基于几何模拟法的板料成形快速评估

自行开发了计算机辅助复杂曲面零件成形几何模拟软件.系统以面积不变的几何模拟法为理论基础,对空间曲面进行全四边形网格剖分,利用逆映射法,对零件进行展开和成形模拟分析,结合FLD图对板料成形性进行评估,并提供了算例.     

数控弯管机机构运动学建模与加工过程仿真技术

针对现有数控弯管加工过程仿真方法通用性差的问题,提出一种基于机构运动学模型的数控弯管加工过程仿真方法。在运用多体系统运动学理论对数控弯管机进行机构运动学分析的基础上,建立了描述数控弯管机运动特征和结构参数的信息模型及机构运动学模型,采用Newton-Raphson迭代法对数控弯管机机构运动学方程进行求解,给出了数控弯管机运动和导管动态成形的运动规划算法,实现了任意结构单头数控弯管机的加工过程仿真。最后开发了原型系统,以SWING和VB200HP两种数控弯管机为例对所提方法进行了验证。     

铝合金汽车覆盖件冲压成形回弹的仿真研究

简要介绍了用于冲压成形回弹的有限元基本理论,提出了复杂汽车覆盖件成形仿真的模式,并以汽车底座横梁外板为例,利用DYNAFORM软件,对其拉延、切边、冲孔和回弹的过程进行了仿真,通过仿真结果与实验结果的比较,证明了所得到的数值参数和仿真方法能获得比较可靠的仿真结果,对实际生产有一定的指导意义。     

等效拉延筋模型及其在板料成形数值模拟中的应用

讨论等效拉延筋的建模方法、常用模型及其在板料成形数值模拟中的应用情况,并指出研究中仍存在的问题及今后的发展方向。     

Modeling and simulation for multiple-step incremental air-bending forming of sheet metal

Based on Hill’s yielding criterion and plane strain condition, the explicit expressions of elastoplastic constitutive model are derived in this paper which takes into account the effects of transverse stress, neutral surface shifting, and sheet thickness thinning on the sheet springback of air-bending. Then, this model is embedded into ABAQUS software platform by means of programming. Finally, 3D ABAQUS finite-element models (FEM), used to form the semiellipse-shaped workpiece with super length and large opening of sheet metal, are established, and the multiple-step incremental air-bending forming and springback processes are simulated. The simulation and experiment results show that the data predicted with the new constructed constitutive model under the plane strain condition are in much better agreement with experimental data than those predicted with the constitutive model built-in ABAQUS. It can be taken as a valuable mathematical tool used for multiple-step incremental air-bending forming simulation of large area sheet metal.     

Analytical model for prediction of sidewall curl during stretch-bend sheet metal forming

Curl is the curvature that results from non-uniform through-thickness strain present in sheet stampings that involve material flow over a die radius. In order to understand and control curl for tight fit-up tolerances, an analytical model that can provide a reliable measure for the amount of curl would be very helpful. In this study, a model is developed based on the moment–curvature relationship during stretch-bend sheet forming operations. The analytical model includes the variables of applied tension, yield strength, elastic modulus, bending radius, and sheet thickness. These are the primary factors affecting curl during sheet stamping operations. For the verification of analytical model, sidewall curl is experimentally measured after deformation of a strip using a bending-under-tension test system. The results show a good relationship between the theoretically predicted value and the experimentally obtained one, especially in the regions of high curl.     

汽车覆盖件冲压成形仿真研究进展

汽车覆盖件冲压成形仿真技术的发展,突破了原有汽车冲压件模具及工艺设计的设计方法,对保证工件质量、减少材料消耗、缩短产品开发周期、降低制造成本具有重要意义.概述了目前汽车覆盖件冲压成形仿真所涉及到的热点领域,如摩擦与接触、回弹分析、模具系统和工艺参数、材料屈服模型和板料形状设计,讨论了这些领域的研究进展和进一步研究的发展方向.     

Multi-scale friction modeling for sheet metal forming: The boundary lubrication regime

A physical based friction model is presented to describe friction in full-scale forming simulations. The advanced friction model accounts for the change in surface topography and the evolution of friction in the boundary lubrication regime. The implementation of the friction model in FE software codes is discussed. Results show that friction coefficients vary in space and time, and depend on local process conditions such as the nominal contact pressure and the plastic strain in the sheet material. The advanced friction model is validated by two small-scale forming processes, proving the enhanced predictive capabilities of FE simulations. The moderate increase in FE computation time, compared to using a Coulomb based friction model, demonstrates the efficiency of the proposed friction model.     

