During the welding process, the workpiece and the solder melt to form a molten area. After the molten pool cools and solidifies, a connection between the materials is formed. This process usually requires the application of pressure. There are many energy sources for welding, including gas flame, arc, laser, electron beam, friction and ultrasonic wave. Before the end of the 19th century, the only welding process was forge welding of metals, which had been used by blacksmiths for hundreds of years. The earliest modern welding technology appeared at the end of the 19th century, first arc welding and oxygen gas welding, and later resistance welding. In the early 20th century, with the outbreak of the First and Second World Wars, there was a great demand for cheap and reliable connection methods for military equipment, which promoted the development of welding technology. Today, as welding robots are widely used in industrial applications, researchers are still deeply studying the nature of welding and continuing to develop new welding methods to further improve welding quality. Welding is a process in which two or more same or dissimilar materials are connected into one body through the bonding and diffusion between atoms or molecules.
The method to promote the bonding and diffusion between atoms and molecules is Heating or pressurizing, or heating and pressurizing at the same time. Metal welding is divided into three categories according to the characteristics of its process: fusion welding, pressure welding and brazing.
In the process of fusion welding, If the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize the metal and various alloying elements. Nitrogen, water vapor, etc. in the atmosphere enter the molten pool, and will also form defects such as pores, slag inclusions, and cracks in the weld during the subsequent cooling process, deteriorating the quality and performance of the weld.
In order to improve the quality of welding, various protection methods have been developed. For example, gas shielded arc welding uses argon, carbon dioxide and other gases to isolate the atmosphere to protect the arc and molten pool rate during welding; another example is when steel welding, ferrotitanium powder with a high affinity for oxygen is added to the electrode coating for deoxidation. It can protect beneficial elements such as manganese and silicon in the welding rod from oxidation and entering the molten pool, and obtain high-quality welds after cooling.
The common feature of various pressure welding methods is that pressure is applied during the welding process without filling material. Most pressure welding methods, such as diffusion welding, high-frequency welding, cold pressure welding, etc., do not have a melting process, so there are no problems like burning of beneficial alloy elements and intrusion of harmful elements into the weld like fusion welding, thus simplifying the welding process. It also improves welding safety and hygiene conditions. At the same time, because the heating temperature is lower than that of fusion welding and the heating time is shorter, the heat affected zone is smaller. Many materials that are difficult to weld with fusion welding can often be welded with pressure welding to form high-quality joints with the same strength as the base metal.
The seam formed during welding and connecting two connected bodies is called a weld. During welding, both sides of the weld will be affected by the welding heat, resulting in structural and performance changes. This area is called the heat-affected zone. When welding, the workpiece material, welding material, welding current, etc. are different. Deterioration of weldability requires adjustment of welding conditions. Preheating of the interface of the weldment before welding, insulation during welding and post-weld heat treatment can improve the welding quality of the weldment.
In addition, welding is a local rapid heating and cooling process. The welding area cannot expand and contract freely due to the constraints of the surrounding workpiece body. After cooling, welding stress and deformation will occur in the weldment. After welding, important products need to eliminate welding stress and correct welding deformation.
Modern welding technology can already weld welds without internal or external defects and with mechanical properties equal to or even higher than those of the connected objects. The mutual positions of the welded bodies in space are called welded joints. In addition to being affected by the quality of the weld, the strength of the joint is also related to its geometry, size, stress and working conditions. The basic forms of joints include butt joints, lap joints, T-joints (orthogonal joints) and corner joints.
The cross-sectional shape of the butt joint weld is determined by the thickness of the welded body before welding and the groove form of the two joining edges. When welding thicker steel plates, various shapes of grooves are made at the joint edge for welding penetration, so that the welding rod or wire can be fed more easily. The groove forms include single-sided welding grooves and double-sided welding grooves. When selecting the groove form, in addition to ensuring weld penetration, factors such as ease of welding, small amount of filler metal, small welding deformation and low groove processing costs should also be considered.
