Development of a novel Fast light Alloy Stamping Technology (FAST) for manufacturing lightweight panel components using high strength aluminium alloys: Experimental studies

Abstract

This study focuses on the development of a novel sheet metal forming process, Fast light Alloy Stamping Technology (FAST), for manufacturing aluminium alloy sheet components through experimental studies. This novel process is distinguished by an ultra-fast heating rate during the heating stage and precision processing parameters control in order to minimize changes to the material microstructure which are detrimental to the post-form strength. As the initial temper and the pre-existing hardening phases of the material could be maintained throughout the heating and stamping stages, the paint bake cycles utilized by different automakers are sufficient for the material to attain its full strength, replacing the need of post-form artificial ageing. The forming temperature selection for the process therefore depends only on the level of formability required, further reducing the energy consumption and cycle time of the process. The proof-of-concept and the mechanism of FAST were studied through a series of the heat treatment tests using the aluminium alloy AA6082 in naturally aged T4 temper and artificially aged T6 temper. Traditional warm and hot stamping processes in which the specimens were heated at a slow heating rate were conducted at the identical forming temperature range as a comparison. It has been proved that the post-form strength of the specimen after the FAST process and paint bake cycles could achieve 112 Hv, more than 95% of the as-delivered T6 condition. In addition, the thermal-mechanical properties of the material under the ultra-fast heating conditions were investigated using the Gleeble 3800 thermal-mechanical simulator. The true fracture strain was as high as 0.85 at 450℃ for both materials and over 0.50 and 0.32 at 300℃ for the AA6082-T4 and T6 respectively. A dedicated pilot production line Uni-Form for the FAST process was designed, fabricated and used for conducting the forming tests. As a highly integrated test facility, Uni-Form is able to conduct the forming trials in an automated manner. In this work, a U-shape forming tool was utilized to enable the study of mechanical properties of the FAST formed components. The influence of forming temperature and forming speed on the springback was investigated. The post-form strength and the surface roughness of the formed components were examined. Furthermore, a benchmark study on the manufacturing cycle time was carried out. It was determined that FAST is able to reduce the manufacturing cycle time to less than 8.5 seconds to produce the component with the desired mechanical properties from the metal blank, which is only 4.3% of the warm forming process time currently used in the automotive industry. The experimental forming trials confirmed that the FAST process can be scaled up to a forming process in industry for manufacturing the lightweight stampings with the required strength and geometrical accuracy. With the advantages of the FAST process presented in this study, further investigation of this novel forming technology could be conducted in order to expand its application to other types of heat treatable aluminium alloys and the tailor welded blanks of different series aluminium alloys.