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摇架压力分配杆冲压模具设计【含CAD图纸、说明书】
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J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318 DOI: 10.1007/s12204-010-1009-zA Reconfigurable Stamping Die and Its Stamping ProcessSONG Ai-ping (宋爱平), WU Wei-wei (吴伟伟), ZHANG Jun (张 军)(College of Mechanical Engineering, Yangzhou University, Yangzhou 225009, Jiangsu, China) Shanghai Jiaotong University and Springer-Verlag Berlin Heidelberg 2010Abstract: A reconfigurable flexible poles die was developed. The die can be used to implement the process of “the multi-point pressing and forming sheet”. Sheet metal is restricted by the elastic pressing forces putting on the upper and lower surfaces of sheet in stamping process. The method is an effective way to enhance the buckling critical stresses and reduce wrinkling of sheet. The results of tests indicate that the die can achieve “one die brings multi-purpose” and suppress the wrinkle of sheet. The process of the multi-point pressing and forming sheet provides a practical and effective way for the curved sheet metal forming.Key words: stamping process, wrinkle, reconfigurable, dieCLC number: TG 386 Document code: A1IntroductionWrinkling of sheet metal seriously influences the forming quality and the life of die. It may make the forming process unable to carry on. So effectively sup- pressing wrinkle seems to be highly important1. In recent years, in order to meet the demand of light and tough sheet metal, thin sheet metal parts are widely ap- plied in various fields. The study of Wrinkling becomes one of the hottest research topics2.Since the near century, many scholars have brought massive studies and discussions into the instability of sheet. These researches covered from the experimental study and the theoretical analysis to the numerical sim- ulation, from the sheet drawing and the bend forming to the hydroforming, from the wrinkle forecast to the buckling control and so on1-3.Recently, numerical simulation of a forming process is applied to study on wrinkle. Depending on the mod- ern advanced research methods, numerical simulation based on the finite element method has become the main tool of study wrinkling in decades4.However, majority studies encircle wrinkling bifurca- tion of sheet metal and the situations of wrinkling at the present time. But these cannot bring any feasible method for controlling the wrinkles in stamping.Currently, the representative research and applica- tion of the reconfigurable die technology is the multi- point forming technology. The basic principle is using aReceived date: 2009-04-02Foundation item: the National Natural Science Foundation of China (No. 50975249) and the Natural ScienceRe- search Fund of Yangzhou University (No. YZ2009093)E-mail: apsongseries of regular and adjustable the basic bodies (poles) to construct the structure of a die. Thus, the recon- struction of die can be achieved, but the wrinkling in the sheet metal has not been suppressed5.The paper emphasizes how to control wrinkle of sheet forming. Main ideas in the paper are two: One idea is to improve the supporting condition of sheet metal and increase its buckling critical stresses. Thus, “the multi-point pressing and forming sheet” technique will be proposed. Another idea is to explore a reconfigurable die which is combining the technique of “the multi-point pressing and forming sheet”.4 Poles Flexible DieIn order to reduce the wrinkling of sheet, a method of using elastic pressing