Welding, also called fusion welding, is a method of joining metal or other materials by heating, high temperature or high pressureThermoplasticityManufacturing process andtechnology。
modernThere are many energy sources for welding, including gas flameelectric arc, laserelectron 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.Possible injuries to human body caused by welding includeburnElectric shock, vision damage, inhalation of toxic gas, excessive ultraviolet radiation, etc.
Before the end of the 19th century, the only welding process wasblacksmithMetal that has been used for hundreds of yearsForge welding。The earliest modern welding technology appeared at the end of the 19th centuryArc weldingandOxy fuel gas welding, came laterResistance 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 popularManual arc welding, and such asGMAW、Submerged arc welding(submerged arc welding)Flux cored wire arc weldingandElectroslag weldingSuch automatic or semi-automatic welding technology.
In the second half of the 20th century, welding technology developed rapidly,Laser weldingandElectron beam weldingWas developed.today,welding robot It has been 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.
The history of metal connection can be traced back thousands of years. The early welding technology can be seen inBronze AgeandIron AgeOfEuropeAnd the Middle East.Thousands of years agoBabylon, CubaMesopotamian civilization Started usingSoft solderingTechnology.In 340 BC, the ancient India weighing 5.4 tons was manufacturedIron pillar People use welding technology.
In the Middle Ages, blacksmiths forged red hot metal to connect it. This process is calledForge welding。Vinajong BiringesseoPublished in 1540《Flame science》Secretary 1 described forging and welding technology.EuropeRenaissanceOur craftsmen have mastered forging and welding very well. In the following centuries, forging and welding technology continued to improve.By the 19th century, the development of welding technology had advanced rapidly, and its style and features had changed greatly.In 1800,humphry davy Sir found outelectric arc；Later, along with Russian scientistsNikule SlavyenovWith American scientistsC. L. GoffinThe metal electrode invented by C. L. Coffin promoted the forming of electric arc welding process.Arc welding and later developedCarbon arc welding, widely used in industrial production.Around 1900,A. P. StroganovThe metal coated carbon electrode that can provide more stable arc has been developed in the UK;In 1919,C. J. Holsrag(C. J. Holslag) for the first timealternating currentIt was used for welding, but this technology was not widely used until ten years later.
Resistance weldingDeveloped in the last decade of the 19th century, the first patent on resistance welding wasElihu ThomsonHe applied in 1885 and continuously improved this technology in the next 15 years.Thermit weldingandGas weldingIt was invented in 1893.Edmund David discovered acetylene in 1836. By 1900, due to a newGas torchThe emergence of combustible gas welding began to be widely used.Due to its low cost and good mobility, combustible gas welding has become one of the most popular welding technologies at the beginning.However, with the continuous improvement of metal coating technology on electrode surface by engineers in the 20th century (i.escaling powderThe new electrode can provide a more stable arc and effectively isolate the base metal and impurities,arc weldingTherefore, it can gradually replace combustible gas welding and become the most widely used industrial welding technology.
the First World WarAs a result, the demand for welding has soared, and all countries are actively studying new welding technologies.The UK mainly uses arc welding, and they have built the first all welded hull ship, the Frago.During the war, arc welding was also used in aircraft manufacturing for the first time. For example, the airframe of many German aircraft was manufactured in this way.In addition, it is worth noting that the world's first all welded highway bridge was built in Poland in 1929WofqiS nearbyłBuilt on the udwia Maurzyce River, the bridge is composed ofWarsaw Institute of TechnologyStefan Bryła) Designed in 1927.
In 1920s, the welding technology achieved a major breakthrough.Automatic welding appeared in 1920, and the continuity of the arc was ensured through automatic wire feeding device.Shielding gasDuring this period, it received extensive attention.Because in the process of welding, the metal under high temperature willoxygenandnitrogenhappenchemical reaction, resulting inVacuoleAnd compounds will affect the strength of the joint.The solution is to use hydrogenargon 、heliumTo isolate the molten pool from the atmosphere.In the next 10 years, the further development of welding technology has madealuminumAnd active metals such as magnesium can also be welded.1930s tothe Second World WarDuring this period, the introduction of automatic welding, alternating current and active flux greatly promoted the development of arc welding.
In the middle of the 20th century, scientists and engineers invented a variety of new welding technologies.Invented in 1930stud welding (Nail welding), which was soon widely used in shipbuilding and construction industry.Invented in the same yearSubmerged arc welding, which is still popular today.Gas tungsten arc weldingAfter decades of development, it was finally perfected in 1941.Then in 1948,GMAWThe rapid welding of non-ferrous metals is possible, but this technology needs to consume a lot of expensive shielding gas.Using consumable electrode as electrodeManual arc weldingIt was developed in the 1950s and quickly became the most popular metal arc welding technology.In 1957,Flux cored wire arc weldingFor the first time, the self-protection welding wire electrode can be used for automatic welding, greatly improving the welding speed.In the same year,Plasma arc weldinginvention.Electroslag weldingInvented in 1958,Gas electric weldingIt was invented in 1961.
The development of welding technology in recent years includes:Electron beam weldingIt can heat a small area, making it possible to weld deep and long workpieces.laterLaser weldingIt was invented in 1960 and proved to be the most effective high-speed automatic welding technology in the following decades.However, the application scope of electron beam welding and laser welding is limited due to their high price.[1]
Welding purpose
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Welding achieves the purpose of joint through the following three ways:
1. Fusion welding - heating the workpiece to be joined to make it locally melt and formMolten poolAfter cooling and solidification of the molten pool, it can be joined, if necessaryMelt fillAuxiliary, it is suitable for welding of various metals and alloys without pressure.
2. Pressure welding - the welding process must apply pressure to the weldment, which belongs to variousMetallic materialsAnd processing of some metal materials.
