Welding Of Electrical Contacts Research Articles

PROGRAM AND ANALYTICAL COMPLEX OF THE INDUSTRIAL SAFETY AND HEALTH ANALYSIS SYSTEM

Aim. To investigate the quantitative characteristics of magnetic fields created during electric contact welding by various methods: contact point, arc-contact, capacitor point, contact-contact continuous and pulsating reflow. The problem being solved is the lack of necessary information on the electromagnetic safety of the specified welding methods. Methodology. A description of the proposed methodical approaches to determining the levels of magnetic fields, means of measuring them, and methods of assessing their impact on the welder's body is provided. Based on the analysis and processing of the received oscillograms and spectrograms of magnetic fields, measurements of their quantitative characteristics were performed. To determine the general level of the multifrequency magnetic field that occurs during contact welding, the proposed generalized indicator of the level of the magnetic field was used. Implications of research. It was established that during contact spot welding with a stationary machine, the magnetic field level exceeds the maximum permissible value at the workplace in the range of 50-1000 Hz at a distance of 0.3 m from the welding electrodes. During manual welding by this method, the level of the magnetic field exceeds the permissible level in the frequency ranges of 5-50, 50-1000 Hz directly near the electric cable. Condenser spot welding with direct current is characterized by exceeding the maximum allowable MP at the workplace in the high-frequency range of 1000–10000 Hz. During arc-joint welding at the workplace, exceeding the maximum allowable levels of the magnetic field was not detected. Practical implications. It is shown that the spectral composition and magnitude of the magnetic field signal is determined by the welding method itself and the initial parameters of the power sources. The obtained results can be used in the field of welding production and labor protection for the improvement of contact welding technologies and the development of measures to protect welders from the magnetic field.

COATINGS MADE BY ELECTRIC CONTACT WELDING OF METAL POWDERS

Powder additive materials for electrocontact welding are rarely used due to the loss of expensive powder during welding and the difficulty of cooling the welding zone. However, the use of powder materials allows you to obtain a variety of coating properties and increase the adhesion strength of the powder coating to the base metal of the part. (Research purpose) The research purpose is evaluating the effect of the composition of powder on the hardness, adhesion strength and wear resistance of coatings obtained by electrocontact welding. (Materials and methods) Metal powders of the FBH-6-2, PG-C1, PG-C27M, Sormayt, PZHR3.200.28, PR-NH17SR4, PZH1S brands were used. The adhesion strength was determined by the cut-off method on a P-125 brand press. Hardness was evaluated according to the standard Rockwell method on a TC-2 hardness tester; wear resistance was evaluated on a SMC-2 friction machine. (Results and discussion) It was revealed that the greatest adhesion strength to the base metal of the part (steel 45) is observed in the coating of the powder of the PGS-27M brand during electrocontact welding on "hard" modes. The highest hardness was recorded in the coating of "Sormite" powder. The least wear was observed in coatings obtained by electrocontact welding of powder compositions PZHR3.200.28+Sormayt and PZHR3.200.28+VK8. (Conclusions) The use of powder additive materials to obtain coatings on machine parts by electrocontact welding makes it possible to obtain coatings that are superior to coatings obtained by electrocontact welding of steel tapes. The adhesion strength of steel tapes welded by electric contact welding on "soft modes" is about 100-200 millipascals, which is 1.2-1.4 times less than the adhesion strength of powder coatings. The hardness of coatings made of steel tapes and wires reaches HRC 60, and powder coatings up to HRC 65.

Determining patterns in the generation of magnetic fields when using different contact welding techniques

The object of this study is the quantitative characteristics of magnetic fields induced during electric contact welding in various ways: contact point, arc-butt, capacitor point, contact-butt continuous, and pulsating fusion. The problem to be solved is the lack of necessary information regarding the electromagnetic safety of these welding techniques. A description of the proposed methodological approaches to determining the levels of magnetic fields, their measurement tools, and methods for assessing their impact on the welder's body is given. Based on the analysis and processing of the acquired oscillograms and spectrograms of magnetic fields, their quantitative characteristics were measured. To determine the general level of the polyfrequency magnetic field arising at contact welding, the proposed generalized indicator of the level of the magnetic field was used. It was established that during contact point welding by a stationary machine, the level of the magnetic field exceeds the maximum permissible value at the workplace in the range of 50–1000 Hz at a distance of 0.3 m from the welding electrodes. When manually welding in this way, the magnetic field level exceeds the permissible level in the frequency bands of 5–50, 50–1000 Hz directly near the electrical cable. Capacitor spot welding with direct current is characterized by exceeding the maximum permissible MP at the workplace in the high-frequency range of 1000–10000 Hz. During arc-butt welding, no excess of the maximum permissible levels of the magnetic field was detected at the workplace. It is shown that the spectral composition and magnitude of the magnetic field signal is determined by the welding technique and the initial parameters of power supplies. Orimani results can be used in the field of welding production and labor protection.

