Numerical modelling of the material flow during extrusion of aluminium alloys and transverse weld formation

A comprehensive numerical model of the hot extrusion process for aluminium alloys has been developed and validated. Reflecting the complex thermomechanical changes effected in the alloys during extrusion, the model incorporated heat flow and plastic deformation during extrusion. This paper presents the overall numerical development of a hot extrusion process for AA3003 and validation of the numerical model, by comparison to industrial data. The plasticity module was developed using a commercial finite element package, DEFORM^®, a 2-D transient Lagrangian model which couples the thermal and deformation phenomena and is able to predict the temperature, strain rate and strain distribution in the billet/extrudate at any position in the container and die. A new algorithm using MATLAB was also developed so that details of the material flow and formation of the transverse weld and how it is affected by the feeder geometry could be quantified. Validation of the DEFORM model and the MATLAB algorithm of the material flow against industrial data indicated that it gave excellent predictions of the pressure and temperature history during extrusion as well as material flow effects such as surface cladding as one billet is fed in after another through the die. The results indicated that the die feeder design has a significant effect on the transverse weld formation with tapered dies showing lower transverse weld lengths compared to regular feeder plates.     

A stress ratio parameter for studying the workability of metals—Extrusion

The extrusion process has been simulated using the rigid-viscoplastic finite element analysis code ALPID 2.1. Various die geometries, billet materials, and ram speeds were included in the intrinsic workability studies. Conical dies, constant strain rate, and streamlined dies of different length with 9:1 as well as 4.4:1 reduction ratios were studied. Hypothetical materials with various strain rate sensitivities as well as aluminum 2024 and aluminum 1100 were used in the simulations. The rate of change of the square of the stress ratio (mean stress/effective stress) with respect to the log of strain rate as well as several other parameters were plotted for materials in the deformation region of the die. These plots are used to illustrate the stability of materials during the extrusion deformation process. Four different experimental process conditions were used with a streamline die to help confirm the results from the simulations.     

Investigation into the thermo-viscoplastic finite element analysis of square die extrusion of square section with Lagrangian description

An analysis of three-dimensional hot extrusion through landless square dies is carried out as a nonsteady-state problem. In the problem, difficulties arise from the severe distortion and die interference of elements at the aperture rim of the die, even with a small punch travel. Finite element simulation is impossible without intermittent remeshing procedures. To overcome these difficulties, an automatic remeshing technique is proposed by employing a modular conceptual mesh structure. In the analysis of temperature distribution, conduction, convection and radiation are considered in connection with a deformation analysis of a visco-plastic material. The effect of the mesh structure on the present scheme as well as material properties and temperatures associated with punch travel is discussed. As an example, an extrusion of a square section is simulated. In order to confirm the present scheme, experiments are carved out using aluminium at the elevated temperature.     

Finite element simulations of deformation behavior in equal channel angular pressing using a rotated die

A new die design for equal channel angular pressing (ECAP) of square cross-section billet was proposed by a 45 rotation of the inlet and outlet channels around the channel axes. ECAP utilizing the rotated and conventional dies was simulated in three dimensions using the finite element method. Conditions with different material properties and friction coefficients were studied. The billet deformation behavior was evaluated in terms of the spatial distribution of equivalent plastic strain, plastic deformation zone and load history. The results show that the rotated die appears to produce billets with a smaller deformation inhomogeneity over the entire crosssection and a greater average of equivalent plastic strain at the cost of a slightly larger working load. The billet deformation enters into a steady state earlier in the case of the rotated die than the conventional die under the condition of a relatively large friction coefficient.     

