Vol 21, No 1 (2019)

Purpose. The use of diamond grinding wheels on a metal bond for grinding high-speed steels is recommended by most literature sources using electrophysical, electrochemical, or combined processing methods. At the same time, it is recommended to limit the field of application to the final circular grinding, due to the appearance of a defective layer on the processed surface. Its signal features include systematic chips along the cutting edge and microchips on the front surface of the samples, the size of carbide particles, individual craters or holes in the front surface, a decrease in hardness and an increase in the height of asperity profile. This paper is devoted to the determination of such technological regimes of the combined electric diamond processing of tools made of high-speed steel M2, when grinding, on which there would be no signal signs of the defect layer. The solution to this problem will allow expanding the scope of application of diamond grinding wheels on a metal bond when processing tool steels. The subject of research is the condition of the surface and cutting edge of high-speed plates of metal-cutting tools, depending on the technological modes of the combined electric diamond grinding (CEDG). The purpose of the work is to study the influence of the technological modes of CEDG on the nature of changes to the surface layer of high-speed steel tools. Materials and methods. The grinding operation is carried out on a universal sharpening machine, model 3D642E, modernized under the technology of CEDG. The following grinding diamond cup on a metal bond is used: AC6 80/63 M1 100%. The electrical parameters, studied in this range, are: ipr = 0.17…0.25 A/cm2; itr = 3.125…9.375 A/cm2, respectively. Mechanical parameters, studied in this range, are: V = 17…35 m/s; t = 0.01…0.03 mm/doub.st; S = 1.5 m/min. Grinding is performed using standard electrolyte: NaNO3 – 3 %, NaNO2 – 1 %, Na2CO3 – 0.5 %, and the rest is water. Microstructural studies are performed on microsections of the samples after etching. The surface quality is studied using scanning electron microscopy (Carl Zeiss EVO50 XVP); light microscopy (METAM LV-42); roughness is determined using a profilograph-profilometer (Abris-PM7); HRC hardness is determined using a hardness tester (600 MRD). Results and discussion. It has been established that the best combination of technological modes, which guarantee the absence of signal signs of a defective layer and the high quality of metal-cutting tools made of high-speed steel is maintained, are the following: V = 35 m/s; S = 1.5 m/min; t = 0.02 mm/doub.st; ipr = 0.25 A/cm2; itr = 6.25 A/cm2. It is found that when processing in the recommended modes, the cutting edge is even with shallow notches, the size of carbide particles is, on average, 2…5 μm. The established modes make it possible to obtain a roughness of the front surface Ra = 0.070 μm. It is found that the obtained hardness is 6 % higher than the initial hardness and is 67…70 HRC.

Introduction. The development of modern processing technologies for structural materials has significantly increased the requirements not only for equipment, accessories and tools for implementing processes, but also for the quality of machined surfaces. Particularly acute this problem can be traced when creating products of an individual complex profile, often produced by individual technologies, which leads to the need to reduce costs while maintaining production efficiency. The most widely used parts of this type were found in shipbuilding, aircraft manufacturing, mechanical engineering, and medicine. For the mechanical (manual) processing of the metal frame during dental prosthetics, rotary instruments are used, including dental drills. They are equipped with collet chucks, in which carbide mills, grinding corundum heads on a ceramic bond and diamond heads on a metal bond are installed. Diamond heads on a metal bond are used only for processing products that are not then covered with ceramics. It is not recommended to use them for machining metal frames under ceramic coating, as diamond heads on a metal bond leave scratches in which gases can accumulate and stagnate during the ceramic firing process, leading to defects in the ceramic coating. In addition, during the treatment, the tool becomes “salted”. It became necessary to interrupt the process and clean the diamond heads in a sandblaster. Objective. The paper solves the problem associated with ensuring the possibility of using high-performance diamond heads on a metal bond for mechanical (manual) finishing of metal frames for further coating with ceramics by applying and combining known methods of electrochemical grinding and electrochemical polishing of products (hybrid finishing technologies). Results and discussion. Studies are carried out by mechanical (manual) processing of samples of steel 12Cr18Ni10Ti. On the laboratory bench we assembled, comparative tests are carried out on three methods for processing metal blanks: traditional grinding of samples with a dental diamond head, electrochemical grinding of samples with a dental diamond head and electrochemical grinding of samples with a dental diamond head followed by electrochemical polishing of samples with a round electrode made of wire DKRNM 2.5 L63 (GOST 1066-2015). Images of the surface of samples processed in different ways and the chemical composition of the surface of the sample are obtained on a Hitachi TM4000Plus desktop scanning electron microscope. Measurement of the roughness of the treated surface is carried out on a Model 130 profilometer. Applying an electrochemical grinding method with a diamond head on a metal bond followed by electrochemical polishing with a round electrode eliminates scratches from the diamond head treatment and creates the necessary surface topography to provide a mechanical connection between the metal frame and ceramic. Analysis of the results of comparative studies allows to conclude that the best, in terms of quality, processing efficiency and conditions for providing surface topography, suitable for ensuring a stable mechanical connection between the metal frame and ceramics, is a hybrid processing technology on one processing equipment using diamond electrochemical grinding head on a metal bond, followed by electrochemical polishing with a round electrode.

