凸环管件颗粒介质内高压成形工艺理论解析

离散体颗粒介质使颗粒介质内高压成形工艺中的传压具有非均匀性、颗粒介质与管件之间摩擦作用显著等特征,基于此,建立了颗粒介质非均匀载荷传压模型,对凸环管件胀形工艺过程进行了理论推导和数值解析,探讨了内压状况和摩擦条件对管件成形性能的影响,并通过工艺试验对理论分析结果进行了验证。分析结果表明,颗粒介质内高压成形工艺所具有的内压非均匀性、介质与管坯摩擦作用显著两大特征可有效减小胀形过程中的壁厚减薄和成形压力。对比试验与理论分析结果表明,壁厚分布和成形压力的理论计算结果与试验结果一致,颗粒介质非均匀载荷传压模型的构建策略可用于管件成形的预测和分析。     

基于三维成形极限应力图的AA6061挤压管材成形性能分析

为解决AA6061挤压管材成形性能极差的问题,建立了“固溶水淬+颗粒介质胀形+人工时效”的铝合金管件成形工艺流程。研究了固溶水淬和人工时效工艺参数对材料性能影响规律,并建立了考虑厚向应力的三维成形极限应力图;建立了管件颗粒介质胀形有限元仿真模型,分析管件变形特征质点的运动轨迹和应力应变状态,并应用理论成形极限图对管件破裂失稳点和胀形极限进行分析和预判。四方截面管件胀形工艺试验结果表明,颗粒介质胀形工艺与合适的热处理工艺相结合能够有效地解决AA6061挤压管材的成形问题;考虑厚向应力的三维成形极限应力图可作为铝合金管件胀形工艺方案制定的破裂失稳判据。     

加载路径对AA5083管件热态非金属颗粒介质成形性能的影响

将颗粒介质作为传力介质,应用于铝合金管件内高压热成形工艺。通过热单向拉伸试验建立AA5083板材的本构模型。通过管材热态颗粒介质胀形数值模拟,结合AA5083理论成形极限图的分析,研究了不同加载路径对管件壁厚分布、管端缩料量和主应变曲线的影响规律,并进行了相应的工艺试验验证。研究结果表明,合理匹配初始压头力和管端进给量参数,使预成形管坯在胀形区形成有益皱纹,可为胀形区管坯变形提供聚料作用,从而提高管件成形质量和胀形极限。     

Q235/AA5052复合凸环管颗粒介质胀形工艺研究

钢/铝复合管内衬的AA5052挤压铝管成形性能极差,室温下难以与外覆钢管协调变形至目标管件的形状要求。基于此,提出了挤压铝管退火处理、复合装配、颗粒介质胀形的工艺流程,使复合管胀形比达到1.40,成功制备了厚径比为3/102的复合凸环管件,最大减薄率不超过20%,满足产品技术要求。试验研究表明,AA5052挤压管材采取加热440℃保温60min的退火处理后成形性能最优,延伸率提高了3倍以上;复合管胀形过程中的壁厚分布规律与管层间摩擦因数相关,降低管层间摩擦作用能够抑制内衬铝管减薄,有利于复合管胀形极限的提高。颗粒介质胀形工艺对胀形管坯的尺寸精度要求较低,可采用通用设备和简便的模具装置实现成形工艺。     

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。     

基于有限元模拟的铝合金管液压胀形的工艺研究

在研究管材液压胀形工艺的基础上,采用理论分析和计算机数值模拟相结合的方法对铝合金管液压胀形过程进行研究。通过理论分析计算出胀形力的大小,利用有限元软件,分析比较了胀形压力、胀形速度和摩擦因数对管件胀形成形质量的影响。模拟结果表明:胀形压力与胀形速度必须相匹配;管坯与模具之间的摩擦因数在成形力允许的情况下,尽可能的大一些。     

基于离散元法的固体颗粒介质传力特性研究

固体颗粒介质成形工艺是采用固体颗粒介质代替刚性凸模(凹模)的作用,对金属板料、管材拉深胀形的先进工艺,在复杂零件精密成形、难加工材料成形、温热成形等方面具有独特优势.为揭示该工艺中固体颗粒介质的传力特性,采用离散元法(Discrete/distinct element method,DEM)数值模拟固体颗粒介质在单轴压缩下的受力过程,从力链角度分析固体颗粒介质在压缩过程中细观结构的变化规律,并以直径1mm不锈钢球为传力介质,自行设计颗粒介质传力性能试验,数值模拟结果与实测值吻合较好.研究发现颗粒配位数与体积份额呈幂函数关系,侧压系数与压应力亦呈幂函数关系,且当内部力链结构趋于稳定时,侧压系数趋于定值.应用散体力学研究方法推导出固体颗粒介质压力衰减规律,进而得到介质传力极限距离,这对如何准确控制成形中颗粒介质压力分布,提高加工工件的成形性能具有重要意义.     

