[introduction] chemical equipment installation is a key step before the production of chemical equipment, welding technology directly affects the performance of the equipment, most of the operating environment in chemical equipment is bad, so the welding is of great significance for the manufacture and use of chemical equipment. Below, for everyone to collect a variety of welding technology.
Welding introduction
Welding: usually refers to the metal welding. By heating or pressing, or both simultaneously, the two separated objects are formed by the combination of the atoms and the forming method.
Classification: according to the welding process, the welding process can be divided into three categories according to the heating degree and the process characteristics.
(1) welding
The workpiece welding at the local heating to the melting state and the formation of molten pool (usually also add filler metal), cooling crystallization formed after welding, the welding workpieces combine as a whole can not be separated. There is a common welding method for welding, arc welding, electroslag welding, plasma arc welding, electron beam welding, laser welding etc..
(2) pressure welding
During the welding process, the welding method is required. Common welding resistance welding, friction welding, cold pressure welding, diffusion welding, explosive welding, etc..
(3) brazing
When the melting point is lower than the metal of the metal being welded (filler metal), the gap of the joint is filled, and the connection is realized. In the brazing process the welding workpieces does not melt without plastic deformation.
Characteristics of welding production:
(1) metal materials are saved, the structure is light.
(2) in order to create a large, small, large, complex machinery parts and components, to simplify the casting, forging and machining process, to obtain the best technical and economic results.
(3) welded joints have good mechanical properties and sealing performance.
(4) to make a double metal structure, so that the performance of the material is fully utilized.
Application: Welding Technology in machinery manufacturing, shipbuilding industry, construction engineering, electrical equipment production, aviation and aerospace industry and other applications are very extensive.
Disadvantages: welding technology also has some shortcomings, such as welding structure can not be disassembled for maintenance, inconvenience; welding structure will exist in the welding stress and deformation; microstructure and properties of welded joint are not uniform, and the welding defects etc..
Introduction of various welding techniques
Electric arc welding
Arc: a strong and lasting gas discharge phenomenon, between the positive and negative electrodes with a certain voltage, and the gas between the two electrodes should be in the state of ionization. Ignition arc welding, the two electrode (usually a workpiece, the other pole is filled with metal wire or electrode) connected to the power supply, short contact and rapid separation, short poles contact each other, forming arc. This way is called contact arc ignition. After the arc is formed, the electric arc can be maintained as long as the power is kept between the two poles of the electric potential difference.
Arc characteristics: low voltage, high current, high temperature, high energy density, good mobility, generally 20 ~ 30V arc voltage can be maintained stable combustion, while the current in the arc from tens of amperes to several thousand amps to meet different welding requirements of the workpiece, the arc temperature can reach more than 5000K, can melt all metal.
The arc consists of three parts: the cathode area, the anode area and the arc column area.
Arc welding power supply: arc welding arc welding power supply, usually can be divided into four categories: AC arc welding power supply, DC arc welding power supply, pulse arc welding power source and inverter arc welding power source.
DC welding machine when the workpiece is connected to the anode, the electrode is connected to the cathode, known as the DC is connected, at this time the workpiece is heated, suitable for welding thick workpiece.
When the workpiece is connected to the cathode, the electrode is connected with the anode, which is called direct current reverse connection. At this time, the workpiece is less heated and is suitable for the welding of thin and small workpieces. When the AC welding machine is used for welding, because of the change of the polarity of the poles, there is no positive or reverse connection problem.
Welding metallurgy process:
In the welding process, the interaction of slag and gas liquid metal, three, is a process of metal smelting. However, due to the particularity of the welding conditions, the welding process of chemical metallurgy has different characteristics with the general smelting process.
First of all, welding metallurgy high temperature, phase boundary, fast reaction speed, when the arc in air, liquid metal oxidation and nitridation reaction strongly, there are a large number of hydrogen atoms and metal evaporation, the moisture in the air and the workpiece and the welding material in the oil, rust, water in the arc under high temperature decomposition can be dissolved in liquid metal, lead to joint plasticity and toughness decreases, and cracks (hydrogen embrittlement).
Secondly, the weld pool is small, fast cooling, the metallurgical reaction is difficult to reach the equilibrium state, the weld in inhomogeneous chemical composition, and gas and oxide in the molten pool not surfaced, easy to form pores, slag and other defects, and even cracks.
In order to ensure the quality of the welding seam, the following measures are usually taken during the welding process:
(1) mechanical protection of the molten metal during the welding process to separate the air from the air. There are three kinds of protection modes: gas protection, protection and protection of slag slag.
(2) the metallurgical processing of weld pool, mainly through the welding material (electrode, welding wire and flux) deoxidizer adding a certain amount of (mainly ferromanganese and ferrosilicon alloy elements) and a certain amount of exclusion in the molten pool during the welding process of FeO alloy, while the elements loss compensation.
