Research of bimetallic cutting tools and development of production technology

. This article presents studies related to the development of the technology of obtaining bimetallic plates for obtaining external grooves by the model gas-spinning casting method. In the scientific work, the mechanism of formation of the joining of the bimetallic composition consisting of XVCG steel and 40XL steel was investigated, consequently, partial melting of the deposit is observed, as a result of the interaction of the liquid metal with the constituent deposit (insert) of the bimetallic composition, and as a result, a single joint occurs in the intermediate zone characterized by its composition and structure between the steel and the components of the compound


Introduction
Solid multi-blade cutting tools are now a solid volume, and certain technological operations are superior to other operations.Despite the greatest relative consumption of expensive tooling materials and the loss of operability due to the breakage of one tooth of the tool, these tools have some undeniable advantages.The most important of these achievements is the production of multi-tooth tools with a small pitch and the operation of the tools with high stability and reliability, which ensures high quality and precision in the processed surfaces, which is associated with the smoothness of the milling process, high uniformity and the possibility of multiple sharpening.It can be said with great confidence that this tool shows a monopoly in clean and precision processing, but its use in other operations remains high [1][2][3].One of the more important aspects is the possibility of making devices of various shapes and sizes, including several tens of millimeters.
In addition, the fact that the integrated tool can be sharpened multiple times makes it possible to choose the optimal angle of the cutting wedge for each processed material and thus creates the possibility of full operation of the tooling material.
In terms of reliability, multi-shaped multi-blade tools are made integrally.As an example, we can show worm, slotted, and modular milling cutters, shaped milling cutters, taps, and plates, but we can emphasize that the list also includes tools from the list of tools given above [4][5][6][7][8][9][10][11][12][13][14].Thus, from a practical point of view, we have to look at the construction of all-around cutting tools as objectively necessary in connection with the provision of high requirements such as geometry, accuracy, and stable operation of the tools.
The integral cutting tool, in turn, does not meet the conditions of saving valuable tooling materials, and their production technology is contrary to the requirements in terms of resource and energy saving [4].
The creation of cutting tools consisting of assemblers and organizers is logically the stage of its improvement.
The construction of a compound milling cutter with constituent cutting plates (blades) made of high-speed steel or hard alloy plate undoubtedly leads to the economy of tooling materials.But the small number of teeth compared to integrated tools is explained by the fact that the condition for fixing elements and cutting plates requires additional space for their placement.This, in turn, leads to an increase in the number of pitches between the teeth, which ultimately increases uneven milling and vibration during cutting [3][4][5][6].

Material and methods
The main goal of replacing solid cutting tools with sheet metal processing tools is to reduce the consumption of rare tool steels.Therefore, it was not difficult to choose the material for the working elements, that is, the working, and cutting elements of the metal-layered composite tools.40 XL and XVCG steels according to GOST 5950-83 for cutting elements of round plates (table 1).Insert -the working element of the composition made of tool steel is made of graded rolling with mechanical processing.But technologically and economically, it is desirable to make them from specially shaped rolls, which in turn leads to a reduction of metal that is additionally lost.Finished elements are cleaned of oils.Degreasing is carried out in laboratory conditions with a solution of caustic soda and acetone, and in production conditions in an ultrasonic bath (8-10 minutes in chlorine, then washing in water solutions of Na2CO3, Na3PO4 with added emulsifier) [7].After degreasing, the castings are dried, then coated with a layer of flux that has a binder.Flux is dipped into it and covered, and the thickness of the film layer is up to 0.5...0.7 mm.Boron (Na2B2O7) was used as a flux for cutting elements made of XVG, and XVCG steels, and a mixture of boron with potassium fluoride (90% Na2B2O7 + 10% KF) was used for cutting elements made of high-speed steel.Fine-grained flux powder is mixed in a 4% alcohol solution of polyvinyl butyral after 15-16 seconds according to the viscosity shown on the viscometer.The flux-coated ingot is dried again and placed in a press mold.
Based on the results of studies on the technological operations of the production of multi-blade tools with a cast metal layer, a block diagram of the technological processes of the casting of these tools was developed (Fig. 1).The developed block-scheme model serves as a basis for the preparation of the technological process of obtaining various types of multi-blade tools by gas-spinning casting method.Qualitative phase X-ray structural analyzes were additionally performed in Fek radiation on the DRON-2.0device [16].
The macrostructure of the composition was studied using the MBC-2 device, and the integrity of the composition and its quality were determined in this analysis.The joining of the intermediate layer of the composition was studied in MIM-8 and Neofot-21 brand metallographic microscopes at magnifications from 100 times to 1500 times.
The change in the properties of the intermediate layer of the composition on the crosssectional surface was evaluated by the microhardness distribution (PMT-3 microhardness measuring device, P= 50 g load, h=0.1 mm).

