Spot Welding
What makes spot welding different from arc welding?
Spot welding uses contact resistance and pressure between copper electrodes to create a localized nugget, while arc welding uses an electric arc and typically adds filler material. Spot welding is fast, repeatable, and does not require filler metal or extensive post-processing.
Why is copper commonly used for spot welding electrodes?
Copper alloys are used because they conduct current well while withstanding repeated thermal cycling and pressure loading during the weld sequence. Proper tip geometry and condition are critical because electrode wear changes resistance and affects nugget consistency.
What does CNC add to spot welding in a production environment?
CNC adds positioning, sequencing, and repeatability, allowing programmed weld coordinates, consistent cycle timing, and automated multi-point production runs. Operators define the weld pattern by coordinates, ensuring each spot lands on the correct lap joint with stable clamping and consistent stack-up thickness.
Spot welding is a resistance welding process that joins overlapping sheet metals by clamping them between copper-alloy electrodes, applying pressure, and passing a high electrical current through the contact area. Localized resistance generates heat and fuses the sheets at a small weld nugget, using no filler metal. The process is fast, repeatable, and easily automated.
In a CNC or automated shop-floor cell, spot welding is programmed as a coordinate-driven cycle. The machine moves the workhead or table to programmed X-Y positions, applies electrode force, delivers a set current and time pulse, then indexes to the next spot for repeatable production welding. Critical setup variables are electrode force, weld current, weld time, tip geometry, and part fit-up; these determine nugget size, penetration, and repeatability. Operators define the weld pattern by coordinates, ensuring each spot lands on the correct lap joint with stable clamping and consistent stack-up thickness. The process suits thin sheet and overlapping parts, producing localized joints with a clean exterior finish rather than long continuous beads. In automated fixtures, one station can be loaded while another welds, improving throughput. Because no filler metal or extensive post-processing is required, it is common in sheet-metal fabrication, wire mesh, cages, racks, and thin-gauge assemblies.
Weak nugget under peel testing: Insufficient current or weld time leaves the sheets only partially fused, usually because settings are too low for the material thickness or electrode wear has increased tip resistance. The joint fails in shear or peel.
Expulsion and deep electrode indentation: Excessive current, force, or dwell overheats the joint and ejects molten metal, thinning the parent sheet and distorting the assembly. This usually happens when parameters drift above the window for the stack-up.
Skipped and inconsistent welds: Dirty surfaces, scale, oil, coatings, gaps, or mushroomed tips concentrate heat unpredictably, causing varying nugget size, skipped welds, or electrode sticking. The weld quality becomes impossible to control in production.