Common arc welding method:
1, hand arc welding
Hand arc welding is one of the earliest and most widely used welding methods in various arc welding methods. It is based on the external electrode coated with a coating for the electrodes and filler metal, the arc is the electrode end and between the workpiece surface combustion. Paint in the arc thermal effect on the one hand, can produce gas to protect the arc, on the other hand can produce slag covering the surface of the molten pool, to prevent the interaction of molten metal with the surrounding gas. The more important role of the slag to produce physical and chemical reaction with the molten metal or alloy element, can improve the weld metal. Hand arc welding equipment is simple, portable, flexible operation. Can be applied to repair and assembly in the short seam welding, in particular, can be used for difficult to reach the parts of the welding. Manual arc welding with the corresponding electrode can be applied to most industrial carbon steel, stainless steel, cast iron, copper, aluminum, nickel and its alloy.
2, submerged arc welding metal Arc Welding Submerged (SMAW)
Submerged arc welding is a kind of melting electrode welding method, which is based on the granular flux as protecting medium and is covered by arc. The welding process of submerged arc welding is composed of three parts:
1, in the welding parts to be welded joints at the uniform heap enough granular flux;
2, the conductive nozzle and the welding parts are respectively connected to the welding power source two to produce the welding arc;
3, automatic feeding wire and moving arc welding.
The main characteristics of submerged arc welding are as follows:
1, arc unique performance
(1) high welding quality slag air protection effect is good, the main component of the arc zone is CO2, the oxygen content is greatly reduced the nitrogen content in the weld metal, and automatically adjust the welding parameters, arc walking mechanization, pool there a long time, the metallurgical reaction fully, strong wind resistance, so the weld composition and stability, good mechanical properties;
(2) good working conditions for the welding arc slag isolation operation; mechanization of walking, lower labor intensity.
2, arc column electric field strength is higher than the melting pole gas shielded arc welding has the following characteristics:
(1) the equipment has good regulation performance, because the electric field intensity is high, the automatic regulation system's sensitivity is high, the stability of the welding process is improved;
(2) the lower limit of welding current is higher.
3, the production efficiency is high due to shorten the length of conductive wire, current and current density increased, the penetration ability of the arc and the wire melting rate is greatly improved; because the insulation effect of flux and slag, the overall thermal efficiency is greatly increased, so that the welding speed is greatly improved.
Metallurgical reaction: the flux to participate in the metallurgical reaction, Mn, Si was reduced, C partially burned, limiting impurities S, P to H, to prevent hydrogen porosity.
Droplet transition: slag wall transition
Power supply: DC power supply for small current situation, constant speed wire feeding, self arc regulation; high current general use AC power supply, variable speed wire feeding (SAW welding wire generally coarse), arc pressure feedback arc regulation.
Welding material: welding wire and flux. Welding wire and flux must be guaranteed to obtain high quality welding joints, at the same time to reduce costs as much as possible, but also pay attention to the application of the current type and polarity.
Scope of application: the submerged arc welding deep penetration, high productivity, high degree of mechanical operation, thus is suitable for welding long weld plate structure. Is widely used in shipbuilding, boilers and pressure vessels, bridges, machinery, nuclear power plant structure, heavy marine structures and weapons manufacturing sector, is one of the most commonly used welding method in welding production. In addition to the connection of the component in the metal structure, the submerged arc welding can also be deposited on the surface of the base metal to wear resistance and corrosion resistant alloy layer. With the development of welding technology and welding metallurgy materials production technology, submerged arc welding welding materials from carbon steel structure to the development of low alloy steel, stainless steel, heat-resistant steel and nonferrous metals, such as nickel base alloy, titanium alloy, copper alloy etc.. Due to its own characteristics, its application also has certain limitations.
Mainly as:
(1) the limits of the welding position, because of the reasons for the flux to maintain, if not the use of special measures, submerged arc welding is mainly used for horizontal and vertical position welding, and can not be used for cross, vertical and overhead welding;
(2) the limits of the welding materials, can not be welded aluminum, titanium and other strong oxidizing metals and their alloys, mainly for the welding of ferrous metals;
(3) only suitable for long welding seam welding, and can not weld the space position of the limited weld; (4) can not directly observe the arc; (5) does not apply to the sheet, small current welding.
3, gas tungsten arc welding
This is a non consumable electrode gas shielded arc welding, which uses the arc between the tungsten electrode and the workpiece to melt the metal into the weld. Tungsten welding process to melt, only play the role of the electrode. Sent by the welding torch nozzle argon or helium for protection. Can also be added in accordance with the need for metal. In the international arena known as TIG welding. Gas tungsten arc welding as well to control the heat input, so it is an excellent way to connect the sheet metal and welding primer. This method can be used for the connection of all metals, and is especially suitable for welding aluminum and magnesium which can form refractory oxides and the active metal such as titanium and zirconium. This kind of welding method has high welding quality, but the welding speed is slower than that of other arc welding.
4, gas shielded arc welding (GMAG)
(GMAG) belongs to the welding method of heat source by arc weld pool as the arc welding wire is established with the parent metal mixed melting between the wire and the continuous feeding of the molten pool and the heat removed in the arc weld and base metal crystallization separation by metallurgy connected.
