Ch10

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian • Schmid© 2008, Pearson EducationISBN No. 0-13-227271-7

Polymer PropertiesElongation Poisson’sin 50 mm ratio

Material UTS (MPa) E (GPa) (%) (!)ABS 28–55 1.4–2.8 75–5 –ABS (reinforced) 100 7.5 – 0.35Acetals 55–70 1.4–3.5 75–25 –Acetals (reinforced) 135 10 – 0.35–0.40Acrylics 40–75 1.4–3.5 50–5 –Cellulosics 10–48 0.4–1.4 100–5 –Epoxies 35–140 3.5–17 10–1 –Epoxies (reinforced) 70–1400 21–52 4–2 –Fluorocarbons 7–48 0.7–2 300–100 0.46–0.48Nylon 55–83 1.4–2.8 200–60 0.32–0.40Nylon (reinforced) 70–210 2–10 10–1 –Phenolics 28–70 2.8–21 2–0 –Polycarbonates 55–70 2.5–3 125–10 0.38Polycarbonates (reinforced) 110 6 6–4 –Polyesters 55 2 300–5 0.38Polyesters (reinforced) 110–160 8.3–12 3–1 –Polyethylenes 7–40 0.1–0.14 1000–15 0.46Polypropylenes 20–35 0.7–1.2 500–10 –Polypropylenes (reinforced) 40–100 3.6–6 4–2 –Polystyrenes 14–83 1.4–4 60–1 0.35Polyvinyl chloride 7–55 0.014–4 450–40 –

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


Polymer Structure


FIGURE 10.1 Basic structure of some polymer molecules: (a) ethylene molecule; (b) 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.

Polypropylene

Polystyrene

Polyvinyl chloride

Polytetrafluoroethylene(Teflon)

Polyethylene

H

C

H

H

C

H

Fl

C

Fl

Fl

C

Fl

H

C

H

H

C

Cl

CH3

H

C

H

H

C

C6H5

H

C

H

H

C

n

H

C

H

H

C

H

nCH3

H

C

H

H

C

n

H

C

H

H

C

Cl

nC6H5

H

C

H

H

C

n

Fl

C

Fl

Fl

C

Fl

H

C

H

H

C

H

(a) (b)

Polyethylene

Mer

n

Heat, pressure,

catalyst

(c)

H H H H

C C C C

H H H HHH

C

HH

C

Polymer repeating unitMonomer


Effect of Molecular Weight

FIGURE 10.2 Effect of molecular weight and degree of polymerization on the strength and viscosity of polymers.

104 107

Molecular weight, degreeof polymerization

Pro

pert

y

Tensile andimpact strength

Commercial

polymers

Viscosity


Polymer Chains

FIGURE 10.3 Schematic illustration of polymer chains. (a) Linear structure; thermoplastics such as acrylics, nylons, polyethylene, and polyvinyl chloride have linear structures. (b) Branched structure, such as polyethylene. (c) Cross-linked 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.

(a) Linear (b) Branched

(c) Cross-linked (d) Network


Effect of Temperature

FIGURE 10.4 Behavior of polymers as a function of temperature and (a) degree of crystallinity and (b) cross-linking. The combined elastic and viscous behavior of polymers is known as viscoelasticity.

(a) (b)

Amorphous

Glassy

Increasingcrystallinity

Ela

stic m

odulu

s (

log s

cale

)

Temperature

Tg Tm

100% crystalline

Leathery

Rubbery

Viscous

No cross-linking

Increasingcross-linking

Ela

stic m

odulu

s (

log s

cale

)

Temperature

Tm

Leathery

Rubbery

Viscous

Glassy


Crystallinity

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.

Amorphous region

Crystalline region


Glass-Transition 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.

