If your design requires varying thicknesses, use a chamfer or fillet.
Plastic shrinks as it cools. Thick sections take longer to cool than thin sections. When different parts of a piece cool at different speeds, it creates internal stress. This leads to defects like sink marks (dimples on the surface) and warping (twisting of the part). Design Guidelines
Undercuts are features like side holes, clips, or threads that prevent the part from ejecting in a straight line. They require complex mold mechanisms like side-actions (slides) or lifters, which add significant cost. Whenever possible, design features to avoid undercuts by orienting them to align with the main opening direction.
Once the plastic has cooled, the part must be ejected from the mold. If the walls of your part are perfectly straight (parallel to the direction the mold opens), they will act like a suction cup, sticking firmly to the mold. This leads to scraped surfaces, damaged parts, and broken tooling. injection molding part design for dummiespdf exclusive
This guide is designed for beginners ("dummies") to help you understand the core principles, avoid common pitfalls, and prepare your designs for successful manufacturing. What is Injection Molding?
If an undercut is mandatory, the mold maker will need to use sliding cores or lifters. This adds mechanical complexity, increases the risk of part defects, and significantly raises the initial cost of the mold. Conclusion
: While digital versions exist, you can sometimes request a physical copy directly from Protolabs. Core Design Principles from the Guide If your design requires varying thicknesses, use a
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If you need additional visuals or more technical depth without the jargon, these manufacturers offer similar high-quality "exclusive" e-books: Fictiv Injection Molding Design Guide When different parts of a piece cool at
Sharp corners are the enemy of a good plastic part. They create "stress concentrators" where the part is likely to crack under pressure. They also make it harder for the molten plastic to flow through the mold.
To prevent ribs from causing cosmetic issues on the visible opposite surface of your part, follow these precise geometric ratios: