**1. Introduction**

 In connection with the change in the profile geometry of the wheel tread due to mechanical wear and plastic deformations, as well as appearance of thermomechanical damages, which result from braking of the rolling stock and which occur as flat sections of cold hardening (slides) with the formation of local martensitic structures with hardness of up to 850–900 HV (white spots), there is a need for a regular reprofiling of the wheel treads. Considering the fact that Russia possesses one of the longest rail networks in the world (the second only to the USA), it is clear that the specified challenge is very comprehensive (given more than 6 million wheel sets in operation). There are two main methods of reprofiling: milling and turning. At the same time, the performance and tool life indicators of cutting tools (carbide inserts) are an important and sometimes a critical factor. Milling the profile of wheel treads is the most common process applied to machine wheel sets for locomotives and electric trains.

 The existing technology for machining wheel sets on KZH-20 machines is one of the most complex and time-consuming machining operations performed in depot conditions during maintenance and current repairs of locomotives and multiple-unit and

 subway rolling stocks. KZH-20 is a wheel-milling machine to mill wheel sets without rolling them out from under a locomotive, manufactured at the KZTZ (Kramatorsk Heavy Duty Machine Tool Building Plant, Ukraine, see **Figure 1a**). A similar pattern to restore the profile of wheels with a special shaped milling cutter with replaceable carbide inserts, except for machines of KZH-20 type, is also implemented on machines of Simmons Machine Tool Corporation (USA) and Kawasaki Inc. (Japan). The main advantages of the above method, in comparison with turning, are as follows:


Furthermore, it was found that milling, in contrast to turning, provides practically unimpeded mechanical machining of the wheel tread profile of reinforced tires and tires with increased hardness.

Despite the above advantages, the most widespread pattern for wheel milling with shaped cylindrical cutters (see **Figure 1b**) has the following significant drawbacks:


**Figure 1.** 

*Process of machining wheel treads on KZH-20 machines (a) and a milling cutter for wheel tread machining (b).* 

*Main Ways to Improve Cutting Tools for Machine Wheel Tread Profile DOI: http://dx.doi.org/10.5772/intechopen.80302* 


 The on-the-site studies found that to date, locomotive depots use various replaceable and brazed carbide inserts. The diagram to show ranges for shapes of carbide inserts used in locomotive depots in different regions of Russia is presented in **Figure 2** [1].

 As can be seen from the diagram, ISO RNGN 121200 carbide inserts used in shaped milling cutters in machines of KZH-20 type are the most widely used cutting tools for mechanical machining of the wheel tread profile. With the actual distribution of average annual consumption in absolute quantitative terms, i.e., in the weight of the consumable carbide, inserts of the RNGN 121200 type gain 53.9% of the weight of the carbide consumed at locomotive and multiple-unit rolling stock repair enterprises of the JSC Russian Railways. Meanwhile, inserts of the LNMX type are also widely used for turning the railway wheel sets with rolling out from under the rolling stock on wheel-turning machines RAFAMET S.A. (Poland) Model UBB-112, and Hegenscheidt-MFD GmbH (Germany) (Model U2000-400) [1].

The process of manufacturing critical parts of railway rolling stock (turning of wheel sets, boring of wheel bands, turning of axes, etc.) is accompanied by:


 Edge machining of workpieces under the above conditions produces elevated heating of the cutting area (up to 800–1000°C), which results in high concentration of thermal stresses directly at the contact areas of carbide inserts (for example, inserts of LNMX ISO shape) used in this process of manufacturing products for rail transport [2–7]. The studies of wear mechanisms of cutting carbide inserts with coatings of various compositions have shown [3, 9–16] that the process of wear of inserts under conditions of the high thermal stresses is accompanied by thermoplastic deformation of a cutting edge. This in turn is connected with the subsequent intense failure of coating and high adhesion and fatigue wear, which is accompanied by chipping of cutting edges or complete failure of fragile cutting part of a tool [3, 9–11, 14–16].

In this regard, the decrease in thermal stress of the cutting area by the deposition of nanoscale multilayer composite coatings (NMCCs) on the working surfaces of the tool, which reduce friction and capacity of heat sources, as well as the general improvement of the conditions of heat transfer out of the cutting area improves the tool life and the efficiency of the HPC processes. The studies of the effect of wearresistant coatings on the thermal state of the cutting system under severe cutting conditions [11–13] have shown that they reduce thermal and mechanical loads on the tool and increase its efficiency.

 The standard method for reducing thermal stress of the cutting process includes the use of cutting fluids. However, under heavy conditions of machining, the efficiency of cutting fluids decreases significantly. Besides, specialized machine equipment (including wheel turning machines and vertical turning machines), intended for manufacturing of products (wheel sets, wheel bands, axles, etc.) used in rail transport, does not use the systems of supply of liquid fluids because of high probability of their intense damage. Thus, the main objective of this study was to develop a tool system improving the efficiency of the technology of heavy machining of workpieces of rail rolling stock products by reducing the thermal stress of the cutting process and cutting tools.
