The manufacturing or sculpting process of joining metals
Metal welding is a manufacturing or sculpting process that connects metals.weldingIn the process, the workpiece and solder are melted or not melted, forming a direct connection weld of the material.During this process, pressure is usually also required to join the weldment.
The difference between ordinary welding and brazing and soldering is that soldering forms a connection by melting the solder with a lower melting point (lower than the melting point of the workpiece itself) without heating the workpiece itself.
There are many energy sources for welding, including gas flame, arc, laser, electron beam, friction, ultrasonic, etc.In addition to being used in the factory, welding can also be carried out in a variety of environments, such as the field, underwater and space.No matter where, welding may bring danger to the operator, so appropriate protective measures must be taken when welding.The possible injuries to human body caused by welding include burns, electric shock, vision damage, inhalation of toxic gases, excessive ultraviolet radiation, etc.
Operation method
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There are more than 40 metal welding methods, which are mainly divided into fusion welding, pressure welding and brazing:
Fusion welding
Fusion welding is a method of heating the workpiece interface to the melting state during welding, and completing the welding without pressure.During fusion welding, the heat source will rapidly heat and melt the interface of the two workpieces to be welded to form a molten pool.The molten pool moves forward with the heat source and forms continuous weld after cooling, connecting the two workpieces into one.
During fusion welding, if the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize metals and various alloy elements.When nitrogen and water vapor in the atmosphere enter the molten pool, they will also form pores, slag inclusions, cracks and other defects in the weld during the subsequent cooling process, which will deteriorate the quality and performance of the weld.
In order to improve the welding quality, various protection methods have been developed.For example,Gas shielded arc weldingArgoncarbon dioxideAnd other gases to isolate the atmosphere, so as to protect the arc during welding from oxidation and avoid the formation of defects;For another example, when welding steel, add ferrotitanium powder with high oxygen affinity into the electrode coating for deoxidation, which can protect the beneficial elements such as manganese and silicon in the electrode from oxidation and enter the molten pool, and obtain high-quality welds after cooling.
Pressure welding
Pressure welding is to realize atomic bonding between two workpieces in solid state under pressure, also known as solid state welding.The common pressure welding process is resistance butt welding. When the current passes through the connecting end of two workpieces, the temperature rises due to the high resistance. When heated to the plastic state, it is connected as a whole under the axial pressure.
The common feature of various pressure welding methods is that pressure is applied during welding without filler materials.Most pressure welding methods, such as diffusion welding, high-frequency welding and cold pressure welding, have no melting process, so there is no burning loss of beneficial alloy elements like fusion welding, and the problem of harmful elements invading the weld, which simplifies the welding process and improves the welding safety and health 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 be welded by fusion welding can often be pressure welded into high-quality joints with the same strength as the base metal.
Brazing
Brazing is a method of using a metal material with a lower melting point than the workpiece as brazing filler metal, heating the workpiece and brazing filler metal to a temperature higher than the melting point of the brazing filler metal and lower than the melting point of the workpiece, wetting the workpiece with liquid brazing filler metal, filling the interface gap and realizing the mutual diffusion of atoms with the workpiece, thus realizing welding.
Laser welding
It is composed of an optical oscillator and a medium placed between mirrors at both ends of the oscillator cavity.When the medium is excited to the high energy state, it starts to produce in-phase light waves and reflect back and forth between the mirrors at both ends, forming the photoelectric cascade effect, amplifying the light waves, obtaining enough energy and starting to emit lasers.
Laser can also be interpreted as a kind of equipment that converts electrical energy, chemical energy, thermal energy, light energy or nuclear energy and other raw energy into electromagnetic radiation beam of certain light frequency (ultraviolet, visible or infrared light).The transformation form is easy to be carried out in some solid, liquid or gaseous media.When these mediums are excited in the form of atoms or molecules, a beam laser with almost the same phase and nearly a single wavelength will be generated.Due to the same phase and single wavelength, the difference angle is very small, and the transmission distance is quite long before being highly concentrated to provide welding, cutting, heat treatment and other functions.
