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     Welding of low carbon steel and low alloy steel

Low carbon steel and low alloy steel belong to ordinary ferritic steel, and the welding between them and the welding between low alloy steel of different materials belongs to the welding of the same heterogeneous steel. The welding between such steels is done according to the low-grade material, which refers to the material with low strength level or alloying element content, to ensure that the weld metal performance meets the low-grade material. The selection of low-grade materials also has better welding performance than high-grade materials, and the price is cheaper, which is conducive to reducing manufacturing costs.

                 Welding of low alloy and medium alloy steels

Because of the discontinuity of the chemical composition of the weld, the discontinuity of the performance will be produced. If this discontinuity has a greater impact on the performance of the service, the welding material can not be selected according to the low-grade principle.

 For example, SA213-T91 and SA213-T22 material welding, if according to the usual low-grade principle, the selection of 2.25Cr-1MO welding material for welding, then the T91 base metal near the fusion line on the T91 side will be seriously carburized, resulting in a decarburized layer, and the weld near the fusion line on the T91 side will be seriously decarburized, resulting in a decarburized layer. This is because the chromium content of T91 is about 9%, and the carbon content of 2.25Cr-1Mo welding wire is about 2.25%. Then, after annealing treatment, the chromium content of the heat affected zone on the T91 side is far greater than that on the weld side, and a large amount of carbon will shift to the base material to produce a carburized layer, resulting in increased hardness, more hardened organization, and serious decarburization on the weld side. The hardness is low, the structure softens, and the joint performance deteriorates. If the 9Cr-1Mo welding material is selected, the weld carburization and decarburization of the base material will occur on the side of the T22 fusion line.

                Welding material selection of dissimilar steel welding

For welding of carbon steel, low alloy steel and austenitic stainless steel, welding materials should be selected according to the working temperature of the joint and the stress condition of the joint.

  When the working temperature of such dissimilar steel joints under bearing pressure is below 315 ° C, austenitic stainless steel welding materials with high Cr and Ni alloy content can be selected. According to the chemical composition of carbon steel (alloy steel) and austenitic steel and the size of the fusion ratio of welding, austenitic stainless steel welding materials with appropriate Cr and Ni content are selected according to a certain nickel equivalent and chromium equivalent microstructure diagram to avoid a large number of martensitic tissues in the weld. Of course, a narrow martensitic band will be produced near the fusion line of carbon steel or low alloy steel. By reducing the carbon content of the welding material, the martensitic structure is low carbon martensitic with good plasticity, and the joint can also ensure good performance.

 When bearing and bearing dissimilar steel joints work at temperatures above 315 ° C, nickel-based welding materials should be selected. For example, ECrNiFe 2,ERCrNiFe 3, etc., the main reasons are as follows.

 If the ordinary austenitic stainless steel welding material is selected, the following problems will occur:

 a) Due to the large difference in the coefficient of thermal expansion between ferrite and austenite, thermal stress and thermal fatigue damage will occur when running at high temperatures.

 b) Due to the large difference in alloying element content, welding joints working at high temperatures will produce serious decarburization layer and carburization layer, which deteriorates the high temperature performance.

 c) Due to the martensitic band organization near the fusion line, the local tissue of the weld is hardened.

 The selection of nickel-based welding materials can avoid the above phenomenon, for the following reasons:

 a) The coefficient of thermal expansion of nickel-based materials is between ferrite and austenite.

 b) Nickel-based materials do not produce decarburization and carburization when welded joints.

 c) Welding of nickel-based materials will not produce martensitic structure.

 However, for non-load-bearing welded joints under high temperature work, the selection of nickel-based electrode can meet the performance requirements, but the manufacturing cost is expensive, and there is no need to use. The use of other inexpensive welding materials can also achieve the purpose.

 A large number of experimental studies abroad have shown that for the non-bearing fillet welds of pipes and accessories in boiler manufacturing, when the pipes are carbon steel and low alloy steel materials, and the accessories are austenitic stainless steel, the welding materials should be selected according to the low grade materials.

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Sources and hazards of radiation

  Thorium tungsten electrodes used in argon arc welding and plasma arc welding contain 1-1.2% thorium oxide, a radioactive substance that is affected by radiation during welding and contact with thorium tungsten rods.

  Radiation acts on the human body in two forms: one is external irradiation, and the other is internal irradiation which occurs when it enters the body through the respiratory and digestive systems. From a large number of investigations and measurements of masked argon arc welding and plasma arc welding, it has been proved that their radioactive harm is small, because the consumption of thorium tungsten rods is only 100-200 mg per day, and the radiation dose is extremely small, which has little impact on the human body.

  But there are two things to be aware of:

  First, when welding in the container, the ventilation is not smooth, and the radioactive particles in the smoke may exceed the health standard;

  Second, the concentration of radioactive aerosols and radioactive dust in the grinding of thorium tungsten rods and the locations where thorium tungsten rods are present can meet or even exceed health standards.

Radioactive substances into the body can cause chronic radiation disease, mainly in the general functional state weakened, you can see obvious weakness, resistance to infectious diseases significantly reduced, weight loss and other symptoms.

             Measures to prevent radiation damage

(1) Thorium tungsten rod should have special storage equipment, a large number of storage should be hidden in the iron box, and installed exhaust pipe.

(2) When welding with a closed cover, the cover body should not be opened during the operation, and the air supply protective helmet or other effective measures must be worn during manual operation.

    (3) Special grinding wheels should be provided to grind thorium tungsten rods, dust removal equipment should be installed in the grinder, and the grinding chips on the ground of the grinder should be often wet swept and intensively buried.

(4) Wear a dust mask when grinding thorium tungsten rod. Wash hands with running water and soap after contact with thorium tungsten rod, and wash clothes and gloves frequently.

 (5) Select reasonable specifications when welding and cutting to avoid excessive burning of thorium tungsten rod.

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1. Hydrogen embrittlement

 Hydrogen embrittlement usually manifests as delayed fracture under stress. There have been galvanized parts such as automobile springs, washers, screws, and blade springs, which have broken in succession within a few hours after assembly, and the proportion of breakage has reached 40% to 50%. A special product cadmium plating parts in the use of the process has appeared batch crack fracture, has organized a national research, the development of strict hydrogen removal process. In addition, there are some hydrogen embrittlement does not show delayed fracture phenomenon, for example: electroplating hangers (steel wire, copper wire) due to multiple electroplating and pickling plating, hydrogen infiltration is more serious, and the phenomenon of embrittlement often occurs when a break occurs in use; A mandrel used for precision forging of a hunting gun, after several times of chromium plating, fell and broke; Some hardened parts (large internal stress) will crack when pickling. These parts are so heavily hydrogen-permeated that cracks occur without external stress, and it is no longer possible to use hydrogen removal to restore the original toughness.

 2. Hydrogen embrittlement mechanism

 The phenomenon of delayed fracture is caused by the diffusion and accumulation of hydrogen in the parts to the parts where the stress is concentrated, and there are many metal defects in the parts where the stress is concentrated (dislocation of atomic lattice, holes, etc.). Hydrogen diffuses to these defects, hydrogen atoms become hydrogen molecules, creating a huge pressure, this pressure and the residual stress inside the material and the external stress on the material, forming a resultant force, when this resultant force exceeds the yield strength of the material, resulting in fracture. Since hydrogen embrittlement is related to the diffusion of hydrogen atoms, diffusion takes time, and the speed of diffusion is related to the concentration gradient, temperature and material type. Therefore, hydrogen embrittlement usually appears as delayed fracture.

 Hydrogen atom has the smallest atomic radius, and it is easy to diffuse in steel, copper and other metals, while it is difficult to diffuse hydrogen in cadmium, tin, zinc and their alloys. The cadmium plating layer is the most difficult to diffuse, and the hydrogen produced during cadmium plating, which initially stays in the coating and the metal surface beneath the coating, is difficult to diffuse outward, and dehydrogenation is particularly difficult. After a period of time, hydrogen diffuses into the metal, especially the hydrogen that enters the metal's internal defects, it is difficult to diffuse out. The diffusion rate of hydrogen at room temperature is quite slow, so it needs to be heated immediately to remove hydrogen. The temperature increases, increasing the solubility of hydrogen in steel, too high temperature will reduce the hardness of the material, so the stress before plating and the temperature of dehydrogenation after plating must be considered not to reduce the hardness of the material, not to be in the brittle tempering temperature of some steel, not to destroy the performance of the coating itself.

 Measures for avoidance and elimination

 1. Reduce the amount of hydrogen infiltration in the metal

  When removing rust and oxidation, try to use sand blowing to remove rust, if using pickling, it is necessary to add rhodin corrosion inhibitor in the pickling solution; In the oil removal, the use of chemical oil removal, cleaning agent or solvent oil removal, less hydrogen infiltration, if the use of electrochemical oil removal, first cathode after anode; In electroplating, alkaline bath or bath with high current efficiency has less hydrogen infiltration.

