Polymer Properties. TABLE 10.1 Approximate range of mechanical properties for various engineering plastics at room temperature.

Transcription

1 Polymer Properties Elongation Poisson s in 50 mm ratio Material UTS (MPa) E (GPa) (%) (ν) ABS ABS (reinforced) Acetals Acetals (reinforced) Acrylics Cellulosics Epoxies Epoxies (reinforced) Fluorocarbons Nylon Nylon (reinforced) Phenolics Polycarbonates Polycarbonates (reinforced) Polyesters Polyesters (reinforced) Polyethylenes Polypropylenes Polypropylenes (reinforced) Polystyrenes Polyvinyl chloride TABLE 10.1 Approximate range of mechanical properties for various engineering plastics at room temperature.

2 C C eat, pressure, catalyst C C C C C C Mer n Polyethylene Polymer Structure Monomer Polymer repeating unit C C C C Polyethylene n C C C C Polypropylene C 3 C 3 n C C C C Polyvinyl chloride Cl Cl n C C C C Polystyrene Fl C Fl C 6 5 Fl C Fl Fl C Fl C 6 5 Fl C Fl n (c) n Polytetrafluoroethylene (Teflon) FIGURE 10.1 Basic structure of some polymer molecules: ethylene molecule; polyethylene, a linear chain of many ethylene molecules; (c) molecular structure of various polymers. These molecules are examples of the basic building blocks for plastics.

3 Effect of Molecular Weight Commercial polymers Property Tensile and impact strength Viscosity Molecular weight, degree of polymerization FIGURE 10.2 Effect of molecular weight and degree of polymerization on the strength and viscosity of polymers.

4 Polymer Chains Linear Branched (c) Cross-linked (d) Network FIGURE 10.3 Schematic illustration of polymer chains. Linear structure; thermoplastics such as acrylics, nylons, polyethylene, and polyvinyl chloride have linear structures. Branched structure, such as polyethylene. (c) Crosslinked structure; many rubbers and elastomers have this structure. Vulcanization of rubber produces this structure. (d) Network structure, which is basically highly cross-linked; examples include thermosetting plastics such as epoxies and phenolics.

5 Effect of Temperature Elastic modulus (log scale) Glassy Leathery Rubbery 100% crystalline Amorphous Increasing crystallinity Elastic modulus (log scale) Glassy Leathery Rubbery No cross-linking Increasing cross-linking Viscous Viscous T g T m T m Temperature Temperature FIGURE 10.4 Behavior of polymers as a function of temperature and degree of crystallinity and crosslinking. The combined elastic and viscous behavior of polymers is known as viscoelasticity.

6 Crystallinity Amorphous region Crystalline region FIGURE 10.5 Amorphous and crystalline regions in a polymer. Note that the crystalline region (crystallite) has an orderly arrangement of molecules. The higher the crystallinity, the harder, stiffer, and less ductile is the polymer.

7 Glass-Transition Temperature Specific volume Cooling: rapid slow Amorphous polymers T g Temperature FIGURE 10.6 Specific volume of polymers as a function of temperature. Amorphous polymers, such as acrylic and polycarbonate, have a glass-transition temperature, Tg, but do not have a specific melting point, Tm. Partly crystalline polymers, such as polyethylene and nylons, contract sharply at their melting points during cooling. T m Partly crystalline polymers Material T g ( C) T m ( C) Nylon 6, Polycarbonate Polyester Polyethylene igh density Low density Polymethylmethacrylate 105 Polypropylene Polystyrene Polytetrafluoroethylene (Teflon) Polyvinyl chloride Rubber -73 TABLE 10.2 Glass-Transition and Melting Temperatures of Selected Polymers

8 Deformation of Polymers Strain t 0 t 1 Time Strain t 0 t 1 Time Increasing viscosity Rigid and brittle (melamine, phenolic) Tough and ductile (ABS, nylon) Strain Recovered strain Strain Recovered strain 0Stress Soft and flexible (polyethylene, PTFE) Strain t 0 t 1 Time (c) t 0 t 1 Time (d) FIGURE 10.7 Various deformation modes for polymers.: elastic; viscous; (c) viscoelastic (Maxwell model); and (d) viscoelastic (Voigt or Kelvin model). In all cases, an instantaneously applied load occurs at time to, resulting in the strain paths shown. FIGURE 10.8 General terminology describing the behavior of three types of plastics. PTFE is polytetrafluoroethylene (Teflon, a trade name). Source: After R.L.E. Brown.