Characteristics of CO2 welding:
(1) in arc welding under high temperature CO2 can be decomposed into CO, O2 and O, has called the compression function of the arc, which leads to the welding arc shape method with arc column with smaller diameter, arc area is small and often difficult to cover the end of wire all droplet characteristics, so the transition resistance of droplet the (spotted force) and the large droplet coarsening, the transition path of the axial variation, splash rate;
(2) the protection of the weld area is good, CO2 density is commonly used to protect the gas in the largest, coupled with the CO2 gas thermal decomposition, the volume increases, so the protection is better;
(3) the energy is relatively concentrated, and the penetration ability is relatively large;
(4) low production cost, energy saving;
(5) technology and technology also has good visibility is easy to observe the welding area, and operation; welding heat affected zone and welding deformation is small; molten pool small crystallization speed, all position welding performance is good; the advantages of rust low sensitivity.
Metallurgical characteristics:
(1), the oxidation of CO2 alloy elements in welding, arc under high temperature, CO2 can be decomposed into CO, O2 and O, in the welding conditions, CO insoluble metal, did not participate in the reaction, while CO2 and O have strong oxidation, the oxidation of Fe and other alloy elements.
(2), deoxidation and weld metal alloy? Deoxidation, deoxidizing agent usually by adding a certain amount of wire in addition, Deoxidizer remaining as alloy elements in the weld, to compensate for the loss of oxidation and chemical composition of weld requirements.
Droplet transfer:
(1) short circuit transition (short arc, filament, small current) is suitable for all position welding of thin plate;
(2) transition of fine particles, thick wire, long arc, high current welding; (3), submerged arc droplet transfer (rarely used).
Power supply: oubtePower supply (single knob control), DC reverse, constant speed wire feeding welding material: CO2 gas and welding wire.
Scope of application: CO2 gas protection welding is widely used in locomotive manufacturing, shipbuilding, automobile manufacturing, coal mining machinery manufacturing and other fields. Suitable for welding low carbon steel, low alloy steel, low alloy high strength steel, but it is not suitable for welding non-ferrous metals, stainless steel. Although there is information showing that CO2 gas shielded arc welding can be used for stainless steel welding, but not the first choice for welding stainless steel.
5, plasma arc welding
Help the water-cooled nozzle and other measures, can make the arc column arc cross-sectional area decreases, temperature, energy density, plasma arc velocity increased significantly, the external constraint that is compressed by the arc column arc called plasma arc.
Plasma arc is a special form of arc, which is a kind of arc with high energy density, and is still a gas conduction phenomenon. Plasma arc welding is a method of using plasma arc heat to heat and melt the workpiece and base metal.
Classification: keyhole plasma arc welding and micro plasma arc welding.
Keyhole plasma arc welding current of 100 ~ 300A, joint without groove preparation, don't leave a gap. When welding, plasma arc welding can be completely fused and formed a small hole, the molten metal being squeezed around the hole, the arc movement, holes move, and weld is formed in the rear, so as to realize the one side welding with back. This method can be welded to the upper limit of plate thickness: carbon steel 7mm, stainless steel 10mm.
Micro beam plasma arc: the welding current is 0.1 ~ 30A, the thickness is 0.025 ~ 2.5mm. In addition, there are suitable for copper and copper alloy welding penetration type plasma arc welding, can be used for thick or thin plate welding and deep penetration welding high-speed plasma MIG welding, plasma arc welding can solve the Aluminum Alloy AC (variable polarity plasma arc welding) process. The main process parameters of plasma arc welding with welding current, welding speed, gas flow, plasma gas flow and welding torch nozzle structure and aperture.
Plasma arc cutting: the use of high temperature and high speed arc flow of plasma arc to melt the metal part of the incision so that evaporation, and the use of high-speed air flow or water flow will melt the material from the formation of the cutting process of the cutting method.
Characteristic：
(1) plasma arc arc energy density, high temperature, strong penetrating ability, 10 ~ 12mm thickness steel groove, a double-sided welding forming, welding speed, high productivity, small deformation stress.
(2) the cross section of the weld is a goblet shape, and the problem of non finger penetration.
(3) arc straight, affected by the fluctuation of arc length, the small fluctuation of molten pool.
(4) 0.1A still has a stable arc, the static characteristic is relatively flat, with a constant current source, can be very good for thin plate welding (0.1mm).
(5) the shrinkage of the tungsten electrode to prevent the welding of tungsten
(6) using small hole welding technology, realize one side welding.
(7) complex device, gas consumption, only suitable for indoor welding. The accessibility of the torch is worse than TIG.
(8) the arc diameter is small, need the torch axis and the weld centerline more accurately in the.
Metallurgical reaction: single, only evaporation.
Power supply: steep down power supply, DC is connected; welding aluminum and magnesium with AC, steep down power, arc, arc stability measures. Welding material: protective gas, tungsten electrode
Application scope: widely used in industrial production, especially the welding of copper and copper alloy, titanium and titanium alloy, alloy steel, stainless steel, molybdenum and other metal used in aerospace and military industry cutting-edge technology, such as missile shell of titanium alloy, on the plane some thin vessel etc..