铝型材宽展挤压数值模拟及模具参数优化

在Deform-3D分析软件平台上,以卷帘门三扇门片为例,采用有限元法对铝型材宽展挤压过程进行了数值模拟,分析了铝型材宽展挤压金属流动过程及变形规律。通过对不同导流孔尺寸宽展挤压模拟结果进行对比分析,得出导流孔中段宽度L取值为19 mm时,金属流出模孔流速均匀,能够实现平稳挤压。根据数值模拟结果设计出的宽展模具能够顺利挤出合格的型材,说明有限元数值模拟能够为宽展模具设计提供有力的技术支持。     

A universal formulation for the extrusion of sections with no axis of symmetry

The subject of theoretical analysis for the extrusion of profiled sections has been heavily worked on by many researchers. However most of these have concentrated on the extrusion of sections with some axes of symmetry. This paper aims to provide a new formulation for the analysis of the extrusion process for non symmetric profiled sections with no axis of symmetry. The upper bound theorem has been used to obtain an approximate solution. Both flat faced dies and bilinear dies were used in the present work. In fact this formulation could be applied to the extrusion process of hollow sections as well as solid parts. The advantage of the proposed method is the new way of discretizing the deforming region in the extrusion of shaped sections based on which a generalized kinematically admissible velocity field was formulated. For a given extruded profiled section this method employs fewer number of sub-divisions than before, giving a lower upper bound value for the extrusion power. The generality, easy application to different sections, short computing time and fairly realistic outcomes of the analysis could be regarded as other strengths of the present method. The lack of incorporation of temperature effects for hot extrusion processes could be mentioned as one of the disadvantages of the present method. The position of the die cavity was also optimized using the new method. A design map for the extrusion die geometry was also given as a graph of extrusion pressure versus the optimum die length for the bilinear dies with different frictional conditions and reductions of area. The extrusion of L-shape profiled section was chosen as a sample since it had no axis of symmetry. Extrusion dies were also manufactured and experiments carried out to verify the theoretical results. Finite element simulation for the extrusion of U, T and I-shape profiled sections was also carried out using ABAQUS\CAE\Explicit commercial software.     

神经网络在模具型腔温升预测中的应用

挤压成形过程中由于坯料和模具之间的滑动接触摩擦和坯料的塑性变形产生热而使模具型腔表面温度升高,加剧模具的磨损。采用热力耦合有限元法计算挤压成形过程中模具型腔表面的温升,将模拟结果与人工神经网络相结合,以有限元模拟结果作为学习样本,训练BP神经网络模型,以此模型预测模具型腔表面的温升。根据预测结果分析了挤压锥角、挤压速度和摩擦系数对型腔温升的影响,为进一步建立挤压成形过程中模具型腔表面的温升模型和磨损预测模型奠定了基础。     

Investigation on Effects of Die Orifice Layout on Three-Hole Porthole Extrusion of Aluminum Alloy 6063 Tubes

Currently, with the increasing demand of high production output, much attention is paid to the research and development of multi-hole extrusion die. However, owing to the complexity of multi-hole porthole extrusion technology, it has not been applied widely in practice for the production of aluminum profiles, especially for porthole die with an odd number of die orifices. The purpose of this study is to design a three-hole porthole die for producing an aluminum tube and to optimize the location of die orifices based on computer-aided design and engineering. First, three-hole extrusion dies for different locations of die orifices are designed. Then, extrusion processes with different multi-hole porthole dies are simulated by means of HyperXtrude. Through numerical simulation, metal flow, temperature distribution, welding pressure, extrusion load, and die stress, etc. could be obtained, and the effects of the location of die orifices on extrusion process are investigated. With the increasing distance between die orifice and extrusion center (described as eccentricity ratio), metal flow becomes nonhomogeneous, and twisting or bending deformation of profile occurs, but the welding pressure rises, which improves the welding quality of profiles. However, the required extrusion force, billet and die temperature, die displacement, and stress induce no significant changes. In comparison with the extrusion force during single-hole porthole extrusion, there is 18.5% decrease of extrusion force during three-hole porthole extrusion. Finally, design rules for this kind of multi-hole extrusion dies are summarized.     