ТЕХНОЛОГИЧЕСКИЕ ПРОЦЕССЫ ПОЛУЧЕНИЯ ФУНКЦИОНАЛЬНЫХ ПОКРЫТИЙ МЕТОДОМ ЭЛЕКТРОКОН ТАКТНОЙ ПРИВАРКИ

Electric contact welding (ECW) is a promising resource-saving technology for obtaining functional coatings from the waste of tool-making and machine-building production. A clear methodology is a pre-requisite for selecting the materials, equipment, and tools used; stating the order and describing the operations (transitions) performed; and choosing technological modes (parameters). To develop a technique for obtaining, strengthening, and restoring machine parts, the authors studied functional coatings obtained by electric contact welding at the 011-1- 10 “Remdetal” installation. The duration of the welding pulse and pauses was set using the RVI-501 controller. The welding current strength was calibrated through a strip made of 5 mm thick copper grade with the welding current meter IST-02. Based on the analysis of the ECW zone resistance, he authors found that, for the steel belt U12, the optimal value of the compression force of the welding electrodes on the plowshare made of 65G steel will be 1.7 kN. To ensure the highest effi ciency of the ECW process and complete overlap of welding sites, and taking into account the mutual movement of electrodes and parts, the authors present the relationships that help pre-set the main parameters of electrical contact welding for all circuits and equipment options: the strength of welding current, its fl ow time and the pause between pulses, the compression force of welding electrodes, welding speed, overlap coeffi cients of welding points fl ow rate of the cooling liquid and their infl uence on the process fl ow and the quality of coatings obtained. The presented algorithm can be used in machine-building production and, in particular, repair production for designing technological processes of obtaining functional coatings during the hardening and restoration of machine parts.

Phase and structural transformations when forming a welded joint from rail steel. Report 3. The use of thermokinetic and isothermal diagrams of austenite decomposition for selection of optimal modes of electric contact welding

During contact flash welding of rails, the metal is heated and continuously cooled in the zone of thermal influence. Accelerated heating and subsequent intensive cooling, implemented by the pulsed flashing-off method, lead to the formation of quenching structures. Subsequently, during the operation of the rails welded joint, this leads to the formation of cracks and to brittle destruction. We have investigated the possibilities of using contact heating after welding to avoid the formation of quenching structures in the metal of the welded joint made of R350LHT rail steel. The thermal cycles during welding and subsequent contact heating were recorded. The regularity of formation of the weld metal structure was established including the zone of thermal influence during pulsed contact heating for R350LHT rail steel. It is shown that contact pulse heating slows down the welded joint cooling and prevents the formation of quenching structures. However, contact pulse heating when using suboptimal modes can also lead to the opposite effect. It is determined that with a significant investment of heat by contact heating, cooling rate of the metal exceeds the critical one, transformation process passes through a diffusion-free mechanism with the formation of martensite coarse-grained structure. The use of thermokinetic and isothermal diagrams of austenite decomposition at known thermal welding cycles allows us to significantly narrow the search limits for optimal modes of contact butt welding of railway rails and subsequent contact heating. The use of optimal contact heating modes makes it possible to obtain a minimum length of heat-affected zones with reduced hardness without the formation of quenching structures in the welded joint of railway rails.

Improvement of rail strings durability used for access railways at mines

The study of the structure of welded joints of E76KhF rail steel at new modes of electric contact welding with the use of additional treatment with electric current was carried out. It was found that the structure of lamellar pearlite prevails in the weld zone. In the course of the study, the optimal welding parameters were determined, due to which it is possible to obtain the required favorable material structure.