Temperature

Tg Tm

Amorphous polymers

Cooling:

rapid

slow

Sp

ecific

vo

lum

e

Partly crystalline polymers

Material Tg (!C) Tm (!C)Nylon 6,6 57 265Polycarbonate 150 265Polyester 73 265Polyethylene

High density -90 137Low density -110 115

Polymethylmethacrylate 105 –Polypropylene -14 176Polystyrene 100 239Polytetrafluoroethylene (Teflon) -90 327Polyvinyl chloride 87 212Rubber -73 –

TABLE 10.2 Glass-Transition and Melting Temperatures of Selected Polymers


Deformation of Polymers

FIGURE 10.7 Various deformation modes for polymers.: (a) elastic; (b) 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.

(a) (b)

(c) (d)

Str

ain

Time

t0 t1

Increasing viscosityS

tra

in

Time

t0 t1

Recoveredstrain

Str

ain

Time

t0 t1

Str

ain

Time

t0 t1

Recovered strain

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.

Rigid andbrittle(melamine,phenolic)

Soft and flexible(polyethylene, PTFE)

Tough and ductile(ABS, nylon)

0

Str

ess

Strain


Temperature Effects

FIGURE 10.9 Effect of temperature on the stress-strain 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 H.K. Nason.

00 0

10

20

30

40

50

60

70225°C

25°

50°

65°

80°

0°10

8

6

4

2

5 10 15 20 25 30

Str

ess (

psi x 1

03)

MP

aStrain (%)

FIGURE 10.10 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.

Impact str

ength

Low-densitypolyethylene

High-impactpolypropylene

Polyvinyl chloride

Polymethylmethacrylate

Temperature (°F)

°C

0 32 90

218 0 32


Viscosity of Melted Polymers

FIGURE 10.11 Parameters used to describe viscosity; see Eq. (10.3).

v

y

t

t

FIGURE 10.12 Viscosity of some thermoplastics as a function of (a) temperature and (b) shear rate. Source: After D.H. Morton-Jones.

Low density polyethylene

Polypropylene

Rigid P

VC

Acrylic

Nylon

140 160 180 200 220 240 260 280 300 320

Vis

co

sity (

Ns/m

2)

10

102

103

104

Temperature (°C)

(a)

1 10 102 103 10410

102

103

104

Ap

pa

ren

t vis

co

sity (

Ns/m

2)

Shear rate, ! (s-1)

Polycarbonate

Rigid PV

C (190°C

)

Acrylic (240°C) LDPE (170°C)

Nylon (285°C)

Polypropylene (230°C)

(b)

! = 1000 s-1

Viscous behavior:

τ= η

!dvdy

"= ηγ̇


Polymer Behavior in Tension

FIGURE 10.13 (a) Load-elongation curve for polycarbonate, a thermoplastic. Source: After R.P. Kambour and R.E. Robertson. (b) High-density polyethylene tension-test specimen, showing uniform elongation (the long, narrow region in the specimen).

(a) (b)

0 25 50 75 100 125

mm

16

14

12

10

8

6

4

2

0

(psi x

10

3)

100

80

60

40

20

0

Str

ess (

MP

a)

0 1 2 3 4 5

Elongation (in.)

Molecules arebeing oriented

FIGURE 10.14 Typical load-elongation curve for elastomers. The area within the clockwise loop, indicating loading and unloading paths, is the hysteresis loss. Hysteresis gives rubbers the capacity to dissipate energy, damp vibration, and absorb shock loading, as in automobile tires and v i b r a t ion dampener s fo r machinery.

Loading

Unloading

Load

Elongation


Applications for PlasticsDesignRequirement

Typical Applications Plastics

Mechanicalstrength

Gears, cams, rollers, valves, fanblades, impellers, pistons.

Acetals, nylon, phenolics, polycarbonates,polyesters, polypropylenes, epoxies, poly-imides.

Wearresistance

Gears, wear strips and liners, bear-ings, bushings, roller-skate wheels.

Acetals, nylon, phenolics, polyimides,polyurethane, ultrahigh-molecular-weightpolyethylene.

Frictional prop-erties

High Tires, nonskid surfaces, footware,flooring.

Elastomers, rubbers.

Low Sliding surfaces, artificial joints. Fluorocarbons, polyesters, polyethylene, poly-imides.

Electricalresistance

All types of electrical components andequipment, appliances, electrical fix-tures.

