Significance-based optimization of processing parameters for thin-walled aluminum alloy tube NC bending with small bending radius

Thin-walled aluminum alloy tube numerical control （NC） bending with small bending radius is a complex process with multi-factor coupling effects and multi-die constraints. A significance-based optimization method of the parameters was proposed based on the finite element （FE） simulation, and the significance analysis of the processing parameters on the forming quality in terms of the maximum wall thinning ratio and the maximum cross section distortion degree was implemented using the fractional factorial design. The optimum value of the significant parameter, the clearance between the tube and the wiper die, was obtained, and the values of the other parameters, including the friction coefficients and the clearances between the tube and the dies, the mandrel extension length and the boost velocity were estimated. The results are applied to aluminum alloy tube NC bending d50 mm×1 mm×75 mm and d70 mm×1.5 mm×105 mm （initial tube outside diameter D0 × initial tube wall thickness t0 × bending radius R）, and qualified tubes are produced.

Cross-sectional distortion behaviors of thin-walled rectangular tube in rotary-draw bending process

The cross-sectional distortion usually appears during rotary-draw bending process of thin-walled rectangular tube with small bending radius.To study the cross-sectional distortion of the tube,a three-dimensional finite-element model of the process was developed based on ABAQUS/Explicit code and its reliability was validated by experiment.Then,the cross-sectional distortion behaviors of the tube were investigated.The results show that a zone of larger circumferential stress appears on the tube when bending angle reaches 30°.And in the larger circumferential stress zone,the sagging phenomenon is produced obviously.The maximum cross-sectional distortion is located in the larger circumferential stress zone and the angle between the plane of maximum cross-sectional distortion and the bending reference plane is about 50°.The position of the maximum cross-sectional distortion keeps almost unchanged with the variation of the clearances between dies and tube.

Experimental and numerical assessment of energy absorption capacity of thin-walled Al 5083 tube produced by PTCAP process

The energy absorption capacity of the Al5083 thin-walled tube produced by parallel tubular angular pressing(PTCAP) process was evaluated. Also, microstructure, mechanical properties, and anisotropy coefficients were studied in the peripheral and axial directions. Results showed that values of energy absorption decreased with processing pass increasing and the values for the unprocessed, first and second passes were obtained to be 167, 161.4 and 160.7 J, respectively. The differences between the simulation results for the energy absorption values and their experimental values for the unprocessed, the first and the second PTCAP passes samples are about 5%, 10%, and 13%, respectively. The energy absorption capacity was related to the anisotropy coefficient and microstructure. The results demonstrated that grain refinement occurred and ultimate tensile strength(UTS) and microhardness after the first and second PTCAP passes were enhanced, while the increase rate in the first pass was much severer. Also, by applying PTCAP, the deformation modes were altered, such that the deformation mode of the annealed tube was quite symmetrical and circular while for the first and second passes there have been triple and double lobes diamond. The results of the numerical simulation for the deformation mode of the annealed and PTCAPed tubes were consistent with the experimental results. The deformation mode of tubes is dependent on their mechanical properties and variation of the mechanical properties during PTCAP process.

6063-O铝合金Y型形管接头电磁成形

基于逆向识别结合平板电磁翻边实验建立6063-O铝合金的Johnson-Cook本构和失效判据,对比分析Y型管分离工序电磁翻边与电磁冲孔翻边复合成形两种方式下的电磁力分布、成形过程及变形特征,表明复合成形能成形出更高的支管并提高成形效率,更为有效地改善壁厚周向分布。在此基础上,进行电磁冲孔翻边复合成形实验,获得成形质量良好的Y型接头,探讨放电电压及管坯厚度对支管成形高度、端部壁厚以及贴模间隙的影响,分析成形支管轴向壁厚分布特征与典型缺陷。

Forming limits under multi-index constraints in NC bending of aluminum alloy thin-walled tubes with large diameters

