Brazing and Welding Fundamentals

Below are some of the most frequently asked questions with answers.

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Welding – It’s all about the fusion, which takes place when melting both the base metal and usually a filler metal. We have written an article regarding brazing vs welding (insert hyperlink on website). However simply, the two metals must be similar, this is the biggest difference.

Brazing – Brazing is defined by a group of joining processes involving two or more metal items. They are often joined together by heating and melting a filler alloy however the filler must have a temperature below the metal pieces. Another bonus of brazing is that this process can join dissimilar metals such as copper, silver, gold, nickel and aluminium. Flux is often an essential part of brazing.

Soldering – Essentially it is the same definition as brazing, the AWS defines soldering takes place with fillers (also known as solders) that melt at below 840 °F (450 °C). Soldering uses metals such as gold, copper, silver, brass and iron. The filer (aka solder) melts so when it solidifies, it bonds to the metal and joins them. The bond isn’t as strong as a brazed joint or welded one.

  • An extremely good joint appearance
  • Can be done on an automated process
  • Very strong joints
  • Lower temperature and lower cost
  • Maintains Integrity of base metals

Occasionally you may need to disassemble your brazed joint. Remembering how important flux is you must use on the whole joint area first. This will help the filler metal flow at virtually its original flow point and importantly it will keep the parts clean. Then heat the joint evenly and then you can separate the separate the joint easily.

When you have metals that are exposed to oxygen you create oxygen atoms and said oxides prevent the heated alloy from joining to the metal.

Flux is a chemical Compound that is applied and shields the joint surface to prevent oxide formation. Remember the metal that is being joined must be cleaned prior to brazing.

Essentially the easiest way is to clean flux off the brazed joint, then quench and soak the assembly in hot water. Stubborn flux HCI can be added or special cleaners can be purchased cost effectively.

The strength of a brazed joint is dependant on several different factors. A few examples are:

  • Following the correct procedure to ensure the metal is joined properly
  • The filler metal used
  • The clearance.

When the liquid is essentially forced into contact with a solid and then distributed between closely fitted surfaces of the joint, you can then braze or solder.

Quite simply, it’s a material used on the surfaces adjacent to the joint to limit the spread of the brazing filler metal whilst it’s in a liquid state.

It may sound obvious, but ensure your working area is well ventilated. Ensure the base metals are clean as this may create fumes when you heat the metal. Be careful not to overheat the assemblies and remove the toxic coatings.

This is the spreading of a molten brazing alloy over the surface of the base metals being brazed. The correct wetting will occur if both the base metals and the brazing alloy reach the working temperature of the alloy.

An assembly gap is the space between the base metals that will be brazed at room temperature and the brazing gap is the space between the base metals to be brazed at the brazing temperature. When you have dissimilar base metals with different thermal expansion, the brazing gap will be different from the assembly gap.

So brazing can be separated often into two methods. Localised heating techniques and diffuse heating techniques:

Localised heating technique (Only the joint)

  • Torch Brazing
  • Induction Brazing
  • Resistance Brazing

Diffuse Heating Technique (Heating the entire assembly)

  • Furnace Brazing

You can weld aluminium with either a TIG welder or a MIG welder. Provided that you have the right electrode and filler metal for your TIG welder, you don’t need to add anything to your setup. Of course many welders sing the praises of foot pedals for controlling the heat input better and water-cooled torches for working on longer stretches of a project.

MIG welding aluminium is another story. The lighter aluminium wire that you’ll feed through your MIG torch will get jammed up inside of the welder’s wire feeder. That’s why it’s essential to pick up a spool gun that feeds the aluminium wire right into your torch as you weld. This eliminates jams and makes it significantly easier to weld without stopping to fix a jammed wire.

This welding process works in almost exactly the same way as if you were welding two similar metals together. Using a laser beam which is precisely focused on the metals, you melt each of the metals together until they form one connected joint. If the two metals are not two wildly dissimilar, such as if you were using two austenitic steels as we mentioned earlier, the two will often join seamlessly together.

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