Spot Welding

Spot welding joins overlapping metal sheets using localized electrical resistance heat, ideal for high-speed, repeatable lap joints in thin-gauge materials.

Overview

Spot welding, or resistance spot welding, forms a fused “nugget” between overlapping metal sheets by passing high current through electrodes under pressure. It excels at fast, repeatable lap joints in thin to medium-gauge sheet metal, especially in automated production cells and robotic welding lines. Cycle times are short, and welds require no filler metal or consumable electrodes.

Use spot welding when you need many similar joints, consistent strength, and clean surfaces on large assemblies like body structures, enclosures, and brackets. It delivers low cost per weld at medium to high volumes but requires access from both sides of the joint and consistent sheet contact. Limitations include shallow weld penetration, sensitivity to coatings and fit-up, and aesthetic electrode marks on visible surfaces. Engineers must design for electrode access, controlled stack-up thickness, and realistic weld spacing to get reliable strength and lean production costs.

Common Materials

  • Low carbon steel
  • Galvanized steel
  • Stainless steel 304
  • Stainless steel 430
  • Aluminum 5052
  • Nickel alloys

Tolerances

±0.020" on weld location; weld nugget size per AWS or customer spec

Applications

  • Automotive body-in-white panels and brackets
  • Appliance housings and doors
  • Battery pack tabs and busbars
  • Sheet metal enclosures and cabinets
  • Wire mesh and wire frame assemblies
  • HVAC ducts and thin-gauge structural frames

When to Choose Spot Welding

Choose spot welding for overlapping sheet-metal joints where you can access both sides with electrodes and need many repeatable welds at low cost per joint. It fits best with thin to medium gauges, stable fixturing, and automated or semi-automated production. Use it when joint loads are well understood and a series of discrete weld nuggets can provide the required strength and stiffness.

vs Seam Welding

Pick spot welding when you need discrete, spaced welds rather than continuous leak-tight seams. It suits structural joints, brackets, and stiffeners where full-length welds would add cost, distortion, or unnecessary continuity. Use it when you want simpler fixturing and shorter weld times per joint.

vs MIG Welding

Choose spot welding over MIG when joining thin sheets in lap configuration with high part counts and repeatable weld locations. It avoids filler metal, reduces heat input and distortion, and is easier to automate with short, consistent cycle times. MIG is better for thicker sections, non-lap joints, or when access is limited to one side.

vs Laser Welding

Select spot welding when you want robust, low-cost equipment and don’t need continuous or ultra-precise, narrow welds. It tolerates slight joint gaps better and is often cheaper to deploy on high-volume stamped assemblies. Laser welding is preferable for one-sided access, very tight heat-affected zones, or aesthetic continuous seams.

vs Mechanical Fastening

Use spot welding instead of bolts or rivets when you want permanent joints, reduced hardware and assembly steps, and better stiffness in overlapped sheet metal. It lowers part count and assembly time at volume but eliminates disassembly, so it’s best for structures not intended to be serviced at the joint level.

Design Considerations

  • Maintain consistent sheet stack-up thickness and material type in a weld group to simplify parameter setup and ensure consistent nugget size
  • Leave sufficient flange width and edge distance (typically ≥2x sheet thickness) to avoid edge blowout and strength loss
  • Design joints so both sides are accessible with standard spot welding guns and electrodes; check reach and throat depth in CAD
  • Specify practical weld spacing and patterns based on load paths, not just aesthetics; avoid unnecessary welds that add cost and distortion
  • Control surface condition and coatings in the weld area; thick coatings or contamination require higher currents and increase variability
  • Dimension weld locations with realistic tolerances and provide datums for fixturing so the shop can design rigid, repeatable welding fixtures