Throughout the injection molding process, there are several factors that affect efficiencies and viability of a plastic part. Before production begins, there are important design elements to consider – particularly when a part requires the use of a high heat or exotic resins. These design considerations improve the moldability of parts, and ultimately, may reduce the chance of defects and other issues. In the beginning design stages of a plastic part, engineers should work closely with a trusted injection molder who can provide suggestions on how to best optimize the design and make critical material suggestions.
Some characteristics of high heat and exotic resins are unique and may perform differently from one application to another. To realize both the design and material’s fullest benefits, experienced design engineers and injection molders have a number of factors to consider. In this post, outlined are a few basic and advanced tips that should be taken into account when designing parts for injection molding with the use of high-heat or exotic resins.
1. Material Shrink Rate:
Shrinkage is the contraction of the molded part as it cools after injection. All materials have different shrink rates depending on resin family (amorphous vs. crystalline materials), mold design, and processing conditions. Resin may also shrink differently depending on direction of flow. As a general rule of thumb, a 10% change in mold temperature can result in a 5% change in original shrinkage. In addition, injection pressure has a direct effect on shrinkage rates. The higher the injection pressure, the lower the shrinkage rate. View typical mold shrink rates, as well as tonnage recommendations and vent depth values, for some moderate-to-commonly used materials and high heat resins:
