Welding titanium?

[boodlefoof]

Hey guys,

Did a bit of a search through the archives and didn't find any mention of this.



I've been putting together an open road racing Datsun 240-Z. The car in factory form only weighed about 2400 pounds, but I plan on building a complete spaceframe chassis which will add some weight. I'll be shedding some weight elsewhere, but I don't think it will get me down to my target. I'm aiming for a curb weight of about 2000 pounds.

Hence my question... I've read that titanium can be MIG welded, and that, being a ferrous metal, it can be welded to mild steel. However, Ti also has a much higher melting point then steel, so I'm guessing MIG welding might be a little different.

Just curious if anyone has experience welding titanium. It looks like using it for the frame could shave quite a bit of weight (it is about 40% lighter than steel, and perhaps I could also get away with thinner wall tubing at the same time).

This is just an idea... and I'll probably end up going with steel (for cost purposes and if I decide I want to be legal for any sort of club racing... they tend to DQ titanium frames).

Thanks for any thoughts or comments.

[dipren443]

Here, this link should help you out. Should just about have anything you need to know about welding Ti.

http://www.timet.com/fab-p27.htm

Also, Ti is a non-ferrous alloy and welding to dissimilar metals is not recommended.

[race-rodz-inc]

i weld Ti from time to time (motorcycle exhaust), as far as i know... it can be mig welded, you must also do all welding in an inert atmosphere(argon bubble).... material has to be absolutley clean, and cool down after welding is key. they say it can be welded in a clean area with no air drafts...but i have never had any luck with it. as for doin a complete frame..... yes it could be done, but the cost involved both in materials and set-up would make me think its not much of an option.

if your looking for lightwieght material... look to chrome moly, but once again it also needs to be tig welded. if you looking to be able to "tie" the frame back to the body... then mild steel is gonna be your best choice. i would think the cost involved doing anything other than mild steel would outwiegh the 75-100lbs weight savings. that figure is based on a full tube chassis drag car, chrome moly vs mild steel.

good luck...let us know what direction you go

[Matt@RFR]

Ti can be MIG welded, it's done every day. Just apply the same principals (including trailing and back purge gas shielding) and it works great. (Edit: I read "can't be MIG welded" in the above post, but I'll leave this anyway)

You do not need an argon chamber to weld Ti. It's nice for small parts, sure. The article linked above outlines everything you need to know about welding Ti in open air.

And just a note since it sounds like you're starting from scratch: Chrome Moly is not any lighter than mild steel. The weight savings comes from being able to use thinner material to acheive the same strength.

[David Pozzi]

Crome molly is heavier than steel. That's why Cro Mo cranks are heavier than stock cranks unless they drill and shave them down.

I don't think you are going to get near 2000 lbs and have a safe car, the vintage race cobras are heavier than that and have aluminum bodies. You'd be lucky to get it down to 2500 lbs.

No group would let you race a car with a ti chassis. McLaren did race at Indy with one long ago.

[Matt@RFR]

According to this, they weigh the same. 0.284lbs/ cubic inch

1018

4130N

[boodlefoof]

Thanks for the thoughts guys.

Yes, the price is a bit prohibitive... and the race sanctioning is kind of a bummer... and I will probably go with mild steel. It was just something I was curious about. I'm looking to drop weight anywhere I can.

Strange, the book I read (I think it was called "The Welder's Handbook") said that it was a ferrous metal and could be welded to mild steel. If it isn't, that would be a deal breaker, as I plan to weld the frame to the body...

Thanks for the link too. Very helpful.

[dipren443]

Strange, the book I read (I think it was called "The Welder's Handbook") said that it was a ferrous metal and could be welded to mild steel. If it isn't, that would be a deal breaker, as I plan to weld the frame to the body...

Thanks for the link too. Very helpful.

Some stainless or non stainless steels may be alloyed with Titanium to increase corrosion resistance, strength, etc and those may be ferritic. But titanium alone is non-ferritic. I get to play with Ti6AL-4V at work quite often in developing inspections for turbine components and am fairly well versed in it's material properties.

Here is a quote taken from Global Spec, one of our material suppliers...

"Titanium and Titanium Alloys - Titanium and titanium alloys are non-ferrous metals with excellent corrosion resistance, fatigue properties and a high strength to weight ratio."

And one more from a Metals handbook here at my desk:

"Another important characteristic of titanium- base materials is the reversible transformation of the crystal structure from alpha (a, hexagonal close-packed) structure to beta (b, body-centered cubic) structure when the temperatures exceed certain level. This allotropic behavior, which depends on the type and amount of alloy contents, allows complex variations in microstructure and more diverse strengthening opportunities than those of other nonferrous alloys such as copper or aluminum."

[boodlefoof]

Thank you. That is very helpful.

Well, if I can't weld the body to it... I guess I'll be going with steel! I'll have to find some other places to cut weight... I'm guessing the frame will come in around 400 pounds if I go with mild steel.

Bummer that lightweight parts have to be so expensive!

[Matt@RFR]

John, just for clarity because it wasn't specifically mentioned yet: Chrome Moly is easily welded to mild steel.

[boodlefoof]

Thanks Matt. Unfortunately, I do not have a TIG, and hoped to do all of the work with my trusty Millermatic 175.

[David Pozzi]

Matt,
I was told Cro Mo was heavier by David Crower, he was referring to their crankshafts and rods. He told me the percentage difference, but of course I forgot it. Their steel cranks are lighter than their Crome Molly cranks when machined in identical ways.

I have not tried to verify it, but from the site you quoted by clicking on the metric weight link:
1018 0.2843218 /cu in
4130 0.2835992 /cu in
4340 0.2835992 /cu in
That's a fraction of a percent difference but Crower had told me it was several percent. Now I'm confused...

[Matt@RFR]

As you know, Chrome Moly is a generic name for high Chromium and high Molybdenum content steel. Crower is using 4340, and from what I could tell, it's the exact same weight as 4130. Even the 5xxx series steels that I randomly looked at weighed the same. Nitriding didn't have any effect on weight.

I'd like to know what Mr. Crower was refering to! I also wonder if I'm getting bogus numbers.