Ring rolling is a versatile incremental bulk forming process. Due to the incremental character of the process, it consists of a large number of deformation and dwell steps. Finite element (FE) simulations of bulk forming processes are capable of predicting loads, stresses and material flow. In recent years, the finite element analysis of ring rolling processes has become feasible both in terms of calculation time as well as regarding the closed loop control of the kinematic degrees of freedom [1]. Accordingly, the focus of interest now includes the prediction of the microstructure evolution. The accuracy of such numerical simulations strongly depends on the models characterizing the material behavior and boundary conditions. In this paper, a finite element based simulation study was conducted, in order to evaluate the impact of boundary conditions such as transfer time, radiation, heat transfer and friction on the target values of the ring rolling process. The results of the simulation study were compared to ring rolling experiments on an industrial size ring rolling device. A good accordance regarding the evolution of the outer diameter and radial force was observed. Strong contingencies of transfer time on the forces throughout the process were detected and considered in the simulation study. In a post processing step, the evolution of the microstructure considering the dynamic and static recrystallization as well as the grain growth was calculated using the FE results. The calculated grain sizes show good accordance with the experimentally observed microstructure of the ring before and after the rolling. Furthermore, the impact of process parameters on the evolution of the grain size was investigated.

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Abstract. Roll bonding is a well-known process to produce composite sheet metals. Transferring this principle to ring rolling would allow to produce seamless radial composite rings, which combine the advantages of different material properties. This process is studied, both experimentally and using FEM-simulation. For the FEM an explicit model is applied including the kinematic control algorithms of the radial-axial ring rolling machine. In the used model the occurrence of unexpected asymmetrical joints can be reproduced, which are observed during the rolling experiments. By varying the influencing parameters on the asymmetric joint in the FEM a plausible reason was found.

Ring Rolling is a versatile metal-forming process to manufacture seamless rings of various cross-sectional geometries. Rings with a “dish shape” are used in different areas such as offshore, aeronautics or the energy sector. Current ways to produce dish shaped rings have the disadvantages of limited or inflexible geometries and either high material waste, additional costs for special tools or long process time. Instead, when manufacturing dish shaped rings on conventional radial-axial ring rolling mills, ring producers will be able to expand the range of their products easily. In a prior investigation, the general feasibility of an alternative to the current manufacturing processes was shown in experiments and in finite element method (FEM) simulations, avoiding major additional machining and material costs. Resulting from an analysis of the geometrical requirements and material flow mechanisms for dishing and ring climbing, a rolling strategy was derived, applying a large height reduction of the ring. A major problem of this rolling strategy is that whenever the contact between the ring and the main roll is lost in the process, the ring starts to oscillate around the mandrel and neither dishing nor ring climbing can be observed. In order to ensure a permanent contact between ring and main roll and in order to stabilize the ring in its inclined position in the rolling mill, additional stabilizing measures of the process will be developed and investigated. With the developed FE-model, a stabilizing measure by the use of pressure rolls and automatic guide roll movement for ring climbing was tested and appears promising for the application in a real experimental environment.