Carbon graphite's brittle properties create unique conditions when milled.
Carbon graphite fiber sheet materials and solid carbon graphite blocks present unique characteristics to the professional machinist. Carbon graphite materials are extremely light yet incredibly hard, so their applications in the marketplace are expanding. However, because their structural characteristics are brittle, carbon graphite composite materials must be milled with specialized equipment in order to successfully create the engineered pieces.
Choosing Cutting Tools
Use carbide- or diamond-tipped cutting tools for the milling procedure. When milling any material, the cutting tool must be harder than the milled surface. Otherwise the cutting tool is damaged while the milled part remains. Only a carbide- or diamond-tipped cutter has the tensile strength to mill carbon graphite without fracturing.
Selecting Spindle Speeds
Choose high-spindle speeds when milling carbon graphite fiber. Cutting carbon graphite material generates low temperatures because the CNC tools actually chip small amounts of the carbon fiber away from the milled part. Higher spindle speeds provide the best environment to cleanly chip, or mill, the carbon materials without chipping or shattering the piece.
Selecting Feed Rates
When milling carbon graphite fiber, choose slow material-feed rates. The carbon fiber material easily fractures if the feed rates are too fast. When drilling completely through carbon graphite material, higher success is achieved by drilling halfway through the middle part from each direction. This strategy prevents the graphite from chipping as the cutting tool exits are graphite material. The high-density properties of the carbon fiber are also likely to snap off the cutting tool if fed through the equipment to quickly.
Keeping the Work Area Clean
Use a shop vac during the milling process to remove the large amounts of carbon dust created when milling carbon fiber. The milling process creates carbon dust and even small shards of carbon graphite which break away from surface. These particles fill the milling area quickly and can create visibility problems. The graphite dust also contains larger chips of carbon graphite which will be quite sharp. Removing the dust and chips from the work surface protects the milling machine operator.
