I. Electrode arc welding (I) Welding arc is a permanent and intense gas discharge phenomenon between two charged conductors.
1. Formation of an arc (1) Short-circuiting of the welding rod to the workpiece When the short-circuit is short-circuited, the current-condensed individual contact points are heated by the resistance heat Q=I2Rt, and the electric field strength of the extremely small air gap is high.
Result: 1 A small amount of electrons escaped. 2 Individual contact points are heated, melted, and even vaporized and vaporized. 3 Many metal vapors with low ionization potential appear.
(2) Lifting the electrode to maintain the proper distance Under the action of thermal excitation and strong electric field, the negative electrode emits electrons and performs high-speed directional motion, which strikes neutral molecules and atoms to excite or ionize them.
Result: The gas between the air gaps rapidly ionizes, and in the impact, excitation, and positive and negative charged particle recombination, its energy is converted and light and heat are emitted.
2. Arc structure and temperature distribution The arc consists of three parts, namely the cathode area (usually the white spot on the electrode face), the anode area (the thin bright area in the bath corresponding to the end of the electrode), and the arc column area (two Air gap between electrodes).
3, the conditions of the stable arc burning (1) should meet the welding arc electrical characteristics of the power requirements a) when the current is too small, the air gap between the ionization is not sufficient, the arc resistance is large, requires a high arc voltage, can only be maintained The degree of ionization.
b) As the current increases, the degree of gas ionization increases, the conductivity increases, the arc resistance decreases, and the arc voltage decreases. However, when it is reduced to a certain degree, in order to maintain the necessary electric field strength and ensure the emission of electrons and the kinetic energy of charged particles, the voltage must not change with increasing current.
(2) Do a clean-up work and use a suitable electrode for welding.
(3) Prevent partial blows.
(4) Polarity of electrode In welding, when using a DC welding machine, there are two methods: forward connection and reverse connection. However, AC arc welding equipment is widely used, and the polarity of the electrodes is frequently changed. There is no polarity problem.
1) Positive connection - the power supply is connected to the positive terminal of the weldment, and the electrode is connected to the negative terminal. General welding operations are using positive connection.
2) Reverse connection—The negative terminal of the power supply is connected to the weldment and the positive electrode is connected to the weldment. When welding thin sheets, in order to prevent burn-through, reverse welding is used for welding.
(II) Welding process of electrode arc welding
1. Welding process
2. Electrode arc welding heating characteristics (1) heating temperature is high, but also to local heating. Extremely uneven heating of the metal near the weld can cause workpiece distortion, residual stress, and non-uniform tissue transformation and performance changes.
(2) The heating speed is fast (1500 degrees per second), the temperature distribution is not uniform, and the structures and defects that may not appear in the heat treatment may occur.
(3) The heat source is moving, and the heated and cooled areas constantly change.
(III) Metallurgical characteristics of arc welding (1) The temperature in the reaction zone is high, which strongly evaporates and oxidizes the alloy elements.
(2) The metal pool is small in volume and has a short time in the liquid state, which leads to uniform chemical composition, gas and impurities are too late to float, and defects such as pores and slag inclusions are easily generated.
(d), welding rod
1. The composition of the electrode The arc welding electrode consists of a core and a sheath.
(1) The welding core 1 is used as an electrode for arc welding, and an arc is formed between the welding member and the welding member.
2 In the welding process, it is continuously melted, and it transits to a moving molten pool. Together with the molten parent metal, it forms a weld joint.
(2) The function of the coating of the electrode of the welding rod 1
a) Effective combined gas and slag protection of the bath;
b) Deoxidation and desulfurization of the molten metal in the bath and infiltration of alloy into the bath metal to improve the mechanical properties of the weld;
c) Stabilize the arc to improve the welding process.
