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.     

FE analysis of extrusion defect and optimization of metal flow in porthole die for complex hollow aluminium profile

To solve the defects of bottom concave appearing in the extrusion experiments of complex hollow aluminium profiles, a 3D finite element model for simulating steady-state porthole die extrusion process was established based on HyperXtrude software using Arbitrary Lagrangian–Eulerian (ALE) algorithm. The velocity distribution on the cross-section of the extrudate at the die exit and pressure distribution at different heights in the welding chamber were quantitatively analyzed. To obtain an uniformity of metal flow velocity at the die exit, the porthole die structure was optimized by adding baffle plates. After optimization, maximum displacement in the Y direction at the bottom of profile decreases from 1.1 to 0.15 mm, and the concave defects are remarkably improved. The research method provides an effective guidance for improving extrusion defects and optimizing the metal flow of complex hollow aluminium profiles during porthole die extrusion.     

螺塞复合挤压的材料分配规律研究

针对螺塞零件复合挤压时的材料分配规律进行研究,推导出圆杯正六边形杆复合挤压的材料分配公式,提出材料分流层的形状是旋转抛物面。应用Deform软件对螺塞零件的挤压成形进行数值模拟,得到成形应力图和挤压力行程曲线,研究发现,螺塞的成形过程实际上分为2个阶段:复合挤压和反挤压。最终进行产品试制,试验结果表明:正反挤两个出口高度的实际数值和理论值吻合较好。     

The origin of weld seam defects related to metal flow in the hot extrusion of aluminium alloys EN AW-6060 and EN AW-6082

Longitudinal weld seams are an intrinsic feature in hollow extrusions produced with porthole dies. As these joins occur along the entire extruded length, it is desirable that these weld seams have a minimal impact on the structural integrity of the extrudate. In particular, defects associated with weld seam formation should be avoided. In this research, the occurrence of defects related to material flow inside the extrusion tooling is studied. In lab-scale experiments, EN AW-6060 and EN AW-6082 aluminium alloy billets are formed into strips by means of the direct hot extrusion process. By utilising model dies with an internal obstruction similar to the supports present in porthole dies, a strip with a central longitudinal weld seam is formed. The effects of different geometries of the weld-chamber and the processing conditions on the quality of the weld seam are investigated. Characterisation is performed through mechanical testing, focusing on the ability of the weld seam area to accommodate plastic deformation, and microstructural analysis provides insight into the defects related to unsound metal flow. Through computer simulations, conditions related to weld seam formation are modelled and correlated with the experimental results. The experimental results demonstrate that metal flow controlled by the die geometry causes defects leading to inferior mechanical performance of the extrudate. It is further argued that current weld seam formation criteria utilised in finite element modelling need enhancement to incorporate these flow related defects.     

Optimisation of flow balance and isothermal extrusion of aluminium using finite-element simulations

There is significant demand to reduce variations in the shape and mechanical properties of the aluminium extrusion process to meet tighter tolerance requirements. To reduce variations, the flow and temperature evolution in the container and die must be controlled. To study how the process parameters influence the temperature evolution and the material flow, the effects of ram speed, initial temperature distribution in the billet and container cooling rate have been studied. This work is divided into three parts which examine the different aspects of the extrusion process. (1) To minimize the radial variations of temperature and velocity fields over multiple press cycles. (2) To obtain isothermal extrusion of aluminium. (3) To understand and formulate the effect of an undesired lateral temperature gradient in the billet on the exit velocity of the aluminium sections. In each part, the effect of different process parameters on the flow balance and temperature evolution of the extruded sections is shown and discussed.     

Microstructure and flow behaviour during backward extrusion of semi-solid 7075 aluminium alloy

The microstructure and flow behaviour during thixo backward extrusion of 7075 aluminium alloy were investigated. Reheating the steel die and the aluminium billet placed into the die at the same time using an induction furnace provides rapidly a very homogeneous microstructure suitable for thixoforming. During thixoextrusion, despite the high solid fraction, the solid globules are weakly connected and slide over each other without any plastic deformation. The flow remains quasi homogeneous resulting in homogeneous induced microstructure of the component.     

径向挤压的金属流动分析

以十字轴的径向挤压为例，较为详细地论述了径向挤压的流动规律，这些流动规律为径向挤压件工艺方案的制定和径向挤压件的有限元分析提供了实验依据。     

热反挤压过程中金属不稳定流动状态的研究

利用有限元软件Deform-3D对厚壁钢管热反挤压制坯过程进行数值模拟,分析了摩擦系数和壁厚对金属流动状态的影响.结果表明:反挤压件管壁内侧的金属在向上平移的同时还伴有径向移动,摩擦系数越大、管壁越厚,径向移动的程度越大,越容易造成凸模抱模的现象.根据模拟结果,提出了一种新增径向塑性变形区的大型厚壁钢管热反挤制坯的变形...     