6, tubular wire arc welding
Tubular welding wire arc welding is also used in the continuous feeding of the welding wire and the workpiece between the burning of the arc as heat source for welding, can be considered to be a type of gas arc welding. The welding wire used is a tubular welding wire, and the flux of various components is arranged in the pipe. Welding, plus the protection of gas, mainly CO2.
Flux thermal decomposition or melting, slagging protection plays a bath, alloying and arc stability role. Arc welding of tubular welding wire has the advantages of arc welding with the arc welding electrode, because of the effect of the flux in the tube. Tubular welding wire arc welding can be used in the welding of various kinds of joints. Tubular wire arc welding has been widely used in some advanced industrial countries.
Two, welding
1, gas welding
The use of gas: combustible gas combustion in oxygen when the heat generated by the base metal melting and welding a welding connection. The gas is used as a method of gas flame welding heat source. The most widely used is oxygen acetylene flame of acetylene gas as fuel. Because the equipment is simple to operate, but the gas heating rate and low productivity, heat affected zone, and easily lead to large deformation. The gas can be used for the welding of ferrous metal, nonferrous metal and alloy.
Can be gas: acetylene, liquefied petroleum gas, etc.. Acetylene, for example, the flame temperature of combustion in oxygen up to 3200. There are three kinds of oxygen acetylene flame:
Neutral flame: the mixing ratio of oxygen to acetylene volume is 1 ~ 1.2, acetylene is fully burnt, which is suitable for welding carbon steel and non ferrous alloy.
Carbon flame: oxygen and acetylene volume mixing ratio of less than 1, acetylene excess, suitable for welding of high carbon steel, cast iron and high speed steel.
The mixture of oxygen and acetylene oxidizing flame: volume ratio is larger than 1.2, excess oxygen, suitable for brazing brass and bronze.
Welding flame temperature is low, slow heating, heating area wide, HAZ width, welding deformation, and the welding process, the protection of molten metal by poor welding quality can not be guaranteed, so its application has very little. But the gas has no power, simple equipment, low cost, convenient movement and strong commonality, so in the situation without power and the field work has practical value. At present, mainly used for the welding of thin steel plate (thickness 0.5 ~ 3mm), copper and copper alloy and cast iron.
2, gas pressure welding
Gas pressure welding and gas welding, pressure welding gas flame as heat source. When welding, the end of the two butt joint of the workpiece is heated to a certain temperature, and then a sufficient pressure is applied to obtain the solid joint. Is a solid state welding. Air pressure welding is not filled with metal, commonly used in rail welding and steel welding.
3, electro slag welding
Electroslag welding is the resistance to heat of slagEnergy welding method. The welding process is in the position of the vertical welding, in the assembly space formed by the two end face of the workpiece and the water cooled copper sliding block. The use of current through the slag resistance heat generated when welding the workpiece end of melting. According to the shape of the electrode for welding, electroslag welding wire for electroslag welding, electroslag welding and melting mouth electroslag welding.
Characteristics of electro slag welding: in the process of electro slag welding, there is an arc process in addition to the beginning stage, and the rest are stable electro slag process, which is essentially different from the submerged arc welding process.
Electro slag welding has the advantage of: the thickness of the workpiece can be welded large (from 30mm to more than 1000mm), high productivity. Mainly used for welding in the cross-section butt joints and t-joint. Electro slag welding can be used for welding of various steel structures, and can also be used in the welding of castings. Electroslag welding joint is slower due to heating and cooling, heat affected zone width, coarse microstructure and toughness after welding generally require normalizing.
Limitations of electro slag welding:
(1) due to the weld pool, heating and cooling slowly, in the weld and heat affected zone is easy to overheat the formation of thick tissue, so usually after welding with electroslag welding joint in eliminating coarse normalizing.
(2) electroslag welding to welding always, cannot welding, electroslag welding for the workpiece thickness below 30mm, weld should not be too long.
Classification and application of electro slag welding
The classification of electroslag welding, electroslag welding with wire electrode, electroslag welding, melting mouth electroslag welding and electroslag welding tube.
Electroslag welding with wire electrode electroslag welding is the most commonly used method, it is used for the electrode wire according to the welding thickness is different, can use one or more single wire welding wire, welding thickness to welding for 40 ~ 60mm, when the welding thickness is greater than 60mm, the wire for horizontal swing; three wire can swing 450mm thick weldments. Wire electrode electro slag welding is mainly used for the welding of 40 ~ 450mm of the thickness of the welding parts and longer welding parts, but also can be used for large welding parts of the ring weld.
Application: mainly used for heavy machinery manufacturing, manufacturing forged welded structures and cast - welding structure, such as heavy machine machine, high pressure boiler, the welding thickness is 40 ~ 450mm, the material is carbon steel, low alloy steel, stainless steel etc..
