Effects of forming media on hydrodynamic deep drawing

Apart from the punch and the die, a pressurized fluid (water or oil) is used in hydroforming. The presence of such pressure media is the main difference between hydroforming and conventional deep drawing. No comprehensive study has yet been conducted on the effect of forming media on the formation of cylindrical cups via hydrodynamic deep drawing assisted by radial pressure. This study investigated the formation of such cups through Finite element (FE) simulation and experiments. First, the process was modeled numerically using ABAQUS FE software. After simulation, copper and St14 sheets were formed with water and oil as the forming media. The effect of these forming media on thickness distribution and maximum punch force was investigated. By examining the thickness distribution curve of the hydroformed cup, a close agreement was found between experimental and numerical results. Using oil as the forming media reduced thinning at the corner radius zone of the punch and increased the maximum punch force. Changing the forming media does not significantly influence the maximum thickening at the cup wall region.

     

Influences of lubrication conditions and blank holder force on micro deep drawing of C1100 micro conical–cylindrical cup

Lubrication conditions and blank holder force (BHF) are two key processing parameters in deep drawing. This is more obvious in micro forming because of the miniaturization of the specimen size. Micro conical–cylindrical cups with internal conical bottom diameter of only 0.4 mm were well formed. The influences of lubrication conditions and BHF on micro deep drawing of micro conical–cylindrical cups were investigated using a micro blanking–deep drawing compound mold. Pure copper C1100 with a thickness of 50 μm, which was annealed at 450 °C for 2 h in vacuum condition, was chosen as the specimen material. The experiments were conducted on a universal testing machine with a forming velocity of 0.05 mm/s under 4 kinds of lubrication conditions and BHF. The experimental results showed that a micro conical–cylindrical cup with internal conical bottom diameter of only 0.4 mm was well formed, and the limiting drawing ratio (LDR) reached 2.1. The polyethylene (PE) film, which decreased the drawing force and increased the drawing ratio (DR), was superior to castor oil, petroleum jelly and dry friction, and can be chosen as a proper lubricant for micro deep drawing. The rim of the micro cup seriously wrinkled when BHF was less than 4.2 N. The bottom of the micro cup cracked when the BHF was larger than 5.6 N.     

Increasing the drawing height of conical square cups using anti-lock braking system (ABS)

This paper deals with increasing the drawing height of metal conical square cups with anti-lock braking system (ABS). A novel technique enabling higher drawing height than that achieved in the conventional deep drawing process is introduced, and the principle of the process is explained in this paper. Results of experiments conducted using aluminum alloyed Al-1050 blanks of thickness of 1 mm to draw conical square cups are reported here. Measured drawing load, drawing height and thickness distributions were compared with those obtained from the conventional method. The experimental results showed that higher drawing height of the cup can be achieved by the use of ABS.     

Investigation of hydrodynamic deep drawing for conical�Ccylindrical cups

Forming conical parts is one of the complex and difficult fields in sheet-metal forming processes. Because of low-contact area of the sheet with punch tip in the initial stages of forming, bursting occurs on the sheet. Moreover, since most of the sheet surface in the area between the punch tip and blank holder is free, wrinkles appear on the wall of the drawing part. Thus, these parts are normally formed in industry by spinning, explosive forming, or multi-stage deep drawing processes. In this paper, forming pure copper and St14 conical?Ccylindrical cups in the hydrodynamic deep drawing process was studied using finite element (FE) simulation and experiment. The effect of pressure path on the occurrence of defects and thickness distribution and drawing ratio of the sheet was studied. It was concluded that at low pressures, bursting occurs on the contact area of sheet with punch tip. At higher pressures, the cup was formed, but the wall thickness distribution depends on the pressure path. It was also illustrated that for the pressure path with a certain maximum amount, the workpiece was formed adequately with minimum sheet thickness reduction. Internal pressures more than this maximum amounts did not affect on the thickness distribution. By applying the desired pressure path, conical?Ccylindrical cups with high deep drawing ratio were achieved.     

Study on process parameters and its analytic application for nonaxisymmetric rectangular cup of multistage deep drawing process using low carbon thin steel sheet

Multistage deep drawing process is widely used to obtain various nonaxisymmetric rectangular cups. This deep drawing scheme including drawing and ironing processes consists of several tool sets to carry out a continuous production within one progressive press. To achieve the successive production, design and fabrication of the necessary tools such as punch, die, and other auxiliary devices are critical, therefore, a series of process parameters play an important role in performing the process design. This study focuses on the tool design and modification for developing the rectangular cup with an aspect ratio of 5.7, using cold-rolled low carbon thin steel sheet with the initial thickness of 0.4 mm. Based on the design results for the process and the tools, finite element analysis for the multistage deep drawing process is performed with thickness control of the side wall in intermediate blanks as the first approach. From the results of the first approach, it is shown that the intermediate blanks could experience failures such as tearing, wrinkling, and earing by excessive thinning and thickening. To solve these failures, the modifications for the deep drawing punches are carried out, and the modified punches are applied to the same process. The simulation results for the multistage rectangular deep drawing process are compared with the thickness distributions before and after the punch shape modifications, and with the deformed shape in each intermediate blank, respectively. The results of finite element reanalysis using the modified punches show significant improvement compared with those by using the original designed punch shapes.     

