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.     

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。     

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.     

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。     

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。     

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.     

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.     

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.     

SX55冷轧双相钢成型性能评定

在“七五”期间,鞍钢开发并生产出冷轧罩式炉退火双相钢(SX55),本文阐述SX55钢研制中的成型性能评定,指出该材料具有优越的拉胀成型性能、理想的拉深成型性能及较差的平面应变成型性能,据此,指导生产试冲及应用,取得了较好的效果。     

IF板与08Al板的成形性能研究

通过模拟成形性试验，对新型超深冲用IF钢板和传统冲压用08Al钢板的冲压成形性能进行了研究．结果表明：IF板的拉深性能、扩孔性能、胀形性能以及“拉深-胀形”复合性能等均优于08Al板，其中，扩孔性能和平面各向异性的改善最为显著；各项试验中，IF板的成形力普遍小于08Al板。     

7075铝合金板材热冲压成形中的高温摩擦

采用自制的板带高温摩擦试验机模拟实际固溶–冲压–淬火一体化热成形工艺下7075铝合金的高温摩擦过程,分别对上下摩擦头进行冷却和加热以模拟实际热冲压过程对模具和压边圈的冷却和加热,分析了下模加热温度、法向载荷和滑动速度对7075铝合金摩擦行为及磨损机理的影响。结果表明:铝合金摩擦系数随着下模加热温度的升高而增大,磨损机制由300 ℃时的黏着磨损转变为500 ℃时的黏着磨损、氧化磨损和磨粒磨损;施加法向载荷越大,摩擦系数越大,不同载荷下磨损机制均为黏着磨损及轻微的磨粒磨损,且随着载荷增大,黏着磨损程度有所加深;高滑动速度导致了磨损表面局部氧化物的生成,使摩擦系数随着滑动速度增大而减小,滑动速度为30 mm·s?1时,磨损机制主要是氧化磨损、磨粒磨损和黏着磨损。      

Effects of Thickness Ratio and Length of Thickness Transition Zone on the Tensile Behavior of Tailor Rolled Blanks

In the present work, tensile behavior of tailor rolled blanks (TRBs) made of DP590 was studied. The TRBs were produced by variable gauge rolling. The tensile specimens of TRB had thickness ratios (T_r) of 0.47, 0.52, 0.68, 0.78 and 0.89, whereas the lengths of thickness transition zone (TTZ) were 58, 75 and 110 mm. The results of tensile test along with SEM and EBSD observations revealed that the total elongation of TRBs is strongly dependent on the TTZ geometry. Accordingly, it was found out that the total elongation increases with increasing T_r. However, unprecedented results were obtained for variations of total percent elongation versus the length of TTZ. In case of tensile specimens with identical gauge length, the total elongation decreases with increasing the length of TTZ. To justify the results, a novel geometrical parameter called effective length ratio (ELR) was introduced. This new parameter showed a meaningful relation with the total elongation. Accordingly, the effects of TTZ position and geometry on the total elongation were studied utilizing ELR parameter. It was concluded that the total elongation increases with increasing the ELR parameter. Furthermore, a linear correlation between ELR and total elongation was established. This can be used to interpolate the tensile behavior of TRBs for any intermediate conditions which can be more applicable for prediction of tensile behavior without performing any tests. Finally, the influence of thickness ratio on the probability of fracture from a certain region was discussed.     

Gas‐pressure Forming of an AlMg‐Alloy Sheet at Elevated Temperatures

Forming of automotive leightweight parts using aluminium offers numerous advantages. Compared to other wrought aluminium alloys, in particular AlMg‐alloys generally show a good formability which is favourable for the production of complex parts. However, forming of Mg‐containing alloys at room temperature leads to yielding patterns preventing their implementation for class‐A‐surface applications. Furthermore, the formability of steel still exceeds that of AlMg‐alloys at room temperature. Thus, in the present study, sheet metal forming is applied at a temperature range that is typical for warm forming. It is supposed to profit from the advantages of warm forming like high achievable strains and improved surface quality of the formed part, while not having the disadvantages of long production times and high energy consumption, which is correlated with superplastic forming. Applying fluid‐based sheet metal forming in this paper, nitrogen is used as fluid working medium to satisfy the demand on high temperature resistance. Concerning the blank material used, formability of Mg‐containing aluminium alloys shows strong strain rate sensitivity at elevated temperatures. To figure out the optimal strain rates for this particular process, a control system for forming processes is developed within the scope of this paper. Additionally, FE‐simulations are carried out and adapted to the experiment, based on the generated process data. FE‐investigations include forming of domes (bulging) as well as shape‐defined forming, having the objective to increase formability in critical form elements by applying optimal strain rates. Here, a closed‐loop process control for gas‐pressure forming at elevated temperatures is to be developed in the next stages of the project.     

