Injection Mold Design Guide

This is a comprehensive guide to Injection Mold Design. It covers the fundamental principles, component terminology, design best practices, and the critical interaction between the part design and the mold tool.

9. Tolerances and Dimensional Control

• Typical tolerances: +/- 0.1–0.5 mm depending on size, geometry, and material. Tight tolerances increase tooling cost.
• Critical dimensions: Isolate critical features near datum features and plan for post-molding machining if needed.
• Shrink and warpage compensation: Use mold-flow simulation and iterative prototyping; adjust cavity dimensions for expected shrink.

Part 9: The Ejection System

The mold opens, but the part sticks to the core (B-side). How do you get it off? injection mold design guide

• Ejector Pins: The standard. Place them near ribs, bosses, and corners. Avoid placing them on cosmetic surfaces (they leave a witness mark).
• Sleeve Ejectors: Used around core pins (e.g., for round boss holes).
• Stripper Plate: A plate that pushes the periphery of the part. Best for thin-walled, round, or cosmetic parts (no pin marks).
• Air Poppers / Valve Ejectors: For deep-draw parts prone to vacuum lock.

Rule of thumb: You need enough ejection force to overcome the shrinkage friction (approx. 10% of clamping force). Increase pin diameter if the plastic is soft (TPU, silicone). This is a comprehensive guide to Injection Mold Design

1. Core Principles of Mold Design

Before detailing features, understand the three golden rules: Typical tolerances: +/- 0

• Fill, Pack, Cool, Eject – The mold must enable each cycle step.
• Steel is the limit – Mold geometry must be machinable (EDM, CNC, grinding).
• Profit = Cycle time + Yield – A 10% faster cycle or 2% less scrap pays for the mold quickly.