超塑成形的钛合金波纹管壁厚分布规律研究

以DN250双波Ti-6A l-4V钛合金波纹管为例研究了采用超塑胀形/轴向加载复合超塑成形工艺成形的钛合金波纹管的壁厚分布规律。用ARVIP3D刚粘塑性壳单元有限元软件模拟了波纹管在胀形、合模和充满3个阶段的壁厚减薄情况,分析了筒坯长度和胀形阶段的变形量对超塑成形后波纹管厚度分布情况影响。通过实验研究了波纹管的实际壁厚分布曲线。结果表明,与其它成形方法相比,超塑成形的波纹管波峰壁厚减薄率较大,壁厚分布可用JIS公式粗略估算。     

TA1板单点渐进成形壁厚变化规律的数值模拟研究

钛及其合金应用越来越广泛,目前单点渐进成形技术已经开始运用于钛及其合金的成形加工,但仍存在成形件壁厚过度减薄的问题,严重影响了成形件的成形质量。文章以TA1钛合金板材成形方锥形件为研究对象,运用Abaqus有限元仿真软件,依据单一变量原则,分别探究工具头直径、底面边长、板材原始厚度和螺距等工艺参数对成形件平均壁厚减薄率与最大壁厚减薄率的影响规律。结果显示:增大工具头直径,平均壁厚减薄率随之增大,最大壁厚减薄率随之减小;平均壁厚减薄率和最大壁厚减薄率都随着底面边长的增加而增加;板材原始厚度增加,平均壁厚减薄率与最大壁厚减薄率都随之减小;随着螺距的增加,平均壁厚减薄率逐渐减小,最大壁厚减薄率逐渐增大。     

金属板料单点增量成形厚度减薄率的预测与控制

金属板料单点增量成形过程中成形区域厚度减薄率过大是影响成形极限的一项重要因素,预测成形区域壁厚是控制减薄率的重要方法。选取1060铝板,对单点增量成形过程中的壁厚变形过程进行分析,利用Abaqus有限元分析软件,建立单点增量成形有限元模型,利用仿真结果拟合出精度较高的壁厚预测公式,分析工具头直径、层间距、进给速度、板料厚度、成形角度等工艺参数对减薄率的影响规律,并通过试验验证有限元模拟的正确性,并提出通过改变成形轨迹控制减薄率的方法。结果表明:拟合出的壁厚预测公式所求得壁厚值比正弦定理所求得的壁厚值更接近实验值;壁厚减薄率值随着工具头直径、成形角度和板料厚度的增大而增加,随层间距的增加而减小,进给速度对减薄率影响不显著,成形角度是影响减薄率的最重要因素;采用压入点均布的成形轨迹可有效减小减薄率。     

工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性分析

为实现21-6-9高强不锈钢管数控弯曲精确成形,提高其成形质量与成形极限,需要对弯曲过程中壁厚减薄进行有效控制。基于ABAQUS/Explicit有限元软件平台,建立了21-6-9高强不锈钢管数控弯曲三维弹塑性有限元模型,并对其可靠性进行了验证。通过有限元模拟和正交试验,研究了工艺参数对21-6-9高强不锈钢管数控弯曲壁厚减薄影响的显著性及规律。结果表明,影响壁厚减薄的显著性工艺参数依次为芯棒伸出量、管材与芯棒间隙、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数和弯曲速度,其影响规律为：壁厚减薄率随着芯棒伸出量、管材与防皱块摩擦因数、管材与芯棒摩擦因数、管材与压块摩擦因数、弯曲速度的增大或管材与芯棒间隙的减小而增大。采用多元线性回归方法建立了最大壁厚减薄率与显著性工艺参数之间的回归预测模型,经对比验证,回归预测模型结果与正交试验结果之间的相对误差不超过5%。     

