This paper reports a study and analysis of non-even wire tension in high-speed wire electrical discharge machining (HSWEDM). This problem has been a challenge since HSWEDM was invented. The tensions of the wire electrode at both ends of a wire-winding cylinder become inconsistent when the wire electrode continues discharging for a certain period. Studies have suggested that the amount of dielectric fluid added into the discharging gap differs depending on the positive and negative moving directions of the electrode. The resistances experienced by the electrode differ because of the discharging explosion. Meanwhile, the elongations of the electrode differ according to positive and negative moving directions. Therefore, tensions are inconsistent, and non-even wire tension occurs. Factors that affect non-even wire tension are studied, and a new mode of variable wire speed reciprocating WEDM is designed. Experiments show that the machining effects in the new mode are better than those in the traditional mode under the same cutting conditions. Processing accuracy, surface quality, and cutting speed are increased. Moreover, the service life of the electrode is extended three times or more with the new mode compared with that in the traditional mode.

The ever changing principles regarding cutting efficiency,workpiece surface microstructure,ablation efficiency,electrical conductivity,the pH value and concentration of the dielectric liquid in the process of HSWEDM are studied,and the machining waveform of electro-discharge in the process is tested. The analysis shows that the method previously determining the functional performance of dielectric fluid is short of scientificity,hence using ablation efficiency as the life index of a compound dielectric fluid is more accurately represented,and the change of ablation efficiency has great relevance with electrical impulses utilization rate in this process. This perception points out the direction for establishing the evaluation system regarding the life expectancy of HSWEDM dielectric fluid.

Life test of dielectric fluid in high speed wire-cut electrical discharge machining (HSWEDM) was carried out to analyze the relationship between the dielectric fluid life and the discharge pulse probability. In terms of the working fluid properties and the effect on the discharge characteristics of discharge gap,discharge gap and discharge characteristics before and after the failure of dielectric fluid were analyzed. The relationship between the dielectric fluid life and the discharge pulse probability was proposed. The relationship between the discharge pulse probability and the cutting efficiency and surface quality was studied ,when the effective discharge pulse pro-bability is less than 70 %,the cutting efficiency is reduced and the surface quality becomes poor ,which can be used as the index of the failure of dielectric fluid. Whereby the device of detecting the dielectric fluid life was invented which can monitor the life condition of dielectric fluid effectively.

This paper studied and analysed "non-even wire tension" in HSWEDM,which has existed since the invention of HSWEDM. That is to say,when the processing of wire electrode continues discharging a period of time,the tensions of the wire on both ends of tube are inconsistent. Studies suggest that the amount of dielectric fluid brought into the discharging gap is different as the positive and negative moving direction of the electrode. Then the resistances suffered by the electrode are not the same which are caused by the discharging explosion. And the elongations of the electrode with positive and negative moving direction are different. Thereby the tensions are inconsistent and the "non-even wire tension" occurred. The factors affecting the non-even wire tension are studied,a new machining mode of variable wire travelling speed reciprocating WEDM is designed. Experiments show that with the same cutting conditions,the machining effects in the new mode are better than that in the traditional mode. The processing accuracy,the surface quality and the cutting speed are increased observably. Especially the life of the electrode is extended 3 times or more.

The influence of different sizes of discharge debris on microprocess in HSWEDM was studied.In a new filtration system designed,the influence of which on process index such as wire wear,cutting speed,surface quality of workpiece and lifetime of dielectrics was studied.Results show that,the best size for discharge debris should be 3~5 μm,in which condition,for the same cutting area,wire wear decreasing by 25 %~50 %,cutting speed increasing by 2 %~12.4 %,surface roughness Ra decreasing by 3.7 %~12.6 % and lifetime of dielectrics increasing by 25 %~50 %.