11-24

Summary of welding techniques for MIG welding process

2022-11-24

MIG gas shielded welding: 1. Maintain 1/4-3/8 inch wire extension (length of wire extending from torch tip). 2. Use a small diameter wire when welding thin plates. Large diameter welding wire and high current welding machine are used for thick plate welding. Check the specific performance recommendations of the welder. 3. Welding the workpiece with the correct welding wire. Stainless steel welding wire welding stainless steel, aluminum welding wire welding aluminum, steel welding wire connecting steel. 4. Use the correct protective gas. Carbon dioxide is very suitable for welding steel, but it may be too hot for welding thin plates. When welding thinner materials, a mixture of 75% argon and 25% carbon dioxide should be used. Only argon can be used for welding aluminum. When welding steel, a mixture of three gases (helium + argon + carbon dioxide) may be used. 5. For better control of the weld bead, keep the wire aligned with the joint edge of the puddle. 6. When the welding operation is in an abnormal position (vertical welding, horizontal welding, top welding), the molten pool should be kept small to achieve the best control of the weld, and the smallest diameter wire should be used as much as possible. 7. Ensure that the correct wire size is used for the nozzle, liner and drive roller. 8. Always clean the welding gun liner and drive roller, so that the welding gun mouth no splash. If the welding gun is blocked or the wire feed is not smooth, please replace it. 9. Try to keep the welding torch straight during welding to avoid wire feeding problems. 10. Use both hands at the same time during the welding operation to ensure the stability of the welding gun and do this as much as possible. (The same applies to stick welding, TIG welding and plasma cutting). 11. Adjust the tightness of the spool and drive roller of the wire feeder so that it can just feed the wire, not too tight. 12. When the welding wire is not in use, it should be kept in a clean and dry place to avoid pollution and affect the welding effect. 13. Use DC reverse polarity DCEP power supply. 14. The drag (pull) torch technology provides deeper penetration and narrower welds. Pushing gun technology produces shallow penetration and wider weld.

11-23

Application of Welding Robot in Welding processing

2022-11-23

Welding robots are mostly positioning arm robots, with two types of teaching and intelligent. Teaching robot: through teaching, memory welding trajectory and welding parameters, in strict accordance with the teaching program to complete the product welding. With only one teaching, the robot can accurately reproduce each step of the teaching. This type of welding robot is widely used and suitable for mass production. For fixed stations on the assembly line. Its function is mainly to teach and reproduce, and its adaptability to environmental changes is poor. It is useless for small batch production of large structural parts on the construction site. Intelligent robot: It can automatically determine the starting point, spatial trajectory and related parameters of the weld according to simple control instructions, and can automatically track the weld trajectory according to the actual situation, adjust the welding torch posture, adjust the welding parameters, and control the welding quality. This is the most advanced welding robot, it has the characteristics of dexterity, light, easy to move and so on. Can adapt to different structures, different positions of the welding task. At present, there are few practical applications and it is still in the research and development stage. In welding robots, spot welding robots account for 50%-60%, which consists of three parts: robot body, spot welding system and control system. The degree of freedom of the robot body is 1~5, and the control system is divided into body control and welding part control. Welding system mainly includes: welding controller, welding tongs and water, electricity and other auxiliary components (underwater welding). 2 computer software applications. The application of computer software system in the field of welding mainly has the following aspects:. 1. Computer simulation technology includes simulation of welding thermal process, welding metallurgical process, welding stress and deformation. Welding is a complex process involving disciplines such as arc physics, heat transfer, metallurgy and mechanics. By simulating the various processes of welding by computer, the computer system can determine the best design scheme, process method and welding parameters for welding various structures and materials. Traditionally, the welding process is always determined through a series of tests or based on experience to obtain a reliable and economical welding structure. Computer simulation only needs a small number of verification tests to prove the applicability of numerical methods in dealing with a certain problem, and a large number of screening work can be done by the computer, which saves a lot of test work, thus greatly saving manpower, material resources and time, which is of great significance in the welding of new engineering structures and new materials. The level of computer simulation technology also determines the scope of automated welding. In addition, computer simulation is widely used to analyze the strength and performance of welded structures and joints. 2. Using database technology and expert system, the welding process design and process parameter selection, welding defect diagnosis, welding cost budget, real-time monitoring, welding CAD, welder assessment and so on are studied. Database technology has penetrated into all aspects of the welding field, from raw materials, welding tests, welding processes to welding production. Typical database systems include welding procedure qualification, welding procedure planning, welder file management, Welding materials, material composition and performance, weldability, welding CCT chart management and welding standards consulting systems. These database systems provide favorable conditions for the management of various data and information in the welding field. Welding expert system mainly focuses on process formulation, defect prediction and diagnosis, computer-aided design and so on. In the existing welding expert system, process selection and process formulation are the most important application fields, and the real-time control of welding process is an important development direction. Computer-aided quality control (CAQ) is used for data analysis of products and real-time monitoring of welding quality. In addition, computer-aided design/manufacturing (CAD/CAM) is increasingly used in Welding processing, mainly for CNC cutting, welding structure design and welding robots.

