When selecting inserts for machining operations, the physical and chemical properties of the workpiece material are the deciding factor. Under international standards (ISO), inserts are classified with specific letter and colour codes according to the workpiece material groups. Choosing the wrong insert leads to rapid tool wear, breakage, built-up chips or poor surface finish on the workpiece.
Watch Temak Teknik’s information video on carbide inserts, ISO material classes and choosing the right insert below:
ISO Material Groups and Colour Codes
Indexable carbide inserts are divided into 6 main groups according to the workpiece material:
1. P Group: Steels (Blue)
- Scope: Carbon steels, alloy steels, cast steels and non-heat-treated tool steels (1020, 1040, 1045, 4140, 2379 etc.).
- Chip Formation: Generally produces continuous, helical chips. Cutting resistance is moderate and machinability is very good.
2. M Group: Stainless Steels (Yellow)
- Scope: Stainless steels containing at least 12% chromium, nickel or molybdenum (e.g. 304, 316, duplex stainless steels).
- Characteristics: Built-up edge and notch wear occur during cutting. Sharp insert geometries with high heat resistance should be selected.
3. K Group: Cast Iron (Red)
- Scope: Grey cast iron, nodular (ductile) cast iron and malleable cast iron.
- Chip Formation: Produces short, brittle chips (like grains of bulgur or wheat). As little chip breaking is required, the chipbreaker forms on these inserts are generally flat or plain.
4. N Group: Non-Ferrous Metals (Green)
- Scope: Aluminium alloys, copper, brass, bronze and various plastics such as polyamide, Delrin and cast nylon.
- Characteristics: These inserts have polished (bright) and extremely sharp geometries to reduce friction and prevent material smearing. They offer long life at high cutting speeds.
5. S Group: Heat-Resistant Superalloys and Titanium (Orange / Brown)
- Scope: Nickel-, cobalt- or titanium-based high heat-resistant alloys (Inconel, Hastelloy, titanium etc.).
- Characteristics: These materials are much harder to cut than stainless steels, generate high heat during machining and cause work hardening. Tool life is short, and inserts with special coatings are required.
6. H Group: Hardened Materials (Grey)
- Scope: Heat-treated hardened steels and cast irons between 45 and 65 HRC (Rockwell).
- Characteristics: Extremely high cutting temperatures and high strength are involved. In conditions free of impact and vibration, ceramic or CBN (Cubic Boron Nitride) inserts are also preferred alongside carbide inserts.
Key Recommendations for Choosing the Right Insert
- Part Form and Surface Brightness: When machining aluminium and plastics, green-coded (N class) bright polished inserts should be chosen to avoid dulling or built-up edge (BUE) [01:38].
- Recommendation for Plastics: For plastic-based materials such as polyamide, Delrin and cast nylon, inserts with aluminium geometry (N) provide a smooth cut and prevent the part from melting and burring [01:53].
- Ceramic Alternative: In hardened materials (H group), where there is no risk of impact, heat-resistant ceramic inserts or CBN inserts can increase cutting life many times over