Basic Knowledge of Injection Mold Structure: From Beginner to Master
一、Overview of Injection Molds
Injection molds are the core tools in plastic product manufacturing, determining the shape, dimensions, and surface quality of products. During the injection molding process, plastic pellets are heated to a molten state and injected into the mold cavity, where they cool and solidify into the desired product. A high-quality injection mold not only improves production efficiency but also ensures product consistency and reduces manufacturing costs.
二、Basic Components of an Injection Mold
1. Molding System
The molding system is the core part of the mold, directly determining the product shape:
Cavity: The concave part forming the outer surface of the product;
Core: The convex part forming the inner surface of the product;
Insert: Replaceable local molding components for easy maintenance and modification;
2. Gating System
The gating system guides molten plastic into the cavity:
Sprue: The channel connecting the injection machine nozzle to the runners;
Runner: Distributes plastic from the sprue to multiple cavities;
Gate: The narrow channel connecting the runner to the cavity;
Cold Slug Well: Collects cooled plastic at the front end;
3. Ejection System
The ejection system pushes the molded product out of the mold:
Ejector Pin: Directly contacts and ejects the product;
Ejector Plate: The plate securing the ejector pins;
Return Pin: Resets the ejection system during mold closing;
Ejector Guide Pin: Ensures smooth ejection;
4. Cooling System
The cooling system controls mold temperature:
Cooling Channel: Circulates cooling medium;
Baffle: Changes water flow direction to improve cooling efficiency;
Bubbler: Cools deep cavity areas;
5. Guiding and Positioning System
Ensures precise mold alignment:
Guide Pin: Cylindrical guiding component;
Guide Bush: Sleeve that pairs with the guide pin;
Locating Ring: Ensures alignment between the mold and injection machine;
6. Side Core-Pulling System
Handles undercuts or side features on the product:
Slider: Laterally moving molding component;
Angle Pin: Drives the slider movement;
Lock Block: Locks the slider during mold closing;
7. Venting System
Removes air from the cavity to prevent defects like gas marks, achieved via slots or gaps between components.
三. Classification of Injection Molds
1. By Structure
Two-Plate Mold: The simplest structure, consisting of a fixed and moving plate;
Three-Plate Mold: Includes an additional runner plate for automatic gate separation;
Hot Runner Mold: Keeps the gating system molten, eliminating waste;
2. By Cavity Number
Single-Cavity Mold: Produces one product per cycle;
Multi-Cavity Mold: Produces multiple identical products per cycle;
Family Mold: Produces multiple different products per cycle;
4. Key Design Considerations
Parting Line: Positioned at the product’s largest contour, considering draft angles and aesthetics.
Draft Angle: Typically 0.5°–3° to prevent sticking.
Uniform Wall Thickness: Avoids sink marks and warpage (generally 1.5–4mm for plastic parts).
Rib Design: Thickness ≤ 50%–60% of the main wall.
Fillet Transitions: Reduce stress concentration and extend mold life.
5. Common Injection Mold Materials
Pre-Hardened Steel: E.g., P20 (HRC 28–32), for standard molds.
Hardened Steel: E.g., H13 (HRC 48–52), for high-demand molds.
Stainless Steel: For transparent or medical products.
Aluminum: For prototyping or low-volume production.
6. Mold Maintenance
Regular Cleaning: Remove residual plastic and debris.
Rust Prevention: Apply anti-rust oil for long-term storage.
Lubrication: Regularly lubricate moving parts like guide pins and ejectors.
Damage Inspection: Periodically check cavity surfaces and critical components.
7. Trends in Injection Molding
High Precision: Meets demands for electronic components.
Smart Molds: Integrated sensors for real-time monitoring.
Quick Mold Change (QMC): Reduces setup time.
3D Printing: For complex cooling systems or conformal channels.
Tianjin Xuansheng Technology Co., Ltd. is a professional injection mold manufacturer offering one-stop customized solutions, integrating material selection, product development, mold design, injection molding, and assembly. With over 20 years of industry experience, the company is equipped with German and Swiss precision machining tools, a 100,000-class cleanroom, and achieves mold accuracy up to 5μm. Certified with IATF 16949 and ISO 13485, this injection mold manufacturer leverages digital intelligent manufacturing, combining Mold 3D simulation, smart CAD design, and CRM management to provide end-to-end services from design validation to mass production. Specializing in automotive parts, medical devices, and electronics, Xuansheng’s expert team ensures shortened development cycles and higher success rates, delivering cost-effective localization and iterative upgrades. As a leading injection mold manufacturer, Xuansheng embodies the value of "intelligent mold-to-product integration."
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