THE LASER USER ISSUE 87ISSUE 87 WINTER 2018 THE WINTER 2018 LASER IN THIS ISSUE:

USER Powder Bed Fusion Vertical Laser Cladding

Laser Welding Plastics

Laser Shock Peening

Medical Device Ablation

Bill Steen Reflects

OPTICAL INNOVATION IN MIRRORS & LENSES: SHAPING BEAMS FOR PRECISION MANUFACTURING

1 ISSUE 87 WINTER 2018 THE LASER USER

THE LASER USER

Editor: Dave MacLellan Sub-Editor: Catherine Rose

ISSN 1755-5140

© 2018 – Association of Industrial Laser Users

The Laser User is the house magazine of the Association of Industrial Laser Users. Its primary aim is to disseminate technical information and to present the views of its members. The views and opinions expressed in this magazine belong to the authors and do not necessarily reflect those of AILU.

The Editor reserves the right to edit any submissions for space and other considerations.

Authors retain the right to extract, in part or in whole, their material for future use. The Laser User is published quarterly in February, May, August and November by AILU for its members and is available in print or online.

Editorial Board for this issue: Ric Allott STFC Ravi Aswathanarayanaswamy Renishaw Paul Goodwin TWI Cover image: An axicon lens (with a conical surface) is Lin Li University of Manchester used to generate Bessel beams for femtosecond laser James McDowell Litron Lasers micromachining of glass and other materials. Jonathan Magee Coherent | Rofin Image courtesy of Rémi Meyer , FEMTO-ST Institute, Mark Millar Essex Laser Besançon, France. Andy Toms TLM Laser

ADVERTISING AILU STEERING COMMITTEE ENQUIRIES 2017-18 +44 (0) 1235 539595 President: Lin Li (University of Manchester) [email protected] Vice President: Jon Blackburn (TWI) Advertising rates at: Exec. Director: Dave MacLellan (Anode Marketing) http://bit.ly/AILU_MEDIA_GUIDE_2018 Elected until 2020 Shireen Khanum (GF Machining) Anke Lohmann (Anchored In Ltd) Vojtech Olle (OSI Optoelectronics) Mike Poulter (SPI Lasers)

Elected until 2019 Duncan Hand (Heriot-Watt University) WELCOME TO NEW Louise Jones (KTN) AILU MEMBERS Jonathan Lawrence (Coventry University) Ian White (Yamazaki Mazak) ES Precision Andrew May Elected until 2018 [email protected] Paul Goodwin (TWI) Roger Hardacre (ALT) Lumentum Tony Jones (Cyan Tec Systems) Adrian Norton (thinklaser) Association of Industrial Laser Users Philippe Leopold Oxford House [email protected] Co-opted 100 Ock Street Adam Clare (University of Nottingham) Abingdon NKT Photonics Mark Millar (Essex Laser) Oxfordshire Paul Fitzsimons Stan Wilford (IPG Photonics) OX14 5DH [email protected]

Past presidents and founder members are also able to Tel: +44 (0) 1235 539595 Proform Laser Services attend committee meetings. Anyone wishing to join the E-mail: [email protected] Laura Canner AILU Steering Committee please contact the Executive Web: www.ailu.org.uk [email protected] Director.

2 THE LASER USER ISSUE 87 WINTER 2018 CONTENTS HIGHLIGHTS...

Powder Bed Vertical Laser Laser Welding Fusion 16 Cladding 18 Plastics 20

Laser Shock Medical Device Bill Steen Peening 22 Ablation 24 Reflects 26

ASSOCIATION NEWS MAIN FEATURES CONTENT BY SUBJECT First Word 4 Fluid and particle dynamics in Business Laser Ablation President’s Message 4 laser powder bed fusion Members' News 5 Main Feature 24 Ric's Ramblings 4 Ioannis Bitharas et al. 16 AILU Interview 12 Professor Bill Steen Reflects Energy Bill & Non-Commodity MEMBERS’ NEWS Study on powder blown laser Main Feature 26 Costs Member & Business 5 cladding of vertical surfaces Short Feature 31 Events Diary 36 Case Studies 10 Piotr Lubaszka & Bernd Baufeld 18

Laser welding plastics – Product News 32 EARLY CAREER a short guide RESEARCHERS Laser Processing Ian Jones 20 Laser processing of Plastic Automotive Components hard-to-weld materials 8 Laser shock peening of metals Short Feature 7 and advanced ceramics Photo competition 9 Industrial R&D 7 Pratik Shukla 22 SHORT FEATURES Hard-to-Weld Materials Laser ablation: layer removal and Short Feature 8 Industrial R&D 7 surface treatments Plastic automotive component David Van de Wall 24 Job Shop processing 7 News 14 Non-commodity business costs 31 The laser: from burning paper to Chair’s Report 15 mainline manufacture EDITORIAL William Steen 26 Additive Manufacturing Main Feature 16 Interview: Paul Maclennan, ULO Optics 12 Observations 28 Laser Cladding Job Shop Corner 14 Main Feature 18 A Funny Thing... 34 Laser Welding Plastics PRODUCT NEWS Main Feature 20 Systems 32 Laser Shock Peening Processing Heads 32 Main Feature 22 Beam Measurement 32 Ancillaries 33 EVENTS 29, 35 3 ISSUE 87 WINTER 2018 THE LASER USER ASSOCIATION NEWS

FIRST WORD PRESIDENT'S MESSAGE The 9 years of studying and working life with Bill laid down a solid foundation on which The last couple of months have seen a ramp In this issue we have the honour of publishing to build my entire career in the area of laser up of activity in the AILU office for our next 3 an article by Professor Bill Steen (p. 26-27) engineering. Bill was a most inspiring teacher, events which I hope that all of our members will outlining the history of laser processing in his supervisor and a friend. He always inspired get involved with. research groups from the 1970s to the 2000s. and encouraged students and researchers Some of the photos in the article are published and gave them the opportunities and freedom Over the last two years (and more) a team of for the first time. The article is extracted from to solve challenging scientific and engineering people and a number of working groups have a longer document which I'm sure Bill would problems. Everyone was happier after talking pulled together a national strategy for laser be happy to share if you interested - please to Bill in technical discussions. material processing and the report “Lasers contact him via the AILU office. for Productivity: A UK Strategy”, outlining the Students and researchers were often invited to recommendations, is to be launched at the Reading this article brought me back to the Bill’s house and annual barn dances were held Houses of Parliament on 6 March at 2.30pm. 1980s and 1990s. I joined Bill’s laser group for the laser group members and friends. He We are hoping to see 100 AILU members there at Imperial College London in 1985 as a PhD regularly sent PhD students and post-docs to and as many MPs as we can get to call in student working on intelligent adaptive control various conferences to learn and interact with during the afternoon to meet their constituents of the laser cladding process. The project wider laser communities. and familiarise themselves with the capabilities involved the closed loop control of laser power, of the laser in manufacturing. If you are powder flow-rate, clad deposition height and Bill received the Arthur Schawlow Award interested to find out more, you can register dilution using a hierarchical, multiple sensor from the Laser Institute of America in 1996 your interest in the events pages on the AILU and multiple loop structure combined with and the prestigious Honorary Fellow of the website (there is a link to Eventbrite on that artificial intelligence (AI). Institution of Mechanical Engineers in 2017. We congratulate Professor page and registration is free). We are also In 1988 I followed Bill to Liverpool University, Steen on his lifetime looking for a good cross-section of samples working as a research assistant and later achievements that to display on the day – showing some typical research fellow in a number of projects, have changed the examples from manufacturing to highlight where including monitoring of high speed laser welding manufacturing world. lasers can be used. for industrial packaging and laser based nuclear MACH 2018 takes place on 9-13 April and decommissioning, until 1994 when I joined Lin Li there will be a Lasers for Manufacturing Zone, UMIST (University of Manchester Institute of lin.li@manchester. in place of the AILU Pavilion we have had in Science and Technology) as a lecturer. ac.uk previous shows. Come along during the week or join us in the Zone as exhibitors. Finally, we are getting closer to LPM 2018 RIC'S RAMBLINGS and we all benefit as a society from it –“oh ok, (that’s Laser Precision Microfabrication in case sounds cool, on you go Sir”. Phew I thought, you hadn’t heard) which gives our members a Dear Readers, for this latest edition of The that was a close one. But on reflection that is unique opportunity to visit this Symposium in Laser User my ramblings have taken me much what Photonics West is all about - and from Edinburgh from 25-28 June. Why not submit further afield than usual. I write to you from what I can see this week there is a whole load an abstract before it is too late? Registration SPIE Photonics West in San Francisco – a big of business being done. is open, so register this week and get your old US style celebration of all things photonic. I One of the most interesting sessions I attended accommodation booked! Those companies have been coming to Photonics West for quite was a panel discussion on taking Quantum looking to sell into this market should a while now (though not every year) and it never Technologies into industry. Lots of opportunities also consider sponsorship and exhibiting fails to impress me; the sheer number and in security, communications, next generation opportunities. This event is more international range of companies exhibiting and the myriad computing and so on, but whenever the panel than ILAS, so we expect a significant number of of applications of “light” almost too numerous experts specified where an application will be attendees from Japan, China, USA, Lithuania… to list. realised they were not able to say when with I am hoping for a significant turnout – even My story starts at the US border, standing in any certainty at all – good old Heisenberg must more than the 220 we had at ILAS 2017. the seemingly never-ending queue waiting to have been looking down and chuckling to show my passport and mentally preparing for himself. I think a whole load of wave-functions the forthcoming rapid-fire inquisition as to why will need to collapse before we see Quantum I feel I have the right to enter the country. The fully integrated in our everyday lives, but it is first part went fine – name, hotel etc. then the coming and lasers have a big role to play. heat got turned up, “Why are you here?” oh I’m attending Photonics West, “What’s that?” I thoroughly recommend a trip to Photonics it’s a big science conference on lasers and West – it makes you glad you chose photons optics and stuff, “What do you do?” well I’m in as your choice of career, and if nothing else business development, “business – what on you get to eat lunch earth has that got to do with science!? What under blue skies and o can you possibly get out of attending that?”… 20 C at the back end well that stopped me in my tracks for a few of January. What’s not to like? Dave MacLellan seconds, my mind racing, my hands beginning AILU Executive Director to sweat at the thought of a small room and the Ric Allott unmistakable sound of marigold gloves being [email protected] [email protected] put onto large clumsy hands. Then I hit it – it's 07473 121142 all about the applications – the science feeds the applications and that generates business 4 THE LASER USER ISSUE 87 WINTER 2018

MEMBER AND BUSINESS NEWS

BILL STEEN INDUCTED AS SPI LASERS APPOINTS WORK STARTS ON NEW HONORARY FELLOW NEW CEO COHERENT PREMISES We are delighted to share the news that on 1st SPI Lasers has announced the appointment of Work is under way at a Daventry business November 2017 Professor William Steen was its CTO Dr Mark Greenwood to the position of park to construct a new £2.3m purpose- inducted as an Honorary Fellow of the Institution CEO effective 1st January 2018, succeeding built UK sales and service headquarters for of Mechanical Engineers. Bill founded the world’s Dr Thomas Fehn who is moving to take up a Coherent | Rofin. Following site clearance work first laser materials processing research group at position at SPI’s parent company, TRUMPF. in December, foundations have been laid for Imperial College in 1968 and pioneered scientific the new premises, which is expected to be Mark has a long track record in the laser research in this area. completed later this year. industry gained over 20 years in developing This developed into a major manufacturing field lasers for a wide range of applications and including laser cutting, drilling, welding, surface industries. He joined SPI Lasers in 2015 as hardening, surface cladding, material surface part of the acquisition of JK Lasers where he modification and additive manufacturing. was responsible for establishing the fibre laser technology base and product portfolio. Bill is commonly referred to as the ‘Father of Laser Materials Processing’ within the laser Contact: Matt Wallis processing community. He co-founded AILU and [email protected] was its president for the first eight years. www.spilasers.com

Bill has documented his career leading research groups at Imperial College and later the University of Liverpool, a summarised version of MTC TO LEAD £14M AM which can be found on pages 24 and 25 of this AEROSPACE PROJECT magazine issue. Groundbreaking: L-R Daventry District Following the launch of the Industrial Strategy Councillor Colin Poole; Alan Knape (Financial For further information visit http://www.imeche. white paper on 27 November 2017, Business Controller) and Allan Hardisty (Head of Service org/news/ Secretary Greg Clark announced £53.7 million of for UK & Ireland), both of Coherent | Rofin. funding for seven R&D projects. Contact: Alan Knape One of those seven projects is The DRAMA [email protected] (Digital Reconfigurable Additive Manufacturing www.rofin.co.uk facilities for Aerospace) led by the Manufacturing www.coherent.com Technology Centre (MTC) with partners ATS Global, Autodesk, Granta Design, Midlands Aerospace Alliance, National Physics Laboratory, ES PRECISION: NEW Renishaw and the University of Birmingham. START-UP COMPANY The project will showcase the use of digital In October 2017, ES Precision opened its technologies to drive productivity and reliability doors to offer laser processing to industries in AM, leading to increased adoption of AM such as medical device, Formula 1, aerospace, technologies by the aerospace sector and, in electronics and general engineering. Business Bill Steen being presented with his Honorary the long term, other industrial sectors. It will has started well and the 6 staff have been busy Fellowship by Institution President Carolyn also deliver the world’s first digitally-twinned running jobs on the 8 laser workstations in their Griffiths. reconfigurable AM facility and establish the UK Oxfordshire premises. ES Precision is able to drill as a global leader in AM technology. and cut organic materials at very high speed, mark label data onto any shape label and mark The project, part of the ATI programme, has virtually all materials including all metals, most RIC ALLOTT BECOMES received a grant of £11.2 million through the plastics as well as coated materials. VISITING PROFESSOR Industrial Strategy Challenge Fund. AILU ex-President Ric Allott has been appointed Visiting Professor in the Faculty of Engineering, Environment and Computing at Coventry University. This follows on from a number of years working closely with Coventry on applications of high power lasers, such as laser peening and surface modification techniques and is in recognition of Ric’s academic and industrial contribution to lasers and photonics over his career.