9 Temperature Effects C Stress (psi x 10 3 ) C MPa Impact strength Low-density polyethylene igh-impact polypropylene Polyvinyl chloride Polymethylmethacrylate Strain (%) FIGURE 10.9 Effect of temperature on the stressstrain curve for cellulose acetate, a thermoplastic. Note the large drop in strength and increase in ductility with a relatively small increase in temperature. Source: After T.S. Carswell and.k. Nason Temperature ( F) FIGURE Effect of temperature on the impact strength of various plastics. Note that small changes in temperature can have a significant effect on impact strength. Source: P.C. Powell.

10 Viscosity of Melted Polymers y v t Viscous behavior: ( ) dv τ = η = η γ dy t FIGURE Parameters used to describe viscosity; see Eq. (10.3). FIGURE Viscosity of some thermoplastics as a function of temperature and shear rate. Source: After D.. Morton-Jones. Viscosity (Ns/m 2 ) Rigid PVC Acrylic Polypropylene Low density polyethylene! = 1000 s -1 Nylon Temperature ( C) Apparent viscosity (Ns/m 2 ) Acrylic (240 C) LDPE (170 C) Nylon (285 C) Polypropylene (230 C) Polycarbonate Rigid PVC (190 C) Shear rate,! (s -1 )

11 Polymer Behavior in Tension mm Molecules are being oriented Stress (MPa) (psi x 10 3 ) Load Loading Unloading Elongation (in.) FIGURE Load-elongation curve for polycarbonate, a thermoplastic. Source: After R.P. Kambour and R.E. Robertson. igh-density polyethylene tension-test specimen, showing uniform elongation (the long, narrow region in the specimen). Elongation FIGURE Typical loadelongation curve for elastomers. The area within the clockwise loop, indicating loading and unloading paths, is the hysteresis loss. ysteresis gives rubbers the capacity to dissipate energy, damp vibration, and absorb shock loading, as in automobile tires and vibration dampeners for machinery.

12 Applications for Plastics Design Requirement Mechanical strength Wear resistance Typical Applications Gears, cams, rollers, valves, fan blades, impellers, pistons. Gears, wear strips and liners, bearings, bushings, roller-skate wheels. Frictional properties igh Tires, nonskid surfaces, footware, flooring. Electrical resistance Plastics Acetals, nylon, phenolics, polycarbonates, polyesters, polypropylenes, epoxies, polyimides. Acetals, nylon, phenolics, polyimides, polyurethane, ultrahigh-molecular-weight polyethylene. Elastomers, rubbers. Low Sliding surfaces, artificial joints. Fluorocarbons, polyesters, polyethylene, polyimides. All types of electrical components and Polymethylmethacrylate, ABS, fluorocarbons, equipment, appliances, electrical fixtureslenes, nylon, polycarbonate, polyester, polypropy- ureas, phenolics, silicones, rubbers. Chemical resistance eat resistance Functional and decorative features Functional and transparent features ousings and hollow shapes Containers for chemicals, laboratory equipment, components for chemical industry, food and beverage containers. Appliances, cookware, electrical components. andles, knobs, camera and battery cases, trim moldings, pipe fittings. Lenses, goggles, safety glazing, signs, food-processing equipment Power tools, housings, sport helmets, telephone cases. Acetals, ABS, epoxies, polymethylmethacrylate, fluorocarbons, nylon, polycarbonate, polyester, polypropylene, ureas, silicones. Fluorocarbons, polyimides, silicones, acetals, polysulfones, phenolics, epoxies. ABS, acrylics, cellulosics, phenolics, polyethylenes, polpropylenes, polystyrenes, polyvinyl chloride. Acrylics, polycarbonates, polystyrenes, polysulfones. laboratory hardware. ABS, cellulosics, phenolics, polycarbonates, polyethylenes, polypropylene, polystyrenes. TA B L E G e n e r a l recommendations for plastic products.

13 Reinforced Polymers Laminate Particles Foam oneycomb Short or long fibers, or flakes Continuous fibers (c) (d) FIGURE Schematic illustration of types of reinforcing plastics. Matrix with particles; matrix with short or long fibers or flakes; (c) continuous fibers; and (d) and (e) laminate or sandwich composite structures using a foam or honeycomb core (see also Fig on making of honeycombs).

