Welding metals: the main processes

Arc welding is a process of raising the temperature to the melting point of the metal to be welded, using an electric arc. It is the heat generated by the resistivity of the metals in contact with the electricity that raises the temperature to the welding point, until the metals reach their melting point.

Many welding processes use the electric arc as the source of the fusion energy, since the heat of the arc can easily be concentrated and controlled. Electric-arc welding can be divided into different methods: MIG-MIG welding, TIG welding, plasma welding, etc.

The arc welding equipment is made up of several parts:

-              The welding station (electricity generator). There are also portable electric welding stations.

-              The welding electrode: The vector of transport of the electric energy. It may either be meltable (i.e. the electrode melts and thereby becomes a filler metal) or non-meltable (i.e. the electrode does not melt).

-              The welding wire: The welding wire is the filler metal that provides the connection between the two parts to be welded; it also serves as a conductor for the electric current.

-              The welding rod: The welding rod serves (similar to the welding wire or the meltable electrode) as a filler metal. It provides a connection between the two metal parts to be assembled.

The filler metal is not systematically required in the welding process. Thin metal parts can be welded without using a filler metal. Arc welding processes can be divided into various techniques: such as MIG-MAG welding or plasma welding.

When welding aluminium, copper, steel, stainless steel, zinc or cast iron, bear in mind that every metal requires a welding method suited to its structure and to the thickness of the parts to be welded.

The same applies to plastic welding or PVC welding.

TIG welding is an arc welding process with a non-meltable electrode, in the presence (or not) of a filler metal. TIG is an acronym for Tungsten Inert Gas. Tungsten refers to the electrode and the inert gas, and is the type of plasma-forming gas used. The arc is created between the electrode and the part to be welded under gas shielding.

With the development of semi-automatic welding, TIG welding has replaced the meltable wire with a non-meltable electrode, while retaining the advantage of protecting the welding zone via a protective gas.

Since the electrode does not melt, TIG welding requires filler metal.

TIG welding requires a non-meltable tungsten welding electrode to be incorporated in the torch.

The gas is stored in a cylinder connected to the torch. The flow rate and pressure are controlled using a solenoid valve.

The TIG electric welding station is a generator connected by a cable to the part to be welded, and by a wire to the welding torch. A semi-automatic or automatic control unit allows varying the intensity of the welding current depending on the desired arc and the size of the filler metal rod.

The TIG welding torch is equipped with a ceramic nozzle that enables the flow of gas to be directed to the welding zone.

MIG-MAG welding is a semi-automatic welding process. The metals are fused by the energy generated by an electric arc that forms between a meltable electrode wire and the parts to be assembled. The acronyms MIG and MAG stand for Metal Inert Gas and Metal Active Gas respectively. The difference between the two lies in the composition of the gas.

The MIG process uses a neutral gas that does not react with the weld metal, unlike the MAG process. The MIG/MAG is used systematically when the primary concerns are efficiency (continuous welding) or when the bead thicknesses are greater, as is the case in structural steelwork.

The required equipment generally comprises an MIG-MAG welding station with a continuous feed roll of welding wire. The gas is filled in the cylinders connected to the welding torch.

Mostly used in mechanical construction, the plasma arc is a highly efficient welding process. The plasma is an ionised gas. The plasma welding process also requires using an electric arc for welding the metal, but the energy generated here is greater. This energy allows for local melting of the part to be assembled and the metal filler wire, in order to create the molten pool, and the weld bead, upon cooling.

The benefits of plasma welding lie in the quality and accuracy of the welds, which are difficult to spot. This process also allows very thin parts to be welded (0.05 mm in the case of micro-plasma). The equipment required for plasma welding is made up of several parts: a non-meltable welding electrode incorporated into the torch, a meltable welding wire, and obviously the gas in the cylinders connected to the torch.

The energy is generated by a laser beam that greatly and very quickly increases the temperature of the materials to be welded. Laser welding provides extremely high precision and speed. Moreover, the welds made using this process are almost invisible.  

This is why this process is recommended for any application requiring extreme precision in different industries, including automotive, medicine and even goldsmithing. Laser welding is executed using a laser welding machine.

This process does not involve many separate parts, as is the case for the various electric-arc welding techniques.

This is a special welding process that involves the continuous, 360° rotation of an arc around a cylindrical part. Cylindrical shapes such as pipes make manual welding difficult, but not impossible. Mechanised orbital welding allows the operation to be controlled with programmed welding parameters.

Most metals can be welded using this process: The strongest steels, the steels most resistant to heat and corrosion, non-alloy or low-alloy carbon steels, nickel alloys, as well as titanium, copper, aluminium and their alloys.

In France, there are 200,000 employees whose main activity is welding. They use specialised protective equipment to protect themselves from the risks related to this activity. The main risks related to this activity are chemical (welding fumes), thermal (heat released by the welding processes), ocular (emitted radiation) and electrical.  

The personal protective equipment of the welder includes:

-  a welder’s helmet or welding helmet with a visor made from a suitable material (for electric welding) or goggles with suitable lenses (for blowtorch welding). If necessary, a welding hood. 
- leather gloves with cuffs
- protective footwear and leggings
- workwear (overalls with trousers, vest and hood) made of fire-resistant cotton or non-flammable technical textile, with a leather apron
- Noise protection depending on the level of noise.

The personal protective equipment complements the collective protective equipment that is found in workshops or on jobsites. When possible: specific precautions must be taken, such as the local exhaust ventilation of welding smoke.

Or, the UV protection of the staff, using opaque welding screens of a sufficient length to separate the work stations. 

The Expo Permanente website allows you to get in touch with specialised suppliers of welding equipment or the protective equipment related to the activity. You can contact them to ask for advice and quotes free of charge.