Strange "hammered" surface while turning Titanium grade 5 Ti6Al-4V (annealed)
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    Default Strange "hammered" surface while turning Titanium grade 5 Ti6Al-4V (annealed)

    A subsupplier is currently experiencing a strange phenomenon while turning a workpiece for my company. Serial production. CNC-lathes. We start with a forged blank approx. Ø 100 mm by 1000 mm long, with a bore hole Ø 80 mm. A forged and annealed tube actually. Ti6Al-4V. The blank is in step 1 turned from the inside. In step 2 the workpiece is put on a rather tight mandrel and we turn the outside and most of the material is cut away. The remaining wall thickness of the tube, in finished condition, is only approx. 0,5-0,8 mm.

    In both step 1 and step 2 we sometimes observe a strange surface. The Surface appears to be hammered. This happens more often on the outside (step 2) than on the inside. This hammered surface is not all over the cylindrical Surfaces, mostly partially only and it is not present on all pieces. Some looks "normal".

    The Surface roughness is the same on the hammered and on the regular Surface. Within spec.

    I realise there is a problem with the thin-walled machining and I understand that it is a challange, but what causes this? Vibrations? Heat? Material variation/structure?

    We're Clueless and we've tested lots of different Tools and cutting parameters.

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    You said it was a forged tube? My GUESS would be the forging could have been partially done outside of the proper forging temperatures.
    Do you know how these are forged?
    Hammer, press, ringroller? My bet would be hammer, and forging may have been done as the part cooled and those hits are what you are seeing. But again just a guess... will it show up in a picture?

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    Do you guys like my new hair cut??? Answer me!!

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    Quote Originally Posted by litlerob1 View Post
    Do you guys like my new hair cut??? Answer me!!
    Hey at least he is a step or two ahead of alot of the new posters "Hey my machine ain't working, what's wrong??"
    At least he was specific about the material and a basic outline of the process.

    OP, need to post up speeds/feeds/doc and machine type (toy lathes unmentionable here) and what you are using to cut with, insert size, shape etc.

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    And a close up picture of the surface finish.

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    Quote Originally Posted by litlerob1 View Post
    Do you guys like my new hair cut??? Answer me!!

    No sir, I do not. And I hate your shoes.

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    Quote Originally Posted by litlerob1 View Post
    Do you guys like my new hair cut??? Answer me!!
    Thanks for such a nice attitude. I feel so welcome here and Your comment is so Fruitful. I guess you won´t have an answer even if you had the full picture. Loser!

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    He may be an ass but why would you ask for help without providing the full picture?

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    Quote Originally Posted by RicoRider View Post
    Thanks for such a nice attitude. I feel so welcome here and Your comment is so Fruitful. I guess you won´t have an answer even if you had the full picture. Loser!
    With respect, I suggest it is you who has the wrong attitude. Lighten up and smile. Litlerob1's comment was quite civil considering how others have been treated here. This site is not for the thin-skinned.

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    Quote Originally Posted by RicoRider View Post
    Thanks for such a nice attitude. I feel so welcome here and Your comment is so Fruitful. I guess you won´t have an answer even if you had the full picture. Loser!
    Too bad for you that "looser" likely has the answer to your question, though I doubt you could beat it out of him now.....

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    Hi RicoRider:
    I have seen this phenomenon before too, when turning Ti6Al4V titanium and this is how it was explained to me:

    Titanium exists in two main crystalline microstructures; alpha and beta which are governed by the other alloying elements.
    Alpha is the strong hard microstructure and Beta is the more ductile microstructure.
    Ti6Al4V is a mix of Alpha and Beta, so it's sometimes called a "mixed phase alloy".
    In addition, titanium is notorious for organizing its crystals in several varieties of bigger structures each of which results in different material properties where they occur.

    The management of these microstructures is an imperfect art, and sometimes you can get pockets within the material where one form predominates over another.
    Heat treating or forging the material can make this problem worse.

    Obviously if you have zones in the material that have different hardness and ductility, you will get this weird appearance when you try to machine it and the cutter plows into the softer bits while bouncing over the harder bits.

    So for what it's worth, that is how it was described to me when I bitched about a batch of bar stock I'd gotten that I couldn't turn for shit and couldn't buff nicely either.
    It was Ti6Al4V alloy.

    Cheers

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

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    Quote Originally Posted by RicoRider View Post
    A subsupplier is currently experiencing a strange phenomenon while turning a workpiece for my company. Serial production. CNC-lathes. We start with a forged blank approx. Ø 100 mm by 1000 mm long, with a bore hole Ø 80 mm. A forged and annealed tube actually. Ti6Al-4V. The blank is in step 1 turned from the inside. In step 2 the workpiece is put on a rather tight mandrel and we turn the outside and most of the material is cut away. The remaining wall thickness of the tube, in finished condition, is only approx. 0,5-0,8 mm.

    In both step 1 and step 2 we sometimes observe a strange surface. The Surface appears to be hammered. This happens more often on the outside (step 2) than on the inside. This hammered surface is not all over the cylindrical Surfaces, mostly partially only and it is not present on all pieces. Some looks "normal".

    The Surface roughness is the same on the hammered and on the regular Surface. Within spec.

    I realise there is a problem with the thin-walled machining and I understand that it is a challange, but what causes this? Vibrations? Heat? Material variation/structure?