Electric Contact Welding of a Perforated Steel Strip

Electric Contact Welding of a Perforated Steel Strip

Features of structure formation of surface layers with high content of boron on steel 15Х11МФ in the conditions of furnace and induction heating

The results of obtaining borated layers on 15H11MF high-alloy steel under equilibrium and non-equilibrium heating conditions are presented. Equilibrium conditions were achieved by slow furnace heating (with a heating rate of 0.1 oC/s), non-equilibrium – by induction heating (with a heating rate of 100 oC/s). The heating was controlled by measuring the thermoelectric power by a thermocouple welded to the surface of the sample by electric contact welding. The signal from the thermocouple was digitized by the ADC and transmitted to a computer where, at high speed, an array of data of temperature-time dependence of the process was formed. Furnace heating was carried out in a laboratory electric furnace at 1130 оС ± 5 оС, 1150 оС ± 5 оС and 1160 оС ± 5 оС. Induction heating was carried out to temperatures of 1180 oC ± 20oC, 1200 oC ± 20oC, 1220 oC ± 20oC. The possibility of significant reduction of the treatment process from 3 hours to 2 minutes due to the intensifying action in non-equilibrium conditions of structure formation is shown. Boron saturation came from the paste. Saturating paste consisted of 60% boron carbide, 30% NaF, 10% CaF2. The method of metallographic research shows not only the morphological differences of the obtained surface layers, but also established the predominant mechanism of boron diffusion into high-alloy martensitic steel. During furnace heating (1150оС), a solid boron with a thickness of up to 50 μm and a hardness of 15100 MPa is formed. At a depth of up to 150 μm, grain boundary diffusion is noticeable, which obviously dominates in the processes of boron saturation of high-alloy steels. At temperatures of 1160 oC and furnace heating under a solid layer of boride with a thickness of 110 μm, a two-phase zone is formed, which consists of boride and a solid solution with a thickness of 70 μm. This layer is more defective. Induction heating with boron saturation forms a thick (up to 200 μm) layer of coarse boride crystallites (18900 – 9270 MPa) with an eutectic structure (6440 MPa), which becomes coarser with increasing temperature from 1180 to 1220 оС. The ability to obtain solid hardened layers in a short treatment time makes boron saturation from pastes a more attractive alternative among other chemical-heat treatment technologies.

Investigation of pre-sprayed powders for electric contact welding

There are a number of difficulties in the electrical contact welding of powder materials: shedding of powder from the surface of a cylindrical part, impossibility of hardening the layer during welding due to flushing of the powders with coolant and unstable flow of powder into the welding zone. One solution is pre-spraying the powder in some way. (Research purpose). The research purpose is investigating the possibility of electric contact welding of metal powders preliminarily sprayed by a gas-flame method, namely, adhesion strength and losses during preliminary gas-flame spraying of powders. (Materials and methods) Powders of grades PG-NA-01, PrKhIIG4SR, PRZh3.200.28 were sprayed onto flat samples of St3 steel, polished to a roughness of Ra 1.25. The strength of powder adhesion to the base was studied by the cut method. (Results and discussion) The percentage loss of the powder as a whole is 3-23 percent for all the distances studied. The greatest powder losses appear at a distance of more than 180 millimeter from the tip of the burner for powders of grades PG-NA-01 and PrKhIIG4SR. The smallest powder losses were observed for PrZh3.200.28 powder, which totaled 3-7 percent. The maximum adhesion strength of the sprayed powders to the surface was 22.1 megapascals' when spraying the PG-NA-01 powder. The adhesion strength of powders of the grades PrKhIIG4SR and PrZh3.200.28 is small and amounts to 0.2-3 megapascals'. (Conclusions) The use of preliminary flame spraying of powders for their further electric contact welding is possible using PG-NA-01 grade powder, while the best adhesion to the base (that is more than 20 megapascals') is achieved with a spraying distance of 120-140 millimeter. The smallest powder losses during flame spraying are achieved at a spraying distance of 100-160 centimeters', at which the powder loss for the studied grades was 4-12 percent.

Methods of elimination of rails increased damage in the area of weld joints

Rail weld joints from electric-contact welding in stationary and fi eld conditions, as well as those from aluminothermic welding are weak points on tracks that are easily damaged compared with rails outside the weld joints. Currently, these weak points are the defects connected with lack of penetration in the welding area, burns at the points of poor contact of the rail foot with the current-carrying contact tips, or with defects of the weld joint machining after welding, as well as the local hardness reduction in areas affected by heat after welding, and local heat treatment after welding. Elimination of wide areas of reduced hardness at the weld joint points producing saddles, cracks, and chipping, and promoting rails damage next to such joints is a major challenge for increasing the serviceability of weld joints. This study introduces three avenues for elimination of increased damage of rails at weld joints including:• Improvement of technology and equipment for electriccontact welding and local heat treatment after welding in the stationary and fi eld conditions.• Development of technology and equipment for induction welding in the stationary and fi eld conditions.• Development of technology and equipment for differentiated induction tempering of rails preliminary welded in strings 800 m long.

