Ultrasonic Vibration assisted Similitude of Metal Forming Processes

Abstract

Introducing new complex metal forming processes in industry commonly involves a trial and error approach to ensure that the final product requirements are met. Detailed process modelling, analysis and small-scale feasibility trials could be carried out instead. A fundamental concern of scaled experiments, however, is whether the results obtained can be guaranteed to be representative of the associated industrial processes. Presently, this is not the case with classical approaches founded on dimensional analysis providing little direction for the design of scaled metal-forming experiments. The difficulty is that classical approaches often focus predominantly on constitutive equations (which indirectly represent micro-structural behaviour) and thus focus on aspects that invariably cannot be scaled. The research aims to introduce a novel technique for scaling metal forming processes, founded on the idea that scaling can be achieved by scaling space itself. With this approach, the physics in two spaces is described using transport equations and are deemed to possess finite similitude if found to be proportional. Finite similitude can be shown to always exist in continuum mechanics for isotropic scaling and it is demonstrated here how the concept can be used to design experiments. Validation of the approach is achieved by means of scaled experimental, numerical and analytical solutions of scaled upsetting tests (i.e. cylindrical and ring samples) and extrusion process . Three trial materials with different dimensions are tested and distinguished by the degree of strain softening, strain hardening and near perfect-plastic behaviour. Finite similitude results confirm that any discrepancies between the maximum loads are substantially reduced when the new scaling theory is applied. Best results are obtained when the same material is adopted for both full and small-scale experimentation. In addition, this work examines the idea of applying ultrasonic vibration to trial models in order to reduce the mismatch in the results between the trial and scaled models. The goal here is to improve trial-space models so that they are more representative of the behaviour of larger scaled processes.

Date of Award	31 Dec 2018
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Keith Davey (Supervisor) & Rooholamin Darvizeh (Supervisor)