Plastic Injection Mold Design Guidelines

Plastic Injection Mold Design Guidelines

Plastic injection mold design is a complex art that requires a thorough understanding of material properties and molding processes.plastic injection mold design While CNC machining allows for design changes to be made by a software engineer, changes to an injection molding mold are costly and time consuming due to the high-grade steel used in injection molds. A few simple design guidelines can help make a significant impact on the quality of a final product.

Injection molded parts are made by injecting hot melted plastic into a hollow cavity.plastic injection mold design The molten plastic travels through a runner and into one or more specialized gates before reaching the cavity where the desired part is formed. The sprue (a tube that draws the melted plastic into the mold) and the parting line must be carefully designed to avoid core pulling, reduce seam lines and extend mold life.

Wall thickness in injection molded parts is critical to the success of the finished part. A good rule of thumb is to allow the walls to be a maximum of 10% thicker than the core. Thicker sections take longer to cool, and uneven cooling can cause warping, sink marks and cracking. It is also important to minimize the number of thick sections in the part, if possible.

A smooth transition between thick and thin sections is ideal, but if this is not practical, the thickness change should be as gradual as possible. Abrupt changes in wall thickness can lead to stress concentrations and uneven shrinking, which may result in warping or twisting of the part.

Another common problem in injection molded parts is the formation of drag marks during ejection. These marks are caused by a high amount of friction between the part and the injection mold, and they can significantly reduce the appearance of a finished product. These marks are most often found in corners and ribs, but can occur anywhere in the part.

To minimize drag marks, it is recommended to use a minimum of 2 degrees of draft on vertical surfaces. This will help the molded part slide freely from the tool when it is opened. It is also important to design the part with a sufficient amount of clearance between tall features like cams and other undercuts. If a draft angle is not applied to these features, the part will be stuck in place and require more force to be removed from the injection mold, leading to damage.

Texturing is a popular way to improve the appearance of an injection molded part, but it should only be done after the part has been produced. The texture must be matched to the part and the mold, and a good rule of thumb is to apply the heaviest amount of texture to the areas that will show the most wear.

Injection molded parts with threaded portions are generally fastened to other components through the use of threaded inserts or threaded bosses. It is best to design these elements into the B side of the part so they will not be visible and will not interfere with the functionality of the part.

Tags:3d printed injection mold | automotive plastic injection molding