PPT_MFG_Chapter19_Lect 2.pptx

Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 19: Plastics and Composite Materials: Forming and Shaping Chapter Outline 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Introduction Extrusion Injection Molding Blow Molding Rotational Molding Thermoforming Compression Mo...

Manufacturing Engineering Technology in SI Units, 6th Edition Chapter 19: Plastics and Composite Materials: Forming and Shaping Chapter Outline 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Introduction Extrusion Injection Molding Blow Molding Rotational Molding Thermoforming Compression Molding Transfer Molding Casting Foam Molding Cold Forming and Solidphase Forming Processing Elastomers Processing Polymermatrix Composites Processing Metal-matrix and Ceramic-matrix Composites Design Considerations Economics of Processing Plastics and Composite Materials Introduction    Processing of plastics and elastomers is similar to forming and shaping of metals Thermoplastics melt and thermosets cure at low temperatures, easy to handle and require less force and energy to process Plastics can be molded, cast, formed and machined with ease and at high production rates Introduction Introduction Extrusion  In extrusion, the raw materials are in the form of thermoplastic pellets, granules or powder  https://www.youtube.com/watch?v=WaB-dsB1Kfk Extrusion  1. 2. 3.    Screws have three distinct sections: Feed section Melt section Metering or pumping section Molten plastic is forced through a die in a process similar to that of extruding metals Controlling the rate and uniformity of cooling is important to minimize product shrinkage and distortion Complex shapes with constant cross section can be extruded with inexpensive tooling Extrusion (a) Coat-hanger die for extruding sheet (b) Round die for producing rods (c) Non-uniform recovery of the part after it exits the die https://www.youtube.com/watch?v=3BFV-2jZliw Extrusion : Miscellaneous Extrusion Processes Plastic Tubes and Pipes  These are produced in an extruder with a spider die https://www.youtube.com/watch?v=SqyrJUNhXwg Extrusion : Miscellaneous Extrusion Processes Rigid Plastic Tubing  The die is rotated and rigid plastic tubing causes the polymer to be sheared and biaxially oriented during extrusion Coextrusion for producing bottle  Involves simultaneous extrusion of two or more polymers through a single die Extrusion : Miscellaneous Extrusion Processes Plastic-coated Electrical Wire  Electrical wire, cable, and strips are extruded and coated with plastic by this process Polymer Sheets and Films  These can be produced by using a specially designed flat-extrusion die  Also known as the coat-hanger die  Designed to distribute the polymer melt evenly throughout the width Extrusion : Miscellaneous Extrusion Processes Polymer Sheets and Films Extrusion : Miscellaneous Extrusion Processes Thin Polymer Films  Common plastic bags and other thin polymer film products are made from blown film, which in turn is made from a thin-walled tube produced by an extruder Extrusion : Miscellaneous Extrusion Processes Thin Polymer Films  Common plastic bags and other thin polymer film products are made from blown film, which in turn is made from a thinwalled tube produced by an extruder Extrusion : Miscellaneous Extrusion Processes EXAMPLE 19.1 Blown Film Assume that a typical plastic shopping bag made by blown film has a lateral dimension (width) of 400 mm with an expansion ratio of 2.5. (a) What should be the extrusion-die diameter? (b) These bags are relatively strong in use. How is this strength achieved? Extrusion : Miscellaneous Extrusion Processes Solution Blown Film a. The perimeter is (2) (400) = 800mm Blown diameter should be πD = 800 D = 255mm For 2.5 times, the die diameter is 255/2.5 = 100mm b. The resulting biaxial orientation of the polymer molecules significantly improves the strength and toughness of the plastic bag Extrusion : Production of Polymer Reinforcing Fibers     Synthetic fibers used in reinforced plastics are polymers that are extruded through the tiny holes of a device called a spinneret Process of extrusion and solidification of continuous filaments is called spinning Spinning is used for the production of natural textiles where short pieces of fiber are twisted into yarn There are 4 methods of spinning fibers: melt, wet, dry, and gel spinning Extrusion : Production of Polymer Reinforcing Fibers  In melt spinning, the polymer (thermoplastics) is melted for extrusion through the spinneret and then solidified directly by cooling Extrusion : Production of Polymer Reinforcing Fibers   Wet spinning is the process for fiber production and used for thermoset polymers that have been dissolved in a solvent. The spinneret is submerged in a chemical bath that causes the fiber to precipitate by dilluting the solvant in liquid bath, and then solidify, as it emerges. The process gets its name from this "wet" bath. Acrylic, rayon, aramid, modacrylic, and spandex are produced via this process. Extrusion : Production of Polymer Reinforcing Fibers  Dry spinning is used for thermosets carried by a solvent  It differs from wet spinning in that the solidification is achieved through evaporation of the solvent. This is usually achieved by a stream of air or inert gas. Because there is no precipitating liquid involved, the fiber does not need to be dried, and the solvent is more easily recovered.  