Silicon Bronze MIG Brazing Basics

MIG brazing benefits

MIG brazing may not be a familiar process to many, and in some cases it may even be considered a new technology; but it is no stranger in the welding world. MIG brazing is a welding process that has been around for years and the process is gaining popularity recently by professionals and hobbyists alike due to the benefits it can offer, especially with silicon bronze filler metal. 

This article will provide the basics of MIG brazing silicon bronze including advantages and disadvantages, where this process can be used, and how to properly set up a welding power source for MIG brazing silicon bronze.

What is MIG brazing?

Traditionally, brazing processes have used an oxy-fuel acetylene torch to melt the filler metal, but in MIG brazing, a standard MIG gun is used to run brazing wire. Brazing filler metal melts at 840 degrees Fahrenheit, which is lower than the melting point of the base metals being joined. Due to the lower melting point the filler metal provides capillary action – fluid being drawn into the weld joint – when brazed.

What is silicon bronze?

Silicon bronze filler metal is mostly comprised of copper, silicon, tin, iron and zinc. The composition of the wire provides some unique benefits such as the ability to weld dissimilar metals together, reduce distortion and provide a visually appealing finish.

Welding dissimilar metals

When braze welding with silicon bronze filler metal, the molten metal bonds the base materials together, but does not provide fusion like mild steel filler metal. Because of this, silicon bronze can be used for welding dissimilar materials together, such as cast iron to steel, stainless steel to steel, etc.

Reducing distortion

The low melting point of silicon bronze also provides a cooler welding process, putting less heat into the material that is being welded. Reduction in heat input leads to less distortion and the ability to weld on heat sensitive materials without compromising the physical properties. It is an ideal process for joining thinner metals together, filling gaps, and sheet metal work such as HVAC and auto body welding.

Gold finish

When done correctly, a silicon bronze weld will have a gold colored finish that provides contrast to the base metal. Gold colored welds are often used for aesthetic appeal in metal art applications.

MIG brazing does have a few disadvantages to consider. Generally, silicon bronze wire is more expensive than mild steel wire. Additionally, because of the composition, the wire is softer than a mild steel filler metal and occasionally can cause birdnesting or other feeding issues. It also has a lower tensile strength than mild steel filler metal.

Machine setup

MIG brazing can be done with short-circuit transfer, and the arc characteristics will be like a mild steel filler metal arc.

When setting up a machine for MIG brazing, there are several key components that must be correct to achieve the best results possible. 

• Shielding gas: It is critical that 100 percent argon shielding gas is used with silicon bronze wire. 
• Drive rolls: Since silicon bronze wire is softer than steel, U-groove drive rolls are recommended, but V-groove drive rolls will also work. 
• Process selection: When setting up this process up on a piece of Miller® equipment that allows you to select the MIG process, best results are achieved when setting the machine to the C25 setting. 
• Polarity: Polarity should be set to DCEP. 
• Gun liner: A Teflon liner is recommended due to the softness of the silicon bronze wire, but a regular steel liner will also work. 
• Technique: MIG brazing uses the same welding techniques as short circuit MIG.

For many of the Miller machines, parameters for MIG brazing silicon bronze have been developed. PDFs of the parameters are available for reference:

           Millermatic 252 Parameters                         Millermatic 212 Parameters 

            Millermatic 211 Parameters                         Millermatic 190 Parameters

             Millermatic 141 Parameters                         Multimatic 215 Parameters 

           Multimatic 200 Parameters