Exploratory experiment and numerical simulation investigation on a novel flexible skew rolling of hollow shafts

Flexible skew rolling (FSR) with two rollers is a new technology for forming large shaft parts, which is especially suitable for manufacturing the shafts with small-batch and multi-variety. Hollow shaft parts can achieve lightweight forming of parts under the premise of meeting strength. In this paper, an exploratory study of the hollow shaft in FSR of 40Cr steel has been conducted for estimating the technological potential of FSR. The effects of the hot rolling main parameters (roll swing angle, compression ratio, initial wall thickness, and mandrel diameter) on forming quality have been investigated by means of finite element (FE) analysis and experiments. The data gained from the experimental tests conducted on the FSR mill was used to validate the model and the research results. The forming characteristics and forming precision of this process were investigated, and the microstructure of outer and inner surfaces of the hollow shaft was observed. The dimensional accuracy of the FSR hollow shaft decreases with the increase of the compression ratio, the relative mandrel diameter, the swing angle, and increases with the increase of the relative wall thickness. The microstructure near outer surface of the FSR hollow shaft is the first to be refined, the grain size of the inner wall is larger than the grain size of the outer wall and the mechanical properties of the rolled piece are significantly enhanced.