forces putting on surfaces of sheet in stamping process was presented, it can improve the stability of sheet metal.A new reconfigurable die was developed. The die has high efficiency in reconfiguration so that it can achieve multi-purpose use. Simultaneously the die can be car- ried out the process of “the multi-point pressing and forming sheet”.Curved sheet metal parts are used in many products such as aerospace products, military products, ships and engineering machines, the batch of parts is small. Different shape requires different die for forming sheet metal. It leads to high cost and long cycle6-7. To meet this situation, the reconfigurable stamping die has been explored. The die can be applied to forming a variety of sheet parts by reconfiguring. The novel die is named as “poles flexible die”.Poles flexible die is a kind of reconfigurable stamping314J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318die. Figure 1 shows the structure. The die is com- bined with some discrete adjustable poles which are assembled in an array. The length of pole can be ad- justed. After analyzing 3D models data of sheet part, the length of each pole can be adjusted accurately8.1Frame, 2Screw rod, 3Adjustable sleeve, 4Baffle 5Jointer, 6Punch head, 7Blank-holder, 8Sheet metalFig. 1 The structure of poles flexible diePunch head located in the end of pole can be replaced with relevant shape head. All heads are constituted the surface of die so that it is conformed to the shape of sheet part.The die is composed with flexible poles. In order to realize the multi-point pressing and forming sheet process, the adjustable pole is designed as a flexible pole with the function of “pressing sheet” and “forming sheet”. Figure 2 shows the scheme of the flexible pole.In the process of sheet metal forming, the correspond- ing flexible poles of the upper and lower dies firstly pro- ceed to “press sheet” by the pressure spring. With the descending of the upper die, punching heads and sleeves are retracted inward. Pressing force of punching head is gradually increased under the effort of spring. After all punching heads and sleeves are retracted a definite distance (pressing distance), the adjusted nuts will re- sist sleeves and locate the sleeves. Consequently, the heads and sleeves cannot retract inward and all punch- ing heads will be combined to form the die surface, so that a sheet metal can be forced to forming. The length of pressing-distance slot has various sizes. The long pressing-distance slot may be used for construct- ing the blank-holder. Pressing force on sheet metal is produced by pressure spring inside die. Changing the corresponding coefficient of elasticity of spring can gen- erate desired pressing force. Pressing force on sheet metal is far smaller than forming force, and the press- ing force applied on a sheet metal is from 50 to 600 N. Figure 4 shows the upper die fixed on the upper worktable of the press machine. The surface of the die is spherical face composed by some punching heads of poles.Poles in the periphery of die are blank-holder poles.1234567 8 ABABAABB1Stepping motor, 2Frame, 3Screw rod 4Pressure spring, 5Adjustable nut, 6Adjustable sleeve7Punch head, 8Pressing distanceFig. 2 The schematic of the flexible poleIt can be seen from Fig. 2 that position of sleeve is restricted by the adjustable nut in flexible pole. Rotat- ing screw rod can control the position of sleeve. Sleeve is tightly held the adjusted nut under the effort of pres- sure spring. Figure 3 shows the materialization of the flexible pole.1Screw rod, 2Pressure spring, 3Adjustable nut 4Pressing-distance slot, 5Adjustable sleeve 6Punching headFig. 