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Title: An investigation into vibration assisted machining : application to surface grinding processes
Author: Tsiakoumis, Vaios I.
ISNI:       0000 0004 2718 5279
Awarding Body: Liverpool John Moores University
Current Institution: Liverpool John Moores University
Date of Award: 2011
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The purpose of this study was to apply vibrations to the workpiece during surface grinding in order to improve the performance of the process. In addition to this, further necessary parameters were examined and analysed. A first step was to design the vibrating rig and after a number of different designs the most suitable model was selected for the conduction of the preliminary studies. However, a novel-improved system was designed and manufactured in order to undertake the full volume of experimental work. A number of simulations including stress and modal analysis were carried out and all the static and dynamic characteristics of the rigs were identified. Moreover, the exact dynamic behaviour of the rigs - including their natural frequencies - was established though real experiments. Sweep - sine and impact tests were employed in order to identify these dynamic parameters and the results were compared to those of simulation with the intention to detect the amount of error between these techniques. The rigs were vibrated at their resonant frequencies in order to achieve high values of amplitude with low voltage input. The static and dynamic characteristics of the grinding machine tool were identified. Similar methods such as sweep-sine test were employed in order to find the natural frequency of the machine tool's spindle unit. Static and dynamic stiffness of the machine tool's spindle unit as well as its compliance were identified. The preliminary studies showed an improvement in surface quality of the workpiece as well as a small reduction in cutting forces. This reduction was getting bigger with the increase of depth of cut. The main body of experimental work followed and showed that for 25 urn depths of cut, the vibration-assisted method could decrease up to 22.5 % the tangential forces. Furthermore, the effect of vibration was getting more noticeable at higher wheelspeeds and workspeeds. At those speeds the reduction in workpiece surface roughness reached 12.6%. Moreover, it was found that the application of vibration increased the material removal rate, reduced the cutting forces, increased the G-ratio and produced lower values of wheel wear compared to conventional grinding. Finally, an innovative closed-loop vibration control system was used for the process which could control the amplitude and the frequency of vibration in the actual grinding cycle. This I A Abstract system managed to control the applied values of vibration amplitude at resonant or near resonant frequencies. It was found that for higher depths of cut the closed-loop vibration control reduced the normal forces by 19% compared to open-loop control and 21 % compared to conventional grinding. Furthermore, the closed-loop control system performed better in terms of workpiece surface quality when grinding mild steel compared to conventional grinding and open-loop vibration control.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: TJ Mechanical engineering and machinery