Effect of Machine Stiffness on Cutting Performance

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The cutting characteristics of a point attack bit, especially the effects of cutting speed and depth of cut on cutting force were investigated. Point attack bits are becoming more popular as a cutting tool for boomheader, but its performances are still open to discussion. A series of rock cutting experiments were conducted with various cutting depths and speeds.It was found that the horizontal component of cutting force increases linearly with cutting depth. This simple relation is true all for the mean, the mean peak and the peak values. It was also found that the build-up nose develops on the clearance face of the bit when a hard andesite is cut at higher cutting speed. As a result, cutting force, especially its vertical component, increases considerably with cutting speed.The effects of cutting machine stiffness are discussed. Machine stiffness is regarded as one of the important factors in rock cutting, but its effects on cutting performance have scarcely been studied. In this study, a test rig with variable stiffness was designed and manufactured with which a series of cutting experiments were performed.It was iound that the horizontal-vertical (cross) component of compliance matrix has significant importance. If it is negative, the vertical component of cutting force increases and decreases harmonically with the horizontal component during a cutting process. If positive, however, the vertical component increases when the horizontal component decreases, and vice versa. It was also found that machine stiffness has effects on the mean, the mean peak and the maximum values of cutting force. The mean peak and the maximum values increase with stiffness against the force parallel to the bit axis, that is, stiffness corresponding to the sum of the cross and the vertical components of stiffness.