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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
Milling graphite and carbon
Turning graphite and carbon
Drilling graphite and carbon
Sawing graphite and carbon
Grinding graphite and carbon
Surface finishing graphite and carbon

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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