The analysis of ultrasonic machining systems using wholefield interferometric techniques

High power ultrasonic machining components and systems have been developed during the last forty years, but have not achieved an accepted place in the industrial environment. This has been a factor of competing traditional machining techniques which offer consistent performance, as opposed to ultrasonic equipment which has limited theoretical background and poor reliability. Niche applications involving polymer welding have been secured, but the ultrasonic equipment in these cases is very simple in form, generally being composed of three components; a transducer, a velocity transformer and the welding tool. Interest in ultrasonic machining is being expressed by certain manufacturing companies, which demand more complex systems, with as many as twenty ultrasonic components. However, design and operation of these systems using traditional methods have not been systematic, and there has been a requirement for improved analytical approaches and design rigour and design validation. The research described within this thesis is concerned with the novel analysis, understanding and design of high power ultrasonic cutting systems for the food industry. The operational behaviour of individual resonant components, sub-assemblies and complete cutting systems have been examined, in order to determine how design boundary conditions may be altered, such that the performance of the cutting system is improved or optimised. Analysis of experimental data produced by single point, wholefield optical techniques, and software based models (produced via Finite Element Analysis), have allowed the introduction of new designs of cutting system which achieve better cut quality parameters than original equipment. A major component of the research has been the evolution of new experimental techniques employed for the ultrasonic analysis. Recent work in this area had shown the applicability of Electronic Speckle Pattern Interferometry (ESPI), but was found to have limited range and sensitivity in industrial operating conditions. Questions of detail concerning the linear or non-linear behaviour of the ultrasonic cutting systems at high powers whilst cutting material, in comparison to low power laboratory investigations, generated the fundamental requirement for analysis in the industrial environment. Therefore it was necessary to evolve the wholefield techniques to answer these questions. Novel experimental techniques have been developed and applied in the form of Electronic Speckle Pattern Shearing Interferometry (ESPSI), for the analysis of low and high amplitude dynamic displacements. The versatility and simplicity of this technique has allowed the examination of ultrasonic phenomena from low power to high power excitation, thus providing a gauge of the linearity of the cutting systems behaviour. The novel application of speckle shearing interferometry has been extended to the analysis of ultrasonic and sonic components in harsh, arduous industrial conditions, obtaining interferometric data of unprecedented quality. This has centred around the ultrasonic cutting systems during cutting trials of various confectionary products, and a minor examination of f1extensional sonar transducers whilst operating in large scale underwater testing facilities. The success of this work has been made possible by the use of pulsed lasers within the interferometers, and the integration of the interferometric systems with laser vibrometer synchronisation. A final aspect of the research has been to consider the interaction of the ultrasonic cutting systems with the materials being machined. This has required further development of speckle shearing interferometry in order to investigate and utilise its ability to measure out-of-plane and in-plane strain values.