COMPOSITE FABRICATION TECHNIQUES

The fabrication methodology of a composite part depends mainly on three factors:
(i) the characteristics of matrices and reinforcements,
(ii) the shapes, sizes and engineering details of products, and
(iii) end uses.

The composite products are too many and cover a very wide domain of applications ranging from an engine valve to an aircraft wing.

The fabrication technique varies from one product to the other.

1. COLLOQUIUM PRESENTATION ON COMPOSITE FABRICATION TECHNIQUES 1 Supervisor – Dr. V.R.Komma Mechanical Engg . Deptt . MNNIT Allahabad Submitted by – Sandeep Kashyap(2015PR21) M.Tech . (Prod. Engg .)

2. 1. INTRODUCTION 2. FABRICATION PROCESSES FOR POLYMER MATRIX COMPOSITES( PMC ) 3. FABRICATION PROCESSES FOR METAL MATRIX COMPOSITES(MMC) 4. FABRICATION PROCESSES FOR CERAMIC MATRIX COMPOSITES( CMC ) 5. FUTURE CHALLENGES 6. CONCLUSION REFERENCES 2 OUTLINE

3. The fabrication methodology of a composite part depends mainly on three factors: (i) the characteristics of matrices and reinforcements , ( ii) the shapes, sizes and engineering details of products, and ( iii) end uses . The composite products are too many and cover a very wide domain of applications ranging from an engine valve to an aircraft wing. The fabrication technique varies from one product to the other. 3 1. INTRODUCTION

4. Important moulding methods for fabrication of polymer matrix composite structural parts may be classified under :- Matched Die Mould – Some of it includes Compression Moulding, Cold Stamping, Press Moulding and Injection M oulding. Contact M ould (also called open mould ) – Some of it includes Vacuum B ag M oulding, Pressure Bag Moulding and Autoclave. Filament W inding and Pultrusion 4 2. FABRICATION PROCESSES FOR PMC

5. The common feature in this technique is moulds are usually fabricated with cast iron, steel and aluminium alloy . Fibre reinforced plastics or wooden moulds are also used in some cold moulding processes. The mating surfaces of the moulds are first polished, cleaned and coated with a release agent . Next a gel coat is applied. The gel coat is not provided, when the moulded part is to be adhesively bonded to another part, as the coat may not allow proper bonding . Venting ports are provided in the moulds for escape of excess resin and volatile matters. 5 a. Matched-Die Mould Methods

6. (i) Compression Moulding : Moulding material may be predetermined quantity of BMC, SMC or prepregs . The moulds can have a single cavity or multiple cavities with complex curved shapes . The pressure is applied by mounting the moulds in a mechanical or hydraulic press or by some external means. On application of pressure and temperature, the mould material softens and then flows and fills the mould cavity. Further, continuation of heat and pressure accelerates curing . 6 (PMC, Defense Handbook (2002))

7. It is employed in fabrication of automobile body panels, housings for electrical appliances and machines, covers, and several other parts. (ii) Cold stamping Moulding : In this, the thermoplastic sheets are preheated, laid on the mould along with reinforcements and then cold pressed. An extension of this method is continuous production of fibre reinforced thermoplastic laminates is illustrated in Fig. below. Alternate layers of fibre fabrics and thermoplastic films are fed through hot rollers that melt the resin and force it to penetrate and coat the individual fibres. The consolidated laminate is then passed through cold rollers which cure and harden the laminate. 7 PMC, Defense Handbook (2002)

8. (iii) Press Moulding : I t is used to make flat, slightly curved and corrugated laminates. On the application of pressure the excess resin is squeezed out and passes through the pores of nylon cloth(i.e. peel ply to achieve required surface finish) and perforations of Teflon film and gets absorbed by the bleeder (e.g., jute cloth). The pressure is applied normally to allow uniform resin distribution. The uniform flow of excess resin out of the moulding can be achieved by applying vacuum to one of the surfaces of the mould cavity. 8 (PMC, Defense Handbook (2002))