11-22

Characteristics of high frequency induction heating welding

2022-11-22

Fast heating speed and high production efficiency. The unit power of high-frequency induction heating is as high as 500-1 000/kw², so the heating speed is extremely fast, and the time required for large-area welding is only a few seconds, which can greatly shorten the welding time, improve productivity and reduce production costs. (2) The heat affected zone is small, and the damage to the substrate is small. The skin effect of high-frequency induction heating makes the heating depth of the welded workpiece very shallow, even reaching a few tenths of a millimeter. Relying solely on heat transfer from the workpiece to the core, any point of the workpiece is heated to melt upon entering the sensor. Temperature, it enters a rapid cooling state after leaving the sensor, there is almost no heat preservation time, and the heating time is extremely short, so the heat affected zone is very small, and the substrate is basically not damaged. In addition, there is little scale formation, and even if heated in air, there is little oxidation and decarburization on the billet surface. To avoid or reduce the formation of brittle compounds at the interface, the mechanical properties of welded joints are excellent. Due to the fast induction heating speed, energy concentration, short cooling time, the resulting austenite grains are small, and the workpiece after induction heating has a very good metallographic organization. For dissimilar metal welding, a very short heating time can reduce the formation of brittle compounds at the interface and effectively improve the mechanical properties of the welded joint. (4) to achieve the welding of complex interface. The sensor heating head can be designed into the corresponding shape according to the heating needs of different workpieces, and the extremely short heating time can realize local heating, the temperature of the heating zone is quickly established, and the temperature transition zone is narrow, so that the sensor can move along the complex interface, so as to realize the welding of the complex interface. In addition, high-frequency induction heating welding also has the advantages of energy saving, repeatability, and easy automatic production. The disadvantage is that the heating temperature is not easy to control accurately, and the electromagnetic field generated is more harmful to the human body.

11-21

Heating principle and characteristics of high frequency induction welding

2022-11-21

High frequency welding uses solid resistance heat as energy source. During welding, the resistance heat generated by high-frequency current in the workpiece is used to heat the surface of the welding zone of the workpiece to a molten or nearly plastic state, and then apply (or not apply) upsetting force to achieve metal bonding. So it is a solid phase resistance welding method. High-frequency welding can be divided into contact high-frequency welding and induction high-frequency welding according to the way that high-frequency current generates heat in the workpiece. In contact high-frequency welding, high-frequency current is transmitted to the workpiece through mechanical contact with the workpiece. In induction high-frequency welding, a high-frequency current generates an induced current in the workpiece through the coupling of an induction coil outside the workpiece. High frequency welding is a highly professional welding method, should be equipped with special equipment according to the product. High productivity, welding speed up to 30 m/min. It is mainly used for welding longitudinal seams or spiral seams in pipeline manufacturing. The principle of high-frequency induction heating: Put the workpiece into the inductor (the coil is usually made of copper tube). When the inductor is connected to a certain frequency of alternating current, an alternating magnetic field will be generated around it. The electromagnetic induction of an alternating magnetic field produces a strong magnetic flux that changes instantaneously. When a heated object such as metal is placed in the induction coil, the magnetic flux will penetrate the entire heated substance, and a large magnetic field opposite to the direction of the heating current will be generated inside the heated substance. Because the resistance in the heated substance generates Joule heat, the large eddy current causes the temperature of the substance itself to rise rapidly, which is the principle of induction heating.

