Today machining of hard materials is state-of-the-art. Materials up to 70HRc are processed. This not only applies to hardened steel or high-grade steels but also to hard coatings of like electroless nickel platings and special materials such as molybdenum or tungsten.
Mold cavities and mold inserts used in injection moulding are usually machined in the hardened state because no quenching distortion of the finished mold cavity geometry occurs. Since the smallest possible structures are frequently required, the hard materials must be micro machined. 

Various manufacturers supply coated micro milling tools made from fine-grained solid carbide. With these tools the machining of materials to approximately 60HRc is possible. Tools with diameters down to 50µm are available and very serviceable. Tools with smaller diameters are available on the market, however, they are usually so fragile that normally safe handling or processing is impossible.
CBN micro milling tools can be found on the market starting from diameters of approximately 100µm. With these tools the machining of materials to 70HRc is possible. With suitable materials, diamond can also be used instead of CBN or solid carbide. For example, electroless nickel coatings can be successfully processed with single-crystal diamond milling tools. Here also tools with diameters up to 100µm can be used.

The attainable surface roughness of hardened steel using solid carbide tools lies between 80 and 150nm Ra. However, the surface quality decreases with increased tool usage. During the processing of hard materials, solid carbide tools quickly show signs of wear that also substantially affect the geometrical tolerance and accuracy of the workpiece. Therefore, the choice of the correct tool and the correct process strategy is crucial.
Exotic materials such as molybdenum, gold platinum alloys, tungsten but also full form cast iron or high-grade steels have already been successfully processed with Kugler micro machining equipment. The experience that we have gained in this area has shown that the determination of the process parameters is going to be of ever increasing importance. Therefore, before processing any new material detailed cutting and production trials are carried out. Only then can the production goal of the customer be achieved.

By Roland Bohr
Technical Manager Micro Machining

Head of Department:
Mandy Jacobs
mandy.jacobs@kugler-precision.com