Master Thesis Master's Programme in Mechanical Engineering, 60 Credits

Design and Fabrication of Moulds using Additive Manufacturing for producing Silicone Rubber Products

Thesis in Mechanical Engineering, 15 credits

Halmstad 2020-05-29 Shreyas Kantharaju, Jobin Varghese HALMSTAD UNIVERSITY PREFACE

Industries all around the world is looking forward to reducing their investments in design, production and manufacturing processes. They are implementing new technologies to their business for improving performance and productivity. Additive manufacturing is one among those booming technologies which opens new revolutionary methods in the field of manufacturing. It enables to produce complex shaped objects in a less costly and time-consuming ways, it also allows designers to directly test their designs by prototyping and make any design changes if required to improve or optimize the designs. Along with low production cost and less production time the other factors like the product functionality and other properties like strength, surface quality etc., becomes important.

This thesis is a part of an on-going project of DiSAM – Digitalization of supply chain in Swedish Additive Manufacturing in collaboration with Halmstad University and Unimer Plast & Gummi AB. The aim of this project is to implement Additive manufacturing technology into the supply chain industry. In this thesis we mainly focus on design and fabrication of a simple and a complex mould geometry for producing Silicone Rubber products using Additive Manufacturing and to test the quality of the product obtained in terms of surface topography. In addition, post- processing methods are implemented to enhance the quality of the moulded silicone rubber products and compared to the reference injection moulding parts.

Abstract

Now a days. additive Manufacturing is becoming a major part of the manufacturing industries all around the world. Even, it is still a developing field. Its main advantage is its ability to print different types of shapes, in different sizes and good quality. The additive manufacturing technologies is capable of bring down the costs of the manufacturing when compared to other traditional methods of manufacturing. This technology gives the flexibility to making complex shapes according to the clients and customers requirements also this technology can reduce time and human effort/involvement needed in the manufacturing industries. Now 3D printing has more influence in Swedish market more than ever and this thesis is a part of a project of DiSAM – Digitalization of supply chain in Swedish Additive Manufacturing to implement 3D Printing into Swedish market. This thesis describe how advance materials and new manufacturing technologies can play a very important role in building the future and from this study we are trying to find out whether the additive manufacturing technology can replace the traditional manufacturing process like injection molding. The main aim of the thesis is to design and fabricate a simple mould geometry for producing Silicone Rubber products using additive manufacturing and to assess the quality of the obtained product in terms of surface topography, dimensional accuracy and mechanical properties. Our project partner Unimer Plast & Gummi AB who is a major producer of plastics and rubber products is facing a problem in the production of silicone rubber products. They want to produce a mould for producing silicone rubber products using additive manufacturing. In this thesis we had made the study in two parts, a design part and an analysis part. In the design part we sorted out one material which is suitable for our application that is to produce a mould for making silicone products while in analysis part we made a study about the surface topology and its quality to see whether 3D printed moulds could produce silicone rubber products with same or better surface quality than the one which are produced using conventional injection moulding process. As a result of our study we came to know that high temperature resin can be used for making moulds to produce silicone products and only factor affecting the quality of the surface of mould or silicone product is built orientation and other factors like layer thickness, curing temperature and time does not have any impact on the surface quality.

ACKNOWLEDGEMENT

This thesis is a part of a major project developed by DiSAM for implementing additive manufacturing in Swedish supply chain. We were able to achieve satisfying results from this research. We take this opportunity to thank who all have become a part and helped us to achieve and complete this project. First and foremost, we like to thank God Almighty in helping us in completing this project. We express our sincere gratitude to our Prof. Bengt-Göran Rosén, Department of Mechanical Engineering, Halmstad University, Sweden for his help, generous guidance and support. We express our heartful gratitude to our Supervisor Mr. Amogh Vedantha Krishna, Department of Mechanical Engineering, Halmstad University for being with us in every step, continuous guidance and moral support. We also express our thanks to Mr. Stefan Rosén, Toponova AB, for his help and guidance for taking measurements using GFM MikroCAD and Interferometer instruments. We also express our thanks to FabLab crew, Halmstad University namely Martin Bergman, Joakim Wahlberg, Tim Malmgren and Andre Stadelmann for their help, guidance and support

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LIST OF CONTENTS

PREFACE i ABSTRACT ii ACKNOWLEDGEMENT iii LIST OF FIGURES vi LIST OF TABLES viii LIST OF GRAPHS xi

1. INTRODUCTION 1 1.1 BACKGROUND 1 1.1.1 REPRESENTATION OF OUR CLIENT 2 1.2 AIM OF THE STUDY 3 1.2.1 PROBLEM IDENTIFICATION 3 1.3 LIMITATIONS 3 1.4 STUDY ENVIRONMENT 4 2. THEORY 5 2.1 ADDITIVE MANUFACTURING 5 2.2 SILICONE RUBBER 10 2.3 DESIGN OF EXPERIMENTS 11 2.4 SURFACE MEASUREMENTS 12 2.5 DATA ANALYSIS 19 3. METHOD 21 3.1 RESEARCH METHODOLOGY 21 3.2 ALTERNATIVE METHODS 21 3.3 CHOOSEN METHODOLOGY 22 3.4 DATA COLLECTION 31 4. RESULTS AND DISCUSSIONS 33 4.1 PHASE 1 33

4.2 PHASE 2 54 5. CONCLUSION AND FUTURE ACTIVITIES 57 5.1 CONCLUSION FROM OUR RESEARCH 57 5.2 FUTURE RESEARCH ACTIVITIES 57 6. CRITICAL REVIEW 58

REFERENCE 59 APPENDIX 62

LIST OF FIGURES

Figure 1: Classification of Additive Manufacturing 5 Figure 2: FDM Printer Principle 6 Figure 3: FDM Printing Process 7 Figure 4: SLA Printer Working Principle 8 Figure 5: SLA Printer Process 9 Figure 6: GFM MikroCAD Instrument 13 Figure 7: Average Roughness and Root Mean Square Roughness 16 Figure 8: Abbott Curve 16 Figure 9: Material Ratio Curve from MountainsMap 17 Figure 10: Str and Sal Surface Parameters 17 Figure 11: Texture Direction 18 Figure 12: Root Mean Square gradient (Sdq) (Sa = 80 nm, Sdq=11.0 deg). 18 Figure 13: PEEK Printer and the Filament 21 Figure 14: PEEK Printed moulds 21 Figure 15: Methodology Chart 22 Figure 16: Step wise procedure to capture images in GFM MikroCAD 26 Figure 17: Mountains Map software Logo 27 Figure 18: History of Operation Chart for flat surface 28 Figure 19: History of Operation Chart for curved surface 28 Figure 20: Data Analysis Process Flow Chart 29 Figure 21: Part 1 – Identification of significant parameters 30 Figure 22: Part 2 – Identification of significant influence of independent variable on significant parameter 30 Figure 23: Trail testing of silicone sample 33 Figure 24: Silicone Rubber tested at different temperatures according to the table 1 34 Figure 25: PLA and ABS Mould 36 Figure 26: Silicone sample from PLA mould 36 Figure 27: Basic design of the mould in PEEK 36 Figure 28: Silicone sample obtained from PEEK 36 Figure 29: Actual Design of the mould in PEEK with 30*13 mm 37 Figure 30: Silicone samples obtained by using PEEK mould 37 Figure 31: Design 1 Mould printed in HT 39 Figure 32: Silicone Sample from HT 39 Figure 33: Mould break after testing 39 Figure 34: Design 2 Mould 40 Figure 35: Silicone sample D2 -1 41 Figure 36: Silicone sample D2 -2 41 Figure 37: Design 3 Mould 41 Figure 38: Silicone sample of D3 42

Figure 39: Design 4 Mould-CAD Images 43 Figure 40: Design 4 actual printed mould 43 Figure 41: Silicone sample of D4 43 Figure 42: Silicone samples obtained using Taguchi Experimentation 44 Figure 43: Reference Silicone Sample 45 Figure 44: Solid Block Design 54 Figure 45: 4-Part Mould Design 55 Figure 46: Sample obtained using 4-Part Mould Design 55 Figure 47: CAD Model of Complex shape silicone sample 56 Figure 48: Sustainability 58 Figure 49: Other silicone samples used for testing and observations with different time and time 59 Figure 50: 3D Printed Tool used to shape silicone rubber 60 Figure 51: Other Mould Design (PLA) 60 Figure 52: Other version of design 4 61 Figure 53: Basic Mould Design (PLA) 61 Figure 54: Design 4 mould under pressure 61 Figure 55: SLA Printed Mould Part (90 Build Inclination) 62

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LIST OF TABLES

Table 1: Surface Parameters Table 14 Table 2: Outline to capture the observations of Silicone Samples 24 Table 3: Taguchi Orthogonal Experimental Design 25 Table 4: Observations from testing silicone rubber without mould 34 Table 5: Observation from the testing of different moulds 38 Table 6: Observation Table on Tested Silicone Samples 44 Table 7: Observation of Silicone Rubber using Taguchi Experimentation 45 Table 8: Comparison in 3D images build inclination of silicone samples at 0 and 90 47 Table 9: Regression Analysis Statistics 48 Table 10: Significant Parameters Table 49 Table 11: Most Significant Parameters obtained using Correlation Analysis 50 Table 12: Taguchi Experiments with Coatings 62 Table 13: Taguchi Experiments without Coatings 62

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LIST OF GRAPHS

Graph 1: Average Roughness Graph 51 Graph 2: Void Volume Graph 52 Graph 3: Core Roughness Depth Graph 53 Graph 4: Density of Peaks Graph 53

1. INTRODUCTION

Manufacturing is a process in which the conversion of raw materials into a finished product. There are 2 types of the manufacturing process which are traditional methods and advance methods. Both methods are involved in the todays industries. Traditional methods are good for mass production, fast and convenient operations. But in some cases, the traditional methods lack quality in dimension, in surface finish etc. In case of advance methods, they are not efficient in mass production but excellent for high quality products in small scale. In traditional methods, the heavy machines are required to machine the products and requires different machines for different operations. This will increase the need of work force, cost and other resources. Also, traditional methods have limitations like for producing complex shape because of the number of the processes involved and skills required. In case of advance methods like additive manufacturing, there is no limitations of shape that is manufacturing of complex shapes are easy and simple and no requirement of multiple machines to produce an end use product. [1,3] Compared to traditional methods (injection moulding, casting, machining etc), additive manufacturing generates less waste and no polluting fumes and chemicals during its operation. Also, it can be used to produce the products with high quality and surface finish and are best suit for customization of product. Even though AM manufacturing has many advantages, it also has some disadvantages like special materials like Photopolymerization Resins used in stereolithography printers are carcinogenic in uncured form and post processing are required after printing. In this thesis, special materials High Temperature Vulcanized silicone rubber (HTV) is considered, 3D printing with this material is still in the stage of development because of its high viscosity of the material and high curing temperature. So, this research shows an alternative method to manufacture silicone rubber products using 3d printed moulds using photo polymerization high temperature resin. [4,5,6]

1.1 BACKGROUND This thesis is mainly focused on the design and fabrication of a mould geometry for producing Silicone Rubber products using additive manufacturing, which can give the product quality same as the one’s produced using conventional methods like injection moulding. This thesis comes under project from DiSAM - Digitalization of Supply Chain in Swedish Additive Manufacturing where the focus is on implementation of Additive Manufacturing (AM) technology into the supply chain of the industry, which is funded by Vinnova and KK - stiftelsen – Swedish knowledge foundation.

