Desenvolvimento de neutralizadores dinâmicos viscoelásticos para redução de vibrações em torneamento simultâneo

Abstract

Regenerative vibrations have been a chronic problem studied due to the complexity of factors that arise during machining. When it comes specifically to simultaneous external turning, there are few studies that address the incidence of regenerative vibrations in machines with this construction characteristic. Machines with greater material removal capacity have been increasingly present in the metallurgical industries. Decreased productivity, reduced tool life and surface quality problems are common challenges in this type of machine in a stage of dynamic instability, due to low dynamic stiffness in situations such as shaft machining. The objectives of the present work correspond to a greater understanding of the main factors associated with the dynamics of the simultaneous external turning process of electric motor shafts in the roughing operation, to propose a solution to reduce vibration arising from dynamic instability known as chatter by means of neutralizers viscoelastic dynamics, build such devices and carry out experiments to verify their effectiveness. To this end, the influence of the machine-support-tool assembly on the cutting parameters was analyzed, taking into account the dynamic stability of the process. The natural frequencies of tools and supports of both towers were determined through impact tests with simultaneous measurement of the vibration response. Additionally, a numerical analysis was carried out in finite elements considering the boundary conditions to obtain the numerical natural frequencies with the aim of understanding the dynamic behavior of the electric motor shaft during machining. Subsequently, the design, optimization and manufacture of viscoelastic dynamic neutralizers to be applied to tool holders for turning electric motor shafts were carried out. The process stability assessment was carried out by monitoring vibration acceleration signals. As a result, an average vibration of 7.74 g was obtained in the upper tower with the neutralizer, compared to 18.8 g without the neutralizer, corresponding to an average reduction of 58.7%. In the upper tower, the average vibration with the neutralizer was 7.28g, while without the neutralizer it was 18.47g, corresponding to a reduction of around 61% in vibration levels. The average roughness of the surfaces machined with the neutralizer was 5.68 µm, while without the neutralizer it was 10.13 µm, representing a reduction of around 44%. With this study, it was possible to obtain a greater understanding of the behavior of regenerative vibrations in simultaneous external turning, as well as verify the effectiveness of the neutralizer for minimizing vibrations in machines with this dynamic characteristic through the use of passive viscoelastic neutralizers.