11-20

How to realize invisible weld and change the operation of welding method

2022-11-20

1. The non-magnetic metal ring is required to use non-magnetic A- body stainless steel, because other metals leave the magnetic field (the magnetic field is removed); There will be remanence. However, the remanence of stainless steel after leaving the magnetic field (removing the magnetic field) is almost zero. 2. The metal ring requiring magnetic permeability should use pure iron or iron cobalt alloy with good magnetic permeability. The cobalt content is 27% ~ 50%, which has a high saturation magnetization. Low resistivity. Suitable for manufacturing pole shoes, motor rotors and stators, small transformer cores, etc. 3. In order to ensure the dimensional accuracy and welding strength of the components, the original design of the fillet weld to plug weld; 4. In order to ensure welding quality and control welding deformation, the original welding method is changed to vacuum brazing method, 5. In order to make the weld beautiful and improve the strength of the weld, the original obvious weld design is changed to invisible weld, 6. Solder Solder is a silver-free solder paste composed of copper, tin, nickel and phosphorus. 7. The particle size of silver-free solder paste is 200um, 8. Melting point of silver-free solder paste: 580 ℃ ~ 620 ℃, 9. During trial welding, increase the vacuum degree from × 10-3 Torr to × 10-4 Torr, 10. Welding temperature: 670 ℃ ~ 720 ℃, 11. According to the design requirements of the above technology, the expected purpose of the design is achieved through welding experiments; 12. Post-weld inspection: all technical indicators have achieved the expected results.

11-19

Effect of different silver-based brazing filler metals on brazing quality of copper tube

2022-11-19

Pure copper is widely used in heat exchange equipment and refrigeration pipes because of its good thermal conductivity, ductility and corrosion resistance. However, due to the high thermal conductivity and high linear expansion coefficient of copper, incomplete penetration and cracks are likely to occur in fusion welding. Compared with the effect of melting different silver-based solder on the quality of copper pipe brazing welding, brazing is widely used in the connection of copper pipe joints because the base metal does not melt, reduces the residual stress of the joint and avoids the formation of the above defects. The flame brazing process of copper tubes in different industries has been widely studied. The processing conditions of copper pipe in air-conditioning manufacturing industry are analyzed, and the application of flame brazing process in air-conditioning pipe processing is studied. The brazing connection technology of gas copper pipe is studied. According to the characteristics of the heat exchanger industry, measures to improve the copper tube brazing process are proposed. An important aspect that affects the quality of brazing is the choice of brazing filler metal. Silver-based solder is a kind of medium temperature solder widely used in production. It has a low melting temperature and good wettability. The resulting brazed joint has high strength and good plasticity, and can be brazed with most metals except aluminum and magnesium. However, silver is a precious metal. In order to reduce the cost, it is of great significance to correctly select and reasonably use silver-lead materials.

11-18

Flame brazing process, precautions for welding process

2022-11-18

Flame brazing uses an oxyacetylene neutral flame to heat the base metal and the solder. During brazing, in order to ensure the relative position of the welded parts, use the vise on the pre-assembly platform for positioning and pre-assembly. Before brazing, chamfer the copper pipe joints, remove burrs, and then wipe the copper pipes and pipe fittings to be welded with acetone to clean the surface oil. During brazing, the distance between the welding nozzle and the base metal should be controlled at 30~70mm, and the entire joint area should be heated, and the heating time should be shortened as much as possible. When the copper tube is heated to dark red, the silver brazing filler metal is dipped in the end of the silver-based brazing filler metal and placed in the place to be brazed. The wire ends are heated to melt and flow along the joint gap. Continue to heat the joint and continuously add solder to fill the joint gap. At the same time, the flame should move back and forth evenly along the joint until a smooth brazed seam is formed. In the brazing process, the shaking of the workpiece should be reduced as much as possible to reduce the occurrence of defects. If the brazing position is not good, you can put a mirror on the back to observe the brazing seam. After brazing, the appearance of the brazed joint shall be observed. For poorly formed or suspected to have pores in the brazing seam, should be reheated, if necessary, can be filled with solder. After brazing, chemical cleaning is carried out, and the brazing samples before and after cleaning are shown in Figure 1. There are many residual flux and discoloration on the surface of the copper pipe before cleaning. After cleaning, the surface of the copper pipe is smooth and the cleaning effect is remarkable.

