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AIM Processing Small Plastic Parts Blog

5 Design Tips for Problem-Free Plastic Injection Molding

[fa icon="calendar"] Sep 30, 2016 1:15:00 PM / by Jon Gelston


The process of plastic injection molding can produce the perfect parts for your needs quickly and cost effectively. However, as with any manufacturing process, there are certain “gotchas” that can cause less than optimal results. Below are five design guidelines you should follow to help ensure that your production runs deliver an outstanding finished product.

It’s All in the Design Details

  1. Determine ideal wall thickness. In designing parts, thinner walls require less raw material and can be produced faster thanks to more rapid cooling. However, a thicker wall is, of course, stronger. It’s important that you think carefully about product requirements as you design a part and find the right balance of production time and cost versus the strength of the finished product.
  2. Maintain consistent wall thickness. In order to be structurally sound, plastic parts must have walls that are uniform in thickness. This characteristic helps prevent warping and variable shrinkage and ensures that molds will fill properly. Wall thickness variations of more than 10% can lead to processing challenges and quality issues.
  3. Choose the proper gate location. The position of a gate dictates how a mold is filled. Ideally, material should enter through a gate positioned at the thickest part of the cavity and then make its way into more narrow areas. Gate location is especially important if slight variations in wall thickness can’t be avoided.
  4. Design corners with a generous radius. As plastic moves into a mold it must navigate corners. The more rounded the turns, the more easily the material will flow through them and continue to other areas. By comparison, sharp corners tend to cool and harden with uneven shrinkage that produces stress points and can result in sink marks.
  5. Use the appropriate draft angle. The best draft angle, in terms of cost and manufacturability, is the greatest angle that will not negatively affect your satisfaction with the product. As for the minimum angle, the resin supplier is in the best position to make that judgement. Generally speaking, between 2° and 5° per side is preferable, although 1° per side is sufficient in selected cases. Even a small draft angle is preferable to none.

Two Decades of Design Review Experience

Throughout our more more than 20 years in the plastic injection molding business, we’ve worked with many designs that were perfectly optimized for production, and some (despite our advice) that were not. As a result, we can bring a great deal of expertise to a conversation about your design. We’re happy to share our insights on a design you are contemplating or have already completed. Give us a call and let’s talk about how to make your upcoming project a tremendous success.

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Topics: Plastic Injection Molding, Plastic Injection Molding Defects

Jon Gelston

Written by Jon Gelston