Resistance welding refers to processes that use electrically generated heat and pressure to create bonds between materials. Such processes usually pertain to connecting metals but the term resistance welding may also be used in plastic bonding. This type of welding is regarded as quick and efficient when done properly. Mistakes during such a process can result in problems such as cracking, deformed surface appearance, and cavities.
The machines normally used for resistance welding utilize copper electrodes. These are used to inject the materials with electrically generated heat. The machine’s operator can control the amount of heat and the heating period. After a sufficient amount of heat is injected, the materials may be cooled on the outside while the inner, molten materials are left to cool more gradually. When this phase is complete, bonds should be formed.
Generally, the higher the melting point of the metal, the less heat that is needed. A metal that conducts heat well, such as aluminum, requires more heat for resistance welding. This is because the heat tends to spread through the material instead of being trapped at the melting point.
Resistance welding also requires force. Pressure is used to hold layers of metal together while they are cooling. If this is not done, cohesion may never occur. The necessary pressure is usually applied by the machine that supplies the electrical current. The machine’s operator can also usually control the amount of pressure.
Spot welding is an example of a resistance welding process. It can be used to connect multiple layers of metal without filler materials. Since copper is an excellent conductor of heat, pointed, copper electrodes, are used to clamp the metal together and send electrical currents through them.
Many metals do not conduct heat well. The heat created within the layers of the project is therefore trapped and results in melting. Pressure from the electrodes then causes the layers to connect.
Seam welding is similar to spot welding. Instead of creating bonds at various points, however, this process allows the creation of long, continuous bonds. Round electrodes are used in this process to roll over the outsides of the materials, feeding them with electrical current and applying pressure.
There are several types of resistance welding bonds. Fusion bonding involves materials that bind because their melting points are reached, allowing the molten materials to mix together. A solid state bond, on the contrary, is one that involves minimal melting.