線切割放電加工角隅精度之改良

Abstract

現今的製造工業正朝向高精密加工的趨勢。由於能加工堅硬及複雜的 材質，線切割式放電加工在一些重要的製造領域佔有重要的地位，但是因 為線撓曲和擺振等現象，加工精度將被破壞，尤其是角隅部份更明顯。本 論文的目的在發展一控制策略，使線切割放電加工角隅部份的精度可以獲 得改良。 因為使用了低剛性的線當作電極，必須對加工過程中線的行為 有所認識，角隅部份精度失真的主要原因也作了概括的介紹。為了維持角 隅加工品質，以模糊邏輯為基礎的控制策略被提出。經由線切割放電加工 的物理特徵、實驗資料和使用者經驗訂出了模糊法則，放電強弱的調整比 例可藉由多變數模糊邏輯控制器計算出。放電強弱經由調整放電參數（ OFF-TIME）來調變，這種改變不但可達到上述目的還可使加工過程中的影 響減到最小。整個控制的目的在改善加工精度且維持加工進給速度在一合 理之值。 在本篇論文，被認為與精度失真有關的現象可藉由提出的控制 策略來改善。實驗結果特別在粗加工時，角隅的加工誤差減到正常加工的 一半以下，且加工時間維持在增加不超過百分之十。 Manufacturing industry of nowadays follows a trend towards high precision machining. Wire electrical discharge machining (Wire-EDM) has almost occupied an important position in some production fields, due to its capability of machining hard materials and intricate shapes. However, the machining accuracy, especially at corner parts, may be destroyed because of some phenomena such as wire deflection and vibration, etc. The purpose of this thesis is to develop a control strategy so that the machining accuracy at corner parts for wire-EDM can be improved. Because of the use of low-rigidity wire electrodes, it is essential to understand the behavior of wire electrodes in machining process. The main causes of inaccuracies due to wire- EDM process at corner parts are illustrated. In order to maintain machining quality at corners, a control strategy based on fuzzy logic is proposed. The fuzzy rules based on the wire- EDM's physical characteristics, experimental data, and operator' s experience are constructed, so that the reduced percentage of sparking force can be determined by a multi-variables fuzzy logic controller. Sparking force is modified by means of regulating the machining coefficient, OFF-TIME. Thechange of the OFF-TIME of the discharging pulse can not only achieve the above aim but also have a little influence in the machining process. The objective of the total control is to improve the machining accuracy at corner parts, but still keep the cutting feedrate at fair values. In this thesis, the main phenomena thought to be predominantly related to inaccuracies at corners can be improved by the proposed control strategy. As a result of experiments, machining errors of corner parts, especially in rough-cutting, can be reduced to less than 50% of those in normalmachining, while the machining process time increases not more than 10% of the normal value.