Baeg-Soon Cha

OPTIMUM JOINING CONDITIONS IN A MECHANICAL PRESS JOINT

Mechanical press joining has been used in sheet metal work because it is a simple process and offers the possibility of joining dissimilar sheet metals, such as steel and aluminum alloy sheets. The mechanical press joint strength was found to vary with joining conditions, such as sheet thickness and punch diameter. The optimum joining conditions of the mechanical press joint under complex loading can be determined by correlating strength ratio with diameter ratio and sheet thickness ratio. The failure mode was considered during estimation of the joining strength. Under this experimental condition, the optimum strength ratio was acquired at a sheet thickness ratio of 1.0 and a diameter ratio of 1.683.

A Study on the Void Formation in Residual Wall Thickness of Fluid-Assisted Injection Molding Parts

In fluid-assisted injection molding, the distribution of the residual wall thickness on the inside and outside of the curved area is different, and void is formed due to the effect of the shrinkage on the outside where the residual wall thickness is thicker. The shrinkage that takes place in the residual wall is affected by the rheological changes in the polymer caused by temperature change and also by the thermal properties of the penetration fluid. In this study, the different effects on void formation in residual wall during fluid-assisted injection molding were analyzed, and water and silicone oil that had different thermal properties were used for the fluids. For this, heat transfer analysis and injection molding analysis were conducted. The void formation occurred due to the different temperature distribution and volumetric shrinkage in the direction of the residual wall in the curved area with a hollow section. It was also found that the void formation in the curved area decreased in the case of silicone oil compared to the case of water from simulation and experiments.

Experimental and Numerical Investigation of the Effect of Process Conditions on Residual Wall Thickness and Cooling and Surface Characteristics of Water-Assisted Injection Molded Hollow Products

Recently, water-assisted injection molding was employed in the automobile industry to manufacture three-dimensional hollow tube-type products with functionalities. However, process optimization is difficult in the case of water-assisted injection molding because of the various rheological interactions between the injected water and the polymer. In this study, the boiling phenomenon that occurs because of the high melt temperature when injecting water and the molding characteristics of the hollow section during the water-assisted injection process were analyzed by a water-assisted injection molding analysis. In addition, the changes in the residual wall thickness accompanying changes in the process conditions were compared with the analysis results by considering water-assisted injection molding based on gas-assisted injection molding. Furthermore, by comparing the cooling characteristics and inner wall surface qualities corresponding to the formation of the hollow section by gas and water injections, a water-assisted injection molding technique was proposed for manufacturing hollow products with functionality.

A Study on the sealing Characteristic of Automobile Waterproof Connector

Abstract Liquid silicone rubber(LSR) has been applied to various products such as electronic devices owing to its excellent thermal and chemical resistance. Hyperelastic materials, however, have properties distinguished from generalmetal materials. Hyperelastic materials show elastic behaviors in the range of large deformation in which load has the nonlinear relation with deformation. In addition, they have characteristics of nonlinearity, incompressibility, in large scale. On account of such characteristics, there are many difficulties in design and production using these materials. In this study, the load-deformation relation obtained from tension and compression tests was applied to finite element analysis in order to design waterproof connectors for automobiles. Furthermore, the effectiveness of thefinite element analysis was confirmed by comparing the results of analysis with those of performance tests. Key Words : Hyperelastic material, Liquid silicone rubber, Sealing, Waterproof connector