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Re: [multimachine] Re: Large lathe for flame spray operations

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  • Dr. Alexis O'Neill
    Dave, This helps enormously. I think we can try almost all of your suggestions, as the speeds we tried are way above what you ve listed and we didn t do any of
    Message 1 of 12 , Feb 4, 2013
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      This helps enormously. I think we can try almost all of your suggestions, as the speeds we tried are way above what you've listed and we didn't do any of this. Also, the soda water would be helpful. All we want to do is take off about 200mils or less of the coating to polish it, as the sprayed surface is not very pretty and hard to seal for use around food stuffs.

      I will get all this ready and we'll try more samples. At least now we have a direction to move in.

      Thanks very much, we'll make more samples and see what happens.


      Enviado desde mi oficina móvil BlackBerry® de Telcel

      -----Original Message-----
      From: "David G. LeVine" <dlevine@...>
      Sender: multimachine@yahoogroups.com
      Date: Mon, 04 Feb 2013 01:52:24
      To: <multimachine@yahoogroups.com>
      Reply-To: multimachine@yahoogroups.com
      Subject: Re: [multimachine] Re: Large lathe for flame spray operations

      On 02/03/2013 10:16 AM, Dr. Alexis O'Neill wrote:
      > We need to finish a 316 stainless steel thermal sprayed coating on a
      > carbon steel plate, well, several, but this is the sample, and we
      > can't seem to get the job done. We've done everything up to the first
      > sealing correctly, the technicians think, and this type of coating has
      > a hardness of 81 HRb only, not very hard. Yet the machine shop, using
      > a fly cutter, burned up 7 cutting blades trying to finish the sample,
      > which was only 63cm by 30cm on 1" carbon steel, which makes no sense.
      > I have samples on plates and cylinders sent to me from our suppliers
      > in England and Asia and I have been assured by everyone there that fly
      > cutting the stainless steel is no problem, but we can't seem to get it
      > done. We have taken samples to 2 machine shops here, one of which has
      > around 15 CNCs and plenty of experience, but they said it was too hard
      > a finish. One of my engineers brought me one of the small cutting
      > blades, I don't know what to call them in English, about 3/4 " square
      > and 3/8" thick, and it indeed was blacken with the heat during
      > cutting. The edge was smoothed completely. They ruined 7.

      Hmmm... Okay, let's go back to basics.

      Stainless is NASTY to machine, it work hardens. If your feed is too
      slow, you won't be able to machine it, ever.

      If your SFM is too high, stuff burns right up, so generally it is large
      chip load, no fine cuts and slower than...

      I can assume this is what you are doing, but if not, don't feel too bad,
      I have seen a huge number of burned out tools from too light a cut on SS.

      Another well known issue is machine rigidity for exactly the same
      reasons. The machine flexes a little (or is a little loose), the bit
      rides on top of the affected layer and it can't ever get back.

      Some experiments:


      Try fly cutting as slow as your machines can go (on the order of 35-70
      SFPM, no faster!) and cutting completely through the stainless in one
      pass. It will destroy the test piece, don't worry. Watch the cutter,
      if it gets hot STOP! You are running way too fast, cut the RPMs in
      half, the chips should NEVER turn blue, at worst brown or straw
      colored. Eventually you will find a feed and speed which work. For a
      100mm diameter fly cut, I would try 30 RPM or less, I don't know the
      feed or depth of cut, but I would guess it would be pretty high and the
      chip load would be pushing the machine's limits.

      You also need to look at tooling, TiAlN coatings (the purple ones) or
      TiCN or one of the new SilliconNitride/Aluminum Titanium Nitride coated
      tools may be a big win in dry cutting. Read completedetails in this
      Cutting Tool Engineering article

      Now, take another test sample and prove you can fly cut ALL the
      stainless off without destroying the tooling. Once you can do this, try
      leaving a VERY thin layer of stainless. My guess is that you will find
      the ripples will be horrible because the machine is not rigid enough, or
      the tool will start to burn up. Slow down and try again. After a short
      while it should be obvious that feed and speed are critical and you will
      probably find a few combos which allows you to cut the coating without
      getting molten chips. After that, it is just fine tuning. Remember,
      using coolant to find the range which works and then going dry and
      getting the new parameters is not a bad idea.

      This chart:

      may be of help.

      You may also find an FDA approved cutting fluid (like soda water) which
      will transfer heat out of the cut, my best guess would be to find a food
      grade surfactant (detergent) to use in the water, if only to pull heat
      out of the cut. Cool the tool bit and it might just last much longer.

      Does this help at all?

      P.S. There is no room or the chart would also be in the FILES area.

      Dave 8{)


      /"Among the many misdeeds of British rule in India, history will look
      upon the Act of depriving a whole nation of arms as the blackest."/

      Mohandus Ghandi, An Autobiography, Page 446.
    • pokerbacken
      Stainless can harden when worked, it can harden hard enough to require carbide to cut and even then wear can be excessive. actually a light cut of 0.01mm can
      Message 2 of 12 , Feb 4, 2013
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        Stainless can harden when worked, it can harden hard enough to require carbide to cut and even then wear can be excessive.

        actually a light cut of 0.01mm can be on tools than 1mm deep cut if tool is not extremely sharp and can "lift" the chip from the surface without rubbing the surface.
        success is dependent on machine and tool is being rigid and "high feed and slow speed".
        Least bit of squeal and/or vibration and the part is "lost" to workhardening.

        One of my teachers in school told us to set speed we thought and reduce to half of that and increase feed and depth of cut to 125-150% of what we would use on regular steel.
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