2007 Volume 57 Issue 8 Pages 351-356
Dieless drawing technique can thin down tubes by combining locally heating and tensile deformation of tubes without dies and tools. In this study, the dieless drawing process is applied to non-circular 1100 and 3003 aluminum alloy extruded tubes with double hollow section for heat exchangers. Fundamental deformation behavior of the tubes in the dieless drawing is investigated experimentally. Multi-pass dieless drawing is performed for the tubes to obtain larger reduction in area. The limiting reduction in area of A3003 tubes is 40% larger than 35% of A1100 in a singles pass drawing. Reduction in area 57.75% is obtained by two-pass dieless drawing for A3003 tubes. Geometrical similarity law in cross section is satisfied for the aluminum extruded tubes with double-hollow-section. In addition, surface characteristic and microstructure of the tubes after the dieless drawing is observed to investigate the effect of microscopic factors on the deformation behavior and the drawability in the dieless drawing. The results show that the surface roughness of the tubes increases with increasing reduction in area. Furthermore, the rate of increasing surface roughness depends on the grain size of initial tubes. It is found that the microstructure and the surface characteristic affect the deformation behavior and the drawability in the dieless drawing.
