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The heat generated during spot welding of lithium battery spot welding machine is determined by the following formula

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The heat generated during spot welding of lithium battery spot welding machine is determined by the following formula

Release time:2018-11-29 Author: Click:

The heat generated in spot welding of lithium battery assembly equipment lithium battery spot welding machine is determined by the following formula: Q=IIRt(J)-(1):Q-generated heat (J), I-welding current (A), R-electrode resistance (Ohm), T-welding time (s)。 Resistance R and the factors affecting R include resistance Rw of workpiece itself, contact resistance between two workpieces。 Resistance Rc, contact resistance between electrode and workpiece Rew。 That is R=2Rw+Rc+2Rew-(2) When workpiece and electrode are fixed, the resistance of workpiece depends on its resistivity。 Therefore, resistivity is an important performance of the welded material。 Metals with high resistivity have poor electrical conductivity (e。g。 stainless steel) and metals with low electrical resistivity have good electrical conductivity (e。g。 aluminium alloy)。 Therefore, spot welding of stainless steel is easy to produce heat and difficult to dissipate heat, while spot welding of aluminum alloy is difficult to produce heat and easy to dissipate heat。 In spot welding, the former may use a small current (thousands of amperes), while the latter must use a large current (tens of thousands amperes)。 Resistivity depends not only on the type of metal, but also on the state of heat treatment, processing mode and temperature of metal。 Contact resistance exists for a short time, generally in the initial stage of welding。 It is formed by two reasons: 1) the oxide or dirty material layer with high resistance coefficient on the surface of workpiece and electrode will greatly hinder the current。 Too thick oxide and dirty matter layers can even prevent current from conducting。 2) Under the condition that the surface is very clean, because of the micro-roughness of the surface, the workpiece can only form contact points on the part of rough surface。 A current line is formed at the contact point。 The resistance at the contact is increased due to the reduction of the current path。 Compared with Rc and Rw, the resistance Rew between electrodes and workpieces is smaller and has less effect on nugget formation, because the resistivity and hardness of copper alloys are generally lower than that of workpieces。

Effect of Welding Current


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It can be seen from formula (1) that the effect of current on heat production is greater than that of resistance and time. Therefore, in the welding process, it is a parameter that must be strictly controlled. The main cause of current variation is voltage fluctuation of power grid and impedance change of secondary circuit of AC welding machine. The impedance change is due to the change of the geometry of the circuit or the introduction of different quantities of magnetic metals into the secondary circuit. For DC welding machine, the change of secondary circuit impedance has no obvious effect on current.

Effect of Welding Time

In order to ensure nugget size and weld strength, welding time and welding current can complement each other in a certain range. In order to obtain a certain strength of solder joints, high current and short time (strong condition, also known as hard specification) can be used, but also small current and long time (weak condition, also known as soft specification). The choice of hard or soft specifications depends on the performance, thickness of the metal and the power of the welding machine used. There is a upper and lower limit for the current and time required for metals with different properties and thickness, which shall prevail when used.

Effect of Electrode Pressure

The total resistance R between the two electrodes is obviously affected by the electrode pressure。 With the increase of the electrode pressure, R decreases significantly, but the increase of welding current is not significant, which can not affect the heat production reduction caused by the decrease of R。 Therefore, the strength of solder joint always decreases with the increase of welding pressure。 The solution is to increase the welding current while increasing the welding pressure。

Effect of Electrode Shape and Material Properties

Because the contact area of the electrode determines the current density, the resistivity and thermal conductivity of the electrode material are related to the generation and loss of heat, therefore, the shape and material of the electrode have a significant impact on the formation of nuggets。 With the deformation and wear of the electrode end, the contact area increases and the strength of the solder joint decreases。

The influence of workpiece surface condition

Oxides, dirt, oil and other impurities on the surface of the workpiece increase the contact resistance. Excessive thickness of oxide layer may even prevent current from passing through. Local conduction, due to the current density is too high, will produce splash and surface burnout. The existence of oxide layer will also affect the inhomogeneity of solder joints heating, resulting in the fluctuation of welding quality. Therefore, thorough cleaning of the workpiece surface is a necessary condition to ensure the quality of joints.