This thesis is a part of the three phases project. The first phase involves in identifying an alternative material for silicone rubber, that is comparatively easier

1 to 3D print and at the same time fulfilling the mechanical properties. So, in first phase priority is given for identifying an alternative material to replace silicone rubber which is compatible with 3D printers and shows mechanical properties like silicone rubber.

The second phase involves in design and fabrication of moulds using Additive manufacturing. As explained in the above paragraph silicone rubber is difficult to 3D print so, in this phase the project intends to develop a mould using additive manufacturing in order to reduce the massive costs of redesign and alteration of moulds for producing prototype or pilot batches.

Third phase involves in the development of AM systems for printing silicone rubber. This is totally a different thought, where the intention is to develop a new branch in the additive manufacturing technology that is to develop a method to 3D print silicone directly without using a mould.

In this thesis the focus is on second phase that is to design and fabrication of moulds using Additive manufacturing. The research is conducted in two phases. In the first phase the main interest is to design and fabricate a simple mould and to create a silicone rubber samples using the mould to study about its surface quality. In the second phase, a complex mould is designed and fabricated to create the silicone rubber samples using the mould. Due to the short time limit we have kept the study on dimensional accuracy and mechanical properties of the mould and silicone sample for the future.

1.1.1 REPRESENTATION OF OUR CLIENTS Unimer Plast & Gummi AB is a market-oriented and competency-driven company in the industrial sales of hoses, plastics and silicone rubber products. The head office is in Halmstad and sales companies with logistics and production centres are in Suzhou, Jiangsu, China and Minneapolis, USA. Unimer was founded in 1974 by Olle Olsson and half-owner Lennart Jönsson. In the beginning, they produced rubber tensioner with patented fastening strap. Several variants of rubber tensioner were then developed for elastic clamping of truck hoods. Flexible tubing and punching of foam plastic details were other important products. Now Unimer has a turnover of approximately SEK 100 million and has nearly 40 employees on three continents with over 1500 active customers This thesis is a part of an ongoing project in collaboration with Halmstad University and Unimer Plast & Gummi AB. The company follows strict quality requirements and provides reliable products to customers at competitive rates.

1.2 AIM OF THE STUDY This research focuses towards design and development of 3D printed moulds to produce silicone rubber (unknown grade) products. The design of moulds should be stable and stiff to withstand high temperature and pressure due to thermal expansion of silicone rubber for prolonged time. This study is carried out for the purpose of implementation of additive manufacturing in Swedish supply chain management. This research has important areas such as: • To know the behaviour of silicone rubber when it is subjected to heat. • Design and development of 3d printed moulds to test silicone to obtain required shape • Measurement of obtained silicone samples will be done by using surface measurement instruments and 3d images of same will be obtained • Implementation of design of experiments (DOE) to select which sample data is best match with the reference (Injection Mould) data.

1.2.1 PROBLEM IDENTIFICATION Unimer Plast & Gummi AB is producing certain component made of Silicone Rubber material using injection moulding process for the purpose of mass production. The need of this project arised when the company realised the expense to invest in new or redesign of moulds, usage of labour, usage of available resources to make the mould is too high. Hence, the company is looking to implement Additive Manufacturing into their supply chain for fabricating pilot and customized orders. 3D printing of silicone rubber products is very difficult because of many reasons. So, this project intends to overcome those challenges and difficulties related to 3D printing and to obtain the results required by the company.

1.3 LIMITATIONS This research is divided into 2 phases which are designing for simple and complex shapes. Firstly, the indentation is to design the simple moulds and make silicone samples by using the moulds. The surface measurements and data analysis are made on the simple shape silicone samples. Since, this research is a very much time consuming. The time consumed in printing the moulds, time consuming in curing the silicone samples are the major one. Due to the time shortage, we have obtained the results with the phase 1 simple design only. The same procedure and the results of phase 1 may be applicable on the complex design shape in phase 2.

1.4 STUDY ENVIRONMENT All the work related to this research is conducted in Halmstad University. Facilities of FABLAB to produce 3D printed mould and tests the silicone using lab oven. The moulds were, printed using stereolithography (SLA) and Fused Deposition Modelling (FDM) printers which are available in the lab. Library to access for the research papers and articles. Rydberg Laboratory to Applied Science (RLAS) and Toponova AB Company to make the surface measurements. Worked in computer lab to design and develop the moulds by using Catia V5 CAD designing software and with Mountains Map for analysis of surfaces images.

2. THEORY In this section a detailed literature review is presented on various topics related to the thesis such as additive manufacturing, mould design, silicone rubber, testing of materials, surface measurements, surface and data analysis.

2.1 ADDITIVE MANUFACTURING Additive manufacturing (AM) is fast growing technology and were widely accepted in sectors of manufacturing all over the world. It is also known as additive fabrication, 3D printing, direct part manufacturing, layered manufacturing, and freeform fabrication. According to international standard ISO/ASTM 52900, AM is defined as a “process of joining materials to make parts from 3D model data, usually layer upon layer” [3]. It is also defined as the process of joining materials to make objects from three- dimensional (3D) model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies such as machining. [2] This technique was developed and used in research and development for prototyping and, but it is now used in industries for producing end-use parts because of its cost and time efficiency and is becoming an alternative to conventional manufacturing processes, like moulding, machining, etc.

CLASSIFICATION OF ADDITIVE MANUFACTURING

Figure 1: Classification of Additive Manufacturing [4]

Additive manufacturing process is mainly classified into three, liquid based, solid based and powder-based processes.

Solid-based AM processes: In this AM technologies the input raw material is in solid state. Among so many existing solid-based AM technologies, fused deposition modelling (FDM), freeze- form extrusion fabrication (FEF), laminated object manufacturing (LOM), and direct ink writing (DIW) are the most popular. [4]

Liquid based AM processes: In liquid-based AM technologies, mostly photocurable polymer resins are used as the input raw material. The common types of liquid-based AM technologies in use are stereolithography (SLA), multi-jet modelling (MJM), rapid freeze prototyping (RFP), and digital light processing (DLP) are the most prominent. Parts produced using this process shows good surface quality a dimensional accuracy. [4]

Powder based AM processes: In powder-based AM technologies, powder state raw materials are used as the input. Common powder-based AM technologies are, three-dimensional printing (3DP), electron beam melting (EBM), SLS, selective laser melting (SLM), laser engineered net shaping (LENS), and pro metal and laser metal deposition (LMD). [4]

Fused Deposition Modelling (FDM): It is a cheaper 3D printing technique based on the principle of layered manufacturing technology mainly developed for the additively manufacturing of polymer materials. During the manufacturing process, the plastic raw materials (filamentous polymer) is first melted in the printing nozzle at a temperature slightly higher than the melting point of the printing polymer and extruded through the nozzle, then deposited onto the printer hot bed layer by layer. The nozzle head and printer bed move according to the tool path, which is generated for each layer under the control of computer. [4]

Figure 2: FDM Printer Principle [22]

FDM Printing Process: To print using FDM printer we need to follow some steps and these steps may change according to different FDM printers. But in general to print with a FDM printer first we will import the digital file of the object into the slicing software usually in STL file format, then we will adjust the print settings like selecting the material to print the object, moving and orienting the object on print platform, resizing if required, adding supports, setting infill, raft and brim, etc.

Figure 3: FDM Printing Process After setting the print settings we will slice the 3D object in the software that is converting the 3D object model to specific instructions for the printer and will be saved as a graphics file. Then this will be uploaded to the 3D printer for printing.

Common materials used in FDM: PLA – PLA is Polylactic Acid, one of the most popular materials used in 3D printing. PLA is renewable and most importantly biodegradable because it is made from organic materials, namely corn-starch and sugarcane. It is safer and easier to use, and with no toxic fumes and is easy to print, very inexpensive, and creates parts that can be used for a wide variety of applications. PLA print temperature range: 180°C – 230°C. [21] ABS - Acrylonitrile Butadiene Styrene (ABS) is an opaque thermoplastic and amorphous polymer, it can be easily recycled, ABS have a strong resistance to

7 corrosive chemicals and/or physical impacts, tough, and has impact-resistant properties. ABS is a great choice for printing plastic automotive parts, moving parts, musical instruments, kitchen appliances, electronic housings, and various toys. ABS print temperature range: 210°C – 250°C. [21]

Stereolithography Apparatus (SLA): In SLA process a liquid photopolymer resin is used print the part or product in a layer-by-layer fashion on a platform. UV laser is used to cure or solidify the liquid resin. The fabrication of part or product in SLA technologies requires supporting structures to attach the part or product on the building platform and hold the object as it floats in the liquid resin and the support structures are fabricated using the same material as that of the actual part. After printing the product is removed from the platform and post cured for some time in a UV chamber.[4]

Figure 4: SLA Printer Working Principle [10]

SLA Printing Process:

Figure 5: SLA Printer Process Printing procedure for SLA is also like FDM printing and print procedures varies depending on printers. Here also we need a digital file of the objected needed to be printed and this file will be loaded to the slicing software. The we will make some adjustments to the print settings like selecting the printer, print material, setting the layer thickness, adjusting the shape and size of the object, orienting the object on the platform, adding supports and rafts etc. some slicing software’s will be having options to apply the auto settings. After applying the settings, the object will be sliced and will be read for uploading to the printer to start printing.

