The reliability test of motorized spindle is an important method to study the failure mode and mechanism of motorized spindle in CNC machine tools. However, simulating the real working conditions of motorized spindle is a prerequisite for carrying outreliability tests which needs to study the loading condition and compile the load spectrum of motorized spindle. The previous methods of compiling the load spectrum can only make the cutting force, torque and rotational speed into the spectrum separately, and neglect the effect of cutting time and the corresponding relations among 3 parameters which is inconsistent with the actual working conditions. In view of this problem, a method which compiles multi-dimensional load spectrum of motorized spindle considering the coupling effect of cutting force, Torque and rotational speed is discussed. By analyzing and processing the field load data of NC machine tools, the operating time, rotating speed, cutting force and cutting torque of the spindle are calculated. The number of machining cycles of spindle is obtained by multiplying the operating time and rotating speed. Then, normalize the data to get 4 parameters including the relative machining cycles, relative rotating speed, relative cutting force and relative cutting torque. A multi-dimensional load spectrum including rotational speed, axial force, radial force, torque and relative cycle times in different levels is compiled. Compared with the former load spectrum, the reliability test of the motorizedspindle based on new multi-dimensional load spectrum doesn't change the failure mode and mechanism of the motorized spindle.
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