Numerical and experimental study of the taper-rolling process for producing a helical blade from a metal strip

In-depth understanding and quantification of the forming characteristics of the taper-rolling process are crucial for process design and parameters determination in order for producing a desired precise helical blade from a metal strip. To this end, a quantitative study is carried out on this process through finite element (FE) simulation and experiment. For the FE simulation, a 3D model is established by handling problems observed in experiments about strip bite, sideways movement, and interference with the rolls and then is calibrated in numerically dynamic effect and validated by experiment. The results show that the plastic hoop and thickness strain components exhibit linearly increasing distributions from the inner to outer rim of the blade, which is a result of the hyperbolic-curve distributed roll gap. Thus, small radial strain that coordinates the deformation in hoop and thickness directions varies from positive to negative across the blade width. As a result, less spread and smaller bending radius have been achieved on the blade than that on the in-plane bent ring under the same conditions. Screw diameter increases with increasing initial position of the strip (H), initial roll gap (S 1) and rolls offset (S 2), and screw pitch increases with increasing S 1 and S 2 but is uncertain with increasing H, the rules of which are quantified. The reason is attributed to the change of roll gap and thus the change of strain distribution with varying H, S 1, and S 2. Then, three forming defects (turning-I, turning-II, and wrinkling) are defined and correspondingly the stable condition is determined as 0.9 <= a z/b 0 <= 1.6 and t 1/t 0 ≥ 0.3. Thus, a formable window of H, S 1, and S 2 for sound formation is determined, within which the forming limit defined as the achievable minimum relative bending radius R in/b 0 is quantified by simulation and validated by experiment.