A general forming limit criterion for sheet metal forming

The forming limit of sheet metal is defined to be the state at which a localized thinning of the sheet initiates during forming, ultimately leading to a split in the sheet. The forming limit is conventionally described as a curve in a plot of major strain vs. minor strain. This curve was originally proposed to characterize the general forming limit of sheet metal, but it has been subsequently observed that this criterion is valid only for the case of proportional loading. Nevertheless, due to the convenience of measuring strain and the lack of a better criterion, the strain- based forming limit curve continues to play a primary role in judging forming severity. In this paper it is shown that the forming limit for both proportional loading and non-proportional loading can be explained from a single criterion which is based on the state of stress rather than the state of strain. This proposed criteria is validated using data from several non-proportional loading paths previously reported in the literature for both aluminum and steel alloys. In addition to significantly improving the gauging of forming severity, the new stress-based criterion is as easy to use as the strain-based criterion in the validation of die designs by the finite element method. However, it presents a challenge to the experimentalist and the stamping plant because the state of stress cannot be directly measured. This paper will also discuss several methods to deal with this challenge so that the more general measure of forming severity, as determined by the state of stress, can be determined in the stamping plant.     

Modified membrane finite element formulation considering bending effects in sheet metal forming analysis

A modified membrane finite element formulation is derived to take the bending effect into account for sheet metal forming analysis. The algorithm developed is applied to a cylindrical and a square cup drawing problem to confirm its validity. The results show that the bending effect is appreciable in a class of deep drawing problems. It is also noted that the present algorithm enhances the convergence of a solution procedure and prevents numerical buckling.     

Substepping algorithms with stress correction for the simulation of sheet metal forming process

The finite element analysis of the sheet metal forming process involves various nonlinearities. To predict accurately the final geometry of the sheet blank and the distribution of strain and stress and control various forming defects, such as thinning, wrinkling and springback, etc., the accurate integration of the constitutive laws over the strain path is essential. Our objective in this paper is to develop an effective and accurate stress integration scheme for the analysis of three-dimensional sheet metal forming problems. The proposed algorithm is based on the explicit “substepping” schemes incorporating with the stress correction scheme. The proposed algorithms have been implemented into ABAQUS/Explicit via User Material Subroutine (VUMAT) interface platform. The algorithms are then employed to analyze a typical deep-cup drawing process and the accuracy of these algorithms has been compared with the implicit “return” algorithm and explicit forward algorithm. The results indicate that the explicit schemes with local truncation error control, together with a subsequent check of the consistency conditions, can achieve the same or even better level of accuracy as “return” algorithm does for integrating large plastic problems like sheet metal forming process.     

A new sheet metal forming system based on the incremental punching, part 1: modeling and simulation

In heavy forging, a manipulator is indispensable to assist and help the precision of the forming process. This paper presents a multi-system simulation methodology combining the forging finite element method (FEM) simulation and the kinematics analysis to evaluate the mutual reaction loads between the forging process and the assisting manipulator. The forging is realized by the thermal–mechanical FEM simulation and the kinematics movements are analyzed based on the statics and dynamics modeling of the manipulator. The reaction load generating from the forging process to the manipulator clamps is treated as an input parameter for the kinematics analysis system, which will then calculate the movement of the manipulator. And this movement is regarded as the passive compliant movement constraint and applied on the forging process through the manipulator clamps. Using this coupled system, the study compares the reaction loads with and without the active vertical compliant movement and/or the passive horizontal compliant movement and reveals the effect of these compliant movements on the reaction loads.     

Lubricant test methods for sheet metal forming

Sheet metal forming of tribologically difficult materials such as stainless steel, Al-alloys and Ti-alloys or forming in tribologically difficult operations like ironing, punching or deep drawing of thick plate requires often use of environmentally hazardous lubricants such as chlorinated paraffin oils in order to avoid galling. The present paper describes a systematic research in the development of new, environmentally harmless lubricants focusing on the lubricant testing aspects. A system of laboratory tests has been developed to study the lubricant performance under the very varied conditions appearing in different sheet forming operations such as stretch forming, deep drawing, ironing and punching. The laboratory tests have been especially designed to model the conditions in industrial production. Application of the tests for evaluating new lubricants before introducing them in production has proven successful and has in a number of examples assisted the substitution of environmentally hazardous lubricants by more friendly ones in industrial production.     

