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Manufacturing, Engineering & Technology, Fifth Edition, by Serope
Chapter 19
Forming and Shaping Plastics and
Composite Materials

Characteristics of Forming and Shaping Processes
for Plastics and Composite Materials

Forming and Shaping Processes for Plastics, Elastomers, and
Composite Materials
Figure 19.1 Outline of forming and shaping processes for plastics, elastomers, and composite
materials. (TP = Thermoplastics; TS = Thermoset; E = Elastomer.)

Extruder Schematic
Figure 19.2 (a) Schematic illustration of a typical screw extruder. (b) Geometry of an
extruder screw. Complex shapes can be extruded with relatively simple and inexpensive dies.

Extrusion Die Geometries
Figure 19.3 Common extrusion die geometries: (a) coat-hanger die for extruding sheet;
(b) round die for producing rods; and (c) dies for producing square cross-sections. Note
the nonuniform recovery of the part after it exits the die. Source: (a) Encyclopedia of
Polymer Science and Engineering (2nd
ed.). Copyright © 1985. Reprinted by permission of
John Wiley & Sons, Inc.

Extrusion of
Tubes
Figure 19.4 Extrusion of tubes.
(a) Extrusion using a spider die
(see also Fig. 15.8) and
pressurized air. (b) Coextrusion
for producing a bottle.

Production of Plastic Film and Bags
Figure 19.5 (a) Schematic illustration of the production of thin film and plastic bags from
tube – first produced by an extruder and then blown by air. (b) A blown-film operation. This
process is well developed, producing inexpensive and very large quantities of plastic film and
shopping bags. Source: Courtesy of Windmoeller & Hoelscher.
(b)

Melt-Spinning
Process
Figure 19.6 The melt-spinning process
for producing polymer fibers. The fibers
are then used in a variety of
applications, including fabrics and as
reinforcements for composite materials.

Injection Molding
Figure 19.7 Schematic
illustration of injection molding
with (a) plunger and (b)
reciprocating rotating screw.

Injection Molding Sequence
Figure 19.8 Sequence of operations in the injection molding of a part with a reciprocating
screw. This process is used widely for numerous consumer and commericial products,
such as toys, containers, knobs, and electrical equipment (see Fig. 19.9).

Products Made by Injection Molding
Figure 19.9 Typical products made by injection molding, including examples of insert
molding. Source: (a) Courtesy of Plainfield Molding, Inc. (b) Courtesy of Rayco Mold and
Mfg. LLC.
(b)(a)

Mold Features for Injection Molding
Figure 19.10 Illustration of mold features for injection molding. (a) Two-plate
mold with important features identified. (b) Four parts showing details and the
volume of material involved. Source: Courtesy of Tooling Molds West. Inc.

Types of Molds used in Injection Molding
Figure 19.11 Types of molds used in injection molding: (a) two-plate mold; (b) three-plate
mold; and (c) hot-runner mold.

EPOCH Hip Stem
Figure 19.12 The EPOCH hip stem. This
design uses a PAEK (polyaryletherketone)
layer and bone-ingrowth pad around a
cobalt-chrome core in order to maximize
bone ingrowth. Source: Courtesy of
Zimmer, Inc.
Figure 19.13 An EPOCH hip is
removed from the mold after an
insert injection-molding operation.
Source: Courtesy of Zimmer, Inc.

Injection-Molding Machine
Figure 19.14 A 2.2-MN (250-ton) injection molding machine. The tonnage is the
force applied to keep the dies closed during the injection of molten plastic into the
mold cavities and hold it there until the parts are cool and stiff enough to be removed
from the die. Source: Courtesy of Cincinnati Milacron, Plastics Machinery Division.

Reaction-Injection Molding Process
Figure 19.15 Schematic illustration of the reaction-injection molding
process. Typical parts made are automotive-body panels, water skis,
and thermal insulation for refrigerators and freezers.

Blow-Molding
Figure 19.16 Schematic illustrations of
(a) the extrusion blow-molding process
for making plastic beverage bottles; (b)
the injection blow-molding process;
and (c) a three-station injection
molding machine for making plastic
bottles.

Rotational
Molding Process
Figure 9.17 The rotational molding
(rotomolding or rotocasting)
process. Trash cans, buckets, and
plastic footballs can be made by
this process.

