Question Mark
Expert guidance helps welders better understand weld strength, machine capacity, filler metal selection, puddle control, and best practices for producing high-quality welds.
Is a MIG weld stronger than a TIG weld?
When properly executed, the MIG and TIG processes both make for strong, reliable welds. The difference between the two processes is the way the filler metal is deposited – and more importantly, the heat involved. It helps if we know the application of the weld. What does the weld need to do? How will it be stressed? How will it be finished? The filler metal for both is the same – usually an ER70S-X – so the major difference between the two is the way the filler is entered into the weld pool. With MIG welding, the electrode is the filler. With TIG, the filler is fed by hand and thus easier to control. The TIG welding process requires cleaner materials, but generally results in better fusion.
Each process has advantages and disadvantages, but if performed correctly, both MIG and TIG can produce welds with excellent strength and integrity.
How thick of a metal can I weld with my small MIG welder?
The real question being asked is: How thick of metal can I weld with a single-pass weld? Thick materials can be welded with smaller machines if you have a good understanding of welding technique and welding process. However, as the material thickness increases, so does the need to prepare the weld joint to accept the weld metal. For example, performing a butt joint on 3/8-inch material requires the edges of the metal to be beveled in order to get full penetration at the root of the weld. Even large industrial welding machines have a hard time penetrating through thick materials with a single pass.
A single-pass weld is usually sufficient for a material thickness of 3/16-inch or less, but things change as the material reaches ¼-inch or thicker. The thicker the material, the more prep is necessary, and multi-pass weld layers will be required. Slowing down and making bigger welds is not the solution. On the contrary, it will cause problems with weld integrity. Always remember that no matter how big of a machine you’re using, you must stay on the front edge of the puddle to ensure fusion. For most hobby/garage applications, a 200-amp machine would be ideal. If you want to fabricate ½-inch plate, you’ll need a larger machine. More importantly, you need proper technique and understanding how to make multipass welds.
Why does the filler metal ball up before I can reach the puddle when I TIG weld?
One reason this happens is because of improper travel angles of the torch – or more simply, the torch is laid over too much. Remember that the arc is shaped like a cone or a bell, and when the torch is angled more into the material the arc is directed into the base metal. The filler rod balls up because the arc is being redirected too much from a bad torch angle and is actually deflecting off the metal – much like a Frisbee skipping on concrete. It’s often the result of our natural inclination to lay the torch over too far in order to get a better view of the puddle.
When this happens, the arc is not pointed in the proper direction. Try working on body and head positioning so you can see the puddle better. Being comfortable and creating clear sight lines is very important before even striking the arc.
Is a hotter, larger weld stronger than a smaller weld?
One of the biggest misconceptions is that a hot, oversized weld is stronger than a smaller one. I want to address the old saying, “Turn it up and burn it in,” “The bigger the weld, the stronger the weld,” and some of the other “helpful” mottos we’ve all heard over the years.
When we do various destructive testing with welds, a good weld often breaks next to the weld, depending on the base metal. This area where the metal was heated almost to melting temperature but did not become liquid is called the HAZ (heat affected zone). Heat changes metal on a molecular level, and the change is usually not for the better. A hotter weld, laid down larger than necessary, is not stronger. It actually weakens the base metal in different ways with the excessive and unnecessary heat from the larger weld. The thickness of the materials determines the size of the weld.
When a weld is tested for integrity, we remove the weld reinforcement on the top and bottom of the weld. The only weld metal being tested is the same thickness as the base material. It’s important to remember that bigger welds cannot make the material any stronger. Use the correct size welds for the given material and forget the advice about bigger and hotter.
What size TIG filler should I use for welding sheet metal?
Selecting the diameter of TIG filler for a weld is partly a matter of preference, but the filler should never be thicker than the material to be welded, especially when working with thin materials. If you’re welding 16-gauge sheet metal, the filler should be the same thickness or thinner. It takes a certain amount of heat to melt the filler, but if you use filler metal that requires more heat to melt than the base metal, you’ll simply burn the material away before the filler can melt.
I prefer .045 filler for 16-gauge and .035 for 18- to 20-gauge. When done correctly, the small fillers produce a small flat weld that requires very little finish work. The wire on your MIG welder can also be cut and used, as it’s the same filler that’s used for TIG. Smaller TIG filler can also be purchased in .035 and .045 diameters and 36-inch lengths. Once you get into the thicker materials, the filler size must increase too. Thicker materials will require more joint design, material prep, multipass welds and welding technique. Use the size filler that works best for you.