There are many factors, which can influence the welding effort of resistance welding, which is applied tungsten copper as electrodes, such as welding current, time, pressure, electrode shape and properties and workpiece surface condition.
The influence of current on heat generation is greater than both resistance and time. Therefore, in the spot welding process, it is a parameter that must be strictly controlled. The main causes of current changes are grid voltage fluctuations and changes in the impedance of the AC welder's secondary loop. Impedance changes are due to changes in the geometry of the loop or due to the introduction of different amounts of magnetic metal in the secondary loop. For DC welding machines, the impedance change of the secondary loop has no obvious effect on the current.
In addition to the total welding current, the current density also has a significant effect on heating. The shunting of the welded joints and the increase of the electrode contact area or the bump size during projection welding will reduce the current density and the heat of welding heat, thereby significantly reducing the strength of the joint.
2.0 Effect of welding time
In order to ensure the size of the nugget and the strength of the solder joint, the welding time and the welding current can complement each other within a certain range. In order to obtain a certain strength of the solder joints, high current and short time (strong condition, also called strong specification) can be used, or small current and long time (weak condition, also called weak specification) can be used. The choice of strong condition or weak condition depends on the properties, thickness and power of the welder used. However, there are still upper and lower limits for the current and time required for metals with different properties and thicknesses. If these limits are exceeded, a qualified nugget will not be formed.
3.0 Influence of electrode pressure
The electrode pressure has a significant effect on the total resistance R between the two electrodes, and as the electrode pressure increases, R decreases significantly. Although the welding current increases slightly at this time, it cannot affect the reduction in heat generation caused by the decrease in R. Therefore, the strength of the solder joint always decreases as the electrode pressure increases. While increasing the electrode pressure, increase the welding current or prolong the welding time to compensate for the effect of the decrease in resistance and keep the strength of the solder joint unchanged. The use of this welding condition is beneficial to improve the stability of the solder joint strength. If the electrode pressure is too small, it will cause spatter and reduce the strength of the solder joint.
4.0 Influence of electrode shape and material properties
Since 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, so the shape and material of the electrode have a significant impact on the formation of the nugget. With the deformation and wear of the electrode tip, the contact area will increase and the strength of the solder joint will decrease.
5.0 Influence of the surface condition of the workpiece
Oxides, dirt, oil and other impurities on the surface of the workpiece increase the contact resistance. An oxide layer that is too thick may even make the current flow impossible. Partial conduction, due to excessive current density, will produce splashes and surface burns. The inhomogeneity of the oxide layer will also affect the inconsistency of the heating of each solder joint, causing fluctuations in the welding quality. Therefore, thorough cleaning of the surface of the workpiece is a necessary condition to ensure high-quality joints.
Besides the above mentioned influential
factors, the workers’ operation and machines are also important in welding. The
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