Potakhov D. A.

Petersburg State Transport University, Russia

Strength Evaluation of cutting tools for wheel lathes

Worn wheel sets surface riding profile is periodically restored by machining using a cutting tool equipped with removable carbide plates. The performance of recovery processing is often limited by the lack of strength and durability of cutting tools, as evidenced by statistics about the use of machining equipment. The cutting tool durability reduction is also caused by the increasing hardness and strength characteristics of the wheel steel that increases its consumption [1-3] and, as a result, increases the cost of repairing the wheels. In practice, the cutting modes are often reduced to prevent the destruction of cutting tools when turning the wheels. Therefore, increasing the strength of the tool's cutting surface is a very important issue. Studies were performed to evaluate the stress-strain state and the strength of the cutting tool in the process of force and temperature-force loading on the basis of a systematic approach for different operating conditions, based on which the shape of cutting edge is proposed, that provides the lowest tensions in the body of the plate during the wheel turning.

The key strength values of cutting tools have been developed mainly by the accumulation and analysis of a large amount of experimental data. Analytical description of all the processes, and in particular the boundary conditions when cutting materials, only until recently allowed to establish functional relationships with a lot of assumptions. The use of numerical methods made it possible to switch to the more accurate solution of engineering problems, but the complexity of an accurate analytical description of the boundary conditions for the different methods and processing conditions hinders their widespread usage. SolidWorks system, which uses numerical methods based on the finite element method [4], provides a wide range of integrated tools of engineering analysis, using specialized calculation modules of CAD system. It can take the complex boundary conditions of cutting into account and give a fairly accurate result in comparison with the real process.

The problem of the tool's strength is primarily related to the definition of its stress-strain state under the loads, that appear during cutting the materials. In general, the tensions in the contact area of the cutting tool are defined by the contact tensions on the front and rear surfaces as well as the rounded contour of the cutting edge. The examination of the failure mechanism of tool materials makes it is clear that the most common method of the strength calculation is the calculation using the allowable tensions of the first kind. In general, the tensions of the first kind in the cutting surface are defined as the sum of tensions that appear under influence of cutting forces and temperature field and residual stresses that arise during the manufacturing of the tool material and sharpening [5]. The applied loads determine the main stresses. Further, according to the theory of limiting stress states by Pisarenko-Lebedev [6], the equivalent stresses are defined, ie uniaxial tensile stresses, that are equally dangerous th the given the complex stress state. The maximum equivalent stress is compared to the permissible stress, that takes the safety factor into account. To simplify the calculations the influences of the temperature field and residual stresses are usually ignored. The practice of the tool usage shows that in many cases they are the heat loads that determine its strength and durability. Given this fact, the model considered the thermal loads at the contact surfaces of the cutting tool. The research results demonstrate the significant reduction of safety margin, taking into account the influence of temperatures, accompanying the process of restoring the wheel profile. The pattern of distribution of equivalent stress contours in the body of the cutting tool is determined, based on an analysis which revealed the pockets of stress concentration. The safety factors of carbide cutting plate of the standard form in the processing of the wheels of varying hardness are analyzed.

At the present stage of development of means of computer simulation the process of designing any product cannot be imagined without conducting various types of engineering analysis, such as the strength calculations, modeling of kinematic mechanisms or checking the behavior of the product according to the different thermal and other conditions. Engineering calculations are designed to reduce the time spent to the search of the rational design solutions and also to minimize the number of full-scale tests, and as soon as possible to get the best result. [7]

In the SolidWorks system with the application of the design study, the geometry of the cutting tool was considered. The geometry optimization was carried out for removable multi-faceted plates based on the data of stress-strain states in the chip formation zone. The following plate geometry parameters were chosen as the research variables: the front angle, the reinforcing chamfer angle and its width. By solving the optimization problem the rational variant of geometry was found, which provides the lowest stresses in the plate body from the wheels turning with temperature and force influence. This will improve the efficiency of the cutting tools and performance of the mechanical operation of turning of railway wheels by raising the modes of the profile recovery. In this case, the likelihood if the tool breakage is reduced, as well as the cost of its purchase in case of working on the applied modes.

References:

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2. Ivanov, I.A. Improving efficiency of rail transport wheels at repair by technological methods / I.A. Ivanov, S.V. Urushev, M. Sitazh, A.M. Budyukin. – St. Petersburg: Petersburg State Univ. of Railways, 1995. – P. 124.

3. Potakhov, D.A. Use of wheel sets of increased hardness on rolling stock / D.A. Potakhov // Petersburg Transport University. – 2013. – №1 (34) – Pp. 139-147.

4. Chaskalovic J. Finite Element Methods for Engineering Sciences. – Springer, 2008. – P. 267.

5. The development of the science of metal cutting / ed. by N.N. Zorev. – Moscow: Mashinostroyeniye, 1968. – 416 p.

6. Pisarenko, G.S. Deformation and strength of materials under complex stress state / G.S. Pisarenko, A.A. Lebedev. – Kiev: Naukova Dumka, 1976. – P. 415.

7. Alyamovskiy, A. A. Engineering calculations in Solidworks Simulation / A. A. Alyamovskiy – Мoscow: DMK Press, 2010. – P. 464.