Introduction. Tooling equipment plays a major role for machine-building enterprises. The most important part in equipping the metal-cutting tool is the replacement of the cutting part from the group of high-speed steels by the cutting part made of hard alloy, which in turn gives an increase in durability and overall performance of the cutting tool. When cutting power of the tool increases then its changeability decreases. That is the reason why it is more rational to use complete approach which takes into account designing of a tool using a hard alloy WC–Co. Designing, production and test of gear cutting tools, development of cutting modes should be carried out in relation to a particular workpiece and its material. The purpose of the work: to study the influence of the geometry of the removable insert on distribution of dangerous tensile stresses. The paper studies the results of the calculation of the stress-strain state in a removable plate made of a WC-Co material. Tension and compression zones are observed on the main cutting edge. The concentration of dangerous tension stresses is located in the transition zone between the straight side cutting edge and the top, since there is the greatest constraint on cutting in this zone. Accordingly, the greatest destruction will occur in this zone. It is important that in this part of the cutting edge there will be the largest wear on the back surface. The research methods: ANSYS finite-element analysis program is used to detect dangerous tensile stresses s1. Results and Discussion. Analysis of the stress distribution isolines showed that tensile stresses along the front surface of the removable cutting insert are reduced due to the fact that each removable cutting insert cuts off its part of the material. First, a narrowed cutting insert enters the work, which cuts off the metal with the upper part of the cutting insert, and then an understated cutting insert operates, which works with side cutting edges. As a result of the study, it was found that with a progressive cutting scheme, compared to the standard one, in which the original profile of the counterpart rack was made according to DIN3972 during gear milling, dangerous tensile stresses in cutting carbide plates are significantly reduced.

Introduction. The solution on improving the speed and volume of cargo transportation by railway transport is connected with increased requirements to critical parts of the rolling stock. One of such details is a side bearing cap. The cap is installed on the support in the truck bolster and designed to hold a car body of the lateral forces. Method. The previous studies have shown that gray cast iron, in particular, SCH35 grade, is an effective material with satisfactory performance properties under high loads. Gray cast iron contains graphite which in the frictional couples can serve as cutting oil. However, these properties are not always sufficient for the buffing loading conditions, subjected to the slid bearing cap. Results and Discussion. Achieved results and the patent search allowed declaring the resulting iron as an invention (patent number 2562554). In the course of the investigation, it is possible to establish the influence of the concentration of alloying elements of nickel and molybdenum on the mechanical properties of the developed cast iron. The quality of the new iron and its characteristics are assessed within laboratory and stand tests. Polished sections analysis of non-etching samples allowed identifying graphitic phase. Study of metal matrix has shown that metal backing of the cast iron has perlite alongside with acicular perlite. Besides, this iron CHMN-35M metal matrix has perlite-ferritic metal backing. As reflected by the results, in all combinations iron of CHMN-35M grade has shown the best (approximately in 1.5 times) wear resistance in comparison with SCH35 iron. Therefore, the total value of accumulative wear (hob and shaft wear) in couples with CHMN-35M iron is also lower.

Introduction Currently, a significant part of the cutting elements of the processing equipment is made of composite materials based on a metal matrix with dispersed ceramic inclusions. As a rule, such compositions are synthesized by powder metallurgy methods from a mixture of powders with a characteristic particle size from a few micrometers to tens of micrometers. Durability of cutting element is determined by the mechanical properties (including strength, hardness and fracture toughness) of thin surface layers of the composite. It is known that mechanical properties of the surface layers of the composites with microscale reinforcing ceramic inclusions are significantly inferior to the properties of these same compositions with characteristic sizes of reinforcing ceramic particles of tens to hundreds of nanometers. One of the successful ways to solve this problem is to modify the structure of the surface layers of synthesized composite with microscopic ceramic inclusions by the method of high-energy pulsed electron-beam irradiation in inert gas plasma. In the previous papers, the authors have shown that such processing leads to qualitative change in the structure of the surface layers, namely, to multiple crushing of original stochastically packed ceramic inclusions, their dissolution and subsequent precipitation in the form of regularly packed columnar particles with the preferential orientation normal to the surface. The change in the parameters of the internal structure determines a significant change in the mechanical properties of the surface layers and requires detailed parametric study. The aim of the work was to numerically study the influence of the key structural parameters, namely, the type of packing, the size and non-equiaxiality of ceramic particles on strength and fracture toughness of the modified surface layers. Results and discussion. The performed numerical analysis has revealed the key factors that determine the increase in the mechanical and tribological properties of modified surface layers of metal-ceramic composites. These are the features of packing and geometrical characteristics of ceramic inclusions. We showed that multiple decrease in the size of inclusions together with a change in their shape from equiaxial to substantially non-equiaxial and regular packing of inclusions with a preferential orientation normal to the surface lead to change in the pattern of stress distribution under compression from dispersed to frame-like as well as to elongation and complication of crack paths. This results in increase in the values of strength, yield stress and strain hardening of the surface layers. We explained that by varying the degree of non-equiaxiality of ceramic inclusions it is possible to achieve a necessary balance of competing mechanical characteristics like strength and fracture toughness.