Common materials(resins) used in SLA1: Grey Pro Resin - It gives high precision, high resistant to deformation, moderate elongation, and low creep. This material is great for concept modelling and prototyping. High Temperature Resin - This resin has a high deflection temperature which is the ability to withstand high temperature without deforming under specific pressure.

1 Formlabs, https://formlabs.com/eu/materials/engineering/#high-temp-resin

The heat deflection temperature for this resin is 120°C for 0.45MPa or 238°C on additional thermal curing.

2.2 SILICONE RUBBER

Silicone rubber is a high-performance elastomer composed of silicone (polymer) containing silicon together with other molecule like carbon, hydrogen and oxygen. It has high commercial importance because of its properties like durability, thermal resistance at high and low temperatures ranging from -50°C to 350°C, weatherability - when exposed to wind, rain and UV rays for long periods result in virtually no change in physical properties, high gas permeability, low surface energy, electrical insulation, transparency and proven biocompatibility and has applications in many fields like engineering, manufacturing, biomedical, aerospace, automobile etc. Silicone rubbers are used to make products like sealants, cooking utensils, thermal and electrical insulation etc. [5,6]

Silicone rubber is available in three main forms: [5,6]

• Solid Silicone Rubber or High Temperature Vulcanized, HTV - Solid silicone rubber contains polymers with a high molecular weight and relatively long polymer chains. They are higher viscosity rubbers that are mixed and processed like other elastomers and are available in uncured form and required traditional rubber processing techniques. They are cured at elevated temperature, either by means of chemical method using organic peroxides or with platinum catalyst or by conventional thermal oven curing methods. In this thesis we are using this Solid Silicone Rubber or High Temperature Vulcanized for testing.

• Liquid Silicone Rubber, LSR - contains polymers of lower molecular weight and hence shorter chains. It has better flow properties. It is processed on specially designed injection moulding and extrusion equipment. • Room Temperature Vulcanized, RTV – RTV silicone rubber is a type of silicone rubber made from one-part (RTV-1) or two-component (RTV-2) systems where their hardness range of very soft to medium. They are available for potting, encapsulations, sealants etc. [5]

Applications of Silicone Rubber: [5] Some of the common applications of silicone rubber are:

• Construction & Restoration - Due to its adhesive properties, it can be used to bind together important building materials, such as concrete, plastics, glass, metal, and granite

• Electronics – Used to seal the inner circuits and processors of most electronic gadgets, protecting them from heat, corrosion, moisture and other conditions that can cause wear and tear

• Aviation - Silicone adhesives are used to seal crucial parts of planes like doors, windows, fuel tanks, vent ducts etc.

• Healthcare - Used for making prosthetics, infant care products and other medical articles that must match safety standards.

• Domestic Uses - Non-stick, sturdy and durable cookware is manufactured using a silicone coating

• Paints and Adhesives – Due to its adhesive and pigmentation qualities, silicone greatly enhances the quality of paints and sealants. It also provides better resistance against weather changes and most kinds of stains.

2.3 DESIGN OF EXPERIMENTS: DOE refers to the process of planning, designing and analysing the experiment so that valid and objective conclusions can be drawn effectively and efficiently. In order to draw statistically sound conclusions from the experiment, it is necessary to integrate simple and powerful statistical methods into the experimental design methodology (Vecchio, 1997). The success of any industrially designed experiment depends on sound planning, appropriate choice of design, statistical analysis of data and teamwork skills. [7] In our thesis we followed Taguchi method for carrying out the design of experiments. Taguchi method: The Taguchi method is used whenever the settings of interest parameters are necessary or for finding the best combinations of the control factors to make the product or process insensitive to the noise factors (Phadke, 1989; Ross, 1996). The Taguchi method is based upon the technique of matrix experiments. Taguchi method is based on mixed levels, highly fractional factorial designs and other orthogonal designs. It distinguishes between control variables and noise variables. Experimental matrices are special orthogonal arrays OAs (Phadke, 1989; Ross, 1996) which allow the concurrent effect of numerous process parameters to be

11 studied capably. The purpose of conducting an orthogonal experiment is to determine the optimum level for each parameter and to establish the comparative significance of individual factors in terms of direct effects on the response the purpose of conducting an orthogonal experiment is to determine the optimum level for each parameter and to establish the comparative significance of individual factors in terms of direct effects on the response. Taguchi suggests the S/N ratio as the objective function for matrix experiments (Phadke, 1989; Ross, 1996). The S/N ratio is used to measure the quality characteristics and the significant process parameters through analysis of variance (ANOVA). [8] It is one of the most common methods used for analysing the data. ANOVA is a statistical technique that assesses potential differences in a scale-level dependent variable by a nominal- level variable having two or more. The ANOVA is developed by Sir Ronald Fisher in 1918. It is the extended version of T test and Z test. [9] The Taguchi method is applied in many fields such as environmental sciences, agricultural sciences], physics, statistics, management and business, medicine and chemical processes [9]

Steps for implementing Taguchi experimental design:

1. Step 1. Selection of the output or target parameters. 2. Step 2. Identification of the input parameters and their levels. 3. Step 3. Determining the suitable orthogonal array (OA). 4. Step 4. Assign factors and interactions to the columns of the array. 5. Step 5. Conduct the experiments. 6. Step 6. Statistical analysis and the signal-to-noise ratio and determining the optimum setting of the factor levels. 7. Step 7. Perform confirmatory experiment (if necessary). [9]

2.4 SURFACE MEASUREMENTS: Surface measurement or Surface metrology is the measurement of the features like regular patterns, irregularities, roughness, waviness, critical dimensions, etc.) of a surface. In another view it is the measurement of small-scale features on surfaces. Surface metrology includes the measurement of surface texture and surface form errors. Surface primary form, surface fractality and surface roughness are the parameters most commonly associated the with Surface metrology. [11,12] Surface metrology methods are used to examine and measure the topography at different length scales and spatial frequencies of a surface. Roughness is typically determined by measuring the height, width and periodicity/frequency of surface patterns or irregularities. Waviness is defined by surface irregularities on a larger scale (lower frequency range) than the roughness. A uniform surface is isotropic. Lay refers to the directionality of surface features (anisotropic) which is often due to material manufacturing or treatment. [13]

Instrument used for surface measurement: The below instrument is used in capturing the images of the surface of any object for the further process. GFM MikroCAD:

Figure 6: GFM MikroCAD Instrument [19] MikroCAD is the first surface metrology system to use structured light fringe projection profilometry to generate 3D surface scans with microscopic level of detail for small volume measurement. [19] Surface metrology software – MountainsMap: Mountains is an image analysis and surface metrology software platform published by the company Digital Surf. Its core is micro-topography, the science of studying surface texture and form in 3D at the microscopic scale. The software is dedicated to profilometers, 3D light microscopes ("MountainsMap"), scanning electron microscopes ("MountainsSEM") and scanning probe microscopes ("MountainsSPIP"). [20] Surface parameters: In this thesis we considered surface parameters which comes under ISO 25178 which is an International Organisation for Standardisation collection of international standards relating to the analysis of 3D areal surface texture. ISO 25178 consist of surface parameters like Height Parameters, Functional Parameters, Spatial Parameters, Hybrid Parameters, Functional Parameters (Volume), Feature Parameters and Functional Parameters (Stratified surfaces). [23]

Table 1: Surface Parameters Table

Height Parameters Sq µm Root-mean-square height Ssk Skewness Sku Kurtosis Sp µm Maximum peak height Sv µm Maximum pit height Sz µm Maximum height Sa µm Arithmetic mean height Functional Parameters c = 1 µm under the highest Smr % Areal material ratio peak Smc µm p = 10% Inverse areal material ratio Sxp µm p = 50%, q = 97.5% Extreme peak height Spatial Parameters Sal µm s = 0.2 Autocorrelation length Str s = 0.2 Texture-aspect ratio Std ° Reference angle = 0° Texture direction Hybrid Parameters Sdq Root-mean-square gradient Developed interfacial area Sdr % ratio Functional Parameters (Volume) Vm µm³/µm² p = 10% Material volume Vv µm³/µm² p = 10% Void volume Vmp µm³/µm² p = 10% Peak material volume Vmc µm³/µm² p = 10%, q = 80% Core material volume Vvc µm³/µm² p = 10%, q = 80% Core void volume Vvv µm³/µm² p = 80% Pit void volume Feature Parameters

pruning = Spd 1/µm² Density of peaks 5% pruning = Spc 1/µm Arithmetic mean peak curvature 5% pruning = S10z µm Ten point height 5% pruning = S5p µm Five point peak height 5% pruning = S5v µm Five point pit height 5% pruning = Sda µm² Mean dale area 5% pruning = Sha µm² Mean hill area 5% pruning = Sdv µm³ Mean dale volume 5% pruning = Shv µm³ Mean hill volume 5% Functional Parameters (Stratified surfaces) Sk µm Not filtered Core roughness depth Spk µm Not filtered Reduced summit height Svk µm Not filtered Reduced valley depth Smr1 % Not filtered Upper bearing area Smr2 % Not filtered Lower bearing area

Spq Not filtered Plateau root-mean-square roughness

Svq Not filtered Valley root-mean-square roughness

Material ratio at plateau-to-valley Smq Not filtered transition

In the surface measurements 35 surface parameters are considered which belongs to families like Height Parameters, Functional Parameters, Spatial Parameters, Hybrid Parameters, Functional Parameters (Volume), Feature Parameters and Functional Parameters (Stratified surfaces).