 2. Low hydrogen diffusivity and low hydrogen solubility of the plating coating

  It is generally believed that when electroplating Cr, Zn, Cd, Ni, Sn, Pb, hydrogen infiltrated into steel parts is easy to remain, and Cu, Mo, Al, Ag, Au, W and other metal coatings have low hydrogen diffusion and low hydrogen solubility, and hydrogen infiltration is less. In the case of meeting the requirements of the technical conditions of the product, the coating that will not cause hydrogen infiltration can be used, such as dacromet coating layer can replace galvanized, will not occur hydrogen embrittenness, corrosion resistance is improved by 7 to 10 times, good adhesion, film thickness of 6 to 8um, equivalent to a thinner galvanized layer, does not affect the assembly.

 3. Stress before plating and remove hydrogen after plating to eliminate hydrogen embrittlement

  If the internal residual stress of the parts is large after quenching, welding and other processes, tempering treatment should be carried out before plating to reduce the hidden danger of serious hydrogen infiltration.

  Parts with more hydrogen infiltration during electroplating should in principle be dehydrogenated as soon as possible, because the hydrogen in the coating and the hydrogen in the surface substrate metal are diffused into the steel substrate, and the amount increases with the extension of time. The new draft international standard states that "it is best to carry out dehydrogenation treatment within 1h after plating, but no later than 3h". There are also corresponding standards in China, which stipulate the dehydrogenation treatment before and after electrogalvanizing. The process of hydrogen removal after electroplating is widely used in heating and baking, and the commonly used baking temperature is 150 ~ 300℃, and the heat preservation is 2 ~ 24h. The specific treatment temperature and time should be determined according to the size of the part, strength, coating properties and the length of plating time. Dehydrogenation is usually carried out in an oven. The dehydrogenation treatment temperature of galvanized parts is 110 ~ 220℃, and the temperature control level should be based on the base material. For elastic materials, thin-walled parts below 0.5mm and steel parts with high mechanical strength requirements, hydrogen treatment must be carried out after galvanizing. In order to prevent "cadmium brittleness", the dehydrogenation treatment temperature of cadmium-plated parts can not be too high, usually 180 ~ 200℃.

  Three, should pay attention to the problem

  The greater the strength of the material, the greater its hydrogen embrittlement sensitivity, which is the basic concept that surface treatment technicians must be clear when preparing electroplating process specifications. International standards require steel with tensile strength σb>105kg/mm2 to be stressed before plating and dehydrogenated after plating. The French aviation industry requires corresponding dehydrogenation of steel parts with yield strength σs>90kg/mm2.

  Because the strength of steel has a good correspondence with the hardness, it is more intuitive and convenient to judge the hydrogen embrittlement sensitivity of the material by the hardness of the material than by the strength. Because a perfect product drawing and machining process should be marked with steel hardness. In electroplating, we found that the hardness of steel began to show the risk of hydrogen embrittlement fracture when it was about HRC38. For parts higher than HRC43, dehydrogenation treatment should be considered after plating. When the hardness is about HRC60, it must be dehydrogenated immediately after the surface treatment, otherwise the steel will crack within a few hours.

  In addition to steel hardness, the following points should also be considered:

 (1) The use of safety factor of parts: parts with large safety importance should be strengthened to dehydrogen;

 (2) The geometry of the parts: with a gap that is easy to produce stress concentration, parts such as small R should be strengthened to dehydrogen;

 (3) Cross-sectional area of parts: small spring steel wire and thin blade spring are easily saturated with hydrogen, and dehydrogen should be strengthened;

 (4) The degree of hydrogen infiltration of parts: in the surface treatment of more hydrogen, long processing time parts, should be strengthened to dehydrogen;

 ⑤ Type of coating: such as cadmium plating layer will seriously block hydrogen diffusion, so it is necessary to strengthen dehydrogenation;

 The mechanical properties of parts in use: when the parts are subjected to high tensile stress, dehydrogen should be strengthened, and hydrogen embrittlement will not be produced only when the stress is compressed;

 ⑦ Surface processing state of parts: for parts with large internal residual stress such as cold bending, drawing, cold bending, quenching, welding, etc., it is not only necessary to strengthen dehydrogen after plating, but also to remove stress before plating;

 ⑧ Historical situation of parts: Special attention should be paid to parts that have been hydrogen embrittlement in the past production, and relevant records should be made.

 Dehydrogen embrittlement

  The main reason is the metal "hydrogenation" phenomenon caused by the electroplating process, and the unqualified products you use are not the plating process itself has a problem, because electroplating (except vacuum plating) will cause metal hydrogenation, but at present, many metal surface treatment providers have removed the last process (especially for elastic components are deadly) : That is the "dehydrogen treatment" process, that is to say, under normal circumstances, for metal parts with strength requirements need to be dehydrogenated before they can be handed to the user, but in order to save production costs, and the user does not understand the case or has never required, accepted the case, omitting this process can save 5~15% of the cost. So you feel that the bolts, spring washers and other parts after electroplating are "brittle" after electroplating treatment.

  Generally speaking, the dehydrogenation treatment requirements for metal parts with strength requirements are: 120 degrees ~220 degrees high temperature maintained for 1 to 2 hours (after electroplating), and the specific 

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1 What is acid electrode?

Electrode containing more acid oxide in the coating, such as junction 422 (E4303), junction 502 (E5003) and other AC-DC dual electrode.

2 What is alkaline electrode?

The electrode containing a large amount of alkaline oxide and fluoride, such as junction 507 (E5015), junction 506 (E5016) and other electrodes.

3 What is cellulose type (downward vertical welding special) electrode？

Welding rod containing a large amount of organic matter in the coating, pipe and thin plate structure downward vertical welding.

< 1 > For example, E6010 (equivalent to E4310, J425G) is suitable for bottom welding, hot welding, fill welding.

< 2 > E8010 (equivalent to E5511, J555) is suitable for hot welding, filling welding, cover welding layer.

Generally use low hydrogen down electrode cover welding; E7048 (equivalent to J506X) weld is clean and beautiful.

4 Why should the electrode be strictly dried before welding?

The welding rod will often deteriorate the process performance due to moisture absorption, resulting in unstable arc, increased spatter, and easy to produce porosity, cracks and other defects. Therefore, the electrode must be strictly dried before use. The drying temperature of the general acid electrode is 150 ~ 200℃, and the time is 1 hour. The drying temperature of the alkaline electrode is 350 ~ 400℃, the time is 1 ~ 2 hours, and the electrode is placed in the insulated box of 100 ~ 150℃ after drying.

5 What is welding wire?

A wire used as a filler metal in welding and used to conduct electricity at the same time - called a welding wire. There are two kinds of solid wire and flux-cored wire. Common solid wire model: ER50-6 (grade: H08Mn2SiA).

6 What is flux-cored wire?

A kind of welding wire made by drawing a thin steel strip rolled into a round steel pipe, which is filled with a certain composition of powder.

7 Why is the flux-cored wire protected with CO2 gas?？

There are two types of flux-cored wire according to the protection mode: flux-cored gas-protected wire and flux-cored self-protected wire. The flux-cored gas-protected welding wire is generally protected by CO2 gas, which belongs to the form of gas-slag combined protection. It has good weld forming and high comprehensive mechanical properties.

8 When is the welding material scrapped？

Corrosion of welding core, adhesion, peeling, serious moisture (especially low hydrogen type electrode, heat-resistant steel electrode, low-temperature steel electrode), such electrode can no longer be used, to be scrapped.

9 What are the effects of moisture on the electrode?

After the electrode is damp, the color of the general coating is dark, the collision of the electrode loses the crisp metal sound, and some even appear "white flowers".

Influence of damp electrode on welding process:

(1) The arc is unstable, the splash is increased, and the particles are too large.

(2) deep penetration, easy to bite edge.

(3) The slag is not covered well and the welding wave is rough.

(4) It is difficult to remove slag.

Influence of damp electrode on welding quality:

(1) Easy to cause welding cracks and pores, especially alkaline electrode.

(2) The values of mechanical properties are easy to be low.

10 What are the effects of damp welding wire?

Moisture absorbing welding wire can increase the content of diffused hydrogen in the deposited metal, resulting in pits, pores and other defects, welding process performance and mechanical properties of weld metal become worse, and serious weld cracking can be caused.

 After nitriding, quenching and low temperature tempering are also required.

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1.Anneal

1. Treatment Method:

The steel parts are heated to a temperature below Ac3 +30 ~ 50℃ or Ac1+30 ~ 50℃ or Ac1, and generally cooled slowly with the furnace after thorough burning and heat preservation.

2. Purpose:

① Reduce hardness, improve plasticity, improve cutting and pressure processing performance;

② Refine grain, improve mechanical properties, prepare for the next step;

③ Eliminate the internal stress caused by hot and cold processing.

3. Application:

① Applicable to alloy structural steel, carbon tool steel, alloy tool steel, high-speed steel and other forgings, welding parts and supply of unqualified raw materials;

② Generally annealed in blank state.

                           2. normalizing

1. Treatment Method:

The steel parts are heated to 30 ~ 50℃ above Ac3 or Accm, and the cooling rate is slightly greater than that of annealing after insulation.

2. Purpose:

The purpose of normalizing is similar to annealing.

