CVD Diamond Coated Endmills and Coolant
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  1. #1
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    Default CVD Diamond Coated Endmills and Coolant

    Hello everyone, long time lurker here, I think this is the first time I had a question that I haven't seen answered here, but this week I was really thrown a curveball that I hope someone might have some input on. So the material is some kind of quartz/silica type aggregate in a polymer, think composite countertop material. I have to machine various test specimens from this material, and the only thing that will hold up at all are these CVD Diamond coated endmills my coworker has for machining graphite.

    My question is does running coolant have any detrimental effect on this coating this would cause them to wear faster than they would without? Also, if anyone has done a similar job and found some parameters (feeds/speeds) or tooling that was a magic bullet, advice would be appreciated.

    My coworker is a longtime toolmaker that insists these mills be run without coolant. I believe (and my boss has my back) that this material must be worked under flood coolant at all time due to the silica dust hazard. I suspect coolant or not, they are going to wear unacceptably because WE ARE MILLING ROCKS. We are going to call the manufacturer tomorrow morning, but I'm hoping maybe someone here has some additional insight because if they can be cut with coolant I know engineering is going to try to push to proceed and it has just been a nightmare to work with this material.

    If anyone is wondering why I am attempting to mill ROCKS, I am a machinist at a material science company and we are trying to make various standard specimens out of this material (tensile, compression, TMA, DMA, flexure, etc etc). This is my 3rd year in this field if you include 2 years of school, so I am very green and the knowledge of these forums has been and will be very much appreciated.

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    Pretty sure you want to use coolant. The only diamond coated end mills I have used were Dataflutes 15 years ago milling plastic. It sounds to me you should be using diamond tools to machine stone, or quartz countertop material, which I do a lot of. Keep in mind this is going to be REAL hard on your way covers, vises, and anything else it touches. For a speeds feeds reference a high end with the proper tools is 1 ipm per thousand rpm with a 1/4" tool, and 3-4 ipm per thousand rpm with a 3" tool. Proper tools are diamond crystals held in a metal bond, with LOTS of coolant in a 360 degree ring.

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    Once the coating is gone the tool is toast. Carbide does not hold up to quartz very well. You really want the diamond/metal matrix as per DavidScott and you will need a rougher and a series of finishers. Rougher wears quickly so accuracy drops quickly.

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    I ran CNC saws for a couple years that sliced pure silicon rods for the electronics industry. Computer chips
    We used a stainless steel blade with a bonded diamond edge. The coolant was a slick soapy with the viscosity of water.
    Without coolant to keep the diamond edge cool and flushed of slurry the edge would only last minute's.
    Our coolant was plumbed in from another room. It went down one night and 10 saw blades were wiped out before the saws could coast to a stop.

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    I am curious about "diamond coated end mills". A search obtained many places that sell them, but no explanation of just what they are. Is this some kind of coating like a plating or a paint which adheres to the tool on it's own - diamond and nothing else? Or is it a diamond abrasive, perhaps very fine, that is cemented to the tool? Or some other process? For that matter, is it really actual diamond?

    I have never heard of any process for actually plating with diamond. If such a process existed, couldn't you use it to grow larger diamonds from smaller ones? $$$$$$$$! On the other hand, I would think that an end mill has most of it's cutting action right at the edge and conventional wisdom says the sharper that edge, the better the cutting action, well up to a point, anyway. It would seem that coating a sharp edge with a diamond abrasive, no matter how fine, would just dull it. And that coating would wear away fairly fast at the cutting edge, exposing the substrate which would then wear even faster. Why would that be better than a diamond burr?

    So, I am curious, just what is a "diamond coated end mill"?

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    The Dataflutes I have had the diamond "grown." on the carbide endmill like a coating. It's about .002" thick and in coating the end mill it rounded the cutting edge. Terrible burrs in ABS.

    By the way the 3" face mill I use for stone and quartz wears about .001" per 5ish pounds of material removed, wear is pretty minimal.

    I just remembered the company that did the coating, it was Crystallume.

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    Here is a bit of information about the process. It may not be the only process but there isn't much online about how its done.

    US4155721A - Bonding process for grinding tools
    - Google Patents

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    That is for single layer bonds, you want a thick bond with the diamond throughout so there is 1/4" or more of tool that has to wear off before it's toast. Bonding metal to diamond is very difficult, you need to use a reactive metal alloy to do it right. Diamond is an incredibly interesting material.

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    This patent appears to be for binding abrasive particles to a tool. It says diamond or other abrasive.



    Quote Originally Posted by mllud22 View Post
    Here is a bit of information about the process. It may not be the only process but there isn't much online about how its done.

    US4155721A - Bonding process for grinding tools
    - Google Patents

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    And this one appears to be an actual diamond plating process. Very interesting.

    Thanks for the reference. I could have searched for hours to find that.



    Quote Originally Posted by DavidScott View Post
    The Dataflutes I have had the diamond "grown." on the carbide endmill like a coating. It's about .002" thick and in coating the end mill it rounded the cutting edge. Terrible burrs in ABS.

    By the way the 3" face mill I use for stone and quartz wears about .001" per 5ish pounds of material removed, wear is pretty minimal.

    I just remembered the company that did the coating, it was Crystallume.

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    Sandvik has developed a way to 3d print diamond materials. Diamond tooling is about to get really interesting!


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