Acetate, triacetate, acrylic, modacrylic, polybenzimidazole fiber, spandex, and vinyon are produced via this process. Extrusion : Production of Polymer Reinforcing Fibers  Gel spinning is used to obtain high strength or special fiber properties. Gel spinning, also known as dry-wet spinning. The polymer is in a "gel" state, only partially liquid, which keeps the polymer chains somewhat bound together. These bonds produce strong inter-chain forces in the fiber, which increase its tensile strength. The polymer chains within the fibers also have a large degree of orientation, which increases strength. The fibers are first air dried, then cooled further in a liquid bath. Some high strength polyethylene and aramid fibers are produced via this process. Dry Spinning Wet Spinning Melt Spinning Gel Spinning Injection Molding  Injection molding is similar to hot-chamber die casting Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding    Pellets or granules are fed into the heated cylinder The melt is forced into the mold either by a hydraulic plunger or by the rotating screw system of an extruder Modern machines are of the reciprocating or plasticating screw type Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding  Some injection-molded products Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding   Molds with moving and unscrewing mandrels are used in injection molding They allow the molding of parts to have multiple cavities or internal and external threaded features Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding  1. 2. 3. 3 basic types of molds: Cold-runner, two-plate mold (a) Cold-runner, three-plate mold (b) Hot-runner mold (c) Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding   Multicomponent injection molding allows the forming of parts with a combination of various colors and shapes Insert molding involves metallic components that are placed in the mold cavity prior to injection and then becoming an integral part of the molded product Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding Overmolding  A process for making products in one operation and without the need for post molding assembly http://www.youtube.com/watch?v=eUthHS3MTdA&NR=1&feature=endscreen Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding Overmolding  In ice-cold molding, the same type of plastic is used to form both components of the joint  Operation is carried out in a standard injection-molding machine and in one cycle Process Capabilities (~70-200 MPa)  Injection molding is a high-rate production process and permits good dimensional control  Capable of producing complex shapes with good dimensional accuracy  Thermosets are molded at 2000C and Thermoplastics at 900C Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding Machines  Injection-molding machines are horizontal  Vertical machines are used for making small, closetolerance parts and for insert molding  Machines are rated according to the capacity of the mold and the clamping force  High-volume production is essential to justify high expenditure 2.2 MN Horizontal injection molding machine Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding EXAMPLE 19.2 Force Required in Injection Molding A 2.2-MNn injection-molding machine is to be used to make spur gears 110 mm in diameter and 2.5 mm thick. The gears have a fine-tooth profile. How many gears can be injection molded in one set of molds? Does the thickness of the gears influence your answer? (assume that the pressure required in the mold is 100 Mpa) Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding Solution Force Required in Injection Molding The pressures required in the mold cavity will be on the order of 100 MPa. Cross-sectional (projected) area of the gear is π(1002)/4 = 9500mm2 The force required is (9500)(100) = 0.95 MN We have 2.2 MN of clamping force available, the mold can accommodate two cavities and produce two gears per cycle. As it does not influence the crosssectional area of the gear, the thickness of the gear does not have influence. Copyright © 2010 Pearson Education South Asia Pte Ltd Injection Molding: Reaction-injection Molding  In the reaction-injection molding (RIM) process, a monomer and two or more reactive fluids (can be other monomers) are forced at high speed into a mixing chamber and into the mold cavity Nylon, polyurethane and epoxy Applications: bumpers & fenders, steering wheels & instrument panels Pressure: 10-20MPa Chemical reaction Copyright © 2010 Pearson Education South Asia Pte Ltd Blow Molding   Blow molding is a modified extrusion- and injection-molding process In extrusion blow molding, a tube is first extruded, then clamped into a mold with a cavity and blown outward to fill the mold cavity Copyright © 2010 Pearson Education South Asia Pte Ltd Blow Molding  In injection blow molding, a short tubular piece (parison) is injection molded into cool dies  The dies then open and the parison is transferred to a blow-molding die by an indexing mechanism Copyright © 2010 Pearson Education South Asia Pte Ltd Blow Molding Blow Molding Video Copyright © 2010 