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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.