Preform optimization for hot forging processes using an adaptive amount of flash based on the cross section shape complexity

In multistage hot forging processes, the preform shape is the parameter mainly influencing the final forging result. Nevertheless, the design of multistage hot forging processes is still a trial and error process and therefore time consuming. The quality of developed forging sequences strongly depends on the engineer’s experience. To overcome these obstacles this paper presents an algorithm for solving the multi-objective optimization problem in designing preforms. Cross wedge rolled preforms were chosen as subject of investigation. An evolutionary algorithm is introduced to optimize the preform shape taking into account the mass distribution of the final part, the preform volume and the shape complexity. A crucial factor in preform optimization for hot forging processes is the amount of flash. Therefore an equation for improving the amount of flash is derived. The developed algorithm is tested using two connecting rods with different shape complexities as demonstration parts.     

基于UBET和FEM的模锻件预成形设计

提出了一种用于锻造过程预成形模拟设计的新方法——基于 U BET和 FEM的混合正 /反向模拟预成形设计技术 ,即先用 UBET进行反向模拟 ,快速找出可能的预锻件或初始坯料 ,再用 FEM进行正向模拟验证 ,必要时可根据正向模拟结果对坯料或预锻件进行修改 ,使之能够达到完全充满型腔且飞边尽可能小的最佳效果。应用 U BET和FEM的混合正 /反向模拟预成形设计技术进行预成形设计 ,并与实验结果进行对比 ,结果与实测值基本吻合。     

An axisymmetric forging approach to preform design in ring rolling using a rigid–viscoplastic finite element method

In this paper, a new method for approximately predicting the deformation of material in ring rolling is presented. The plastic flow of material in ring rolling is assumed to be axisymmetric and thus the ring rolling process is considered as a sequence of consecutive forging processes. The problem, having tool velocity as well as material velocity field as unknown variables, is formulated by an axisymmetric rigid–viscoplastic finite element method. The unknown tool velocity is determined by making the circumferential stress on the ring cross-section exist in the range of user-specified values. The approach is applied to preform shape design in ring rolling of bearing races. The predicted results are compared with the experimental ones. It has been shown that the approximate approach presented is useful for engineering design of preform in ring rolling of bearing race-like rings.     

A die forging design approach for controlling metal flow way and its application in practice

In this paper a novel idea about die forging process design in relation to metal flow is presented. The purpose is to almost completely fill a die cavity before flash starts to form. The paper shows that preform design is the way to realize this situation. The paper describes a method in which metal flow is simulated using UBET in reverse sequence to that occurring in practice. The successful application of the method in production is shown.     

Sensitivity analysis based preform die shape design for net-shape forging

A sensitivity analysis method for preform die shape design in net-shape forging processes is developed in this paper using the rigid viscoplastic finite element method. The preform die shapes are represented by cubic B-spline curves. The control points or coefficients of B-spline are used as the design variables. The optimization problem is to minimize the zone where the realized and desired final forging shapes do not coincide. The sensitivities of the objective function, nodal coordinates and nodal velocities with respect to the design variables are developed in detail. A procedure for computing the sensitivities of history-dependent functions is presented. The remeshing procedure and the interpolation/transfer of the history-dependent parameters, such as effective strain, are stated. The procedures of sensitivity analysis based preform die design are also described. In addition, a method for the adjustment of the volume loss resulting from the finite element analysis is given in order to make the workpiece volume consistent in each optimization iteration. The method developed in this paper is used to design the preform die shape of H-shaped forging processes, including plane strain and axisymmetric deformations. The results show that a flashless forging with a complete die fill is realized using the optimized preform die shape.     

A new upper-bound elemental technique approach to axisymmetric metal forming processes

A new upper-bound elemental technique (UBET) is proposed to improve the ineffectiveness of UBET for solving forging problems that are geometrically complex or need a forming simulation for predicting the profile of free boundary. This method combines the advantages of the stream function and the finite element method (FEM); specifically, the curve fitting property of FEM and the fluid incompressibility of the stream function. The formulated optimal design problems with constrained conditions are solved by the flexible tolerance method. Three forming problems (ring upsetting, closed-die, and backward-extrusion forging) are used to illustrate this method: the results of ring upsetting show a good ability of simulating for predicting the forming profile of a free boundary; the closed-die forging produces a lower upper-bound solution than UBET; and backward-extrusion forging demonstrates the flexible curve fitting property for a complex geometric boundary.     

