Technological support of strength and durability at the manufacture and repair of component parts for branch mechanical engineering

Abstract

This dissertation is dedicated to solving practical scientific and technological problems in the branch mechanical engineering field: Friction causes a large number of mechanical products to be damaged. Human beings have been exploring theories and methods to prolong the life of mechanical equipment and parts. The research of wear mechanism has positive significance for improving the life of mechanical parts and repairing parts. Wear is generated on the surface of mechanical equipment. The failed parts can be repaired by surface processing technology. Surface processing technology has been used in remanufacturing engineering. The research of wear and wear-resistant materials has always been the most active field of tribology research. The development of new materials and processes has been the hotspot of wear application research. The application research of surface coating and surface modification has become the most active field of tribology research. The present research focuses on wear caused by linear reciprocating motion in an open environment. It explores the theory and methodology of using remanufacturing technology to continuously improve the wear resistance and enhance the life of parts. One of the difficulties in wear research is the research on the anti-wear and anti-friction properties of coatings under extreme conditions. With the rapid development of composite surface coating theory, new coating theories appear. It is of great significance to redesign the anti-wear and anti-friction coating by using the new theory. Since electro-spark deposition (tantamount to electro-spark alloying) has the characteristics of energy saving and environmental protection, low use cost and convenient operation, it is of positive significance to combine ESD technology with composite coating theory to explore new coatings. In this study, high toughness materials, high wear-resistant materials, and friction-reducing materials are used for composite, in order to explore new friction-reducing and wear-resistant coatings. The development of pneumatic impact deposition technology can improve the traditional deposition process and greatly improve the quality of friction-reducing coating, which is a new attempt in science. This new composite coating solution reduces energy consumption and pollution, which is important for low wear and high service life of mechanical equipment. It has promotional value for parts with the same wear mechanism. It is also very important to save a lot of resources and reduce a lot of business money. The object of research is a technological process for forming functional coatings on the pin shaft of the locking mechanism for the lifting device. The subject of research is the regularities of the technological process for forming a surface with specified performance properties, which ensure the necessary quality (durability, wear resistance, workability) of the pin shaft surface of the locking mechanism for the lifting device. The purpose of the study is to improve the quality of the surface layers at manufacturing and remanufacturing the pin shaft of the locking mechanism for the lifting device of an electric car battery by forming the composite multilayer coatings of the SKH51+WC+B83 composition on its wear surfaces with the use of the method of electro-spark deposition. To achieve this goal, it is necessary to solve the following tasks: 1. To conduct an analysis of the existing modern methods and technologies for repairing component parts for branch mechanical engineering in accordance with the ESD characteristics. 2. To conduct an analysis of modern materials for electrode – tools to provide for a comprehensive assessment of the properties of the surface coatings applied to improve the overall technical characteristics of the surface. 3. To conduct a research on the formation of wear-resistant composite coatings and compare various surface properties. 4. To conduct a research of the defects of low-temperature soft metal deposition and improve the existing repair technology. 5. To investigate the effect of the ESD coating repair technology on the accuracy of the surface obtained. 6. To introduce the research results into the engineering practice of enterprise remanufacturing. In the introduction, the topic and scientific task of the thesis are described, the aims and tasks of the research are formulated, and the scientific novelty and practical value of the received results are specified, as well as information on the approval, structure and scope of work. In the First Chapter, the development of remanufacturing engineering was introduced, and several major remanufacturing common processes were compared. Because of the cost and convenience, electro-spark deposition technology was emphasized. This chapter provided an overview of the history of ESD deposition, the recent research progress and optimization of the ESD process. In the Second Chapter, the basic theories and research methods were mainly introduced. The working principle of the ESD deposition method was introduced. Three different principles of vibrating electrodes were presented. The basic theory of coating formation by the ESD method was analyzed. It included corrosion mechanism of ESD, pulse energy theory, the metal melting theory and heat transfer simplified model. Also in the chapter, there was presented the surface property testing equipment, which could perform surface morphology, elemental composition, roughness, hardness and tribological properties. Finally, experimental methods and coating deposition processes were described. In the Third Chapter, there were described the methods for increasing surface abrasion resistance coating, which have been being constantly improved. (1)Graphite deposited on the surface of 45 steel can improve the abrasion resistance of the material surface. According to abrasion width, Taguchi orthogonal method was used to find out the optimum process on the graphite deposition. Thereby, the optimum parameters of ESD process were determined, which were efficiency, voltage, current frequency and work time. Since the surface had hard phase Fe3C, the carburized surface was 59.96% less abrasion mark width than the non-carburized surface. The surface wear resistance of the substrate was increased. (2)The high-speed steel SKH51 was used for electro-spark deposition on the surface of 45 steel. The SKH51 material has good wear resistance and excellent impact toughness, which is better than that of carburized 45 steel. Therefore, the SKH51 material was used as a transition layer, so that the more wear resistant material WC can be deposited later to form a gradient coating. The normalization method and weighting factor method were used to evaluate the different performance parameters of the coating, and the optimal coating deposition process parameters were obtained. (3)Titanium and titanium alloys, Nb, and Zr were carburized on the surface, and hard phases such as TiC, ZrC, and NbC were formed in situ. The graphene oxide gel coatings were obtained by coating materials. By comparing these coatings, it was found that SKH51+WC+B83 composite coating had better