Wear mechanisms of TiN-coated CBN tool during finish hard turning of hot tool die steel

Abstract

The aim of the present investigation was to identify the wear mechanisms of TiN-coated CBN tools prevalent under different machining conditions during hard turning of hot tool die steel. The different wear mechanisms observed were abrasion wear at low cutting speed, low feed rate, and high workpiece hardness; formation of a transferred layer resulting from tribochemical reactions between constituents of the tool and workpiece material at high speed; and the formation of built-up edges at moderate cutting speed. Hard carbide particles of the work material at higher feed rate severely abraded the tool flank land, resulting in shallow grooves due to the detachment of CBN grains. At greater depth of cut, the built-up edges and transferred layer reduced friction and tool wear. Excessive adhesion of workpiece material followed by plastic deformation and notching were clearly visible at low workpiece hardness (47 HRC). The influence of cutting speed, feed rate, depth of cut, and workpiece hardness on the progressive tool flank wear, i.e. flank wear rate (VB_r, μm/mm) in the steady wear region, was also analysed. The flank wear rate was observed to decrease with increase in cutting speed, depth of cut, and workpiece hardness, but after an initial decrease it increased with increase in feed rate.