Su Wenjun

Bio: Su Wenjun is an academic researcher from Xi'an Jiaotong University. The author has contributed to research in topics: Bearing (mechanical) & Machine tool. The author has an hindex of 4, co-authored 11 publications receiving 65 citations.

Active damping of milling chatter vibration via a novel spindle system with an integrated electromagnetic actuator

Abstract: Self-excited vibration, widely referred to as chatter, has always been a limitation and challenge in machining. To suppress milling chatter vibration and improve surface finishes, a novel spindle system is proposed in this study. A noncontact electromagnetic actuator with two degrees of freedom is developed and integrated into the designed spindle system compactly. A differential driving mode is utilized for the electromagnetic actuator to obtain a linear output of actuator force, making the actuator more applicable for vibration control. Displacement sensors mounted near the actuator measure the vibration of the rotating spindle shaft and provide feedback signals for the developed proportional-derivative controller. The active damping performance of the designed spindle system with an integrated electromagnetic actuator, in both x and y directions, is also validated with impact tests and milling experiments, and a maximum increase (by factors of 3.67 and 2.89 in x and y directions, respectively) of dynamic stiffness at the first modal frequency is obtained. Milling experiment results with and without active damping also illustrate that milling chatter vibration has been well damped actively with the developed spindle system.

Device and method for testing the dynamic characteristics of high-speed machine tool spindle

Abstract: The invention discloses a device and a method for testing the dynamic characteristics of a high-speed machine tool spindle. The test system comprises a virtual cutter mounted on the machine tool spindle, and a three-direction force measuring instrument and magnetic meter bases which are mounted on a machine tool workbench. The three-direction force measuring instrument is equipped with an electromagnetic loading device, the virtual cutter is inserted into the electromagnetic loading device, and the bottom of the electromagnetic loading device is provided with a through groove in the same direction as the electromagnetic force. The magnetic meter bases are arranged at the two sides of the three-direction force measuring instrument. Each magnetic meter base is equipped with a laser displacement sensor of which the light spots can penetrate through the through groove. Different radial directions of the spindle can be loaded simultaneously, the loading device does not need to be adjusted, and analysis of the static and dynamic stiffness of the machine tool spindle in different radial directions is facilitated. The electromagnetic loading device is equipped with a cooling device, so that the current problem that a large amount of heat is generated in the electromagnetic loading process with the increase of the loading time to influence the performance of the spindle is effectively solved.

Online monitoring system and method for spindle colliding and tool breakage based on mixed supporting electric spindle

Abstract: The invention discloses an online monitoring system and method for spindle colliding and tool breakage based on a mixed supporting electric spindle. The electric spindle in the system comprises a spindle body, a tool handle with a tool, a front bearing set, a stator, a rotor and a rear bearing set. The tool handle, the front bearing set, the stator, the rotor and the rear bearing set are mounted on the spindle, a motor is mounted in the stator, and a motor is mounted in the rotor. An electromagnetic bearing and a signal collecting and processing device are further included. Mixed supporting on the spindle is formed by the electromagnetic bearing, the front bearing set and the rear bearing set. The electromagnetic bearing comprises an electromagnetic bearing rotor arranged at the front end of the spindle in a sleeving manner through interference fit, an eddy current displacement sensor, an electromagnetic bearing controller and an electromagnetic bearing stator. The eddy current displacement sensor, the electromagnetic bearing controller and the electromagnetic bearing stator are connected in sequence. The eddy current displacement sensor is mounted at the front end of the spindle and used for measuring radial displacement at the front end of the spindle. The input end of the signal collecting and processing device is connected with the eddy current displacement sensor, the electromagnetic bearing controller and the output end of an encoder arranged on the spindle. The output end of the signal collecting and processing device is connected with the input end of a CNC system.

Milling chatter detection based on VMD and difference of power spectral entropy

Abstract: Chatter is a kind of unstable vibration in high-speed milling process, leading to poor surface quality of workpiece, significant tool wear, and severe noise. In order to avoid these negative effects of milling chatter, the detection of chatter at early stage is highly needed. In this paper, an early-stage chatter detection method based on variational mode decomposition (VMD) and difference of power spectral entropy (ΔPSE) is presented. Considering that the existence of possible colored noise in the monitoring signals, which might lead to the misjudgment of chatter detection, the signals monitored at spindle’s idling is utilized to identify these noise components. In order to separate the needed chatter-sensitive sub-signals, VMD is utilized to decompose the original signals into a series of intrinsic mode functions (IMFs), and the chatter-sensitive sub-signals are obtained by adding the IMFs whose central frequencies are closed to the milling system’s natural frequency. After that, an adaptive filter is utilized to filter out the harmonics of spindle-speed frequency and the identified colored noise components. Then, a dimensionless indicator is designed, which is determined as the difference of power spectral entropy (ΔPSE) of signals without and with filtering. A series of experiments are also performed, and the results indicate that the presented methodology can detect the chatter at early stage and is applicable in different cutting conditions, which is very important in the practical application.