Composition of 2 drug skins
a) Arc stabilizers: Compounds of potassium, sodium, and calcium that are easily ionized are mainly used.
b) Slagging agent: the slag formed on the surface of the molten pool is not covered by the atmosphere, and it does not allow the atmosphere to invade the molten pool.
c) Gasification agent: Decompose CO and H2 and other gases to surround the arc and the molten pool, which acts as a barrier to the atmosphere, protecting the droplets and the molten pool.
d) Deoxidizer: The main application of ferromanganese, ferrosilicon, titanium iron, aluminum iron and graphite, etc., to remove the oxygen in the molten pool.
e) Alloying agent: Ferro-manganese, ferrosilicon, ferrochromium, ferromolybdenum, vanadium iron, ferro-tungsten and other iron alloys are mainly used.
f) Binder: commonly used potassium, sodium water glass.
(3) Types of electrode coating
a) Acid electrode - The coating contains a large amount of acidic oxides, such as SiO2, TiO2, and Fe2O3.
b) Basic electrode - The coating contains a large amount of alkaline oxides, such as CaO, FeO, MnO, Na2O, MgO, etc.
2. The types of welding rods are divided into ten categories, namely structural steel electrodes, low temperature steel electrodes, molybdenum and chromium-molybdenum heat resistant steel electrodes, stainless steel electrodes, surfacing electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes. , aluminum and aluminum alloy welding rods and special purpose welding rods.
3. Selection principle of electrode (1) Select the electrode with the same or similar chemical composition as the base metal (2) Select the electrode with the same strength as the base metal (3) Select the type of the electrode coating according to the conditions of use of the structure
(E) Changes in the metal structure and properties of welded joints
1. The change of temperature on the weldment and the distribution of the weld zone metal undergoes a state where the state of steady state begins to be heated to a higher temperature, and then gradually cools to a normal temperature such a thermal cycle.
2. Changes in the microstructure and properties at the welded joints (taking low-carbon steel as an example)
3. Main defects of welded joints (1) Blowholes Air voids are voids that remain in the weld pool when the weld seam fails to escape when the weld seam solidifies.
Prevention:
a) Dry the electrode and carefully clean the welding surface and nearby area of ​​the weldment;
b) Proper operation with proper welding current.
(2) Slag inclusions are slags that remain in the weld after welding.
Precaution:
a) carefully clean the soldered surface;
b) Thorough slag removal between layers during multilayer welding;
c) Slow down the crystallization speed of the bath.
(3) welding crack
a) Hot cracking Hot cracking is the welding crack that occurs when the metal of the welded joint cools to a high temperature zone near the solid line during welding.
Precaution:
Reducing structural rigidity, preheating before welding, reducing alloying, and selecting low-hydrogen type electrodes with good crack resistance.
b) Welding cracks produced when a cold cracked joint is cooled to a lower temperature.
Precaution:
a) Use a low-hydrogen type electrode to dry and remove oil and rust on the surface of the weldment;
b) Preheating after welding and heat treatment after welding.
(4) Incomplete penetration Failure of the welded joint is not fully penetrated.
cause:
Groove angle or clearance is too small, blunt edge is too thick, groove is dirty, electrode is too thick, welding speed is too fast, welding current is too small and improper operation.
(5) Unmelted unfused is the phenomenon that the weld joint and the base metal are not completely melted.
cause:
Detrimental groove, excessive electrode diameter, improper operation, etc.
(6) Undercut The undercut is a phenomenon of grooves or depressions generated along the base material of the weld toe.
cause:
Excessive welding current, long arc, improper electrode angle, etc.
(VI) Welding deformation
1. Causes of welding stress and deformation Local heating during welding is the root cause of weld stress and deformation.
2. The basic form of welding deformation
3. Measures to prevent and reduce welding distortion (1) Anti-deformation method (2) Adding allowance method (3) Rigid clamping method (4) Selecting a reasonable welding process
4. Process Measures for Reducing Welding Stress (1) Choosing a Reasonable Welding Sequence (2) Preheating (3) Post-weld Annealing
Second, submerged arc welding arc burning in the welding layer under the welding method, known as submerged arc welding. Submerged arc welding arc welding, feeding electrode are generally completed by the automatic device, it is also known as submerged arc welding.
