Welding fatigue
Introduction
Spot welding is a resistance welding method that is based on pressure, intensity "Intensity (physical)") and time.
In this welding, a part of the pieces to be welded are heated by electric current to temperatures close to fusion and pressure is exerted between them. It is generally intended for welding metal sheets or sheets, normally applicable between 0.5 mm and 3 mm thick. It is advisable that the two sheets have the same thickness.
Spot welding is the most difficult and complicated of the resistance welding procedures. The base materials must be arranged overlapping between electrodes, which are responsible for sequentially applying the pressure and current corresponding to the cycle, producing one or more welding points.
Process characteristics
It is a type of welding that is classified as welding without fusion of the base metal to be welded. It is considered a process in which the electrodes used are not consumables. In addition, no filler material is needed to produce the union between the two pieces. It is considered a type of fast, clean and strong welding.
The material used for the electrodes is a copper alloy with Cd, Cr, Be, W so that it has low resistance and high opposition to deformation under pressure, its hardness being between 130 and 160 HB.
This type of welding also requires a transformer where the secondary coil supplies a voltage to the electrodes of 1 V to 10 V and a large current, because generally the resistance of the pieces to be welded is very low, therefore the current that must pass through the area to be welded must be of the order of 500 A.
Welding process
Contenido
El principio de funcionamiento de este proceso consiste en hacer pasar una corriente eléctrica de gran intensidad a través de los metales que se van a unir. Como en la unión de los mismos la resistencia es mayor que en el resto de sus cuerpos, se genera el aumento de la temperatura en juntura, Efecto Joule (Q = I^2 R t).
Donde:.
Aprovechando esta energía y con una determinada presión se logra la unión. Solamente se obtienen soldaduras uniformes si las chapas a soldar están limpias, ya que los óxidos superficiales son causa de variaciones en el tamaño y resistencia de los puntos de soldadura. Esto es especialmente cierto en el aluminio. La presencia de óxidos o suciedad puede aumentar diez veces o más la resistencia total entre los puntos de los electrodos.