Extrusion A typical extruder. Extrusion is the method that produces the largest volume of plastic products Extruded products are generally long uniform and solid or hollow complex cross-sections

Sheet and Film Extrusion Other types: Tubing, Electrical wire coating, Pipes To extrude thin film, air is forced into an extruded sheet and then either pinched or cut. A common dye to produce sheets is referred to as the coathanger dye.

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: Uses: 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 turbine wheel

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-Carbide tools

Two-phase processing Slurry infiltration 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.

Fuse-deposition Modeling (a) (a)

Stereolithography

Selective Laser Sintering

Selective Laser Sintering