轧制差厚板方盒形件拉深成形起皱缺陷影响因素

轧制差厚板由于板料厚度、力学性能的不均匀,在成形过程中容易发生起皱缺陷。综合采用数值模拟和冲压实验2种手段对差厚板方盒形件拉深成形起皱缺陷进行研究。讨论了差厚板方盒形件起皱缺陷的发生机理,并以厚度应变为评价指标,分析了板料尺寸、过渡区长度、过渡区位置、板料厚度等板料几何参数对差厚板起皱缺陷的影响,最后给出了抑制起皱缺陷的措施。研究表明:差厚板方盒形件最容易发生起皱的部位是薄板侧和厚板侧的法兰区以及过渡区法兰部分。板料尺寸越小,过渡区长度越短,则差厚板越不容易发生起皱,采用较大或者较小的板厚差均能够抑制起皱现象的出现,而过渡区中心位置偏离板料中心则可能导致差厚板起皱现象的发生。     

轧制差厚板纵向弯曲回弹规律分析

为了推动轧制差厚板在汽车梁结构件上的应用,以U型件为对象,研究了轧制差厚板的纵向弯曲回弹特性。首先完成了差厚板U型零件纵向弯曲成形数值模拟,分析了差厚板的回弹趋势,讨论了差厚板的应力分布,揭示了差厚板弯曲回弹规律,探讨了差厚板等效应力的影响因素,并通过试验对回弹仿真结果进行验证。结果表明,不均匀的应力分布是纵向弯曲的差厚板U型件沿弯曲轴方向上回弹不一致的根本原因,退火处理能够减小差厚板卸载前后的应力差,从而实现抑制差厚板回弹的作用。差厚板的板料尺寸、厚度、过渡区长度均会对差厚板的等效应力造成较大影响,从而改变差厚板的回弹大小及分布。另外,差厚板零件不同厚度部位的回弹相互牵制,使得各部分的回弹量趋向一致,从而导致差厚板的回弹量均介于薄、厚等厚板之间。     

轧制差厚板纵向弯曲回弹分析与预测

将轧制差厚板应用于梁类零件的制造能够实现汽车轻量化，但同时也带来了更为复杂的回弹问题。为了掌握差厚板梁类零件的回弹机理并获取各种工艺参数对回弹的影响规律，通过仿真与试验手段研究差厚板U型件纵向弯曲回弹问题。首先，建立差厚板U型件纵向弯曲成形与回弹有限元模型，完成成形与回弹过程仿真，并通过冲压试验对仿真结果进行验证，讨论差厚板回弹分布情况及其原因，分析退火工艺对差厚板回弹的影响规律及内在机理。接着，基于差厚板U型件回弹仿真结果，进行正交试验设计，在此基础上完成回弹影响因素的灰色关联分析，获取各因素的影响水平以及优化的参数组合。最后，完成BP神经网络模型的构建，实现差厚板U型件的回弹预测。研究结果表明，双斜率退火工艺能够减小差厚板的回弹，并且使得回弹分布更加均匀。灰色关联分析获取的最优工艺参数组合为过渡区位置-20 mm、过渡区长度50 mm、板料厚度1.6/2.0 mm、板料尺寸80 mm×230 mm,采用最优工艺参数组合成形的差厚板U型件可以获取更低水平的回弹量。不同工艺参数对差厚板U型件弯曲回弹的影响程度按降序排列为板料尺寸、过渡区位置、过渡区长度、板料厚度。建立的神经网络模型具有...     

冷轧差厚板轧制极限差厚量研究

为研究冷轧差厚板轧制时厚度过渡段的极限差厚量,采用相关轧制理论建立了差厚板轧制过程的轧制力模型、电机功率模型和轧制力矩模型,并根据设备能力得到轧制力、电机功率及轧制力矩的约束条件,通过编写程序得到了多工况的批量计算。研究结果表明,来料厚度和厚区厚度对极限差厚量有很大影响。同一来料当厚区厚度越大时,极限差厚量也越大。来料相同且在差厚过渡区以一定轧制力轧制时,随着厚区厚度的逐渐减小,极限差厚量出现先减小后增加的情况。当厚区厚度一定时,若轧制力不变,随着来料厚度的增加,差厚板过渡区极限差厚量逐渐减小。     