Ric said “Being appointed visiting professor is a real honour for me and it will be an ideal platform from which to build on our collaborations with Coventry University and the broader community". Contact: Kevin Withers Contact: Andrew May Contact: Ric Allott [email protected] [email protected] [email protected] www.the-mtc.org www.esprecision.co.uk

5 ISSUE 87 WINTER 2018 THE LASER USER BUSINESS NEWS

BYSTRONIC'S TUBE PRO-LITE DISTRIBUTE NEWS FROM TLM LASER

PROCESSING PARTNERSHIP LIGHT SHAPING DIFFUSERS Partnership agreement Bystronic has entered a partnership with tube The Pro-Lite Group Ltd (Cranfield, UK) has TLM Laser has further enhanced its laser processing specialist TTM Laser S.p.A, based been appointed as pan-European distributor for products and systems portfolio through a in Italy. Bystronic CEO Alex Waser explained, the holographic, light shaping optical diffusers partnership agreement with LasX Industries, "TTM Laser is an ideal specialist partner (LSDs) made by Luminit LLC (Torrance, CA, producers of high performance production class for Bystronic, as it allows us to expand our USA). Compared with traditional transmission laser converting systems and services. existing portfolio with additional tube and profile diffuser material, a holographic light shaping processing technologies and know-how. This diffuser provides for higher efficiency and more Under this new partnership, TLM Laser will be partnership allows Bystronic and TTM Laser to precise control of the shape and direction of responsible for the sales, marketing, installation offer customers an even more versatile range of propagation of the transmitted beam, in addition and servicing of LasX Industries laser systems solutions." to homogenising the light and providing for throughout the United Kingdom and Ireland. excellent hiding of the light source and reduction Contact: David Larcombe of undesirable hot-spots. [email protected] www.bystronic.com Contact: Robert Yeo [email protected] www.pro-lite.co.uk BOFA’S GLOBAL GROWTH PROMPTS UK EXPANSION BOFA International is increasing its UK footprint TANNLIN'S NEW SCANNING by 25% to meet growing worldwide demand for ELECTRON MICROSCOPE its fume and dust extraction technology. Work Tannlin has recently invested in a Scanning has started on creating an additional 12,000 sq Electron Microscope (SEM) which allows ft of space in the company’s home town of Poole magnification of ×15 to ×60,000 (and up to TLM Laser Director Andy Toms (left) with in Dorset to house its corporate functions, along ×240,000 with digital zoom) and Roughness William Dinauer, President of LasX Industries Inc. with a state-of-the-art research and development Analysis. The addition of the SEM will centre. New Business Development Manager, allow Tannlin to measure within sub-micron New laser converting system David Thompson, will be working with BOFA’s parameters, rigorously inspect laser cut edges TLM's portfolio has been enhanced with the existing customer base and developing new and take detailed, three dimensional images. addition of LaserSharp® digital converting opportunities. technology. The comprehensive laser processing Contact: John Horsey systems developed by LasX are used for laser john.horsey.bofa.co.uk cutting, scoring, and perforating processes, www.bofa.co.uk eliminating the need for costly tooling and lengthy set-up times.

The digital converting technology opens up TRUMPF UK'S SALES many new opportunities for TLM Laser within the Packaging sector. The company will initially GROW focus on “Breathable Packaging” and “Easy TRUMPF UK recorded an order intake of £57.1 Contact: Fraser Shaw Open” applications. million, an increase of 50% on the previous [email protected] Contact: Andy Toms fiscal year. Preliminary operating profit is shown www.tannlin.com [email protected] as £988,239. Machines and systems across www.tlm-laser.com all TRUMPF technologies continue to prove popular with UK manufacturers, with notable AMADA UK SCOOPS new additions, such as the TruPrint Series for 3D POWERPHOTONIC'S MAJOR printing and the TruBend Center 5030 for semi- APPRENTICESHIP AWARD automated bending, contributing to the total. AMADA UK has been crowned ‘Large EXPANSION PLANS The UK workforce also grew substantially in the Employer of the Year 2017’ at the prestigious PowerPhotonic has announced plans to last 12 months with technical service accounting Worcestershire Apprenticeships Awards. The invest in a new facility that will triple its current for most of the new staff members. award is seen as recognition for the company’s manufacturing capacity. In a move, which is highly successful apprenticeship programme, scheduled to be completed by the end of 2018, which has been in place since 2006. At the company will transfer its operations into present, AMADA employs 17 apprentices, a larger, 15,820 square foot facility at the St mostly in engineering, but also in accountancy David’s Business Park, Dalgety Bay to capitalise and business administration schemes. The on global growth opportunities. The investment programme supports AMADA UK’s mantra will include the creation of a new class 1000 of “growing our own talent pool” providing clean room facility, which expands production management candidates of the future with capacity for PowerPhotonic’s unique micro-optic “AMADA DNA”. technology.

Contact: Gerry Jones Contact: Gary Belfort Contact: Roy McBride [email protected] [email protected] [email protected] www.uk.trumpf.com www.amada.co.uk www.powerphotonic.com 6 THE LASER USER ISSUE 87 WINTER 2018 FEATURES

INDUSTRIAL R&D BEGINS ON NUCLEAR AMRC'S POWERFUL NEW DISK LASER CELL

The UK's Nuclear Advanced Manufacturing Research Centre (Nuclear AMRC) is now starting industrial R&D on a powerful new disk laser cell. The cell is designed to produce high- quality deep penetration joins, from around 15 mm, in stainless steel. It features a 16 kW disk laser which is believed to be the most powerful of its kind in the UK.

The laser head is carried by a six-axis gantry over a two-axis manipulator table, which can carry components up to 15 tonnes, all contained in a safety enclosure. The cell was designed and built by Cyan Tec Systems, who integrate robotic and laser systems for industrial applications.

The Nuclear AMRC team will initially use the cell to investigate the viability of using a solid state laser to weld seams on large intermediate-level waste containers for the nuclear decommissioning sector.

Laser welding promises to significantly reduce manufacturing times and costs while The team now wants to talk to manufacturers processes, plus large-scale electron beam and maintaining a high quality of weld seams. who are interested in developing laser welding mechanised arc welding cells. Thanks to a strictly localised high-energy processes for their own production, or who input and high travel speeds of up to 10 m/min The Nuclear AMRC is part of the UK want to investigate innovative applications of or more, the laser produces a much lower government-backed High Value Manufacturing the technology. heat input than other welding technologies, Catapult, and managed by the University of significantly reducing thermal stress and The Nuclear AMRC works with companies Sheffield. Its facilities and services are open distortion. along the supply chain to improve to companies of all sizes for commercial and manufacturing capabilities and performance for collaborative R&D projects. The cell can also deliver a simultaneous MIG the nuclear industry. Its 8,000 sq m research weld for hybrid welding, which offers a better factory on the Advanced Manufacturing Park in fit-up tolerance than laser alone, with less heat Contact: Bernd Baufeld South Yorkshire contains over £35 million worth distortion than arc. The technique is used in [email protected] of state-of-the-art manufacturing equipment the shipbuilding industry to join steel plates of www.namrc.co.uk tailored for nuclear industry applications. up to 50 mm. Facilities include a 15 kW Laserline fibre- Contact: Tony Jones With further development, the cell could also coupled diode laser cell, used to develop [email protected] be used to investigate laser cutting techniques automated cladding and additive manufacturing www.cyan-tec.com for decommissioning.

LASER PROCESSING OF PLASTIC AUTOMOTIVE COMPONENTS Laser marking head. This will allow processing options such The use of direct part marking on automotive as marking of oblique, convex and concave components has to guarantee high readability surfaces. for safe traceability, and must also be resistant Laser welding to abrasion, temperature, light and lubricants, to ensure that marks last the life span of the Laser welding joins plastic pieces by emitting product. laser radiation and generating heat at the boundary surface without using any adhesive. Original Equipment Manufacturers (OEMs) and The laser beam must pass through the laser 1st/2nd tier suppliers require a system that is transparent (upper) material, and then will be able to mark both metals and plastics. Fibre absorbed by the laser absorbing (lower) material. laser technology in particlular offers an energy- and at low pressure into the joining surface. This efficient and cost-effective way of laser marking The laser welding of plastics offers significant not only leads to a stress-free and low-distortion these materials. advantages over conventional joining methods: it joining of the components but is also extremely does not cause adhesive residues and also does energy efficient. Automotive components come in a variety of not produce any abrasion particles which may different geometries and 3D markings have to be lead to problems with the finished component. In Contact: Bob Norfield applied accurately and quickly without the need addition, it is possible to introduce the process [email protected] to reposition or move the product or marking energy required for joining in a targeted manner www.laser.panasonic.eu 7 ISSUE 87 WINTER 2018 THE LASER USER EARLY CAREER RESEARCHERS

COLLABORATE WITH SPOTLIGHT ON ECRS AT CRANFIELD UNIVERSITY CRANFIELD UNIVERSITY Name: Goncalo Nuno Name: Armando The Welding Engineering and Laser Processing Rodrigues Pardal Caballero Ramos Centre (WELPC) at Cranfield University has Nationality: Portuguese Nationality: Venezuelan been established for more than 50 years. The main laser processing activities at the Centre Age: 35 Age: 28 include welding, cutting, micro joining, peening Academic history: Academic history: and additive manufacturing. The centre has partnerships with many different companies I finished my masters in I completed my and several funding bodies, and is open to mechanical engineering at bachelor degree in collaboration with new partnerships and research Instituto Superior Técnico, Lisbon in 2011 and Metallurgy at Universidad Central de Venezuela projects. came to the UK to start my PhD in welding in 2012 and moved to the UK to complete engineering at Cranfield University. a Masters degree in Welding Engineering at The main facilities that are available for research Cranfield University. I gained experience in in the WELPC centre are: I studied the possibility of joining steel to laser processing and investigated the feasibility aluminium and titanium to stainless steel using Laser facilities: 8 kW CW IPG fibre laser; 3 kW of using a nanosecond laser for welding different welding techniques, several interlayers CW SPI fibre laser; 500 W CW SPI fibre laser; applications. and the use of additive manufacturing to build 100 W ns pulsed fibre laser; High energy ns

transition components. After completing my MSc I joined the Welding pulsed Litron laser; Synrad 200 W CO2 laser. Engineering and Laser Procesing Centre team At the end of my PhD I was invited to stay at Arc facilities: Many welding arc power sources as research assisstant and started a part time the Welding Engineering and Laser Processing that can be combined with laser facilities for PhD. The main focus of my thesis is to develop Centre as a Research Fellow which is my hybrid processing. a phenomenological model for controlling current position. Residual stress mitigation facilities: Including depth and size of the meltpool, based on the laser shock peening. I have been involved in high power laser spatial and temporal distribution of energy in welding, laser and arc hybrid additive the selective laser melting process (SLM). This Monitoring facilities: Including laser profilers manufacturing projects and the development project includes the use of different laser delivery and power meters. of new facilities and equipment for the WELPC systems and multi-beam processing of the All laser and arc systems can be coupled to department. powder bed. robotic or automatic motion systems to develop fully automated processes capable of processing Hobbies: Hobbies: components up to 10 metres. I have a passion for 3D printing and use a I like to read, build scale car models and I If you would like to view our facilities please plastic 3D printer at home. I also enjoy walking, manage several social media pages to promote contact Goncalo Pardal: g.pardal@cranfield. listening to music and watching TV. and celebrate Afro Natural Hair. ac.uk.