3 The flexible pole1Blank-holder, 2Surface of dieFig. 4 The upper die with spherical surface5 The Stamping Process of the Multi- point Pressing and Forming SheetPoles flexible die can be realized the stamping pro- cess of “the multi-point pressing and forming sheet”. The stamping process with discrete flexible poles can be seen in Fig. 5. It must be gone through four steps that are “holding blank”, “pressing sheet”, “pressing and forming sheet” and “shaping sheet”.At the first stage of the forming, blank holders of the die achieve “holding blank” as shown in Fig. 5(a). Then both upper and lower punching heads of dies are pressing sheet, and the process is called “multi-point pressing sheet”, as shown in Fig. 5(b). In the process of stamping, some sleeves reach the designated point firstly and other sleeves and punching heads are press- ing sheet surfaces, as shown in Fig. 5(c). Finally, allJ. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318315sleeves and punching heads of poles reach the desig- nated point, surfaces of punching heads are combined the surface of die, the sheet metal is shaped by the die, as shown in Fig. 5(d). During the process, the sheet metal is always confined by punching heads.In the process of forming sheet metal, poles flexible die composed by “flexible poles” proceeds to “pressing sheet” and “forming sheet” at the same time. The pro- cess of “the multi-point pressing and forming sheet” can prevent buckling and wrinkling of sheet. In the stamp- ing process the force of pressing sheet is far smaller than the force of forming sheet, and the force of pressing sheet is produced by springs and the force of formingsheet is produced by press machine.Experiment results indicate that poles flexible die has good forming characteristics and can suppress wrinkle of sheet. The upper and lower surfaces of sheet metal in the forming process are pressed by elastic poles, in order to improve the stability of sheet metal.It can be seen from Fig. 6(a) that sheet metal is pressed by loads Px, the elastic pressing forces Fe are located in the upper and lower surfaces of sheet metal. Pressing forces are produced by springs in flexible poles. The upper elastic pressing force equals to the lower cor- responding force and the condition of sheet metal main- tains plane, as shown in Fig. 6(a).1Coupled pole, 2Blank, 3Blank-holder, 4Variant headsFig. 5 The stamping processes of the multi-point pressing and forming sheetze1e4Fe Fe Fe FezF Fe2 Fe3FPxPxPxOxOPxxFePx ya OFe Fe Fe Fe x OxKPx a bbFePxPx OLy5.2 Pressing forces on surfaces of sheet5.3 Pressure differences of surfaces5.4 Pressure difference by pressure springsFig. 6 The relationship of elastic pressing forces on sheet and buckling critical stressK is the coefficient of elasticity of the spring inside the flexible pole, L is the compressed length of the spring, as shown in Fig. 6(c). When sheet metal is gen- erated deflection , spring in the convex side of sheet can be further compressed and elastic force made by spring is increasing. Springs on the concave side of sheet will relax a bit. The elastic pressing force differ- ence Fe made by the two side springs can be obtained as Fe = 2K.When sheet metal occurs bending made by the pres-sure load Px as shown in Fig. 6(b), it will produce force differences Fe1, Fe2 at the pressing points. These pressure differences may inhibit