When two steel plates with different thicknesses are butted together, in order to avoid severe stress concentration caused by sharp changes in cross-section, the thicker edge of the plate is often gradually thinned until the two joined edges are of equal thickness. The static strength and fatigue strength of butt joints are higher than other joints. For connections that work under alternating and impact loads or in low-temperature and high-pressure vessels, welding of butt joints is often preferred.
The pre-welding preparation of lap joints is simple, easy to assemble, and the welding deformation and residual stress are small, so it is often used to install joints and unimportant structures on construction sites. Generally speaking, lap joints are not suitable for working under conditions such as alternating loads, corrosive media, high or low temperatures.
The use of T-joints and corner joints is usually due to structural needs. The operating characteristics of incomplete fillet welds on T-joints are similar to those of fillet welds on lap joints. When the weld is perpendicular to the direction of the external force, it becomes a front fillet weld. At this time, the surface shape of the weld will cause varying degrees of stress concentration; the stress situation of the penetration fillet weld is similar to that of a butt joint.
The load-bearing capacity of corner joints is low and is generally not used alone. It can only be improved when welding is penetrated or when there are fillet welds both inside and outside. It is mostly used at the corners of closed structures.
Welded products are lighter than riveted parts, castings and forgings, which can reduce the weight and save energy for transportation vehicles. Welding has good sealing performance and is suitable for manufacturing various types of containers. Develop joint processing technology to combine welding with forging and casting to produce large-scale, economical and reasonable cast-welded structures and forged-welded structures with high economic benefits. The welding process can effectively utilize materials. The welded structure can use materials with different properties in different parts, giving full play to the strengths of various materials to achieve economy and high quality. Welding has become an indispensable and increasingly important processing method in modern industry.
In modern metal processing, welding developed later than casting and forging processes, but it developed very quickly. The weight of welded structures accounts for approximately 45% of steel production, and the proportion of aluminum and aluminum alloy welded structures is also increasing.
For future welding processes, on the one hand, new welding methods, welding equipment and welding materials must be developed to further improve welding quality, safety and reliability, such as improving existing arcs, plasma arcs, electron beams, and lasers. and other welding energy; use electronic technology and control technology to improve the process performance of the arc and develop a reliable and lightweight arc tracking method.
On the other hand, it is necessary to improve the level of welding mechanization and automation, such as realizing program control and digital control of welding machines; developing special welding machines that automate the entire process from preparation process, welding to quality monitoring; in automatic welding production lines , the promotion and expansion of CNC welding manipulators and welding robots can improve the level of welding production and improve welding hygiene and safety conditions. Welding technology emerged with the smelting production of copper, iron and other metals and the application of various heat sources. The ancient welding methods are mainly cast welding, brazing, forge welding and riveting welding. Before 2500 BC, the ancient Babylonians and the Indus Valley Civilization had reached a high level of hot and cold processing of copper and iron metals. They could use forge welding, cast welding and other welding methods to make metal utensils and engraved them with text. The representative culture at this time was the Harappan culture.
