In process design of bar rolling with multi-passes, accurate prediction of deformed geometry of the rolled workpiece is crucial. Unlike the 2-roll system for which many models are already available in predicting deformed geometry, many studies have not been carried out for the 3-roll system. Recently, finite element (FE) analyses have been applied for accurate prediction of the deformed geometry in the 3-roll rolling process. However, it requires large computation time. Thus, development of an analytical model for predicting accurate rolled geometry with less computation time will be beneficial for practical purpose.
In the present study, a model for prediction of deformed shape was developed first. And, based on this model, a model for prediction of strain of the workpiece was developed. For this purpose, the model for prediction of deformed shape in the 3-roll system with multi-passes was developed by deriving spread and geometrical configuration formula from FE analysis results. Among the proposed formulae for prediction of deformed geometry, the equivalent rectangular transformation method applied to the spread formulae was used to develop a model for prediction of strain. It was assumed that deformation of the workpiece was occurred in the directions of principal coordinates. And then, calibration coefficient was introduced to consider the characteristics of each pass.
For FE simulations an in-house FE program CAMProll, developed based on the rigid-thermoviscoplastic approach was used. In FE simulations, process parameters such as the initial workpiece geometry and amounts of roll draft and rolling speed were varied. By comparing spread ratios of FE simulation results five representative geometry changes (round ― semi-hexagonal, semi-hexagonal ― hexagonal, hexagonal ― hexagonal, hexagonal― oval, and oval ― round) were identified. For each representative geometry change those two formula were determined in the present investigation.
