In this article, we will introduce 8 different types of welding methods and processes in detail, including definitions, working principles, characteristics, advantages, etc.
I believe you will have a new understanding of welding methods after reading this.
Let's dive right into it.
Shielded Metal Arc Welding
Principle
Electric arc welding with welding rod is a process method that uses the stable burning arc established between the welding rod and the workpiece to melt the welding rod and the workpiece so as to obtain a joint firm welding.
During welding, the coating is continuously decomposed and melted to generate gas and slag, which protects the electrode end, arc, weld pool and its surrounding areas, and prevents harmful pollution from the atmosphere to the molten metal.
The welding core also melts continuously under the action of arc heat and enters the weld pool to form the weld filler metal.
Feature
1. Compared with other arc welding methods, stick arc welding has the following advantages:
1. Simple equipment, flexible and convenient operation, strong adaptability, good accessibility, free from welding location and position restrictions, and welding can generally be carried out where the electrode can reach.
These are important reasons for the wide application of shielded metal arc welding.
2. There are a wide variety of weldable metal materials.
Almost all metals can be welded, except those that are insoluble or easily oxidized.
3. Requirements for joint assembly quality are low. During the welding process, the arc is manually controlled by the welder.
Welding process parameters can be modified by timely adjusting the arc position and electrode speed, reducing the quality requirements for joint assembly.
2. Compared with other arc welding methods, stick arc welding has the following disadvantages:
1. Welding productivity is low and labor intensity is high.
Compared with other arc welding methods, the welding current is low and the welding rod must be replaced after each welding rod is completed.
Slag cleaning is also necessary after welding.
Production efficiency is low and labor intensity is high;
And the arc light is strong and the smoke is heavy.
2. Welding quality is highly dependent on people.
As manual welding electrodes are used for welding, there are requirements for the welder's operational skills, work attitude and performance in the field.
The quality of welding largely depends on the operational level of the welder.
Welding process
Electric arc welding with welding rod is composed of welding power source, welding cable, welding tongs, welding rods, weldments and electric arcs.
During welding, welding rods and workpieces are used to contact and ignite electric arcs, and then the welding rods are lifted and held at a certain distance.
Under the condition that the welding power source provides adequate arc voltage and welding current, the electric arcs burn continuously to produce high temperatures, and the welding rods and weldments are locally heated to the molten state.
The molten metal at the end of the electrode is fused with the molten molten metal to form a molten pool.
In welding, the arc moves with the electrode, and the liquid metal in the molten pool gradually cools and crystallizes to form a weld, and the two welds are welded together.
In welding, the electrode welding core is transferred to the molten pool in the form of molten droplets after melting, and the electrode coating generates a certain amount of gas and liquid slag.
The generated gas is filled around the arc and weld pool to isolate the air.
The density of liquid slag is lower than that of liquid metal and it floats in the weld pool to protect it.
When the metal in the molten pool cools and solidifies, the slag also solidifies to form welding slag covering the weld surface, preventing the high-temperature weld metal from being oxidized and reducing the cooling rate of the weld.
In the welding process, complex metallurgical reactions such as deoxidation, desulfurization, dephosphorization and dehydrogenation are carried out between liquid metal and liquid slag and gas, so that the weld metal can obtain suitable chemical composition and structure.
TIG welding (tungsten inert gas welding)
Definition
TIG welding is also known as non-consumable inert gas arc welding.
Whether manual or automatic welding of stainless steel with a thickness of 0.5 to 4.0 mm, TIG welding is the most commonly used welding method.
The filler wire TIG welding method is often used for pressure vessel backing welding, because TIG welding has good gas tightness, which can reduce the porosity of welds during pressure vessel welding.
The heat source of TIG welding is DC arc, the working voltage is 10~95V, but the current can reach 600A.
The correct connection mode of the welding machine is that the workpiece is connected to the positive pole of the power supply, and the tungsten electrode on the welding torch is used as the negative pole.
The inert gas is usually argon.
Tig w learning process
Inert gas is fed through the welding torch to form a shield around the arc and in the welding puddle.
To increase the heat input, 5% hydrogen is usually added to the argon.
However, when welding ferritic stainless steel, hydrogen cannot be added to argon. Gas consumption is about 3 to 8 liters per minute.
In addition to blowing inert gas from the welding torch, it is best to also blow the gas used to protect the back of the weld under the weld.
If necessary, the weld pool can be filled with welding wire of the same composition as the austenitic material to be welded.
When welding ferritic stainless steel, type 316 filler is generally used.
