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Dimensional Accuracy and Design Limitations in Plastic Injection Molding

Introduction

When your product enters the injection molding stage, whether using rapid tooling or traditional mass production molds, the underlying physical principles and design limitations apply. To ensure smooth, stable production and the desired quality, it’s crucial to understand the design specifications for dimensional accuracy, minimum wall thickness, and internal angles.

Dimensional Accuracy

Injection molding is a highly precise mass production process. Generally, the dimensional tolerance of finished products can be consistently controlled within a ±0.1mm range. For critical dimensions with strict fit requirements (such as clips or bearing holes), precision mold manufacturing and process control can even achieve higher accuracies of ±0.05mm. This ensures high consistency across every product produced on a large scale.

Minimum Wall Thickness

To ensure that the molten plastic flows smoothly and completely fills the mold cavity, the part’s walls must be kept to a minimum. Too thin a design can lead to problems such as underfill, structural fragility, or warping in the finished product.

A general design principle is to design plastic parts with a wall thickness between 1.0mm and 3.0mm. Of course, different plastic materials have different flow properties, and the minimum wall thickness recommendations vary slightly. For example, the recommended minimum wall thickness for commonly used ABS and PC materials is 1.0mm; while PA66 (nylon) with 30% glass fiber has poor flow properties, the recommended minimum wall thickness is 1.2mm or above.

Minimum Inner Corner Radius

In plastic part design, avoid sharp right-angled internal corners. Structurally, right-angled corners cause stress concentrations, making them the most vulnerable and prone to fracture. From a manufacturing perspective, mold cavities are milled by CNC tools, which are inherently rounded, making it impossible to achieve perfect right angles.

To ensure smooth material flow, reduce stress, and extend mold life, it’s strongly recommended to design rounded corners (R) on all internal corners. A safe design guideline is to maintain a minimum radius of at least R0.5mm for internal corners.

Conclusion

In summary, a successful injection molded product is one that fully considers manufacturing feasibility during the design phase. When planning your product, following these two basic principles—maintaining a uniform wall thickness of at least 1.0mm and a radius of at least R0.5mm on all internal corners—will significantly improve production efficiency and quality consistency, effectively avoiding unnecessary mold modifications and increased costs later on.