The iron-edged copper yue made in the Shang Dynasty of China is a casting and welding piece of iron and copper. The fusion line of copper and iron on its surface is winding and well-joined. During the Spring and Autumn Period and the Warring States Period, there were many coiled dragons on the bronze drum base in the tomb of Zeng Houyi, which were soldered together in sections. After analysis, the composition of the solder used is similar to that of modern solder. Swords made during the Warring States Period had steel blades and wrought iron backs, which were usually heated and forged and welded. According to the book "Tiangong Kaiwu" written by Song Yingxing of the Ming Dynasty: In ancient China, copper and iron were heated together in a furnace and forged to make knives and axes; yellow mud or finely sieved old wall soil was sprinkled on the joints. Forging and welding large anchors in sections. In the Middle Ages, forge welding was also used to make weapons in Damascus, Syria. Ancient welding technology has long stayed at the level of cast welding, forge welding, brazing and riveting. The heat sources used are furnace fires. The temperature is low and the energy is not concentrated. It cannot be used for welding workpieces with large cross-sections and long welds. Can be used to make decorations, simple tools, living utensils and weapons. At the beginning of the 19th century, Davis of the United Kingdom discovered arc and oxyacetylene flame, two high-temperature heat sources that can locally melt metals; from 1885 to 1887, Bernardos of Russia invented the carbon electrode arc welding clamp; in 1900, aluminum appeared again Heat welding. At the beginning of the 20th century, carbon arc welding and gas welding were applied. At the same time, thin-coated electrode arc welding also appeared. The arc was relatively stable, the welding pool was protected by slag, and the welding quality was improved. Manual arc welding entered the practical stage. Welding has become an important welding method since the 1920s. It also became the beginning of the development of modern welding technology. During this period, Noble in the United States used arc voltage to control the feeding speed of the welding rod and made an automatic arc welding machine, which became the beginning of welding mechanization and automation.
In 1930, Robinov in the United States invented submerged arc welding using welding wire and flux, and welding mechanization was further developed. In the 1940s, in order to meet the needs of welding aluminum, magnesium alloy and alloy steel, tungsten electrode and melting electrode inert gas shielded welding were successively introduced.
In 1951, the Patton Welding Research Institute of the Soviet Union invented electroslag welding, which became an efficient welding method for large-thickness workpieces. In 1953, Lyubavsky and others in the Soviet Union invented carbon dioxide gas shielded welding, which promoted the application and development of gas shielded arc welding, such as mixed gas shielded welding, flux cored wire gas slag combined shielded welding and self-shielded arc welding. wait. In 1957, Gage of the United States invented plasma arc welding; in the 1940s, Germany and France invented electron beam welding, which was also practical and further developed in the 1950s; in the 1960s, the emergence of laser welding plasma, electron beam and laser welding methods marked the With the new development of high energy density fusion welding, the weldability of materials has been greatly improved, allowing many materials and structures that are difficult to weld by other methods to be welded.
Other welding technologies include resistance welding invented by Thompson in the United States in 1887 and used for spot welding and seam welding of thin plates; seam welding is the earliest semi-mechanized welding method in pressure welding. As the process proceeds, the workpiece is pushed forward by two rollers; in the 1920s, flash butt welding began to be used to weld bars and chains. At this point, resistance welding has entered the practical stage. In 1956, Jones of the United States invented ultrasonic welding; Chudikov of the Soviet Union invented friction welding; in 1959, the Stanford Research Institute of the United States successfully studied explosive welding; in the late 1950s, the Soviet Union made vacuum diffusion welding equipment. Development Trend of Welding Technology 1. Improving welding productivity is an important driving force for the development of welding technology
There are two ways to improve productivity: First, increase the welding deposition rate, such as three-wire submerged arc welding. The parameters are 220A/33V, 1400A40V, and 1100A45V. With a small groove section and a baffle or liner behind it, a 50~60mm steel plate can be welded and formed in one go. The welding speed can reach more than 0.4m/min. Its deposition rate is more than 100 times compared with electrode arc welding. , the second way is to reduce the groove section and metal deposition. The most outstanding achievement is narrow gap welding. Narrow gap welding is based on gas shielded welding, using single wire, double wire, or triple wire for welding. Regardless of the thickness of the joint, the butt joint can be used. For example, if the thickness of the steel plate is 50~300mm, the gap can be designed to be about 13mm, so The required amount of deposited metal is reduced several times or dozens of times, thus greatly improving productivity. The main technical key of narrow gap welding is to see how to ensure penetration on both sides and ensure that the arc center automatically tracks and is on the center line of the groove. To this end, countries around the world have developed a variety of different solutions, resulting in a variety of narrow gap welding. Law.
In electron beam welding, plasma welding, and laser welding, butt joints can be used without beveling, so it is a more ideal narrow gap welding method, which is one of the reasons why it is widely valued. .
