TERMS AND DEFINITIONS

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

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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.

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Bubbles – Similar to blisters, gas pockets, or voids that have formed inside the plastic.

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Cavity - The machined shape within a mold which created the form of the plastic part.

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Clamp – The mechanism that holds the mold in location during the molding process.

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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.

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

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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.

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Crazing – A defect that causes small cracks often caused by over-stressing the plastic material.

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Creep – The “set” that a molded part takes under stress and does not return to its original shape. Also known as “memory”.

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Cure – The process of allowing a plastic to harden or stabilize.

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Cycle – The overall time it takes for the plastic injection process to complete a finished part.

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Density – Mass per unit volume of a substance.

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Draft – The angle or degree of taper in a side wall to help facilitate removal of the parts from the mold.

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Ejection pin – Metal rods in the mold which push the parts from the mold.

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Ejector return pins – Pins that push the ejectors back into position once the parts have been released.

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Ejector rod – A bar that engages the ejector assembly and pins when the mold opens.

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Fan gate – A gate with a wider width that helps reduce warping through stress.

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Fill – The packing of material into the mold.

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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.

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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.

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

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Flow rate – The volume of material passing a fixed point per unit time.

 

Gate – The channel into which melted plastic flows into a mold.

 

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.

 

Insert – An object, such as a magnet or screw, which is inserted into the molded part.

 

Machine shot capacity – The maximum volume of resin which can be injected in a single stroke.

 

Mold – A hollow form that plastic is injected or inserted into to manufacture a plastic part.

 

Mold release – A surface preparation used to aid in the ejection of the part from the mold.

 

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.

 

Nozzle - The hollow-cored metal nose screwed into the injection end of the barrel which forms a seal under pressure.

 

Orange peel – A patchy rough surface defect caused by moisture in the mold cavity, or by incomplete pack-out.

 

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.

 

Parting line – A line on a part formed when the two sides of the mold come together.

 

Pinpoint gate – A very small gate, used in hot runner molds, to control the flow of material.

 

Platens – Steel plates in the molding machine onto which the mold is fastened.

 

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.

 

Purging – The process of cleaning the injection machine of remnant color or materials prior to running a new part.

 

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.

 

Runner – The channel system that allows the flow of the melted material to fill the part cavities.

 

Short shot – A defect where the material does not fully fill the part cavity.

 

Shot – A complete cycle of the injection machine.

 

Shrinkage – The amount of volume reduction that takes place when a plastic material cools.

 

Sprue – The opening feed that conveys material from the nozzle to runner system in the mold.

 

Tool – The mold used to form plastic parts in an injection machine.

 

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.

 

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.

 

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.