If you have taken a look under the hood of your car lately, you likely have seen parts that were brazed using a Controlled Atmosphere Brazing (CAB) process. As more and more automotive manufacturers switch to aluminum components to increase performance and decrease car weight, the demand for strong, leak tight joints increases. These types of joints can be found throughout a typical vehicle from the radiator to the A/C condenser.
Key aspects of Controlled Atmosphere Brazing (CAB)
Many automotive manufacturers use the CAB process in critical automotive applications because it ensures superior joint strength. When brazing with aluminum, the CAB process incorporates the following key aspects:
- Filler Metal: most commonly an aluminum-silicon alloy that will flow quickly when melted and create strong joints post braze
- Furnace: Inert/Controlled Atmosphere - retort and continuous (straight and humpback) furnaces
- Flux: generally non-corrosive for aluminum applications; helps to reduce oxides on the metal surface which allows for filler metal to flow
- Furnace Atmosphere, either:
- Nitrogen (N2) - displaces air/oxygen in the furnace atmosphere
- Inert gases - helium and argon; used in brazing metals and ceramics
Providing a good joint in an automotive application is key—low strength return bend joints on a radiator can lead to failures once in service. Similarly, small leak paths in braze joints can be hard to access and repair once a vehicle is assembled. For such applications, a controlled, repeatable process that forms high quality joints is necessary.
Common automotive applications for CAB
A general procedure for a CAB process in an automotive application would be as such: aluminum parts—heat exchangers for example—are preloaded with a braze preform such as Lucas Milhaupt’s Handy 1 AL 718 ring. The furnace then utilizes a conveyor that holds the parts in place while moving slowly enough to allow the parts to reach temperature and complete a proper braze. While heating, a cover gas, such as nitrogen or argon, flows over the parts to inhibit oxide formation, which helps the alloy melt properly once at temperature and fill the joint as desired.
Prevent base metal damage with controlled heat
This process allows for a number of benefits. First, the slow and even heat that the furnace provides helps prevent localized overheating and damaging of base materials. Overheating is common when brazing manually with torch and can weaken the joint.
Reduce flux use to improve aesthetics
Another benefit of CAB is the use of a cover gas—while flux is still required in a CAB process for aluminum, the controlled atmosphere helps minimize the amount of flux needed. This means less flux voids in joints and less flux residue after brazing, which offers an improved aesthetic benefit. The protective atmosphere also helps to keep further oxidation from occurring which allows for the braze alloy to flow more freely and form higher quality joints.
Reduce variation in large batch brazing
While Controlled Atmosphere Brazing is a slower heating process than torch or induction, it is very efficient in mass production as large quantities can be run continuously. The furnace will also allow for even heating of all parts, big or small, while the controlled atmosphere keeps a constant flow of protective gas around every braze joint simultaneously.
By using a CAB process that provides even heat for every joint, variation from part to part is decreased and the final joints formed are much more robust. This allows for a more economical braze process as more parts can be brazed at once while leaks and costly repairs are minimized.
CAB as a robust process for automotive manufacturers
Controlled Atmosphere Brazing, or CAB, is an economical process that can be used in many mass production environments such as the brazing of aluminum parts in the automotive industry. The consistent temperature it provides keeps variation low and quality high on each joint, while the protective gas helps to provide a cleaner surface for the filler metal to flow across.
Lucas-Milhaupt provides a complete line of braze alloys, including preforms and pastes, for Controlled Atmosphere Brazing and the repair thereafter. Please contact us for assistance with your brazing program.