3. Brazing - using a metal material with a lower melting point than the base metal as the solder, wetting the base metal with liquid solder, filling the joint gap, and diffusing with the base metal to realize the bonding weldment.It is suitable for welding of various materials, and also suitable for welding of different metals or dissimilar materials.
Metal welding
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Welding classification
During welding,workpieceandsoldermeltForming a melting zone,Molten poolThe connection between materials is formed after cooling and solidification.In this process, it is usually necessary to applypressure。There are many energy sources for welding, includingGas flame、electric arc, laserelectron beam, friction, ultrasonic, etc.Before the end of the 19th century, the only welding process wasblacksmithMetal that has been used for hundreds of yearsForge welding。The earliest modernwelding technique At the end of the 19th centuryArc weldingandOxy fuel gas welding, came laterResistance welding。In the early 20th century, with the firstthe Second World WarAt the beginning of the war, there was a great demand for cheap and reliable connection methods of military equipment, which promoted the development of welding technology.Today, withwelding robot stayIndustrial applicationsThe researchers are still deeply studying the nature of welding and continue to develop newwelding method To further improvewelding quality 。
Physical essence
Welding is a process in which two or more materials of the same or different species are bonded and diffused into one by atoms or molecules
The method to promote the combination and diffusion between atoms and molecules is heating or pressurizing, or heating and pressurizing at the same time
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 metals and variousalloying element。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 and molten pool rate during welding;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.
Bench type cold welding machine
The common feature of various pressure welding methods is that the pressure is applied in the welding process without filler materials.Most pressure welding methods, such asDiffusion welding、High frequency welding、Cold pressure weldingThere is no melting process, so there is no burning loss of beneficial alloy elements and invasion of harmful elements into the weld, as in fusion welding, which simplifies the welding process and improves the safety and health conditions of welding.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 are difficult to useFusion weldingThe welded materials can often be pressure welded into high-quality joints with the same strength as the base metal.
The joint formed during welding to connect two connected bodies is called weld.During welding, both sides of the weld will be affected by welding heat, and the structure and properties will change. This area is called heat affected zone.Due to workpiece material during weldingwelding material 、welding current And so on.To worsen weldability, it is necessary to adjust the welding conditions, preheat the weldment interface before welding, heat preservation during welding andPost weld heat treatment, which can improve the welding quality of weldments.
In addition, welding is a local rapid heating and cooling process, and the welding area cannot be controlled by the surrounding workpiece bodyFree expansionAnd shrinkage, which will be generated in the weldment after coolingWelding stressAnd deformation.All important products need to be relieved of welding stress and rectified after weldingwelding deformation 。
Modern welding technology has been able to weldMechanical propertiesWelds equal to or even higher than the connected body.The mutual position of welded bodies in space is calledwelded joint The strength of the joint is not only affected by the weld quality, but also related to its geometry, size, stress and working conditions.The basic forms of joints include butt joint, lap joint and T-joint (positive joint)
The cross section shape of the butt joint weld depends on the thickness of the welded body before welding and thegrooveForm.When welding thicker steel plates, various shapes of grooves shall be made at the edges for penetration, so that the welding rod or welding wire can be easily fed.The groove forms include single-sided groove and double-sided groove.When selecting groove type, in addition to ensuring penetration, it is also necessary to consider the convenience of welding and fillingAmount of metalLess welding deformation and low cost of groove processing.
Two pieces with different thicknesssteel plateDuring butt joint, in order to avoid serious stress concentration caused by sharp change of cross section, thicker plate edges are often gradually thinned to equal thickness at two joint edges.The static strength and fatigue strength of butt joints are higher than those of other joints.stayalternating、Impact loadButt joint welding is often preferred for the connection under or in low temperature and high pressure vessels.
The pre welding preparation of lap joints is simple, the assembly is convenient, and the welding deformation and residual stress are small, so they are often used in the field installation of joints and unimportant structures.Generally speaking, lap joints are not suitable for working under alternating load, corrosive medium, high temperature or low temperature.
The use of T-joints and corner joints is usually due to structural needs.On T-jointIncomplete penetrationThe working characteristics of fillet weld of lap joint are similar to that of fillet weld of lap joint.When the weld is perpendicular to the direction of external force, it becomesFront fillet weldAt this time, the shape of the weld surface will cause different degrees of stress concentration;The stress of fillet weld with penetration is similar to that of butt joint.
The bearing capacity of the corner joint is low, and it is generally not used alone. It can be improved only when it is fully welded or when there are fillet welds inside and outside. It is mostly used at the corners of closed structures.
Compared with riveted parts, welded productscastingAnd forgings, forMeans of transportationIt can reduce self weight and save energy.The welding has good sealing property and is suitable for manufacturing various containers.The development of joint processing technology can combine welding with forging and casting to produce large, economical and reasonable cast welding structures and forge welding structures with high economic benefits.The welding process can effectively use materials, and the welding structure can use materials with different properties in different parts, giving full play to the advantages of various materials, so as to achieve economic and high-quality.Welding has become an indispensable and increasingly important processing method in modern industry.
In modern metal processing, welding is better than castingforging and pressingThe process developed late, but at a fast speed.The weight of welded structure accounts for about 45% of the steel output, and aluminum andaluminium alloyThe proportion of welded structures is also increasing.
The future welding process, on the one hand, should develop new welding methodsWelding equipmentAnd welding materials to further improve welding quality and safety reliability, such as improving existing welding energy sources such as arc, plasma arc, electron beam and laser;Use electronic technology and control technology to improve the arc resistanceProcess performanceA reliable and lightweight arc tracking method is developed.
On the other hand, it is necessary to improve the level of mechanization and automation of welding, such as program control and digital control of welding machine;Develop a special welder that automates the whole process from preparation, welding to quality control;stayAutomatic weldingConnecting to the production line, promoting and expanding the numerical control welding manipulator and welding robot can improve the welding production level and improve the welding health and safety conditions.
