Analytical Prediction of Three Dimensional Cutting Process—Part 2: Chip Formation and Cutting Force with Conventional Single-Point Tool

The cutting model and the energy method to predict chip formation and cutting force, which were proposed in the previous part of this study, are extended to machining with conventional single-point tool. The prediction is always possible in the practical range of cutting conditions regardless of size of cutting and tool geometry, if only orthogonal cutting data under equivalent cutting conditions are in hand. The predicted results are verified to be in good agreement with the experimental results in a wide variety of depth of cut, side and back rake angles, side cutting edge angle, and nose radius.

The Theory of Plasticity Applied to Machining With Cut-Away Tools

Cut-away tools have a strong tendency to produce a complicated plastic flow ahead of the restricted tool-chip contact area as far as the restriction is in effect. The paper stresses the importance of the plastic field for better understanding the machining characteristics with cut-away tools. By applying the theory of ideal plasticity, the plastic field is found to be composed of one centered fan and two straight slip-line fields. The stress and velocity fields are then calculated based upon the construction of slip lines. The plastic deformation during chip-forming process is obtained analytically as a deformed pattern of originally square grids printed on the side of workpiece. The analytical pattern is verified to be in good agreement with the pattern actually produced in experiments. A quantitative analysis for variation of coefficient of friction on rake face with the artificial reduction of tool-chip contact area is proposed, in comparison with experimental results. The experimental results appear to support the analysis.

Free Machining Steel—IV: Tools With Reduced Contact Length

Tools which provide controlled contact on the tool face are used to study the action of free machining steels. The mean normal stress on the tool face σc is found to increase with increased undeformed chip thickness (t = feed) or with a reduction in the controlled length of tool face contact. An increase in σc in turn is found to promote the stability of the built-up edge to higher speeds. The high-speed finish produced with a cut-away tool is thus found to be inferior to that produced with a conventional tool. Manganese sulfide is found to have a similar effect on surface finish, but lead tends to improve the finish obtained at a high cutting speed. The cut-away tool provides improved low-speed finish in all cases as does the addition of either manganese sulfide or lead to the steel. Manganese sulfide is found to become more effective with increased undeformed chip thickness t, while lead behaves in the opposite manner. This observation along with several others is in agreement with the idea that manganese sulfide is a poor solid “lubricant,” while lead is an effective solid lubricant. An optimum chip-tool contact length appears to exist at which the tool life will be a maximum at any combination of cutting speed and feed. From this it follows that an optimum combination of sulfur or lead content, degree of cold work, cooling capacity of cutting fluid, or extent of tool-face limitation exists, since all of these quantities influence the resultant length of contact between chip and tool.

A Photoelastic Analysis of Machining Stresses

Direct measurements of the distributions of normal and frictional stresses on a rake face under cutting conditions have been considered to be practically impossible. However, as reported in this paper, the stress distributions have been successfully obtained photoelastically by using a tool made of a photoelastic material. According to the authors’ experiment, the frictional stress on the rake face is distributed uniformly over a wide range of the tool-chip contact length, but it decreases rapidly near the point of chip-separation on the rake face. As to the normal stress, it has a peak near the cutting edge, being rather stationary in the middle part of the contact length and decreasing gradually toward the point of chip-separation.