Analysis of Pulse Trains and Machining Characteristics of Ultrasonic Vibration Assisted Wire-EDM for High Thickness Workpiece
| Autor: | LIN, YANG-LEI, 林洋磊 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 It is difficult to apply conventional machining processes to hard material; hence, the electrical discharge machining (EDM) is generally adopted as an alternative method. However, material removal rate of EDM is much lower than that of conventional machining, in addition, it is a great concerned issue in wire-EDM that instability gap status or even wire rupture leading to low efficiency and poor profile for high thickness (above 150mm) workpiece. Therefore, this thesis is first aimed at the fundamental studies on degradation of Wire-EDM status through pulse-trains analysis, and then be verified through acoustic signal. At the other hand, a hybrid technique of ultrasonic assisted wire-EDM (UA-WEDM) is proposed to overcome the risk of wire-rupture and increase machining stability.The EDM pulse-trains are acquired through a multi-channel oscilloscope in sub-micro second order with differential voltage probes and isolator, high frequency current probe, and be verified through a PCB measurement microphone. The features of pulse-trains can be classified in to open, normal spark, arcing and short-circuit based upon the gap voltage and current waveforms. Each normal spark, arcing or even wire rupture pulse is reflected onto an higher frequency acoustic pulses with respective characteristics. Besides the succeeded clustering of arc pulses is identified as the sign of high rupture risk, the relationship between gap-status and the operation conditions, and the precaution period for wire rupture alarm of 500 to 1100 μs are established. It is suggested to prolong discharge off-time directly through power generator hardware as the gap status reaches such a precaution status. In our research design, an UA-WEDM by vibrating the wire electrode at point between the upper guide and workpiece is proposed. The wire vibration frequency up to 40 kHz is proposed to avoid the succeeded clustering of arcing pulses, and the many antinodes increase the liquid pressure difference and flushing speed, allowing higher efficiency of debris expelling.Experiment results reveal that with ultrasonic power of 100W, although the UA-WEDM increases 3-8 % of kerf width compared to conventional cutting, it increases 38 % of average feedrate and reduce the risk of wire rupture significantly up to 60% (by comparison to 3 times wire rupture of conventional wire-EDM). Furthermore, it also reduces the drum factor of lateral wall significantly up to 20-40%. Not only the explanation of fundamental gap status is achieved, but also the optimization of operational conditions to material removal rate and drum factor through Taguchi’s design of experiment are conducted. And the optimization is verified through confirmation experiment that there is only minor error. The effect of proposed UA-WEDM strategy is further verified though cutting of 150 mm height of punches that not only stable prevention from wire-rupture is achieved, but also the machining precision on less and more uniform drum factor aspects are improved. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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