Injection molding plastic parts has some fantastic advantages, including scalability, the ability to manufacture simple to extremely complex parts, and uniformity, the ability to manufacture hundreds of millions to millions of nearly identical parts. However, injection molds can be expensive to build and maintain, and changing tools can be challenging.

Maximize the Advantages of Injection Molded Parts

1. The uniformity is the best. A constant wall thickness throughout the part will provide optimum flow. The nominal wall thickness should be between 2-3mm. For traditional injection molding processes, the recommended minimum is 1mm and the maximum is 4mm.

2. Smooth is better than sharp. Use radii whenever possible and avoid sharp transitions between wall sections.

3. Draft angles are your "friend and foe". Adding draft angles to the face of a part helps release it from tooling, but it can present design challenges, especially for mating parts. The recommended minimum draft angle is 1 degree on untextured cores and at least 3 degrees on textured cavity surfaces.

4. Avoid using zero-draft faces unless necessary. If you really need zero draft area to ensure proper part fit and tolerance, try minimizing it to just a portion of the face, not the entire surface.

5. The simpler the better. Avoid undercuts (areas that cannot be formed by the simple opening/closing direction of the tool). Lifters and slides allow the formation of undercut features in the main pull direction when simple methods are not feasible. If so, leave at least 2 to 3 times the feature width to allow for lift or slide movement.

6. Transition from thick to light. The part will mold better if the plastic moves from the larger wall thickness to the smaller wall thickness starting at the gate (where the plastic flows first to fill the part).

7. Denting (localized surface denting of the part due to slower cooling of the thicker part of the plastic) is not good. To reduce or eliminate the visibility of cosmetic surface blemishes, be sure to follow some recommended guidelines:

Try to avoid gates, ribs, screw bosses, etc. on the back of important decorative surfaces;

The rib height should be 3 times the wall thickness or less;

The bottom of the rib should be 60% or less of the wall thickness.

8. Datum definition area. Use benchmarks (characteristics that serve as reference points to define each part) to establish part interfaces and interactions with the overall system. Using a baseline structure that matches the design intent of the assembly can mean the difference between a product performing well or not.

9. Inspection is important. Take DFM (Design for Manufacturing) reports seriously as they convey the mold maker's understanding of the design, especially things like ejector pin locations (which may conflict with planned design changes), gate locations (which may cause cosmetic issues) and parting lines information such as location (which may affect interaction) and supporting parts). Use the inspection report to review the design. An example DFM report shown here:

10. Prototype early and often. Current prototyping methods, including 3D printing, allow early testing of design concepts, allowing partial and/or entire parts to be modeled before expensive tooling is built.