Metallographic Cutting for accurate, low-deformation sectioning

Metallographic cutting or sectioning usually marks the first step of the metallographic sample preparation process. In most cases it is necessary because the part or solid body is too large for the following metallographic grinding and polishing steps carried out on a laboratory scale.

Depending on part geometries and material hardness as well as employed analytical techniques, different cutting techniques and consumables are used.

QATM is a leading manufacturer and supplier of high-quality consumables as well as a range of innovative metallographic cutting machines with a choice of manual or automatic axes. The QATM application experts combine decades of experience with thousands of processed materialographic samples and will be happy to assist with your application.

Metallographic cutting machines

In metallographic sample preparation, mostly abrasive cut-off machines are used for sectioning of workpieces. Optimum cooling is just as important for the sectioning result as precise movement. Common cooling media consist of a mixture of a boric and amino acid-free corrosion protection agent with water. An appropriate concentrate is diluted with water in a ratio of e. g. 1:30. The manufacturer's instructions should be carefully observed. Cleanliness (generally the top priority in metallographic sample preparation) must be ensured for the inside of the chamber as well as the draining system – this influences the precision and the service life of the machine.

The different metallographic sectioning techniques

Traverse Cut

Two versions are possible in this case:

1. The sample table with the workpiece previously fixed on is moved to the fixed wheel manually or automatically.
2. The wheel is moved accordingly.

Chop Cut

The workpiece is firmly fixed on the table. The wheel is then manually or automatically guided from top to bottom into the fixed workpiece.

Step Cut X

The workpiece is not sectioned in one step, but in layers (stepwise). This type of sectioning is particularly suitable for large, thick workpieces of solid material.

Step Cut Y

The workpiece is not sectioned in one step, but in layers (stepwise). This type of sectioning is particularly suitable for large, thick workpieces of solid material that must be clamped on edge (plates, angles, etc.).

Diagonal Cut

In case of a diagonal sectioning, the table moves backwards (X axis) while the wheel moves downwards (Y axis). This type of sectioning is particularly suitable for asymmetrical workpieces, or for compensating the wear of the wheel in order to obtain a constant cutting depth.

Zig-Zag Cut

The workpiece is not sectioned in one step, but in layers (stepwise). The zig-zag cut is made in the middle of the component.

Care Cut

During manual operation, the clamping table (X axis) moves back and forth until the cut is completed. It starts with the movement from front to back. This type of sectioning is particularly suitable for workpieces where a clean edge and material-friendly processing (temperature, deformation) is required due to the smallest possible contact surface.

Rotation Cut

This process is most often used on precision cutters. It can also be used for large workpieces with corresponding rotary sample holders. The sample is turned clockwise or anti-clockwise towards the cut-off wheel. Quarter or half rotations are also possible. For a round workpiece with a diameter of 50 mm, only a cutting distance of 25 mm is required.

The area between sectioned workpiece and the wheel should be as small as possible.

Large contact zone

Small contact zone

Grain size of the abrasives

The grain size of the abrasive in the cutting wheel is an aspect that must not be neglected in metallographic sample preparation. It should be between 45 and 180 µm and will result in a surface that allows further metallographic preparation without removal-oriented planar grinding, if all parameters are set correctly. A very fine grain size is recommended when using thin wheels. A fine grain size is also important if burr-free sectioning is required. The degree of hardness of the wheel itself does not impact the hardness of the abrasive grains, but rather the hardness of the bond, i. e. about the resistance of the individual abrasive grain to breaking out of the bond material.

• A softer bond should be used for large-area contact points. This also ensures that worn abrasive grains are broken out. This type is also well suited for heat-sensitive materials.
• In the case of smaller contact areas, a harder and more stable wheel material is suitable. Those are also used for sectioning tubes and profiles. The advantage here is that it has less contact with the workpiece since the wall thickness is usually small.