Study On Cutting Performance And Its Extended Application Of Coated Silicon Nitride Cutting Tool

High speed, high precision, high efficiency, intelligent and environmental protection becomes more and more popular in today’s machining area, it’s difficult to improve the tool performance single by good design of cutting tool materials or its shape. Moreover, throughout the tool failure of a large number of examples in machining, we can realize that the tool surface property is the key point on the tool failure. Ceramic cutting tools with high hardness, high wear resistance and heat resistance, is widely chosen as proper cutting tool in automobile and mould industry. But, ceramic cutting tool is very sensitive to surface state with its poor toughness. Therefore, ceramic tool surface modification has become a hot topic at present.With the development of coating technology in recent years, covering the ceramic tool with thin wear resistance PVD/CVD coatings has become possible. In this paper, through a lot of cutting experiment, two mainly aspects of coated silicon nitride cutting tool was researched according to the characteristics of its application. On the one hand, TiN+Al2O3coated silicon nitride cutting tool’s tool life and wear mechanisms were researched when machining HT250. According to the experimental results, because of the excellent mechanical and physical properties of matrix and the wear/chemical resistance of TiN+Al2O3coating material, make the tool can under a more high cutting parameter and greatly improve the machining efficiency. The tool failure forms include abrasive wear, oxidation and adhesion wear, and the main failure form is abrasive. Moreover, according to the knowledge of mathematical statistics, the generalized Taylor formula between the cutting tool life and cutting parameters has been established.On the other hand, the paper made a research on the extended application of coated ceramic cutting tool, a Al2O3/TiN coated silicon nitride cutting tool was used as a example when machining alloy steel AISI4340. In the test, the life of coated silicon nitride tool and the tool wear mechanism have been investigated. According to the performance of uncoated one, it can be found that the wear mechanisms of coated tool was changed by the adding the Al2O3/TiN coating when machining AISI4340steel. The dominant failure mode crater wear by uncoated tool was transformed into flank wear. Also, found that the coating has a significant effect to inhibit the boundary wear. In the machining test process, it is big problem to remove the chip safely. Through a lot of experiments, found that an ideal state of chip removal, the chip was fly out along the direction away from the workpiece and the cutter bar after removed from the workpiece, can be achieved by reasonable selection of cutting parameters when nitride tool machining AISI4340steel. And the selection of parameter follows some rules, first of all, a high cutting speed Vc is needed, such as500m/min or above in experiment tests; Second, the selection of feed rate f and depth of cut ap should be selected according to the workpiece material and the mutual adaptation between the two.