Main advantages
Gas shielded arc welding is a type of arc welding method that uses external gas as the shielding medium.
Its advantages are good visibility of the arc and weld pool and easy operation;
There is no slag or little slag, so there is no need to clean the slag after welding.
However, special windproof measures must be taken when working outdoors.
According to whether the electrode is melted during welding, gas shielded welding can be divided into gas shielded welding with non-melting electrode (tungsten electrode) and gas shielded welding with consumable electrode.
The first includes tungsten inert gas welding, plasma arc welding and atomic hydrogen welding.
At present, atomic hydrogen welding is rarely used in production.
Tungsten inert gas (TIG) welding is a welding method that uses the arc generated between the tungsten electrode and the workpiece to melt the base metal and filler wire (if filler wire is used) under inert gas protection.
During welding, shielding gas is continuously sprayed from the welding gun nozzle, forming a protective gas layer around the arc to isolate the air, so as to prevent its harmful effects on the tungsten electrode, weld pool and in the adjacent heat affected. zone, in order to obtain high quality welds.
Argon, helium or a mixture of argon and helium can be used as shielding gas.
In special applications, small amounts of hydrogen may be added.
Argon is used as a shielding gas for tungsten and argon arc welding, and helium is used for tungsten and helium arc welding.
Due to the high price of helium, argon tungsten arc welding is much more widely used in industry than helium arc welding.
Classification
TIG welding can be divided into manual welding, semi-automatic welding and automatic welding according to the operation mode.
During manual argon tungsten arc welding, the movement of the welding gun and the addition of filler wire are completely manual;
During semi-automatic argon tungsten arc welding, the movement of the welding gun is manually operated, but the filling wire is automatically fed by the wire feeding mechanism;
During automatic argon tungsten arc welding, if the workpiece is fixed and the arc moves, the welding gun will be installed on the welding cart, and the cart displacement and filler wire can be added in the form cold wire or hot wire.
Hot wire refers to the increase in deposition speed.
In some cases, such as sheet metal welding or backing pass, it is sometimes unnecessary to add filler wire.
Among the above three welding methods, manual argon tungsten arc welding is the most widely used, while semi-automatic argon tungsten arc welding is rarely used.
Welding Power Source
During TIG welding, due to the low current density and low thermal conductivity of argon, the arc is basically not compressed and the static characteristics of the arc are horizontal.
According to the requirements of arc static characteristics on the external characteristics of the power supply, the power supply with reduced external characteristics must be used regardless of whether AC power supply or DC power supply is used.
During TIG welding, small changes in arc length will cause large fluctuations in the welding power source.
Therefore, the ideal power source for TIG welding is a power source with vertical vertical drop external characteristics (such as magnetic amplifier-type silicon arc welding rectifier), which can eliminate current fluctuations caused by changes in arc length .
AC power supply is generally used for TIG welding of aluminum, magnesium and their alloys.
MIG welding
Definition
MIG welding (MIG welding) is an electric arc welding method that uses the melting electrode, external gas as the arc medium, and protects metal droplets, welding puddle and high temperature metal in the welding area. It's called MIG welding.
Arc welding with inert gas (Ar or He) with solid wire is called MIG welding.
Related Reading: MIG vs TIG Welding
Principle
Unlike TIG welding, MIG (MAG) welding uses a fusible welding wire as an electrode and uses the burning arc between the continuously fed welding wire and the workpiece to be welded as a heat source to melt the welding wire and the base metal.
During the welding process, argon shielding gas is continuously transmitted to the welding area through the welding gun nozzle, so that the arc, molten pool and nearby base metal are free from the harmful effects of the surrounding air.
The continuous fusion of the welding wire will be transferred to the welding pool in the form of droplets, and the weld metal will be formed after melting and condensation with the molten base metal.
Feature
1. Just like TIG welding, it can weld almost all metals, especially suitable for welding aluminum and aluminum alloys, copper and copper alloys, stainless steel and other materials.
In the welding process, there is almost no oxidation burning loss, only a small amount of evaporation loss, and the metallurgical process is relatively simple.
2. High labor productivity.
3. MIG welding can be DC reverse connection. Welding aluminum, magnesium and other metals has a good cathodic atomization effect, which can effectively remove the oxide film and improve the welding quality of the joint.
4. Tungsten electrode is not used and the cost is lower than TIG welding; It is possible to replace TIG welding.
5. When MIG welding aluminum and aluminum alloy, underjet droplet transfer can be used to improve the quality of welded joints.
6. Because argon is an inert gas and does not react with any substances, it is sensitive to oil stains and rust on the surface of the welding wire and base metal, and is easy to generate air holes.
