PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE RED BANNER OF LABOR
named after S. M. KIROV

Vol. 157                    1970

ON THE METHODOLOGY FOR SEPARATING CUTTING FORCES IN FACE MILLING OF NON-FERROUS METALS

G. L. KUFAREV, A. A. KOZLOV

(Submitted by the scientific seminar of the departments of machine tools and metal cutting
and mechanical-engineering technology)

In works [1, 2], a derivation is given of theoretical two-term equations for calculating cutting forces in face milling. The derivation of these equations and the methodology for separating the forces into two independent groups are based on the following propositions:

1. The forces on the rake face of the tool, at a constant degree of deformation, vary in direct proportion to the cross section of the layer being cut.

2. The forces on the flank face are practically independent of the thickness of the layer being cut.

In the machining of ferrous metals, it has been demonstrated on the basis of extensive experimental material [3, 4, etc.] that the regime of constant temperature on the rake face corresponds to the regime of a constant degree of plastic deformation of the layer being cut and, consequently, the separation of forces can be carried out both at constant chip shrinkage and at constant temperature. In order to determine whether such a methodology for separating forces is applicable in the machining of non-ferrous metals, special experiments were carried out.

In conducting the experiments, the cutting temperature was measured by means of a natural thermocouple, and its shrinkage was determined from the collected chips. The cutting forces (the tangential force \(P\) and the feed force \(P_s\)) were measured by means of elastic-electric apparatus with inductive sensors.

The experiments were carried out with face mills made of high-speed steel and carbide, with cutters made of alloy VK8. The materials studied were ductile non-ferrous metals: brass L62, bronze BrA Zh9-4, red copper M1, and duralumin D-1.

Figure 1 presents the dependence of the change in chip shrinkage on temperature (the temperature is indicated in microammeter readings) for the case of milling brass L62 with a carbide mill.

As can be seen from the graph, the experimental points reliably lie on a single curve. This indicates that, despite the wide range of variation in cutting speed and feed \((v = 19—980\ \text{m/min};\ S_z = 0.02 \div 0.503\ \text{mm/tooth})\), the constant-temperature regime is close to the constant-shrinkage regime. Similar results were obtained in milling bronze and duralumin with a face mill having a rake angle \(\gamma = +10^\circ\).

A qualitatively different picture is obtained when milling copper. The experiments showed that the scatter of the experimental points in this case

considerably greater than for the preceding metals; moreover, this scatter is not random, but has a definite regularity—with increasing feed, chip shrinkage at constant temperature decreases.

When milling copper with a cutter having a rake angle \(\gamma = +18^\circ\), the absolute value of chip shrinkage decreases, and the scatter of the experimental points also decreases; however, the character of this scatter remains the same as for \(\gamma = +10^\circ\).

Fig. 1

A similar picture, in which, with increasing feed, chip shrinkage under the constant-temperature condition decreases, is observed not only in the machining of copper, but also in the machining of L62 brass with a face mill having a rake angle \(\gamma = 0^\circ\), whereas when milling the same brass with a cutter having \(\gamma = +10^\circ\) (Fig. 1), the scatter of the experimental points is entirely insignificant.

A similar picture was also obtained in milling the indicated metals with high-speed-steel face mills.

Analysis of the experimental data on face milling of the investigated ductile non-ferrous metals showed that the constant-temperature condition corresponds to a condition of constant shrinkage over a wide range of changes in cutting conditions and tool geometry only when milling BrAZh9-4 bronze. Thus, only for it is it possible to separate the forces into two independent groups under the condition of constant temperature.

At the same time, as can be seen from Fig. 2 (straight line 3), the dependence of the circumferential force \(P\) on the feed per tooth \(S_z\) is a straight line that does not pass through the origin. The intercept cut off by it on the ordinate axis corresponds to the value of the force on the flank surface in the direction of cutting.

When machining copper over a wide range of changes in cutting conditions and tool geometry, the constant-temperature condition corresponds to different chip shrinkage, and it is greater the smaller the feed. It follows from this that, at constant temperature, the cutting forces will not increase in proportion to the increase in feed; the dependence \(P = f(S_z)\) at \(T = \mathrm{Const}\) will not be a straight line, but some curve (Fig. 2, curve 1), and, consequently,

the separation of forces into two groups at a constant temperature cannot be carried out. The separation of forces into forces on the front and on the rear surface when machining copper can be carried out only under a regime corresponding to constant chip shrinkage. In this case (Fig. 2, curve 2) the dependence \(P=f(S_z)\) is a straight line and, consequently, the cutting force changes in direct proportion to the cross-section of the layer being removed.

Fig. 2

For the two remaining non-ferrous metals—brass L62 and duralumin D-1—as analysis of the experimental material has shown, the regime of constant temperature corresponds to constant shrinkage only at positive rake angles. Therefore only for these conditions can the forces be separated into forces on the front and rear surfaces under the condition of constant temperature. In the general case, however, in milling non-ferrous metals, constancy of temperature does not correspond to constancy of chip shrinkage, and the separation of forces should be carried out not at constant temperature but at constant shrinkage.

LITERATURE

1. Cutting of Metals and the Tool. Edited by A. M. Rozenberg. Mashinostroenie, Moscow, 1964.

2. A. M. Rozenberg, G. L. Kufarev, Yu. A. Rozenberg. New relationships for calculating cutting forces in milling. Machinability of Heat-Resistant and Titanium Alloys. Proceedings of the All-Union Interuniversity Conference. Kuibyshev, 1963.

3. A. M. Rozenberg, A. N. Eremin. Elements of the Theory of the Metal Cutting Process. Mashgiz, 1956.

4. A. I. Promptov. Dynamics of High-Speed Milling of Steels with Face Mills. Dissertation. Tomsk, 1953.

5. A. M. Rozenberg, G. L. Kufarev, Yu. A. Rozenberg, A. A. Kozlov, S. I. Takhman. Calculation of cutting forces in face milling. Izv. TPI, vol. 138, 1966.