(I) Submerged Arc Welding Process
(B), the main features of submerged arc welding
1, high productivity
2, the welding quality is high and stable
3, saving welding materials
4, improved working conditions
5. Applicable to flat welding long straight welds and larger diameter annular welds. For short welds, zigzag welds, narrow locations, and welding of thin plates, their strengths cannot be exercised.
(III) Welding wire and flux
(4) Process characteristics of submerged arc welding
1, strict preparatory work before welding
2, welding deep penetration
3, the use of arc plate and lead plate
4, using solder pads or steel pads
5, using guide device
V. The concept of plasma arc welding and cutting (I) and plasma arc
1. The general welding arc is free arc. Only part of the gas in the arc zone is ionized and the temperature is not concentrated enough.
2. When the free arc is compressed into an arc of high energy density, and the arc column gas is sufficiently ionized to become a state containing only positive ions and negative ions, the fourth state of matter, the plasma, occurs.
Plasma arc with high temperature (15000 ~ 30000K), high energy density (480 kW/cm2) and plasma flow at high speed (maximum multiples and speed of sound)
3, the three kinds of compression effects of plasma arc welding
(1) Mechanical Compression Effect In the plasma gun, when the high-frequency oscillation ignites the arc, the arc formed by the gas ionization passes through the small nozzle tip and is mechanically compressed by the inner wall of the nozzle.
(2) Thermal compression effect Due to the cooling water in the nozzle, the temperature and the ionization degree of the gas near the inner wall of the nozzle are drastically reduced, forcing the arc current to pass through the center of the arc cylinder, so that the center current density of the arc column increases sharply. Further reduced, this is the second compression of the arc.
(3) Electromagnetic contraction effect The arc current density is greatly increased and the associated electromagnetic contraction force causes the arc to be compressed for the third time.
Due to the three compression effects, the diameter of the plasma arc is only about 3mm, and the energy density, temperature, and air velocity are greatly improved.
(B), the characteristics of plasma arc welding
1. The energy density is large, the temperature gradient is large, the heat affected zone is small, and materials with strong thermal sensitivity or bimetal can be welded.
2. It has good arc stability, high welding speed, and can be used for penetrating welding, so that the weld seam can be formed on one side of both sides with a beautiful surface and high productivity.
3, high air flow spray speed, mechanical flushing force, can be used to weld large thickness workpieces or cut large thickness of stainless steel, aluminum, copper, magnesium and other alloys.
4, arc ionization is sufficient, the current limit of less than 0.1A can still work stably, suitable for micro-plasma arc (0.2 ~ 30A) welding ultra-thin plate (0.01 ~ 2mm), such as film boxes, thermocouples and so on.
VI. Vacuum Electron Beam Welding Vacuum electron beam welding is the use of directional high-speed electron beam jets that impinge on the workpiece to convert kinetic energy into heat energy and melt the workpiece to form a weld seam.
Vacuum electron beam welding features:
1. Welding in a vacuum, the weld is clean, smooth, mirror-like, free from defects such as oxidation.
2. The electron beam energy density is as high as 108 W/cm2, which can quickly heat the weldment metal to a very high temperature, thus melting any refractory metal and alloy. With deep penetration, fast welding speed and minimal heat affected zone, the impact on the performance of the joint is small, and there is no deformation of the joint.
7. Laser welding Laser welding is a method in which a focused laser beam is used as an energy source to bombard the heat generated by the weldment.
Laser welding features:
1, laser welding energy density, the role of a short time, heat affected zone and deformation is small, can be welded in the atmosphere, without gas protection or vacuum environment.
2, the laser beam can be used to change the direction of the mirror, the electrode does not touch the weldment during the welding process, which can be welded to the general welding process is difficult to weld the site.
3, laser welding of insulating materials can be directly, welding dissimilar metal materials is relatively easy, and even can weld metal and non-metal together.
