OD CNC Grinding
Close
Login to Your Account
Results 1 to 11 of 11

Thread: OD CNC Grinding

  1. #1
    Join Date
    Mar 2016
    Country
    UNITED STATES
    State/Province
    Alabama
    Posts
    333
    Post Thanks / Like
    Likes (Given)
    364
    Likes (Received)
    92

    Default OD CNC Grinding

    Hi all,

    My workplace is wanting to do CNC grinding on ceramic coatings on aerospace fins. Looking that the profile, they could certainly be ground in a 3 axis CNC machine. My question is more of related to machine longevity. Are there any machines well suited to this sort of work? Something I'm presuming with good coolant filtration and way coverings. Should I be looking into specific grinding machines?

    Some specs
    • The current fins are about 4" long, so small work envelope. Maybe bigger in the future.
    • I'd assume a wheel of about 2" diameter, but with the current geometry there is no reason they couldn't be bigger or smaller.
    • There is currently no geometry that couldn't be done with a 3 axis mill and slightly rounded stone. I don't see a need for 4 or 5 axis.
    • Tolerances are +/- 1 thou.


    We have a CNC mill that I'm sure could do it, but it's limited to 15k spindle speed and is only used for graphite with no flood coolant of any sort.

    Just getting me pointed in the right direction would be huge. I'm just a dumb engineer at a small company. I have no CNC manufacturing experience and I've already tapped out the guys at work.

    TIA.

  2. #2
    Join Date
    Oct 2005
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    21,114
    Post Thanks / Like

    Default

    I keep thinking Makino has something....I know they make the carbon milling machines (for EDM electrodes).

  3. #3
    Join Date
    Jul 2006
    Location
    Hillsboro, New Hampshire
    Posts
    12,441
    Post Thanks / Like
    Likes (Given)
    2848
    Likes (Received)
    8658

    Default

    Quote Originally Posted by ClappedOutBport View Post
    Hi all,

    My workplace is wanting to do CNC grinding on ceramic coatings on aerospace fins. Looking that the profile, they could certainly be ground in a 3 axis CNC machine. My question is more of related to machine longevity. Are there any machines well suited to this sort of work? Something I'm presuming with good coolant filtration and way coverings. Should I be looking into specific grinding machines?

    Some specs
    • The current fins are about 4" long, so small work envelope. Maybe bigger in the future.
    • I'd assume a wheel of about 2" diameter, but with the current geometry there is no reason they couldn't be bigger or smaller.
    • There is currently no geometry that couldn't be done with a 3 axis mill and slightly rounded stone. I don't see a need for 4 or 5 axis.
    • Tolerances are +/- 1 thou.


    We have a CNC mill that I'm sure could do it, but it's limited to 15k spindle speed and is only used for graphite with no flood coolant of any sort.

    Just getting me pointed in the right direction would be huge. I'm just a dumb engineer at a small company. I have no CNC manufacturing experience and I've already tapped out the guys at work.

    TIA.
    Grinding ceramic coated "fins" (turbine blades?) isn't a trivial matter - you have to worry about compromising the coating by inducing microcracks (which can spread to the substrate), overheating if the diamond (no stone wheels unless these are soft coatings) isn't the right grit, bond, dress, etc., and adhesion compromising if the grind isn't uniform relative to the underlying material.

    Perhaps you can tell us more about the actual parts, the contours to be ground, the ceramic coating and application method, and whatever else? At the least, I'd also want to talk with Norton/Saint-Gobain, or another major player in the diamond wheel game.

  4. #4
    Join Date
    Aug 2005
    Location
    Raymond , CA
    Posts
    372
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    268

    Default

    Quote Originally Posted by ClappedOutBport View Post
    Hi all,

    My workplace is wanting to do CNC grinding on ceramic coatings on aerospace fins. ............... Should I be looking into specific grinding machines?

