Controlled shot www.cwst.co.uk

COMPANY PROFILE Why does controlled shot Curtiss-Wright Surface Technologies (CWST) offers a single source solution and point of contact for all your surface peening extend part life? treatments. We can reduce your turnaround times and costs through our Critical component failure can very often be traced network of over 75 worldwide facilities. back to residual tensile stresses that are introduced Our proven surface treatments meet during the manufacturing process. Processes such as industry demands for lighter materials, welding, laser cutting and electric discharge as well improved performance and life extension in key markets such as Aerospace, as milling, turning, drilling and grinding can produce Automotive, Energy and Medical. We can residual tensile stresses which will reduce prevent premature failures due to fatigue, corrosion, wear, galling and fretting. strength and shorten a component’s life.

With the application of controlled shot is a process peening to the surface of a component that involves creating an indentation on the any residual tensile stresses are converted surface of a component to a technically to compressive stresses which have been defined specification using small high quality proven to prevent typical failure modes such spherical media called shot. as metal fatigue, corrosion fatigue, corrosion cracking, intergranular corrosion, The surface yields but it is restrained fretting, galling and wear. by the substrate, with the result that a residual compressive stress is introduced Controlled shot peening has long been which makes the surface resistant to associated with engineered crack initiation and propagation. The shot of metals including steels, stainless steels, media can be steel, stainless steel, glass aluminium, titanium and copper alloys. It or ceramic beads and controlling the forms an essential part of the manufacturing size, intensity and coverage will result in process used within the engineering industry a residual compressively stressed layer of Surface Technologies is a Division of to improve wear and corrosion resistance uniform magnitude and depth. Curtiss-Wright (NYSE:CW) a global and prevent premature fatigue failures. innovative company that delivers highly Impact at high speed creates a dimple engineered, critical function products and Shot peening – what is it and how Dimple services to the commercial, industrial, does it work? defense and energy markets. Building on the heritage of Glenn Curtiss and the Shot peening is a highly cost effective Wright brothers, Curtiss-Wright has a long treatment which can be performed on tradition of providing reliable solutions components of any shape and size and stretched surface through trusted customer relationships. can even be done on site, which when combined with the reduced maintenance costs achieved by extended part life, you COMPRESSION can clearly see why leading manufacturers specifically include this process in their

specifications. Shot peening process For more information on all our services and full worldwide contact details: www.cwst.co.uk For more information on all our services and full worldwide contact details: www.cwst.co.uk Controlled Shot Peening www.cwst.co.uk

Process specification criteria

To ensure the shot peening process meets Tension 0 Compression all its requirements certain criteria has to be considered and these are: Stress from applied load from shot peening PARAMETER SELECTION Resultant stress

The choice of shot peening parameters is dependent on:

l knowledge of the application of the Shot peening influence on applied stress component – algebraic reductions l component geometry l manufacturing method impact, although the thickness of the How did the shot peening process l mechanical properties of the base section is also a factor. A deeper layer begin? material is generally desired for optimum crack growth resistance and protection again Hammering or cold hammering stresses l strain sensitivity of the base material severe environmental conditions. a material through force beyond its yield l operating environment strength, so allowing it to be shaped l service conditions, loads and cycles SURFACE STRESS and hardened. The earliest example of l cost sensitivity this process can be traced back to a This magnitude is usually less than the l gold helmet circa 2700 B.C. The helmet turnaround time maximum compressive stress, which is featured the trademark dimpling effect subsurface but can be tailored to suit the that is induced by hammering an object application. into shape. The process was widely used CONTROLLING THE PROCESS to shape and harden armour during the crusades (1100-1400 A.D.). To ensure accuracy, reliability and repeatability the variable parameters of the The process remained relatively shot peening process have to be carefully unchanged until the industrial revolution controlled. when there were many experiments on the manipulation of metals, usually termed as Controlled shot peening is different from “cold rolling” which essentially replaced most manufacturing processes in that cold hammering and through trial and there is no non-destructive method to error this brought about improvements in confirm that it has been performed to the surface hardness and fatigue life. proper specification. Techniques such as x-ray diffraction require the part be During the 1920’s the benefits of sacrificed to generate a full compressive mechanical pre-stressing had become depth profile analysis. more understood and A C Sampietro, a renowned automotive engineer, was However, to ensure peening specifications reputed to have said that fillets of are being met for production batches, crankshafts in European race cars were the following process controls must be hand peened to improve fatigue life. maintained: media intensity, coverage, shot direction and repetition. After much research the question of when and how the process of shot peening We have developed robotic and was formally discovered appears to have DEPTH OF COMPRESSIVE LAYER specialised mechanical equipment that been between 1927 and 1929, with the ensures that the motion of the component automotive industry taking a further lead by This represents the depth of material that is resistant to crack initiation and to shot flow is consistent – hence the term introducing it into their specification for the controlled shot peening. manufacture of the Cadillac Valve springs propagation. This layer is controlled by in December 1929. predetermining the energy of the peening

