Saturday 22 September 2018
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Understanding The Difference Between DC and AC Welding

Welding refers to the combining of two metal parts or more together. Although it is often mistaken for being the same as soldering, it is different in that soldering is just using molten metal to attach two separate surfaces of metal together. An electric current powering specialist welding equipment is used to weld pieces of metal together because the majority of most metals have a high melting point.

Shielding, Filler Metal and Welding Arc

Welding as a process is broken down into three parts – welding arc, the filler metal and shielding for the weld. What is known as a welding arc is the continuous spark started from a piece of welding equipment and heats the metal with 1000s+ degrees Fahrenheit. A circuit that is sent through the equipment to the metal that needs to be welded creating a spark. The filler metal is an extra metal that is added during the welding process to strengthen the newly welded joint. Air can contaminate welds when they are not set, so a shielding of some kind has to be used until this happens to protect it from the air. Shielding is generally accomplished by using a shielding gas during welding. This can either be done using filler metal with a special formulation that releases gas as it starts to melt or by using a shielding gas during the welding process.

Polarity of Welding Arc

Similarly to any other form of current passing through an electrical circuit, welding arcs have a polarity, with both a negative and positive pole. The weld strength is effected significantly by the polarity. A positive or electrode-negative polarity causes a more shallow penetration in the weld than reverse or electrode-positive polarity. That being said, for quicker filler metal deposition, electrode-negative polarity is best. The polarity will always be a constant when a DC or direct current is used. In a 60 hertz current though, using an AC or alternating current, it switches 120 times every second.

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Which Is Best?

The welding type that most people tend to prefer is DC welding. A smoother weld is produced by DC, regardless of whether you use electrode-negative or electrode-positive polarity. While DC delivers a current that is consistent and continuous, AC by its very nature produces one that swings between positive and negative. While the polarity swings, it will eventually pass an area with zero output current. Though this only usually occurs for a small fraction of a second, it is enough of a disruption to cause the arc to extinguish flutter or even just fluctuate. See for a great range of machines available.

When Do Welders Use AC?

AC welding is only rarely used because DC welding is far superior. When there are no DC welding machinery available, AC welding equipment may be used. Often, in an unflattering way, these are called buzz boxes and are seen as beginner’s technology. Arc blow problems can sometimes be fixed with AC welding. This happens when an arc blows or wanders out of the joint that is being welded. Which normally occurs when working with high level current, large-diameter electrodes.

As we are living in a very digital-centred world these days, this has changed the landscape of welding too. In keeping with the evolution of technology, we have started shifted towards using more welding machines.

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