Titanium Machining Troubles
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  1. #1
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    Default Titanium Machining Troubles

    I am working on an order of 25 parts made out of Ti 6Al HTa. I have only machined Titanium a few times so I am no expert.

    The dimensions of the finished part will end up being (Inches) .25 X 1.522 X 21.640 with a fairly loose tolerance of +- .005. The Stock measures .4 X 2. X 22.

    I am having a hell of a time keeping it flat on the .250 thickness. Currently held in two kurt vises and jack screws under in a few spots.

    I am using generic end mills at this point but will probably order titanium specific tomorrow.I am considering building a fixture as well so I can clamp it against a solid plane and play the musical clamp game for a while.

    I guess my question is, does any one have any tips on how they would do this, and will this part still spring like a pringles chip once I un-clamp it from the fixture. Would proper tooling help significantly? Machines a Mazak 510C

    Thanks in advance fellas!

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    mill,flip repeat.

    Flood the hell out of it,don't let the tool rub or get hot.
    And use SHARP TOOLING!

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    Quote Originally Posted by PegroProX440 View Post
    I am working on an order of 25 parts made out of Ti 6Al HTa. I have only machined Titanium a few times so I am no expert.

    The dimensions of the finished part will end up being (Inches) .25 X 1.522 X 21.640 with a fairly loose tolerance of +- .005. The Stock measures .4 X 2. X 22.

    I am having a hell of a time keeping it flat on the .250 thickness. Currently held in two kurt vises and jack screws under in a few spots.

    I am using generic end mills at this point but will probably order titanium specific tomorrow.I am considering building a fixture as well so I can clamp it against a solid plane and play the musical clamp game for a while.

    I guess my question is, does any one have any tips on how they would do this, and will this part still spring like a pringles chip once I un-clamp it from the fixture. Would proper tooling help significantly? Machines a Mazak 510C

    Thanks in advance fellas!
    Dump the jack screws they are useless on small thin parts.
    get 2 sets of vise jaws 10" wide mill your jaws and your golden

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    Helical makes good cutters for Ti. I would never run generic.

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    Quote Originally Posted by Delw View Post
    Dump the jack screws they are useless on small thin parts.
    get 2 sets of vise jaws 10" wide mill your jaws and your golden
    The long vise jaws won't do much if machining with the stock flat. They could help if used as described below.

    What's going on is release of internals stress in the (presuming) rolled sheet part, and new stresses added during the cutting itself. Ti is both tough and of low modulus of elasticity, and this fights you when trying to maintain flatness over long, thin parts.

    The toughness resists cutting, which means more "pushing" of material over slicing, introducing stress and warping. The low modulus means the material deflects more easily as it's being cut, and it can then return to the original (or new) position after the tool has passed by.

    If this is a relatively simple part (the .250 flatness is a uniform plane), you can try starting with the stock set vertically in the vise jaws, and side mill with a ~5/8" or so endmill on both sides of the ~1.55" sticking out. Take balanced (cut both sides equally), small WOC, full DOC passes so that you put little stress into the part as you cut it. Yes, use sharp cutters and good, lubricious coolant.

    You can try doing this with a pair of passes, release stock and check for warp, then a new set of passes. You might have some issue with a change in flatness after you arrive at final thickness and and flip to mill off the remaining stock. Which brings up the question - if the part is flat, can you just start with the right thickness to begin with? What's the final general shape, it would help knowing for more tailored suggestions.

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    Quote Originally Posted by Milland View Post
    The long vise jaws won't do much if machining with the stock flat. They could help if used as described below.

    What's going on is release of internals stress in the (presuming) rolled sheet part, and new stresses added during the cutting itself. Ti is both tough and of low modulus of elasticity, and this fights you when trying to maintain flatness over long, thin parts.

    The toughness resists cutting, which means more "pushing" of material over slicing, introducing stress and warping. The low modulus means the material deflects more easily as it's being cut, and it can then return to the original (or new) position after the tool has passed by.

    If this is a relatively simple part (the .250 flatness is a uniform plane), you can try starting with the stock set vertically in the vise jaws, and side mill with a ~5/8" or so endmill on both sides of the ~1.55" sticking out. Take balanced (cut both sides equally), small WOC, full DOC passes so that you put little stress into the part as you cut it. Yes, use sharp cutters and good, lubricious coolant.

    You can try doing this with a pair of passes, release stock and check for warp, then a new set of passes. You might have some issue with a change in flatness after you arrive at final thickness and and flip to mill off the remaining stock. Which brings up the question - if the part is flat, can you just start with the right thickness to begin with? What's the final general shape, it would help knowing for more tailored suggestions.
    Mtndew had that part covered basically, I was stating the obvious get rid of the jack screws there useless.
    theres a million ways to skin a cat but you sure the hell aint going to do it with Jack Screws

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    You really need to ditch the vice for that part, no matter what jaw configuration you come up with you're going to be constantly chasing your tail.

    The part needs to be fixed to a static plane to stand much of a chance of coming out flat after multiple flips.

    If you have the parts laying around, a simple vacuum fixture is probably the best option, but .005" final tolerance means you will have to be careful, and probably experiment a bit, with o ring protrusion.

    Double sided tape is another option, although I have much less experience with that.

    Freeze clamping would be a neat way to do this, but I've never tried it and I doubt many people have that kind of equipment lying around a job shop.

    End/side stops in any case, positioned to react directly opposite the cutting forces.

    Finally, ditch the endmill. 45 degree high positive facemill with uncoated polished aluminium geometry inserts. A 2-3" one that will pass over the full surface in one pass.

