Slight Moisture Ingress into Sandwich Panel 2

[SAITAETGrad]

Is this a method of sandwich panel cutting people are familiar with?

Link

 

[MikeHalloran]

I've had 12 gage stainless steel sheet cut by waterjet, with generally satisfactory results.

I've understood that it could be used to cut sandwich panels; I just haven't seen a video before.

Are you concerned about some part of the process?


Mike Halloran
Pembroke Pines, FL, USA

 

[verymadmac]

Well if you bake out the moisture and inspect for delam, then it might be fine, but why would you.
Water jet limits you to through cuts only, no pre-drilled holes for potted inserts etc.

 

[SAITAETGrad]

Mike, I just don't know - even if you bake & inspect as madmac suggests, what confidence could one have?

 

[MikeHalloran]

What confidence does one want?

I said I was familiar with the process, not that I would recommend it for an application so far unrevealed.

I think I read somewhere that the waterjet doesn't seriously affect even paper-based core, because the flow is actually pretty low, but I would worry about abrasive contamination for aerospace panels.

Most people today don't bother to prepend 'abrasive assisted' to 'waterjet cutting'. I think the high pressure water alone will cut most materials, but feeding some grit into the stream makes it cut _much_ faster, certainly enough to change the economics of the business.

Then, someone has to remove the stray grit from the workpiece. The local waterjet cutter associated with my former employer doesn't do it, probably because their entire facility is awash in abrasive dust.



Mike Halloran
Pembroke Pines, FL, USA

 

[Sparweb]

Oh my god

STF

 

[Compositepro]

Waterjet cutting is very commonly used for all types of composite parts.

 

[SAITAETGrad]

Sorry Mike- I brought this up for discussion as a curiosity - not for a particular application. The video was strange to my eyes but certainly I know little of a great many things.

Thank you for mentioning the abrasive - informative.

While flow may be low, the pressure is of course very high. Wouldn't you be concerned about moisture penetrating into the honeycomb?

For an application, how about a galley structure of a pre-existing design with adhesive bonded structural joints previously validated by test. If the tested part was done by pin router could you cut the parts by water jet without need for additional structural tests? Presumably, disbond & other NDE checks make water jet more expensive than pin routing - so can we rule them out?

 

[MikeHalloran]

The pressure forcing the water through a sapphire orifice is quite high, but that results in high velocity of the exiting jet. There is essentially no velocity in a radial direction, else the jet would expand rapidly. The extreme velocity of the water and of the entrained abrasive tends to carry the detritus along the same axis. The pool of water under the workpiece is intended to slow down the jet so it doesn't cut the submerged grid supporting the workpiece. The used abrasive and bits of whatever is cut settle on the bottom of the tank.

Routers, on the other hand, tend to throw chips radially, i.e., into the cavities within the core, so cleanup may be more difficult than for a waterjet. OTOH, they do allow making blind cuts and even undercut pockets for embedded attachment points.

I think galleys and beverage carts are already made from sandwich panels, and have been for a long time. Maybe a little social engineering could net you a tour.



Mike Halloran
Pembroke Pines, FL, USA

 

[WKTaylor]

SAITAETGrad

We manufacture honeycomb floor panels this way. The floor panels consist of aluminum skins [pre-PAA/primed], aluminum honeycomb core [PAA], film adhesive and edge potting compound.

Here's how we make them...
Per each panel drawing there is a common 'raw stock size' for both the (2) skins and the honeycomb core. In most cases there are skin thickness differences [upper VS lower] and obvious differences due to LH-RH mirror-image construction. It used-to drive the shop nuts making LH and RH panels from finish-trimmed materials.

Duhhh... then we had an idea...

We tried bonding the raw-stock skins to the raw-stock core, then routing these raw HC raw-panels to either a LH or RH configuration. Almost instantly, the idea of cutting these raw HC panels to final LH or RH trim using NC water-jet cutting [W/WO abrasives] was proposed and tested successfully. The 'GREAT CAUTION NOTE' here is that the upper-surface has to be identified so that the panels aren't inadvertently trimmed backwards [IE: MUST maintain thick-skin side UP]. Various sandwich construction test methods proved that this method worked without any deleterious effects to the panel structure [shear, t-peel, crush, etc]. Many man-hours and much 'frustration' have been saved with this method.

After water jet-cutting, the next step is to under-cut [recess-cut-out] the exposed edge HC-core by hand; and then potting the recessed HC edges with low-density potting compound [filled-epoxy] for moisture sealing and edge-crushing strength. The finished panel is then coated with epoxy primer, all-over. NOTE. The time between water-jet cutting and under-cutting the exposed HC edges, and then potting the edges, is sufficient to allow the trimmed area to be thoroughly dry long-before the potting step.

NOTE. This 'process' also works well for constant thickness crushed-core HC panels; and sandwich panels with non-metallic HC core.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
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[SAITAETGrad]

Many thanks Wil.

 

[WKTaylor]

OH yeah forgot to clarify...

Any minor disbonding between skins and core that might occur along the water-jet cut edges is pretty-much eliminated by the HC-core under-cutting/potting procedure.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can b

 

[tbuelna]

I've seen WJ used to trim solid carbon composite laminate, but not (what appears to be) carbon skins with a fairly thick aramid honeycomb core. The issue I have seen with WJ of solid panel skins with a large separation between them is that the jet tends to disperse when it exits the back side of each upper panel. This "kerf" effect results in a variation of the upper/lower panel trimmed edges. In the video linked above, there are two stacked honeycomb panels being WJ trimmed at the same time. I don't see how this would produce an accurate trimmed profile (assuming an accurate profile is required).

Even a small amount of humidity or trapped moisture in the cell spaces of a honeycomb material can cause delamination problems if the panel is processed in an autoclave or oven at elevated temps. Also, recall how moisture trapped in the spaces of the aluminum honeycomb used for the X-33 composite cryo fuel tank structure caused delamination failure during testing.