A few weeks ago, I wrote about a greener way to Solder. Today I want to talk about a natural extension of this technology, Ultrasonic Brazing. Brazing is a joining method commonly used in various industries resulting in higher joint strengths than soldering. It has the ability to join dissimilar materials, join complex assemblies, and to be batch processed. In the advanced energy field, brazing is an attractive option for joining stainless steels to zirconia for solid oxide fuel cell applications.
Typically, you can not braze in air without the use of VOC containing fluxes. To avoid flux, the common solution is to use expensive vacuum furnaces. But is a vacuum brazing process always green? Not necessarily. Even under vacuum, materials like ceramics, stainless steels, titanium, etc are usually metallized to improve wetting. Electroplated nickel is a common metallization but electroplating is not a green process due to discharge of toxic chemicals and heavy metals through wastewater (effluents). Even electroless plating is not a green process as this usually contains formaldehyde in the waste stream. When you consider the entire process of joining how do you use a green brazing process in your manufacturing process? The answer is ultrasonic brazing.
Ultrasonic brazing is an extension of ultrasonic soldering process to include higher temperature brazing filler metals. This process can be done in air thus avoiding the need for costly vacuum furnaces. Furthermore, this process permits brazing of non-metals without metallization/plating. These two advantages make this a truly green process with the added benefit of potential cost savings arising from the freedom from vacuum furnaces.
EWI has developed ultrasonic brazing process that can be performed in air without the use of flux, thus avoiding VOC emissions. Ultrasonic brazing in air has been demonstrated on similar metals – 304 Stainless Steel, Ti6Al-4V using Al-12Si filler metals at ~600C. Furthermore, this process has also been demonstrated in brazing of boron nitride to aluminum using a commercially available Al-12Si filler metal. In addition, EWI has demonstrated this process on tubular geometries such as the 321 stainless steel to 17-4PH stainless steel shown in the picture below.
Posted by Mark Norfolk