We also offer a one-stop PVD coating – TOOL GRINDING SERVICE which will restore your tools to their original specifications. Beyond the obvious advantage to you of less headaches and simpler, more convenient service, as a rule the end product is a much higher quality tool.
As a service to our clients, we pre-select high quality grinders, provide rigorous quality control of the grind quality, and coat the tools after we making sure that the grind satisfies the highest standard.
You should be aware of the fact, that burring at edges of high speed steel tools is a sign of plastic deformation. A hardened tool steel does not deform, it can only break, chip. The reason for the formation of burrs as a result of grinding is invariably incorrect technology or careless, bad workmanship. If for example the grinding wheel is not dressed correctly or frequently enough, or the wrong wheel grade is used for the job, then during grinding, the edges can overheat to high temperatures. This over-heating can cause softening of high speed steels, enabling plastic deformation and burr formation. Because of the small volume of the burrs and the associated edge itself, these areas will cool quickly, transferring the steel at the very edge, and the burr itself, into a glassy, brittle, un-tempered martensitic state. The visible signs of this mistreatment can be easily eliminated by removing/breaking off the burr with a brass stick or a wire brush, and the discoloration or darkening can be etched off. However, the tool performance is permanently impaired.
Incorrect grinding procedures can also affect the performance of carbide tools. Exposure to high temperatures will reduce the WC, breaking the carbon-tungsten bonds, which will lead to the loss of some of the carbon from the surface. The free tungsten which is left behind is available to form a brittle, mechanically inferior intermetallic compound with the cobalt binder. The structure thus formed is called the eta (η) phase. Eta phase is formed preferentially at cutting edges – areas of the highest thermal exposure, rendering these edges brittle, prone to micro-chippage and rapid edge breakdown.
Another potential problem during grinding of cobalt-cemented tungsten carbide tools is leaching of the cobalt binder. This can occur if the lubricant/coolant used during wet grinding turns acidic due to neglect, incorrect handling, or incorrect selection. The acidic chemical environment dissolves and removes some of the cobalt binder from the surface, thus weakening the anchoring of tungsten carbide (WC) particles, and causing their loss. Cobalt leaching reduces the adhesion of PVD coatings, thereby greatly reducing the beneficial effects of coatings. Cobalt leaching can also occur if carbide tools are left wet, exposed to atmospheric air after grinding, even if they are carefully washed with pure water. The wet surface will turn acidic due to absorption of atmospheric carbon dioxide, which will lead to similar results as a turbid coolant.
These are wide-spread, commonly encountered problems in grinding, and we can make sure that these and other problems will be avoided by selecting high quality, reliable grinding vendors and conducting scrupulous inspection of the ground tools prior to PVD coating.