New Algorithms for Thermo‐mechanical FE‐Simulation of Quasi‐periodic Processes

With the aid of the finite element method, a lot of mechanical and thermal phenomena in forming processes can be analysed successfully. However, for industrial purposes the necessary computational time for complex processes is often not acceptable. Many researches have attempted to reduce the computational time which is needed to find a solution. In this paper, new algorithms are described which make use of the existing similarity in some forming processes, especially incremental forming process. Incremental forming processes are characterised by very small deformation zones and approximate self similarity. The described algorithms are based on the transformation and interpolation of already computed solutions. The results from transformation and interpolation are verified by means of some physical constraints. If the results pass the latter check, they will be archived as solution. Consequently, at this time step, no iterative computation will be accomplished by the mechanical solver. Then the calculations by the thermo solver are accomplished conventionally in dependence on the archived mechanical results. With the help of these algorithms, the number of iterations will obviously be reduced and the results will be reasonably acceptable. In this paper, all details are described and two forming processes as validation occur to depict the advantages of this method.     

半固态加工技术的进展及我国应对措施

半固态金属成形技术具有高效、节能、近终形生产和成形件性能高等许多优点，被专家们称为21世纪最具前景的加工方法。本文介绍了半固态金属成形的成形工艺、坯料制备工艺、微观组织、数值模拟状况及国内外研究应用情况，展望了半固态金属 的前景，提出了我国的应对措施，     

Linear contact algorithm for rigid-plastic finite element simulation

The rigid-plastic finite element analysis of metal forming processes is known to be much more efficient and stable than the elastic-plastic one. This efficiency results from the absence of kinematical nonlinearities in the formulation. Contact algorithms used in rigid-plastic models must agree with this fact, otherwise the efficiency can be damaged seriously. The aim of this paper is to present a linear contact algorithm designed specially for rigid-plastic analysis of metal forming problems. The linearization is achieved by dictating constancy of boundary conditions during one increment according to the requirement of the variational principle by Markov. The algorithm consists of two parts: the contact search and the contact control. The procedure has been implemented for two-dimensional cases. However, the generalization to three dimensions is straightforward. The efficiency and the stability of the proposed procedure has been validated by means of examples of application such as extrusion and forging. Furthermore, parametric studies of the contact variables have been performed.     

半固态加工技术的进展、前景及对策

半固态金属成形技术具有高效,节能,近终形生产和成形件性能高等许多优点,被专家们称为21世纪最具前景的加工方法,介绍了半固态金属成形的成形工艺,坯料制备工艺,微观组织,数值模拟状况,国内外研究应用情况,展望了半固态金属的前景,并提出了应对措施。     

Rapid Finite Element Analysis of Bulk Metal Forming Process Based on Deformation Theory

 The one-step finite element method (FEM), based on plastic deformation theory, has been widely used to simulate sheet metal forming processes, but its application in bulk metal forming simulation has been seldom investigated, because of the complexity involved. In this paper, a bulk metal forming process is analyzed by using a rapid finite element simulation method based on deformation theory. The material is assumed to be rigid-plastic, strain hardening. The constitutive relationship between stress and total strain is adopted, whereas the incompressible condition is enforced by penalty function. The geometrical non-linearity in large plastic deformation is taken into consideration. Furthermore, the force boundary condition is treated by a simplified equivalent approach, considering the contact history. Based on constraint variational principle, the deformation finite element method is proposed. The one-step forward simulation of axisymmetric upsetting process is performed by this method. The results are compared with those obtained by the traditional incremental FEM to verify the feasibility of the proposed method.     

Finite-Volume Model for Shallow-Water Flooding of Arbitrary Topography

A model based on the finite-volume method is developed for unsteady, two-dimensional, shallow-water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession. The model uses Roe’s approximate Riemann solver to compute fluxes, while the monotone upstream scheme for conservation laws and predictor-corrector time stepping are used to provide a second-order accurate solution that is free from spurious oscillations. A robust, novel procedure is presented to efficiently and accurately simulate the movement of a wet/dry boundary without diffusing it. In addition, a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed. Model predictions compare favorably with analytical solutions, experimental data, and other numerical solutions for one- and two-dimensional problems.     

Fast Algorithms for the Simulation of Electromagnetic Metal Forming

Despite the comprehensive understanding of the modelling and numerical simulation of electromagnetic metal forming that has recently been gained, the simulation of real forming situations is still a challenging task due to the large computational resources required. A bottleneck is the computation of the electromagnetic fields, since 100 000 up to several million unknowns are required to represent the geometry of a typical forming device. The purpose of this article is to present new techniques to speed up the simulation of electromagnetic metal forming with particular emphasis on the computation of the electromagnetic fields. An acceleration of the electromagnetic field computation is a significant step towards a virtual design of electromagnetic forming processes.     

Experimental Analysis of Hydraulic Solver Convergence with Genetic Algorithms

A procedure for the experimental convergence evaluation of a hydraulic-network solver is proposed, based on using genetic algorithms to search for network parameter values that maximize the number of iterations of the hydraulic-network solver under test. The efficiency of the method is demonstrated by the example of convergence evaluation for the EPANET hydraulic simulator. Examples of a pipe network and of combinations of parameter values for which the static solver of the simulator fails to converge in a reasonable number of iterations are given. The features of the EPANET 2.00.12 solver responsible for loss of convergence are discussed. New criteria for the automatic start of solution damping aimed at improving the convergence of the solver are proposed. The better convergence of the EPANET solver modified in accordance with these criteria is confirmed by the random and the proposed search-based testing method.     