3. Application:

Normalizing is usually used as a pre-heat treatment process for forgings, welds and carburized parts. For low carbon and medium carbon carbon structural steel and low alloy steel parts with low performance requirements, it can also be used as the final heat treatment. For general medium and high alloy steels, air cooling can lead to complete or partial quenching and therefore cannot be used as the final heat treatment process.

                           3.quenching

1. Treatment Method:

The steel is heated to a phase change temperature of Ac3 or Ac1, held for a certain time, and then quickly cooled in water, nitrate, oil or air.

2. Purpose:

Quenching is generally to obtain a high hardness of martensitic structure, and sometimes for some high alloy steels (such as stainless steel, wear-resistant steel) quenching, it is to obtain a single uniform austenitic structure to improve its corrosion resistance and wear resistance.

3. Application:

① Generally used for carbon steel and alloy steel with ω greater than 0.30%;

②Quenching can give full play to the strength and corrosion resistance potential of steel, but at the same time it will cause a lot of internal stress, reduce the plasticity and impact toughness of steel, so it is necessary to temper in order to obtain better comprehensive mechanical properties.

4. Tempering

1. Treatment Method:

The quenched steel is reheated to Ac, the following temperature, after insulation, in air or oil, hot water, water cooling.

2. Purpose:

① Reduce or eliminate the internal stress after quenching, reduce the deformation and cracking of the workpiece;

② Adjust the hardness, improve the plasticity and toughness, and obtain the mechanical properties required by the work;

③ Stabilize the workpiece size.

3. Application:

① Low temperature tempering is used to maintain the high hardness and wear resistance of the steel after quenching; Moderate temperature tempering is used to improve the elasticity and yield strength under the condition of maintaining a certain toughness; To maintain high impact toughness and plasticity, but also have enough strength with high temperature tempering. Public number "Mechanical Engineering Literature", the engineer's gas station!

② General steel try to avoid at 230~280 ° C, stainless steel between 400 ~ 450 ° C tempering, because this will produce a tempering brittleness.

                          5.modulation

1. Treatment Method:

High temperature tempering after quenching is called tempering, that is, the steel is heated to a temperature of 10 to 20 ° C higher than the quenching, the quenching after holding the heat, and then the tempering at a temperature of 400 to 720 ° C.

2. Purpose:

① Improve the cutting performance and improve the finish of the machined surface;

② Reduce the deformation and cracking during quenching;

③ Good comprehensive mechanical properties are obtained.

3. Application:

① Suitable for alloy structural steel, alloy tool steel and high-speed steel with high hardenability;

② It can not only be used as the final heat treatment of various more important structural parts, but also as the pre-heat treatment of some precision parts, such as the lead screw, to reduce deformation.

                            6.ageing

1. Treatment Method:

The steel parts are heated to 80~200℃, held for 5~20h or longer, and then taken out to cool in the air.

2. Purpose:

① Stabilize the microstructure of steel parts after quenching, reduce the deformation during storage or use;

② Reduce the internal stress after quenching and grinding, and stabilize the shape and size.

3. Application:

① Suitable for all kinds of steel after quenching;

② It is often used in precision work that requires the shape to no longer be deformed, such as precision lead screws, measuring tools, bed boxes, etc.

7.Cooling treatment

1. Treatment Method:

The quenched steel parts are cooled to -60~-80℃ or lower in low temperature media (such as dry ice, liquid nitrogen), and the temperature is uniform after taking out the temperature to room temperature.

2. Purpose:

① All or most of the residual austenite in the hardened steel is transformed into martensite, thereby improving the hardness, strength, wear resistance and fatigue limit of the steel;

② Stabilize the structure of the steel to stabilize the shape and size of the steel parts.

3. Application:

① Steel parts should be cold treated immediately after quenching, and then tempered by low temperature to eliminate the internal stress during low temperature cooling;

② Cold treatment is mainly suitable for precision cutting tools, measuring tools and precision parts made of alloy steel.

                           8.Flame heated surface

1. Treatment Method:

The flame of oxygen-acetylene gas mixture combustion is sprayed onto the surface of the steel, rapidly heated, and immediately sprayed when the quenching temperature is reached.

2. Purpose:

Improve the surface hardness, wear resistance and fatigue strength of steel parts, and the heart remains ductile.

3. Application:

① It is mostly used for medium carbon steel parts, and the depth of the quenched layer is generally 2-6mm;

②It is suitable for large workpieces produced in a single piece or small batch and workpieces requiring local quenching.

9.Induction heating surface hardening

1. Treatment Method:

The steel is placed in the sensor, so that the surface of the steel generates an induced current, which is heated to the quenching temperature in a very short time, and then immediately sprayed with water to cool.

2. Purpose:

Improve the surface hardness, wear resistance and fatigue strength of steel parts, and the heart remains ductile.

3. Application:

① Mostly used in medium carbon steel and medium carbon alloy structural steel parts;

② Due to the skin effect, the high-frequency induction heating hardening layer is generally 1-2mm, the medium frequency induction heating hardening is generally 3-5mm, and the power frequency induction heating hardening is generally greater than 10mm.

                       10.carburization

1. Treatment Method:

The steel parts are placed in the carburizing medium, heated to 900 ~ 950℃ and heat preservation, so that the surface of the steel parts to obtain a certain concentration and depth of carburizing layer.

2. Purpose:

Improve the surface hardness, wear resistance and fatigue strength of steel parts, and the heart remains ductile

3. Application:

① It is mostly used for low carbon steel and low composite steel parts with carbon content of 0.15% ~ 0.25%, and the general carburizing layer is 0.5 ~ 2.5mm;

②After carburizing, the surface must be quenched to obtain martensite in order to achieve the purpose of carburizing.

                        11.

1. Treatment Method:

Using active nitrogen atoms decomposed by ammonia gas at 500 ~ 600℃. The surface of the steel is saturated with nitrogen to form a nitriding layer.

2. Purpose:

Improve the hardness, wear resistance, fatigue strength and corrosion resistance of the steel surface.

3. Application:

It is mainly used in medium carbon alloy structural steel containing aluminum, chromium, molybdenum and other alloying elements, as well as carbon steel and

cast iron. Generally, the depth of the nitriding layer is 0.025 ~ 0.8mm.

12.Nitrocarburizing

1. Treatment Method:

Carburizing and nitriding the steel surface simultaneously.

2. Purpose:

Improve the hardness, wear resistance, fatigue strength and corrosion resistance of the steel surface.

3. Application:

① Mostly used in low carbon steel, low alloy structural steel and tool steel parts. Generally, the depth of nitriding layer is 0.02 ~ 3mm;

② After nitriding, quenching and low temperature tempering are also required.

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At present, although welding technology and equipment have been developed in terms of automation, completely replacing welding workers is still a distant goal. Welding is a job that requires a high degree of skill and precision, involving the selection of materials, the application of welding methods, the operation of equipment and the quality control of welds.

Although automated welding technology has been applied in many industrial fields, manual welding can still play a unique role in complex welding tasks, welding of special materials and structures, and welding tasks requiring high quality. Welders, through their rich experience and skills, are able to flexibly respond to different welding needs and are able to make timely adjustments and repairs.

In addition, the welding process also needs to carry out the visual inspection of the solder joint, adjust the welding Angle and speed, deal with irregular shape and other work, which need human operation and judgment. Machines are not yet able to completely replace these complex manual operations and judgment capabilities.  

Therefore, despite the progress of automation technology in the field of welding, manual welding is still indispensable in many fields. Learning welding techniques is still highly valuable, and there are still broad employment prospects in the future.

               Welding employment

Welding as a basic and important manufacturing technology, for various industries, there are broad employment. Here are some of the main areas and opportunities for welding employment:

1. Manufacturing: Manufacturing is the main employment area of welding technology. Whether it is automotive manufacturing, aerospace, shipbuilding, building structures, machinery manufacturing or electronic equipment manufacturing, a large number of welders are needed to produce, assemble and maintain parts.

 2. Construction and infrastructure: The field of construction and infrastructure requires welding technology to connect and strengthen structures, such as Bridges and steel structures of buildings. In addition, pipe welding is also an important application area in the construction and infrastructure sector.

 3. Oil and gas industry: The oil and gas industry requires welding technology for pipeline connection and maintenance to ensure the safety and operation of pipelines.

             4. Energy industry: The energy industry, including nuclear, wind and solar energy, requires welding technology to manufacture and maintain equipment.

             5. Car repair and boat repair: car repair shops and boat repair shops need skilled welders to carry out car and boat repair and chassis structure repair.

             6. Maintenance of manufacturing equipment and mechanical equipment: welding technology also plays an important role in the field of maintenance of manufacturing equipment and mechanical equipment.

Development prospect

After entering the 21st century, welding is an important part of the manufacturing industry, and the rapid development, so the welding industry has brought unprecedented opportunities for development, and with the progress of The Times, the development of science and technology, the manufacturing industry continues to develop and grow, more and more manufacturing industry demand for welding continues to expand.

Welding technology has not only become an indispensable production technology for industrial production and manufacturing, but also the demand for welding technology gaps in the above manufacturing sectors will only become larger and larger!

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The flux-cored wire does not need additional protective gas, wind resistance and porosity resistance during welding, and the operation process performance is good!