4, the power is small, welding thickness subject to certain restrictions.
VIII. Resistance welding Resistance welding is a process in which pressure is applied through the electrodes after the weldment is assembled, and current is applied through the contact surface of the joint and the resistance heat generated in the adjacent area.
There are many types of resistance welding, commonly used are spot welding, seam welding and butt welding.
(I) Spot welding Spot welding is to assemble a weld joint into a lap joint and press it between two electrodes, and the resistance welding heat is used to melt the base metal to form a solder joint resistance welding method. Spot welding is mainly used for thin plate welding.
Spot welding process:
1, pre-pressure, ensure good contact with the workpiece.
2, electricity, so that the formation of welding nugget and plastic ring.
3, breaking point forging, so that the nugget cooling and crystallization under the pressure continue to form a dense, non-shrinkage, crack solder joints.
(2) Seam Weld Seam Welding is the assembly of welded parts into lap joints or butt joints and is placed between two roller electrodes. The roller pressurizes the weldment and rotates. Continuous or intermittent power transmission forms a continuous weld seam. Resistance welding method.
Seam welding is mainly used to weld a relatively regular weld structure that requires sealing, and the plate thickness is generally less than 3mm.
(III) Butt butt welding is a resistance welding method that welds the weldment along the entire contact surface.
1. Resistance butt welding resistance Butt welding is assembling the weldment into a butt joint so that the end face is in close contact, heated to the plastic state by resistance heating, and then the power is turned off and the top forging force is rapidly applied to complete the welding.
Resistive butt welding is mainly used for weldments with simple cross-sections, diameters or side lengths of less than 20 mm and less stringent strength requirements.
2, flash butt welding flash butt welding is to weld the fittings into butt joints, turn on the power, so that the end gradually moved closer to the local contact, the use of resistive heat to heat these contact points, in the role of high current, produce flash, so that the end When the metal melts until the end reaches a predetermined temperature within a certain depth, the power is turned off and the upsetting force is rapidly applied to complete the welding.
The quality of flash-welded joints is better than that of resistance welding. The mechanical properties of welds are comparable to those of the parent metal, and there is no need to clean the pre-welding surfaces of the joints before welding. Flash butt welding is often used for the welding of important weldments. Can weld the same kind of metal, but also can weld dissimilar metal; Solderable 0.01mm wire, but also can weld 20000mm metal rod and profile.
Nine, friction welding Friction welding is the use of the heat generated by the surface of the weldment to rub the heat, so that the end surface to achieve thermoplastic state, and then quickly upset the welding of a pressure welding method.
Friction welding features:
1. Due to friction, the oxide film and impurities on the contact surface of the weldment are clear, which makes the welded joint dense and does not produce defects such as pores and inclusions.
2, can weld the same kind of metal, more suitable for dissimilar metal welding.
3, high productivity.
Ten brazing
(I) Types of brazing Brazing is classified into brazing and soldering depending on the solder melting point.
1. Braze brazing with a melting point higher than 450°C for hard solder brazing is brazing.
Hard solder has copper base, silver base, aluminum base and other alloys.
Flux commonly used Pengsha, boric acid, fluoride, chloride and so on.
Heating methods include flame heating, salt bath heating, resistance heating, high frequency induction heating, and the like.
The brazed joints have a strength of up to 490 MPa and are suitable for workpieces with high stress and high operating temperatures.
2. Solder brazing with a melting point of less than 450°C for solder brazing is soldering.
Common solder is tin-lead alloy.
Commonly used fluxes are rosin and ammonium chloride solutions.
Commonly used iron and other flame heating.
(B), the characteristics of brazing
1, the weldment heating temperature is low, the metal structure and mechanical properties change little, the weldment deformation is small, the joint is smooth, the weldment size is accurate.
2, can weld the same or dissimilar metals.
3, weldable by a plurality of welds of complex shapes of the weldment.
4, the equipment is simple.
