Plastics Processing - Process & Materials in Manufacturing

Plastic Pros:

• Good strength to weight ratio
• No painting - built in color
• Produce complex shapes
• Good design versatility

Polymers: Chemical compound (or mixture of compounds) formed by polymerization and is a chain of repeating structural units. Made up of many molecules to form a chain.

Thermoplastic Polymers: These plastics can be recycled. Examples: polyethylene(PE), polypropylene(PP), nylon(PA).

Thermosetting Polymers: These plastics can not be recycled. Examples: epoxy(EP), urethanes(PU or PUR), polyester(PET). Make good insulators. Heavy and dense.

Elastomers: rubbery(SI).


Forming and Shaping Processes:

• Forming: vacuum and thermoforming.
• Extrusion: profile, sheet, and blown film.
• Molding: compression, injection, blow molding.

Thermoforming: low cost, make large parts, oldest plastics process.
Extrusion: thermoplastic process, low tooling cost, this process is the highest plastic production by volume. Products with constant cross section. Examples: pipe, straws, fishing line.

• Blown Film Extrusion: Examples: thin-film sheets, plastic bags, zip lock bags.

Injection Molding: mostly a thermoplastic process. Parts include: sprue(material entry), runner(distribution), gate, part(cavity). The liquid plastic flows from the sprue and ends in the cavity. Makes expensive, complex, high volume products.

Compression Molding: mostly a thermoset process.

Other Polymer Processes:

• Rotational Casting - thermoplastic
• Casting - thermoplastic and thermoset
• Structural Foam Molding - thermoplastic and thermoset
• Reaction Injection - thermoset
• Transfer Molding - thermoset

Reinforced Plastics: thermoplastic and thermoset polymers with interspersed fibers that strengthen the finished part.

Polymer parts have low stiffness and strength, which can be offset by increasing section modulus and with reinforcements.

Polymer parts have a high coefficient of thermal expansion which can lead to warping and inaccurate dimensional accuracy.


Info on Metal Casting found here.