Study on ultrasonic vibration-assisted micro extrusion

• Main Authors: Chia-Hsien Kao, 高嘉賢
• Other Authors: Jung-Chung Hung
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/95907367555996495355

碩士 === 國立勤益科技大學 === 機械工程系 === 101 === With the trend of smaller elements, the mechanisms in micro metal forming due to minimized sizes are different to that in conventional macroscopic forming. Further, ultrasonic vibration-assisted forming could reduce the forming stress and exceed the forming limit of conventional forming process; hence adopting the characteristics of ultrasonic vibration-assisted forming to overcome the problems caused by micro forming is a feasible method. This study comprises three topics including the development of the apparatus for ultrasonic vibration-assisted micro forming, the effects of ultrasonic vibration on micro upsetting and the ultrasonic vibration-assisted micro extrusion. With the goal of minimizing the apparatus and upgrading the control precision, the apparatus for ultrasonic vibration-assisted micro forming was firstly designed and manufactured, and the apparatus was then used in the experiments of ultrasonic vibration-assisted micro upsetting and micro extrusion. By the similarity principle, the specimen was minimized with a ratio (λ) and used in the experiments of conventional micro upsetting (CMU) and axial ultrasonic vibration-assisted micro upsetting (AUMU) to investigate the size effect to the forming characteristic and the impact of ultrasonic vibration. At last, this study proposed the transverse ultrasonic vibration method to overcome the difficulties of ultrasonic vibration-assisted extrusion. The die for micro gear extrusion was designed as bisected die, and longitudinal vibration was applied to the bisected die to produce the transverse vibration during the micro gear extrusion experiment. As the apparatus for ultrasonic vibration-assisted forming was built, the laser displacement meter was used to measure the actual displacement and the linear errors were then calibrated. In this manner, the actual displacement precision in this experimental flatbed was successfully improved form 30μm to within 3μm, and the load precision was 0.5N. In the results form micro upsetting, the plastic stresses decreased with smaller specimens, and the smaller size, the larger stress reduction. As the grain size increased the plastic stress also decreased but the effect was relatively less significant. When ultrasonic vibration was applied to forming process, the plastic stresses were all decreased. By smaller specimen sizes, the stress reduction was more significant than that in conventional upsetting. In the results of micro extrusion, ultrasonic vibration effectively decreased the forming force during the micro gear forming, and the reduction increased with the increase energy of ultrasonic vibration. The surface roughness was decreased by ultrasonic vibration, and the decreasing trend in roughness increased with the higher ultrasonic energy.