You are hereBase Metal, Filler Metal, and the Art of Welding
Base Metal, Filler Metal, and the Art of Welding
Welding always involves at least two separate pieces of metal – after all, the very definition of a weld is a heat-created join between workpieces that had formerly been separate. A weld bead could theoretically be laid down directly on the surface of a single piece of metal, but unless you are creating a piece of artwork with a TIG welding machine, then it would serve no practical purpose.
The pieces of metal which are actually being joined together are called the base metal. The welding arc usually melts the edges or surfaces of both pieces of base metal, allowing the two masses to flow together at that point and form a joint. Elements of both pieces of metal, in other words, are rendered molten and become part of the final weld bead, uniting the base metal into a single overall piece.
The use of filler metal
The base metal itself, however, rarely supplies enough metal to create a good weld bead. Instead, extra metal needs to be added during the welding process, often a considerable amount thereof. This metal is known as filler metal, and is added in one of several ways.
In both MIG (metal inert gas) and stick welding, the filler metal is also the electrode, and is fed through the welding gun, carrying the electric arc at the same time as it is melted by it. MIG filler metal comes in a long wire which comes off a spool through a series of rollers, while stick welding involves using short, inflexible “sticks” instead.
TIG welding, on the other hand, uses a tungsten electrode which is not consumed during the welding process, and a separate welding rod that is added to the pool by hand. This is a skilled operation that requires a steady hand and good judgment, but can produce some of the best welds possible – narrow, clean, strong, and extremely precise.
Welding metals by type
It is one peculiarity of welding that a true weld can only be created between two pieces of the same base metal, usually using filler metal of exactly the same type of metal, too. There is a simple reason for this, rooted in the basic physics of metal.
Each metal has its own melting point, so if you try to weld two different kinds of metals, either one will still be solid and inert when the other is turning molten, or else you will need to use such extreme heat to melt both that the metal with the lower melting point will either become completely liquid and run away, with the arc blowing holes through it, or else it will actually vaporize – either outcome, of course, ruining the weld and probably both pieces of base metal as well.
The only instance of welding different metals is braze welding, which is effectively no more than soldering on a grand scale, using brass filler metal as the “solder”. This produces welds of inferior quality and lessened strength, but can be used when it is absolutely necessary to weld dissimilar metals.