Height(Amplitude) Parameters: Height parameters are those which describes the highest peaks and deepest valleys on a surface, and it includes Root-mean-square height, Skewness, Kurtosis, Maximum peak height, Maximum pit height, Maximum height, and Arithmetic mean height. As the name suggests, this group of parameters provides information on the amplitude features and generally used to represent overall measure of the texture comprising the surface, the degree of symmetry of the surface heights about the mean plane. Detailed explanation about this parameter is given in the book Characterization of Areal Surface Texture. [23]

Figure 7: Average Roughness and Root Mean Square Roughness

Functional Parameter (Volume): It represents an evolution of the functional indices and are defined as the functional indices and the family of Sk parameters, with respect to the Abbott curve.

Figure 8: Abbott Curve The parameters are defined with respect to two bearing ratio thresholds, set by default to 10% and 80%. Two material volume and two void volume parameters. It is used to determine the amount of bearing area remaining after a certain depth of material is removed from the surface, assure that an optimum crevice volume is produced for a sealing surface to allow for some lubricant entrapment (to prevent running dry) but not be too deep to prevent leakage.

Figure 9: Material Ratio Curve from MountainsMap The figure 45 represents the material ratio curve of the sample material. It can be clearly witnessed the regions on the top represent the peak areas, the deepest regions represent the valley and the intermediate regions represent the core areas. Detailed explanation about this parameter is given in the book Characterization of Areal Surface Texture. [23, 28] Spatial Parameters: These parameters consist of Autocorrelation length (Sal), Texture-aspect ratio (Str) and Texture direction (Std). Str is useful in determining the presence of lay in any direction, Str may be used to detect the presence of underlying surface modifications, Str may find application in detecting subtle directionality on an otherwise isotropic texture. Sal is useful in establishing the distance between multiple measurements made on the surface to adequately determine the general texture specification of the surface. Sal may find application related to the interaction of electromagnetic radiation with the surface and tribological characteristics such as friction and wear.

Figure 10: Str and Sal Surface Parameters Std is useful in determining the lay direction of a surface relative to a datum by positioning the part in the instrument in a known orientation. Std may also be used

17 to detect the presence of a preliminary surface modification process (e.g. turning) which is to be removed by a subsequent operation. Detailed explanation about this parameter is given in the book Characterization of Areal Surface Texture. [23, 28]

Figure 11: Texture Direction Feature parameters: This parameter are derived from a segmentation of the surface into motifs (dales and hills). Segmentation is carried out using a watershed method and it includes density of peaks, Arithmetic mean peak curvature, Ten point height, Five point peak height, Five point pit height, Mean dale area, Mean hill area, and Mean dale volume. Detailed explanation about this parameter is given in the Detailed explanation about this parameter is given in the book Characterization of Areal Surface Texture. [23, 28] Hybrid Parameters: These are the parameters which are having a combinational with roughness and spacing parameters. Hybrid parameters includes Root-mean-square gradient (Sdq) and developed interfacial area ratio (Sdr). Sdq is a general measurement of the slopes which comprise the surface and may be used to differentiate surfaces with similar average roughness. for a given Sa, a wider spaced texture may indicate a lower Sdq value than a surface with the same Sa but finer spaced features.

Figure 12: Root Mean Square gradient (Sdq) (Sa = 80 nm, Sdq=11.0 deg).

Sdr may further differentiate surfaces of similar amplitudes and average roughness. Sdr is useful in applications involving surface coatings and adhesion. Detailed explanation about this parameter is given in the Detailed explanation about this parameter is given in the book Characterization of Areal Surface Texture. [23,28] 2.5 DATA ANALYSIS After successfully collecting all the information and reliable data, using different techniques from different sources, next is to extract the significant and useful information from all the collected data to make certain observation or conclusion and to discuss about the findings. This process of performing certain calculations and evaluation on the collected data in order to extract relevant information from data is called data analysis. The data analysis may take several steps to reach certain conclusions. Simple data can be organized very easily, while the complex data requires proper processing. [14] The word analysis refers to a closely related operation those are performing with the purpose of summarizing the collected data and organizing in such a manner yielding answer to the questions. Analysis of data involves organizing the data in several steps in a proper way. Those steps include classification & tabulation, graphical representation, measure of location, measure of variability, measure of relationship, estimating the unknown and testing of hypothesis. In this thesis we used regression analysis tool in MS Excel for analysing the data we collected. Regression analysis: Regression analysis is a way of mathematically sorting out which of dependent and independent variables does indeed have an impact [15] In a regression analysis we study the relationship, called the regression function, between the variable, called the dependent variable, and several others, called the independent variables. Regression function also involves a set of unknown parameters. If a regression function is linear in the parameters, we term it a linear regression model. Otherwise, the model is called non-linear. Linear regression models with more than one independent variable are referred to as multiple linear models, as opposed to simple linear models with one independent variable. [16] In this study, the dependent variables are the areal surface texture parameters and the independent are the build inclination, layer thickness, curing time and temperature. The relationship between these variables can be established via regression analysis. It answers the question: which variables matters the most? Which can we ignore? How do those variables interact with each other? And, perhaps most importantly, how certain are we about all these variables?

Correlation Analysis: Correlation analysis is a statistical method used to evaluate the strength of relationship between two quantitative variables. A high correlation means that two or more variables have a strong relationship with each other, while a weak correlation means that the variables are hardly related. [18]

3. METHOD

3.1 RESEARCH METHODOLOGY In this research we study about how the silicone rubber products can be made by using advance manufacturing process like additive manufacturing (3D Printing). This research work was carried out under continuous improvement on design of moulds, quality of the silicone sample after subjected to the heat with respect to time. Later, the obtained silicone samples were undergone testing and measurement and comparison is made with the reference data and results are obtained.

3.2 ALTERNATIVE METHODS Here, this research methodology remains constant. The alternative was considered only in printing of moulds by using different technology printers. Firstly, we have considered fused deposition modelling (FDM) printers to print the mould by using Polyether Ether Ketone (PEEK) filament.

Figure 13: PEEK Printer and the Filament [24,25]

These PEEK filaments are having a glass transition temperature of 143 C, with young’s modulus of 3.6 GPa and melting point temperature of 343 C. But we have rejected printing moulds with FDM because of low surface quality prints.

Figure 14: PEEK Printed moulds

The above figure 14 shows the object/mould which are printed by using FDM printer. The image shows quality on surface of the moulds were poor. But our aim is to achieve the high-quality surface of the silicone samples. There was breakage of mould layers occurred that is the bonding between the layers of the moulds were weak and it affects the silicone sample when it is subjected to heat and time. So, we have rejected printing with the PEEK moulds. The quality of the silicone surface is directly proportional to the quality of the mould printed by using 3D printing technology.

3.3 CHOOSEN METHODOLOGY In our research, we have considered qualitative and quantitative methods to carry out the experiments, measurements and analysis. For the development of mould and to carry out the preliminary tests on silicone rubber materials quality, we have chosen qualitative approach and for detailed surface quality assessment of silicone product. we have chosen quantitative approach.

Figure 15: Methodology Chart

Our research methodology is divided into 7 steps. In the phase 1 of our research we follow these steps to achieve the results for the simple design. After we achieve results in phase 1, we will conduct the research on complex shape in the phase 2 using this same chosen methodology. The steps which are involved in our research methodology are explained below:

STEP 1: LITERATURE SURVEY AND STUDY OF THE MATERIAL (SILICONE RUBBER) Planning: Here, where we had made detailed discussions with our thesis supervisor about this topic and got a clear idea about the purpose of this topic and the problems that should be solved. In this section we must concentrate on two phases: Phase 1- Simple design; Phase 2: Complex design. We have conducted brainstorming on how to understand and solve the problem. Literature Survey: Literature survey is very important stage where we begin to understand background of the subject. We go through some book, scientific articles, research papers etc., which were available in Google scholar, Science Direct, Scopus and University Library Database and, we gathered some information about our client “Unimer Plast & Gummi AB” form their company website. We did some back-end research and studied about the silicone rubber, design of moulds, additive manufacturing, curing of silicone, 3d printing and many more. We have gathered all the data and implemented on the research which we are conducting. Testing silicone without mould: This is the preliminary step of our research. Here, are testing samples at different temperature and time to identify its behavioural change when it is subjected to heat. We made observations about formation of air bubbles in silicone rubber, deformation, stickiness and removability. We made observations about these factors based on the visual observations. We define stickiness as level of adherence of silicone sample to a surface after curing. Removability as the ease at which the samples can be removed from the oven platform. Air bubbles is an intensity of air trapped in the samples and deformation is a change in the shape of the sample after and before curing. We have prepared one table using excel to capture the observation from testing silicone samples. The below table 2 shows the outline to follow to record the observations for all other experiments on silicone samples.

Table 2: Outline to capture the observations of Silicone Samples

Process variables Observations Material for mould or Sample

Temperature in  C

Time/ Layer Thickness Number of Trials 1 2 3 4 5 Very      Stickiness Moderate      Not      Moderate      Deformation Structured      Easy      Removability Difficult      Less      Air Bubbles Moderate      High/Many     

STEP 2: SELECTION OF MATERIAL AND AM PROCESS

Here the aim is to find the material to make a mould using 3d printing technology for making silicone samples. We have considered the mould material based on the important criteria’s like capacity to withstand high temperature, good surface finish, stiffness in the mould, ability to print complex designs, easily available, less expensive, easy to handle. By keeping these into considerations we have choose the materials like Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS), Polyether Ether Ketone (PEEK) in FDM printers. We have even selected Hight Temperature resin (HT) in stereolithography apparatus (SLA) printers. To select the most suitable material among the 4 above mentioned materials we printed moulds using all 4 materials and tested with the silicone samples at different temperatures of 120C, 130C, 150C and 165C. The observations from these results are tabulated and explained in section 4.

STEP 3: FINALIZING MOULD DESIGN

This is the crucial step in our research that is the design factors will influence quality of the output object that is silicone sample. Initially we have come up with the 3- part mould design, they are top cap, bottom base and side wall. For finalizing our mould design, we design and considered many designs using trial and error

24 methods. We carried out several iterations because we were visually inspecting the moulds behaviour when it was tested. In this process we identified some flaws in our design, according to these observations we have made some design changes till we achieved a stable mould design. To find the stable design, we tested each mould with the silicone sample for different temperature with respect to time. All the results and observations about testing and moulds are explained in detail in section 4 step 3.