9. (iv ) Injection Moulding : It is suitable for thermoplastic resin systems. If the reinforcements are in the form of particles or very short fibres. The mix is first heated in an injection chamber and then forced into the closed mould cavity under high pressure and is allowed to cure . It is suitable for fabrication of small to medium size parts such as valves, gears, instrument panels, etc . 9 If the reinforcements are in the form of preforms, they are laid in the mould cavity and the fluid resin is then injected into the mould cavity. The process is known as resin injection moulding. For larger mouldings such as boat hulls, resin is injected at several locations . (NV Srinivasulu (2012))

10. 10 Some Applications of Match-Die Mould Method

11. In this there is only one mould (Male or female), the surface of which is first polished, cleaned and coated with a release agent & gel. The moulding materials are laid on the mould by either the hand lay-up process or the spray-up process . 11 2.2 Contact Mould (also called open mould) In the hand lay-up process, woven rovings, or chopped strand mats are placed layerwise, with each layer coated with resin using a brush or a spray gun. Some time gap is allowed for the applied resin coat to gel, before laying the next layer and applying resin to it. Squeeges or rollers are used for uniform distribution of resin and consolidation for the laminate. In the spray-up process, chopped strands or particulate reinforcements and the resin are sprayed separately/simultaneously to the mould surface. After which, the moulding is allowed to cure. (PMC, Defense Handbook (2002))

12. For compact and voidless finished products, other improved techniques are vacuum bag moulding, pressure bag moulding processes and autoclave moulding. (i) Vacuum Bag Moulding : The whole moulding system is covered with a flexible vacuum bag. The edge of the bag is sealed using vacuum sealing compounds. 12 Layers of bleeder, perforated Teflon film, and nylon peel ply, in order . When vacuum is applied, volatiles, trapped air and excess resin escapes out and further consolidates the laminate. The whole assembly can be put in an oven, if a high temperature curing is needed. (PMC, Defense Handbook (2002))

13. ( ii) Pressure Bag Moulding : In this case, the vacuum bag is replaced by a pressure bag and the whole system is covered by a pressure plate. The required pressure is then applied through an inlet pipe located at the cover plate. The higher pressure ensures proper consolidation and densification of the composite lay-up. However, the method cannot be applied to a male mould. 13 (PMC, Defense Handbook (2002))

14. ( iii) Autoclave Moulding : It is a highly sophisticated process in which controlled temperature and pressure can be applied. In addition, vacuum is also applied to suck volatile matters and entrapped air or gases. The whole assembly is put inside an autoclave. Curing takes place in presence of simultaneous. pressure and temperature. 14 After curing, the mould is taken out of the autoclave. It yields highly densified products and is therefore favoured in fabrication of major aerospace components like aircraft wing parts, helicopter blades, etc . (PMC, Defense Handbook (2002))

15. 15 Some Applications of Contact Mould Method

16. 16 2.3 Filament Winding The filament winding process is employed for fabrication of a continuous fibre reinforced composite structure having an axis of revolution. Continuous fibre strands or rovings are first coated with resin in a resin bath and then fed through rollers to squeeze out excess resin and finally wound, under constant tension, around a collapsible mandrel . The mandrel is usually made of steel. However, other materials like plastic foam and rubber are also used in fabrication of some mandrels. (PMC, Defense Handbook (2002)) (PMC, Defense Handbook (2002))

17. There are basically 2 types of filament winding patterns: helical winding and biaxial winding . After winding is complete, the mandrel is removed from the carriage and placed in an oven, if required, for curing. Filament wound products for aerospace applications are normally cured in an autoclave. Common examples are tubes, pipes, cylindrical tanks, pressure vessels, rocket motor cases, etc . 17