14 Properties of Reinforcing Fibers Strength/density (m x 10 4 ) Kevlar 29 Kevlar 49 Kevlar 129 Spectra 900 S-glass E-glass Thornel P-100 igh-tensile graphite Spectra 2000 Celion 3000 Boron igh-modulus graphite Thornel P-55 Titanium Steel Aluminum Stiffness/density (m x 10 6 ) Tensile Elastic Density Relative Type Strength (MPa) Modulus (GPa) (kg/m 3 ) Cost Boron ighest Carbon igh strength Low igh modulus Low Glass E type Lowest S type Lowest Kevlar igh igh igh Nextel igh igh Spectra igh igh Note: These properties vary significantly, depending on the material and method of preparation. Strain to failure for these fibers is typically in the range of 1.5% to 5.5%. FIGURE Specific tensile strength (ratio of tensile strength-to-density) and specific tensile modulus (ratio of modulus of elasticity-to-density) for various fibers used in reinforced plastics. Note the wide range of specific strength and stiffness available. TABLE 10.4 Typical properties of reinforcing fibers.

15 Metal and Ceramic Matrix Composites Material FIBER Glass Graphite Boron Aramids (Kevlar) Other MATRIX Thermosets Thermoplastics Metals Ceramics Characteristics igh strength, low stiffness, high density; E (calcium aluminoborosilicate) and S (magnesiaaluminosilicate) types are commonly used; lowest cost. Available typically as high modulus or high strength; less dense than glass; low cost. igh strength and stiffness; has tungsten filament at its center (coaxial); highest density; highest cost. ighest strength-to-weight ratio of all fibers; high cost. Nylon, silicon carbide, silicon nitride, aluminum oxide, boron carbide, boron nitride, tantalum carbide, steel, tungsten, and molybdenum; see Chapters 3, 8, 9, and 10. Epoxy and polyester, with the former most commonly used; others are phenolics, fluorocarbons, polyethersulfone, silicon, and polyimides. Polyetheretherketone; tougher than thermosets, but lower resistance to temperature. Aluminum, aluminumlithium alloy, magnesium, and titanium; fibers used are graphite, aluminum oxide, silicon carbide, and boron. Silicon carbide, silicon nitride, aluminum oxide, and mullite; fibers used are various ceramics. TABLE 10.4 Types and General Characteristics of Reinforced Plastics and Metal-Matrix and Ceramic-Matrix Composites

16 Fiber Spinning Polymer chips Feed hopper Spinneret Cold air Melter/extruder Melt spinning Bobbin Stretching Twisting and winding FIGURE 10.1 The melt spinning process for producing polymer fibers. The fibers are used in a variety of applications, including fabrics and as reinforcements for composite materials.

17 Composite Material Microstructure Matrix Kevlar fibers Graphite fibers Tungsten diameter mm Boron diameter 0.1 mm Matrix FIGURE Cross-section of a tennis racket, showing graphite and aramid (Kevlar) reinforcing fibers. Source: After J. Dvorak and F. Garrett. Cross-section of boron-fiber-reinforced composite material.

18 Effect of Fibers Tensile strength (psi x 10 3 ) Carbon fibers 300 Long glass fibers Short glass fibers Reinforcement (%) MPa Impact energy (ft-lb/in.) Long glass fibers Short glass fibers Carbon fibers Reinforcement (%) J/m Flexural modulus (psi x 10 6 ) Carbon fibers Long and short glass fibers Reinforcement (%) FIGURE Effect of the percentage of reinforcing fibers and fiber length on the mechanical properties of reinforced nylon. Note the significant improvement with increasing percentage of fiber reinforcement. Source: Courtesy of Wilson Fiberfill International. (c) GPa Flexural strength (psi x 10 3 ) Carbon fibers Long glass fibers Short glass fibers Reinforcement (%) (d) MPa

19 Strength and Fracture of Composites Tensile strength (psi x 10 5 ) Random Orthogonal Unidirectional MPa Glass content (% by weight) 0 FIGURE Fracture surface of glass-fiberreinforced epoxy composite. The fibers are 10 µm (400 µin.) in diameter and have random orientation. Fracture surface of a graphite-fiber-reinforced epoxy composite. The fibers are 9-11 µm in diameter. Note that the fibers are in bundles and are all aligned in the same direction. Source: Courtesy of L.J. Broutman. FIGURE Tensile strength of glass-reinforced polyester as a function of fiber content and fiber direction in the matrix. Source: After R.M. Ogorkiewicz.

