On the Forces on the Flank Face of a Cutting Tool
Abstract Generated abstract
This paper examines the normal and tangential forces acting on the flank face of a cutting tool during machining of different materials. Using dynamometer measurements of total cutting forces and extrapolation to zero chip thickness at constant chip shrinkage, the study estimates flank-face forces for sharp tools with minimal wear. The results indicate that these forces increase with chip compression and, at comparable compression, tend to be larger for work materials with higher hardness and strength, while the flank-face friction coefficient also varies with chip compression and material plasticity. The paper argues that this dependence links flank-face contact conditions to plastic deformation ahead of the tool, challenging a strictly autonomous view of processes on the flank face.
Full Text
ON THE FORCES ON THE REAR FACE OF A CUTTING TOOL
M. F. POLETIKA
Below we present some results of determining the forces on the rear face when machining various materials. The forces \(N_1\) and \(F_1\) on the rear face (Fig. 1) were calculated from the total forces \(P_z\) and \(P_{xy}\), measured with a dynamometer, by the method of extrapolating to zero chip thickness the dependences \(P_z, P_{xy}=f(a)\), obtained at constant chip shrinkage.
Fig. 1. Diagram of the forces acting on the cutting tool
The measurement of forces was carried out with wear on the rear face not exceeding \(0.05 \div 0.07\) mm. Such a cutting tool we conventionally call “sharp.” Measurement of the forces on the rear face made it possible to reveal two clearly expressed tendencies in the behavior of these forces. For the given machin—
of the work material (and, of course, at constant cut thickness), the forces on the rear face increase with increasing chip compression. At constant compression, but for different materials, these forces are greater the higher the hardness and other strength characteristics of the work material.
Fig. 2. Forces and friction coefficients on the rear face when cutting beryllium bronze
As an illustration of what has been said, Fig. 2 may serve; it presents the values of the forces \(N_1\) and \(F_1\), as well as the coefficient of friction on the rear face \(\mu_1\), as functions of chip compression when cutting beryllium bronze BrB2, heat-treated to different hardnesses. Beryllium bronze does not change its microstructure during heat treatment, and therefore the dependences shown in Fig. 2 reflect the direct influence of the mechanical properties of the work material on the forces.
The coefficient of friction \(\mu_1\) also increases with increasing chip compression. It also increases with increasing plasticity (decreasing hardness) of the work material. It is characteristic that, on average, the coefficient of friction on the rear face of the tool is higher than on the front face.
Figure 3 gives summary plots of the values of the forces \(N_1\) and \(F_1\) for all the work materials we investigated. Both show that the dependence of the forces on the rear face on chip compression is fairly general, since it is retained when cutting metals with the most diverse properties.
The tendency of the forces to increase with increasing hardness of the work material is especially clearly expressed for the normal force \(N_1\) (Fig. 3). The higher the hardness, the higher the corresponding curve \(N_1=f(\xi)\) is located. It is noteworthy that for three materials having approximately
identical mechanical properties: annealed U12 steel, beryllium bronze tempered to hardness HB-200, and technical titanium VT-1, the curves \(N_1=f(\xi)\) practically coincide, although the characteristics of chip formation when cutting these metals differ substantially from one another.
Fig. 3. Normal and tangential forces on the rear face when machining various materials
The curves \(F_1=f_1(\xi)\) are arranged less regularly, although the general tendency for the curve to shift upward with increasing hardness is approximately maintained. The dependence of the forces on the rear face on the hardness of the material being machined was not unexpected for us. Similar results had previously been obtained by N. N. Zorev when machining hardened steels with a cutter having an artificial blunting along the rear face [1].
It appears that no one had previously paid attention to the relationship between chip shrinkage and the forces on the rear face. The existence of such a relationship even somewhat contradicts the established view that the processes occurring on the rear face are autonomous and completely independent of the phenomena on the front face of the cutter. The point is that, when considering contact processes on the rear face, it is usually not taken into account that the front of the wave of plastic deformation propagating ahead of the cutter descends below the cutting line. Therefore the rear face comes into contact with material that has already been deformed, the degree of deformation of which is directly related to the magnitude of chip shrinkage. The more
the greater the shrinkage, the greater the volume ahead of the tool that is encompassed by plastic deformation, and the higher the degree of deformation of the metal in the layers adjacent to the cutting surface. The forces on the rear face should also increase in this case.
In conclusion, we note that the observed dependence of the forces \(N_1\) and \(F_1\) on shrinkage does not cast doubt on the generally accepted method, used by us, for separating the forces on the rear and front faces, since all calculations by this method (extrapolation to zero chip thickness) are carried out at constant chip shrinkage.
REFERENCES
- N. N. Zorev. Problems in the Mechanics of the Metal-Cutting Process. Mashgiz, Moscow, 1956.