轧制差厚板横向弯曲成形仿真与试验

为了抑制轧制差厚板在横向弯曲成形过程中的缺陷问题,采用仿真和试验方法研究轧制差厚板U型件的横向弯曲过程。分析差厚板U型件在横向弯曲过程中的成形特点,探讨弯曲回弹以及过渡区移动等缺陷的发生机理。结果表明,横向弯曲的差厚板U型件在成形过程中除了会产生回弹缺陷外,还会发生厚度过渡区移动;差厚板薄、厚板侧的厚度以及性能差异是差厚板产生缺陷的根本原因;采用退火处理能够减小差厚板的回弹量,但是会导致过渡区移动量增大;板料尺寸越大,回弹量与过渡区移动量也随之增大。     

基于AutoForm的超深冲汽车电池盒成形工艺设计与仿真

以拉延深度高达238 mm的新能源汽车电池盒上板为研究对象,通过分析零件图的结构形状特征,利用Auto Form有限元分析软件建模及数值模拟方法对板料的冲压成形过程进行了多种拉延方案的工艺模拟分析,依据有限元软件的成形仿真结果预测板料在拉延过程中出现的开裂、起皱等成形缺陷,研究分析了缺陷产生的原因,确定了零件的最佳成形方案,并优化了成形工艺参数。     

整体式侧围冲压成形仿真过程中影响因素窗口分析

整体式侧围外板是汽车覆盖件中形状复杂、尺寸大以及表面质量要求高的零件。由于零件的材料厚度薄、各区域变形状态和变形量差异大,其冲压过程的拉深变形容易受材料性能、形状尺寸、模具状态、接触润滑和工艺参数的影响而产生成形缺陷。尤其在模具状态和工艺参数一定的情况下,其成形性对材料性能参数变化较为敏感。因此采用数值模拟技术对左侧围外板零件成形过程进行大量的成形仿真,考虑多个重要影响因素对板料成形性能的影响,以确定此零件冲压成形时易失稳部位的关键影响参数,并确定该零件材料参数和冲压工艺参数窗口。     

TC4盒形钣金零件气压成形工艺的研究

采用普通工业TC4板料,在MTS高温拉伸试验系统上进行了不同变形条件的恒速拉伸试验,研究材料的高温变形行为.分析了5类通用高温本构关系对该材料真实应力应变曲线的拟合情况.最终,采用经典的Kumar模型建立了TC4的高温本构关系.利用MARC分析TC4机身盒形零件的气压成形过程,依据正交试验原理确定FEA仿真方案,并对成形模具进行了设计.以壁厚标准差为评价指标,采用极差分析法确定各因素对指标的影响程度和最佳工艺参数,并通过气压成形试验获得满足质量要求的零件.     

基于M-K理论的6016铝合金成形极限曲线预测

近年来,为实现汽车车身轻量化,大量的铝合金材料被用于汽车车身制造,由于6016铝合金具有良好的烘烤性能,被大量使用.但是传统的冷成形技术并不能成形复杂零件,因此热冲压-冷模具淬火成形技术被用到铝合金的成形过程中,板材成形领域中一个重要的性能指标是成形极限.本论文使用理论预测和试验两种方法对6016铝合金成形极限曲线进行了研究.首先,建立了考虑应变强化和应变速率强化的Fields-Bachofen本构方程,并将此本构方程引入到成形极限理论推导过程中;然后,基于M-K凹槽理论,对6016铝合金成形极限曲线进行了理论预测,并且采用Nakazima试验方法对预测结果进行了验证.结果显示,随着初始厚度不均度的增加,预测曲线向纵坐标的正方向移动;通过实验值和预测值的对比发现M-K凹槽理论对成形极限曲线的预测是可行的、准确的.      

