Design and fabrication of gypsum mold for injection molding

Traditionally, a mold made of gypsum can only be used in a low-pressure molding, e.g. casting, due to the weak strength of gypsum material. This study addresses the potential of gypsum as a candidate for rapid tooling used in injection molding. The ingredients for the gypsum mold were decided upon, and an additional compression with a vibration process was introduced to enhance the mechanical strength of the gypsum mold. Scanning electron microscope (SEM) results show that the amount of void inside the gypsum mold is reduced, and more interlocking of the microstructure of gypsum is formed by increasing the intensity of the compression with a vibration process. A higher degree of interlocking produces a significant enhancement of the compressive strength of the gypsum. Two samples were selected as master designs for testing the replication performance and lifetime of the gypsum mold. The dimensional replication accuracy of the molded part was over 99.9%. The maximum lifetime of the gypsum mold is about 210 cycles of injection shots. This work provides an alternative tooling for injection molding that can allow manufacturers to produce a small quantity of prototypes in an efficient and cost-effective way in the early stages of product development.