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All plastics shrink (0.3% for ABS, up to 2.5% for POM). The mold cavity must be cut to account for shrinkage.
Used in hot runner systems, these feed plastic directly into the top of the part, leaving a minimal vestige and generating zero runner scrap. 4. Cooling System Engineering
: Mandatory when molding corrosive plastics like PVC, which release hydrochloric gas when melted. Summary Checklist for Mold Designers
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❌ Never vent into ejector pin holes unless pin has a flat.
An injection mold is a high-precision tool used to mass-produce plastic parts by injecting molten material into a carved cavity. Proper mold design directly impacts part quality, production speed, and manufacturing costs. This comprehensive guide outlines the foundational principles, mechanical systems, and material selection criteria required to design a successful injection mold. 1. Core Principles of Part Design Compatibility All plastics shrink (0
| Material | Shrinkage | Mold Steel | Vent Depth | Corrosion Risk | | :--- | :--- | :--- | :--- | :--- | | | Low | P20 (standard) | 0.03mm – 0.05mm | Low | | PC (Polycarbonate) | Low | H13 / Stainless | 0.02mm – 0.03mm | Low (requires dry steel) | | PVC | High | Stainless (420) | 0.01mm – 0.02mm | High (releases HCl gas) | | POM (Acetal) | High | P20 / H13 | 0.01mm | Moderate (degassing needed) | | Glass-filled Nylon | Low | Hardened H13 | 0.02mm (abrasive) | Low (abrasive wear on gates) |
Before diving into the details of injection mold design, it's essential to understand the basic components of a mold. A typical injection mold consists of:
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Use ribs to increase structural stiffness instead of thickening the walls. Rib thickness should be 50% to 60% of the main wall thickness to prevent sink marks on the cosmetic flip side. Bosses used for fasteners should follow the same thickness rules and include internal gussets for reinforcement.
This data will allow us to map out the ideal gate sizing, shrinkage rates, and side-action mechanisms for your design. AI responses may include mistakes. Learn more Share public link
Ignoring any of these four pillars results in catastrophic failure.
Injection mold design is a complex process that requires careful consideration of several key factors. By following best practices, avoiding common mistakes, and using simulation to optimize the design, designers can create high-quality molds that produce consistent, accurate parts. Whether you're a seasoned designer or just starting out, this injection mold design guide provides a comprehensive overview of the key considerations and best practices for designing high-quality injection molds.
When a part contains through-holes, the steel of the core must meet the steel of the cavity to block plastic flow. This contact area is a shut-off. Designing shut-offs with a slight angle (typically 3 to 5 degrees) prevents the steel faces from rubbing directly against each other, reducing tool wear. Dealing with Undercuts
