Plastic Injection Glossary

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A-Side

The negative side of the mold, sometimes called the cavity, which often forms the exterior of the plastic part.

Anneal

The process of gradually cooling a plastic part after it has been heated to a temperature just below its softening point, making the material tougher.

Assembly

Joining completed molded parts together to form a final product.

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B-Side

Sometimes referred to as the core, this is the side of the mold containing the injectors; most often forms the interior of the plastic part.

Barrel

The section of the molding machine containing the screw which melts resin pellets and injects the compressed material into the runner of the mold.

Boss

A protrusion on a plastic part or mold used to add strength to the piece or create alignment for fasteners. 

Bubble

Gas pockets or vacuum voids which occasionally occur inside plastic during the injection molding process.

Burn Marks
Typically black or brown-colored discolorations on an edge or surface of a molded plastic component.
Blister
A raised area on the surface of a molding caused by the pressure of gases inside it
Bloom
A visible exudation or efflorescence on the surface of a plastic part
Backing Plate
A plate used as a support for the cavity blocks, guide pins, or bushings
Breathing
Allowing gasses to escape the mold early in the molding cycle. Also known as degassing.
Burn
Thermal decomposition through discoloration, distortion or localized destruction of the surface of the plastic part.
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CAD
Acronym for Computer Aided Design
Cavity
The negative shape formed in a steel tool in which plastic is injected to create the mold.
Charge
A portioned out amount of material loaded by the screw into the mold during a single cycle.
Cure
The process of hardening of injection molded parts.
Cycle
The time is takes for the plastic injection process to complete. One plastic part can sometimes take multiple cycles to complete.
Color Streaking
Also known as “discoloration”, occurs when a plastic part is a different color than intended.
Chalking
A dry chalk-like appearance or deposit on the surface of a plastic part. Also known as Blooming.
Core Pin
Pin used to mold a hole.
Curing Temperature
Temperature at which a cast or molded part is cured.
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Draft
The degree of taper a side wall has to facilitate removal of plastic parts from a mold.
Durometer
A measure of the hardness and resistance to marring in a material.
Discoloration
Also known as “color streaking”, occurs when a plastic part is a different color than intended.
Degassing
Allowing gasses to escape the mold early in the molding cycle. Also known as breathing.
Deterioration
A permanent change in the physical properties of a plastic component.
Deflashing
A range of finishing techniques used to remove the excess material on a plastic molding. These techniques can range from filing, sanding, milling, tumbling, and more.
Diaphragm Gate
The gate used in molding annular or tubular articles which forms a solid web across the opening of the part.
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EDM (Electric Discharge Machining)
A type of precision machining process used to build tools for plastic injection molding; utilizes electrical charges to erode metal.
Ejector Pin
A pin used to push the plastic molding out of its cavity or mold.
ERP
Acronym for Enterprise Resource Planning; a software dedicated to managing manufacturing processes and automating administrative functions for greater efficiency.
Extrusion
The compacting and forcing of a plastic material through an orifice.
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Finish

The final surface texture of a part.

Flow Lines
Discolored lines that show up on a prototype part. Flow lines usually happen when the injection speed is too low, causing the plastic to solidify too soon.
Flexural Strength
Ability of a plastic component to flex without permanent distortion or breaking.
Flow Marks
Wavy surface marks on a molded object caused by irregular or improper flow of the plastic material into the mold.
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Gate

The opening in the mold where the molten plastic is injected into the final part.

Gloss
The shine or luster of the surface of a plastic material.
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Hardness
The level of resistance a plastic material has to compression or surface damage.
Hot-Runner Mold
Heated molds that melt plastic and send it to nozzles which fill the plastic part cavities. 
Hot Stamping
An engraving process where a heated die is used to apply pressure to the plastic part, transferring pigment onto it.
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Injection Molding
A manufacturing process where melted plastic is injected into a negative of the part being produced, known as a mold cavity. After the plastic cools, it becomes a solid of the positive component.
Impact Strength
The ability of plastic material to withstand shock loading. Molded plastics are usually given a value on an Izod scale.
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Jig
Apparatus which holds and guides the tool during the plastic injection machining process.
Jetting
When molten plastic fails to stick to the mold surface due to the speed of the injection.
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Knit Lines
Discolored lines that show up on a plastic prototype part. See Flow Lines.
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Laminar Flow
Thermoplastic resin poured into a mold is accompanied by solidification of the layer in contact with the mold surface. This resin acts as an insulating tube through which material flows to fill the remainder of the cavity, and is essential to duplication of the mold surface.
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Molding Material
Types of plastic material used in injection molding. These materials can comprise of resin, filler, pigments, plasticizers, or other ingredients.   
Mold Release
A material used to prepare a part’s surface for easier ejection of a mold.
Melt Strength
The strength of the plastic while in the molten state.
Molding Cycle
In molding, the cycle time is the period or elapsed time between a certain point in one cycle and the same point in the next.
Monomer
A simple compound which can react to form a polymer.
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Nozzle
The hollow nose attached to the end of the injection machine which transfers melted plastic into the mold.
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Orientation
The alignment of the crystalline structure in plastic material so as to produce a uniform structure.
Olefins
A group of unsaturated hydrocarbons named after the corresponding paraffins by the addition of “ene” or “ylene" to the stem (ie propylene)
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Pad Printing
The process where ink is taken from an etched design and deposited on a molded plastic part to create a design.
Parting Line

A line formed on the seam of the part where two molds meet.

Plastic
A polymeric material which can be melted under heat and pressure.
Plasticizer
A certain material incorporated in melted plastic to increase its flexibility when hardened.
Purging
Cleaning one type of material out of the cylinder of an injection molding machine by forcing it out with new material.
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Resin
Generic term for a chemical compound injected in to a mold.
Runner
The channel that connects the sprue and nozzle to the gate of the mold cavity.
Residence Time
Duration of time an injected material charge sits in the heating cylinder before its injection into the mold
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Screw
A device housed in a barrel which portions out resin pellets and melts them on before they are injected into the mold.
Shot
A single complete cycle of the screw in the barrel of the molding machine.
Shrink Rate
The amount of shrinkage that occurs during plastic cooling (Usually between .004” and .20”)
Sprue
Opening feed that sends material from the nozzle to the runner.
Sink Mark
Depressions which form in certain areas of a plastic molded part. They’re usually caused when the cooling device is insufficient and doesn’t fully cure the product.
Surface Delamination
When thin layers on the surface of a plastic part appear and peel off piece by piece
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Thermoplastic
A recyclable polymeric material that can be heated and cooled repeatedly without changing the structure of the plastic.
Tool
The solid mold in which resin is injected to for the plastic part.
Thermoset
A material that will has undergone a chemical reaction through heat and pressure
Tie Bars
Bars which provide structural rigidity to the clamping mechanism of a press
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Ultrasonic Welding
A process of welding that produces a molecular bond between compatible thermoplastic parts.
Undercut
A protrusion or indentation that impedes withdrawal from a two-piece, rigid mold
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Vent
A shallow channel or minute hole cut in the mold cavity to allow air to escape as the material enters the mold
Void
A void or bubble occurring in the center of a thermoplastic part usually caused by shrinkage.
Vertical Flash Ring
The clearance between the core and the vertical wall of the cavity in a positive or semi-positive mold.
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Warping
Uneven shrinkage in different parts of the molded component. This usually occurs when there’s non-uniform cooling of the plastic material.
Weld Lines
Lines that can appear on the surface of a molded part where the molten material has converged after splitting off in a mold.
Water Absorption
The ability of thermoplastic material to absorb water.
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