船用大直径厚壁管数控弯曲工艺参数对壁厚影响的显著性分析

为实现船舶管件数控弯曲精确成型,更好地研究船用大直径厚壁管壁厚变化率,提高其成型质量,需对其弯曲过程中壁厚减薄进行有效控制。基于有限元分析软件Dynaform建立船用20#管绕弯成型过程有限元模型,对其进行可靠性验证,再通过有限元分析和虚拟正交试验对弯曲段外侧最小壁厚数据进行极差分析和方差分析,研究工艺参数对于壁厚减薄影响的显著性及规律。结果表明:管件数控弯曲成形过程中工艺参数对最大壁厚减薄率影响的显著性顺序依次为:芯棒与管材摩擦系数、芯棒前伸量、芯棒与管材间隙、夹模与管材间隙;壁厚减薄率随着芯棒与管材摩擦系数、芯棒前伸量以及夹模与管件间隙的增大而增大,随着芯棒与管件间隙增大而减小。同时利用多元线性回归方法建立显著性工艺参数与最大壁厚减薄率之间的回归方程,经对比验证,对于规格为Φ140mm×4.5mm(t)×420mm(R)船用20#大直径厚壁管,此回归预测模型结果与正交试验之间的相对误差不超过5%。     

工艺参数对汽车副车架内高压成形质量的影响

采用有限元分析软件Dynaform,对某汽车副车架的内高压成形工艺进行数值模拟。研究不同初始管坯尺寸和内压加载路径对壁厚分布和零件成形质量的影响。分析结果表明,合理的初始管坯尺寸和内压加载路径能够改善零件壁厚分布的不均匀性,提高材料的成形极限和产品质量。该分析结果为内高压成形工艺的制定提供依据。     

材料成形性能对空心曲轴内高压成形模拟结果的影响

用数值模拟的方法研究材料成形性能对空心曲轴内高压成形结果的影响,分析了管材的厚向异性系数与硬化指数的变化对壁厚分布的影响,结果表明,内高压成形件的壁厚分布与材料的硬化指数n值、厚向异性指数r值密切相关,n值越大,壁厚分布越均匀,r值越大,壁厚减薄率越小,可减小破裂的可能性。     

AZ31B镁合金管材液压胀形数值模拟分析

基于管材轴向补料液压胀形技术,采用Dynaform有限元仿真软件对0.75mm厚的AZ31B镁合金管材的胀形过程进行了数值模拟分析。研究了模具圆角半径、液压力、模具间隙等工艺参数对镁合金管件壁厚分布和最大壁厚减薄量Δt的影响规律,并探索了相对合理的工艺参数。研究结果表明,镁合金管件的最小壁厚通常分布在最大胀形直径处,除非模具间隙过小;由于受到轴向作用力,管材两端会随模具间隙的改变而出现不均匀的壁厚增厚现象,并且受轴向压头作用的一端的壁厚增厚量相对较大;胀形过程中,当模具圆角半径为5mm,模具间隙为0.8mm时,获得的镁合金管件壁厚分布较均匀,成形效果较好。     

液压成形S500MC高强钢汽车轮辋疲劳性能的有限元模拟

以厚度为2.0 mm的S500MC微合金高强钢板为材料,采用液压成形工艺制造汽车轮辋,通过有限元方法分析该轮辋的疲劳性能,并与常规滚压成形2.3 mm均匀壁厚SPFH540中强度低合金钢轮辋和2.0 mm均匀壁厚S500MC微合金高强钢轮辋进行对比.结果表明:液压成形轮辋壁厚的最大减薄率为10.9％;液压成形轮辋的截面弯曲应力和径向应力变化趋势与2种滚压成形轮辋的一致,说明轮辋局部减薄不会使其所受应力发生明显变化;液压成形轮辋的最大弯曲应力和最大径向应力低于该钢的屈服强度,最大弯曲应变和最大径向应变均远小于屈服应变,且疲劳性能安全系数均大于1,表明壁厚局部减薄不会影响轮辋的弯曲和径向疲劳性能.     

基于POA-BP的TP2管材自由弯曲成形结果预测

将壁厚减薄率和椭圆率作为管材自由弯曲成形结果的评价指标,选取弯曲模与管材间隙值、弯曲模圆角半径值、管材弯曲变形区长度、导向机构圆角半径值、导向机构与管材间隙值作为影响因子。利用数值模拟方法对管材自由弯曲成形结果的评价指标和影响因子建立样本库,并随机选取6组作为测试样本,其余的作为训练样本,结合BP神经网络和鹈鹕优化算法对预测模型进行训练,构建POA-BP神经网络预测模型对管材自由弯曲成形结果进行预测。结果表明,POA-BP预测模型的壁厚减薄率和椭圆率的最大预测误差不超过2%,故POA-BP预测模型能够有效预测管材成形结果。     