基于插值多项式的成形极限图数据处理方法

为了获取准确的金属板材成形极限曲线,采用成形极限实验数据路径选择和分区域多项式拟合的方法处理实验数据。数据路径曲线根据最小主应变划分为左侧曲线和右侧曲线,采用多项式法对曲线进行拟合计算,然后合并形成成形极限曲线。计算结果表明,采用该方法可以快速准确地生成需要的成形极限曲线。     

Forming Limit and Thickness Transition Zone Movement for Tailor Rolled Blank during Drawing Process

The process of automobile lightweight can be promoted by the application of tailor rolled blank(TRB)in the automobile industry.Therefore,research on the formability of TRB is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight.Aiming at the present condition of lack of researches on the influence of characteristic parameters on TRB drawing process,the drawing formability of TRB was studied with a combination method of simulation and experiment by taking square box as the research object.Firstly,drawing simulation and experiment of TRB were carried out.Then,effects of thickness transition zone(TTZ)position and blank size on the drawing formability of TRB were analyzed.Forming limit and TTZ movement for TRB square box during the drawing process were respectively discussed,when transition zones of TRB were located at different positions and blanks were of different sizes.The results indicate that lubrication condition exerts greater influence on TRB forming limit in comparison with TTZ movement,and the smaller blank size and TTZ being located at the blank center or slightly offset to the thinner side are preferable for acquiring greater forming limit and smaller TTZ movement.     

Influencing factors of wrinkle defects of tailor rolled blank for square box in drawing process

Tailor rolled blank(TRB) is inclined to wrinkle during the forming process because of the nonuniformity of blank thicknesses and mechanical properties. The wrinkle defect of TRB square box in deep drawing was studied by numerical simulation and stamping experiment. The mechanism for the wrinkle defect of TRB square box was discussed, and effects of blank size, thickness transition zone length and position, and blank thickness on the wrinkle defect of TRB were analyzed by taking thickness strain as an evaluating indicator. Finally, the measures restricting the wrinkle defects were presented. The results indicate that the spots inclined to wrinkle for TRB square box are the flange on the thinner side, the flange on the thicker side, and the flange in the thickness transition zone. The smaller the blank size and the thickness transition zone length are, the harder TRB is to wrinkle. Greater or smaller thickness difference can both restrain the wrinkle phenomenon, and thickness transition zone center offset from the blank center may lead to the occurrence of wrinkle.     

Numerical Simulation and Experimental Investigation of Springback in U-Channel Forming of Tailor Rolled Blank

 In order to grasp the springback rule of TRB (tailor rolled blank) parts after forming, the springback behavior of TRB was investigated by integrating such three means as theoretical research, numerical simulation and stamping experiments. Fundamental theories of springback were analyzed. The stamping and springback processes of annealed 1.2/2.0 mm TRB, 1.2 mm and 2.0 mm plates for U-channel were simulated, and the simulation results were compared with the experiments. The results indicate that the springback of TRB falls in between those of the 1.2 mm and 2.0 mm plates. It is desirable for the TRB U-channel to have die clearance of 1.1 times maximum blank thickness and friction coefficient of about 0.12, and longer thickness transition zone is preferable. The simulation data demonstrate reasonably good agreement with the experiments.     

Transverse Bending Characteristics in U-channel Forming of Tailor Rolled Blank

Research on the formability of tailor rolled blank (TRB)is of good practical significance and application value because of the enormous potential of TRB in the aspect of automobile lightweight.However,the forming of TRB is problematic because of the varying properties;especially,springback is a main challenge.The transverse bending (bending axis is perpendicular to the rolling direction)of TRB U-channel was studied through simulation and experiment.The forming characteristics of TRB U-channel during transverse bending were analyzed.The mecha-nisms of forming defects,including bending springback and thickness transition zone (TTZ)movement,were re-vealed.On this basis,effects of blank geometric parameters on springback and TTZ movement were discussed.The results indicate that springback and TTZ movement happen during transverse bending of TRB U-channel.Nonuni-form stress distribution is the most fundamental reason for the occurrence of springback of TRB during transverse bending.Annealing can eliminate nonuniform stress distribution,and thus diminish springback of TRB,especially springback on the thinner side.Therefore,springback of the whole TRB becomes more uniform.However,annealing can increase the TTZ movement.Blank thickness and TTZ position are the main factors affecting the formability of TRB U-channel during transverse bending.     