Before welding, the welding wire and workpiece must be thoroughly cleaned.
laser welding
Definition
Laser welding is a welding method that uses a focused laser beam as energy to bombard the heat generated by welding.
Due to the optical properties of the laser, such as refraction and focusing, laser welding is very suitable for welding micro parts and parts with poor accessibility.
Laser welding also has the characteristics of low heat input, small welding deformation and immunity to electromagnetic field.
At present, laser welding has not been widely used due to the high price of laser and low electro-optical conversion efficiency.
Related reading: Laser welding: the basic guide
Classification
1. Laser welding can be divided into manual laser welding machine, automatic laser welding machine and galvanometer laser welding machine according to the control mode
2. According to the laser source, it can be divided into: YAG laser welding machine, semiconductor laser welding machine and fiber laser welding.
There are two basic modes of laser welding: laser thermal conduction welding and laser deep penetration welding.
The first uses a low laser power density (105 ~ 106 W/cm 2 ).
After the workpiece absorbs the laser, it only reaches the melting surface, and then relies on heat transfer to guide the internal heat transfer of the workpiece to form a molten pool.
This welding mode has shallow penetration and small depth-to-width ratio.
The latter has a high laser power density (106 ~ 107 W/cm 2 ).
After absorbing the laser, the part quickly melts and even vaporizes.
The molten metal forms a small laser beam under the action of vapor pressure, which can shine directly into the bottom of the hole, causing the hole to extend continuously until the vapor pressure in the hole is balanced with the surface tension and the gravity of the liquid metal.
When the keyhole moves along the welding direction with the laser beam, the molten metal in front of the keyhole flows around the keyhole backwards, and the weld is formed after solidification.
This welding mode has great penetration and a large depth/width ratio.
In the field of mechanical manufacturing, except for thin parts, deep penetration welding must generally be used.
The metal vapor and shielding gas generated during deep penetration welding are ionized under the action of the laser, thus forming plasma inside and above the keyhole.
Plasma can absorb, refract and scatter laser, so generally, plasma above the molten pool will weaken the laser energy reaching the workpiece.
It also affects the beam focusing effect and is unfavorable for welding.
It is usually possible to expel or weaken the plasma by blowing from the side.
The formation of the keyhole and the plasma effect mean that the welding process is accompanied by characteristic sound, light and electrical charge.
It is of great theoretical significance and practical value to study the relationship between them and welding specifications and weld quality, and to monitor the process and quality of laser welding using these characteristic signals.
Laser welding one advantage is
1. Heat input can be reduced to the minimum required amount, the metallographic change range of the heat-affected zone is small, and the deformation caused by heat conduction is also minimal.
The process parameters of single-pass welding of 2.32mm thick plates are qualified after verification, which can reduce the time required for welding thick plates and even save the use of filler metal.
3. There is no need to use electrodes, and there is no concern about pollution or damage to the electrodes.
And because it is not a contact welding process, wear and deformation of the machine can be minimized.
4. The laser beam is easy to focus, align and be guided by optical instruments, can be placed at a suitable distance from the workpiece, and can be guided again between the machines and tools or obstacles around the workpiece.
Other welding rules cannot be used due to the above space restrictions.
5. The workpiece can be placed in a closed space (under the control of vacuum pumping or internal gas environment).
6. The laser beam can be focused on a very small area and can be used to weld small parts with similar spacing.
7. The range of weldable materials is wide, and various heterogeneous materials can also be joined.
8. It is easy to carry out high-speed welding automatically and can also be controlled by digital or computer.
9. When welding thin materials or thin diameter wires, there will be no reflow problem like arc welding.
10. It is not affected by magnetic field (arc welding and electron beam welding are easy) and can accurately align the welding.
11. Can weld two metals with different physical properties (such as different strengths).
12. No vacuum or x-ray protection required.
13. If piercing welding is adopted, the depth-to-width ratio of the weld bead can reach 10:1.
14. The device can be switched to transmit the laser beam to multiple workstations.
Electron beam welding
Principle
Electrons are one of the basic particles of matter, which generally revolve around the nucleus at high speed.
When electrons receive a certain amount of energy, they can jump out of their orbit.
Heat a cathode to release and form a free electron cloud.
When the voltage is increased to 30 to 200 kv, the electrons will be accelerated and move towards the anode.
The basic principle of electron beam welding is that the cathode of the electron gun emits electrons due to direct or indirect heating.
With the acceleration of the high-voltage electrostatic field, electrons can form an electron beam with high energy density through focusing the electromagnetic field.