STEP 4: DESIGN OF EXPERIMENTS BY TAGUCHI METHOD AND TESTING

The moulds are printed with different layer thickness to know whether layer thickness affects the quality of the silicone rubber. The finalized design moulds are printed with 50µm and 100µm. In the previous steps, we have finalized the design, the material to print with and the process to print the mould. In this step, we are printing the final mould design for varying layer thickness of the mould. In the before steps we have not considered the layer thickness to print the moulds. So, we wanted to know by considering all the parameters and factors which affects the silicone rubber samples clearly and to check if it gives the same result of the reference silicone sample. We are applying L8 (2^3) Taguchi Orthogonal Design in design of experiments. This analytical tool helps us to know by considering all the factors and parameters, which experiment gives the best result and resembles the same as the reference. This step includes two stages, in the first stage we generated a set of experiments using Taguchi method were 4 sets of experiments are highlighted which will influence the surface properties of silicone sample. For this we considered factors like layer thickness, curing temperature and curing time. In the 2nd stage, we are testing the silicone in the moulds which are printed with the different layer thickness.

Table 3: Taguchi Orthogonal Experimental Design

L8 (2^3) Taguchi Orthogonal Design ‐ limited experiments

Curing Experiments Layer thickness Curing Time Temperature

1 50μm 120° C 3 hours 2 50μm 160° C 4 hours 3 100μm 120° C 4 hours 4 100μm 160° C 3 hours

STEP 5: SURFACE MEASUREMENTS

Since we have carried out the qualitative work in the previous steps, from step 5 we are conducting the quantitative work. We managed to achieve the good results with the silicone samples, we have carried this research further to know more about the surface of the silicone rubber by using advance instruments like GFM MikroCAD optical microscope. The company named Toponova AB, gave us a great opportunity and our supervisor guided and helped to us in taking the measurement silicone rubber and the mould (Top, Bottom surface and side walls) in every step. This instrument uses Stripe Projection Technique to measure the surface of the objects. The step wise procedure to capture the image of the surfaces are shown in the figure 16.

Figure 16: Step wise procedure to capture images in GFM MikroCAD The general steps involved in the capturing the images of the surface of the objects are as follows: i. Placing an object on platform: Firstly, we must place the object on the platform which the images of the surface as to captured. ii. Alignment: Aligning the object in the required direction or in the required angle that is at 0 to 90 so that when the beam of light projects from the instrument will fall on the surface to be measured and it is properly levelled on the platform. iii. Focusing: After levelling the object on the platform, we must adjust the focus knob to focus on the surface which has to be captured till the visual image of the surface appears on the computer screen. iv. Adjustment: After focusing, the visual image appears on the computer screen, we need to align the crosshair to the surface of the object as shown in the figure 16.

v. Image generation: After adjustment, we must capture the image of the surface. It is a process of generating a digital image of the surface. We have got quality specimens in step 4 with the silicone rubber and HT mould. We have 50µm and 100µm 3d printed mould by using HT material and silicone rubber with the 4 samples. We have measured surfaces and side walls of all silicone rubber and the mould. On one surface we have taken the 3 set of the measurements which means on the side walls and on the surface of the silicone rubber and mould is measured in the different positions on each surface. We are using the captured image to analyse them by using analyzation software called Mountains Map.

STEP 6: SURFACE AND DATA ANALYSIS

Surface Analysis: The images from the surface measurements are imported to the mountainsmap software for the further analyzation. We are considering silicone rubber images because we are aiming to achieve good quality of silicone samples that can be produced by using SLA 3D printing. In silicone rubber we have captured the images of side walls and top, bottom surfaces of all 4 samples including reference sample.

Figure 17: Mountains Map software Logo We have taken measurements from all 4 silicone samples and analysed using mountains map software. Below steps shows the process of analysing surface images using mountainsmap software. The process is divided into types of analyzation: i. Image analyzation for flat surfaces (0 build Inclination): In this step, images obtained from surface measurements are imported to the MountainsMap software and the image is processed using the tools like mirror, levelling, etc., to make the surface image even and the surface parameters are captured.

Figure 18: History of Operation Chart for flat surface ii. Image analyzation for curved surfaces (90 build Inclination):

Figure 19: History of Operation Chart for curved surface

In this step, the analyzation of raw surface image is processed to get the final 3D image by following steps for curved surface. The operations like mirroring, removal of form, fill in non-measured points are carried out using the software tools and the required surface parameters are obtained.

Data Analysis: In research fields, the analysis of the data by using statistical tools are very important. In our research to analyse the data we have used Regression Analysis in Design of Experiments. It is one of the important tools to find the most significant parameters by comparing the dependent and independent variables. Here dependent variables are surface parameters and independent variables are curing temperature, layer thickness, curing time and build inclination. In this step, we analyse the data generated using mountainsmap software using Microsoft Excel, we follow the below steps.

Figure 20: Data Analysis Process Flow Chart i) Data Import from MountainsMap Software: From mountainsmap software we obtained the data of 35 surface parameters from the measurements of all 4 samples.

ii) Performing Regression analysis Here to perform the regression analysis using the data from mountainsmap. In statistical modelling, regression analysis is a set of statistical processes for estimating the relationships between a dependent variable and one or more independent variables. The most common form of regression analysis is linear regression, the linear regression is divided into two types, simple and multiple. For our research we are using multiple regression analysis, in which a researcher finds the line that most closely fits the data according to a specific mathematical criterion. In our research, we are doing the regression analysis for 35 surface parameters. But in here, we are showing only the regression analysis process applied on the parameter Sq (Root mean square height) (µm) as an example to understand the methodology.

iii) Identification of Significant parameters: For identifying the significant parameters, we consider results of regression analysis. The steps of this process are shown below in figure 21.

Figure 21: Part 1 – Identification of significant parameters [27] In this part 1, we are checking the influence of all four variables (Build Inclination, layer thickness, curing temperature and time) in each parameter. Here we have considered the adjusted R2 value and significant F value. Firstly, we will check the value of adjusted R2 value if it is high (above 80% User defined) will accept the parameter and we will move to significant F value where we check if the significant F value is less than 0.05 or not. If it is greater than 0.05 then we will reject that analysis. But if the significant F value is less than 0.05 then we will accept the analysis and move forward to check the influence of independent variable.

Figure 22: Part 2 – Identification of significant influence of independent variable on significant parameter [27]

In part 2, of identification of significant influence of independent variable on the significant parameter depends on the P value of independent variable. If its value is also less than 0.05 then we can say that this independent variable has a significant influence on the respective significant surface parameter which in turn influences the surface quality. From the part 1 analysis, a significant parameter can be identified and from part 2 analysis it can be understood which independent variable (layer thickness, build inclination, curing time and temperature) has the most significant effect on the identified significant parameter.

iv) Performing Correlation Analysis: In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. In the broadest sense correlation is any statistical association, though it commonly refers to the degree to which a pair of variables are linearly related. Correlations are useful because they can indicate a predictive relationship that can be exploited in practice [18]. In this step we are checking the influence of one surface parameter to another surface parameter using correlation analysis and identifying the most relevant significant parameters from the identified significant parameters

v) Plotting Graphs:

From the regression and the correlation analysis, we obtained the most significant/most influencing parameters, one variable (build inclination) which will affect the quality of the surface. From this data we will plot the graph between the surface parameters and the variable. For plotting the graph one surface parameter from each category which are “Height parameter”, “Functional Parameter (Volume)”, “Functional Parameters (Stratified Surfaces)”.

3.4 DATA COLLECTION The data about the silicone rubber, mould and about implementation of 3d printing in supply chain are collected from research articles and scientific papers. Observations are made on the silicone to know the behaviours like air bubbles stuck inside the silicone, stickiness, deformation of the shape, removability from the mould when it is subjected to temperature with respect to time. Trial run is applied with the mould and the silicone samples. Then surface measurements are captured with the actual silicone samples and imported to Mountains Map software for surface imaging and analysing. The parameter values are extracted to Microsoft

Excel for further statistical experimental approach. All the data which we are obtained are stored safe and secured and compared with the reference data. All the data which are generated are kept for the further investigations.

4. RESULTS AND DISCUSSIONS

4.1 PHASE 1

This phase of the report highlights the observations we obtained from conducting the experiments on different silicone samples generated by using the simple mould geometry. We have used the facility and the resources which are available in the fablab in Halmstad university like 3d printers (SLA) to print moulds, lab ovens for curing the silicone samples. Also, we have used the optical microscope to capture the images of the silicone surface. The parameters which are involved in the surface measurements are defined by ISO 25178. By using Mountains Map software, the 3d images of silicone samples are generated. Then those 3d images are compared to the reference silicone samples to make observations.

STEP 1: LITERATURE SURVEY AND STUDY OF THE MATERIAL (SILICONE RUBBER)

The recommended temperature and time for curing the silicone rubber material was at 165 C for 155 minutes and post curing at 200 C for 4 hours. Working at this temperature limits the availability of materials for 3D printing moulds, since a few materials have a continuous work temperature of above 165 C. Hence, some tests were conducted to see if silicone rubber can cure at lower temperature for prolong exposure of heat. Firstly, the raw silicone is taken and subjected to the temperature of 165C for 15 min (as recommended by material provider) in the lab oven. We have made some observation in the below table 4, the sample looks like as shown in the figure 23.

Figure 23: Trail testing of silicone sample

After this we have tested the silicone samples at temperatures of 120, 130, 140 and 150 C with respect to 1 hour. Images of testing of samples with the above- mentioned temperatures are shown below. As the results are obtained, they are tabulated in the table 4 below.