基于Ayada损伤模型的板料冲裁过程数值模拟

使用DEFORM-2D软件对AISI-1045钢的冲裁工艺过程进行弹塑性大变形有限元数值模拟,采用Ayada断裂准则,预测了材料变形过程中静水应力、等效应力和等效应变的分布以及发展趋势、冲裁最后阶段微裂纹产生发展和最终断裂,模拟结果中的材料断裂和冲裁力的变化与实验结果一致.     

One step positive approach for sheet metal forming simulation based on quasi-conjugate-gradient method

In one step inverse finite element approach, an initial blank shape is normally predicted from the final deformed shape. The final deformed shape needs to be trimmed into a final part after stamping, the trimmed area, therefore, needs to be compensated manually before using one step inverse approach, which causes low efficiency and in consistency with the real situation. To solve this problem, one step positive approach is proposed to simulate the sheet metal stamping process. Firstly the spatial initial solution of one step positive method is preliminarily obtained by using the mapping relationship and area coordinates, then based on the deformation theory the iterative solving is carried out in three-dimensional coordinate system by using quasi-conjugate-gradient method. During iterative process the contact judgment method is introduced to ensure that the nodes on the spatial initial solution are not separated from die surface. The predicted results of sheet metal forming process that include the shape and thickness of the stamped part can be obtained after the iterative solving process. The validity of the proposed approach is verified by comparing the predicted results obtained through the proposed approach with those obtained through the module of one step inverse approach in Autoform and the real stamped part. In one step positive method, the stamped shape of regular sheet can be calculated fast and effectively. During the iterative solution, the quasi-conjugate-gradient method is proposed to take the place of solving system of equations, and it can improve the stability and precision of the algorithm.     

Review: geometric and dimensional tolerance modeling for sheet metal forming and integration with CAPP

The focus of this publication is a review of the state of the art in tolerance analysis, synthesis, and transfer for geometric and dimensional tolerances in sheet metal forming and the integration solutions with computer-aided process planning systems. In this context, the general tolerance methods are first described. Then, the mathematical models for sheet metal tolerance analysis and synthesis are examined in detail. To address the CAPP modeling concerns, the paper is then followed up with a brief review of past research works related to feature-based process planning. Finally, those imperative future research areas are identified.     

Experiment and numerical simulation on delamination during the laminated steel sheet forming processes

Laminated steel sheets, which have advantages in reducing vibration and noise, are widely used in home appliances, automotive components and building structures. With polymer layer laminated in steel sheets, the unique failure mode—delamination may occur in the forming process if the process parameters are defined improperly. In the presented work, firstly, the delamination is investigated by U channel forming in bending mode. Then, a step-bottom square cup drawing is also conducted to study the delamination in the deep drawing of the laminated sheet metal in more complex stress state. Nonlinear visco-elastic material model is applied to describe the mechanical behavior of polymer layer. Cohesive element and continuum shell elements are utilized to discretize the polymer layer and the outer steel sheets, respectively. The results of U channel forming indicate that increasing forming speed somewhat decreases the tendency of delamination, and increasing blank holding force (BHF) significantly diminishes the occurrence of delamination. Meanwhile, the results of the step-bottom square cup drawing reveal that the wrinkling of facial sheets often induces delamination. Increasing the BHF and the frictional coefficient prevents the occurrence of wrinkling and the delamination induced by wrinkling. However, when wrinkling is suppressed, further rising in BHF and frictional coefficient will increase the risk of direct delamination.     

Principles and apparatus of multi-point forming for sheet metal

As a flexible forming method for sheet metal part, multi-point forming (MPF) technology is discussed in the paper. It employs two reconfigurable element groups to approximate the continuous upper and lower solid dies. With the technique, rapid fabrication of 3D sheet metal part is realized. The principles of multi-point die forming (MPDF) and multi-point press forming (MPPF) are described and then the rules to determine the size of the element are given. For any spatial shape surface to be formed, all elements’ height can be calculated through the contacting point calculation equation. On the computer control, the shape of the two element groups can be adjusted by serial adjusting mode or parallel adjusting mode. MPDF apparatus that includes CAD software, computer control system, two element groups, hydraulic press and laser CMM is developed. Following the given MPF procedure, 3D sheet metal part was formed without failure. Due to the rapid change characteristics of the two element groups, several special MPF forming techniques that are impossible in conventional sheet forming have been investigated in detail. By flexible blank holder technique, thin sheet MPDF is realized. With sectional MPF, large size sheet would be formed on small scale MPF apparatus. Through closed loop MPF, spring-back would be compensated cycle by cycle, and large deformation part is obtained with incremental MPDF successfully.