18. 18 2.4 Pultrusion In this continuous fibre strands taken from a number of spools are sequentially pulled through a resin bath, a shaping guide and a hot die. The fibres are coated in the resin bath and the excess resin is squeezed out. The shaping guide provides a gradual change from a simpler to a more complex pre-formed shape close to that of the pultruded part. The final shape is realized when the preformed shape is pulled through a hot die and gets cured. (PMC, Defense Handbook (2002))

19. Continuous strand mats and woven fabrics can also be pulled along with filament strands to provide better transverse properties to the pultruded sections. The die is a very critical component in the fabrication process. It is usually made of chromium plated steel and should have a highly smooth surface. 19 Thermosets like epoxies and polyesters are normally used in the pultrusion process. A pultrusion machine SPACETRUDER (developed at Vikram Sarabhai Space Centre, Trivandrum, India). It can produce continuous lengths of FRP sections such as rounds, square bars, channels, angles , etc.

20. 20 Aluminium , magnesium, titanium and nickel alloys are commonly used as metal matrices, although several other matrix materials including super alloys have also been used. Both metal and ceramic reinforcements are employed . Important moulding methods for fabrication of MMC parts may be classified under :- (i) Diffusion Bonding (ii) Powder Metallurgy Process (iii) Casting 3. FABRICATION PROCESSES FOR MMC

21. Composite laminates are produced by consolidating alternate layers of precursor wires or fibre mats and metal matrix sheets or foils under temperature and pressure. A monotape (i.e., a unidirectional lamina) in which a fibre mat is sandwiched between two metal sheets or foils, forms the basic building block. Several complex composite components can be fabricated by stacking monotapes as per design requirements . Under temperature and pressure metal sheets or foils diffuse through fibre layers to form a laminate. A multilayered laminate may have any desired stacking sequence . Carbon fibres have been successfully combined with matrices like aluminium, magnesium, copper, tin, lead and silver to make a wide range of carbon fibre reinforced metal composites . 21 (i) Diffusion Bonding

22. One interesting example is the 3.6m long high gain antenna boom that acted as a wave guide for the Hubble space telescope . The boom is made with diffusion bonded carbon fibre reinforced aluminium composite. 22 (MMC, Defense Handbook (2002))

23. Almost all metals and their alloys can be converted into powder form by atomization techniques. In one process (known as powder cloth process ), metal matrix powders are mixed with an organic binder and then blending with a high purity Stoddard solution. On application of low heat, Stoddard solution evaporates leaving behind dough-like mixture which, on rolling, yields a metal powder cloth. Alternate layers of powder clothes and fibre mats , when hot press bonded, form a composite laminate. B inders usually burn out without leaving any residue. When reinforcements are in form of short fibres and particulates , metal matrix powder and reinforcements are thoroughly blended and degassed to remove volatiles and then composite ingot is formed by hot pressing in vacuum. Composite ingot is then used to fabricate structural components using secondary fabrication processes . 23 (ii) Powder Metallurgy Process

24. In thermal spray processes , metal powders, are deposited on fibre substrates using either plasma spray or arc spray techniques. P lasma spray technique is employed to deposit spherical metal powders that are injected in the plasma stream (the temperature is about 10,000K and the traveling speed is around Mach 3 ) within the throat of the gun. P owder particle should melt, but not vaporize before reaches substrate. A rc spray technique uses continuous metal matrix wires of 0.16-0.32 cm dia. 2 wires of opposite charge are fed through an arc spray gun. E lectric arc produced causes tips to melt. Argon gas stream carries and deposit them on substrates. 24 ( Kaczmara J.W . (2000)) ( Kaczmara J.W . (2000))

25. Monotapes produced by thermal spray processes are fabricated by diffusion bonding processes for structural components The powder metallurgy process has been used to produce composites such as boron and carbon fibres with aluminium alloy, SiC fibres with chromium alloys, boron and Al 2 O 3  fibres with titanium alloy , and several other composite systems . 25 Some Applications of Powder Metallurgy Process :

