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.

Numerical simulation of aluminum alloy ladder parts with viscous pressure forming

Viscous pressure forming (VPF), a recently developed flexible die forming process that is suitable for difficult to form material, can obtain the better stress states of sheet blank during forming process in manufacturing complex shape parts. The process of manufacturing aluminum alloy ladder parts with VPF and solid metal punch was simulated by the FE software DEFORM. Under different blank holder pressure (BHP), the stress state, the strain state, the forming of small radius curved face and the distribution of thickness were analyzed. The simulation results show that, compared with solid metal punch forming, the sheet blank can flow into die cavity more easily with VPF due to the improvement of the stress states; the severe thickness reduction can be avoided, the sheet blank can contact the die perfectly and the parts have high dimensional accuracy.

Effect of blank holder pressure on viscous pressure forming aluminum alloy ladder parts

Viscous pressure forming (VPF), is suitable for forming difficult to form sheet metal parts. An investigation in the effect of blank holder pressure (BHP) on VPF aluminum alloy ladder parts was conducted. Based on experimental and numerical simulation results of the effect of BHP on dimensional accuracy, wall thickness reduction, forming pressure, material flow and defects (such as wrinkling and fracture) of specimens, the effect patterns of BHP load path on VPF ladder parts were explained. The limits of BHP corresponding to specimens with no defect and with wrinkling or fracture defect were determined. In the limits of formable BHP, the variable load path of BHP was beneficial to drawing blank into the die and decreasing wall thickness reduction of specimens. The experimental results show that the ladder parts of good surface fineness and high dimensional accuracy can be obtained by variable load paths of BHP.

Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation

Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1mm. Therefore, in this study, thin-walled die casting of aluminum （Al-Si-Cu alloy： ALDC 12） in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation （MAGMA soft） and actual casting experiment （Buhler Evolution B 53D）. Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.

Machining Deformation Prediction of Thin-Walled Part Based on Finite Element Analysis

For the problems of machining distortion and the low accepted product during milling process of aluminum alloy thin-walled part,this paper starts from the analysis of initial stress state in material preparation process,the change process of residual stress within aluminum alloy pre-stretching plate is researched,and the distribution law of residual stress is indirectly obtained by delamination measurement methods,so the effect of internal residual stress on machining distortion is considered before finite element simulation. Considering the coupling effects of residual stress,dynamic milling force and clamping force on machining distortion,a threedimensional dynamic finite element simulation model is established,and the whole cutting process is simulated from the blank material to finished product,a novel prediction method is proposed,which can availably predict the machining distortion accurately. The machining distortion state of the thin-walled part is achieved at different processing steps,the machining distortion of the thin-walled part is detected with three coordinate measuring machine tools,show that the simulation results are in good agreement with experimental data.

Microstructure and mechanical properties of 7075 aluminum alloy during complex thixoextrusion

7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM,TEM and other analytical methods.The results show that different parts in 7075 aluminum alloy show quite different microstructures.The microstructure of the thin walls formed by back-extrusion is stratified,and the bottom of the parts formed by angular extrusion is obviously deformed.Shear forces contribute to the crushing of grains and the coarse second phase.The main strengthening phases in the material areηphase and E phase,whose amounts greatly decrease during heating to semi-solid and thixoextrusion.After heat treatment,they can precipitate evenly to improve the mechanical properties of the material.The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa,while the average elongation is 5.49%.

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.

Residual Stress Relaxation of Thin‑walled Long Stringer Made of Aluminum Alloy 7050‑T7451 under Transportation Vibration

Thin-walled long stringer made of aluminum alloy 7050-T7451 is prone to deformation during transportation,so a research of residual stress relaxation was launched in this paper.The transport resonance stress of long stringer was analyzed based on the power spectral density of road transport acceleration.The residual stress relaxation experiment of aluminum alloy 7050-T7451 under different equivalent stress levels was designed and carried out.According to the amount of residual stress relaxation in the experiment,an analytical model was established with the equivalent stress level coefficient.The deflection range of long stringer was evaluated under different damping ratios.The results show that when the equivalent stress exceeds 0.8σ0.2,the residual stress relaxation of the thin-walled samples occurs.The residual stress relaxation increases linearly with the equivalent stress,which is logarithmically related to the loading cycle.The deformation caused by residual stress relaxation of the long stringer is proportional to the square of the length and the bending moment caused by stress rebalance,and inversely proportional to the moment of inertia of the structure.As the damping ratio decreases from 0.03 to 0.01,the total deflection of the long stringer increases from 0 to above 1.55 mm.

