Study on forming process of equal wall thickness metal spiral pipe by single screw pump

To solve the problems of poor high temperature resistance of conventional screw pump stator and difficult machining of screw pump stator with equal wall thickness, this paper created a finite element model of equal wall thickness metal spiral pipe for single screw sump with 42CrMo based on tube hydroforming (THF). In this paper, the forming effects of different processes were evaluated by analysing the average pitch, wall thickness thinning rate and inner contour accuracy. Due to the particularity of design section and irregular plastic flow of material, the wall thickness of internal high pressure forming decreases seriously; on the other hand, because the diameter of the designed section is relatively large, the minimum ratio of D₂ to D_min is 1.12, which shows that wrinkles appear in external high pressure forming. As a result, based on the problems of internal and external high pressure forming, a coupling forming process was proposed. The results show that different parameters of coupling forming have little effect on the average pitch of metal spiral tube, and its maximum deviation is 1.08%; while thickness reduction ratio is proportional to initial diameter and thickness. Besides, when the liquid pressure is 350 MPa, the diameter is 60 mm and the wall thickness is 7.5 mm, the contour matching degree is higher; but the material accumulation and wrinkling will happen when the pipe diameter greater than 60 mm.