Production of Structure Components with Selective Properties by means of Action Media based Cold Forming

Minimising a metallic component's weight can be achieved by either using lightweight alloys or by improving the component's properties. In both cases, the material formability affects the utilisability for mass production processes. Most of the high‐strength materials show a material‐restricted formability and are difficult to forge. The formability of a material is described by its maximum forming limit. Large plastic strains can lead to mechanical damage within the material. A promising approach of handling low ductile, high‐strength alloys in a forming process is deformation under superimposed hydrostatic pressure by active media. In the present study, the influence of superimposed hydrostatic pressure on the flow stress is analysed as well as the forming ability for different sample geometries at different hydrostatic pressure and temperature levels. The experimental results show that the superimposed pressure has no influence on the plastic deformation, nor does a pressure dependent near‐surface material hardening occur. Nevertheless, the formability is improved with increasing hydrostatic pressure. The relative gain at room temperature and increase in the superimposed pressure from 0 bar to 600 bar for tested materials was at least 140 % and max. 220 %. Therefore, a cold forming process under superimposed pressure is developed to produce structure components with selective properties. For example, the gain in formability will be used to enlarge local plastic strains to higher limits resulting in higher local strain hardening and hardness. This offers new design possibilities with selectively adjusted local structure or structure component properties, especially adapted to their technical application. Additionally, by applying damage models, finite‐element analysis is used in order to predict damage occurring in the cold forming process under superimposed hydrostatic pressure for various sample geometries.     

Design of hydroforming process for an automobile subframe by FEM and experiment

Tube hydroforming technology has shown the attention of the automotive industry due to its advantages over conventional stamping and welding methods.In this study,the tube hydroforming process including tube bending,preforming and hydroforming process for an automobile subframe is analyzed and designed by the simulation software AutoForm of a finite element method (FEM) program.A parametric study is carried out to obtain the effect of the forming parameters such as initial tube size and loading path on the forming results.The simulation results are also compared with experiment results.The research indicates that the multiple forming operation of the tube hydroforming process can be simulated accurately by using the implicit code AutoForm,and the formability of tube hydroforming can be improved by designing suitable forming parameters.     

深冲搪瓷钢DC03EK析出物及其抗鳞爆性能分析

对DC03EK深冲用冷轧搪瓷钢铸坯、热轧基料进行析出物检测,对其冷轧成品卷进行析出物、抗鳞爆敏感性TH值、成形极限FLD测试。结果表明,DC03EK深冲用冷轧搪瓷钢材料中存在弥散分布的Ti(C,N)、TiN、TiC、TiS、Ti4C2S2和极少量的MnS等析出物,铸坯中析出物颗粒较大,经热轧轧制较大颗粒析出物变小,经冷轧轧制及罩式退火后,析出物变得细小并弥散分布,使得DC03EK具有高的抗鳞爆敏感性TH值,同时又具有良好的成形性。     

铍板材深冲压成形异形件探讨

冲压成形是金属板材加工异形件的最基本方式。金属材质不同,冲压成形异形件的难易程度不同,主要影响因素是冲压成形性能和冲压成形极限。文章结合铍板材的冲压成形性能和冲压成形极限,对铍板材冲压成形异形件的难易性作了探讨。     

Study of Forming Limit for Rotational Incremental Sheet Forming of Magnesium Alloy Sheet

As a lightweight material, magnesium is being increasingly used for automotive parts. However, due to a hexagonal-closed-packed (hcp) crystal structure, in which only the basal plane can move, magnesium alloy sheets exhibit a low ductility and formability at room temperature. Press forming of magnesium alloy sheets is conventionally performed at elevated temperatures of 200 °C to 250 °C and thus is known as energy consumed forming. Therefore, in view of an energy saving forming technology, we study magnesium alloy sheet forming by a rotational incremental sheet forming (RISF) at room temperature, where the rotational tool generates local heat of specimen enough to accelerate plastic deformation. The flow curves of the magnesium alloy sheet are obtained and calculated at elevated temperatures, while the yield loci of the magnesium alloy sheet are measured at room temperature. Using RISF, a square cup of 80-mm width, 80-mm length, and 25-mm height is then formed from a magnesium alloy sheet at room temperature. In addition, the strain distribution is obtained and compared with the forming limit curve (FLC) by considering the effect of the tool radius and is found to effectively predict the forming limit of a magnesium alloy sheet in RISF.