Design of high power ultrasonic manufacturing tools: a systematic approach

High power ultrasonics is currently under-utilised as a manufacturing technology. The potential of the technology in areas such as welding, fastening and cutting has not been fully realised because the beneficial mechanisms available in ultrasonic systems are not always understood and therefore are not fully utilised. The empirical approach to much of the design process often results in unreliable operating performance in customised tools. The aim of the research reported in this thesis, is to develop a structured approach to the design and optimisation of high power ultrasonic systems. Furthermore, this research demonstrates how the use of such an approach can benefit the understanding of the fundamental ultrasonic process, which in turn leads to more informed system design criteria. Initially a combined analytical and experimental approach is proposed and is demonstrated using an ultrasonic welding tool as the focus. Finite element analysis is used to predict the vibration behaviour of the welding tool and models are validated by experimental vibration analysis techniques; electronic speckle pattern interferometry and experimental modal analysis. It is determined that the problematic behaviour of the welding tool results from high modal density and modal coupling, both of which are common problems associated with high power ultrasonic tooling. Sensitivity analysis with degree of freedom ranking using finite element analysis, detunes the coupled flexural vibration from the operating frequency of the system, successfully isolating the required response. The approach is extended to ultrasonic fastening, whose performance is known to be influenced greatly by fastener geometry. The technique is applied to develop a series of fasteners, each having an alternative critical vibration parameter during insertion. Insertion tests demonstrate that a particular torsional mode family promotes improved insertion performance and resulting join quality. Finally the approach is extended to a novel ultrasonic cutting application. The potential of the cutting process is assessed using finite element analysis to verify the cutting mechanism as one of controlled crack propagation which is dependent on the vibration characteristics of the cutting blade. Using a combination of vibration analysis and fracture analysis, the ultrasonic cutting process is optimised for blade mode of vibration, leading to improved cutting performance and control. A significant advance is made in the understanding of the fundamental mechanisms of ultrasonic cutting and in cutting system design.