The Spot Welding Process

on the process of spot welding

The process of spot welding

After switching current passes from one electrode to another through the metal parts and metal heats up more than just a place of contact details. Heating of the metal surface under the electrodes when properly conducted process is negligible, since the contact electrode - the product has relatively little resistance due to the softness and high electrical conductivity of the electrode metal and the electrode is cooled rapidly under running water. The passage of current causes heating and melting the metal in the welding zone, creating the flow core, having a lenticular shape (see Fig.). The diameter of the core weld point in ordinary cases, has a value of 4-12 mm. Spot welding without melting the metal core point though is possible (for mild steel), but is not sufficiently reliable and, therefore, in practice almost never used. Welding of metals having poor weldability in a plastic state, is only possible with sufficient molten metal in the core point.

Spot welding is a unique process that combines the melting of metal and molded to obtain the structure of a welded joint with a large sediment pressure. Pressure should be sufficient to overcome the rigidity of the product and carry out the necessary plastic deformation, ensuring adequate strength of welded points. The required pressure increases rapidly with increasing thickness of the base metal. Air pressure is fully transmitted to the electrodes, having a small work surface, carrying a large thermal and electrical load. In a large thickness of the base metal electrode load is so high that their life is declining rapidly. Therefore, spot welding is used primarily for the small thickness of the metal, not more than 5-6 mm. The diameter of the nucleus determines the strength of the points mainly depends on the diameter of the working electrode surface, plate thickness, pressure, current, and the time of his passing. If incorrectly chosen mode of welding can not occur enough melting point metal and get imperfections. When the core is molten, the adjacent area around the circumference of the metal is in a plastic state, impact pressure of the electrodes. The pressure creates the seal ring ductile metal, retaining the liquid metal core. With low pressure sealing ring can not retain the liquid metal core and the inner splash occurs in the gap between the metal sheets.

With increasing time of passage of the current diameter and height of the growing nucleus. An excessive increase in the size of the nucleus weakens its shell from the heated solid metal, and there is a strong indentation of the metal under the electrodes, leading to the outdoor splash of molten metal and reduce the strength of the point. After switching off the current starts cooling and solidification of the molten core point.

The crystallization of the molten metal comes from the surface of the nucleus to the middle. As a result, the kernel has a columnar dendritic structure.

See also:
Electric Resistance Welding
Pliers for Welding
Spot Welding
The Spot Welding Process
The Spot Welding Process (Part 2)
Special Types of Spot Welding