An Experimental Study on Superplastic Hemispherical Forming of Aluminum Lithium 2195 Alloy

Abstract

Abstract-Superplastic forming (SPF) technology is currently being used to produce a number of components for aerospace vehicles. The most important advantages of using SPF technology is the process simplicity and economy in tooling. The widely used superplastic materials are titanium alloys and aluminum alloys, which are the workhorse alloys of the aerospace industry. The low density and good mechanical properties of Aluminum-Lithium 2195 alloy make them successfully used in cryogenic tank of space vehicles. In this study, a hemispherical dome is produced with this alloy by superplastic forming. By controlling hydraulic gas pressure, it was possible to maintain the superplastic condition during the forming process. The forming temperature was 460℃ to form a complete hemispherical dome with diameter of 350 mm for 3,420 sec. The programmed gas pressure was applied and the maximum pressure was limited to 5 MPa to protect the forming tool. The distribution of thickness within the hemisphere was investigated and confirmed the analysis result. The process development for the production of a hemisphere with 2195 aluminum alloy has been achieved. The hemispherical dome is in good conformity with drawing dimensional and tolerance specifications.Index Terms-Aluminum lithium alloy, gas pressure forming, hemisphere, superplastic forming.

Manufacturing Titanium and Al-Li Alloy Cryogenic Tanks

“…Finite element analysis has been carried out using MSC MARC® with MANTAT®, which has a module for hot forming analysis [9]. The gas pressure profile obtained from the analysis was employed in the superplastic forming process as shown in Figure 3(a) [8]. Initially, low gas pressure of about 1 MPa was applied until the 2,900 sec, and then the pressure was increased to 5 Mpa.…”

“…This is because it is the free bulging without any friction in the first stage of forming. When circumferential area begins to contact the tool, the material movement is relatively limited and the material in contact with the tool deform plastically [8].…”