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.     

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。     

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.     

轧制差厚板成形极限场

摘要：轧制差厚板板料厚度和材料性能分布不均匀,准确预测差厚板零件的成形极限变得十分困难。首先将差厚板的过渡区离散成若干等厚板的组合,对每一个厚度下的板料进行不同路径的凸模胀形数值模拟,拟合出不同厚度板料的成形极限曲线,对厚度进行插值获取差厚板的成形极限场。最后,采用成形极限场对差厚板筒形件的成形极限进行预测。研究结果表明：采用数值模拟、拟合以及插值的方法得到的成形极限场,可以较为准确地预测实际差厚零件的成形极限。     

Springback behavior of tailor rolled blank in U-shape forming

The springback of tailor rolled blanks with quenching and partitioning steels was investigated.In order to find out the springback behavior and related influence factors for the novel sheets,both experimental and simulation methods have been used to compare and analyze the springback characteristics of equal thickness blanks and tailor rolled blanks in U-channel forming.From the results,the overall springback angles of tailor rolled blanks at thin and thick sides are respectively 106.79° and 99.705°,which are both lower than those of the corresponding equal thickness blanks.Due to the existence of the thickness transition zone,the stress distribution in thin and thick sides of blanks is changed.The location of dangerous region in thin side of tailor rolled blanks is closer to the end of side,and the thick side moved to the middle of straight wall,which are different with the equal thickness blanks.Afterwards,the released quantitles of tangential stress and strain per unit section of blank are adopted to calculate relative springback angles and give novel evaluation criteria for qualitatively analyzing the amount of springback angles.By comparing the results,it shows that the tangential strain method is more suitable for the actual situation.     

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.     

基于Autoform的汽车门背板成形仿真分析

基于Autoform有限元仿真分析软件,对汽车门背板冲压过程中孔边缘冲压开裂原因进行分析,孔边缘减薄率较大是引起汽车门背板孔边缘冲压开裂的原因。为此,分别调整压边圈冲程、孔半径、孔间距和孔向上偏移量,分析其对冲压过程中孔边缘减薄率的影响。结果表明,增加或减小压边圈冲程、减小孔半径、增加孔间距和孔向上偏移量均有利于汽车门背板孔边缘减薄率的改善;调整孔半径和压边圈冲程对汽车门背板孔边缘减薄率影响较大,而调整孔间距和孔向上偏移量对孔边缘减薄率影响较小。结合现场实际情况,将孔半径由40 mm调整为30 mm,试冲压后汽车门背板孔边缘冲压开裂问题得到有效解决。     

基于Autoform的汽车门背板成形仿真分析

基于Autoform有限元仿真分析软件,对汽车门背板冲压过程中孔边缘冲压开裂原因进行分析,孔边缘减薄率较大是引起汽车门背板孔边缘冲压开裂的原因。为此,分别调整压边圈冲程、孔半径、孔间距和孔向上偏移量,分析其对冲压过程中孔边缘减薄率的影响。结果表明,增加或减小压边圈冲程、减小孔半径、增加孔间距和孔向上偏移量均有利于汽车门背板孔边缘减薄率的改善;调整孔半径和压边圈冲程对汽车门背板孔边缘减薄率影响较大,而调整孔间距和孔向上偏移量对孔边缘减薄率影响较小。结合现场实际情况,将孔半径由40 mm调整为30 mm,试冲压后汽车门背板孔边缘冲压开裂问题得到有效解决。     

Experimental Analysis and Prediction of Springback in V-bending Process of High-Tensile Strength Steels

Experimental setup has been designed, to study the effects of thickness, width, bend angle and machine tool parameters on the springback, in two high-tensile strength steel grades, namely JSC440 and JSC590, during the V-bending process. Relationship between the springback and the parameters are analyzed using plots. Optimal combination of parameters for the minimum springback is evaluated. Analysis of variance has been carried out to analyze the magnitude of influence of these parameters on the springback. Using the experimental results, analytical models for the prediction of springback for the combinations of blank thickness, width, bend angle and machine tool parameters have been developed. Results reveal that in V-bending of JSC440, thickness and width are the dominant factors influencing the springback, whereas in JSC590 steel, insignificant change in springback is observed with the change in width of blank and using the hydraulic press with holding. However, thickness of steel sheet and bend angle influence significantly the springback in JSC590 steels.

