High Performance Manufacturing of Advanced Thin Plates ─ Forming of Titanium and Stainless Steel Materials
Sammanfattning: The manufacturing industry represents a highly important sector of the Swedish economy. The increasing demands placed on the quality and performance of products that are manufactured places increasing demands on the manufacturing processes involved. The aim of the dissertation has been to study how a particular forming process used in the production of thin sheet-metal parts of advanced character can best be analyzed, optimized, controlled and monitored, and how the processing results can best be predicted and be expressed in economic terms. The sheet-metal parts in question are composed of either stainless steel or pure titanium, formed into complex and intensive patterns, high demands being placed upon their precision of manufacture. An overarching goal was to be able to continuously and adaptively optimize the manufacturing process in terms of quality, process stability, production speed and sustainable resource utilization. To facilitate achievement of this ultimate goal, a laboratory platform was developed providing the testing methodology needed for process studies of different aspects of forming of critical importance. Use of this platform made it possible to focus on specific problems encountered industrially in the forming of the geometric patterns called for. Under the laboratory conditions created, knowledge and experience concerning relationships between important processing factors and the processing results obtained could be studied. In many cases, the results of the studies carried out could be combined with those obtained through use of more traditional testing methods, either to simplify or to verify results obtained. The laboratory platform and the studies carried out enabled the formability of the different materials involved to be rank-ordered and each of them to be assigned a formability index. The effects of different factors that affect the friction that occurred were also studied with the aim of being determining what forming conditions were optimal. It was found to be possible, with use of the methodology developed and of the increased knowledge and understanding it provided of the sheet-metal surfaces involved, of the lubrication employed, and of the formability of the sheet-metal material in question, to improve the performance of the process that was studied. Tool wear was assessed in a laboratory platform by means of appropriate measurement techniques. In order to keep the tool cost in an industrial setting as low as possible per part produced, it is important that the tool material and the coating of it employed be selected with adequate attention to both cost and performance. Various tool solutions for low-, medium- and high-volume production were studied. Taking account of the relationship between the costs associated with a reference tool and the wear index that applies can help to optimize the relationship between price and performance. The use of FE-analysis was seen as an important step in efforts for improvement aimed at creating a high-performance production system. Virtual aids can be useful in this context, contributing to time effectiveness in optimization of both the product in question and the manufacturing process involved. The laboratory platform made it possible to verify the results of the FE-analyses performed, enabling improvements both of the product and of the forming process employed to be implemented. A new control system that was developed based on use of AE (Acoustic Emission), able during the forming process to ensure virtually in real time the quality of the products being manufactured, was studied, as were various methods for describing the production system as a whole from the standpoint of cost. A method for analyzing production performance in terms of downtimes, in particular their character, effects and the costs per unit produced, was presented. A cost model likewise developed enabled both the downtimes and their causes to be expressed in economic terms. The dynamic downtime behavior of a production system was also studied from a cost perspective. There was found to be considerable potential for improvement of the production process as a whole. It was also shown that selection of the appropriate level of automation is important for achieving a production system having both a high level of performance and long-term sustainability. In connection with this, an economic model was presented for determining the optimal automation level under a given set of conditions.
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