It can also be used for welding various types of steel structures, including low carbon steel, low alloy high strength steel, low temperature steel, heat resistant steel, stainless steel and wear-resistant surfacing.

Therefore, the flux-cored wire is more widely used than the solid wire

                    The difference between flux-cored wire and solid wire

1. Production efficiency

In terms of production efficiency, the flux-cored wire adopts continuous welding mode, so the production efficiency is high. Compared with solid wire, the time of removing spatter and polishing weld surface is reduced because of less spatter and better weld forming.

2. Adaptability to steel

Compared with solid wire, because flux-cored wire generally transfers alloying elements through the flux-cored wire, the alloy composition can be easily adjusted from the formula to suit the requirements of the steel to be welded like a manual electrode. The solid welding wire each adjustment of the alloy composition, it must be re-smelted, the process is many, difficult to control, so it is difficult to meet the requirements of less and more varieties. And some alloy steel solid core wire drawing performance is poor, it is difficult to pull into the required wire. At this time, flux-cored welding wire shows its unique advantages.

3. Operating cost

Compared with manual electrode and solid wire, the price of flux-cored wire itself is very high. However, for large enterprises, after the use of flux-cored wire, the production cycle is shortened and the weld quality is easy to ensure, so the comprehensive benefits are very high.

4. Moisture resistance

 Common cartridge wire has a continuous gap on the side of its steel skin due to the constraints of its manufacturing form. Therefore, the shelving time of the flux-cored wire after opening the package can not be too long to prevent excessive moisture absorption and affect the welding quality.

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Like many other solid-state processes, resistance spot welding (RSW) relies on the material's inherent volume resistivity as a means of generating heat when an electric current passes through it. This physical phenomenon is described by Joule-Lentz's law (Joule's first law), which states that the heat (Q) generated by an electrical conductor is equal to the current (I) multiplied by the voltage (V) and the time (t) that the current is allowed to flow, or Q = IVt. Ohm's law states that voltage (V) is equal to current (I) multiplied by resistance (R), or V=IR. This means that Joule's law can also be written (after substitution) as Q=I2Rt.

In other words, the heat entering the weld is equal to the current multiplied by the resistance and the square of the time the current flows through the weld. Incidentally, this equation assumes that resistance and current are constant, which is not always the case with resistance welding. To help us further understand resistance heating (and subsequent resistance welding), it may help us to understand the relationship between the bulk resistivity of some materials and others. For the purposes of this talk, we'll limit things to a few materials that are common in our lives. Finally, resistivity is indicated by the Greek letter rho (ρ) in ohm-meters (Ω•m).

The volume resistivity of the materials we use in everyday life varies greatly. Here are some simple conclusions:

Copper has a very low volume resistivity value. That means it's a good conductor. It is this low volume resistivity that allows us to weld aluminum and iron alloys with electrodes made of copper without having to weld copper electrodes to parts.

The difference in bulk resistivity between aluminum and iron is large (about three times). However, it's not so big that we can't relate one to the other.

So how does the above information help us connect various aluminum alloys or any other material using the RSW process? Part of the reason is that the material generates heat when an electric current passes through it, and this is where volume resistivity comes into play. As we mentioned earlier, the total heat entering the weld can be expressed as Q=I2Rt. With this in mind, it makes sense that when comparing aluminum to iron, we would need more current or welding time to make up for the difference in total heat reduction due to loss of resistance. Often, however, when determining the best method for resistance spot welding, we cannot focus on just one material property, in this case volume resistivity.

First, because aluminum has a lower melting point, it reaches the plastic range at much lower temperatures than iron. This also means that the same volume of aluminum requires less heat to produce a melting temperature than iron. However, for aluminum alloys, it is more difficult to maintain sufficient plasticity to constrain melting because the plasticity range is very narrow. (The actual process window for acceptable spot welding for aluminum welding will be smaller than for welding with iron because we have a narrower range of allowable variations in current and welding time).

We now know the challenges we face. In order to successfully connect aluminum using the RSW process, we must take into account its lower (relative to iron) body resistivity, melting point, and plastic range. To help put it all together, the following rules of thumb may be helpful.

Rule of thumb

For RSW processes, there are a number of standardized welding procedures available, and they come in many forms. With the above in mind, is it possible to relate the information contained in the steel welding procedure to the information contained in the aluminum welding procedure? More importantly, is it possible to see how the welding industry explains the difference between these two materials? The short answer is yes. Although not accurate, a review of the steel (uncoated high strength low alloy) and aluminum welding diagrams should yield the following rough approximations. I call it the 3-1-1/3 rule.

Rule 3: For a given specification and control metal thickness (GMT), the typical current value of aluminum is approximately three times that of steel. This higher current requirement is caused both by the lack of bulk resistivity in the aluminum required to generate the heat required for melting, and by the heat drawn from the weld by the surrounding material. One place this rule is broken is if the surface of the aluminum has been freshly cleaned (think aerospace applications). In these cases, it is not uncommon for the secondary current required to be four times or more than the current in steel.

Rule 1: For a given specification and GMT, the welding forces of steel and aluminum will be roughly the same. A certain amount of unaffected substrate must be present to enclose the newly formed solder core, although depending on many factors, aluminum and steel weld forces are roughly the same. Note that we are not talking about the forging power that many aluminium can benefit from when joined by the RSW process. That's another subject.

1/3 rule: For a given specification and GMT, the welding time for aluminum is about 1/3 of the welding time for steel.

This is where the narrow plastic range really comes into play. This narrowing means that the process window for aluminum is smaller. Therefore, low and very targeted welding time values must be used.

Now that we know how to do resistance spot welding in aluminum, the next step is to understand that not all aluminum is created equal. Regardless of the alloy, or the post-treatment solution, the complete labeling should specify the required information.

Once the type of aluminum alloy to be treated is determined, the next step is to use this information and consult the compatibility chart to understand the best treatment method. These diagrams are available from a variety of sources, including AWS C1.1 Recommended Procedure for Resistance Welding or RWMA Resistance Welding Manual. Finally we can create the following categories:

1) The degree of difficulty of combination in welding problems. This category is usually sorted by difficulty and can even include recommendations not to weld materials together.

2) Pre-cleaning requirements. This can range from never requiring (very rare) to surfaces that require chemical and/or mechanical cleaning before they can be welded. It is important to note that I have yet to see how the existing surface pretreatment on the market is included in these charts. If your material has such a coating, it may be beneficial to consult the manufacturer.

3) Corrosion resistance of the obtained weld metal. In particular, it is either as good as the base material or it is not.

4) Admit that the chart is incomplete. Just like surface pretreatment, the world of substrates is constantly evolving, so you may want to contact manufacturers to see how compatible they are with the material.

Once the compatibility problem has been solved, it is now only necessary to use the basic principles of RSW for welding. Anyone who has read the RWMA Q&A column for a long time will know this: Use the right sized device and have a power supply with the right electrode cap on the right designed part. If you do this, you will have a cost-effective and robust welding process. So, although there are other ways to connect metal materials, RSW is not going away anytime soon.

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Virtual welding is one of the most common defects.

Sometimes after welding it seems that the front and back of the steel belt welded together, but in fact did not achieve the degree of integration, the strength of the combination surface is very low, the weld in the production line to go through a variety of complex processes, especially through the high temperature furnace area and high tension tension area, so the weld in the production line is very easy to "cause broken belt accident," It has great influence on the normal operation of the production line.

The essence of virtual welding is that the temperature of the joint surface of the weld is too low during welding, the core size is too small or even has not reached the degree of melting, but has only reached a plastic state, and is barely combined after rolling, so it looks welded well, but in fact, it is not fully integrated.

Analysis of the causes and steps of virtual welding can be carried out in the following order:

(1) First check whether the weld joint surface has impurities such as rust and oil, or uneven and poor contact, which will increase the contact resistance, reduce the current, and the welding joint temperature is not enough.

(2) Check whether the amount of overlap of the weld is normal, and whether the amount of overlap on the drive side is reduced or cracked. The reduction of the amount of overlap will make the joint area of the front and rear steel strips too small, so that the total force surface will be reduced and can not bear the greater tension. In particular, the phenomenon of driving side cracking will cause stress concentration, and the cracking will become larger and larger, and finally pull off.

(3) Check whether the current setting conforms to the process regulations, and whether the current setting does not increase correspondingly when the thickness of the product changes, resulting in insufficient current in the welding and poor welding.

(4) Check whether the welding wheel pressure is reasonable, if the pressure is not enough, it will be due to the contact resistance is too large, the actual current is reduced, although the welding controller has a constant current control mode, but the resistance increases beyond a certain range (generally 15%), it will exceed the limit of current compensation, the current can not increase with the increase of resistance and the corresponding increase, can not reach the set value. In this case, the system will issue an alarm when it is working properly.

In actual operation, if the exact cause of the virtual welding can not be analyzed for a while, you can clean the head and tail of the steel strip, increase the amount of welding overlap, appropriately increase the welding current and welding wheel pressure again, and pay close attention to the formation of the weld during welding, in most cases, you can deal with the problem in an emergency.

Of course, if there are control system problems, or grid voltage fluctuations, so that the weld welding must be taken other measures to solve.