Polymethylmethacrylate, ABS, fluorocarbons,nylon, polycarbonate, polyester, polypropy-lenes, ureas, phenolics, silicones, rubbers.

Chemicalresistance

Containers for chemicals, laboratoryequipment, components for chemicalindustry, food and beverage contain-ers.

Acetals, ABS, epoxies, polymethylmethacry-late, fluorocarbons, nylon, polycarbonate,polyester, polypropylene, ureas, silicones.

Heat resistance Appliances, cookware, electrical com-ponents.

Fluorocarbons, polyimides, silicones, acetals,polysulfones, phenolics, epoxies.

Functional anddecorativefeatures

Handles, knobs, camera and batterycases, trim moldings, pipe fittings.

ABS, acrylics, cellulosics, phenolics,polyethylenes, polpropylenes, polystyrenes,polyvinyl chloride.

Functional andtransparent fea-tures

Lenses, goggles, safety glazing, signs,food-processing equipment

Acrylics, polycarbonates, polystyrenes, poly-sulfones. laboratory hardware.

Housings andhollow shapes

Power tools, housings, sport helmets,telephone cases.

ABS, cellulosics, phenolics, polycarbonates,polyethylenes, polypropylene, polystyrenes.

TA B L E 1 0 . 3 G e n e r a l recommendations for plastic products.


Reinforced Polymers

FIGURE 10.15 Schematic illustration of types of reinforcing plastics. (a) Matrix with particles; (b) 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. 7.48 on making of honeycombs).

Particles

Continuous fibers

(a)

(c) (b)

Short or long fibers, or flakes

Laminate

Foam

Honeycomb

(d)


Properties of Reinforcing Fibers

FIGURE 10.16 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.

Kevlar 49

S-glass

Boron

High-modulus

graphite

E-glass

Celion 3000

Thornel

P-55

Titanium

Steel Aluminum

Kevlar 29

Kevlar 129 Spectra 900

Spectra 2000

Str

ength

/density (

m x

10

4)

40

30

20

10

0

Stiffness/density (m x 106)

0 105 15 20

Thornel P-100

High-tensilegraphite

Tensile Elastic Density RelativeType Strength (MPa) Modulus (GPa) (kg/m3) CostBoron 3500 380 2600 HighestCarbon

High strength 3000 275 1900 LowHigh modulus 2000 415 1900 Low

GlassE type 3500 73 2480 LowestS type 4600 85 2540 Lowest

Kevlar29 2800 62 1440 High49 2800 117 1440 High129 3200 85 1440 High

Nextel312 1630 135 2700 High610 2770 328 3960 High

Spectra900 2270 64 970 High1000 2670 90 970 High

Note: These properties vary significantly, depending on the material and methodof preparation. Strain to failure for these fibers is typically in the range of 1.5% to5.5%.

TABLE 10.4 Typical properties of reinforcing fibers.


Metal and Ceramic Matrix Composites

Material CharacteristicsFIBER

Glass High strength, low sti!ness, high density; E (calcium aluminoborosilicate) andS (magnesiaaluminosilicate) types are commonly used; lowest cost.

Graphite Available typically as high modulus or high strength; less dense than glass; lowcost.

Boron High strength and sti!ness; has tungsten filament at its center (coaxial); highestdensity; highest cost.

Aramids (Kevlar) Highest strength-to-weight ratio of all fibers; high cost.Other Nylon, silicon carbide, silicon nitride, aluminum oxide, boron carbide, boron

nitride, tantalum carbide, steel, tungsten, and molybdenum; see Chapters 3, 8,9, and 10.

MATRIXThermosets Epoxy and polyester, with the former most commonly used; others are pheno-

lics, fluorocarbons, polyethersulfone, silicon, and polyimides.Thermoplastics Polyetheretherketone; tougher than thermosets, but lower resistance to temper-

ature.Metals Aluminum, aluminumlithium alloy, magnesium, and titanium; fibers used are

graphite, aluminum oxide, silicon carbide, and boron.Ceramics 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


Fiber Spinning

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.

