基于Autoform的冷冲压成形模拟研究
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摘要
随着汽车市场竞争的白热化，外观设计成为重要的一环，用户对汽车整体的色彩、手感、精度、造型等都提出新要求。业内人士普遍认为，大型、精密、设计合理的冷冲模具将得到市场的欢迎。在各种类型的汽车中，平均一个车型需要冲压模具2000套，其中大中型覆盖件模具300套。据统计，汽车上60%-80%的零件都是利用冲压工艺生产出来的。在车身开发过程中，模具的开发所需要的工作量占整个工作量的近70%，所需时间通常为8-12个月，模具的开发既影响着开发的时间也影响着开发成本的控制。因此，为了提高市场竞争力，提高模具开发能力，降低成本这个课题也日益被各大车企提上日程。
传统覆盖件模具的开发是在设计中依据长期积累的经验，再对设计好的模具进行反复试模，并提出修改意见。但是传统的模具开发方法加大了成本投入，在模具制造和调模试模阶段也增加了难度，如果设计中出现工艺过程判断错误不仅浪费人力物力甚至还可能导致模具的报废。
目前，板料成形有限元仿真技术广泛应用于汽车领域，为模具设计，工艺制定等多种实际应用过程提供了积极有效的途径。据保守估计，采用这一系统可以使整个模具的设计和制造周期缩短约2/5，整个模具生产成本降低约1/3，进而整车成本也得到了大大的降低，提高了市场竞争力。
板料有限元仿真通过将连续体进行离散为有限个依靠节点相互连接的单元体，将外加载荷及约束条件施加在节点上，再利用单元位移模式或应力模式对每个单元节点建立平衡方程，最后引入边界条件求解方程求得此结构的位移分布或应力分布。
在车身覆盖件的冲压仿真过程中关于单元的选择，选用壳单元比选用膜单元更加精确，因为壳单元在厚度方向上对变化的体现比膜单元更加准确。同时，静态隐式算法在时间步长上的优势使得我们本文选择利用Autoform软件来进行分析。
将模拟结果计算出来之后，我们需要对处理结果进行分析，通常我们采用的最简单直接的方法就是利用材料的成形极限图。AUTOFORM根据板料的材料性能和应变状态将成形极限图分成7个区：塑形破裂区，临界破裂区，过度减薄区，安全区，拉伸不足区，起皱趋势区及起皱区，并对各个区域的颜色分区和各区域判定准则加以说明。
利用Autoform软件对汽车左/右侧围内板前段进行实例分析。首先确定工序过程，再确定坯料形状，之后再确定拉延造型。合理的拉延造型决定了板料的成形结果的优良，为此我们必须合理配置各个能控制板料流动阻力的因素来达到最优解。我们对配置过程中压边力，压料面的形状以及拉延筋和摩擦阻力几个因素的确定进行了详细的讲解，最终确定了本次模拟的各个参数，利用此参数仿真出来的最终板料的成形极限图上的点大部分都落在了绿色区域，符合要求。
最后对模拟过程中个几个关键因素进行说明，第一，初始压边力，若初始压边力不足以使板料在拉延筋处充分变形，则拉延筋就不能起到阻碍板料流动的作用；第二，毛坯形状，优化前的毛坯比优化后的毛坯在成形过程中所提供的成型阻力要大；第三，拉延筋，在模拟过程中通常用虚拟拉延筋代替实际拉延筋来实现模拟过程。
Along with the competition becomes white-hot in the automotive market,appearance design has become an important link, the consumers also raise new claimsconcerning about color, hand feel, precision, shape and other aspects.People in thefield generally accept that large, sophisticated， rational design cold stamping die willget the welcome of the market. In all types of vehicles, an average of a new car modelneed about2000sets of stamping dies, in which there are300sets of large andmedium-sized automobile panel dies. According to the statistics,60%-80%of theparts on the car are produced by the stamping process.In auto-body development, diedevelopment course usually takes about8to12months, accounting for nearly70%ofall theworkload. It affects not only the time of the whole development course but alsothe development cost control. Therefore, in order to improve the marketcompetitiveness, research about enhancing abilities of the die development to reducecost has been taken into agenda by every automobile enterprises.
The traditional automobile panel die development is based on the long-termaccumulated experience and take measures to test mold over and over again after thedie design has finished. In this course, workers can find out the problems and proposetheir amendments. But this method can lift the input costs, can also increase thedifficulties in the phase of both manufacture and adjustment. An error in the designprocess is not only a waste of manpower and material resources, it can even result inthe mold scrapped.
