Zhengkun Feng

Modeling and simulation of asymmetrical three-roll bending process

Abstract Asymmetrical three-roll bending is one of the three-roll bending processes widely used in metal forming due to its simple configuration. Modeling and simulation of the process based on finite element analyses has great interests to industrial practices. This paper deals with the prediction of the position of the lateral roll during cylindrical roll bending. In the numerical model, the rolls are assumed to be rigid bodies and the plate is assumed to be made of elasto-plastic material, with a bilinear material model corresponding to the results from tensile tests. Shell elements are applied to the plate and automatic node-to-surface contacts are selected for the interfaces between the plate and the rolls. The nonlinear equations are resolved by fully integrated Belytschko–Tsay shell formulation under the well-known ANSYS/LS-DYNA environment with explicit time integration. The positions of the lateral roll predicted by the numerical simulations agree well with experiments.

Numerical study of non-kinematical conical bending with cylindrical rolls

Abstract Although desired cones can be manufactured by kinematical conical roll bending, less manufacturing cost is still largely required. This paper presents the modelling and simulation of non-kinematical conical roll bending process with cylindrical rolls. Such process is achieved by using attachments to reduce the velocity on the area close to the top edge of the plate. In contrast with a kinematical conical roll bending machine, the driving outer rolls of a non-kinematical conical roll bending machine are allowed to slide on the plate close to the top edge. The modelling is based on finite element method under ANSYS/LS-DYNA environment. The bent cones obtained from numerical simulations compare well with the desired cones. Numerical simulation investigations show that the adaptive capacity of the model is available within a range of the top–bottom radius ratio of the desired cones between 0.44 and 0.8.

Three-stage process for improving roll bending quality

Abstract Continuous pyramidal three-roll bending process has the simple configuration. However, two planar zones exist near the leading and trailing edges after a conical roll bending. This paper proposes a three-stage process to improve the geometrical quality of a bent cone for providing an alternative process for the manufacture of the crowns of Francis turbines for hydro plants or the towers of wind power plants. The process was simulated under the commercial software LS-DYNA with an explicit scheme and ANSYS with an implicit scheme. The geometrical quality of the bent cone was improved after the final stage of the process.

Investigation of non-kinematic conical roll bending process with conical rolls

Abstract Although high quality cones can be produced with kinematic conical roll bending due to the non-slide condition between the conical rolls and the plate, the process flexibility is limited because the conical rolls cannot be reused to produce cones of different cone angles. In this paper, a non-kinematic three-roll bending process is proposed to reduce manufacture costs by reusing existing conical rolls. In this process, an attachment is added to the top edge of the plate to obtain required circumferential velocity as the top/bottom radius ratio of the desired cone is smaller than the rolls. The top sides of the conical rolls slide on the plate to reduce the local velocity near the top edge and an appropriate velocity near the top edge of the plate can be obtained by adjusting the friction coefficients between the rolls and the plate. This flexible process can provide performance similar to the kinematic conical roll bending process. The process modeling is based on the finite element method under ANSYS/LS-DYNA environment. A relation between the gap size of the bent cone and the friction at the plate/attachment contact interface has been investigated by using numerical simulations. The simulation results give a well bent cone compared with an ideal cone.

Heat-Assisted Roll-Bending Process Dynamic Simulation

Abstract The forming forces during roll-bending process can be reduced by heating the workpieces. Heat-assisted roll-bending is a promising alternative to the costly and time-consuming casting process that is usually selected for manufacturing large and thick axisymmetric parts made of high-strength steel. In this paper, a computer-aided simulation program has been built in the Ansys/LS-Dyna environment to study the relationships between temperature, applied forces and plate thickness. The finite element modelling of the formed geometry is sequential with first a thermal simulation followed by a structural one. The numerical results are then compared to analytical ones. The analyses of the process with numerical simulations yield a better understanding of the mechanism of the process and provide an opportunity for the design of an efficient heating system to control the heat energy to be input in the workpiece during the roll-bending process.

