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

[Bill Macfarlane]

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.

Mike:
I work for a large aircraft Co. We do a lot of drilling on composets and we use a drill/reamer tool that we call a dreamer. You may want to contact; Quality Carbide Tool. They are the suplier for this drill/reamer. It works very well.

[vettespeed]

OK,
I guess this stuff is "prepreg" carbon fiber composite, probably baked in an oven I suppose after it's layed up. Anyway I lit into a piece today with a new 3 flt aluminum cutting style 1/2" endmill. It cut great, left a smooth nice finish, but created heat and yes did dull very quickly. I cut it dry. You guys keep mentioning diamond tooling, what do you mean? Diamond coated carbide? Diamond incrusted? What manufacturers, flute style, whatever? I used some endmills today that had little diamond bits incrusted to them and it did not leave a nice finish, rather course and porous compared to the fluted endmill. The parts I will be cutting will need about 1.5 flute length to cut the profile then have the top side contour hemstitched. It looks like maybe there won't be any hole drilling after all, so I mainly need advice on endmills. Thanks, Mike.

[crazyneosimpson]

Vettespeed,
Speed? It's a plastic keep the speed up, this is nothing like tooling metals, I find the speed comparable to aluminium. This needs to be tempered with your wear rate, carbon is abrasive, if you only have a few holes to drill it won't change your speed.
Feed? Again it is soft, measure it, same as AL!
To get a neat hole in the B787 we slotdrill 1mm smaller then circular interpolate to finish to size.

[chineguy]

Use Diamond coated endmills. You will not believe the difference in tool life. Spindle speed should be relatively high. When cutting epoxy bonded fiber they usually recommend to use a higher feed to break the fiber. I have heard the diamond coated bits that look like steel grinding wheels with grooves work well. They have to be run at router bit type speeds though. I never could try them. The company I worked for insisted on trying to use antiques (20 yr. old) with slow spindles. You can get some good end mills from Garr. They have some speed feed info in the catalog. Otherwise its just trial and error. The composite articles mentioned would be well worth your time to read.

[mechanical]

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.

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

Scott,

I am a composites design engineer for one of the major aero companies. I was just trying to offer a quick bit of public common knowledge that is available on the web thru any major search engine. Since they are trying to determine if they will bid on the package or not I don't know what engineering has been provided to them. I would first check the engineering package and see what spec's govern what you can and can't do. If there are question's about the spec's contact the buyer for clarification. The spec's must be obeyed unless a deviation is permitted on the engineering dwg itself. In this case I know water is allowed as a coolant while machining on a "cured" composite part. There are also various other coolants allowed but he must read the spec and see what the program has qualified to use at this point. Just a guess i'm sure he will see Boelube, Coolube 21, Water, and Cetyl Alcohol as approved coolants. If the part will be bonded to another part then that will cause a few of the coolants to drop off the list and will require a good cleaning to remove all traces of coolant afterwards.

As far as recomending PCD tooling, it's recommended by experience of living with this stuff daily. Yes you can use HSS or Carbide cutters, but why take the chance of ruining a part with so much labor involved. Remember machining is normally the last step of the labor intensive layup process. I would hate to scrap months of work because I wouldn't spend an extra $100 bucks on a PCD cutter. I just know if he is looking to maximize his machining efforts I would start looking at PCD ball end mills for all profiling efforts.

I will take a stab at your question about using a water jet to cut composites. It seems like you are thinking of cutting uncured composites with a waterjet? If so then that is not allowed to the best of my knowledge on any program I have worked on. Also, there are requirements in place that govern the moisture content of the fiber before it can be accepted for use. Using a waterjet to cut cured composites depends on the final application and what level of inspection (NDI) that the part will recieve when finished. Speaking of NDI most ultrasonic inspection systems use water as the coupler or transfer medium. Most critical composite parts are either submerged or flooded with water during the UT inspection.

[unterhaus]

This is bringing back bad memories from my days as an engineer in the Air Force. I'm pretty sure the manufacturing standards for the aircraft I worked on were called out on the drawing for the part. Assuming you won a bid from the government, they should be able to provide them for you. I don't think that they were usually provided in the bid package that we sent out.

The General Dynamics standards were pretty good, there was a huge book of them.

[vettespeed]

Brand of tooling? Type and style of tooling? Spindle speed or surface footage suggestions? Feedrate or in/rev suggestions. Dry or coolant? I will be cutting on HAAS mills with max 10,000 RPM spindle, maybe less depending on machine the parts go on. Someone mentioned PCD? I tried a cutter that appeared to be tiny diamond chunks bonded to a shank and it did not leave a very nice finish, do you think they were PCD? Maybe my feed was too fast or spindle speed too slow? I ran a 1/2" cutter at S1528 & 15.0 in/min on a finish profile cut. If anyone suggests tooling types please provide brand, type of cutter, spindle speed or surface footage suggestion, feed or in/rev suggestions. I will be cutting it dry or with a typical coolant flood, the machines currently have Hangsterfer's coolant in them, I can't see running water in these machines, everything would rust. Thanks, Mike.

[BptRoadman]

When You say "carbon fiber" is it like cloth or already autoclaved? If it's still cloth then you need something like a Gerber Cutter if its cured then a waterjet ... that stuff is brutal

[mxtras]

Google around for more info on the specific cutters and such.

I used standard Micro grain carbide (Micro 100 brand, avail through MSC) end mills with TiCN coating but this was in the early to mid 90's and I was not allowed to use coolant of any kind other than a cold air gun. There have been many advances in coatings and tooling technology as well as composites since that time. I ran these on a 8,000 RPM spindle. Later in that career I ran high speed spindles (25K) but still used standard tooling with various coatings - out of convenience and availability. As far as the feed - I can not recall an exact number but as mentioned before - adjust as deemed necessary. The feed will likely be relatively slow - probably near what you would use for steel but I think that depends on your DOC and panel composition. For some panels (polyester resins) you would likely see very rapid feeds that would nearly mimic Aluminum or maybe faster. I conducted numerous tooling life tests but no longer have access to that information - sorry to be of such little help with the specifics. I know that's what you are looking for and hopefully someone will chime in and tell you exactly what to buy and exactly how to run it, but I would be suprised as we have no way to know exactly how the material you are dealing with reacts to cutting.

From what I recall, you want to use pretty aggressive tooling goemetry with a high shear angle. Maybe look at Rob Jack tooling - they have many unique tools with high helix and high rake angles for various composites. Google them and give them a call - from what I understand they will help you out and maybe even offer sample tools for you to evaluate - especially if you are running production and might buy numerous tools from them. I have dealt with them in the past, but in a slightly different situation.

Sorry to be of such limited help!

Scott

[mxtras]

BptRoadman -

This guy is cutting a cured panel.

For cloth, look at American GFM ultrasonic cutters (Chesapeake, VA and Steyr, Austria) - this is absolutley the way to go for cutting Kevlar, Carbon, Glass and any other cloth or prepregs.

Scott

[ultra]

I've been water jet cutting carbon/epoxy plate for years with no problems. Never seen a water migration problem due to H2O cutting but this will depend on the quality of the composite structure and of course the end use and environment of the finished structure. Most of the stuff I have cut has been autoclave cured prepreg or vacuum infused at room temp so its very compact and with low void content. In any case I've also machined holes in this material and overheating your tool can cause the resin to burn locally which is a bad thing. I would suggest finding out what resin is being used and go from there. I'm with everyone else on diamond coated tools.

[Joe Brennan]

I just found this site and would like to participate in the discussion if people are still interesed. Please post