With this electron beam to bombard the workpiece, the enormous kinetic energy is converted into thermal energy, so that the workpiece at the welding point is melted, forming a weld pool, thus realizing the welding of the workpiece.
Application
Electron beam welding is widely used in aerospace, atomic energy, national and military defense, automobile and electrical instrument industries due to its advantages of no welding rod, no oxidation, good process repeatability and small thermal deformation.
In heavy industry, the power of electron beam welding machine has reached 100 kilowatts and can weld stainless steel plates with a thickness of 200 mm.
When welding large parts, a large-volume vacuum chamber must be used or a moving local vacuum must be formed at the welding position.
In automobile production, electron beam welding is mainly used to process parts of engines, transmissions, etc.
These parts are relatively less machined, which meets the economic requirements of electron beam welding.
As a modern advanced welding technology, electron beam welding also plays an important role in the aerospace field.
The uniqueness of materials and welding requirements for aerospace components, ranging from micro pressure sensors to spacecraft hulls, means that electron beam welding is quickly becoming a necessary process for processing these important components, which is Widely used in welding important parts of aircraft bearings and engine rotors. components.
Technical requirement
High voltage power supply for electron beam welding machine has different technical characteristics compared with other types of high voltage power supply.
According to the factory standards of foreign electron beam welding machine manufacturers, German DIN standards and the technical requirements of China electron beam welding machines, the high voltage power supply requirements for electron beam welding machines electron beam welding are as follows:
As there is no uniform standard at home and abroad for the technical requirements of high-voltage power supply for electron beam welding machines, the technical requirements proposed by some manufacturers are mainly ripple coefficient and stability.
The ripple coefficient should be less than 1% and the stability is ±1%.
Almost all manufacturers of electron beam welding machines have put forward such requirements.
Germany's PTR also put forward the technical requirements for the medium voltage type, which requires the relative ripple coefficient to be less than 0.5%, the stability to be ±0.5%, and the repeatability to be less than 0.5 %.
The above requirements are determined according to the electron beam spot and the welding process.
Furthermore, the German Pro-beam Group proposed that the carbon content of steel produced by electron beam hardening should be greater than 0.18%.
The advantage of vacuum is that there is no color change and hydrogen embrittlement after annealing, the depth is between 0.1-1.7mm, and there is no surface dissolution.
Plasma arc welding
Brief introduction
Plasma arc welding is a fusion welding method that uses a high-energy density plasma arc beam as a welding heat source.
Plasma arc welding is characterized by energy concentration, high productivity, fast welding speed, small stress deformation, stable arc and suitable for welding thin plates and boxes.
It is especially suitable for welding various refractory, easily oxidized and heat-sensitive metal materials (such as tungsten, molybdenum, copper, nickel, titanium, etc.).
The gas dissociates when heated by the arc and is compressed as it passes through the water-cooled nozzle at high speed, increasing the energy density and degree of dissociation, forming a plasma arc.
Its stability, calorific value and temperature are higher than those of the general arc, which is why it has greater penetration force and welding speed.
The gas that forms the plasma arc and the shielding gas around it generally uses pure argon.
According to the material properties of various workpieces, helium, nitrogen, argon or a mixture of both are also used.
Principle
Plasma arc cutting is a common cutting process for metallic and non-metallic materials.
It uses high-speed, high-temperature and high-energy plasma gas flow to heat and melt the material to be cut, and uses internal or external high-speed gas flow or water flow to discharge the molten material until the beam Plasma gas flow penetrates the back to form a cut.
Feature
1. Micro plasma arc welding can weld thin sheets and plates.
2. It has the effect of small hole and can better realize the free forming of single-side and double-side welding.
3. The plasma arc has high energy density, high arc column temperature and strong penetration ability.
Steel with a thickness of 10 ~ 12 mm can be welded without groove.
It can be welded once and molded on both sides.
The welding speed is fast, the productivity is high, and the tension deformation is small.
4. The equipment is complex, the gas consumption is large, the assembly clearance and part cleaning are strict, and it is only suitable for internal welding.
Power supply
When plasma arc welding is used, DC current and sag characteristic power supply are generally used.
Due to the unique operating characteristics obtained from the special torch arrangement and the separate flow of plasma and shielding gas, a common TIG power supply can be added to the plasma console, and a specially constructed plasma system can also be used.
It is not easy to stabilize the plasma arc when using sine wave alternating current.
When the distance between the electrode and the workpiece is long and the plasma is compressed, the plasma arc becomes difficult to perform its role.