4, electron beam welding
Electron beam welding is a method for welding the heat energy produced by the high speed electron beam bombardment of the surface of the workpiece. Electron beam is produced by electron beam welding and is accelerated by electron gun. Commonly used in electron beam welding are high vacuum electron beam welding, low vacuum electron beam welding and non vacuum electron beam welding. The first two methods are carried out in a vacuum chamber. Welding preparation time (mainly vacuum pumping time) is longer, and the size of the workpiece is limited by the size of the vacuum chamber. Electron beam welding and arc welding, the main feature is the weld penetration, weld width and weld metal of high purity. It can be used for precise welding of very thin materials and can be used in a very thick (up to 300mm) component welding. All metals and alloys which can be melted and welded by other welding methods can be welded by electron beam. Mainly used for the welding of high quality products. It can also solve the welding of dissimilar metals, metal oxides and refractory metals. But it is not suitable for mass production.
Electron beam welding machine: the core is the electron gun, it is to complete the electron generation, the electron beam forming and the convergence device, mainly by the filament, the cathode, the anode, the focusing coil and so on. Electric heating and heating the cathode filament, namely electronic emission when the cathode reaches about 2400K, high voltage electric field between the cathode and the anode, the accelerated electrons (about 1/2 light), through the anode hole injection, and then the focusing coil, converging into a diameter of 0.8 ~ 3.2mm electron beam welding, and in the welding surface and the kinetic energy is converted into heat, so that the welding joint of rapidly melting, by cooling crystallization after the formation of weld.
According to the different degrees of vacuum of the welding workshop (the position of the welding parts), the classification of the electron beam welding:
(1) high vacuum electron beam welding. The studio and the electron gun are in the same room, the vacuum degree is 10-2 ~ 10-1Pa, is suitable for the difficult to melt, the activity, the high pure metal and the small parts precision welding.
(2) low vacuum electron beam welding. Studio and the electron gun is divided into two vacuum chamber, the vacuum chamber of 10-1 ~ 15Pa, suitable for larger structures, and the oxygen, nitrogen is not too sensitive to refractory metals.
(3) non vacuum electron beam welding. The distance between the welding part and the electron beam exit should be controlled at about 10mm to reduce the scattering caused by the collision between the electron beam and the gas molecule. Non vacuum electron beam welding is suitable for welding of carbon steel, low alloy steel, stainless steel, refractory metal and copper, aluminum alloy, etc..
Advantages of vacuum electron beam welding:
(1) electron beam energy density is large, up to 5× 108W/cm2, about 5000 to 10000 times the normal arc, heat concentration, high thermal efficiency, small heat affected zone, narrow and deep weld, welding deformation is very small.
(2) welding in the vacuum environment, the metal does not function with the gas phase, the joint strength is high.
(3) the focus radius of the electron beam can be adjusted in a large range, flexible control, strong adaptability, can be welded 0.05mm thin pieces, but also can be welded 200 ~ 700mm thick plate.
Application: especially suitable for welding some refractory metal, active or high purity metal and thermal sensitive metal. But the complexity of the equipment, the cost is high, the welding size by vacuum chamber, high precision and easy assembly, excited X ray, auxiliary welding time is long, low productivity, wide application of these weaknesses are limited to electron beam welding.
5, laser welding
Laser welding is the welding of the laser beam which is focused by high power coherent monochromatic photon flow. This kind of welding method usually has continuous power laser welding and pulsed power laser welding. Laser welding has the advantage that it does not need to be carried out in a vacuum, the disadvantage is that the penetration is not as good as the electron beam welding. Precise energy control can be carried out in laser welding, so the welding of precision micro devices can be realized. It can be used in many kinds of metals, in particular, can solve some difficult to weld metal and dissimilar metal welding.
The generation of a laser: a beam of light, wavelength, frequency, and direction, which is produced when the material is excited.
Laser features: with good color, good direction, high energy density, high energy density, laser transmission or mirror after focusing, can beTo obtain a diameter less than 0.01mm, power density of up to 1013W/cm2 of energy, can be used as welding, cutting, drilling and surface treatment of heat source. Laser produced substances are solid, semiconductor, liquid, gas, etc., which is used for welding, cutting and other industrial processing is mainly yttrium aluminum garnet (YAG) solid laser and CO2 gas laser.
Main advantages of laser welding:
(1) laser can be transmitted through optical fiber, prism and other optical methods, suitable for micro parts and other welding methods can not reach the parts of the welding, but also through the transparent materials for welding.
(2) high energy density, high speed welding, heat affected zone and welding deformation are small, especially suitable for heat sensitive materials.
(3) laser radiation is not affected by the electromagnetic field, does not produce X rays, vacuum protection, can be used for large-scale structure of the welding.
(4) can be welded directly without pre insulated conductors, insulating layer can be peeled off; physical properties of different welding dissimilar materials.
The main disadvantage of laser welding is expensive equipment, low energy conversion rate (5% ~ 20%), welding interface processing, assembling and positioning requirements are very high, mainly used for welding of micro devices and instrument industry in the electronics industry, welding and silicon steel sheet, galvanized steel sheet etc..