Figure 24: Silicone Rubber tested at different temperatures according to the table 1

Table 4: Observations from testing silicone rubber without mould Material Silicone Rubber Trails Set 1 Set 2 165 Temperature in  C (Recommended 120 130 140 150 by company) Time 15 Min 1 Hour 1 Hour 1 Hour 1 Hour Very      Stickiness Moderate      Not      Moderate      Deformation Structured      Easy      Removability Difficult      Less      Air Bubbles Moderate      High/Many     

The table shows the observation of silicone samples are captured by curing them for different temperatures in order to observe how silicone will behave to different temperature at normal atmospheric pressure while curing and also we observed for physical parameters like stickiness, deformation, removability from the surface and presence of air bubbles trapped inside the silicone samples. Table 4 shows in set 1, small quantity of silicone rubber is subjected to the temperature of 165 C for 15 min. We have observed that the silicone sample shows stickiness, moderately getting deformed, it was difficult to remove from the surface it was kept, many air bubbles were trapped in it. In set 2, at 120 C for 1 hour, we have observed that the silicone sample shows moderate stickiness, moderately getting deformed, it was easy to remove from the surface it was kept, many air bubbles were suspended in it. At 130 C for 1 hour, we have observed that the silicone sample shows moderate stickiness, structured in the shape, it was easy to remove from the surface it was kept, many air bubbles were suspended in it. At 140 C for 1 hour, we have observed that the silicone sample shows moderate stickiness, structured in the shape, it was easy to remove from the surface it was kept, many air bubbles were suspended in it. At 150 C for 1 hour, we have observed that the silicone sample shows no stickiness, structured in the shape, it was easy to remove from the surface it was kept, many air bubbles were suspended in it. From these observations we understood how the property changes of silicone when it is subjected to heat at atmospheric pressure with respect to the time and we have a picture of how the silicone rubber responds to the temperature and time without mould. In the next step we are testing the silicone rubber by keeping it inside different types of the 3d printed mould to know silicone’s behaviour.

STEP 2: SELECTION OF MATERIAL AND AM PROCESS

Finalizing the mould material and 3D printing process:

Material selection is a step in the process of designing any physical object. In the context of the product design, the main goal of material selection is to minimize cost while meeting product performance goals. Appropriate selection of the material is significant for the safe and reliable functioning of a part or a component. Initially, we have used FDM technology to print the mould for making the silicone samples. To print the mould, we have used Flashforge finder printers for printing the mould by using PLA, Zortrax to print ABS, Creatbot to print with PEEK. We have made some basic design and printed by using ABS and PLA materials. The material shows some deformity in the shape when it is kept under heat.

Figure 25: PLA and ABS Mould The above picture shows how the PLA and ABS deformed when it is heated up to 120C. In PLA, the mould shows the deformation in the shape and the material was cured partially Silicone is cured in the top portion and not cured in the bottom. In the ABS mould, the subjected temperature is absorbed by the mould and the silicone wasn’t cured. It showed the same physical properties as how it was initially. The image shown below is the silicone sample which we have obtained by using PLA mould.

Figure 26: Silicone sample from PLA mould From the above observations we understand these 2 materials will not withstand the high temperature when it is kept in the oven for curing. Further, we have observed from the market survey, Polyether Ether Ketone (PEEK) shows the material properties which suits to our requirements. We have decided to move further printing the mould by using PEEK material by using Creatbot 3d printers. The PEEK print settings are mentioned below table. The basic design is created by using CAD software to print with the PEEK material. The basic design printed PEEK mould material images are shown in the figure 27.

Figure 27: Basic design of the mould in PEEK Figure 28: Silicone sample obtained from PEEK

In the above figure 27, we wanted to test the silicone in the mould. So, we made basic design to know how the silicone rubber behaves when it is kept in the PEEK moulds. These PEEK materials have a capability to withstand the pressure in the container area, on the walls, and doesn’t deform in its shape when it is subjected to heating at 165C (recommended) and we have tested the 1st sample for 120C for 30 min. We did this because even though we know the recommended temperature, we wanted to try for the lower temperature for lower time as we are using the polymer-based materials. But the recommended temperature was carried out in the metal moulds in the company. The product outcome was slightly better with the PEEK than with the other two moulds. The samples images are shown in the figure 28 above. The outcome with the PEEK was appreciative. So, we have decided to print the mould by increasing the size of the mould. The dimensions are set according to the actual size of the sample which was provided by the company as a reference. The cavity diameter 30mm and cavity depth are 13mm. The image of the printed mould is shown in the figure 29.

Figure 29: Actual Design of the mould in PEEK with 30*13 mm

Figure 30: Silicone samples obtained by using PEEK mould

The mould shows the dull and bad surface finish with the same printing settings which we have selected to print basic designs. We are aiming to have a high surface finish from the PEEK printing. So, we have just tested with the same mould. The result with the silicone sample is shown figure 30. The samples which are obtained was having very poor surface finish and the colour of the samples changed and the sample was getting deformed and lot of air bubbles stuck in the silicone rubber. So, we decided to reject the PEEK material to print the moulds by using FDM process. The below table shows the observations captured of curing of silicone sample with the basic design of the moulds with the different materials like PLA, ABS and PEEK.

Table 5: Observation from the testing of different moulds

Product material Silicone Rubber Mould material PLA ABS PEEK

Trails Set 3 Set 4 Set 5 Set 6 Set 7 Set 8 Set 9

Temperature in C 120 120 120 120 130 150 165

Time 1 hour 1 hour 30 min 1 Hour 30 Min 1 hour 15 Min

Very        Stickiness Moderate        Not        Moderately        Deformation Structured        Easy        Removability Difficult        Less        Air bubbles Moderate        Trapped More       

From the above observations, we have concluded that we are not using the FDM method of technology to print the moulds to make silicone rubber products. We have decided to move to another material called High Temperature Resin. It is a liquid vat photopolymer and it can be 3d printed by using Stereolithography apparatus (SLA) printers. From the literature study we understand that this material can satisfy our requirements2 like capacity to resist high temperature up to 238C under the pressure. So, we decided to print the mould by using HT resin in SLA printer. The figure 31 shows printed mould using HT material in SLA printer.

2 Formlabs, https://formlabs.com/eu/materials/engineering/#high-temp-resin

Figure 31: Design 1 Mould printed in HT From the figure 31, the mould has a fine surface finish. We have tested the silicone rubber by keeping in the mould for 140C for 1 hour. The results are shown in the figure 32 and figure 33.

Figure 32: Silicone Sample from HT Figure 33: Mould break after testing From the results we have observed that, • Lot of air bubbles in the silicone rubber. • Mould break due to thermal expansion of silicone rubber and thin mould walls. • Surface finish of the silicone rubber is good. • Easily removable from the mould. • Less stiffness and rigidity in the mould walls to hold the pressure.

From the observation we are concluding that, we can select the High Temperature resin to print the moulds using Stereolithography apparatus (SLA) printers in our further research. We did this because, • Mould surface has a greater surface finish • It can with stand higher temperature. • We can strength the mould by improving the design and by increasing the wall thickness. • Efficient and Consistent prints compared to the FDM printers.

STEP 3: FINALIZING MOULD DESIGN:

The observations and results of this step is very important in our research. We have carried out trial and error method to obtain the stable mould design. The details are explained below. In the previous step for the finalization of mould material, we have developed a mould design (Design 1) and we observed that on testing the moulds failed due to thin walls of the mould, thermal expansion of the silicone during curing process, no room for the expansion of the silicone during curing, no rigid supports between the bottom base and top cap. From these observations we concluded that there is a requirement of improvement to the design 1. Design Improvements: Design 2: As we have seen the results of the design 1 mould printed by using high temperature resin in the step 2, by considering the observations from that we have decided to make some improvements in the design so that to achieve the expectations and to obtain the results. The implemented design improvements are increasing the thickness of the walls, adding the grooves on the bottom base so that the side walls can perfectly fit and provide a stable support between bottom and top cap. The improvement in the design are shown in the figure 34.

Figure 34: Design 2 Mould After the improvements in the design, we printed design 2 mould using High temperature resin in SLA printer and tested with silicone for different temperatures and time that is for 120C and 150C for 3 hours and 4 hours respectively. Here we have increased the curing time from 1 hour to 3 and 4 hours because to combine the pre and post curing process and to observe will there be any effect of curing time on stickiness of the sample. But this attempt was also a failure. The observation of silicone samples is given below.

Figure 35: Silicone sample D2 -1 Figure 36: Silicone sample D2 -2 We observed that the mould broke but only the top cap was broken. In case of silicone sample, the observations are, • Silicone samples appeared non-sticky. • the surface quality was good and • intensity of air bubbles was less. • Difficulty in removal from the mould Then these observations are compared with the previous experimental observations and concluded that the presence of air bubbles in the silicone samples are occurring due to the breaking of the mould.

Design 3:

From the observation from the previous design, we decided to redesign the mould. Here, we made some changes in the shape in top and bottom caps of the mould. That is the circular shape of caps to triangular, so we can add three additional supports between the caps and the thickness of the side walls and caps were increased to 4 mm. Also, we added a hole on the side walls. This is done because during the curing process, excess silicone from inside the mould can be pushed out as a result of thermal expansion in the silicone rubber and given some room/space (clearance) in millimetres for the silicone for expansion which can prevent the breakage of the mould.Then we are printed design 3 and tested with the silicone rubber and observations are noted.

Figure 37: Design 3 Mould

From the testing of the mould using design 2, the results obtained were not satisfactory.

Figure 38: Silicone sample of D3 We observed that the top and bottom caps of the mould as broken and faced difficulty for the removal of silicone sample from the mould. The observation in the silicone sample are: • Breakage in the mould • The sample was non-sticky in nature. • Surface quality was improved than in design 2 • Air bubbles are reduced • Sample was more elastic in nature As a result, we once again revised design 3 mould and upgraded to design 4.

Design 4: Here the mould parts are changed from 3-part mould to 4-part mould. There are two separate side walls and separate top and bottom caps. Even we have provided additional support structures on the top and bottom caps such that the stress on the caps will be evenly distributed and rigid grip in the corners section for the purpose to increase the supports between the top and bottom caps.

Figure 39: Design 4 Mould-CAD Images

Figure 40: Design 4 actual printed mould

Figure 41: Silicone sample of D4 Observation from the test using this mould design 4 was satisfying and we have observed that • No breakage in the mould. • The removability of silicone sample from the mould was effortless. • The silicone samples appeared well structured. • Free of air bubbles. • Surface quality was good compared to the other samples • The visuality appearance of the samples are good compared to the other mould design samples. • The mould can be reusable.

