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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): 313-318DOI: 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 onthe upper and lower surfaces of sheet in stamping process. The method is an effective way to enhance the bucklingcritical stresses and reduce wrinkling of sheet. The results of tests indicate that the die can achieve “one diebrings multi-purpose” and suppress the wrinkle of sheet. The process of the multi-point pressing and formingsheet provides a practical and effective way for the curved sheet metal forming.Key words: stamping process, wrinkle, reconfigurable, dieCLC number: TG 386Document code: A1IntroductionWrinkling of sheet metal seriously influences theforming quality and the life of die. It may make theforming process unable to carry on. So effectively sup-pressing wrinkle seems to be highly important1.Inrecent years, in order to meet the demand of light andtough sheet metal, thin sheet metal parts are widely ap-plied in various fields. The study of Wrinkling becomesone of the hottest research topics2.Since the near century, many scholars have broughtmassive studies and discussions into the instability ofsheet. These researches covered from the experimentalstudy and the theoretical analysis to the numerical sim-ulation, from the sheet drawing and the bend formingto the hydroforming, from the wrinkle forecast to thebuckling control and so on1-3.Recently, numerical simulation of a forming processis applied to study on wrinkle. Depending on the mod-ern advanced research methods, numerical simulationbased on the finite element method has become themain tool of study wrinkling in decades4.However, majority studies encircle wrinkling bifurca-tion of sheet metal and the situations of wrinkling atthe present time. But these cannot bring any feasiblemethod 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 Foundationof 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 inthe sheet metal has not been suppressed5.The paper emphasizes how to control wrinkle of sheetforming. Main ideas in the paper are two: One ideais to improve the supporting condition of sheet metaland increase its buckling critical stresses. Thus, “themulti-point pressing and forming sheet” technique willbe proposed. Another idea is to explore a reconfigurabledie which is combining the technique of “the multi-pointpressing and forming sheet”.2Poles Flexible DieIn order to reduce the wrinkling of sheet, a method ofusing elastic pressing forces putting on surfaces of sheetin stamping process was presented, it can improve thestability of sheet metal.A new reconfigurable die was developed. The die hashigh efficiency in reconfiguration so that it can achievemulti-purpose use. Simultaneously the die can be car-ried out the process of “the multi-point pressing andforming sheet”.Curved sheet metal parts are used in many productssuch as aerospace products, military products, shipsand engineering machines, the batch of parts is small.Different shape requires different die for forming sheetmetal. It leads to high cost and long cycle6-7. To meetthis situation, the reconfigurable stamping die has beenexplored. The die can be applied to forming a varietyof sheet parts by reconfiguring. The novel die is namedas “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 areassembled 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, 4Baffle5Jointer, 6Punch head, 7Blank-holder, 8Sheet metalFig. 1The structure of poles flexible diePunch head located in the end of pole can be replacedwith relevant shape head. All heads are constituted thesurface of die so that it is conformed to the shape ofsheet part.The die is composed with flexible poles.In orderto realize the multi-point pressing and forming sheetprocess, the adjustable pole is designed as a flexiblepole with the function of “pressing sheet” and “formingsheet”. Figure 2 shows the scheme of the flexible pole.12345687AAAABBBB1Stepping motor, 2Frame, 3Screw rod4Pressure spring, 5Adjustable nut, 6Adjustable sleeve7Punch head, 8Pressing distanceFig. 2The schematic of the flexible poleIt can be seen from Fig. 2 that position of sleeve isrestricted by the adjustable nut in flexible pole. Rotat-ing screw rod can control the position of sleeve. Sleeveis tightly held the adjusted nut under the effort of pres-sure spring. Figure 3 shows the materialization of theflexible pole.1Screw rod, 2Pressure spring, 3Adjustable nut4Pressing-distance slot, 5Adjustable sleeve6Punching headFig. 3The flexible poleIn 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 thedescending of the upper die, punching heads and sleevesare retracted inward. Pressing force of punching headis gradually increased under the effort of spring. Afterall punching heads and sleeves are retracted a definitedistance (pressing distance), the adjusted nuts will re-sist sleeves and locate the sleeves. Consequently, theheads 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. Thelength of pressing-distance slot has various sizes. Thelong pressing-distance slot may be used for construct-ing the blank-holder. Pressing force on sheet metal isproduced by pressure spring inside die. Changing thecorresponding coefficient of elasticity of spring can gen-erate desired pressing force.Pressing force on sheetmetal 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 upperworktable of the press machine.The surface of thedie is spherical face composed by some punching headsof poles.Poles in the periphery of die are blank-holder poles.1Blank-holder, 2Surface of dieFig. 