Investigation into the formability of Al-1050 tailor-welded blanks with antilock braking system

Tailor-welded blanks (TWBs) have been widely used in the automotive industry as they reduce car weight and manufacturing cost. A new deep drawing system with an antilock braking system (ABS) was used for the improvement formability of tailor-welded blanks. In this study, Al-1050 aluminum alloy sheets, having a thickness of 1.5 and 2 mm, were welded using both a metal inert gas (MIG) and a laser welding. The effect of the conventional and ABS methods on the limiting drawing ratio (LDR), punch force, weld line movement, and wall thickness is investigated. The experimental results showed that tailored blanks produced using laser welding are not suited for deep drawing. In contrast, however, the MIG-welded blanks are suitable for deep drawing. These TWBs were deep drawn with both the conventional and ABS methods. The ABS method improved the LDR from 2.06 to 2.15 and decreased the maximum load from 17.31 to 16.53 kN when compared with the conventional method.     

The effect of a multistep deep-drawing process with circular and rectangular shapes on the deformation of AZ31 magnesium sheets

This study has mostly focused on the forming limit, microstructural change, and anisotropy that arise from rectangular and circular deep drawing of magnesium sheets. Moreover, this study predicts the change in the material thickness and the forming depth at the first forming process that produces the rectangular cup by the deep drawing of the rectangular blank. Further, by using the rectangular cup that is formed by the first forming process, when the circular and square cups in the rectangular cup are simultaneously manufactured in the so-called second forming process, the effect of the clearance between the die and punch on the change in the product thickness according to forming depth associated with microstructural analysis is investigated. The forming temperature is optimized to maximize formability. The results obtained in this study are utilized as data for predicting the die clearance and the change in the thickness.     

圆筒形件拉深失稳及各因素影响分析

对板料成形中圆筒形件拉深的破裂失稳及产生破裂失稳的临界压边力进行研究.由于凸、凹模圆角及其间隙的存在,圆筒形件拉深的筒壁区实际为凸、凹模圆角之间的公切线部分.根据Mises-Hill屈服函数及Tresca准则求出凸缘变形区、凹模圆角区和筒壁区的应力分布,得到危险断面处的应力表达式,从而求出不产生破裂失稳的临界压边力的解析表达式,并进一步分析获得拉深比、硬化指数、厚向异性系数、摩擦因数以及径向推力等因素对临界压边力的影响规律.采用液压压边与周缘加径向推力的拉深模具对08Al板料进行拉深试验,试验结果与理论计算结果具有很好的一致性.     

圆杯无压边锥模拉深皱曲强度与拉深极限预测

采用能量法导出圆杯无压边锥模拉深的皱曲强度,考虑了材料性 能,径向和周向弯曲作用,厚度变化及加工硬化效应。应用该强度预测无皱极限拉深比,与 Sowerby等人使用3种材料3种板厚作的无压边锥模拉深试验结果完全一致,最大相对误差不 超过8%。提出的研究方法同样适用于轴对称非直壁零件拉深凸凹模间悬空区的切向压缩失稳 分析。     

Hydrodynamic deep drawing process assisted by radial pressure with inward flowing liquid

A radial pressure can reduce drawing force and increase drawing ratio in hydrodynamic deep drawing. However, conventional hydrodynamic deep drawing cannot attain a radial pressure higher than the pressure in the die cavity. In this research, a modified method, named hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid, was proposed and investigated using both primarily experimental and numerical simulation analysis. A radial pressure higher than the pressure in the die cavity was realized by means of the inward flowing of the liquid during this process. After preliminary experimental validation, FEM was used to explore the forming process. The results from the simulation were compared with those from the experiment. The effects of the radial pressure on the wall thickness distribution, punch force, and compressive stress in the blank flange were studied with assistance of numerical simulation. The process window for radial pressures versus drawing ratios was established in 2Al2O alloy experimentally and cups with drawing ratio of 2.85 were successfully formed.     