汽车驱动桥壳液压胀形试验的失效研究

对0.75t汽车桥壳进行了液压胀形试验,分析了管件胀形的两种失效形式:胀裂和起皱。通过管件胀裂实验数据绘制出胀形极限图,并得到胀形系数和轴向应变之间存在线性比例关系Kr=l+δ-1.72ε2,揭示了管件材料的固有属性与外界加载条件对成形共同起着决定性作用。管件胀形中的起皱行为分为有益皱纹和有害皱纹。前者作为一种预成形方法能够为进一步成形聚集材料,管件成形的界限可得到扩大。     

AA6061铝合金正方形截面管胀形工艺研究

AA6061铝合金挤压管材在常温下强度高但塑性差,难以成形复杂形状零件。基于此,提出了固溶处理+固体颗粒介质胀形+人工时效的工艺流程,通过固溶、淬火和时效等热处理工艺调整铝合金变形前后的力学性能,应用固体颗粒介质胀形技术实现管件塑性成形。以AA6061挤压铝合金管为研究对象,分析了固溶处理工艺参数对合金力学性能的影响,发现管材经固溶温度560℃且保温120min处理后,其延伸率提高3倍以上,强度和硬度也大幅降低,使合金管材的成形性能指标显著提高,具备了固体颗粒介质胀形管件的条件;对合金固溶处理后再人工时效处理的试验研究表明,人工时效温度180℃且保温360min时合金塑性下降,强度和硬度等性能指标均可恢复至初始状态。基于铝合金热处理工艺特征的研究,采用固溶处理+固体颗粒介质胀形+时效处理的工艺流程,成功试制了AA6061铝合金典型的正方形截面管件,其环向最大展长率可达34%。     

薄壁深抛物线形零件固体颗粒介质成形工艺

薄壁抛物线形壳体成形过程为拉深和胀形两种变形模式的复合,极易发生起皱和破裂。固体颗粒介质成形是采用固体颗粒代替刚性凸模或凹模(或弹性体、液体)对板料进行成形的工艺。板材在颗粒介质内压的作用下成形,可以有效防止抛物线形件拉深成形过程中侧壁的起皱;由于颗粒内压是非均匀分布的,故可以有效控制抛物线形件成形过程中的破裂,提高板材的成形极限。根据固体颗粒介质成形工艺的特点,提出了两次成形薄壁深壳体零件的工艺,建立了数值分析模型,通过数值模拟和试验对该成形过程和工艺参数进行了分析。结果表明,采用固体颗粒介质成形工艺过程简单、成形工件壁厚分布均匀、表面质量好、回弹小。     

径压胀形中管材的填充性及成形性分析

通过对不锈钢管材径压胀形过程进行有限元数值模拟，对成形管材断面对角线长度变化趋势及壁厚分布规律进行了分析与比较，探讨了加载方式、管端约束条件（管端自由与管端固定）及摩擦条件对管材填充性及成形性的影响规律。结果表明，自由胀形直径或内压力越大，则管材的填充性越好，但成形性越差；管端固定时会使管材的填充性及成形性变差；摩擦使胀形管材断面形状不完全对称，且随着自由胀形直径或内压力的增大而显著。     

Analytical model of corner filling with granular media to investigate the friction effect between tube and media

In a tube forming process, granular matter is used as pressure transmission medium instead of liquid to expand a circular tube into one with square section. In this process, the friction at media/tube interface has a significant effect on the final result. In this paper, an analytical model was developed to determine the influence of the friction on the deformation developing process and final thickness distribution along the tube section. Experimental researches were also implemented to evaluate the analytical model in the end. In this model, four friction situations were applied to the numerical analysis process according to the active or negative function of friction on the flow of metal. The analysis result showed that different friction situations could lead to different deformation processes and thickness distributions. The examination on experiments of AA6061 tube indicated that the experimental data of thickness was extremely close to the analysis result with the friction situation in which the metal flow toward the corner of square section die was impeded by the friction force. However, the analytical prediction of thinning trend of thickness had a deviation compared with the experimental data in the corner region. In addition, the breaking and caking of granules in the tube forming process make the friction situation between the tube and media very complex. Therefore, a further research needs to be conducted from the direction of granular matter mechanics and friction mechanism in order to acquire a more explicit result.     

An examination of the effect of target thickness in the perforation of mild steel plate by a flat-ended projectile

Results of experiments on the high-speed perforation of different thicknesses of mild steel plate are presented, for impact velocities of up to 300 m/sec, and compared with the results of static perforation tests.Plate profiles, thinning of perforated plugs and energy requirements for perforation, are presented and discussed.It is found that the bulging of the target plate is greatest when the projectile is just contained, and that the bulging at containment increases with plate thickness over the early stages of the thickness range, after which it decreases with increasing plate thickness. This is contrary to the static case, in which the bulging continually increases. A photomicrograph of the material at the plug-plate interface is provided to support the view that thermo-plastic instability occurs when perforating thicker plates at high speed.     

On the tube hydroforming process using rectangular,trapezoidal, and trapezoid-sectional dies: modeling and experiments

It is generally known that the contact between tube and die, in the case of tube hydroforming process, leads to the appearance of friction effects. In this context, there are many different models for representing friction and many different tests to evaluate it. In the present paper, the pin-on-disk test has been used and the theoretical model of Orban-2007 has been chosen and developed to evaluate friction coefficient. The main goal is to prove the capacity of theoretical model to present the friction conditions in comparison with the pin-on-disk test. From the Orban model, values of 0.05 and 0.25 of friction coefficient have been found under lubricated and dry tests, respectively. On the other hand, by the classical pin-on-disk test, other values were experimentally obtained as friction coefficient at the copper/steel interface. In the case of pure expansion hydroforming, based on an internal pressure loading only, a “corner filling” test has been run for tube hydroforming. Both dry and lubricated contacts have been considered. Various configurations and shapes have been studied such as the rectangular, trapezoidal, and trapezoid-sectional dies. Finite element simulations with 3D shell and 3D solid models have been performed with different values of friction coefficients. From the main results, it was found that the critical thinning occurs in the transition zone for the square and rectangular section die and in the sharp angle for the trapezoidal and trapezoid-sectional die. The comparison between numerical data and experimental results shows a good agreement. Moreover, the thickness distribution along the cross section is relatively consistent with those measured for the 3D shell model; however, the 3D solid models do not provide a realistic representation of the thickness distribution in the shaped tube. Finally, the results obtained from the theoretical model were more efficient than the results obtained from the pin-on-disk test.