titanium tapping and welding questions

i_r_machinist · Jul 17, 2013

I have to make a valve gag out of titanium. It will be welded after tapping. First, I can't remember ever tapping Ti. I know that if you let a drill dwell it will work harden like hell. Any problems tapping 1/2"-13 by 1.25" thru? I'm planning on putting 1/4" beads on the sides. Warpage or hardening problems? Post weld heat treat?
Engineers are beating the doors down.
Any help much appreciated!
i_r_machinist

welds will be along the length of the cylinder. Cylinder is 1 1/2" od 3/8" long with two 3/8" grooves along the side. Plate is 3/8" thick.

Limy Sami · Jul 17, 2013

I'd tap it post welding, that way you won't run the risk of distortion - because taking a whisker out of a Ti thread with a tap is not fun.

IIRC Welded Ti squirms about nearly as much as stainless steel - yuk.

allloutmx · Jul 17, 2013

you shouldnt have much warping problems but to be safe you should try to hold it against a block of aluminum...i recommend a large gas lense on the torch.

JRIowa · Jul 17, 2013

TI can be a real bitch when welded. If we had a part like that, we'd send it out to get welded in a glove-box. Hydrogen, Oxygen, and Nitrogen all cause embrittlement in TI. The back side of the joint should be shielded also.

On the cylindrical part, drill 1/4" through. Clean the weld joints with acetone. Argon or He/argon mix for shield gas. IIRC, the argon gives a little better penetration.

You can do an stress relieve on the assembly after welding. Depending on the alloy, it's usually around 1,000 F. Section IX gives alloys 1,2, & 3 a P number. You should also have a Class D fire extinguisher close by.

I'm out of the office for a couple of hours, but if you need anything else, call or send me an email.
JR

allloutmx · Jul 17, 2013

JRIowa said:
TI can be a real bitch when welded. If we had a part like that, we'd send it out to get welded in a glove-box. Hydrogen, Oxygen, and Nitrogen all cause embrittlement in TI. The back side of the joint should be shielded also.

On the cylindrical part, drill 1/4" through. Clean the weld joints with acetone. Argon or He/argon mix for shield gas. IIRC, the argon gives a little better penetration.

You can do an stress relieve on the assembly after welding. Depending on the alloy, it's usually around 1,000 F. Section IX gives alloys 1,2, & 3 a P number. You should also have a Class D fire extinguisher close by.

I'm out of the office for a couple of hours, but if you need anything else, call or send me an email.
JR

are you sure you dont mean that the helium provides better penetration?
i use to weld ti in a bubble filled with argon, but have had very good results with extra large gas diffuser

MH1 · Jul 17, 2013

tapping should be done with high end titanium specific taps (had a lot of success with Emuge Rekord series), biggest tap drill you can get away with. tapping last is probably not a bad idea as the Ti likes to close up tapped holes anyway and the welding won't help that. 1/4" is way too much fillet on that part, rule of thumb for fillet welds is 1/2 the thickness of the thinner base metal so i wouldn't go any larger than 3/16 you will see drastically less distortion reducing the fillet size even that little bit (it will still try to be a potato chip when you're done, though!). no post weld HT per se but we generally stress relieve helps "undo" some of the distortion. I ASSume GTAW welding? Argon/helium? start gas early if you can and keep the gas on after arc off for 15 seconds or so until the weld cools will help with contamination. Filler should be ELI/Gr23 if you can get it. will help with contamination/reduce cracking chances.

MH1 · Jul 17, 2013

allloutmx said:
are you sure you dont mean that the helium provides better penetration?
i use to weld ti in a bubble filled with argon, but have had very good results with extra large gas diffuser

View attachment 81396

it does here on the east coast. maybe not in the middle! large gas cup should do fine, his weld length is fairly short. we regularly do out of chamber GMAW with 7/8 and 1" gas cups it really only needs to be shielded until it's cools down closer to 1000 deg F.
back shielding is a good idea but difficult on this part, the second side fillet should be re cleaned/wire wheeled shiny again before welding though.

JRIowa · Jul 17, 2013

OK, so I didn't remember correctly! WTF, I've got all of this information stored and sometimes it comes out wrong. Just wait 'til you guys get to be as old as me. It's been 6 years since I had the weld engineers.
Young punks from back east. Geez!

JR

allloutmx · Jul 17, 2013

JRIowa said:
OK, so I didn't remember correctly! WTF, I've got all of this information stored and sometimes it comes out wrong. Just wait 'til you guys get to be as old as me. It's been 6 years since I had the weld engineers.
Young punks from back east. Geez!
JR

partial credit for being close....the way i learned was helium is to welding as nos is to a gas engine..it gives you some boost when you run out of amps.