Polymerchips

Feedhopper

Cold air

Spinneret

Meltspinning

Melter/extruder

Bobbin

Stretching

Twisting andwinding


Composite Material Microstructure

FIGURE 10.18 (a) Cross-section of a tennis racket, showing graphite and aramid (Kevlar) reinforcing fibers. Source: After J. Dvorak and F. Garrett. (b) Cross-section of boron-fiber-reinforced composite material.

(b)(a)

Kevlar fibers

Graphite fibers

Matrix

Matrix

Borondiameter 0.1 mm

Tungstendiameter 0.012 mm


Effect of Fibers

FIGURE 10.19 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.

Short glass fibers

Carbon fibers

Long glass fib

ers

Short glass fibers

Carbon fibers

Long glass fibers

Reinforcement (%)

Impact energ

y (

ft-lb/in.)

J/m

0

1

2

3

4

5

6

0 10 20 30 40

10 0 40 20 30

0

100

200

300

Reinforcement (%)

Fle

xura

l m

odulu

s (

psi x 1

06)

Long and short

glass fibers

0

1

2

3

4

5

6

10

0

30

40

20 GP

a

Short glass fibers

Long glass fibers

Carbon fib

ers

10 0 30 40 20

Reinforcement (%)

Fle

xura

l str

ength

(psi x

10

3)

0

10

20

30

40

50

60

100

0

200

300

400

MP

a

Carbon fibers

Reinforcement (%)

(b)

(c) (d)

(a)

Tensile

str

ength

(psi x 1

03)

MP

a

0

10

20

30

40

50

60

0 10 20 30 40 0

100

200

300

400


Strength and Fracture of Composites

FIGURE 10.20 (a) Fracture surface of glass-fiber-reinforced epoxy composite. The fibers are 10 µm (400 µin.) in diameter and have random orientation. (b) 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.

(a) (b)

FIGURE 10.21 Tensile strength of glass-reinforced polyester as a function of fiber content and fiber direction in the matrix. Source: After R.M. Ogorkiewicz.

Te

nsile

str

en

gth

(p

si x 1

05)

20 40 60 80

Unidirectional

Orthogonal

Random

Glass content (% by weight)

MP

a

10001.5

2.0

1.0

0.5

0

500

0


Plastics ProcessesProcess CharacteristicsExtrusion Long, uniform, solid or hollow, simple or complex cross-sections; wide range

of dimensional tolerances; high production rates; low tooling cost.Injection molding Complex shapes of various sizes and with fine detail; good dimensional

accuracy; high production rates; high tooling cost.Structural foam

moldingLarge parts with high stiffness-to-weight ratio; low production rates; lessexpensive tooling than in injection molding.

Blow molding Hollow thin-walled parts of various sizes; high production rates and lowcost for making beverage and food containers.

Rotational molding Large hollow shapes of relatively simple design; low production rates; lowtooling cost.

Thermoforming Shallow or deep cavities; medium production rates; low tooling costs.Compression molding Parts similar to impression-die forging; medium production rates; relatively

inexpensive tooling.Transfer molding More complex parts than in compression molding, and higher production

rates; some scrap loss; medium tooling cost.Casting Simple or intricate shapes, made with flexible molds; low production rates.Processing of

reinforced plasticsLong cycle times; dimensional tolerances and tooling costs depend on thespecific process.

TABLE 10.6 Characteristics of processing plastics and reinforced plastics.


Extrusion

FIGURE 10.22 Schematic illustration of a typical extruder.

Thrust bearing

Hopper

Throat

Screw

Barrelliner

Barrel

Barrelheater/cooler

Thermocouples

Wire filterscreen

Breakerplate

Die

Melt-pumping sectionMelt sectionFeed section

Throat-coolingchannel

Gear reducerbox

Motor

Adapter

Meltthermocouple


Extrusion Mechanics

FIGURE 10.23 Geometry of the pumping section of an extruder screw.

W

w

H

D

!

Barrel

Pitch

Flight

Barrel

FIGURE 10.1 Extruder and die characteristics for Example 10.5.