    We're Clueless and we've tested lots of different Tools and cutting parameters.
    This weekend I had to do a bit of "tractor surgery" replacing various hydraulic bits and pieces and then replace some really close fitting bushings/ sleeves to worn large pins.

    I'm not proud of the fact that I got a little frustrated and not using the correct tools or patience but managed to hammer the sh*t out of certain things and file back some stuff for a pretty freaking tight and precise fit that should last another ten years. [Precision black smithing is sort of an oxymoron.].

    So some pictures would be amazing ! @RicoRider

    cuz I'm wondering if they are literally hammering the sh*t out of things with this "Mystery mandrel" ?

    Have you tried regular turning with offcuts of the stock , just too see how it goes ?

    Do you know what cnc machines they are using + use of steady rests etc.

    vibration can be an issue .

    There are firms that make precision tubes/ specialize in (particularly in Germany).

    that's all I got for three "brain farts".

    Eric

    Photos of the set up and mandrel would be super cool

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    Quote Originally Posted by implmex View Post
    Hi RicoRider:
    I have seen this phenomenon before too, when turning Ti6Al4V titanium and this is how it was explained to me:

    Titanium exists in two main crystalline microstructures; alpha and beta which are governed by the other alloying elements.
    Alpha is the strong hard microstructure and Beta is the more ductile microstructure.
    Ti6Al4V is a mix of Alpha and Beta, so it's sometimes called a "mixed phase alloy".
    In addition, titanium is notorious for organizing its crystals in several varieties of bigger structures each of which results in different material properties where they occur.

    The management of these microstructures is an imperfect art, and sometimes you can get pockets within the material where one form predominates over another.
    Heat treating or forging the material can make this problem worse.

    Obviously if you have zones in the material that have different hardness and ductility, you will get this weird appearance when you try to machine it and the cutter plows into the softer bits while bouncing over the harder bits.

    So for what it's worth, that is how it was described to me when I bitched about a batch of bar stock I'd gotten that I couldn't turn for shit and couldn't buff nicely either.
    It was Ti6Al4V alloy.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    I just read this … What he said too ;-)

    Was wondering about the scale / size of hammered apparent finish ?

    If you take close ups try to put a scale in the shot.

    @RicoRider
    do you have shop microscope or dissecting microscope ?

    And what are the "form" tolerances for the tube ? When finished etc. ?

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    Still waiting for a picture....

    R

    I am an ass. I am an ass. I am an ass. IMNS is my new tag.

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    Sorry for the previous post, but I really think the hair cut comment was a bit rude. Never mind. I will try to get a Picture as soon as possible. Also Micro structure Pictures.

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    Quote Originally Posted by implmex View Post
    Hi RicoRider:
    I have seen this phenomenon before too, when turning Ti6Al4V titanium and this is how it was explained to me:

    Titanium exists in two main crystalline microstructures; alpha and beta which are governed by the other alloying elements.
    Alpha is the strong hard microstructure and Beta is the more ductile microstructure.
    Ti6Al4V is a mix of Alpha and Beta, so it's sometimes called a "mixed phase alloy".
    In addition, titanium is notorious for organizing its crystals in several varieties of bigger structures each of which results in different material properties where they occur.

    The management of these microstructures is an imperfect art, and sometimes you can get pockets within the material where one form predominates over another.
    Heat treating or forging the material can make this problem worse.

    Obviously if you have zones in the material that have different hardness and ductility, you will get this weird appearance when you try to machine it and the cutter plows into the softer bits while bouncing over the harder bits.

    So for what it's worth, that is how it was described to me when I bitched about a batch of bar stock I'd gotten that I couldn't turn for shit and couldn't buff nicely either.
    It was Ti6Al4V alloy.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Thanks alot for great and interesting information. I will get some pics of the Surface and the Micro structure

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    Quote Originally Posted by implmex View Post
    Hi RicoRider:
    I have seen this phenomenon before too, when turning Ti6Al4V titanium and this is how it was explained to me:

    Titanium exists in two main crystalline microstructures; alpha and beta which are governed by the other alloying elements.
    Alpha is the strong hard microstructure and Beta is the more ductile microstructure.
    Ti6Al4V is a mix of Alpha and Beta, so it's sometimes called a "mixed phase alloy".
    In addition, titanium is notorious for organizing its crystals in several varieties of bigger structures each of which results in different material properties where they occur.

    The management of these microstructures is an imperfect art, and sometimes you can get pockets within the material where one form predominates over another.
    Heat treating or forging the material can make this problem worse.

    Obviously if you have zones in the material that have different hardness and ductility, you will get this weird appearance when you try to machine it and the cutter plows into the softer bits while bouncing over the harder bits.

    So for what it's worth, that is how it was described to me when I bitched about a batch of bar stock I'd gotten that I couldn't turn for shit and couldn't buff nicely either.
    It was Ti6Al4V alloy.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    This has been my experience too. When you encounter a piece of Gr5 that does this, you also cannot polish it out. That's the way it looks and that's that.

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    Implement has the answer. I have seen the same surface conditions in Ti investment castings being machined. It’s not an issue just related to forging.

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    Quote Originally Posted by RicoRider View Post
    Sorry for the previous post, but I really think the hair cut comment was a bit rude. Never mind. I will try to get a Picture as soon as possible. Also Micro structure Pictures.
    Haha! You haven't seen anything yet!

    Hope you stick around to learn a bit, and eventually be able to help others here.

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    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.

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