The stagnant region often appears in front of the tool cutting edge, which is caused by mechanical inlay and excessive pressing in plastic metal cutting with large negative rake angle tools at a low speed. It results in the change of the effective negative rake angle which can affect the flow characteristics of material, the quality of machined surface and the abrasion loss of cutting tools. However, the critical negative rake angle model based on the existence of the stagnant region has not been reported yet. Therefore, in order to investigate the critical negative rake angle value considering the stagnant region, a critical negative rake angle model based on the principle of minimum required energy is established, and the correctness of the theoretical model is verified by orthogonal cutting experiments. At the same time, the influence of the critical value of the large negative rake angle tool on the machined surface quality is studied through different cutting experiments. These experimental results show that the deviations of both experimental and theoretical critical negative rake angle are less than 5% during the orthogonally cutting of the aluminium (AL1060) and copper (T2) materials by the negative rake angle tool. Meanwhile, the critical negative rake angle is related to the adhesive friction coefficient of tool–workpiece contact surface. The analysis of friction characteristics shows that the deviation values of both theoretical and experimental critical negative rake angle are proportional to the coefficient of adhesive friction and the thickness of the stagnant region. Critical negative rake angle has a significant effect on roughness and residual stress of the machined surface.

With the high-speed development of the delicateness grinding, mechanical scratching and micro-cutting technology, scholars have become more and more interested in the forming mechanism and related characteristics of the negative rake angle tool. Based on DEFORM-2D forming software, this paper investigates the forming mechanism and related characteristics of the negative rake angle tool. Through the simulation comparison analysis, it is clear that as the negative rake angle decreased form 0° to 60° (the negative rake angle does not attain to the critical value), the shear angle becomes smaller, the ability of the chip formation in the front of the tool surface becomes weaker, the chip shape becomes blunter, the action state of the tool effect on the material is cutting and ploughing, and the tangential force and normal force increase, significantly. When the negative rake angle reaches the critical value (no chip formation, negative rake angle is approximately equal to -80°), the shear angle is approximately equal to 0°, no chip formed in front of the tool surface, the tool pure ploughing the material, and the tangential force and normal force both show a significant downward trend. Meanly, a triangular stagnant region appears in front of the tool surface when the negative rake angle decreased form -20° to -80°.

No abstract

No abstract

No abstract