楔横轧梯形螺纹轴成形模设计与轧制工艺

介绍了一种楔横轧轧制梯形螺纹轴的模具设计方法,模具由预坯段和螺纹段组成。预坯段由起楔段、展宽段和圆弧精整段组成。螺纹段模具孔型以模具齿顶宽不变和侧壁张角不变为条件,通过楔横轧上、下模对滚,模具齿形根据咬入和挤出工件材料体积相等理论设计。通过DEFORM-3D有限元软件模拟验证轧件质量,验证了模具进行螺纹轴轧制的可行性,该模具设计方法为楔横轧螺旋轴类件轧制技术研究提供理论依据和参考。     

Extrusion through controlled strain rate dies

The workability of a material during deformation processing is determined by (a) the die geometry which, in turn, determines the flow field during deformation, and, (b) the inherent workability of the material under the imposed processing conditions of strain rate and temperature. Most common alloys have good inherent workability and can be successfully formed over wide ranges of temperature and strain rate. Products can be successfully formed from these alloys even with dies which impose large variations in strain rate during deformation. However, many of the new alloys and composites can be deformed only in very narrow processing regimes, and control of the strain rate during deformation of such materials becomes important. For example, extrusion of a whisker-reinforced aluminum alloy composite is possible only when the strain rate is controlled to within one order of magnitude. This paper describes the development of a method for obtaining preliminary shapes of controlled strain rate extrusion dies, a special case being the constant strain rate die. The theoretical basis for such die design processes is presented, followed by some examples of die geometries. Since this design procedure ignores the material flow properties, the designed die shapes must be verified using the finite element method or physical modeling. Results of simulations with the program ALPID are also presented.     

热锻成形过程数值模拟与多目标设计优化技术研究

提出了一种基于有限元分析和序列二次规划的热锻成形工艺多目标优化方法,优化目标包含锻件的内部损伤值和变形均匀性两个方面。用锻件所有单元的最大损伤值作为衡量锻件变形损伤的指标,用锻件所有单元体的等效应变与整个终锻件的平均等效应变的均方差,作为锻件变形均匀性的指标,构造了多目标优化问题的评价函数。在设计过程中,优化变形工艺参数使得工件内部损伤值最小,同时工件内部变形均匀。以零件毛坯的初始高径比为设计变量,建立了热锻成形过程多目标优化设计的数学模型。应用该方法对齿轮齿圈毛坯非等温热锻成形工艺参数进行优化,取得了良好的效果。     

亚热精密成形过程模具磨损的数值模拟研究

采用数值模拟技术分析了亚热挤压成形阶段坯料及模具上的参量变化。基于修正的磨损模型,将其引入到有限元数值模拟软件中,对亚热挤压过程中模具磨损量的变化情况进行了分析,得到了不同变形阶段的瞬时磨损曲线及一次成形结束时的综合磨损曲线。利用研究结果对模具的磨损寿命进行了预测,与实际情况对比,两者吻合较好。     

A APPLICATION OF ANSYS ON A SECTION EXTRUSION DIE

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Damage prediction for magnesium matrix composites formed by liquid-solid extrusion process based on finite element simulation

A damage prediction method based on FE simulation was proposed to predict the occurrence of hot shortness cracks and surface cracks in liquid-solid extrusion process. This method integrated the critical temperature criterion and Cockcroft &; Latham ductile damage model, which were used to predict the initiation of hot shortness cracks and surface cracks of products, respectively. A coupling simulation of deformation with heat transfer as well as ductile damage was carried out to investigate the effect of extrusion temperature and extrusion speed on the damage behavior of C_sf/AZ91D composites. It is concluded that the semisolid zone moves gradually toward deformation zone with the punch descending. The amplitude of the temperature rise at the exit of die from the initial billet temperature increases with the increase of extrusion speed during steady-state extrusion at a given punch displacement. In order to prevent the surface temperature of products beyond the incipient melting temperature of composites, the critical extrusion speed is decreased with the increase of extrusion temperature, otherwise the hot shortness cracks will occur. The maximum damage values increase with increasing extrusion speed or extrusion temperature. Theoretical results obtained by the Deform?-2D simulation agree well with the experiments.     

