What is the Brazing Process?

4 August 2023

Brazing is a type of joining method in which two or more metal (or ceramic) parts are joined together using a filler material with a lower melting temperature than the base materials. In this process, the parts to be joined are first temporarily fixed using a fixture, clamp, or spot welding. The selected filler material, depending on the main material type, is applied to the joint, and then the filler material is melted by applying a temperature above its melting point but lower than the melting temperature of the base materials. The molten filler material advances through capillary action, filling the gap between the joined parts and creating a strong bond.

The filler material not only fills the gap between the two pieces but also penetrates both materials to create a very strong welding joint. Depending on the geometries of the parts to be used and the application purpose and method, the filler material can be used in different forms such as powder, or slurry mixed with a binder, foil, tape, or wire.

What are the Main Brazing Methods?

This process, widely used in various industries, especially in aviation, has several methods depending on the heat source used to melt the filler material. The main brazing methods are as follows:

  • Furnace brazing: In this process, the heat to melt the filler material is provided by a furnace. Vacuum furnaces are commonly used, but other types of furnaces can be used under a protective gas atmosphere. 
  • Torch brazing: In this process, heat is generated using the flame produced by oxyacetylene gas. The melted filler material is applied to the joint area by the heat of the flame. A material called flux is used to protect the molten filler material from the oxidizing effect of the air. 
  • Induction brazing: In this process, heat is generated by induction current. A material called flux is used to protect the molten filler material from the oxidizing effect of the air. 
  • Resistance brazing: In this process, heat is generated using the electric arc method in gas-shielded welding. Inert gases such as Argon or Helium are used to protect the molten filler material from the oxidizing effect of the air.

What are the Key Points to Consider in the Brazing Process?

The most important factors to consider in this process are:

  • The cleanliness of the materials to be joined and the environment. 
  • The suitability of the joining surfaces of the parts for brazing. 
  • Proper adjustment of the gap between the parts to be joined. 
  • Selection of the correct filler material and its form suitable for the base materials. 
  • Application of the appropriate protective atmosphere and temperature.

What are the Common Applications of Brazing in Aviation?

In aircraft and helicopter engines, many parts are joined using the brazing process in vacuum furnaces. Especially in recent years, this method has been developed and preferred for joining ceramic parts used in engines operating at higher speeds and temperatures. Micro-cracks observed in various parts of the turbine area are also repaired using the brazing method before being put back into service. The joining process of the honeycomb (named because of its honeycomb-like appearance) parts, which are frequently used in aircraft engines and also referred to as sealing elements, is also done using this method.

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