Optimization of Hot Metal Gas Forming by Taguchi Method for Production Step-tubes from AA6063

The applications of aluminum alloys are limited due to the low formability at ambient temperature. To overcome such limitations, hot metal gas forming is developed as a new process. In this paper, the hot metal gas forming for production of cylindrical step tubes from 6063 aluminum alloy is studied experimentally. For this purpose, Taguchi method of experimental design was used to optimize the process parameters such as axial feed, forming temperature and gas pressure. Seamless tubes with an outer diameter of 25 mm and 1.3 mm thickness were used. After deformation, the specimens were cut and the die filling and thickness distribution were measured. At a constant temperature, with increasing pressure at low axial feed, the specimens burst, while with increasing axial feed at low pressure the specimens were wrinkled. The results indicate that if the axial feed increases in proportion to the pressure, the risk of bursting and wrinkling decreases. The analysis of variance indicated that from the three parameters studied, the effect of axial feeding on filling percentage was of prime importance. The main effects plots for signal-to-noise ratio showed that the optimum arrangement of parameters were at 580°C, 0.6 MPa and an axial feed of 14 mm. In this condition, the die filling of 92% and maximum thinning less than 10% were achieved.