1. Formation of an arc (1) Short-circuiting of the welding rod to the workpiece When the short-circuit is short-circuited, the current-condensed individual contact points are heated by the resistance heat Q=I2Rt, and the electric field strength of the extremely small air gap is high.
Result: 1 A small amount of electrons escaped. 2 Individual contact points are heated, melted, and even vaporized and vaporized. 3 Many metal vapors with low ionization potential appear.
(2) Lifting the electrode to maintain the proper distance Under the action of thermal excitation and strong electric field, the negative electrode emits electrons and performs high-speed directional motion, which strikes neutral molecules and atoms to excite or ionize them.
Result: The gas between the air gaps rapidly ionizes, and in the impact, excitation, and positive and negative charged particle recombination, its energy is converted and light and heat are emitted.
2. Arc structure and temperature distribution The arc consists of three parts, namely the cathode area (usually the white spot on the electrode face), the anode area (the thin bright area in the bath corresponding to the end of the electrode), and the arc column area (two Air gap between electrodes).
3, the conditions of the stable arc burning (1) should meet the welding arc electrical characteristics of the power requirements a) when the current is too small, the air gap between the ionization is not sufficient, the arc resistance is large, requires a high arc voltage, can only be maintained The degree of ionization.
b) As the current increases, the degree of gas ionization increases, the conductivity increases, the arc resistance decreases, and the arc voltage decreases. However, when it is reduced to a certain degree, in order to maintain the necessary electric field strength and ensure the emission of electrons and the kinetic energy of charged particles, the voltage must not change with increasing current.
(2) Do a clean-up work and use a suitable electrode for welding.
(3) Prevent partial blows.
(4) Polarity of electrode In welding, when using a DC welding machine, there are two methods: forward connection and reverse connection. However, AC arc welding equipment is widely used, and the polarity of the electrodes is frequently changed. There is no polarity problem.
1) Positive connection - the power supply is connected to the positive terminal of the weldment, and the electrode is connected to the negative terminal. General welding operations are using positive connection.
2) Reverse connection—The negative terminal of the power supply is connected to the weldment and the positive electrode is connected to the weldment. When welding thin sheets, in order to prevent burn-through, reverse welding is used for welding.
(II) Welding process of electrode arc welding
1. Welding process
2. Electrode arc welding heating characteristics (1) heating temperature is high, but also to local heating. Extremely uneven heating of the metal near the weld can cause workpiece distortion, residual stress, and non-uniform tissue transformation and performance changes.
(2) The heating speed is fast (1500 degrees per second), the temperature distribution is not uniform, and the structures and defects that may not appear in the heat treatment may occur.
(3) The heat source is moving, and the heated and cooled areas constantly change.
(III) Metallurgical characteristics of arc welding (1) The temperature in the reaction zone is high, which strongly evaporates and oxidizes the alloy elements.
(2) The metal pool is small in volume and has a short time in the liquid state, which leads to uniform chemical composition, gas and impurities are too late to float, and defects such as pores and slag inclusions are easily generated.
(d), welding rod
1. The composition of the electrode The arc welding electrode consists of a core and a sheath.
(1) The welding core 1 is used as an electrode for arc welding, and an arc is formed between the welding member and the welding member.
2 In the welding process, it is continuously melted, and it transits to a moving molten pool. Together with the molten parent metal, it forms a weld joint.
(2) The function of the coating of the electrode of the welding rod 1
a) Effective combined gas and slag protection of the bath;
b) Deoxidation and desulfurization of the molten metal in the bath and infiltration of alloy into the bath metal to improve the mechanical properties of the weld;
c) Stabilize the arc to improve the welding process.