At present, the sheet forming simulation based on the finite element technologyis widely used in the automotive field for the reason that it can provide a positive andeffective way in mold and process design courses. According to conservativeestimates, using this system can make the whole die design and manufacturing cycleshortens about2/5, the whole mold production costs lowered about1/3, the wholevehicle cost also get greatly reduced, meanwhile the market competitiveness of thistype of vehicle can be highly improved.
The sheet finite element simulation process is to decompose the continuumstructure into limited amount of unit bodies, which are interconnected by nodes. Theapplied load and constraint conditions are imposed on these nodes, then we can usedisplacement mode or stress mode to establish balance equations for each node on theunit body, finally we can figure out the displacement or stress distribution of thisstructure through adding the boundary conditions.
In the automobile panel stamping simulation process involves the question aboutchoosing the reasonable element, the results of choosing the shell element is moreaccurate than that choosing the membrane element because the shell element canreflect the thickness change more accurately. Meanwhile, the advantage in time stepof static implicit method makes me finally choose the software Autoform to completethe paper.
Accompanied by the simulation results, we need to deal with these results. Thesimplest and most direct way we usually adopt is to use the material forming limitdiagram. Autoform devices the forming limit diagram into7areas based on thematerial properties and strain state of the sheet, the crack area, the risk of crack area,the excessive thinning area, the safe area, the insufficient stretching area, the wrinkletendency and the wrinkle area. Then illustrate the color of each region and its regionalcriteria.
We take use of Autoform software to complete the B/S Inner LH or B/S InnerRH’s example analysis. Determine the processes at first, then decide about the shapeof the blank, after that the drawing modeling should be determined. A reasonable drawing modeling can influence the forming result, for which we must make the bestfiguration on these factors to control the flow resistance. We give the figurationprocess a detailed explanation, include factors about the determination of the binderforce, the shape of the binder, the set of drawbead and the frictional resistance. Weultimately determine the various parameters of the simulation, and most of the pointson the forming limit diagram of the blank finally fall on the green zone, the resultscomply with the requirements.
At last, we give explanation to several key factors in the simulation process. First,the initial blank-holder force, if the initial blank-holder force is insufficient to makethe deformation of the sheet fully done in the drawbead, then the drawbead cannotplay the role of blank flow obstacle. Second, shape of the blank, the resistanceprovided by the optimized blank is larger than that provided by the blank beforeoptimization. Third, the drawbead, we usually use virtual drawbead instead of actualdrawbead in the simulation process.
传统覆盖件模具的开发是在设计中依据长期积累的经验，再对设计好的模具进行反复试模，并提出修改意见。但是传统的模具开发方法加大了成本投入，在模具制造和调模试模阶段也增加了难度，如果设计中出现工艺过程判断错误不仅浪费人力物力甚至还可能导致模具的报废。
目前，板料成形有限元仿真技术广泛应用于汽车领域，为模具设计，工艺制定等多种实际应用过程提供了积极有效的途径。据保守估计，采用这一系统可以使整个模具的设计和制造周期缩短约2/5，整个模具生产成本降低约1/3，进而整车成本也得到了大大的降低，提高了市场竞争力。
板料有限元仿真通过将连续体进行离散为有限个依靠节点相互连接的单元体，将外加载荷及约束条件施加在节点上，再利用单元位移模式或应力模式对每个单元节点建立平衡方程，最后引入边界条件求解方程求得此结构的位移分布或应力分布。
在车身覆盖件的冲压仿真过程中关于单元的选择，选用壳单元比选用膜单元更加精确，因为壳单元在厚度方向上对变化的体现比膜单元更加准确。同时，静态隐式算法在时间步长上的优势使得我们本文选择利用Autoform软件来进行分析。
将模拟结果计算出来之后，我们需要对处理结果进行分析，通常我们采用的最简单直接的方法就是利用材料的成形极限图。AUTOFORM根据板料的材料性能和应变状态将成形极限图分成7个区：塑形破裂区，临界破裂区，过度减薄区，安全区，拉伸不足区，起皱趋势区及起皱区，并对各个区域的颜色分区和各区域判定准则加以说明。
利用Autoform软件对汽车左/右侧围内板前段进行实例分析。首先确定工序过程，再确定坯料形状，之后再确定拉延造型。合理的拉延造型决定了板料的成形结果的优良，为此我们必须合理配置各个能控制板料流动阻力的因素来达到最优解。我们对配置过程中压边力，压料面的形状以及拉延筋和摩擦阻力几个因素的确定进行了详细的讲解，最终确定了本次模拟的各个参数，利用此参数仿真出来的最终板料的成形极限图上的点大部分都落在了绿色区域，符合要求。
最后对模拟过程中个几个关键因素进行说明，第一，初始压边力，若初始压边力不足以使板料在拉延筋处充分变形，则拉延筋就不能起到阻碍板料流动的作用；第二，毛坯形状，优化前的毛坯比优化后的毛坯在成形过程中所提供的成型阻力要大；第三，拉延筋，在模拟过程中通常用虚拟拉延筋代替实际拉延筋来实现模拟过程。
