Material groups in machining
The workpiece material is one of the most important variables with influence on the machining process. The preparation for successful machining always starts with the correct understanding of the material that is going to be cut.
The metalworking industry produces a huge variety of components machined from a wide diversity of raw materials, where each workpiece material has unique machinability properties.
Material ISO groups
To make life easier, ISO standard has split the workpiece materials into 6 groups, each group having distinct machinability properties.
A letter and a color has been given to each group.
Material groups and subgroups
The classification into 6 main groups (PMKSNH) is a very good start, as the materials inside each group have similar machinability properties. However, depending on their alloying elements and/or hardness level, the machinability of materials of the same main group can still vary quite a lot, this is the reason why we need to further split them into subgroups. By identifying the right subgroup of a workpiece material, we will be able to make correct choices regarding the selection of inserts and cutting parameters. Let’s see the 6 ISO groups, with their respective Lamina material subgroups.
P – Steels
«P» comes from the German word «Plastisch», and means plastic (malleable)
Steels are alloys with Iron as major element (Fe-Based)
Typical components: structural parts, cam shafts, molds, dies, hydraulic components, etc.
Machinability is good in general. Group 1 can be very sticky and requires positive chipbreakers.
M – Stainless Steels
«M» comes from the German word «Mischgruppe», and means mixed group
Stainless steels are alloys with Iron as major element and Chrome content higher than 12%
Typical components: parts for pumps, water turbines, food processing industries, etc.
Machinability is good for Ferritic and Martensitic, considerably complex for Austenitic and difficult for Duplex.
K – Cast Irons
«K» comes from the German word «Kurzspanend», and means small-chipping
Cast irons are Fe-C composition with percentage of Silicon in between 1 and 3%.
Typical components: Engine blocks, gears, brake discs, crankshafts, etc.
Cast irons are abrasive materials, but their machinability is good in general.
S – High Temp Alloys (Super Alloys)
«S» comes from the German words «Spezialle-gierungen», and means special alloys
High TempAlloys (Nickel, iron or cobalt-based) and Titanium.
Typical components: aerospace engine and turbines, oil and gas marine applications, medical implants
This group of materials is very difficult to machine, due to poor thermal conductivity and strenght retention at high temperatures.
H – Hardened materials
«H» comes from the German word «Hart», and means hard
Hardened and thermal treated materials with hardness higher than 45HRc.
Typical components: Transmission shafts, gear box housings, stamping dies, etc.
Machinability is difficult, due to very high cutting forces.
N – Non-ferrous materials
«N» comes from the German word «Nichteisenmetalle», and means non-ferrous metals
This group is composed by non-ferrous, soft metals with hardnesses under 130 HB Aluminum is the most common.
Typical components: engine block, wheels, transmission housings, aerospace frame components
Machinability is good. It generates low cutting forces, but has tendency to produce long chips, reason why very positive chipbreakers are required.
Cutting Tools consumption in the World by workpiece material
On the left, we can see the popularity of the main material groups in the metalworking industry.
This chart is based on the money spent with cutting tools.
Material reference list
In our catalogue, from page 329 to page 335, you can find a list of materials in Lamina material groups, considering also different norms.
In summary, machinability varies a lot depending on the type of workpiece material. Before selecting tools and cutting parameters, it is very important to verify in which Lamina material group the workpiece is classified.