Welding is essential in the manufacture of buildings, bridges, cars, aeroplanes, pipelines, power stations and a host of other structures and objects. There are four main welding techniques used in the modern manufacturing and construction industries.
Welding is a process that is rarely seen, oft-forgotten, and largely invisible – out of sight, out of mind. Disregarding it, however, could also leave you severely out of pocket. That’s why it pays to take welding and fabrication seriously in the steel window industry.
But this begs a fundamental question – given that there are so many different welding techniques, which is the right one for a specific application? There are essentially four main types of welding.
Gas metal arc welding (GMAW) and flux core arc welding (FCAW) use the same core process – consumable electrode wire is automatically fed into the welding arc so that users do not need to replace the electrode as often as they do in, say, shielded metal arc welding (SMAW).
A wire feeder synchronises with the power supply to deliver wire from a spool at the appropriate speed. Most electrode wires also require a shield gas which feeds through the same cable as the wire. However, with self-shielded flux-core wire, the wire produces its own shield gas and protective slag.
The tip conducts electricity through the electrode wire. A gas diffuser releases the gas into the nozzle, which then blows out around the weld puddle to repel contaminants. When gas, wire and electric power are united properly, the wire melts steadily into the workpiece.
The amperage, voltage and wire speed used in GMAW/FCAW will vary depending on the metal being welded and the type of wire being used.
GMAW and FCAW have many different options for nozzles, tips and diffusers. Protruding tips and tapered nozzles can aid welding in narrow spaces while recessed tips enable higher burn-off rates.
Self-shielded FCAW does not normally require a nozzle as there is no external shield gas. However, FCAW with a shield gas is extremely resistant to atmospheric interference like wind.
GMAW and FCAW welding tips
- Be sure to follow safety and setup procedures in the owner’s manual.
- Varying the wire feed speed/amperage must be done manually. The thicker the electrode wire, the higher the wire feed speed and the more amperage that is required to burn off the electrode wire.
- Increasing wire feed speed and voltage or increasing wire thickness will increase the rate that filler metal is deposited to the workpiece.
- Most automatic wire systems maintain a voltage. However, voltage can be varied on a machine manually to alter the distance between the tip and the point where wire burns out (the ‘stick-out distance’).
- How a user welds can greatly affect weld properties. The angle of the tip and the travel speed while welding can alter the weld depth.
Shielded metal arc welding (SMAW) – commonly known as ‘stick welding’ – is one of the most widely used welding processes for joining metal. For stick welding, each electrode has a metal core that can contain different types of metal and an outer covering of flux.
The flux coating shields the arc from contaminants in the air, making the finished weld stronger. Flux also helps eliminate tiny holes that can form in the weld (metal porosity), as well as cracking, undercutting, and spatter.
If an electrode has absorbed moisture, using an electrode oven to dry it out can restore its ability to deposit quality welds.
Mastering the following five elements should ensure successful stick welding:
- Current: using the appropriate current (AC or DC) is imperative.
- Length of arc: the distance between the electrode and workpiece should be the length of the diameter of the electrode’s core wire.
- Angle of electrode: the angle of the electrode affects weld penetration. Too much penetration can make the weld brittle and lead to stress cracking and create holes in the metal; too little penetration can result in a weak weld.
- Manipulation of weld pool: as stick welding is performed, gas pockets can form which can compromise weld integrity. These can be eliminated with a slight side-to-side motion when welding.
- Speed of travel: A weld speed that is too slow leads to a weld bead that is too large while a fast weld can lead to a weld bead that is too narrow.
SMAW welding tips
- Take care when handling stick welding electrodes. Rough handling can cause the flux coating to break loose from the core wire, rendering the electrode unusable.
- Don’t use an electrode if the core wire is exposed because the missing flux will cause welding defects and result in a poor weld.
- Keep electrodes dry; wet electrodes can result in porous, weak finished welds.
- During set up, set the amperage on the welding machine to match what is required by the electrode being used. If stick welding for the first time, set the amperage exactly in the middle of the range suggested for the electrode.
- If using DC machine, set the polarity according to the requirements of the electrode being used.
Gas tungsten arc welding (GTAW), commonly known as TIG (or tungsten inert gas) welding, is a versatile welding process for joining metal. Both AC and DC power sources can be used in TIG welding; which is chosen will depend on the type and thickness of the metal to be welded.
A TIG torch is an electrode holder that supplies welding current to the tungsten electrode and an inert shield gas to the arc zone. A collet-like clamping device allows adjustment so that the right length of electrode extends beyond the shielding gas cup.
TIG welding uses a non-consumable tungsten electrode and has an extremely high melting point which means that TIG electrodes can heat other metals to their melting points without themselves melting.
Argon and helium are the main shielding gases used in TIG welding. In some applications, however, a mixture of the two gases can prove advantageous. On occasion, hydrogen is mixed with argon or helium for special applications.
TIG welding tips
- A foot pedal allows the user to adjust the amperage of the machine without having to manually turn the amperage knob and is highly recommended.
- Torch position is important in TIG welding. The ideal position is 90°. However, the weld pool will be blocked from view by the torch. Angle the torch 15° to see the weld pool while maintaining great results.
- Some TIG welding requires the use of a filler metal in the form of a filler rod when there is insufficient metal present to complete a strong joint.
- Torches may be air- or water-cooled.
- GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium, magnesium, and copper alloys.