Heat Balance and Heat Dissipation

During spot welding, the heat generated by spot welding machine is determined by the following formula: Q=IIRt(J)-(1):Q-generated heat (J), I-welding current (A), R-electrode resistance (Ohm), T-welding time (s)。 Resistance R and the factors affecting R include resistance Rw of workpiece itself, contact resistance Rc between two workpieces。 The contact resistance between the electrode and the workpiece is Rew。 That is R=2Rw+Rc+2Rew-(2) When the workpiece and the electrode are fixed, the resistance of the workpiece depends on its resistivity。 Therefore, resistivity is an important performance of the welded material。 Metals with high resistivity have poor electrical conductivity (e。g。 stainless steel) and metals with low electrical resistivity have good electrical conductivity (e。g。 aluminium alloy)。 Therefore, spot welding of stainless steel is easy to produce heat and difficult to dissipate heat, while spot welding of aluminum alloy is difficult to produce heat and easy to dissipate heat。 In spot welding, the former may use a small current (thousands of amperes), while the latter must use a large current (tens of thousands amperes)。 Resistivity depends not only on the type of metal, but also on the state of heat treatment, processing mode and temperature of metal。 Contact resistance exists for a short time, generally in the initial stage of welding。 It is formed by two reasons: 1) the oxide or dirty material layer with high resistance coefficient on the surface of workpiece and electrode will greatly hinder the current。 Too thick oxide and dirty matter layers can even prevent current from conducting。 2) Under the condition that the surface is very clean, because of the micro-roughness of the surface, the workpiece can only form contact points on the part of rough surface。 A current line is formed at the contact point。 The resistance at the contact is increased due to the reduction of the current path。 Compared with Rc and Rw, the resistance Rew between electrodes and workpieces is smaller and has less effect on nugget formation, because the resistivity and hardness of copper alloys are generally lower than that of workpieces。

Effect of Welding Current

It can be seen from formula (1) that the effect of current on heat production is greater than that of resistance and time。 Therefore, in the welding process, it is a parameter that must be strictly controlled。 The main cause of current variation is voltage fluctuation of power grid and impedance change of secondary circuit of AC welding machine。 The impedance change is due to the change of the geometry of the circuit or the introduction of different quantities of magnetic metals into the secondary circuit。 For DC welding machine, the change of secondary circuit impedance has no obvious effect on current。

Effect of Welding Time

In order to ensure nugget size and weld strength, welding time and welding current can complement each other in a certain range. In order to obtain a certain strength of solder joints, high current and short time (strong condition, also known as hard specification) can be used, but also small current and long time (weak condition, also known as soft specification). The choice of hard or soft specifications depends on the performance, thickness of the metal and the power of the welding machine used. There is a upper and lower limit for the current and time required for metals with different properties and thickness, which shall prevail when used.

Effect of Electrode Pressure

The total resistance R between the two electrodes is obviously affected by the electrode pressure。 With the increase of the electrode pressure, R decreases significantly, but the increase of welding current is not significant, which can not affect the heat production reduction caused by the decrease of R。 Therefore, the strength of solder joint always decreases with the increase of welding pressure。 The solution is to increase the welding current while increasing the welding pressure。

Effect of Electrode Shape and Material Properties

Because the contact area of the electrode determines the current density, the resistivity and thermal conductivity of the electrode material are related to the generation and loss of heat, therefore, the shape and material of the electrode have a significant impact on the formation of nuggets. With the deformation and wear of the electrode end, the contact area increases and the strength of the solder joint decreases.

The influence of workpiece surface condition

Oxides, dirt, oil and other impurities on the surface of the workpiece increase the contact resistance. Excessive thickness of oxide layer may even prevent current from passing through. Local conduction, due to the current density is too high, will produce splash and surface burnout. The existence of oxide layer will also affect the inhomogeneity of solder joints heating, resulting in the fluctuation of welding quality. Therefore, thorough cleaning of the workpiece surface is a necessary condition to ensure the quality of joints.

