Hiroki Kiyota

Experimental Research of Micro-Textured Tool for Reduction in Cutting Force

An effect of micro-textured tool on a reduction in cutting force has reported in recent years. Some researchers have discussed that the microstructures contribute to the reduction in friction force at tool-chip interface by acting as cutting fluid reservoirs. In this study, on the other hand, a reduction in cutting force achieved by using the textured tools was confirmed even under dry condition. The results of orthogonal cutting tests employing AISI 1045 steel with non-textured and textured tools indicated that the cutting force and calculated friction coefficient at the tool-chip interface definitely reduce at relatively high cutting speed. For this friction reduction effect, effective texture patterns and optimal area ratio of concave portion to total surface were empirically suggested. Moreover, from results of the tests using tools with sectionally textured surface, it was revealed that the texture only around the position in which the chip flow separates from the tool rake face is effective to reduce the cutting force. Close observation of both tool edges and formed chips under various cutting tests indicated that changes in geometry and dimensions of dead metal formed around the cutting edge is essential for the reduction in cutting force. Finally, a mechanical cutting model having an agreement with the experimental results was discussed by employing the slip-line field method.

Control of Built-Up Edge Behavior by Chamfered Cutting Edge Preparation and Surface Modification

A chamfered cutting edge, which is commonly shaped in order to strengthen an edge of a cutting tool consisting of brittle material, easily causes an enhanced adhesion and a burr formation due to high compressive stress anterior to the edge. These problems lead to a detachment of tool material and a notch wear at depth-of-cut line, which would result in unexpected tool fracture. On the other hand, the edge shape promotes formation of a built-up edge (BUE) as a dead metal and can maintain it stably. Actually, the formed BUE is plastically extruded along to the chamfered edge and can prevent formation of the notch wear. In this study, basic experiments to reveal effects of chamfered tool edge preparation, such as chamfer angle, chamfer width and rake angle, on the BUE behavior were conducted. Additionally, the results suggested that the plastic flow in the BUE extrusion can suppress the adhesion if the extrusion is arisen uniformly. Therefore, attempts to control the BUE flow by chamfer surface modification were carried out.

Size Effect in Machining on Initial Tool Wear in Heat-Resistant Alloy Cutting

Ni based heat-resistant alloys have high strength at high temperature. In addition, they have low thermal conductivity and work-hardening properties. Therefore, Ni based heat-resistant alloys are known as a difficult-to-cut material. The final goal of our study is to develop a cutting method for extending the life of cutting tools for Ni based heat-resistant alloys. As a first step, this study investigated the size effect in machining on initial tool wear in Ni based heat-resistant alloys cutting. Using two types of Ni based heat-resistant alloys with different average grain size, orthogonal cutting tests were performed under changing uncut chip thickness from 12.5 to 200 μm. The cutting speed and width of cut were 30 m/min and 1 mm, respectively. As a result, it was found that when the uncut chip thickness is less than the average grain size, the initial tool wear strongly depends on the average grain size. In contrast, when the uncut chip thickness is sufficiently larger than the average grain size, the initial tool wear does not depend on the average grain size. These results indicate that the ratio of the uncut chip thickness to the average grain size is an important factor to extend the life of cutting tools for Ni based heat-resistant alloys.