What is Spot Welding?
Resistance welding is a procedure that involves spot welding, also called resistance spot welding. Applying pressure and heat from an electric current to the weld area typically uses this welding procedure to join two or more sheets together.
It applies pressure and electric current to the surfaces of copper alloy electrodes, generating heat as the current passes through resistive materials like low-carbon steel.
How Does Spot Welding Work?
One of the earliest methods of joining two or more sheets of metal together is spot welding, a type of resistance welding in which no filler material is used.
The procedure entails applying pressure and heat to the weld region by using shaped alloy copper electrodes that conduct an electrical current through the weld pieces. When the material melts and fuses the components, the current is cut off, the electrodes’ pressure is maintained, and the liquid “nugget” solidifies to create the joint.
Electric current, transmitted to the workpiece through copper alloy electrodes, produces the welding heat. The use of copper for the electrodes ensures that heat is generated preferentially in the workpieces rather than the electrodes since copper has high thermal conductivity and low electrical resistance compared to most other metals.
The heat produced is influenced by the metal’s electrical resistance, thermal conductivity, and the time the current is applied. The equation: can be used to describe this heat.
The terms “Q” and “I” in this equation stand for heat energy, current, electrical resistance, and application time, respectively.
Materials Appropriate For Spot Welding
Steel is relatively simple to spot weld due to its lower heat conductivity and better electrical resistance, with low-carbon steel being the best choice. However, because they tend to create complex and brittle microstructures, high carbon content steels (Carbon Equivalent > 0.4wt %) are susceptible to low fracture toughness or cracking in the welds.
Due to its excellent electrical resistance and lower heat conductivity, steel—low carbon steel is the ideal option—is very easy to spot weld. High carbon content steels (carbon equivalent > 0.4wt %) are prone to low fracture toughness or cracking in the welds because they tend to produce complex and brittle microstructures.
Other frequently spot-welded materials include titanium, nickel alloys, and stainless steels, particularly austenitic and ferritic grades.
Although copper and aluminium have similar electrical and thermal conductivities, welding is possible because aluminium has a lower melting point. But when welding aluminum, very high current levels are required due to the material’s low resistance (in the order of two to three times higher than for steel of equivalent thickness).
Additionally, aluminium damages the surface of copper electrodes in a small number of welds, making it highly challenging to produce stable, high-quality welds. Due to this, the industry mainly uses aluminium spot welding in specialized applications. Thanks to several recent technological breakthroughs, it is now possible to spot-weld aluminum with stability and good quality.
Resistance spot welding can also be used to join copper and its alloys. However, because the heat generated by the electrodes and the workpiece is so similar, spot welding copper is difficult to accomplish with standard copper alloy spot welding electrodes.
Using an electrode formed of an alloy with high electrical resistance and a melting temperature significantly higher than the melting point of copper (far higher than 1080 °C) is the solution for welding copper. Molybdenum and tungsten electrode materials are frequently used for spot welding copper.
Where Is Spot Welding Used?
Numerous industries use spot welding, including automotive, aerospace, rail, white goods, metal furniture, electronics, medical buildings, and construction.
Spot welding is the most frequent joining procedure in high-volume manufacturing lines. It has, in particular, been the primary joining process in the construction of steel cars for over 100 years due to how easily it can be automated when combined with robotics and manipulation systems.
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