In injection molding, it is important to know the solidification behavior of the resin in the cavity. However, the solidification behavior has not been experimentally clarified. On the other hand, it is difficult to monitor when the moldings pulls away from the cavity surface at cooling stage.
In this study, the resin state in the cavity has been monitored by using an ultrasound. The solidification thickness in the cavity has been measured by the ultrasonic echo. Moreover, the amplitude, the phase and the mean velocity of the sound propagated through the resin have been also investigated in order to detect the resin state.

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In this report, a method to adhere ABS resin and phosphor bronze in a mold by injection-molding is proposed. For this investigation of adhesion, a phosphor bronze plate treated with 1, 3, 5-triazine-2, 4-dithiol-6-sodium mercaptide (TTN) aq. solution was inserted in a mold and then ABS resin was injected. ABS resin showed good adhesion to the phosphor bronze plate treated with TTN as the ABS resin showed cohesive failure in the matrix but not at the interface in a shearing test. The adhesive strength was dependent upon the conditions of TTN treatment and the molding and the content of the polybutadiene component in the ABS resin. A TTN concentration in the range of 0.8-1×10^-3mol/l and an immersion time in the TTN soln. in the range of 10-60s were the optimum conditions. Mold temperatures above 80°C gave higher adhesive strength and ABS containing 19-20% polybutadiene component gave the highest adhesive strength. Under optimum conditions, the adhesive strength exceeded 4MPa. The mechanism of adhesion is believed to be the formation of chemical bonding between the Cu-triazine mercaptide coating on the phosphor bronze plate and the butadiene component in the ABS resin.

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Failure under a static load was studied for a plastic part which included a metal reinforcement. The metal part was inserted into the mold prior to the injection molding process. The short-glass fiber reinforced PA 66 was then injected into the mold. It was observed in a fracture test that the plastic part was separated from the metal insert at the failure site. Since the contact state between the plastic and the metal was difficult to be experimentally examined, finite element analysis was utilized. The plastic and the metal were considered as two separated structures in the analysis. The boundary conditions were applied so that force was carried across the boundary only if the boundary was closed. To verify the analysis results, the strains in the plastic part were measured at locations near the failure site. It was deduced from the comparison of the analysis with the experiment that the separation of the plastic from the metal at a portion of the boundary yielded stress concentration at the closed portion of the boundary. It was also deduced that this stress concentration induced local plastic deformation of the polymer. It has been clarified that the separation of the plastic part from the metal part is the primary failure mechanism of the plastic part. It has also been clarified that the plasticity of the polymer affects the fracture load of the part.

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