Tech Tips

5 Tips for Quality Plastic Part Design

You’ll save time and money with plastic parts designed to be cost efficient and as easily moldable as possible. And remember, after you start building the mold or worse, once your parts are in the production phase, problems are much more expensive to fix.

Here are 5 tips to keep in mind for better plastic part design:

1) Think about adding draft angles to make sure that we can readily get your parts out of the mold. Larger draft angles may work better with parts that have longer or deeper side wall surface areas. The same is true for textured surfaces that may stick. Larger draft angles here will help make the parts easier to remove.

2) Remember that even with draft added, we need to still remove the parts from the mold. For more cost effective molds, try to leave areas for ejector pins whenever possible. Some designs may require ejector blades or a stripper plate, but remember that these will add additional cost. Try to indicate the places you want the pins clearly in your drawings and keep in mind that you will have a visible indentation in these places.

3) Do your best to maintain a uniform wall thickness throughout your part. This helps prevent voids, warpage, and molded-in stresses. It also facilitates proper melt flow. To steer clear of sink marks, make every attempt to keep ribs or internal wall features approximately 2/3’s thickness of the main wall. Also, be sure to design the part with the thinnest wall possible. The thinner the wall, the quicker the cooling rate and the less expensive your parts.

4) One way you can achieve a uniform wall thickness is by taking the edges and rounding them. It’s good to avoid sharp corners (insufficient radius) as you design your plastic part. This helps you minimize stress concentrations and various defects.

5) If you’re designing plastic parts, you must also pay attention to gate type and location. Some of the choices you have include a direct sprue gating into the part, tab, gates, fan gates and tunnel gates (just to name a few). It is important to consider the gate type and location because they help determine how the plastic streams through the part. The thing is, the gate will leave a mark that you can see or a small vestige that may look wrong in some areas or could hamper the part’s intended function.

If you have any questions on plastic part design, please call me at 315.841.4101 or email at

I look forward to speaking with you about any design issues you might have. You can check out our pre-quote engineering checklist to get an idea of what we look at during the design/engineering phase.

Until next time,