Spot Welding

Spot welding joins overlapping sheet metal by localized resistance heating, creating quick, repeatable lap joints for high-volume assemblies with minimal distortion and preparation.

Overview

Spot welding is a resistance welding process that fuses overlapping sheet metal by passing high current through clamped electrodes to form a localized weld nugget. It creates strong lap joints rapidly with no filler metal and minimal edge preparation, making it a staple for thin-gauge steel and some aluminum assemblies.

Use spot welding when you need fast, repeatable joints on accessible, overlapping sheets, especially in medium to very high production volumes. It excels at dense weld patterns, controlled heat input, and low distortion, but it does require access from both sides and consistent part fit-up. Weld quality depends heavily on material type, thickness, surface condition, and electrode design. You trade off flexibility in joint type and thickness range for speed, automation potential, and low per-weld cost once tooling and parameters are dialed in.

Common Materials

  • Low carbon steel
  • Galvanized steel
  • Stainless steel 304
  • Stainless steel 316
  • Aluminum 5052
  • Aluminum 6061

Tolerances

±0.03" on spot location; weld nugget size and strength per print or AWS specification

Applications

  • Automotive body panels and brackets
  • Battery tabs and busbar connections
  • Sheet metal enclosures and cabinets
  • HVAC duct flanges and frames
  • Appliance housings and inner panels
  • Wire mesh and light bracket assemblies

When to Choose Spot Welding

Choose spot welding for overlapping sheet metal joints where you have access from both sides and need fast, repeatable welds. It fits best for thin-gauge lap joints in medium to high production runs, especially when weld locations are standardized and you can justify simple fixtures or automation.

vs Seam Welding

Pick spot welding when you need discrete welds at defined locations rather than a continuous, leak-tight seam. It is usually simpler to fixture, more forgiving on part fit-up, and faster to set up for multiple short joints spread across a large assembly.

vs MIG welding

Choose spot welding when joining thin overlapping sheets where speed and minimal post-processing matter more than joint accessibility or thickness range. It avoids filler wire, reduces spatter and distortion, and is easier to automate for repetitive weld patterns.

vs TIG welding

Use spot welding when you need high throughput and consistent lap joints instead of precision, operator-intensive weld beads. It delivers adequate structural strength on thin sheet at a fraction of the cycle time and skill level required for TIG.

vs Riveting / mechanical fastening

Select spot welding when you want permanent joints without added hardware, minimal assembly time, and cleaner aesthetics. It reduces BOM count and assembly steps, provided serviceability and disassembly are not required.

Design Considerations

  • Keep total sheet stack thickness within the spot welder’s qualified range and specify material thicknesses clearly on the print
  • Provide sufficient lap joint width for electrode diameter plus edge distance; avoid placing spots too close to edges or bends
  • Ensure electrode access from both sides with enough clearance around flanges, beads, and hardware for the chosen electrode shape
  • Call out weld pattern, minimum nugget size, and strength or pull-test requirements instead of vague notes like “spot weld as required”
  • Avoid heavy coatings, sealants, or adhesives between faying surfaces at weld locations, or clearly indicate zones to be masked or cleaned
  • Control part flatness and fit-up in the joint area; poor contact increases variability in weld size and strength and drives reject rates up