| Summary: | 碩士 === 國立中山大學 === 機械與機電工程學系研究所 === 104 === In this study, a pinless tool made of tungsten carbide rod with 6 mm in diameter is used as the welding tool at high rotating speed and constant downward load conditions to conduct the friction stir lap welding (FSLW) for thin galvanized steel sheets. To understand the lap mechanism, a shear tensile test is conducted to measure the fracture load after welding. The lap mechanism and characteristics of thin galvanized steel sheets, in terms of weld surface profile, interface temperature, failure load, and plunge depth, were investigated under different operation conditions, such as the downward load (150~500 N), the rotating speed (3000~24000 rpm), the dwell time (5~30 sec) and the feeding rate (0.5~2 mm/sec). Under a rotating speed 18000 rpm, a downward load of 300 N and a dwell time of 20 sec, the shear strength for the galvanized steel is about 1.8 times as strong as the cold rolling steel. Experimental results show that the failure load is significantly influenced by the downward load, the rotating speed, and the feeding rate. An empirical equation of failure load (F_f) suitable for the thin galvanized steel sheets of the FSLW process is derived in terms of load (〖F_d〗^ ), rotating speed (〖N_s〗^ ), feeding speed (f^ ) as F_f=0.0302∙〖F_d〗_^0.8289∙〖N_s〗_^0.6312∙f^(-0.43). This formula indicates that F_f is proportional to the product of〖 F〗_d and N_s, but inversely proportional to 〖 f〗^ . Moreover, the influence of downward load on the failure load is greater than that of rotating speed.
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