호스니플재의 마찰용접 최적화에 관한 연구

Abstract

Friction welding is a very useful joining process to weld metals which have axially symmetric cross section. In this paper, for the friction welding with tube-to-tube shape for excavator hose nipple, the feasibility of industry application was determined using analyzing mechanical properties of weld and optimized welding variables was suggested. In order to accomplish this object, rotating speed(n), friction heating pressure(HP), and friction heating time(HT) were selected as the major process variables and the experiment was performed in three levels of each parameter. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Virkers hardness surveys of the bond of area and heat affected zone(HAZ), and microstructure investigations. The specimens were tested as-welded and post-weld heat treated(PWHT). Weld characteristic was investigated in terms of weld shape and metal loss, and 7.5mm of metal loss was regarded as the optimal metal loss. By tensile test, tensile strength and yielding strength was measured and fracture was occurred at base metal. In order to optimize the welding condition, fitness function was defined with respect to metal loss and yielding strength and the fitness values for each welding condition could be calculated in experimental range. Consequently, we set the optimal welding condition as the point which had maximum value of fitness function. As the result of this paper the optimal welding variables could be suggested as rotating speed was 1000rpm, friction heating pressure was 10MPa, and friction heating time was 9sec. Two similar materials are strongly mixed to show a well-combined structure of micro-particles without any molten material and particle growth or any defects. An acoustic emission(AE) technique was applied to evaluate the optimal friction welding conditions nondestructively. AE parameters of accumulative count and event were analyzed in terms of generating trend of AE signals across the full range of friction weld. The typical waveform and frequency spectrum of AE signals which is generated by friction weld were discussed.