LASER PROCESSING OF HARD-TO-WELD MATERIALS

Ni-based superalloys are used in high performance applications in the aerospace industry for their strength capabilities in harsh conditions. Unfortunately, many of them are not suitable for additive manufacturing by selective laser melting (SLM) because of the high cooling rates that introduce a lot of residual stresses. These are relieved in the material through the formation of cracks. Hot isostatic pressing can heal these cracks post-processing, but this is not favoured since there is the risk of them reopening under loading leading to catastrophic failures. Therefore, it is essential to eliminate them in-situ, i.e. in the as-SLM state.

The superalloy CM247LC is highly un-weldable. When processed by SLM, the material showed stresses build-up. These strategies push the extremely shorter scan vectors. The latter micro-cracks along the grain boundaries. theory behind checkerboard strategy by reducing produced parts with higher bulk density. Researchers at Nottingham aimed at reducing the length of the scan vector to the extreme Furthermore, the orientation and density of cracks by generating custom scan strategies. (~100 µm), reducing the distance over which cracks changed with the fractal scan strategies. Using the common strategies has not been the stresses build up. This targets producing Although the crack density was reduced, they successful, e.g. the checkerboard strategy a uniform thermal profile with reduced residual became wider and their orientation was found to increased cracks at the overlap between the stresses and cracking. follow the scan vectors. scanned islands. So Catchpole-Smith et al. [1] They reported more localised stress distribution [1] Additive Manufacturing 15 (2017), p.113-122. investigated the feasibility of using fractal scan in each island in the checkerboard strategy and Contact: Nesma Aboulkhair strategies where large areas are divided into a more uniform one in the fractal scan strategy [email protected] much smaller regions to control the residual across the material during processing for the www.nottingham.ac.uk 8 THE LASER USER ISSUE 87 WINTER 2018 EARLY CAREER RESEARCHERS

NEW! PHOTO COMPETITION OPEN TO AILU MEMBERS

The Early Career Researchers Committee is introducing a photo competition which is open to all AILU members. Here are the details:

• Images must relate to laser materials processing. • The competition will run for a year covering 4 magazine editions (issues 88-91). • Entrants will submit photos by a given deadline for each issue of the magazine. • One winner will be chosen for each magazine issue, and will go forward to the Grand Final to win a prize. • The prize is a £25 Amazon voucher, and the image will be featured on the front cover of The Laser User if suitable. • The images will be judged by Dave MacLellan (AILU Executive Director) and the winner will be announced in each magazine issue. 3. The entrant must also provide: Competition dates • title/caption for each submitted photograph, The competition is now open. • a short description of the photograph, noting whether the photograph The closing date for Issue 88 (Spring 2018) is 9TH APRIL 2018. is a composite of several images or has been enhanced in any way, • any due acknowledgements. Competition rules 1. Photographs must be submitted by email to [email protected] 4. Photographs submitted previously cannot be re-submitted, but you may submit more than one image to each issue. 2. The entrant must include the following statement in the text of the email submission: 5. Photographs should be of good print quality, at 300 dpi, ideally portrait orientation and at least 2000 pixels wide. I have the relevant permission to enter the attached photograph(s) in the competition and give the AILU the right If you have any queries, please do not hesitate to contact us at to publish the photograph(s) in the magazine (print and online). [email protected].

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Get our FREE brochure Capabilities in Laser Processing and Micromachining at www.aerotech.co.uk/resources/brochures.aspx www.aerotech.co.uk • +44 (0)1256 855055

AH0118A-LPM-LTD 9 AH0118B-LPM-LTD-LaserMicromachining-190x126.indd 1 1/11/2018 10:17:19 AM ISSUE 87 WINTER 2018 THE LASER USER CASE STUDIES

LVD PHOENIX BRINGS CONTROL AND CUTTING PRODUCTIVITY

For brothers Darren and Ashley Churchill, going to work each day is more than just a job. Their company, JC Engineering, based in Reading, was started 51 years ago by their father John Churchill who is still very active within the business.

The small family business has recently invested in a new LVD Phoenix 3015 4kW fibre laser machine. “We hadn’t bought a laser before because we felt that the technology wasn’t right for us,” says Darren. “We were carrying out a lot of second and third operations on the punch – countersinking, forming, and putting on part identification, and so on. This meant we could keep the parts on the punching machine for all these operations and keep our labour costs down.” He adds that the company undertakes a lot of work in aluminium, which again suited the punching technology. that now was the time to invest in a fibre laser, Ashley concludes: “We cover a lot of areas – “If stainless steel had been a big part of our the technology was ready for the work we do.” aircraft work, the computer industry, point of business then we would probably have bought sale, we do anything really. You never know Once it had been established that the a laser 10 to 15 years ago, but until now we felt what the next job is going to be. There are jobs technology was right, one of the key drivers for that the technology and running costs for cutting we have shied away from in the past that we JC’s investment decision was gaining control aluminium were not going to give us any benefit are now taking on because we now have the over its production processes. over what we had.” With the laser now up and laser. The laser has transformed the way we do running this is no longer a problem! Ashley says: “We were sub-contracting work to things.” laser companies and we felt the quality wasn’t Darren continues: “We are generally working with there, so we were losing control of what we materials up to 6 mm-thick, with the majority could do for our customers. We felt that the next Contact: Chris Phillips 3 mm or below. The fibre laser is cutting it at step for us was to have control in-house so that [email protected] such a rate that I don’t see how you could do it we were not reliant on subcontractors.” www.lvdpullmax.co.uk any other way more cost-effectively. We realised

UK AEROSPACE COMPANY EXPANDS WITH LASERDYNE FIBRE

Paul Fabrications, a Derby-based Unitech Aerospace company, is involved in the development of major aero-engine programmes for both civil and military applications. The company has recently expanded its laser processing capabilities with a six axis LASERDYNE 795XL machine. Paul Fabrications is the first and only manufacturing facility in the UK to possess this combination of technology. The machine incorporates LASERDYNE SmartTechniques™ processing technology for high speed, high precision laser cutting, welding and drilling.

“The LASERDYNE system is a fantastic addition

to our existing 5-axis CO2 laser technology,” commented Gary Hemmings, Paul Fabrications’ Business Improvement Director. “In certain applications, it is four times faster than to the surface in uncoated and thermal barrier with excellent intermediate temperature tensile technology that was available previously and coated heat resistant materials.” ductility and high strength. The LASERDYNE gives us the ability to add enhanced features to system allows us to easily achieve a tolerance “We’re operating the system for trepanning using our customers' parts.” range from 0.3 mm down to 0.05 mm on part both continuous wave and peak power pulsing,” features including inner and outer profiles and Mark Barry, Vice President of Sales for Prima reports Sean Ahern, CAD/CAM Laser Engineer hole sizes of 0.6, 0.9, 1.5 and 26 mm. ” Power Laserdyne added, “There are a number of for Paul Fabrications. “We are laser processing unique capabilities with this fibre laser processing silencers and liner assemblies made from Contact: Mark Barry system. The 795XL adds capacity for complex nickel alloy C263 and C625. These materials [email protected] o laser hole drilling at angles as shallow as 10 have exceptional fabrication characteristics www.primapower.com 10 THE LASER USER ISSUE 87 WINTER 2018

CASE STUDIES

BYSTRONIC AIDS PROFITABLE LOW-VALUE MANUFACTURING Eastern Attachments manufactures construction and agricultural attachments, supplying to companies such as Persimmon Homes, Taylor Wimpey and JCB. Director Daniel Leslie said, “The UK is known for its strength in high added value engineering, such as aerospace for example, but there is a perception that we cannot compete with low-wage countries in Eastern Europe and the Far East when it comes to manufacturing relatively low value, simple items.

“In 2007, most handling buckets for construction and agricultural equipment in the UK came from overseas, but these days imports are becoming a rarity. Within six months of entering the sectors we had taken half the market for products we manufacture – buckets, handling grabs, forklift attachments and tipping skips – and now produce the vast majority of units sold in the UK.” When Bystronic launched the first high power originally planned output was only possible due 10 kW fibre laser machine at the end of 2016, to automation of the fibre laser cutter. Mr Leslie Attachments can be made considerably capable of cutting up to 25 mm mild steel, estimates that the cell, which runs around the lighter, so a construction firm or farmer can lift Eastern Attachments decided it was time to act. clock with eight hours of operator attendance, more material to achieve higher productivity, can typically produce as much in 24 hours as a or downsize the machine to reduce capital The 3 x 1.5 m capacity fibre laser cutter, manually-loaded plasma machine produces in expenditure. A spin-off advantage of these high equipped with a ByTrans Cross for sheet storage five 8-hour day shifts. strength steels is fewer impurities such as silicon, and automated material handling to and from which is beneficial for achieving better edge the machine, was installed at the beginning of quality when laser cutting, especially 12 mm and summer 2017, just in time to prevent the need Contact: David Larcombe under when using nitrogen rather than oxygen as for a second shift on the two manually-loaded [email protected] the cutting gas. plasma cutters. Achieving more than double the www.bystronic.com

11 ISSUE 87 WINTER 2018 THE LASER USER INTERVIEWINTERVIEWPRODUCT NEWS

GROWTH THROUGH DIVERSIFICATION AN INTERVIEW WITH PAUL MACLENNAN SALES & MARKETING DIRECTOR, ULO OPTICS

Q. Can you tell us about the history of ULO Optics and the company today?

ULO Optics was founded strong relationships with key In 2017 ULO acquired in 1982 by David Greening industrial OEMs. Laser Beam Products in as V&S Scientific, operating Biggleswade and renamed Following the untimely death out of a factory unit in North it LBP Optics. The two of David Greening in 1999, London. The business at facilities are run as separate the company was sold to that time focused on CO business units and across 2 Belgian company Umicore laser optics and grew rapidly the two sites there are and became part of its in the 1980s into a one stop 34 employees with a Electro Optics Division. It shop for high quality laser turnover of £5.5 million and subsequently relocated to components and beam anticipated annual growth its current modern facility in delivery solutions. During in excess of 20% year on Stevenage. The company the 1990s the company year projected until 2023. was sold to the UK developed a range of Currently the business management team in 2006 scanner optics and high supplies close to 50,000 and renamed ULO Optics. power laser optics which optical parts per year. enabled the development of 12 12 THE LASER USER ISSUE 87 WINTER 2018

INTERVIEW

Q. How does the acquisition of LBP Optics rely on this approach for around a third of our turnover. We export change your capabilities and objectives? over 80% of what we make in Stevenage, whilst at LBP, excluding a couple of major UK based customers, we export roughly 60% We’ve worked closely with LBP founder Mark Wilkinson since the of what we make. One of our largest export customers is based in 1980s and have always held a broadly similar business outlook. the EU medical sector. In all the years we’ve ordered mirrors from LBP, we have never had to reject a single optic - so we always knew the optical quality Q. How do you see UK market conditions and was literally second to none. More recently, Mark’s business has seen the potential for significant growth in two key areas: medical future business with Europe post-Brexit? and defence. This ties in very well with ULO’s aim to further Since the referendum we’ve seen over 50% growth in Europe, the develop our presence in both these market sectors. Combining favourable exchange rates having given us a competitive edge. the metrology and experiences of both companies with our ISO How this will play out post-Brexit next year remains to be seen, 9001:2015 accreditation will help that process. but we are in a highly specialised market sector and our quality and service are excellent so we are confident that we will continue to remain competitive especially as much of our competition for

CO2 products comes from outside the EU. “ Regarding the one micron sector, our philosophy has always been The success of fibre lasers to stay ahead of the competition by entering the market at the high value added end. We’ve been lucky enough to have been invited is hugely important to our onto a couple of innovative projects; LaserSnake and ModuLase. The experience we’ve drawn from working on these programmes growth plans. has given us a wonderful insight into the optics that are required to GROWTH THROUGH work properly at high power levels (greater than 5 kW).

