Request for material recommendation (probably a Titanium alloy

[John2004]

Hi everyone,

I need to machine two small parts. One part requires a yield strength of 100,000 PSI and one part requires a yield strength of 200,000 PSI. It's probably best to machine the parts from stock that has a thickness near the part thickness. There are some small internal radii and a small cutter of 1/4" OD will probably be needed for much of the
machining and a 3/6" OD cutter for a few other small inside radii. I need a lightweight material preferably similar in weight to Aluminum. I'm guessing that Titanium is the best compromise (perhaps the only one) even though it's a little heavier than aluminum it's still lighter than steel.

I've listed the overall dimensions of the two parts below along with the required yield strengths.

Part #1 overall dimensions (required yield is 100,000 PSI)

2.557” Long
3.873” wide
2.139” thick

Part # 2, overall dimensions (required yield is 200,000 PSI)

Part 2.339” thick
2.557” Long
3.873” Wide

Here is what I found in Machineries Handbook...

5 Al, 2.5 Sn Alpha yield = 117 KSI condition is annealed

5 Al, 2.5 Sn (low O2) Yield = 108 KSI condition is annealed

3 Al, 8 V, 6 Cr, 4 Mo, 4 Zr Condition is Solution + age KSI yield = 200 KSI This is a beta alloy

I have no real experience with Titanium, they list Alpha, Alpha-Beta, Near-Alpha, & beta alloys but I'm not sure what the real differences are.

For a few parts this small, what is the general difference in cost (materials plus labor) as compared to making the part from aluminum or steel ? Aluminum and non-hardened steel are probably out of the question at both the required yields, but I'm just curious how titanium would compare.

How hard is Titanium to machine ? How does it compare to Aluminum and say 4140 pre-hard ? I'm guessing it must fall somewhere between these two ranges.

I would appreciate any recommendations for a specific grade of material and any tips for machining.

Thanks
John

 

[metengr]

John2004;
For a decent background on Ti alloys, I would suggest you go here and download their Technical Manual. This has excellent information for design purposes and handling;

http://www.timet.com/Index2_content.html

Second, make sure you understand that Ti does have limitation in terms of stiffness, it is more flexible in comparison to other metals.

 

[John2004]

Thanks for the link Metengr, I will check out the information.

As far as stiffness, as long as the elastic modulus is at least as good as Aluminum, I should have no problems.

 

[GregLocock]

I was involvd in a project that involved machining tons (literally) of Ti bar stock.

Any competent machine shop with modern machines will find TiAl6V4 easy to machine. Segregate the waste and sell it back.

Our machining cost was substantially greater than the material cost.

One nice thing with Ti is that if you have a decent order size they supply barstock to your spec for OD, given six months lead time.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

6Al 4V is "common" in airplanes ... fty between 120 and 160ksi ... in our material reference AR-MMPDS-01 or Mil-Hdbk-5 (available on-line) don't include fty near 200ksi ... i suspect that pushing the materila strength that much indicates that you've lost something somewhere else ... machinabiity, fatigue, ...

 

[CoryPad]

Were you planning to buy plate and use a milling machine to make the parts? What are your volumes? The high strength alloys may not be available for small orders.

Ti-3Al-8V-6Cr-4Mo-4Zr (also known as Beta C) can have yield strength above 1400 MPa (200 ksi), but it probably will only be available in bar/wire. Ti-10V-2Fe-3Al or Ti-6Al-2Sn-4Zr-6Mo can have strength near 1400 MPa and should be available in plate.

For the 700 MPa (100 ksi) strength parts, you could use the standard Ti-6Al-4V alloy.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[John2004]

Thanks for the additional feedback everyone.

I was planning to buy plate and mill the parts. Initially, the volumes are just a few pieces to test.

I will check into the Ti-6A1-4V for a 100 KSI yield and the Ti-10V-2Fe-3Al or Ti-6Al-2Sn-4Zr-6Mo for a 200 KSI yield. Hopefully, I can find the material in plate and in a small enough quantity.

Thanks again,
John