Plastic Molding Mfg., is a Massachusetts based injection molder specializing in tight tolerance precision molding, insert molding, over molding and a variety of part joining processes. We are an engineering driven company, providing our customers with "one stop solutions" for the design and production of polymer based products.
Injection Molded Part Design
Injection-molded part design is a complex process requiring considerations for mechanical part function, processing and materials. Each part has it’s own unique set of requirements and challenges. The most important guideline to designing an injection-molded part is to ensure function and manufacturability is co-existent in part design. Consideration for generally accepted design guidelines when engineering your injection-molded components will provide for a cost-efficient, seamless launch when paired with the right partner such as Plastic Molding Mfg. Some of these guidelines include:
- Design parts with a uniform wall thickness to provide for even material flow, cooling and shrinkage. When uniformity is not possible the transition should be made gradually on the order of 3 to 1 in the direction of material flow during injection to avoid areas of stress and uneven cooling.
- Generous Radius should be supplied at all corners to avoid stress areas in the part; sharp corners should be avoided. Fillet radii should be at least 25% and up to 60% if load bearing, of the nominal wall thickness. The outside corner radius should be equal to the inside radius plus the wall thickness for uniformity and stress reduction.
- To ensure quicker cooling, shorter cycle times and minimum material costs, use the least wall thickness that will accomplish the mechanical features of the part.
- Add plenty of draft to the part (in the direction of the mold opening or closing) to ensure easy de-molding (2-5 degrees is preferable)
- Instead of adding thick sections to increase the structural integrity of a part, use ribs or gussets. This will improve cycle time; reduce part weight and material costs. Maximum rib height should not exceed 3 times the nominal wall thickness to avoid fill and sticking issues in processing. A draft of at least 0.5 degrees per side is necessary on ribs; a draft of 1-1.5 is preferred. A radius of 25 - 50% the nominal wall section should be included at the intersection of the nominal wall and rib base in order to eliminate stress concentration and improve material flow around the rib. The addition of gussets to a part design should follow the same rules as ribs. The height of the gusset can be up to 95% of the height of the rib or boss it is attached to and up to 4 times the nominal wall thickness depending on the height of the rib being supported. The base length of the gusset is typically twice the nominal wall thickness.
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