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.

Effect of blank quenching on shear spinning forming precision of 2219 aluminum alloy complex thin-walled components

The quenching-spinning(Q-S)process,i.e.,shear spinning after blank quenching,has been increasingly utilized to form 2219 aluminum alloy complex thin-walled components.However,the changes in material property,shape and stress of the blanks after quenching will affect the spin-ning forming precision.In this study,the rules and mechanisms of these effects are investigated based on a combined finite element(FE)model including blank quenching and component spinning process.The results indicate that the increase of material strength and the existence of distortion of the quenched blank lead to a notable increase in the non-uniformity of the circumferential compres-sive stress in the spinning area and the increase of the flange swing height during spinning.These changes result in an increase in the wall thickness and component-mandrel gap of the components.The quenching residual stress has little effect on wall thickness and roundness but can noticeably reduce the component-mandrel gap.This is because that the existence of quenching residual stress of the blank can lead to the decrease of the maximum circumferential compressive stress of the workpiece in spinning and an obvious drop in the maximum compressive stress after reaching the stress peak.Quenching distortion is the main factor affecting the roundness.Moreover,the opti-mized installation way of the blank for spinning is obtained.

Effect of depressurizing speed on mold filling behavior and entrainment of oxide film in vacuum suction casting of A356 alloy

The effect of depressurizing speed on mold filling behavior and entrainment of oxide film of A356 alloy was studied. Themold filling behavior and velocity fields were recorded by water simulation with particle image velocimetry. The results show thatthe gate velocity first increased dramatically, then changed with the depressurizing speed: the gate velocity increased slowly atrelatively high depressurizing speed; at reasonable depressurizing speed, the gate velocity kept unchanged; while at lowerdepressurizing speed, the gate velocity decreased firstly and then kept unchanged. High gate velocity results in melt falling backunder gravity at higher speed. The falling velocity is the main factor of oxide film entrainment in vacuum suction casting. The designcriterion of depressurizing rate was deduced, and the A356 alloy castings were poured to test the formula. The four-point bend testand Weibull probability plots were applied to assessing the fracture mechanisms of the as-cast A356 alloy. The results illuminate amethod on designing suitable depressurizing speed for mold filling in vacuum suction casting.

考虑各向异性的回转曲面件蠕变时效成形数值模拟与实验

针对铝锂合金回转曲面件蠕变时效成形各向异性问题,开展了基于Barlat91屈服各向异性准则和蠕变各向异性本构模型的回转曲面件蠕变时效成形数值模拟与实验研究。仿真结果表明,构件加载阶段发生塑性变形,呈现出■的塑变各向异性现象;考虑蠕变各向异性行为的构件的蠕变应变分布发生明显改变。进一步通过开展回转曲面件蠕变时效成形实验发现,所建立的蠕变各向异性模型对厚度变化、残余应力分布预测准确;相对于各向同性模型,型面精度的整体预测偏差减小9.3%,焊接边预测偏差减小91.5%,证明了所建铝锂合金蠕变时效各向异性本构模型的准确性和实际应用价值。

大型7085铝合金筒形件淬火残余应力及其消减工艺研究

以大型7085铝合金筒形件为研究对象,研究了在最大程度保证铝合金大锻件性能的同时尽可能减小其淬火残余应力的方法。基于Abaqus平台,分别建立了大型筒形件淬火有限元模型和淬火后冷胀形有限元模型,考虑了淬火工艺和冷胀形工艺间的数据继承关系,分析了工艺参数对锻件性能及残余应力的影响规律。针对大型7085铝合金筒形件的淬火过程,将7085铝合金的等温转变曲线和时间-温度-性能曲线写入Abaqus用户子程序USDFLD中,计算了大型筒形件在不同淬火工艺条件下的析出相含量和分布、对应的硬度变化以及残余应力分布,获得了35℃的淬火水温是最优的选择。在消减淬火残余应力的冷胀形工艺中,基于不同的淬火水温条件开展了胀形量、胀形道次和每道次之间环转动角度的正交模拟实验,结果显示胀形量对残余应力消减的影响最显著,胀形量为4.5%时大型7085铝合金筒形件的应变均匀性最好且残余应力消减最充分。将仿真获得的优化淬火工艺和胀形方案应用于生产试制,所获得的大型筒形件各项力学性能达到设计要求,其残余应力实测结果与仿真结果对比具有较好的一致性。