Q. Is there anything new and exciting in the DIVERSIFICATION ” pipeline? Q. How does the shift from CO2 to fibre lasers, We are currently launching a new version of our affordable and

especially in the past 5-10 years, affect your modular CO2 beam delivery named Compact2, which offers business? double the aperture of our Compact Series, and twice the power (up to around 1 kW). We will soon launch a range of user-friendly beam collimators for one micron. Our Technical Director, Nick Ellis, Historically ULO and LBP have been mainly associated with CO2 laser optics. In the 1990s we took a long hard look at our product continues to design amazing multi-element scanner lenses for both CO , used extensively in the manufacture of smart phones, and range; most of our business was UK based and CO2 related, so 2 we realised that targeting the export market was needed as well one micron where they are used in the automotive sector. as more than one wavelength band.

I think it was at an AILU Jobshop Meeting in Coventry, many years ago, that I first heard the phrase “Growth Through Diversification”. It impressed me as a concept and since then we’ve worked hard “ to attract business from new products and new sectors. We have We have been hugely recently diversified into one micron products, and hired Stuart McCulloch from SPI Lasers to grow that business. The success of impressed with the fibre lasers is hugely important to our growth plans with products such as multi-element scanner lenses, protection windows and a ILAS events. newly launched range of collimators.

Intriguingly, the percentage of LBP’s customer base that have changed up to high power fibre lasers is only 15%. We’ve put this

surprisingly low number down to mainly supplying low power CO2 OEMs, where applications such as polymer processing can’t easily ” be replaced with solid state laser alternatives. We have not seen Q. How has AILU membership benefited your a decline in demand for CO 2 optics, despite the often announced company? demise of CO2, and this is complemented by additional growth in one micron optics and the new business from LBP. We have been hugely impressed with the ILAS events. They are very well run, always useful and enjoyable (even more so in the evenings). We’ve also enjoyed having a platform to deliver information through Q. Is your biggest market OEMs or end users? making presentations at workshops. Finally we regard the magazine How much of your business is export? as AILU’s pivotal epicentre – described by our founder David Greening as being the best of its type anywhere in the world. Overall ULO supplies 40% of its turnover to OEMs; LBP a much higher amount at 70%. With reference to the end user sector, Contact: Paul Maclennan ULO supplies 20% of its turnover and LBP 13%. ULO’s traditional [email protected] route to market is via a strong network of distributors; currently we www.ulooptics.com 13 ISSUE 87 WINTER 2018 THE LASER USER

JOB SHOP CORNER

GRATNELLS INVESTMENT EXPANDS CAPABILITIES

Gratnells Engineering has recently invested in MIDTHERM HELPS CREATE MALTON LASER GROWTH a new state-of-the-art BLM LT Fiber machine, allowing the company to expand their LOCAL HISTORY ARTWORK AND TRAINING capabilities in 2018 and ensure clients benefit Midtherm Laser recently worked with community Increase in profits for 3rd consecutive year from even faster turnaround times. artist Luke Perry to produce an art installation Malton Laser has reported a turnover of £2.2 The new machine sits next to an existing commemorating the mining heritage of what is million for the past year, an increase of 18% laser tube cutting machine which is designed now Silverdale Country Park, Staffordshire. compared to the previous 12 months. Moving forward, the company is aiming to increase to cut from small to medium diameters and The 3 m high sculpture depicts an ex-miner on its turnover by a further 20% over the next thicknesses of metal tubular sections. The one side and a leading local community figure on year, in order to position the business as one LT Fiber allows tubes of any shape to be cut the reverse. Midtherm Laser cut 5 mm, 15 mm of the most forward-thinking, cutting-edge without any additional special equipment and 20 mm mild steel which created the desired companies in the industry. This recent growth is required. effect. partly thanks to the business’ investment in the The new machine is already helping to most advanced, revolutionary laser cutting and increase factory efficiency by allowing welding technology. unloading to various positions, with finished parts from one machine being unloaded MD graduates from prestigious training whilst production continues uninterrupted programme on the other. The need to manually separate Managing Director, Charles Corner, graduated parts from different orders has also now been from the 10,000 Small Businesses Training eliminated. Programme at Oxford University after being Tube laser cutting continues to grow in selected from hundreds of business leaders popularity as it offers a quick route to a to take part in the course. Set up with the precise finish, eliminating conventional, aim of assisting businesses in reaching their time-consuming stages such as marking full potential, the course aims to provide small out, sawing and finishing whilst delivering business leaders with the skills and tools they significant cost savings. need to effectively grow their businesses.

Contact: Murray Hudson Charles Corner, MD Malton Lasers [email protected] www.gratnellslasercutting.com

Contact: Paul Lake Contact: Dean Cockayne Contact: Charles Corner [email protected] [email protected] [email protected] www.blmgroup.com www.midthermlaser.co.uk www.maltonlaser.com

14 THE LASER USERUSER ISSUEISSUE 8787 WINTERWINTER 20182018 CHAIR’S REPORT

THE GREAT CARILLION DEBACLE ...

No doubt you will have seen the spectacular failure of Carillion in and the customers. Possibly you are both a supplier and a the news recently. Possibly some of you have been affected by customer in a way, as this company had fingers in many pies. The it. Companies going bang is nothing new, but this time there is a main difference here though is that the Government was one of the difference. customers and so will also suffer as a result of this failure. When running any company there are always issues with trying to Selfishly, I’m most interested in what is happening to the suppliers. chase debtors and deal with customers that go bust. In the Job The Government has now stepped in to try and help, however, Shop market we seem to have much more than our fair share of supply chains being what they are, I suspect very few of us failing companies that leave us high and dry; they often open up supplied Carillion directly, more likely we were much further down again a few days later with a slight name change and are back at the line. In some ways, that should help insulate many of us from it again. Yes there are various, often expensive, ways to protect the worst, however it also means I would not hold my breath for yourself, and some costs can be retrieved, but in the most part a any of that Government money. few pennies in the pound does not make up for what has been Carillion is a rare case due to its size but perhaps, as the lost. I certainly feel like it is an all-too-frequent occurrence and Government have now been landed with this burden, they might the Government seems completely oblivious to the scale of the spot the wider problem that it is all too easy for companies to rack problem. up large debts then fold, leaving everyone else high and dry. It In the case of Carillion, the Government’s first reaction was that happens far too often. they were a private company and would not receive Government assistance, typically short sighted if you ask me! The people they wanted to target were the senior managers who have been paid Mark Millar the big bucks. Senior managers were given the option to repay [email protected] some of their large bonuses, all of whom declined. Those that are www.essexlaser.co.uk actually suffering are the employees, pension holders, suppliers

15 ISSUE 87 WINTER 2018 THE LASER USER ADDITIVE MANUFACTURING

FLUID AND PARTICLE DYNAMICS IN LASER POWDER BED FUSION IOANNIS BITHARAS ET AL.*

Laser powder bed fusion (LPBF) is zoom of 7:1. All the experiments reported here and spatter are in the upper forward direction currently the most widely adopted process were undertaken with gas-atomised stainless with respect to the laser scan direction. The for the additive manufacture of metallic steel 316L powder (Renishaw PLC) with particle induced flow of the ambient gas entrains powder components. Detailed visualisation studies diameters in the range 15–45 μm and a mean particles in towards the melt pool from all recently revealed that the process is more diameter of 30 μm. Powder layers were melted directions on the powder bed. Particles behind dynamic than is generally appreciated and on to 2 mm thick stainless steel 304 L coupons, the melt pool are lifted off the powder bed, as can involve considerable motion of powder using a single mode fibre laser (SPI 400 W seen in the side view of Figure 1(a). Entrained particles and agglomerates in and above continuous wave, 1070 nm) which was scanned particles are unlikely to be consolidated into the the powder bed. This motion is driven by over the powder surface (Raylase MS-II-14 track and are mostly ejected by the laser plasma the laser-induced plume of metal vapour scanner with 163 mm focal length f-theta lens) and gas flow. At the 100 W condition, the and plasma above the melt pool. with a 50 μm diameter Gaussian beam profile. plasma and spatter are directed predominantly The shielding chamber was purged with argon vertically upwards, resulting in less momentum Metal LPBF is a category of additive manufacture until the measured oxygen concentration was in the shield gas flow at the powder level and (AM) process in which thermal energy selectively <0.1%. consequently less denudation. At the 200 W fuses regions of a powder bed. Commercial condition, the plasma and spatter are directed LPBF systems are already used to manufacture Single line scans backwards with respect to the scan direction. components, but they require intensive, part- Figure 1 shows high-speed imaging for side and The induced gas flow is at a sufficiently low specific process setting refinements in order top views of the powder bed during laser line angle that it impinges on the powder bed and to reduce the distortions caused by residual scans at three different combinations of laser causes denudation by blowing particles away stresses, to determine process settings that power and scan speed. The two latter parameter from the track. reduce defects and to determine acceptable sets have the same line energy (laser power positions for support structures. In the future, divided by scan speed) at 200 J/m, while the first Multilayer island scans software will simulate a full-build and reduce the one has a line energy of 500 J/m. In all cases a Figure 2 shows top views whilst building time required to determine process settings, melt pool is formed, containing a characteristic rectangular islands through multiple layers using but that approach still requires better process “moving crater” at the spot where the laser the 100 W, 0.5 m/s setting, shown by the single understanding so that residual stresses, energy is maximum. Vapourised iron and plasma line scans to be more favourable in terms of porosity and surface finish are predicted reliably expands rapidly from this position, with velocities denudation. For the first layer, Figure 2(a), the first for different process regimes. Imaging and reaching several hundreds of m/s. Recent scan line shows relatively little denudation and simulations are the two main approaches being studies have shown that this vapour plume the laser plasma is vertical as observed in Figure used to achieve this improved understanding. induces a gas flow in the inert atmosphere [3], 1(b). From the second scan lines onwards, the It is extremely challenging to record images causing the removal of powder in the spread laser plume points away from the previously built, through the viewing window of commercial layer – an effect termed denudation. adjacent track. As the first layer progresses, the LPBF systems with sufficient magnification or denudation increases and a sizeable region next The results in Figure 1 show that the direction contrast to see individual powder particles in the to the scanned island remains stripped of powder. of the plume changes with process parameters, powder bed. Due to this, such methods have After six layers in the build, Figure 2(b), the creating a different denudation pattern on the been used mainly for build monitoring, rather denudation is less severe, both between adjacent powder bed. At the 50 W condition, the plasma than to understand the physics of the process. tracks and around the edges of the island. To overcome this problem, we have utilised an experimental open architecture LPBF system, designed to allow easy access to imaging whilst maintaining the capacity to print millimetre- scale fully dense parts. More details about this system have been presented in Issue 80 of The Laser User and in [1]. In this visualisation study [2], we employ a combination of high- speed imaging and schlieren imaging, as well as multiphysics modelling, to elucidate the effects of the interaction between the laser beam and the powder bed.

