Research on Stability of Robotic Longitudinal-Torsional Ultrasonic Milling With Variable Cutting Force Coefficient

With their successful applications in handling, spraying, arc welding and other processing fields, industrial robots are gradually replacing traditional CNC machine tools to complete machining tasks due to the wider working envelope and the higher flexibility. Aiming at the chatter problem, a robotic longitudinal-torsional ultrasonic milling method with variable force coefficient is proposed in this paper. Taking Carbon Fiber Reinforced Plastics (CFRP) as the processing object, the influence of the fiber layup angle on the milling force are analyzed first; then the robot milling force parameters are determined and the robot milling kinematics model is established. Furthermore, the ultrasonic function angle is defined, and the cutting layer thickness model, the dynamic milling force model and the dynamic differential equation under ultrasonic vibration are established to analyze the stability of robotic longitudinal-torsional ultrasonic milling of CFRP. Finally, the full discrete method is used to obtain stability lobe diagrams.

Investigation of tool-workpiece contact rate and milling force in elliptical ultrasonic vibration assisted milling

Elliptical ultrasonic vibration assisted milling (EUVAM) is widely used as an efficient processing method for hard-to-machining materials such as titanium alloy, superalloy, and hard-brittle materials. To uncover the mechanism of the intermittent cutting characteristics in EUVAM, the tool-workpiece contact rate model is developed by combining with the kinematic relationship between the tool edge and the workpiece in the process. According to the analysis of the contact rate model, the phenomenon that the contact rate increases rapidly with the time-varying tooth position angle in one-dimensional ultrasonic vibration assisted milling can be improved in EUVAM. In addition, considering the variation of window function and undeformed cutting thickness, a force model is established. And the experiment of EUVAM is performed to verify the model of ultrasonic milling force, and the influence of process parameters (amplitude, cutting speed, feed rate and cutting depth) on ultrasonic milling force is also analyzed.

Comparison of Conventional and Hybrid Ultrasonic Milling in the Processing of Improved Steel

The combination of conventional milling and ultrasonic processing, more precisely ultrasonic vibrations, belongs to the newer types of hybrid processing. The realization of vibration sources as well as parameters that are variable in the realization of this process capture the attention of readers. In this paper, in addition to the application and possibility of installing different types of ultrasonically supported milling, the emphasis is given in the field of the surface quality. Namely, the application of ultrasonic vibrations in the processing of steel for improvement, which are characterized by higher hardness and toughness, and as such are a challenge for finding the most favorable processing. The quality of the processed surface as a function of the mean arithmetic roughness and the mean height of the unevenness measured in 10 points obtained in the classical conventional milling and the new hybrid process are presented.

Chatter Suppression and Stability Analysis of Rotary Ultrasonic Milling Titanium Alloy Thin-walled Workpiece

Titanium alloy and its thin-walled structures are widely used in the aerospace field. Aiming at the processing chatter and difficult-to-machine problem of titanium alloy thin-walled workpieces, rotary ultrasonic milling technology (RUM) is employed to restrict machining vibration in this paper. Firstly, the titanium alloy web with low stiffness is equivalent to a mass-spring-damping system with three degrees of freedom for describing its dynamic characteristics. Then, a novel stability analysis method is proposed for RUM thin-walled workpiece (RUM-tww) through defining an ultrasonic function angle. Furthermore, RUM-tww stability lobe diagrams (SLDs) are achieved based on the semi-discrete method (SDM). The simulation results show that the milling stability of titanium alloy webs is improved effectively under the effect of ultrasonic vibration energy. Compared with conventional milling thin-walled workpiece (CM-tww), the stability region of RUM-tww is increased by 80.32% within the spindle speed from 1000r/min to 5000r/min. Finally, milling experiments are carried out to verify the validity and rationality of SLDs via analyzing chatter marks, cutter marks and flatness on the machined surface. The experimental results are in good agreement with the theoretical prediction.