Evolution process
Hammer anchor drawing in Heavenly Creations
Welding technology appears with the smelting production of copper, iron and other metals and the application of various heat sources.The ancient welding methods are mainlyCast welding、Brazing、Forge welding、rivet and solder。2500 BCBabylon, CubaThe people and the Indus River civilization have reached a high level in the hot and cold processing of copper and iron metals, and can use forging welding, casting welding and other welding methods to manufacture metal appliances, and engraved with characters.At this time, the representative culture isHarappa Culture。
Made in the Shang DynastyIron edged bronze axeIt refers to the cast weldment of iron and copper. The fusion line of copper and iron on the surface is zigzag and well connected.Spring and Autumn Period and Warring States PeriodIn the tomb of Marquis Yi of Zeng, there are many coiled dragons on the bronze base of Jiangu, which are brazed in sections.After analysis, the composition of the solder used is similar to that of modern soft solder.The sword is made in the Warring States Period. The blade is steel and the back isWrought ironIt is generally formed by heating, forging and welding.According to Song Yingxing of the Ming Dynasty《Tiangong Kaiwu》A book records that in ancient China, copper and iron were heated together and forged to make knives and axes;Use yellow mud or sifted Chenjiubi soil to sprinkle on the interface, and forge and weld large anchors in sections.In the Middle Ages, weapons were also forged and welded in Damascus, Syria.
Modern development
The ancient welding technology has remained at the level of casting welding, forging welding, brazing and riveting for a long time. The heat source used is furnace fire, which is low in temperature and not concentrated in energy. It can not be used for welding workpieces with large sections and long welds, but can only be used to make decorations, simple tools, living appliances and weapons.
Shielded metal arc welding
At the beginning of the 19th century, Davies in England found thatelectric arcandOxyacetyleneFlame is two high temperature heat sources that can locally melt metal;From 1885 to 1887, Russia's Benaldos invented the carbon electrode arc welding clamp;It appeared again in 1900Thermit welding。At the beginning of the 20th century, carbon electrode arc welding and gas welding were applied. At the same time, thin coated electrode arc welding appeared. The arc was relatively stable, and the welding pool was affected byslagProtection, improved welding qualityManual arc weldingIn the practical stage, electric arc welding has become an important welding method since the 1920s.It has also become the beginning of the development of modern welding technology.During this period, Noble in the United States usedarc voltage Control the feeding speed of welding rod to make automatic arc welding machine, thus becoming the beginning of welding mechanization and automation.AmericanJeff Robinov Invention using welding wire andfluxOfSubmerged arc weldingWelding mechanization has been further developed.In the 1940s, in order to adapt to aluminum, magnesium alloys andAlloy steelThe need for welding, tungsten electrode andMIG weldingOne after another.
In 1951, the Soviet Union's Barton Electric Welding Research Institute createdElectroslag weldingIt becomes an efficient welding method for thick workpieces.In 1953, the Soviet Union's Lyubavsky and others inventedCO2 gas shielded welding, promoting the application and development of gas shielded arc welding, such as mixed gas shielded weldingFlux cored wireGas slag joint shielded welding and self shielded arc welding, etc.The invention of Gage in 1957Plasma arc welding；Invented in Germany and France in the 1940sElectron beam welding, which was also practical and further developed in the 1950s;In the 1960s, laser welding plasma, electron beam andLaser weldingThe appearance of the method indicates thatenergy density The new development of fusion welding has greatly improved the weldability of materials, making it possible to weld many materials and structures that are difficult to weld by other methods.
Other welding technologies include 1887, AmericanThompsonResistance welding is invented and used for spot welding andSeam welding；Seam welding is the earliest semi mechanized welding method in pressure welding. With the seam welding process, the workpiece is pushed forward by two rollers;Used since 1920sFlash butt weldingMethods Welding bar and chain.So far, resistance welding has entered the practical stage.In 1956, Jones of the United States inventedUltrasonic welding；Invented by Chudikov in the Soviet Unionfriction welding；In 1959,Stanford, USAResearch success of the InstituteExplosive welding；In the late 1950s, the Soviet Union made vacuum diffusion welding equipment.
Development trend
Development trend of welding technology 1. Improving welding productivity is an important driving force to promote the development of welding technology
There are two ways to improve productivity: first, improve the welding deposition rate, such as three wire submerged arc weldingprocess parameters 220A/33V, 1400A40V and 1100A45V respectively.The groove section is small, and a baffle or pad is set at the back. The 50~60mm steel plate can be formed by one-time penetration welding. The welding speed can reach more than 0.4m/min, and the deposition rate is more than 100 times higher than that of shielded metal arc welding. The second way is to reduce the groove section and metal deposition. The most prominent achievement is narrow gap welding.Narrow gap welding is based on gas shielded welding. Single wire, double wire and three wire welding can be used regardless of joint thickness. For example, the thickness of steel plate is 50~300 mm, and the gap can be designed to be about 13 mm. Therefore, the amount of deposited metal required is reduced by several times or ten times, thus greatly improving productivity.The key technology of narrow gap welding is to ensure the penetration of both sides and the automatic tracking of the arc center on the groove centerline. For this reason, many different schemes have been developed in the world, and many narrow gap welding methods have emerged.
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 improve the welding speed, such as 5mm steel plate or aluminum plate. The welding speed can reach 2~3m/min, which can obtain good shape and quality, and the welding deformation is small.
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, only starting from the welding process has certain limitations, so countries around the world pay special attention to the technical transformation of workshops.The main processes of the preparation workshop include material transportation, material surface degreasing, sand blasting, and protective paint coating;Steel plate scribing, cutting and beveling;partsAssemble and fix.The above processes have been mechanized and automated in modern factories.Its advantage is not only to improve the productivity of products, but also to improve the quality of products.
3. Automatic and intelligent welding process is an important direction to improve the stability of welding quality and solve severe working conditions.