铝合金薄壁件超声振动铣削形变量研究

针对铝合金薄壁件加工中形变量较大的问题,这里提出了超声振动辅助铣削的方法对铝合金薄壁结构进行加工,以提高薄壁件的加工质量。首先采用ABAQUS软件建立了T形薄壁结构的热力耦合仿真模型,从温度场和应力场两方面对薄壁的变形因素进行了分析。然后设计了铝合金薄壁件铣削实验,研究了薄壁区域温度和受力的变化规律。最后通过测量试验后薄壁件的最大形变量,对仿真模型的准确性进行了验证。研究结果表明:薄壁结构的形变量随主轴转速的升高逐渐降低,随进给速度的增加逐渐增加。超声振动可以有效的降低薄壁结构的温度和受力,从而降低薄壁结构的形变量。超声振动铣削时形变量平均减小了22.8%。实验和仿真之间两者之间形变量的平均误差为4.3%,薄壁铣削形变量模拟具有较高的准确性。

基于固有应变法的中空薄壁铝合金结构件焊接变形及残余应力预测

为提升中空薄壁铝合金结构件焊接变形与残余应力预测精度。基于固有应变法与焊接热输入参数对焊接等效载荷开展求解,利用有限元仿真方式从变形及应力的角度出发,分别对焊接变形及残余应力进行分析,并通过焊接试验进行验证。结果表明:焊缝左右两侧的边缘区域是产生焊接残余应力的主要位置,横向、纵向残余应力分别为275 MPa、181 MPa,结构件上蒙板呈马鞍形分布,焊接所导致的最大变形分布在上蒙板左右两侧,左右两侧仿真最大值分别0.299 mm、0.274 mm,左右两侧试验最大值分别0.37 mm、0.34 mm,试验变形值略大于仿真变形值,两侧变形预测误差率分别为19.1%、19.4%。研究结果可为类似中空薄壁铝合金结构件焊接变形及残余应力预测提供一定参考依据。

铝合金抛物线形零件反向粘性介质压力成形工艺研究

针对铝合金抛物线形零件在成形时容易出现拉裂、起皱等问题,提出了采用反向粘性介质压力成形方法进行此类零件成形。通过对抛物线形零件的成形过程进行有限元分析,得到不同反向粘性介质压力下试件等效应力及变化趋势,并采用实验方法对其过程进行验证。研究结果表明,反向粘性介质压力成形不仅改善了板料应力状态,使最大等效应力减小,同时也改变了板料变形路径,有效提高了板料成形性能,在反向粘性介质压力为9.2MPa时成形出了满足要求的零件。

铝合金汽车覆盖件材料特性的应用评价方法

汽车轻量化是大势所趋,铝合金替代传统钢材已成为轻量化重要的技术途径。汽车属于耐用消费品,用车环境复杂多变,为满足消费者使用需求,整车制造厂要研究铝合金替代件的品质管理要件。文章以汽车覆盖件常用的6000系列铝合金板材材料特性评价为例,从定量及定性两方面介绍了评价铝合金板材的指标与验证方法,可作为汽车制造厂的研究参考。

铝合金薄壁角片数控加工方案分析与论证

对小型铝合金薄壁角片零件的结构与材料进行了工艺性分析,设计出两种数控加工工艺方案。通过对两种加工方案所采用的加工方法进行整体论证,对比得出一种高质量的适合批量生产的加工方案,并总结出最优的数控铣切的切削参数。

高速动车组铝合金零件CNC铣削加工工艺研究

高速动车组应用了较多铝合金零件。此类零件存在较高的加工装夹难度,若无法准确把握加工工艺,易出现加工缺陷。结合铝合金零件性能,详细分析零件计算机数字控制机床(Computer Numerical Control,CNC)铣削加工工艺特点,并从多个角度研究铝合金零件的CNC铣削加工工艺及其热处理技术。合理优化加工参数和热处理技术,可提高铝合金零件的加工质量和机械性能,促进高速动车组铝合金零件加工工艺水平的提升,进而推动我国高速动车组的发展。