Spot Welding

Spot welding joins overlapping sheet metal with localized resistance-heated nuggets, delivering fast, repeatable joints for thin-gauge assemblies with access from both sides.

Overview

Spot welding is a resistance welding process that clamps two overlapping sheets between copper electrodes and passes current to form a fused “nugget” at each spot. Cycle times are short, heat input is localized, and joints are consistent when surface condition, fit-up, and electrode force are controlled.

Choose spot welding for lap joints in thin to medium gauge sheet metal where you can reach both sides and want high throughput with minimal distortion. It’s common in brackets, enclosures, frames, and subassemblies where weld appearance isn’t the primary requirement.

Tradeoffs: it’s not a continuous seal (no leak-tight seam), joint strength depends on nugget size and spacing, and access/stack-up limits apply. Coatings, scale, adhesives, and gaps can reduce weld quality and electrode life. Aluminum and stainless are weldable but typically require higher current, tighter process control, and more electrode maintenance than mild steel.

Common Materials

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

Tolerances

±0.010"

Applications

  • Sheet metal enclosures and cabinets
  • Appliance panels and frames
  • Automotive brackets and reinforcements
  • HVAC duct and bracket subassemblies
  • Wire mesh to frame attachments
  • Battery tray and bracket assemblies

When to Choose Spot Welding

Spot welding fits high-volume or repeat-production sheet metal assemblies with lap joints and two-sided electrode access. It works best on clean, well-fitting parts with consistent thickness and repeatable fixturing. Expect discrete attachment points rather than a continuous, sealed joint.

vs Seam Welding

Choose spot welding when you only need discrete attachment points and want maximum speed with minimal heat input and distortion. Seam welding makes a continuous weld line for sealing and higher continuity but usually costs more in tooling/fixturing and is less tolerant of variable fit-up.

vs MIG Welding (GMAW)

Choose spot welding when you can overlap sheets and access both sides, and you need fast, repeatable joints with minimal cleanup. MIG is better for single-sided access, thicker sections, and longer continuous welds, but typically adds more heat and post-weld finishing.

vs TIG Welding (GTAW)

Choose spot welding when appearance isn’t the driver and you need high throughput on thin sheet with consistent strength. TIG can produce cleaner-looking, continuous welds and handles complex joints, but it’s much slower and more operator-dependent.

vs Riveting / Blind Rivets

Choose spot welding when you want a low-profile joint without added hardware and you can weld the chosen material/coating. Rivets work with dissimilar materials and single-sided access, but add BOM cost, hole prep time, and potential leak paths.

vs Structural Adhesive Bonding

Choose spot welding when you need immediate handling strength and robust performance at elevated temperatures or in oily/dirty environments. Adhesives can spread load and join dissimilar materials, but require surface prep, cure time, and process controls for consistent bondline thickness.

Design Considerations

  • Design lap joints with sufficient overlap for electrode contact and nugget placement, and keep overlap consistent along the joint
  • Provide clear two-sided access for electrodes and allow space around the weld for electrode diameter and squeeze force
  • Control fit-up: minimize gaps, warpage, and stack-up variation; spot welding quality drops quickly with poor contact
  • Specify spot weld size and spacing (or call out number of welds per flange) to make strength and quoting unambiguous
  • Avoid welding through heavy coatings, adhesives, paint, or scale unless the process is qualified; call out coating condition and removal requirements
  • Add locating features or fixturing tabs/holes when repeatability matters; consistent clamping improves weld consistency and reduces rework