Projection welding is a modification of spot welding, working on the same general principle but with fewer variables that affect the resistance welding process.
In projection welding, the weld is localized by means of a raised section or sections (called projections) on one or both workpieces to be joined. The two metal surfaces are held together under pressure by electrodes, and when electrical current is sent through the weld electrode, the projections melt and fuse the materials, creating the weld joint.
In this photo, red arrows point to the metal fastener projections. (Photo credit: JHP Fasteners Inc.)
Weld joint strength is dependent on the nature of the projections used. Three types of projections are commonly used: button, cone, and spherical.
Button projections are generally used to join thin, flat sheet metals, from 24 to 13 gauge. Cone projections are usually used with 12 to 5 gauge metal sheets. Spherical projections are best for thicker metal materials.
Advantages of Projection Welding
Projection welding is an easily maintainable and repeatable process if its fundamentals are taken into account from the start. Numerous weld joints can be created at once with proper design and jigging, allowing for faster processing—the projections themselves can serve as a means of positioning the workpieces.
Because the heat is concentrated at the projections, heavier sections can be welded, and welds can be spaced closer than when using other processes. Additionally, projection welding provides better heat control for different material compositions and thicknesses. Parts with little to no heat surface marks on one side can be produced by processing projections on the opposite part and using large electrodes contoured to the finished part.
Electrode life tends to be longer in projection welding than in spot welding, thanks to lower resistance. When performed properly, projection welding produces very little expulsion.
- “How Projection Welding Works” http://www.typesofwelding.net/projection_welding.html
- “Projection Welding Process” http://www.weldtechcorp.com/welding_concepts/projectionweld.html