further bending of sheet and can suppress wrinkling of sheet as well.The upper and lower surfaces of sheet metal are ap- plied loads Fe. When sheet metal occurs buckling, it must overcome the work produced by pressure differ- ence Fe of load. The work is W = mFe/2.There m is the number of pressing points, is max- imum value of deflection after buckling and /2 is the316J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318average deflection of m pressing points approximately. When the surfaces of sheet arent applied with pres- sure forces Fe, the sheet metal is pressed with face-parallel load Px.Critical compressive stress is calculated with energy approach, the formula of buckling critical stresses crof sheet9-10:blank-holder force. The way may decrease wrinkles of sheet. However, if the value of the blank-holder force is too large, cracking may occur in sheet metal12. How to control wrinkle of sheet is the key of the experiment. Simulation of the forming process is performed with the software DYNA-form. It is shown from Fig. 7 that the material is prone to wrinkle along the section M-N.cr =2D a2da2 21 +b2.(1)When the surfaces of sheet are applied with pressure forces Fe, the buckling critical stress crq can be got.2D a2 24mFecrq =1 +a2db2+ 2d ,Fig. 7 Stresses status in the forming of sheetaccording to Fe = 2K,2D a2 22mKIn the course of reconfiguration, the 3D model of sheet part should be analyzed, the extension elongationcrq =1 +a2db23+ 2d ,(2)of each pole and the shape of each punching head are calculated firstly. Subsequently, it is to adjust the posi- ETd )where D = 12(1 2 , d is the sheet metal thickness,ET is the tangent modulus, is Poissons ratio.It is noted from Eqs. (1) and (2) that crq is greater than cr obviously. Comparing Eq. (1) with Eq. (2), it can be discovered from Eq. (2) that the buckling critical stress of sheet metal increases along with the increasing of elastic coefficient of springs. Increasing the elastic coefficient of springs will lead to enlarge the pressure difference Fe and improve the buckling critical stress. It indicates that the elastic pressing force applied to the surfaces of sheet can improve the buckling critical stresses of sheet metal. The process of the multi-point pressing and forming sheet can suppress buckling and wrinkling of sheet effectively.2 TestsThe process of “the multi-point pressing and form- ing sheet” is carried out by the poles flexible die. Poles flexible die has the ability of quick reconfiguration. The die can be constructed by adjusting the length of poles and choosing sleeves and fitting the suitable spring in poles and changing corresponding heads. Poles flexi- ble die has many advantages to surpass traditional die. It can effectively suppress wrinkle of sheet, also it can bring new method into the sheet metal forming. Follow- ing experiments will show the characteristics about the process of “the multi-point pressing and forming sheet”.4.1The Forming of Spherical Sheet PartA spherical sheet metal part is a typical kind of curved sheet metal part. If the sheet metal part was formed by traditional die, wrinkles often occur in the surrounding area as well as blank-holder area11. A common way for solving the wrinkles is increasing thetion of the adjustable nuts and to change the punching heads, and to construct the surface of the die. Next step is to constitute the blank-holder structure of the die. Some surrounding poles of die are used for blank- holder. The sheet metal part with the spherical shape has