矩形盒拉深变压边力加载规律及预测

目的解决板料拉深过程中出现拉裂、起皱、拉深不充分等缺陷的问题。方法利用专业分析板料成形的软件Dynaform,研究分析了非轴对称件矩形盒,在几种典型的变压边力下的拉深成形性能,获得了成形效果较好的加载模式,进而利用仿真软件Dynaform获取了样本数据。结果建立了矩形盒拉深成形变压边力网络模型并对其学习训练,最后对神经网络预测结果及仿真结果所得到的变压边力加载曲线进行多项式拟合,获取了最佳压边力控制曲线。结论在板料拉深过程中,通过控制压边力的大小,能够较好地发挥材料的流动性,改善制件的最终成形效果。     

复杂轿车前底板变压边力数值模拟和物理模拟研究

为了有效地解决实际生产中如何优化复杂轿车前底板拉深成形过程中的变压边力工艺,首先基于相似物理模拟理论建立了前底板的简化物理模拟模型,其次通过数值模拟手段从众多典型变压边力模式中得到一条最优化变压边力加载曲线,使拉深件不出现起皱和拉破现象,且厚度分布最均匀.最后通过实际物理模拟实验对比来验证所得结果.数值模拟和物理模拟最终结果均表明:U型变压边力加载模式是复杂轿车前底板拉深成形的较优压边力控制曲线,其状态下不仅拉深工件的厚度最大减薄率最小,而且工件的最终厚度变化率的整体均方差为最小.     

控制压边力改善铝合金板成形性能的研究

以5052H32铝合金板为研究对象,以有限元数值模拟和基于计算机控制多点变压边力液压压力机的实验为手段,研究随位置变化的压边力对铝合金板成形性能的影响.研究结果表明:合理地控制随位置变化的变压边力可以显著提高铝合金板的成形性能,增加盒形件的拉深深度(最大拉深高度提高约12%);随位置变化的压边力对铝合金成形性能改进的主要原因是减少破裂危险区域壁厚减薄和应变的峰值;采用Barlat 96屈服准则描述铝合金的屈服行为具有较高精度,数值模拟和实验的偏差较小.     

基于变压边力的侧围外板成形研究

目的 为了提高侧围外板成形裕度,降低拉延开裂风险。方法 运用CATIA软件设计了侧围外板精细化工艺模面,并借助AutoForm软件对侧围外板拉延成形过程进行了有限元分析。结果 在恒定压边力加载的工况下,侧围外板在后三角窗及后门洞区域发生轻微开裂,无法满足成形要求。基于恒定压边力工况条件,对压边力加载方式进一步研究,提出变压边力工况条件,并模拟了9种变压边力加载方式下的成形效果,从中筛选出最优变压边力工况条件,改善了侧围外板拉延成形性,消除了开裂风险。将最优仿真数据用于侧围外板实际试模,试模结果与仿真结果基本一致,零件成形良好,最大减薄率为19.8%,最大增厚率为6.7%,符合产品质量需求,证明了变压边力工艺方案的可行性。结论 变压边力工况条件可以提高零件成形裕度。     

锥形件拉深智能化控制中压边力的控制规律

法兰起皱、侧壁起皱和侧壁破裂是拉深成形的主要障碍,而合理控制压边力是防止起皱破裂的关键所在.在总结前期研究成果的基础上,结合拉深成形过程的特点,在成形三极限图中给出了圆锥形零件拉深成形的成功区域,并提出了获得最佳压边力控制规律的方法.这为圆锥形零件拉深成形中的模具设计、工艺参数的制定提供了依据,也为拉深智能化控制提供了保证.     

TA1纯钛微型杯件软模微拉深成形工艺研究

目的 提高现有微成形工艺的可成形性,解决薄板易破裂等缺陷,探究薄板软模微拉深成形工艺的工艺参数对成形性的影响,致力于制造具有更大拉深比的微型杯件。方法 采用退火后的纯钛薄板作为原始板材,设计了薄板的软模微拉深成形模具进行实验。实验中探讨了工艺参数和材料参数对微型杯件极限拉伸比的影响。工艺参数包括压边力、橡胶性能和润滑方式,材料参数主要是晶粒尺寸。结果 通过控制压边力能够避免微拉深工艺中的缺陷。压边力过低会导致法兰区域起皱,压边力过高会导致上圆角部位破裂。采用刚度系数为72N/mm的压边弹簧能够有效避免起皱和破裂。选用硬度为65HA的聚氨酯橡胶能够成形出极限拉深比最大（为2.64）的纯钛微型杯件。软模微拉深工艺必须采用有效的润滑方式来提高板材的流动行为。采用蓖麻油润滑能够有效避免微型杯件的破裂缺陷。板材的晶粒尺寸对极限拉深比的影响是最强烈的。晶粒尺寸为8.4μm的纯钛薄板能够制造出极限拉深比为2.64的微型杯件,而随着晶粒尺寸的增大,微型杯件的极限拉深比显著下降。结论 通过软模微拉深工艺并且采用合适的工艺参数成功制备了极限拉深比为2.64的微型杯件,与现有工艺相比,所获得的微型杯件的极限...     

