PROCEEDINGS

of the Tomsk Polytechnic Institute
named after S. M. Kirov,
Order of the October Revolution and Order of the Red Banner of Labor

Vol. 225 1972

ACCELERATED METHOD FOR EXPERIMENTAL DETERMINATION OF FORCES ON THE FLANK FACE OF A TOOL IN FACE MILLING

V. V. Ovcharenko, G. L. Kufarev

(Presented by the scientific seminar of the Department of Machine Tools and Metal Cutting)

Considering the components of cutting force that arise on the surfaces of the tool, they can be divided into two groups: forces on the rake face and forces on the flank face of the tool, which are fundamentally different in the nature of their occurrence.

The need to study the forces on the flank face is due not only to the need to determine their share in the overall balance of forces, but also to the fact that, from the change in the forces on the flank face, one can judge the influence of various factors on the conditions of contact between the flank surface and the material being machined and, consequently, on tool wear along the flank surface.

In the milling process, even with large feeds per tooth, cutting is carried out at small chip thicknesses; and in full and side milling, at chip thicknesses close to zero. In such cases, the forces on the flank face must by no means be neglected. To determine cutting forces in milling by theoretical equations [1, 2], accounting for the forces on the flank face is also necessary in order to avoid substantial errors when performing calculations.

Of all the methods encountered in the literature for experimentally determining forces on the flank surface, the most widespread is the method of extrapolating force relationships to zero chip thickness, proposed by A. M. Rozenberg [3]. The more substantiated approach to separating the forces on the tool surfaces and the sufficient accuracy of this method make it more preferable than others.

The described procedure is based on the following assumptions:

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

2. The forces on the flank surface of the tool do not participate in the process of deformation of the chip metal and are practically independent of the thickness of the layer being cut.

Along with its advantages, this method also has a substantial drawback. To obtain reliable results by this method

it is necessary to carry out a large number of experiments—35–40 tests, since a constant chip-deformation regime can be isolated only when the feed and cutting speed are varied over sufficiently wide limits. Naturally, this entails large expenditures of time for carrying out the experiment, increased consumption of the sometimes costly work material, cutting tool, etc. At the same time, in order to investigate the general regularities in the variation of forces, stresses, and other characteristics of the cutting process as functions of machining conditions and tool geometry, it is desirable to conduct tests on a larger number of machined metals differing in their properties.

The proposed method for determining the forces on the flank face is, in essence, a more accelerated and simplified method than that of Prof. A. M. Rozenberg.

It is assumed here that regimes of a constant degree of deformation are simultaneously also regimes of constant cutting temperature [3, 4, etc.].

In carrying out all dynamic tests, the cutting temperature was measured by means of a natural thermocouple, and the chip shrinkage was determined from the collected chips. The cutting forces were measured by means of elastic-electric equipment with resistance sensors. The instantaneous values of cutting forces and temperature, as the tooth of the milling cutter moved along the contact arc, were recorded on the film of an MPO-2 oscillograph.

From the oscillogram one can easily determine the instantaneous values of temperature and force for different chip thicknesses. Therefore, by conducting tests at different speeds (5–7 tests) at one value of feed per tooth, it is possible to plot the dependence of force on chip thickness under constant-temperature conditions.

By the proposed method, the forces on the flank surface of the tool were determined in face milling of steels 2Kh13, 40Kh, and 45 under the following cutting-process conditions: \(V_{\text{cut}} = 30 \div 190\ \text{m/min}\); \(S = 0.05 \div 0.2\ \text{mm/tooth}\); \(B = D = 150\ \text{mm}\); \(t = 3\ \text{mm}\). Tool geometry: \(\gamma = 10^\circ\); \(\alpha = 10^\circ\); \(\varphi = 90^\circ\); \(\lambda = 0^\circ\). A single-tooth milling cutter with a T15K6 hard-alloy insert was used.

In Fig. 1, graphs are presented of the dependences of the maximum values of cutting temperature, chip shrinkage, and circumferential force on cutting speed in milling steel 40Kh with different feeds. Because of the limited scope of the article, the results obtained for steels 2Kh13 and 45 are not given in the present work.

The graph in Fig. 2 clearly confirms the constancy of chip shrinkage under conditions of constant cutting temperature. On the basis of these data, it is possible to separate the forces on the flank face both under the condition of constant chip shrinkage and under the condition of constant cutting temperature.

Figure 3 gives graphs of the instantaneous values of cutting temperature and circumferential force obtained as a result of processing the oscillogram of one test.

Having, for each machined material, oscillograms of 5–7 tests obtained at different cutting speeds with one feed, it is possible to plot the dependence of the circumferential force on chip thickness under the condition of constant temperature.

The results of force separation obtained by the proposed accelerated method were compared with the results obtained by the method of Prof. A. M. Rozenberg when carrying out a large series of tests. Analysis of the results obtained (Fig. 4) showed complete agreement of the values of the forces on the flank face of the tool determined by the method proposed...

Fig. 1

Visible labels in the figure:

• \(T\)
• Temperature, °C, on the axis \(\times 10\)
• Shrinkage
• \(P_o\)
• Circumferential force, kg
• Cutting speed, m/min
• \(V\)

Conditions shown inside the graph:

Steel 40Kh; T15K6; \(\gamma = 10^\circ\); \(\varphi = 90^\circ\)

\(z = 1,\quad t = 3\ \text{mm};\quad D = B = 150\ \text{mm}\)

Curve labels:

• \(S_z = 0.2\)
• \(S_z = 0.12\)
• \(S_z = 0.08\)
• \(S_z = 0.05\)
• \(S_z = 0.03\)

Fig. 2

Fig. 3

by us (symbols on the graphs), and according to the method of Prof. A. M. Rozenberg (solid lines on the graphs).

Thus, the use of the proposed method for separating the forces on the cutting tool, with a considerably smaller number of experiments performed, makes it possible to obtain results with the same accuracy as by the method of Prof. A. M. Rozenberg.

Fig. 4

REFERENCES

1. Cutting of Metals and Tools. Edited by Prof. A. M. Rozenberg. Mashinostroenie Publishing House, Moscow, 1964.

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

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

4. A. A. Kozlov. Milling of Nonferrous Metals and Alloys. Dissertation. Tomsk, 1965.