Effect of process parameter characteristics on joint strength during ultrasonic metal welding of electrical contacts

Modern customer durable products are subjected to severe operating conditions and require a variety of quality electrical contacts for improved performance and service life in diverse applications. Over a few decades, ultrasonic metal welding process has evolved as a suitable manufacturing technique for large-scale rapid manufacturing of such electrical contacts. In this investigation, the welding parameters such as clamping pressure, amplitude of vibration of the sonotrode, weld time and the part dimensions such as diameter of wire and thickness of the sheet are considered for joining electrical contacts comprising of copper wire and sheet. Experiments are conducted according to the response surface method with two replications to obtain the response of T-peel strength of the joint. The effect of process parameters on the strength of joint is vividly investigated, and a process characteristic map is developed for improvement of the process to produce defect-free electrical contacts. The lower level of clamping pressure (2 bar), medium level of amplitude of vibration of the sonotrode (47.5 μm), weld time (2.5 s), diameter of the wire (1.2 mm) and thickness of the sheet (0.2 m) are found to be effective to produce electrical contacts with maximum strength of the joint of more than 220 N. The results from experiments are utilized to develop a mathematical model for prediction of strength of the joint. The results predicted by using the model are in good agreement with results from experiments.

Electric Arc Surfacing of Defective Plots of Rails in the Area of Electrocontact Welded Joint

One of the main causes for the failure of the rails of a continuous joint made by electric contact welding is defects in collapse and wear in the joint zone. We address the usage of electric arc surfacing to repair defective rails. The structure and hardness are studied of the defective areas of rails recovered by electric arc surfacing performed in one and two layers. Static tests and fatigue tests of pilot samples of rails with eliminated defects were carried out. The pilot samples with defects eliminated by electric arc surfacing meet the criteria of static strength to the same degree as the rail samples without surfacing. The surfacing technology that we examined should be adjusted by applying preheating to reduce the cooling rate of metal in the weld zone. Fatigue tests showed a positive effect from surfacing at the wear sites in the welded joint. Performance tests confirm that electric arc surfacing is promising to eliminate defects in the collapse and wear of the rails in the area of the electric contact welded joint.

Calculation of optimal modes for electric-contact welding of rails of mine haulage tracks

The choice of thermal regime is based on the exclusion of formation of quenching structures (martensite and bainite), causing additional stresses and cracks which lead to the destruction of rails. After welded joint upset and cooling at the time of reaching the required temperature it is proposed to perform quasi-isothermal exposure by passing pulses of alternating current through the welded joint. The method for calculating the quasi-isothermal exposure is described that depends on the strength of the welding current and different rails section. It is suggested that after welding the rails during quenching, a quasi-isothermal holding is carried out in the temperature range of the formation of the fine-dispersed structure by passing pulses of alternating electric current through the welded joint maintaining this temperature until the end of the transformation. It is shown that the use of quasi-isothermal exposure at a chosen temperature of 600 – 650 °C makes it possible to obtain a finely dispersed structure of the welded seam of rails of mine haulage tracks without additional heat treatment.

