During any braze process, the temperature of an assembly is raised high enough to melt a brazing filler metal (BFM) placed in, or next to, a joint in that assembly that is to be permanently joined together when the BFM melts and flows into the joint by capillary action. After brazing, the assembly is then cooled back down to room temperature, inspected/tested and placed into service.
Now, if I go back and braze that assembly a second time to add another component to it, I am technically re-brazing the assembly because I’m sending the assembly back into the furnace a second time for another brazing process to be conducted on the part. In such a description, re-brazing is a general term that can be applied to that total assembly.
However, there is a fine line between the description I’ve just given in the previous sentence and a very specific question that some people ask. This is, “If I send that assembly back into the furnace a second time to add on a new component to the previously brazed part, am I actually re-brazing the first joint again?” Technically speaking, you are NOT re-brazing that first joint IF the temperature of the second braze is much lower than the brazing temperature used the first time the assembly was brazed. So, there would be no chance of that first brazed joint remelting at the brazing temperature used for that second braze.
The brazing industry is very familiar with another phrase applied to multiple braze runs performed on one assembly for the purpose of adding components onto the part in each subsequent braze run and not remelting any of the previous brazements. The phrase for such a procedure is known as step-brazing.
Step-brazing can occur as many times as needed, as long as each subsequent braze run is done at a lower temperature than the previous braze runs so that the previous BFMs cannot possibly be remelted. As an example, step-brazing is the term to be used if I were to make a first braze using a nickel-based BFM at 2000°F (1100°C), add a new part to the assembly and silver-braze it at 1700°F (925°C), and do a third addition to the part, brazing it with a low-melting silver-braze at 1350°F (730°C). In this step-brazing process, each subsequent braze is done at a much lower temperature than the previous one to prevent any possible melting of any of the previous brazements. Again, such a process is called step-brazing and should not to be called a re-braze of any specific joint in the assembly.
Having said that, what do we call a process in which I add a component to a previously brazed assembly and use a BFM for the second braze that melts/flows at about the same (or higher) temperature than the first braze? Under such a situation, you would be bringing the first brazed joint back up to (or higher than) its original braze temperature with the possibility that that BFM might remelt. In such a case, it can correctly be called a re-braze because you are bringing the part back up to its original brazing temperature (or higher). This is true even though the purpose of that second braze was to merely add on a component to the assembly and not merely to reflow the first braze.
Obviously, if you reheat the first braze joint above its original braze temperature for the purpose of correcting a problem with that first joint, and you want the BFM in the joint to reflow, then we are all familiar with using the phrase re-braze in such a situation.
But, as mentioned earlier, the phrase re-braze could also be correctly used whenever you are raising the furnace temperature to (or above) the original braze temperature since it is possible during that second braze run to reflow (or significantly enhance the diffusion of) the BFM in that first joint.