Strange "hammered" surface while turning Titanium grade 5 Ti6Al-4V (annealed) - Page 2
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  1. #21
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    Quote Originally Posted by RJT View Post
    Using the ignore feature will lower your blood pressure. I find this forum much more enjoyable after I found that feature. You will learn who you don't want to view comments from. I don't need the aggravation, life is too short.
    But that would be boring

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  3. #22
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    Quote Originally Posted by RJT View Post
    Using the ignore feature will lower your blood pressure. I find this forum much more enjoyable after I found that feature. You will learn who you don't want to view comments from. I don't need the aggravation, life is too short.
    Me too, to the above, and how appropriate for a member with a Titanium "rating" to comment on a post with a question about titanium!

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    Some images of the surface...
    1.jpg3.jpg

  5. #24
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    Got any close-in pics of the inserts you were cutting with?

  6. #25
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    Looks like a serious chatter problem. And the underlying finish doesn't look that great, either. I'm gonna go with basic workholding problem, compounded by maybe not a good insert for the job.

  7. #26
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    Quote Originally Posted by RicoRider View Post
    Some images of the surface...
    1.jpg3.jpg
    Quote Originally Posted by Milland View Post
    Got any close-in pics of the inserts you were cutting with?
    That's a lot more severe than what I envisioned from your original comments.

    That's how Ti turns when you use an unsuitable geometry insert, like one with a micro-radiused edge for steel, and/or negative rake.

    Switch to an upsharp uncoated aluminium insert and most likely that problem will go away.

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  9. #27
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    What Gregor said.

  10. #28
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    Quote Originally Posted by litlerob1 View Post
    What Gregor said.
    I third it.

    On another note. I think your haircut looks pretty good.3779869050_216363986c_b.jpg

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    Quote Originally Posted by AARONT View Post
    I third it.

    On another note. I think your haircut looks pretty good.3779869050_216363986c_b.jpg
    This site is on its way down anyway. Let me help it.

    mr-penis_o_3986567.jpg

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    Hi All:
    I'm going to argue against chatter as the root cause, and I say so because the OP pointed out in his first post that the problem is inconsistent not just between parts but within a single part.
    Also, chatter in titanium typically shows a different pattern than what I'm seeing.
    Here's a photo of what chatter on a thinwall titanium tube typically looks like to me (I had a helluva time making this sample...it's a 1" thinwall tube hanging out a fair ways and the 1/2" square tool is sticking out from the toolpost almost 4 inches).

    Next, look at how widely the zones of dimpling are separated by zones where the turned finish is completely different in the original photos.
    Look also at how narrow those zones are and how weirdly they're distributed around the part.

    Last; the customer is subbing these parts out to a vendor who sounds like they are fully capable of machining titanium...after all they're boring these things 80 mm diameter and a METER deep before they turn the outsides.
    This is not some dude with a Southbend in his garage, learning how to do basic turning from Youtube videos.
    So I'm having a hard time believing they are too dumb to identify and correct something as basic as a chatter problem.

    Cheers

    Marcus
    www.implant-mechanix.com
    www.vancouverwireedm.com
    Attached Thumbnails Attached Thumbnails dscn5023.jpg  

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  15. #31
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    So Marcus do you still think the OP's issue is the structure of the material?

    R

    BTW... I think you should fire your pet Beaver and get a new one to machine those parts. Lol

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    Hi litlerob1:
    Yeah I do.
    If you look closely at the lower right corner of the first picture, you can see a pattern of dots with craters around them, almost as if someone had taken a welder and hard faced little dots, and then a ring around them, then turned the material away.
    If you've ever turned a weldment on something like 4140 you can see a similar pattern on the welded area where it's gotten harder than the base material.
    I'm pretty sure that pattern is from the way the Alpha phase crystals have organized themselves into little nodules in a sea of Beta phase, and the cuttere is bouncing over the nodules.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    I'm definitely not arguing with you Marcus. I would defer to you in almost everything. BUT, what I see is a progressively worsening surface finish, as the diameter get larger. To me that says Harmonics.

    R

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    Hi again litlerob:
    Until a sample is sectioned and examined for its microstructure we'll never know for sure, so all we can do is speculate.
    What does surprise me is that the vendor the OP is using had not thought to do that examination as a first step in solving his problem.

    These parts cannot be cheap to produce, and the microstructure of Ti6Al4V titanium is no big secret, so one would think to look there early especially if you can make good parts all day and then, all of a sudden, one goes to shit in only one spot.

    A similar experience turning aluminum or steel, would probably have most of us blaming the material pretty quickly.

    As I said; I have no way of knowing if I'm right or not, but that's where I'd look first, and that was what was blamed when I struggled with a very similar problem on some turned parts back in the distant past.
    (BTW, no one analyzed those parts either: I tipped them in the scrapper, the titanium vendor supplied me with a new bar for free, and the problem went away, so we all accepted the explanation pretty uncritically and moved on)

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Thank you all for your effort to help me solve this problem. At the moment we have not done any microstructure analysis on the particular hammered surfaces, but we have made it on Another tube during a problem with the cylindricity. The microstructure analysis was done in 4 areas in the front of the tube and 4 in the rear.

    I would appreciate if you could give me your opinion/experience regarding machinability after seeing these Pictures. The 2 first is from the front and the others are rear pics. front.jpgfront2.jpgrear.jpgrear2.jpg

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  22. #36
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    That microstructure looks beta annealed especially at the rear. Does this part have any strength requirements?


    https://image.slidesharecdn.com/05ti...?cb=1456959617

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    Quote Originally Posted by RJT View Post
    Using the ignore feature will lower your blood pressure. I find this forum much more enjoyable after I found that feature. You will learn who you don't want to view comments from. I don't need the aggravation, life is too short.
    Unfortunately you can't ignore a moderator.

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  25. #38
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    It will be interesting to see a picture as all of us probably describe things differently. I don't think I have ever used the word "hammered" to describe a turned finish. Maybe this will be something I have never seen before.
    I somehow skipped over the pic, all I can say is WTF!!! Unless that is at an extremely high magnification I have never seen such a thing.

  26. #39
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    Quote Originally Posted by RicoRider View Post
    Some images of the surface...
    1.jpg3.jpg
    I have to admit this application problem has been bugging me a bit , at the back of my mind.

    So first brain fart that occurred to me is a possible interaction with thermal effects (through cutting) and the mandrel.

    So the surface is heated up and further annealed through cutting causing thermal expansion locally of the work piece and then the area behind the cut starts to cool, (but the mandrel is cooler than the thin walled work piece and more of a constant diameter and of a different material or Ct (effectively) ) so as that part of the freshly cut 'Tube" cools and shrinks onto the mandrel it causes localized stretching perpendicular to the direction of the turned cut. These semi circular stretch lines could be as a result of cooling onto the mandrel.

    This "Pattern" occurred to me when looking how tin foil/ aluminum foil can have these wrinkles when wrapped not very well around a tube.

    @RicoRider I think it's essential to show the design of the mandrel and a video of the actual cutting process.

    What level of coolant might be used ? To take heat away in a big way ?

    Does make me think of cryogenic cutting methods ????

  27. #40
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    If I saw something like that my first inclination would be to drop the RPMs and bump the feed rate up.

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