Brazing is a joining operation that’s used to attach individual components together where other attachment or joining methods such as riveting, fasteners or welding are not possible. There are two common types of brazing methods used in aerospace, Torch Brazing and Induction Brazing. Advance Welding is Nadcap accredited for both processes.
Brazing involves holding two or more parts in the right position for the final assembly and flowing a ‘melt’ or low melting point metal into the joints between the components being joined. Brazing is most often done to metal parts where the high temperature required for welding would distort the parts or cause damage to perhaps electrical or electronic components mounted on the parts or there is no space or accommodation for other joining methods. In order to avoid high temperatures that would affect the parts themselves, a filler metal with a much lower melting point than the base metals is used. This means that brazing is most often done with silver, copper, silver-copper alloys and sometimes aluminum.
Aerospace Torch Brazing
Torch brazing is a method of joining two materials together by adding a filler metal with a protection of flux such that the metal flows between the work pieces and when cooled it forms a bond combining the two components. This process is called wetting. In brazing, a material is used for the filler with a melt and oxidation point significantly below the workpieces temperature, which separates it from welding where the workpieces are joined through melting and fusing of the component parts.
Torch brazing is ideal for small scale production and specialized operations, it can also prove useful in hard to reach applications. It is versatile and has an ability to produce high quality and repeatable attachments where welding is not possible.
Aerospace Torch brazing can be done in three methods: Manual, Machine and Automatic
Manual torch brazing involves a hand held or fixed torch, it requires skill and is labor intensive but it is the most versatile means of brazing. Machine torch brazing is great for repetitive processes where an operator needs to precisely control the placement of the attachment point. In machine torch brazing, the actual brazing operation is handled entirely by the machine under the direction of a skilled operator. Automatic torch brazing allows for a fully mechanized brazing machine that will retrieve the materials to be joined, adjust the pieces, perform the brazing operation and ensure that the assembly properly cools before any loads are applied on the joint. In automatic torch brazing an operator may monitor the process and may provide pallets or bins of parts and remove completed assemblies to the next staging area or operation. Automatic torch brazing allows for higher production rate and more uniform quality. Advance Welding provides Manual Torch Brazing.
Aerospace Induction Brazing
An alternative to torch brazing is induction brazing. In induction brazing, an AC coil is used to stimulate a current in the materials to be joined. This causes the materials to heat up to the point where a brazing melt (filler) can flow.
Induction brazing has the advantage of not using a flame which can be advantageous in certain environments as well as not discoloring the base materials. Without a flame from a torch less oxidation occurs which means that there can be less cleaning to take place after joining. Since removing oxidation often requires acids, this can be an important consideration.
Induction brazing as it’s defined requires a magnetic metal as the base materials which will allow the induction coil to energize the currents in the base material to a degree to produce heat. Non-magnetic metals such as certain stainless steels or even ceramics are sometimes brazed by using an induction coil to heat a magnetic metal plate that they are fixed to.
Because lots of energy can be applied to a very small area with a precisely designed coil and part positioning strategy, induction brazing can deliver faster cycle times than torch brazing and is usually used in larger production runs. Targeting a very small area of a component to be heated means that secondary effects such as distortion or metal fatigue are eliminated. There is also less wear and tear on fixtures using induction brazing as the heat is tightly located in the part and little transfers to fixtures or mounting plates.
The ability to very tightly control the heated area means that higher quality joints are often produced with induction brazing.
In aerospace manufacturing, advanced military aircraft and commercial aerospace engine components, fan blades and vanes for the compressor and turbine are often fabricated using aerospace brazing methods.
The Following are Aerospace Brazing Standards
AWS C3.4 Specification for Torch Brazing
AWS C3.5 Specification for Induction Brazing
MIL-B-7883 Brazing of Steels, Copper, Copper Alloys, Nickel Alloys, Aluminum and Aluminum Alloys-Military Specification
To learn more about Nadcap and Aerospace Welding and Brazing, visit our guide here.