Projection Welding
Projection welding is a resistance welding process that joins metal parts by applying current, force, and time through raised projections, embossments, or intersecting features. The small contact area at each projection concentrates resistance heating at predetermined points, causing the projections to collapse and fuse the parts together under pressure. This produces a localized, repeatable weld without requiring special electrode shapes.
On the shop floor, projection welding is a staple in automated cells for attaching nuts, studs, bolts, and brackets to sheet metal or formed parts. Operators fixture parts so the raised projections align precisely under flat electrodes; the machine then applies controlled force, power, and time. The projections act as heat concentrators, collapsing during the weld to forge a consistent joint. Because the weld location is defined by the embossment or coined feature, repeatability is far better than with free-form spot welding. Multiple projections can be welded in a single stroke when the press and frame are rigid enough to resist flexing. This process is particularly valuable in metal fabrication and sheet-metal assembly, where parts are designed with repeatable projection geometry. Weld schedules must balance force, current, and time for each material stack-up, and stainless steel or titanium often demands higher force and tighter control.
- Projection Geometry Drift: Poorly formed or worn projections reduce current density, so the weld lands off-center or weak. The heat is no longer concentrated exactly where intended.
- Insufficient Machine Force or Frame Stiffness: If the frame flexes, multiple projections collapse unevenly, causing inconsistent nuggets, electrode sticking, or expulsion. Rigidity and follow-up force are essential.
- Wrong Weld Schedule for Material Stack-Up: Stainless steel, titanium, or multiple projections need more force and precisely controlled power/time; otherwise surface burn, excessive indentation, or incomplete fusion occurs.
Why use projections instead of a flat spot-weld interface?
A projection creates a very small initial contact area, which raises electrical resistance and concentrates heat exactly where the weld is intended. That localized heating makes the weld position more repeatable and predictable than a free-form spot weld.
Can projection welding make more than one weld at once?
Yes. Multiple embossed or designed projections can be welded in a single stroke, provided the welding machine has enough force and power to collapse all projections uniformly and maintain consistent pressure across the joint.
What controls weld quality most tightly?
Projection consistency, electrode alignment, and the force/power/time schedule are the primary controls. If any of these drifts, the heat balance changes and weld quality suffers, especially with multiple projections or harder materials.