Some observations on surface damage during machining of a bearing bronze

Abstract

The effect of the tool rake angle, depth of cut (feed), tool wear land length and cutting speed on the nature of the surface generated in machining a bearing bronze (free machining) under dry unlubricated orthogonal conditions was determined. Machined workpieces were examined with an optical microscope and a scanning electron microscope equipped with an energydispersive X-ray analysis system. The surface roughness was determined with a profilometer. The results of the investigation show that during machining considerable surface damage in a wide variety of forms is produced. The intensity of the surface damage and the surface roughness increases with an increase in feed rate, an increase in rake angle and an increase in tool wear land length, but is independent of the cutting speed. The results also show that lead is readily lost from surface cavities and is deposited on the rake and flank faces of the cutting tool as a smeared layer. In addition, lead globules were found on the tool holder, the freshly machined workpiece surface and other regions close to the tool cutting action. The results are interpreted in terms of the type of chip produced, the stress concentrations associated with the presence of second-phase particles (lead) and the nature of the interaction between the tool cutting edge and the workpiece.