Annealing - Annealing is the heating and slow cooling of a plastic part which allows the polymer chains to recoil and relieve internal stresses.

Release agent – A compound, which is sprayed on the mold, or as an additive, molded into the part to help facilitate the release of the part.

Thermoset – A material, which when heated, is pressed or molded into a shape.  The heating process changes the structure of these materials, and for this reason they cannot by re-heated.

Blow molding – The process follows the basic steps found in glass blowing. A parison (heated plastic mass, generally a tube) is inflated by air. The air pushes the plastic against the mold cavity to form the desired shape. Once cooled, the plastic is ejected.  This method is used to make plastic bottles.

Flash gate – An alternative to a fan gate, which conveys the melted resins into a thinner gate section creating a linear melt flow into the cavity.

Flow marks - A wavy pattern or discoloration caused by a slow injection speed which allows the material to cool too quickly.

EDM or electric discharge machining - A manufacturing process used to create molds, where the shape of the mold cavity is obtained by removing metal material using electrical discharges.

Additives – These compounds are added to resins to improve the overall performance and appearance of finished products.  A key trend in this area today is using additives that are made from organic materials such as eggshells, wood pulp, rice hulls or materials that improve the biodegradability of the plastic.

Blister – As the name says, this is a part defect which appears as a small bubble or blister on the surface of a part and it generally created by gas or air bubbles.

Flash or burrs – A thin lip or protrusion beyond the body of the part that is generally caused by poor clamping force, improper mold design and/or mold damage.

Polymer - A substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together, e.g., many synthetic organic materials used as plastics and resins.

Hot-runner mold – Hot runner molds consist of 2 plates that are heated with a manifold system.   The manifold sends the melted plastic to nozzles which fill the part cavities.

Cold slug – A defect characterized by a small non-uniform area on the part caused by an improperly heated piece of plastic becoming attached to the part.

Bridge tool – An injection mold that makes parts until the final tool is completed.  These molds or tools are not meant to be production tools.

Compression molding - The name of this molding method says everything.  A heated plastic material is placed in a heated mold and is then compressed into shape. The plastic can be in bulk but often comes in sheets. The heating process, called curing, insures the final part will maintain its integrity. This molding method is often used to make large objects such as automobile components.

Masterbatch – A solid or liquid additive for plastic used for coloring plastics or imparting other properties to plastics.

Multi-shot molding – A process where two or more plastic substances are injected into the mold to form a part.  Toothbrushes are often manufactured using this technique.

Over molding – A two-shot process, in which two plastic substances, are injected into a mold sequentially, usually a harder base material with a coating of softer material.

Core - A protrusion or set of matching protrusions, which form the inner surface of a plastic part. They are often considered they “male” side of the part.

Undercut – Can be a design flaw that results in an indentation or protrusion that inhibits the ejection of the part from the mold.  Other times undercuts are designed into a mold to ensure a part holds onto the correct side of the mold.

Alloy – A plastic alloy is a physical modification of an existing plastic to achieve higher performance and or functionality.  These alloys are often used in the automobile industry and to replace metal parts.

Delamination - This defect appears as a flaky surface layer on the part and is often caused by contamination or moisture in the resin pellets.

Colorant – A pigment system, usually in pelletized form, powder or liquid, which is mixed with resin to produce the desired color.

Vent – A channel from the mold cavity that allows gas and air to escape as resin is being injected into the cavity to prevent many types of defects from occurring.

Thermoplastic - A material that can be heated and cooled repeatedly without changing the material structure.  Highly recyclable.

Degassing – Opening and closing of a mold to allow gas to escape.  Trapped gas and/or air can cause parts defects such as blistering and bubbles.

Posted by Kyle Coblentz | 02 / 19 / 14 0 Comments

Weld line - Also called a knit line, the juncture where two flow fronts meet and are unable to join together during the molding process. These lines usually occur around holes or obstructions and cause localized weak areas in the molded part.

Tie bars - Bars which provide structural support to the mold in the press.  The spacing between the tie bars dictates the size of the mold that can be placed into the injection machine. The mold opens and closes riding on the tie bars.

Prototype tool – Also called a soft tool, a preliminary mold built to produce prototype parts and used to make adjustments to the final production tool.

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