Modal convection and its effect on the stability of EDM wires

Abstract

Recently, it has been shown that EDM wires undergo thermal buckling at low axial transport speeds and a series of transport instabilities at high axial transport speeds. Hence, only intermediate speeds ensure the straight wire configuration, which is needed for high-accuracy cutting. These conclusions are based on the assumption that the convective heat transfer coefficient remains piecewise constant along the length of the wire. However, a recent study on convection from a vibrating, flexible body shows that the convection coefficient becomes modal. The present study re-examines the wire stability problem with this modal effect in mind. It is shown that at low axial transport speeds, the straight wire configuration may be stable. Its stability hinges on vibration—large amplitude motion implies increased convection and increased stability from thermal buckling. At high transport speeds, the system still undergoes the reported transport instabilities. This work shows that the well-defined intermediate speed range is not so well-defined in the presence of wire vibrations.