The newly developed laser arc hybrid welding method can increase the welding speed. For example, for a 5mm steel plate or aluminum plate, the welding speed can reach 2~3m/min, achieving good shape and quality with small welding deformation.
2. Improving the mechanization and automation level of the preparation workshop is the key development direction of the world's advanced industrial countries.
In order to improve the production efficiency and quality of welded structures, there are certain limitations in starting from the welding process alone. Therefore, countries around the world pay special attention to the technical transformation of workshops. The main processes of preparing the workshop include material transportation, material surface degreasing, sandblasting, and protective paint application; steel plate scribing, cutting, and beveling; and component assembly and fixing. The above processes have been mechanized and automated in modern factories. Its advantage is not only to improve the productivity of the product, but more importantly, to improve the quality of the product.
3. Automation and intelligence of the welding process are important directions to improve the stability of welding quality and solve harsh working conditions.
4. The development of emerging industries continues to promote the advancement of welding technology.
Welding technology has a history of more than 100 years since its invention. It can meet the needs of almost all important product manufacturing in the current industry. However, the development of emerging industries still forces welding technology to continue to advance. The development of the microelectronics industry promotes the development of micro-connection processes and equipment; and the development of ceramic materials and composite materials promotes vacuum brazing and vacuum diffusion welding. The development of aerospace technology will also promote the development of space welding technology.
5. The research and development of heat sources is the fundamental driving force for the development of welding processes.
The welding process uses almost all available heat sources in the world, including flame, arc, resistance, ultrasonic, friction, plasma, electron beam, laser beam, microwave, etc. (Our company mainly uses arc welding. , resistance welding automated welding equipment, mainly). The emergence of every heat source in history is accompanied by the emergence of new welding processes. However, the development and research of welding heat sources has not ended so far.
6. Energy-saving technology is a common concern
As we all know, welding consumes a lot of energy. Taking electrode arc welding as an example, each unit is about 10KVA, and each submerged arc welding machine is 90KVA. Resistance welding machines can reach thousands of KVA, and many new technologies have emerged to achieve this energy-saving goal. In resistance spot welding, using the development of electronic technology, changing the AC spot welding machine into a secondary rectifier spot welding machine can improve the power factor of the welding machine and reduce the welding machine capacity. A 1000KVA spot welding machine can be reduced to 200KVA. The same welding effect can still be achieved. The emergence of inverter welding machines is another successful example. It can reduce the weight of the welding machine and improve the control performance of the power factor of the welding machine. It has been widely used in production.
Welding methods
Welding technology is mainly used on metal base materials. Commonly used ones include arc welding, argon arc welding, CO2 shielded welding, oxygen-acetylene welding, laser welding, and electroslag There are many types of pressure welding, and non-metallic materials such as plastics can also be welded. There are more than 40 metal welding methods, which are mainly divided into three categories: fusion welding, pressure welding and brazing.
Fusion welding is a method in which the workpiece interface is heated to a molten state during the welding process and the welding is completed without applying pressure. During welding, the heat source rapidly heats and melts the interface between the two workpieces to be welded, forming a molten pool. The molten pool moves forward with the heat source, and after cooling, a continuous weld is formed to connect the two workpieces into one body.
Pressure welding is to achieve interatomic bonding between two workpieces in a solid state under pressurized conditions, also known as solid-state welding. The commonly used pressure welding process is resistance butt welding. When current passes through the connection end of two workpieces, the temperature rises due to the large resistance. When heated to a plastic state, the connection becomes one under the action of axial pressure.
Brazing is to use a metal material with a lower melting point than the workpiece as the filler metal. The workpiece and the filler metal are heated to a temperature higher than the melting point of the filler metal and lower than the melting point of the workpiece. The liquid filler metal is used to moisten the workpiece. A method of filling the interface gap and achieving interdiffusion of atoms with the workpiece to achieve welding.
