Resistance Welding Machine Contact Resistance Exists For A Short Time
Resistance welding machine contact resistance exists for a short time
When the workpiece and the electrode is constant, the resistance of the workpiece depends on its resistivity. Therefore, Resistance welding machine the resistivity is the important performance of the material being welded. High resistivity of the metal its poor conductivity (such as stainless steel) low resistivity of the metal its good conductivity (Such as aluminum). Therefore, the spot welding of stainless steel heat and easy to heat difficult, spot welding aluminum alloy heat and heat easy. Spot welding, the former can use a smaller current (thousands of amps), while the latter must use a large current Million amperes). Resistivity depends not only on the type of metal, but also with the metal heat treatment state, processing methods and temperature.
Resistance welding machine contact resistance exists for a short time, generally exists in the initial welding, formed by two reasons:
1) the workpiece and the electrode surface with high resistance coefficient of oxide or dirt layer, Resistance welding machine the current will be a greater obstruction. Too thick oxide and dirt layer can even make the current can not turn on.
2) in the surface is very clean conditions, due to the surface of the micro-roughness, so that the workpiece can only be in the rough surface of the local contact points. Forming a current line at the point of contact. The resistance at the contact is increased due to the reduction of the current path.
The resistance between the electrode and the workpiece Rew Compared to Rc and Rw, the precision welding of copper alloys is generally lower than that of the workpiece, so it is small and has little effect on the formation of nuggets, and we consider less of its influence.
2. Effect of welding current
The effect of current on heat production is greater than both resistance and time. Therefore, in the welding process, Resistance welding machine it is a must control the parameters. The main reason for the current change is the voltage fluctuation of the grid and the secondary circuit impedance change of the AC welding machine. Impedance changes are due to changes in the geometry of the circuit or the introduction of different amounts of magnetic metal in the secondary circuit. For DC welding machine, secondary circuit impedance changes, no significant impact on the current.