半固态金属成形技术及应用

半固态金属加工是近年来金属加工技术研究的热点。本文论述了半固态金属坯料制备、成形方法、微观组织及其数值模拟，并阐述了其发展应用和前景。     

金属增材制造数值模拟研究进展

作为高性能复杂金属构件的新兴制造技术,增材制造已被应用于航空航天、汽车工业、医疗和核电等领域.金属增材制造工艺涉及传热、热力、相变及流动等复杂物理现象,不同尺度及跨尺度数值模拟结合实验验证可实现对增材制造过程中复杂物理现象的理解、调控及优化,为高质量、高精度、高性能金属构件的成形提供有力支撑.本文综述了宏观、介观、微观...     

Calculation of metal forming processes by means of FEM

The simulation of metal forming processes with the finite element method (FEM) is becoming more and more significant for process analysis and optimising. With regard to the quality of the calculations care must be taken to select a suitable FE model. Possibilities for FEM applications will be shown using the examples of die bending sheets and profile bending. A practical extension of this application is the support of the FE systems user by access to a material database.     

Application of computer modelling in part,die, and process design for manufacturing of automotive stampings

Recent studies in sheet metal forming, conducted at universities world wide, emphasize the development of computer aided techniques for process simulation. To be practical and acceptable in a production environment, these codes must be easy to use and allow relatively quick solutions. Often, it is not necessary to make exact predictions but rather to establish the influence of process variables upon part quality, tool loads, material flow, and material thickness variation. In cooperation with its industrial partners, the ERC for Net Shape Manufacturing at the Ohio State University has applied a number of computer codes for analysis and design of sheet metal forming operations. This paper gives a few selected examples taken from automotive applications and illustrates practical uses of computer simulations to improve produtivity and reduce tool development and manufacturing costs.     

High-Resolution Method for Modeling Hydraulic Regime Changes at Canal Gate Structures

A method for modeling flow regime changes at gate structures in canal reaches is presented. The methodology consists of using an approximate Riemann solver at the internal computational nodes, along with the simultaneous solution of the characteristic equations with a gate structure equation at the upstream and downstream boundaries of each reach. The conservative form of the unsteady shallow-water equations is solved in the one-dimensional form using an explicit second-order weighted-average—flux upwind total variation diminishing (TVD) method and a Preissmann implicit scheme method. Four types of TVD limiters are integrated into the explicit solution of the governing hydraulic equations, and the results of the different schemes were compared. Twelve possible cases of flow regime change in a two-reach canal with a gate downstream of the first reach and a weir downstream of the second reach, were considered. While the implicit method gave smoother results, the high-resolution scheme—characteristic method coupling approach at the gate structure was found to be robust in terms of minimizing oscillations generated during changing flow regimes. The complete method developed in this study was able to successfully resolve numerical instabilities due to intersecting shock waves.     

Modelling and Numerical Simulation of Ductile Damage in Bulk Metal Forming

A complete set of fully coupled constitutive equations accounting for both combined isotropic and kinematic hardening as well as the ductile damage under anisothermal conditions at finite (visco)plastic strain is developed and implemented into the general purpose Finite Element code for metal forming simulation. First, the fully coupled anisotropic constitutive equations in the framework of Continuum Damage Mechanics are presented. Attention is paid to the strong coupling between the main thermomechanical fields as thermal effects, elasto‐viscoplasticity, mixed hardening, ductile isotropic damage and contact with friction. The associated numerical aspects concerning both the local integration of the coupled constitutive equations as well as the (global) equilibrium integration schemes are presented. The local integration is outlined thanks to the Newton iterative scheme applied to a reduced system of two differential equations. For the global resolution of the equilibrium problem, the classical dynamic explicit (DE) scheme with an adaptive time step control is used. A fully adaptive 2D methodology with mesh and loading sequences adaptation based on some appropriate error estimates is used. For 3D simulations only a constant appropriately refined 3D mesh is used. Various 2D and 3D examples are given in order to show the capability of the methodology to predict the ductile damage initiation and growth during metal forming processes.     

Numerical Simulation of Viscoplastic and Frictional Heating During Finite Deformation of Metal. Part I: Theory

This paper is concerned with the numerical simulation of hot metal forming, especially superplastic forming. In this first part, a complete thermo-viscoplastic formulation at finite strains is derived and a unified stress update algorithm for thermo-elastoplastic and thermo-elasto-viscoplastic constitutive equations is obtained. The resulting unified implicit algorithm is both efficient and very inexpensive. A staggered scheme is used for the global resolution of the thermomechanical problem. We will also describe the basis of our thermomechanical frictional contact model. Discussion of computational aspects and efficiencies will be assessed in the second part of this work.     

Process Modeling for Precision Forming of Discrete Parts – State of the Technology and Critical Issues

This paper presents an overview on the application of FE simulation as a virtual manufacturing tool in designing manufacturing processes for precision parts. The processes discussed include forging, sheet metal forming and hydroforming. Determination of reliable input parameters to simulate a process is a key element in successful application of process simulation for process design in all the mentioned areas. These issues are discussed in detail. Practical examples of application of FE simulation are presented for improvement of the existing metal forming process and/or designing new metal forming process for manufacturing discrete precision parts in forging, sheet metal forming and hydroforming.     

数值模拟在汽车板成形中的应用

在汽车和冶金工业中,板成形数值模拟广泛地应用于零件的选材和模具的设计.文章论述了板成形数值模拟的基本方法及其发挥的重要作用,并采用动力显式有限元软件DYNA3D对轿车顶板的冲压成形过程进行仿真计算,分析了成形安全裕度.