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What are the differences between 7075 and 6061 aluminum alloys

1. Different ingredients

The 7075 series mainly uses zinc as the main alloy, and the composition ratio reaches 6%. The 6061 series mainly uses magnesium and silicon as the main alloys, and the total composition ratio is low.

2. Different intensity

In terms of strength, 7075 is stronger, no less than steel, but only a little stronger than 6061.

3. The price is different

7075 is the lightest and strongest aluminum, and the price is super expensive, while 6061 is the most common aluminum, light, strong, and affordable.

4. Different practicability

7075 contains a high proportion of other metals, so welding, processing are more difficult, its proportion is higher, so it is generally not used as a frame material. 6061 Due to the low proportion of other metals, it can increase its strength and reduce its wind resistance through special shape and various treatments, and even reduce the weight by three times pumping the tube. On the whole, 6061 is a better material.

Second, the difference between zinc alloy and aluminum alloy

1. Different raw materials

Zinc alloy is an alloy with other elements added on the basis of zinc, and the commonly added alloy elements are low-temperature zinc alloys such as aluminum, copper, magnesium, cadmium, lead and titanium. Zinc alloys are manufactured by melting and become materials in die casting and stamping processes. Aluminum alloy is a general term for aluminum-based alloys, the main alloying elements are copper, silicon, magnesium, zinc, manganese, secondary alloying elements are nickel, iron, titanium, chromium, lithium and so on.

2, different scope of application

Zinc alloy can be divided into cast zinc alloy and deformed zinc alloy according to the manufacturing process, which can be used for die-casting meters, galvanized corrosion prevention on the surface of automobile parts shell poles, and galvanized treatment of boiler water wall pipes to improve high temperature corrosion resistance. Aluminum alloy is the most widely used non-ferrous structural material in industry, widely used in aviation, aerospace, automotive machinery manufacturing, shipbuilding, chemical industry and so on.

3, the soup temperature is different during processing

Zinc alloy at more than 400 degrees; Aluminum alloy more than 700 degrees.

4, processing equipment is different

Although both are called die casting machines, they can not be universal at all.

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About spot welder Contact welder electrode material composition

1, CuCr (chromium copper) and CuCrZr (chromium zirconium copper) What is the difference?

Common ground: all are copper alloy material, suitable for resistance welding electrode, with high hardness, strength; It has the characteristics of high temperature softening, can resist high temperature and maintain its chemical and physical properties at about 450℃ ~ 550℃; With certain wear resistance, long service life; It has good electrical conductivity.

Difference: In copper alloy smelting, CuCr only adds Cr element to copper; CuCrZr, in addition to adding a certain component of Cr element, also added Zr element, and Zr element has wear resistance, toughness and other characteristics, so CuCrZr compared with CuCr, the material has better wear resistance, has a longer service life, but also improve the high temperature softening temperature, so CuCrZr as an electrode material is more superior.

2. Why does the electrode stick when welding the galvanized sheet?

This is because the electrode material used is CuCr or CuCrZr, when the Cu in the material is welded to produce high temperature melting, the zinc (Zn) of the galvanized plate will react with Cu and Zn alloy, and CuZn is just the brass alloy composition, and a chemical reaction occurred, the loss of the electrode material, resulting in the phenomenon of sticking.

3, how to solve the bonding phenomenon when welding galvanized sheet?

a) The best solution is to use dispersion strengthened copper (CuAl2O3),CuAl2O3 is a superior resistance welding electrode material, its softening temperature is up to 900°, is a good electrical conductivity strength and wear resistance, long service life, does not produce electrode and workpiece sticking phenomenon.

b) If you want to use CuCr or CuCrZr, you can use two current welding method, spot welding machine must have two current output, the first current (small) will first break down the coating, the second current to weld the workpiece, so that the workpiece will be firmly welded, the electrode sticking phenomenon will also be improved.

4, what is KCF, why welding nuts, bolts to use it?

KCF is a special ferrochrome alloy, which is characterized by good hardness and strength toughness, and after special heat treatment process, it has the characteristics of low pressure insulation on the surface, and when welding nuts or bolts, the thread part is required to make insulation protection to prevent the burn of the screw due to shred; Because KCF is used as a bar forming material, the processing is more convenient and the cycle is shorter; Therefore, it is ideal to use KCF material as the positioning core.

Of course, ceramic materials can also be used as the positioning core, the hardness of ceramics is completely no problem, but because it is easy to break and break, it is not ideal, and the molding needs a mold, so the processing of special cores is more difficult, the production cycle is longer, and the cost of small batches is very high. If the batch is large and standardized, the cost will be lower.

5, electrode material introduction:

Chromium-zirconium copper (CuCrZr)

Chromium zirconium copper (CuCrZr) is the most commonly used resistance welding electrode material, which is determined by its excellent chemical and physical properties and good cost performance.

1) Chrome-zirconium copper electrode It achieves a good balance of the four performance indicators of the welding electrode:

Excellent electrical conductivity ---------- ensures the minimum impedance of the welding circuit and achieves excellent welding quality.

High temperature mechanical properties ---------- High softening temperature guarantees the performance and life of electrode materials under high temperature welding environment.

Wear resistant ---------- electrode is not easy to wear, prolong life, reduce costs?

High hardness and strength ---- ensure that the electrode head under a certain pressure is not easy to deformation and crush, to ensure the welding quality.

Instructions:

1) Chemical composition analysis of the alloy according to ZBH62-003.1-H62003.8;

2) The hardness of the alloy is measured according to GB230, and the average value is taken at three points for each sample;

3) Eddy current conductance meter for conductivity measurement (eddy current comparison method). Each sample is measured at three points, and its average value is taken. Samples with a diameter less than 15mm can be measured according to GB3048.2;

4) For softening temperature test, the sample is placed in the furnace with the temperature rising to 550℃ (after closing the furnace door, it is required to return to this temperature for 2h within 15Min and then quench water cooling, and the temperature value of the sample room is measured (taking the average value of three points).

5) Electrode is an industrial production of consumables, the amount is relatively large, so its price and cost is also an important factor to consider, chromium zirconium copper electrode relative to its excellent performance, the price is relatively cheap, can meet the needs of production.

6) Chromium-zirconium copper electrode is suitable for spot welding and convex welding of carbon steel plate, stainless steel plate, plated plate and other parts, chromium-zirconium copper material is suitable for manufacturing electrode caps, electrode connecting rod, electrode head, electrode grip, convex welding special electrode, welding wheel, conductive nozzle and other electrode parts.

Beryllium copper (BeCu)

Beryllium copper (BeCu) electrode material has higher hardness (up to HRB95~104), strength (up to 800Mpa/N/mm2) and softening temperature (up to 650℃) than chromium-zirconium copper, but its conductivity is much lower and poor. Beryllium copper (BeCu) electrode material is suitable for welding under high pressure sheet parts, as well as harder materials, such as welding wheels for welding seams; It is also used for some electrode accessories with high strength requirements, such as crank electrode connecting rod, converter for robots; At the same time, it has good elasticity and thermal conductivity, and is suitable for manufacturing stud welding collet. Beryllium copper (BeCu) electrodes are expensive, and we usually list them as special electrode materials.

Copper alumina (CuAl2O3)

Copper aluminum oxide (CuAl2O3) is also known as dispersion strengthened copper, it compared with chromium zirconium copper, has higher strength (up to 600Mpa/N/mm2), excellent high temperature mechanical properties (softening temperature of 900℃) and good electrical conductivity (conductivity 80~85 IACS%), with excellent wear resistance, long life. Copper aluminum oxide (CuAl2O3) is a kind of excellent performance electrode material, whether its strength, softening temperature or conductivity are very superior, especially for welding galvanized sheet, it does not produce the phenomenon of electrode and workpiece sticking as chromium zirconium copper electrode, without frequent grinding, effectively solve the problem of welding galvanized sheet, improve efficiency, reduce production costs. Aluminum oxide copper electrode has excellent welding performance, but its current cost is very expensive, so the current use can not be widely used, but the excellent welding performance of galvanized sheet and the widespread use of galvanized sheet, making its market prospects. Aluminum oxide copper electrode is suitable for welding of galvanized steel plate, aluminum products, carbon steel plate, stainless steel plate and other parts.

Tungsten (W), Molybdenum (Mo)

Tungsten electrode materials are pure Tungsten, tungsten-based high-gravity alloy, and tungsten-copper alloy. Tungsten-based high-gravity alloy is sintered by adding a small amount of nickel-iron or nickel-copper to tungsten, and tungsten-copper composite materials contain 10-40% Copper by weight.

Molybdenum tungsten electrode has high hardness, high melting point, high temperature performance and other characteristics, suitable for welding non-ferrous metal copper, aluminum, nickel, such as the switch of copper braided strip and metal sheet welding.

Appendix: Chemical and physical properties of electrode materials

1) Chromium-zirconium copper (CuCrZr) molding process:

Vacuum melting → hot forging (extrusion)→ solid melting → cold forging (drawing)→ aging treatment

The above process, coupled with strict quality control, ensures excellent electrical conductivity, high strength and good wear resistance of the material.