MODERN WELDING METHODS OF THE RAILS OF NEW GENERATION

Nowadays, the railways in the Russian Federation are moving to the path of seamless construction. The development of technologies to ensure the possibility of continuous welded rail track with the desired quality characteristics is the actual direction now. One of the key technologies for the construction, repair and maintenance of a seamless path is welding of rails, for which various methods have been developed and are used, such as: electric-contact, gas-press, induction, laser welding, friction welding, aluminothermic, electric arc electrodes, in the environment of protective gases, electroslag, powder wires, etc. The article describes the advantages and disadvantages of the main types of welding rails that are most widespread today: resistance flash welding and aluminothermic welding. It is shown that as the primary method of rails welding in Russia, electric-contact welding is used. However, in connection with the inability to weld rails in the zones of turnouts by contact machines, the use of aluminothermic welding of rails started on the railways of Russia. It has been shown that the most important factors that determine the quality and reliability of welded rails are metallurgical and welding technologies, as well as subsequent processing methods that reduce the impact of high temperature effects. The technological features of these methods, advantages and disadvantages of modern methods of solving problems in welding, as well as economic costs were considered taking into account operational properties of joints. Experience has shown that during the exploitation of welded joints made by aluminothermic method on the railway and at testing on the experimental ring of JSC All-Russian Scientific Research Institute of Railway Transport, their quality is slightly inferior of electric-contact welding. Special attention is paid to the peculiarities of welding technology for differentially thermally strengthened rails. The analysis of existing methods of rails welding allows working out the main directions of research to solve this problem.

Laser beam welding of electrical contacts for the application in stationary energy storage devices

The energy sector has been changing in the past few years, driven by the transition toward renewable energy. This affects the technologies, as well as the structure of energy production by means of a decentralized and time-dependent energy generation. The resulting effects on the power grid require local storage systems to store the surplus energy and to limit the feed-in power. For these energy storage systems, the use of commercial 26650 LiFePO4 battery cells is highly promising. Since the capacity of these cells is comparatively low, a large quantity of cells is needed to match the storage requirements. For this reason, the interconnection between individual battery cells is the basic prerequisite for the production of energy storage systems. Recent research has shown that laser beam welding is suitable for the welding of small electrical contacts. However, the welding process of 26650 cells with contacts made of nickel plated steel is very complex. The requirements regarding the heat input during the joining process are high due to a low thickness of the case in the range of a few hundredth of a millimeter and a high temperature sensitivity of the battery materials. Within this work, experiments on laser beam welding of nickel-plated DC04 steel on copper, aluminum, and steel were carried out. The electrical and mechanical properties of the connection joints were evaluated within a comparative study. For the investigation of the heat input during the welding process, the change of temperature inside the battery case was measured. The results presented in this paper show that laser beam welding with continuous wave radiation is a suitable joining process for the electrical connection of 26650 battery cells, while avoiding a critical temperature change within the cells. Electrical joints with a low contact resistance and a high mechanical strength can be achieved. Furthermore, a clamping device for battery modules consisting of 24 battery cells is presented and the application of the welding process for a large scale production of energy storage systems is demonstrated.

Laser beam welding of electrical contacts of lithium-ion batteries for electric- and hybrid-electric vehicles

Lithium-ion batteries are preferred in electric and hybrid-electric vehicles due to their high energy density. In the course of developing high performance battery systems, which consist of over a hundred single cells, the energy efficiency still needs to be increased. One promising measure concerning this purpose is to reduce the electrical losses of contacts between the lithium-ion cells using laser beam welding. This joining technology offers the opportunity to vary the contact area as well as its geometry or position in the joining zone. Nevertheless, aging effects of the cells result in a mechanical stress at the joints between the terminal and the busbar. Varying the geometrical shape of the contact area opens a high potential to reduce these mechanical stresses of the contacts within a high voltage battery. This work presents a method to optimize the addressed geometrical shape of the weld seam in order to minimize the mechanical stresses of electrical contacts. A solution is proposed to calculate the optimum weld seam shape by the use of a genetic algorithm (GA) linked with a solid mechanics FEM simulation. The GA compiles alternative weld seam shapes, while the FEM simulations evaluate their mechanical properties. The optimised result is further verified within an experimental study.

Formation of bonding regions in homogeneous metals in electric resistance welding

Based on the dislocation hypothesis of the formation of welded compound without the melting of combinable metals the theoretical model is developed of the forming of the centres of gripping homogeneous metals during the electric-contact welding. Dependences for the calculated estimation of the sizes of the centres of gripping are obtained.

Application of a wear-resistant sintered surface layer by electric contact welding

1. The proposed method for the surfacing of machine components makes it possible to produce sintered compacts of various compositions and weld them onto parts with a surface area of up to 8.5 cm2. 2. The physicomechanical properties of such a facing layer depend chiefly on the composition of the starting powder mixture, the particle sizes of its components, and the parameters of the compact sintering and welding processes. 3. Of the materials tested, the sintered alloy No. 36 possesses the highest wear resistance and hardness. 4. The production and weld bonding of facing layers by this technique lend themselves to mechanization, and all the fabrication operations involved can be automated.