Part Details Review
Part drawing defines a design concept. Assigning tolerances to the dimensions defines its character. Much too often, part tolerances are specified without simultaneously considering functional and molding issues. This results in cost escalation and production difficulties. As a designer, you must clearly identify the functionally critical dimensions and assign tolerances accordingly. The practice of assigning blanket tight tolerances leads to needless expense in mold building. If necessary, involve the molder early on in the design process for discussion and feedback regarding the tolerance issues. Some part tolerances may be unachievable using the commercially viable production methods. In such cases a total redesign of the part may be necessary. Achievable tolerances for injection molded parts depend on material shrinkage characteristics, part geometry, tool dimensions, and processing conditions. As a designer, your objective should be to select the material with shrinkage characteristics suited to your application, obtain accurate shrinkage information, consider the effect of geometry on achievable tolerances, and assign tolerances prudently. Try to keep an open communication link with your mold maker and molder. Their feedback can be invaluable in understanding what is achievable and the corresponding cost impact. |