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

Doktorsavhandling, 2019

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 understand 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.