For more information on all our services and full worldwide contact details: www.cwst.co.uk MEDIA CONTROL COVERAGE CONTROL substrate surface of the part to correct the distortion and in the process replace any Controlling the shape and size of the Complete coverage of a shot peened tensile stresses with beneficial compressive shot will result in a residual compressively surface is crucial in performing high quality stresses. stressed layer on the surface of uniform shot peening. Coverage is the measure magnitude and depth: of original surface area that has been covered by the shot peening indentations. C.A.S.E.™ super finishing Coverage should never be less than 100% This technique is combined with controlled as fatigue and stress corrosion cracks can shot peening and is particularly suited to develop in any non-peened area that is not gears and results in a mirror like finish on encased in residual compressive stress. the component’s surface for resistance Some strain sensitive materials perform to crack initiation and propagation, whilst better with levels of coverage in excess of retaining the natural valleys for lubricant 100%. retention to reduce operating temperatures and friction and to improve overall life and Shot peen forming performance. This process is particularly suited to gears and transmission The process of controlled shot peening components and any situation which can also used to create a change in Poor shot shape and size will result in an involves metal to metal contact. the shape of a component, for example irregular residual stress profile, excessive to create the aerodynamic contours of surface disruption and potential stress aircraft wing skins where within the elastic Surface texturing/Peentex raisers. range of the material gentle curves are Controlled shot peening can be used to formed to consistent tolerances. Parts that create a range of surface textures from a have been peen formed have increased non-slip textured finish for handgrips on resistance to flexural bending fatigue and tooling to a mirror like finish for decorative even if the material is peened on one purposes and on various surfaces such as side only, the process causes both sides metals, glass and acrylic. to have compressive stresses which has been proven to inhibit stress corrosion For high traffic areas and internal cladding cracking and improve fatigue strength. and railings, surface texturing will diffuse direct light and glare thus disguising Correction of distortion fingerprints and mild blemishes. The finish is also non-directional so ideally suited for Controlled shot peening can also be used jointed and welded frames and structures INTENSITY CONTROL to correct distortion typically caused by disguising unsightly weld beads giving a manufacturing processes such as casting, more uniform appearance. In addition Shot peening intensity is the measure of rolling, forging and heat treatment which textured finishing can provide substantial the energy of the shot stream. It is one of can also dramatically alter the stress resistance to wear, scratching, written the essential means of ensuring process pattern of the final machined part making it graffiti and stickers as well as making repeatability. The energy of the shot stream vulnerable to stress corrosion cracking and cleaning easier so ideal for architectural is directly related to the compressive fatigue. With the application of controlled applications. stress that is imparted into a component. shot peening it is possible to stretch the Intensity can be increased by using larger media and/or increasing the velocity of the shot stream.

Other variables to consider are the impingement angle and peening media. Intensity is measured using Almen test strips and must be conducted initially during set up and repeated at approved intervals.

For more information on all our services and full worldwide contact details: www.cwst.co.uk Surface Technologies www.cwst.co.uk

Why should you choose Curtiss-Wright Proud history of experience and Surface Technologies (CWST) to deliver innovation dating back to the Wright your surface treatments: Brothers and Glen Curtiss who formed the Curtiss-Wright Corporation in 1929 A worldwide supported network service of over 75 facilities, including on site field As a single source for all your surface crews treatments we can improve your turnaround times and save you money We offer a diverse range of quality surface treatments including: Customer’s trust us to improve the performance, strength and life of their l Controlled shot peening components, including the repair and l Shot peen forming overhaul of worn components l Long experience in protecting components from fatigue, corrosion, l Engineered coatings wear, galling, fretting and environmental attack in key industries l C.A.S.E.™ super finishing We maintain all appropriate customer l Surface texturing and industry quality approvals including l Material testing ISO 9001, NADCAP, AS9100 and ISO 13485 l Repair and overhaul The Dublin Spire – a stunning example of our Tailoring our services to meet your needs surface texturing technique showing the versatility of controlled shot peening

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Metal Improvement Company Metal Improvement Company Curtiss-Wright Corporation Curtiss-Wright Curtiss-Wright 13925 Ballantyne Corporate Place Hambridge Lane, Newbury 80 Route 4 East, Suite 310 Suite 400, Charlotte, NC 28277 Berkshire RG14 5TU, UK Paramus, New Jersey 07652, USA l T: +1 (973) 541 3700 l T: +44 (0)1635 279621 l T: +1 (201) 843 7800 l F: +1 (973) 541 3699 l E: [email protected] l E: [email protected] l W: www.curtisswright.com l W: www.cwst.co.uk l W: www.cwst.com

For more information on all our services and full worldwide contact details: www.cwst.co.uk