The standard electrode head, electrode cap and shaped electrode are produced by cold extrusion process and precision machining to further improve the density of the product, and the product performance is more excellent and durable to ensure stable welding quality.

Round rod specifications φ3.0 ~45mm, the box or disk is generally forged according to the requirements of customers.

Chemical composition and physical properties of Al 2 O 3 Cu and BeCu

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Clear View tanks are unparalleled in the safe handling of propane, are extremely weather and corrosion resistant, lightweight and offer the ability to view the level of fuel through the tank.

  Corrosion / Weather Resistant

  Due to the composite fiberglass construction, Clear View propane tanks can be used in manyenvironments. By design and materials, the fiberglass tank may be used on a vessel, a forklift or an outdoor BBQ alike with little worry of the effects of sun, salt or weather. For aesthetic purposes, cylinders can be easily be cleaned by power-washing with a soap and water solution. Sand-blasting or painting of the cylinders is not necessary. UV additives and stabalizers have been applied to the casing material. Finally, as part of the approval, Clear View fiberglass tanks are tested and approved down to -40F / -40C.

  Lightweight, with a Clear View
  Fiberglass propane tanks weigh 50% less than steel counterparts and 20% less than aluminum. This lighter weight makes the tanks easier to handle. The ability to view the propane through the fiberglass tank removes all guessing as to the level. Additionally, the translucent quality of the tank allows you to view fuel level as the tank is being filled.

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It is difficult to operate stably because people are in an unnatural position during the welding. At the same time, the operation also has to lift the heavy welding torch and cable, which increases the difficulty of the operation. In addition, the molten iron in the molten pool is easy to sag and form a convex weld pass, which causes the molten iron to flow in serious cases. Therefore, the welding parameters should be strictly controlled in order to obtain a good weld formation.

First of all, ensure that the butt gap between the two plates is guaranteed to be 3mm, not too large or too small, too large will cause breakdown, welding tumor, the phenomenon of concave welding pass, too small will cause the back is not welded through, not fused.

                            Backing weld

Welding process: The welding parameters are set to 18.5V and 130A.

Angle before welding: Keep 90° on both sides of welding gun and groove, and 80-90° on the back side. When transporting the bar, the zigzag shape or positive crescent type is used, and the middle is stopped on both sides to prevent the edge from biting on both sides, and the middle is too high or through the silk.

                            Filler welding

Clean up the spatter and welding slag produced by the base welding before welding.

Welding process: Welding parameters are set to voltage 19V, current 140A.

Angle before welding: Keep 90° on both sides of welding gun and groove, and 75-85° on the back side. When the bar is used, the zigzag shape or positive crescent type of rod is used. The middle belt is stopped on both sides, which can prevent the appearance of too high in the middle of the biting edge on both sides. The short arc welding is used when welding. Cover welding begins when the weld pass is about 1mm lower than the base material.

                            Capping weld

Clean up the spatter and welding slag produced by the base welding before welding.

During the welding process, the welding parameters are set to the voltage 18V and the current 110-120A.

Angle before welding: Keep 90° on both sides of welding gun and groove, and 75-85° on the back side. When transporting the bar, the zigzag shape or positive crescent type transporting bar is used, the middle belt is paused on both sides, and the left and right sides are fully integrated with the base material to swing, which can prevent the appearance of the middle of the biting edge on both sides from being too high.

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1) Personal protective equipment Metal welding and cutting workers should wear appropriate labor protection products before work, such as dust masks, welding gloves, welding work clothes; Wear safety goggles or face mask when operating; Wear rubber shoes when working in wet places or on rainy days. For special operations, you can also wear a long tube breathing apparatus to prevent smoke hazards. To prevent arc damage, choose different types of filters according to the strength of the current. Wear light colored canvas work clothes, tie the cuffs, buckle the neckline, can reduce its damage to the skin.

2) Pre-work inspection and cleaning Before the operation of various containers, pipelines, workpieces stained with flammable gas and solution, should be inspected first, wash away toxic and harmful, flammable and explosive substances, relieve the pressure of containers and pipelines, and eliminate the closed state of containers. Before the fire, the material in the container should be sampled and analyzed, and the work should be carried out after it is qualified; When welding and cutting closed hollow workpieces, air holes must be left. Work in the container, there should be human supervision, and have good ventilation facilities and lighting facilities.

3) Pay attention to site safety details In order to prevent fire and explosion accidents, the workplace should be carefully checked before operation, and flammable and explosive items should not be stored around the workplace. When performing gas welding or gas cutting operations, it is necessary to carefully check the bottle valve, pressure reducing valve and hose, and there can be no air leakage phenomenon; Screw and remove the valve should be done according to the operating procedures.

In the welding operation, it should be noted that the current is too large, the wire sheath damage will produce high temperature; Poor contact at the joint can cause a fire. Therefore, the operation should be carefully checked before the replacement of defective equipment. In addition, it should also be noted that when welding, cutting pipes, equipment, heat conduction may cause flammable and explosive items at the other end to catch fire or even explode. Check carefully before operation and remove dangerous items at the other end.

When cutting old equipment and scrap steel, pay attention to removing flammable and explosive items included in them. At the job site, a sufficient number of fire extinguishing equipment should be equipped, and the effective period of the fire extinguishing equipment should be checked to ensure its effective use. After the welding and cutting operations, the site should be carefully inspected to eliminate the remaining kindling and avoid future problems.

4) For the prevention of electric shock accidents, the welding machine shell and non-charged metal components must protect the ground (or zero), and the insulation resistance should be large enough. The terminal should be covered with a cover; Welding handle, welding pliers and welding cable insulation; At the same time, distance should be kept between charged bodies and between charged bodies and other objects. The welding machine and the power cord should be placed in a place that is not accessible to the human body.

When climbing and welding, it should be noted that the distance from the high-voltage grid is not too close, the cable used for operation can not be wrapped around the body or on the shoulder, the cable should be tied to the scaffolding and other facilities, so as not to step on the foot, resulting in damage to the insulation layer. When moving, repairing and repairing the welding machine, replacing the fuse, changing the polarity and other operations, the power switch must be cut off.

Wear insulated gloves when pushing and pulling the power knife, and the person should stand on the side to prevent the arc spark from burning the face. In the event of electric shock, the power supply should be cut off immediately and on-site first aid should be carried out.

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Copper contact tip, the color is purple, but not entirely pure copper, sometimes it also adds a small amount of deoxidation elements or other elements to improve the material and performance, so it is also a copper alloy. At present, domestic copper processing materials can be divided into four types according to the composition: oxygen-free copper, deoxidized copper, ordinary copper and special copper with a small amount of alloying elements. Copper is widely used in the production of conductive and thermal equipment. It is also used in some non-oxidizing acids, bases, salt solutions and a variety of organic acids, which have good corrosion resistance and are used in the chemical industry. Although the electrical and thermal conductivity of copper is second only to silver, it has good weldability, and can be made into various semi-finished products and finished products by cold and thermoplastic processing.

        Chromium zirconium copper contact tip, with high strength, hardness, conductivity and thermal conductivity, and wear resistance, crack resistance and softening properties, after a long time after treatment hardness, strength, conductivity and thermal conductivity are significantly improved, easy to weld. Widely used in motor commutator, welding machine, seam welding machine and so on.

        Chromium zirconium copper contact tip, has good electrical conductivity, thermal conductivity, high hardness, wear resistance and explosion resistance, crack resistance and high softening temperature, welding electrode loss is less, welding speed is fast, the total cost of welding is low, suitable for welding welding machine electrode related accessories, in Europe and the United States welding gun, mainly with copper conductive contact tip, mainly used in Europe and the United States protective gas to argon gas mixture. The arc is long, the gas cooling performance is poor, the main way of the failure of the conductive contact tip is caused by the micro arc between the hole wall of the conductive contact tip and the welding wire, so the conductive copper with better conductive conductivity is used as the conductive contact tip, and the CO2 gas is used as the protective gas in Asia, the arc is short, the gas cooling ability is strong, and the conductive contact tip is mainly chromium zirconium copper on the welding gun in Japan and South Korea. Japan believes that the failure of the conductive contact tip is mainly caused by the friction loss between the inner hole wall of the conductive contact tip and the welding wire, so the harder chromium zirconium copper material is mainly used. Since China mainly uses CO2 gas as a protective gas, chrome zirconium copper conductive contact tip should be selected. The national standard for the conductive contact tip is 9mm, but most of the existing conductive contact tip on the domestic market is far lower than this standard, the process standard is uneven, resulting in the conductive contact tip inner hole wall burr, the wire is not smooth, good conductive contact tip in the unit price is relatively high but the reaction in the service life, is often several times the general conductive contact tip. It also reduces the disadvantages of frequent replacement of the conductive contact tip (time saving). The most important thing is that the good welding effect greatly improves the production efficiency, and brings greater development and benefits to the production enterprises!

Comparison of life of conductive contact tip

1. Material is the main reason affecting the life of the conductive contact tip. The conductivity test confirmed that the conductivity of the common copper contact tip on the market is only about 80%IACS, which is far lower than the national standard, so the service life is low.

Good conductive contact tip copper material/chromium zirconium copper material strictly implement national standards, conductivity above 100%IACS, so it has a long service life.

