Welding & Metalwork: Fundamentals
Put simply, welding is a process that uses heat to join metal to create a strong bond.
The heat, commonly generated with an electric arc or gas flame, needs to be hot enough to melt the metals being welded. the melting process is usually accompanied by a filling process, where additional metal is added to make a strong joint.
Brazing and soldering are not welding processes by definition as the parent metal is not heated to a temperature sufficient to melt it. Instead, silver, copper or lead alloys are used to 'glue' the metals together - the heat simply melts the glue and encourages it to adjere to the parent metal.
As most welding methods use an electrical arc to generate heat, it is useful to have a basic understanding of how electricity works during welding.
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Heat and Electricity - The Basics of Welding