4The upper die with spherical surface3The 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 canbe seen in Fig. 5. It must be gone through four stepsthat are “holding blank”, “pressing sheet”, “pressingand forming sheet” and “shaping sheet”.At the first stage of the forming, blank holders ofthe die achieve “holding blank” as shown in Fig. 5(a).Then both upper and lower punching heads of dies arepressing sheet, and the process is called “multi-pointpressing sheet”, as shown in Fig. 5(b). In the processof stamping, some sleeves reach the designated pointfirstly 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 combinedthe surface of die, the sheet metal is shaped by the die,as shown in Fig. 5(d). During the process, the sheetmetal is always confined by punching heads.In the process of forming sheet metal, poles flexibledie composed by “flexible poles” proceeds to “pressingsheet” and “forming sheet” at the same time. The pro-cess of “the multi-point pressing and forming sheet” canprevent buckling and wrinkling of sheet. In the stamp-ing process the force of pressing sheet is far smaller thanthe force of forming sheet, and the force of pressingsheet is produced by springs and the force of formingsheet is produced by press machine.Experiment results indicate that poles flexible die hasgood forming characteristics and can suppress wrinkleof sheet. The upper and lower surfaces of sheet metalin the forming process are pressed by elastic poles, inorder to improve the stability of sheet metal.It can be seen from Fig. 6(a) that sheet metal ispressed by loads Px, the elastic pressing forces Fearelocated 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. 5The stamping processes of the multi-point pressing and forming sheetPxPxPxPxPxzPxxxPxPxbyaxxOObFeFeFeFe1Fe2Fe3Fe4FeFeKOLFeFeFeFeFezOOay(a) Pressing forces on surfaces of sheet(c) Pressure difference by pressure springs(b) Pressure differences of surfacesFig. 6The relationship of elastic pressing forces on sheet and buckling critical stressK is the coefficient of elasticity of the spring insidethe flexible pole, L is the compressed length of thespring, as shown in Fig. 6(c). When sheet metal is gen-erated deflection , spring in the convex side of sheetcan be further compressed and elastic force made byspring is increasing.Springs on the concave side ofsheet will relax a bit. The elastic pressing force differ-ence Femade by the two side springs can be obtainedas Fe= 2K.When sheet metal occurs bending made by the pres-sure load Pxas shown in Fig. 6(b), it will produceforce differences Fe1, Fe2 at the pressing points.These pressure differences may inhibit further bendingof 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, itmust overcome the work produced by pressure differ-ence Feof 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 energyapproach, the formula of buckling critical stresses crof sheet9-10:cr=2Da2d?1 +a2b22.(1)When the surfaces of sheet are applied with pressureforces Fe, the buckling critical stress crqcan be got.crq=2Da2d?1 +a2b22+4mFe2d,according to Fe= 2K,crq=2Da2d?1 +a2b22+2mK2d,(2)where D =ETd312(1 2), d is the sheet metal thickness,ETis the tangent modulus, is Poissons ratio.It is noted from Eqs. (1) and (2) that crqis greaterthan crobviously. Comparing Eq. (1) with Eq. (2), itcan be discovered from Eq. (2) that the buckling criticalstress of sheet metal increases along with the increasingof elastic coefficient of springs. Increasing the elasticcoefficient of springs will lead to enlarge the pressuredifference Feand improve the buckling critical stress.It indicates that the elastic pressing force applied tothe surfaces of sheet can improve the buckling criticalstresses of sheet metal. The process of the multi-pointpressing and forming sheet can suppress buckling andwrinkling of sheet effectively.4TestsThe process of “the multi-point pressing and form-ing sheet” is carried out by the poles flexible die. Polesflexible die has the ability of quick reconfiguration. Thedie can be constructed by adjusting the length of polesand choosing sleeves and fitting the suitable spring inpoles and changing corresponding heads. Poles flexi-ble die has many advantages to surpass traditional die.It can effectively suppress wrinkle of sheet, also it canbring new method into the sheet metal forming. Follow-ing experiments will show the characteristics about theprocess of “the multi-point pressing and forming sheet”.4.1The Forming of Spherical Sheet PartA spherical sheet metal part is a typical kind ofcurved sheet metal part. If the sheet metal part wasformed by traditional die, wrinkles often occur in thesurrounding area as well as blank-holder area11.Acommon way for solving the wrinkles is increasing theblank-holder force. The way may decrease wrinkles ofsheet. However, if the value of the blank-holder force istoo large, cracking may occur in sheet metal12. Howto control wrinkle of sheet is the key of the experiment.Simulation of the forming process is performed withthe software DYNA-form. It is shown from Fig. 7 thatthe material is prone to wrinkle along the section M-N.Fig. 7Stresses status in the forming of sheetIn the course of reconfiguration, the 3D model ofsheet part should be analyzed, the extension elongationof each pole and the shape of each punching head arecalculated firstly. Subsequently, it is to adjust the posi-tion of the adjustable nuts