High‐Pressure Sheet Metal Forming of Large Scale Structures from Sheets with Optimised Thickness Distribution

In order to manufacture components optimised in regard to lightweight construction, the use of innovative forming processes like high‐pressure sheet metal forming (HBU) in combination with the use of tailor rolled blanks (TRB) as innovative semi‐finished materials is a promising solution. To realise a sufficient forming process reliability, at first, investigations on the seal system were carried out. Hereby, a non‐adjustable as well as a new adjustable seal system have been investigated and qualified as sufficient solutions for this process depending on thickness ratio and thickness gradient within the TRB. One typical workpiece geometry which offers a promising lightweight potential and which can be manufactured from TRB with the HBU‐process is the class of body structures. Therefore, an idealised large scale structure has been designed and investigated in theoretical (numerical) and experimental research. The research work has shown that this large scale structure can be manufactured sufficiently by the HBU of TRB.     

Forming Limit Investigation of AA6061 Friction Stir Welded Blank in a Single Point Incremental Forming Process: RSM Approach

In the present work, an experimental study was made to identify formability characteristics of aluminum 6061 fiction stir welded blank in an incremental forming process. Forming limit diagram, bowl height, minimum thickness and thickness distribution were studied to find formability of tailored welded blank. Firstly, series of experiments were carried out to find which joining direction caused higher formability and desired forming limit curve. For this purpose, joints with three different directions (i.e. rolling direction, transverse direction and diagonal direction) were prepared and formability i.e. formed bowl height until failure along with forming limit curves were compared. After finding the best joining direction, effect of welding process parameters i.e. rotational speed, plunge depth and travel speed on formability of welded blanks were analyzed by using response surface methodology (RSM). The results were discussed according to microstructure and fractography analysis obtained by scanning electron microscopy. After finding the effects, welded blanks with optimal parameter combination were fabricated and effect of incremental forming parameters i.e. spindle speed, feeding rate and axial step on thickness distribution were analyzed. Here, RSM was also used to find parametric and optimum setting of parameters. From the results, it was obtained that joints with diagonal direction caused higher value of bowl height. Also, tool rotary speed of 1600 RPM, travel speed of 40 mm/min and plunge depth of 0.15 mm caused higher value of bowl height implying high formability. Furthermore, it was found that selection of 0 RPM spindle speed, 600 mm/min feeding rate and axial depth of 0.6 mm resulted in higher thickness distribution.     

Properties of Large‐Scale Structure Workpieces in High‐Pressure Sheet Metal Forming of Tailor Rolled Blanks

In order to manufacture components optimised in regard to lightweight construction, the use of innovative forming processes like high‐pressure sheet metal forming (HBU) in combination with the use of tailor rolled blanks (TRB) as innovative semi‐finished material is a promising solution. Fundamental investigations on the HBU of TRB have been carried out in a joint research project at the Institute of Forming Technology and Lightweight Construction (IUL), University of Dortmund, and the Institute of Metal Forming (IBF), RWTH Aachen. The experiments performed with cylindrical parts have provided basic knowledge on the sheet material flow and resulting part properties. To achieve sufficient process reliability, a non‐adjustable as well as an adjustable seal system have been tested and proved to be suitable solutions, depending on thickness ratio and thickness gradient within the TRB. In order to demonstrate the lightweight potential of this process chain, a forming tool for an automotive body structure has been designed and tested. The experiments have shown that this large‐scale structure can well be manufactured in the HBU process from a TRB.     

Prediction and Control of Wrinkle and Fracture for Stamping Regular Polygonal Box

Based on the deformation characteristic of regular polygonal box stamped parts and the superfluous triangle material wrinkle model, the criterion of regular polygonal box stamped parts without wrinkle was deduced and used to predict and control the wrinkle limit. According to the fracture model, the criterion of regular polygonal box stamped parts without fracture was deduced and used to predict and control the fracture limit. Combining the criterion for stamping without wrinkle with that without fracture, the stamping criterion of regular polygonal box stamped parts was obtained to predict and control the stamping limit. Taken the stainless steel 0Cr18Ni9 (SUS304) sheet and the square box stamped part as examples, the limit diagram was given to predict and control the wrinkle, fracture and stamping limits. It is suitable for the deep drawing without flange, the deep drawing and stretching combined forming with flange and the rigid punch stretching of plane blank. The limit deep-drawing coefficient and the minimum deep-drawing coefficient can be determined, and the appropriate BHF (blank holder force) and the deep-drawing force can be chosen. These provide a reference for the technology planning, the die and mold design and the equipment determination, and a new criterion evaluating sheet stamping formability, which predicts and controls the stamping process, can be applied to the deep drawing under constant or variable BHF conditions.