Results and discussion
Control batches of M30x1.0 and M30x1.5 and M30x2.0 (Fig. 2) plates were prepared to study the formation of a bimetallic cast composition consisting of tool steel and structural steel, taking into account all improvements.The shape and dimensions of the composition insert correspond to the drawings (Fig. 2, b).The resulting foam models in the press mold (Fig. 3) were attached to the collector using a fastener, 6 pieces for the M30x1.0plate and 7 pieces for the M30x2.0plate.To reduce the dimensions of the height gauge for the new M30 size plates, the dimensions of the fuses have been proportionally reduced, for the controlled plates their surface is 1.2...1.5cm 2 , and for the new variants 0.6......0.8 cm 2 .
The reduction of the cross-sectional area is explained by the reduction of the filling speed when filling the mold with liquid metal and the elimination of the occurrence of gas voids, in this case, when increasing the filling speed with liquid metal, expanded polystyrene does not have time to fully gasify and is retained by the liquid alloy [8][9][10][11][12][13][14][15][16].
As a liquid alloy, we used 40XL steel, heated at a low temperature.Castings from similar foam models are shown in Fig. 4, a, b.At this stage, very important and necessary research was carried out -assessment of the permeability level.casting was 1.5 ... 2.0%, which corresponds to the coefficient of permeability of ordinary steel castings.The coefficient of permeability in terms of internal dimensions is small and equal to 1.0...1.5%.
Research and development works have been done to evaluate the strength and reliability, research of structures before and after heat treatment, micro-hardness distribution, and determination of joint stress state of all M30 size insert castings -finished XVCG steel cutting element and 40XL steel body.
The results of the shear resistance test are shown in Table 2 and characterize the strength of the joint.The shear force in the M30x1.0plate is 1.5...2.0 times greater than in the M30x2.0plate, and is 14.2...18.6 kN and 8, 8.....11.6 kN respectively (Table 2).However, when we calculate the shear strength concerning the actual contact surface in the joint, it is approximately the same for all sizes of M30 plates and varies in the range of 9.7...14.4 MPa.
The reliability of the joint in the composition was evaluated based on macrostructural analyzes (Figure 5), and through these analyzes, it is possible to discuss the integrity of the joint formed by the body and the body in the bimetallic plate with all contact surfaces.Studies have shown that the joint is intact on different surfaces of the bimetallic composite deposit height, and especially along the entire perimeter of the bottom, tail portion of the composite, along the upper toreted surface (relative to the casting of the metal into the mold) (Figure 5).In the lower border of the composition, except for the tail part, there is a violation of the integrity of the composition in the composition.Here, the situation is mainly related to the positive effect of the additional metal volume up to 2 mm thick, for the same purpose, this volume is removed on the toretized surfaces in steel castings (Fig. 4) [16][17][18].
Microstructural analysis of the composition in the cast state.On the contact surface of the steel that makes up the composition of composition with the deposit, a single system of pearlite grains with a cementite network in the lower and tail part is formed, which, in turn, is caused by the carbonization of the liquid alloy with the dissociation products of Thermal treatment in the low-temperature release scheme transforms the structure (Fig. 7): pearlite turns into a martensite-cementite mixture.In this case, this structure is characteristic of the deposited material in the composition, but it occupies almost the entire volume of the intermediate zone (0.2...0.4 mm) and then passes into the trostit-martensite structure, which is characteristic of the condition of incompletely obtaining steels up to the eutectoid.The results obtained on the determination of microhardness of the intermediate layer of the composition confirmed the results of metallographic studies, in this case, the thickness of the intermediate zone of the composition in the M30 plate was 0.2...0.4 mm (Figures 8  and 9).X-ray determination of the level of macro stress that occurs in the cast bimetallic composition made of XVCG steel.When transitioning from the M30x1.0plate to the M30x2.0plate, the compressive stress is partially replaced by the tensile stress, which, in turn, decreases the total volume of the metal when the plate body changes to smaller dimensions.and, in turn, is related to the change of thermal conditions in the formation of the compound.Heat treatment leads to an increase in the absolute value of the macro stress without changing the nature of the distribution [18][19][20].
2. The condition of the formation mechanism of the intermediate zone between the surface of the cutting deposit and the liquid structural alloy in the cast metal layered composition was determined.As a result, the thickness of the intermediate layer increases to 0.2 -0.4 mm, and the hardness after heat treatment increases from 300 HV to 700 HV.

Fig. 1 .
Fig. 1.Block diagram of the technological process of casting bimetallic cutting tools, the working element of which consists of high-speed tool steelThe mutual contact-intermediate layer formed by the liquid alloy of structural steel, which makes up the composition, with the deposit made of tool steel, was involved in comprehensive research.The composition, structure, and properties of the intermediate layer of the composition were studied sequentially.Qualitative phase X-ray structural analyzes were additionally performed in Fek radiation on the DRON-2.0device[16].The macrostructure of the composition was studied using the MBC-2 device, and the integrity of the composition and its quality were determined in this analysis.The joining of the intermediate layer of the composition was studied in MIM-8 and Neofot-21 brand metallographic microscopes at magnifications from 100 times to 1500 times.The change in the properties of the intermediate layer of the composition on the crosssectional surface was evaluated by the microhardness distribution (PMT-3 microhardness measuring device, P= 50 g load, h=0.1 mm).

Fig. 7 .
Fig. 7. Microstructure of the joint of XVCG grade steel and casting 40XL steel in the M30 cast bimetallic composition plate (in the heat-treated state)

Fig. 8 .Fig. 9 .
Fig. 8. Distribution of microhardness in the intermediate layer at the junction of XVCG steel and 40XL steel in the form of M30 round bimetallic composite plate before heat treatment

Table 1 .
Chemical composition of non-heat-resistant tool steels with high indentation depth for cast metal layer composition to deposit visible plaques

Table 2 .
The results of shear strength of XVCG steel compared to 40XL steel in the joints of M30 and M30x2 cast round plates (after heat treatment)