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Sheet metal forming process and tools optimisation

Exploitable results

The punch and die stamping process is widely used for forming sheet metal in modern industry, ranging from automotive, or appliance manufacturing to aerospace industry. The high standards and fierce competition which are the norm in these industries force the suppliers of parts to continuously improve the quality of the parts while reducing production costs (typically through higher productivity) and lead times, in order to maintain their market share. At the same time they have to deal with ever increasing part complexity in terms of geometry and material. This requires the optimization of the part design and the development of the production means (presses, tools and feeding systems), along with the optimization of the manufacturing process. The Protool project addresses the incorporation of new technologies into sheet metal forming systems. The idea was to develop new devices for the control of some relevant parameters of the stamping process. The project research and work was oriented in four key areas: - A detailed specification of user requirements for the improvement of stamping process was obtained through a survey among press users. - Development of measurement and data acquisition system for the process parameters such as the drawing force, blank holding force and blankholder travel. - Development of a PC-based controller to automatically detect the defects in a zone. The controller uses features extraction techniques and neural network to detect these defects. A fuzzy logic controller then suggests new values of the process parameters for each zone. This ensures that the next part is of improved quality. - Design and development of new devices to be included in a standard press: - Pin-adjustment device allows a more precise regulation of the force supported by each of the blank holder pins. Therefore the blankholder force can be distributed according to the needs of the part. - Ram Parallelism device compensates unbalanced loads and keeps the parallelism of the ram during the press stroke. This prevents faults due to undesirable load distribution and increases tool life. - Deceleration of the Slide device reduces slide speed at the time of impact. This has several benefits. Impact force, tool wear, machine vibrations and noise are reduced. As a result drawability and cycle time are improved. The tests conducted showed that the system was able to predict splitting and wrinkling. However, the system was not able to detect very small splits. In the case of wrinkles, although the predictions were generally correct, it was difficult to obtain precise values of wrinkle heights especially when small wrinkles were involved. One other disadvantage of the system was the high number of electrical connections giving rise to several failure points. It was discovered that the blank size could be reduced in size and still give an acceptable part. This change has now been introduced into production and yielded savings of £0.12 per part or £69,000 per annum. Reduction of cycle times in a 10%, minimization of idle times up to a 30% and enhancement of part quality in a 20% can be achieved.