Heat Balance and Heat Dissipation

During spot welding, only a small part of the heat generated is used to form solder joints, and most of it is lost due to conduction or radiation to the adjacent materials. The heat balance equation is Q=Q1+Q2-(3). Among them, Q1-the heat to form nuggets and Q2-the loss of heat effective heat Q1 depends on the thermal physical properties of metals and the amount of melted metals, but not on the welding conditions used. Guan. Q1 = 10% - 30% Q, the lower limit of metal with good thermal conductivity (aluminium, copper alloy, etc.) and the upper limit of metal with high resistivity and poor thermal conductivity (stainless steel, superalloy, etc.). The loss of heat Q2 mainly includes the heat conduction through the electrode (30% - 50% Q) and the heat conduction through the workpiece (about 20% Q). About 5% of the heat radiated into the atmosphere.

 

The lead wire of welding machine should not be too thin or too long. The voltage drop during welding should not be greater than 5% of the initial voltage, and the initial voltage should not deviate from the power supply voltage (+10%). Gloves, aprons and protective glasses should be worn when the welding machine is operated to avoid burns caused by Mars flying out. The sliding part should be well lubricated and the metal spatter should be removed after use. The screw of each part should be tightened once 24 hours after the new welding machine starts to use, especially the connection screw between copper flexible connection and electrode must be tightened well, and the oxide between electrode rod and electrode arm should be removed regularly after use to ensure good contact.

If the AC contactor is not sucked properly when welding machine is in use, it indicates that the voltage of power grid is too low. Users should first solve the problem of power supply, and the power supply can be used only after it is normal. It should be pointed out that the newly purchased welder can replace the new welder or the main parts if the quality problems of the main parts occur within half a month. Welding machine mainframe part guaranteed for one year, long-term maintenance services. Usually, after the user notifies the factory, the service is in place within three to seven days according to the distance. Damage to welder due to user's reasons is not covered by warranty. Fragile parts and consumables are not covered by warranty.

Because the contact area of the electrode determines the current density, the resistivity and thermal conductivity of the electrode material are related to the generation and loss of heat, therefore, the shape and material of the electrode have a significant impact on the formation of nuggets。 With the deformation and wear of the electrode end, the contact area increases and the strength of the solder joint decreases。 Oxides, dirt, oil and other impurities on the surface of the workpiece increase the contact resistance。 Only a small part of the heat is used to form solder joints, and most of it is lost due to conduction or radiation to the adjacent material。 The heat balance equation is Q=Q1+Q2-(3)。 Among them, Q1-the heat to form nuggets and Q2-the loss of heat effective heat Q1 depends on the thermal physical properties of metals and the amount of melted metals, but has nothing to do with the welding conditions used。 Q1 = 10% - 30% Q, the lower limit of metal with good thermal conductivity (aluminium, copper alloy, etc。) and the upper limit of metal with high resistivity and poor thermal conductivity (stainless steel, superalloy, etc。)。 The loss of heat Q2 mainly includes the heat conduction through the electrode (30% - 50% Q) and the heat conduction through the workpiece (about 20% Q)。 About 5% of the heat radiated into the atmosphere。

The lead wire of welding machine should not be too thin or too long. The voltage drop during welding should not be greater than 5% of the initial voltage, and the initial voltage should not deviate from the power supply voltage (+10%). Gloves, aprons and protective glasses should be worn when the welding machine is operated to avoid burns caused by Mars flying out. The sliding part should be well lubricated and the metal spatter should be removed after use. The screw of each part should be tightened once 24 hours after the new welding machine starts to use, especially the connection screw between copper flexible connection and electrode must be tightened well, and the oxide between electrode rod and electrode arm should be removed regularly after use to ensure good contact.

If the AC contactor is not sucked properly when welding machine is in use, it indicates that the voltage of power grid is too low。 Users should first solve the problem of power supply, and the power supply can be used only after it is normal。 It should be pointed out that the newly purchased welder can replace the new welder or the main parts if the quality problems of the main parts occur within half a month。 Welding machine mainframe part guaranteed for one year, long-term maintenance services。 Usually, after the user notifies the factory, the service is in place within three to seven days according to the distance。 Damage to welder due to user's reasons is not covered by warranty。 Fragile parts and consumables are not covered by warranty。

Because the contact area of the electrode determines the current density, the resistivity and thermal conductivity of the electrode material are related to the generation and loss of heat, therefore, the shape and material of the electrode have a significant impact on the formation of nuggets. With the deformation and wear of the electrode end, the contact area increases and the strength of the solder joint decreases. Oxides, dirt, oil and other impurities on the surface of the workpiece increase the contact resistance.


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