2. The manufacturing process is the second reason that affects the life of the conductive contact tip. The forming of holes is the bottleneck of making conductive contact tip. Due to the difficulty in forming the inner hole of the conductive contact tip, the "extrusion forging" forming method of the copper pipe with larger aperture is generally adopted in our country. The so-called "extrusion forging" is to insert a steel wire with a suitable diameter into the copper pipe with a large hole, rotate the copper pipe at one end, reduce the inner hole of the copper pipe by reducing the outer diameter of the copper pipe, and finally extract the steel wire to make the hole shape.

This production method only partially solves the forming problem of the inner hole of the conductive contact tip, and has disadvantages. See Figure 1 - Common market conductive contact tip. The conductive contact tip is suitable for welding wire diameter of 0.8mm. The aperture on the right side of the contact tip after extrusion forging is 1.01mm, which is the working part of the contact tip. The left aperture without extrusion forging is 1.39mm, the hole depth is 18mm, and this part is basically not working. It is calculated that the length of the non-working part of the hole accounts for 40% of the total length, which greatly reduces the life of the conductive contact tip.

 The good conductive contact tip is produced by copper tube produced by patented technology. The diameter of the inner hole of the copper tube is as small as 0.9mm, and the aperture is consistent and smooth on the full length of the conductive contact tip, which greatly improves the service life of the conductive contact tip.

Combined with the above two life factors, the service life of the good conductive contact tip is more than double that of the common conductive contact tip on the market.

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1. Welding splash

The splash produced by laser welding seriously affects the surface quality of the weld and can contaminate and damage the lens. Generally, after laser welding is completed, many metal particles appear on the surface of the material or workpiece, attached to the surface of the material or workpiece.

Spatter cause: The surface of the processed material or workpiece is not cleaned, there are oil stains or pollutants, and it may also be caused by volatilization of the galvanized layer.

The solution:

A. Pay attention to cleaning materials or workpieces before laser welding.

B. Splash is directly related to power density. Appropriate reduction of welding energy can reduce spatter.

                2.  Cracks

2. The cracks produced by continuous laser welding are mainly hot cracks, such as crystal cracks, liquefaction cracks, etc.

The cause of the crack is mainly caused by excessive shrinkage force before the weld is not completely solidified.

Solution: Filling wire, preheating and other measures can reduce or eliminate cracks.

3.  Stomata

The surface porosity of weld is a defect that is easy to appear in laser welding.

Causes of stomata:

A. The laser welding pool is deep and narrow, and the cooling speed is fast. The gas produced in the liquid molten pool is too late to overflow, which easily leads to the formation of pores.

B, the weld surface is not cleaned, or galvanized zinc vapor volatilization.

Solution: Clean the surface and weld surface before welding to improve the volatilization of zinc when heated. In addition, the blowing direction also affects the formation of stomata.

4.  Bite the edge

The biting edge refers to: the weld is not well combined with the base material, there is a groove, the depth is greater than 0.5mm, the total length is greater than 10% of the weld length, or greater than the length required by the acceptance standard.

Reasons for edge biting:

A. The welding speed is too fast, and the liquid metal in the weld will not be redistributed on the back of the small hole, forming A biting edge on both sides of the weld.

B, the joint assembly gap is too large, the molten metal in the joint filling is reduced, and it is also easy to bite.

C, at the end of laser welding, if the energy decline time is too fast, the small hole is easy to collapse, and it will also cause local edge biting.

The solution:

A. Control the processing power and speed matching of laser welding machine to avoid edge biting.

B. The edge of the weld found in the inspection can be polished, cleaned and repaired to make it meet the requirements of the acceptance standard.

                     5.  Weld accumulation

The weld is obviously overfilled, and the weld is too high when it is filled.

The cause of weld accumulation: the wire feed speed is too fast or the welding speed is too slow.

Solution: Improve the welding speed or reduce the wire feed speed, or reduce the laser power.       

6.  Welding deviation

The weld metal does not solidify in the center of the joint structure.

The reason for this situation: inaccurate positioning during welding, or inaccurate filling welding time and welding wire alignment.

Solution: Adjust the welding position, or adjust the repair welding time and the position of the welding wire, as well as the position of the lamp, the welding wire and the weld.

7.  The weld is dented

Weld concave refers to the phenomenon of concave weld metal surface.

The reason for the weld depression: when brazing, the solder joint center is poor. The center of the spot is close to the lower plate and deviates from the center of the weld, resulting in partial melting of the base material.

Solution: Adjust the light matching.

8.  Bad weld forming

Poor weld forming includes: poor weld ripple, uneven and irregular weld, uneven transition between weld and base material, poor weld and uneven weld.

The reason for this situation: when the weld is brazed, the wire feed is unstable, or the light is discontinuous.

Solution: Adjust the stability of the equipment.

9.  Uneven weld bead

Uneven weld path refers to: when the weld trajectory changes greatly, the corner is prone to uneven weld path or molding.

Cause: the trajectory of the weld changes greatly, and the teaching is uneven.

Solution: Welding under the best parameters, adjust the Angle of view, so that the Angle is consistent.

10.  Surface slag inclusion

Surface slag inclusion refers to: in the welding process, the skin slag inclusion that can be seen from the outside mainly appears between layers.

Cause analysis of surface slag inclusion:

A, multi-layer and multi-pass welding, the interlayer coating is not clean; Or the surface of the previous layer of weld is not smooth or the surface of the weldment does not meet the requirements.

B, welding input energy is low, welding speed is too fast and other improper welding operation technology.

The solution:

A. Select reasonable welding current and welding speed. The interlayer coating must be cleaned during multilayer and multipass welding.

B. Polish the weld to remove the slag on the surface, and repair the weld if necessary

What are the laser welding processes? Laser welding is a new type of welding, laser welding is mainly for thin-wall materials, precision parts welding, spot welding, butt welding, overlap welding, sealing welding, etc., its characteristics are: with a high depth to width ratio, small weld width, small heat affected zone, small deformation, fast welding speed. The weld is smooth and beautiful, and there is no need to handle or only a simple processing procedure after welding. The weld has high quality, no porosity, can reduce and optimize the impurities of the base material, the tissue can be refined after welding, and the strength and toughness of the weld are at least equal to or even more than the base metal. Precise control, small focus point, high precision positioning, easy to achieve automation. It can realize the welding between some dissimilar materials.

1, laser self-fusion welding

Laser welding is the use of laser beam excellent directivity and high power density and other characteristics of the work, through the optical system to focus the laser beam in a very small area, in a very short time to be welded to form a highly concentrated energy heat source area, so that the solder to be melted and formed a solid solder joints and welds. Laser welding: the depth to width ratio is large; High speed and high precision; Small heat input, small deformation; Non-contact welding; Not affected by magnetic field, no need to vacuum.

2, laser wire welding

Laser wire filling welding refers to the method of pre-filling a specific welding material in the weld and melting it with laser irradiation or filling the welding material at the same time of laser irradiation to form a welding joint. Compared with non-wire welding, laser wire filling welding solves the problem of strict requirements for workpiece processing and assembly. Smaller power welding thicker parts; By adjusting the composition of the filler wire, the microstructure properties of the weld area can be controlled.

3, laser flight welding

Remote laser welding is a kind of laser welding method which uses high-speed scanning lens to process long working distance. High positioning accuracy, short time, fast welding speed, high efficiency; Will not interfere with the welding fixture, optical lens pollution less; Arbitrary shape welds can be customized to optimize structural strength, etc. Generally, the weld has no gas protection, and the splash is larger. It is widely used in thin high-strength steel plate and galvanized steel plate such as body covering parts.

4, laser brazing

The laser beam emitted by the laser generator is focused on the surface of the welding wire and heated, so that the welding wire is heated and melted (the base material is not melted) to wet the base material, fill the joint gap, and combine with the base material to form a weld to achieve a good connection

5, laser swing welding

By swinging the reflection lens inside the welding head, the laser swinging is controlled to stir the welding solution pool to promote the gas overflow from the solution pool and refine the grain. At the same time, the sensitivity of laser welding to incoming material gap can be reduced. Especially suitable for aluminum alloy, copper and dissimilar materials welding.

6, laser arc composite welding

Laser-arc composite welding combines two kinds of laser and arc heat sources with different physical properties and energy transmission mechanisms to form a new and efficient heat source. Composite welding features: 1, compared with laser welding, bridge ability is enhanced, improve the organization. 2, compared with arc welding, small deformation, high welding speed, deep penetration. 3, and the length of each heat source and make up their own shortcomings, 1+1>2.

Welding is a processing process and connection method that combines atoms between two workpieces by heating, pressurizing, or both. Welding is widely used for both metals and non-metals.

Development history of welding technology

Forge welding technology appeared in Egypt in 3000 BC.

In 2000 BC, the Yin Dynasty of China used casting and welding to make weapons.

1801 - H.Davy of England discovers electric arc.

1836 - Edmund Davy discovers acetylene gas.

1856 - James Joule, an English physicist, discovers the principle of resistance welding.

1959 - Deville and Debray invent hydrogen - oxygen welding.

