Spot welding machine buying guide
Michael, Professional and passionate welder, Sheffield62 guides
How does spot welding work?
What phases does the process consist of?
- Docking: metal sheets are placed between the electrodes;
- Welding: current is applied across the plates;
- Forging: sheets are held under pressure;
- Release: electrodes are pushed apart to release the plates.
What does a spot welding machine look like?
As is often the case with machine tools, there are two types: portable (for ease of use but with limited performance); and stationary (better suited to intensive work and thicker metal sheet).
- Portable spot welders are compact, lightweight and handy for difficult-to-access joints. As such, they are most commonly used in coachbuilding. They have an average welding capacity of 2 + 2mm and are relatively inefficient due to the fact that the electrodes aren't cooled between cycles. Automatic adjustment makes it easier to adjust the spot parameters according to the thickness of sheet and welding head used.
- Stationary spot welders are mounted on a column with a jack and mobile arms. The frame is heavy and bulky and the machine has a welding capacity of 0.5–10mm. The body of the machine often equipped with a 380V generator and two arms with a mechanical, pneumatic or hydraulic jack to adjust operating height, as well as heat-resistant electrodes made of copper or copper-chromium alloy. No electric arc is produced, and the arms are water-cooled in closed circuit. The arms and electrodes are interchangeable to vary spot size and form across different types of weld.
What type of sheets can be welded?
Metals such as stainless steel, aluminium, steel alloys and galvanized steels can be spot welded, subject to operating adjustments (current, welding time, intensity of compression).
Unbuttoning - or how to check weld quality
How to choose your generator?
- Mains voltage (i.e. 230V) will allow you to run a portable machine; for a fixed welder, you'll need 400V and probably a compressed air supply for the actuator;
- Power has a direct influence on a machine's ability to weld thicker sheet metal;
- Operating factor is expressed as a percentage, for a given amperage (eg 70% at 100A): for 10 minutes of use, this corresponds to 7 mins of welding and 3 mins of cooling. This factor is inversely proportional to the operating current (so a higher-current device offers better operating efficiency).
- Spot current is of the order of 3–6000A for portable machines, and up to 15000A for stationary machines, its value dictating the quality of the weld;
- Secondary vacuum voltage is the voltage measured at the terminals of the welding machine before the welding current is applied - a key indicator of priming quality;
- An isolator fuse provides protection against voltage surges.
- Interchangeable arms to suit different formats of metal parts;
- A wide range of electrodes will let you produce a range of different spot welds.
Are there other variants of spot welding machines?
Yes - two!
Can you summarize the applications of a spot welder?
A word about safety
Learn more about metalworking tools...
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Michael, Professional and passionate welder, Sheffield 62 guides écrits
I was trained as a pipe worker and welder and worked in the industry for 15 years, going all over the UK for large-scale projects. When I decided it was time to stay closer to home - to have time for my own DIY - I took over a local metal shop and eventually went on to become head of a professional engineering firm.
I'm retired now, but I haven't stopped working with my hands. I recently built my own metalwork studio at home - a lifelong dream! I use my welding skills to make sculptures and bespoke furniture. With my studio, I managed to find a piece of paradise where I can let my imagination run wild.
I also love going around to local auctions and boot sales. I always find some interesting old object or tools that I can add to my collection or transform into works of art.
Now that I have the time, I've turned my hand to decorating, painting on canvas and gardening. I'm always developing new technologies and tools to bring my ideas to life. And I'm always happy to give others advice on how they can make their dreams a reality, too!