5. Brazing and Welding – Important Differences

In welding two metals are melted together.   In brazing two or more materials are joined by the use of a third, dissimilar material.  In brazing the greatest strength is achieved by a chemical reaction between the braze alloy and the metals on either side.  To do this the materials need to be in close contact with no interfering layer.    

1.  Cleanliness is much more important in brazing than welding.   Good welders clean before welding.  However the heat of welding does burn out contaminants.  In cases where the contaminants do not ‘burn out’ the residue is mixed in with the molten metal. 

In brazing there is less heat so the contaminants are less likely to burn out.  Instead the contaminants are often transformed into a hard layer that prevents bonding.   

See articles on ‘Cleaning Steel Before Brazing’ and ‘Trying To Clean By Burning With A Torch’

2.  Joint design is very different in the two processes.  In welding the two pieces are placed in contact and a bead is run down the edges.  The joining is done on the edges.

In brazing the joining is done over the entire surface of the two mating parts.  In many cases leaving small fillets on the sides can increase joint strength by up to 40%.   

See article on ‘Brazing carbide in a Notch’