    Milling the top with an endmill and a stepover will not only warp, but also twist the part.

    It's daunting running a facemill over the top of a small thin piece that's only held down by air pressure, but I've done it a fair bit now and I've not had a part let go underneath the cutter yet (touch wood).

    Smallest part I've successfully held in a vacuum fixture was some aluminium plates about 2.5" sq. 6mm thick down to 4.5mm. I was really skeptical there was enough surface area to hold the part, but it worked completely fine.

    Honestly though, if I was in your shoes I'd be trying really hard to find a way to not have to thickness that plate...

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    The material cannot be changed. Its a government part and they stock is already defined by their print and is already sitting on my floor. I'm going to make a fixture to clamp them against and I will order some cutters today. Since starting this new job I'm taken more out of my mold and die background and leaning towards small batch government and aerospace parts. I have a lot of learning ahead.

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    Just use a magnetic chuck, and grind the thickness.....

    I agree with Gregor though, it doesn't sound like vise work to me. Even fucking around with Destaco clamps would be a better option for the .22 thickness. Vacuum is a little sketchy IMO, but it might work.

    R

    EDIT; I have no idea what condition the stock is in. But maybe use a vacuum fixture for a sub section of the sheet and work the Thickness that way-then nest the parts out of that.

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    Quote Originally Posted by gregormarwick View Post
    Double sided tape is another option, although I have much less experience with that.
    I would give this a shot, but just for finishing the .250 thickness. You have to test how it reacts with your coolant first.

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    Cut the first side flat in a vice with face mill, drill mounting and locating holes around the perimeter, slot mill perimeter of part finished .03" past other floor. Flip and bolt onto flat fixture plate cut second side, leaving .005"-.008" thick x .25" long vertical tabs every three inches or so holding the part into the window frame. Release and break part out, block sand or file tabs flush with flat surface.
    f
    For endmills, Kennametal Harvi III are hard to beat, and are designed for roughing and finishing Ti. For facemills, if you have a positive 45 degree tool, use that. If not, find one you have been wanting or needing on other projects and buy it.

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    Shots in the dark. ;-) Not even a SWAG

    hold in low melting pt alloy, eg. Chamber Casting Alloy Ingot aka low 158-190F - RotoMetals

    Of course you have to keep it cool; not always easy.

    I don't suppose the spec will let you stress relieve.

    Hope you are getting good $$ for this job.

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    Our coolant Blaser eats through adhesive in seconds, titanium is not magnetic. Clamping it in multiple spots on a fixture and flipping it a few times is probably my best bet i am thinking. If I had more than 25 to make I would be looking at other avenues. We have a vacuum chuck but I cant get it to hold worth anything. Its suction is generated by a venturi off an airline and in my opinion does not produce enough suction for most applications. Whats your experience with them?

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    Quote Originally Posted by PegroProX440 View Post
    We have a vacuum chuck but I cant get it to hold worth anything. Its suction is generated by a venturi off an airline and in my opinion does not produce enough suction for most applications. Whats your experience with them?
    They can work, but it helps to have either a flat part to start with, or something compliant to "give" and conform to the chuck face. Otherwise you get too much vacuum leaking. If need be, add o-ring grooves or other gasket methods for less flat stock. But Ti, since it moves and is tough to cut, is among the more difficult materials to hold in a vac-chuck.

    Any thoughts on my suggestion to hold the part vertically and try side cutting each way with long endmills? You do have enough remaining width to hold the part in some vises.

    Or hell, send the stock out for double-disk or blanchard grinding, let it be someone else's headache...

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    Venturi vacuum generators can produce a very strong vacuum but low volume so they don’t tolerate leaks. A vacuum gauge would be important if it is not holding.

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    Quote Originally Posted by litlerob1 View Post
    Just use a magnetic chuck, and grind the thickness.....
    You got one of those Titanium magnets laying around I could borrow?

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    Just a note on vacuum chucks- you can suck as hard as you want, but the most force you'll ever get is 14.7 pounds per square inch, the result of atmospheric pressure. A 50 HP vacuum pump can't make it any better. Thus, they work better for large areas and are pretty terrible for tiny parts.

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    Quote Originally Posted by PegroProX440 View Post
    Our coolant Blaser eats through adhesive in seconds, titanium is not magnetic. Clamping it in multiple spots on a fixture and flipping it a few times is probably my best bet i am thinking. If I had more than 25 to make I would be looking at other avenues. We have a vacuum chuck but I cant get it to hold worth anything. Its suction is generated by a venturi off an airline and in my opinion does not produce enough suction for most applications. Whats your experience with them?
    Venturi vacuum generator is what I have too.

    Creates a pretty effective vacuum but doesn't have the capacity to tolerate any leakage, so a very good seal is important. Sometimes you need to help it by pushing the part down until it creates the seal, it can't always do it on it's own, but then when it's got it held it keeps it held pretty good.

    It works surprisingly well for small parts, in that it will keep them held down pretty well, but they can be pushed around pretty easily, so you need side stops on all sides, or if the part has holes in you can dowel it through those etc.

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    Quote Originally Posted by mhajicek View Post
    You got one of those Titanium magnets laying around I could borrow?
    You know me so well. I've one specifically for Ti, one for Plastic, one for Brass, and one for Metal.

    R

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    Quote Originally Posted by mhajicek View Post
    You got one of those Titanium magnets laying around I could borrow?

    Ti IS a tad magnetic (as compared to other ferromagnetic materials) to a strong, external magnetic field, but probably not enough to hold for a 2" wide face path.
    Just my $0.02

    Doug


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