复杂盒形零件成形金属流动控制研究

用挤压工艺代替冲压、机加工等生产盒形件，是一种很有发展前途的工艺方案。复杂盒形件的挤压不同于规则盒形件的成形，本文从复杂盒形件挤压的金属流动特点入手，提出了挤压模的具有方向性的止流槽。同时对该零件的变形过程进行了实验研究，验证了止流槽控制金属流动的可行性，为同类型零件的成形提供了借鉴。     

型材挤压过程金属变形流动的有限元仿真

采用大变形弹塑性有限元理论,对典型型材角铝零件的挤压成形过程进行了全面有限元仿真和分析。深入研究了了型材挤压变形过程中金属变形流动规律和力学特征,对挤压工艺参数合理选择和优化奠定了基础。     

Control of material flow in a combined backward can - forward rod extrusion

The paper deals with an analysis of an extrusion process with a divided material flow. As we are forced to seek for optimal technological solutions with short testing times and low risks and costs, a reliable process evaluation is of the greatest importance.

The paper discusses the influences of tool geometry, friction and lubrication as well as workpiece properties on balanced material flow in a combined extrusion process. The FEM analysis applying the DEFORM code has been used in order to predict the process parameters and to estimate its stability. The subsequent experimental verification has resulted in a conclusion that modern computer aided tools, tuned by proper experimental sets, can be used for fast and reliable cold metal forging process planning.     

Application of auger electron spectroscopy and inert metal marker techniques to determine metal and oxygen transport in oxide films on metals

Auger electron spectroscopy in combination with depth profiling by Ar ion sputtering was employed as a surface analytical technique to determine the positions of thin (3–5 nm) inert Pd markers during growth of oxide films on Al, Ni, and -NiAl. Alumina films 35 and 120 nm thick formed on Al and -NiAl, respectively, grew by inward diffusion of oxygen. Metal migration accounted predominantly for the growth of a NiO film 150 nm thick on the (111) crystal face of Ni. However, an assessment could not be made with respect to oxygen diffusion, if any, in this film due to the limitations imposed on precise depth profiling of the marker position caused by uneven sputtering of the oxide and metal phases.     

金属三维挤压成形过程数值模拟的若干关键技术

推导了采用六面体等参单元网格划分的金属三维挤压成形过程数值模拟中的摩擦力功率泛函在局部坐标系的一阶和二阶偏导数的表达式 ,提出了有效的三维六面体网格划分和网格质量控制技术处理方法。以此为基础 ,建立了三维刚塑性有限元数值模拟系统和六面体网格再划分系统。方坯料反向挤压过程数值模拟的结果与实验非常吻合 ,验证了所推导的公式和开发的系统 ;圆坯料侧向挤压过程的模拟验证了提出的网格质量控制技术的第三种方法。     

Tribological measures for controlling material flow in sheet-bulk metal forming

Sheet-bulk metal forming (SBMF) is characterized by successive and/or simultaneous occurrence of quite different load conditions regarding stress and strain states. These conditions significantly influence the material flow and thus the geometrical accuracy of the components. To improve the product quality a control of the material flow is required. An appropriate approach is given by locally adapted tribological conditions due to surface modifications of tool and workpiece, so-called tailored surfaces. Within the present study different methods to adapt the surfaces are presented and investigated with respect to their tribological effectiveness in SBMF. In a first step, requirements regarding necessary adaptions of the friction values for two SBMF processes are numerically defined. Based on the requirements different tailored surfaces are presented and analyzed regarding their tribological influence. Finally, the potential of surface modifications to improve SBMF processes is shown.     

Raising productivity of aluminium extrusion with nitrogen

Abstract

Nitrogen has been used for cooling and/or inerting aluminium extrusion dies for more than 35 years. Although it has not been widely investigated, the process is reported to improve quality and extrusion speed. Several techniques exist to apply the process in practice. Some of these techniques inert only the die exit. Others additionally use liquid nitrogen to cool the die and the exiting product simultaneously, and it is results from these techniques that are reported in the present paper. Although the gains to be made are very dependent on the profile being extruded and the design of the die set, the use of these techniques significantly improves all the measured parameters. In some cases increases in extrusion speed of over 100% are reported and in one case die life increased by 200%. Several methods of introducing the liquid nitrogen are described. Results are presented for each and the advantages of each technique are discussed. It is shown that liquid nitrogen injection via the bolster is particularly efficient when long runs can be extruded and when the peripheral conditions such as the section shapes, dimensional stability, die design and the plant as a whole, permit the extrusion speed to be increased substantially.     