Three, pressure welding
1, resistance welding
This welding method is the resistance of the heat energy, including the slag resistance heat for electroslag welding energy and a solid resistance heat energy resistance welding. As the electro slag welding has more unique characteristics, it is put in the back of the introduction. This paper introduces several kinds of solid resistance heat energy resistance welding, spot welding, seam welding, the main welding and butt welding etc.. Resistance welding is generally to make the workpiece under the action of a certain electrode pressure and the use of current through the workpiece generated by the resistance heat will be the contact between the two workpiece surface melting and welding method to achieve the connection. Usually use a large current. In order to prevent the occurrence of arc on the contact surface and to forging the weld metal, the welding process is always to put pressure. This type of resistance welding, welders surface good for stable welding quality is the most important. Therefore, the contact surface between the electrode and the workpiece, and the workpiece and the workpiece must be cleaned before welding.
Advantage：
1) when the fusion core is formed, the plastic ring is always surrounded by the plastic ring, which is separated from the air, and the metallurgical process is simple.
2) the heating time is short, the heat is concentrated, the heat affected zone is small, the deformation and the stress are small, and usually do not have to arrange the correction and the heat treatment process after welding.
3) does not need the welding wire, welding rod and so on, as well as oxygen, acetylene, argon and so on the welding material, the welding cost is low.
4) the operation is simple, easy to realize mechanization and automation, improve the working conditions.
5) high productivity, no noise and harmful gas, in large volume production, and other manufacturing processes can be assembled together with the assembly line. But because of the flash butt welding spark splash isolation.
Disadvantages:
1) there is still a lack of reliable non-destructive testing methods, the welding quality can only rely on the process of test specimens and the destructive testing of the workpiece, and rely on a variety of monitoring technology to ensure.
2) lap joint seam welding point, not only increased the weight of components, and because between two plates around the nugget formation angle, the tensile strength and the fatigue strength of the joints is low.
3) the equipment power is big, the mechanization automation degree is high, the equipment cost is high, the maintenance is more difficult, and the common high power single phase AC welding machine is not conducive to the normal operation of the power grid.
Scope of application: in the automotive, aircraft, equipment, home appliances, construction steel, and other industries have a wide range of applications, widely used materials, but easy to oxidation resistance of metal resistance welding is slightly worse. Thin plate assembly, which is mainly used for welding thickness less than 3mm. All kinds of steel, aluminum, magnesium and other non-ferrous metals and alloys, stainless steel, etc. can be welded.
2, friction welding
Friction welding is a solid state welding with mechanical energy as the energy source. It is the use of mechanical friction between the two surfaces generated by the heat to achieve the connection of metal. The heat of friction welding is concentrated in the joint surface, so the heat affected zone is narrow. Two the surface to be applied pressure, most of the time is to increase pressure on the end of the heating, so that the hot metal by the top of the forging, the general combination of surface does not melt. Friction welding productivity is higher, the principle of almost all can be hot forging of metal friction welding. Friction welding can also be used for welding of dissimilar metals. To be applied to the workpiece with a maximum diameter of 100mm of circular cross section. By using the heat generated by the mutual friction between the contact surfaces of the welding parts, the end face can reach the thermoplastic state, and then the top forging force is quickly applied to realize a solid state welding method of welding.
Friction welding has the following advantages:
(1) stable welding quality, the welding joint of high dimensional accuracy, scrap rate is lower than the resistance welding and flash butt welding.
(2) high productivity welding, flash butt welding than high 5 ~ 6 times.
(3) suitable for welding of dissimilar metals, such as connection between carbon steel, low alloy steel and stainless steel, high-speed steel, stainless steel, copper connection between copper and aluminum, aluminum steel, steel zirconium etc..
(4) low processing costs, power saving, welding parts without special cleaning.
(5) easy to realize mechanization and automation, simple operation, no spark arc welding work site, and harmful gas.
Disadvantages: by the workpiece rotation, welding non circular cross section is more difficult. The disc shaped workpiece and the thin wall pipe fittings are difficult to weld due to the difficulty of clamping. Due to the limitation of the power of the main spindle motor, the maximum cross section of friction welding is 20000mm2. Friction welder one-time investment cost is large, suitable for mass production.
Application of dissimilar metal and steel products, such as the electric power industry in the copper aluminum transition joint, high speed steel structure with metal cutting tool steel; steel products, such as boiler serpentine pipe, valves, bearings and other tractor.
3, diffusion welding
Diffusion bonding is generally a solid state welding method with indirect heat energy as the energy source. Usually carried out in a vacuum or protective atmosphere. When welding the two welders surface in high temperature and high pressure contact and heat preservation time, to achieve the distance between atoms together after atomic simple interdiffusion. Not only need to clean the surface of the workpiece before welding impurities such as oxides, and surface roughness to be less than a certain value to ensure the quality of welding.
Diffusion welding in vacuum or protective atmosphere, at a certain temperature (below the melting point of the base metal) and pressure conditions, make contactThe smooth surface of the treated surface is closely contacted with the surface of the micro plastic flow, and the atoms are mutually diffused. After a long period of time, the original interface disappears, and the welding method of the complete metallurgical bonding is achieved.
Diffusion welding has the following advantages:
(1) in the case of almost no damage to the performance of the welded materials, the welding between the various kinds of materials and dissimilar materials can be realized, which can be used to manufacture the double-layer or multilayer composite materials.
(2) welding complex structure and thickness is large workpieces.
(3) the composition and microstructure of the joint are uniform, and the stress corrosion tendency is reduced.
(4) welding distortion is small, the joint precision is high, can be used as part of the final assembly connection method.
(5) can be processed simultaneously with other processes (such as vacuum heat treatment, etc.), can be completed at the same time a number of joint welding, so as to improve productivity.
Disadvantages: diffusion welding welding parts surface processing and cleaning requirements, welding time is long, low productivity, high cost, large investment in equipment.
Application: welding, metal and ceramic welding between dissimilar metals with different melting point and metallurgical, and welding of titanium, nickel and aluminum alloy structures. It is not only used in the advanced technology of atomic energy, aerospace and electronics industry, but also has been extended to the general machinery manufacturing industry department.
Four, brazing
Brazing of energy can be chemical reaction heat, also can be indirect heat energy. It is the melting point than the material being welded with low melting point metal solder, the solder melts after heating, capillary action and solder into the gap of the joint contact surface, wetting welded metal surface between the liquid and solid phase diffusion and the formation of brazed joints. Therefore, brazing is a kind of solid phase and liquid phase welding method.
1, brazing characteristics and Applications
The melting point is lower than that of the base alloy brazing material for brazing, heating and melting, and by wetting and wicking fill in and keep the joint gap, and the parent material in solid, liquid and solid base metal solder on the mutual diffusion between the formation of brazed joint. The physical and chemical properties of the base metal brazing effect, welding stress and deformation is small, can be welding of dissimilar metals different properties, can simultaneously complete weld seams, joint appearance neat, simple production equipment, small investment. But the strength of the solder joint is low, and the heat tolerance ability is poor.
Application: hard alloy cutting tools, drilling bit, bicycle frame, heat exchanger, tube and all kinds of containers; in the manufacture of microwave waveguide, electronic tube and electronic vacuum devices, brazing even the only possible connection method.
2, solder and flux
The filler metal is formed in the solder joint, and the quality of the solder joint is largely determined by the solder. Solder should have appropriate melting point, good wettability and sealing ability, and can mutual diffusion of the parent material, but also should have the mechanical properties and physical and chemical properties, in order to meet the requirements of the use of joints. According to the melting point of the solder, brazing is divided into two categories: soldering and brazing.
(1) soft soldering:
Brazing filler metal with a melting point less than 450 degrees C is called soft soldering. It is commonly used as tin lead solder. It has good wettability and electric conductivity. It is widely used in electronic products, electrical appliances and auto parts. Soft soldering joint strength is generally 60 ~ 140MPa.
(2) brazing:
Solder melting point above 450 DEG C, called the brazing filler metal is used, brass and silver based solder solder. With high strength, conductivity and corrosion resistance of the solder joint with silver brazing filler metals, low melting point, good technology, but the price is higher than for brazing, welding demanding, general welding with brass solder. Hard soldering is used for the welding of steel and copper alloys, and of the tool. Hard solder joint strength is 200 ~ 490MPa.
Note: the contact surface of the parent material should be very clean, so it is in flux. The flux function is to remove the base metal and oxide solder surface and oil impurities, protect the solder and base metal contact surface is not oxidized, increase the wettability and capillary flow of solder. Flux should be lower than the melting point of solder, corrosive flux residue on the base metal and the joint should be small. Soldering flux is rosin or commonly used zinc chloride solution, commonly used solder brazing agent is a mixture of borax, boric acid and alkaline fluorides.
According to the heat source or heating method, brazing can be divided into: flame brazing, induction brazing, furnace brazing, dip soldering, resistance brazing, etc.. Due to the low heating temperature, the performance of the workpiece material is small, and the stress and deformation of the welded parts are small. But the strength of the solder joints is generally low, and the heat resistance is poor.
Brazing heating methods: almost all of the heating heat source can be used as brazing heat source, and so will be brazing classification.
Flame brazing: using gas flame for heating, for carbon steel, stainless steel, hard alloy, cast iron, copper and copper alloy, aluminum and aluminum alloy brazing.
Induction brazing: the use of alternating magnetic field in the part of the induction current resistance heat welding parts, used to have a symmetrical shape of the welding parts, especially the tube shaft type of brazing.
Dip soldering: the welding part or whole immersed in a molten salt mixture of molten solder or melt, by these liquid medium heat to achieve the brazing process, which is characterized by rapid heating, uniform temperature, small welding distortion.
Furnace brazing using resistance furnace heating welding, resistance furnace by vacuum or by reducing gas or inert gas protection welding.
In addition, there are iron brazing, resistance brazing, diffusion brazing, soldering, brazing, the infrared response of electron beam brazing, laser brazing etc..
Brazing can be used for welding carbon steel, stainless steel, high temperature alloy, aluminum, copper and other metal materials, but also can connect dissimilar metals, metal and nonmetal. Suitable for welding joint loading or not working at normal temperature, the micro joints and complex brazing precision, especially suitable for welding.