4、Emerging industryThe development of welding technology has been constantly promoted.
Welding technology has a history of more than one hundred years since its invention. It can almost meet the needs of production and manufacturing of all important products in the current industry.However, the development of emerging industries still forces the welding technology to advance continuously.The Development of Microelectronics Industry Promotes MicroelectronicsConnection processDevelopment of equipment;For another example, the development of ceramic materials and composites has promoted 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 source is the fundamental power to promote the development of welding technology.
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 focuses on arc welding, resistance welding automatic welding equipment). The emergence of each heat source in history is accompanied by the emergence of new welding processes.However, up to now, the development and research of welding heat source has not ended.
6. Energy saving technology is a common concern
As we all know, welding consumes a lot of energy. For example, welding rod arc welding, about 10KVA for each, submerged arc welding, 90KVA for each, and resistance welding can reach thousands of KVA. Many new technologies have emerged to achieve this energy saving goal.In resistance spot welding, with the development of electronic technologyAC spot welderChange toSecondary rectifier spot welderIt can improve the power factor of the welding machine and reduce the capacity of the welding machine. The 1000KVA spot welding machine can be reduced to 200KVA, while still achieving the same welding effect.Inverter welderIt 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 method
The welding technology is mainly applied to the metal base metal. The common welding technologies include electric arc welding, argon arc welding, CO2 shielded welding, oxygen acetylene welding, laser welding, electroslag pressure welding, plastic, etcNon metallic materialsIt can also be welded.There are more than 40 metal welding methods, which are mainly divided into fusion welding, pressure welding and brazing.
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.
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.
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.
The seam connecting two connected bodies formed during welding is called weld.Both sides of the weld will be subject to welding heat during welding, and the structure and properties will change. This area is called 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 seam and heat affected zone after welding, which also reduces the performance of the weldment and worsens the weldability.This requires adjustment of welding conditions. Preheating at the interface of weldment before welding, heat preservation during welding and post welding heat treatment can improve the welding quality of weldment.[2]
Industrial art
The emergence of welding caters to the needs of the development of metal art for new techniques.
Overlap
Art creation and craft methods are always inseparable.As an industrial technology, the emergence of welding caters to the needs of the development of metal art for new technological means.On the other hand, the unique and wonderful changes of metal under the action of welding heat also meet the needs of metal art for new artistic expression language.In today's metal art creation, welding is being expressed as a unique artistic expression language.Metal weldingArt, as a relatively independent art form, can be separated from traditional metal art in a branch way, because welding is artistic.Welding can produce rich expression language of artistic creation.Welding is usually carried out at high temperature, and metal will produce many wonderful and rich changes at high temperature.The metal base metal will undergo color change and thermal deformation (i.eWelding heat affected zone）Welding defectsIt is often used in welding art.Welding defects refer to the defects that do not meet the design or process requirements during welding.Its manifestations mainly include welding cracks, pores, undercuts, incomplete penetration, incomplete fusion, slag inclusionOverlapCollapse, pit, burn through, inclusion, etc. This is a very interesting phenomenon: in today's metal art creation, the artistry of welding is usually reflected in some failed operations of industrial welding, or hidden in some welding defects that industrial welding strives to avoid.Secondly, the language of welding art is unique.
For a welding sculpture, the rough weld is exposed on the surface of the sculpture, and various irregular cutting marks have also become the artist's beautiful artistic language. In many cases, due to the rough and simple style of welding sculpture, the corrosion and defects of metal are mostly reserved according to the needs of the work. Therefore, a kind of non carvedOriginal beauty.
The welding seam at the splicing of the steel plate at the lower part of the sculpture is very thick. From the perspective of the firmness of the welding process, it is obviously not only out of the consideration of the solidity of the sculpture. In this sculpture, several twisted welding seams at the lower part have become an indispensable part of the sculpture as an important factor in its overall aesthetic.From the perspective of sculpture as a whole, no matter the character modeling in the upper part or the texture processing in the lower part, there are distorted welding traces everywhere, and the whole work has reached the unity of the overall visual language.In the manual plasma cutting method, the heat generated by the current during cutting is used to make the cutting edge produce a heat affected zone, which will "dye" the bright white stainless steel with a slightly gradual color.At the same time, through the adjustment of welding specifications, the strong air flow from the cutting gun will blow a circle of randomly formed texture at the cutting edge at the moment of melting the cutting steel plate.The formation process of this random effect has certain 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 welding art wall decorations, and manual tungsten electrode can be used for smaller onesArgon arc welding。
If a mural work is regarded as a painting, the processing of points, lines, surfaces, black, white, gray and even colors in the picture can be achieved by welding.Metal wires of various models and materials will appear in different forms on the screen when different welding processes are applied.Different metals have different colors, bright silver of stainless steelAluminiumOf carbon steel,Titanium steel, bronze, red copper, brass, and as for steel, different steels will have different color changes when heated at high temperature, namelyWelding heat affected zoneIs different.In addition, cutting is also one of the methods of creating welding art murals, which can be used either in combination with welding or alone, depending entirely on the creator's creative intention and mastery of technology and effect.Taken together, the above methods are rich in changes.
Plastic welding
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Apply heat and pressure or other methods toThermoplasticA method of fusing two or more surfaces of a product into a whole.
Causes of fire and explosion accidents
Plastic welding machine
(1) During welding and cutting operations, especially gas cutting, sparks, molten beads and iron slag are splashed around (larger molten beads and iron slag can be splashed 5m away from the operating point) due to the use of compressed air or oxygen flow jet. When there are flammable and explosive substances or gases in the operating environment, fire and explosion accidents may occur.
(2) When welding and cutting at heightinflammables and explosives If it is not cleaned up, the operators throw welding rod heads in the process of work, and do not carefully check whether there is kindling after the operation.