As we got a stable simple mould, we finalised this mould design based on the observations and proceeded to the next step. The observation table for the above experiments with the design 2,3 and 4 with the high temperature resin mould is shown below in table 6.

Table 6: Observation Table on Tested Silicone Samples

Product material Silicone Rubber Mould material HT Mould Set 10 Set 11 Set 12 Set13 Set14 Trails D1 D2 D2 D3 D4 Temperature in C 150 120 150 150 150

Time 1 hour 3 hours 4 hours 4 hours 4 hours

Very Stickiness Moderate     Not      Moderately     Deformation Structured      Easy      Removability Difficult     Less     Air bubbles No air Moderate     Trapped bubbles More    

STEP 4: DESIGN OF EXPERIMENTS BY TAGUCHI METHOD AND TESTING Based on this matrix shown in the table 2, we made different mould sets of the finalized design with the chosen material (HT) using 3D printing (SLA) with different layer thickness (50 and 100 microns). In the second stage we tested the silicone samples using the moulds of 50µm and 100µm layer thickness according the experiment matrix developed using Taguchi experimentation. The images of the samples are shown in the figures below.

1 2 3 4

Figure 42: Silicone samples obtained using Taguchi Experimentation

Figure 43: Reference Silicone Sample From the above figure 42, the silicone samples obtained using Taguchi experimentation table and the reference silicone sample, the sample from 1st experiment with 50µm layer thickness, curing temperature 120C with curing time 3 hours shows the maximum resemblances of the reference silicone sample shown in figure 42. From this we may conclude that using settings of experiment 1, we can develop a silicone sample which almost resemblances the required surface quality. The observation made by using the taguchi experiments are shown in the below table 7.

Table 7: Observation of Silicone Rubber using Taguchi Experimentation

Product material Silicone

Mould material HT Trails 1 2 3 4 Temperature in C 120 160 120 160 Time 3 hours 4 hours 4 hours 3 hours

Layer Thickness 50 50 100 100 in µm

Very Stickiness Moderate Not     Moderately Deformation Structured     Easy     Removability Difficult Less Air bubbles Moderate No air bubbles Trapped More

From the experimental table 7 we observed the all the four samples are giving same results in case of stickiness, deformation, removability and air bubbles. But other than these factors we got some other important observations that is the samples which are cured at 160C appeared to be darker than the samples which are cured at 120C. Also, when compared with the reference sample the sample which is cured at 120C for 3 hours shows the maximum resemblance to the reference than the other 3 samples. However, further quantitative analysis is required to discriminate the samples and to validate the above assumption.

STEP 5: SURFACE MEASUREMENTS In this step, we have observed that replicas were used to capture the surface of the silicone samples and it was easy to capture the Images of flat surfaces of the replica. But for the round surface (side surface) of the silicone, it was difficult to capture the measurements because of the shape and the placing of the replica on the platform to take the measurements were difficult. So, we have managed to capture 3 images for each surfaces of the silicone samples.

STEP 6: SURFACE AND DATA ANALYSIS

Surface Analysis: In this step, we have analysed the images and generated the 3d view and parameters of the surface of the silicone samples. The below table shows the 3D images which are generated by using MountainsMap Software. We have shown the comparison of silicone samples cured at the different temperatures at different time using HT printed moulds of 50μm and 100μm with the reference. It also shows the difference in surface roughness with 90° and 0° build inclination. From the 3D views of samples, we have observed that with the 0° build inclination, we can achieve the similar surface quality of reference silicone samples and with the 90° build inclination, we have the surface roughness of the silicone samples are more and shows least resemblance with the reference silicone surfaces as we can see in the table 8.

Table 8: Comparison in 3D images build inclination of silicone samples at 0 and 90

Experiments/Samples Build Inclination 0 Build Inclination 90

Reference Sample

Sample 1

LT-50μm, 120° C, 3hrs

Sample 2

LT- 50μm, 160° C, 4hrs

Sample 3

LT-100μm, 120°C, 4 hrs

Sample 4

LT-100μm, 160°C, 3 hrs

We have also generated the values of the surface parameters of all the samples (0 and 90° build inclination) and tabulated in the Microsoft excel sheet for the further analysis of data. Data Analysis: Here, we analysed the data imported from the previous surface analysis step to find the most significant surface parameters to plot the graphs. First, we carried out regression analysis, using Microsoft excel. Here we can’t show of all the results of regression analysis for 35 parameters analysis result, so we are showing analysis of Sa (Athematic Mean Height) (μm) from Height parameter family group.

Table 9: Regression Analysis Statistics

Regression Statistics Multiple R 0.934173397 R Square 0.872679935 Adjusted R Square 85% Standard Error 0.622371119 Observations 24

ANOVA df SS MS F Significance F Regression 4 50.44413 12.61103 32.55755 2.91445E-08

Residual 19 7.35957 0.387346 Total 23 57.8037

Standard Coefficients Error t Stat P-value Intercept 4.383797458 1.326347 3.305167 0.003722 Layer thickness 0.004919211 0.005082 0.968036 0.345188 Curing Temperature -0.009922798 0.006352 -1.56214 0.134757 Curing Time -0.390008027 0.254082 -1.53497 0.141276 Build inclination 0.031499975 0.002823 11.15781 8.76E-10

Above table 9 shows the result of regression analysis. From the result, we have considered 3 values which are Adjusted R2 values, Significant F value and P-Values for identifying the significant parameters and we have observed that 10 parameters are showing the significant of influence on the surface quality of silicone samples.

Table 10: Significant Parameters Table

P-value Sl Significant Adj. Description Unit Sig. F Layer Build No parameters R2 Curing Temp Curing Time Thickness Inclination Root-mean- 3.59E- 1 Sq µm 84% 0.313 0.159 0.132 0.000 square height 08 Arithmetic 2.91E- 2 Sa µm 85% 0.345 0.135 0.141 0.000 Mean Height 08 Smc (p = Inverse Areal 2.80E- 3 µm 85% 0.284 0.112 0.137 0.000 10%) Material Ratio 08 Sxp (p = Peak Extreme 1.62E- 4 50%, q = µm 81% 0.331 0.354 0.373 0.000 Height 07 97.5%) Vv (p = 3.30E- 5 Void Volume µm3/µm2 84% 0.286 0.111 0.124 0.000 10%) 08 Vmc (p = Core Material 3.36E- 6 10%, q = µm3/µm2 84% 0.421 0.131 0.166 0.000 Volume 08 80%) Vvc (p = Core Void 3.87E- 7 10%, q = µm3/µm2 84% 0.305 0.098 0.110 0.000 Volume 08 80%) Vvv (p = Pit Void 2.74E- 8 µm3/µm2 80% 0.225 0.532 0.552 0.000 80%) Volume 07 Spd Density of 2.52E- 9 (pruning = 1/µm2 88% 0.807 0.849 0.025 0.000 Peaks 09 5%) Sk (Not Core Roughness 5.97E- 10 µm 83% 0.605 0.121 0.149 0.000 filtered) depth 08

We can further shortlist the significant parameters by, performing Correlation analysis on significant parameters which are obtained and shown in table 10.

Table 11: Most Significant Parameters obtained using Correlation Analysis

Sxp Vmc Vvc (p = Spd Sk Smc Vv (p (p = (p = Vvv 50%, (pruni (Not Surface Sq Sa (p = = 10%, q 10%, (p = Parameters q = ng = filtere 10%) 10%) = q = 80%) 97.5 5%) d) 80%) 80%) %)

Sq 100%

Sa 100% 100%

Smc (p = 100% 100% 100% 10%)

Sxp (p = 50%, q = 99% 99% 98% 100% 97.5%)

Vv (p = 100% 100% 100% 98% 100% 10%)

Vmc (p = 10%, q = 100% 100% 100% 99% 100% 100% 80%)

Vvc (p = 10%, q = 100% 100% 100% 98% 100% 100% 100% 80%)

Vvv (p = 98% 97% 96% 100% 96% 97% 96% 100% 80%)

Spd (pruning -84% -84% -83% -86% -83% -83% -82% -87% 100% = 5%)

Sk (Not 99% 100% 99% 98% 99% 100% 99% 96% -82% 100% filtered)

From table 11, it can be understood that all the parameters are highly correlated with each other, this indicates that these parameters behaviour similarly although it explains different parts of the surface. These highly correlated parameters may then be chosen as per the relevance of the study. However, Spd parameter has negative and slightly lower correlation compared to other parameters and hence it becomes

50 an interesting parameter to consider for analysis. From this methodology, the significant relevant parameter chosen for analysis were Sa, Average roughness, Vv, Total void volume, Spd, Density of peaks and Sk, Core roughness depth. In the following sections, the graphical representations of these parameters are provided to understand its influence on surface quality.

Graph 1: Average Roughness Graph

Sa, Average Roughness 7.0 6.0 5.0 4.0 3.0 2.0 50µm_1 1.0 Heightin µm 0.0 50µm_2 0° 90° 50µm_1 1.9 5.5 100µm_3 50µm_2 2.2 3.6 100µm_4 100µm_3 2.1 5.0 Reference 100µm_4 1.9 5.2 Reference 2.42 2.15 Build Inclination

The graph 1 is plotted between average roughness and build inclination. The arithmetic mean height or Sa parameter is defined as the arithmetic mean of the absolute value of the height within a sampling area [23] Build inclination can be defined as the angle at which the object is aligned to the printer platform.

From graph 1, it can be understood that the average roughness is higher at build inclination 90° and lower at 0° surfaces. It is difficult to derive the relationship between build inclination and roughness parameter since there are only two build inclinations are used. Studies have shown that at 0° flat surface have lowest surface roughness and highest at 10-30°. The surface roughness in general, decreases with increase in build inclination, however, 0° surfaces form an exception.

Further, the average roughness of samples at 0° made from the HT moulds is less than or similar to average surface roughness of the reference samples made by injection moulding method and in case of 90° build inclination, the average surface roughness of the samples made from HT mould is more than the samples made from injection moulding method.

