TOOL WEAR MECHANISMS IN INTERMITTENT CUTTING OF METAL-MATRIX COMPOSITES

Cutting of fibre and particle reinforced light alloys is known to cause extensive wear of cutting tool edges. With the objective to identify the mechanisms responsible for this, single edge cutting experiments on 20% alumina fibre reinforced SS 4103 and 30% SiC particle reinforced SS 4244 were performed. A modified Sharpy impact strength tester (the Uppsala Pendulum) was used to conduct the experiments. This set-up provides an excellent quick-stop facility which was used to freeze the cutting action. The tools were used for one single, quick-stopped, cut only. Then both tool and work material were studied in the scanning electron microscope. As expected, the hard reinforcing phases in both composites were found to cause severe abrasive wear on the tool. Contrary to the case when cutting ordinary, unreinforced metals and alloys, distinctive traces of single abrasive tool wear events were found on the cut surfaces of the composites. However, the whiskers reinforced alloy caused considerably less wear on the rake face than on the flank face of the tool. This was explained by the whiskers fragmenting when passing the primary shear zone. Thus, only smaller whisker fragments, less firmly situated in the matrix, reached the rake face. An experiment with diamond coated cemented carbide tools was also performed. The coatings showed no signs of abrasive wear but failed by spalling off the rake face at the moment of quick-stop. It was concluded that diamond coatings offers very good wear protection, provided that the adhesion between the tool and coating is strong enough.