⑶ Gas welding and gas cutting are not placed according to the specified requirementsAcetylene generatorThe welding (cutting) torch, rubber pipeline andacetyleneGenerator safety device.
(4) There are deficiencies in the formulation of gas cylinders, as well as in the storage, filling, transportation and use of gas cylindersSafe Operation ProceduresEtc.
(5) There are defects in the formulation and installation of acetylene, oxygen and other pipelines, which are not found and rectified in time during use.
(6) Relevant measures were not taken as required when repairing fuel containers and pipes.When carrying out replacement welding repair, the replacement is not complete, and when carrying out pressure non replacement welding repair, the pressure is not enough, leading to the introduction of external open fire.
Preventive measures
(1) During welding and cutting operations, all inflammable and explosive materials within 10M of the operating environment shall be cleaned up, and the trenchsewerWhether there is combustible liquid and gas inside, and whether it is possible to leak combustible and explosive substances into the trench and sewer, so as to avoid disasters and accidents caused by welding slag and metal sparks.
(2) When welding and cutting at heights, it is forbidden to throw welding rod heads randomly. The lower part of welding and cutting operations should be isolated. After the operation is completed, careful inspection should be carried out and no fire hazard can be confirmed before leaving the site.
⑶ Cylinders that meet the requirements of relevant national standards and regulations shall be used, and the storage, transportation and use of cylinders shall be strictly followedSafe Operation Procedures。
⑷ Pipelines conveying combustible gas and combustion supporting gas shall be installed, used and managed according to regulations, and special safety technical training shall be provided for operators and inspectors.
(5) When repairing the fuel container and pipeline, the welding method shall be determined according to the actual situation.When the replacement method is implemented, the replacement shall be thorough. During the work, the presence of combustible substances shall be strictly controlled. When the replacement method is implemented under pressure, a certain voltage shall be maintained as required.The oxygen content shall be strictly controlled during work.It is necessary to strengthen detection, pay attention to monitoring, and take safety organization measures.
Content abstract: As an industrial technology, the emergence of welding caters to the needs of new technology means for the development of metal art.On the other hand, the unique and wonderful changes of metal under the action of welding heat also meet the needs of metal art for new artistic expression language.
Key words: metal art welding
Art creation and craft methods are always inseparable.As an industrial technology, the emergence of welding caters to the needs of new technological means for the development of metal art.
Metal welding art can be separated from traditional metal art as a relatively independent art form in a branch way, because:
First, welding is artistic.
Welding can produce rich expression language of artistic creation.Welding is usually carried out at high temperature, and the metal will produce many wonderful and rich changes at high temperature: the metal base metal will undergo color change and thermal deformation (i.e. welding heat affected zone);The welding wire will form some beautiful texture after melting;Welding defects are often used in welding art.Welding defects refer to the defects that do not meet the design or process requirements during welding.Its manifestations mainly include welding cracks, pores, undercuts, incomplete penetration, incomplete fusion, slag inclusion, weld beading, collapse, pits, burn through, inclusions, etc.
Secondly, the language of welding art is unique.
The manifestations of the above welding defects andWelding heat affected zoneIt is formed by welding operations under certain specifications, and only by welding can these artistic languages be produced.The surface effect of welding art works is impossible or difficult to achieve by other metal processing processes, so welding art has unique artistry.
Using different metal materials and different welding processes, the art of welding can be brought into full play in different metal art forms:
1. Metal welding sculpture
In the welding sculpture works, the weld and cut marks do not exist passively as traces of technical processing, but are embodied in a wonderful and indispensable expression language.A welding sculpture, with thick weld exposed on the surface of the sculpture, and various irregular cutting marks have become the artist's beautiful artistic language
2. Metal welding wall decoration
If a mural work is regarded as a painting, the processing of points, lines, surfaces, black, white, gray and even colors in the picture can be achieved by welding.Metal wires of various models and materials will appear in different forms on the screen with different welding processes.
The work shown in Figure 3 adopts the method of manual plasma cutting. Using the heat of the current during cutting, the cutting edge produces a heat affected zone, which "stains" the bright white stainless steel with a slightly gradual color.At the same time, through the adjustment of welding specifications, the strong air flow from the cutting gun will blow a circle of randomly formed texture at the cutting edge at the moment when the cutting steel plate melts. After the metal is cooled after cutting, it will solidify into a beautiful cut mark, which is flat and bright in the middleStainless steel plateIt forms a contrast of texture.The formation process of this random effect has certain 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 welding art murals, and smaller ones can be usedManual argon tungsten arc welding。
Characteristics of welding system
System structure characteristics
1. Mechanical device
mash welderThe system consists of three parts: mechanical device, power supply device and control device.In order to adapt to the welding process requirements of the spot welder, the pressurizing mechanism (welding tongs) adopts a double stroke fast pneumatic transmission mechanism. The opening of the welding tongs can be changed by switching the stroke control handle, which can be divided into large opening and small opening to meet the welding operation requirements.Generally, the state is short stroke opening of welding tongs. When the control button is switched to the "power on" position, the welding tongs will be clamped and pressurized when the handle switch is pulled. At the same time, the current will return to the short stroke opening state after completing a welding cycle under the control of the control system.
2. Power supply device
Main power routeResistance welding transformer, thyristor unit, main power switch, welding circuit, etc.The welding equipment we use is a single phase with power of 200kVA and secondary output voltage of 20Vpower frequencycommunicationResistance welding machine。Since multiple models are produced in the same line, welding tongs need to be weldedHigh strength steel plateandmild steelThe thin plate and welding tongs' gun arm shall transmit large mechanical force and welding current, so the strength, rigidity and heating of welding tongs shall meet certain requirements and shall be of good qualityelectric conductionandThermal conductivityAt the same time, the welding tongs are required to be cooled with water, so a new type of welding tongs whose electrode arm can withstand 400kg pressure is selected.
3. Control device
The control device mainly provides signal controlResistance welding machineOperate to switch on and off the welding current, control the welding current value, and conduct fault monitoring and handling.
