Spot Welders and Spot Welding equipment. How it works.
Resistance Seam Welding
Trading for over 50 years, Westermans International has built up a huge knowledge of all types of spot welding equipment and machinery which we now stock from our East Midland warehouse.
Do you want information immediately? Call +44 (0)116 2696941 now
Spot Welding – Technical Details
Spot welding is a resistance process, relying on the electrical resistance of the components to generate heat when a current is passed through them. The heat generated is proportional to
- The square of the current
- The resistance of the components
- The time for which the current is passed
Weld currents typically vary from 500A on very thin
materials (<0•2mm) up to 30kA for heavy sheet of
projection weld applications.
The thicker the material, the longer it will take to heat it
up to the required temperature. In general, therefore,
weld times increase in proportion to the thickness of the
The purpose of the force applied to the welding electrodes is to contain the expansion which occurs when the metal is heated. If this expansion is not contained, metal will be expelled from the weld area, leaving reduced nugget size and the possibility of an incomplete nugget composition, adversely affecting weld strength.
As metal thickness increases, the expansion force increases, so the weld force must increase. Thicker materials therefore require higher forces.
Metal type will also affect force required:-
Galvanised metal has a low initial electrical resistance requiring higher currents to generate the heat. Higher currents cause faster expansion, so higher forces are required.
Stainless steels are harder and require more force to create a join at the sheet interface during the weld, so require high forces, typically 50% above those for mild steel.
The heat generated must be thought of as ‘heat per unit area’. Spot diameter increases with material thickness (too small a spot on sheet of a given thickness which requires a given current to heat it up and a given force will indent too far into the sheet, causing splashing (metal expulsion) and adversely affecting weld strength.)
A standard 5mm dia spot has a surface area of 19mm2. If this is allowed to increase to 7mm, with an area of 38mm2, visually not very different, and the current is not increased, the ‘heat per unit area’ has halved and spots will fail.
Tip dressing is therefore the single most critical area affecting weld quality.
Weld current is concentrated in a small area by shape of the welding electrode.
Weld current is concentrated by one or more projections
raised in one component.
The same current and force is required for each projection, so large machines capable of delivering these are required.
Used for welding of nuts and bolts and for annular ring projections (tube to sheet).
Current is concentrated by use of a narrow wheel which rotates, driving the components through the weld heads.
The welds can be overlapped, producing a gas-tight join.
Duty cycle is very high, so large transformers are necessary.
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
High frequency welding (HFI, ERW) For producing continuously welded metal tube and pipe, finned tube and for butt welding; applications include exhaust pipes, fuel lines, hydro-formed tube, and tailored blanks
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
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
Resistance spot welding The principal process for joining sheet metal components such as vehicle body parts together. Resistance Spot Welding (RSW) is widely used in the high-volume manufacture of sheet metal products. The automotive industry has relied on RSW as a principal joining method for many decades. A typical car contains between 2000 and 3000 spot welds. Take a detailed look at images and instruction on Resistance seam welding
Would you like to talk to our Team?
Maybe you are not sure which welding machine is best for you? Our Sales Team is more than happy to discuss your welding requirements.
With extensive knowledge on ALL makes and models, they can suggest the most suitable machine for your application and budget.
Between Monday and Friday during our working day of 8am – 5pm GMT, we aim to reply to your request within 2 hours of receiving your email.
Remember; we are not restricted to any one brand of Welding Machine.
Do you want a price immediately?
Call +44 (0)116 269 6941 or +44 (0)771 1919906 now