Spot Welding

Spot welding joins overlapping sheet metal by clamping electrodes and using electrical resistance heat to form fast, repeatable weld nuggets at discrete points.

Overview

Spot welding (resistance spot welding) clamps two or more overlapping sheets between copper electrodes and drives high current for a short time to create a localized weld nugget. It’s a high-speed, low-consumable process that’s easy to automate and repeat in production.

Choose it for lap joints in thin-to-medium sheet where you can access both sides with electrodes and you need many discrete attachment points. It works best on steels and many stainless grades; aluminum is weldable but more sensitive to surface condition, electrode wear, and process control.

Tradeoffs: joints are discrete points (not sealed), strength depends on nugget size and spacing, and cosmetics can show electrode marks. Fit-up, stack-up, coatings, and access drive variability; the process is less suited to thick sections, one-sided access, or assemblies requiring continuous leak-tight seams.

Common Materials

  • Mild steel
  • HSLA steel
  • Stainless steel 304
  • Stainless steel 430
  • Galvanized steel
  • Aluminum 5052

Tolerances

±0.010"

Applications

  • Automotive body-in-white panels
  • Sheet metal enclosures and cabinets
  • Appliance chassis and brackets
  • HVAC duct and fittings (non-sealed joints)
  • Battery pack tabs and busbar-to-tab joints
  • Wire mesh and sheet attachments

When to Choose Spot Welding

Spot welding fits production sheet-metal assemblies with lap joints, consistent material thickness, and repeatable part location features. It’s most cost-effective when you need many joints quickly with minimal filler/consumables and can fixture for two-sided electrode access. Expect best results when surface condition and coatings are controlled and joint spacing is defined.

vs Seam Welding

Choose spot welding when the joint can be discrete points and you don’t need a continuous, leak-tight seam. It’s typically faster to fixture and cheaper per joint for intermittent attachments, especially where heat input and distortion must stay localized.

vs MIG Welding (GMAW)

Choose spot welding when parts are thin sheet with lap joints and you want high repeatability with minimal operator dependency. It avoids filler wire and generally reduces spatter, cleanup, and heat distortion compared to arc welding on light-gauge assemblies.

vs TIG Welding (GTAW)

Choose spot welding when you need high throughput and consistent joints rather than continuous, cosmetic beads. It’s better suited for repeated attachments across large panels where TIG time and heat input would drive cost and warpage.

vs Self-Piercing Riveting (SPR)

Choose spot welding when the materials are weldable and you can tolerate local electrode marks. It eliminates rivet hardware and typically reduces part cost and mass versus mechanical fastening when access and coatings allow stable welding.

Design Considerations

  • Provide flat, parallel electrode landing areas and avoid embosses or hems at the weld point
  • Keep consistent stack thickness at weld locations; avoid mixing large thickness ratios in the same weld schedule
  • Call out nugget diameter and weld spacing/pattern, not just “spot weld,” to control strength and inspection criteria
  • Design in positive locating features and fixture datums to control fit-up and prevent shunting through unintended contact points
  • Maintain adequate edge distance and pitch to prevent tear-out and excessive sheet indentation
  • Specify coating/plating condition (e.g., galvanized, pre-painted) at weld areas and note any required post-weld corrosion protection