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Machining graphite and carbon

Dr. Dmitri Kopeliovich

Cutting Graphite (or carbon) is different from cutting Metals. Metal exerts plastic deformation when a tool edge cuts it producing a curl or chips.
When a graphite is machined small powder-like particles separate from the workpiece as a result of brittle fracture caused by the stress produced by the cutting tool edge.
Cutting graphite operation consumes much less energy and generates much less heat than in cutting metals.

General guidelines for machining graphite and carbon

  • Graphite is abrasive material causing fast wear of metallic uncoated cutting tools. Only diamond (preferable) or carbide tools may be used for cutting graphite.
  • Graphite and carbon are generally machined dry without using Cutting fluids (coolants). If coolants are used in some machining operations (grinding, honing, polishing) the workpiece should be dried at 300-400°F (150-200°C) to remove liquids absorbed by the material.
  • Graphite as compared to metals is machined at higher cutting speed, feed speed and depth of cut;
  • Chipping (breakage) of the material in the exit of a cutting pass may be avoided by limiting the depth of cut to a half of the insert length;
  • Lowering feed rate in the exit of a pass also prevents chipping;
  • Chamfer at the end of the workpiece makes the tool entrance and exit easier and diminishes chipping;
  • Machining graphite and carbon produces dust with particles size in the range 0.0004”-0.005” (10-130μm). The dust mast be removed from the machining region by a dust extraction system providing a minimum air velocity of 6 ft/s (20 m/s).


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Milling graphite and carbon

Milling graphite and carbon
Tools: with inserts of 1/64-1/32” (0.4-0.8 mm) nose radius, clearance angle at least 10°
Parameter Value in metric unit Value in US unit
General purpose
Cutting speed 100-300 m/min 333-1000 ft/min
Feed speed 0.1 mm/(tooth*revolution) 0.004 inch/(tooth*revolution)
Depth of cut 5-10 mm 0.2-0.4 inch
Finish
Cutting speed 150-600 m/min 500-2000 ft/min
Feed speed 0.013-0.05 mm/(tooth*revolution) 0.0005-0.002 inch/(tooth*revolution)
Depth of cut 0.5-2 mm 0.02-0.08 inch

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Turning graphite and carbon

Square nose tools are not recommended since they increase chipping.

Turning graphite and carbon
Tools: with inserts of 1/64-1/32” (0.4-0.8 mm) nose radius, angle 20°
Parameter Value in metric unit Value in US unit
General purpose
Cutting speed 100-300 m/min 333-1000 ft/min
Feed speed 0.13 mm/(revolution) 0.005 inch/(revolution)
Depth of cut 10-20 mm 0.4-0.8 inch
Finish
Cutting speed 200-600 m/min 666-2000 ft/min
Feed speed 0.025-0.076 mm/(revolution) 0.001-0.003 inch/(revolution)
Depth of cut 0.2-0.5 mm 0.008-0.02 inch

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Drilling graphite and carbon

Drilling graphite and carbon
Tools: point angle 70°-100°, clearance angle 10°-15°
Parameter Value in metric unit Value in US unit
Cutting speed 60-900 m/min 200-3000 ft/min
Feed speed
drill diam. 1/32-3/16” (1-5 mm)
0.025-0.1 mm/rev. 0.001-0.004 in/rev.
Feed speed
drill diam. 3/16-1/4” (5-6 mm)
0.05-0.13 mm/rev. 0.002-0.005 in/rev.
Feed speed
drill diam. 1/4-5/16” (6-8 mm)
0.05-0.15 mm/rev. 0.002-0.006 in/rev.
Feed speed
drill diam. 5/16-3/8” (8-10 mm)
0.05-0.2 mm/rev. 0.002-0.008 in/rev.
Feed speed
drill diam. 3/8-1/2” (10-12 mm)
0.05-0.25 mm/rev. 0.002-0.010 in/rev.

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Sawing graphite and carbon

Graphite is cut by band saws (5 teeth/inch) at speed 1000-2000 ft/min (300-600 m/min).
Carbon is cut by diamond cutting wheels at speed 170-200 ft/s (50-60 m/s).

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Grinding graphite and carbon

Milling graphite and carbon
Tools: grinding wheel with the structure parameter between 6 to 9
Parameter Value in metric unit Value in US unit
General purpose (made by silicon carbide wheels of grit 20-46)
Cutting speed 20-30 m/s 65-100 ft/s
Feed speed 300-600 mm/min 12-24 inch/min
Depth of cut 0.5-5 mm 0.02-0.2 inch
Finish (made by electro-corundum wheels of grit 120-160)
Cutting speed 20-30 m/s 65-100 ft/s
Feed speed 150-300 mm/min 6-12 inch/min
Depth of cut 0.05-0.3 mm 0.002-0.012 inch

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Surface finishing graphite and carbon

  • lapping.

Lapping is carried out by aluminum oxide/silicon carbide powder with grain size 12-16 μm.

  • Polishing.

Polishing is carried out by diamond/aluminum oxide powder with grain size 6-10 μm.

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machining_graphite_and_carbon.txt · Last modified: 2013/06/22 by dmitri_kopeliovich
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