Cast iron can be divided into malleable, gray, nodular, compact graphite iron (CGI), and austempered ductile iron (ADI).
Gray cast iron
Material Classification: K2.x
- The dominant wear criteria when milling gray cast iron are abrasive flank wear and thermal cracks.
- On the component, frittering at the cutter exit side of the workpiece and surface finish problems are the main issues.
Suitable cutters and inserts
There are several cutter concepts that have been developed primarily for milling gray cast iron:
- CoroMill 365 general purpose cutter.
- AUTO R roughing cutter.
- AUTO-AF adjustable finishing cutter.
- AUTO-FS non-adjustable finishing cutter. CoroMill 245 cassettes are available for AUTO-AF cutter bodies as an alternative.
- Wiper inserts, are available for all of the above cutter concepts.
- Most other CoroMill cutters can also be used in gray cast iron simply by choosing a dedicated insert geometry and grade.
- CoroMill 345 is a good choice for mixed production of steel and cast iron.
- Use K-geometries -KL, -KM, -KH and -KW (wiper).
- Grade recommendations for indexable insert cutters, see Application hints below.
- For CoroMill Plura solid carbide endmills, grade GC1620, and for CoroMill 316, grade GC1030, are the basic choices.
Typical insert wear
Frittering on the component
- Preferably run dry, without cutting fluid, to minimize problems with thermal cracks. Use carbide inserts with thick coatings. GC3040 is the first choice and GC3220 an optimizer for higher speeds.
- If workpiece frittering is a problem
– check flank wear
– lower the feed, fz, in order to reduce chip thickness.
– use a more positive geometry, -KL
- If cutting fluid must be used to avoid dust, etc. choose the wet milling grades. K20W is the basic choice and K15W and GC3040 are complementary grades.
- Coated carbide is always the first choice, but ceramics (CC6190) can also be used. Note that the cutting speed, vc, should be very high, above 2624 ft/min. Burr formation on the workpiece limits the cutting speed. No cutting fluid should be used.
- Use carbide inserts with thin coatings, e.g., GC3220 in dry and K15W in wet conditions, or alternately, an uncoated carbide.
- Cubic boron nitride (CB50) can be used for finishing at high speeds in gray cast iron. No cutting fluid should be used.
Nodular cast iron
Material Classification: K3.x
Ferritic and ferritic/perlitic nodular cast iron
The machinability of ferritic nodular cast iron is very similar to that of low alloyed steel. Therefore, the milling recommendations provided for ISO P materials should be used regarding selection of tools, insert geometries and grades. The first choice grade is GC1020.
Pearlitic nodular cast iron
Is more abrasive, therefore ISO K grades are recommended.
Compact graphite iron (CGI)
Material Classification: K4.x
Perlitic content less than 90%
This type of CGI, which often has a pearlitic structure of around 80%, is the most common being milled. Typical components are engine blocks, cylinder heads and exhaust manifolds.
Cutter recommendations are the same as for gray cast iron; however, sharper, more positive insert geometries should be selected, for example –KX and –KL for AUTO-R cutters, to minimize burr formation on the component.
The first choice grade is GC1020.
GC1020 is the basic choice for both dry and wet conditions. An alternative for dry conditions is K20D, and for wet conditions K20W.
Circular milling can be a very good alternative method to conventional cylinder boring in CGI.
Austempered ductile iron (ADI)
Material Classification: K5.x
Roughing is normally carried out in the non-hardened condition and can be compared with milling of a high alloyed steel.
The finishing operation, however, is performed in the hardened material, which is very abrasive. This can be compared with milling of hard steels, ISO H. Grades with high resistance against abrasive wear are preferred. GC1020 is the first choice for both dry and wet conditions; the complementary grade for harder ADI-materials is GC1010.
In comparison with NCI, the tool life in ADI is reduced to approx. 40%, and the cutting forces are approx. 40% higher.