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.     

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.     

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。     

叶片精锻三维有限元反向模拟脱模准则的确定

叶片精锻过程的预成形设计是提高叶片锻件质量和降低产品成本的一个极其重要的方面,基于有限元法的反向模拟技术能够从叶片终锻件形状反演出预成形毛坯形状。为此,本文介绍了有限元反向模拟的基本步骤,综述了确定反向模拟中边界节点脱模准则的方法。针对叶片精锻三维有限元反向模拟过程,提出用跟踪拟合修正的方法来确定边界节点脱模的时间序列,确定了反向模拟的脱模准则。将所确定的脱模准则应用到叶片精锻三维有限元反向模拟程序中,可得到合理的叶片预成形毛坯形状。     

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.     

中心管胎模锻造工艺研究

通过对8MN快锻液压机上采用胎模锻造中心管锻件的工艺方案的分析,研究了锻造制坯、模具设计的特点和要点,提出了液压机胎模锻造变形力的计算方法,指出锻造难点、可能出现的问题及预防纠正措施,还提出了液压机胎模锻造模具材料的选用方法.     

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.     

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.     

基于灵敏度分析的预锻模具形状优化设计

以最终锻件的形状为目标,采用塑性有限元、灵敏度分析和工程优化算法相结合的方法,对预锻模具形状进行了设计。针对下模速度为零时,下查形状不能优化有的情况,提出了一种处理速度灵敏度边界条件的方法,该方法可同时对上下模具形状进行优化。针对程度耗时较问题,提出了贮存灵敏度刚度矩阵,减少优化设计变量的方法,大大提高了程序的运行速度。最后,给出了优化设计实例,验证了该方法的可靠性。     

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.     

Preform Design for Large-Sized Frame Forging of Ti-Alloy Based on 3-D Electrostatic Field Simulation and Geometric Transformation

Large-sized frame forging of Ti-alloy is an important forced component of aircraft. The frame forging has complicated shape which leads to great difficulties in deformation. Some defects may be produced during the forming process such as un-filling or overlapping. Preform design is an effective method for producing qualified forging. In this article, a new method based on 3-D electrostatic field simulation is proposed to design preform of a large-sized frame forging of Ti-alloy and a geometric transformation method is introduced to obtain the preform dimension. In order to select more suitable preform of large-sized frame forging, FEM software Deform-3D is employed to simulate the isothermal forming process of designed preform. Deformation uniformity index ψ is introduced as a criterion to judge the forging quality and the most appropriate preform is obtained by virtual orthogonal test design.     

UBET-based numerical modeling of bulk deformation processes

The paper summarizes the development of numerical procedures for modeling bulk deformation process and preform designing techniques based on the upper bound elemental technique (UBET). UBET has a unique place where an approximate, but faster solution is needed for decision making. In designing and optimizing multistage forging and profile ring-rolling processes, an approximate solution can be used to identify the most influential process parameters. Once an optimum combination of process conditions are determined, computationally intensive, but more accurate finite element analysis can be used to verify and refine results. In this paper, UBET procedures for closed-die forging and profile ring rolling are high-lighted. Experimental investigations are used to validate the model predictions. Also, the UBET-based preform design tool is presented as a process and die design tool for multistage forging processes. Application of these techniques is presented with evidence of effective material usage and extended overall die-life.     

7050铝合金等温模锻坯料设计

设计合适的锻压坯料是保证锻压后锻件具有良好综合性能的基础,通过改进锻压坯料的尺寸来改善锻件各部位的变形程度以获得具有良好组织及性能的锻件。运用有限元模拟软件Deform-3D模拟联接轴等温模锻过程,对不同尺寸的坯料模拟等温锻造过程,随着坯料在Z向厚度尺寸的增加,模锻后锻件的等效应变随之逐渐增加。选择成形效果较佳且模锻后锻件变形程度逐渐增加的锻压坯料进行实验。对热处理后的等温模锻件进行室温拉伸、硬度、电导率、疲劳以及金相实验检测。结果显示:对于横截面沿长轴突变的联接轴锻件,锻件各部位间性能差异较大;等温模锻后,变形程度大的锻件能够获得更好的微观组织和力学性能。     

材料塑性成形过程最优化设计—Ⅰ有限元灵敏度分析方法

本文采用有限元方法建立了一种非稳态材料塑性成形过程的灵敏度分析理论和模具形状优化设计方法。采用三次Ｂ样条函数描述预成形模具形状,Ｂ样条函数的控制点坐标（系数）作为优化设计变量,通过对控制点坐标的优化设计,使实际终成形件形状与理想终成形件形状之间的差别最小,从而实现预成形模具形状的优化设计,详细建立了目标函数、有限元节点坐标、节点速度对优化设计变量的解析灵敏度方程及其彼此之间的数学关系,并给出了节点速度灵敏度的边界条件     

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.     

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.     

金属体积成形预成形设计的现状及发展

金属体积成形预成形设计 ,是材料多工序成形工艺与模具设计的中心工作。如何设计预锻件形状和预锻模形状是生产合格终锻件的关键 ,也是模具设计的难点之一。预成形优化设计是采用了优化技术的预成形设计 ,是发展的预成形设计 ,在国内外得到了广泛研究。本文首先介绍了预成形设计所依据的知识和采用的主要手段 :基于以往丰富经验的经验性指导原则、物理模拟技术和基于数值模拟的计算机辅助设计。然后对处于当今预成形设计的主流方法—基于数值模拟的预成形设计的两个发展阶段 ,即预成形设计和预成形优化设计进行了介绍。其次对常用的正向模拟和反向模拟预成形设计方法和常用的基于灵敏度分析的正向模拟优化法、直接微分法、拟合优化法、微观遗传算法等预成形优化设计方法的基本原理、特点及应用进行了介绍和总结。最后指出了预成形设计的发展趋势。     

基于响应面法（RSM）的锻造预成形多目标优化设计

以航空发动机涡轮盘锻件为研究对象,应用响应面法(Response surfce Methodology,RSM)和有限元数值模拟(FEM)对锻造过程预成形设计的多目标优化问题进行了研究.首先以模具充填完整和提高锻件内变形均匀性为目标,建立了有限元数值模拟与响应面法相结合的二阶分析模型,并对优化结果进行了讨论.其次,在原优化设计的基础上以降低锻造过程的成形载荷为目标进行了预成形再设计.结果表明,应用响应面法可灵活有效的对难变形材料锻造预成形坯料形状进行多目标优化设计.     

STUDY ON THE NUMERICAL SIMULATION OF MULTI-STAGE ROTARY FORGING OF A NON-AXISYMMETRIC PART AND THE CAE ANALYSIS OF THE DIE STRENGTH

Traditionally a rotary forging process is a kind of metal forming method where a conic upper die, whose axis is deviated an angle from the axis of machine, forges a billet continuously and partially to finish the whole deformation. For the rotary forging process simulation, more researches were focused on simulating the simple stage forming process with axisymmetric part geometry. Whereas in this paper, the upper die is not cone-shaped, and the billet is non-axisymmetric. So the movement of the punch is much more complicated than ever. The 3D FEM simulation models for the preforming ＆ final forming processes are set up aider carefully studying the complicated movement pattern. Deform-3D is used to simulate the material flow, and the boundary nodal resisting forces calculated by the final stage process simulation is used to analyze the final forming die strength. The CAE analysis of the die shows that the design of the final forming die is not reasonable with lower pre-stress which is easy to crack at the critical corners. An optimum die design is also provided with higher pre-stress, and verified by CAE analysis.     

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。