Filler Rod Basics
This filler material is a metal alloy specifically designed to withstand the high heat of welds and to fuse the two pieces of stock together as a composite.
So, not surprisingly, the alloy and size of filler rods vary for the varying stock thicknesses and types of base metals people weld.
TIG filler rods typically come in 3-foot lengths, packed in 10 or 50-pound boxes (or tubes). The diameter usually ranges from 1/16 to 1/4 inch.
The filler rods are also made with several alloys to handle different metals.
Since the TIG filler rod composition needed is often the same as that used for MIG filler material, some of the MIG wires are also sold for TIG welding. These are identified as “TIG cut lengths.”
Choosing A Filler Rod:
Unfortunately, there is no definitive answer for the filler rod you “must” use for a weld. However, the weld you need to make defines certain parameters.
This criterion can then be used to follow certain guidelines. Also, manufacturers usually have detailed charts to help select a filler rod.
In general, the important parameters include the base metal thickness, its composition, and the type of weld joint (butt vs. fillet).
Using this criterion, you can use certain guidelines to zero in on the filler rod alloys and diameters you might want to use.
Filler Rod Alloys: (“Composition”)
The American Welding Society (“AWS”) has categorized the various alloys and assigned special AWS “ER” numbers to more easily identify them.
Each number represents a “recipe” of chemical additives in the filler metal to address specific base metals and weld conditions.
The number of alloys available can be overwhelming.
Below you can find some simple guidelines to help you zero in on some common compositions of the filler rod.
Also, manufactures often have charts you can consult to find their best product for a given weld.
- ER70S-2, ER70S-6, and several other ER70S-series options with different digits at the end to address specific conditions of the metal (e.g., dirty or clean) or the type of joint being welded.
- ER70S-6 is generally used for mild steel welding.
- ER308 & ER308L: One of the most common welding rods. It’s the choice for welding 304 stainless steel, which is widely used in manufacturing. In addition, this filler rod alloy is used with 200-series and other 300-series stainless steels.
- ER309 & ER309L: Used for welding dissimilar metals. It can handle higher heat and has good corrosion resistance.
- ER316 & ER316L: Commonly used for pressure vessels, valves, chemical equipment, and marine applications. (The “L” refers to extra low carbon in the rod, less than 0.08%, which adds corrosion resistance.)
- The numbers above are some of the more popular, but the roster of stainless steel base metals manufactured today is vast.
- ER4043: is a good general filler material for most aluminum applications. However, welding of 2xxx and 7xxx series aluminum is generally not recommended.
- ER5356: is used for 5xxx series aluminum and is generally preferred if the finished piece will be anodized.
Filler Rod Diameter:
The thickness of the stock you TIG weld will suggest a filler rod diameter. There are all kinds of opinions on the right filler rod diameter.
Below I have assembled some guidelines to help you cut through the static.
In general, use a filler rod with a diameter less than the thickness of the metal being welded.
With a base metal thickness under 1/8 inch, the rod diameter should be slightly thinner than the metal being welded.
For stainless sheet metal, use one size lower than you would use for carbon steel. This helps because you typically use less amperage on stainless steel thin stock, compared to carbon steel. At low amperage, a large rod chills the puddle and can cause an irregular bead.
For aluminum, the same rules that you would use for steel sheet metal apply. In my experience, 1/16″ (1.6mm) wire can be used for sheet aluminum as thin as 0.040 inches.
For thicker aluminum, sometimes the rod balls before it even reaches the puddle. If that happens, try a tighter arc and less torch angle. If that does not work, go up one size with your filler rod.