Analytical model of corner filling with granular media to investigate the friction effect between tube and media

In a tube forming process, granular matter is used as pressure transmission medium instead of liquid to expand a circular tube into one with square section. In this process, the friction at media/tube interface has a significant effect on the final result. In this paper, an analytical model was developed to determine the influence of the friction on the deformation developing process and final thickness distribution along the tube section. Experimental researches were also implemented to evaluate the analytical model in the end. In this model, four friction situations were applied to the numerical analysis process according to the active or negative function of friction on the flow of metal. The analysis result showed that different friction situations could lead to different deformation processes and thickness distributions. The examination on experiments of AA6061 tube indicated that the experimental data of thickness was extremely close to the analysis result with the friction situation in which the metal flow toward the corner of square section die was impeded by the friction force. However, the analytical prediction of thinning trend of thickness had a deviation compared with the experimental data in the corner region. In addition, the breaking and caking of granules in the tube forming process make the friction situation between the tube and media very complex. Therefore, a further research needs to be conducted from the direction of granular matter mechanics and friction mechanism in order to acquire a more explicit result.