We looked at stick welding in December, used mostly for repair and fabrication, depending on time available and an individual’s ability.

Not so commonly found on farms are metal inert gas (MIG) welders, sometimes referred to as CO2 welding.

MIG welders have a role on farms, but lack the flexibility of a stick welder.

They require some form of Argon-based gas for shielding the welding process. The wire consumed in the process is prone to rust if not kept in the proper environment or used quickly.

An MIG welder is a workshop machine. It is neither suitable for use outside nor very mobile.

MIG welders do not like rust or paint and will not burn through to weld like a stick welder does.

On the plus side, MIG welding is a much faster process. It is very clean welding with no slag produced.

MIG welding is also very easy and fast to learn and perform to a reasonably competent level. Someone who struggles with a stick welder could potentially pick up the MIG process quite easily.

Welding light material is far easier. The process can be controlled by triggering the welding torch or spot welding to affect a repair. If required, vertical welding is much easier to do.

How MIG welding works

MIG and metal active gas (MAG) welding are both types of gas metal arc welding (GMAW).

GMAW is a welding process in which an electric arc forms between a consumable wire electrode (similar to stick) and the work piece metal or metals. The process heats the work piece metal or metals, while the welding wire is fed into the molten pot and all are joined together in the process. A shielding gas is also fed out through the welding torch or gun to protect the weld from external contaminants in the air.

Today, GMAW is the most common industrial welding process preferred for its versatility, speed and the relative ease of adapting the process to robotic automation.

Gas

Shielding gases fall into two categories; inert and semi-inert. Inert or noble gases are stable and are useful in preventing undesirable reactions from taking place. In welding, this reaction is generally with oxygen or moisture which would contaminate and/or weaken a weld.

Semi-inert shielding gases, or active shield gases typically include carbon dioxide, oxygen, nitrogen and hydrogen. When used in small controlled quantities, they can improve weld characteristics.

Picture one

There are many MIG welding unit options, with prices typically starting at around €250 for a 100 amp unit. This could rise to around €3,500 for a 400 amp unit (all single-phase).

Unit choice will depend on your budget and what you intend using it for. A mid-range 180 amp MIG welder will happily handle 0.8mm welding wire at a range of amperages. This would allow satisfactory repair of light panels, while also fabrication of standard wall 2in box section, for example.

Heavier fabrications involving a 10mm plate for example may require up to 100 more amps and 1mm wire for comfortable fabrication.

Picture two

Choose a detachable welding torch assembly, where elements can be replaced as they become worn or damaged.

For example, coiled in the centre of the picture is a liner through which the welding wire is fed through to the welding torch. These can become worn or damaged requiring replacement.

Picture three

This is a dismantled view of the business end of a larger welding torch. Just protruding is a liner through which the welding wire is fed.

Next is the gas diffuser for shielding the welding process.

The welding tip screws into this and is available is different sizes to suit different diameter welding wire. A two-piece cone shield directs the gas around the weld. Cones become damaged during the welding process and this two-piece design allows the nose section alone to be replaced.

Picture four

Welding wire is available for mild steel, stainless steel, aluminium and more. Diameters include 0.6mm, 0.8mm, 1mm and 1.2mm. The 1mm diameter wire is by far the most commonly used. Roll sizes include 15kg, 5kg and 0.8kg (for mild steel). The 5kg roll size is useful for a farm where a MIG would occasionally be used.

For farm workshops, it is advisable to remove the roll of welding wire to a dry environment. A rusty roll will cause trouble and could damage a perfectly good liner.

Picture five

The range and variety of gas bottle sizes is extensive and limited by their cost. That is the cost of the gas and rent of the gas bottle.

There are rent-free options available, so check pricing options before purchasing a MIG welder for the farm.

Pictured are three typical gas bottle size options from IIG-Irish Industrial Gases c/o JJ Bolger Ltd, Enniscorthy; 11.27m3, 4.84m3 and 2.42m3.

Picture six

These are the essentials for MIG welding – a standard flip-up welding mask, a pair of welding gloves, a wire brush and a snips for trimming wire over-runs. Other PPE-should include safety glasses, flame resistant/cotton overalls and suitable boots.

Picture seven

There are a couple of different gas regulator options. On the left is the vertical unit with a float inside it while on the right is a conventional gauge. The typical gas flow rate is around eight litres/min, read while welding/torch is triggered. If the weld is porous or the workplace draughty, then the rate will have to be increased to produce an effective weld.

Picture eight

Welding with a MIG unit is slightly different than a stick welder in the sense that you push the torch in front of you rather than dragging it along. This can take getting used to and practice makes perfect. If you hold the welding tip too low, the shielding cone picks up on the molten weld – too high, and the weld is not shielded properly and is porous.

Weld number one is what you aim for, a nice rounded profile with decent weld penetration.

The second weld is when the amperage is set too low, producing this high-ridged weld with no penetration.

At the end of weld three, you can see where the gas runs out/switched off. The weld takes on a porous appearance. Weld four is produced with the shielding gas off – it is porous, which compromises the weld strength and integrity.

Picture nine

Welder settings are pretty basic – amperage and wire feed speed. Wire feed speed can take a bit of fiddling with to get right. Too fast and the wire pushes the torch away, jumping off the work piece. Too slow and weld splatters onto the work piece or wire burns back into the tip.

Just right and you hear a constant frazzle, a bit like rashers frying on the pan but at a much faster rate.

Picture 10

A common mistake when setting up an MIG for the first time is not setting enough tension on the welding wire drive wheel. This can cause uneven wire feed or burn-back into the tip, particularly if the welding torch lead is at an acute angle.

Too much can cause nesting of the welding wire in the feed house if the wire feed speed or amperage settings are not in sync to burn what is being fed out of the torch.

Health and safety