Thermoforming Process
Figure 19.18 Various thermoforming processes for a thermoplastic sheet. These processes
commonly are used in making advertising signs, cookie and candy trays, panels for shower
stall, and packaging.

Compression Molding
Figure 19.19 Types of compression molding – a process similar to forging: (a) positive,
(b) semipositive, and (c) flash, which is later trimmed off. (d) Die design for making a
compression-molded part with external undercuts.

Transfer Molding
Figure 19.20 Sequence of operations in transfer molding for thermosetting plastics.
This process is suitable particularly for intricate parts with varying wall thickness.

Processes for Plastics and Electrical Assemblies
Figure 19.21 Schematic illustration of (a) casting, (b) potting, and (c) encapsulation
processes for plastics and electrical assemblies, where the surrounding plastic serves as a
dielectric.

Calendering
Figure 19.22 Schematic illustration of calendering. Sheets produced by this
process subsequently are used in thermoforming. The process also is used in
the production of various elastomer and rubber products.

Motorcycle Components
Figure 19.23 Reinforced plastic components for a Honda motorcycle. The
parts shown are front and rear forks, rear swing-arm, wheel, and brake disks.

Tapes used in Making
Reinforced Plastic Parts
Figure 19.24 (a) Manufacturing process for polymer-matrix composite tape. (b) Boron-
epoxy prepreg tape. These tapes are then used in making reinforced plastic parts and
components with high strength-to-weight ratios, particularly important for aircraft and
aerospace applications and sports equipment. Source: (a) Courtesy of T. W. Chou, R. L.
McCullough, and R. B. Pipes. (b) Courtesy of Avco Specialty Materials/Textron.
(b)

Tape and Tape-Laying System
(b)(a)
Figure 19.25 (a) Single-ply layup of boron-epoxy tape for the horizontal stabilizer for an
F-14 fighter aircraft. (b) A 10-axis computer-numerical-controlled tape-laying system.
This machine is capable of laying up 75- and 150-mm (3- and 6-in.) wide tapes on
contours of up to +/- 30 degrees and at speeds of up to 0.5m/s (1.7 ft/s). Source: (a)
Courtesy of Grumman Aircraft Corporation. (b) Courtesy of The Ingersoll Milling
Machine Company.

Production of Fiber-Reinforced Plastic Sheets
Figure 19.26 Schematic illustration of the manufacturing process for producing fiber-
reinforced plastic sheets. The sheet still is viscous at this stage and later can be shped
into various products. Source: After T. W. Chou, R. L. McCullough, and R. B. Pipes.

Vacuum-Bag Forming and Pressure-Bag Forming
Figure 19.27 Schematic illustration of (a) vacuum-bag forming, and (b) pressure-bag forming.
These processes are used in making discrete reinforced plastic parts. Source: After T. H.
Meister.

Open-Mold Processing
Figure 19.28 Manual methods of processing
reinforced plastics: (a) hand lay-up, and (b)
spray lay-up. Note that, even though the
process is slow, only one mold is required.
The figures show a female mold, but male
molds also are used. These methods also
are called open-mold processing. (c) A boat
hull made by these processes.

Filament-Winding
(b)
Figure 19.29 (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. The
products made by this process have high strength-to-weight ratio and also serve as
lightweight pressure vessels. Source: Courtesy of Brunswick Corporation.

Pultrusion
Figure 19.30 (a) Schematic illustration of the pultrusion process. (b) Examples of
parts made by pultrusion. The major components of fiberglass ladders (used
especially by electricians) are made by this process. Unlike aluminum ladders, they
are available in different colors but are heavier because of the presence of glass fibers.
Source: Courtesy of Strongwell Corporation.
(b)

Design Modifications to Minimize Distortion in Plastic Parts
Figure 19.31 Examples of design modifications to eliminate or minimize distortion in
plastic parts: (a) suggested design changes to minimize distortion; (b) stiffening the
bottoms of thin plastic containers by doming – a technique similar to the process
used to shape the bottoms of aluminum beverage cans; and (c) design change in a
rib to minimize pull-in (sink mark) caused by shrinkage during the cooling of thick
sections in molded parts.

Production Characteristics of Molding Methods

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