Chronicle of Events
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Early development
History of metal welding and cutting:
Over 3000 BC, forging and welding technology appeared in ancient Egypt
Over 2000 BC, China's Yin Dynasty used cast welding to make weapons
Before 2000 BC, China had mastered the brazing of bronze and forging and welding of ironware
1911: Philadelphia&Suburban Gas Company built the first 11 mile long pipe welded by oxygen solvent gas welding
1912: The first oxyacetylene gas welded steel pipe was put on the market
1912: Edward G. Budd Company in Philadelphia, USA produced the first all steel automobile body welded by resistance spot welding
About 1912: In order to produce the famous Model T car, Ford Motor Company of the United States completed the modern welding process in its own factory laboratory.
1913: Avery and Fisher in Indianapolis, USA perfected acetylene cylinder
In 1916, Ansel Xiante, Jr. invented the X-ray nondestructive testing method for welding area
1917:the First World WarDuring this period, 109 marine engines seized from Germany were repaired by arc welding, and these repaired ships were used
Shipped half a million American soldiers to France
In 1917, Webster&Southbridge Electric Company, located in Massachusetts, USA, used electric arc welding equipment to weld 11 miles long with a diameter of
3-inch pipeline
1919: Comfort A. Adams formed the American Welding Society (AWS)
Commemorative photos of American Welding Society activities in 1924
1919: CJ. Halslag invented AC welding
1920: Gerdien discovered the thermal effect of plasma flow
1920: The first all welded hull steamship Fulagar was launched in Britain
About 1920: began to use arc welding to repair some valuable equipment
Circa 1920: resistance weldingWelded steel pipeThe Johnson Process was patented
About 1920: The first oil tanker, the Poughkeepsie Socony, was launched in the United States by welding
About 1920: flux cored wire was used for hardfacing
In 1922, Prairie Pipeline Company successfully completed the welding from Mexico to Dexas with a diameter of 8 inches and a length of
The laying of 140 miles of crude oil pipeline
1923: Stody invented surfacing
1923: The world's first floating roof tank (used to store gasoline or other chemicals) was built;The advantage is that the floating roof and tank wall formed by welding
The tank can be raised or lowered like a telescope, so that the volume of the tank can be easily changed
1924: Magnolia Gas Company built a 14 mile long all welded natural gas pipeline using oxyacetylene welding technology
1924: In the United States, HH. Lester first used X-ray photography to test the steam pressure for the power plant of Boston Edison
8.3 Mpa casting quality to be installed
matters needing attention
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1、 Length of arc
The length of the arc is related to the type of electrode coating and coating thickness.However, short arc, especially low hydrogen electrode, shall be adopted as far as possible.A long arc may cause porosity.Short arc can avoid the invasion of harmful gases such as O2 and N2 in the atmosphereweld metal The formation of oxides and other undesirable impurities will affect the weld quality.
2、 Welding speed
Appropriatewelding speed There are corresponding changes in the welding rod diameter, coating type, welding current, heat capacity of the object to be welded, structure start and other conditions, and no standard provisions can be made.Keep proper welding speed, and the slag can cover the molten pool well.Make all kinds of impurities and gases in the molten pool have sufficient time to float out, and avoid the formation of slag inclusion and pores in the weld.If the bar moving speed is too fast during welding, the shrinkage stress will increase when the welding part is cooled, which will cause cracks in the weld.
Key points of welding wire selection
The selection of welding wire shall be based on the type of steel to be welded, quality requirements of welding parts, welding construction conditions (plate thickness, groove shape, welding position, welding conditions, post weld heat treatment and welding operation waiting), cost, etc.
The sequence of welding wire selection shall be considered as follows:
① According to the welded structureSteel gradeSelect welding wire for carbon steel andLow alloy high strength steel, mainly according to the principle of "equal strength matching"mechanical property Welding wire required.aboutHeat resistant steelAnd weathering steel, mainly focusing on the consistence and similarity of chemical composition of weld metal and base metal to meet the requirements of heat resistance and corrosion resistance.
② Select welding wire, welding conditions, groove shapeShielding gasThe mixing ratio and other process conditions are related, and the maximum welding efficiency and reduction shall be selected on the premise of ensuring the performance of welded jointsWelding costWelding materials.
③ According to the siteWelding positionSelect the welding wire diameter corresponding to the plate thickness of the weldment to be welded, determine the current value to be used, refer to the product introduction data and use experience of each manufacturer, and select the welding wire brand suitable for the welding position and use current.
Welding process performance includes arc stability, size and quantity of spatter particles, slag removal, weld appearance and shape, etc.For carbon steel andlow alloy steelWelding methods and welding materials are mainly selected according to welding process performance (especially semi-automatic welding).
2. Selection of solid wire
(1) Submerged arc welding wire
High chromium cast iron surfacing welding wire (HS101)
Welding wire and flux are consumable materials for submerged arc weldingcarbon steelreachHigh nickel alloyvariedMetallic materialsThe welding wire and flux can be used for submerged arc welding.The selection of submerged arc welding wire should consider both the influence of flux composition and the influence of base metal.In order to obtain different weld composition and mechanical properties, one kind of flux (mainly melting flux) can be used to match with several welding wires, or one kind of welding wire can be used to match with several welding fluxes (mainly sintering flux).A. Welding wire for low carbon steel and low alloy steel
The common welding wires for submerged arc welding of low-carbon steel and low-alloy steel are as follows:
① Low manganese welding wire (such as H08A) is often used with high manganese flux to weld low carbon steel with low strength low alloy steel.
② Medium manganese welding wire (such as H08MnA H10MnSi) is mainly used for low alloy steel welding, and can also be used with low manganese flux for low carbon steel welding.
③ High manganese welding wire (H10Mn2 H08Mn2Si) is used for welding low alloy steel.
