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Defining Plastic Injection Molding Key Terms

Sep 15, 2016

The collaborative nature of ERC’s culture is shared among our designers, engineering staff, and of course, our partners. Learning common plastic injection terms is a must! Here is a glossary of plastic injection molding key terms commonly used at the Engineering Resource Center:

AspectRatio: Ratio of total flow length to average wall thickness.

Assembly: The process of joining parts by any of several methods.

Cavity: A depression, or a set of matching depressions, in a plastics-forming mold which forms the outer surfaces of the molded articles.

Clamp: The part of an injection molding machine incorporating the platens that provides the force necessary to hold the mold closed during injection of the molten resin and open the mold to eject the molded part.

Ejection Pin: A rod, pin or sleeve that pushes a molded part off of a core or out of a cavity of a mold.

Ejector Return Pins: Projections that push the ejector assembly back as the mold closes. Also called surface pins or return pins.

Ejector Rod: A bar that actuates the ejector assembly when the mold opens. 

Elasticity: The ability of a material to quickly recover its original dimensions after removal of a load that has caused deformation.

Flash: Any excess material that is formed with and attached to the component along a seam or mold parting line.

Gate: The channel through which the molten resin flows from the runner into the cavity.

Injection (also known as Fill Time): Time required to fill the cavity or mold.

Injection Molding: The method of forming objects from granular or powdered plastics, most often of the thermoplastic type, in which the materials is fed from a hopper to a heated chamber in which it is softened, after which a ram or screw forces the material into a mold. Pressure is maintained until the mass has hardened sufficiently for removal from the mold.

Insert: a removable part of the mold imparting increased resistance to wear, heat transferability, or changeable part shape to that area of the mold.

Knockout Pin: A pin that ejects a molded article from the mold.

Mold (n): A hollow form or matrix into which a plastic material is placed and which imparts to the material its final shape as a finished article.

Mold (v): To impart shape to a plastic mass by means of a confining cavity or matrix.

Mold Frame: A series of steel plates which contain mold components, including cavities, cores, runner system, cooling system, ejection system, etc.

Multi-Cavity Mold: A mold having two or more impressions for forming finished items in one machine cycle.

Packing: The filling of the mold cavity or cavities as full as possible without causing undue stress on the molds or causing flash to appear on the finished parts. Over- or under-packing results in less than optimum fill.

Prototype Tool: A preliminary mold built upon which the final mold will be based.

Resin (Synthetic): The term is used to designate any polymer that is a basic material for plastics.

Runner: In an injection mold, the feed channel, usually of circular cross section, which connects the sprue with the cavity gate. The term is also used for the plastic piece formed in this channel.

Scrap: any output of a mold that is not usable as the primary product.

Shot: One complete cycle of a molding machine.

Sprue: The feed opening provided in injection molding between the nozzle and cavity or runner system.

Toggle: A type of clamping mechanism that exerts pressure by applying force on a knee joint. A toggle is used to close and exert pressure on a mold in a press.

Tool: In injection molding, the term sometimes used to describe the mold.

Undercut: A protuberance or indentation that impedes withdrawal from a two-piece rigid mold

Vent: A shallow channel or opening cut in the cavity to allow air or gases to escape as the melt fills the cavity.

Void: An unfilled space within a solid material.

Warpage: Distortion caused by nonuniform internal stresses.


To learn more plastic injection molding terms visit the online link by clicking here.

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