Numerical and Experimental Investigation of Low Pressure Hydroforming of Aluminum Tubes

Tube hydroforming process is used widely in production of car structural parts. High strength to weight ratio is one of the properties of parts which is produced using this process. Low pressure tube hydroforming (LPTH) is one method recommended for solving problems of tube hydroforming such as requiring high pressure of fluid and sealing problems. LPTH method is similar to crushing a hollow solid body. Unlike high pressure tube hydroforming, upper die is not fixed in this process and it moves at the same time by applying internal pressure and squeezes the tube. Main defects in low pressure hydroforming are tube wall thinning and geometric errors at final form of the part. In this paper, LPTH of AA6063 aluminum tubes was carried out and circular cross section of tube was deformed to rectangular. Thickness distribution, formed corner radius and flatness of top surface of part was investigated under three different loading paths. Results show that lower corner radius can be achieved with higher internal pressure while thinning is increased. Maximum of flatness was obtained when moving of the upper die was carried out after reaching the maximum of internal pressure. Minimum of radius was formed at upper corner equal to 5.63mm and at lower corner equal to 5.62mm under internal pressure of 10MPa. Concavity of upper surface of part was decreased to 0.2mm by applying 10MPa internal pressure.