TOOL WEAR IN FINISH TURNING OF MEDIUM-CARBON STEEL WITH COATED CARBIDE TOOLS

Multilayer-coated cemented carbide inserts were used to machine 080M40 steel under finish machining conditions in order to assess their over all performance and also to identify factors responsible for tool fail ure at different speed, feed rate and depth of cut conditions. Detaile d examination of worn fools were carried out after the machining tests in addition to recordings of the wear regions, surface finish generat ed, component forces and chip formation during machining. Comparative tests were also carried out with similar fools with a different chip b reaker (MA style) in order to study the effect of chip breaker groove on tool performance. The test results show that tool performance is ad versely affected by increasing cutting conditions, especially cutting speed and feed rate, due to increased temperatures and stresses genera ted at the cuffing edges during machining. Flank wear and chipping/fra cture of the tool edges were the major failure modes at the cutting co nditions investigated. Random chipping of the insert edges is more pro nounced at higher speed conditions and tends to be accelerated by inhe rent vibration of the machine tool during cuffing operation. The diffu sion wear mechanism is dominant at a speed of 300 m/min. where high te mperatures sufficient to promote interatomic diffusion at the chip-too l interface are generated during machining. This is compounded by plas tic deformation and fracture mechanisms when machining at higher speed s and feed rates where much higher temperatures and compressive stress es are generated closer to the cutting edge, causing the softening of the tool and the likely elimination of the clearance face. Forces gene rated during machining are not affected by increasing cutting speed bu t by increase in feed rate and depth of cut under the finish machining conditions investigated.