Advantages of Injection Mold with Hybrid Process of Metal Powder Bed Fusion and Subtractive Process

Abstract

This paper focuses on the hybrid process combining metal additive manufacturing (AM) and subtractive processing developed for application to injection molds. The basic concept is a combination of laser powder bed fusion of metal powder and subtractive processing. This process is characterized by alternating buildup and milling processes. Even the inner surface of deep grooves, which conventionally required electrical discharge machining, can be machined with small-diameter tools with a short flute length. Therefore, molds with complex shapes that previously required electrical discharge machining can be manufactured in a single process. Moreover, a dimensional accuracy and surface roughness of levels equal to those achieved by machining with the machining center can be ensured. In the hybrid process, it is necessary to minimize the surplus solidified area (which is the area milled by the small-diameter tool). Therefore, the formation mechanism of the surplus solidified region is verified. It is shown that the power distribution of the laser beam significantly affects the size (width and depth) and density distribution of the excessively solidified region. In addition, the effective value of metal AM mold is introduced. The 3D cooling circuit improves the efficiency of the injection molding process. If the temperature balance between the cavity side and core side is achieved, the distortion of the molded product would be suppressed. If the cooling effect is promoted, the molding cycle would be shortened substantially. Second, the effect of the gas vent function by a permeable structure is explained through actual examples. The effect of the gas vent function by the permeable structure is explained. It is indicated that stable molding can be achieved. In addition, the appearance defects of molded products can be reduced when the air inside the cavity is exhausted sufficiently from the mold through the permeable structure.