Machining of cast irons
Cast irons, which make up the ISO K group, are Fe-C compositions with a relatively high percentage of Si (1-3). They are short-chipping materials with good chip control in most conditions, though their machinability varies. Added elements such as Cr (chromium), Mo (molybdenum) and V (vanadium) form carbides, which increase strength and hardness but lower machinability. All cast irons contain SiC, which is very abrasive to the cutting edge.
There are 5 main types of cast iron. Although they all belong to the family of cast irons, the range of properties and applications means that choosing the right tool coating – something the Ionbond engineers would be happy to discuss with you – is of particular importance.
Easy to machine:
- Gray Cast Iron (GCI)
- Malleable Cast Iron (MCI)
More difficult to machine:
- Nodular Cast Iron (NCI)
- Compacted Graphite Iron (CGI)
- Austempered Ductile Iron (ADI)
The specific cutting force of cast irons falls between 790 and 1,350 N/mm². Machining at higher speeds, especially of cast irons with sand inclusions, creates abrasive wear.
NCI, CGI and ADI require extra attention, compared to normal GCI, due to the different mechanical properties and the presence of graphite in the matrix.
Cast irons are traditionally machined dry, but can also be used in wet conditions, mainly to keep the contamination of dust from carbon and iron to a minimum. There are also grades available that suit applications with coolant supply.