Grinding carbon fiber
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  1. #1
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    Default Grinding carbon fiber

    I was asked about possibly grinding a single carbon fiber part on my cylindrical grinder, it is about 5" diameter and 8" long. I know that carbon fiber (CFRP) makes a mess, that it destroys machines if not properly worked, and there are the obvious health risks. I can only run a 7" diameter grinding wheel on the machine, and I will be working between centers. The machine does have flood and mist coolant as well as a dust extractor system, and the machine was strategically placed close to a man door for even better dust evacuation. I wanted to know if there were any special types of grinding wheels that would be best suited for this application. Would I be ok with a standard alum-oxide wheel, ceramic wheel, or composite wheel? What grit, hardness, bond size is best? Would I be better off with a diamond wheel in this instance?
    I do not know the surface finish desired yet, although I don't predict I will be given one as this seems to be more of a size application not necessarily a surface finish application. From what I was told the part was wound with long strand fiber, vacuum bagged to remove air, and finally heated for cure. My intent is to grind between centers on the mandrel the part was originally set on. This is a new one for me as I know enough to be dangerous with traditional grinding of tool steels and other alloys, but nothing of the sort with respect to carbon fiber. If I get any additional information I will be sure to pass it along.

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    Well, I can't offer you any advice on Carbon fiber, but I know when I was young I spent about a month grinding Carbon plates for a sintering operation. If it is anything like that, I would pass on the job unless they were bringing it with a considerable pile of cash.

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    I think a good grinding wheel for this would be an electroplated diamond wheel of the appropriate grit. Nice free-cutting open structure. And yes, any way you look at it, it's going to be messy. I think I would shoot for dry grind and serious vacuum/dust collection.

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    When machining carbon fiber I prefer flood coolant in addition to a vacuum to keep the dust down. I've wanted to try using a thin layer of Anchorlube over the surface to try and keep the dust trapped in the gel. Flood usually does a pretty good job, you just want to control the coolant so it can be filtered before going back into your sump. I usually rig up a trough out of cardboard because I'm only do a few parts at a time. The exit of the trough goes into a container with a coarse filter. The exit of the container then runs through a finer filter paper. It takes 20 minutes to setup and some care while using to ensure the filter paper doesn't get clogged up.

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    remember that carbon fiber is electrically conductive. Get the dust in electronic places and you're gonna be hating life!

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    Quote Originally Posted by greggv View Post
    remember that carbon fiber is electrically conductive. Get the dust in electronic places and you're gonna be hating life!

    I second that
    We had 2 VFD blown when testing a big carbon braiding machine Just a hour or so
    Peter

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    All the grinding I have done on CF was with abrasive paper. We had separate clean areas that were only used for composite work, and usually used a downdraft table with LOTS of air flow. Like you could gronk a big grinding disk into a fiberglass part, and the stream of powdered part would go about two inches sideways, and then straight down into the table collection area.

    But I would say that a HEPA rated Vac system and some creative work around the workspace using cardboard and tape to make a pickup area under the wheel work space would not be a terrible idea.

    And a respirator with a decent particulate rating. The resin is crap in your lungs, the carbon fiber is worse.

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    I think first you have to realize you can't really "grind" carbon fiber. Grinding implies a specific process where the swarf ignites into sparks, and burn off so you don't clog the wheel (I had to yell at several engineers for clogging up our good ruby wheel with aluminum, it's rather dangerous) . Usually only iron or titanium based alloys. You are abrading carbon fiber, so you need to look for an abrasive that's hard enough and open enough to not load up. We had an aluminum wheel that we glued sandpaper around the outside, using fabric backed sandpaper off a shop roll, in a water bath to help clear it and keep the dust down. We could load it up and run it at high speed with no worry about it exploding like a vitrified wheel. It worked reasonably well, but it was not what I would call a "professional" solution.

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    Quote Originally Posted by Winterfalke View Post
    I think first you have to realize you can't really "grind" carbon fiber. Grinding implies a specific process where the swarf ignites into sparks, and burn off so you don't clog the wheel (I had to yell at several engineers for clogging up our good ruby wheel with aluminum, it's rather dangerous) . Usually only iron or titanium based alloys. You are abrading carbon fiber, so you need to look for an abrasive that's hard enough and open enough to not load up. We had an aluminum wheel that we glued sandpaper around the outside, using fabric backed sandpaper off a shop roll, in a water bath to help clear it and keep the dust down. We could load it up and run it at high speed with no worry about it exploding like a vitrified wheel. It worked reasonably well, but it was not what I would call a "professional" solution.
    Grinding does not inherently need to involve iron based alloys, nor ignite the swarf... Aluminum can be ground just dandily with the correct wheel - which is silicon carbide or diamond grit based.

    I do agree with the open free-cutting wheel thoughts for sure. You don't want heat building up, it will probably melt or burn the epoxy. I still would go dry with a serious vacuum setup. Hepa filter or even better a wet particle trap of some sort. Maybe both.

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    I have two methods of vacuum that I intend to use, one is a HEPA vacuum, one is a standard dust collection vacuum, plus I have a full PAPR system hood that I am going to be wearing while grinding. I also am going to use flood coolant, I am trying to determine what I can use. If I just use plain water it is going to cause chaos with rusting the machine ways, if I use a synthetic coolant from concentration I am worried about the synthetic causing an issue with the carbon fiber. One of the things I am considering is using cryogenic fluid/gas to cool the part and help the fibers shear easier for a better surface finish. I was told by the owner of the part that the surface finish is not critical, however the OD is +000/-.005 I was provided a test part to try out, hopefully this works out. I found a ceramic wheel with an open structure in 46 grit that I am going to try out, the bond is pretty open.


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