An arc welding machine may appear to be a mysterious piece of equipment that has many inexplicable features to the layman, but in fact, it is a highly developed and eminently practical tool for bonding two pieces of metal together almost as strongly as if they had been made in one piece to begin with. Each part has its function, and this is true whether the is a large, wheeled ‘shop’ model or a compact type that can be carried with a shoulder strap wherever the user can go – onto ladders, into difficult corners, and so on.
Creating the weld with electrode heat
Arc needs several features to produce a strong, viable weld over a long period of working time. The first necessity is to create molten metal at the join between the two pieces of metal that are to be welded. This can be accomplished by heating the edges of the two pieces of metal to the melting point or, in many cases, by melting a piece of ‘filler metal’ which acts as a kind of solder for the welding process. The filler metal may be a short metal rod which doubles as the arc welder’s electrode, a continuously-fed wire which operates in the same way but without the need for constant changes of rod, or a separate filler metal wire melted by a permanent electrode.
In all cases, the metal is heated to the melting point by electricity in the ’s welding gun. The electrode can be positively or negatively charged, depending on the type of weld desired, and it is usually possible to switch between a positive and negative electrode charge in the same . A positive charge produces intense heat, which makes the welding process faster and increases the penetration of the weld, making it suitable for thicker metals. A negative charge produces cooler, slower, shallower welding that is good for finer work and thinner metals.
The role of gas shielding
In order to make a successful weld, several other factors are needed besides heat and molten metal at the join. When metal is heated intensely and rapidly, it tends to rust or oxidize at an extremely fast rate – within a second or two when it is heated enough to be molten. If the metal in a welding join were to oxidize, it would leave brown stains on the finished metal, and almost certainly weaken the weld – possibly enough to render it almost useless, and certainly enough to cause a risk of ongoing oxidation damage.
Oxidation only occurs when there is oxygen in physical contact with the metal, however – so all arc make use of gas to shield the hot metal from the air. The time that the metal needs to be shielded is very brief, so the gas shielding is provided at the point of the weld itself by various mechanisms. One way is to coat the filler metal with a flux that vaporizes into a gas around the molten metal, which effectively blocks air but leaves a lot of residue, or slag, on the project’ surface. Another solution is to have a gas tank in the itself to feed gas through a hose that blows it out around the welding point. The gas used is generally argon, sometimes mixed with helium, since it will not combust or explode in the electric arc of the welder.
The grounding clamp and welding gun
In order to create a complete electrical circuit through the , the welding gun, and the object to be welded – a circuit necessary for the arc welder to work – a grounding clamp must be attached to either the piece of metal being welded or the welding table. Once this is in place, arc welding becomes possible, although it also means that a good deal of care should be exercised by the welder, since a live current is present in the metal that is being welded. Finally, there is a welding gun – the piece of equipment the operator holds and actually uses to carry out the welding job.