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Extruded aluminum alloys, which are highly versatile, have relatively modest prototyping cost, good strength and corrosion resistance. Because there is no weld seam, the circumferential mechanical properties may be uniform and advantageous for hydroforming. However, surface defects such as die lines and pick-up can be generated during the extrusion especially due to imperfections on the die surface. In this study, the extent of the crack propagation caused by die lines is evaluated according to the deformed shape of the tube in hydroforming process. And when forming a extruded aluminum tube, the deformed surface of the tube frequently becomes rougher with increasing plastic strain. This is well known as orange peel phenomenon and it has a significantly effect not only on the surface quality of a final product but also on the forming limit. To evaluate the effects of the orange peel on the hydroformability, the inter-stage polishing has been performed. Through the several tests including hydroforming test, the effect of surface defects on the hydroformabilities are well defined.

Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.

In the tube hydroforming process, a tube is placed into the die cavity and the ends of the tube are sealed by fixing the axial cylinder piston into the ends. Then the tube is pressurized with a hydraulic fluid and simultaneously the axial cylinders move to feed the material into the expansion zone. In this study, the empirical and the quantitative relationship between process parameters and hydroformabillity are analyzed by fuzzy rules. Fuzzy expert system is an advanced expert system which uses fuzzy rule and approximate reasoning. Many process parameters are converted to the quantitative relationship by use of approximate reasoning of fuzzy expert system.