智能化拉深控制中的侧壁起皱临界条件

建立了轴对称件拉深侧壁起皱的数学模型。从能量平衡原理出发,通过对屈服准则的线性化处理,推导了考虑几何参数、摩擦系数和材料性能参数、板材皱曲时约束条件的轴对称拉深成形过程中侧壁起皱临界压边力的变化规律,给出了皱曲判据。理论分析与实验吻合较好,为拉深过程的智能化控制提供了理论依据。     

板料成形有限元模拟的压边力控制方法研究

采用新的研究方法模拟水槽拉伸的实际压边过程。压边力采用不同的压边间隙和施加不同的分离力来实现。通过一个系统的研究方案来确定一个优化的压边力和压边间隙。研究发现 ,板料的法兰区域随着压边间隙的增加起皱变形严重 ,由于起皱引起的板料刚度上升导致压边力迅速上升。采用分离力时的模拟厚度比压边间隙小是由于法兰区域的变压边力。通过厚度和法兰边缘实验和模拟结果的比较 ,发现采用压边间隙可以更好地模拟板料成形的压边过程     

可控变压边力的盒形件拉深模具设计

压边结构及压边力对板料拉深成形质量有着重要影响。由于盒形件成形时具有应力分布不均匀、变形分布不均匀以及变形速度不均匀的特点，拉深模具压边结构采用了分区方式，将压边圈分为直边部分和圆角部分，各部分可以协调运动。拉深过程中压边力通过控制系统可以随拉深起皱规律而合理变化，有效地改善法兰区变形的不均匀性，提高盒形件的成形质量。     

Adaptive FEM simulation for prediction of variable blank holder force in conical cup drawing

Fracture and wrinkling are two primary failure modes in deep drawing of sheet metal parts. Previous studies showed that properly selected variable blank holder force (BHF) profile, i.e. variation of BHF with punch stroke, can eliminate these failures to draw deeper parts. In this study, an adaptive simulation strategy was developed to adjust the magnitude of the BHF continuously during the simulation process. Thus, a BHF profile is predicted in a single process simulation run and the computation time is reduced. The proposed strategy has been applied successfully to two conical cup drawing operations. The predictions have been compared with experiments and the results indicate that the adaptive simulation strategy can also be used to improve the drawing process for forming non-symmetric parts.     

铝合金车门防撞梁热冲压成形缺陷(英文)

通过试验和数值仿真研究生产车门防撞梁中经常出现的减薄、破裂、起皱和回弹成形等缺陷。建立了适用于350~500°C的本构模型,并用于铝合金热冲压数值仿真。进行冲压试验和数值模拟以弄清成形缺陷的量化规律并分析工艺参数对成形缺陷的影响。研究结果表明:铝合金热冲压中破裂现象得到改善,回弹基本消除。增大压边力可减轻起皱的程度,但压边力超过15 kN将导致工件最大拉深处破裂。在压边力为3~5 kN,冲压速度为50~200 mm/s及有润滑的条件下,可以避免成形缺陷的产生。     

圆筒件拉深成形临界防皱变压边力加载曲线研究

针对板料拉深成形过程中如何最优控制压边力的难题,文章首先从理论上分析了圆筒件拉深成形过程中法兰上任一点处的承载能力,建立其应力应变平衡关系,从而得到法兰上任一点处的瞬时径向拉应力和周向压应力公式;其次结合法兰起皱有关能量守恒定理和Hill厚向异性理论,推导出了包含摩擦系数和板料厚向异性系数在内的法兰起皱临界最小压边力公式,并分析了各种拉深成形工艺参数对此法兰起皱临界最小压边力大小的影响规律;最后应用数值模拟软件eta/DYNAFORM验证此临界变压边力加载曲线的可行性,并修正其表达形式。最终板厚变化量的均方差计算结果表明,理论推导的起皱临界最小压边力修正加载曲线,不仅比常见的最小压边力恒定加载模式更节省能量,而且其厚度分布也更加合理、均匀。     

