Gas blowforming of grooves on superplastic aluminum alloy sheet to increase the surface area

摘要

The purpose of this study is to investigate the application of superplasticity to blowforming. To form an efficient heat exchanger plate, blowforming is carried out to increase the surface area of the plate as much a~ possible. A plate made of7475 aluminum alloy (t = 1.5 mm) is placed over the hot die which results in the formation of concentric grooves on the plate. The formability of grooves was examined by using two types die shapes with a constant gas pressure of 0. 5MPa. One of theshapes has four grooves (depth : H = 8 mm) and the other has three grooves (H = 10 mm), both of which have a surface area 2.5 times larger than the original area. In the latter case, the ratio of the number of specimens blowformed without fractures tothe total number of specimens blowformed was small (~30%). The distributions of the thickness strains were not symmetrical with respect to the center of grooves, and the value of the strain at the groove wall on the side of the die center was greater than that on the outer side of the die. Thus, it is necessary to consider the fluidity of the material which flows into the grooves. On the other hand, the radius of the die corner, R, may have little influence on the blowformability.