Fusion Welding is defined as melting together and coalescing materials by means of heat.

The word coalescing means to unite, to merge, to join, to combine, to fuse or to amalgamate.

But in this Fusion Welding principals, coalescing means the used of Filler Metals which are metals added to the weld area during welding.

For your information, not all Fusion Welding requires Filler Metal.

There are also Non Fusion Welding techniques and approaches. Fusion welds made without the use of filler metals are known as Autogenous welds. Autogenous means "arising from within or from a thing itself. But in this case, Autogenous welds means "the welding done either without solder or with a filler of the same metal as the pieces being welded".

[caption id="attachment_376" align="aligncenter" width="300" caption="Coalescing means the used of Filler Metals which are metals added to the weld area during welding"][/caption]