26. Casting or liquid infiltration is process in which molten matrix is infiltrated into a stack of continuous fibre or discontinuous reinforcements and is then allowed to solidify between the inter-reinforcement spaces. Some important casting methods are stir castings, pressure/squeeze castings, and centrifugal casting. In stir casting , required amount of metal matrix is weighted and placed in graphite crucible and heated to melt using furnace. All the pre- weighted reinforcing elements are mixed with molten metal and a constant vigorous stirring was done for 15 to 20 minutes until a clear vortex formed. 26 ( iii) Casting

27. At the pouring temperature, the molten mixture was poured into the permanent mould and allowed to solidify for few minutes. After complete solidification it is withdrawn and machined accordingly. In Centrifugal casting , solidification takes place in a rotating mould. In this process, the centrifugal acceleration forces the heavier discontinuous reinforcements to concentrate near the outer periphery and the lighter ones lie closer to the axis of rotation. Pressure/Squeeze casting is the process in which the molten matrix is infiltrated, under high pressure, onto a preheated stack of discontinuous reinforcements or fibre preforms laid on a metal die. Solidification takes place also under pressure. The Toyota piston, made of ceramic fibre and aluminium matrix, is one such example. 27

28. 28 Some Applications of Casting Process :

29. 29 Ceramic such as glass, glass-ceramics, borides, carbides, graphite, nitrides and silicates reinforced with ceramic particles, whiskers and fibers provide enhanced strength and toughness even at high temperatures. Important moulding methods for fabrication of CMC parts may be classified under :- ( 1 ) Hot Press Sintering (2) Liquid Infiltration (3) Reaction Sintering (4) Chemical Vapour Deposition Process 4. FABRICATION PROCESSES FOR CMC

30. SiC whiskers are very commonly used to reinforce matrices such as glass, ZrO 2 , B 4 C, Al 2 O 3 , Si 3 N 4  and several other ceramics . N umber of glass systems such as lithium aluminosilicate (LAS), magnesium aluminosilicate (MAS ) etc . have been hot pressed at relatively lower temperature without causing any damage to the reinforcement. 30 4.1 Hot Press Sintering (Mehdi Shahedi Asl (2015))

31. Infiltration of molten ceramics is similar to the resin injection molding process. The high melting points of ceramics , may degrade the reinforcements. This problem can be overcome by the use of polymer precursors that bring down the process temperature. 31 4.2 Liquid Infiltration However , during the conversion of a polymer precursor to the ceramic matrix, a lot of volatile matters escape causing shrinkage of the matrix. The matrix also becomes porous. The porosity can be reduced to a large extent by reimpregnation. Several precursor polymers have been studied to produce SiC  and Si 3 N 4 matrices .

32. Reaction sintering eliminates problems associated with hot press sintering and liquid infiltration, such as fibre damage, matrix shrinkage , etc . In this process, ceramic matrices are reaction formed . For eg ., silicon nitride( RBSN ) is made from finely divided silicon powders and subsequently reacted in a mixed nitrogen/hydrogen atmosphere at 1,200 to 1,250 ° C. The nitrogen permeates the porous body and reacts with the silicon to form silicon nitride within the pores. The piece is then heated to 1,400 °. The entire reaction-sintering process can last up to two weeks. Although up to 60 percent weight gain occurs during nitriding, dimensional change is less than 0.1 percent . The SiC matrix has also been successfully reaction bonded with SiC and carbon mixture powder exposed to a liquid/ vapour Si. This is a “net shape” process . M ain drawback is that resulting composite may have excessive porosity. 32 4.3 Reaction Sintering

