Introduction of rolling motion at the tool-tip in metal cutting

Highlights

• Tool-tip rolling motion in RTC-tool disrupts the severe sliding contact at tool-chip interface.

• Material flow characteristics around the tool-tip are investigated by in-situ image analysis.

• Tool-tip rolling motion promotes nearly laminar flow and increases the shear velocity in the primary shear zone.

• Small and stable retardation region in RTC-tool reduces chip thickness, cutting force and surface roughness.

• Highly non-laminar plastic flow and unstable retardation region cause cracking at the tool-tip.

Abstract

In metal cutting, severe sliding contact at the tool-chip interface is unavoidable by a conventional cutting tool, which results in sloth motion of chip, higher chip thickness, formation of stagnation zone, higher power consumption, and poor surface finish. To overcome this limitation, rolling motion is introduced at the tool-chip interface by mounting a roller at the tip of a cutting tool – termed as Rotating Tip Cutting Tool (RTC-tool). The roller in RTC-tool rotates during cutting and establishes rolling-sliding contact. A model in-situ experimental configuration is used to study the plane strain flow characteristic of pure copper, notoriously known for higher chip thickness and power consumption, during cutting at low speed. The performance of RTC-tool is compared with sharp cutting-edge and blunt cutting-edge tools (fixed curvature and stationary-roller-tip tool). It is found that rolling motion at the tool-tip decreases the chip thickness and average plastic strain within the chip by about two times than sharp tool and more than two times than the blunt tools. Additionally, there is a significant improvement in surface roughness than the sharp tool. The digital image correlation techniques reveal that flow characteristics within the chip and near the tool-tip interface (retardation region) are influenced by the non-laminar plastic flow of materials. As opposed to the unstable retardation region and periodic cracking at the tool-tip of sharp tool, additional rolling motion at the tool-tip cuts the chip at the incipient stage, forms a stable retardation region, and increases the average velocity of the material in this region. Large retardation region and sloth motion of materials within the retardation region produce large chip thickness during cutting by blunt edge tool. As the chip thickness rather power consumption of the sharp tool is less than the blunt tool, force measurement in nearly orthogonal cutting configuration of RTC-tool compared with the sharp cutting edge. These tests are performed at moderate speed range in a lathe machine. The force measurement data and post-cutting characterization are aligned with the in-situ observations. As the frictional resistance of the roller controls the chip thickness further improvement in the performance of the RTC-tool is possible by reducing the frictional resistance of the roller.