Composition of 2 drug skins
a) Arc stabilizers: Compounds of potassium, sodium, and calcium that are easily ionized are mainly used.
b) Slagging agent: the slag formed on the surface of the molten pool is not covered by the atmosphere, and it does not allow the atmosphere to invade the molten pool.
c) Gasification agent: Decompose CO and H2 and other gases to surround the arc and the molten pool, which acts as a barrier to the atmosphere, protecting the droplets and the molten pool.
d) Deoxidizer: The main application of ferromanganese, ferrosilicon, titanium iron, aluminum iron and graphite, etc., to remove the oxygen in the molten pool.
e) Alloying agent: Ferro-manganese, ferrosilicon, ferrochromium, ferromolybdenum, vanadium iron, ferro-tungsten and other iron alloys are mainly used.
f) Binder: commonly used potassium, sodium water glass.
(3) Types of electrode coating
a) Acid electrode - The coating contains a large amount of acidic oxides, such as SiO2, TiO2, and Fe2O3.
b) Basic electrode - The coating contains a large amount of alkaline oxides, such as CaO, FeO, MnO, Na2O, MgO, etc.
2. The types of welding rods are divided into ten categories, namely structural steel electrodes, low temperature steel electrodes, molybdenum and chromium-molybdenum heat resistant steel electrodes, stainless steel electrodes, surfacing electrodes, cast iron electrodes, nickel and nickel alloy electrodes, copper and copper alloy electrodes. , aluminum and aluminum alloy welding rods and special purpose welding rods.
3. Selection principle of electrode (1) Select the electrode with the same or similar chemical composition as the base metal (2) Select the electrode with the same strength as the base metal (3) Select the type of the electrode coating according to the conditions of use of the structure
(E) Changes in the metal structure and properties of welded joints
1. The change of temperature on the weldment and the distribution of the weld zone metal undergoes a state where the state of steady state begins to be heated to a higher temperature, and then gradually cools to a normal temperature such a thermal cycle.
2. Changes in the microstructure and properties at the welded joints (taking low-carbon steel as an example)
3. Main defects of welded joints (1) Blowholes Air voids are voids that remain in the weld pool when the weld seam fails to escape when the weld seam solidifies.
Prevention:
a) Dry the electrode and carefully clean the welding surface and nearby area of ​​the weldment;
b) Proper operation with proper welding current.
(2) Slag inclusions are slags that remain in the weld after welding.
Precaution:
a) carefully clean the soldered surface;
b) Thorough slag removal between layers during multilayer welding;
c) Slow down the crystallization speed of the bath.
(3) welding crack
a) Hot cracking Hot cracking is the welding crack that occurs when the metal of the welded joint cools to a high temperature zone near the solid line during welding.
Precaution:
Reducing structural rigidity, preheating before welding, reducing alloying, and selecting low-hydrogen type electrodes with good crack resistance.
b) Welding cracks produced when a cold cracked joint is cooled to a lower temperature.
Precaution:
a) Use a low-hydrogen type electrode to dry and remove oil and rust on the surface of the weldment;
b) Preheating after welding and heat treatment after welding.
(4) Incomplete penetration Failure of the welded joint is not fully penetrated.
cause:
Groove angle or clearance is too small, blunt edge is too thick, groove is dirty, electrode is too thick, welding speed is too fast, welding current is too small and improper operation.
(5) Unmelted unfused is the phenomenon that the weld joint and the base metal are not completely melted.
cause:
Detrimental groove, excessive electrode diameter, improper operation, etc.
(6) Undercut The undercut is a phenomenon of grooves or depressions generated along the base material of the weld toe.
cause:
Excessive welding current, long arc, improper electrode angle, etc.
(VI) Welding deformation
1. Causes of welding stress and deformation Local heating during welding is the root cause of weld stress and deformation.
2. The basic form of welding deformation
3. Measures to prevent and reduce welding distortion (1) Anti-deformation method (2) Adding allowance method (3) Rigid clamping method (4) Selecting a reasonable welding process
4. Process Measures for Reducing Welding Stress (1) Choosing a Reasonable Welding Sequence (2) Preheating (3) Post-weld Annealing
Second, submerged arc welding arc burning in the welding layer under the welding method, known as submerged arc welding. Submerged arc welding arc welding, feeding electrode are generally completed by the automatic device, it is also known as submerged arc welding.