Q235覆管对AA5052铝合金基管颗粒介质胀形行为的影响

采用AA5052铝合金挤压管作内层基管、Q235碳素结构钢卷焊管作外层覆管的钢铝复合管对复合管颗粒介质胀形行为进行研究。通过塑性理论分析胀形过程中管间切向摩擦力及法向压力对基管应力大小的影响;利用数值模拟分析管间摩擦因数和覆管各向异性对基管的应变成形极限的综合影响,并给出单管、复合管胀形时的壁厚减薄情况和基管的应力、应变分布;通过管材颗粒介质内高压胀形试验,对比单管和复合管胀形条件下铝合金管的极限胀形比,分析复合管的变形协调性。结果表明：通过施加Q235碳素结构钢覆管,减小了AA5052基管胀形区中间截面处的双向拉应力,基管胀形区壁厚减薄变小,胀形比提高了22%,复合管下基管最大减薄率为17.5 %,成形性能显著提高。     

金属波纹管单点增量成形过程研究

将单点增量成形技术引入金属波纹管成形,提出了一种金属波纹管单点增量成形工艺。基于ABAQUS/Explicit建立增量成形波纹管仿真模型,分析成形过程中成形力的演变,以及成形应力、材料局部变形位移和塑性应变分布的特点;建立了波纹管单点增量成形实验平台,采集成形过程数据并分析实验数据。结果表明：X向分力在增量成形管壁中的数值最大,其次是Y向分力和Z向分力;斜面拉伸区和圆弧过渡区的塑性应变大,该区域管壁容易发生过度减薄和断裂。     

微小尺寸等壁厚不锈钢螺旋管充液压制成形方法研究

为了解决常规螺杆钻具寿命短与微小尺寸螺杆钻具等壁厚定子难加工的问题,本文采用充液压制成形工艺加工微小尺寸等壁厚螺旋管,基于304不锈钢拉伸实验,建立了充液压制成形等壁厚螺旋管有限元模型,用数值模拟方法研究管件外径、壁厚、液压力大小、液压力加载路径、压制速度、摩擦系数对螺旋管质量的影响。结果表明,管件外径为51.8 mm,壁厚为5.3 mm时,螺旋管质量较好,最大液压力为650 MPa,液压力加载路径为路径5,模具挤压速度为0.429 m/s,摩擦因数不超过0.125时,螺旋管加工质量较好,导程误差近似为0,壁厚误差小于8%,平均厚度为5 mm,螺旋管中部壁厚误差小于3%。研究结果可为生产实际中微小尺寸等壁厚不锈钢螺旋管的成形工艺提供参考。     

Plugging criteria for thinned high-pressure feedwater heater tubes considering pressure and thermal loading

When heat exchanger tubes have critical thinning which could cause unsafe conditions, it is general practice to plug the tubes so that they are out of service to prevent rupture failure at the thinnest location. Plugging criteria for the high-pressure feedwater heater tubes of fossil power plant were studied. Tubes in the desuperheating zone were considered due to their high internal pressure and the high temperature difference across the tube wall. Theoretical analysis of uniform thinning and eccentric thinning of the tube was conducted to determine the stress conditions at the thinnest location under internal/external pressure and thermal gradient across the tube. The minimum required tube thickness was determined using the maximum shear stress criterion (Tresca theory). Accuracy and effectiveness of the analytic solutions of the stresses were verified by comparing the results obtained with those obtained from finite element analysis. Using finite element analysis, the stresses for eccentric thinning were determined. Thermal loading due to temperature difference across the wall was considered even though the contribution of pressure loading to the stress of the tube was known to be higher than that of the thermal loading. As case studies, the tube plugging criteria of three high pressure feedwater heaters were determined using actual temperature and design pressure industry data. The procedure used in this study can be applied to different pressure and temperature operating conditions, and different tube materials.     

