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Does The Resistance Of Spot Welder Depend On The Type Of Metal?
Jan 16, 2019

The resistance of spot welder 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. 8594 2. The influence of welding current on spot welding machine can be seen from formula (1) that the influence 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. 3. The influence 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. Spot welding machine has a upper and lower limit for the current and time required for metals with different properties and thickness, which is used as the criterion. 4. The effect of electrode pressure on total resistance R of spot welding machine is obvious. With the increase of electrode pressure, R decreases significantly, but the increase of welding current is not large, so it can not affect the decrease of heat production 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. 5. Effect of Electrode Shape and Material Properties

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