Abstract: According to the geometry characteristics of helical flutes of the high speed end milling cutter, the general mathematical model of the flute outline in radial section is established. Based on the model and the basic theories of dynamic balance, a mathematical model of mass eccentricity and imbalance value of the high-speed end milling cutter with three unequal blade spaces is deduced. The unbalance value of the end milling cutter is measured by a dynamic balance measuring instrument, and compared with the calculated value. The result shows that the mathematical model of mass eccentricity and imbalance value is completely reliable. According to the model of mass eccentricity, the influencing factors thereof are analyzed and it is found that the helical angle and the length of the cutting edge have the most influence on the mass eccentricity. According to this, the optimal design method for the high-speed end milling cutter with three unequal blade spaces is proposed. In order to investigate the influence of unbalance value and the structure of unequal blade spaces on cutting force and vibration , the comparative tests of high speed milling are carried out. The results show that the structure of unequal blade spaces can suppress vibration and has little influence on cutting force, and the increase of unbalance leads to obvious increase of cutting force and vibration.

Key words: Dynamic balance, End milling cutter, High speed cutting, Unequal blade space