What is projection welding?

Welders should wear hard hats and gloves for protection.

Projection welding is a variation of the spot welding process in which raised projections on one or both sheets locate and concentrate welding energy. This technique allows closer weld spacings on thicker materials than is possible with the conventional approach. Projection welding is commonly used to attach connection points such as studs and nuts to sheet metal assemblies, particularly in the automotive industry. Suitable materials for the projection welding process include aluminum, low carbon steel and stainless steel.

Projection welding is commonly used for sheet metal fabrication.

Conventional spot welding involves passing a high voltage electric arc between two electrodes on either side of the material to be welded. This causes localized fusion of the two materials, thus creating a spot weld. Projection welding uses the same basic principle, but uses a shallow projection on one or both surfaces at the weld points. These projections face inward towards the inner surfaces of the solder sheets and concentrate the heat generated during solder discharge. This maximizes the potential of the weld pool and allows thicker materials to be welded with the same current settings.

Projections on workpieces are typically of spherical or blunt conical cross-section. Where both sheets are embossed, carefully calculated projection patterns ensure accurate indexing. Projections are also often used to accurately align workpieces. As in conventional spot welding, the rotating electrodes are held static while the parts advance between them. The feed rate must be carefully adjusted to ensure that the projections match the time of the welding arc as they pass between the electrodes.

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The automotive construction industry uses projection welding extensively in the assembly of body plates. Attachment points, such as integral nuts and nails, used to secure seats, panels, seat belts and interior trim, are usually secured by projection welding. This technique also offers the added benefit of minimal shrinkage and distortion at the weld location. Post-production parts are easier to plate or paint, with little grinding or finishing required. Different thickness materials are also easier to weld using this method.

Projection welding is a suitable process for many metals, including low carbon steel, stainless steel and aluminum. Increased efficiency means sheet thicknesses of up to 0.125 inches (3 mm) can be welded successfully. This process has some disadvantages, such as extra steps in the production process and limitations regarding the materials that can be used. The benefits, however, often outweigh the disadvantages; Projection welding is a good alternative to conventional spot welding.

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