Extruder characteristic

Die characteristic

Operating point

3

2

1

0

Flo

w r

ate

, q

x 1

0-5

(m3/s

)

0 5 10 15

Pressure (MPa)

Drag flow:

Pressure flow:

Die characteristic

K for circular cross-sections:

Qd =π2HD2N sinθcosθ

2

Qp =WH3p

12η(l/sinθ)=pπDH3 sin2θ

12ηl

Qdie = Kp

K =πD4d128ηld


Blown-Film Manufacture

FIGURE 10.25 (a) Schematic illustration of production of thin film and plastic bags from a tube produced by an extruder, and then blown by air. (b) A blown-film operation. Source: Courtesy of Windmoeller & Hoelscher Corp.

(a) (b)

Wind-up

Pinch rolls

Guide rolls

Blowntube

Mandrel

Die

Extruder

Air

(a)


Tube Extrusion

FIGURE 10.26 Extrusion of plastic tubes. (a) Extrusion using a spider die (see also Fig.6.59) and pressurized air; (b) coextrusion of tube for producing a bottle.

(b)

(a)

Breaker plate

Spider die

Co-extrusion blow molding

Extruder barrel

Extruder 1

Extruder 2

Screen pack

Melt flowdirection

MandrelA

v

A

B

B

Polymer melt

Spider legs (3)

Spider legs (3)

Air channel

Mandrel

Plastic melt:two or more layers

Parison

Air in

SectionB–B

Section A–A


Injection Molding

FIGURE 10.27 Injection molding with (a) a plunger and (b) a reciprocating rotating screw. Telephone receivers, plumbing fittings, tool handles, and housings are examples of parts made by injection molding.

Powder,Pellets

Hopper

Heatingzones Nozzle Mold

Vent

Ejector pins

Cylinder(barrel)Cooling

zone

Piston(ram)

Injectionchamber Torpedo

(spreader) Sprue

Moldedpart Vent

Press(clamp)force

Rotating and reciprocatingscrew

(b)

(a)


Mold Features

FIGURE 10.28 Illustration of mold features for injection molding. (a) Two-plate mold, with important features identified; (b) injection molding of four parts, showing details and the volume of material involved. Source: Courtesy of Tooling Molds West, Inc.

(b)

Mainrunner

Gate

Cavity Guidepin

Guide pinSprue

Cavity

Branchrunner

(a)

Gate

Sprue

Part

Mainrunner

Cold slug wellBranchrunner


Mold Types

FIGURE 10.29 Types of molds used in injection molding. (a) Two-plate mold, (b) three-plate mold, and (c) hot-runner mold.

(c)

Parts

Sprue

bushing

Plate

Plate

Hot plate;Runner stays molten

Ejectorpins

(a) (b)

Parts

Sprue

bushing Sprue

Runner

GatePlate

Part

Plate

Ejectorpins

Part

Ejectorpins

Sprue

bushing

Plate Plate

Stripper

plate


Insert Molding

FIGURE 10.30 Products made by insert injection molding. Metallic components are embedded in these parts during molding. Source: (a) Courtesy of Plainfield Molding, Inc., and (b) Courtesy of Rayco Mold and Mfg. LLC.

(a) (b)


Reaction-Injection Molding

FIGURE 10.31 Schematic illustration of the reaction-injection-molding process.

Mixinghead

Recirculationloop

Pump

Monomer 2

Stirrer

Pump

Heatexchanger

Heatexchanger

Recirculationloop

Displacementcylinders

Mold

Monomer 1

Stirrer


Blow Molding

FIGURE 10.32 Schematic illustrations of (a) the blow-molding process for making plastic beverage bottles and (b) a three-station injection-blow-molding machine.

(c)

(a)

(b)

Heatingpassages

Mold closedand bottle blown

Tail

Blown bottle

Extrudedparison

Knife

Bottlemold

Blow pin

Extruder

Injection-moldingmachine

Parison

Coolingpassages

Parison transferredto blow mold

Blow pin

Blow pinremoved

Blownbottle

Parison mold

Blown-mold station

Blown bottle

Stripper station3

Bottle

Reciprocating-screw extruder

Transferhead

Blow mold

Preformneck ring

Parison

Preformmold

Preformmold station

Core-pin opening(Blown air passage)

Blow-moldneck ring

Indexingdirection

Blow-moldbottom plug

1

2

Stripper plate


Rotational Molding

FIGURE 10.33 The rotational molding (rotomolding or rotocasting) process. Trash cans, buckets, carousel horses and plastic footballs can be made by this process.

