How to bevel Nomex Honeycomb

Discussion in 'Composites' started by PittsS1S, Oct 26, 2019.

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  1. Oct 26, 2019 #1

    PittsS1S

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    What are the ways to bevel and at which angle Nomex Honeycomb .I saw that some kind of "resin" can be used to fill the cells where the bevel will be,to get that area of the Honeycomb more rigid and give a clean transition where the upper and lower skins join .
    Is that kind of "resin" some sort of micro balloon or a specific product ?
    I will use 2 and 3 mms thick
     
  2. Nov 7, 2019 #2

    Scheny

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    Hi, it is a combination of resin and micro balloons, as resin alone would get too heavy and you loose the benefit of honeycomb.

    I have not done it personally yet, but we are intending to use a belt-grinder which we mount inclined at an angle on a slider plate. Then we can slide it along the edge creating the bevel.

    As for the angle, we intend to do 3:1, so it will be approximately 30°.
     
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  3. Nov 10, 2019 #3

    PittsS1S

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    Thank you Scheny
     
  4. Nov 10, 2019 #4

    AdrianS

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    We used a custom router bit set to the exact depth. Filled the exposed core with resin/microballons : it takes more than you'd expect.

    We were machining a slot in the inner skin and core and inserting a ?balsa? former, then folding the panel and gluing the joint.
    That was a long time ago - techniques may have changed.
     
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  5. Nov 10, 2019 #5

    Toobuilder

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    Honeycomb should be rigid enough to mill. That's how we do it at my company. Filling the voids eliminates the advantage of the honeycomb core.
     
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  6. Nov 10, 2019 #6

    Aviacs

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  7. Nov 10, 2019 #7

    User27

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    Build a jig to hold the nomex vertical (or just off vertical) and pass it by a table saw with the blade extended as far out as possible
     
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  8. Nov 10, 2019 #8

    BoKu

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    How do you get down off of an elephant? You don't, you get down off of a duck.

    In the vast majority of cases where folks ask how to handle honeycomb, they'd be better off using pvc foam core.
     
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  9. Nov 11, 2019 #9

    Scheny

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    I think the questions and answers somehow got in different directions.

    Original question from PittsS1S: joining upper and lower skins
    1. Either you bevel it and then join beyond the bevel --> this case you can even do it without filling (in theory)
    2. Joining without a bevel --> fill the last inch with balloons and then cut a clean edge after it has cured
    Here is a project with 3mm honeycomb done totally without bevels (method 2):
    https://www.r-g.de/w/images/3/3c/PIK20_E_-_Ein_Großmodell_in_Wabenbauweise.pdf

    As for the answers we got here, most are for how to join bulkheads at 90° angle. Here you also have two possibilities:
    1. interrupt the honeycomb (or for a finished sandwich use the routher or saw method the colleagues have described above)
    2. put ballons in the area of joining and then attach it to the inner skin (as in the PDF I linked)

    BR, Andreas
     
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  10. Nov 11, 2019 #10

    geraldmorrissey

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    If you live in a cold environment, fill the cells with water and do your cutting outside. An "ice chuck", a milling machine with a refrigerated top was used to machine aluminum honetcomb at a company I worked for. However not sure if nomex absorbs water and if so degrades its properties.Try a test panel.
    Gerry
     
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  11. Nov 11, 2019 #11

    PittsS1S

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    thank you all for those very helpfull advices...
     
  12. Nov 11, 2019 #12

    BoKu

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    In the range of 2-3mm, Soric might be a reasonable alternative to honeycomb. It might be a bit heavier, but it is much easier to use and process. We've started using it for small compound curved parts like winglet transitions etc.
     
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  13. Nov 12, 2019 #13

    RSD

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    Cheers BoKu - I just tooks a look at the Soric and it looks like a very useful product to have a roll of!
     
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  14. Nov 12, 2019 #14

    RSD

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    BoKu - do you have any information on the weights of Soric vs Nomex honeycomb of the same mm thickness? I haven't seen a lot of info that enables a like for like comparison of weight for the same thickness.
     
  15. Nov 12, 2019 #15

    stanislavz

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    Will show myself like noob, but just tried this think in shop, and ordered it online : [​IMG]

    Feels right in a hand, for any small foam cutting. And nomex filled with ice too :)
     
  16. Nov 12, 2019 #16

    cheapracer

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    I just had an amusing thought, but one that would actually work, dip what ever you don't want into swimming pool acid, i.e. hydrochloric acid.

    What you don't want will be gone in about 15 minutes!
     
  17. Nov 12, 2019 #17

    BoKu

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    Sorry, I have no information on that. I have only used Soric on relatively small parts where the weight was relatively inconsequential. Everywhere where weight per unit area mattered to my design, I made coupons using the candidate materials and processes and weighed them.
     
  18. Nov 12, 2019 #18

    Scheny

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    Hi, Soric has an impregnated density of 470kg per cubic meter. Laminated glass has 1450kg if I calculated correctly.

    Honeycomb has 27kg per cubic meter, but requires a coupling layer that adds another at least 150g per m2 and side. This idea not bad, as some foams can soak twice that.

    So, for 2mm you have 900g/m2 for Soric, vs. 350g/m2 for honeycomb very roughly calculated.

    BR, Andreas
     
  19. Nov 12, 2019 #19

    BoKu

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    From what I've seen of honeycomb, you really have to use prepregs and the adhesive film "coupling layers" to get uniformly good weight properties. If you're using wet layups, even with very careful saturation, you can get much higher weights per unit area. What happens is that surface tension tends to draw epoxy out of the laminate and onto the surfaces of the cells, which also causes dryer laminates than you want. It doesn't take much of that before you're better off using PVC foam cores.

    When using PVC foam cores, how much resin the foam soaks up is entirely a function of the cell size. And to some degree, you want that to happen, because that's how you get a good bond between the face plies and the core foam.

    Bottom line, the fastest and most effective way to find the material properties is to use the materials to make test coupons under practical conditions, and then measure the properties.
     
  20. Nov 12, 2019 #20

    RSD

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    I did find this online which may help some people -
     

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