An electric welder has become a staple in the workshop these days, modern machines making welding much more accessible to more people. In some cases prices have come right down too, which should make them a tempting prospect for anyone who looks after their own cars.
Welding with an electric arc has been around in various forms since the 19th century but the favourite for home mechanics today is the Metal Inert Gas (MIG) welder. Since they’ve become so widely available, MIG welders have been a revelation because in some instances they produce far better results than oxy-acetylene or straight arc welding.
MIGs are beautiful, simple things and with a bit of practice, a following wind and good preparation, it’s relatively easy to get a good result on thin as well as thick steel. Preparation is the key word here because MIG welding won’t tolerate a rusty or dirty surface. The closer to forensically clean the surface is, the better quality the weld.
MIGs feed wire through a torch which also carries a stream of inert gas from a canister or cylinder. The wire forms one electrode and the work piece (connected to the other terminal of the welder) the other.
When welding starts, an electric arc is created between the wire and the job and because it’s shrouded in inert gas the weld should be uncontaminated, strong and shiny. The wire also acts as the filler rod, fed through the torch by a powered spool in the machine body as it melts into the weld pool. It’s such a perfect concept, the MIG welder is probably one of the most fun tools to use in the entire workshop.
£250-£300 will buy a decent quality MIG welder with perhaps high and low power settings and two voltage settings which can be selected at each level, giving four settings in all. It will also have a wire spool speed control which can be set for set according to the power setting and the rate at which the wire is being gobbled up. The operating range will typically be around 30-135amps and it should take a variety of wire sizes (maybe 0.6mm-0.8mm).
The choice of wire diameter is linked to the thickness of the material and the power being used. Thinner wire and a low power setting are ideal for car bodywork and thicker wire in combination with a high power setting for thicker gauge work pieces. A machine like this can weld steel with a thickness of around 0.7mm up to 5mm or 6mm. A 5kg spool of wire costs under £20 and is easy to swap out, along with a screw-in feed tip of the corresponding size.
To confuse matters a little, some (but not all) MIG welders these days can be used in both gas and gasless mode. A different kind of wire with a flux core is used for gasless welding. As the wire melts, the flux emits an inert vapour which shields the weld from the surrounding oxygen and for that reason they should only be used in well ventilated conditions.
Gasless welding has an advantage in outdoor, windy conditions where a gas shield would be blown away, producing a slag-infested, poor-quality weld. If pushed, they can also handle metal that isn’t perfectly clean and de-rusted. In the workshop though, the gas version is the best option so look for welders that are advertised as “gas” or capable of both and make sure what you’re buying comes with a regulator and hose ready to go.
Gas MIG welders can come set up with small, cheap pressure taps for use with disposable gas canisters but for frequent use it makes more sense to use larger industrial cylinders. In that case, the cylinders themselves are rented, either by paying a deposit, or in the case of British Oxygen, opening an account and paying an annual rental fee. In both cases the cost of the gas for each fill goes on top. Using a cylinder requires the use of a proper regulator with a pressure gauge so it’s worth checking what your choice of welder is supplied with.
Welders usually come with a basic, fixed lens mask to protect the eyes but they’re so dark it’s virtually impossible to see anything through them until the arc strikes up. An essential part of the kit is an auto-darkening helmet which is clear until the instant the arc strikes. Luckily, the price of these has fallen and they can be picked up for just over £20 from tool stores or online.
Safety-wise, an electric MIG welder is unlikely to kill anyone as the combination of voltage and current isn’t high enough. The main danger is to the eyes and under no circumstances should an electric arc be looked at directly by either the welder or a bystander. Welding without gloves or covering up is a bad move too because spattering from the weld burns the skin and ultra violet light from the arc causes sunburn. A pair of lightweight leather welding gauntlets is ideal, giving protection but also plenty of feel.
Tune in next time for some tips on using MIG welders, what steps to take when working on the vehicle rather than the bench and how to get good results using them.