Diode laser brazing of aluminium alloy to steels with aluminium filler metal

Abstract

Diode laser brazing of aluminium alloy (A5052) to interstitial free steel (IF steel) or type 304 stainless steel (SUS304) was conducted using aluminium filler metal (BA4047) with Nocolock flux. The processing parameters of laser power, wire feed rate and travel speed were varied. The strength of lap joints of A5052 on steels was evaluated by tensile shear test. The joint strength of A5052/steels was increased with increasing laser power and reached the maximum strength, more than approximately 80% of the A5052 base metal strength, at a laser power of 1300 W. Voids and incomplete penetration of filler metal were observed at the A5052/braze layer interface when the laser power was below 1100 W. The Fe–Al intermetallic compounds were formed at the steel/braze layer interfaces and grew drastically when the laser power exceeded 1300 W. Superior brazability of A5052/steels was found at brazing conditions corresponding to a temperature of filler metal droplet of 1050–1250 K.     

基于金属流线分析的三柱槽壳温挤件工艺优化

挤压件体积成形过程中,金属流线对其使用性能影响很大。针对三柱槽壳温挤件金属流线不佳现象,分析了流线的形成过程,研究了正挤工艺、反挤凸模形状和尺寸、摩擦力和挤压速度对金属流线的影响规律。据此提出改善流线结构的方案,并进行实验验证。结果表明:相对于平底和梯形反挤冲头,三角冲头结构对金属流线的引导作用更佳,且在保证沟道尺寸的前提下,三角冲头底面倾斜角、引流圆锥凸台顶角圆弧半径和底面直径越大越好;正挤凹模锥角取60°~90°最为合理;摩擦力对金属流线影响较大,摩擦力越大,金属流线越差;挤压速度对金属流线的影响不大。     

Kinematics of metal flow during twist extrusion investigated with a new experimental method

We propose an experimental method for investigating the kinematics of metal flow in twist extrusion (TE). The method is based on a theoretical model of the velocity field. The parameters of this model are determined to satisfy the observed flow-line for characteristic points of the specimen. The model incorporates two physical constraints: (1) metal flow is limited by the surface of the die; (2) metal volume remains constant. The advantage of this method is that it takes into account the actual rheology of the metal and friction conditions.We show that TE forms a vortex-like flow that stretches metal particles. The stretching increases with subsequent TE passes. The equivalent strain increases from 0.3 to 0.5 in the paraxial zone of the specimen to 2.0–2.5 at the periphery.We analyze different sources of inaccuracy of the method and show that its error in estimating the equivalent strain is of the order of 0.1, which is perfectly acceptable when investigating severe plastic deformations.     

Influence of punch geometries on the divided material flow in a double cup extrusion process

This paper provides an analysis of the deformation patterns in a backward can extrusion combined simultaneously with a forward can extrusion process, which is known as a double cup extrusion process. The main objective of this study is to examine the divided material flow characteristics in DCEP. Analyses were conducted in a numerical manner by employing a rigid-plastic finite element method. Among many process parameters, the major design factors chosen for analysis include the reduction in area (RAB), the wall thickness ratio (TR), the punch nose radius (R), and the friction condition. The simulation results were summarized in terms of relationships between the process parameters and the ratios of extruded length and volume, and between the process parameters and force requirements, respectively. Comparisons between a multi-stage forming process in sequential operations and one-stage combined operation were also made in terms of the forming load and pressure exerted on the tool. The force requirement and self-regulating characteristics were more greatly influenced by the wall thickness ratio among the selected major design factors. And more severe load to form the same shape is expected in sequential operations than in a combined extrusion process.     

阻流阴极铝电解槽流场数值模拟研究

运用商业流体计算软件ANSYS CFX,研究了阻流阴极铝电解槽熔体流场分布,分析了阻流阴极能够提高电解槽磁流体稳定性、降低极距的原因.数值模拟结果表明,阻流阴极电解槽铝液平均流速较传统电解槽降低了60%,电解质平均流速降低了40%;两相稳态界面向上隆起量和向下凹陷量之间的差值减小1cm,界面变形趋于平缓.