Welding is a process in which both the participating metals are metaled and re solidified to complete as one metal. Proper melting of mating parts is a basic criteria to result a sound weld.
In case of Brazing both the participating metals are not melted but a third metal of lower melting point is used to be filled in between the two. The solidification of this third metal results the joining.
The filler metal is drawn into the gap between the closely fitted surfaces of the joint by capillary action.
The design of the joint should incorporate a minimum gap into which the braze filler metal will be drawn.
Welding joints are strongest joints used to bear the load. Strength of the welded portion of joint is usually more than the strength of base metal.
Brazing joints are weaker than welding joints. This can be used to bear the load up to some extent.
In Welding,To join, work pieces need to be heated till their melting point.
in brazing Work pieces are heated but below their melting point.
In Welding, Heat cost is involved and high skill level is required.
In Brazing, Cost involved and skill required is lower than welding.
In Welding, Mechanical properties of base metal may change at the joint due to heating and cooling.
In Brazing, mechanical properties may change at joint but it is almost negligible.
In Welding, Temperature required is 3800°C in welding joints.
In Brazing, Temperature may go to 600°C in brazing joints.
In Welding, Heat treatment is generally required to eliminate undesirable effects of welding.
In Brazing, No heat treatment is required after brazing.
In Welding, No preheating of workpiece is required before welding as it is carried out at high temperature.
In Brazing, Preheating is desirable to make strong joint as brazing is carried out at relatively low temperature.