Thesis
The influence of tool excitation on material deformation
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2003
- Thesis identifier
- T10777
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- “Forming with ultrasonic excitation” refers to the plastic deformation of engineering materials while the forming tool is excited at ultrasonic frequency. The original research in this subject was initiated about five decades ago but this subject continues to remain popular. Reports on the use of ultrasonics for material deformation tend to focus on parametric conditions that are beneficial to the process; little is stated of the need to develop tool design methodologies and acceptable tool geometries, and the limitations to the application of excitation to material-deformation processes. The objective of this thesis is to assess the applicability of ultrasonic vibrations to industrial metal forming processes; this is an essential prerequisite to decision making by industrial process designers. To achieve this, it was necessary to perform experimental and analytical assessments of equipment design and manufacturing requirements. Two sets of equipment were designed and constructed. In both, the forming tool vibrated in the longitudinal mode; in the first, the tool vibrated in the direction perpendicular to the forming force while in the second vibrations were parallel to this force. The potential for applying ultrasonic excitation to industrial processes was evaluated with reference to currently known processes. Those selected were indentation, heading, wire-flattening and back-extrusion. Experiments were conducted to determine the influence of vibration on the reduction of forming forces. Finite element (FE) analysis was used to support tool design, particularly for the design of tool geometry to minimise vibration-induced stresses and for tuning the tools, the latter was essential for attaining resonance without the need for proving trials. This relied on the use of Finite Element techniques for determining the modal behaviour of tool-configurations. FE techniques were also used to identify the zones of high stress-concentration with a view to refining tool geometry. FE simulations were also used to simulate material flow in back extrusion under various excitation conditions. Two Finite Element models were developed for these; the first modelled the tools as rigid bodies while, in the second the punch of dimensions complying with the resonant conditions was modelled as an elastic body. Simulations showed that the decrease in forming force could be partially attributable to changes in the direction of friction forces. It was also revealed that the amplitude of vibration at the working surface of the punch was smaller than that measured at remote points on the tooling. A kinetic model of ultrasonically-assisted forging operations, based on the interaction between the rigid tool and the elasto-plastic work material was proposed. The model has been used successfully to describe experimental result, qualitatively. Experiments revealed that the forging force is inversely proportional to excitation amplitude and directly proportional to process velocity. The influence of excitation diminishes at a rapid rate with process velocity; thus, ultrasonic excitation is particularly suitable for application to relatively slow deformation-rate processes. The dominant consideration in such applications is the extent to which the process is sustained in a steady-state over the duration of the process; processes in which the work-material is subjected to continuously changing deformation fields would show, neither economic nor tool-performance related gains. Further, high-strength work materials and/or large components would require a level of excitation, which would demand the use of large generators. Conventional tool-steels would not be able to withstand the induced stresses and thermal changes. The power required for the excitation of tools and the poor efficiency of the ultrasonic systems will remain a constraint to the applicability of ultrasonics to material-deformation processes. The cost of power expended may outweigh the tool-force related advantages.
- Advisor / supervisor
- Balendra, Raj
- Resource Type
- DOI
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