Computer aided preform design in forging using the inverse die contact tracking method

The inverse die contact tracking method presented in this paper utilizes both the forward and inverse finite element simulations to design the preform shapes in forging processes. The procedure starts with the forward simulation of a candidate preform into the final forging shape. A record of the boundary condition changes is produced by identifying when a particular segment of the die makes contact with the workpiece surfaces in forward simulation. This recorded time sequence is then optimized according to the material flow characteristics and the state of die fill to satisfy the requirement of material utilization and forging quality. The modified boundary conditions are finally used as the boundary condition control criterion for the inverse deformation simulation. Additionally, a procedure to determine process staging points using trial forward simulation is given. As an example, the preform design of a plane strain forging process is performed. The fuller, buster and blocker dies are designed by using the inverse deformation simulation.     

基于有限元法的正反向模拟技术在链轨节锻造中的应用

锻造过程的预成形设计是提高锻造质量和降低产品成本的一个极其重要的方面，基于刚一粘塑性有限元法的正反向模拟技术能够从最终的锻件形状直接得出坯料的预成形形状，通过改善设计制坯操作来减少作为飞边的材料浪费。中介绍了覆带链轨节锻造的常规工艺，说明了目前覆带链轨节锻造中存在的问题，阐述了有限元法、预成形设计思想和正反向模拟技术以及它们在覆带链轨节锻造中的应用。     

Optimum design of forging dies using fuzzy logic in conjunction with the backward deformation method

A novel shape optimization method is presented for the design of preform die shapes in multistage forging processes using a combination of the backward deformation method and a fuzzy decision making algorithm. In the backward deformation method, the final component shape is taken as the starting point, and the die is moved in the reverse direction with boundary nodes being released as the die is raised. The optimum die shape is thereby determined by taking the optimum reverse path. A fuzzy decision making approach is developed to specify new boundary conditions for each backward time increment based on geometrical features and the plastic deformation of the workpiece. In order to demonstrate this approach, a design analysis for an axisymmetric disk forging is presented in this paper.     

A design approach for intermediate die shapes in plane strain forgings

A new technique has been developed for the design of die shapes in the plane strain forging process. The objective of this research work is to develop a design procedure to obtain the number of stages and the shape of each die for manufacturing a desired product. Metal flow during the forging is considered in the design of the intermediate die shapes in multistage forgings. The two approaches developed for the preform shapes design are conformal mapping techniques and ideal material flow simulations. The forging process is simulated using a nonlinear rigid visco plastic finite element program ALPID (analysis of large plastic incremental deformation). Staging criteria is developed from the results of the forging simulation and the number of stages are based on the stress ratio parameterg (mean stress/effective stress) and strain rate gradient information. This paper presents two examples of forgings to demonstrate an optimal die shape design methodology.     

Sensitivity analysis based preform die shape design using the finite element method

This paper uses a finite element-based sensitivity analysis method to design the preform die shape for metal forming processes. The sensitivity analysis was developed using the rigid visco-plastic finite element method. The preform die shapes are represented by cubic B-spline curves. The control points or coefficients of the B-spline are used as the design variables. The optimization problem is to minimize the difference between the realized and the desired final forging shapes. The sensitivity analysis includes the sensitivities of the objective function, nodal coordinates, and nodal velocities with respect to the design variables. The remeshing procedure and the interpolation/transfer of the history/dependent parameters are considered. An adjustment of the volume loss resulting from the finite element analysis is used to make the workpiece volume consistent in each optimization iteration and improve the optimization convergence. In addition, a technique for dealing with fold-over defects during the forming simulation is employed in order to continue the optimization procedures of the preform die shape design. The method developed in this paper is used to design the preform die shape for both plane strain and axisymmetric deformations with shaped cavities. The analysis shows that satisfactory final forging shapes are obtained using the optimized preform die shapes.     

Forging preform design with shape complexity control in simulating backward deformation

This paper presents a preform design method which employs an alternative boundary node release criterion in the finite element simulation of backward deformation of forging processes. The method makes use of the shape complexity factor which provides an effective measure of forging difficulty. The objective is to release die contacting nodes in a sequence which will minimize the geometric complexity throughout the backward deformation simulation. This is done by calculating the effect of releasing each of a select group of boundary element nodes at each finite element solution step. The particular detached node which results in the minimum shape complexity factor will be released for the current step. This process continues for each backward step until the last few nodes remain in contact. This design method is demonstrated through the simulated forging of an integrated blade and rotor turbine disk blank. A preform shape developed by this method is compared with an empirically designed preform. Performance parameters for comparison include die fill, flash volume, effective strain variance, frictional power and die load. Comparing the results of the forward simulations indicates improved performance of the preform design using FEM based backward deformation method over that of the empirical design.     

A new approach to optimal design of multi-stage metal forming processes with micro genetic algorithms

This paper describes a new method for design optimization of process variables in multi-stage metal forming processes. The selected forming processes are multi-pass cold wire drawing, multi-pass cold drawing of a tubular profile and cold forging of an automotive outer race preform. An adaptive micro genetic algorithm (μGA) scheme has been implemented for minimizing a wide variety of objective-cost functions relevant to the respective processes. The chosen design variables are die geometry, area reduction ratios and the total number of forming stages. Significant improvements in the simulated product quality and reduction in the number of passes has been observed as a result of the micro genetic algorithms-based optimization process.     

