Knowledge

Selecting the correct indexable inserts – what do I need to know?

Indexable inserts offer a significant advantage compared to other cutting tools: If a cutting edge of the indexable insert is worn, it is simply turned to an unused cutting edge – no need for regrinding. This ensures that ongoing production is only interrupted briefly and there is no need for a time-consuming setup of the tool.

Which cutting insert to use depends on the type of production and the material to be machined, and its level of hardness. There is a wide range of indexable inserts of different shapes and material, which makes selecting the correct indexable inserts tricky. 

Indexable inserts to international standard

In order to prevent wrong decisions from being made, indexable inserts are standardised internationally. This ISO standardisation specifies the size, shape, mounting, material properties and coating. The cutting machine operator uses the ISO indexable insert designation to select the appropriate indexable insert needed for the relevant application.

The ISO code can include up to twelve characters. The first to seventh characters indicate mandatory information. The eighth and ninth provide optional information which is used as required. The tenth to twelfth are optional manufacturer details and are added separately to the ISO code using a hyphen.

The seven mandatory fields indicate the insert shape or the clearance angle and other core features of the cutting insert. The characters have individual identification letters and numbers which clearly identify an indexable insert. In order to be able to assign the appropriate dimension to these identification letters, tables conforming to DIN4983 are available which can be looked up in a table book.

Manufacturer-specific details are indicated after a hyphen and, depending on the company, specify the chamfer width, chamfer angle, cutting material or shape of the chip breaker. The relevant legend is taken from the manufacture catalogues.

1 = insert shape | 2 = clearance angle | 3 = tolerances

4 = machining and fixing characteristics | 5 = cutting edge length | 6 = insert thickness

7 = corner rounding | 8 = cut development | 9 = cutting direction

10 = manufacturer's information

The ISO code comprises 9 symbols, of which symbols 8 and/or 9 are only used as required. The manufacturer can add other symbols, which are added to the ISO code by a hyphen (e.g. for the shape of the chip breaker).

Tips for selecting the correct indexable insert

To achieve good chip control and the best machining results, the geometry, grade, shape (point angle), size, corner radius and setting angle of the indexable insert should be selected carefully.

Select the indexable insert geometry based on the selected application

For roughing, we recommend a combination of large cutting depth and high feed rate. Roughing applications place high demands on the cutting edge dependability. Finishing is an application which requires low cutting forces as shallow cutting depths and low feeds are generally needed.

Select the largest possible point angle

A large point angle is stable, requires increased machine output, but can also tolerate higher feed rates. High cutting forces are therefore possible, but the tendency for vibrations also increases. With a small point angle, the cutting edge is less stable and it has a small cutting edge engagement; thereby increasing the thermal sensitivity. The insert has a smaller cutting force.

1. RE = corner radius

2. I = cutting edge length (indexable insert size)

3. Point angle

Selecting the indexable insert size based on the cutting depth

Select the indexable insert size depending on the machining requirements and the space which is available for the tool in the application. A larger indexable insert offers greater stability. For difficult machining, the indexable insert size is usually above IC 25 mm (1 inch). During finishing, the size can often be reduced in most cases. Proceed as follows: First, determine the largest cutting depth and then set the required cutting length, whilst taking into account the setting angle of the tool holder. You can then select the correct cutting edge length for the insert.

Selecting the largest possible corner radius

The corner radius is selected depending on the cutting depth and feed and influences the surface quality, chip breakage and stability of the indexable insert – the corner radius is therefore an extremely important factor when it comes to turning operations. A small corner radius is ideal for shallow cutting depths, reduces vibrations and produces a good chip breakage. However, the cutting edge is less stable than with a large corner radius. This allows a high feed with greater cutting depths and high cutting edge dependability. However, with the large corner radius, greater radial forces occur. This can impair the cutting effect and lead to a poorer surface quality. You should therefore select a smaller corner radius if there is a tendency for vibrations to be generated with your configuration.  Always select a corner radius which is not larger than the cutting depth.

Selecting the correct setting angle

The setting angle KAPR is the angle between the cutting edge and feed direction. It influences the chip formation, direction of the cutting forces and the cutting edge length being engaged. With a large setting angle, the forces are directed towards the chuck, thereby producing a reduced tendency to generate vibrations. It allows shoulders to be turned and produces higher cutting forces during entry and exit. However, with the large setting angle there is a tendency towards notch wear in HRSA and case-hardened materials. The smaller setting angle increases the tendency for vibrations to be generated as higher radial forces are directed into the component. But on the other hand, the cutting edge is under less strain and a thinner chip is created, which allows for increased feed rates, and the notch wear is lower. However, it is not possible to turn against a 90-degree shoulder.

Selecting the correct cutting material and coating

The material of the cutting insert should essentially be hard and resistant to deformation, whilst at the same time also tough, in other words, not brittle, should not react to the material and should be overall chemically stable, i.e. resistant to sudden thermal alternating stress, oxidation and diffusion. Cutting inserts are available made of carbide, ceramic, boron nitride and diamond. Indexable insert geometry and grade complement each other: the degree of toughness of one grade can compensate for the lack of stability of an indexable insert geometry.

  • Carbide: Temperature resistant up to 1000 degrees, high wear resistance and high pressure resistance  
  • Ceramic: Temperature resistant up to 1200 degrees, great hardness, high degree of toughness and suitable for increased cutting speeds
  • Boron nitride: Temperature resistant up to 200 degrees, high wear resistance, great hardness
  • Diamond: Extremely high wear resistance

To improve the properties, indexable inserts are often coated with hard materials such as titanium carbide or titanium nitride in order to further improve the wear resistance and heat resistance.

  • Typical applications of uncoated carbide grades include the machining of heat-resistant super alloys (HRSA) or titanium alloys and the turning of hardened materials at lower speed. The result is increased wear compared to coated grades.
  • CVD-coated grades are the first choice for a wide range of applications where wear resistance is the deciding factor. CVD stands for chemical vapour deposition. The CVD coating is applied through chemical reactions at temperatures of 700-1050 degrees. These applications are found with general turning operations and when drilling into steel, where the thick CVD coatings provide resistance to crater wear, and with general turning operations of stainless steels and milling grades in ISO P, ISO M and ISO K. When drilling, the CVD grades are usually used in the outer cutting edge.
  • PVD-coated grades, i.e. with coatings produced by means of physical vapour deposition (PVD), are also recommended for adhesive material due to their tough, yet sharp cutting edges. The application range is diverse and includes all solid carbide milling cutters and drills and most grades for grooving, thread cutting and milling. PVD-coated grades are also used on a large scale for finishing operations and as centre cutting grades when drilling.

Now find the suitable indexable insert and insert holder: