The heat generation mechanism in ultrasonic welding by a torsional vibrator is discussed based on a simple theory of viscoelasticity. It is concluded that the principal heat source in ultrasonic torsion welding is friction loss at the interface, not viscous dissipation. However, near the resonant frequency, which is much higher than practical frequencies, viscous dissipation becomes the main cause of the heat generation. Optimum welding conditions are also discussed. A loose interface and non-slip conditions at the anvil are preferable for welding. The present discussions will contribute to a further development of the ultrasonic welding technology.

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BMC (Bulk molding compound) is composed of glass fiber, unsaturated polyester and filler. Aluminum sludge has been used as the filler for BMC composite materials used in injection molding. The molding conditions were investigated in terms of mechanical strength and shrinkage of the specimen with varied aluminum sludge contents within the range of 10 to 40%. With a sludge content of 40% and the glass fiber content maintained at a constant 10%, the tensile strength of the specimen showed the highest value and the shrinkage ratio of the specimen showed the lowest. When viewing the fracture surface through a scanning electron microscope, it was observed that the highest tensile strength which is at the sludge content of 40% was attributed to the uniform distribution of glass fiber. From the comparison of the sludges of three kinds of heat treatment -423K, 773K and 1573K- the sludge structure fired at 773K crystalized into γ alumina and the product containing γ alumina showed the highest mechanical strength and the lowest shrinkage. The cause of the improvement of mechanical property is attributed to the finest particle size (6.58 μm) of γ alumina, which is superior for unloosing the chopped strand fibers in the BMC mixing process and the uniform scattering of glass fibers not only in the internal area but also near the surface area of the material during injection molding.

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In this study, development of conductive plastics was attempted by using soldering power as the conductive filler. But, it was difficult to get the uniform dispersal solder. And, in order to obtain stability in a solder dispersed conductive plastics, kneading experiments were performed in which the solder dispersed in the plastic was made even finer and a slight amount of short copper fibers was added to ensure good fluidity. The addition of the short copper fibers showed remarkable effects and was found to enable the solder to be dispersed even more finely. The results also confirmed that uniform and fine dispersal of the solder helps prevent surface defects caused by the stretching of the solder at the surface of injection molded product and the coagulation of the solder inside the conductive material. When the fibers are joined by the dispersed solder, conductivity is stable. However when the amount of solder is insufficient, conductivity was found to deteriorate, indicating that the joining of the fibers by solder is an important factor. Experiments confirmed that the addition of copper fibers and copper powder has little effect for increasing conductivity, but increasing the solder amount improves conductivity.

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