Friction behavior modeling and analysis in micro/meso scale metal forming process

Currently, a lot of know-how in conventional metal forming process cannot be directly applied to micro/meso forming processes due to so-called size effects. As a very important phenomenon in metal forming process, friction size effects are observed with an increasing degree of miniaturization. For microforming application, the input data of friction behaviors becomes critical to obtain accurate results for process simulation and traditional friction models are not reliable. In this paper, the evolution of friction behaviors from micro size to macro size is studied and a new uniform friction model is proposed based on the assumption of open-close lubricant pockets. A function of real contact area (RAC) image and normal press image is established by introducing size/scale factor image to describe the influence of size effects. Therefore, the development of the friction behavior from micro/meso scale to macro scale could be depicted by this new uniform friction model. It indicates that the friction curves of micro/meso size are between those of the dry friction (upper boundary) and conventional lubricant friction (lower boundary). Moreover, finite element (FE) simulations are performed, based on the new friction model, to analyze the friction size effects in ring compression process. It is found that the radial friction forces with the change of inner and outer diameters are totally different and their tendencies are in good accordance with the experimental results. The new uniform friction model enables more flexible modeling of friction behaviors.