Common Mistakes To Avoid When Designing Injection-Molded Parts

Common Mistakes To Avoid When Designing Injection-Molded Parts
  • Opening Intro -

    Injection molding is a fantastic tool for manufacturers on many fronts, namely cost, speed, and product reliability.

    The process best suits scenarios where a project requires significant quantities of highly reproducible, uniform parts at a cost-effective per-piece rate.


However, the flexibility of injection molding doesn’t mean the process is simple. Designers and manufacturers can endure various problems if they fail to consider every aspect of the process. The results of design mistakes include poor product quality, production delays, and unexpected cost overruns.

Read on to discover the five common mistakes to avoid when designing injection-molded parts!

Variations in Wall Thickness

Injection-molded parts usually look alike: thin, shell-like objects without deep sections of solid material.

This nature is due to the injection molding process. After loading the mold with a liquid substance, that substance must undergo a cooling process to become solid. If there is a variation in cooling, then some parts will solidify and contract before others, posing problems that lead to the deformation of the part.

An efficient way to prevent this deformation is to emphasize consistency in both the substance’s thickness and the cooling pace. However, reaction injection molding (RIM) is a more flexible molding alternative that allows for varying wall thickness in the same part. If achieving a consistently thin final product isn’t your goal, RIM is a fantastic option that negates this issue.

Wrongly Parting the Lines

In injection molding, the parting line is the line that separates the core and cavity molds. Its positioning can impact the success and appearance of the molded part.

Improper positioning of the parting line gives rise to various issues. One significant issue caused by improper positioning is flash, a term used to describe excess material that spills out through the miniature opening between the cavity and mold core.

Failure To Remove Undercuts in Molded Part Designs

One of the most common mistakes to avoid when designing injection-molded parts is failing to remove undercuts from the final design. Undercuts make it extremely challenging to remove a part from its mold. Occasionally, designers implement pick-out inserts and side-action cams to make undercuts possible, but these extend the manufacturing time.

Where possible, consider removing undercuts from the design to cut down on manufacturing time and create a more efficient part-making process.

Lack of Prototyping

Creating a prototype of your part is an effortless way to measure manufacturability and reliability. Prototyping is more efficient when performed using CNC machining and 3D printing rather than an injection molding service, which is better suited to mass manufacturing.

You can evaluate your component’s structural solidness, shape, and various crucial factors necessary for effective manufacturing. Early prototyping allows for easy, successful testing over multiple design iterations.

Ignoring Draft During Design Stages

Draft, or the tapering of a design’s faces, is one of the most crucial factors to emphasize when building injection molded components. Integrating draft into your product design ensures that you make the component more favorable to immediate release or removal from the mold.

Parts that cannot eject from the mold are more vulnerable to degradation and can extend the cycle times, negating the benefits of using plastic injection molding services.

Image Credit: common mistakes to avoid when designing injection molded parts by Adobe Stock royalty-free image #122562046

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