How do I cut carbon fiber (Joint Strike Fighter)?

[vettespeed]

I've been in the CNC world of exotic metals for 10+ years machining such materials as 625/718 Inconel, 6AL6V Ti, 13-8 Stainless, 4000/300 series steels, etc. Got a new job at a mold/tooling shop and the company is considering bidding on a Joint Strike Fighter carbon fiber package. What's it take to cut this stuff. I couldn't tell you type/grade, just know I got a piece to test and it seems like some dense stuff. What cutters would I use to cut profiles up to .750 deep or so and maybe drill a few holes around 1/4"? Thanks, Mike.

[mxtras]

Are you talking about a laminate, fabric or prepreg? If it's a laminate, do you know what the resin is?

Hate to answer your question with questions, but....

After re-reading your post, it appears that this is already laminated. Standard carbide end mills will work most of the time. I have encountered only a few composites that were extremely difficult to cut and for those, diamond tooling was used to basically sand the part to shape. I have turned end mills into semi-molten blobs trying to cut composite armor plating so I can attest that it can be a challenge. Most of the cutting I did was with either dry fabrics or pre-preg materials but had to rout laminated panels from time to time and I would typically use Micro grain, high helix end mills and adjust as necessary to keep the tool from overheating. Watch the dust.

Scott

[vettespeed]

It must be laminate? It's not fabric. I guess I'l looking at resin and fabric, is that laminate? It's dense and feels rock hard to the touch. I'm not sure I know what prepreg is? We made the molds, now they are laying up the cabon fiber into the molds then we are going to 5 axis trim the profiles, 3-D contour the top side, and drill some holes.

[mxtras]

Drilling can be a challenge depending on the resin and the density, I guess. I have seen issues with the entry and exit de-laminating. If this is a highly stressed part, the holes would likely be molded in or have bushings molded in place, so I am guessing this is not a super-critical component? Edge sealing is an issue with carbon laminates and the trend was heading towards net shape molding when I exited the field a few years ago.

Scott

[vettespeed]

Huh? How do I cut it? Endmill material/style/type, speed/feeds, etc?

[mechanical]

Don't even bother with carbide tooling just go ahead and set up using diamond coating tooling. Trust me you will thank yourself later. You will have great sucess using diamond coated drill bits to drill the composite. The main thing to watch is your feed rate, if you feed to high or with a dull bit you will break out the back side of the composite (aka delamination). The main thing to do early on is monitor your tooling extremely close to determine the point of replacement. Don't try stretching your tooling past this point with composites it will bite you every time. You can get assorted end mills that coated and you can have those end mills recoated a few times to save some money. To answer your questions on feeds and speeds you will have to just go to the machine and start cutting to find out what works best. Also you will probably be using water as your main form of coolant with the allowance of rust inhibitors to protect your machine. Let me know if you have any more questions.

[whirlybomber]

I've worked with cutting cured composite panels (that's what you're doing, btw) for 13 years now.

Without the exact details of what you are cutting (and no, don't post them. the men in the black helicopters would be around to send you on a one-way trip to gitmo vi rendition-air so fast you would not believe it. More seriously, what the JSF is made out of (in detail) is probably an export-controlled secret. posting it here would break all sorts of laws) we would not be able to tell you exactly what type of tool to use to cut the stuff.

contact the people you are bidding with for the contract, and ask them nicely to tell you what they use. Read some composite magazines and get local cutter vendors to visit you and display what they sell. Experiment on your own with all sorts of stuff.

Although to drill holes, we use standard drills for low-tolerance holes one-shot drill/reamers for close tolerance holes, and standard countersink cutters in cages for countersinks. All in comercial product's you understand.

Although if you have made the LM's (layup mandrels) and are producing test pieces/first articles, I would say you already have the contract, as you obviously have the engineering data....

Oh yeah. don't breath the dust. that stuff makes asbesdos look harmless. And be careful which solvents you use to clean up uncured resins. some of those things will do nasty stuff to your kidneys/liver. And lets not get started on mould release agents.....

Why oh why won't they just let us make this sort of stuff out of large monolithic alloy high-speed machined frames and ribs? Al-li is souch a nice alloy when designed and manufactured properly.

[mxtras]

Originally Posted by mechanical Don't even bother with carbide tooling just go ahead and set up using diamond coating tooling. Trust me you will thank yourself later.

Are you here to tell me that carbon laminates can not be cut with end mills? This is simply not the case. It is done effectively daily.

Originally Posted by mechanical The main thing to do early on is monitor your tooling extremely close to determine the point of replacement.

Very true. The tools go from cutting fine to too dull to work very rapidly and without much warning. It's best to log cutting distances for each cutter to forcast failure rates and to judge coating performance and tooling geometries. Cutting carbon/epoxy laminates is a very abrasive thing. You may also want to try ceramic tools - a bit more costly but they perform well under heat.

Originally Posted by mechanical Also you will probably be using water as your main form of coolant with the allowance of rust inhibitors to protect your machine.

Say what? Not a good idea. Ask the designer of this panel if using water on his laminate is OK. Carbon and water do not and have never gotten along. Edge sealing is such a huge issue with carbon parts to prevent delamination that the use of water for cooling would send any composites engineer into convultions. Use a cold air gun and possibly a mist system (and definately a vacuum system for the dust) and get approval from the company you are making these things for. If they are doing any bonding or sealing they are going to want to know exactly what it is that you are using and in what concentration. Do NOT use water as coolant when cutting carbon composites. Ever.

There are a lot of folks cutting carbon laminates with water jet and for this I have no explanation. I can not understand how they get away with this. I have seen dry goods cut with a water jet and I understand that it leaves little moisture on the part but I am not a chemist nor do I have experience with water jet cutting so I can not speak intelligently on this. I am aware of longevity issues caused by (presumably) moisture induced de-lamination involving carbon laminates. Perhaps someone with a bit more experience can enlighten me on this aspect.

Scott

[mxtras]

Originally Posted by whirlybomber Without the exact details of what you are cutting (and no, don't post them. .

Uh - very good point! My question was a bit on the un-sensitive side, I guess! I assume he knows not to divulge the sensitive info.

I was first thinking he could be cutting fabric - it was not really clear to me that he was cutting a cured laminate.

Scott

[alucarD]

I helped in a shop that used "WATER" to cool the cutting ... back in the day H2o was a bad thing to use on laminates <forgive my spelling> they were black in color and this was after the 2 weeks in the ovens to cure them.. yes Gov. contracts.. nasty stuff after curing you coulden't put a .38 cal bullet throught a 1/32 inch sheet... stuff scared me to death.... ok the gov. provided stuff they called "water" looks clear and tasts like rusty piping and almost instantly eats plane steal bits you use this "water" on CARBON STEEL only they will tell you this very adamintly <roughly: the guy that told my friend was screaming it at him> the color of the material is a big issue at this point... mind you i have note worked with the stuff since the black,green,gold and yellow days the color will or at least should help you to know what the strength of the stuff is. Black is the toughtest and you can only cut it with a sand cutter or diamond bit but the stuff is very easy to work with once you know what your doing.....
The shop i helped in used 4 pieces about a foot long and did lots of test cutting..
The pieces they were making were dash board type of thing lots of holes and recesses.. One piece took a week to do by one guy.. good luck and i hope that helped

[pvogtcharlotte]

This month's "Manufacturing Engineering"
www.sme.org/manufacturingengineering
has a detailed article about cutting composites.
It seems that waterjet works well.
Paul Vogt,
Charlotte, NC

[mxtras]

Here's another pretty decent article on cutting composites:

http://www.mmsonline.com/articles/120501.html

Scott