Along with the competition becomes white-hot in the automotive market,appearance design has become an important link, the consumers also raise new claimsconcerning about color, hand feel, precision, shape and other aspects.People in thefield generally accept that large, sophisticated， rational design cold stamping die willget the welcome of the market. In all types of vehicles, an average of a new car modelneed about2000sets of stamping dies, in which there are300sets of large andmedium-sized automobile panel dies. According to the statistics,60%-80%of theparts on the car are produced by the stamping process.In auto-body development, diedevelopment course usually takes about8to12months, accounting for nearly70%ofall theworkload. It affects not only the time of the whole development course but alsothe development cost control. Therefore, in order to improve the marketcompetitiveness, research about enhancing abilities of the die development to reducecost has been taken into agenda by every automobile enterprises.
The traditional automobile panel die development is based on the long-termaccumulated experience and take measures to test mold over and over again after thedie design has finished. In this course, workers can find out the problems and proposetheir amendments. But this method can lift the input costs, can also increase thedifficulties in the phase of both manufacture and adjustment. An error in the designprocess is not only a waste of manpower and material resources, it can even result inthe mold scrapped.
At present, the sheet forming simulation based on the finite element technologyis widely used in the automotive field for the reason that it can provide a positive andeffective way in mold and process design courses. According to conservativeestimates, using this system can make the whole die design and manufacturing cycleshortens about2/5, the whole mold production costs lowered about1/3, the wholevehicle cost also get greatly reduced, meanwhile the market competitiveness of thistype of vehicle can be highly improved.
The sheet finite element simulation process is to decompose the continuumstructure into limited amount of unit bodies, which are interconnected by nodes. Theapplied load and constraint conditions are imposed on these nodes, then we can usedisplacement mode or stress mode to establish balance equations for each node on theunit body, finally we can figure out the displacement or stress distribution of thisstructure through adding the boundary conditions.
In the automobile panel stamping simulation process involves the question aboutchoosing the reasonable element, the results of choosing the shell element is moreaccurate than that choosing the membrane element because the shell element canreflect the thickness change more accurately. Meanwhile, the advantage in time stepof static implicit method makes me finally choose the software Autoform to completethe paper.
Accompanied by the simulation results, we need to deal with these results. Thesimplest and most direct way we usually adopt is to use the material forming limitdiagram. Autoform devices the forming limit diagram into7areas based on thematerial properties and strain state of the sheet, the crack area, the risk of crack area,the excessive thinning area, the safe area, the insufficient stretching area, the wrinkletendency and the wrinkle area. Then illustrate the color of each region and its regionalcriteria.
We take use of Autoform software to complete the B/S Inner LH or B/S InnerRH’s example analysis. Determine the processes at first, then decide about the shapeof the blank, after that the drawing modeling should be determined. A reasonable drawing modeling can influence the forming result, for which we must make the bestfiguration on these factors to control the flow resistance. We give the figurationprocess a detailed explanation, include factors about the determination of the binderforce, the shape of the binder, the set of drawbead and the frictional resistance. Weultimately determine the various parameters of the simulation, and most of the pointson the forming limit diagram of the blank finally fall on the green zone, the resultscomply with the requirements.
At last, we give explanation to several key factors in the simulation process. First,the initial blank-holder force, if the initial blank-holder force is insufficient to makethe deformation of the sheet fully done in the drawbead, then the drawbead cannotplay the role of blank flow obstacle. Second, shape of the blank, the resistanceprovided by the optimized blank is larger than that provided by the blank beforeoptimization. Third, the drawbead, we usually use virtual drawbead instead of actualdrawbead in the simulation process.
引文
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[2]林忠钦.汽车板精益成形技术[M].北京：机械工业出版社，2009.
[3]李树新.日本当代汽车模具业的发展动向[J].模具工业，1993(12):53-56.
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