Warm hydroforming of magnesium alloy tube with large expansion ratio

Process of warm tube hydroforming was experimentally investigated for forming an AZ31B magnesium alloy tubular part with a large expansion ratio.Effects of temperature on the mechanical properties and formability were studied by uniaxial tensile test and hydraulic bulge test.Total elongation increases with temperature up to 250 °C,but uniform elongation and maximum expansion ratio get the highest value at 175 °C.Different axial feeding amounts were applied in experiments to determine the reasonable loading path.A preform with useful wrinkles was then realized and the tubular part with an expansion ratio of 50% was formed.Finally,mechanical condition to produce useful wrinkles is deduced and the result illustrates that useful wrinkles are easier to be obtained for tube with higher strain hardening coefficient value and tubular part with smaller expansion ratio.     

镁合金管材的热态内压成形起皱行为分析

利用数值模拟和塑性理论分析AZ31B镁合金管材的热态内压成形过程的变形机理,找出临界起皱应力、应力状态及皱纹形状的变化规律。结果表明:随着温度升高,管材轴向抗起皱能力下降,其机理是材料的屈服强度和弹性模量随温度升高而下降;皱峰和皱谷处应力轨迹均在环向应变伸长和轴向应变压缩的区域;随着补料量的增大,皱峰处应力向壁厚减薄的方向发展,皱谷处应力向壁厚增加的方向发展;内压与材料屈服强度之比(相对压力)决定初始屈服时皱峰和皱谷处壁厚的变化情况,即温度较高时,相对压力较大,初始屈服时皱峰和皱谷处应力状态越易处于管壁呈减薄趋势的区域;当温度较低时,相对压力较小,初始屈服的皱峰和皱谷处的应力状态越易处于管壁有增厚趋势的区域;随着温度升高,相同加载路径下皱纹的高度和波长增大,皱纹趋向于向中间移动,且波数减少。     

内高压成形起皱行为的研究

对内高压成形起皱过程进行了理论分析、数值模拟和实验研究．分析了加载路径、成形区长径比等因素对皱纹数量和工件成形效果的影响．结果表明：不是所有的皱纹都是失效形式，在某些情况下，管料起皱后仍然可以成形，关键是获得有益皱而不是死皱，通过起皱在成形区聚料是一种有效的预成形方法，该方法拓宽了内高压成形区间．     

Analysis on critical conditions of sidewall wrinkling for hydroforming of thin-walled Tee-joint

Based on the sidewall wrinkling phenomena in hydroforming of thin-walled Tee-joint, an analytical model for tube wrinkling under double side constraints was proposed to calculate the critical wrinkling stress. The effects of stress ratio, diameter-to-thickness ratio and tube material properties on critical condition of sidewall wrinkling were investigated. It is found that the middle of the main tube side wall is the most dangerous position for wrinkling within hydroforming of thin-walled Tee-joint. At a certain internal pressure, the critical wrinkling stress increases with increasing of ratio of hoop stress to axial stress and material strength coefficients, but decreases with increasing of work-hardening exponent and ratio of diameter to thickness. Through the analytical model combining FEM simulation, the critical wrinkling loading path according to the relation between axial feeding and internal pressure was obtained. Experimental results validates that wrinkle can be avoided if the pressure is above the critical wrinkling loading path, otherwise, wrinkle occurs. It is also verified that the analytical model of critical wrinkling stress is reasonable for the thin-walled Tee-joint hydroforming process.     

Mechanical property and formability of AZ31B extruded tube at elevated temperature

The mechanical properties of AZ31B magnesium alloy tube were tested by ring hoop tension test at different temperatures. The formability for tube hydroforming was also evaluated by flee-expansion test.The results show that there exists a quick decrease of total elongation along hoop direction at the temperature range of 150-230℃,which is quite different from that along axial direction.The total elongation along hoop direction of welded tube is quite close to that of seamless tube until 230℃is reached.At ...     

镁合金管件热态内压成形研究进展

首先简介了热态内压成形国内外研究现状,然后重点介绍了哈尔滨工业大学在热态内压成形装置和镁合金热态内压成形方面的研究进展。所研制的热态内压成形装置可在一定温度下实现镁舍金大膨胀率变径管、弯曲轴线变截面管的研制。采用AZ31B镁合金管材获得膨胀率30％,最大减薄率6．7％的变径管件;采用AZ61A镁合金管材试制了正方形截面件和某轿车样件,采用AZ31镁合金管材试制了截面带有小圆角的管件。介绍了上述样件的工艺过程,表明镁合金热态内压成形工艺具有广阔的应用前景。     

单侧双排四通管液压胀形壁厚与补料规律研究

以单侧双排四通管液压胀形工艺为研究对象,运用数值模拟方法分析不同加载参数条件下单侧双排四通管液压胀形支管高度、壁厚分布和补料情况,得出单侧双排四通管液压胀形壁厚分布和补料的一般规律.结果表明:单侧双排四通管液压胀形以两支管外侧主管补料为主,支管间内侧主管补料很少.加载参数对支管高度和外侧主管补料影响较大,对最大、最小壁...     