The application of abductive networks and FEM to predict the limiting drawing ratio in sheet metal forming processes

The deep drawing process, one of the sheet metal forming methods, is very useful in the industrial field because of its efficiency. The limiting drawing ratio (LDR) is affected by many material and process parameters, such as the strain-hardening exponent, the plastic strain ratio, friction and lubrication, the blank holder force, the presence of drawbeads, the profile radius of the die and punch, etc. In order to verify the finite element method (FEM) simulation results of the LDR, the experimental data are compared with the results of the current simulation. The influences of the process parameters such as the blank holder force, the profile radius of the die, the clearance between the punch and the die, and the friction coefficient on the LDR are also examined. The abductive network was then applied to synthesize the data sets obtained from the numerical simulation. The predicted results of the LDR from the prediction model are in good agreement with the results obtained from the FEM simulation. By employing the predictive model, it can provide valuable references to the prediction of the LDR under a suitable range of process parameters.     

The design of blank’s initial shape in the near net-shape deep drawing of square cup

Deep drawing process is very useful in industrial field because of its efficiency. The deep drawing is affected by many process variables, such as blank shapes, profile radii of punch and die, formability of materials and so on. Especially, in order to obtain the optimal products in deep drawing process, blank shape is very important formability factor. In this paper, the finite element method is used to investigate the cup height of the square cup drawing process. In order to verify the prediction of FEM simulation of the product’s height and forming load in the square cup drawing process, the experimental data are compared with the results of the current simulation. A finite element analysis is also utilized to acquire the designed profile of the drawn products, a reverse forming method for obtaining the initial blank’s shape according to the forward square cup drawing simulation is proposed. The design of initial blank’s shape is also certified to obtain the designed profile of drawn cups by experiment. The influences of the blank’s shape on the height of product, the forming load, the maximum effective stress and the maximum effective strain are also examined.     

圆锥形凹模径向分块压边拉深工艺实验研究

采用圆锥形凹模拉深工艺可以提高成形极限,但需要用压边圈将板坯先压成与凹模面吻合的形状,当变形程度较大时,板坯很容易起皱。为了克服这一缺点,提出了将圆锥形凹模与径向分块压边方法结合的工艺,该工艺可有效改善压边圈与板坯的约束状态,从而达到抑制起皱的目的。对圆筒形件的拉深成形,采用了刚柔复合的径向分块压边圈结构,设计了圆锥形凹模径向分块多压边圈拉深模,取不同凹模半锥角的圆锥形凹模进行了圆筒形件的拉深成形实验。实验表明,新的压边方法能有效克服初始成形过程的起皱,可与锥度较小的凹模一起使用。采用凹模半锥角为45°的凹模,得到AA5754、AA6061和08Al三种板材的极限拉深系数分别为0.410、0.431、0.373,显著提高了成形极限。对圆锥形凹模的拉深成形,给出了理论计算成形极限的方法,理论与实验结果非常接近。     

Hydrodynamic lubrication of the ironing process

A theoretical model is presented to calculate the lubricant film thickness in an unsteady hydrodynamic lubrication of cup-shaped products to be formed by the ironing process. The model covers the development of hydrodynamic lubrication in various phases of the ironing process. The model provides equations for estimating the lubricant film thickness for each phase. Experiments were conducted to study the effect of lubricant viscosity on die expansion and punch force in making cup-shaped products by the ironing process. It was found that the die expansion varied between unlubricated and lubricated cups and depended on the lubricant viscosity. The film thickness was estimated from the difference between the increased die/punch clearance, which was calculated from the expansion, and the lubricated cup wall thickness. The theoretical film thickness was compared with the estimated film thickness based on the die expansion measurement.     

Experimental study on multi-stage deep drawing for rectangular cup with high aspect ratio

Multi-stage deep drawing process for rectangular cup using finite element method has been analyzed to understand the main process parameters, to modify the tool configurations for achieving sound intermediate blanks, and to obtain the rectangular deep-drawn cup in the prior study. As shown in the results of the numerical analysis, it has been ensured that the rectangular deep-drawn cup could be obtained. In this study, the tool fabrication and development considering the effects of the intake angle and the ironing operation are performed. The developed tool sets are applied to the multi-stage deep drawing process of this study, and a systematic experiment for the rectangular deep drawing process is carried out. From the first trial in the experiment, several failures are predicted. To solve these failures, the contact surface on the lower die is modified. As shown in the experimental results for the second trial by applying the modified lower die, it is investigated that the failures such as wrinkling and tearing phenomena are not observed, and the excessive deformation behavior due to thinning and thickening effects is decreased. Furthermore, the thickness distributions on the major axis and the minor axis of the intermediate blanks are investigated to be already satisfied by the target (ironing) thickness, respectively. By this systematic approach, it is confirmed that the experimental results show a good agreement with the designed and required configuration of the final product.     

