简介概要

复杂空心铝型材的挤压缺陷仿真分析及材料在分流模中的流动行为优化

来源期刊:中国有色金属学报(英文版)2018年第10期

论文作者:易杰 王震虎 刘志文 张见明 何芯

文章页码:2094 - 2101

关键词:空心铝型材;挤压缺陷;材料流速;阻流块;ALE算法

Key words:hollow aluminium profile; extrusion defect; metal flow velocity; baffle plate; ALE algorithm

摘    要:为了解决复杂空心铝型材在挤压试验中出现的截面内凹缺陷,基于Arbitrary Lagrangian-Eulerian (ALE)算法,利用HyperXtrude软件平台建立型材在多孔分流挤压模具挤压过程中的三维稳态有限元模型。定量分析型材挤压出口不同方向的金属流速及焊合室内不同高度的压力分布。为实现出模口型材横截面材料流速的均匀性,采用增加阻流块方法对模具结构进行优化。优化后进行挤压试验,型材底面Y方向的最大位移由1.1 mm减小到0.15 mm,内凹缺陷得到显著改善。研究方法为复杂空心铝型材分流模挤压缺陷的改善和材料流动行为的优化提供理论指导。

Abstract: 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.



详情信息展示

Trans. Nonferrous Met. Soc. China 28(2018) 2094-2101

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

Jie YI1,2, Zhen-hu WANG1, Zhi-wen LIU1,3, Jian-ming ZHANG1,2, Xin HE1

1. State Key Laboratory of Advanced Design and Manufacture for Vehicle Body, Hunan University, Changsha 410082, China;

2. School of Mechanical Engineering, Hunan Industry Polytechnic, Changsha 410208, China;

3. School of Mechanical Engineering, University of South China, Hengyang 421001, China

Received 12 March 2018; accepted 13 June 2018

Abstract: 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.

Key words: hollow aluminium profile; extrusion defect; metal flow velocity; baffle plate; ALE algorithm

1 Introduction

Aluminium alloys have lots of advantages and economic predominance in engineering because of their low density, high specific strength and specific stiffness, good collision energy absorption and recyclability [1,2], which are widely used in automobiles, rail transits, aerospace and construction. Extrusion is a highly efficient and low-energy-consumption process and is the main manufacturing procedure for hollow aluminium profiles. Thin-wall hollow aluminium profiles are usually extruded by the porthole dies [3]. Firstly, a billet is forced to flow through a splitter bridge and then split into multiple metal streams. Subsequently, the billet is allowed to flow into the welding chamber and welded each other under high temperature and pressure conditions. Finally, the billet is allowed to flow out of the die orifice between the die mandrel and the lower die to form hollow profiles of desired shape and size. The higher the design complexity of the profile section is, the more inhomogenous the extrusion deformation is, and the more difficult to control the metal velocity at the die exit is.

The porthole die plays a key role in aluminum hollow profile production, which directly affects the product quality and service life of porthole die [4,5]. If the metal flow velocity on the cross-section of extrudate at the die exit is nonuniform, the performance and quality of extruded profiles will be seriously affected. In the traditional trial-and-error design, extrusion die design is mainly based on the practice experience and expertise of die designers [6]. Usually, after a porthole die is manufactured, it will undergo several modifications and tests until an acceptable profile is obtained, which causes additional cost and waste of time. With the rapid development of numerical technology, many researchers have performed some simulation work on aluminum alloy extrusion to provide accurate and theoretical guidance for die design [7]. CHEN et al [8] revealed the material flow during multi-hole extrusion process for producing a hollow and thin-walled profile by means of numerical simulation based on the Arbitrary Lagrangian- Eulerian (ALE) algorithm. SUN et al [9] carried out the numerical simulation of extrusion process for a complex hollow magnesium doorframe using HyperXtrude software. BASTANI et al [10] performed a transient simulation of the aluminum extrusion process based on ALE algorithm in order to study how process parameters that influence flow balance and exit temperature. CHEN et al [11] carried out FE analysis on the extrusion process of a large hollow profile and modified the porthole die by reducing the area of porthole, adding baffle plate, and adjusting the length of bearing to obtain uniform velocity and temperature distributions of the extrudate. MAHMOODKHANI et al [12] investigated the influence of die feeder geometry on the formation of transverse weld using FE simulation.

In the present study, in order to solve the bottom concave defect of a complex hollow aluminum profile in the extrusion experiments, a 3D FE model for simulating the steady-state porthole die extrusion process was established based on HyperXtrude software using ALE algorithm. The velocity distribution on the cross-section of extrudate at die exit and pressure distribution in the welding chamber were quantitatively analyzed. The porthole die structure was optimized by adding baffle plates to obtain uniform metal flow velocity at the die exit. The research method and results are helpful to improve the extrusion defects of complex hollow aluminum profiles and optimize the porthole die structure.

2 Defects in initial extrusion experiment

The research object of this study is a complex hollow profile of 6063 aluminium alloy produced by an extrusion factory. Figure 1 shows the geometrical dimensions of the profile. The wall thickness of profile was 1-3 mm, the length and width dimensions were 107.46 and 62.62 mm, respectively. In actual extrusion experiments of the profiles, the bottom edge B of profile presents an inward depression that generates a small gap with the ruler, which is circled in red in Fig. 2. This defect is undetected with eye observation, but a noticeable depression can be observed when touching bottom edge B. As the reference, palpable depression is unnoticeable at position C.

3 Establishment of 3D FE model for porthole die extrusion

3.1 Geometry and FE modelling

Unigraphics NX software was used to establish the geometric model of the initial die design, extract the region boundary of metal flow through the container, portholes and welding chamber. Then, the model with Step format was imported into the HyperXtrude software for preprocessing. The geometrical model was divided into five parts: billet, porthole, welding chamber, die bearing and free surface. The basic principle of mesh generation was from small to large to ensure continuity of different parts of the extruded workpiece. The division order was as follows: die bearing, free surface, welding chamber, porthole and billet. To improve the accuracy and efficiency of FE simulations, the free surface length of extruded profile was set to be three times the length of die bearing, whereas the billet length is two times of the inner diameter of container. The pentahedron mesh was used in the components of profile and die bearing, while tetrahedron mesh was adopted in the billet, portholes and welding chamber. Die bearing was required to secure at least four free nodes in the thin area of the section. The mesh size was not larger than 1/5 of the size in the thinnest position, and mesh width should not be greater than 3 mm. Other parts were based on the mesh size of the die bearing. The mesh size of the welding chamber was 2.5 times of the die bearing, the mesh size of the portholes was three times of the welding chamber, and the mesh size of the billet was three times of the portholes. After mesh division, continuity between different mesh parts and their quality was checked. The ideal mesh quality must satisfy the following basic conditions: (1) minimum unit size >0.1 mm; (2) minimum unit angle >15°, maximum angle <165°; (3) length/width ratio of the unit: tetrahedron <8, triangular prism <12; (4) Jacobian >0.7. Figure 3 shows the FE model for steady die extrusion process of the hollow profiles.

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