Loading path optimization of tube hydroforming process

Optimization methods along with finite element simulations were utilized to determine the optimum loading paths for closed-die and T-joint tube hydroforming processes. The objective was to produce a part with minimum thickness variation while keeping the maximum effective stress below the material ultimate stress during the forming process. In the closed-die hydroforming, the intent was also to conform the tube to the die shape whereas in the T-joint design, maximum T-branch height was sought. It is shown that utilization of optimized loading paths yields a better conformance of the part to the die shape or leads to a higher bulge height. Finite element simulations also revealed that, in an optimized loading path, the majority of the axial feed needs to be provided after the tube material yields under the applied internal pressure. These results were validated by conducting experiments on aluminum tubes where a good correlation between the experimental results and simulations were obtained.     

Experimental Observations of 5A02 Aluminum Alloy in Electromagnetically Assisted Tube Hydroforming

To establish the efficiency of electromagnetically assisted tube hydroforming, a typical experimental test for hydroforming, i.e., hydrobulging, was carried out on a 5A02 tube blank by using a combined quasi-static axial feeding and pulsed electromagnetic hydrobulging method. Data on the formability of an aluminum alloy 5A02 tube employing this combined loading method is compared with data for traditional quasi-static tests. The results show that the formability of aluminum alloy undergoing a quasi-static–dynamic process is dramatically increased beyond that exhibited in quasi-static or fully dynamic tests. The ultimate expansion ratio of an aluminum alloy tube undergoing a pulsed electromagnetic hydrobulging process is greatly increased beyond that exhibited in quasi-static hydrobulging tests. Both the expansion ratio and the effective strain exhibited in electromagnetically assisted tube hydroforming tests are about four and two times of that in quasi-static and fully dynamic hydrobulging tests, respectively. The forming limits of aluminum samples with both low and high prestrain levels are almost similar in the electromagnetically assisted tube hydroforming process, which makes it possible to stretch the aluminum alloy to a higher quasi-static prestrain level without weakening its total quasi-static–dynamic formability.     

空心双拐曲轴内高压成形数值模拟

应用动态显式有限元法对空心双拐曲轴的内高压成形过程进行了模拟分析,研究了加载路径对内高压成形的影响,指出了在加载曲线中存在着最佳成形区间,成形压力小于20MPa时,管坯产生起皱,成形压力大于32MPa时,管坯发生开裂,只有合理的应用加载路径,成形压力介于20MPa与30MPa之间,使轴向进给量可以正好补偿径向的变形量才能获得壁厚较为均匀的合格零件。     

Optimization of loading conditions for tube hydroforming

Tube hydroforming is a developing technology with advanced features of lightness and unified part. This study investigates the best possible regulation for loading conditions between the internal pressure and the axial feeding by hydroforming of a T-shape metal tube. Using conjugate gradient method with finite element method, a program module is generated to check the hydroformed tube quality about its thickness uniformity and the geometry accuracy. Thereby, a batch mode and a sequential mode to optimize the loading conditions of the tube hydroforming process are created and investigated. Regarding the tube quality from the simulation results, the hydroforming process, which follows the loading curve generated by the sequential mode, is better than by the batch mode. The optimal loading procedure generated by this article can offer another possibility for engineer by determining the internal pressure and the axial feeding in tube hydroforming.     

RESEARCH ON HYDROFORMING TUBULAR PART WITH LARGE PERIMETER DIFFERENCE

The tube hydroforming process for manufacturing the tubular part with large perimeter difference was studied by means of experiments and FE simulation. It is an asymmetrical one and the expansion ratio is 70 percent. The part is successfully hydroformed by applying the useful wrinkles to accumulate suffcient metal in the area with large expansion ratio. The thickness distribution is analyzed, and the maximum thinning ratio of the part is 21.6 percent. It is shown from the experiment and simulation results that the tubular part with large perimeter difference, long expansion area and asymmetrical shape can be obtained in one step, applying the useful wrinkles. Typical failure modes were analyzed.     

Research on Hydroforming Tubular Part with Large Perimeter Diffierence

The tube hydro forming process for manufacturing the tubular part with large perimeter difference was studied by means of experiments and FE simulation. It is an asymmetrical one and the expansion ratio is 70 percent. The part is successfully hydro formed by applying the useful wrinkles to accumulate sufficient metal in the area with large expansion ratio. The thickness distribution is analyzed, and the maximum thinning ratio of the part is 21.6 percent. It is shown from the experiment and simulation results that the tubular part with large perimeter difference, long expansion area and asymmetrical shape can be obtained in one step, applying the useful wrinkles. Typical failure modes were analyzed.     