Numerical and experimental investigation of pulsating blankholder effect on drawing of cylindrical part of aluminum alloy in deep drawing process

In this study, the effect of a new pulsating blankholder system has been investigated on improving the formability of aluminum 1050 alloy. By using this system, during each pulsating cycle, first, the metal was easily flowed into the die through removing the blankholder force, and then the blankholder force applied by springs was employed to prevent excessive metal flow and wrinkling. Deep drawing of cylindrical cup was simulated by ABAQUS6.7 software. Cup depth, tearing, and thickness distribution of the experimental and numerical analyses were then compared. The results indicated that by using the pulsating blankholder system coupled with proper frequency and gap, the cup depth can be increased and thickness distribution can be improved. Further, good agreement was observed between simulation and experimental results.     

An Analysis of Draw-Wall Wrinkling in a Stamping Die Design

Wrinkling that occurs in the stamping of tapered square cups and stepped rectangular cups is investigated. A common characteristic of these two types of wrinkling is that the wrinkles are found at the draw wall that is relatively unsup-ported. In the stamping of a tapered square cup, the effect of process parameters, such as the die gap and blank-holder force, on the occurrence of wrinkling is examined using finite-element simulations. The simulation results show that the larger the die gap, the more severe is the wrinkling, and such wrinkling cannot be suppressed by increasing the blank-holder force. In the analysis of wrinkling that occurred in the stamping of a stepped rectangular cup, an actual production part that has a similar type of geometry was examined. The wrinkles found at the draw wall are attributed to the unbalanced stretching of the sheet metal between the punch head and the step edge. An optimum die design for the purpose of eliminating the wrinkles is determined using finite-element analysis. The good agreement between the simulation results and those observed in the wrinkle-free production part validates the accuracy of the finite-element analysis, and demonstrates the advantage of using finite-element analysis for stamping die design.     

Experimental and numerical analysis of hydrodynamic deep drawing assisted by radial pressure at elevated temperatures

Nowadays, due to the demand for lightweight construction and fuel consumption reduction, especially in automotive and aerospace industries, the use of aluminum alloys has drawn much attention. Nevertheless, poor formability at room temperature is the main drawback of using these alloys. To overcome the problem, the work material is formed at elevated temperatures. In the present paper, Hydrodynamic Deep Drawing assisted by Radial Pressure (HDDRP) process has been selected over other forming methods. The aim of the study is to investigate the applicability of this process in conjunction with warm forming. For this purpose, experimental and numerical attempts have been made on warm forming of flat-bottom cylindrical cups in isothermal condition. At first, a series of warm hydroforming experiments were performed to determine the effect of tool temperature and forming speed on the thickness distribution of the final part and on the required forming load. Then, a set of finite element analyses (FEA) were performed using ABAQUS explicit to extend the findings. The Response Surface Method (RSM) was then used to build the relationship between the input parameters such as temperature and forming speed, and output responses including minimum part thickness and maximum punch force. It is demonstrated that the required forming force was decreased with increase in punch speed and tool temperature. Additionally, minimum thickness of the part is increased with increasing temperature and decreasing punch speed. Studying the Limiting Drawing Ratio (LDR) revealed that elevating the forming temperature causes reduction in LDR, while rising the punch speed leads to a slight enhancement in it. For the evaluation of part dimensional changes after forming, springback analysis was done via studying the through-thickness hoop stress distribution. It is found that using warm isothermal HDDRP in high forming rate results in more uniform stress distribution and lower level of stress and so a better springback behavior.     

先进充液柔性成形技术及其关键参数研究

基于所提出的具有均匀压边力并轴向加压的板材充液柔性成形技术,面向板材液压柔性成形技术的普遍规律,成形出拉深比较高的铝合金筒形件以及其他复杂形状的零件如方锥盒形件、方盒形件、轴对称锥形件等,对其中的关键技术如初始液压加载状态、液压加载最优路径、破裂控制等一些关键参数进行了研究和优化;考虑板平面方向性系数的影响,利用数值模拟的手段对其成形过程进行了分析,指导实验研究,得出了有益的结论。     

差厚激光拼焊板盒形件的数值模拟研究

拼焊板技术在汽车制造业中得到了广泛的应用。焊缝存在是拼焊板成形性能降低的一个重要因素,因此研究控制焊缝移动非常重要。通过对盒形件拉伸的应力分析,得到焊缝移动规律;基于非线性隐式算法,选用各向异性屈服准则,采用阶梯压边圈,精确建立了焊缝模型,对盒形件拉深进行了数值模拟,并与试验结果进行了比较。通过对模拟结果的应力、单元厚度分析,比较模拟和试验的吻合程度,验证了应力分析和模拟的正确性。