33. The preform is kept in a high temperature furnace (reactor ). A carrier gas (H 2 , Ar , He, etc.) stream passes through a vessel containing gaseous reagents and carries their vapour into the reactor. C hemical reaction of reagents leads to the formation and deposition of ceramic matrix vapour on the heated surface of the preform . Other reaction powders diffuse out of the preform and are carried by the flowing gas stream out of the furnace. The deposition process continues, until all the inter fibre spaces are filled up resulting in a homogeneous and more or less void free composite. M ain advantage is that it causes minimum damage to the fibres(due to low pressure & temperature) and also this process permits fabrication of composite parts with irregular shapes. A typical reaction such as                      CH 3 + SiCl 3   → SiC +   3HCL is responsible for deposition of SiC vapour . 33 4.4 Chemical Vapour Deposition Process

34. This process been found to yield superior carbon-carbon composites and has been used to produce aerospace components such as aircraft brake discs and engine exit nozzles, rotors, etc . 34 Some Applications of CMCs :

35. A major challenge relating to composite design is the unavailability of simulation tools and a general lack of composite material characterization. Manufacturing is an issue for composites in the automotive sector when one considers the high production volumes required . One reason is the cost of the raw materials, and the lack of suitable manufacturing processes. There is an ever-increasing demand for the manufacturing of large and complex shaped parts , which are either quite expensive or very difficult to fabricate . More improved fibres are needed that are stable for long times at high temperature. 35 5. Future Challenges

36. Due to their higher strength-to-weight ratios, composite materials have an advantage over conventional metallic materials; although, currently it is expensive to fabricate composites. Components must be designed with composites in mind from the onset of the design process. For this reason, the designer must have a good understanding of the candidate materials and must be well versed in the manufacturing techniques that may be employed . Day by day, there is an increased n umber of developments in the area of fabrication science in tune with the requirement of dimensions, strength, applications of composite. 36 6. Conclusion

37. Basutkar A.G. and Kolekar A., ” A Review on Properties and Applications of Ceramic Matrix Composites”, IJRSI , Vol. II, Issue XII, 2015, pp:28-30 Awalellu K.A ., “ A Review on Properties and Applications of Polymer Matrix Composites”, IJRSI , Vol. III, Issue IA, 2016, pp:53-55 Begg A.R., ”Application of Metal Matrix Composite”, BP Metal Composites Ltd. , 1991, pp:42-45 Akay M., “An Introduction to Polymer Matrix Composites”, Bookboon.com, Vol. 1, 2015. “Metal Matrix Composite Handbook”, Department of Defence USA , Volume 4 of 5, 2002. “Polymer Matrix Composite Handbook”, Department of Defence USA , Volume 4 of 5, 2002. “Ceramic Matrix Composite Handbook”, Department of Defence USA , Volume 4 of 5, 2002 . Krishnakanth K. and Sivakuma E.R ., “ Design and Fabrication of Composite Gears “, IJIRSET , 2015, pp:364-372 Rawal S., “Metal Matrix Composites for Space Application”, MMC for space:Overview , 2001, pp:14-17. Divya H.V ., Naik L.L., and Yogesha B.,”Processing Techniques of Polymer Matrix Composites – A Review” International Journal of Engineering Research and General Science , Volume 4, Issue 3, 2016, pp : 357-362. 37 REFERENCES

38. Halbig M.C., Jaskowiak M.H ., Kiser J.D. and Zhu D., “Evaluation of Ceramic Matrix Composite Technology for Aircraft Turbine Engine Applications”, NASA Glenn Research Centre, 2013, pp:1-11. 12. Kaczmara J.W., Pietrzakb K., and Włosinskic W., “The production and application of metal matrix composite materials “, Journal of Materials Processing Technology , 2000, pp : 58-67 13. Donato et al., “Process for producing ceramic matrix composite by liquid infiltration”, U.S. Patents , 1998, Patent No. 5,853,653 14. Macke A., Schultz B.F., and Rohatgi P., “MMC for Automotive Industry”, Center for Composite Materials,University of Wisconsin– Milwauke ”, 2012,pp :19-23. 38 REFERENCES (Contd.)