Slender single point boring tools are damped with tuned mass dampers (TMD) to increase their resistance against chatter. A TMD with fixed parameters may weaken its effectiveness when it is coupled with spindles or bars with different lengths. This paper presents a tunable and parametric, digital design of boring bars. The large length to diameter boring bar is modeled using Timoshenko beam elements and the effects that the TMD head has on the dynamics of the assembled boring bar-TMD system is modeled using a derived analytical expression. A universal TMD head that consists of a carbide mass, oil pocket, and two rubber O rings with experimentally calibrated stiffness and damping as a function of compression is designed. The boring bar has an internal compression shaft that can be pressed against the O ring to vary its stiffness using an integrated power screw. The complete TMD boring bar system is mathematically modeled to determine the Frequency Response Function (FRF) including the required TMD natural frequency and damping ratio to maximize the chatter-free depth of cut. The digital model is verified by comparing the simulated and experimentally measured FRF of the TMD bars. The bars are also tested in boring experiments successfully. 

Parametric design of boring bars with adaptive tuned mass dampers



When driving and working, the engine, working equipment and uneven road sur-face will cause severe vibrations to the wheeled excavator, 1which can affect efficiency and comfort. This paper discusses various patents and presents a new method of vibration reduction for excavators.



The purpose of the research is to design the counterweight of the excavator as tuned mass of tuned mass damper (TMD) to reduce body vibration.



The recent patents of TMD were investigated in this research. In this paper, the coun-terweight of the excavator is designed as a non-linear TMD system. The vibration models were established under driving and crushing conditions, respectively. The vibration response of the vehicle body was calculated and analyzed through MATLAB/Simulink under driving and crush-ing conditions. Finally, the damping characteristics of the TMD system were discussed.



The vibration of the car body can be reduced by TMD. 2The improvement rates in ver-tical acceleration were 8.05%, 11.85% and 11.15% for the three classes of road surfaces for the driving conditions. The improvement rates of 3vertical acceleration for the three powers of crushing conditions are 16.18%, 18.32% and 23.48%, respectively.



The vibration damping performance of the excavator was effectively improved by TMD in the main working conditions. The variation of body vertical acceleration with TMD parameters indicates the existence of optimal damping characteristics parameters for the TMD system at a fixed road surface and vehicle speed.


Research on Vibration Damping of Tuned Mass Damper for Wheeled Ex-cavator

Ultrasonic elliptical vibration cutting has a wide range of applications in the field of precision cutting of difficult-to-machine metal materials. However, due to its intermittent cutting characteristics and the weak rigidity of the horn, cutting chatter is prone to occur during its cutting process, which has an important impact on cutting surface quality and tool wear. In this paper, the rigid/viscoplastic rod model is used to simulate the horn in the ultrasonic elliptical vibration cutting device, and the influence factors of the amplitude-frequency response of the horn are analyzed. The influence of cutting speed and cutting depth on cutting chatter was studied by ultrasonic elliptical vibration cutting experiment of tungsten heavy alloy, and the influence of cutting chatter on cutting surface morphology and diamond tool wear was studied. The research shows that cutting speed will change the excitation frequency of the horn, and reasonable cutting speed can inhibit the occurrence of cutting chatter and avoid resonance of the horn. The cutting depth will affect the excitation amplitude and amplify the vibration amplitude when chatter or resonance occurs. The experimental results show that in ultrasonic elliptical vibration cutting of heavy tungsten alloy, chatter suppression can significantly improve the quality of the cutting surface and reduce the wear of diamond tools.

Cutting Chatter in Ultrasonic Elliptical Vibration Cutting and Its Influence on Surface Roughness and Tool Wear

Abstract In this study, a milling tool with variable mass and stiffness is developed for chatter reduction. The proposed milling tool is hollow with a solid core threaded inside it. As the core is screwed in or out of the tool body, the equal mass and stiffness of the tool are changed. Therefore, the tool's frequency response function (FRF) is changed to affect the stability lobe diagram (SLD) position. Moving the SLDs can stabilize an unstable cutting process. With respect to the FRFs obtained from modal test, the idea is proven using an experimental and analytical approach. The optimum core position for every spindle speed is also presented. The developed tool stability is then investigated in a realistic cutting condition. The cutting process sound analysis and surface finish visual inspection results reveal the performance of the proposed system in chatter reduction of a slender milling tool. 

https://www.researchsquare.com/article/rs-2443716/latest.pdf

Chatter Stability Improvement of a Slender Milling Tool via a Dynamics Variation Mechanism

Blast polishing offers an operator-friendly solution to many of the previously encountered polishing difficulties. However, the process lacks studies into the control of key parameters, one of which is viscoelasticity (particularly present in biological-based abrasive medias). Together with analytical-empirical models, a vibrational spring-dashpot model is presented, which characterizes the impact force, contact time, and damping ratio/coefficient of polishing media upon impact; as well as the effects of damping on contact parameters: stress, deformation, and area of contact. These are compared to experimentally gathered results for verification of the model. Impact force is shown to decrease dramatically with increasing hydration while increasing linearly with an increase in kinetic energy. Experimental findings reveal that 50% wet contact exhibits a 340% reduction in force magnitude compared to dry contact. Contact time results show an exponential increase with an increase in hydration. Research findings also show that higher hydration levels result in lower damping ratios and that higher kinetic energies (related to higher hydration levels) tend toward a decrease in damping ratio. Similarly, media damping coefficients decrease with both hydrational increases and kinetic energy increases. Results show that contact stress is reduced at higher hydration levels, which is mainly due to higher contact areas, and hence it was noticed that an increase in hydration prevents occurrence of chipping and brittle failure on the workpiece surface. Contact stress is shown to reduce by 325% from a 10% wet contact to a 50% wet contact. A high hydration of 30 to 50%, a high impinging velocity of value 31.4 m/s and above, a low stand-off distance of value 20 mm and below, a 45° polishing angle, and a polishing time of 20 to 40 min provide the most optimal parameters for efficient polishing to achieve a mirror finish on an additive manufactured Ti-6Al-4V component. The findings stipulated provide a base on which to further characterize the process and aim to promote further development and optimization of the blast polishing process. 

/pdf/spring-dashpot-vibrational-model-for-the-investigation-of-13q01q63.pdf

Spring-dashpot vibrational model for the investigation of viscoelasticity in gelatinous abrasive media and subsequent control of parameters for the blast polishing of Ti-6Al-4 V alloy

Yanlin Zhang

Papers

Improving optimal chatter control of slender cutting tool through more accurate tuned mass damper modeling