Experimental Measurement of Wire-lag Effect and Its Relation with Signal Classification on Wire EDM

In this paper, direct measuring of the influence of wire deformation on part geometry is proposed. Classical methods presented in literature are optical or are based on measuring wire-lag using electrical contact between wire and workpiece. The idea that the effect of wire deformation can be directly measured by suddenly stopping the machine is developed in this contribution. Using this approach, the effect of wire deformation can be measured even when cutting circular paths of small radius. A complete set of experimental tests is presented under different WEDM cutting conditions; including the effect of low dielectric pressure, part radius and part thickness. Analysis of discharge patterns has also been carried out, so that the lack of accuracy in WEDM'ed parts can be correlated with the quality of discharges. Results show that wire deformation increases as much as 45% when cutting a circular interpolation of radius 0.8 mm if compared with a straight cut on a part of similar thickness. This fact has direct implications on the error caused by the tractrix effect when cutting small circular paths. Likewise, the relation between wire-lag and discharge type percentages (based ionization time) stablishes that, as the radius increases the percentage of discharges without ionization time raises, decreasing the one that has an ionization time above 10 μs.