    TIA.
    Short answer- Cylindrical Peel grinding

    Long answer follows:

    When a turbine engine is taken out of service for repair the owner can either send the engine back to the manufacturer and pay the high price or it can send it out to a independent repair shop and pay a reasonable price. The repair of the turbine blades involves removing the outer layer yttria stabilized zirconium oxide thermal barrier and the underlying -Nickle -Cobalt-Chrome-Aluminum-Yttrium hot corrosion protective coating. The eroded sections of the blade are repaired by welding. The repaired areas are then blended in by hand grinding followed by drilling out the cooling passages. The blades are then recoated. The corrosion barrier layer is reapplied by plasma spraying. The ceramic thermal barrier is applied by electron beam evaporation. The coatings are not ground. The plasma spraying and electron beam evaporation involve manipulating the blade to insure a uniform coating.

    The original turbine blade manufacturer might do enough volume to justify the cost of a cylindrical peel grinder to replace the hand grind blending operation. The original turbine blade geometry would be available for programing the peel grinder.

    This is how it was done 20 years ago. There may have been improvements in the process since then.

  5. Likes dian liked this post
  6. #5
    Join Date
    Oct 2005
    Country
    UNITED STATES
    State/Province
    Pennsylvania
    Posts
    21,114
    Post Thanks / Like

    Default

    Quote Originally Posted by Robert R View Post
    When a turbine engine is taken out of service for repair the owner can either send the engine back to the manufacturer and pay the high price or it can send it out to a independent repair shop and pay a reasonable price. The repair of the turbine blades involves removing the outer layer yttria stabilized zirconium oxide thermal barrier and the underlying -Nickle -Cobalt-Chrome-Aluminum-Yttrium hot corrosion protective coating. The eroded sections of the blade are repaired by welding. The repaired areas are then blended in by hand grinding followed by drilling out the cooling passages. The blades are then recoated. The corrosion barrier layer is reapplied by plasma spraying. The ceramic thermal barrier is applied by electron beam evaporation. The coatings are not ground. The plasma spraying and electron beam evaporation involve manipulating the blade to insure a uniform coating.

    The original turbine blade manufacturer might do enough volume to justify the cost of a cylindrical peel grinder to replace the hand grind blending operation. The original turbine blade geometry would be available for programing the peel grinder.

    This is how it was done 20 years ago. There may have been improvements in the process since then.
    That's all well and good.
    Doo you have a machine recommendation for the OP ?

  7. #6
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    10,157
    Post Thanks / Like
    Likes (Given)
    572
    Likes (Received)
    8311

    Default

    This is a nice machine:Kingsbury | Haas | CNC Grinding Multigrind CB (Turbine Blade) - YouTube
    If 3 axis CNC your idea of a fancy machine be sitting and strapped when you open the quote.
    This not the same Haas that everyone knows. Different company with the same name.
    Bob

  8. Likes digger doug liked this post
  9. #7
    Join Date
    Mar 2016
    Country
    UNITED STATES
    State/Province
    Alabama
    Posts
    333
    Post Thanks / Like
    Likes (Given)
    364
    Likes (Received)
    92

    Default

    Not turbine blades. Rocket fins. Brand new.

    Additive spray coated. I'm not 100% sure of the coating.

    We're not talking about taking off lbs of metal here. More like grams. It could be done by hand with diamond sponges, and we do that a lot, but we are looking for something faster that can hit that tolerance. That's all. Nothing crazy.

    My supervising engineer is wary of flood coolant due to the non-100% dense nature of the ceramic coating, having to get it out afterwards. I think it's relatively important. I also think that distinction is a big factor, as to whether we go for a grinding style machine meant for flood coolant, or a Makino for graphite like Doug suggested. Or get a used VMC, guard everything as well as possible and hope for the best.

  10. #8
    Join Date
    Aug 2005
    Location
    Raymond , CA
    Posts
    372
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    268

    Default

    Quote Originally Posted by ClappedOutBport View Post
    Not turbine blades. Rocket fins. Brand new.

    Additive spray coated. I'm not 100% sure of the coating.

    .
    There are ceramic coatings that are applied by painting or dipping,
    For example:
    Ultra High Temperature Ceramic Coatings | Aremco

    The coatings would be soft enough to machine rather than grind. A better approach would be to invest in spray equipment that will apply a uniform coating so that no machining is required.