The welding wire for low-alloy high-strength steel contains more than 1% Mn and 0.3% - 0.8% Mo, such as H08MnMoA and H08Mn2MoA, which are used for welding low-alloy high-strength steel with high strength.In addition, Ni, Cr, V, RE and other elements can also be added to the welding wire to improve the performance of the weld according to the requirements for the composition and performance of low-alloy high-strength steel.
The weld metal with strength level of 590Mpa mostly adopts Mn Mo welding wire, such as H08MnMoA, H08Mn2MoA, H10Mn2Mo, etc.
C. Welding wire for stainless steel
When welding stainless steel, the composition of welding wire shall be basically the same as that of the stainless steel being welded.H0Cr14 H1Cr13 H1Cr17 and other welding wires can be used for welding chromium stainless steel, and H0Cr19Ni9 H0Cr19Ni9Ti and other welding wires can be used for welding chromium nickel stainless steel;When welding ultra-low carbon stainless steel, the corresponding ultra-low carbon welding wire, such as H00Cr19Ni9, shall be used.Flux can be of smelting type or sintering type. It is required that the oxidizability of flux should be small to reduce the burning loss of alloy elements.
D. Welding rod (electric welding)
J422 is a carbon steel electrode with titanium calcium coating.Both AC and DC can be used for all position welding.Excellent welding process performance and good mechanical properties;Stable arc, small spatter, easy slag removal and arc striking;The welding seam is beautiful, the welding wave can be wide, narrow, thin, thick, easy to weld and high efficiency.
Purpose:It is used for welding important low-carbon steel structures and low-alloy steel structures with low strength grade, such as Q235, 09MnV, 09Mn2, etc.
Welding quality standard
1. Welding quality GB6416-1986 Technical factors affecting the quality of steel fusion welded joints
2. Welding quality GB6417-1986 Classification and description of weld defects of metal fusion welding
3. Welding quality TJ12.1-1981 Regulations on welding quality of construction machinery
4. Welding quality JB/ZQ3679 Quality of welding parts
7. Welding quality JB3223-1983 Welding rod quality management procedure
8. Welding Standards Abolished in 2005 GB/T 12469-1990 Welding Quality Assurance Requirements and Defect Classification for Steel Fusion Welded Joints
Welding type
1. Welding rod arc welding:
Principle - electric arc welding method of welding with manual welding rod.The stable burning arc established between the welding rod and the weldment is used to melt the welding rod and weldment, so as to obtain a solid welding joint.It belongs to gas slag joint protection.
Main features - flexible operation;Low assembly requirements for joints to be welded;Wide range of weldable metal materials;Low welding productivity;The weld quality is highly dependent (depending on the welder's operating skills and on-site play).
Application - widely used in shipbuilding, boiler and pressure vessel, machinery manufacturing, building structure, chemical equipment and other manufacturing and maintenance industries.It is suitable for welding of various metal materials, thicknesses and structural shapes (in the above industries).
2. Submerged arc welding (automatic welding):
Principle - The arc burns under the flux layer.The heat generated by the burning arc between the welding wire and the weldment is used to melt the welding wire, flux and base metal (weldment) to form a weld.It belongs to slag protection.
Main features - high welding productivity;Good weld quality;Low welding cost;Good working conditions;It is difficult to weld in space;High requirements for assembly quality of weldments;It is not suitable for welding thin plates (when the welding current is less than 100A, the arc stability is poor) and short welds.
Application - widely used in shipbuilding, boiler, bridge, lifting machinery and metallurgical machinery manufacturing industry.Submerged arc welding can be used for all weldments whose welds can be kept in horizontal position or with small inclination angle.The plate thickness shall be greater than 5mm (burn through prevention).weldingCarbon structural steel、Low alloy structural steelStainless steel, heat-resistant steel, composite steel, etc.
3. CO2 gas shielded welding (automatic or semi-automatic welding):
Main features - high welding productivity;Low welding cost;Small welding deformation (concentrated arc heating);High welding quality;Simple operation;High splash rate;It is difficult to weld with AC power supply;Poor wind resistance;Non ferrous metals that are easy to oxidize shall not be welded.
Application - mainly welding low carbon steel and low alloy steel.Suitable for various thicknesses.Widely used in automobile manufacturing, locomotive and vehicle manufacturingChemical machinery, agricultural machinery, mining machinery and other departments.
MIG welding principle - usinginert gasAn electric arc welding method that uses welding wire as the melting electrode as the shielding gas.
The shielding gas is usually argon or helium or their mixture.MIG uses inert gas. MAG adds a small amount of active gas, such as oxygen and carbon dioxide, into the inert gas.
Main features - good welding quality;High welding productivity;No deoxidation and dehydrogenation reaction (easy to form welding defects, especially strict requirements for surface cleaning of welding materials);Poor wind resistance;The welding equipment is complex.
Application - It can weld almost all metal materials, mainly used for welding nonferrous metals and their alloys, stainless steels and some alloy steels (too expensive).The thinnest thickness is about 1mm, and the large thickness is basically unlimited.
Principle - atinert gasUnder the protection, the welding method is to use the arc generated between the tungsten electrode and the weldment to heat melt the base metal and filler wire (or without filler wire) to form a weld.The electrode does not melt during welding.
Main features - strong adaptability (stable arc, no splash);Low welding productivity (poor current carrying capacity of tungsten electrode (anti melting and evaporation of tungsten electrode, anti tungsten inclusion in weld));The production cost is high.
Application - It can weld almost all metal materials, commonly used in stainless steel,SuperalloyWelding of aluminum, magnesium, titanium and their alloys, refractory active metals (zirconium, tantalum, molybdenum, niobium, etc.) and dissimilar metals.Weldments with welding thickness generally less than 6mm, or backing welding of thick parts.The narrow gap TIG automatic welding with thickness of more than 90mm can be realized by using small angle groove (narrow groove technology).