20 Plastics Processes Process Extrusion Injection molding Structural foam molding Blow molding Rotational molding Thermoforming Compression molding Transfer molding Casting Processing of reinforced plastics Characteristics Long, uniform, solid or hollow, simple or complex cross-sections; wide range of dimensional tolerances; high production rates; low tooling cost. Complex shapes of various sizes and with fine detail; good dimensional accuracy; high production rates; high tooling cost. Large parts with high stiffness-to-weight ratio; low production rates; less expensive tooling than in injection molding. ollow thin-walled parts of various sizes; high production rates and low cost for making beverage and food containers. Large hollow shapes of relatively simple design; low production rates; low tooling cost. Shallow or deep cavities; medium production rates; low tooling costs. Parts similar to impression-die forging; medium production rates; relatively inexpensive tooling. More complex parts than in compression molding, and higher production rates; some scrap loss; medium tooling cost. Simple or intricate shapes, made with flexible molds; low production rates. Long cycle times; dimensional tolerances and tooling costs depend on the specific process. TABLE 10.6 Characteristics of processing plastics and reinforced plastics.

21 Extrusion Throat Barrel Thrust bearing Throat-cooling channel Gear reducer box opper Feed section Motor Barrel liner Melt section Barrel heater/cooler Thermocouples Melt-pumping section Wire filter screen Melt thermocouple Breaker plate Adapter Die Screw FIGURE Schematic illustration of a typical extruder.

22 Pitch Barrel Extrusion Mechanics Flight D w W! Drag flow: FIGURE Geometry of the pumping section of an extruder screw. 3 Barrel Q p = Q d = π2 D 2 N sinθcosθ 2 Pressure flow: W3 p 12η(l/sinθ) = pπd3 sin 2 θ 12ηl Flow rate, q x 10-5 (m 3 /s) Extruder characteristic Die characteristic Operating point Pressure (MPa) FIGURE 10.1 Extruder and die characteristics for Example Die characteristic Q die = K p K for circular cross-sections: K = πd4 d 128ηl d

23 Blown-Film Manufacture Pinch rolls Wind-up Guide rolls Blown tube Mandrel Extruder Die Air FIGURE Schematic illustration of production of thin film and plastic bags from a tube produced by an extruder, and then blown by air. A blown-film operation. Source: Courtesy of Windmoeller & oelscher Corp.

24 Tube Extrusion Breaker plate Spider die Extruder barrel Screen pack Polymer melt A B Section B B Section A A Melt flow direction v B Spider legs (3) Spider legs (3) Mandrel A Air channel Air in Co-extrusion blow molding Extruder 1 Plastic melt: two or more layers Mandrel Parison FIGURE Extrusion of plastic tubes. Extrusion using a spider die (see also Fig.6.59) and pressurized air; coextrusion of tube for producing a bottle. Extruder 2

25 Injection Molding Powder, Pellets opper eating zones Nozzle Mold Vent Piston (ram) Cooling zone Cylinder (barrel) Injection chamber Torpedo (spreader) Sprue Ejector pins Press (clamp) force Molded part Vent Rotating and reciprocating screw FIGURE Injection molding with a plunger and a reciprocating rotating screw. Telephone receivers, plumbing fittings, tool handles, and housings are examples of parts made by injection molding.

26 Mold Features Gate Cavity Sprue Main runner Part Gate Cold slug well Branch runner Cavity Main runner Sprue Guide pin Branch runner Guide pin FIGURE Illustration of mold features for injection molding. Two-plate mold, with important features identified; injection molding of four parts, showing details and the volume of material involved. Source: Courtesy of Tooling Molds West, Inc.

27 Mold Types Plate Gate Plate Plate Stripper plate Plate Sprue bushing Part Sprue Ejector pins Sprue bushing Ejector pins Part Runner Parts Plate ot plate; Runner stays molten Plate Sprue bushing Parts (c) Ejector pins FIGURE Types of molds used in injection molding. Two-plate mold, three-plate mold, and (c) hot-runner mold.

