MIG WELDER

▶ There are plenty of MIG welders in this price category, but which one should you choose? There are a few considerations to note when deciding. The first is whether to buy a gasless MIG welder or one that uses a gas cylinder. Strictly speaking, there’s no such thing as gasless welding. The purpose of the gas is to form a barrier around the weld pool to protect it from oxygen in the air that results in contamination. This is achieved with a gas cylinder containing carbon dioxide or argon and carbon dioxide, whereby the gas provides that protection. If a MIG welder doesn’t have a gas cylinder, then a self-shielding MIG wire is used, which provides its own barrier to oxygen in the form of a gas – so there’s really no such thing as gasless MIG welding. Gasless welding produces a fierce arc that’s not suitable on steel thinner than 1.2mm thick. It should only be conducted in the open air (well-ventilated) because of the amount of smoke and waste gases produced. Due to the availability and low cost of small gas cylinders (some can be hired), we recommend investing in a MIG welder with a gas cylinder. MIG welders are rated in amps, which provides some indication as to the thickness of two pieces of steel they are capable of welding together. These claims or figures vary between manufacturers, but as a rough guide, a 90-amp MIG welder is a suitable ‘hobby’ machine that can weld steel up to 2mm in thickness. Find out what the minimum amperage is on a MIG welder as this is useful for welding thin steel. 30amps for example is suitable for 1mm-thickness of steel (not to be confused with a MIG welder that needs a 30amp supply). The amperage is adjusted by the power range control on a MIG welder. Whilst most entry-level MIG welders are powered by standard 13amp mains electricity, a MIG welder with an amp rating greater than 150 needs a 32amp round blue plug and dedicated wiring, unless you only operate it on its lower amperage settings. If your garage or workshop doesn’t have such a supply, then it may be possible to connect a suitable 6mm cable from a domestic fusebox and install an additional one with the required socket. A qualified electrician will have to do this job and it should cost around £200. Check the duty-cycle of a MIG welder. This is a rating for how much time you can spend welding before the welder has to be left to cool down to avoid overheating it. These figures are provided by the manufacturer of the welder. They may stipulate for instance, a 70% duty-cycle at 90 amps over 10 minutes. This means you can weld at 90 amps for 70% of 10 minutes (seven minutes) before you have to stop for three minutes. Fortunately, most car bodywork welds are performed at low amps, so the duty-cycle may not apply. However, some welders have a thermal cut-out to safeguard against overheating. Turbo welders have a fan to help with cooling. When you’ve acquired a MIG welder, read through any literature supplied with it to find out what thickness of welding wire is recommended along with the settings for wire feed and power. There should also be instructions on how to correctly fit a reel of welding wire and how to properly maintain your welder. Do not buy a MIG welder with a permanently live torch. This is where the MIG welder doesn’t have a contactor that activates the supply of electricity to the welder’s torch when the trigger is pressed. Instead, it’s permanently live, which means you’ll start welding whenever you touch something the torch can earth to. Always check this with the manufacturer of the MIG welder before buying one. Some of the latest MIG welders use an inverter. Traditionally, a MIG welder uses a copper wound transformer to regulate the power output, which usually provides a range of fixed power output settings. The latest MIG welders use an inverter (look for IGBT – insulated gate bipolar transistor), which is lighter than a transformer, smaller, requires less power input, offers a higher duty-cycle and provides finer control of the power output so there’s more chance of finding the right power setting when welding.