Numerical simulation and analysis on the deep drawing of LPG bottles

Deep drawing is one of the most used sheet metal forming processes in the production of automotive components, LPG bottles and household goods, among others. The formability of a blank depends on the process parameters such as blank holder force, lubrication, punch and die radii, die-punch clearance, in addition to material properties and thickness of the sheet metal. This paper presents a numerical study made on the deep drawing of LPG bottles. In particular, the application of both variable blank holder forces and contact friction conditions at specific location during deep drawing are considered. The numerical simulations were carried out with DD3IMP FE code. A variable blank holder force strategy was applied and the numerical results were compared with results from other blank holder force schemes. It is evident that the proposed variable blank holder force scheme reduces the blank thinning when compared to other schemes; the friction coefficient also has a significant influence on the stress–strain distribution.     

板料成形中的新型可控压边力技术研究

板料成形中,压边力是控制板料流动的重要因素。前人大量的研究表明,在拉伸成形的不同行程施加合适的变压边力(VBHF),可有效避免板料成形中起皱和破裂的缺陷。文章基于压边力成形窗口的定义和分析,提出新的控制目标,并采用PID闭环控制策略来优化不同冲压行程中分块压边圈上的压边力。针对一个具有不同角部半径的盒型件进行了闭环的变压边力优化模拟,得到其不同位置的分块压边圈随行程变化的最优压边力曲线,并在变压边力压机上进行实验验证,结果表明,使用铝合金板料并在恒定压边力下难以成形的盒形件,在最优变压边力下成功成形。     

基于板料冲压的压边力拉深成形数值模拟分析

压边力是板料拉延成形过程的重要工艺参数之一,合理控制压边力的大小,可避免成形件起皱或破裂等缺陷.建立了三角冲压件的有限元模型,利用DYNAFORM软件,采用数值模拟的方法研究了三角形冲压件拉深时,压边力随时间及位置变化对成形性能的影响.分析结果表明,通过控制拉深过程压边力值的大小和分布,能有效地控制金属的流动,提高板材的成形性能.     

变压边力对铝合金板料拉深成形性能的影响

利用数值模拟软件对5A02铝合金板料进行了随时间变化和随压边圈位置变化的变压边力拉深研究,分析了变压边力对拉深成形性能的影响。研究表明,采用先增后减的压边力可以显著提高铝合金板料的成形性能,但压边力达到最大值的时间有一个合理范围。施加分块压边力时,应根据压边圈相对位置材料流入凹模速度和变形程度来确定各部分压边圈的压边力大小。     

数值模拟波动压边力对拉深件成形质量的影响

钣金成形拉深工艺中,压边力的数值大小和方向是一个重要的工艺参数,在拉深过程中,对压边力大小和方向的控制,往往决定了拉深件的成形质量。然而,现有对变压边力的研究较多集中于线性且稳定的加载。从压边力波动变化的角度分析波动压边力对拉深件成形质量的影响,并考虑不同波形对这一影响有何变化,提出了一种更为有效的提高拉深件成形质量的方法。     

Optimal Programming of Multi-point Cushion Systems for Sheet Metal Forming

Numerical optimization technique coupled with finite element analysis of the stamping/sheet hydroforming process was developed to predict four possible modes for application of blank holder force (BHF) in multiple-point cushion systems, namely a) BHF constant in space/location and time/stroke, b) BHF variable in time/stroke and constant in space/location, c) BHF variable in space/location and constant in time/stroke and d) BHF variable in space/location and time/stroke. The BHF was predicted by (a) minimizing the risk of failure by tearing (thinning) in the formed part and (b) avoiding wrinkling. The developed technique was applied to predict the BHF to form a) an automotive part (liftgate-inner) from AA6111-T4 aluminum alloy, b) an asymmetric part from aluminum alloy AA5083-H32 by sheet hydroforming process with die (SHF-D) and c) a round cup by sheet hydroforming with punch (SHF-P). Experimental results showed that the FEM based optimization methodology can reduce trial and error effort and is able to predict the blank holder force necessary to form the parts without fracture and wrinkling in the investigated stamping and sheet hydroforming operations.     

