Application Cases

Experiment Name: Research on Vibration Suppression in Machining of Thin-Walled Parts Based on Magnetorheological Damping Control

Research Direction: Mechanical Machining

Test Objective:
To dynamically control the magnetorheological (MR) damping effect and compensate for the loss of dynamic characteristics during the milling of thin-walled parts, a vibration suppression method using a Smith-Active Disturbance Rejection Controller (S-ADRC) to adjust the MR damping is proposed. Based on the established milling dynamics model of the MR-thin-walled part system, an active vibration control method combining a Smith predictor and an ADRC is used to eliminate the effects of time delay and disturbances during the control process. The stability of the S-ADRC is then analyzed by solving the closed-loop control differential equation of the MR vibration suppression system. The controller and the vibration suppression system were established using MATLAB/Simulink. The transient control performance and disturbance rejection capability of the S-ADRC were analyzed and compared with those of PID and ADRC controllers. Simulation results indicate that the proposed control method possesses high robustness and superior transient control performance.

To verify the effectiveness of the MR damping control vibration suppression method based on the S-ADRC, a milling vibration suppression system for thin-walled parts based on MR damping control was developed. The system includes a thin-walled part vibration suppression control test bench and corresponding control software. The controller adjusts the MR damping in real-time based on the vibration displacement of the thin-walled part, thereby altering its dynamic characteristics to achieve vibration suppression. Finally, modal impact tests and thin-walled part milling vibration tests were conducted. The test results demonstrate that the vibration suppression method based on MR damping control and the S-ADRC can effectively suppress milling chatter in thin-walled parts.

Testing Equipment: ATA-304 Power Amplifier, Magnetorheological Damping Vibration Suppression Device, Eddy Current Sensor, Data Acquisition Card, Host Computer (Laptop), S-ADRC Controller.

Experimental Procedure:

Figure: Milling Vibration Control System for Thin-Walled Parts Based on MR Damping Device

A typical cantilevered T-plate was selected as the control object for the milling vibration suppression test. A vibration control system for thin-walled parts based on MR damping was developed. This system comprises both hardware and software components. The S-ADRC controller was integrated into the thin-walled part vibration suppression control software written in LabVIEW and applied to the MR damping device. Using this control system, side milling tests on thin-walled parts were conducted on a machining center. Real-time adjustment of the MR damping by the controller successfully suppressed vibrations during the side milling process of the cantilevered thin-walled part.

Figure: Diagram of the Test Setup and Control System for the Thin-Walled Part Milling Vibration Suppression Experiment

Before conducting the MR damping-controlled milling vibration suppression tests on the thin-walled part, a series of preparations were required, such as writing the G-code for the milling process, installing the MR damping device, connecting the circuits between hardware components, debugging program parameters, and preparing the MR fluid.

An eddy current sensor was used to measure the vibration displacement of the thin-walled part. Its linear operating range is 0.6-2.6 mm, with a calibration coefficient of 2.5 relative to the voltage signal. The initial gap between the sensor and the thin-walled part was set to 1 mm; therefore, the target value v0 for the controller was set to 2.5. After all preparations were complete, the milling tests began. The milling tests were divided into two groups: one group used 150 mL of MR fluid in the container without applying MR damping control, and the other group also used 150 mL of MR fluid but with MR damping control applied during machining. The cutting parameters for both groups were identical: spindle speed 3000 rpm, axial depth of cut 2.5 mm, and radial depth of cut 0.5 mm. The thin-walled part material was aluminum 7075 with a thickness of 5 mm. A three-flute carbide end mill with a diameter of 10 mm was used.

The eddy current sensor was fixed by a bracket on the non-cutting side of the workpiece, positioned 1 mm from the workpiece surface. Its output was connected to the data acquisition card, with a sampling frequency of 19200 Hz. The vibration status was transmitted to the controller. The calculated control signal was sent from the acquisition card's output to the power amplifier. After amplification, it was fed back to the MR damping device to suppress workpiece vibration.

Experimental Results:

The thin-walled part cutting tests were divided into two groups. The cutting parameters for the first group (no MR damping control) were: spindle speed 3000 rpm, axial depth of cut 2.5 mm, radial depth of cut 0.5 mm, and feed rate 300 mm/min. The cutting parameters for the second group were identical to the first, but the S-ADRC controller was activated, adjusting the output voltage in real-time based on the acquired vibration signal to modify the damping characteristics of the MR fluid and the machining system. The vibration curves for the thin-walled part during the two cutting tests are shown in the figure below.

Figure: Vibration Signals During Cutting (a) Without Control (b) With MR Damping Control

The vibration signals from both tests were analyzed using Fourier transformation to observe the difference in chatter frequencies. Figure 4 shows the Fourier spectra under the two milling conditions (without and with MR damping control). Furthermore, the surface textures and 3D topographical images of the machined workpiece under different conditions are shown in Figure 5.

Figure 4: Frequency Spectrum (a) Without Control (b) With MR Damping Control

Figure 5: Surface Textures and 3D Topographical Images of the Machined Workpiece Under Different Milling Test Conditions

Analysis of the first group of tests (without MR damping control) showed that the workpiece vibration amplitude during milling reached 0.15 mm. Besides the spindle frequency (50 Hz) and the tooth passing frequency (multiples of the fundamental frequency), the frequency spectrum also exhibited chatter frequencies at 257 Hz and 768 Hz. This indicates that selecting machining parameters within an unstable cutting region and conducting the milling test without MR damping control induced chatter, also verifying the accuracy of the milling stability lobe diagram. Furthermore, 3D topography measurements of the machined surface using a ZYGO profilometer showed that without control, the average surface roughness (Sa) after milling was 0.347 μm, with a peak-to-valley (P-V) roughness of 15.716 μm. The machined surface exhibited明显的 (obvious) chatter marks.

In the second group of tests (with MR damping control), the results showed that the time-domain vibration amplitude of the workpiece during milling attenuated to 0.08 mm, half of that observed without control. In the frequency domain, the chatter frequencies at 257 Hz and 768 Hz completely disappeared from the spectrum. This suggests that applying MR damping control increased the system's stability limit, causing the machining parameters to fall within a stable region. ZYGO measurements showed that with control, the average surface roughness (Sa) after milling was 0.130 μm, and the P-V roughness was 2.301 μm, significantly lower than the results without control. Moreover, the machined surface was noticeably smoother and flatter compared to the uncontrolled case. The results of these two comparative tests demonstrate that the controller, by enhancing the damping effect of the MR fluid, strengthens the dynamic characteristics of the thin-walled part, suppresses vibrations during the milling of cantilevered thin-walled parts, and improves machining stability.

Figure: ATA-304C Power Amplifier Specifications and Parameters