Plastic Shaping Processes Quiz

An injection molding process where a gas is mixed with the polymer melt, creating a tough outer skin surrounding a foam core.

Injection molding of thermosets uses shorter barrels, lower temperatures, and heated molds to initiate cross-linking.

Mixing two reactive liquids and injecting them into a mold, where chemical reactions solidify the material.

Blow molding creates hollow, seamless containers, like bottles.

Thermoforming starts with a thermoplastic sheet or film.

A mold with a convex shape.

A mold with a concave cavity.

Mechanical thermoforming molds are more costly due to needing matching mold halves, unlike pressure or vacuum thermoforming which only need a single mold.

The line where the two mold halves meet.

Removing the molded part from the mold cavity.

Automatic separation of the part from the runner.

Gating usually at the base—reduces weld lines.

Flash (excess plastic)

Short Shots (incomplete filling)

Sink Marks (uneven cooling)

Force of gravity

Blow Molding

Gravity forces plastic into mold.

Foaming plastics involves three main methods: mechanical agitation, using blowing agents (like gas), and chemical blowing agents.

Mixing a liquid resin with air, then hardening the polymer with heat or chemicals.

Mixing a gas (like nitrogen or pentane) with a polymer; the gas expands when pressure is released.

Mixing a polymer with compounds that release gases (like CO2 or N2) at high temperatures.

Plastics are generally weaker and less stiff than metals.

Plastics generally have good impact resistance, better than many ceramics.

Plastics have limited service temperatures compared to metals and ceramics.

Plastics expand more with temperature changes than metals.

Plastics can degrade from sunlight, radiation, oxygen, ozone, and some solvents.

Four key elements influence injection molding: material properties, mold design, process parameters, and injection settings.

The four main factors influencing injection molding: molder, material, injection machine, and mold.

Cold runner two-plate, cold runner three-plate, hot runner (runnerless), and insulated runner molds.

A hydraulic, three-platen system is the most prevalent type in industry.

Common materials include HDPE, MDPE/LDPE, PET, PP, PVC, TPE, PS, PC, PTFE, and polyimide/nylon.

Extrusion blow molding, injection blow molding, biaxial stretch blow molding, and co-extrusion blow molding are the main ones.

Plasticizing the resin, parison production, parison inflation and cooling, ejection from the mold, and finishing/trimming.

Degating, deflashing, cleaning, and decorating are the main types of plastic finishing.

Various methods can be used to decorate plastic parts (specific details not provided).

Degating, deflashing, cleaning, and decorating are the four most common plastic finishing operations.

Process of injecting molten plastic into a mold to create a desired shape.

The viscosity of a polymer melt decreases with increasing shear rate, exhibiting 'pseudoplasticity'.

The main categories are: extrusion, molding, forming continuous sheets & films, fibers, foamed products, and discrete formed sheets & films.

Many plastic shaping processes are 'net shape' processes, meaning less energy is required compared to metalworking. They also require lower temperatures than metals or ceramics, offer flexibility in geometry, and generally don't require painting or finishing.

Die swell is the expansion of the extrudate's cross-section upon exiting the die orifice. This occurs because of the viscoelastic properties of the polymer melt.

Viscosity is affected by temperature, shear rate, and the molecular weight of the polymer.