氣中放電放電狀態監測系統之開發

Development of monitoring system of discharge state in Dry EDM

許克宇(Ke-Yu Shue)

指導教授 ： 蔡曜陽

國立臺灣大學/工學院/機械工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.10622

摘要

氣中放電加工技術具有環保、高材料移除率與低電極消耗率等優點，但過小的放電間隙導致大量電弧放電的產生使放電不穩定。因此本研究針對此問題開發一套適於氣中放電之放電狀態監測系統，分別記錄每一單發放電延遲時間(Discharge delay time, Td)、實際放電持續時間(Real discharge duration time, RTon)及實際開路電壓狀態(State of real open voltage, SRVo)，並在加工過程中任意取出一萬發連續放電波形資料，藉由波形分類統計結果找出最適於本系統之放電方式。
實驗中將空氣導入紅銅中空電極中並用由內而外噴出的方式，對SKD-11工件進行放電加工。由實驗結果可知，其放電電壓約為6 V ~ 13 V，而在加工過程中當兩極間進入放電狀態，過小的放電電流設定值會致使放電電流持續時間未達所設定之Ton便降至零準位。接著，將所記錄之一萬發連續放電波形資料進行分析與波形分類統計，根據每單發放電波形所擷取得之Td與RTon將波形分類成正常(Normal)、電弧(Arc)、點火失敗(Ignition failure)及短路(Short)四種狀態。由本實驗可知僅改變脈衝休止時間(Poff)導致放電頻率改變的情況下進行加工，開路電壓並無電容充電效應。由統計結果可知，當降低Poff時Arc總發數發數逐漸增加而使部份實驗結果中Ignition failure總發數會有先增後減的情況。而在使用雙迴路-先引弧後放電且Vo = 180 V時Ignition failure總發數皆比使用雙迴路-同時放電的放電方式時低，但Vo = 380 V時則相反。
根據上述實驗結果，本研究建議此放電狀態監測系統應選用雙迴路-先引弧後放電的放電方式與Vo = 380 V以降低Arc發數。若以較低Ignition failure發生率為前題下則應選用雙迴路-先引弧後放電並設定Vo = 180 V與Toff = 80 us以穩定放電狀態。

關鍵字

氣中放電 ； 放電狀態監測 ； 空氣 ； FPGA

並列摘要

Dry EDM processing technology has environment-friendly, high material removal ratio and low electrode ware ratio, etc., but the discharge gap, which is too small, having led to a large number of arc caused discharge instable. Having this in mind, this research has developed a monitoring system of discharge state for this issue in Dry EDM. This system is able to recorded discharge delay time (Td), real discharge duration time (RTon) and state of real open voltage (SRVo) for a single discharge. During the discharge process, 10 thousands continuous discharge waveforms are able to being sampled. This research uses the waveforms classification by the statistical results to identify an appropriate method for the gap state monitoring system.
This research uses a method which blown air into tubular copper electrode and spray out while the SKD-11 work-piece is processing by discharge. From experimental results, the discharge voltage is about 6 V ~ 13 V. In the discharge state, the set of discharge current which is too small is going to reduced discharge current to zero between the gap before the current duration time reach to the set of discharge duration time(Ton). The continuous discharge waveform recorded in process would be analysis, statistic, and classify. According to Td and RTon which was captured in every single discharge, the waveform was classified to four states such as normal, arc, ignition failure, and short. The open voltage (Vo) has no capacitor charging effect while the discharge frequency changes with pulse pause time (Poff) in discharge process. When Poff decreases, the ignition failure has increased first and decreased with the increases of arc in part of the experimental results. When Vo = 180 V, the amount of ignition failure in using the double loop - ignition before discharge mode is lower than in the double loop – both discharge in same time mode, but the results is contrary to Vo = 380 V.
Based on the results above, this research suggests these this discharge state monitoring system should be used 380 V as Vo and the circuit should be double-loop – ignition before discharge mode to reduce the quantity of arc. Supposing a lower probability of ignition failure is the most important premise, double-loop – ignition before discharge mode, Vo = 180 V and Toff = 80 us is suggested to provide a stable discharge.

並列關鍵字

Dry EDM ； gap state monitoring ； air ； FPGA

參考文獻

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