     

Robustness of the sheet metal springback cup test

The robustness of a proposed test for elastic springback characterization of sheet metal has been examined using a matrix of defined experimental errors. A series of flat bottom deep drawn cups made from AISI 1010 steel sheet were examined. It was found that misalignment of the blank over the forming tool and error in the vertical location where the springback ring was cut from the cup sidewall had the largest effect on the resulting springback opening. Other experimental errors involving cup height and ring width were found to be less important. The effect of in-plane anisotropy of mechanical properties on springback was negligible. The results are examined in terms of measured through thickness residual stresses and elastic bending of beams with circumferential thickness gradients.     

薄腹板近终形异形坯连铸温度场数值模拟

 薄腹板异形坯更体现了近终形的特点。采用有限元数值模拟计算了薄腹板异形坯连铸温度场,分析了不同拉速、比水量对连铸过程温度、坯壳厚度和液芯长度的影响。结果表明：异形坯不同位置的温度和坯壳厚度不均匀,当异形坯腹板较薄时,腹板处凝固传热较慢,腹板处和R角处坯壳最薄弱,比翼缘边部薄约4mm;拉速每提高0.1m/s,异形坯出结晶器时的表面温度会提高约80～100℃,坯壳厚度会减薄0.8～1.2mm,液芯长度增加1.2～1.6m;比水量每提高0.05L/kg,异形坯出二冷段时的表面温度会降低约8～16℃,液芯长度缩小0.13m。     

Status and Innovation Trends in Hot Stamping of USIBOR 1500 P

Thanks to its superior mechanical properties after hot stamping, USIBOR 1500 P experiences a very rapid growth in anti‐intrusion applications of automotive structures (bumpers, doors, bodies‐in‐white). As the blank is stamped at high temperature (typically between 600°C and 800°C) and then immediately quenched in the closed forming die, the very high strength level of 1500 MPa can be achieved without shape deviation or springback, and for very complex shapes. This performance cannot currently be matched by any other cold stamped material. This paper intends to give a short overview of the current status in application of USIBOR 1500 P, with a specific focus on the thermomechanical modelling of its stamping behaviour in finite element simulation. Current innovation trends with respect to the material itself, its processing and the opportunities it offers in terms of tailored mechanical properties will be presented and discussed.     

热冲压工艺参数对零件成形性影响规律分析

主要研究了热冲压工艺参数对热冲压后零件成形性的影响规律。热冲压工艺参数主要包括冲压速度、压边力、摩擦因数和板料温度,每个工艺参数均分为低、中、高3个水平。结合测试方案设计和仿真模型,利用方差分析研究不同工艺参数对零件成形性的影响程度;同时,利用量化分析方法确定不同水平的工艺参数对零件成形性影响程度的量化值。结果表明,工艺参数对零件减薄率的影响程度由重到轻的顺序为摩擦因数、板料温度、冲压速度和压边力,其中摩擦因数影响程度的量化值约为97.3%。     

Stretch Bending of Z-section Stainless Steel Profile

The stretch bending properties of a new Z-section stainless steel profile were investigated by simulation.The causes of the forming defects,such as section distortions and poor contour precision,were analyzed,and the corresponding controlling methods were proposed.The results show that the main forming defects for the stretch bending of the Z-section profile were the flange sagging,the sidewall obliquing inward,the bottom surface upwarping,and the bad contour accuracy;the cross-section distortions were mainly induced by the shrinkage of the sidewall,which could be eliminated by increasing the sidewall height of the profile reasonably;the poor contour precision was mainly due to springback,which could be controlled by modifying the die surface based on the springback amount;for the investigated bending beam,the proper sidewall height compensation was 2mm,and the suitable die surface modification amount was 1.2times of the springback amount,when the elongation was 10% of the initial profile length.Stretch bending tests were conducted on a new type of die with adjustable bending surfaces,and high quality components were achieved,which verified the effectiveness of the defect controlling measures.     

