How to Make Successful Aluminum TIG Repairs
Repairing aluminum tools and parts can be a hassle, but some basic welding advice can make it easier. Keep this article handy as a “cheat sheet” for your next repair to make sure you get back to work with the strongest tool possible.
To weld or not to weld? And, how?
Each repair is unique and should be evaluated to determine the most effective course of action for your production schedule and tool availability. First, don’t burden yourself by trying to salvage a component that is beyond repair. A part with multiple fractures and/or one that is easily and inexpensively replaced should be replaced; it will save you time, money and frustration in the future. On the other hand, if the tool has only a few cracks or it is a part that can undergo proper and timely welding repairs, then do proceed.
As a rule, the TIG welding process is best for repairing aluminum. To ensure arc stability, you should use a power source with high frequency capabilities. All AC/DC machines have this built-in feature, but an AC-only machine may require an add-on external high-frequency component. Balanced wave control is also a necessary feature when TIG welding aluminum, as it increases cleaning action to remove surface oxides.
Most aluminum TIG welding repairs won’t exceed 80-100 amps, so a 200-amp power source matched to a 200-amp air- or water-cooled TIG torch will suffice. Also, be certain your power source has post-flow capabilities to prevent tungsten and weld puddle contamination.
Be Prepared for Welding Success
Proper joint preparation is the most important step in aluminum TIG welding repair. Dirt, grease, oil and aluminum’s natural oxides can weaken the repaired part by causing porosity, inclusions and other discontinuities. Follow these steps for the cleanest and strongest possible TIG welds.
1. Disassemble and remove the part (if part of a larger component) whenever possible. Heat from the TIG welding process can be dangerous to surrounding items such as motors and wiring.
2. Bevel the crack/joint down to a “V” halfway through the damaged part. Then tack weld it together and flip the part over. Bevel out an identical “V” groove on the opposite side and tack that together (Figure 1). Welding on both sides adds strength and reduces any chance of breaking. If you cannot access both sides of a damaged piece, simply bevel deeper so that 70-80 percent of the damaged part’s thickness can be filled with weld metal. Use a hand grinder with a 4-1/2-in. diameter wheel and 36-80 grit to bevel the damaged crack/joint. Grit finer than 300 can clog the grinding wheel and won’t effectively grind the joint. It may even embed impurities deeper into the aluminum. You can also use a bench grinder to bevel the part.
3. Use a stainless steel wire brush designated for aluminum to clean out the joint. A wire brush removes dirt and any of the oxides that may still reside on aluminum’s surface.
4. Use a specifically designated aluminum cleaner to remove any lasting remnants of oil, grease and moisture from the joint. One suggested cleaner is XeroTri Cleaner /Degreaser by LPS. Also wipe the opposite side clean so that no impurities are pulled through the aluminum and into the weld puddle. Most TIG power sources provide good cleaning action, however, you should never rely solely on this feature to do the job for you.
Make the Right Choices
Shielding Gas: Pure Argon is the recommended gas for aluminum welding and is suitable for 95 percent of all repairs. An Argon/Helium mix can be used when welding on thicker materials (greater than 3/8 in.). The addition of Helium creates a hotter weld puddle, as compared to pure Argon, thus enabling the operator to weld on thicker material.
Shielding gas flow should be set at 15-20 cubic feet per hour (CFH) when welding in the flat position. For out-of-position welds, or when welding where there is air movement, adjust the flow rate to 20 CFH. Be careful not to use too much shielding gas, as it can lead to turbulence in the weld puddle. This can create porosity and pinholes.
Tungsten: For welding repairs on aluminum, 2% ceriated tungsten sharpened at the tip is a good all-purpose tungsten for AC welding, as it allows for the use of 30-percent more amperage compared to pure tungsten. Sharpened (or pointed) tungsten also offers easy arc starts and a narrow heat-affected zone, along with the ability to control penetration more accurately. A 3/32-in. diameter tungsten is adequate for most repairs but an 1/8-in. diameter tungsten should be used on 3/8-inch or thicker materials and larger castings.
Not surprisingly, tungsten preparation and cleanliness is just as important as joint preparation. Grind the tungsten on a grinding wheel so that the grind marks run lengthwise, as this helps control arc wandering. If the tungsten accidentally becomes contaminated during the weld process, cut back ½ in. from the contaminated point and reshape the tungsten. Simply grinding off the surface at the contaminated point won’t work because there is no way to determine how deep the contamination runs.
The tungsten should extend no more than 1 and 1/2 times the diameter of the tungsten. Following this basic rule increases visibility and reduces the possibility of touching the tungsten to the weld puddle.
Filler Metal: There are two major classifications of TIG filler rods used to repair aluminum: ER4043 and ER5356. ER4043 is a general-purpose filler rod to use if you are unsure of the exact chemical makeup/composition of the part. ER5356 is used when TIG welding on anodized aluminum, because it provides proper color match after the anodizing process is completed; if an ER4043 rod is used and the part is anodized, the weld zone will appear as a dark gray, unattractive area.
The diameter of the filler rod is determined by the thickness of the broken part; however, the most common are 3/32-in. and 1/8-in diameter. To ensure the filler rod is free of contaminants that can result from open storage, or from laying on dirty work surfaces, use a Scotch Brite™ pad to clean it before welding.
Tune in Your Technique
Always (if possible) situate the part in a flat position. Hold the tungsten 1/8-in. away until the arc is initiated (Figure 3). Do not to touch the tungsten to the aluminum at the risk of contaminating the work piece. Also, using a lift arc start with a conventional AC machine is not recommended for aluminum TIG welding.
A good practice is to maintain an arc length equal to the diameter of the tungsten you are using. For example, if you are using 3/32-in. tungsten, you should have a 3/32-in. arc length.
Once you’ve started your arc, the first pass on the aluminum is going to be dirty even if you have cleaned it perfectly. Aluminum acts as a sponge and there is almost always contaminants embedded in it. For this reason, weld the first pass down the length of the beveled joint without adding any filler rod. This will allow you to “boil” out as much dirt as possible. Then brush off any contaminants that came to the surface on the first pass.
Begin to add filler rod on the second weld pass. There may still be some dirt surfaces in the weld bead, but the joint will become cleaner with each pass (Figure 4). Brush the joint and repeat this process until you have completely built-up and repaired the part. If pinholes or porosity show up, do not hesitate to grind them down, brush the area, and weld again. Doing so ensures a stronger weld and helps remove even more contaminants.
A Word about “Holes”
The TIG welding process is slightly different when repairing a hole in a part instead of a crack. First, you need to clean out the hole with a toothbrush-sized stainless steel brush and then weld around the edges of the hole to remove any contaminants without adding filler rod. Next, you should use a file to remove any jagged edges. Once you have gotten the hole down to good material you can begin welding and adding filler rod.
Weld in a circular pattern around the hole to build it up from the outside in. Fill in the hole and then weld around the top of the hole to flatten out the weld. Finally, grind off any weld that may be protruding from the backside.
Get Back to Work
Always remember to use the utmost discretion when repairing your aluminum parts. First determine whether the part can and should be repaired, and take the proper precautions during the TIG welding process to expedite the repair. After all, the goal is to get the part back to work in a timely and efficient manner, and, of course, to save time and money for future repairs.