Page 16 - ISCAR_WORLD_2021

CAST-IRON

LOGIQ

As can be construed from its name, cast iron
is intended for castings. Machining cast iron
parts involves removal of non-uniform and For example, machinability of Ni-resist cast iron can be
variable stock - for example sand inclusions, compared with grey cast iron; however, the required
casting skin, blowholes, hot tears and other cutting geometry seems more suitable for austenitic
casting defects, which affects cutting tools. stainless steel. Workpieces from austenitic ductile iron
From a machining point of view, the higher (ADI) are delivered in different material conditions and
graphite content also has a disadvantage: it hardness level that impact on selecting right cutting
accelerates abrasion wear. This means that the tools. Machinability of ADI before hardening is sufficient
cutting tools must have good wear resistance and is similar to cutting high-alloy steel. Nevertheless, if
to ensure high productivity. It is also worth this cast iron is machined in a high hardness condition,
noting that the term “cast iron" may in fact only the tools intended for the ISO H application group
refer to different types of ferrous alloy, for will meet the customer's expectations.
which machinability can vary significantly.
The latter is often neglected, which can lead The situation with cast iron of high hardness in ISO
to wrong choice of cutting tools and incorrect H group is challenging. Machining cast iron with a
definition of cutting data. hardness of HB 400…440 is usually less of a problem
for manufacturers. However, the picture changes
There are several types of cast iron. Grey, nodular and radically when dealing with hard abrasion-resistant
malleable cast iron form the application group K (red high-chrome cast iron. The general hardness may
identification color) in accordance with the ISO 513 be around HRC 52…54 but in the thin-wall areas of
Standard classification. Hardened and chilled cast a machined part, the hardness can reach HRC 60
iron relate to group H (grey identification color). These and even more. In combination with the high chrome
specifications offer clear guidelines for manufacturers content, it makes machining extremely difficult and
regarding the application of cutting tools - correct tool significantly diminishes tool life.
material, cutting geometry and cutting data selection.

Usually, machining ISO K cast iron is not a problem for
manufacturers. Ferritic grey cast iron, for example, is
an easy-to-cut material. However, machining ISO H
cast iron is more difficult. Although similar to conditions
for machining hard steels, the material’s specific
features demand appropriate solutions from cutting
tool producers. In addition, some types of cast iron
demonstrate a certain duality in their machinability,
emphasizing the broadness and heterogeneity of
the definition "cast iron".

16 ISCAR 17