Minimizing drum-shaped inaccuracy in high-speed wire electrical discharge machining after multiple cuts

Drum-shaped inaccuracy increases dramatically in high-speed wire electrical discharge machining (HS-WEDM) after multiple cuts when very thick workpiece (> 100 mm) are used. To tackle this problem, a positional change model of the wire electrode was established to analyze the main causes of the drum-shaped inaccuracy. In HS-WEDM, the conductivity of the working fluid is very high. As the workpiece thickness increases, the “leakage current” at the machining gap increases, and more energy is required for the trim cuts. In addition, to maintain stable trim cuts, a long pulse-on time is needed. As a result, the high discharge energy inevitably results in a large explosive force, which increases the wire bending deformation due to long durations under this force. To solve these problems, novel measures were taken in this study. First, an improved working fluid was proposed to reduce the conductivity so that the energy loss between the electrodes can be decreased. The discharge energy used for the trim cuts was diminished to reduce the impact of the discharge explosive force. Second, a short pulse-on time and a high peak current were utilized for the trim cuts to reduce the impulse from the effect of the discharge explosive force on the wire electrode. Third, a closed-loop tension mechanism was designed to increase the wire tension, thereby improving the stability and rigidity of wire electrode. Finally, the rigidity of wire electrode was further improved by utilizing a unique trim-cut method proposed in this study. The experimental results showed that the drum-shaped inaccuracy of a workpiece with a thickness of 150 mm was reduced to 10 μm from 25 μm after three cuts (one roughing cut and two finish/trim cuts) under normal machining and the quality and uniformity of the machined surface were improved.