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Title: Modelling of laser forming at macro and micro scales
Author: Griffiths, Jonathan
ISNI:       0000 0004 2745 2795
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2012
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Laser forming (LF) offers industry the promise of controlled shaping of metallic and nonmetallic components in prototyping, correction of design shape or distortion and precision adjustment applications. In order to fulfil this promise in a manufacturing environment the process must have a high degree of controllability, which can be achieved through a better understanding of its underlying mechanisms. The work presented in this thesis is primarily concerned with the use of modelling of the LF process at macro and micro scales as a means of process development. At the macro scale, finite element (FE), finite difference (FD) and analytical modelling were used to gain a better understanding of the complex interrelation between the various process parameters for specific geometries, reducing the need for extensive empirical investigations. A particular focus of the investigation was ascertaining which of these parameters influenced the fall off in bend angle per pass in multiple pass LF, along with the magnitude of their influence. The development of a full thermal-mechanical model of the LF process is detailed, as well as its application in a feasibility study into the forming of square section mild steel tubes for the automotive industry. Using this model, experimental observations were rationalized and novel scan strategies were developed which optimized the efficiency and accuracy of the process, something hitherto not possible using empirical methods alone. At the micro-scale, FE modelling was used to determine the mechanism of deformation in a novel laser micro-forming (LμF) technique, in conjunction with a full empirical study. The technique combined short pulse durations (20 ps) with high repetition rates (500 kHz) to generate localized heat build-up on the top surface of micro-scale stainless steel components, allowing for controlled and repeatable micro-adjustment. Modelling results suggest the mechanism works by confining the heating effect to the surface of the material, thereby selectively inducing thermal stresses and avoiding thermal damage of the component.
Supervisor: Watkins, Ken; Dearden, Geoff Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral