非对称管件内高压成形过程研究

为了改善两端不对称形状管件内高压成形后的壁厚均匀性,提高管件内高压成形极限,采用Dynaform有限元模拟软件并结合实验,研究了补料压力、轴向补料量对管件成形过程中起皱和破裂的影响.结果表明:当补料压力低于32 MPa时,失效形式为死皱;当补料压力高于42 MPa时,失效形式为破裂,适宜的补料压力区间为34~42 MPa;当左右补料量分别为42和22 mm,整形压力126 MPa时,可得到合格非对称瓶形管件,管件最大膨胀量为70.75%,壁厚最大减薄率为27.12%。通过控制管材在内压和轴向力的作用下发生合理的预成形,包括管材两端的合理补料量以及合理的起皱形状和数量,可在最终的内高压成形中实现更好的壁厚均匀性,提高成形极限。     

加载路径对扭力梁内高压成形壁厚分布和精度的影响

为研究加载路径(内压力和轴向补料的匹配关系)对扭力梁内高压成形的影响,通过数值模拟和试验研究的方法,研究了不同加载路径对局部截面壁厚分布和管件成形精度的影响规律.研究发现:当补料初始压力过低时,在端部区域起皱;当补料初始压力过高时,补料全部集中在端部区域;当补料量过小时,壁厚改善不明显;补料量过大时,端部区域起皱.研究结果表明:初始压力为30 MPa,补料量15 mm时为合理加载路径,此时内高压成形件壁厚减薄较小,成形精度较高.     

加载路径对不锈钢球形件内高压成形过程影响

为了研究加载路径对不锈钢球形件内高压成形过程的影响,采用实验方法分析了加载路径对成形过程中缺陷形式的影响,获得了80%膨胀率成形管件的壁厚分布规律.结果表明:当初始内压与屈服强度比值小于0.21时,管坯形成两个皱纹,在整形阶段发生开裂;当初始内压与屈服强度比值大于0.25时,管坯在轴向进给阶段即发生开裂.在初始内压与屈服强度比值为0.21～0.25时,可以成形出合格管件,合格管件最大减薄点位于球形件的最大截面处,最大减薄率为24.5%.本文所成形不锈钢球形件内高压成形区间,合理初始内压与屈服强度比值范围为0.21～0.25.     

钛合金管件高压气胀成形工艺研究进展

高压气胀成形是在内高压成形基础上发展起来的管件成形技术,采用气体介质加载,可在高温下成形钛合金构件。以Ti-3Al-2.5V钛合金管材为实验材料,开展了矩形截面构件和大截面差构件高压气胀成形工艺研究,提出了气压阶梯加载方法和气压与轴向位移匹配的加载方法。结果表明,利用Ti-3Al-2.5V钛合金在一定温度和应变速率范围的应变和应变速率双硬化机制,采用合理的加载路径,能够消除开裂缺陷,以较高的效率实现钛合金异形管件的成形制造,并且构件壁厚相对均匀,形状和组织性能均可得到有效控制。     

780 MPa 超高强钢扭力梁内高压成形研究

目的为了适应载荷和安装空间及轻量化的要求,轿车扭力梁正趋于设计成空心封闭变截面高强钢结构,但高强钢成形存在着回弹大、成形精度低等缺点。方法针对这一问题,采用数值模拟和实验的方法,开展了780 MPa超高强钢扭力梁内高压成形研究,重点研究了预制坯形状对扭力梁内高压成形的影响,并采用响应面模型,优化了预制坯,获得了最优的预制坯形状。在此基础上,研究了加载路径对扭力梁内高压成形过程的影响。结果当扭力梁预成形压下量为62.2 mm,下模引导角为29.2°时,得到了最优的预制坯形状。后续内高压成形过程中,支撑压力过小或补料量过大,在试件端部引起起皱缺陷;支撑压力过大或者补料量过小,补料主要集中于端部,对大膨胀量区域影响较小;当采用补料量为8%的加载路径时,可以有效改善壁厚的分布,避免起皱缺陷。结论合理的预制坯形状能够有效避免超高强钢扭力梁内高压成形过程中的飞边缺陷,而加载路径控制是扭力梁内高压成形过程中避免起皱缺陷和过度减薄,提高成形极限和零件成形精度的重要途径。     

扶梯上侧板横撑液力成形仿真研究

目的 缩短上侧板横撑胀形件的开发周期,降低开发成本。方法 采用理论研究与仿真分析相结合的方法对胀形管件的壁厚分布及加载路径进行研究。首先,借助ABAQUS有限元软件,对简单管件两次液压成形过程进行仿真模拟,通过对比仿真结果与实验结果,验证仿真建模的正确性。其次,基于有限元软件对横撑管件液力成形、退火等过程进行仿真分析。最后,通过分析、总结获取合理的加载路径。结果 通过理论计算得到了预胀形所需的内压力值,为横撑管件预胀形仿真分析提供了参考。在预胀形阶段,当内压力<65 MPa时,由于内压力不足,管件无法成功胀形,当内压力>65 MPa时,管件中间胀形区域存在应力集中现象,不利于后续管件胀形,所以预胀形阶段的合理加载路径为常压65 MPa。在终胀形阶段,常压加载路径下的胀形结果不理想,而在多线性加载路径4下退火件及未退火件都能获得理想的胀形结果,因此,多线性加载路径4为终胀形的合理加载路径。结论 相较于常压加载,终胀形阶段采用多线性高压加载,管件成形效果更好;终胀形前进行退火处理,可以降低胀形管件的残余应力,壁厚分布也更加均匀。     

管件液压成形中加载路径的确定方法研究

加载路径是影响管件液压成形结果的关键因素,为了快速准确地确定管件液压成形中的加载路径,提出了利用理论计算与数值模拟相结合的方法来优化和调整成形的加载路径,确定最佳的成形区间.根据塑性力学理论计算出成形的初始内压,确定出成形区间,然后调整不同的轴向补料量进行数值模拟,并根据数值模拟的分析结果确定最佳的补料量,最终通过调节加载路径的斜率,获得合理的成形加载路径.实验结果表明:针对非对称结构的空心轴类件的液压成形,应用本方法快速地确定出合理的加载路径,零件顺利成形,且成形零件的减薄率在整个成形区间里是最小的.     

大截面差空心件内高压成形研究

截面周长差较大的空心零件的内高压成形需要解决膨胀区的轴向补料问题和预成形问题,才能获得壁厚分布较为均匀的合格零件.以某轿车转向节臂零件的成形过程为例,对上述问题进行了试验研究.首先设计、试制了瓶形预制件,在预成形中利用"有益起皱"实现了大量的补料,获得了壁厚分布符合要求的预制件;然后在终成形前使零件截面具有合理的形状,再进行终成形,既保证了圆角部位的外形尺寸,又提高了壁厚均匀性.采用本文介绍的方法实现了截面周长差达70%的瓶形预制件的制备,从而获得了壁厚、外形尺寸均满足设计要求的转向节臂零件.     

空心双拐曲轴加载路径优化与成形规律

目的研究加载路径对空心双拐曲轴成形效果的影响。方法基于有限元分析软件,对304不锈钢双拐曲轴内高压胀形工艺进行有限元仿真,分析了加载路径对双拐曲轴胀形高度与壁厚的影响,并对开裂、起皱等缺陷产生的原因进行分析,最后,根据数值模拟结果,对双拐曲轴进行实际成形试验,并将数值模拟结果与试验结果进行对比。结果成形压力小于20 MPa时,管坯产生起皱;成形压力大于60 MPa时,管坯产生开裂。通过试验获得了壁厚分布均匀的双拐曲轴零件,并且数值模拟结果和试验结果基本一致。结论轴向进给大、内压不足容易导致过渡圆角处起皱;轴向进给小、内压过大容易导致拐部顶端开裂。只有设置合理的加载路径才能成形出壁厚均匀性好,胀形高度达到要求的双拐曲轴。     

补料比及反冲推头倾角对Y型管内高压成形质量的影响研究

目的 解决5A02铝合金Y型管在内高压成形过程中易出现破裂和内凹缺陷的问题,以获得最佳成形质量的管件,对成形中的补料比和反冲推头倾角进行研究。方法 使用内高压成形机进行实验,分析了管件的表面质量、管件壁厚分布情况,研究了补料比和反冲推头倾角对Y型管成形质量的影响。选取端面倾角大小分别为0°、13.5°、27°的反冲推头进行实验,设计了1.5∶1、2∶1、2.5∶1和3∶1 4组补料比进行对比分析。结果 比较3种不同反冲推头成形得到的管件,通过对支管成形效果的分析,确定13.5°为最佳反冲推头倾角;补料比在1.5~2.5时可成形出Y型管,补料比为2∶1时,Y型管成形质量最好。为获得成形质量高的Y型管,需选择补料比为2∶1的加载路径和端面倾角为13.5°的反冲推头进行实验。结论 采用合适的反冲推头端面倾角,既可以使Y型管获得理想高度的支管,又可有效地抑制成形中期支管出现的破裂缺陷;选择合理的补料比可以避免过渡圆角内凹缺陷,也可以改善Y型管的壁厚分布情况,进一步提升管件最终的成形质量。     

Effect of loading paths on hydroforming tubular square components

The influence of loading path on tube hydroforming process is discussed in this paper with finite-element simulation. Four different loading paths are utilized in simulating the forming process of square tubular component with hydroforming and the result of different loading path is presented. Among the result, the thickness distribution of bilinear loading path is the most uniform one. It shows that the increase of punch displacement in the stage of high pressure is beneficial to the forming of component for optimized stress condition.     

Effect of Loading Paths on HydroformingTubular Square Components

［1］F.Dohamann, Ch. Hartl: J. Mater. Proc. Technol.,1996, (60), 669. ［2］A.Mustafa, K.Sutter, X.Li and A.Altan: Proc. of 2nd Inter. Conf. on Innovations in Hydroforming Technology, Ohio, USA, 1997. ［3］H.L.Xing and A.Makinouchi: Numisheet′99-13-17September, Beasncon-France, 1999, 479.     

Effect of Prestrain on Formability and Forming Limit Strains During Tube Hydroforming

The tube hydroforming process is a relatively complex manufacturing process; the performance of this process depends on various factors and requires proper combination of part design, material selection and boundary conditions. In manufacturing of automotive parts, such as engine cradles, frames rails, sub-frames, cross members, and other parts from circular tubes, pre-bending and per-forming operations are often required prior to the subsequent tubular hydroforming process to fit the tubular blank in the complex die shape. Due to these pre-- hydroforming operations, some of the strains are already developed before going to the actual hydroforming process. Such developed strains before hydroforming process in the part is called as prestrain. In this paper the study of effect of prestrain on formability and forming limit strains during tube hydroforming is done by simulation by taking the material prestrain value. The forming limit strains of pre-strained tube during hydroforming are predicted. A series of tube bulge tests for tube hydroforming are simulated by a commercial finite element solver to predict the limit strains. Numerical simulation of forming limit strains in tube hydroforming with different internal pressure and different simulation set up with or without axial feeding are considered to develop wide range of strain paths in the present work. The effects of process conditions on the forming limit strains are detailed. In this paper the forming limit strains during tube hydroforming are simulated for prestrain and compared with zero prestrain. Prediction of limits strains is based on a novel thickness based necking criterion.     

预拉深对气胀钛合金筒形件壁厚均匀性的影响

以钛合金筒形件为研究对象,针对传统气胀成形存在减薄率过大问题,开展了预拉深-气胀复合成形方法研究。采用数值模拟分析了传统气胀成形中筒底减薄率过大的原因,实验研究了不同加载路径对TA15筒形件减薄率的影响。结果表明:气胀成形的加载速度对减薄率有一定的影响,慢速气胀和快速气胀成形件最大减薄率分别为63.2%、54.2%,仅提高加载速度并不能满足壁厚均匀性要求;在有一定预拉深的情况下,通过热拉深-气胀复合成形,最大减薄率可减小到36.7%。热拉深-气胀复合成形工艺可有效改善成形件的壁厚分布均匀性.     

带壁厚偏差管坯液压胀形加载路径的研究

建立了带壁厚偏差管坯液压胀形的力学模型,揭示了不同轴向应力状态下壁厚偏差对管坯成形的影响规律,给出了带壁厚偏差管坯液压胀形加载路径设计的标准.针对某重型卡车桥壳预成形管坯的液压胀形工艺,进行了3种不同壁厚偏差管坯在不同典型加载路径下的有限元模拟,结果表明:内压升高至最大保持恒定,管坯薄壁侧均在合模前发生开裂且薄壁侧与厚...     

FEA comparison of high and low pressure tube hydroforming of TRIP steel

The increasing application of hydroforming for the production of automotive lightweight components is mainly due to the attainable advantages regarding part properties and improving technology of the forming equipment. However, the high pressure requirements during hydroforming decreases the costs benefit and make the part expensive. Another requirement of automotive industries is weight reduction and better crash performance. Thereby steel industries developed advanced high strength steels which have high strength, good formability and better crash performance. Even though the thickness of the sheet to form the component is reduced, the pressure requirement to form the part during expansion is still high during high pressure hydroforming. This paper details the comparison between high and low pressure tube hydroforming for the square cross-section geometry. It is determined that the internal pressure and die closing force required for low pressure tube hydroforming process is much less than that of high pressure tube hydroforming process. The stress and thickness distribution of the part during tube crushing were critically analysed. Further, the stress distribution and forming mode were studied in this paper. Also friction effect on both processes was discussed.