Secondaryaxis

Spindle

Pressurizingfluid

Inlet

Outletvent

Mold

Primaryaxis


Thermoforming

FIGURE 10.35 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.

(a) Straight vacuumforming

(b) Drape vacuumforming

(c) Force above sheet (d) Plug and ring forming

RingClamp

Plasticsheet

Ram

Mold

Mold

Vacuum line

Vacuumline

Plasticsheet

Clamp

Heater


Compression Molding

FIGURE 10.35 Types of compression molding, a process similar to forging: (a) positive, (b) 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.

(a) (b) (c)

Open

OverlapLand

Knockout(ejector pin)

(d)

Part

Plug

Heatingelements

Punch

Mold

Charge

Moldedpart

ClosedFlash


Transfer Molding

FIGURE 10.36 Sequence of operations in transfer molding of thermosetting plastics. This process is particularly suitable for making intricate parts with varying wall thicknesses.

Transfer plunger

Transfer pot andmolding powder

2. Mold closed and cavities filled

Knockout(ejector) pin

3. Mold open and molded parts ejected

1. Insert polymer in mold

Sprue

Punch

Moldedparts


Casting, Potting, Encapsulation & Calendering

FIGURE 10.38 Schematic illustration of calendering. Sheets produced by this process are subsequently used in processes such as thermoforming.

Liquid plastic

Mold

Electrical coil

Housing or case

Coil Mold Mold

1. 2. 3.

FIGURE 10.37 Schematic illustration of (a) casting, (b) potting, and (c) encapsulation of plastics.

Finished film

Rubber feed

Calender rolls

Takeoff orstripper roll


Reinforced Plastic Components

FIGURE 10.39 Reinforced-plastic components for a Honda motorcycle. The parts shown are front and rear forks, a rear swing arm, a wheel, and brake disks.


Manufacture of Prepregs

FIGURE 10.40 (a) Manufacturing process for polymer-matrix composite. Source: After T.-W. Chou, R.L. McCullough, and R.B. Pipes. (b) Boron-epoxy prepreg tape. Source: Textron Systems.

(a) (b)

Continuousstrands

Spools

Surfacetreatment

Resin

Backing paper

Continuousstrands

ChopperResinpaste

Resinpaste

Compactionbelt

Carrierfilm

Carrierfilm

FIGURE 10.41 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.


Vacuum and Pressure Molding

FIGURE 10.42 (a) Vacuum-bag forming. (b) Pressure-bag forming. Source: After T. H. Meister.

Atmosphericpressure

Flexible bag

Gasket

Vacuumtrap

Vacuumtrap

Resinand glass

Gelcoat

Mold

Clampingbar

Moldrelease

Moldrelease

Room-temperature or oven cureHand or spray lay-up

Air pressure345 kPa (50 psi)Clamp

Gelcoat

Resin andglass

Metal orplastic mold

Steam orhot water

Hand or spray lay-up

(a) (b)

Flexible bag


Open Mold Processing

FIGURE 10.43 Manual methods of processing reinforced plastics: (a) hand lay-up and (b) spray-up. These methods are also called open-mold processing. (c) A boat hull made by these processes. Source: Courtesy of Genmar Holdings, Inc.

(c)

(a) (b)

Mold

Boat hull

Mold

Gantry crane

Lay-up ofresin and

reinforcement

Mold

Roller Brush

(a) (b)

Mold

Roving Resin

Chopped glassroving

Spray


Filament Winding

FIGURE 10.44 (a) Schematic illustration of the filament-winding process. (b) Fiberglass being wound over aluminum liners for slide-raft inflation vessels for the Boeing 767 aircraft. Source: Advanced Technical Products Group, Inc., Lincoln Composites.