2A12 铝合金平底筒形件充液拉深数值模拟研究

目的研究工艺参数对2A12铝合金平底筒形件充液拉深成形的影响规律。方法采用数值模拟方法,研究了液室压力加载路径、成形液室压力、压边力和压边间隙对板材充液拉深成形效果的影响。结果获得了充液拉深成形的失效形式,以及不同工艺参数下零件壁厚减薄率的变化规律。成形前期,液室压力不宜过大,最大液室压力在10~25 MPa之间,压边间隙在1.05~1.15mm之内,可有效避免零件过度减薄和法兰起皱。结论合理的液室压力加载路径和压边间隙,可以有效地控制零件法兰区起皱,防止凸模圆角处破裂。     

双曲扁壳类汽车覆盖件刚度的试验研究

为进一步掌握汽车覆盖件刚度控制机制,建立了以双曲扁壳件为研究模型的成形试验及刚度测试分析系统.分别完成了成形工艺条件中不同压边力、拉深深度条件下,双曲扁壳件的成形试验,5种约束方式下的双曲扁壳件刚度测试试验.分析了压边力、拉深深度和约束方式对刚度的影响规律.研究表明:刚度测试时的约束方式对刚度有重要影响,约束越大,刚度越大;约束的改变对刚度的影响远大于其他工艺条件(压边力和拉深深度)对刚度的影响,提出刚度测试时为准确获得成形工艺条件等对刚度影响的最佳约束方式;工艺条件中压边力及拉深深度的变化对刚度亦有不同程度的影响,刚度随着压边力的增加而增大;成形时的拉深深度越大,刚度值也越大.上述工艺条件的改变对刚度的影响远大于厚度减薄对刚度的影响,在实际生产中,可以通过调整成形时的工艺参数提高汽车覆盖件的刚度.     

简单形状零件拉深成形智能化控制技术研究

板材成形智能化是冲压工艺的一项新技术.以圆锥形件和锥壁盒形件为研究对象,分别讨论了实现实时监测、实时识别、实时预测和实时控制所需的关键技术,逐步形成了拉深成形智能化控制的理论基础.在实时识别和实时预测阶段采用人工神经网络,在压边力控制阶段采用基于破裂临界曲线的控制方法,能够得到较满意的结果.研究过程中开发了智能化拉深实验系统,实验证明识别、预测精度较好.     

贮箱箱底充液拉深成形工艺参数的多目标优化

充液拉深成形技术能够实现大型贮箱箱底的整体成形,然而成形件的质量受到许多工艺参数的影响.不合适的工艺参数会导致成形件的起皱甚至破裂.在本文中,针对预胀压力、液室压力、压边力、压边圈圆角半径这些关键的工艺参数,以提高成形件的质量、降低起皱和破裂缺陷为目标,利用NSGA-Ⅲ算法进行多目标优化,得到了最优的工艺参数.通过实验验证了提出方法的有效性和结果的准确性.     

Springback reduction with control of punch speed and blank holder force via sequential approximate optimization with radial basis function network

This paper proposes a springback reduction technique with the control of punch speed and blank holder force (BHF) via sequential approximate optimization (SAO). Springback is one of the major defects in sheet forming and its reduction is a crucial issue for improving product quality. Computer-aided-engineering is one of the helpful tools for predicting springback and widely used in automotive industries. Various approaches are considered for springback reduction, and we optimize the punch speed as well as BHF (variable BHF). Sheet forming simulation is generally costly and time-consuming, and the SAO with the radial basis function network is used to determine the optimal punch speed and variable BHF. The U-shaped forming in NUMISHEET’93 is used in the numerical simulation. The standard deviation of the bending moment is minimized subject tearing evaluated with the forming limit diagram. The punch speed and the variable BHF are taken as the design variables. The validity is examined through numerical simulation.     

The effect of blank holder force on the stamp forming behavior of non-crimp fabric with a chain stitch

A blank holder force (BHF) is applied to a fabric preform in stamp forming operations to impose a tension onto it, which helps to reduce the occurrence of defects such as wrinkles. The current study aims to quantitatively investigate BHF’s effect on formed shapes by carrying out a stamp forming operation on non-crimp fabrics with various BHFs. A non-crimp fabric (NCF) with chain stitches was used as the fabric preform. The NCF exhibits asymmetrical shear behavior due to its stitches, which can be confirmed from a picture frame test. This asymmetrical shear behavior causes NCFs to be formed into asymmetrical shapes when stamped by a symmetrically spherical forming tool. The asymmetrical forming behavior was scrutinized using various BHFs and measuring the local change in fiber angle along the formed parts’ arc lines. It was observed that BHF lessens the formed shape’s asymmetry and influences the NCF’s in-plane buckling and wrinkling behavior. The BHF’s effect on wrinkling behavior was quantitatively characterized using an image processing method that can assess a fabric preform’s wrinkling level. Finally, using these experiments and simulations, we discuss the feasibility of finding the optimized forming condition that can process the NCF preform into complex shapes with few or no wrinkles.     

