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Production Resistance Welding

What Is Resistance Welding?

Resistance welding is a process that takes advantage of a workpiece's inherent resistance to the flow of electrical current. As current is passed through the parts to be welded, the parts resist the passage of the current, thus generating the welding heat. A force is simultaneously applied, and the parts are joined together.

Unlike other forms of welding, resistance welding does not utilize additional materials such as fluxes and filler rods. The weld nugget is formed directly from the base materials.

There are three main resistance processes: Spot, Projection, and Seam Welding.

Spot Welding

	Spot welding is a process typically used in high-volume, rapid welding applications, such as those found in the automotive, appliance and aerospace industries, to join sheet metal up to 1/8 of an inch (3mm) in thickness. The advantages of this process are that it is not labor-intensive and can easily be automated.
Resistance spot weld section

Projection Welding

	Projection welding is a variation of resistance welding in which current flow is concentrated at the contact surface of interest by an embossed or machined projection. Because the projection effectively localizes the current, resistance welding can be done in a wide range of applications not addressable by conventional resistance spot welding.
Resistance projection welding

Seam Welding

Mash seam welding

Seam welding is similar to spot welding except that rotating wheel electrodes are used. The process is used when leak-tight welds or long strings of spot welds are required. Three forms of seam welding exist: standard seam, mash seam, and roll spot welding.

In standard seam welding, a series of overlapping weld nuggets are formed by rotating the wheel electrodes along the workpieces and firing a continuous series of current pulses. This action forms a continuous, leak-tight joint.

In mash seam welding, there is a small overlap of sheets, typically about one to two times the sheet thickness. Sheets are then mashed together, making a solid state joint. The resulting welded joint is generally 110-150% of the original sheet thickness. This final joint thickness can be reduced by postweld planishing.

Mash seam welding

Production Resistance Welding at LSA

LSA is a leading supplier of high volume projection welded and mash seam welded sheet metal assemblies and components.

We have successfully combined our expertise in mash seam welding, precision blanking and forming to reduce the cost of manufacturing components by as much as 40%. Our capability in mash seam welding extends to the development of welding equipment and fixtures, process development and control, understanding the metallurgy behind resistance welding and development of material specifications. We currently have five seam mash welding machines, using AC and DC transformers and state of the art weld controllers, capable of welding parts over 36 inches in diameter.

LSA has refined the science of projection welding enough to bring our reject rate down to less than 5 parts per million. This has been achieved through a combination of carefully controlled manufacturing of the associated sub assemblies, comprehensive and strict process control during the welding process and a quality control program that is designed to detect any deviation from our high quality standards. Currently we have six, high volume, automated projection welding cells. Our projection welding experience includes un-coated and coated materials.