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.     

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.     

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.     

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.     

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.     

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.     

基于有限元灵敏度分析的锻造成形微观组织优化设计

采用有限元、灵敏度分析与工程优化算法相结合的方法,以能充满型腔且少无飞边的终锻件的晶粒度分布均匀化为目标,以预成形形状为优化对象,对锻造成形过程的微观组织进行了优化设计。采用三次B样条函数描述预成形模具形状,并以B样条函数的控制点坐标为设计变量,给出了锻造过程微观组织演变的模型,建立了衡量锻件充型性能及微观组织分布均匀化的目标函数,推导了目标函数对设计变量的灵敏度,给出了优化设计步骤。并以一典型H型锻件为例,对锻件的微观组织进行了优化,取得了较好的结果。     

Finite element analysis of die wear in hot forging processes

Design optimization of hot forging dies requires an accurate estimation of die wear. The presented paper introduces a finite element model for wear estimation that includes the process related thermal effects on hardness of the tool material. Fundamental investigations concerning the hardness evolution due to thermal softening of the tool material are presented. To obtain necessary data for model calibration by means of statistical analysis, optical measurements are performed on several industrial forging dies. The introduced model is proved to be applicable in wear estimation of hot forging dies over a large number of operating cycles.     

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.     

Influence of the shape and position of the preform in the precision forging of a compressor blade

The influence of the shape and the initial position of the preform in precision forging of a compressor blade has been studied by 3D rigid–viscoplastic finite element method (FEM) in this paper. The results show the following: (1) a short and thick preform results in necking at the arc transition zone between the tenon and the blade body, and at the zone near the tip of the blade during deformation; (2) a long and slender preform produces bending in the middle of the blade body during deformation; (3) if a long and slender preform is bent in advance, an advisable product without flash can be obtained; (4) a reasonable initial position of the preform deviates to the thinner side of the blade die cavity; (5) this research is beneficial for the practice of the precision forging process of a compressor blade and it has a general significance for other types of blade.     

The Effect of Geometric Parameters of Conical Cups on the Preform Shape in Two-Stage Superplastic Forming Process

A combination of sensitivity analysis and finite element simulation has been developed for the preform design in two-stage superplastic forming process. The aim is to present a simple approach to generate an estimate for the preform shape. In this respect, the commercial finite element software ABAQUS/Standard 6.8 was used as a computational tool and sensitivity analysis was used for preform design by minimizing the mean fractional deviation from the target thickness as an objective function. The predicted preform was verified through comparison with experimental results by investigating the deformation of AA5083 sheet at temperature of 500 °C. The effect of the geometric parameters of conical cups on the preform shape was examined. The results showed that the geometric parameters have a significant effect on the preform shape. By increasing the height and the cone angle of the final cup, the depth of the preform in the inner cavity decreases and the dome region is approached to the center of the preform cup. By increasing the corner radius of the final-die, only the height of the dome region decreases.     

滑动叉无飞边锻造工艺有限元模拟研究

滑动叉传统上采用开式模锻工艺生产,飞边大,材料浪费严重且尺寸精度差。为了降低锻件成本,针对滑动叉的形状特征,提出一种少无飞边模锻的新工艺,使预制毛坯在封闭的模膛内成形,实现锻件近净成形。根据体积不变原则对计算毛坯进行处理得到预制毛坯。应用DEFORM 3D软件模拟研究了滑动叉无飞边和小飞边锻造工艺过程,模拟验证结果表明,新工艺显著地提高了材料利用率和成形质量,降低了锻造载荷。     

转轮叶片热模压成形压力中心的动态计算

为确保实际生产中压力中心的波动始终处于设定的公差范围之内,提出一种基于刚塑性有限单元法,通过实时节点力的计算来获取非均匀厚度板料成形压力中心的动态算法.推导了相应的计算列式,采用DEFORM软件二次开发实现了该算法.同时,建立了水轮机转轮叶片热模压成形过程的有限元模型,结合上述算法给出了具体的压力中心坐标值,为压力中心的优化提供了必要的数值基础.     

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。     

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.     

板料冲压成形有限元反向分析中初始解确定方法的研究

初始解的确定是板料冲压成形有限元反向分析中的一个重要环节,初始解的好坏会影响后续计算的收敛性以及分析计算的效率。文中介绍了板料冲压成形有限元反向分析的基本原理,对反向法计算中的初始解确定方法进行了研究,总结并分析了国内外关于初始解确定方法的研究概况,提出了一种高效实用的方法,最后给出了计算实例。     

金属成形建模中的快速拟逆方法和塑性直接算法(英文)

逆方法 (IA)是一种基于产品最终形状的,应用于构建轴对称冷锻造过程模型的简单方法。由于是假设在简单路径下变形,而且简化了工具的作用形式,因此该方法计算速度很快;数值测试显示,该种方法因为没有考虑变形历史,因而只能较好的估算应变,但是应力估算的误差较大。该文提出了一种新方法——拟逆方法 (PIA:Pseudo Inverse Approach),这种方法是在保留IA优势的基础上,考虑了工件的加载历史,因而可以较好的估算应力。PIA引入了多个中间构型来考虑变形路径,摒弃了传统的接触问题的处理方法,采用自由表面法对中间构型进行修正。另外,基于等效应力的概念和拉伸应力应变曲线,提出了一种全新的塑性积分的直接算法,并编写了快速健强的计算程序。通过和ABAQUS的计算结果的比较,研究了PIA的计算效率和局限性,结果表明,该方法可以应用于初始预成形的设计以及锻造工艺的参数优化。     

On process parameter estimation for the tube hydroforming process

Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.     

差温无模预成形锻造的有限元模拟研究

利用热力耦合有限元方法 ,对AISI10 4 5钢圆柱体坯料在环形加热源局部加热下的差温无模预成形锻造过程进行了模拟研究。模拟结果表明 ,在坯料中获得和控制大梯度分布的不均匀温度场是实现无模预成形锻造的关键。复杂零件成形必须合理地组合加热源和冷却源 ,以便产生所需的温度梯度场。在快速变形条件下 ,变形过程中的持续加热对金属的流动影响甚微 ,变形前的温度分布基本上决定了金属的流动 ,但在慢速变形条件下 ,变形过程中的持续加热对金属的流动产生一定的影响 ,其影响程度视零件复杂程度而异。从该文研究结果可以预见 ,差温无模锻造可以发展成为一种无模锻造制坯新工艺     

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.