Projection welding uses surface protrusions on one or both sheets to concentrate welding energy, allowing for closer weld gaps on thicker materials. It is commonly used in the automotive industry for connecting studs and nuts to sheet metal assemblies. The process is suitable for low carbon steel, stainless steel, and aluminum, with plate thicknesses up to 0.125 inch (3 mm). While it has some downsides, projection welding is generally a good alternative to conventional spot welding.
Spot welding is a variation of the spot welding process in which raised protrusions on one or both sheets locate and concentrate the welding energy. This technique allows for closer weld gaps on thicker materials than is possible with the conventional approach. Butt welding is commonly used to connect 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.
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 surface projection on one or both surfaces at the weld points. These protrusions face inward towards the inner surfaces of the weld sheets and concentrate the heat generated during weld discharge. This maximizes the potential of the melt pool and allows thicker materials to be welded at the same current settings.
The protrusions in the workpieces are typically of spherical or blunt conical cross section. Where both sheets are embossed, carefully calculated projection patterns ensure accurate indexing. Bosses are also often used to accurately align workpieces. As with conventional spot welding, the rotating electrodes are held static as the workpieces are advanced between them. The feed rate must be carefully matched to ensure that the projections match the timing of the welding arc as it passes between the electrodes.
The automotive industry uses spray welding extensively in the assembly of body pans. Connection points such as integral nuts and studs used to attach seats, dashboards, seat belts, and interior trim are typically attached by spray welding. This technique also offers the added benefit of minimal shrinkage and distortion at the weld site. Post production pieces are easier to plate or paint with little grinding or finishing required. Materials of different thicknesses are also easier to weld with this method.
Projection welding is a process suitable for a number of metals including low carbon steel, stainless steel and aluminium. The increased efficiency means that plate thicknesses up to 0.125 inch (3 mm) can be successfully welded. This process has a couple of downsides such as additional steps in the manufacturing process and limitations regarding the materials that can be used. The advantages, however, generally outweigh the disadvantages; projection welding is a good alternative to conventional spot welding.
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