線切割放電加工對厚工件精修之研究

Abstract

線切割放電加工是精密零組件及模具或耐高溫航太材料等不可或缺的一種材料移除方法，而當線切割放電加工精修厚工件時，往往需要多道次精修以達到所需要的表面粗糙度、加工速度、真直度。 本研究主要在探討厚工件精修製程時電相關參數(放電時間、放電休止時間、伺服電壓)、線相關參數(線張力、線速度)、沖水相關參數(沖水壓力、沖水方式)對表面粗糙度、加工速度、鼓形量的影響。並對鼓形量部分深入探討其放電點位置分佈與短路放電頻率關係。 由實驗結果發現，當放電時間增加使工件表面粗糙度變差，加工速度變快，斷面鼓形量變大；放電休止時間增加對工件表面粗糙度影響並不明顯，但同時降低了加工速度與斷面鼓形量；而伺服參考電壓部分，當伺服參考電壓提升，能有效降低工件表面粗糙度、加工速度、鼓形量。而線相關參數部分，線速度改變對表面粗糙度和加工速度沒有顯著影響，然而線速度如果過慢會造成工件斷面會有線徑消耗誤差存在；當線張力提升，對表面粗糙度影響有限，並會使加工速度下降，也能獲得較好斷面真直度。而沖水相關參數部分，當沖水水壓增加不會改變表面粗糙度結果，但能使加工速度變快，而對工件斷面真直度則有漸增的趨勢；而相同流量不同沖水方式下，對表面粗糙度與加工速度和鼓形量都沒有顯著影響。 而觀察精修時其放電位置分佈的部份，其放電位置分佈主要集中在工件的上半部和下半部；且當短路放電頻率升高，鼓形量也從中凹形貌轉變為中凸形貌。

Wire electrical discharge machining (Wire-EDM) is an essential material removal process in precision components and die or aerospace materials.When Wire-EDM machined thick workpiece,several finishing process was needed to reach the surface roughness and dimensional accuracy that we required. This study focused on the influence of electrical parameters (pulse on time,pulse off tome,servo voltage),wire parameters(wire tension,wire feed rate) and flushing parameters(flushing rate,flushing types) on surface roughness,material remove rate and drum shape error on the thick workpiece in finishing process.And for the drum shape error, probing into the relationships between discharge location distribution and short circuit frequency. The experiment results showed, when pulse on time increases ,the surface roughness is rougher and the drum shape error larger, but the material remove rate becomes higher.The influence of surface roughness isn’t obvious when pulse off time increases,but the drum shape error and the material remove rate become decreased. In the servo voltage part ,It is effective to reduce the surface roughness,material remove rate and drum shape error, when servo voltage is increased.In the wire parameters part,the change of the wire feed rate doesn’t significantly effect on the surface roughness and material remove rate. However, if the wire feed rate is too slow, there will exist some wire consumption error on the machined part.When the wire tension enhances,It limited impacts on the surface roughness,decreased the material remove rate,and a better cross-section straightness.In the flushing parameters part, when flushing pressure is increased, It doesn’t significantly effect on the surface roughness,but it increases the material removal rate and drum shape error. While at the same flow rate but different flushing types, it doesn’t significantly effect on the surface roughness, the material remove rate and the drum shape error. In the discharge distribution part, discharge location mainly concentrated in the upper and lower workpiece.When the short circuit frequency increases,the drum shape error converts convex to concave.