  11. #9
    Join Date
    Nov 2014
    Country
    UNITED STATES
    State/Province
    Colorado
    Posts
    3,750
    Post Thanks / Like
    Likes (Given)
    4202
    Likes (Received)
    1097

    Default

    Quote Originally Posted by ClappedOutBport View Post
    Not turbine blades. Rocket fins. Brand new.

    Additive spray coated. I'm not 100% sure of the coating.

    We're not talking about taking off lbs of metal here. More like grams. It could be done by hand with diamond sponges, and we do that a lot, but we are looking for something faster that can hit that tolerance. That's all. Nothing crazy.

    My supervising engineer is wary of flood coolant due to the non-100% dense nature of the ceramic coating, having to get it out afterwards. I think it's relatively important. I also think that distinction is a big factor, as to whether we go for a grinding style machine meant for flood coolant, or a Makino for graphite like Doug suggested. Or get a used VMC, guard everything as well as possible and hope for the best.
    Guys I spoke to at Makino do have a grinding solution for their V33i and V56i machines.

    I believe they actually use their graphite package with minimal modifications to doooo "Wet" grinding, sort of jig grinding 'Style".

    They were very keen to stress WET grinding. +ve pressure at various joints and moving contact surfaces + wipers and rubber barriers on the machine itself.

    This may be massive overkill for your tolerances. [As it's a ridiculously accurate machine (Vxxi series) .].

    I pressed them further about judicious use of various grinding processes on other machines with reference to machine warranty;

    Like what happens if you circumvent the normal coolant / fluid handling of a more generic (less grinding friendly) machine and are super careful about collection and filtration. ~ Their attitude was somewhat refreshing as essentially the One year warranty runs out and one is unlikely to completely trash a new machine in under 12 months... most of the time - i.e. It's up to you how you want to trash or not trash your machine.

    Some machines like a Hermle are not abrasive friendly by virtue of their layout and exposed linear rail systems + getting gummed up with the media / binder for various wheels. [If you are "thinking" Hermle and abrasives - just don't tell them lol. - EVER ;-) ].

    I have seen the regular HAAS machines (not the one's Carbide Bob is talking about) being pressed into service for larger wheel grinding application + 5 axis trunnions. -The idea is that the machine is destroyed sacrificially for the application. [I believe even using oil in some cases.].

    ~ For Example with most CNC jig grinders their actual X, Y and Z movements are not that much more accurate than a modern CNC mill... Other than Newer Hauser Jig Grinding dual column machines and their ilk. [Low vibration, high spindle speed and zero (spindle) runout is more of a consideration/ priority + thermal management + all the wacky extra movements such a machine requires.)
    ___________

    Apologies for random stream of consciousness here; there are a number of Makino Graphite machines floating out there (Second hand) that are not too expensive you could experiment with. -Makino customer portal for second hand machines is relatively good providing you pay annual fees.

    Hard to answer your question without some vague sketch of at least a facsimile of a part i.e. not the actual part but similar surfaces/ geometry and materials + arse covering for larger process and intended goals.

    __________

    Could this be done on an old school Moore jig grinder + (tilt-able) spin table or regular surface grinder with special rotating (tilt-able) between centers driven attachment ?
    Last edited by cameraman; 04-06-2021 at 09:50 PM. Reason: v56i ~ v55

  12. Likes ClappedOutBport, digger doug liked this post
  13. #10
    Join Date
    Feb 2010
    Location
    ch
    Posts
    3,117
    Post Thanks / Like
    Likes (Given)
    257
    Likes (Received)
    428

    Default

    what is "peel grinding"?

  14. #11
    Join Date
    Jul 2006
    Location
    Hillsboro, New Hampshire
    Posts
    12,441
    Post Thanks / Like
    Likes (Given)
    2848
    Likes (Received)
    8658

    Default

    Quote Originally Posted by dian View Post
    what is "peel grinding"?
    The Powerful Potential of Peel Grinding


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •