Phillip Hoier

The effect of workpiece material and its microstructure on tool wear in metal cutting

Philipp Hoier, Doctoral Student at Materials and manufacture​ IMS, defends his doctoral thesis on September 16, 2019.

​Abstract
In our everyday life we are frequently using different types of mechanical systems like automobiles, home appliances, or airplanes. Each system usually contains many individual components that have to work together properly so that the mechanical system as a whole functions. A modern aircraft engine, for example, contains about 18000 individual components. During manufacturing of most of the components, different metal cutting operations are used to cut the material (also called workpiece) into the desired shape. Obviously, the whole engine can only work safely and reliably if every single component has the exact right shape and dimension. Small deviations due to problems during the cutting processes can cause catastrophic failures during the service life of the aircraft engine. 
One problem that can arise during metal cutting operations is excessive wear of the tools that are used to cut the workpiece. In such a case, the component that is cut can be damaged and has to be scrapped since it cannot be applied for its purpose. This problem can be compared to cutting vegetables with a knife (your cutting tool) in your kitchen at home: After long cutting time and maybe depending on what types of vegetables you cut, the edge of your cutting tool can wear and get blunt. Instead of cutting precise slices of for example tomatoes, you will rather squish the tomato and get “damaged” slices with intolerable dimensions and properties. 
In order to avoid this problem during manufacturing of mechanical components, it is therefore important to know or predict when the cutting tool is too blunt to cut the workpiece precise enough. This is however difficult, because it is not well understood how the different constituents of the workpiece affect the wear of cutting tools. It is further complicated by the fact that workpieces can vary depending on their type and the producer. Similarly, the characteristics of a tomato (for example size and amount of hard seeds) can vary depending on what kind of tomatoes are used and where they were grown.
This thesis aims at increasing the fundamental understanding of how the workpiece material and variations in its microstructure affect the wear of the tools used to cut it. This was achieved by controlled cutting tests during which the amount of tool wear was measured and compared when cutting different workpieces. Furthermore, the workpieces and worn cutting tools were studied at the microscopic scale to identify the mechanisms responsible for the wear. The gained knowledge can help to optimize the cutting process as it allows to predict how fast cutting tools wear down and when they have to be replaced. In that way the risk for having to scrap components can be reduced which is beneficial from an economical and an environmental standpoint and leads to more sustainable processing.


Published: Tue 24 Sep 2019.