(I) Submerged Arc Welding Process
(B), the main features of submerged arc welding
1, high productivity
2, the welding quality is high and stable
3, saving welding materials
4, improved working conditions
5. Applicable to flat welding long straight welds and larger diameter annular welds. For short welds, zigzag welds, narrow locations, and welding of thin plates, their strengths cannot be exercised.
(III) Welding wire and flux
(4) Process characteristics of submerged arc welding
1, strict preparatory work before welding
2, welding deep penetration
3, the use of arc plate and lead plate
4, using solder pads or steel pads
5, using guide device
V. The concept of plasma arc welding and cutting (I) and plasma arc
1. The general welding arc is free arc. Only part of the gas in the arc zone is ionized and the temperature is not concentrated enough.
2. When the free arc is compressed into an arc of high energy density, and the arc column gas is sufficiently ionized to become a state containing only positive ions and negative ions, the fourth state of matter, the plasma, occurs.
Plasma arc with high temperature (15000 ~ 30000K), high energy density (480 kW/cm2) and plasma flow at high speed (maximum multiples and speed of sound)
3, the three kinds of compression effects of plasma arc welding
(1) Mechanical Compression Effect In the plasma gun, when the high-frequency oscillation ignites the arc, the arc formed by the gas ionization passes through the small nozzle tip and is mechanically compressed by the inner wall of the nozzle.
(2) Thermal compression effect Due to the cooling water in the nozzle, the temperature and the ionization degree of the gas near the inner wall of the nozzle are drastically reduced, forcing the arc current to pass through the center of the arc cylinder, so that the center current density of the arc column increases sharply. Further reduced, this is the second compression of the arc.
(3) Electromagnetic contraction effect The arc current density is greatly increased and the associated electromagnetic contraction force causes the arc to be compressed for the third time.
Due to the three compression effects, the diameter of the plasma arc is only about 3mm, and the energy density, temperature, and air velocity are greatly improved.
(B), the characteristics of plasma arc welding
1. The energy density is large, the temperature gradient is large, the heat affected zone is small, and materials with strong thermal sensitivity or bimetal can be welded.
2. It has good arc stability, high welding speed, and can be used for penetrating welding, so that the weld seam can be formed on one side of both sides with a beautiful surface and high productivity.
3, high air flow spray speed, mechanical flushing force, can be used to weld large thickness workpieces or cut large thickness of stainless steel, aluminum, copper, magnesium and other alloys.
4, arc ionization is sufficient, the current limit of less than 0.1A can still work stably, suitable for micro-plasma arc (0.2 ~ 30A) welding ultra-thin plate (0.01 ~ 2mm), such as film boxes, thermocouples and so on.
VI. Vacuum Electron Beam Welding Vacuum electron beam welding is the use of directional high-speed electron beam jets that impinge on the workpiece to convert kinetic energy into heat energy and melt the workpiece to form a weld seam.
Vacuum electron beam welding features:
1. Welding in a vacuum, the weld is clean, smooth, mirror-like, free from defects such as oxidation.
2. The electron beam energy density is as high as 108 W/cm2, which can quickly heat the weldment metal to a very high temperature, thus melting any refractory metal and alloy. With deep penetration, fast welding speed and minimal heat affected zone, the impact on the performance of the joint is small, and there is no deformation of the joint.
7. Laser welding Laser welding is a method in which a focused laser beam is used as an energy source to bombard the heat generated by the weldment.
Laser welding features:
1, laser welding energy density, the role of a short time, heat affected zone and deformation is small, can be welded in the atmosphere, without gas protection or vacuum environment.
2, the laser beam can be used to change the direction of the mirror, the electrode does not touch the weldment during the welding process, which can be welded to the general welding process is difficult to weld the site.
3, laser welding of insulating materials can be directly, welding dissimilar metal materials is relatively easy, and even can weld metal and non-metal together.
4, the power is small, welding thickness subject to certain restrictions.
