ULTRA HIGH-SPEED CUTTING OF CAST IRONS WITH CONTROLLED NONMETALLIC INCLUSIONS BY cBN CUTTING TOOLS

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The aim of this study is to clarify the possibility of ultra-high-speed machining of the cast irons with cBN cutting tool. Ultra-high-speed face milling test tests (up to 4500 m/min) were carried out on several kinds of cast irons using cBN tools with different binders. Tool wear, cutting forces, cutting temperatures and non-metallic inclusions in cast irons adhered on the wear part of the cBN tools were examined.Results obtained were as follows ;1. Oxide protective layer consisted from Al, Si, and Mn was observed on the rake face and flank face of cBN tool when machining cast irons with high content of Al203, and the wear of the tool became small when the layer was adhered.2. The cutting speed at which the protective layer was observed on the tool depended on the content of A1203 in the cast iron, the higher content of A1203 the higher cutting speed. The maximum cutting speed was 4500 m/min at which the protective layer was observed in the tests.3. Formation of the protective layer depended on the binder of the cBN tool, the layer easily tended to adhered on the tool with ceramic binder including TiC, because TiC was oxidized easily and to combine with other oxides.4. In the process of clarifying the bonding mechanisms of cBN tools and the protective layer, it was clarified that boron nitride BN had the effect of making AlN from Al in work material, and the AIN adhered on the tool acted as a very stable protective layer. The results were presented at an International Conference.