|Development of a zero compliance tool holder for precision turning machine
Drilling and boring
Hong Kong Polytechnic -- Dissertations
|xii, 164 leaves : ill. ; 30 cm
|Boring is one of the most common types in machining processes. Unfortunately, errors, chatters and vibrations in boring operation are inevitably caused by micro-displacements of boring bar. These micro-displacements which are due to the low rigidity of boring bar, low rigidity of tool holder or vibrations of machine from external source, etc., adversely affect the surface finish and accuracy of the machined bore. In order to reduce these micro-displacements, there are many methods to maintain the depth of cut within a critical value. In this project, attempts were made to design a boring bar fitted with an active error compensation device in order to maintain the desired 'position-in-space' of the cutting edge during machining. The active error compensation device was based on a PC-controlled piezo-electric actuator which, after the force deflection signals were received from the strain gauges cemented on the boring bar, acts on the boring bar in an opposite direction to offset the movements caused by the cutting force. Control algorithms were written to simultaneously monitor the displacements and activate the compensatory motions. Control parameters were tested to give fast and stable compensation motions. Experiments were conducted to evaluate the effectiveness of this boring set-up. Through the analysis of the experimental results, the average improvement in compensation of diameter variation was found to be 64% (maximum straightness error <=5um) over a 21-mm deep tapered bore with an increasing depth of cut the maximum of 0.14mm. The boring set-up was proved to be successful in compensating micro-displacements and is limited by the maximum force available from the piezo-electric actuator.
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