Pearson Education South Asia Pte Ltd Rotational Molding     Thermoplastics and thermosets can be formed into large, hollow parts by rotational molding A thin-walled metal mold is made in two pieces and is designed to be rotated about two perpendicular axes Liquid polymers (plastisols) can be used in rotational molding The mold is heated and rotated simultaneously Applications: Storage tanks, trash cans, boat hulls, buckets, housings, large hollow toys, carrying cases, footballs and boots Copyright © 2010 Pearson Education South Asia Pte Ltd Rotational Molding Process Capabilities  Can produce parts with complex, hollow shapes with small wall thicknesses  Produce large parts volume  Outer surface finish of the part is a replica of the surface finish of the inside mold walls  Quality-control considerations usually involve accurate weight of the powder, proper rotational speed of the mold Copyright © 2010 Pearson Education South Asia Pte Ltd Thermoforming   Thermoforming is a process for forming thermoplastic sheets or films over a mold through heat and pressure Due to low strength of the materials formed, the pressure difference caused by a vacuum is sufficient for forming Applications: packaging, trays for cookies and candy, advertising signs and refrigerator liners Copyright © 2010 Pearson Education South Asia Pte Ltd Thermoforming Process Capabilities (0.1-2 MPa)  Used to produce packaging, trays for cookies and candy, advertising signs and refrigerator liners  The material must exhibit high, uniform elongation, else it will neck and tear  Molds for thermoforming are made of aluminum because high strength is not required, thus tooling is inexpensive Thermoforming Video Copyright © 2010 Pearson Education South Asia Pte Ltd Compression Molding— Similar to forging   In compression molding, a pre-shaped charge or a powder or a viscous mixture of liquid-resin and filler material is placed into a heated mold cavity Forming is done under pressure from a plug or upper half of the die Copyright © 2010 Pearson Education South Asia Pte Ltd Compression Molding Process Capabilities (10-150MPa)  3 types of compression molds are available: 1. Flash type (c): for shallow or flat parts (low Pressure) 2. Positive type (a): for high-density parts (high Pressure) 3. Semipositive type (b): for quality production (mid pressure) 4. Used mainly for Thermosetting plastics with original materials in partially polymerized state (Thermoplastics and elastomers are also processed) Compression Molding Process Capabilities  Complexity of parts produced is less than that from injection molding  But dies are cheaper due to simplicity  Dimensional control is better Copyright © 2010 Pearson Education South Asia Pte Ltd Transfer Molding   Transfer molding is a further development of compression molding The uncured thermosetting resin is placed in a heated transfer pot or chamber and after the material is heated, it is injected into heated closed molds Copyright © 2010 Pearson Education South Asia Pte Ltd Transfer Molding Process Capabilities (~300 MPa)  Suitable for intricate shapes with varying wall thicknesses (comparable to injection molding)  Molds are more expensive  Some excess material will be left in the channels of the mold during filling  Typical: Electronics Manufacturing =thin intricate parts requires higher pressure than injection molding Copyright © 2010 Pearson Education South Asia Pte Ltd Casting  Thermoplastics and thermosetting plastics can be cast into shapes using rigid or flexible molds  Casting is a slow but simple and inexpensive process  Polymer must have low viscosity in order to flow easily into the mold  Typical: gears, bearings, wheels, thick sheets, components that require resistance to abrasive wear Copyright © 2010 Pearson Education South Asia Pte Ltd Casting Potting and Encapsulation  Potting and encapsulation involve casting the plastic material around an electrical component to embed it in the plastic  Potting is carried out in a housing or case, which becomes an integral part of the component and fixes it in position (b)  In encapsulation the component is coated with a layer of the plastic, surrounding it completely and solidifying (c) Copyright © 2010 Pearson Education South Asia Pte Ltd Casting Centrifugal Casting  Similar to centrifugal metal casting  Used with thermoplastics, thermosets and reinforced plastics with short fibers Copyright © 2010 Pearson Education South Asia Pte Ltd Foam Molding  Products are styrofoam cups, food containers, insulating blocks and shaped packaging materials  In foam molding, raw material is expandable polystyrene beads where products have a cellular structure  Structure may have open and interconnected porosity or have closed cells, depending on polymer viscosity Copyright © 2010 Pearson Education South Asia Pte Ltd Foam Molding    A common method of foam molding is to use preexpanded polystyrene beads with blowing agents (pentane, a volatile hydrocabon or inert gas (nitrogen)) which are then molded in the mold later Another method: the mixture is placed in the mold and heated by steam or hot air /water or oven They can expand as much as 50 times the original size and take the shape of mold cavity Foam Molding Video   Amount of expansion can be