People are familiar with brazing as the metal-joining process in which a flame torch melts and joins metal parts. That process is specifically termed torch brazing, one of the many methods utilized for brazing. Apart from that, there are multiple other brazing types, each using a different heat source—induction brazing, resistance brazing, dip brazing, furnace brazing, and infrared brazing.
This article covers the major brazing types and the scale for which each technique is employed on an industrial level. Read on to get familiarized with all brazing methods.
What is Brazing?
Brazing is a metal-joining process in which a melted filler metal fills the faying (in-contact) surfaces of the joined metal workpieces. In this process, the base metal doesn’t melt. Only the filler melts and strengthens the joint.
Though the joint strength of a brazed joint may be less than that of welding, brazing offers several key advantages over it. For instance, it can join two dissimilar metals and thin-walled parts that cannot be welded.
Brazing has various applications in different industries. It is employed in the automotive industry for joining tubes and pipes, in the electrical equipment industry for joining wires, and for crafting jewelry.
6 Major Types of Brazing
The process of brazing is achieved by various methods, referred to as brazing processes or types. Brazing has six major types based on the heating source employed for heating the filler metal [1, 2].
1. Torch Brazing: A Reliable Skilled Method of Joining Metals
Torch brazing is one of the most used types of brazing. The flux is applied to the two joining surfaces via a flame torch in this brazing process. The torch bears a reducing flame to prevent oxidation. This flame is normally fueled by acetylene or propylene, while the filler material is in the form of wire or rod.
Torch brazing is usually done manually, thus requiring trained workers to configure the flame and operate the hand-held torches. The method is mostly suitable for repair work, where a high level of control is necessary to achieve the desired results. It can also be utilized in production scenarios where most tasks are done manually.
2. Furnace Brazing: A Versatile and Efficient Method for Medium and High Production
Furnace brazing is a method that uses a commercial furnace to supply heat. Since a heat reservoir is used, the method is well-suited for medium and high-scale production needs.
For medium-scale production, the process begins by loading the components and brazing metal in small batches into the furnace. Next, the furnace is heated to the required brazing temperature. Once the heating process is complete, the components are cooled and taken out of the furnace.
High-production operations use flow-through furnaces, where parts are placed on a conveyor and transported through the various heating and cooling sections.
Temperature and atmosphere control are critical in furnace brazing, with the atmosphere requiring a neutral or reducing environment. In some instances, vacuum furnaces can also be used.
3. Induction Brazing: A Rapid Heating Method for Low to High Production
Induction brazing works on the principle of heat generation through electrical resistance. In this brazing method, the parts, loaded with filler metal, are placed inside an induction coil that bears high-frequency AC. The key point to note is that the parts assembly is just placed inside. There is no physical connection with the coil.
The AC frequencies used in induction brazing have a range of 5 kHz – 5 MHz. The higher frequencies are desired to first heat the surface, while lower frequencies cause deeper heat penetration into the workpiece.
Induction brazing is normally utilized to meet low to high-production requirements. Additionally, it offers a rapid heating method for producing high-quality brazed joints in metal parts.
4. Resistance Brazing: A Direct Heating Method for Small Parts
Resistance brazing is a method that obtains heat from the resistance of metal workpieces as current flows through them. In this process, parts, along with the filler metal in between, are held between electrodes. Then high pressure and current flow through the electrodes.
The resistance brazing method follows the same principle as induction brazing. However, there is one difference. In this case, the metal pieces are a part of the electrical loop rather than being placed inside of that loop.
Interestingly, the equipment used in this process is similar to the one used in resistance welding. However, brazing equipment consumes much less power than welding.
Since both induction and resistance brazing offer rapid cycles, they are useful in small-scale production units.
5. Dip Brazing: A Fast-Heating Method for Multiple Parts
Dip brazing is a process in which either a molten metal bath or a molten salt bath is used for heating. As the process name suggests, the assembled parts are dipped in the heated baths, and the solidification process happens when the parts are removed.
In the salt bath method, the molten mixture, fluxing ingredients, and filler metal are placed in the assembly beforehand. While in the metal bath, the molten filler metal acts as the heating medium and gets drawn into the joint by capillary action during the submersion process.
Just like the prior two methods, dip brazing also provides quick cycles. But, it has the advantage of brazing multiple joints on a single component or even several components at once.
6. Infrared Brazing: The Modern Way to Braze Thin Sections
In infrared, the heat for brazing is supplied through high-intensity IR lamps. These lamps can generate around 5,000 W of heat, which, when thrown on metal parts, causes them to melt and then brazed.
The process takes time and is slow compared to the previously explained brazing methods. So, its use case is just limited to joining and brazing thin metal sections.
Conclusion
There are six major types of brazing, each with a different heating source and a set of advantages.
Torch brazing is a reliable, skilled method often used for repair work. Furnace brazing, which involves a furnace, suits medium to high-production applications. Induction and resistance brazing, which employ electrical resistance heat, are rapid heating methods best suited for small parts. Dip brazing is a quick method for brazing multiple joints, while infrared brazing is only limited to thin joints using IR rays.
In short, each of the six brazing methods has its specific use case, and the choice of method depends on the application, production scale, and desired outcome.
References:
[1] M. P. Groover, Fundamentals of Modern Manufacturing: Processes and Systems, 5th ed. Wiley.
[2] American Welding Society. Committee on Brazing and Soldering., Brazing Manual, 3rd ed. Miami: American Welding Society, 1976, pp. ix, 309 p.
