5 Plastic Injection Molding Design Mistakes and How to Avoid Them
Your plastic injection molding design is the foundation of your plastic part. A high-quality, well-developed design can be the difference between a part that performs well and one that doesn't. That's why we're walking you through the Top 5 Plastic Injection Molding Design Mistakes and How to Avoid Them. At Camcar Plastics, we keep these mistakes top of mind throughout every stage of the design process. Understanding why they matter is just as important as avoiding them — because when we get the design right from the start, we save you time and money in the long run.
Mistake #1: Inconsistent Wall Thickness
Inconsistent wall thickness occurs when the walls of a part vary in thickness across its structure. Maintaining uniform wall thickness throughout the entire part is essential. When it's inconsistent this leads to uneven cooling which can cause sink marks, warping, or internal stress. None of these are qualities you want in a finished plastic part.
We avoid this by maintaining a uniform wall thickness, typically between 1.5–4.5mm depending on the material. The material itself plays a big role in determining the right thickness, and accounting for it from the start is key to producing a consistent, high-quality part.
Mistake #2: Not Accounting for Material Shrinkage
Every single thermoplastic material shrinks as it cools. This is something plastic injection molding manufacturers are aware of and should always take into consideration when designing a plastic part. The material shrinkage rate varies widely across materials, and when ignored can affect the spec dimensions — making an especially significant impact on parts with tight-tolerance features.
From day one our design team at Camcar Plastics takes into consideration the shrinkage rate of the material used for your part. After we carefully select a material according to your needs, we then account for all factors that could affect the result before we finalize the dimensions.
Mistake #3: Ignoring Undercuts
Undercuts are features that prevent the plastic part from ejecting straight out of the mold in a clean, efficient way. When undercuts are ignored, they require additional features to be added to tooling, like side-actions or lifters. This can significantly increase the cost and complexity of your tooling, which is what our team works hard to avoid wherever possible.
We address this early on in the design process, working to eliminate any undercuts where we can. If there are undercuts that cannot be avoided, we flag them early so tooling can be planned accordingly. Our team ensures every detail of your design is accounted for before the final tooling production process begins.
Mistake #4: Inadequate Draft Angles
Inadequate draft angles are vertical walls with little or no taper, making it difficult for the part to eject correctly. When a part isn't ejected swiftly and cleanly, it can cause drag marks or parts that get stuck in the mold. This results in slower cycle times and increased plastic scrap.
We avoid this by having our designers review the draft angles for injection molding early in the design-for-manufacturing process. Our team ensures all angles support a successful ejection so your cycle time stays on track and material isn't unnecessarily wasted.
Mistake #5: Sharp Corners and Edges
When a design contains sharp corners and edges with no radius, it results in a weak plastic part. Sharp corners concentrate stress, creating fragile points in both your part and the tooling mold itself, which accelerates wear and costs more time and money down the line.
Our team ensures this doesn’t happen by adding a radius to all internal corners. It improves material flow, produces a stronger part, and extends the life of your tooling mold. It's one of the simplest things we can do in the design process, and it makes a significant difference in the durability of your final product.
Conclusion
These five plastic injection molding design mistakes may seem small, but they can make all the difference in the quality and cost of your plastic part. At Camcar Plastics, we're aware of every one of these mishaps and do everything we can to catch them early. They’re accounted for before they impact your tooling, cycle time, or bottom line. When the effort is taken to get your design right from the start, we save you time and money in the long run.
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