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Cutting force detection can contribute to predicting the productivity and quality of end milling operations. Instantaneous cutting force prediction of digital twins in end milling operations should be near real-time and accurate. This paper proposes an image-based approach that can contain more useful information due to a higher dimension and simplify the complexity of computing geometric data. The cutter frame image (CFI) is utilized as one of the inputs of a convolutional neural network (CNN) to predict instantaneous cutting forces. Considering the convenience of capturing massive data, the approach uses cutting forces generated from a mechanistic force model instead of experimental cutting forces to train the CNN. The correlation coefficient R2 value between predicted results and simulated results is 0.9999 and the average time cost per image is 0.057 s in a cutting condition, which validates the possibility to use the image-based method to predict instantaneous cutting forces accurately and efficiently in the digital twin. [ABSTRACT FROM AUTHOR]

The optimal parameters of a passive damper (i.e., frequency ratio and damping ratio) for the machining vibration attenuation of thin-walled part are quite affected by the material removal process, and the damper becomes ineffective easily due to its narrow vibration band. A design of passive damper with tunable stiffness is proposed for being adaptive to the varying machining process, and the frequency tuning is carried out by orienting the mass block inside the damper. Modal tests are performed to verify the amplitude reduction of the target mode of the thin-walled part. It shows that the optimal vibration suppression is reached when the orientation is 20° due to a smaller frequency difference between the damper and target mode, and the amplitude of the damped frequency response function is reduced to 1.3 %. Finally, machining tests are carried out, and the machining vibration and surface quality validate the large increase of machining stability. The experimental critical depth of cut under optimal tuning is increased by 1.8-folds compared with the most ineffective tuning, and the machined surface roughness is reduced by more than 80 %. [ABSTRACT FROM AUTHOR]

The cutting efficiency and surface quality in the machining of compliant workpieces have been severely affected by machining vibration. As industrial workpieces are most likely to have multiple flexible modes due to its complex geometry and each mode can only be damped by a single vibration mode of a tuned mass damper (TMD), a two-degree-of-freedom (DOF) magnetic TMD (MTMD) is designed for damping the vibration of aluminum thin-frame workpiece with multiple modes. The natural frequencies of the MTMD are designed to be adjustable as evidenced by hammer tests and are tuned to coincide with the modes of the workpiece. Eddy current damping is incorporated for promoting damping by utilizing the relative motion between the mass block and magnets inside the MTMD. Frequency response functions demonstrate that the MTMD is effective in attenuating the amplitude of the first and second modes by 21.6 and 12.1 dB. Milling tests are finally carried out to validate its effectiveness. [ABSTRACT FROM AUTHOR]

Machining vibrations are harmful to workpiece surface quality and tool life, especially for thin-walled parts. A lightweight damping device is proposed by utilizing eddy current damping, and it can be easily attached onto the workpiece surface by glue. The cylindrical device is mainly composed of a magnet, an aluminum cylindrical conductor, and two springs. An induced repulsive force due to the machining vibration is generated and transmitted to the workpiece and then contributed to the vibration attenuation. Dynamic response evaluation on a cantilever beam by hammer tests demonstrates that the device is able to damp vibration mode and the effect of additive mass on the beam dynamics is investigated by roving the attaching point. Moreover, the device is applied to damp multiple modes and attenuate machining vibration of a thin-walled frame. Machining tests under different configurations of cutting parameters are carried out, and its effectiveness of wide band and adaptability to the varying machining processes are validated. [ABSTRACT FROM AUTHOR]

Stability lobes are widely used to avoid chatter which restricts the machining quality and productivity. A lot of work has been done to predict the stability lobes fast and accurately. However, most of them are based on the linear force model, and the chatter stability limit is formulated as independent on the feed rate, which is inconsistent with the machining practice. By referencing with the zero-order solution, this paper investigates the chatter stability prediction based on the exponential force model. Focusing on the cutters with a lead angle (i.e., inserted face mill, the ball-end mill, and bull-nose end mill) where chatter is likely to be brought up in Z direction, the stability model is extended to three-dimensional. Taylor equation is utilized to linearize the exponential expressions when computing the directional coefficients in order to solve the stability limit analytically as the linear force model. Simulation results show that the exponential force model agrees with the measurements as well as the linear force model in the cutting force prediction, and it is able to demonstrate the feed rate effect on the stability limit. The stability limit is found to be increased as the feed rate increases, which is evidenced by the time domain simulation. Cutting tests are performed in the end to verify the stability model. The proposed model could be reduced to either X/ Y dimensional or linear force model-based stability model by further simplifications. [ABSTRACT FROM AUTHOR]