Unit 20 Plastic Parts

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.