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CNC/surface grinding, how is abrasive wear compensated?

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  • CNC/surface grinding, how is abrasive wear compensated?

    I was watching demonstrations of CNC gear grinding on youtube last night. Being unfamiliar with precision surface or tool grinding, I was wondering how compensation for abrasive wear during grinding processes occurs (or does it)???

  • #2
    They use diamond wheels so wear is very minimal. The CNC control allows for wear compensation so if they do inspect the part and determine the wheel has worn it is easy to compensate for it with a few keyboard inputs.
    Mark Hockett

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    • #3
      That's so

      Mark is correct.

      If the job run justifies the cost a diamond wheel is used. Test runs and records will determine when the wheel is to be advanced to compensate for wear or when the wheel is to be dressed or replaced. Inspection is fairly regular on a "batch" basis.

      Otherwise cubic boron or aluminium-oxide wheels are used and re-dressed or replaced accordingly.

      Same applies to "normal" surface, cylindrical, tool/cutter, and centre-less grinding when done on a CNC/NC-controlled process.

      It also applies to tools on auto/CNC machine and machining centres - lathes and mills included.

      Wear-rates are pretty well established as guides and then "fine-tuned" on the specific machine for a specific job.

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      • #4
        i interpret your question as how wear is allowed for in precision grinding in general vs cnc gear grinding -slight differences although cnc gear grinding is beyond my experience. good info on cnc wear compensation is presented, I'd add that I believe the machine knows where the dresser is so knows where the wheel starts off at.

        you guys say they're using a diamond wheel - on what? the gears? given that they are likely ferrous that would seem odd If you're grinding carbide on a T&C cutter you use diamond, if its steel (on t&C or surface) its a grinding wheel

        For non cnc precision grinding, first off, the wheels just don't wear that quickly. at risk of stating the obvious, you are never concerned with the exact wheel dia. you cut, measure and adjust the wheel position.

        on a surface grinder, what wear there is compensated mostly by technique - if the wheel is .500 wide, each pass might .050-.100 so the leading side of the wheel sees the wear and the trailing barely gets touched. when finished, you spark out, that go over and over and over the work until no point the work makes contact. Using this approach the leading side wears and trailing doesn't, or at least since it is hardly cutting, not by enough to matter.

        on a t&c its no much of an issue in that the ground surface is so narrow it is all ground in a pass; ie overlapping strokes aren't needed. For your final (light) cut, on lets say a big 8 flute end mill, i don't think you'd be able to measure the difference created by wheel wear between cutting the 1st and last tooth - at least other variables and sources of error would dwarf it.
        .

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        • #5
          I don't claim to be an expert on this but I've been to a few cnc grind shops doing repairs and have never seen diamond wheels in the machines. One of the shops we go to makes the little fan blades(probably not the correct term ) for jet engines.

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          • #6
            parts are checked constantly, offsets adjusted as necessary to keep parts well within spec, that way if they start to go out, the adjustment brings it back it...meanwhile never really approaching the edge of the tolerance band

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            • #7
              oh, i've seen plenty of diamond wheels, they were about 6" in diameter and had big huge studs on them....they were used to dress the cylindrical grinder wheel

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              • #8
                Originally posted by mochinist
                I don't claim to be an expert on this but I've been to a few cnc grind shops doing repairs and have never seen diamond wheels in the machines. One of the shops we go to makes the little fan blades(probably not the correct term ) for jet engines.
                mochinist,
                My only experience with CNC grinding is in the tool making industry. The industrial supplier (Swift Tool) where I get all of my carbide end mills from manufactures them in house. They use Walter 5 axis CNC grinders with diamond wheels. The machines also have in process gaging capability.
                Mark Hockett

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                • #9
                  Originally posted by Mark Hockett
                  mochinist,
                  My only experience with CNC grinding is in the tool making industry. The industrial supplier (Swift Tool) where I get all of my carbide end mills from manufactures them in house. They use Walter 5 axis CNC grinders with diamond wheels. The machines also have in process gaging capability.
                  Makes sense since they are grinding carbide. I've never seen an endmill being ground but I am sure it is an interesting process.

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                  • #10
                    wow, I know this one!

                    As I happen to do a bit of production precision grinding from time to time at work, this is how it goes..at least for what I do.

                    Dress the wheel with the automatic overhead desser, set the dresser to dress every .002 to .007 or so depending on material and amount of material to be removed, and try to set the dress cycle to dress within the last .0005 to .001 of final dimension, and have at it.

                    The wear is compensated for by the dress cycles during the grinding process. The wheel may only wear a few tenths between dresses, but dressing .001 to .002 off each time ensures that the machine knows where it's at most of the time, as well as having a fresh wheel for further grinding.

                    If needed, the operator can also imput corrections to the machine, for fine adjustments.

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