Resistance Welding

Resistance welding of various types can be catered for using TWI's in-depth know how.

Welds are created between materials by applying localised pressure and resistance heating - applying a high electric current, usually with copper electrodes.

• Resistance spot welding: the principal process for joining sheet metal components such as vehicle body parts. Electrodes concentrate the current at a small point, while electrode force squeezes the materials together. Spot welding requires only short contact time but high current, resulting in melted material at the interface - the weld nugget. It is a fast, reliable process with low distortion.
• Resistance projection welding: a versatile process for joining wire, sheet, machined & formed parts in steel; applications include wire mesh, attachment of brackets, etc in sheet metal assembly, and welded nuts and bolts. Projections on the component, e.g. embossed projections on sheet or formed projections on nuts and bolts, provide the locallised concentration of force and current, so that large flat electrodes can be used and many welds made simultaneously.
• Resistance seam welding: the process for producing leak-tight, continuous joints in sheet metals; applications include vehicle fuel tanks, domestic radiators, tin cans and drums. Welds are produced in long continuous seams by rolling the material sheets between rotating electrode wheels.
• Micro & miniature resistance welding: used extensively in electronic packaging & sensor/transducer assembly, e.g. resistance welding fine-pitch copper transducer interconnections.
• Flash & resistance butt welding: forge butt welding processes for a wide range of metals, section sizes & shapes; applications include wheel rims, starter rings, wire welding & railway track welding. The ends of material to be joined are resistance heated either under pressure (resistance butt) or with intermittent contact (flash welding) to create a softened zone. When the two ends are forced against each other, an upset is formed, eliminating any melted material and contaminants from the interface and creating a solid phase joint.
• High frequency welding (ERW): for producing continuously welded metal tube and pipe, finned tube; applications include exhaust pipes, water and fuel pipelines, and hydro-formed tube. Joints are created using high frequency current to resistance heat the edges of the tube, which are then forged together producing a solid phase weld.

TWI has resistance welding equipment covering spot, seam and projection welding processes with associated power supplies and monitoring equipment.

- Spot, projection and seam welding
- AC/DC up to 100kA short circuit current
- Up to 30kN force capability.
- Special or modified equipment capability
- 1000Hz medium frequency inverter welder
- Parameter monitoring with transient digital storage oscilloscope and
- commercial meters.

For further information on any of these processes, contact us on: lasers@twi.co.uk