Oxyacetylene Welding is not used in high responsibility fusion welding because fusion welding requires two metals to be fused without melting whereas Oxyacetylene Welding involves the melting of metals so this process is not suitable.

By Makeveli

non fusion welding is when there is no filler metal needed...Actually all welding is considered fusion welding, meaning the material fuses together unlike soldering. The material has to melt to fuse.

it should be called solid state welding which does not melt the base... in fusion welding the base melts as you weld.

Fusion is the blending of elements and can only be achieved by melting. Welding by definition is fusion. Brazing ,soldering etc are non fusing.

Fusion welding is just any welding process which inhibites the phase trasition from solid to liquid and then back to solid state, while electric resistance welding is based on purely ohmic heating of the different parts, this heat will create fusion of the metal. So; Electric resistance welding can be said to be a type of fusion welding, but not the other way around.