Navigating the technical terminology of plastic injection mold toolmaking is critical for successful project execution. At CNMOULDING, we believe in clear, engineer-to-engineer communication. This comprehensive glossary defines the essential terms, tolerances, and mechanisms used throughout the mold design, manufacturing, and production phases.
A – C: Core Components & Material Behavior
Anti-Warping & Part Design
- Boss: A cylindrical protrusion or raised feature on a plastic part, typically engineered to accept screws, threaded inserts, or assembly pins.
- Core Out: The engineering process of removing heavy mass from thick sections of a plastic part. This ensures a uniform wall thickness, eliminates cosmetic defects, and minimizes component distortion.
- Rib: A thin, blade-like structural reinforcement feature designed to stiffen part walls and strengthen bosses without increasing the baseline wall thickness, effectively preventing part deformation.
Mold Architecture
- Cavity (Upper/Female Half): The concave portion of the injection mold that forms the external aesthetic surface of the plastic part. Typically, parts do not remain on the cavity side when the molding machine opens.
- Core (Bottom/Male Half): The protruding portion of the injection mold tool that forms the internal geometry of the plastic part. The molded part typically shrinks onto and remains on the core side upon mold separation.
- Cooling System: A network of precisely drilled water channels integrated within the mold plates. Proper cooling regulates tool temperature, optimizes cycle times, ensures proper polymer solidification, and prevents part warping.
Material Selection & Phenomena
- Draft Angle: A mandatory taper or slope applied to all vertical faces of an injection-molded part parallel to the direction of mold opening. It allows the plastic part to release cleanly from the metal tool steel without drag marks. (Refer to our Design Guide for specific material recommendations).
- Shrinkage Rate: The percentage of volumetric contraction experienced by plastic resins as they cool from a molten state to a solid state inside the mold. This rate must be calculated and factored into the initial mold design before cutting steel.
- Example: Polycarbonate (PC) typically shrinks around 0.006 in/in, while Nylon (PA66) can shrink up to 0.015 in/in.
- Sink Mark: A cosmetic defect manifesting as a shallow depression on the surface of an injection-molded part. It is caused by non-uniform wall thickness or excessive thickness ratios at rib/boss intersections during resin cooling.
- Warp (Warpage): A post-molding distortion or geometric twisting caused by non-uniform volumetric shrinkage or uneven cooling across the part’s wall sections.
D – G: Gating, Feeding, and Kinematics
Gating Systems
- Gate: The restricted orifice through which molten plastic enters the mold cavity from the runner system. Common configurations include: Edge Gates, Fan Gates, Cashew/Tunnel Gates, and specialized automatic-shear gates.
- Runner (Hot/Cold): The distribution channel that guides molten polymer from the sprue to the gates. Hot Runner Systems (utilizing components from brands like Yudo, Husky, or Mold Masters) maintain the plastic in a molten state within the manifold, eliminating runner scrap and improving cycle efficiency.
- Sprue: The primary channel oriented perpendicular to the mold parting line that connects the injection molding machine nozzle directly to the runner system.
- Vestige: The minor structural witness mark or material remnant left on the plastic component after the gate/runner has been manually or automatically sheared off.
Dynamic Tooling Mechanisms
- Cam / Horn Pin (Angle Pin): An angled steel pin mounted in the mold plate that mechanically drives the slide/slider mechanism horizontally as the injection molding machine opens and closes.
- Gibs: Precision-ground steel guide rails that guide and retain the slider block along its linear path of motion.
- Heel Block: A heavy-duty wedge block designed to mechanically lock the slider mechanism into its forward position, resisting the immense hydraulic clamping pressures generated during resin injection.
- Slider / Side Action: An automated mechanical module integrated within the injection mold to form undercuts or complex lateral features. Slides move perpendicular to the mold opening direction to release the part without obstruction.
I – W: Production, Prototyping, and Quality
Mold Tooling & Tooling Strategies
- Part: The customized plastic component designed via 2D drawings or 3D CAD models supplied by the OEM or customer.
- Tool (Injection Mold): The high-precision steel assembly (comprising plates, cores, cavities, mechanisms, and ejection units) engineered to shape and solidify molten polymer under high pressure.
- Stock Safe (Steel Safe): An intentional engineering strategy where extra metal is left on the mold core/cavity during initial CNC machining. This allows for precise, fine-tuning adjustments based on actual T1 sample dimensions, as removing metal is significantly cheaper and faster than adding it via welding.
- Example: Leaving a mold dimension at 0.505″ for a targeted 0.500″ inner diameter to evaluate actual material shrinkage.
- Undercuts: Any geometric feature, hole, recess, or protrusion on a part design that prevents direct, straight-line ejection along the mold parting line. Undercuts require Side Actions (Sliders) or Hand-Pulls (Loose Inserts) to be successfully molded.
Manufacturing and Processing
- Ejector Pins: High-strength steel rods driven by the machine’s ejector plate to physically push the cooled plastic part off the mold core.
- Shear / Shear Stress: The internal friction and localized heat generated within the molten plastic as it is forced through narrow gates under high velocity and pressure. Excessive shear causes polymer degradation and material burning; insufficient shear leads to premature freezing and short shots.
- Thin-Wall Molding: A specialized injection molding process focused on parts with nominal wall thicknesses ranging between 0.005″ and 0.060″ (0.12mm to 1.5mm), requiring high-speed injection and high-clamp pressures.
- Wall Thickness: The cross-sectional thickness of the solid plastic sections of a component. Maintaining a uniform wall thickness is paramount to preventing sink marks, voids, and warpage.
Rapid Prototyping & Inspection
- FDM (Fused Deposition Modeling): An additive 3D printing technology that extrudes layers of molten production-grade filaments (such as ABS or PC) to build functional prototypes directly from digital CAD data.
- Reverse Engineering: The process of capturing data from an existing physical plastic part (often via 3D scanning) to reconstruct a precise 3D digital CAD model for mold building or design modification.
- SLA (Stereolithography): A high-precision rapid prototyping technology that utilizes a UV laser or electron beam to cure liquid photopolymer resin layer-by-layer into a highly detailed physical part.
Logistics & Operations
- Bulk Pack: A standard shipping method where molded plastic components are carefully discharged directly from the molding machine into a shipping carton without individualized wrapping or stacking layers.
- Operators: Trained personnel responsible for running the injection molding machine, managing manual insert loads, inspecting parts for defects, and executing manual gate trimming.
Engineered for Perfection. Managed with Integrity.
Understanding these technical terms ensures that you and your manufacturing partner are aligned on every detail. At CNMOULDING in Shanghai, our engineering team utilizes these foundational standards alongside advanced ISO 13485 quality protocols to engineer molds that achieve tolerances up to ±0.005mm.
Whether your project requires complex Unscrewing Molds, Multi-Cavity Hot Runners, or detailed DFM Reviews, we manage the entire manufacturing cycle 100% in-house.
Have a 3D part file ready for an engineering review?
Submit your STEP/STP/IGS files to our engineering team today for a comprehensive DFM assessment and line-item quote.
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