(a) (b)

Rotating mandrel

Traversing resin bath

Continuous roving


Pultrusion

FIGURE 10.45 (a) Schematic illustration of the pultrusion process. (b) Examples of parts made by pultrusion. Source: Courtesy of Strongwell Corporation.

(b)(a)

Infiltration tank

Preforming die

Heated die

PullerCured

pultrusion

Pultrusioncut to length

Prepregfeed system

Saw


Processing of RP Parts

FIGURE 10.46 The computational steps involved in producing a stereolithography file. (a) Three-dimensional description of the part. (b) 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.

(a) (b)

(c) (d)

A

A

Model

Support

Model

Support

Side view


Rapid Prototyping Processes

TABLE 10.7 Characteristics of rapid-prototyping processes.

SupplyPhase

Process Layer CreationTechnique

Phase-ChangeType

Materials

Liquid Stereolithography Liquid-layer cur-ing

Photopoly-merization

Photopolymers (acrylates,epoxies, colorable resins, andfilled resins)

Polyjet Liquid-layer cur-ing

Photopoly-merization

Photopolymers

Fused-depositionmodeling

Extrusion ofmelted plastic

Solidification bycooling

Thermoplastics (ABS, poly-carbonate, and polysulfone)

Powder Three-dimensionalprinting

Binder-dropletdeposition ontopowderlayer

No phasechange

Polymer, ceramic and metalpowder with binder

Selectivelaser sinter-ing

Layer of powder Laser-driven Sintering ormelting

Polymers, metals withbinder, metals, ceramics,and sand with binder


RP MaterialsTensile Elastic Elongation

Strength Modulus in 50 mmProcess Material (MPa) (GPa) (%) NotesStereo-lithography

Somos 7120a 63 2.59 2.3-4.1 Transparent amber; good generalpurpose material for rapid prototyp-ing.

Somos 9120a 32 1.14-1.55 15-25 Transparent amber; good chemicalresistance; good fatigue properties;used for producing patterns in rub-ber molding.

WaterShed 11120 47.1-53.6 2.65-2.88 3.3-3.5 Optically clear with a slight greentinge; similar mechanical propertiesas ABS; used for rapid tooling.

Prototool 20Lb 72-79 10.1-11.2 1.2-1.3 Opaque beige; higher strength poly-mer suitable for automotive com-ponents, housings, and injectionmolds.

Polyjet FC 700 42.3 2.0 15-25 Transparent amber; good impactstrength, good paint absorption andmachinability.

FC800 49.9-55.1 2.5-2.7 15-25 White, blue or black; good humidityresistance; suitable for general pur-pose applications.

FC900 2.0-4.6 – 47 Gray or black; very flexible mate-rial, simulates the feel of rubber orsilicone.

Fused-depositionmodeling

Polycarbonate 52 2.0 3 White; high-strength polymer suit-able for rapid prototyping and gen-eral use.

ABS 22 1.63 6 Available in multiple colors, mostcommonly white; a strong anddurable material suitable for generaluse.

PC-ABS 34.8 1.83 4.3 Black; good combination of mechan-ical properties and heat resistance.

Selectivelaser sinter-ing

Duraform PA 44 1.6 9 White; produces durable heat- andchemical-resistant parts; suitable forsnap-fit assemblies and sandcastingor silicone tooling.

Duraform GF 38.1 5.9 2 White; glass-filled form of DuraformPA, has increased sti!ness and issuitable for higher temperature ap-plications.

SOMOS 201 17.3 14 130 Multiple colors available; mimicsrubber mechanical properties

ST-100c 305 137 10 Bronze-infiltrated steel powder.

TABLE 10.8 Mechanical properties of selected materials for rapid prototyping.


Stereolithography and FDM

FIGURE 10.47 Schematic illustration of the stereolithography process. Source: Courtesy of 3D Systems.