1881: Frenchman De Meritens invents the earliest carbon arc welding machine.

1881: Dr. R. H. Thurston of the United States spent six years to complete all the experiments on the strength and extensibility of a full range of copper-zinc alloy brazing materials.

1882 - The austenitic manganese steel invented by Robert A. Hadfield of England and named after him is patented.

In 1885, Elihu Thompson, an American, patented a resistance welding machine.

1885 - Russian Benardos Olszewski develops carbon arc welding technology.

1888: Russian H. l. C. L.

1889-1890: C. L. Coffin, an American, performed the first arc welding using a light wire as an electrode.

In 1890; The American C. L. Coffin proposed the concept of welding in an oxidizing medium.

1890 - British man Brown makes the first attempt to rob a bank using oxygen and gas cutting.

1895 - Bavarian Konrad Roentgen observes X-rays produced by a stream of electrons passing through a vacuum tube.

1895 - Frenchman Le Chatelier receives a certificate for inventing the oxyacetylene flame.

1898: German Goldschmidt invented thermite welding.

1898: The German Klein. Schmidt invented arc welding of copper electrodes.

1900: Strohmyer invented the thin-coated electrode.

In 1900, the French Fouch and Picard made the first oxy-acetylene cutting torch.

1901 - German Menne invents oxygen spear cutting.

1904: The Swede Oscar. Kjellberg established the world's first electrode factory - ESAB's OK Electrode factory.

In 1904, Avery invented the portable steel cylinder.

1907: When demolishing the old Central railway station in New York, more than 20% of the engineering cost was saved due to the use of oxy-acetylene cutting.

1911 - Philadelphia & Suburban Gas Company builds the first 11-mile line to be welded using oxygen solvent gas welding.

1912: The first oxy-acetylene gas welded steel pipe was put on the market.

1912 - The Edward G. Budd Company in Philadelphia produces the first all-steel automobile body welded with resistance spot welding.

Circa 1912: In order to produce the famous Model T car, the Ford Motor Company in the United States completed the modern welding process in the laboratory of its factory.

1913 - Avery and Fisher perfect acetylene cylinders in Indianapolis, USA.

1916: Ansel. The first is the invention of X-ray nondestructive testing in the welding zone.

1917: During World War I, 109 ship engines captured from Germany were repaired using arc welding, and half a million American soldiers were transported to France using these repaired ships.

1917: Webster & Southbridge Electric Company in Massachusetts used arc welding equipment to weld 11 miles of pipeline with a diameter of 3 inches.

1919: Comfort A. dams forms the American Welding Society (AWS).

1919 - C.J.Halslag invents AC welding.

1920 - Gerdien discovers the heat flux effect.

1920 - Fulagar, the first steamship with an all-welded hull, is launched in England.

Circa 1920: Began using arc welding to repair some valuable equipment.

Circa 1920: The Johnson Process for welding steel pipes using resistance welding is patented.

Circa 1920: The Poughkeepsie Socony, the first oil tanker built using the welding method, is launched in the United States.

Circa 1920: flux-cored wire is used for wear-resistant surfacing.

1922 - Prairie Pipeline Company successfully completes the laying of an 8-inch diameter, 140-mile crude oil pipeline from Mexico to Texas using oxy-acetylene welding technology.

1923: Stody invents surfacing welding.

1923: The world's first floating roof storage tank (used to store gasoline or other chemicals) is built; Its advantage is that the tank can be raised or lowered like a telescope by a welded floating roof and tank wall, so that the volume of the tank can be easily changed.

1924: Magnolia Gas Company builds 14 miles of all-welded natural gas line using oxy-acetylene welding technology.

1924: H.H. ester was the first in the United States to use X-ray photography to test the quality of castings to be installed at a steam pressure of 8.3Mpa for the Boston Edison power plant.

1926: American Langmuir invented atomic hydrogen welding.

1926: Alexandre invented the principle of CO2 gas shielded welding.

1926: A.O.Smih company in the United States took the lead in introducing the production method of applying a protective solid coating (that is, manual arc welding electrode) on the metal electrode for arc welding.

1926: Chromium-tungsten-cobalt alloy receives the first patent for flux-cored wire.

1926: Americans M. Hoart and P.K. evers obtain a patent for the use of helium as an arc protection gas.

1927: Lindberg successfully flew the Ryan monoplane over the Atlantic Ocean, with a fuselage made of welded steel tubes.

1928: The first structural steel welding code, Code for Fusion Welding and Gas Cutting in Building Structures, is published by the American Welding Society, which is the predecessor of today's D1.1 Structural Steel Welding Code.

1930: The Georgia Railroad Center uses a continuous welding method to lay the railroad in two tunnels. The welded track was put into use two years later when the line was through.

1930: The former Soviet Union Robinov invented submerged arc welding.

1931 - The Empire State Building is built with a welded all-steel structure.

1933: The first joint welded using the arc welding process was laid with a long transmission line with no liner construction.

1933 - San Francisco's Golden Gate Bridge, then the highest suspension bridge in the world, opens to traffic, made of 87,750 tons of welded steel.

1934 - Barton Welding Institute is established.

Barton Institute founder Yevkin Oskalovich Barton

The largest welded iron bridge over the River Deniebe in Europe - Barton Bridge

1934: The Unheated pressure Vessel Code is published by the API - ASME collaboration.

1935: Linde Air Products of the United States perfected the submerged arc welding technology.

1936: Wasserman invented low temperature brazing.

1939: American Reinecke invented the ion flow spray gun.

1940 - Exchequer, the first all-welded ship, is launched at Ingalls Shipyard in the United States.

1941: American Meredith invented tungsten inert gas shielded arc welding (helium arc welding).

1941: During World War II, ships, aircraft, tanks and various heavy weapons were manufactured using a large number of welding techniques.

1943: Behl invented ultrasonic welding.

1943: Aircraft builders first welded the hollow blades of aircraft steel propellers using atomic hydrogen welding, submerged arc welding, and MIG welding.

1944: British Carl invented explosive welding.

1947: The invention of electroslag welding in the former Soviet Union by Bopo Noebech (Voroshevich).

1949 - The first FORD car with an all-welded structure made using arc and resistance welding processes rolls off the assembly line.

In 1950, Americans Muller, Gibson and Anderson obtained the first patent for the excessive welding of MIG.

1950 - German F. B. uhorn discovers plasma arcs.

Circa 1950: Electroslag welding is first used in production in the former Soviet Union.

1953: Hunt invented cold pressure welding.

1953: The former Soviet Union Lyupovsky, Japan Sekiguchi and others invented CO2 gas shielded arc welding.

1954: Self-protecting flux-cored wire was put into production at Lincoln Electric Company in the United States.

1954 - The Nautilus, the first welded nuclear submarine, enters service with the U.S. Navy.

1954: Benard invents the tubular electrode.

1955: Thom, USA. Claverd invents high-frequency induction welding.

1956: Harbin Welding Research Institute was established in China.

1956: The former Soviet Union Chudikov invented friction welding technology.

1957: The invention of electron beam welding by Schgill in France.

1957: The former Soviet Union Kazakov invented diffusion welding.

1957: "Welding" is published, which is the first professional welding magazine in China.

Circa 1957: The United States, the United Kingdom, and the former Soviet Union all used CO2 as a protective gas in the process of short circuit welding.

1960: Airco of the United States introduced the metal pulse gas welding process.

1962: The patent for gas welding was granted to the Belgian Arcos.

1962 - Electron beam welding is first used on supersonic aircraft and B-70 bombers.

1964: The patent for the hot wire welding method and the coordinated control of the MIG welding method is granted to the American Manz.

1965 - The welded Appllo 10 spacecraft successfully landed on the moon.

1967: Arada invented continuous laser welding.

In 1967, the world's first submarine pipeline was successfully laid in the Gulf of Mexico, which was manufactured by the Krank Pilia company of the United States using the thermal thread process and welding process.

1968: Welded 22 floors above the John Hancock Center in Chicago to create the world's tallest sharp-angled steel structure at 1,107 feet.

1969: Linde Company of the United States proposed the hot wire plasma arc spraying process.

1970: Thyristor inverter welding machine came out.

1976: Arada invented series electron beam welding.

Around 1980: Semiconductor circuits and computer circuits are widely used to control welding and cutting processes.

Circa 1980: Use steam brazing to weld printed circuit boards.

1983: The circular top of the 160-foot diameter flap structure on the space shuttle was welded using the submerged arc and shielded welding method and inspected using a radiographic flaw detector.

1988: Welding robots began to be widely used in automobile production lines.

Around 1990: Inverter technology has been greatly developed, and the result is a reduction in the weight and size of welding equipment.

1991: The British Welding Institute invented friction stir welding and successfully welded aluminum alloy plates.

1993: The United States Army Abrams main battle Tank was successfully welded using a robot-controlled CO2 laser.

1996: A research group of more than 30 people headed by B.K.Lebegev, academician of the Barton Welding Institute in Ukraine, researched and developed the welding technology of human tissue.

2001: Human tissue welding was successfully applied in clinic.

2002: Welding of the Three Gorges Turbine is completed, the largest turbine in the world that has been built and is currently under construction.

1985:Huarui was established

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