pure molybdenum sheet, milling and drilling

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Thread: pure molybdenum sheet, milling and drilling

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    Default pure molybdenum sheet, milling and drilling

    Hi all --


    Mo has been discussed here a while back, but I thought I could get some job-specific insight. This is for my own lab, not manufacturing/production. So I have the time, but I do not have $$$$ to invest into this.


    I need to make 5 parts out of pure Mo sheet, 3 mm thick. Each part is a rectangle 35x62 mm, with 40+ holes ranging in size from 1.25 mm to 2.0 mm. The 1.25 mm holes are then tapped 0-80. The parts are used as heat sinks in microscopy which experience excursions from -80C to +40C while epoxy-glued to borosilicate glass. The choice of Mo is due to corrosion resistance, low heat expansion, good conductivity, relatively low cost (compared to say Ta), and relatively ok machinnability. Tried Al, numerous SSs, Ta, Ti, Invar, W and none had all of the above properties in one material.


    I just made one of these on a Sherline mill. The part came out OK, it took about 5 hrs, and I am not looking forward to repeating this for 4 more. So I am wondering if there is anything I can do better. I glued the original 3 mm 100 x 100 mmplate to a 10 mm flat Al plate, used RPMs and feeds I would normally for Steel and Ti. There was not much heat/smoke, just very fast wear of the drills and mills. Used TiN-coated centre drills for drilling holes and a 4mm 2-flute carbide endmill. No other drills b.c the part wast thin enough, and the centre drills went through. For 1 part, used up 10 drills and 3 mills. Tapping was OK b.c. the threads were shallow.


    Any specific drill/mill brand recommendations? Special oil? Can these be laser-cut instead? Tried water jet (outsourced), it formed bubbles and delaminated. For now, I ordered a 2mm plate instead of 3 mm, just to make it a bit less epic.

    Thank you all in advance!

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    Moly is nasty to machine and there's only so much you can do to get away from tool wear. Making sure you're tools don't have much run out and your work holding is stable is very important. Make sure you coolant is good and don't be shy with it. As for specific tools there's plenty of high performance tools out there that can get this job done, but that will have a lot to do with how much you're looking to invest in this project. I am a Kennametal guy and swear by their products (especially Mills), but Guhring and Walters both make some amazing drills, but you're going to pay for them. Really any of the larger companies will have multiple options to get this job done for you.


    Quote Originally Posted by runcyclexcski View Post
    Hi all --


    Mo has been discussed here a while back, but I thought I could get some job-specific insight. This is for my own lab, not manufacturing/production. So I have the time, but I do not have $$$$ to invest into this.


    I need to make 5 parts out of pure Mo sheet, 3 mm thick. Each part is a rectangle 35x62 mm, with 40+ holes ranging in size from 1.25 mm to 2.0 mm. The 1.25 mm holes are then tapped 0-80. The parts are used as heat sinks in microscopy which experience excursions from -80C to +40C while epoxy-glued to borosilicate glass. The choice of Mo is due to corrosion resistance, low heat expansion, good conductivity, relatively low cost (compared to say Ta), and relatively ok machinnability. Tried Al, numerous SSs, Ta, Ti, Invar, W and none had all of the above properties in one material.


    I just made one of these on a Sherline mill. The part came out OK, it took about 5 hrs, and I am not looking forward to repeating this for 4 more. So I am wondering if there is anything I can do better. I glued the original 3 mm 100 x 100 mmplate to a 10 mm flat Al plate, used RPMs and feeds I would normally for Steel and Ti. There was not much heat/smoke, just very fast wear of the drills and mills. Used TiN-coated centre drills for drilling holes and a 4mm 2-flute carbide endmill. No other drills b.c the part wast thin enough, and the centre drills went through. For 1 part, used up 10 drills and 3 mills. Tapping was OK b.c. the threads were shallow.


    Any specific drill/mill brand recommendations? Special oil? Can these be laser-cut instead? Tried water jet (outsourced), it formed bubbles and delaminated. For now, I ordered a 2mm plate instead of 3 mm, just to make it a bit less epic.

    Thank you all in advance!


    BBunch
    Machinist @ Knise and Krick inc.


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    Default Re: pure molybdenum sheet, milling and drilling

    Thank you for the note! I went ahead and got two new 4mm dia mills and two new 1.25 mm centre drills, in all-carbide. They were about $50 USD each, and this is 10x of what I normally spend per endmill


    I am in the UK, so my local good supplier is Cromwell Tools, and here is an example. If it does not work out, I will try one of the suppliers you suggested.


    https://www.cromwell.co.uk/shop/cutt.../p/DOR1611761E


    Regarding outsourcing, I have contacted quite a few laser cutting companies, and noone was interested in one-off high-tolerance job. Actually, one indicated they would take this on if I supply a 2 mm Mo sheet in 500 x 500 mm or bigger (about $1K on ebay from China). I could go for this in the future. However, I am in R and D and prototyping. Spending 2K for on a job, just to realize after tests that a few dimensions need to change, is not sustainable. E.g. this particular part I am working on right now is the 9th interation.



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    Default Re: pure molybdenum sheet, milling and drilling

    Just wanted to follow up on my own thread. I got the carbide mill and drill (the parts from Cromwell tools I listed), and the tools made a huge difference. One 1.6 mm OD centre drill survived 30 holes, 2mm thick Mo, about 1000 rpm or so, oil, and I think it has plenty left. The carbide mill and drill were not cheap, never spent so much on tools before.

    Drilling MO was a bit similar to drilling glass: I needed a bottom plate to make exit holes clean, otherwise the material "delaminated" from below. I observed the same with waterjet cutting. Gluing the 2 mm sheet to an Al plate with wax and rosin produced nice and clean holes.



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    Default Re: pure molybdenum sheet, milling and drilling

    Moly is pretty abrasive. I have run a few parts made from it. I don't know that you will be able to use a tap. I wasn't able to get more than one or two holes before that tap wore out and seized in the part. I had to thread mill it, but mine were 10-32 STI so it was easy to thread mill.

    You have to cut it a certain way to keep it from chipping off. I think I worked top down and from the outside to inside. If I tried to machine inside to outside it would chip off the corners.

    Moly is mostly used in space because it has a extremely low coefficient of linear thermal expansion. It can go from -100C to +100C with very little movement.



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