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Title: Characterization of blanking induced magneto-mechanical cut edge defects in non-oriented electrical steel
Author: Al-Rubaye, Ammar Dawood Ghali
ISNI:       0000 0004 7964 5716
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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Electrical steels play a vital role in the generation and use of electricity as they are widely used in a range of electrical equipment for industrial and domestic appliances. The material is usually manufactured in the form of cold-rolled thin strips that are stacked together to form the laminated stacks used to form the stator and rotor parts of electric motors. As the individual layers are made mostly by blanking and piercing processes the quality of the final product directly affects the performance of the electrical machines. The blanking process results in local plastic deformation and texture modification in electrical steels which will affect the magnetic and mechanical performance of the electric motors and transformers. Therefore, the main aim of the project is to obtain a better understanding of the global and local magneto-mechanical properties of the sheet material at the cut edge and vicinity area to optimise design parameters used for the final products. An experimental investigation was designed and implemented to study the mechanism of blanking operation and local magneto-mechanical properties of thin strip electrical steels at the cut edge. The deformation at the cut edges was identified regarding main blanking parameters such as deformation rate, material thickness and sheet orientation at a specific clearance. The thickness of individual laminates plays a critical role in the magnetic performance of the manufactured power units. However, the thinner gauges introduce challenges to the manufacturing and processing of the material, especially in the high-speed cutting operations. Therefore the study was considered using two different thin gauge thickness with different grain orientations of electrical steel with nominated thickness 0.2 mm and compare results with those for 0.35 mm sheet thickness. A novel blanking experiment together with Digital Image Correlation was designed in order to identify local strain distribution in laminates of both the used thicknesses during the blanking process. That was done to achieve a better understanding of deformation induced microstructural damage in the vicinity of the cut edge. Also, a bespoke single sheet magnetic tester was designed and built to determine the effect of blanking induced cut edge damage on magnetic properties in the form of hysteresis losses and quantify magnetic deterioration in the produced laminations. The microstructure of cut edge deformation and the fracture surface was observed using both optical and scanning electron microscopes. Furthermore, Nano-indentations tests were implemented in the deformed area at the cut edges to characterize local deformation. The results showed that the cutting process parameters have a significant impact on the mechanical and magnetic properties and the cut edge quality. The reduced thickness also introduced a great challenge in preparing samples for all the tests that were done. Sheet thickness had a significant role on the hysteresis loss and extension of deformation and strain amount. The results also showed that the blanking speed also has an important influence on blanking results and thereby more affected in mechanical and magnetic properties. However, it was observed that the thickness of the laminations plays an important role due to the small number of grains in the thickness direction causing the individual grains to have a significantly high effect on the local properties of the produced parts. The change in the cutting location regarding the grains could cause different deformation state. This variations in the blanking deformation make it very difficult to determine the extension of deformation or give clear trend to the blanking behaviour effects upon the mechanical and magnetic properties. The achieved results can be used to enhance our knowledge and be practically implemented through the interconnection between the inputs of the cutting process and the outputs represented by the edge quality and affected properties. This investigation can also be incorporated in improving the manufacturing process in order to manage magnetic property deterioration, thereby exploiting the full potential of the magnetic materials; as a result, improving the machine's performance.
Supervisor: Ghadbeigi, Hassan ; Atallah, Kais Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available