Control over Mechanical Properties and Microstructure of BR1500HS Hot-stamped Parts

The hot-stamping processing parameters are of critical importance in transforming ultra-high-strength steel(UHSS)into high-quality parts,which were studied by mechanical properties tests,metallographic observations and calculation analysis method based on hot stamping experiments and numerical simulation technology,the mechanical properties,thickness,dimensional accuracy,and microstructure of the hot-formed parts are analyzed to determine the influence of different processing parameters for UHSS parts formed from BR1500HS.The results indicate that the quenching time had the most significant impact on the mechanical properties of the parts,and longer quenching time resulted in better mechanical properties.In addition,the pressing speed had a significant influence on the thickness of the formed parts,and the part-opening temperature had the most significant effect on the dimensional accuracy of the parts.And to get hot-stamped parts with excellent quality,the optimum process conditions should be set as heating temperature of 930℃,soaking time of 4min,stamping force of 7MPa,pressing speed of 75mm/s,quenching time of 15s,and water-flow rate of 1.1m/s.     

特厚钢板轧制缺陷压合临界条件物理模拟试验

由国内某厂提供的320 mm的有缺陷连铸坯,试样尺寸是160 mm×100 mm×180 mm,在东北大学轧制技 术及连轧自动化国家重点实验室轧制。模拟比为2.0,按平均压下率小、中、大,将试件分成3组,每组轧成3种不 同厚度的成品板,其中中等平均压下率是按缺陷临界压合条件制定,既粗轧道次满足动态临界几何条件 l/ h = 0.53。轧制后经超声波检验合格,验证了缺陷压合的临界条件。     

Experimental Characterization of Heat Transfer Coefficients During Hot Forming Die Quenching of Boron Steel

The heat transfer coefficient (HTC) between the sheet metal and the cold tool is required to predict the final microstructure and mechanical properties of parts manufactured via hot forming die quenching. Temperature data obtained from hot stamping experiments conducted on boron steel blanks were processed using an inverse heat conduction algorithm to calculate heat fluxes and temperatures at the blank/die interface. The effect of the thermocouple response time on the calculated heat flux was compensated by minimizing the heat imbalance between the blank and the die. Peak HTCs obtained at the end of the stamping phase match steady-state model predictions. At higher blank temperatures, the time-dependent deformation of contact asperities is associated with a transient regime in which calculated HTCs are a function of the initial stamping temperature.     

高强高韧性厚规格E36船板生产工艺模拟试验

采用小炉真空冶炼150kgE36坯料,锻造后在实验室进行了热轧模拟试验和正火处理。检测结果表明,TMCP工艺下（二阶段轧制,轧后水冷速度在5～10℃/s）,随成品厚度增加,强度、断后伸长率、冲击功降低,60、70mm钢板中心处的冲击功低于标准要求,且晶粒粗大,并存在轻微带状组织;经过910℃±20℃正火处理工艺,钢板内部混晶组织得到了改善,强度略有降低,断后伸长率和冲击值明显提高。因此,钢板厚度〈40mm时可以采用TMCP工艺进行生产,而厚度〉40mm则需要进行热处理。     

TWIP950在某新车型前纵梁的应用可行性研究

本文对第二代AHSS典型钢种TWIP950的机械性能包括拉伸强度、n值、r值和烘烤硬化性进行了试验.采用1.5 mm厚度TWIP950替代1.6 mm厚度DC05进行轻量化设计的前纵梁正碰仿真结果表明,使用TWIP钢在减重6.25%的同时具有更佳的吸能效果.通过冲压仿真和现场试制对两种材料的冲压成形性进行了比较,结果表明TWIP950在具有更好成形性的同时也面临更大的回弹.总之,在模具设计时进行有效的回弹控制并保证钢板理想的边缘状态,TWIP950具备在前纵梁的轻量化应用可行性.