28 Insert Molding FIGURE Products made by insert injection molding. Metallic components are embedded in these parts during molding. Source: Courtesy of Plainfield Molding, Inc., and Courtesy of Rayco Mold and Mfg. LLC.

29 Reaction-Injection Molding eat exchanger eat exchanger Displacement cylinders Stirrer Monomer 2 Pump Stirrer Recirculation loop Monomer 1 Pump Recirculation loop Mold Mixing head FIGURE Schematic illustration of the reaction-injection-molding process.

30 Extruder eating passages Extruded parison Knife Tail Blow Molding Bottle mold Blow pin Mold closed and bottle blown Blown bottle Blow pin removed Blow pin Injection-molding machine Parison Cooling passages Blown bottle Parison mold Parison transferred to blow mold 2 Blown-mold station Blow-mold bottom plug Blown bottle Blow-mold neck ring Transfer head 3 Stripper station Indexing direction Core-pin opening (Blown air passage) Blow mold Parison 1 Preform mold station Reciprocating-screw extruder FIGURE Schematic illustrations of the blowmolding process for making plastic beverage bottles and a three-station injection-blow-molding machine. Stripper plate Bottle Preform neck ring Preform mold (c)

31 Rotational Molding Inlet Primary axis Outlet vent Pressurizing fluid Mold Spindle Secondary axis FIGURE The rotational molding (rotomolding or rotocasting) process. Trash cans, buckets, carousel horses and plastic footballs can be made by this process.

32 Thermoforming Straight vacuum forming eater Clamp Plastic sheet Mold Vacuum line Drape vacuum forming Mold (c) Force above sheet Vacuum line Clamp Plastic sheet Ram (d) Plug and ring forming Ring FIGURE Various thermoforming processes for thermoplastic sheet. These processes are commonly used in making advertising signs, cookie and candy trays, panels for shower stalls, and packaging.

33 Compression Molding eating elements Punch Open Charge Mold Knockout (ejector pin) Land Overlap Molded part Flash Closed (c) Part Plug (d) FIGURE Types of compression molding, a process similar to forging: positive, semipositive, and (c) flash. The flash in part (c) is trimmed off. (d) Die design for making a compression-molded part with undercuts. Such designs also are used in other molding and shaping operations.

34 Transfer Molding Sprue Transfer plunger Transfer pot and molding powder Punch Knockout (ejector) pin Molded parts 1. Insert polymer in mold 2. Mold closed and cavities filled 3. Mold open and molded parts ejected FIGURE Sequence of operations in transfer molding of thermosetting plastics. This process is particularly suitable for making intricate parts with varying wall thicknesses.

35 Casting, Potting, Encapsulation & Calendering Liquid plastic Mold Electrical coil ousing or case Mold Coil Mold FIGURE Schematic illustration of casting, potting, and (c) encapsulation of plastics. Rubber feed Calender rolls FIGURE Schematic illustration of calendering. Sheets produced by this process are subsequently used in processes such as thermoforming. Finished film Takeoff or stripper roll

36 Reinforced Plastic Components FIGURE Reinforced-plastic components for a onda motorcycle. The parts shown are front and rear forks, a rear swing arm, a wheel, and brake disks.

37 Manufacture of Prepregs Spools Continuous strands Surface treatment Resin FIGURE Manufacturing process for polymer-matrix composite. Source: After T.-W. Chou, R.L. McCullough, and R.B. Pipes. Boronepoxy prepreg tape. Source: Textron Systems. Backing paper Chopper Resin paste Carrier film FIGURE Manufacturing process for producing reinforced-plastic sheets. The sheet is still viscous at this stage and can later be shaped into various products. Source: After T.-W. Chou, R. L. McCullough, and R. B. Pipes. Continuous strands Resin paste Compaction belt Carrier film

38 Vacuum and Pressure Molding Clamping bar Atmospheric pressure Gasket Clamp Air pressure 345 kpa (50 psi) Vacuum trap Flexible bag Vacuum trap Flexible bag Metal or plastic mold Mold Steam or hot water Mold release Gel coat Resin and glass Room-temperature or oven cure and or spray lay-up Mold release Gel coat Resin and glass and or spray lay-up FIGURE Vacuum-bag forming. Pressure-bag forming. Source: After T.. Meister.