A Photron Fastcam Mini UX100 monochrome camera was used for high-speed imaging. The direct imaging experiments reported here were recorded at 8000 fps and 1280 × 616 pixels. Figure 1: High-speed images and schematic when scanning single tracks with laser power and The camera was fitted with a C-mount QiOptiq scan speeds of (a) 50 W and 0.1 m/s; (b) 100 W and 0.5 m/s and (c) 200 W and 1 m/s. The videos Optem Fusion lens, configured to provide a for all figures are available with [2]. 16 THE LASER USER ISSUE 87 WINTER 2018 ADDITIVE MANUFACTURING

Figure 3: Composite image of the heated gas plume for laser power 100 W and scan speed 0.5 m/s towards the viewing direction. Fluid dynamic simulations [2] P. Bidare, I. Bitharas, R.M. Ward, M.M. Attallah, A.J. Moore, Acta Mater. 142 (2018) 107–120. doi:10.1016/j. The background colour distribution of Figure actamat.2017.09.051. 4 shows the high velocities associated with the laser plume due to the evaporation in the [3] M.J. Matthews, G. Guss, S.A. Khairallah, A.M. Knudsen layer. The magnitude of the plume's Rubenchik, P.J. Depond, W.E. King, Acta Mater. 114 velocity scales linearly with power, reaching (2016) 33–42. several hundred m/s at 100 W. However, the * I. Bitharas1, P. Bidare1, R.M. Ward2, M.M. jet velocity decelerates exponentially in the Attallah2, A.J. Moore1 z direction, reaching under 100 m/s over an 1 2 Figure 2: Top views of island scans at 100 W upwards distance of 1.1 mm. The arrows in this Heriot-Watt University; University of Birmingham and 0.5 m/s for (a) layer 1, (b) layer 6. figure show that velocities of the order of a few m/s are induced in the Ar atmosphere by the Contact: Ioannis Bitharas This decrease in denudation is in part due to plume. [email protected] the increase in powder layer thickness between www.applied-optics-photonics.hw.ac.uk layers as it evolves towards the steady state As dictated by momentum conservation, a radial thickness. By the sixth layer, the powder layer flow field is generated in the Ar atmosphere. thickness is already 89.5% of the steady Upwards momentum carried by the plume is state value of ~130 μm [1]. Additional image imparted to the surroundings, while radial gas sequences recorded for layers seven through motion is induced via momentum conservation, ten showed no significant change in behaviour consistently with the mechanism observed from that of layer six. At the steady state powder in the schlieren images, Figure 3. The radial layer thickness, it appears that there is sufficient flow exerts drag forces on particles in the powder adjacent to the track for it to roll towards powder layer, resulting in a net particle motion the track without leaving a completely denuded towards the laser and the denudation observed region. The rough surface of the previously experimentally. built layer also seems to contribute towards decreasing denudation compared to the first Conclusions layer. The combined results showed that the inert atmosphere and laser plume are integral Gas flow visualisation to the heat, mass and momentum transfer Figure 3 shows a composite schlieren image of the process. Their inclusion in numerical sequence at the times indicated after initial models is essential for process optimisation, to illumination of the powder by the laser for a identify parameter sets which result in reduced single track laser scan across the powder bed denudation. Observation of plume and particle towards the camera. Upwards momentum behaviour under cross-flow [2] emphasised the carried by the plume is imparted to the importance of uniform extraction streams above surroundings, as indicated by the observed the bed, carrying enough momentum to prevent convection front while radial gas motion is contamination of the bed from ejected particles. induced by the eddies trailing it. Dark lines in the Taking hydrodynamic phenomena into account initial convection front are visible, and are due to during process planning can improve the overall entrained iron vapour. build quality and limit the adverse effects of ejected vapour and particles. These refractive index gradients are undesirable and can cause variations in the laser position References and focus. In a commercial system, these hot Figure 4: Laser plume (surface) and induced Ar [1] P. Bidare, R.R.J. Maier, R.J. Beck, J.D. Shephard, fluids should be cleared by a flow of shield gas gas flow (arrows) velocity. A.J. Moore, Addit. Manuf. 16 (2017) 177–185. across the powder bed during the process, which can also serve to extract ‘airborne’ particles and prevent them from landing back on Ioannis Bitharas is a Research Associate at Heriot-Watt the powder bed. Cross-flows are typically of the University. His research interests are optical diagnostics order of a few m/s, and so do not interfere with and multiphysics simulations of manufacturing processes. the plasma flow directly.

SEE OBSERVATIONS P28 17 ISSUE 87 WINTER 2018 THE LASER USER CLADDINGPRODUCT NEWS

STUDY ON POWDER BLOWN LASER CLADDING OF VERTICAL SURFACES PIOTR LUBASZKA & BERND BAUFELD

Powder blown laser cladding is widely a b applied in industry to achieve corrosion- or wear-resistance. Commonly, this is carried out in the 1G flat position. However, for certain applications, especially large and heavy components which are difficult to manipulate, the cladding of vertical surfaces would be beneficial. This report presents results observed when depositing powder in 2G horizontal position using a high power diode laser. Figure 1 a: Set-up for 2G cladding with robot arm, process head and substrate. b: COAX12 nozzle Introduction with powder flow directed to a vertical surface. Cladding enables the modification of surfaces to optimise their functionality. For example, stainless This paper reports results obtained at the The hardness above the overlap line is lower steel or nickel base alloys can be utilised for Nuclear AMRC using this COAX12 nozzle for 2G (~220 HV, typical for stainless steel) than below corrosion resistance. A number of different cladding. the line (300 - 400 HV, too high for stainless cladding technologies are available, including steel) (Figure 4a). The difference in hardness plasma transferred arc cladding, submerged Setup and materials above and below the overlap line is highlighted in arc cladding and laser cladding, which result A 15.0-kW Laserline® high power diode laser a hardness map (Figure 4b). in varying properties and quality. For example, with wavelength range of 900 nm to 1070 nm, The chemical composition above the overlap arc-based technologies often exhibit significant a Laserline® process head OTS2, a Fraunhofer line is close to that of the powder, whilst the dilution and thermal distortion [1]. IWS COAX12 nozzle, and a 5-axis KUKA® composition below is somewhere between that robot attached to a Güdel® gantry were used Powder blown laser cladding is characterised of the substrate and the powder. The difference for the cladding process. The powder feed rate, by high power density, low heat input and high in chemical composition above and below the delivered by a GTV hopper was determined for heating and cooling rates [1-3] resulting in low overlap line and the substrate is visible via EDX each experiment. Figure 1a shows the process dilution, chemical composition achieved within mapping (Figure 5a, similar location to Figure 3a). head oriented for 2G, and Figure 1b the 4 few micrometres, and limited thermal distortion powder streams oriented for cladding a vertical of the workpiece [4, 5]. Parameter optimisation surface. Two different optical sets were used with In order to overcome the issues described, a Cladding in the downhand position (1G ASME/ laser beam diameters of ~9 mm and ~7 mm. number of trials with different sets of parameters PA ISO 6947) is most frequently used. In this Each sample consisted of 12 to 13 tracks. The were conducted. The energy density ranged configuration the surface of the component interpass temperature was monitored using between 67 and 161 kW/mm2. The variations is positioned and maintained in the horizontal thermocouples and maintained below 80°C. were for the laser power from 2.5 to 10.0 kW, position. However, for some applications, Argon was used both as a carrier and a shielding for the travel speed 750 to 1500 mm/min, for especially for large and heavy components gas. the powder feed rate 20 to 80 g/min and for this is difficult or even impossible to achieve. the carrier gas feed 4 to 10 l/min. Certain KPV In particular, the tilting of rotating high-mass The substrate was carbon steel S355 with plate combinations resulted in lack of fusion, others to components at high peripheral speeds may be dimensions of 300 mm x 300 mm x 30 mm. extensive penetration depth. inherently dangerous since a difficult-to-control Stainless steel 308L powder by Carpenter with gyroscope is created. particles sizes of 40 µm to 150 µm was used. The laser head was positioned at an angle of 10° either downward to the horizontal plane These problems may be overcome by cladding Results (tilting) or parallel to the horizontal plane opposite vertical walls with the laser beam in horizontal Cladding in 2G position using 1G parameters orientation, either with horizontal tracks (2G a ASME/PC ISO 6947), or with up- or downwards Initially, a cladding parameter set known for tracks (3G ASME/PF or PG ISO 6947). Few good results in 1G was used, but resulted in the commercially available cladding nozzles are following problems: the surface quality of the capable of achieving this type of cladding and, clad was inferior; the average penetration depth to the authors' knowledge, nothing has been into the base material too deep (~750 µm, Figure published in the open literature. 2a); and oxide inclusions (rich in manganese and silicon) developed (Figure 3a). Furthermore, b Fraunhofer IWS has developed a nozzle hardness and chemical composition above (COAX12) where the nozzle inclination does and below the overlap line (from subsequent not influence the powder stream. This nozzle overlapping beads indicating the melt of the last injects powder in four separated homogeneous bead) varied. Figure 2: Cross sections from parameter set 1 streams which are almost unaffected by gravity. (a) and 2 (b). 18 18 THE LASER USER ISSUE 87 WINTER 2018 CLADDING

a a b

b Figure 5: Overlap region of Figure 3 by EDX mapping for parameter set 1 (a) and parameter set 2 (b).

greatly reduced to ~150 µm. Neither lack of penetration depth and dilution, and the fusion nor oxide inclusions were found (Figure occurrence of oxide inclusions. 3b). Furthermore, no significant variation in • The nozzle orientation influences the hardness (220HV to 240HV) and chemical penetration depth, dilution, and surface composition above and below the overlap line smoothness. was observed and agreed with the composition of the powder. Figure 5b shows similar chemical • The demonstrated high quality of cladding Figure 3: Back scattered electron images of the composition below and above the overlap line. in 2G horizontal position with a coverage overlap region (a: parameter set 1, b: parameter rate of 0.19 m2/h creates an opportunity for set 2). Discussion reducing the complexity of large component to the cladding direction (leading). The change The extensive penetration and dilution in the manipulation, decreasing the severity of of nozzle orientation, from downhand tilting to case of parameter set 1 is the reason for the safety issues and the production costs. leading, induced reduced penetration depth and variation in chemical composition and hardness inter-run lack of fusion. above and below the overlap line. Due to the Acknowledgments When the carrier gas flow rate was decreased by high level of dilution, liquid material was pulled The authors wish to acknowledge the UK High 60% (the other parameters remaining the same), from the substrate into the clad causing a Value Manufacturing Catapult for sponsoring this no oxide inclusions developed, the penetration significant change in chemical composition. project. Furthermore the authors are indebted to Stephen Bloomer (Nuclear AMRC) and Holger depth reduced significantly, the clad lift increased While developed for arc welding and not for laser Hillig (IWS Fraunhofer) for their experimental by ~30 % and inter-run lack of fusion occurred. welding, the Schaeffler diagram was used to work and advice. Reducing this rate significantly increased the lift, predict the arising phases. For parameter set 1 indicating an increase in powder efficiency. the area below the overlap line is predicted to be References martensite, while for the area above the overlap The final optimised parameter set 2 is shown [1] Kathuria YP. Surface and Coatings line to be a mixture of austenite (prevailing), in Figure 2b and Figure 3b which show a cross Technology. 2000;132(2–3): p. 262-9. section for this set. The clad lift was ~1.8 mm. ferrite and martensite. The martensite below the overlap line may explain the high hardness in the [2] Vilar R. Journal of Laser Applications. The problems presented for parameter set 1 range of 320 to 420 HV. For parameter set 2 the 1999;11(2): p. 64-79. were resolved. The surface of the clad was composition above and below the overlap line [3] Goodwin P. Laser Cladding of Industrial smoother and less wavy, and penetration was are very similar and within the austenite/ferrite Components. ILAS2015; Kenilworth, UK 2015. a region. Hence, the hardness is similar with a value typical for stainless steel. [4] Weisheit A, Backes G, Stromeyer R, Gasser A, Wissenbach K, Poprawe R. International Conclusion Congress on Advanced Materials, their • The change of the position of the clad Processes and Applications; Munich, 2001. p. 8. surface, from horizontal to vertical, affects [5] Baufeld B, Lawler S. 9th International Laser the cladding process. This is because Symposium; Dresden 2016. gravity affects the powder stream and the melt pool in a different way. This article is an edited version of "Powder Blown Laser Cladding of Vertical Surfaces", • High quality, stainless steel clads can be P. Lubaszka & B. Baufeld, Lasers in Engineering achieved on vertical walls, with optimum b 2018, in print. dilution and penetration depth, smooth surface, and no internal or external defects. Contact: Piotr Lubaszka [email protected] • The carrier gas flow rate affects the www.namrc.co.uk efficiency of the cladding process, the

Piotr Lubaszka is a power beam welding engineer at the Nuclear AMRC, specialising in diode laser cladding.