MH1 · Jul 17, 2013

JRIowa said:
It's been 6 years since I had the weld engineers.
Young punks from back east. Geez!
JR

thats OK a weld engineer's primary job is to remove as much welding as possible anyway!

Limy Sami · Jul 17, 2013

JRIowa said:
OK, so I didn't remember correctly! WTF, I've got all of this information stored and sometimes it comes out wrong. Just wait 'til you guys get to be as old as me. It's been 6 years since I had the weld engineers.
Young punks from back east. Geez!
JR

Thats right JR, give them some stick

OLD FARTS RULE, OK!

JRIowa · Jul 17, 2013

Not our weld engineers! We are covered by ASME Section IX of the B&PV code.
We need to have a procedure for every weld that we do. That's all the P numbers, non P numbers, and any process.
Then, they need to track the performance qualifications and the certifications plus all of the test certificates.
I think that our engineer is working on a WPS and the corresponding WPQR to join some high alloy crap with 2% tungsten. All I know is that tack welds aren't allowed. Nasty stuff.
JR

David J. · Jul 17, 2013

I make odd stray stuff like this fairly often.
I'd weld it first then drill and tap.
Tig, big gas lens, lots of pre and post gas flow.
Usually fit the part in a small, open top box to help contain
the argon around the part. Pretty easy to make a temporary
sealed glove box also but I doubt you'll need it.
As far as heat and puddle control I find Ti to be just
like stainless. Maybe test weld a piece of scrap to check
gas coverage before you cook the finished part.
David

Royldean · Jul 17, 2013

allloutmx said:
...helium is to welding as nos is to a gas engine..it gives you some boost when you run out of amps.

In that case, give me two bottles... the big ones.

/today's terrible movie quote

ritzblitz · Jul 17, 2013

When I had to tap blind 1/4-28 holes about 2in deep, I found the best taps were Emuge taps with a slow twist, they said they were good for nickel IIRC. Cut like butter. Kennametal makes a good tap as well. Good luck.

dave powelson · Jul 17, 2013

Welding Ti without contamination and unacceptable oxidation isn't a walk in the park.
If this is a one-off deal, suggest having it done by one who regularly does chamber work.
That part will need damming and back side purge flow.

Miller - Titanium 101: Best TIG (GTA) Welding Practices

Miller - Only as Strong as the Weld: Best Practices for Welding Titanium Tube & Pipe

Bondo · Jul 17, 2013

The little amount of Ti I have welded/tapped, I have always "pre drilled" then welded, then drilled to finish size and then tapped. This way i am removing as little material as possible in case there is a hard spot from welding.

Edit: Well that is how I was told to do it anyways. I don't have $150,000 worth of student loans so I guess I'm not qualified to give an opinion in this matter to the engineer I dealt with :nutter:

MH1 · Jul 18, 2013

JRIowa said:
Not our weld engineers! We are covered by ASME Section IX of the B&PV code.
We need to have a procedure for every weld that we do. That's all the P numbers, non P numbers, and any process.
Then, they need to track the performance qualifications and the certifications plus all of the test certificates.
I think that our engineer is working on a WPS and the corresponding WPQR to join some high alloy crap with 2% tungsten. All I know is that tack welds aren't allowed. Nasty stuff.
JR

thats why we design out all the welds!!

helterskelter · Jul 18, 2013

We weld a ton of titanium. It needs to be clean, clean, clean, clean, clean. Acid etch it immediately prior to welding (I can give you the solution if you need it). Buy high quality filler rod and acetone wipe it prior to welding. It's highly recommended if at all possible to weld it in a chamber purged with argon. The bead should be bright and shiney with some light straw being acceptable. Dark straw or blue is cause to reject the weld. Also, if you can build some chill blocks to cradle your piece. We use copper with cooling water plumbed through the blocks. Titanium moves and shrinks when you get it too hot. I have a fair bit of titanium welding reference materials available, so if you have any questions feel free to PM me.

Edit: I'd also recommend a heat treat after weld. If you need a baseline one let me know.

JRIowa · Jul 18, 2013

MH1 said:
thats why we design out all the welds!!

Yah! That's why I get stuff that comes across my desk that won't work. The latest was a C5 body with mild steel reducers. Who designed the welds out of that. Then the fact that you can't weld mild steel to a C5 casting.

Here's a part to take the welds out of

The big pipe is 24", everything is 9Cr - 1moly
JR

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