Abstract
This study deals with the technology of the high speed end milling of hardened steel by the milling machine with an air spindle. Lately, high speed milling machines with ball bearing type spindle have been developed, and several tests related to the high speed or high efficient milling of hardened steel have been tried. But, there are a number of unclarified points regarding to the cutting mechanism of the high speed milling. This paper therefore tries to clarify the cutting mechanism and aims to present basic data on practical use for the high speed end milling of hardened steel. The main results are as follows; (1) The dynamic characteristics of the air spindle are obtained by experiments. (2) The stability diagrams are obtained by experiments based on the surface roughness and observation with the eye of machined surface. (3) In case of unstable conditions, selfexcited and forced chatter occur. The later generates because of the excitation by the cutting force of intermittent machining. (4) It is shown that the stability range of machining by 2-flute end mill becomes larger than that by 6-flute end mill, because the frequency of intermittent machining by 2-flute is smaller than the natural frequency of the air spindle.