Furthermore, in the positive half cycle, the superheated electrode will make the nozzle conductive spherical, thus interfering with the stability of the arc.
Special DC switching power supply can be used.
The duration of the positive electrode can be reduced by adjusting the waveform balance, so that the electrode can be fully cooled to maintain the tip nozzle shape and form a stable arc.
Friction welding
Principle
Friction welding is a welding method that uses the heat generated by the friction of the contact surface of the part as a heat source to cause plastic deformation of the part under pressure.
Under the action of pressure, it is under the action of constant or increasing pressure and torque that the relative movement between the welding contact end faces generates friction heat and plastic deformation heat on the friction surface and its surrounding areas, so that the temperature in and around the friction surface rises to a temperature range that is generally below the melting point.
The deformation resistance of the material decreases, plasticity increases, and the oxide film at the interface breaks.
Under the action of disturbed forging pressure, with the plastic deformation and flow of materials, solid state welding is carried out through molecular diffusion and interface recrystallization.
Feature
1. The welding quality of joints is good and stable.
The scrap rate of aluminum and copper transition joints produced by low-temperature friction welding in China is less than 0.01%;
The boiler factory adopts friction stir welding instead of flash welding to produce energy-saving coil, and the welding scrap rate is reduced from 10% to 0.001%.
In West Germany, friction welding was used instead of flash welding to produce automobile exhaust valves, and the welding waste rate decreased from 1.4% to 0.04~0.01%.
As can be seen from the examples above, the scrap rate of friction welding is very low, about 1% of that of general welding methods.
2. Suitable for welding different steels and metals.
Friction welding can not only weld common different steels, but also weld different steels and metals with very different mechanical and physical properties at room temperature and high temperature, such as structural carbon steel, high-speed tool steel, copper – stainless steel, etc.
In addition, it can also weld different metals that produce brittle alloys, such as aluminum, copper, aluminum steel, etc.
3. High dimensional accuracy of welding.
The maximum error of the entire length of the diesel engine pre-combustion chamber produced by friction welding is ±0.1mm.
Some special friction welding machines can ensure that the welding length tolerance is ±0.2mm and the eccentricity is less than 0.2mm.
Therefore, friction welding is not only used to weld raw parts, but also to weld assembled finished products.
4. The welding machine is low power consumption and energy saving.
Compared with flash welding, friction welding saves about 80~90% of electrical energy.
5. Friction welding workplace sanitation
There is no spark, arc light and harmful gases, which is conducive to environmental protection.
It is suitable for automatic production lines along with other advanced metal processing methods.
Classification
After years of development, friction stir welding technology has developed many classifications of friction welding: pin friction welding, surface friction welding, third-body friction stir welding, embedded friction welding, inertial friction welding, friction stir welding, radial friction welding, linear friction welding and friction overlap welding.
Spot welding
Brief introduction
Spot welding refers to the welding method in which a welding spot is formed between the contact surfaces of two overlapping parts using a cylindrical electrode during welding.
During spot welding, pressurize the workpiece so that it comes into close contact, then turn on the current, melt the workpiece contact under the effect of resistance heat, and form a welding spot after cooling.
Spot welding is mainly used for welding stamped parts of sheet metal components with a thickness of less than 4 mm, especially for welding automobile bodies, carriages and aircraft fuselage.
However, containers with sealing requirements cannot be welded.
Spot welding is a type of resistance welding, mainly used for welding thin plate structures and reinforcements.
Feature
During spot welding, the weldment forms a lap joint and is pressed between the two electrodes.
Its main characteristics are the following:
1. During spot welding, the heating time of the connection area is very short and the welding speed is fast.
2. Spot welding only consumes electrical energy and does not require filler materials, flux, gas, etc.
3. The quality of spot welding is mainly guaranteed by the spot welding machine.
Simple operation, high mechanization and automation and high productivity.
4. Low work intensity and good working conditions.
5. Because welding is turned on in a short time, requiring high current and pressure, the process program control is more complex, the welding machine has large capacitance, and the price of the equipment is higher.
6. It is difficult to perform non-destructive testing on welding points.
Operation process
Before welding, the surface of the part must be cleaned.
The common cleaning method is pickling, that is, pickling in sulfuric acid with a heating concentration of 10% and then cleaning in hot water.
The specific welding process is as follows:
1. Place the workpiece joint between the upper and lower electrodes of the spot welder and clamp it;
2. Energize to heat the contact surface of two workpieces, locally melt and form nuggets;
3. Maintain pressure after power off, so that the nugget can be cooled and solidified under the pressure to form solder joints;
4. Remove pressure and remove workpiece.