Principle - the method of obtaining high energy density plasma arc for welding with the aid of the restraint effect of water cooling nozzle on the arc.
Main features (compared with argon arc welding) - ⑴ Concentrated energy, high temperature, pinhole effect can be obtained for most metals within a certain thickness range, and the weld with full penetration and uniform reverse forming can be obtained. ⑵The arc stiffness is good, the plasma arc is basically cylindrical, and the change of arc length has little effect on the heating area and current density on the weldment.Therefore, the arc length change of plasma arc welding has no obvious effect on weld formation. ⑶The welding speed is faster than argon arc welding. ⑷Able to weld thinner and thinner workpieces. ⑷The equipment is complex and the cost is high.
application
⑴Penetrating type(Small hole type)Plasma arc weldingIt is a plasma arc welding method that takes advantage of the characteristics of small diameter, high temperature, high energy density and strong penetration of the plasma arc, and under appropriate process parameters (large welding current of 100A~500A), the weldment is fully penetrated, and under the action of plasma flow force, a small hole through the weldment is formed, and part of the plasma arc is sprayed from the back of the weldment.Can be welded on one side and formed on both sides, most suitable for welding 3-8mm stainless steel, below 12mmtitanium alloy2~6mm mild steel orLow alloy structural steelAnd butt welding of copper, brass, nickel and nickel alloys.(The plate is too thick and affected by plasma arcenergy density It is difficult to form small holes due to the limitation of;The plate is too thin, and the small hole cannot beliquid metalCompletely closed, and small hole welding cannot be realized.)
⑵Penetration type(Dissolved type)Plasma arc welding: Adopt low welding current (30A~100A) and low plasma gas flow, and adopt hybrid plasma arc welding method.No pinhole effect is formed.It is mainly used for welding thin plates (below 0.5~2.5 mm), multi-layer welding, welding of each layer after the back pass and fillet welding.
⑶Micro plasma arc: Plasma arc welding with welding current below 30A.Nozzle diameter is very small（Φ0.5～Φ1.5 mm) to obtain needle like fine plasma arc.It is mainly used for welding ultra thin, ultra small and precise weldments below 1mm.
note appended
1. The above are several common fusion welding methods, each of which has advantages and disadvantages. When selecting a welding method, there are many factors to consider, such as the type of weldment materials, plate thickness, position of weld in space, etc.The principle of welding method selection is to use the welding method with low total cost on the premise of ensuring the quality of welding joints.
Welding temperature control
The temperature of the molten pool has a direct impact on the welding quality. The high temperature of the molten pool, the large molten pool, and the good fluidity of the molten iron make it easy to fuse. However, when the temperature is too high, the molten iron is easy to flow down, and the back side of the single-sided welding and double-sided forming is easy to burn through, forming weld beading, which is difficult to control, and the plasticity of the joint decreases, and the bending is easy to crack.When the molten pool temperature is low, the molten pool is small, the molten iron is dark, the fluidity is poor, and it is easy to produce incomplete penetration, incomplete fusion, slag inclusion and other defects.
The temperature of molten pool is closely related to welding current, electrode diameter, electrode angle, arc burning time, etc. The following measures are taken to control the temperature of molten pool according to relevant factors.
diameter
1、Welding current and electrode diameter: The welding current and electrode diameter shall be selected according to the space position and welding level of the weld. When starting welding, the welding current and electrode diameter shall be larger, and the vertical and horizontal elevation positions shall be smaller.For example, the bottom sealing layer of 12mm flat butt weldingφ3.2mm welding rod, welding current: 80-85A, filling, covering layer selectionφ4.0mm welding rod, welding current: 165-175A, reasonable selection of welding current and electrode diameter, easy control of molten pool temperature, is the basis of weld formation.
method
2、Strip conveying methodThe temperature of the circle shaped electrode welding pool is higher than that of the crescent shaped electrode welding pool, and the crescent shaped electrode welding temperature is higher than that of the zigzag shaped electrode welding pool. When the bottom layer is sealed at 12mm, the zigzag electrode welding is used, and the swing amplitude and pause on both sides of the groove are used to effectively control the temperature of the weld pool, so that the size of the weld hole is basically the same, and the probability of no overlap and burn through at the root of the groove is reduced,The incomplete penetration has been improved, so that the single side welding and double side forming of butt welding and flat welding of the hinge plate are no longer difficult.
angle
3、Electrode angleWhen the included angle between the welding rod and the welding direction is 90 degrees, the arc is concentrated, the molten pool temperature is high, the included angle is small, the arc is scattered, and the temperature of the molten pool is low, such as the 12mm flat welding bottom coat, the angle of the welding rod is 50-70 degrees, which reduces the temperature of the molten pool and avoids the generation of weld beading or rising on the back.For another example, after the bottom layer of 12mm plate vertical welding is replaced with welding rod, the welding rod angle of 90-95 degrees is used during the joint, so that the temperature of the molten pool can be rapidly increased, the molten hole can be opened smoothly, the back surface is formed more smoothly, and the concave phenomenon of the joint point is effectively controlled.
time
4、Arc burning time，φIn the practice teaching of horizontal and vertical fixed welding of 57 × 3.5 pipes, the arc breaking method is used for welding. When welding the bottom layer, the frequency of arc breaking and the arc burning time directly affect the temperature of the molten pool. Because the pipe wall is thin, the ability to bear the heat of the arc is limited. If the arc breaking frequency is slowed down to reduce the temperature of the molten pool, it is easy to produce shrinkage cavities,Only the arc burning time can be used to control the temperature of the molten pool. If the temperature of the molten pool is too high and the molten hole is large, the arc burning time can be reduced to reduce the temperature of the molten pool. At this time, the molten hole becomes smaller and the forming height inside the pipe is moderate, so as to avoid the superelevation of the weld seam inside the pipe or the generation of weld beading.