its spherical radius of 150 mm. Heads in the poles are customized.The upper die is installed in the upper table of the press machine, as shown in Fig.4. The lower die is in- stalled in the lower table. In the process of forming sheet, the blank sheet is placed on the working face of lower die, and then the upper die moves down. Fi- nally the upper and lower dies are matched to finish the forming of sheet metal.The shaped sheet metal part is shown in Fig. 8. No wrinkle exists in the sheet. This is due to the process of “the multi-point pressing and forming sheet”.Fig. 8 Spherical sheet partsThe material of the sheet is AISI1020, of elastic mod- ulus E = 2.06 GPa, of yield strength 0.35 GPa. When the surfaces of sheet arent applied with pressure forces, according to Eq. (1),under the condition of the sheet metal without pressing force, the critical stresses cr can be obtained.cr 3.55 102ETd2 = 34.3 MPa.(3)J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318317There, a, b = 80 mm, d = 1 mm, ET 0.3E.During the forming of the spherical sheet metal, the sheet can be confined by each flexible pole. The surfaces of sheet are applied with pressure forces, according to Eq. (2), the critical stresses of sheet metal with pressing force can be got.crq = 359.3 MPa.(4)Comparing Eq. (3) with Eq. (4), it is easy to know that the value of buckling critical stress crq is obviously bigger than cr under the condition of no pressing forces on sheet metal. The sheet metal cannot be prone to wrinkle with setting bigger coefficient of elasticity of spring inside poles. Elastic pressing forces putting on surfaces of sheet can increase the buckling critical stress and decrease wrinkle of the sheet.(a) The Forming of Hemispherical Sheet Part Hemispherical sheet metal part is an unsymmetrical sheet, as shown in Fig. 9. The opening curved face is inconvenient to set blank-holder. In the forming ofthe sheet metal, it is prone to wrinkle in the unsup- ported area because the sheet metal is applied imbal- ance stamping force. In order to ensure the trouble-free forming, it is necessary to increase the pressing force onto the sheet so as to prevent wrinkle of sheet.Fig. 9 3D model of hemispherical sheet metalBy discharging a half of poles of spherical stamping die, it can be used to form the hemispherical sheet metal part. Now, it can be observed conveniently about the steps of the stamping process. The steps can be seen from Fig. 10. Figure 10(c) shows the step of pressing sheet and forming sheet. Figure 11 shows the hemi- spherical sheet with the thickness of 1.8 mm.Fig. 10 The steps of the multi-point pressing and forming sheet processFig. 11 Hemispherical sheet metal part(b) Forming of Saddle Sheet PartAs shown in Fig. 12, saddle sheet metal is a kind of curved sheet metal part with double curvature. If the sheet is formed directly, wrinkle is often occurred3.The blank-holder is constructed uneasily because the peripheral boundary lines of saddle sheet part are distributed in the different altitude. Currently, it is al- most impossible to form saddle sheet metal by directly using the conventional stamping die. The poles flexible die can be used to form the sheet metal part directly with the multi-point pressing and forming sheet process.Figure 13 shows the flexible die which is finished by re-constructing. During the forming sheet the peripheral poles are retracted corresponding dimension more than other poles. When the upper and lower dies are matched, surfaces of peripheral poles and that of middle poles are combined a continuous forming318J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318surface. Then the sheet is shaped to the saddle sheet metal directly. The structure of blank-holder is called “the multi-point blank-holder”.Rapid prototyping and manufacturing system of fused deposition modeling (FDM) can rapidly manufac- ture all kinds of punching heads. A series of punching heads can be produced in two or three days by using the FDM system. The punching heads are installedin the end of poles separately as shown in Fig. 13. The material of the punching heads manufactured by FDM is acrylonitrile butadiene styrene (ABS) plastic. Punching heads can also be manufactured by rapid prototyping system of selective laser sintering (SLS).Figure 14 shows the saddle sheet part of thick- ness 1.0 mm with stainless steel. Wrinkling can be eliminated by using this method.Fig. 12 3D model of the saddle sheet metalFig. 13 The flexible die with blank-holder at the peripheryFig. 14 The saddle sheet metal formed by the multi-point pressing and forming sheet technology5ConclusionThe experimental results show that poles flexible die has good capability of reconfiguration. It can be used to form sheet metal parts with the thickness ranged from 0.5 to 6 mm. The die has obvious advantages in middle-small batch of curved sheet metal forming. And it achieves multi-purpose only by using one die. Simultaneously the die solves the problem of wrinkle in sheet metal forming with combining the process of “the multi-point pressing and forming sheet”.Cover sheets are widely applied in the industry of avi- ation, aerospace, vehicle, ship and engineering machin- ery. Usually, dies of cover sheets may spend high devel- oping cost and long manufacturing cycle. The reconfig- urable die can reduce the manufacturing cost, shorten manufacturing time and improve the competitiveness of products on the market.References1 Li Heng, Yang He, Zhan Mei,et al. A review of re- search on wrinkling in thin-walled parts plastic form- ing processes J. Journal of Mechanical Science and Technology, 2004, 23(7): 837-841 (in Chinese).2 Prrk R. Wrinkling of tubes in bending from finite strain three-dimensional continuum theory J. Inter- national Journal of Solids and Structures, 2002, 39(3): 709-723.3 Kawka M, Kakita T. Simulation of multi-step sheet metal forming processing by a static explicit FEM code J. 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Interna- tional Journal of Mechanical Science, 2002, 42(12): 2369-2394.10 Xu W L. A simplified method of wrinkling simulation J. Journal of Materials Processing Technology, 2002, 121(1): 19-22.11 Lancaster E R, Calladine C R, Palmer S C. Paradoxical wrinkling behavior of a thin cylindrical shell under axial compression J. International Jour- nal of Mechanical Science, 2000, 42(3): 843-865.12 Wang X, Jian C. On the prediction of side-wall wrin- kling in sheet metal forming processes J. Interna- tional Journal of Mechanical Science, 2002, 42(12): 2369-2394.j .上海交通大学。(Sci),2010,15(3):313 - 318 DOI:10.1007 / s12204 - 010 - 1009 - z一种可重构的冲压模具和冲压工艺宋爱平, 吴伟伟,张军(机械工程学院、扬州大学、扬州225009、江苏、中国)上海交通大学和柏林海德堡斯普林格出版社2010摘要: 可重构的杆系柔性成形模具的发展。这种模具可以应用在多点成形薄板冲 压,在冲压过程中金属板受到施板上、下表面的弹性压力。这是一种有效的提高 屈曲临界压力,减少起皱的方法。测试结果表明,该模具可以实现“一模带来多用” 和抑制板料的起皱。这种多点冲压成形板的过程提供了一个实用和有效的方式弯 曲板料成形方式。关键词:冲压工艺,皱纹,可重构,模具 CLC号码: TG 386 文档代码: A1介绍金属板料起皱严重影响成形质量和模具的生命。它可能使成形过程无法进 行。所以有效地抑制皱纹似乎是非常重要的。1近年来,为了满足金属板轻和强 度的需求,薄板金属零件广泛应用于各个领域。起皱的研究成为最热门的研究主 题。2近世纪以来,许多学者对板料的不稳定性进行了大量的研究和讨论。这些研 究涉及范围从实验研究和理论分析,数值模拟,从薄板拉伸和弯曲成形的液压成 形,从皱纹预测到屈曲控制等等。