Low carbon steel
Issue: Chip formation can be a difficult issue with low carbon steels, which
often are used for welded components. The lower the hardness, carbon and
sulphur content of the steel, the longer the chips are that will be produced.
Recommendations
Solid carbide drills: CoroDrill 860 -PM in grade GC1024 is the first
choice. If problems with chip formation occur, increase the speed, vc, and
decrease the feed, fn (note in normal steels, the feed should be increased).
CoroDrill 880: First choice is geometry -LM and grade GC4024/1044. If
problems with chip formation occur, increase the speed, vc, and decrease the
feed, fn.
Other: Use high pressure and internal coolant supply. Mixture preferably 4-7%.
Example – Low carbon steel
Austenitic and duplex stainless steels
Issue: Austenitic, duplex, and superduplex materials can cause problems with
chip evacuation.
Recommendations
Solid carbide drills: CoroDrill R846 in grade GC1220 is the first choice. CoroDrill 460 -XM in grade GC34 is second choice.
CoroDrill 880: First choice for drill diameter 14.00-63.50 mm is geometry
-MS and grade GC2044/1144. For other sizes use geometry -LM and grade
GC4044 alt. GC4024/1044.
Geometry -GT is a complementary choice for tough conditions.
Other: Internal coolant, high pressure with a mixture of preferably 9-12% or
neat oil.
Example – Austenitic stainless steel
CGI (Compact Graphite Iron)
Issue: CGI does not normally require extra attention. It produces larger chips
than grey cast iron, but they are well broken. Cutting forces are higher, which
affects tool life. Extra wear resistant grades are necessary. Corner wear is
typical as in all cast irons.
Recommendations
Solid carbide drills: CoroDrill R842 in grade GC1210 is the first choice. CoroDrill 460 -XM in grade GC34 is second choice.
CoroDrill 880: First choice is -GR geometry in grade GC4024/1044. If problems with chip formation occur, increase the speed, vc, and decrease the feed, fn.
Other: Internal coolant, mixture of preferably 5-7%.
Example – CGI (Compact Graphite Iron)
Aluminium alloys
Issue: Burr formation and chip evacuation can be a problem.
Recommendations
Solid carbide drills: Use CoroDrill 860 -NM in grade H10F. The optimized
geometry minimizes burr formation at hole exit and can be used with very
high feeds. An economical and more productive alternative to PCD-drills for
aluminium alloys with Si contents up to 12%.
CoroDrill 880: First choice is geometry -LM. Grade H13A is uncoated and
forms a sharper edge which minimizes burr formation. For best chip
formation, use low feed and high speed.
Other: Use emulsion or mist coolant at high pressure.
Example – Aluminium
Titanium and Heat Resistant Alloys
Issue: Thin walled components deflect due to feed force. Work hardening of
hole surface affects subsequent operations. Chip evacuation can be critical.
Recommendations
Solid carbide drills: Geometry R846 is specially developed for this material
group. Large backtaper and a small circular land minimizes work hardening.
The convex edge maximizes peripheral corner strength against notch wear,
reduces the feed force and improves chip formation.
CoroDrill 880: Geometry -LM and grade H13A for titanium and GC4044/1044
for other HRSA.
Other: High pressure (up to 70 bar) coolant improves performance.
Example – Waspalloy
Hard steels
Issue: Notch wear on the peripheral corner.
Recommendations
Solid carbide drills: CoroDrill 460 -XM in grade GC34 is first choice.
CoroDrill 880: Geometry GM and grade GC4024/1044 is the first choice.
Other: Emulsion with a high mixture or neat oil improves tool life. Use
shortest possible drill to maximize the torque strength.
Example – Hardened steel 55 HRc