Comparison of extrusion strains produced by cosine and conical dies

Visioplastic analysis is used to compare strain fields produced in cylindrical aluminum billets extruded at elevated temperature through axially symmetric dies that have either a cosine or a conical profile. The visioplastic method consists of computing strain rates from changes experienced in a flow function as a billet passes through the extrusion die. The flow function is constructed using a grid that is stamped on an axial plane of the billet before extrusion. After the partially extruded billet is removed from the die numerical methods are used to determine the strain rates from the deformed grid. The state of strain over the extrusion region is computed using transformation and then integration of the strain rates. Results show that, unlike the conical die, the cosine die does not produce strains of reversed sign in the die entry region. The consequent benefits of using cosine dies for extrusion of powder metals are discussed.     

Identifying the dominant failure mode in the hot extrusion tooling used to forge nickel based superalloy

The dies used in the extrusion of nickel based super alloys are subject to severe mechanical and thermal stresses, resulting in shortened life and high manufacturing costs. It is necessary to understand the dominant damage mode in order to guide improvements for increased tool life. The operation under examination consists of the hot extrusion of a nickel based superalloy using nitrided hot work tool steel, glassed workpieces and graphite lubrication. The investigation was conducted through a combination of metallurgical analysis, metrology and finite element analysis. Out of the damage modes observed under these conditions, the plastic deformation of the substrate was found to be the cause for tool failure. This paper discusses the relationship between plastic deformation of the substrate and the formation of scoring marks, which fail the die.     

有限体积数值模拟技术在型材挤压变形规律研究中的运用

对基于欧拉描述的金属成形有限体积数值模拟技术进行了概括，通过6063铝合金坯料在挤压模具中变形的过程模拟，分别得到不同时刻的、与实际情况接近的材料变形的速度场、温度场等；该模拟结果反映了挤压时金属的实际变形规律，这表明有限体积数值模拟技术适合解决如挤压这种大变形的三维模拟问题。     

FEA technique of hot plate forming process using cell-typed die with cooling device

Hot plate forming using a cell-typed die is a process for forming a large thick plate with a spherical shape for the manufacture of a large spherical LNG tank.Cell-typed upper and lower dies made of a framework of steel plates fitted to make a grid pattern are used in this process,and an air-cooling device is separately installed inside the lower die.A finite element analysis (FEA) technique was developed,which included hot forming,air flow,cooling and thermal deformation analysis for the hot plate forming process using the cell-typed die.Further,the convective and interface heat transfer coefficients were used to reproduce analytically the effects of the cooling device in the hot plate forming analysis.A small-scale model test of the process was conducted to verify the FEA technique.The analysis results show that the curvature of the final plate agrees well with that of the designed experiment within a maximum relative error of 0.03% at the corner of the plate.     

腹板换热系数对H型钢冷却后变形的影响

针对H型钢易出现上下翼缘内并外扩变形及腹板波浪、裂纹等缺陷的问题,通过H型钢的冷却实验和有限元模拟计算,分析了H型钢冷却后的表面温度场和不均匀变形的规律,研究了上下腹板部位的换热系数对温度场、等效应力场以及变形情况的影响,结果表明冷却后H型钢上下翼缘出现了“内并外扩”现象。运用ABAQUS有限元分析软件建立了二维H型钢冷却模型,通过实验获得了H型钢表面换热系数,并以此作为模拟的边界条件进行有限元模拟分析,得到了H型钢表面温度场;有限元模拟结果同样出现了H型钢上下翼缘“内并外扩”现象,与实验结果相吻合;改变上下腹板部位的换热系数进行有限元模拟,得到了腹板处换热系数对H型钢变形的影响规律,为控制H型钢冷却变形提供了理论基础。     

方圆坯连铸结晶器传热分析及温度场仿真研究

连铸结晶器的工作物理环境极其复杂,其温度场难以确定和分析。本文依据经典传热理论,探讨分析了结晶器的传热现象,建立了描述结晶器温度场的数学和物理模型,并根据实际工况确定了相关参数,对方坯结晶器和圆坯结晶器两种不同简化模型进行了温度场有限元仿真分析,其结果可为结晶器的结构设计和监控提供理论依据和参考数据。