Figure 4: Overlap region (parameter set 1). a: Indents (overlap line indicated by the orange line), b: hardness map. SEE OBSERVATIONS P28 19 ISSUE 87 WINTER 2018 THE LASER USER WELDING PLASTICS

LASER WELDING PLASTICS – A SHORT GUIDE IAN JONES

Lasers are very attractive tools for joining delivered through the upper part to the surface sheet, film and moulded thermoplastics and of the lower part where heating and melting textiles. Their features allow for a precise, takes place. The differential heating is controlled yet rapid, delivery of a controlled amount using laser absorbing additives or coatings at of energy exactly to the point where it is the lower part. A laser with a wavelength in required. Lasers are available with outputs the range 750-1500 nm is used and this may covering a range of wavelengths, which has be provided by diode, fibre and Nd:YAG laser a large bearing on the interaction of the types. In general, this wavelength of radiation light with plastic materials. The nature of is absorbed far less readily in plastics than } the process used is varied depending on the UV or mid-IR radiation. The degree of energy type, thickness and additives in the plastics. absorption in this range depends largely on the Melt zone 0.36mm deep Complex forms can be welded using high presence of additives in the plastics and whether resolution positioning and welds from the plastic is semi-crystalline or amorphous Figure 1: Laser transmission weld in less than 100 μm wide. This makes them (glassy). If no fillers or pigments are present polypropylene showing the melt zone suitable in a wide variety of applications in the plastic, the laser will penetrate a few evenly affecting the carbon black filled and including catheters, microfluidic devices, millimetres into semi-crystalline plastics and and unpigmented plastic layers indicating that all the tubing, packaging, electronic cases and is hardly attenuated at all in amorphous plastics. remaining energy is absorbed immediately at inflatable devices by using different material The absorption can be increased by means of the surface of the black material. Courtesy TWI. handling equipment. additives such as pigments or fillers, especially carbon black pigment. weld at the interface between the two pieces. Plastic types The process is limited by the fact that one side The absorption of radiation by natural of the component has to be black, but is still Thermoplastics are polymer materials made unpigmented plastics increases from 1.6 µm the most common application of the process. from long chain molecules, that, above a certain wavelength upwards until there is very strong The upper part must transmit a proportion of the temperature can be reshaped or welded. Unlike absorption for IR wavelengths longer than laser energy (more that 10% is usually enough), thermoset polymers, the molecular chains in 5 µm. At a wavelength of 2 µm, which may be so that heating preferentially takes place at the thermoplastics are not cross-linked and do not provided by a fibre laser or Holmium:YAG laser, surface of the lower part rather than at the upper have a rigid network. At high temperature the the energy from the beam is deposited in the surface of the top part. An example magnified at molecules are free to move and the material top few millimetres of all plastics (semi-crystalline the joint interface can be seen in Figure 1. This flows as a liquid. Industrial plastics have melting or amorphous). Welding is possible in sheet up image, with an almost equal melt depth in the or softening temperatures in the range to a few millimetres thick without the need for two materials, shows that heating is developed 120-343°C. additional absorbers. This is termed direct laser very locally at the black surface. The black Thermoplastics may be split into semi-crystalline welding because the beam is not transmitted surface acts as a heating element within the (milky appearance) and amorphous (glassy) through an upper part to the joint line. Direct part and provides for rapid processing, minimal types. Semi-crystalline types are a mixture of laser welding is not yet widely applied for joining thermal damage of surrounding components, small crystallites surrounded by amorphous plastics, but has potential for wider use. and minimal distortion or contamination at the material. The crystallites scatter light giving joint. The CO2 laser is a well established materials rise to their outward appearance, and limit processing tool, commonly used for cutting The advent of alternative absorbers for laser the transmission of laser radiation. This in plastics in film, sheet and fabric form. The CO2 welding in 1998 allowed the joint to have turn, limits the maximum thickness that may laser radiation (10.6 µm wavelength) is rapidly much less visible colour. One example is called be transmission laser welded. Some plastics absorbed in the surface layers of all plastics. The Clearweld. It is an infrared absorbing dye, much can be made in both types but generally this energy is delivered as heat in the first 0.2 mm of like other visibly coloured dyes. It can be applied is not the case. Plastics such as polyethylene plastic that the laser is directed to. This leads to as a coating (by spraying, printing, pad, needle (PE), polypropylene (PP), nylon (PA) and rapid heating, and very rapid weld processing or pen) at the joint line or added to the lower polyetheretherketone (PEEK) are semi-crystalline. of thin plastic film is possible, even with fairly part (Figure 2). An example of a welded product Polycarbonate (PC), polymethylmethacrylate modest laser powers (<1000 W). Welding made by applying absorber to the joint surface (PMMA) and polystyrene (PS) are amorphous. speeds in excess of 1000 m/min have been between two transparent parts of PMMA can be Laser types and their interaction with demonstrated. seen in Figure 3. Nearly all colour combinations plastics can now be welded using transmission laser Transmission laser welding welding. The main problems arise with heavily The different applications possible with each When first being reported in 1985, transmission filled plastics, where the upper part will not allow laser type are very dependent on the wavelength laser welding was carried out with an infrared the beam to pass through to the joint. In these of light produced, which dictates the form of transmissive plastic material for the upper cases, the filler must be reduced or changed energy absorption in the plastic. section and a carbon black loaded plastic for in particle size to reduce scattering, or another The most common form of laser welding is the the lower layer. The carbon black absorbs welding process should be considered. transmission method, in which the beam is and heats in the laser beam to generate a 20 THE LASER USER ISSUE 87 WINTER 2018

WELDING PLASTICS

Figure 4: Design for a waterproof jacket that has laser welded seams which are more Figure 2: Diagram of transmission laser welding using IR absorber at the joint interface. effective as a water barrier than the alternative stitched and taped seams. Courtesy TWI. Application areas for transmission laser welding Transmission laser welding can be applied to include: composite materials with glass or polymer fibre • Medical devices reinforcement and matrices that do not have • Packaging high filler content. Where carbon fibre is used or • Automotive components the matrix is black or heavily filled, an alternative • Consumer products process not requiring the beam to pass through • Electronic packages the part is used. This is direct laser welding. • Textiles Direct laser welding The application to textiles is very interesting. The process offers a new method of welding Where laser energy is not transmitted, either textiles that melts only the joint surfaces, not through choice of radiation wavelength, or due the outer surfaces of the material. In that way, a to the materials selected, melting starts at the proportion of the fibres remain unmelted and the upper surface of the plastic. This is described strength and often flexibility of the fabric may be as direct laser welding. The CO2 laser was first Figure 5: Melt run in 3mm thick PMMA using a retained at the seam. Figure 4 shows a design used for this process and welding of thin film 1940nm wavelength Thulium fibre laser, 67W, for a waterproof jacket in which continuous and is possible at very high speeds. Welding has 4.5m/min. Courtesy TWI. hermetic overlap welds are made in waterproof been demonstrated with a range of plastic films fabric laminate. The potential therefore arises for at speeds of up to 1200m/min. A simultaneous materials with radiation wavelengths) and further automation of garment manufacturing for cut/seal may also be carried out for packaging alternative equipment configurations such as waterproof clothing, personal protective clothing, or bag making purposes by controlling the gantry, robotic, scanner or fixed diode arrays. and other textile products. laser beam power distribution to cut two films The laser provides an efficient energy source to in contact whilst leaving a welded region at the give precise heating and localised melting. The The process has also been extended to joining edge of the cut. welds are completed rapidly, with high strength of fibre-reinforced polymer composites. The and good appearance. composite matrix is heated and melted by the For plastics with thicknesses in the range 0.2 mm laser source, whilst the fibre reinforcement to 5 mm, a source with 2-3 µm wavelength may The welding process is efficiently achieved remains unaffected by the process. be used to make conventional butt joints, as using the very compact diode and fibre laser demonstrated by the melt run in Figure 5. There sources, and lends itself easily to high levels of is no need for additional absorber, but the plastic automation. Applications of this technology exist transmission properties must be controlled to for a wide variety of industry sectors and product ensure consistent welding takes place. types.

Summary Contact: Ian Jones Polymer products can be laser welded using [email protected] a variety of process mechanisms (matching www.laserweldplastics.com

Ian Jones is the manager of Laserweld Plastics Ltd, providing consultancy services for companies joining Figure 3: Containers welded in clear PMMA made with IR absorber. The beam may be products made of plastics, textiles and composites. directed down the container walls to make welds that are almost invisible. Courtesy TWI. SEE OBSERVATIONS P28 21 ISSUE 87 WINTER 2018 THE LASER USER LASER SHOCK PEENING

LASER SHOCK PEENING OF METALS AND ADVANCED CERAMICS PRATIK SHUKLA

Laser shock peening is an advanced The pulse repetition rate ranges from 0.5 Hz a glass confinement layer as opposed to a water surface treatment process that is to 60 Hz, and energy level from 1 J to 60 J, confinement layer (at the same laser energy and traditionally deployed to enhance the although much work has been published on the spot size) will result in approximately twice the strength of various metals and alloys. The use of several hundred mJ to undertake laser amount of pulse pressure being induced within benefits of laser shock peening have been shock peening, both with and without coating. the material. However, in terms of practicality, it well documented over the last two decades. Initially, in the early 1970s, long pulse lasers in is more beneficial to use a water layer, due to The process originated in industry and the range of µs were deployed on metals and its flowability over curved surfaces and ease of made its way into academia, where greater alloys, but with advancement in laser technology application, rather than glass. If deep compressive knowledge and understanding was gained and availability of shorter pulses, it was possible stresses are not required, then both can be once metallurgists and engineers made to deliver high energy pulses in a ns time frame – eliminated by applying laser peening alone, in-roads into understanding the way the ultimately making laser shock peening a superior but there is a high risk of losing the efficiency metallic systems responded to the process. process. The pulse duration is usually in the of the process, as the plasma is allowed to range of ns, although the use of ps and fs pulses escape resulting in lesser pulse pressure, plastic The process involves interaction between a high for laser shock peening have also been reported. deformation, and material property enhancement. intensity laser (power density greater than 109 W/ However, the depth of beneficial residual stress is cm2) and generally a metallic object, leading to The cost of lasers has reduced over time, but not readily available with ultra-short pulses as yet. the formation of rapidly expanding plasma away there is still difficulty in deploying a full-scale laser from the surface of the material. To achieve Usually, a top hat beam profile with a distributed shock peening facility for SMEs, job shops, and sufficient shock pulse pressure, the expanding power density is the norm, but Gaussian research labs due to a cost barrier. Depending on plasma is normally confined to the surface of beams have also been reported to be effective the laser energy available (400 mJ to 10 J), the the material using a water confinement layer. For in generating compressive residual stress in a costs range from £30 K to in excess of £300 K the material to plastically deform, the plasma given area over the work-piece. Overlapping is and beyond, for a dedicated, full-scale high energy pressure created by the laser pulse must selective and is typically between 40 - 50%. It is system. If a laser source alone is purchased, exceed the Hugoniot Elastic Limit [1]. To obtain usually correlated with the processing speed of additional costs such as a robotic arm and/or linear a significant level of compressive stress within the work-piece. The faster the pulse repetition stages, appropriate beam delivery, and laser safety the material, the laser process parameters must rate, the faster the required traverse speed of equipment all add up. be carefully considered, so that the laser power the work piece to avoid excessive overlapping, density is sufficient enough to generate shock unless that is desired. In addition, multiple layers Laser Shock Peening at Coventry University pulse pressure that in turn renders beneficial have the tendency to induce greater depth of At Coventry University, research on peening residual stresses. A range of parameters can be compressive stress. science has been conducted since the late employed to undertake laser shock peening in 1990s. More recent research has been focused The selection of the correct ablative overlay also order for the aforementioned to take effect. on residual stress engineering by the structural plays an important role. Laser shock peening integrity group, and applied laser shock peening, was traditionally conducted with black vinyl tape. Parameters and Cost method development and surface engineering by However, aluminium tape overlay introduces Traditionally, a laser of 1064 nm wavelength has the laser engineering and manufacturing group. substantially higher amounts of compressive been used for laser shock peening applications, This latter group are on their way to developing stress in comparison. Nonetheless, it is still time with frequency doubling to give a wavelength a second laser shock peening facility. The consuming in production-based environments of 532 nm, as the effects at this wavelength are group is focused on undertaking research with and so laser shock peening without coating is greater due to better absorption by metals and both peenable and difficult-to-peen materials - practiced, but it often leads to higher material alloys. The energies range from 1 J - 60 J, and titanium and nickel alloys being the former and removal, or surface melting which then has to be some in excess of that for niche applications advanced ceramics and cermet being the latter. removed using additional processes. The use of that require deeper residual stresses, larger spot sizes, faster processing speeds and in turn, throughput. With that said, there has also been much work done on laser shock peening without coating (LSPwC) that can be applied with energy levels in the range of several hundreds of mJ [2]. This leads to small spot sizes, less than a millimetre, rendering high energy density to create sufficient shock pulse pressure and generate plastic deformation within the material with increase in dislocation density. Otherwise, the spot sizes employed range from 1 mm – 10 mm depending on the maximum output energy which the laser is capable of delivering. Figure 1: Laser shock peened surface of Hastelloy-X superalloy (left) and surface hardening phenomena following laser shock peening (right). 22 THE LASER USER ISSUE 87 WINTER 2018

