by Shaun Relyea
Know where the difficulties lie and prepare for them
Titanium has the highest strength-to-weight ratio of any metal and is quite resistant to corrosion. As such, it is often used to help increase the life span of high duty parts. Lightweight titanium alloys are used in many industries including medicine for prosthetics and aerospace for jet engines and spacecraft. While it is highly useful, titanium has a reputation of being difficult to weld. As with any welding application if you know where the difficulty is, you can prepare for it and overcome it. These tips will help you be successful when welding titanium.
Choose your process
Titanium can be welded with several arc-welding processes. One of the more common processes for joining titanium is gas tungsten arc welding (GTAW). Both GTAW and plasma arc welding (PAW) provide very high-quality welds but they require a greater level of skill on the part of the welder. Some power supplies can be used as both GTAW and PAW, giving a lot of versatility for shops welding titanium. If your application requires gas metal arc welding (GMAW), you will need a power supply with pulse capability. GMAW provides a high quality weld, versatility and increased productivity, as it is faster than both GTAW and PAW. Laser hybrid arc welding (LHAW) provides an extremely fast welding speed but it is limited to automation and the part fit up must be precise. Depending on your application, there are different process options available. However, if your application calls for a filler metal, only use titanium, otherwise your weld will turn brittle and crack even before it’s fully cooled.
Shield your weld
Once you’ve decided on your process determine your shielding gas. Shielding gas is especially important when welding titanium because once hot, titanium absorbs atmospheric gases such as nitrogen, oxygen and hydrogen. This absorption causes the weld to become brittle and crack. Shield the arc with an inert gas such as high-purity argon (99.999% pure) or an argon/helium mixture to prevent contamination. Since the welded area must be protected until the weld cools below 500°F, a trailing shield is necessary. Keep all surfaces of the welded part in mind. If the area gets red hot, it must be shielded. In certain welding applications it’s necessary to use a purge gas, for example, to protect the root in a butt joint or to protect the backside of a fillet joint. Depending on the complexity of the part, it may be best to weld inside a glove box to protect all heated areas.
Clean your materials and don’t touch
Now you are ready to prepare your parts. Unlike some other metals, titanium is particularly intolerant of contamination. Parent materials must be cleaned with a non-chlorinated solvent at least an inch around the weld seam prior to welding. Once clean, it’s important not to touch the area with bare skin. The oils from your skin will cause weld contamination and porosity. A common pre-weld procedure includes these 6 steps:
1. Deburr the weld area with a rotary or draw file
2.Wire brush with a dedicated stainless steel brush
3. Solvent clean
4. Tack weld and
5. Wire brush again
6. Solvent clean again and you are ready to weld
What to remember
Welding titanium can be tricky. Just remember the 3 most important points to be a successful titanium welder.
If filler is needed, only use titanium with titanium.
If it gets hot enough to turn red, it has to be shielded.
If it wasn’t clean, it won’t pass.
Happy welding. SMT
Shaun Relyea is technical support manager for Fronius USA, Brighton, MA.