Another observation from the graph is layer thickness does not show much influence on the surface roughness his is due to the selection of surfaces (0° and 90°). Layer thickness may have significant effect for other build inclinations or for

51 other geometries. Further investigations are required to understand the influence of layer thickness in SLA 3D printing. From these observations it is concluded that the average surface roughness of samples made from HT samples are not affected by the layer thickness of the mould and with 0° build inclination silicon products with least surface roughness can be produced. Also, as per the regression table and graphs the effect of curing temperature and time are insignificant on surface roughness. However, it can have a significant effect on the mechanical properties of the sample.

Graph 2: Void Volume Graph

Vv, Void Volume 0.0120 0.0100 0.0080 0.0060 0.0040 50µm_1 0.0020 0.0000 50µm_2

Volume/Area Volume/Area inmm 0° 90° 100µm_3 50µm_1 0.0031 0.009 50µm_2 0.0036 0.006 100µm_4 100µm_3 0.0035 0.008 Reference 100µm_4 0.0030 0.009 Reference 0.0040 0.003 Build Inclination

Graph 2 shows the results obtained from the Void Volume (Vv) parameter. Vv, is the volume of space bounded by the surface texture from a plane at a height corresponding to a chosen material ratio value to the lowest valley. Material ratio may be set to any value from 0% to 100% but usually, 10% and 80% are selected. [28] Sa and Vv is having 100% correlation so the graph 1 and graph 2 are showing a similar result. Hence, similar comments can be made with respect to Vv parameter. Build inclination has a significant effect on this parameter. It can be noticed that 90° build inclination has higher value of Vv than 0°, this is because the 90° surfaces consists of stair-step patterns which in turn leads to the formation of consecutive peaks and valleys on the surface. Furthermore, Void volume parameter can be useful in coating applications. As a future work, it is likely that we use coatings to smoothen the surfaces of the 90° build inclination, in such cases Vv parameter can clarify the amount of coating adhered to the samples.

Graph 3: Core Roughness Depth Graph

Sk, Core Roughness Depth 25.00 20.00 15.00 10.00 5.00 0.00 50µm_1 0° 90° 50µm_1 5.79 18.08 50µm_2

50µm_2 6.86 11.68 100µm_3 Heightin µm 100µm_3 6.64 15.57 100µm_4 100µm_4 5.83 16.17 Reference Reference 7.67 6.77 Build Inclination

Graph 3 represents the core roughness depth it is defined as The Core Roughness Depth, Sk is a measure of the “core” roughness (peak-to-valley) of the surface with the predominant peaks and valleys removed. Sk is also having a 100% correlation with Sa and Vv and as the graph 3 is plotted between the Sk and build inclination, the behaviour of the graph 3 is also similar to the graph 2 and 1. From the observations from graph 1, 2 and 3 it is concluded that the parameters Sa, Vv and Sk of samples made from HT samples are not affected by the layer thickness of the mould and with 0° build inclination silicon products with least surface roughness can be produced. [28]

Graph 4: Density of Peaks Graph

Spd, Density of Peaks 6000.00 5000.00 4000.00 3000.00 2000.00 1000.00 50µm_1 0.00 50µm_2 Density Density 1/mm2 in -1000.00 0° 90° 100µm_3 50µm_1 4298.19 1162.35 100µm_4 50µm_2 3577.83 514.97 Reference 100µm_3 4012.97 309.88 100µm_4 4567.39 921.27 Reference 2360.17 2209.81 Build Inclination

Graph 4 shows the Spd (Density of peaks) parameter which represents the number of peaks per unit area. A large number indicates more points of contact with other objects [29]. Spd is showing negative correlation to other parameters. The graph 4 behaves opposite to the behaviour of other 3 graphs like graph 1, 2 and 3 that is the surface of silicone sample made with HT mould at a 0° inclination has a high density of peaks when compared to the surface of silicone sample made with HT mould at 90°. Also, it is noticeable that the density of peaks on the sample surface is more than the reference surfaces at 90° build inclination, the density of peaks on the samples are less than the reference value with 0° build inclination. 4.2 PHASE 2 This phase composed of design and fabrication of complex mould, surface study on complex silicone sample created by using complex mould. In this phase, development of a complex mould design and its fabrication is successfully carried out and complex shape silicone samples are produced. Due to the time concern, the surface measurement and analysis of the complex shape mould and silicone sample were not carried out and are recommended for future research.

Design and Fabrication of Solid Block Design:

Based on observations and results of phase 1, a solid block design is developed and fabricated using the high temperature resin material and SLA process to print the mould. The solid block design is shown in the figure 44.

Figure 44: Solid Block Design

In this design, the silicone is injected into the mould cavity through the hole provided in the top of the block and is cured at 120C for 3 hours of curing time irrespective to the layer thickness. The observations made from the cured silicone are the sample was partially cured. Since it is a block design, the mould must be

54 broken to remove the silicone sample from it. While removal, the silicone sample is damaged, and it was too adhering to the surface of the mould. Design and Fabrication of 4-Part Mould:

In the previous design, the removal of sample from the mould was difficult. So, to over this issue the block design is upgraded to 4-part design.

Figure 45: 4-Part Mould Design

The sample produced from this mould by curing the sample for 120C for 3 hours (observations from phase 1) shown better results, it was difficult to remove from the mould, even though managed not to damage the sample.

Figure 46: Sample obtained using 4-Part Mould Design

Figure 47: CAD Model of Complex shape silicone sample

The figure 47 shows the CAD model geometry of complex shape silicone rubber. By comparing the figure 47 and 46, we can understand that we can achieve the required complex shape of the silicone by using 3d printing.

5. CONCLUSION AND FUTURE ACTIVITIES

5.1 CONCLUSION FROM OUR RESEARCH

Additive manufacturing is continuously developing field and lot of research are going on in this field. This research was a part of a major project from DiSAM to implement the additive manufacturing into Swedish market. This research is concentrated on design and fabrication of moulds to produce silicone rubber and to conduct study about the surface of the obtained silicone samples. In phase 1, we made a study on samples made from simple mould geometry where we have analysed the qualitative and quantitative results and concluded that it is possible to develop a mould using additive manufacturing for producing silicone rubber products. The important findings of this study are High temperature resin is suitable for making moulds for silicone rubber products, lower temperature than the recommended can be used for curing, pre and post curing can be combined, factors like layer thickness, curing temperature and curing time has a least influence on surface quality of the silicone sample and build inclination plays a crucial role on better outcome of surface quality of silicone sample. This study also shows complexity of the shape is not the limitation for using high temperature resin as a mould material. Based on research observation and results from the phase 1, the development of complex shape mould is carried out and partial results were achieved in phase 2. In order to achieve better results with the complex shape it is recommended to develop a mould geometry with the core and cavity design such that it may give an better outcome with complex shaped silicone products.

5.2 FUTURE RESEARCH ACTIVITIES Due to the time concern, this research is incomplete in case of making study on silicone samples produced using complex mould. So, it is suggested to carry out the surface study on silicone samples produced using complex mould design. This research also suggests making study about PEEK printing to improve the surface quality of PEEK printed objects. Further, dimensional and mechanical property testing must be conducted to arrive at the conclusion of AM can replace traditional methods.

6. CRITICAL REVIEW

Figure 48: Sustainability [26]

Economic Aspect: This research deals with additive manufacturing technology where we can save the cost and time as it allows to directly print the object by using 3D printing regardless of its complexity. Also, many of the materials used in 3d printing can be recycled and can be used for 3d printing again. It can avoid the burden of purchasing costly machines which involves in different process of manufacturing. From this research, it can be noticed that one 3D printer can replace many other expensive machines which are used in conventional methods to manufacture the moulds. Also, the printed moulds can be reused. Society/Social Aspects: In this study shows the conventional method of manufacturing can be replaced by using the Advanced Manufacturing Methods like Additive Manufacturing (3D printing). It helps in reducing of manpower or work force requirement and manufacturing time, it reduces the heavy works that are required in the conventional by avoiding many procedures in conventional method. Environmental Aspect: In our study, by introducing the Additive manufacturing (3D Printing) in the supply chain, the amount of waste (quantity) is reduced drastically. Most of the materials which are made by 3d printing by using polymers, most of all are reusable/recyclable. These methods of manufacturing are environmentally friendly. They won’t cause any pollution in the surroundings compared to conventional methods. The requirement of the resources (Raw material) are less consumed while manufacturing the components.

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APPENDIX 1

Figure 49: Other silicone samples used for testing and observations with different time and time

Figure 50: 3D Printed Tool used to shape silicone rubber

Figure 51: Other Mould Design (PLA)

Figure 52: Other version of design 4

Figure 53: Basic Mould Design (PLA)

Figure 54: Design 4 mould under pressure

Figure 55: SLA Printed Mould Part (90 Build Inclination)

Table 12: Taguchi Experiments with Coatings

L8 (2^4) Taguchi Orthogonal Design Layer Curing Curing Time Experiments Thickness Coatings Temperature In Hrs In µm in C 1 100µm Gold Coating 160 4 2 50 µm No Coating 160 3 3 100 µm Gold Coating 160 3 4 100 µm No Coating 120 3 5 50 µm No Coating 160 4 6 50 µm Gold Coating 120 3 7 100 µm No Coating 120 4 8 50 µm Gold Coating 120 4

Table 13: Taguchi Experiments without Coatings

L8 (2^3) Taguchi Orthogonal Design-Full Factorial Design Layer Curing Curing Time Experiments Thickness Temperature In Hrs In µm in C 1 100µm 120 3 2 100 µm 160 4 If coatings don’t 3 50 µm 160 4 work, use this 4 50 µm 120 3 DoE 5 50 µm 160 3 6 50 µm 120 4 7 100 µm 160 3 8 100 µm 120 4

Shreyas Kantharaju Mechanical Engineering +46767408023 [email protected]

Jobin Varghese Mechanical Engineering +46764474976 [email protected]

PO Box 823, SE-301 18 Halmstad Phone: +35 46 16 71 00 E-mail: [email protected] www.hh.se