Effects of molding conditions on injection molded direct joining under various surface fine-structuring

Abstract

Injection molded direct joining (IMDJ), a metal–polymer joining technique, consists of two basic processes: surface fine-structuring and injection insert molding. During molding, melt polymer infiltrates the surface fine structure on a metal workpiece that is initially placed in a mold; subsequently, the metal workpiece is joined with an injection-molded polymer. This study investigates the effects of molding conditions on the joining strength of IMDJ using two different surface types of fine-structured metal workpieces. The primary difference in the fine structures is size; one has a nanometer scale and the other a micrometer scale. Using two types of metal workpieces, we perform injection molding experiments with six different injection speeds and two different flowing shapes of mold. The results of the joining strength evaluated by tensile shear tests show that the speed–strength correlation depends on the fine structure. To explain this dependency on fine structure size, we assume the infiltration of melt polymer differs between the nanometer scale fine structure and the micrometer scale fine structure. The results also show that the flowing shape affects the joining strength. To confirm the effect of the shape, we measure the time-course variations of the temperature and pressure in the mold, and observe the fiber distribution in the molded polymer parts using X-ray micro computed tomography.