A combined approach to determine workpiece-tool-press deflections and tool loads in multistage cold-forging

Press and tool deflections have significant influence on the accuracy of products and tool service life in cold-forging processes. This paper presents a combined experimental-numerical approach to determine the deflections of the workpiece-tool-press (WTP) system and tool loads to improve product accuracy in a multistage cold-forging process. The measurements of deflections of the vertical mechanical press for the determination of the press flexibility matrix were performed in dynamic operating conditions. Numerical modelling of the vertical mechanical press and a multistage forging system was performed in order to evaluate the tool loads, the displacements and the rotations of the entire WTP system. The press flexibility matrix in combination with finite element (FE) model of the press and multistage process enable predictions of the elastic displacements and rotations of the tool and the press ram as well as determination of the evolution of the resultant force in order to design a reliable multistage cold-forging process. By redesigning the time sequences and evolution of the multistage forming operations during the press stroke, the evolution of the resultant force and the torque are optimized. This approach has been successfully applied to improve the prediction of tool loads, WTP deflections and rotations for the production of the automotive starter side plate.     

Computer-aided preform design in forging of an airfoil section blade

This study attempts to establish systematic procedures for the preform design in forging of an airfoil section blade as a two-dimensional plane-strain problem. Forward loading and backward tracing simulations by the finite element method are used. A circular shape is selected as an original stock, and a side-pressed preform of the circular shape is adopted in view of preliminary simulations using rectangular preforms. The optimal slope angle of the die parting line and the position of the preform within the die, which satisfy the final design condition of flashless forging, are determined from the results of the simulations.     

面向微观组织优化的锻造工艺预成形优化设计及实验研究

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了锻造成形过程微观组织优化目标函数,并确定锻造成形预成形形状作为优化过程的设计变量。采用遗传算法和有限元模拟相结合的方法,开发了锻造过程微观组织优化程序,对典型的H型锻件进行了面向微观组织优化的预成形设计,取得了较好的效果。并根据优化设计的结果进行了实验研究,优化结果的晶粒尺寸及其分布趋势与实验结果比较吻合。     

Fast 3D inverse simulation of hot forging processes via Medial Axis Transformation: an approach for preform estimation in hot die forging

In hot die forging processes, the selection of an ideal preform is of great importance with respect to cavity filling and mechanical load. The common procedure in order to define an adequate preform is the usage of Finite-Element-Analysis (FEA), usually as an iterative process in which various preforms are tested with regard to their suitability. An approach that aims at reducing the number of trials by proposing a first estimation of a suitable preform is presented in this paper. It is conjectured that the material flow paths and resistance can be described by the cavity shape using the Medial Axis Transformation. Based on this, a local inverse material flow for time discrete steps is calculated. The result is a first estimation of an adequate preform shape within a few minutes as an input for further FEA. FE-based parametric design optimization procedure is then presented and compared to the inverse approach, which is identified as a useful complement for the forward simulation technique.     

面向微观组织优化的锻造工艺预成形优化设计

以锻件晶粒尺寸细小均匀为目标,以预成形形状设计为对象,提出了锻造成形过程微观组织优化设计方法,构建了锻造成形过程微观组织优化目标函数,并确定锻造成形预成形形状作为优化过程的设计变量,给出了优化设计的具体步骤,采用微观遗传算法和有限元模拟方法开发了锻造过程微观组织优化程序,并对典型的圆柱体镦粗进行了面向微观组织优化的预成形设计,取得了较好的效果.     

基于Pro/ENGINEER二次开发的筋板类锻件预成形设计

提出一种高筋薄壁类航空锻件预锻成形设计新方法,建立了典型的H型预锻截面数学模型,在Pro/EN-GINEER平台上二次开发了界面友好的预成形设计软件,应用DEFORM-3D有限元软件模拟典型结构件预锻及终锻过程,研究了预成形设计对模锻件变形均匀性及成形载荷的影响。结果表明,预成形设计能使锻件金属流动更加合理,锻件内部的变形更加均匀,同时能降低锻造过程的成形载荷。     

齿轮锻造模具及工艺优化的模拟式设计

齿轮锻造的经验设计方法难以进行锻造模具及工艺的最优化设计,造成了过多的废料和能量消耗。本文根据金属塑性成形理论基础上的上限元模拟技术,通过对齿轮锻造过程的模拟,实现了对齿轮锻造模具及工艺的优化设计,从而大大减少了飞边废料的体积和锻造能耗。