Dynamic FE analysis for reducing the flat areas of formed shapes obtained by roll bending process

Roll bending is a continuous forming process where plates, sheets, beams, pipes, and even rolled shapes and extrusions are bent to a desired curvature using forming rolls. Over the years, with the advantages such as reducing setting up time, the cost in tooling investment and equipment, the roll bending process was fundamental for manufacturing cylindrical shapes. However, the process always leaves a flat area along the leading and trailing edges of the workpiece. Therefore, accuracy could be a challenge when the part to be produced is large and made of high strength steel. There are several methods to minimize the flat area. Among them, for the asymmetrical configuration, moving slightly the bottom roll along the rolling direction may have the highest effect. On the other hand local adjustment of the bottom roll location is also important for providing the pressure needed for gripping and carrying the workpiece through the rolls. Then by optimizing the vertical displacement of the bottom roll one can minimize the span of flat areas.The main objective of this research is to assess 3D dynamic Finite Element (FE) model with Ansys/LS-Dyna for the simulation and analysis of the deformation of the workpiece during the manufacturing of cylindrical parts. Various dynamic simulations based on 3D element are performed to provide better understanding of the whole deformation history and to establish the relationship between the location of the bottom roll and the end shapes of the formed cylinders. The results from FE simulations are then compared with corresponding experimental results from an industrial roll bending machine in order to improve the quality of the final shape.Copyright

Analytical Modeling and FE Simulation for Analyzing Applied Forces During Roll Bending Process

High strength steel is widely used in the manufacturing of parts dealing with heavy cyclic loads and corrosive environments. However, processing this type of steel is not easy, and it becomes a hard-to-solve problem when the part to produce is large, thick and quasi-unique. One example of a thick high strength steel axisymmetric part is the conical shape of the crown of a Francis turbine runner. Some Francis turbine runners installed in the dam basement of a hydraulic power plant are 10 meters in diameter with more than 5 meters in height, while plate thickness can exceed 100 millimeters. Several processes can be envisaged for the manufacturing processes of such large parts (welding or casting…), but few processes can deliver one within a reasonable time and at competitive cost. Among them the roll bending process, causing plastic deformation of a plate around a linear axis with little or no change in plate thickness, is considered as an interesting alternative.The main objective of this research is to assess 3D dynamic finite element and analytical models for the computation of the bending forces during the manufacturing of hollow conical parts made of a thick plate and a high strength steel. Numerous parameters such as thickness, curvature, part size, material properties and friction directly influence the reaction forces on the rolls. Therefore, the results of this research provide a better understanding of the phenomena taking place in the process, and an opportunity to establish relationships between the bending forces and the parameters of a final conical part.Copyright

Piecewise Fifth Order Spline Interpolation for Line Heating Forming Process

A fifth order piecewise spline interpolation model has been developed for computing the evolving geometry of a plate deformed by line heating thermal gradients. 3D formulations are presented and applied to continuously derivable geometries to demonstrate the capability of the methodology. Then the developed formulation is used to form gradually, with a sequence of heating lines, a 3D shape from an initially flat plate. The geometric results obtained from finite element simulations with three heating lines are used to illustrate where heating lines should be applied on a flat plate to achieve the intended geometry of a workpiece. Furthermore, it is shown that applying the developed piecewise fifth order spline interpolation model to the same flat plate produces results very close to the ones obtained from the thermal structural FE simulations.Copyright

Modeling and Simulation for Pressing Process With Reconfigurable Punch and Die

Pressing processes are widely used to reduce manufacturing cost by saving raw material when machining the deformed shapes and by reusing pressing tools. However, the conventional pressing process with matched punch and die is not suitable for flexible process when the shapes are variable and the production batches are small. In this paper, modeling of pressing process with reconfigurable punch and die is presented. The numerical results agree well with those obtained from the model of the conventional pressing process with matched punch and die.Copyright

Analyses of Profile Radial-Axial Ring Rolling Process Based on Explicit Finite Element Method

Profile radial-axial ring rolling is a complex bulk forming used to produce seamless rings for critical structural components in many industries, such as machinery, aeronautics, energy and automotive. The process is characterized by high nonlinearity, unsteady three-dimensional deformation, dynamic contact boundary conditions caused by the rotations of ring and rolls. In this paper, a numerical model based on explicit finite element approach is proposed to simulate and analyze the process. An expanded ring with profile section has been obtained by numerical simulations with the dynamic model based on explicit finite element method.Copyright