Corner Breaks & Fillets
One of the intrinsic benefits of MIM is the ability to produce corner breaks and fillets. Not only do corner breaks and fillets play several important roles in a good MIM component design, but they also provide design engineers with design advantages not readily available in some metalworking processes. In addition to providing improved injection molded part quality, these design advantages include, improved part strength, elimination of stress concentrations, and softening of sharp corners for aesthetics and handling.
Typically, corners breaks should be kept larger than .005" radius. Internal and external corner breaks less than .005" radius will induce stress concentrations in the part and will be difficult to fabricate in the mold. Fig. 13 illustrates an exception where a sharp corner is preferred over a generous radius. The figure shows a MIM component and mold design that benefit from having sharp corners located on the bottom of the part. In this case, the sharp corners allow the part geometry to be kept in one half of the mold, which simplifies the mold design, reduces the mold cost, and does not jeopardize the part's strength. Should a radius be required along the bottom edge of the part, it can be readily produced, but it should be noted that the part must now have portions of it produced in each half of the mold. In addition to adding cost to the mold, the designer should expect a witness line around the profile of the part at the parting-line location.
