What is high-speed machining?

The mechanism of high-speed machining (HSM) has been discussed. The HSM may be defined on the basis of the surface speed, the relative speed between the tool and workpiece, which is essentially a thermal limit because many of the wear mechanisms are temperature dependent. The HSM is defined using the DN number, the product of D that is the diameter in mm of the main bearing bore, and N, the maximum spindle speed in rpm. The DN number is based on the rotation capability of the preloaded spindle bearings. The laboratory spindles although have achieved much higher numbers, the commercial high-speed spindles have remained below 2 million DN for a number of years. One of the main reasons is heat in the bearings and there is also heat from the rotor in an integral spindle and from the drivetrain in a nonintegral spindle. The preload mechanism must allow for thermal growth of the spindle while maintaining preload.