With increasing diameters of aluminum alloy thin-walled tubes (AATTs), the tube forming limits, i.e. the minimum bending factors, and their predictions under multi-index constraints including wrinkling, thinning and flattening have been being a key problem to be urgently solved for improving tube forming potential in numerical control (NC) bending processes of AATTs with large diameters. Thus in this paper, a search algorithm of the forming limits is put forward based on a 3D elastic-plastic finite element (FE) model and a wrinkling energy prediction model for the bending processes under axial compression loading (ACL) or not. This algorithm enables to be considered the effects of process parameter combinations including die, friction parameters on the multi-indices. Based on this algorithm, the forming limits of the different size tubes are obtained, and the roles of the process parameter combinations in enabling the limit bending processes are also revealed. The followings are found: the first, within the appropriate ranges of friction and clearances between the different dies and the tubes enabling the bending processes with smaller bending factors, the ACL enables the tube limit bending processes after a decrease of the mandrel ball thickness and diameters; then, without considering the effects of the tube geometry sizes on the tube constitutive equations, the forming limits will be decided by the limit thinning values for the tubes with diameters smaller than 80 mm, while the wrinkling for the tubes with diameters no less than 80 mm. The forming limits obtained from this algorithm are smaller than the analytical results, and reduced by 57.39%; the last, the roles of the process parameter combinations in enabling the limit bending processes are verified by experimental results.

阻碍角对6063铝合金空心型材“T字位”表面凹痕缺陷的影响

在空心铝型材挤压生产中,型材“T字位”表面常常出现凹痕,导致型材报废。对此,利用Q-Form对6063铝合金空心型材的挤压过程进行数值模拟,获得了型材“T字位”区域的金属流速分布,在此基础上,通过优化模具结构,在型材左右悬臂位置增设一微小阻碍角,使型材“T字位”局部区域金属流速平衡。试模结果表明:型材表面凹痕消失,符合生产要求。

6063铝合金轧制翅片管用铝管工艺研究

采用6063热挤压铝管轧制翅片管,对6063铝管组织、性能指标进行分析,确定化学成分和挤压工艺,合理控制Mg与Si之比,使Mg过剩,最大限度提高铝管的塑性,达到轧制翅片管翅片高度及表面质量要求。

Geometry-dependent springback behaviors of thin-walled tube upon cold bending

As one kind of key lightweight components with enormous quantities and diversities, the bent tubular parts have attracted in- creasing applications in aerospace, automobile, etc. Thus, how the inevitable springback behaves under different bending specifications should be fully addressed to efficiently achieve the precision forming of various bent tubes. Taking the medium strength thin-walled 6061-T4 Al-alloy tube as the objective, via the deformation theory of plasticity, explicit/implicit FE method and experimental approaches, we explored and clarified the nonlinear springback rules of the tubes and corresponding mechanisms in universal rotary draw bending regarding angular springback and radius growth by deliberately changing the tube diameter D and wall thickness t. The geometry dependent springback behaviors of thin-walled tube upon cold bending are thus revealed: 1) With the increasing of D, the tangent tensile strain increases and the proportional coefficient decreases, which causes the angular springback to decrease, while the radius springback increases due to the larger bending radius. 2) With the increasing of t, the tangent tensile strain decreases and the proportional coefficient increases, resulting in the increase of both angular springback and radius springback. 3) Under the same D/t, the angular springback varies little, while the radius springback increases with the larger diameter D. 4) The D/t can be used as a reasonable nondimensional index to evaluate the springback angle; as to the radius growth, the individual effects of the D and t should be considered. 5) The verification of the above results was conducted by experiments and analytical analysis.