coating performance. (4) For low-temperature soft metals, a new deposition process was created to enhance the surface quality. Continuous deposition was carried out with the use of pneumatic impact deposition and RC low-energy circuits. Considering graphite powder for lubrication, it tends to come off easily. (5) GO gel and sodium silicate coatings were utilized. Because graphite power and sodium silicate composite coatings had the poor abrasion resistance, GO gel coating had good wear resistance. It can improve surface accuracy and reduce friction. In the Fourth Chapter, there was described the ESD process, which was applied in the battery replacement equipment of electric vehicle. The test results of the coating for the four versions of solutions were summarized and analyzed, and the best industrial application solution was determined based on the wear resistance test. Because some of the locking device normal cannot return, a composite coating solution was proposed on the pin shafts. The formed coating not only met the requirements of wear resistance, but also had a smaller friction and a certain degree of corrosion resistance. The solution of SKH51+WC+B83 can effectively reduce the cost, reduce the pollution in the electroplating process, and additionally, it can realize the long life of the parts. In the Fifth Chapter, the research work of the PhD is summarized, conclusions are drawn and recommendations for future research are made. According to the set purpose and tasks in work the following results have been obtained: 1. When using Taguchi's orthogonal method, according to the abrasion width, the optimal parameters of the surface carburizing process of steel 45 have been set: the efficiency of 50%, the voltage of 35 V, the current frequency of 180 Hz, and the operating time of 360 s. As a result, the average wear width was 268.206 µm, and the wear depth was 2.999 µm, which is 59.96% less than for steel 45 without carburizing. 2. Using the method of normalization and the method of weighting coefficients to estimate the operating parameters of the coating at the maximum value of the objective function of 0.687887, the optimal parameters of the process of electro-spark deposition of the SKH51 coating on the surface of steel 45, namely, the current frequency of 300 Hz, the voltage of 44 V, the efficiency of 30%, and the rotation speed of 150 rpm have been determined. 3. While comparing the composite coatings of different composition, as an optimal solution, there has been recognized the composite coating formed according to the scheme of SKH51+WC+B83. With the gradient coating of SKH51+ WC, the value of the coating had a gradient wear resistance, the coating of SKH51 had a better morphology and lower roughness (Ra = 1,086µm.) The WC coating had the best wear resistance among all the schemes, and the wear width was 586.12µm. The B83 coating had a very stable friction coefficient of 0.12, which was 48% lower than that of the WC coating. Coating SKH 51+WC+B83 has a good wear resistance and low coefficient of friction, long service life and high reliability. Since the material of B83 is the outer layer of the composite coating of SKH51+ WC+B83, the wear mechanism of the optimal coating is mainly plastic deformation accompanied by slightly polishing. 4. To obtain a better surface quality when providing for a deposition of a soft low-temperature metal by the ESD method, it is necessary to use an RC-discharge circuit and the technology of gas-vibration processing, which makes it possible to control the discharge energy, not to cool the electrode for a long period of time, and to carry out a continuous process of applying a deposition. When the discharge energy is getting greater than the melting energy, the ESD coating would be able to deposit. When the discharge energy is getting less than the melting energy, the electrode performs reciprocating friction on the deposited surface. While processing, the air pressure is in the range of 0.45~0.62MPa, the proper distance of the electrode is to be guaranteed. In this case, a stable vibration frequency is of 310~350 Hz. The pneumatic impact is more stable, and a better deposition effect can be obtained. The mechanism of pneumatic deposition is to control energy through the number of impact discharges per unit time, which reduces the traditional electrode impact force and reduces the deformation of the low-temperature soft metal electrodes. In such a manner, it can enhance the quality of the surface deposition. 5. Graphene oxide gel coating can reduce coating friction and surface roughness. It has a certain wear resistance. It is a new research to modify the surface of ESD coatings with Nano-materials. It was low in cost, very effective in improving surface quality, and easily recognized by the industry. Through the research on the performance of graphene oxide gel, it has been found that the friction coefficient is 0.17, the grinding width is 1283.02μm, the surface quality is the lowest, and the bonding force is of 16.57~20.35N. 6. The ESD process has been applied in the automotive industry to discharge batteries of electric vehicles. Since some locking devices cannot return normally, a solution of SKH51+WC+B83 composite coating on the pin shaft surface of the locking mechanism for the lifting device of a battery for an electric car was proposed. It can effectively reduce costs, reduce pollution during the electro-spark deposition coating process and to ensure a long service life of the remanufactured parts. This method is cheap, easy to operate and easy to maintain, and it is recognized by enterprises. This is expected to save the company 115,000 UAH per year. Scientific novelty of the obtained results: 1. For the first time, high-speed steel SKH51 was studied as a transitional layer of the coating. In this case, the high-speed steel SKH51 has both high wear resistance and impact toughness. During the deposition process, there are almost no micro-cracks on the surface. At the same time, it has a good compatibility with WC coating and can increase the thickness of a composite coating. 2. For the first time, abrasion width method was used to research the wear resistance of ESD coatings. Due to uneven micro-textures of the ESD coating, the abrasive particles can be easily embedded in the micro-texture, which will bring large errors to measure the wear quality of the coating. The wear width is measured by the microscope, which can measure values more conveniently and accurately. 3. For the first time, the evaluation model of normalization method and weighting factors were used for comprehensive evaluation of ESD coating. Deposition quality, coating thickness, roughness, Vickers hardness and wear-resistant width were normalized. Corresponding weighting factors were determined and the total score of each candidate solution was obtained. The test solutions were evaluated to arrive at the optimal solution. The practical significance of the obtained results is to provide technical suggestions for remanufacturing of the core parts of the chassis swap battery box. The given coating scheme solves the technical problem of parts remanufacturing in mechanical engineering with a lower cost. This technical solution is expected to save the enterprise 115 thousand UAH every year.