Five, other welding introduction
High frequency welding
High frequency welding is a solid resistance heat as energy. When welding, the resistance heat generated by high frequency current in the workpiece is heated to heat the surface layer of the workpiece welding area to the molten or close plastic state. So it is a kind of solid state resistance welding method. High frequency welding according to the high frequency current in the workpiece can be divided into thermal contact with high-frequency welding and induction high-frequency welding. When in contact with high frequency welding, the high frequency current is passed through the mechanical contact with the workpiece. The coupling of high frequency current through the outer induction coil of the workpiece in the induction of high frequency weldingInduced current is generated in the workpiece. High frequency welding is a highly specialized welding method, to be equipped with special equipment according to the product. High productivity, welding speed of up to 30m/min. Mainly used in the manufacture of pipe, longitudinal seam or spiral seam welding.
Explosive welding
Explosive welding is another kind of solid state welding method with chemical reaction heat as energy source. But it uses the energy produced by the explosion to realize the metal connection. Under the action of the blast wave, the two pieces of metal can be accelerated in less than one second to form a metal. Among all kinds of welding methods, explosive welding can be welded to the widest range of different metal combinations. Two kinds of metals, which can not be used in metallurgical, can be welded into various kinds of transition joints by explosive welding. The explosive welding is used to cover a large surface area, which is an efficient method for the manufacture of composite plates.
Ultrasonic welding
Ultrasonic welding is a solid state welding method with mechanical energy as the energy source. When ultrasonic welding is carried out, the high frequency vibration of the welding work piece can be caused by the high frequency vibration of the ultrasonic welding, which can cause the bonding surface to generate strong crack friction and heat to the welding temperature. Ultrasonic welding can be used for the welding between the majority of metal materials, metal, dissimilar metal and metal and non metal welding. The repeated production can be applied to metal wire, foil or sheet metal joint of 2 ~ 3mm.
Six, welding new technology, new technology introduction
1, welding robot
The outstanding performance of welding technology progress is the development of welding process from mechanization to automation, intelligence and information. The application of intelligent welding robot is an important symbol of the high degree of automation in the welding process. The welding robot breaks through the traditional way of welding automation, which makes it possible to make small batch automatic production.
Most of the welding robot is the fixed position of the arm, there are two types of teaching and intelligent.
Teach a robot: through the teaching, memory welding trajectory and welding parameters, and in strict accordance with the teaching procedures to complete the welding of products. With only one demonstration, the robot can accurately represent each step of the teaching. This kind of welding robot is widely used, it is suitable for mass production. It is used for the fixed position of the assembly line. The function of this kind of welding robot is mainly to teach and reappear. No place for a small quantity of large structure at the site of production.
Intelligent robots that can automatically determine the starting point of the weld trajectory, control command according to simple and relevant parameters, and can automatically adjust the seam tracking, welding torch attitude, according to the actual situation to adjust the control parameters, the welding quality of welding. This is the most advanced welding robot, with smart, portable, easy to move and other features, can adapt to different structures, different locations of the welding task, the actual application of very few, is still in the research and development stage.
Welding robot, welding robot accounted for 50% ~ 60%, it consists of three parts of the robot body, spot welding system and control system. The degree of freedom of the robot body is 1 to 5, and the control system is divided into two parts, the control system is divided into two parts.
The welding system includes: welding controller, welding tongs and water, electrical and other auxiliary parts (underwater welding).
2, the application of computer software
The application of computer software system in welding field is mainly in the following aspects:
(1) computer simulation technology includes the simulation of welding thermal process, welding metallurgy process, welding stress and deformation, etc.. Welding is a complex process involving arc physics, heat transfer, metallurgy and mechanics. Once the welding process has been realized by computer simulation, it is able to determine the best design scheme, process method and welding parameters for welding of various structures and materials through the computer system. Traditionally, the welding process is always going through a series of experiments or determined by the experience, in order to obtain reliable and economic structure, as long as the applicability of a computer simulation prove that the numerical method in dealing with a problem, a large number of screening work can be done by computer, saves a large amount of testing work, thus greatly save manpower, material resources and time, has very important significance in the welding of new engineering structures and new materials. The level of computer simulation technology determines the scope of automatic welding. In addition, computer simulation is also widely used in the analysis of the strength and performance of welded structures and joints.
(2) welding process design and selection of the process parameters, welding defect diagnosis, welding cost budget, real-time monitoring, welding, welder qualification test for CAD database technology and expert system.
Database technology has penetrated into all aspects of welding field, from raw materials, welding test, welding process to welding production. A typical database system of welding procedure, welding process, welding materials, welding materials, file management, composition and properties of welding, welding and welding standard CCT management consulting system etc.. These database systems provide favorable conditions for the management of various data and information in the welding field.
Welding expert system is mainly focused on process planning, defect prediction and diagnosis, computer aided design and so on. In the existing welding expert system, the process selection and the technology development are the most important application fields. The real-time control of the welding process is an important development direction.
(3) computer aided quality control (CAQ) is used to analyze the data of the products and the real-time monitoring of the welding quality.
In addition, the application of computer aided design / manufacture (CAD/CAM) in welding process is also increasing, which is mainly used in the design of CNC cutting, welding structure and welding robot.