Composites

I've done some graphite type machining long ago that were considered composites. That's about all I know about them. Can anyone give me a
basic breakdown of why they this broad term 'composites' is sometimes used when folks are looking for a CNC programmer?
Is it normally referred to a composite because it takes grinding to remove material?
I don't know, maybe this question seems stupid but I'd appreciate any help getting the basics on it?
Thanks
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Dewittian wrote:

I cut fiberglass woven composites from 1/2" up to 2 inches thick using carbide tools, no grinding no coolant of course. You need a vacuum system to handle the dust which is a huge spindle bearing killer. 4x8 and 5x10 ft sheets that are made into boat transoms, hatches, fuel tanks, bulkheads and stringers just to name a few parts. I currently program for 25 boat companies, been doing boat components for over eight years. There are about 20 grades of boat composite materials. Naturally transoms would be the strongest version. Normal spindle speeds and feed rates do not always apply. On thicker and heavier material grades z level passes can be multiple.
Michael
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Michael Gailey
Artistic CNC Mill, Router and Engraver Programming
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It's considered a composite because it has several different layers or types of material, such as fiberglass composite which has layers of glass fiber held together with epoxy. G10 is another common material, which is a good electrical insulator as well as incredibly strong. Carbon fiber (also fibers and epoxy resin) is considered a composite.
Most composites are cut by grinding or other abrasive processes because they are not consistent density throughout, leading to unpredictable cutting parameters with toothed cutters, and because they tend to be very abrasive, which would rapidly wear down traditional cutters. Machining of composites has been greatly helped by the introduction of PVD-coated tools, particularly diamond coatings.
Graphite is in a similar group because it is very abrasive, but it can be machined with high-performance end mills just fine as long as you have good dust collection and a high-speed spindle. Polycrystalline diamond tools are used almost exclusively for production machining of graphite, such as for sinker edm electrodes. Unlike fiberglass, for example, graphite is very consistent throughout (like normal metal or plastic).
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I guess then that I could get into 5 axis milling with some composites as long as I cut with PVD diamond fast speeds with slow speeds. I once tried drilling through graphite composite and it can be done on a blind hole but breaks out a chunk on the back if you go all the way through. Do you guys think that when somebody is looking for a programmer they are 5 axis grinding or 2 axis routing? The later would pay less and use a low level (cheaper) cam package.
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replying to Dewittian, Gman wrote:

Easy, Machining composites correctly is much more demanding in holding the parts/tools, using the correct cutting tools, using the correct speed/feeds, handling issues like delamination and usually a more complicated part with lots of contours.
So, using the word :composites: is looking for someone who understands how to do this correctly. I've seen many CNC programmers that are very good, but could not do composite parts/tools. Now a days if you do it right you don't need to grind.
In addition, you have many issues with ply drops, cores, plugs, and an unconsistant cross sections. So, you get high frequency vibrations and surface movements.
Mostly, you need people that have do it before and understand all the issues involved. But watch out there is a lot out there that think they know what they are doing, but just break everything.
Regards, Gman
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