铝管材挤压过程中的偏心问题

用空心铸锭挤压铝合金管材时的偏心缺陷是管材的主要缺陷之一。本文研究了影响管材偏心的主要因素,提出了减小管材偏心的一些措施。

空心铸锭壁厚不均对挤压管材偏心的影响

研究了挤压铝合金管材时空心铸锭的壁厚不均对挤出管材头部偏心的影响。指出把铸锭壁较厚的一边朝上、壁薄一边朝下装入挤压筒中,有利于减小挤压管材的头部偏心,偏心部位延伸的长度也较短;反之,则会使偏心程度更加严重。

双杆连续挤压铝管模具结构对成形性能的影响

双杆连续挤压铝管是一种高效率的铝管材制造技术,为保证金属流动均匀性,需要加入汇合模具,而汇合模具结构是影响金属成形的重要因素。根据连续挤压技术成形特点,基于HyperXtrude软件建立双杆连续挤压有限元模拟模型。通过对铝管材连续挤压稳态的数值模拟,对比分析不同汇合模具结构方案的金属流动规律。在LLJ350连续挤压机上进行6063铝合金管材挤压实验,对比观察产品的显微组织及力学性能。结果表明,双杆连续挤压中汇合区域的出口直径对金属流动的均匀性有重要影响,当该出口直径小于3个分流孔的外围直径时,模口处的金属流速更加一致,壁厚更加均匀,塑性明显提高。出口直径的变化对产品的晶粒组织和抗拉强度影响不大。

薄壁矩形管铝型材分流挤压过程挤压力影响研究

以6063铝合金薄壁矩形管为研究对象,首先应用Deform-3D模拟软件分析成形过程中的材料流动与挤压力的变化规律及原因;其次,基于正交试验研究不同工艺参数对挤压力的影响及显著性。结果表明:挤压初期材料处于镦粗和填充状态,挤压力显著上升,而当材料经分流孔进入焊合室后被焊合,分流金属接触到焊合室底部后在焊合室内不断聚集并横向移动,导致挤压力急剧增大;挤压力随坯料温度与模具温度的升高而降低,随挤压速度的增加而增大。最后,基于优选的因素水平,模拟获得了较低的挤压力,将该值与基于主应力法获取的理论最大挤压力进行对比,模拟值与理论值的误差为5.6%。研究成果可为铝型材多孔分流挤压的省力成形和提高模具寿命提供依据。

铝合金管材侧壁增厚成形极限与失稳研究

薄壁管材在增厚变形时容易向外鼓凸并导致折叠缺陷,因此,起皱失稳是主要的成形缺陷。提出了侧壁内、外增厚成形工艺,分别对管材的内(外)表面进行模具限制,使管材侧壁向外(内)增厚成形。通过有限元数值模拟与实验相结合的方法,对两者的成形稳定性进行对比分析,探究侧壁增厚时产生失稳现象的原因,并研究在两种增厚成形方法下,管材的侧壁增厚规律及成形极限。结果表明:与外增厚及传统镦粗成形工艺相比,侧壁内增厚时成形稳定性明显提高。通过对增厚过程进行追踪,可以发现,侧壁的失稳现象与侧壁的增厚方向以及轴向应力分布有关。通过有限元数值模拟及理论分析,得到了侧壁内增厚成形的无失稳条件,内增厚成形的增厚极限受高度的影响小,受高径比的影响大。

钩织烧结多孔管与铝合金薄壁管复合结构的轴向冲击吸能特性

以超细软304不锈钢丝绳为基材,采用短针环形钩织和真空固相烧结的方法制备一种新型多孔管,研究了该多孔管的轴向冲击吸能特性。将多孔管（C）与6063铝合金空心薄壁管（T）复合制备了两种不同复合形式的复合管——外复合管（TC）、薄壁芯复合管（CTC）。对复合管结构及相应的铝合金空心薄壁管进行了轴向冲击吸能性能对比研究。结果表明：新型钩织多孔管具有优良的吸能特性,是良好的吸能结构组件。复合结构的能量吸收（EA）、初始峰值冲击载荷（PCF）和平均冲击载荷（MCF）均大于相应空心薄壁管。复合结构的变形模式受多孔管与空心薄壁管复合效应影响而发生变化。两种复合管中,薄壁芯复合管（CTC）的载荷效率（CFE）最大,并且高于相应的空心薄壁管,具有最好的吸能效果。