Development history
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Before the end of the 19th century, the only welding process was metal forging and welding, 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 oxy fuel gas welding, and later resistance welding.In the early 20th century,the First World Warandthe Second World WarThere is a large demand for military equipment in China, and the corresponding cheap and reliable metal connection process is valued, which promotes the development of welding technology.After the war, several modern welding technologies have emerged, including the most popular manual arc welding, as well as gas metal arc welding, submerged arc weldingFlux cored wire arc weldingAutomatic or semi-automatic welding technology such as electroslag welding.In the second half of the 20th century, with the rapid development of welding technology, laser welding and electron beam welding were developed.Today, welding robots are widely used in industrial production.Researchers are still deeply studying the nature of welding, continuing to develop new welding methods, and further improving the welding quality.
development
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Status and prospect of welding automation technology
With the increasingly mature digital technology, the digital welding machine and digital control technology of the representative office's dynamic ground connection technology have steadily entered the market.Three Gorges ProjectWest East Gas Transmission Project, aerospace engineering, shipbuilding engineering and other national large-scale basic projects have effectively promoted the development and progress of advanced welding, especially welding automation technology.The manufacturing of automobiles and their parts requires the automation of welding with each passing day.China's welding industry is gradually moving towards "high efficiency, automation and intelligence".The welding automation rate in China is still less than 30%, far from 80% in developed industrial countries.Since the end of the 20th century, the country has gradually promoted the basic welding method of automatic welding - gas shielded welding in various industries to replace the traditional manual arc welding, which has achieved initial results.It can be predicted that in the future, the domestic automatic welding technology will develop at an unprecedented speed.
Current status of efficient and automatic welding technology
In the 1990s, China's welding industry took the realization of mechanization and automation of the welding process as its strategic goal, which has been put into practice in the development of science and technology in various industries. In the development of welding production automation, research and development of welding production lines andFlexible manufacturing technology, develop and apply computer aided design and manufacturing;amongFlux cored wireThe growth rate of will increase significantly, and will exceed solid wire in the next 20 years, and will eventually become the leading product of the welding center.
Prospect of welding automation technology
The development of electronic technology, computer microelectronics and automation technology has promoted the development of welding automation technology.Especially, the introduction of cell technology such as numerical control technology, flexible manufacturing technology and information processing technology has promoted the revolutionary development of welding automation technology.
(1) The intellectualization of welding process control system is one of the core issues of welding automation, and also an important direction for future research.Research on optimal control methods should be carried out, including linear and various nonlinear controls.The most representative ones are fuzzy control, neural network control and expert system research of welding process.
(2) Welding flexibility technology is also the focus of research.In the future research, various optical, mechanical and electrical technologies will be organically combined with welding technology to achieve the accuracy and flexibility of welding.The fundamental way to improve the level of welding automation is to transform the traditional welding process equipment with microelectronics technology.It is a current research direction to combine numerical control technology with various welding machinery and equipment to improve its flexibility level;In addition, the combination of welding robot and expert system to realize automatic path planning, automatic trajectory correction, automatic control of penetration and other functions is the focus of research.
(3) The integration of welding control system is the integration of human and technology, and the integration of welding technology and information technology.Information flow and material flow are important components of the integrated system. Promoting their organic combination can greatly reduce the amount of information and real-time control requirements.Attention should be paid to giving play to the response and judgment ability of human in control and temporary processing, establishing a friendly human-computer Christmas interface, and making human and automatic systems harmonious and unified, which are the factors that cannot be underestimated in the integrated system.
(4) Improving the reliability, quality stability and control of welding power source, as well as its excellent dynamic sensitivity, is also an important research topic.Develop and develop high-performance welding machines that can adjust the arc movement, wire feeding and welding gun attitude, detect the beginning of weld slope, temperature field, molten pool status, and penetration, and timely provide welding specification parameters, and actively develop computer simulation technology for welding process.It is an important aspect of realizing welding automation by making welding technology evolve from "skill" to "science".The first ten years of this century will be a favorable period for the rapid development of the welding industry.The majority of our welding workers have a long way to go and must establish the determination to overcome difficulties.Seize the opportunity to strive for the improvement of welding automation in China.