39 Open Mold Processing Roller Brush Roving Resin Lay-up of resin and reinforcement Mold Chopped glass roving Spray Mold Mold Gantry crane Mold Boat hull FIGURE Manual methods of processing reinforced plastics: hand lay-up and spray-up. These methods are also called open-mold processing. (c) A boat hull made by these processes. Source: Courtesy of Genmar oldings, Inc. (c)

40 Filament Winding Continuous roving Traversing resin bath Rotating mandrel FIGURE Schematic illustration of the filament-winding process. Fiberglass being wound over aluminum liners for slide-raft inflation vessels for the Boeing 767 aircraft. Source: Advanced Technical Products Group, Inc., Lincoln Composites.

41 Pultrusion Saw Preforming die Pultrusion cut to length Puller eated die Cured pultrusion Infiltration tank Prepreg feed system FIGURE Schematic illustration of the pultrusion process. Examples of parts made by pultrusion. Source: Courtesy of Strongwell Corporation.

42 Processing of RP Parts Side view A Model A Model Support Support FIGURE The computational steps involved in producing a stereolithography file. Three-dimensional description of the part. The part is divided into slices. (Only 1 in 10 is shown.) (c) Support material is planned. (d) A set of tool directions is determined for manufacturing each slice. Shown is the extruder path at section A-A from (c), for a fused-deposition modeling operation. (c) (d)

43 Rapid Prototyping Processes Powder Selective laser sintering Supply Process Layer Creation Phase Technique Liquid Stereolithography Liquid-layer curing Phase-Change Type Photopolymerization Polyjet Liquid-layer curing Photopolymerization Fused-deposition Extrusion of Solidification by modeling melted plastic cooling Three-dimensional Binder-droplet No phase printing deposition onto change powder layer Layer of powder Laser-driven Sintering or melting Materials Photopolymers (acrylates, epoxies, colorable resins, and filled resins) Photopolymers Thermoplastics (ABS, polycarbonate, and polysulfone) Polymer, ceramic and metal powder with binder Polymers, metals with binder, metals, ceramics, and sand with binder TABLE 10.7 Characteristics of rapid-prototyping processes.

44 Tensile Elastic Elongation Strength Modulus in 50 mm Process Material (MPa) (GPa) (%) Notes Stereolithography Somos 7120a Transparent amber; good general purpose material for rapid prototyping. Somos 9120a Transparent amber; good chemical resistance; good fatigue properties; used for producing patterns in rubber molding. WaterShed Optically clear with a slight green tinge; similar mechanical properties as ABS; used for rapid tooling. Prototool 20Lb Opaque beige; higher strength polymer suitable for automotive components, housings, and injection molds. Polyjet FC Transparent amber; good impact strength, good paint absorption and machinability. FC White, blue or black; good humidity resistance; suitable for general purpose applications. FC Gray or black; very flexible material, simulates the feel of rubber or silicone. Fuseddeposition modeling Selective laser sintering Polycarbonate White; high-strength polymer suitable for rapid prototyping and general use. ABS Available in multiple colors, most commonly white; a strong and durable material suitable for general use. PC-ABS Black; good combination of mechanical properties and heat resistance. Duraform PA White; produces durable heat- and chemical-resistant parts; suitable for snap-fit assemblies and sandcasting or silicone tooling. Duraform GF White; glass-filled form of Duraform PA, has increased stiffness and is suitable for higher temperature applications. SOMOS Multiple colors available; mimics rubber mechanical properties ST-100c Bronze-infiltrated steel powder. RP Materials TABLE 10.8 Mechanical properties of selected materials for rapid prototyping.

45 Stereolithography and FDM UV light source c b a UV curable liquid Liquid surface Formed part Vat Platform FIGURE Schematic illustration of the stereolithography process. Source: Courtesy of 3D Systems. Thermoplastic or wax filament z y FIGURE Schematic illustration of the fused-deposition modeling process. The FDM Vantage X rapid prototyping machine. Source: Courtesy of Stratasys, Inc. eated FDM head moves in x y plane Table moves in z-direction x Fixtureless foundation Plastic model created in minutes Filament supply

46 Support Structures a Gussets Island Ceiling within an arch Ceiling FIGURE A part with a protruding section that requires support material. Common support structures used in rapid-prototyping machines. Source: After P.F. Jacobs.

