Extrusion

Extrusion is the method that produces the largest volume of plastic products

A typical extruder.

Extruded products are generally long uniform and solid or hollow complex cross-sections

Sheet and Film Extrusion

A common dye to produce sheets is referred to as the coathanger dye.

To extrude thin film, air is forced into an extruded sheet and then

either pinched or cut.

Other types: Tubing, Electrical wire coating, Pipes

Injection Molding

Injection molding is similar to extrusion only a mold replaces the die.

Injection Molding Process

• The polymer is pushed into the mold.• The part is cooled within the mold.

• Once cooled, the part is eased out of the mold with ejector pins

Molds

• Cold runner, Two-plate mold• Cold runner, Three-plate mold• Hot runner mold

Machine• Cost range: $85,000 - $140,000

• Die cost: $20,000 - $200,000• Mold cost: approx. $100,000

• Process: 5 sec. – 60 sec.

Extrusion Blow Molding

A polymer is extruded and clamped within a mold. Air is then pushed is and the part is made. The

mold is removed and excess pieces are removed as well.

Injection Blow Molding

The polymer is injected into a closed mold with a blow pin and parison. Air is blown in and the part is made. The blow pin is then removed.

19.6 - Thermoforming• Sheets available in multitude of sizes, thicknesses, and

fillers (to create specific properties).• Parts cannot include holes and openings.• Material: thermoplastics, must exhibit high, uniform

elongation• Packaging trays, signs, appliance housings, refrigerator

liners, shower stalls

19.7 – Compression Molding• Done at temperatures of 200 C (400 F) and higher• Pressures range from 1400- 22000 psi• Material: usually thermosetting plastics, sometimes

thermoplastics• Cures in die• Dishes, handles, container caps, fittings, electrical

components, housings• Fiber reinforced parts with chopped fibers use this

process exclusively.

19.8 -Transfer Molding

• Pressures may reach 43,000 psi• Viscous flow also raises temperature and homogonizes

material• High complexity and dimensional control• More expensive

19.9 - casting• Thermosets and thermoplastics may be used• Slow and simple yet cheap• Flexible molds can be used • Continuous casting can be used• Centrifugal casting• Potting and encapsulation (electrical components)

19.10- foam molding

• Polystyrene beads are the raw material. • Beads, blowing agent, and heat• Pre-expanded beads may be shaped just as plastics• Structural foam molding created hard outer shell and

light cellular core, outside is cooled rapidly• Polyurethane foam processing utilizes chemical

reactions to create foam which is poured into molds or sprayed on surfaces for insulation.

19.11- cold forming and solid phase forming

• Many of the cold working processes that apply to metals can also be used on plastics.

• Thermosets are used because of their ductility at room temperature.

• Advantages: strength, toughness, improved dimensional accuracy, and faster cycle times

• Solid phase forming is carried out at temperatures 10-20 C. Below the melting point.

19.12 Processing Elastomers

•Processing elastomers uses processes similar to shaping thermoplastics•These include:

–Extrusion (tubing, hoses, molding)–Injection molding (components for automobiles

Calendering

• Used to form rubber and thermoplastic sheets.• Process:

– Warm mass fed into series of rolls to create a flat sheet– End product usually 0.3 to 1mm thick

• Uses:– Tines– Belts for machinery

Dipping

• Process:– Dip metal form into a

liquid elastomer compound

– Compound adheres to form, creating item

• Uses:– Rubber gloves

19.13 Processing Polymer-Matrix Composites

• Polymer-matrix composites are also known as reinforced plastics

• Special methods required to shape due to complex structure:– Molding– Filament winding– Pultrusion– Pulforming

Motorcycle parts made of reinforced plastics

Prepegs

• Process: continuous fibers aligned and subjected to surface treatment, then dipped into a resin bath to form a tape

• Uses: flat architectural panelling

• Example of use: F-14 fighter jet horizontal stabilizer F-14 fighter jet

Sheet-Molding Compound (SMC)

• Process: continuous fibers cut into short fibers and deposited in random orientation over layers of resin paste

• Use: random orientation gives the product strength in many directions, instead of just one, like in unidirectional fiber products

Molding of Reinforced Plastics

• Different types of molding used for reinforced plastics:– Compression molding– Vacuum bag molding– Contact molding

Mold for hull of a catamaran

Compression Molding

• Process: Polymer-Matrix composite is placed between two molds and compressed

Vacuum-Bag Molding

• Process: material is placed in a mold, covered by a plastic bag, and a vacuum is created to compress the material into the shape of the mold

Contact Molding

• Two types:– Spray Lay-up:

spray into mold evenly to the thickness desired

– Hand Lay-up: painted onto the mold Jet ski hull made by hand lay-up

Filament Winding

• Resin and fibers are combined at curing

• Process: fiber wound on a rotating mandrel while within resin bath.

• Benefits: very strong and heavily reinforced

• Uses: Aircraft (engine ducts, propellers), spherical pressure vessels

(a)

(b)

Pultrusion

• Process: prepeg pulled through resin bath, heated in a die, and but to length after sufficient cooling time

• Uses: parts with uniform cross-sections that are made continuously (aluminum ladders)

Pulforming

• Process: similar to pultrusion– Prepeg pulled through resin bath, then

clamped between two halves of die. Cut piece and repeat.

• Uses: parts with non-uniform cross-section

19.14 Processing Metal-Matrix and Ceramic-Matrix Composites• Metal-Matrix Composites (MMC)

– Liquid-phase processing– Solid-phase processing– Two-phase (liquid-solid) phase processing

• Ceramic-Matrix Composites (CMC)– Slurring infiltration

Ceramic-matrix turbinewheel

• Liquid-Phase Processing:– Casting together liquid material (ex. Aluminum)

and solid reinforcement (ex. Graphite)

• Solid-Phase Processing:– Consists of powder metallurgy techniques.– Proper mixing important to obtain even distribution

of fibers (ex. Tungsten-carbide tools)

Tungsten-Carbidetools

• Two-phase processing– Involves liquid and solid states– Reinforcing fibers are mixed with a matrix

that contains liquid and solid phases of the metal

• Slurry infiltration– Slurry: mixture of matrix powder, carrier

liquid, and organic binder– Prepare a fiber preform, and hot press it

with the slurry

Chapter 20 Rapid Prototyping

• Produces and example of a part from a CAD drawing before production.

• Additive, subtractive and virtual.

20.3 Additive Processes

• Parts are broken down into layers and constructed slice by slice, usually .004-.020 in. thick.

• Stereolithography, fuse-deposition modeling, ballistic-particle manufacturing, three-dimensional printing, selective laser sintering and laminated-object manufacturing.

(a)

Fuse-deposition Modeling(a)

Stereolithography

Selective Laser Sintering

Selective Laser Sintering