To produce the precise stamping dies for ultra fine LSI lead frame, fatigue strength properties of WC-Co alloy plates of 0.1mm in thickness with different WC particle size, machined by wire electric discharge (WED) and/or by subsequent abrasive flow (AF), were investigated. The WED machining significantly reduced the fatigue strength of the ultra thin alloy plates from about a half to a quarter that of ground specimens. Coarsening of WC particles and surface removal of around 1-2μm by AF machining, however, enhanced the fatigue strength. This was principally caused by that they lowered tensile residual stress in machined surface layer. It was suggested that suppression of initial micro-crack propagation due to coarse WC particles and elimination of surface defects due to the AF machining also improved the fatigue strength although their contributions were very smaller than that of the residual stress.