UV light source

Liquid surface

Vat

c

b

a

Platform

UV curable liquid

Formed part

(a) (b)

Filament supply

Plastic modelcreated inminutes

Thermoplasticor wax filament

Heated FDM headmoves in x–y plane

Tablemoves in

z-direction

z

y

x

Fixturelessfoundation

FIGURE 10.48 (a) Schematic illustration of the fused-deposition modeling process. (b) The FDM Vantage X rapid prototyping machine. Source: Courtesy of Stratasys, Inc.


Support Structures

FIGURE 10.49 (a) A part with a protruding section that requires support material. (b) Common support structures used in rapid-prototyping machines. Source: After P.F. Jacobs.

(a) (b)

Gussets Island Ceiling within an arch Ceiling

a


Selective Laser Sintering

FIGURE 10.50 Schematic illustration of the selective-laser-sintering process. Source: After C. Deckard and P.F. McClure.

Motor

Laser Optics

Motor

Process-controlcomputer

Part-buildcylinder

Powder-feed

cylinder

Roller mechanism

Galvanometers

Process chamber

Environmental-control unit


Three-Dimensional Printing

FIGURE 10.51 Schematic illustration of the three-dimensional-printing process. Source: After E. Sachs and M. Cima.

1. Spread powder 2. Print layer 3. Piston movement

4. Intermediate stage 5. Last layer printed 6. Finished part

Powder Binder

(a) (b)

FIGURE 10.52 (a) 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.


3D Printing of Metal Parts

Binder

Metalpowder

powder

Binder deposition

Particles are loosely sinteredBinder is burned off

(a)

Infiltrated bylower-melting-point metal

(c)(b)

Infiltrating metal, permeates into P/M part

Microstructure detail

Unfused

FIGURE 10.53 The three-dimensional printing process: (a) part build; (b) sintering, and (c) infiltration steps to produce metal parts. Source: Courtesy of the ProMetal Division of Ex One Corporation.


Rapid Manufacturing: Investment Casting

1. Pattern creation

5. Wax meltout/burnout

Heat

2. Tree assembly

6. Fill mold with metal

Moltenmetal

Crucible

3. Insert into flask

7. Cool

4. Fill with investment

8. Finish

FIGURE 10.54 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.


Sprayed Metal Tooling Process

Pattern

Base plate

Alignment tabs

Metalspray

Coating

Aluminum-filledepoxy

Flask

Finished mold half

Pattern

Base plate

Molded part

Second mold half

(a) (b) (c)

(d) (e)

FIGURE 10.55 Production of tooling for injection molding by the sprayed-metal tooling process. (a) A pattern and base plate are prepared through a rapid-prototyping operation; (b) 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.


Example: RP Injection Manifold

FIGURE 10.56 Rapid prototyped model of an injection-manifold design, produced through stereolithography. Source: 3D Systems.


Design of Polymer Parts

(b) (c) (d)

Extruded product

Die shape

Originaldesign

Distortion Modifieddesign

(a)

Thick

Pull-in (sink mark)

Thin

FIGURE 10.57 Examples of design modifications to eliminate or minimize distortion of plastic parts. (a) Suggested design changes to minimize distortion. Source: After F. Strasser. (b) 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.


Costs and Production VolumesTypical Production Volume,

Equipment Production Tooling Number of PartsProcess Capital Cost Rate Cost 10 102 103 104 105 106 107

Machining Med Med LowCompression molding High Med HighTransfer molding High Med HighInjection molding High High HighExtrusion Med High Low *Rotational molding Low Low LowBlow molding Med Med MedThermoforming Low Low LowCasting Low Very low LowForging High Low MedFoam molding High 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.


Case Study: Invisalign Orthodontic Aligners

(a) (b)

FIGURE 10.58 (a) An aligner for orthodontic use, manufactured using a combination of rapid tooling and thermoforming; (b) comparison of conventional orthodontic braces to the use of transparent aligners. Source: Courtesy Align Technologies, Inc.

(a)

(b) (c)

FIGURE 10.59 Manufacturing sequence for Invisalign orthodontic aligners. (a) Creation of a polymer impression of the patient's teeth; (b) 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.

Ch10

Documents

pearson education isbn

john wiley

medium production rates

invisalign orthodontic aligners

low production rates

high production rates

low tooling cost

courtesy align technologies