47 Selective Laser Sintering Galvanometers Laser Optics Process chamber Environmentalcontrol unit Roller mechanism Process-control computer Powderfeed cylinder Part-build cylinder Motor Motor FIGURE Schematic illustration of the selective-laser-sintering process. Source: After C. Deckard and P.F. McClure.

48 Three-Dimensional Printing Powder Binder 1. Spread powder 2. Print layer 3. Piston movement FIGURE Schematic illustration of the threedimensional-printing process. Source: After E. Sachs and M. Cima. 4. Intermediate stage 5. Last layer printed 6. Finished part FIGURE Examples of parts produced through three-dimensional printing. Full color parts also are possible, and the colors can be blended throughout the volume. Source: Courtesy ZCorp, Inc.

49 3D Printing of Metal Parts Binder deposition Infiltrating metal, permeates into P/M part Microstructure detail Unfused powder Binder Metal powder Particles are loosely sintered Binder is burned off Infiltrated by lower-melting-point metal (c) FIGURE The three-dimensional printing process: part build; sintering, and (c) infiltration steps to produce metal parts. Source: Courtesy of the ProMetal Division of Ex One Corporation.

50 Rapid Manufacturing: Investment Casting 1. Pattern creation 2. Tree assembly 3. Insert into flask 4. Fill with investment eat Crucible Molten metal 5. Wax meltout/burnout 6. Fill mold with metal 7. Cool 8. Finish FIGURE Manufacturing steps for investment casting that uses rapid-prototyped wax parts as patterns. This approach uses a flask for the investment, but a shell method can also be used. Source: 3D Systems, Inc.

51 Sprayed Metal Tooling Process Alignment tabs Pattern Metal spray Coating Aluminum-filled epoxy Flask Base plate (c) Finished mold half Molded part Pattern Base plate (d) Second mold half (e) FIGURE Production of tooling for injection molding by the sprayed-metal tooling process. A pattern and base plate are prepared through a rapid-prototyping operation; a zinc-aluminum alloy is sprayed onto the pattern (See Section 4.5.1); (c) the coated base plate and pattern assembly is placed in a flask and back-filled with aluminum-impregnated epoxy; (d) after curing, the base plate is removed from the finished mold; and (e) a second mold half suitable for injection molding is prepared.

52 Example: RP Injection Manifold FIGURE Rapid prototyped model of an injection-manifold design, produced through stereolithography. Source: 3D Systems.

53 Design of Polymer Parts Original design Distortion Modified design Thick Die shape Pull-in (sink mark) Thin Extruded product (c) (d) FIGURE Examples of design modifications to eliminate or minimize distortion of plastic parts. Suggested design changes to minimize distortion. Source: After F. Strasser. Die design (exaggerated) for extrusion of square sections. Without this design modification, product cross-sections would not have the desired shape because of the recovery of the material, known as die swell. (c) Design change in a rib to minimize pull-in caused by shrinkage during cooling. (d) Stiffening of the bottom of thin plastic containers by doming, similar to the process used to make the bottoms of aluminum beverage cans and similar containers.

54 Costs and Production Volumes Typical Production Volume, Equipment Production Tooling Number of Parts Process Capital Cost Rate Cost Machining Med Med Low Compression molding igh Med igh Transfer molding igh Med igh Injection molding igh igh igh Extrusion Med igh Low * Rotational molding Low Low Low Blow molding Med Med Med Thermoforming Low Low Low Casting Low Very low Low Forging igh Low Med Foam molding igh Med Med *Continuous process. Source: After R. L. E. Brown, Design and Manufacture of Plastic Parts. Copyright c 1980 by John Wiley & Sons, Inc. Reprinted by permission of John Wiley & Sons, Inc. TABLE 10.9 Comparative costs and production volumes for processing of plastics.

55 Case Study: Invisalign Orthodontic Aligners FIGURE An aligner for orthodontic use, manufactured using a combination of rapid tooling and thermoforming; comparison of conventional orthodontic braces to the use of transparent aligners. Source: Courtesy Align Technologies, Inc. (c) FIGURE Manufacturing sequence for Invisalign orthodontic aligners. Creation of a polymer impression of the patient's teeth; computer modeling to produce CAD representations of desired tooth profiles; (c) production of incremental models of desired tooth movement. An aligner is produced by thermoforming a transparent plastic sheet against this model. Source: Courtesy Align Technologies, Inc.