When it comes right down to it, the strength, longevity and overall integrity of a weld depends largely upon the filler metal. Failing to select the right filler metal for your welding project promises to compromise the fortitude of your weld.
OK, that totally makes sense, right? But how do you select the right filler metal? And what are the key elements you need to keep in mind in order to make the right choice?
Good question, I’m so glad you asked!
Selecting the right filler metal for your welding projects breaks down to five key considerations:
- Matching the base metal
- Tensile strength
- Welding position
- Number of passes required to complete the weld
- Cleanliness of the base metal
So let’s take a closer look at how each of these key elements relate to the filler metal selection process:
Matching Filler Metal with the Base Metal
The single most important consideration in selecting the right filler metal is matching the filler metal as closely as possible to the base metal.
Whatever type of metal you’re working with – stainless steel, aluminum, bronze or copper alloys, or any of a host of other possible metals – each possesses its own unique properties, which are unmatched by other metals. It’s really pretty elementary chemistry if you think about it – dissimilar compositions aren’t going to bond well (or at all).
The monumental importance inherent in the strength and surety created by the bond between the filler and base metals makes this match the most important consideration in your filler metal selection process.
Selecting the right tensile strength is a almost as important as matching filler and base metal type, coming in a close second among key considerations in your filler metal selection process. Basically, you want the tensile strength of your filler metal to equal or exceed the tensile strength of your base metal – if you can’t match the base metal’s tensile strength exactly, it’s better to exceed than settle for a short fall.
The logic here is also pretty elementary – if you’re bonding two pieces of base metal using a filler metal with a weaker tensile strength than that of your base metal, you’re headed for trouble and will definitely end up creating a weld that’s less than secure.
Filler metals designed for flat or horizontal welding positions are generally less prone to porosity and developing other inclusion related issues, in addition to possessing a faster speed of travel. That means nine times out of ten, your best bet with any welding project is welding in a flat position, i.e. on a work bench or welding table, preferable in a welding shop or some similar work environment. But hey, realistically speaking, that’s not always possible – what’re you gonna do, right?
When you’re making repairs in the field, however, and you don’t have the luxury of a comfy cozy welding shop environment, you gotta do what you gotta do. And that means selecting an all welding position filler metal.
All position filler metals offer a super solidification rate, ensuring the weld puddle remains intact.
Number of Weld Passes
Welding electrodes (filler metal’s delivery agent) are designed for either single or multiple pass use. So when you select your electrode, you need to determine whether or not you can complete your weld in a single pass, or if multiple passes are required to get the job done.
Condition of the Base Metal
Obviously, it’s always best to clean all contaminates from the base metal you’re working with prior to welding. Rust, scale, dirt, paint and other debris all represent impurities with the potential to compromise the strength and integrity of your weld, and removing those materials, in addition to generally making sure your base metal is as clean as possible, is really in your best interest.
Once again, however, it’s not always possible to make this happen. Just as you don’t always have the option of welding in the comfortable confines of welding shop, when making repairs in the field, you’re not always at liberty to clean the metal your working with as well as you would like.
Fortunately, certain filler metals include deoxidizers that are specifically designed to pull rust, dirt and other contaminants to the surface of the weld, and are ideal when you’re forced to weld less than pristine base metals.