Injection Molding and Tooling Glossary

Annealing – The process of heating the plastic parts or steel cavity components and allowing them to slowly cool to strengthen and remove internal stresses.

Bridge Tool – A tool used to mold parts to meet production until the final injection mold is completed. Bridge tools are not used for full production.

Cavity – The carved out depression in a mold where molten plastic flows into to create the molded part according to the design specifications. Injection molds can be either single or multi-cavity tools.

Core – Considered the male element in an injection mold that produces a recessed hole in a part, or part of a complex tool that molds undercut parts, typically withdrawn to one side prior to mold opening.

Degassing – When a mold is opened and closed, allowing gas to escape as trapped air and gas will cause part defects, such as bubbles and blistering.

Ejector Pins – Metal pins used to eject the part from the mold when the mold opens upon cycle completion.

Elastomer – A material that is rubber-like and elastic, snapping back to its original length when stretched under low stress.

Family Tool – One multi-cavity mold that contains different cavities to mold various parts at once, often parts that go together in an assembled product.

Gate – The opening where molten plastic resin flows into the cavity of the mold.

Hot Tip / Hot Gate – A gate used in a hot runner tool which injects the molten plastic directly into the cavity rather than a runner which flows into the cavity. Hot tip gates eliminate a runner or sprue, saving on material in high-volume production runs.

Insert – An object inserted into the part, or a part, such as metal or another plastic part, that plastic is molded around.

Jig – The apparatus that holds the mold and guides it during the injection molding process.

Mold Release – Preparing the surface of the tool to assist in part ejection from the mold.

Overmolding – Also referred to as insert molding, overmolding is when an object, or an insert, is placed in the cavity of a tool prior to injecting the plastic resin so the resin molds over the insert. This is performed in a vertical press, typically a rotary vertical press with 1 top half and 2 or more bottom halves.

Parting Line – The mark or line on a plastic part that indicates where the mold halves join in closing.

Runner – The channel the molten resin flows through to reach the cavities. When the cycle is complete and the parts eject, the runner ejects as well.

Short Shot – A defect created when the cavities in the mold are not completely filled with resin.

Shot Capacity – The maximum material weight a press can produce with one forward motion of the screw or plunger.

Sink Mark – A defect caused by a short shot or shrinkage after the gate seals, creating a dimple or depression on the surface, usually occurring in thick wall sections where material retains heat and shrinks more than it normally should due to the irregularity of the wall thickness.

Tunnel Gate – A gate that allows the flow of material into the cavities but shears off the gate upon ejection to eliminate separation of parts and runner.

Vent – A shallow slot or groove machined into the mold’s parting line to allow gases and air to escape during the molding process.

Warping – A molding defect caused when material shrinks in various ways, causing an irregular shaped part with dimensional distortion.

Contact QT Manufacturing at 972.221.0537 for answers to all your mold making and injection molding questions.