遗传算法结合有限元模拟对液压胀形加载路径的优化

加载路径对液压胀形件的最终质量有着至关重要的影响。在优化加载路径的过程中,设计变量的取值区间对模拟时间的减少及最优解的收敛有重要的意义。文章根据塑性理论分析,给出了管形件液压胀形过程中弹性变形阶段、塑性变形阶段及贴模阶段的轴向喂入量及内压力的工程计算表达式。选取应力比为优化变量,依据屈服准则,得出了胀形过程中合理的变量区间。利用有限元软件包、优化算法及工程计算表达式,得到了液压胀形最优的加载路径。实验结果和有限元模拟结果一致性较好,该方法为轴对称件的加载路径优化提供了新的思路。     

管材液压成形技术的发展——从前8届国际塑性加工会议看管材液压成形技术的发展

文章回顾了前8届国际塑性加工会议论文集中关于管材液压成形方面的文献,发现,早期的管材液压胀形技术内压较低,后来发展到可同时实现超高压和轴向补料;可成形零件的轴线由直线变为二维或三维空间曲线,种类大幅增加;适用于内高压成形的材料也由铝、铜、低碳钢等增加了不锈钢、铝合金、镁合金;同时热态内压成形技术也蓬勃发展起来。     

汽车结构件内高压成形应力极限分析

由极限应力构成的应力成形极限图(FLSD)独立于应变路径,可作为复杂应变路径下成形极限的判据。通过标准成形极限实验获得3A21铝合金板材的成形极限图(FLD);由极限应力应变转换关系,将极限应变转换至主应力空间,建立对应的FLSD;采用LS-DYNA软件对方截面汽车结构件内高压成形过程进行了模拟,应用FLSD预测胀形过程中破裂的发生及极限成形压力。模拟结果与物理实验结果相吻合,证明FLSD可作为管材内高压成形等复杂应变路径下成形极限的判据。     

轴向补料对双金属薄壁管冲击液压成形影响的研究

双金属薄壁管冲击液压胀形技术是在液压胀形与冲压成形基础上发展起来的一种复合成形技术。为了获取更好的成形质量，在液压预成形与冲击液压成形相结合的基础上，通过改变液压预成形的加载路径实现双金属薄壁管成形。介绍双金属薄壁管冲击液压成形原理及内管轴向补料方案；利用Dynaform有限元分析内管轴向补料距离对双金属薄壁管壁厚分布的影响，获得轴向补料距离对双金属薄壁管成形规律；同时，分析内管轴向补料距离对管材中截面的对角线长度变化影响规律，从而获得内管轴向补料距离对双金属薄壁管填充性的影响。通过液压预成形阶段加载路径的研究，探明了轴向补料对双金属薄壁管成形规律的影响，为冲击液压载荷作用下的双金属薄壁管成形提供理论与应用支撑。     

Hydroforming of automotive structural components with rectangular-sections

An experimental and numerical simulation was conducted to investigate hydroforming of automotive rectangular-section structural components and the results were used as guidelines for some prototypes. The effect of loading path on the failures and thickness distribution was discussed and the reasons were analyzed for the failures, such as bursting and folding. Hydroforming with axial feeding is strongly sensitive to the loading path. Bursting occurs in transition zone in the calibration when the internal pressure increases faster than the axial feeding. Otherwise, folding will take place due to too much axial feeding. There is the maximum thickness at central point of the side of cross-section and the minimum thickness at the transition area. If the n value of the tube material is bigger, the thickness of the final part will be more uniform. By using a petal-like perform section shape, the pressure for forming the transition radii was greatly reduced and components with small radii can be formed with relatively low pressure.     

异型变径管内高压成形有限元模拟

通过建立相应的内高压成形有限元模拟模型,用Dynaform有限元分析软件进行模拟分析,研究了异型变径管成形的工艺特点、变形特征及成形参数对成形质量的影响。模拟结果表明,当变径管直径变化率较大时,自由胀形很难成形出理想成品,需采用轴向补料。采用合适的内压加载路径与轴向补料的配合方式能够显著控制起皱、破裂缺陷的产生,使较复杂的异型变径管顺利成形,成形质量较好。     

Experimental investigation of friction coefficient in tube hydroforming

The friction coefficient between tube and die in guide zone of tube hydroforming was obtained. In hydroforming, the tube is expanded by an internal pressure against the tool wall. By pushing the tube through tool, a friction force at the contact surface between the tube and the tool occurs. In guiding zone, the friction coefficients between tube and die can be estimated from the measured axial feeding forces. In expansion zone, the friction coefficients between tube and die can be evaluated from the measured geometries of expanded tubes and FE analysis.