VIII. Resistance welding Resistance welding is a process in which pressure is applied through the electrodes after the weldment is assembled, and current is applied through the contact surface of the joint and the resistance heat generated in the adjacent area.
There are many types of resistance welding, commonly used are spot welding, seam welding and butt welding.
(I) Spot welding Spot welding is to assemble a weld joint into a lap joint and press it between two electrodes, and the resistance welding heat is used to melt the base metal to form a solder joint resistance welding method. Spot welding is mainly used for thin plate welding.
Spot welding process:
1, pre-pressure, ensure good contact with the workpiece.
2, electricity, so that the formation of welding nugget and plastic ring.
3, breaking point forging, so that the nugget cooling and crystallization under the pressure continue to form a dense, non-shrinkage, crack solder joints.
(2) Seam Weld Seam Welding is the assembly of welded parts into lap joints or butt joints and is placed between two roller electrodes. The roller pressurizes the weldment and rotates. Continuous or intermittent power transmission forms a continuous weld seam. Resistance welding method.
Seam welding is mainly used to weld a relatively regular weld structure that requires sealing, and the plate thickness is generally less than 3mm.
(III) Butt butt welding is a resistance welding method that welds the weldment along the entire contact surface.
1. Resistance butt welding resistance Butt welding is assembling the weldment into a butt joint so that the end face is in close contact, heated to the plastic state by resistance heating, and then the power is turned off and the top forging force is rapidly applied to complete the welding.
Resistive butt welding is mainly used for weldments with simple cross-sections, diameters or side lengths of less than 20 mm and less stringent strength requirements.
2, flash butt welding flash butt welding is to weld the fittings into butt joints, turn on the power, so that the end gradually moved closer to the local contact, the use of resistive heat to heat these contact points, in the role of high current, produce flash, so that the end When the metal melts until the end reaches a predetermined temperature within a certain depth, the power is turned off and the upsetting force is rapidly applied to complete the welding.
The quality of flash-welded joints is better than that of resistance welding. The mechanical properties of welds are comparable to those of the parent metal, and there is no need to clean the pre-welding surfaces of the joints before welding. Flash butt welding is often used for the welding of important weldments. Can weld the same kind of metal, but also can weld dissimilar metal; Solderable 0.01mm wire, but also can weld 20000mm metal rod and profile.
Nine, friction welding Friction welding is the use of the heat generated by the surface of the weldment to rub the heat, so that the end surface to achieve thermoplastic state, and then quickly upset the welding of a pressure welding method.
Friction welding features:
1. Due to friction, the oxide film and impurities on the contact surface of the weldment are clear, which makes the welded joint dense and does not produce defects such as pores and inclusions.
2, can weld the same kind of metal, more suitable for dissimilar metal welding.
3, high productivity.
Ten brazing
(I) Types of brazing Brazing is classified into brazing and soldering depending on the solder melting point.
1. Braze brazing with a melting point higher than 450°C for hard solder brazing is brazing.
Hard solder has copper base, silver base, aluminum base and other alloys.
Flux commonly used Pengsha, boric acid, fluoride, chloride and so on.
Heating methods include flame heating, salt bath heating, resistance heating, high frequency induction heating, and the like.
The brazed joints have a strength of up to 490 MPa and are suitable for workpieces with high stress and high operating temperatures.
2. Solder brazing with a melting point of less than 450°C for solder brazing is soldering.
Common solder is tin-lead alloy.
Commonly used fluxes are rosin and ammonium chloride solutions.
Commonly used iron and other flame heating.
(B), the characteristics of brazing
1, the weldment heating temperature is low, the metal structure and mechanical properties change little, the weldment deformation is small, the joint is smooth, the weldment size is accurate.
2, can weld the same or dissimilar metals.
3, weldable by a plurality of welds of complex shapes of the weldment.
4, the equipment is simple.
Cylindrical Lens,Cylindrical Lens,Optical Glass Cylindrical Lens,Pcx Cylindrical Lens
China Star Optics Technology Co.,Ltd. , https://www.opticsrealpoo.com