Analysis of Pulse-Trains and Machining Characteristics of Biaxial Ultrasonic Vibration Assisted Wire-EDM for High Thickness Workpiece

• Main Authors: SU, TZU-HSIU, 蘇子修
• Other Authors: HSUE, WEN-JENG
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/r45257

碩士 === 國立高雄應用科技大學 === 模具系碩士在職專班 === 106 === High-thickness workpieces in wire-cut electrical discharge machining (Wire-EDM) is difficult. Its discharge debris is easily accumulated causing high concentration of debris and difficulty in local processing to prevent from wire breakage. Hence, its machining stability is much lower than the conventional one and both more risks of feed retraction and wire breakage, resulting wire-scratch marks on the works surface. Therefore, the primary goal of this paper is to further improve the machining stability and efficiency of Wire-EDM for high-thickness parts. Although the phenomena and EDM pulse-trains of the uniaxial vibration Wire-EDM had been investigated in previous report in this laboratory, however, the actuator acts only a uniaxial vibration along the feeding direction. Obviously, it is prone to reaming larger expansion slot in the feeding direction, which is not suitable to practical machining. Therefore, in order to overcome the high-thickness wire-cutting characteristics, further development of a novel synchronously biaxial vibration mode with the same amplitude but phase of 90∘is proposed. Accompanied with modification on upper head mechanism and the intake channel, it creates a reasonable short-range of circularly amplitude to achieve the practical vibration-assisted Wire-EDM. Comparing to the conventional cutting and uniaxial-assisted Wire-EDM, the biaxial vibration’s benefits on improving the stability, efficiency, and machining precision are confirmed by Taguchi method and ANOVA analysis. Experimental result verifies that biaxial-vibration contributino of 19% in dominating material removal rate, which is only inferior to the main factor of discharge on-time. It achieves an averaged areal-speed to 90mm2/min with the 56% of increasing over the conventional mode, and also the upper-limit up to 203.6 mm2/min by increasing 9%. On the geometric accuracy, it reducees the drum-shape error of the lateral wall by 6.5%-10% and circular roundness error by uniformly expansion on both axes, which is the cure for the single side reaming of the previsous un-axial mode process. The main reasons of the efficiency improvmenet is the reduction of the typical dischahrge delay from 305 μs to 93 μs resulting in much higher frequency, and also increasing the average normal pulse ratio from 26% to 51%. In cutting a square punch, this method even reduces the risk of wire breakage by 3rd of fourth times. On accuracy improvement, the drum shape and the roundness are attributed to the wire vibration modes under constrained circular vibration by biaxial ultrasonic actuators. That makes the biaxial ultrasonic assisted Wire-EDM a practical applicable process to very high parts.