controlled by varying the temperature and time Small bead size for small thin parts and big size for big and thick parts Copyright © 2010 Pearson Education South Asia Pte Ltd Foam Molding Structural Foam Molding  Molding process used to make plastic products with a solid outer skin and a cellular core structure  Typical: furniture components, computer and business machine housings and moldings  Thermoplastics are mixed with a blowing agent and injection molded into cold molds of desired shapes   The rapid cooling of against the cold mold surfaces produces a rigid 2mm skin and core that is cellular. Overall density is only 40% of solid plastics and has high stiffness-weight ratio Structral Foam Molding Copyright © 2010 Pearson Education South Asia Pte Ltd Foam Molding Polyurethane Foam Processing  Furniture cushions and insulating blocks are made by this process  Starts with the mixing of two or more components and allowing chemical reactions to take place after the mixture is    A) poured into a mold of various shapes B) sprayed over surfaces with a spray gun to provide sound and thermal insulation The mixture solidifies with cellular structures Copyright © 2010 Pearson Education South Asia Pte Ltd Cold Forming and Solid-phase Forming  Used in the cold working of metals and form thermoplastics at room temperature (cold forming: rolling, closed die forging, deep drawing and rubber forming)  Considerations for this process are the polymer must be ductile at room temperature and its deformation must be non-recoverable  Typical materials: polypropylene, polycarbomate, ABS and rigid PVC Cold Forming and Solid-phase Forming  Advantages of the cold forming of plastics are: 1. Strength, toughness and uniform elongation are increased Superior properties using high molecular weights plastics Forming speeds are not affected by part thickness because there is no heating/cooling involved Cycle time is generally shorter than in molding processes 2. 3. 4. Processing Elastomers  In terms of its processing characteristic, thermoplastic elastomer is a polymer  In terms of its function and performance, it is a rubber  Materials used are compound of rubber and various additives and fillers Additives can enhance properties such as tensile and fatigue strength, abrasion and tear resistance, ultraviolet protection and resistance to chemicals Elastomers can be shaped by a variety of processes that are used for shaping thermoplastics   Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Elastomers Thermoplastic elastomers are commonly shaped by       extrusion (fast and economical) injection molding, blowing molding thermoforming Rubber and thermoplastic sheets are formed by the calendering process which can also be used subsequently in thermoforming to produce Calendering is process of smoothing and compressing a material during production by passing a single continuous sheet through a number of pairs of heated rolls. The rolls in combination are called calenders. Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites   Polymer-matrix composites (PMCs) are engineered materials with unique mechanical properties, especially high strength-to-weight ratio, stiffnessto-weight ratio, fatigue strength, creep resistance, and directional properties Polymer-matrix composites can be fabricated to ensure reliable properties in composite parts and structures Reinforced plastic components for Honda motor cycle: front and rear forks, a rear swing arm, a wheel and break disks. Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Fiber Impregnation To obtain good bonding between the reinforcing fibers and polymer matrix and protection during handling, fibers are surface treated by impregnation (sizing) Prepreg Tapes  To produce fiber-reinforced plastic prepreg tapes, the continuous fibers are aligned and subjected to a surface treatment to enhance the adhesion to the polymer matrix  They are then coated by dipping them in a resin bath and are made into a tape  Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Fiber Impregnation Prepregs Tapes   Individual segments of prepreg tapes are then cut and assembled into laminated structures Automated computer-controlled tape-laying machines have been built for laying prepreg tapes Boeing 787 Dreamliner Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Sheet-molding Compound Video Fiber Impregnation Sheet-molding Compound (Thermoset Materials with chopped longer fiber length fibers (up to 2“ or continuous) with good Mechanical Properties)  In making sheet-molding compound (SMC), continuous strands of reinforcing fiber are chopped and deposited in random orientations over a layer of resin paste carried by a polymer film (polyethylene)+ another resin/film layer on top  Primarily used in Compression Molding Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Sheet-molding Compound Video Fiber Impregnation Sheet-molding Compound (Thermoset Materials with chopped longer fiber length fibers (up to 2“ or continuous) with good Mechanical Properties) Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Fiber Impregnation Bulk-molding Compound (BMC) (Thermoset Materials with very short randomly oriented fibers)  BMC are in the shape of billets and are made in similar the manner to