Formation mechanism and control of flaring in forward tube spinning

Forward tube spinning (or flow forming) is usually employed to produce cylindrically tubular components to meet the increasing requirements for manufacturing high-performance and light-weight products at low cost and short lead-time. In forward tube spinning, flaring defect may easily occur at the opening end of tubes, which would deteriorate the quality of the spun tubular parts and reduce the material utilization. In addition, an additional operation is needed to trim away the flared end of the spun tabular parts. Efficient control of flaring formation is thus a non-trivial issue in forward tube spinning process and thus become one of the critical bottleneck issues to be addressed in this unique forming process. In this study, the formation mechanism of flaring was systematically studied via finite element (FE) simulation and an in-depth understanding was thus established, which forms basis for control of flaring forming in forward tube spinning. Based on the simulated material flow behaviour, it is found that flaring is formed by the material in non-spun zone flowing away from the mandrel. This material flow behaviour is caused by the pile up and the decreasing stiffness of the non-spun zone. In addition, the effects of process parameters on flaring were investigated to reduce flaring. The results show that the smaller feed rate and thickness reduction per pass can reduce the maximum flaring to a certain extent, but is very limited. To increase productivity and shorten forming lead-time, an efficient method to control flaring was proposed using a pressing ring in front of the roller based on the formation mechanism of flaring. FE simulation was further used to study the feasibility and demonstrates the validity of the method in terms of reducing and even eliminating the flaring with a short production lead-time. Finally, the forward tube spinning experiments were carried out to validate the formation mechanism of flaring and the method to avoid or eliminate the flaring formation in forward tube spinning.