Resources
Manufacturing Glossary
Plain-language definitions of the injection molding, die casting, and tooling terms that show up in quotes, prints, and DFM feedback — written for people who need to make decisions, not pass a test.
- Cavitation
- The number of part cavities in a single mold or die — e.g., a 4-cavity tool produces four parts per cycle.
- Cavity / Core
- The two halves that form a molded part: the cavity forms the outer surface, the core forms the inner. Parts shrink onto the core, which is why draft and ejection are designed around it.
- Cold runner
- A mold where the runner system solidifies with the part each cycle and is removed afterward. Simpler and cheaper to build than a hot runner; generates runner material that is typically reground or remelted. Most Wrex tooling is cold runner.
- Cold slug well
- A small pocket opposite the sprue that catches the cooled plug of material at the front of a shot, keeping it out of the part.
- Cycle time
- The total time for one complete molding or casting cycle, from mold close through part ejection.
- DFM (Design for Manufacturability)
- Reviewing a part design for how easily and reliably it can be manufactured, before committing to tooling.
- Draft angle
- The taper applied to walls parallel to the mold-opening direction, allowing the part to release without dragging on the tool.
- Draft-free / zero draft
- A wall with no taper. Almost always a design error on molded and cast parts — it drags on ejection, scuffing the part and wearing the tool.
- EDM / Wire EDM
- Electrical discharge machining — a process using electrical sparks to erode metal, used for fine mold and die detail work that's difficult to cut conventionally.
- Ejector pin
- A pin that pushes the part off the core after the tool opens. Leaves a small visible witness mark, so placement on cosmetic surfaces matters.
- Family tool
- A single mold producing several different parts in one shot — economical for matched sets, but all parts must use the same material and be needed in the same ratio.
- First-article inspection (FAI)
- Measuring the first parts produced from a new or modified tool against the customer print before releasing the tool to full production.
- Flash
- Thin excess material squeezed out at the parting line or ejector pins. Removed by trimming or deburring; persistent flash usually signals tool wear or excessive injection pressure.
- Gate
- The point where molten plastic enters the mold cavity; gate location affects fill pattern, cosmetics, and knit lines.
- Hot runner
- A mold with a heated manifold that keeps material molten in the runner, so no runner is ejected with the part. Higher tool cost, less material waste, often faster cycles. Available on request — specify at RFQ.
- Hot-spot porosity
- Voids that form where a casting's last-to-freeze region has no feed path for shrinking metal — typically at isolated heavy sections.
- Insert molding
- Molding plastic directly around a pre-placed insert (often metal) in a single operation.
- Knit line / weld line
- The seam where two flow fronts meet after splitting around a hole or core. Structurally weaker than surrounding material and often cosmetically visible; gate placement determines where they land.
- Living hinge
- A thin flexible section molded integrally with a part, allowing repeated folding. Polypropylene is the classic material for this.
- Machining stock / allowance
- Extra material deliberately cast or molded onto a feature so a machining operation can clean it up to final dimension without cutting into porosity.
- Mold temperature controller
- A unit that circulates temperature-controlled fluid through the tool to hold a target mold temperature. Wrex uses chilled water or water heated below boiling; we do not run hot oil.
- NADCA
- North American Die Casting Association — publishes the tolerance and product specification standards that die cast parts are commonly produced to.
- Nominal wall
- The baseline wall thickness a part is designed around. Ribs, bosses, and transitions are all specified as a proportion of it.
- Overmolding
- Molding a second material (often an elastomer) onto or around an already-molded substrate.
- Parting line
- The line where the two halves of a mold or die meet; often visible as a fine line on the finished part.
- Porosity
- Small voids or air pockets in a cast part, typically caused by uneven wall thickness or process parameters.
- Projected area
- The part's area as seen looking into the mold-opening direction. Multiplied by injection pressure, it determines the clamp tonnage needed to hold the tool closed without flashing — and therefore which press a job can run on.
- Rated shot count
- The number of cycles a tool is quoted and built to produce. Tools within their rated shot count and in active production are maintained and stored at Wrex at no cost.
- Regrind
- Reprocessed plastic material from runners/sprues, sometimes blended with virgin resin — subject to agreement per program.
- Remelt
- Runners, biscuits, and excess material from previous runs of the same alloy, melted down and reused. Standard practice in die casting and a real cost saver; virgin alloy is available on request if specified before casting begins.
- Runner / Sprue / Gate
- The delivery system: material enters through the sprue, travels along runners, and enters the cavity through the gate. All are removed after molding, leaving a gate witness mark.
- Secondary machining
- CNC or other machining performed after molding or casting to achieve tolerances the base process can't hold.
- Shot size
- The volume of material a molding machine injects per cycle, usually stated in ounces. It's the practical limit on part size for a given press.
- Shrink rate
- How much a material contracts as it cools from molten to solid; varies by resin/alloy and affects tool dimensions.
- Shut height
- The closed height of a mold or die. It must fall within a machine's minimum and maximum daylight for the tool to run on that machine.
- Sink mark
- A surface depression over a thick section, rib, or boss, caused by material shrinking as it cools. The most common cosmetic defect on molded parts.
- Slide / Lifter
- Moving tool components that form undercuts and retract before ejection. They add tool cost and maintenance — worth avoiding through design where practical.
- SPI finish
- Society of the Plastics Industry mold surface finish classifications (e.g. SPI-A1 high polish through SPI-D3 dry blast). Required on every new plastic part at Wrex — the tool is cut to the finish you specify.
- Tie-bar spacing
- The clear distance between a press's tie bars, which limits the maximum mold base size that will physically fit in that machine.
- Tonnage / Clamp force
- The force a machine applies to hold the tool closed against injection pressure. Insufficient tonnage causes flash; parts are quoted to a press sized for their projected area.
- Tool class (SPI 101–105)
- An industry classification of expected tool life, from Class 105 (under 500 cycles, prototype) to Class 101 (1,000,000+ cycles, high-volume production). Class determines steel selection and cost.
- Tool transfer
- Moving mold or die tooling from one manufacturer to another, requiring inspection and requalification before production.
- Trim die
- A secondary die used to remove flash, runners, and excess material from a die cast part after casting.
- Undercut
- A feature that would prevent a part from releasing straight out of the mold or die without additional tooling action (a slide or lifter).
- Warp
- Distortion after ejection, caused by uneven cooling or non-uniform shrink. Wall-thickness uniformity is the primary defense.
- Witness mark
- Any small visible artifact left by the manufacturing process — gate, ejector pin, parting line. Not a defect, but its location should be agreed for cosmetic parts.
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