Study on hydromechanical deep drawing with uniform pressure onto the blank

Sheet hydroforming has many virtues and has gained increasing interest in industries recently. In this paper, hydromechanical deep drawing (HDD) with uniform pressure onto the blank is proposed and investigated in detail both primarily in experiments and simulation. Final cups with drawing ratios of 2.46 and 3.11 were, respectively, obtained using Al–Mg–Si alloy (Al6016-T4) and soft aluminum (Al1050-H0) that have the strong anisotropic properties. The influence of process parameters on the sheet deformation was studied and the typical failure types including fracture and wrinkling were discussed. Finally, FEM was used to analyze the forming process, and the results from the FEM simulations were in good agreement with those from the experiments.     

Evaluation of stamping lubricants using the deep drawing test

This paper presents a practical methodology that uses the deep drawing test and finite element (FE) analysis to evaluate stamping lubricants under near production conditions. In stamping operations good lubrication helps to reduce wrinkling, premature fracture, and localized thinning. Furthermore, lubrication also reduces tool wear in large-volume production. Determination of reliable friction data associated with a given lubrication system is also important for successful process design and simulation by FE analysis. In this study, five stamping lubricants (four dry film lubes and one wet lube) were evaluated using the deep drawing test. The performance of the lubricants were evaluated based on: (a) maximum punch force measured, (b) the maximum applicable blank holder force (BHF), (c) the draw-in length, (d) the perimeter of flange after test, (e) the change of surface roughness, and (f) the inspection of surface topography. The coefficient of friction for each lubricant tested was determined through the FE-based inverse analysis by matching the predicted and measured values of the load-stroke curve and the draw-in length. This study showed that one of the tested lubricants was most effective, regardless of test speed and the magnitude of BHF. The methodology used was shown to be effective in evaluating various lubricants for sheet metal forming and accurately differentiating their performances.     

斜壁盒形件多点拉延成形过程中起皱与拉裂预测

借助于LS-DYNA3D软件建立了多点拉延成形用有限元模型,采用BWC壳单元,BT壳单元以及六面体单元,对带法兰的斜壁盒形件多点拉延成形过程进行了数值模拟,获得了压边力和成形深度与起皱与拉裂关系的多点拉延成形的极限图。研究表明,压边力过小,法兰中部将明显起皱;压边力过大,斜壁角部将被拉裂;大小适度的压边力能够得到表面光顺的成形件,即将压边力控制在所给出的起皱极限与拉裂极限之间。     

A Comparative Study on Formability of the Third-Generation Automotive Medium-Mn Steel and 22MnB5 Steel

Third-generation advanced automotive medium-Mn steel, which can replace 22MnB5 steel, was newly developed to improve the lightweight and crashworthiness of automobile. Studies on the formability and simulation method of medium-Mn steel have just been initiated. In this study, finite element simulation models of square-cup deep drawing were established based on various material property experiments and validated by experiments. The effects of blank holder force (BHF), fillet radii of tools (die and punch) on the maximum drawing depth (MDD), thickness distribution of the formed products, and the microstructure before and after forming were investigated and compared with those on 22MnB5 steel. Results show that the MDD of the two steels decreased with increased BHF but increased with the fillet radius of punch; however, the fillet radius of die showed no significant effect on the MDD for both steels. Compared with hot-formed 22MnB5 steel, the martensitic transformation of the hot-formed medium-Mn steel is rarely influenced by the process parameters; thus, it holds the complete, fine-grained, and uniform martensitic microstructure. Moreover, the medium-Mn has better formability, lower initial blank temperature, and smaller impact of BHF and fillet radius of tools on the hot-formed product. Thus, a theoretical basis for the replacement of 22MnB5 steel by medium-Mn steel in hot forming process is provided.     

