Brazing is a welding technique where two pieces of metal are joined using metallic filler that has been melted and then allowed to flow across and into the joint. Once the filler metal cools, a sound and viable weld is formed. The brazing process is known for creating very strong joints that tend to be stronger at the base of the weld. The technique of brazing allows for two pieces of metal to be joined without causing any melting on either of the base metals. Welders tend to use this method when they need to create a weld that is invisible, strong and can be accomplished using a wide range of temperatures.
When brazing it is important that the base metals you will be joining have been thoroughly cleaned. If any contamination is left on the metals, the brazing process will leave you with a brazing mixture that will clump instead of flow freely across the metals, which will result in a weak joint being created. To clean the metals you should wash the surface and then apply a melted flux. The flux is used to remove any oxides and smoothes the surface to allow for the brazing material to flow evenly across the joint you are creating.
The next step in the brazing process requires you to use your torch to melt the brazing materials. It is important that the temperature on your welding machine be set at the right temperature to melt the brazing material but not so high as to cause the base metals to melt. To achieve the proper temperature it is important that you are familiar with the temperature threshold of the base metals you are working with. To control the temperature of your welding torch, you will want to use the sensitivity controls. This will help you make adjustments to the temperature as needed.
The final step of the brazing process requires the completion of the joint by applying the filler metal. Brazing material is typically purchased in stick or wire form. Depending on which type you prefer to use, and the size and shape of the base metal you will be joining, will determine which type is best suited for your project. Once the joint has been heated thoroughly with your torch, you should place the wire or stick on the surface and allow it to melt. As the braze melts, it will flow in and around the surface of the joint creating a weld. Once the metals have cooled, the weld created by brazing will be solid and virtually unbreakable.
Reference: http://www.wisegeek.com/what-is-brazing.htm
