Aviation vacuum brazing process

Brazing, as the earliest material connection method used by humans, has a long history of application in the aviation field. In recent years, with the increase in technical challenges in the fields of aviation manufacturing and aviation maintenance, this technology has also kept pace with the times and its development pace has continued to accelerate. Vacuum brazing refers to a welding method in which the brazing material and the weldment are heated to the melting temperature of the brazing material at the same time, and the gap between the solid workpieces is filled with liquid brazing material to connect the metal materials.
Advantages of vacuum brazing
Taking vacuum brazing as an example, it is a clean, fluorine-free process suitable for high-strength parts with excellent dimensional stability, no voids and impurities, resistant to impact and vibration, and able to withstand high pressure. Vacuum brazing is suitable for the assembly of multiple parts and complex parts, as well as for connecting dissimilar materials, including some non-metals. The parts to be connected can be produced by a variety of methods, such as cold stamping and forming, casting, forging, extrusion, manufacturing or processing, and can be made of almost any metal, alloy or even ceramic. A major advantage of vacuum brazing is that it can connect the same or different metals in a very strong way.
Advances in Vacuum Brazing in Aerospace
The widespread use of vacuum brazing in the aerospace industry is due to its many advantages, such as the ability to process multiple parts simultaneously, which helps save costs; the ability to form multiple joints at the same time; and the ability to heat and cool the entire assembly evenly, minimizing part deformation. In addition, vacuum brazing can also join materials with different thermal expansion coefficients, including ceramics.
Typical Honeycomb Seal Vacuum Brazing
Honeycomb seals are a jet engine component that surrounds propeller or turbine blades to prevent airflow around the blade tips, thereby improving engine efficiency.
Honeycomb seals are made from a variety of nickel-based and cobalt-based superalloys that can withstand the harsh environmental conditions of jet engine applications. Rolling and fixing are the two most important steps in assembly before brazing. In order to ensure close contact and obtain a strong brazed joint, it must be fixed reliably. All dimensions are determined during the fixing stage. Common tolerances for brazing are 0.25 – 0.50 mm.
Proper cleaning is another important step in vacuum brazing preparation. Before vacuum brazing, every effort must be made to ensure that the parts are clean and free of any oxides, contaminants and oils.
Cycle time and component preparation are equally important to the success of the vacuum brazing process. If the temperature is raised too quickly, there is a risk of component deformation or uneven temperatures throughout the assembly. If the components are not positioned securely, the braze will not flow properly. If the assembly is quenched too quickly, deformation, quench cracking of the braze joint or spattering may occur.
Brazing of these high temperature nickel alloys is typically performed at temperatures of 1040°C – 1200°C and vacuum levels of 10^-4 – 10^-5 Torr. Brazing temperatures are 40°C – 65°C above the melting point of the brazing alloy.
Common problems include brazing alloy spattering, quench cracking and deformation. All of these problems can be avoided by controlling component cleanliness, using the correct setup method, properly designing the brazing process and operating the vacuum furnace correctly. Multiple re-welding can be performed at slightly higher temperatures using shorter brazing cycles. A brazing inhibitor (preferably alumina) can be used to reduce the risk of undesired braze flow.

Vacuum Brazing Furnace