The seam formed during welding that connects two connected bodies is called a weld. Both sides of the weld will be affected by the welding heat during welding, resulting in changes in structure and properties. This area is called the heat-affected zone. During welding, due to different workpiece materials, welding materials, welding current, etc., overheating, embrittlement, hardening or softening may occur in the weld and heat-affected zone after welding, which will also reduce the performance of the weldment and worsen the weldability. This requires adjusting the welding conditions. Preheating the interface of the weldment before welding, insulation during welding and post-weld heat treatment can improve the welding quality of the weldment. The emergence of welding caters to the need for new technological means for the development of metal art.
Artistic creation and craft methods are always inseparable. As an industrial technology, the emergence of welding caters to the need for new process methods for the development of metal art. On the other hand, the unique and wonderful changes produced by metal under the action of welding heat also meet the needs of metal art for a new artistic expression language. In today's metal art creation, welding is being emphasized as a unique artistic expression language. Metal welding art can be regarded as a relatively independent art form, separated from traditional metal art in a branched manner. This is because welding has artistic qualities. Welding can produce a rich expression language of artistic creation. Welding is usually performed at high temperatures, and metals undergo many wonderful and rich changes at high temperatures. The metal base material will undergo color changes and thermal deformation (i.e., welding heat affected zone); the welding wire will form some beautiful textures after melting; and welding defects are often used in the art of welding. Welding defects refer to defects produced in the welding joint during the welding process that do not meet the design or process requirements.
Its main manifestations include welding cracks, pores, undercuts, lack of penetration, lack of fusion, slag inclusions, welding nodules, collapse, pits, burn-through, inclusions, etc. This is a very interesting phenomenon: in today's metal art creation , the artistry of welding is usually reflected in some failed industrial welding operations, or is hidden in some welding defects that industrial welding tries to avoid. Secondly, the art language of welding is unique.
In a welded sculpture, thick welds are exposed on the surface of the sculpture, and various irregular cutting marks have become the artist’s beautiful artistic language. In many cases, due to the roughness and simplicity pursued by the welded sculpture The style, metal corrosion and defects are mostly deliberately retained according to the needs of the work. Therefore, you can often feel an uncarved, original beauty in the welded sculptures.
The welds at the joints of the steel plates at the lower part of the sculpture are very thick. Judging from the solidity of the welding process, this is obviously not just for the sake of the strength of the sculpture. In this sculpture, the lower part is almost The twisted welds have become an integral part of the overall aesthetic of the sculpture. From the perspective of the sculpture as a whole, whether it is the text shape of the upper part or the texture treatment of the lower part, there are distorted welding traces everywhere, and the entire work has achieved the unity of the overall visual language. The manual plasma cutting method uses the heat generated by the current during cutting to create a heat-affected zone on the edge of the cutting. In this way, the bright white stainless steel is "dyed" with a slightly gradient color. At the same time, by adjusting the welding specifications, the strong airflow emitted by the cutting gun will "blow" a randomly formed texture around the cutting edge at the moment the cutting steel plate melts. The formation process of this random effect has a certain degree of contingency, but it is an inevitable phenomenon under certain welding specifications. From the perspective of size, semi-automatic CO2 gas shielded welding can be used for larger welded art wall decorations, while manual tungsten arc welding can be used for smaller ones.
If a wall decoration work is viewed as a painting, the processing of points, lines, surfaces, black, white, gray and even colors in the picture can all be achieved through welding. Metal wires of various types and materials, using different welding processes, will appear in different forms on the screen. Different metals have different colors, such as bright silver in stainless steel, sub-silver in aluminum, bright black in carbon steel, titanium steel, bronze, copper, and brass. And as for steel, different steels will appear different when heated at high temperatures. The color change is the difference in the welding heat affected zone. In addition, cutting is also one of the methods for creating welded art wall decorations. It can be used in combination with welding or alone. It all depends on the creator's creative intention and mastery of the process and effect. Taken together, the methods described above can lead to a rich variety of changes.