線切割放電加工之放電延遲時間線上分析系統

Abstract

線切割放電加工時電極與工件之間的間隙狀況，可以反應當時加工狀況的優劣，而每發放電波之放電延遲時間Td可做為描述間隙狀況的指標；過去關於放電Td波列之研究著重於Td統計法以及Td之機率分布情況，但無法直接觀察到放電Td之間的相依存關係，以及放電Td波列的行為是否出現特殊的規律性與相關性。 本研究以時間序列分析的角度出發，應用自行研發之WEDM放電Td時間序列線上分析系統，記錄加工時之Td時間序列，於線上進行相關分析，從Td統計法、不正常放電連續出現的狀況，以及快速傅立葉變換、自相關性分析等方式，交叉比對並深入探討Td時間序列的組成，探討不同加工條件下以時間序列分析法所得到的結果，窺得其中蘊含之物理意義。實驗結果顯示，此WEDM放電Td時間序列線上分析系統可成功對放電Td進行線上分析，由不正常放電波出現比例與連續的情況，以及放電Td累積分布與自相關係數交互分析，可觀察出加工狀況優劣之變化；並發現線電極導具跨距與加工液流量的改變，以及於工件側邊施加振動會導致Td波列當中出現特殊之週期性重複模式。

The situation of the gap between electrode and work piece in WEDM is commonly taken to reflect discharge condition, and each ignition delay time of discharge pulse indicates the real time situation of the gap between electrode and work piece. In the past, investigations about pulse trains of ignition delay time put emphasis on statistical methods and probability distribution, but researchers could not observe the correlation between each pulse and the particular regularity in discharge pulse trains by these methods. An on-line ignition delay time analyzing system based on time series analysis is developed to record the WEDM discharge pulse trains in different parameters and conduct time series analysis by using Td statistical method, abnormal discharge pulse group analysis, fast Fourier transform and auto-correlation analysis in order to realize the physical implications in different kinds of discharge pulse trains. From the experimental results, the on-line ignition delay time analyzing system has practically worked successfully. Researchers can observe variations of discharge conditions by comparing Td statistical chart with auto-correlation analysis, and comparing the proportion of abnormal discharge pulses to all discharge pulses with the number of continuous abnormal discharges analysis. Particular repeated patterns are also observed when changing the distance from the upper guide to the lower guide of the wire, the flow rate of dielectric fluid, and adding vibration on work piece.