Resistance welding is a method to join two metals that involves the application of force or pressure as well as electricity at a spot where the two metals touch. It is also known as resistance spot welding or resistance seam welding. The electricity creates resistance heat at the point where the two metals touch, creating a joint or bond through melting of the metals. The melting of dissimilar metals creates an alloy that is referred to as a weld nugget. Joule heating generates the welding heat in resistance welding, with the amount of heat proportionate to the amount of resistance in weldment (Song, Zhang, and Bay, S-73). In addition, it does not generate splatter or ultraviolet rays. As a result, the process does not require specialized equipment or training for the welding process.
Contact resistance varies substantially in resistance welding and is the main element that creates resistance during most of the welding. Contact resistance depends on the amount of constriction resistance, which is a bundling or constriction of the electric current in the contact spots. It also depends on the amount of film resistance, which is the resistance caused by a film on the surface of the metals such as an oxide or oil (Song, Zhang, and Bay, S-73). The material used in the electrode is important for determining the life and the durability of the weld because it influences the degree of contact resistance (Zhang and Senkara, 1). Other factors affecting contact resistance are the type of base metal as well as temperature and pressure.
Resistance welding occurs rapidly and efficiently, which makes it suitable for use with production of low cost products. It can also be used to produce high volumes of goods in a production process. In general, products using resistance welding are found in the automotive, aerospace, construction, and heating and ventilation systems. Many common products such as metal food and beverage containers were assembled using resistance welding.
Resistance spot welding is commonly used in industry to join metal sheets of varying materials and thicknesses. The resistance spot welding process is very common in automobile manufacturing because it allows the union of two metal sheets using various types of joint configurations. The average car can contain as many as 3,000 different spot welds, with the majority of the welding performed robotically to facility rapid production (European Aluminum Association, 6). The development of effective resistance spot welding techniques contributed to the use of aluminum in automobiles. The resistance spot welding has a very low cost per weld because of the automation of the process, which is important for reducing the cost of production of automobiles and other vehicles. In addition, there are no consumables per weld and very low training costs for employees, particularly if robotic devices are used in to perform the welding processes.
One of the applications of resistance welding is resistance seam welding, which is used in many different types of sheet metal fabrication. The process involves using resistance welding to join the seams of similar types of metals, usually to make a cylindrical type product. Resistance seam welding is used to make cans, fuel tanks, and steel drums. The approach is most effective when the seams is straight or has a regular curvature arc. It is also capable of producing an air tight and leak proof seal, which is important in certain types of metal containers such as engine mufflers or gasoline tanks (Goover, 723). The seam welding method requires the ability to access both sides of the seam and requires a lap joint that binds the two metals at the seam.
The process relies on a device using rotating wheels that moves the two metals through the point of contact with the electrodes at a regular speed. A difference in seam welding from other approaches to resistance welding is that the process is continuous rather than a series of separate welds as in spot welding. The spacing between the weld nuggets is determined by an automated application of the electric welding arc at specified intervals.
Another type of resistance welding is resistance projection welding, which is used in the production of batteries and medical devices. This approach concentrates the heat at the contact surface by using a projection that may be embossed or machined. The projection localizes the current, which forces the parts to heat at the area around the mating surfaces. In practice, this creates a more rapid thermal cycle that prevents the heat from affecting or causing damage to parts adjacent to the weld. It is also useful for jointing metals in which one is considerably thicker than the other and requires more resistance heat to form the weld nugget (Wood, 12).
The resistance projection welding technique is particularly useful in the production of batteries, capacitors, and other electronic devices that rely on wet electrochemical cells that must be sealed. These types of devices are used in medical devices such as defibrillators as well as other types of products that may be embedded in a patient (Wood, 12). This welding process can be used with very small scale welds, which is appropriate for the relatively small medical devices that contain batteries and capacitors because of the ability to use different configurations for the projections.
Flash and resistance butt welding is another resistance welding procedure that can be used to join two metals. The flash approach is normally used in butt welding with the two surfaces are brought into contact or close contact and electric current from the electrode is used to heat the surfaces close to the melting point (Goover, 724). When the surfaces reach the appropriate melt temperature, they are forced together the form the weld. Some of the resistance heat can cause arcing or flashing. The process can lead to some metal as well as contaminants being squeezed from the sides of the joint when the surfaces are pressed together. As a result, the finished product may have to be machined in some cases to ensure that the joint is uniform.
The flash and resistance butt welding process is used in wire drawing, which is intended to reduce the cross-section of the wire. Wire that is broken in the process may have to be reattached or additional wire strands attached to existing strands. The ends to be joined, however, must have the same cross-sections (Goover, 724). The process is also used to join tubular parts. When automated, this type of resistance welding is rapid and economical.
Resistance welding is particularly important for various manufacturing processes because it is inexpensive, reliable, and does not require extensive training for employees. It can be used for producing large durable goods such as automobiles or for precision devices such as medical batteries and capacitors. Resistance welding can be found in can and wire production.
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