Frictional Effect on Ultrasonic-Vibration Forming of Aluminum Alloy

• Main Authors: Jung-Chung Hung, 洪榮崇
• Other Authors: Chinghua Hung
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/43228314505357372958

博士 === 國立交通大學 === 機械工程系所 === 94 === The purpose of this dissertation is to investigate the frictional effect of ultrasonic-vibration during forming of aluminum alloy. This study analyses ultrasonic-vibration drawing and ultrasonic-vibration upsetting, which are extreme cases to each other in terms of relative speed between die and workpiece, to explore the frictional effect of superimposing ultrasonic-vibration during forming processes. The study focuses on four subjects: the set up of an ultrasonic vibration hot upsetting system, the influence of ultrasonic-vibration on hot upsetting, the frictional effect of ultrasonic -vibration during upsetting, and the experiment and simulation of ultrasonic-vibration drawing. In this study, a cooling mechanism was used on an ultrasonic vibration hot upsetting system to overcome high-temperature forming difficulty at the beginning. The effects of ultrasonic-vibration on the upsetting of aluminum alloy was then explored using this system. Results show that the ultrasonic-vibration can significantly reduce the compression force during hot upsetting and the reducing effect of compression force decreases while the temperature increases. Furthermore, upsetting process was used to explore the frictional effect by superimposing an ultrasonic-vibration parallel to the direction of forming. Experimental results of extrapolated compression test also indicate that ultrasonic-vibration can reduce the compressive force when friction is eliminated. The consecutive results of the hot ring compression test and temperature measurements during ultrasonic-vibration on upsetting reveal that increasing temperature by ultrasonic–vibration may reduce the flow stress and increase the interfacial friction. Finally, The ultrasonic-vibration drawing experiments and finite element analysis were performed for CD, AUD and RUD to explore the relative speed effect of workpiece and die by superimposing ultrasonic-vibration parallel as well as perpendicular to the relative speed. For both AUD and RUD, the drawing force fluctuated with the die vibration when drawing speed was below the critical drawing speed and the fluctuation amplitude tended to increase with the decrease of drawing speed. When drawing speed reaches a critical value, the fluctuation of drawing force disappears. On the other hand, results reveal that the critical drawing speed of RUD is higher than AUD and the frictional effect of ultrasonic-vibration vanishes when the interfacial gap speed is zero. From above studies we may conclude that the frictional effect induced by ultrasonic-vibration should associate with both the effect of interfacial gap variation and the temperature increase in general forming processes. The weighting of these two effects depends on the type of forming process. Following this qualitative study, quantitative analysis on the frictional effects of ultrasonic-vibration will be proceeded in the future to be applied in practical forming processes.