LASER SHOCK PEENING

Figure 2: A micrograph of orthopaedic Ti-6Al-7Nb cross-section, post laser shock peening, showing refined grain regions. In particular, laser shock peening of superalloys Compressive stresses of -92 MPa were has drawn significant attention as they are being also measured with increase in laser energy. used in the harsh environment of gas turbine Furthermore, laser shock peening of alumina engines. For example, Hastelloy-X superalloys, ceramics showed an increase in the surface despite having excellent oxidation resistance, hardness by 10%. The respective flaw sizes formability, and high-temperature strength, from the diamond indenter were also reduced Figure 3: A cover page of Issue 1 of Volume 1 fail in elevated temperature environments. by 10.5% - enhancing the KIc by 12%. These for the international journal of peening science Laser shock peening was able to produce findings were a result of grain size reduction, and technology. compressive residual stress through to a depth micro-structural refinement and an induction of of 1 mm which helped in delaying the onset compressive stress layer -64 MPa [6]. The journal reflects the main areas in which of crack initiation and propagation [3]. Laser peening methods are used and developed for shock peening was also beneficial in increasing The International Journal of Peening the surface engineering and for manufacturing dislocation density in the metallic systems, Science and Technology applications. which in turn increased the surface hardening The author has developed a new journal in the Should anyone be interested in submitting a behaviour as shown in Figure 1. area of laser peening: The International Journal manuscript to this journal, further details can of Peening Science and Technology, which he Laser shock peening of titanium alloys has also be found at http://www.oldcitypublishing. also edits. The scope of the journal is broad, proved to be beneficial in strengthening titanium com/journals/ijpst-home/ and papers can be covering, among other things, the following orthopaedic implants that are subject to wear submitted to [email protected]. areas: and material loss. Worn implants often led to References a second and third surgery for the end user, • laser shock peening; resulting in increased pain, cost and time [4]. The • plasma physics and dynamics; [1] Peyre, P. et al. (1996) Journal of Laser SEM image shown in Figure 2 is a cross-section • grit blasting; Applications 8 135-141. micrograph of Ti-6Al-7Nb alloy after laser shock • blast and laser cleaning; [2] Sano, Y. et al. (2006) Materials Science and peening at 3 J, 3 mm spot size, 8 ns pulse • ultrasonic peening, water-jet/cavitation Engineering A 417, 334-340. peening, oil-jet peening, shot peening, ion duration, 1064 nm wavelength to strengthen the [3] Nath, S. et al. (in press) Lasers in Engineering. titanium alloy for biomedical applications. exchange beam peening; • low plasticity burnishing and deep rolling; [4] Shen, X. et al. (2017) Surface & Coatings The laser engineering and manufacturing group is • issues on plastic deformation and Technology, 327, 101–109. also working on laser shock peening of advanced strengthening mechanisms; [5] Shukla, P. et al. (2017) Materials and Design, ceramics which is a new field of application. • residual stress engineering; 134, 523 - 538. Much work is still to be reported in this area, but • finite element analysis and process modelling [6] Shukla, P. et al. (2017) Journal of European initial results have shown some good progress of the peening techniques; Ceramic Society, 37(9), 1728 - 1739. made with both silicon carbide and alumina • topographical and micro/nano structural ceramics. In particular, preliminary studies have characteristics; Contact: Pratik Shukla shown that hardness, fracture toughness, • change in mechanical, electrical and [email protected] microstructures and grain refinement are evident biomedical properties using peening. www.coventry.ac.uk in these materials, as well as induction of some compressive residual stress [5]. With silicon carbide, increases in the surface roughness, Pratik Shukla is a senior lecturer in manufacturing changes to the surface morphology, improved hardness, and a reduction in crack lengths were engineering at Coventry University. His research focuses found. Laser shock peening also improved the on laser processing of materials. fracture toughness from an average of 2.32 MPa.m1/2 to an average of 3.29 MPa .m1/2 . SEE OBSERVATIONS P28 23 ISSUE 87 WINTER 2018 THE LASER USER ABLATION

LASER ABLATION: LAYER REMOVAL AND SURFACE TREATMENTS DAVID VAN DE WALL

Laser ablation is gaining popularity for The laser process imparts no physical force on medical device applications that require the wire during the process, so delicate wires stripping of coatings on cylindrical with diameters as small as 50 microns can be components, such as hypotubes and guide stripped. wires. It is also being widely used for Besides laser processing, other commonly advanced surface treatments, including used processes for removing wire layers include discolouration or foaming of plastics, and mechanical cut and peel, micro-abrasive blasting darkening or annealing of metal parts. (sandblasting), or chemical etching. However, the Offering a repeatable, non-contact process, constantly decreasing diameter and wall thickness laser ablation is a clean, low dust (or of wires makes these competing stripping no-dust) way to selectively remove wire methods impractical, inefficient, or impossible. layers or areas. It is also a fully automated Laser ablation is cleaner, greener, and faster. process, with a very high yield compared to Figure 1: Marking bands by annealing. Top In addition, laser ablation is a fully automated other methods. image - schematic representation of the laser process with a very high yield compared to the processing. Laser ablation: medical device applications other manual methods – approaching 100%. Speeds are fast, and are normally only limited The key applications for laser ablation include: by the amount of laser energy the wire can cope • Layer/coating removal – laser energy is used with. A wide range of lasers are available with to evaporate, melt or oxidise an existing different properties, enabling the end user to layer. The laser can also be used to make a proceed as quickly as their part allows. defined cut in a layer to enable easy removal, either by hand or by an automated method. Helping medical customers improve Wire stripping requirements are constantly production increasing, with both end-span and mid- The laser ablation process has proved to be span parts requiring selective removal. The extremely successful for a variety of medical newest applications include even smaller applications. For example, Amada Miyachi diameter wires, for example those being Figure 2: Jupiter laser ablation system. Europe recently worked on a laser ablation used for transmitting electric signals for brain project with an Irish medical device company stimulation applications. Figure 2 shows an example of a system for a hypotube used in a minimally invasive producing marker bands by annealing the surgical tool for arteries. The application involved • Optional surface roughening – this is useful stainless steel tube. producing a marker band that enabled surgeons for increasing adhesion or increasing friction to know how far to insert the hypotube into the to make handling easier. Laser ablation preferred over mechanical or body. Sandblasting had initially been used to chemical removal methods • Insulation layer removal – electrical isolated remove the nylon coating, but led to scratches wires can be stripped of the polyimide The laser ablation method removes material by on the tube resulting in scrap. The sandblasting insulation layer (tradename Kapton®). directing a focused beam (minimum size around operation was replaced by laser ablation using Kapton absorbs certain wavelength of 25 microns in diameter; a larger size is easier a near infrared (NIR) laser, which performed laser light effectively, leaving a clean to generate) by galvanometers, which are small selective removal of the coating. In addition, the metal surface for electrical contacting fully programmable X and Y mirrors. This enables NIR system removed the coating at the top of afterwards. The laser ablation process can highly tailored removal, so parts or sections the tube, in preparation for gluing another part also remove hydrophobic coatings, like of wire insulation can be removed as needed. on top. Previously, this had involved grinding the polytetrafluoroethylene (PTFE, tradename Changes to the size and location of the removed part down to the bare metal. Teflon®), silicone based coatings, and sections can be made on the fly by calling up Another successful laser ablation project was thermoplastic elastomers (TPE), including a pre-programmed recipes. for a very fine medical spring made by a major wide range of polyamide (nylon) coatings. When used for wire stripping, laser ablation German medical device company. The spring • Marker band annealing – lasers can be simply removes all material from the wire as the had an outer diameter of less than 1 mm and used to anneal stainless steel. This process polymer absorbs the light energy. The material was used in minimally invasive surgical tools darkens the metal to give a distinct contrast is vaporised – effectively ejected away from the that operated through very small incisions. The with the clear surface of the tubes. This can wire. The laser does not affect the wire beneath pull wire inside the spring had to be welded to be used, for example, to create marker bands the insulation, because the power levels needed the spring; any wire coating remaining would be which a surgeon is able to use as a visual to remove the insulation are much lower than burned away, polluting the weld. The ablation aid for guiding and placing catheters during those that would damage the metal wire. This system enabled the company to remove the medical procedures (see Figure 1). advantage can be augmented by selecting a coating to make the end of the spring weldable laser wavelength that is readily absorbed by with a laser in a second process step. the polymers, but reflected by the metal wire. 24 THE LASER USER ISSUE 87 WINTER 2018 ABLATION

wire through the system and then measure the distance from the beginning or end point of the wire to determine whether the system can properly transport it. Several nozzles, feeding and transport wheels are tested to achieve the best result. Their materials, dimensions and coatings vary.

Step 3 is a test of the effectiveness of the actual ablation process once the wire is inside system and positioned correctly.

The testing process takes a few working days and uses Amada Miyachi Europe’s standard laser ablation system as the starting point. About half the wires and assemblies tested can be processed with the standard system, while the Figure 3: Wire stripping using a CO laser. 2 other half requires redesign and modification.

Picking the right laser for the job picosecond and femtosecond lasers. These The clean non-contact laser process reduces or eliminates dust during manufacturing, and can A number of different lasers can be used for two laser families produce pulse widths that are be used to process most plastic and metal parts wire stripping and marker band annealing, extremely short (in the pico- or femto-second fed as a bundle or on a reel. The system is fully depending upon the particular wire diameter, range). The pulses are so short that the coating automated, saves time, and improves production insulation material (e.g. polyimide, Pebax®, evaporates and the material does not have time processes, enabling higher throughput. PET (poly ethylene terephthalate), nylon, and to conduct any heat from the process area into Production yields are nearly 100%, and the laser fluoropolymers), and feature requirements. the surrounding material. process creates a cleaner cut with smoother The sealed CO laser should always be edges when compared to grinding and sand 2 Laser wire stripping and annealing systems considered first. With a wavelength of 10604 nm, blasting, as well as a much cleaner surface after The use of lasers for wire stripping and marker the CO laser is readily absorbed by every processing. 2 band annealing transforms a key step in the polymer, so it will work to a certain degree no process to a lean operation. The key to success The modular system is adaptable to specific matter what insulation material is used. Also, the is in the development of the process. To make product requirements. Customers can select CO laser is not readily absorbed by metals, so 2 the right decision as to which laser source the right laser for their process, including when all the insulation is removed and the laser and removal methodology works best, it is sealed CO , nanosecond pulsed near infra- hits the exposed metal wire, it has little effect for 2 absolutely essential to test possible options in an red 1070 nm, to ultraviolet (UV) 355 nm and a relatively long time. Figure 3 shows the result application laboratory with a range of lasers. The picosecond and femtosecond lasers. System of wire stripping using a CO laser. 2 resulting system solution will then be optimal in options include automatic OK/NOK selection for output bin, in-line on-the-fly wire diameter If a CO2 laser cannot be used for reasons of both process and implementation. heat input control, the nanosecond laser should measurement, and automatic wire length For example, Amada Miyachi Europe consults be considered, specifically those with 532 nm measurement. with customers using a multi-step testing and 355 nm wavelengths. Nanosecond lasers process on wires and assemblies to simulate produce pulses of around 20 ns, removing wire Lasers transform wire coating ablation and the system in a real high volume production insulation material with much less heat input than marker band annealing to a lean, clean environment. operation that of the CO2 laser. Figure 4 illustrates a wire being stripped using a nanosecond laser with a Step 1 involves a simulation of whether the wires Easily automated, the laser transforms a key wavelength of 355 nm. The choice between the can be processed at high volumes. Typically, step in the manufacturing process to a lean 532 or 355 nm is typically made based upon these systems involve processing a wire every operation, reducing and optimising human- the insulation material; the 355 nm is better 10 - 30 seconds. End users want to limit labour dependent processes and providing consistent absorbed by more polymers. and increase throughput by using unassisted part quality. Using lasers rather than manual automatic wire loader/unloader machines. The When extreme quality or minimal heat input chemical-based processes also offers safety test includes bundling up to 2000 wires to is needed, consider the ultra-short pulse benefits from eliminating chemical use, reduces determine whether the system can pick out a chemical handling and disposal costs, and single wire, using either a magnetic or pneumatic supports a company’s ISO 14001 sustainability picking tool, and feed it automatically into the programme. laser ablation system.