11-17

The role of brazing and special joining technology in the development of the aviation industry

2022-11-17

A generation of materials, a generation of manufacturing, a generation of equipment. As one of the important methods of material connection, brazing (including diffusion welding) is recognized as the key connection technology of advanced aircraft and engines together with electron beam welding, laser welding and friction welding. Various titanium alloy and stainless steel pipes on the aircraft body are connected by high-frequency induction brazing during the assembly process to achieve the purpose of weight reduction. A large number of wires and instruments on the onboard equipment are also connected by soldering. For aircraft with a flight Mach number greater than 2.5, brazing or cap welding is increasingly used for honeycomb panels of stainless steel, titanium alloys or high-temperature alloys due to the high temperature of the skin due to friction with the air. The manufacture of a large number of important parts of aero-engines, such as turbine blades, compressor blades, combustion chamber parts, honeycomb sealing structures, blade ring structures, stainless steel heat exchangers, aluminum alloy chassis, fuel manifolds and other pipelines., Without brazing or TLP diffusion welding technology. The engine rectifier, guide vane and casing are connected by brazing, which not only meets the design requirements, but also achieves the effect of weight reduction. According to statistics, an aero-engine core machine brazing area of more than 14000 cm2. It can be said that without advanced brazing and special joining technology, it is impossible to manufacture many important high-temperature structural parts of high-performance aeroengines. With the development of aviation technology, more and more new materials, new structures and new manufacturing technologies will be used in future aviation equipment. Brazing and its derived joining technologies, such as TLP diffusion welding and cap welding, have unique advantages and flexibility in joining new materials and manufacturing complex fine structures. Even for some new materials and complex components, brazing is the only feasible connection technology, which is increasingly used in important load-bearing components. There is no doubt that brazing technology plays an important role in the aviation industry.

11-16

Comparison of brazing and special joining technology level with other countries

2022-11-16

In terms of the development of advanced connection technology and the research of new material connection technology, China has carried out fruitful research work in recent years, which can basically track the world's advanced level. However, compared with the advanced level of foreign countries, there is still a big gap in the basic theory and related numerical simulation technology of brazing and special connection technology, the engineering application of advanced connection technology of new materials, the production and preparation technology of brazing materials, brazing and special connection equipment and control technology. Please describe the development trend and research focus of brazing and special joining. Brazing and related special joining techniques are increasingly used in the manufacture of important load-bearing components and complex components; it plays an important role in the joining of new special materials, and is even the only feasible joining method for certain materials and components. In addition, the integration of brazing and related special connection technology with metallurgy, machinery, electronics, chemical industry, surface engineering, heat treatment, high-energy beam processing and other disciplines can derive many new manufacturing technologies, which is also an important direction for the innovation and development of brazing and related special connection technology. In my opinion, in order to promote the engineering application of advanced materials and their components, in-depth and systematic experimental research should be carried out in the following aspects: 1) Can be used for high-temperature structural parts of ceramics and ceramic and metal connection technology; 2) Connection technology of composite materials (including metal matrix composites, ceramic matrix composites and C/C composites); 3) Intermetallic material connection technology; 4) Connection technology of refractory metal materials; 5) low brittleness brazing technology of titanium alloy; 6) Vacuum brazing technology of heat treatment strengthened aluminum alloy; 7) The application of nanotechnology in brazing and special joining technology. In addition, the research work of basic theory and numerical simulation is still relatively weak, which should be paid enough attention to, and the research intensity and depth should be increased.

11-15

Application of Brazing Technology in Ancient Times

2022-11-15

Diffusion technology also has a long history. In more than 3000 BC, the Egyptians joined two pieces of hot metal together by hammering, which may be the oldest form of solid-phase diffusion welding. In the Bronze Age of 700 BC, the British hammered gold into boxes at room temperature, which should be regarded as the earliest cold welding. Next, diffusion welding technology has experienced a long development process. However, it was not until World War II that diffusion welding technology developed rapidly. This is because the two sides of the war in order to pursue higher aircraft flight performance, the need to achieve a reliable connection of high-strength aluminum alloy components. The rapid development of vacuum technology also promotes the progress of diffusion welding technology. In addition, the development and requirements of the aviation industry have also promoted various forms of diffusion welding. For example, in the 1970 s, TLP diffusion welding techniques were developed primarily for joining high strength cast superalloys. At present, the technology is also used to connect new structural materials such as titanium alloys, ceramics, and intermetallic compounds. Another example is the titanium alloy LID welding process developed in the early 1970 s, which can obtain titanium alloy joints with uniform microstructure and composition. At present, solid-phase diffusion welding is mainly used to manufacture parts of different materials or porous materials, such as streamline analysis elements, porous filter elements, electromagnetic coil skeletons and some bimetal parts. TLP diffusion welding and cap welding are used for high-strength joining of high-temperature alloy and titanium alloy components in the aerospace industry.