带壁厚偏差管大变形推压缩径端部周向褶皱研究

无缝钢管推压缩径生产中的端部内壁周向褶皱会严重影响制件质量。通过测量无缝钢管壁厚,发现壁厚沿周向分布存在薄厚交替性变化规律;通过建立带壁厚偏差管推压缩径力学模型,分析管坯在减径、圆角及出口区的应力及变形特征,得到端部周向褶皱的生成机理。进行不同壁厚偏差管四道次推压缩径试验,结果表明端部不平度均大于初始不平度、定径区不平度均小于初始不平度,与理论分析吻合;总结了壁厚偏差和缩径道次对不平度、相对不平度的影响规律,并给出了产生周向褶皱的工艺参数范围。建立内表面为周期性正弦变化、外表面为圆形的壁厚偏差管几何模型,模拟出周向褶皱的生成与发展过程,得到壁厚、相对不平度在缩径各阶段的演变规律,模拟结果与理论分析吻合、与试验结果趋势一致。采用推压-拉拔缩径,可以大幅降低端部不平度和翘曲,有效提高成形质量。     

An approach to improve thickness uniformity within tailor-welded tube hydroforming

Both experimental and simulation studies were run to investigate the effects of deformation sequence on stress and strain states and thickness distribution during tailor-welded tube hydroforming. The effects of geometrical boundary condition were also studied. Then, an approach to improve thickness uniformity was put forward. Both stress and strain histories indicate that the deformation states of thinner and thicker tubes were obviously different duo to the difference in thickness during tailor-welded tube hydroforming. These induce tensile strain concentrates to happen near weld seam on thinner tube, but compressive strain on thicker tube, which lead to strain mutation around weld seam on tailor-welded tube components. As result, bigger thinning takes place on thinner tube. The difference in thinning ratio between thinner and thicker tubes reaches about 6.6%. By deformation sequence optimization, thickness distribution uniformity can be improved obviously. When deformation sequence altered from thicker tube to thinner tube, the difference in thinning ratio between two segments can be decreased to 1.5%. At last, the effects of geometrical parameters of preform component were analyzed and the suitable parameters were given.     

An experimental and numerical study of necking initiation in aluminium alloy tubes during hydroforming

In this paper, a combined experimental and numerical investigation of free hydroforming of aluminium alloy tubes is conducted. The tubes are subjected to different loading histories involving axial compression and internal pressure. The circumferential and axial strains experienced by the tubes are continuously recorded along with the pressure and axial load. The numerical simulations are carried out using both 2D axisymmetric and 3D finite-element formulations by applying the experimentally recorded axial load and internal pressure. In the latter, a geometric imperfection is introduced in the form of wall thickness reduction at the tube mid-length in order to trigger necking which happens after significant bulging and beyond the stage of peak pressure. The strain histories and peak pressures obtained from the simulations agree well with those determined from the experiments. Further, the forming limit curve predicted by the simulations as well as from a M–K analysis incorporating the computed strain paths corroborate well with the experimental data. The role of nonproportional straining on the mechanics of failure of the tubes due to bulging and necking is studied in detail.     

Analytical model for planar tube hydroforming: Prediction of formed shape, corner fill, wall thinning, and forming pressure

An analytical model for planar tube hydroforming based on deformation theory has been developed. This analytical model can be used to predict hydroformed shape, corner fill, wall thinning, and forming pressure. As the model is based on a mechanistic approach with bending effects included, local strain and stress distribution across the wall thickness can be determined. This includes strain and stress distributions for the outer layer, inside layer, and middle layer. The model is validated using finite element analysis and tube hydroforming experiments on irregular triangular, irregular quadrilateral, and pentagonal hydroformed shapes.     

An investigation into the preforming of tubes

A major disadvantage of traditional cold forging is represented by the inability to forge slender geometries such as tubes, because these tend to collapse under axial forces. Recent research has revealed that, for the forming of hollow flanged components from tubes, a controlled material flow can be achieved by injection forging. However if the height of the flange is high compared to the wall thickness of the tube, instability problems arise causing the tube to buckle. According to previous work by the authors this may be prevented by increasing the wall thickness of the tube locally through the preforming of a simple inner flange on the tube. These preliminary investigations have been restricted to a reduced number of component geometries in terms of the major process parameters; being the inner- to outer-tube diameter proportion and the flange-towall-thickness ratio. In continuation of this work the present paper focuses on a systematic mapping of the optimal preform design in order to allow an establishment of actual preform design rules for the injection forging of tubular components for a whole range of parameter combinations. The analysis builds on a comprehensive finite element analysis in conjunction with experimental tests in aluminium performed for strategically important parameter combinations in order to support the theoretically established formability limit diagrams.