SMC and are extruded to produce a bulk form  BMC are used in compression, transfer and injection molding due to good flow property Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Fiber Impregnation Thick-molding Compound (TMC) (Thermoset Materials with medium length (up to 2") randomly oriented fibers)  Unique process that produces a material with the best combined properties of a BMC (excellent flow properties) and SMC (excellent mechanical properties)  Unlike SMC, TMC is choped into short pieces  TMC are used in compression, transfer and injection molding Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Molding of Reinforced Plastics Compression Molding (for SMC+BMC+TMC)  Material is placed between 2 molds and pressure applied  Sheet-molding compounds also can be processed Vacuum-bag Molding (video1:Carbon fiber / Video2:Turbine blade)  Prepregs(Tapes/fabrics) are laid in a mold to form the desired shape (curing at room temperature or in oven) Pressure-bag molding: bag is placed over the resin and reinforcing fiber mixture and pressure is applied Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Molding of Reinforced Plastics Transfer and Injection Molding for BMC+TMC Resin Transfer mold using fabric+transfer molding Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Molding of Reinforced Plastics Contact Molding  Also referred to as open-mold processing  Use a single male or female mold made of reinforced plastics, wood, metal, or plaster  Contact molding is used in making laminated products with high surface area–to-thickness ratios  2 types: hand layup and spray layup Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Molding of Reinforced Plastics Contact Molding Wind Turbine Blade Manufacturing Wind Turbine Blade   Hand layup: whereby fiber reinforcements (fiber fabrics) are laid and resin mixture then applied layer by layer on a specially designed mould until the desired thickness & shape is formed. A specially designed roller is used by the production operator to roll & apply pressure to make manually mold the product. Spray layup Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming Filament Winding  A process where resin and fibers are combined at the time of curing in order to develop a composite structure  Products made by filament winding are very strong because of their highly reinforced structure Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming Pultrusion  Long parts with various uniform cross sections made continuously by the pultrusion process  Continuous reinforcement, glass roving, or fabric is supplied through several bobbins For curing Pultrusion Video Pulled through a thermosetting polyester bath Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming Pultrusion  Long parts with various uniform cross sections made continuously by the pultrusion process  Continuous reinforcement, glass roving, or fabric is supplied through several bobbins For curing Pultrusion Video Pulled through a thermosetting polyester bath Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming Pulforming After being pulled through the polymer bath, the composite is clamped between two halves of the die and cured into finished product. Examples: hammer handles reinforced by glass fibers and cured automotive leaf springs Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming EXAMPLE 19.3 Polymer Automotive-body Panels Shaped by Various Processes    Polymeric materials are used for automobile bodies Materials are selected for design flexibility, impact strength and toughness, corrosion resistance, high durability, and low mass 3 competing methods: a) injection molding of thermoplastics and elastomers; b) reaction-injection molding of polyurea/polyurethanes; c) compression molding of SMC Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming EXAMPLE 19.3 Polymer Automotive-body Panels Shaped by Various Processes  Polymeric materials are used for automobile bodies  Materials are selected for design flexibility, impact strength and toughness, corrosion resistance, high durability, and low mass  3 competing methods: a) injection molding of thermoplastics and elastomers; b) reaction-injection molding of polyurea/polyurethanes; c) compression molding of SMC Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming EXAMPLE 19.3 Polymer Automotive-body Panels Shaped by Various Processes    Examples: a) body panels & other large exterior components by injection molding; b) outer door panels & rear quarter panels made of polyphenyleneether/nylon or thermoplastic polyester; c) outer door panels made of polycarbonate/ABS; d) facias made of thermoplastic polyolefin Body panels and bumpers are also made of Reactioninjection molded polyurethane/polyureas Thermoset facias are made of reinforced RIM polyurethane Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Filament Winding, Pultrusion, and Pulforming EXAMPLE 19.3 Polymer Automotive-body Panels Shaped by Various Processes   Hoods, roofs and rear decks are made of reinforced polyester or vinylester in compression molding using SMCs Low volume parts are made by resin-transfer molding (RTM) Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Quality Considerations in Processing Reinforced Plastics  Gases must be allowed to