Unit 20Plastic Parts Click icon to add picture

Learning Objectives

• List common names and abbreviations used in the manufacture of plastic parts.

• Explain the difference between thermoplastic and thermoset plastics.

• Explain the processes used in the plastics industry.

Engel, Inc.

Learning Objectives

• Describe methods used to fasten and join plastics.• Read and interpret prints from the plastics industry.

Plastic Parts

• Plastic:– Product of polymer chemistry– Synthetic material formed by chemical reaction, rather than a

substance of natural origin• Thermoplastics: Soften when heated and solid when

cooled• Thermoset plastics: Cannot be softened once cured,

neither by heat nor solvent

Thermoplastics

Thermosets

Plastics Terminology

• Monomer: Low weight molecule capable of reacting to form polymers

• Polymer: Basic molecular structure of a plastic• Polymerization: Joining of two or more molecules to

create a more complex molecule• Resin: Basic organic material from which plastics are

formed• Elastomer: Material with rubber-like characteristics

Plastic Processes

• Molding: Forcing molten plastic into a hollow mold• Thermoforming: Forcing a sheet of softened plastic onto

a mold using vacuum or positive pressure• Extrusion: Pumping molten plastic through a heated die• Casting: Pouring molten plastic into an open mold without

using pressure

Plastic Processes

• Bottles manufactured by blow molding

Uniloy

Plastic Processes

• Car model manufactured by thermoforming

MAAC Machinery

Plastic Processes

• Plastic pipe manufactured by extruding

Polygon Company

Fastening and Joining Plastics

• Mechanical fasteners: Thread-cutting screws, rivets, and press-in inserts

• Mechanical fits: Press-in and snap-on fits• Welding: Ultrasonic welding, heat welding, and spin

welding• Adhesives: Elastomers, epoxies, and solvents

Fastening and Joining Plastics

• An ultrasonic plastic welding machine

Dukane

Plastics Terminology

• Mold: Hollow form into which material is placed to give the material its final shape

• Cavity: Depression or set of matching depressions that shapes the surface of the molded object

• Parting line: Edge of the mold cavity where mold halves come together

• Draft: Slight outward taper in a mold wall designed to facilitate removal of the molded object

Plastics Terminology

• Sprue: Main feed channel that connects the mold orifice to the runners

• Runner: Usually circular channel that connects the sprue with the gate

• Gate: Connects the runner to the part cavity; often 1/8″ diameter or less

nanantachoke/Shutterstock.com

Plastics Terminology

• Mold shrinkage: Shrinking of the plastic part after it has been removed from the mold

• Warpage: Distortion caused by nonuniform shrinkage• Sink mark: Depression or dimple caused by short shot or

local internal shrinkage• Flash: Thin web of excess material forced into crevices

between mating mold surfaces

Plastics Terminology

• Boss: Circular protrusion from the plastic body• Gusset: Angular piece of material designed to strengthen

two adjoining walls• Insert: Material placed into the mold cavity prior to

molding that is then surrounded by the molded material• Overmold: Process of injection molding a plastic over an

existing plastic

What do you see?

Print supplied by Intermatic, Inc.