椭球封头冷拉深缺陷分析

起皱、局部壁厚过度减薄是封头冷拉深常见的缺陷,严重制约着拉深封头质量、成形极限的提高以及生产过程的正常进行。文章采用ABAQUS软件建立椭球封头拉深成形的三维有限元模型,并验证该模型的可靠性;发现了椭球封头拉深过程中易于出现的悬空区起皱和过度减薄两种缺陷,并分析了其形成机理,同时研究了工艺参数对缺陷产生的影响规律。研究发现,悬空区承受双向压应力区域的范围与周向压应力的大小对起皱影响明显,而切向拉应力对壁厚的减薄影响显著。增大压边力、摩擦系数和减小凹模圆角半径,可减小悬空区承受双向压应力区域的面积和周向压应力值,进而减小起皱的倾向,而过大的压边力、摩擦系数和过小的凹模圆角半径,则导致悬空区切向拉应力过大,可加剧壁厚的减薄。     

Process modeling of controlled forming with time variant blank holder force using RSM method

In this paper, a process model of the controlled forming process was proposed based on Response Surface Methodology (RSM). The forming process was controlled through adjusting the blank holder force (BHF) varied with the time and other process parameters. Due to the wide application and the high efficiency of the Finite Element Method (FEM), this is the chief tool used instead of experiments to carry out the controlled forming process. Deep drawing processes of material SPCC were simulated, and the simulation results were verified by the experiments. The forming processes with several types of time variant BHF were simulated and compared to find a suitable one to achieve our desired product shape. The comparison implied that the staircase-shaped time variant BHF can direct the strain path to the desired place to acquire a targeted product.Then the process model was built up using RSM to the forming process with time variant BHF and friction coefficient. The equations explored the relationship between the principal strain of fracture risk elements and the working parameters, including BHF. Three–dimensional (3D) principal strain surfaces of the element were drawn, which visualised the relationship between the principal strain and the working parameters, especially BHF. Using the model, it is feasible to acquire a fracture-free product through regulating the BHF profile.     

镁合金方形件分块压边液压拉深壁厚分析

基于分块压边液压成形装置,运用Dynaform有限元软件对AZ31B镁合金方形件的液压成形过程进行了数值模拟。比较分析了镁合金板在整体式压边和分块式压边条件下的液压成形效果,重点研究了分块压边方式对镁合金方形件的壁厚影响规律,并探索了相对合理的压边力参数。研究结果表明:与整体式压边相比,采用分块式压边能有效改善AZ31B镁合金方形件的壁厚均匀性,提高其成形质量。     

Evaluation of stamping lubricants in forming advanced high strength steels (AHSS) using deep drawing and ironing tests

In forming AHSS, the lubricant must reduce the friction between die and sheet as well as the effect of heat generated from deformation and friction, especially in forming at high stroking rates. In this study, the effectiveness of stamping lubricants was evaluated by using the deep drawing and ironing tests. Various stamping lubricants were tested in forming of DP590 GA round cup samples. In these tests, the performance of lubricants was ranked via evaluation criteria that include punch force and the geometry of tested specimens. Deep drawing tests were conducted at two different blank holder forces, BHF (30 and 70 ton) at a constant ram speed (70 mm/s). The ironing tests were conducted to evaluate the performance of lubricants at higher tool–workpiece interface pressure than that is present in deep drawing. Polymer-based thin film lubricants with pressure additives (e.g. Lubricants A and B) were more effective than other lubricants as shown by the force (e.g. maximum punch force and applicable BHF without cup fracture) and geometry indicators (e.g. draw-in length, flange perimeter and sidewall thinning).The pressure and temperature distributions at the die–sheet interface were predicted by FE simulation of deep drawing and ironing tests. As expected, the value of interface pressure and temperature were maximum at the die corner radius.