escape from the layup through the vacuum bag in order to avoid porosity due to trapped gases  Microcracks may develop during improper curing or during the transportation and handling of parts Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Quality Considerations in Processing Reinforced Plastics CASE STUDY 19.1 (Internally pressurized pressure-bag molding) Manufacture of Head Protector™ Tennis Racquets Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Polymer-matrix Composites: Quality Considerations in Processing Reinforced Plastics CASE STUDY 19.1 (Internally pressurized pressure-bag molding) Manufacture of Head Protector™ Tennis Racquets  Graphite fibers in epoxy matrix using Carbon-epoxy prepregs  Lead Zirconate Titannate (PZT) fibers as integral layers  ChipSystem Prepregs wraps around Polyamide sleeve which itself wraps around a tube inside a mold (outside the prepregs there is another layer of polyamide)  Inside the mold, tube is removed and the hollow passage left behind is internally pressurized and the  Racquet is allowed to cure: a pressure bag Molding Process Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Metal-matrix and Ceramic-matrix Composites  1. 2. 3. Metal-matrix composites (MMCs) can be made into nearnet shaped parts by: Liquid-phase processing: casting the liquid-matrix material (aluminum or titanium) and the solid reinforcement (graphite, aluminum oxide or silicon carbide) together by conventional casting or pressurefiltration casting Solid-phase processing: powder-metallurgy techniques Two-phase (liquid–solid) processing: the reinforced fibers are mixed with a matrix that contains both liquid and solid phases of metal Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Metal-matrix and Ceramic-matrix Composites EXAMPLE 19.4 Metal-matrix Composite Brake Rotors and Cylinder Liners  Brake rotors are made of composites consisting of an aluminum-based matrix reinforced with 20% siliconcarbide particles  To improve the wear- and heat resistance of cast iron cylinder liners in aluminum engine blocks, aluminummatrix liners also are being developed Copyright © 2010 Pearson Education South Asia Pte Ltd Processing Metal-matrix and Ceramic-matrix Composites: Processing Ceramic-matrix Composites  1. 2. 3. Other process used to make ceramic-matrix composites (CMCs): Slurry infiltration: most common—a fiber preform is hot pressed and impregnated with a combination of slurry (contains matrix powder), a carrier liquid and an organic binder. High strength, toughness and uniform structure are obtained. Further processing by reaction bonding or reaction sintering of the slurry possible Chemical-synthesis: the sol-gel and polymer-precursor techniques Chemical-vapor infiltration: a porous fiber preform is infiltrated with matrix phase using chemical vapor deposition technique Copyright © 2010 Pearson Education South Asia Pte Ltd Thermoplastic Properties (Table 2-2) Shigley’s Mechanical Engineering Design Thermoset Properties (Table 2-3) Shigley’s Mechanical Engineering Design Composite Materials Formed from two or more dissimilar materials, each of which contributes to the final properties  Materials remain distinct from each other at the macroscopic level  Usually amorphous and non-isotropic  Often consists of laminates of filler to provide stiffness and strength and a matrix to hold the material together  Common filler types:  Shigley’s Mechanical Engineering Design Fig. 2–14 Material Families and Classes (Table 2-4) Shigley’s Mechanical Engineering Design Material Families and Classes (Table 2-4) Shigley’s Mechanical Engineering Design Material Families and Classes (Table 2-4) Shigley’s Mechanical Engineering Design Material Families and Classes (Table 2-4) Shigley’s Mechanical Engineering Design Design Considerations General design guidelines for the production of plastic and composite-material parts:  1. Complex parts with internal and external features can be produced with relative ease and at high production rates 2. Plastics have much lower stiffness and strength and high thermal expansion, section sizes and shapes should be selected accordingly 3. Overall part shape and thickness determine the shaping or molding process to be selected Copyright © 2010 Pearson Education South Asia Pte Ltd Design Considerations 4. Large variations in cross-sectional areas, section thicknesses, and abrupt changes in geometry, should be avoided to achieve the desired shape (see a & c) 5. Low elastic moduli of plastics requires that shapes be selected properly for improved stiffness of the component (see a & b below) 6. Improper part design or assembly can lead to distortion and uneven shrinking (see a & c) Copyright © 2010 Pearson Education South Asia Pte Ltd Design Considerations 4. Properties of the final product depend on the original material and its processing history 5. Reinforced plastics has directional nature of the strength of the composite Copyright © 2010 Pearson Education South Asia Pte Ltd Economics of Processing Plastics and Composite Materials   Design and manufacturing decisions are based on performance and cost Final selection of a process depends greatly on production volume for justification of equipment costs Copyright © 2010 Pearson Education South Asia Pte Ltd