Dip Brazing

Dip brazing is yet another brazing process which allows the bonding by producing heating in a molten chemical or metal bath. It makes use of a nonferrous filler metal with a melting point above 427°C (800°F) but below that of the base metals. Providing a filler metal whenever there is the usage of metal bath, it is through capillary attraction that the filler metal gets properly distributed in the joint. Dip brazing is popularly associated with aluminum which is the preferred means of fabricating aluminum assemblies. The process offers sturdy joints of supreme quality just like the base metals. By making use of uniform heating, the brazing method produces little or no physical distortion..

It is essential that this joining process allows the metal pieces are joined by means of flowing a filler metal between the joint interfaces. After the filler metal cools down to the solid state, it forms a strong metallic bond throughout the joined area.

Even though there is simultaneous joining of multiple joints accompanied with distinct material thicknesses, these joints are made leak-tight and EMI shielded. Minor distortion occurred due to uniform heating of the parts with minimum fixturing are easily managed with proper tolerancing and component designs.

Aluminum Dip Brazing
Aluminum dip brazing generally include constituents of 88% of filler metal & 12% of silicon. Brazing parts are placed along the joints along with the filler metal once they are chemically cleaned. In order to insure the uniform temperature of dissimilar masses in the assembly, it is preheated in an air furnace to 1,025°F, thereupon, getting immersed in a molten salt bath. These very salts are aluminum brazing flux.

The uniform liquid heat is quiet fast when the bath is maintained at 1,095°F±5°F in a salt bath furnace & molten flux simultaneously comes in contact with both internal & external surfaces once the assembly is immersed or dipped. Supreme quality joints are assured by oxide free surfaces & strong bonding simply because of flux bath.

Aluminum Alloys for Dip Brazing
There are certain considerations to be kept in mind when deciding upon the materials for ideal brazing.

 

MATERIAL	HEAT TREATABLE	NON-HEAT TREATABLE
Wrought Alloys	6061, 6062, 6063, 6053, 6951, 7072	1100, 3003, 3004, 3005
Clad Brazing Sheet	21, 22, and others	11, 12, and others
Cast Alloys		A712.0, C712.0, D712.0, A356.0, A357.0, A359.0, A443.0

 

Aluminum dip brazing follows a particular procedure which allows the aluminum alloys to be perfectly fit for brazing. Let's have a look at the common procedure adopted :

• Cleaning & deoxidization of component parts take place.
• Then, these parts along with brazing filler materials are assembled on the brazing rack. These materials are preplaced in all joints.
• In order to touch the brazing temperature, the assembled parts are preheated.
• The assembly part is made to touch the brazing temperature simultaneously with the fluxing of all joints by dipping the preheated parts into the molten brazing flux. Furthermore, the preplaced filler flows throughout the joints by capillary action once the materials gets liquefied.
• Brazing assemblies are formed when the filler material solidifies after the parts cool.
• Brazed assembly is separated from the residual flux.
• It leads to clean, completed & brazed assemblies.
• There is even optional chem film.

• Once the parts are joined, these are inspected in three ways as per the shape of the product. These are :

1. Naked eye inspection
2. Supersonic waves inspection
3. Leakage inspection.

• The next step is inspection of residual flux, known as Silver nitrate inspection

The many advantages of dip brazing have been mentioned below :

• Dip brazing reduces the tooling cost. Requirement for little & specialized tooling helps in achieving this. Common fixtures allow for quick & inexpensive configuration changes which aid in accomplishing the fixturing.
• One can have material savings. Dip brazing are easily done at near net size which is not possible in case of castings or machined parts.
• Dip brazing provides improved structural integrity. There is leak tight & EMI shielded joint available with varied material thicknesses.
• There is better conductivity which is clearly achieved since the dip brazed joint is aluminum. The result is better than that achieved from an adhesive bond or mechanically attached assembly.
• There is less distortion since the braze process heats all components uniformly which yield less distortion.
• It is quite cheap delivering superior characteristics.
• There is liberty to design using the dip brazed process.

1. Reduced Tooling Costs
2. Reduced Design Change Cost and Implementation Time

• Apt for electronic enclosures
• Heat Exchangers
• Wave Guides
• Antenna
• Microwave Antenna Sector
• Liu EMI Shield Case
• Aircraft makers
• Ideal for air to air technology
• Tube-shell