On the Influence of Tool Material Properties on Chip Shrinkage in Steel Cutting
Abstract Generated abstract
This paper examines how the thermophysical and adhesive properties of cutting-tool materials affect chip shrinkage during steel turning. Building on earlier studies and using experimental measurements for steels 08 and 45 with carbide tool alloys, it relates chip shrinkage to average contact temperature and tool composition. The results indicate that above about 600°C, where built-up-edge formation is absent, higher tool thermal conductivity and greater adhesive capacity increase chip shrinkage and contact length, while below this temperature stable built-up edges reverse the observed ordering through changes in the effective rake angle.
Full Text
On the Influence of the Properties of Tool Material on Chip Shrinkage in Steel Cutting
M. F. Poletika, V. D. Suvorov
As was shown in works [1, 2], when machining steels the properties of the cutting-tool material determine not only the intensity of its wear, but also the characteristics of the chip-formation process. A more in-depth investigation of the influence of the properties of tool material on the parameters of chip formation and on the contact characteristics of the cutting process was carried out by the authors of the present article [3, 4, 5]. Using copper, lead, and aluminum as the materials being machined, and widely varying the properties of the tool materials—including by applying galvanic coatings to the cutting surfaces of the tool—it was possible to separately evaluate the influence on the cutting process of the adhesive and thermophysical properties of the tool material.
When machining steels with high-speed-steel and carbide tools, the above-mentioned properties of the tool material vary within relatively narrow limits, and therefore the corresponding changes in chip shrinkage and other characteristics of chip formation are not as sharp as those we observe, for example, when cutting copper with tools made of specially selected materials [3]. However, the general regularities of their variation remain the same in this case as well. With an increase in the thermal conductivity of the tool material, the length of contact between the chip and the tool and the chip shrinkage increase, while the average contact pressure decreases; the same picture is also observed with an increase in the adhesive capacity of the tool material with respect to the work material.
Two-carbide hard alloys are less thermally conductive than single-carbide ones. The adhesive capacity of tungsten carbide with respect to iron and its alloys is higher than that of titanium carbide. Taken together, both of these circumstances allow one to suppose that, when machining steel with tools made of single-carbide alloys, chip shrinkage and cutting forces will be higher than for tools tipped with two-carbide alloys.
Furthermore, since, with an increase in the cobalt content in a hard alloy, both its thermal conductivity and its adhesive capacity with respect to iron increase, it may be assumed that chip shrinkage and cutting forces will, for example, be higher for a tool made of alloy T5K10 than for a tool made of T15K6.
The considerations presented are confirmed by experimental data. Figures 1 and 2 show the results of measuring chip shrinkage as a function of the average contact temperature when machining two steels: steel 08 and steel 45. We see that at temperatures above \(600^\circ\mathrm{C}\), that is, in the temperature range that excludes built-up-edge formation, the shrinkage curves are arranged in full agreement with the observations made above.
Fig. 1. Dependence of chip shrinkage on the average contact temperature when turning steel 08: \(\gamma=10^\circ\);
\(t=2\) mm; \(S=0.43\) mm/rev
Fig. 2. Dependence of chip shrinkage on the average contact temperature when turning steel 45:
\(\gamma=10^\circ\); \(t=2\) mm; \(S=0.34\) mm/rev
At temperatures below \(600^\circ\mathrm{C}\), when the cutting process is accompanied by the formation of a stable built-up edge on the tool, the arrangement of the branches of the curves changes to the opposite. Shrinkage becomes lowest for the tool made of alloy VK8 and highest for the T15K6 tool. This picture does not contradict what was said earlier. As is known [5], the average (effective) rake angle during cutting under conditions of built-up-edge formation, which determines chip shrinkage and other characteristics of chip formation, depends on two factors: on the actual rake angle of the built-up edge and on the stability of the latter. With an increase in the stability of the built-up edge, the effective rake angle increases.
An increase in the adhesive capacity of the tool material with respect to the chip material leads to stabilization of the built-up edge, to an increase in its stability, and consequently to an increase in
of the actual rake angle. Therefore, for the VK-8 alloy, which has the highest adhesive capacity (among the selected alloys), the actual rake angle will be the greatest, while chip shrinkage, conversely, will be the smallest. For the T15K6 alloy we obtain the opposite picture.
REFERENCES
-
N. N. Zorev. On the influence of the properties of the tool material on the cutting process. Moscow, Vestnik mashinostroeniya, 1953, No. 7.
-
N. N. Zorev. Problems in the mechanics of the process of cutting metals. Mashgiz, Moscow, 1956.
-
M. F. Poletika. Investigation of the influence of the tool material on the process of chip formation. Izv. TPI, vol. 133, 1965.
-
M. F. Poletika, V. D. Suvorov. On the influence of the thermal conductivity of the cutting-tool material on the characteristics of chip formation. Scientific Transactions of the Tyumen Industrial Institute. Collection No. 3, Tyumen, 1967.
-
M. F. Poletika, V. D. Suvorov. On the influence of the chemical properties of the tool material on chip formation. Ibid.
-
A. P. Eremin. The physical nature of phenomena in steel cutting. Mashgiz, Moscow—Sverdlovsk, 1951.