Part Details Review
Thick and thin wall sections in a part lead to differential shrinkage, which can cause warpage and also diminish dimensional precision. Semi-crystalline materials are more sensitive to wall thickness variations as they crystallize more in thick sections resulting in greater local shrinkage. If the material flows from thin to thick, the thin section will get over-packed and shrink less in comparison to the thick section. The thick section will not be packed properly and shrink more. This can make tight tolerance difficult to achieve. Flow obstructions, such as those created by the cores for molding holes, physically restrict shrinkage and in turn experience higher molded-in stress. Portion of the part with numerous holes will shrink considerably less than the portion without any holes. If a uniform shrinkage factor is used for the entire part, it would be difficult to hold the designed dimensional range in some portions of the part. If possible, adjust your design to allow a greater portion of the total tolerance range for the features that are difficult to control and reserve tighter tolerance for the features that can accommodate them easily. |