基于灰色关联分析的轧制差厚板盒形件充液拉深成形工艺参数多目标优化

目的 将充液拉深工艺引入轧制差厚板零件的成形,为了进一步掌握差厚板的充液拉深成形性能,对差厚板盒形件充液拉深成形过程进行研究。方法 通过理论推导获取临界液池压力公式,在此基础上运用数值模拟方法分析液池压力比对差厚板厚度减薄率和厚度过渡区移动量的影响,采用正交试验和灰色关联分析获取成形参数对差厚板盒形件成形性能的影响规律和最优参数组合,实现对差厚板盒形件充液拉深成形工艺参数的多目标优化。结果 随着薄-厚侧液池压力比的增大,差厚板最大厚度减薄率先减小后增大,过渡区移动量先增大后趋于平稳,薄-厚侧液池压力比为2较为合理。厚侧压边力、摩擦因数、薄-厚侧液池压力之比、薄-厚侧压边力之比、厚侧液池压力对差厚板盒形件充液拉深性能的影响程度依次减小。结论 采用灰色关联分析得到的最优工艺参数组合来完成差厚板盒形件的充液拉深成形,能够有效地抑制差厚板零件厚度的过分减薄及厚度过渡区的过度移动,进而提高差厚板的成形性能。     

基于快速成形的低温冰型制造技术研究

研究了冰型制造中的喷射技术和工艺问题。通过实验认为基于电磁阀高频振荡的离散喷射方式最适合于低温冰型成形。提出了临界成形时间的概念，并研究了影响成形质量的诸多因素。通过工艺参数优化，制造出质量较高的冰型。     

Some guidelines for promoting high temperature deformation of metallic alloys

Capacity to reach large deformation at high temperature is an important issue in many forming processes of metallic alloys. It is well known that a low value of the stress exponent (or a concomitant high value of the strain rate sensitivity parameter) is a key point for controlling resistance to necking. A first way for decreasing the stress exponent is to get superplastic properties but it frequently requires dealing with fine microstructures which can be difficult to produce and to preserve. Moreover, in the case of single phase alloys, like aluminum or magnesium alloys, superplastic deformation generally induces damage which can result in premature fracture or damaged components after forming. The aim of this paper is to give some guidelines for promoting high temperature deformation of metallic alloys, with a particular attention given to superplastic forming. The possibility to reduce the temperature of superplastic forming (SPF) for titanium alloys, the capacity to get a better understanding of the specificities of damage process in the case of superplastic deformation and the ability to get large strains to fracture avoiding the production of fine grains before strain are more specifically discussed.     

Extension of the normalized Cockcroft and Latham criterion with temperature-dependent critical damage values for predicting chevron cracks in solid forward extrusion

The fracture criterion according to Cockcroft and Latham in combination with the element deletion method is suitable for a numerical prediction of chevron cracks in solid forward extrusion. Conventionally, the element deletion method uses a constant critical damage value. The exceedance of this value leads to the deletion of elements from the mesh. The use of constant critical damage values leads to an inaccurate prediction of crack location and form when forming takes place at different process temperatures. Therefore, this work proposes the use of a temperature-dependent critical damage value. Implemented in Deform 2D through user subroutines and verified by experiments it is shown that the proposed methodology improves the numerical prediction of chevron crack formation for process temperatures ranging from cold to warm forming.     

Stress and strain based fracture forming limit curves for advanced high strength steel sheet

In this work, strain based fracture forming limit curve (FFLC) of advanced high strength (AHS) steel grade 980 was determined by means of experimental Nakajima stretch-forming test and tensile tests of samples under shear deformation. During the tests, a digital image correlation (DIC) technique was applied to capture the developed strain histories of deformed samples up to failure. The gathered fracture strains from different stress states were used to construct the FFLC. Subsequently, the FFLC in the strain space was transformed to a principal stress space by using plasticity theories. As a result, the fracture forming limit stress curve (FFLSC) of examined steel was obtained. Furthermore, fracture locus (FL) as a relationship between stress triaxialities and critical plastic strains was determined. Hereby, two anisotropic yield functions, namely, the Hill’48 and Yld89 model were taken into account and their effects on the calculated curves were investigated. To verify the applicability of the obtained limit curves, rectangular cup drawing test and forming tests of so-called Diabolo and mini-tunnel samples were performed. Obviously, the FFLSCs and FLs more accurately described the failure occurrences of 980 steel sheets than the FFLCs. In addition, it was found that the drawing depths predicted by the FLs and the Yld89 yield criterion slightly better agreed with the experimental results than those from the FFLSCs and the Hill’48 model, respectively.