What is Resistance Welding?

History of welding technology
In ancient times, metal welding was done in the form of forge welding (metals heated up to melting point are pressed together)�@and brazing (weld using alloy of low melting point). With the advent of electricity, welding technology advanced remarkably; namely, resistance welding, arc welding and gas welding were invented in the end of 19th century. Thereafter, various welding technologies such as ultrasonic, friction, electron beam, plasma, laser welding have been invented.
Though we have very little chance to experience the welding technology, it is applied broadly in the field of industry, whose growth is supported by this technology.

Principle of resistance welding
Welding is to apply electrode to metal workpieces and flow a large current of several tens to several tens of thousands Amperes for several milliseconds to several hundred milliseconds while pressing. Joule heat forms a nugget, resulting in melt joint. Though a large current flows, there is no danger of an electric shock because only low voltage is impressed.

Features of resistance welding
Comparing with other welding methods, resistance welding features as follows:

• Auxiliary material such as solder is not used, resulting in a clean joint which is easy to recycle. Spatter and ultraviolet ray are most unlikely to be generated; consequently, clean and neat worksite is realized.
• As only pressing a switch ensures welding, process is easily automated. Unlike arc welding and gas welding, no skill is required.
• As this welding is performed efficiently in a short period of time, it is suited for a high-volumes production of low-cost products.
• Since welding is done in short time duration, it gives less thermal effect to workpiece, resulting in beautiful appearance with less indentation.
• Since a large current is needed, electric facility is required in some cases. As welding conditions vary with respect to material to be welded and its thickness, welding condition setting must be prepared.
• Visual inspection is difficult because welded portion cannot be checked from the outside.

Example application of resistance welding
Resistance welding is well received in various fields of industry such as automobile, electric car, electric equipment, electronic parts, where metal lap welding, coated-wire welding, etc. are employed. Miyachi Corporation is skillful at precise welding.

Motor	Terminal
Relay	Electronic gun
Halogen lamp	Pressure sensor