1-3最近,一个成形过程的数值模拟应用于研究皱纹。根据现代先进的研究方法, 几十年来基于有限元方法的数值模拟已经成为研究起皱的主要研究工具。4然而,目前多数研究只是围绕分叉钣金的起皱和起皱的情况。这些不能对冲 压中控制起皱带来任何可行的方法。目前,可重构模具技术研究和应用的代表是多点成形技术。基本的原理是利 用一系列的常规和可调的基本体(杆)构建模具的结构。因此,重建模具可以实现, 但在板料起皱现象没有被抑制。5本文强调如何控制板料的起皱成形。本文主要的两个思想是:一是提高支持 条件的金属片和增加其屈曲临界应力。因此,“多点冲压成形板”技术将被提出。 另一个是探索一种结合“多点冲压成形板”技术的可重构模具。2 杆系柔性成形模具为了减少板料的起皱,一种在冲压过程中利用弹性压力挤压板料表面的方法 被提出,这种方法可以提高金属薄板的稳定性。一个新的可重构模具被开发。这 种模具重新配置的效率很高,这样就可以实现多用途使用。同时模具可实现“多 点冲压成形板”的应用。弯曲金属板材零件被用在许多产品上,如航空航天产品、军工产品、船舶、 工程机械、零件的批量很小。不同的形状需要不同的模具成形金属板。它会导致 高成本和长周期6 - 7。为了满足这种情况,可重构冲压模具被发明。这种模具 可通过重构用于形成各种不同板料零件上。这种新奇的模具被命名为“杆系柔性 模”。杆柔性模是一种可重构的冲压模具。图1显示了结构。模具结合了聚集在一 个组里的离散的可调杆。杆的长度可以调整。在分析板材零件三维模型的数据后, 每个杆的长度可以准确调整81 框架,2 螺旋杆,3调节套筒,4 挡板 ,5 连接器,6冲头,7 压边圈, 8 金属板图1.杆系柔性模的结构位于杆末端的冲头可以根据有关形状冲头更换。所有的冲头构成了模具的表 面,以便符合板间的形状。模具是由柔性杆组成的。为了实现多点冲压和板料成形过程,可调杆被设计 为一个具有“压料”和“形成板料”功能的柔性杆,图2显示了该柔性杆的方案。1 步进电机,2 框架 ,3 螺旋杆架,4 压力弹簧、5 调整螺母,6 可调节套筒7 冲头,8 冲压距离图2，柔性杆的原理图可以从图2中看出,套筒的位置被柔性杆上的可调螺母限制。旋转螺旋杆可以 控制套筒的位置。套筒被调整螺母的压力弹簧紧紧地锁住。图3显示了具体的柔 性杆。1 螺旋杆,2 压力弹簧,3 可调节螺母,4 压距离槽,5 可调节套筒,6 冲压头图3柔性杆在金属板料成形过程中,上、下模上相应柔性杆首先被压力弹簧压入“压板”。 随着上模的下行,冲孔头和套筒向内收缩。在弹簧的作用下冲压头压力逐步增加。 当所有冲头和套筒收缩到一定的距离(压距),调节螺母会抵住套筒定位套筒。因 此,冲头和套筒不能缩回，所有冲压头将被组合起来以形成模表面,这样一个金属 板可以被迫形成。压距槽的长度大小有不同的尺寸。压紧行程槽的长度可用于构 建压边。压在金属板的压力是由模具内压力弹簧产生的。改变相应的弹簧弹性系 数可以生成所需的压力。压在金属板上的压力远远小于金属薄板成形力，应用于 金属板上的压力从50到600 。图4显示了固定在冲压机上工作台的上模。模具的表面是由冲头组成的球形 面。模具外围的杆是压边圈杆。1压边圈，2模具表面图4球形表面的上模3多点冲压和板料成型的冲压过程柔性杆可以实现“多点冲压成形”冲压工艺。离散柔性杆的冲压工艺可以在图 5看出。它必须经历四个步骤,是“坯料压紧”、“压板料”、“成形板料”和“塑造板料”。在成形的第一阶段,模具的压边圈实现“压紧坯料”见图5(a)。然后上下模冲 头成形板料,这个过程被称为“多点压板”,见图5(b)。在冲压的过程中,首先一些 套筒到达指定点然后其他的套筒和冲头压紧薄板表面,如图5(c)。最后,所有的套 筒和杆上的冲头到达指定点，冲头面和模具表面结合,金属板受模具挤压成型, 如图5所示(d)。在此过程中,板料总是受冲头限制的。在板料成型过程中、杆柔性模由“柔性杆”“冲压薄板”和“形成薄板”组成。这 个过程的“模内多点压板与成形”可以防止板料的屈曲和起皱。冲压过程中压板力 远小于薄板成形力,压板力是由弹簧产生，成型力是由冲压机产生。实验结果表明,杆柔性模具具有良好的成形特点而且可以抑制板料的起皱。 为了提高金属板的稳定性，成形过程中金属板上下表面被柔性杆挤压。从图6(a)可以看出,金属板受负载Px,弹性压力Fe作用于金属板的上、下表 面。压力是由柔性杆内弹簧产生的。上面的弹性压力等于下面相应的压力，金属 板保持平面,见图6(a)。(a)压紧坯料(b)冲压板料(c)冲压成型板料（d）板料成形1 耦合杆,2 坯料,3 压边,4 变体头图5.模内多点压板与成形的冲压过程.(a)板表面上的压力(b)表面压力差(c)压力弹簧的压力差图6板上弹性压力和屈曲临界应力的关系K是柔性杆内弹簧的弹性系数,L是弹簧压缩长度,见图6(c)。当金属板产生挠 曲变形,板凸侧内弹簧可以进一步压缩，弹簧的弹性力逐渐增加。料板凹侧的弹 簧会放松一点。由两侧弹簧产生的弹性压力差Fe可以获得Fe = 2 k。当板料受压力载荷Px发生弯曲由见图6(b),在压力点将产生压力差, Fe1 Fe2.。这些压力差可抑制板料的进一步弯曲和抑制起皱。 金属板的上下表面受负载Fe,当板料发生屈曲,它必须克服压力差Fe产生的功。这个功是W = mFe/2。这里的m是压力点的数量, 是弯曲后挠度最大值，/2 是m个压力点的平均挠度。当板料表面不受压力F、板料受平行载荷Px。 临界压力用能量法计算,临界应力cr的公式9-10 (1)当板料的表面受压力fe作用,屈曲临界应力crq可以得到根据Fe = 2K (2)当 d是金属板厚度 ET是切线模量,是泊松比。 从方程式中可以看出。(1)和(2)中显然crq大于cr。比较式(1)与式(2),它可以在公式(2)里看出板料屈曲临界应力随着弹簧弹性系数的增加而增加。增加弹簧弹性系数将扩大压力差Fe.提高屈曲临界应力。它表明,作用于板料表面 的弹性压力可以提高板料的屈曲临界应力。多点冲压成形过程可以有效的抑制屈 曲和起皱。4测试“多点冲压成形”的过程由杆系柔性模实现。杆柔性模有快速重构的能力。模 具可以通过调整杆的长度，选择合适的套筒,在杆上装配合适的弹簧，改变相应 的冲头来构建。杆柔性模有许多优点超过传统的模具。它可以有效地抑制板料起 皱,也可以带来板料成形的新方法。接下来的实验将显示“多点冲压成形”的特点。 4.1球形板件的成形球形金属板件是一种典型的弯曲的板件。如果钣金零件是由传统的模具成形, 褶皱通常发生在周围的地区以及压边区域11。一个常见的解决起皱的方法是增 加压边力。这个方法可以减少板料起皱。然而,如果该值的压边力太大,金属板可 能产生开裂12。如何控制板料的起皱是实验的关键。用DYNA-form软件可以模拟成形过程。从图7可看出:材料沿着M-N部分容易起皱。图7板料成形的应力状态在重构的过程中,板件的三维模型可以被分析,扩展延伸的每个杆和每个冲 压头的形状首先被计算出。随后,调整可调螺母的位置，改变冲头的形状,构建模 具表面。下一步是构建模具的压边结构。模具周边的一些杆用于压边。板件的球 形部分球面半径为150毫米。杆上的冲头是定制的。上模安装在冲压机的上工作台上，如图4.下模安装在下工作台上。在板料成 形的过程中，板料的压边部分被固定在下模面上，然后上模下行，最后上下模闭 合，完成板料的成形。图8是成形的板件，没有起皱存在，这归功于“多点冲压成形”。图8球形板件材料AISI1020,弹性模量E = 2.06 GPa,屈服强度0.35 GPa。当板料表面不受 压力时,根据公式(1)板料不受压力的情况下,临界压力cr可以得到。这里, a, b = 80 mm, d = 1 mm, ET 0.3E.在形成球形板件时,板可以被每个柔性杆限制。板料表面受压,根据公式(2), 板料的临界应力和压力可以得到。crq = 359.3 MPa(2)对比公式（3）公式（4），很容易看出，在板料没有受压的情况下临界屈曲 压力crq明显大于cr，杆中弹簧在采用更大弹性系数时板料不易起皱，作用在 板料表面上的弹性压力可以增大临界屈曲压力，从而减少板料的起皱4.2半球形板料的成形半球形金属板件是非对称的,如图9。开幕式曲面不方便设置压边。在板料成
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