The Importance of Uniform Wall Thickness in Plastic Part Design

Uniform Wall thickness guidelines for injection molded parts

Want to know how to optimize your plastic part design for manufacturing with uniform wall thickness?

Wall thickness is one of the most important rules of injection molding part design that you should treat it as an essential part of your overall part design

This is especially important as wall thickness is considered as one of the most importnat factors that determin the success or failure of the plastic product.

In this article we will explore the importance of maintaining uniform wall thickness to get your project going successfully
Why maintain uniform wall thickness?

Metal parts are often designed with thick walls, while plastic products should ideally maintain uniform wall thickness for uniform flow and less shrinkage as illustrated as below. For plastic parts, a gradual change in wall thickness or uniform wall thickness is recommended to reduce stress concentration and other potential issues.

Why do we attach so much attention to wall thickness? Part wall thickness affects quality of plastic molded part in nearly every stage of the injection molding process. Injection molding is a pressure-driven process,. When there is variation in wall thickness, the molten plastic will flow towards the path of least resistance-thicker wall. This results in sink issues, air trapping, welding lines and increased cycle times and ect. On the other hand, molten plastics cools faster as it flows in thin-walled sections. The worst case is that the melt may freeze at the thin wall area and prevents effective pack during the filling process. This leads to an non-fill part.

The results of ueven wall thickness

From above analysis, we could gather a general idea about how uneven wall thickness impact part quality. Please see below for the detailed lists of the results.

Part Cost

For a plastic injecion molded part, thick wall usually requires longer time to cool and more molten plastics to fill. Part cost is primarily calculated by part weight and cycle time. This means that plastic and longer time on the injection molding machine will only increase the cost of production.

Part Look

Variation of wall thickness impacts the look of the plastic part. Uneven wall thickness can cause undesirable physical defects such as sink mark, flow lines, warpage, short shots and so on.

Shear Stress

When uneven wall sections are designed in a plastic part, thin area forces the flow plastic that fills at constant rate to move faster. This increases the shear press accordingly, leading to different degrees of shear stress and warpage.

Gating Issues

Gates should be placed at the thick wall section as molten plastic flows from thick wall to thin wall. When there is varying Uneven Wall thickness, molten plastic may have to flow from thin wall to thicker wall. In this case, plastic material may begin cooling and start freezing in the thin section, effectively blocking the flow to the thicker section. Defects issues such as sink mark and warpage may arise.

In a word, uneven wall thickness produces the most significant effect on final quality, production and cost of a plastic injection molded part. As a leader in the plastic injection molding industry, HS Mold’s experienced engineering team are capable of handling all stages of manufacturing services for your new project, including design for manufacturing, prototype solutions, mold making, in high and low volume production, and custom assembly.

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