Step 2 involves feeding the wire through the system. Optimal wire transportation through Contact: David Van de Wall the system depends on the wire’s stiffness, [email protected] weight and friction. Application experts pull the www.amadamiyachieurope.com

David Van de Wall joined Amada Miyachi Europe in 2012 and manages the Sales Support department for resistance welding, hot bar soldering and laser welding/ Figure 4: Schematic diagram of wire stripping laser marking. using a nanosecond laser. SEE OBSERVATIONS P28 25 ISSUE 87 WINTER 2018 THE LASER USER

MATERIALSPRODUCT NEWS PROCESSING

THE LASER: FROM BURNING PAPER TO MAINLINE MANUFACTURE WILLIAM STEEN

In this article Bill Steen shares his anecdotes from the Imperial College and Liverpool laser research groups (1967- 1998) covering the early pioneering days of laser application work. Bill joined Imperial College as a process metallurgist, lecturing during a time of rapid technological change involving computers and lasers. In 1988 he was offered the James Bibby Chair of Manufacturing Engineering at Liverpool University, with enhanced laser facilities. The research activity moved to Liverpool with a group of about 30 scientists working Researchers in the 1980s: Jack Gabzdyl (L), now VP Marketing and Business Development at SPI on cutting, welding, cladding, weld build, Lasers, and Bill O'Neill R), now Professor of Laser Engineering at the University of Cambridge. cleaning, bending, marking and anything else that they thought the laser could do. deep which was loaded at night and the product manufacturing company. collected the next morning usually only to be Bill was a founder member of AILU and In 1975 I patented the process of arc corrected and recycled. FORTRAN scripting was was the first AILU President, a post that augmented laser processing [1975]. One student most unforgiving. he held from 1995 until 2003. Numerous experimented with arc augmented laser cutting; AILU members have passed through Bill's The founding of a high power laser facility she showed that she could double the cutting tutelage and some are mentioned in his speed but that the arc wandered from side In 1974 I won a grant to have the world’s first recollections below (an edited version of a to side and tended to damage the cut quality 2kW Fast Axial Flow laser made by BOC Power larger piece written by Bill some years ago). [1979]. Beams Division to a design from TWI. We now How it all began had the most powerful laser laboratory in any In the 1980s Jack Gabzdyl studied the effect university in the UK and almost any industry on cut quality of varying the jet angle and jet In 1964, not long after the CO2 laser was invented, I built my own laser from a kit including as well; only TWI had such facilities. This was alignment with the kerf, while skiing near the a glass tube with internal Ge mirrors on flexible no longer dilettante research, this was a real RTM labs in the Alps of Italy on a BRITE project. couplings, supplied by Ealing Scientific. I built responsibility. What could one do with an entirely Other research included the study of the effect a 30,000 V, 100 mA power supply, which was new form of industrial energy? This was the of gas composition, for which we had built a quite a learning curve. The laser was very question we had been entrusted to answer. This precision gas mixing rig to find that the only unstable, could produce up to 5 W on a good account tells how our group invented or were in difference occurred between 99-100% oxygen! day and if my lecture load kept me away from the front line of most of the early laser material Nitrogen was found to cut stainless steel better the lab for too long the mixed gas cylinder of processing developments. with less dross and fewer striations due to no formation of Cr2O3. He, N2, CO2, had to be rolled around on the floor to remix the gases. However it worked and The story of laser cutting By 1993 the subject of laser cutting had been to watch paper burst into flames when placed One thing our new machine could do was cut almost played out since the process was in the invisible infra-red beam was a marvel steel. If paper burning was fun, cutting steel understood, modelled and commercially in use. to entertain the child in anyone; so began my like butter and producing quality cut edges was It was time to look for new processes. But no! fascination with the application of lasers which is even more so. Our first experiment was to cut Bill O’Neill, working with Jack Gabzdyl and using still with me. a sheet of 2mm thick steel that was rotated supersonic Laval nozzles developed an entirely while traversing the beam generating a spiral The story of laser chemical vapour cut showing the cut quality vs. speed in one deposition sample. It showed a step change in the kerf I joined the Royal School of Mines in 1965 and width at one speed. Why the step? We believed an early research topic was to deposit CoO from that the cutting speed driven by the laser was the vapour of cobalt acetyl acetonate, and try slower than the burning rate in oxygen at that to print metallic oxide patterns. It worked, and point causing the step change; we missed the the process of laser chemical vapour deposition concept of polarisation back in 1974. (LCVD) was born and is a recognised process In 1971, TWI had patented oxy/laser cutting today. with a coaxial jet of oxygen – one of the more I made the first mathematical model of a laser obvious patents! This doubled the cutting speed heated spot, even making a 3D graph - without for steel. There was immense rivalry between a software package. Such computing took the the numerous laser manufacturers at that time Paul French in 1987, now Senior Lecturer at form of a deck of punched cards some 30 cm – it was a rich man’s sport to found a laser Liverpool John Moores University. 26 26 THE LASER USER ISSUE 87 WINTER 2018

MATERIALS PROCESSING

was using preplaced powder cladding, which he also cleverly modelled to show why there was such a wide operating range for low dilution cladding.

Leo Sexton made clad tracks of variable composition using a triple hopper feed system, in which lines of variable composition of the system Al-Fe-Co were laid down on a steel surface to map out the entire range of alloys possibilities in that ternary system.

The scabbling story John Powell after the Laser'81 conference. Leo Sexton, Liverpool ca. 1993, now Director Lin Li decided to seal concrete surfaces so that John was a founder member of AILU and is of LaserAge Ltd, Cork, Ireland. Technical Director at Laser Expertise Ltd. they could be clinically cleaned both for hospitals and nuclear plants. He tried melting the concrete new process, LASOX, using the laser as a mapping out the operating region for welding to create a glassy surface and was able to cover match to help the oxygen cutting process. This, and identifying the main parameters, as well fair areas but there were always some stress compared to oxygen cutting alone, gave several as constructing one of the first mathematical cracks on cooling. But Lin Li, being the inventor orders faster penetration of steel sheets of >100 models of a moving laser source. that he is, then used an unfocussed beam to mm thickness and square cut edges, all with At around the time of the transfer of the group simply heat the surface. That chipped off the top less than 1kW of laser power. to Liverpool, 1988, a student joined the group layer of the concrete, which contained the bulk to work on welding Zn coated mild steel, which of the contamination, and so a new process of The drilling story was becoming an important problem in the car laser scabbling was invented, patented by BNFL Lumonics supported us with a Nd:YAG laser, industry. With an Italian partner we developed and is now in use in industry. and Rolls Royce with money for drilling turbine and modelled the gap welding process. blades. Paul French and others provided the muscle and brain power for the work which Around 1995, Geoff Shannon joined the chase included drilling turbine blades at various angles and studied deep section laser welding using and not damaging the inside of the cooling a powder feed system from the work on laser channel. This work, carried out with Heriot-Watt cladding. After his Ph.D he stayed on as a University, developed into a series of instruments research assistant and helped with the rapid for in-process sensing the extent of penetration prototyping work. He is now at Amada Miyachi and when break through occurred. Paul America in California. continued this work at Liverpool John Moores Transformation hardening University. While we were exploring cutting and welding, Laser marking story both of which could be directly applied to This process came to us fully-fledged, it being industry, we were also developing an interest in one of the first industrial applications of lasers laser surface treatment, which was destined to for resistance trimming. Martin Sharp joined us become a main theme of the group activities. Lin Li, Imperial College, 1986. Now Professor, in the 1990s from running a laser job shop; he At that time I ran a third year project on laser Associate Dean and Director of the Laser later took over managing the Laser Engineering transformation hardening. I remember one Processing Research Centre at the University Centre in Birkenhead, an off-shoot of our student, with a cynical streak, who took his of Manchester. Currently AILU President. laboratories in the University, and is now at small sample of En8 steel and passed the laser Liverpool John Moore’s University. In 2011 he over the surface without any melting or any Other processes became President of AILU. other visible effect; looked at it, shrugged his Work was funded by BAe on laser bending and shoulders as if to say “these barmy academics”, carried out by Jonathan Magee, (now working The laser welding story and came back with a look of awe having tested for Coherent). Zhu Liu, married to Lin Li, joined In 1974 research began on the laser welding it and seen that the hardness had more than the group working on laser cladding and surface of mild steel and titanium which included doubled on the stripe he had made. This was alloying and now both are at Manchester how he entered the fascinating world of scientific University. Janet Folkes also worked on surface research. alloying, she worked for Nissan in Japan and then Nottingham University until her untimely Laser surface cladding death in 2012. Cladding or alloying was originally carried out by preplacing the powder, usually sticking it down with alcohol – glue tended to curl up and take Contact: Bill Steen the powder away from the beam. John Powell [email protected]

William Steen was at the forefront of research into laser materials processing for over 40 years. He has over 280 scientific publications in peer-reviewed journals Geoff Shannon ca.1996, now Manager, Advanced and international conferences and 15 patents. Technology at Amada Miyachi America. 27 ISSUE 87 WINTER 2018 THE LASER USER OBSERVATIONS

FLUID AND PARTICLE LASER WELDING PLASTICS LASER ABLATION: LAYER DYNAMICS IN LASER – A SHORT GUIDE REMOVAL AND SURFACE POWDER BED FUSION Ian Jones TREATMENTS

Ioannis Bitharas et al. The article by Ian Jones is very well written and David Van De Wall Good to see a second paper on this topic extremely informative in relation to the different David has provided us with a useful white by Heriot-Watt University and the University types of laser, and the laser-welding techniques paper on the types of laser ablation and of Birmingham. This paper highlights the used for plastics. It also delivers a clear and marking applications found in medical device importance of finding a good process parameter concise understanding of the science behind the manufacture. The classic application over the to minimise the denudation effect. The high- process. last twenty years has been laser stripping marker speed images of single tracks backed up this From a production perspective however, many bands on guidewire and hypotube over-jackets suggestion as the direction of plume changed plastic parts will have been manufactured by made from PTFE coatings, using q-switched and created a different denudation pattern for injection moulding. These components can lasers at 1064 nm. As David points out selective different process parameters. I am happy to see become slightly distorted during the post roughening of areas of the underlying bare metal that this work was extended to multiple tracks moulding cooling process or through improper for gluing can also be performed, and with the and for multiple layers, as single line scans do handling prior to welding. It is essential therefore, same laser tool. not fully represent conditions of all real-time that variations with the manufacturing processes These devices are used in delivery systems for applications. however slight, are understood by both the stenting blocked arteries. Many of us will know product designer and the supplier of the laser Ravi Aswathanarayanaswamy, Renishaw someone that has had heart stents placed and welding system. carried on an active lifestyle after this minimally Joint design, specifically in relation to the invasive procedure. Laser technology plays a positioning and dimensions of any joint melt/ major role in the entire manufacture of these collapse area, requires careful consideration devices from the delivery system that deploys STUDY ON POWDER to ensure that this remains consistent. Other the stent, to the stent itself with processes in key factors are the design of the component cutting, welding, marking and ablation of both BLOWN LASER CLADDING fixtures and the clamping pressure to be polymer and metal components. As David OF VERTICAL SURFACES applied during welding. Too little pressure may remarks the demands on laser wire stripping processes are steadily increasing due to Piotr Lubaszka & Bernd Baufeld result in no fusion between the parts, and too much pressure could cause the weld joint miniaturisation. Components such as the tiny This is an interesting article which tackles the above to collapse prior to the welding process electrodes used for brain stimulation and control general assumption that laser cladding cannot commencing. Dissimilar materials may heat up at in diseases like Parkinsons and Benign Essential be used in configurations requiring significant different rates, causing distortion during welding. Tremor require laser ablation often with ultrashort deviations from the downhand position (1G pulsed lasers. It is great that our industry enables ASME/PA ISO 6947). While it is true that laser Andy Toms, TLM Laser so many of these lifesaving and transforming cladding process parameters developed for activities. cladding in the downhand positon cannot be Jonathan Magee, Coherent | Rofin simply transferred to other orientations, due to the effect of gravity on the powder stream and LASER SHOCK PEENING OF melt pool, this does not mean that appropriate parameter sets cannot be developed for such METALS AND ADVANCED configurations. The authors have very clearly CERAMICS LASERS FOR demonstrated not only the ability to develop KPV Pratik Shukla MANUFACTURING combinations which produce claddings in the horizontal (2G ASME/PC ISO 6947) position, but As a manufacturer of high-energy nanosecond ZONE that the parameters can be refined to ensure lasers, Litron has watched the Laser Shock that the resultant microstructure is comparable Peening application develop with interest. For to that obtained by conventional cladding in the a number of years, we have been supplying downhand position. custom built lasers for LSP to increase the life of components within nuclear reactors, where This is a very positive step in addressing what is this application has been field-proven and commonly seen as one of the limitations of the successful. laser cladding process. It would be interesting to see more work like this applied for use with In recent times we have seen a sharp increase mobile laser cladding equipment which can in the research into and applications of this then be used for the performance of repairs to technique for other industrial processes in other components ‘in