TPi January 2020

Choosing the right welding technique for the task at hand By ESAB, Germany

GMAW and FCAW welding tips

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. 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 modern manufacturing industry and construction, as explained below. 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 is why it pays to take welding and fabrication seriously. 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.

1. Be sure to follow safety and setup procedures in the owner’s manual. 2. 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. 3. Increasing wire feed speed and voltage or increasing wire thickness will increase the rate that filler metal is deposited to the workpiece. 4. 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’). 5. 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. If there is too much penetration it can

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TUBE PRODUCTS INTERNATIONAL January 2020

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