and to change the punchingheads, and to construct the surface of the die. Nextstep is to constitute the blank-holder structure of thedie. Some surrounding poles of die are used for blank-holder. The sheet metal part with the spherical shapehas its spherical radius of 150 mm. Heads in the polesare customized.The upper die is installed in the upper table of thepress machine, as shown in Fig.4. The lower die is in-stalled in the lower table.In the process of formingsheet, the blank sheet is placed on the working faceof lower die, and then the upper die moves down. Fi-nally the upper and lower dies are matched to finish theforming of sheet metal.The shaped sheet metal part is shown in Fig. 8. Nowrinkle exists in the sheet. This is due to the processof “the multi-point pressing and forming sheet”.Fig. 8Spherical sheet partsThe material of the sheet is AISI1020, of elastic mod-ulus E = 2.06 GPa, of yield strength 0.35 GPa. Whenthe surfaces of sheet arent applied with pressure forces,according to Eq. (1)，under the condition of the sheetmetal without pressing force, the critical stresses crcan 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, thesheet can be confined by each flexible pole. The surfacesof sheet are applied with pressure forces, according toEq. (2), the critical stresses of sheet metal with pressingforce can be got.crq= 359.3 MPa.(4)Comparing Eq. (3) with Eq. (4), it is easy to knowthat the value of buckling critical stress crqis obviouslybigger than crunder the condition of no pressing forceson sheet metal. The sheet metal cannot be prone towrinkle with setting bigger coefficient of elasticity ofspring inside poles. Elastic pressing forces putting onsurfaces of sheet can increase the buckling critical stressand decrease wrinkle of the sheet.4.2The Forming of Hemispherical Sheet PartHemispherical sheet metal part is an unsymmetricalsheet, as shown in Fig. 9.The opening curved faceis 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-freeforming, it is necessary to increase the pressing forceonto the sheet so as to prevent wrinkle of sheet.Fig. 93D model of hemispherical sheet metalBy discharging a half of poles of spherical stampingdie, it can be used to form the hemispherical sheet metalpart. Now, it can be observed conveniently about thesteps of the stamping process. The steps can be seenfrom Fig. 10. Figure 10(c) shows the step of pressingsheet and forming sheet.Figure 11 shows the hemi-spherical sheet with the thickness of 1.8 mm.Fig. 10The steps of the multi-point pressing and forming sheet processFig. 11Hemispherical sheet metal part4.3Forming of Saddle Sheet PartAs shown in Fig. 12, saddle sheet metal is a kind ofcurved sheet metal part with double curvature. If thesheet is formed directly, wrinkle is often occurred3.The blank-holder is constructed uneasily becausethe peripheral boundary lines of saddle sheet part aredistributed in the different altitude. Currently, it is al-most impossible to form saddle sheet metal by directlyusing the conventional stamping die. The poles flexibledie can be used to form the sheet metal part directlywiththemulti-pointpressingandformingsheetprocess.Figure 13 shows the flexible die which is finishedby re-constructing.During the forming sheet theperipheral poles are retracted corresponding dimensionmore than other poles.When the upper and lowerdies are matched, surfaces of peripheral poles and thatof middle poles are combined a continuous forming318J. Shanghai Jiaotong Univ. (Sci.), 2010, 15(3): 313-318surface. Then the sheet is shaped to the saddle sheetmetal directly. The structure of blank-holder is called“the multi-point blank-holder”.Rapid prototyping and manufacturing system offused deposition modeling (FDM) can rapidly manufac-ture all kinds of punching heads. A series of punchingheads can be produced in two or three days by usingthe FDM system.The punching heads are installedin the end of poles separately as shown in Fig. 13.The material of the punching heads manufactured byFDM is acrylonitrile butadiene styrene (ABS) plastic.Punching heads can also be manufactured by rapidprototyping system of selective laser sintering (SLS).Figure 14 shows the saddle sheet part of thick-ness 1.0 mm with stainless steel.Wrinkling can beeliminated by using this method.Fig. 123D model of the saddlesheet metalFig. 13The flexible die withblank-holderattheperipheryFig. 14The saddle sheet metal formedby the multi-point pressing andforming sheet technology5ConclusionThe experimental results show that poles flexible diehas good capability of reconfiguration. It can be usedto form sheet metal parts with the thickness rangedfrom 0.5 to 6 mm.The die has obvious advantagesin 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 insheet metal forming with combining the process of “themulti-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, shortenmanufacturing time and improve the competitivenessof 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 andTechnology, 2004, 23(7): 837-841 (in Chinese).2 Prrk R. Wrinkling of tubes in bending from finitestrain 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 sheetmetal forming processing by a static explicit FEM codeJ. Journal of Materials Processing Technology, 1998,80(8): 123-133.4 Liu Hong-wen. Shell theory M. Hangzhou: ZhejiangUniversity Press, 1988 (in Chinese).5 Li Ming-zhe, Cai Zhong-yi, Cui Xiang-ji. Multi-pointformingA new flexible forming process for sheetmetal J. Metal Forming Technology, 2002, 20(6): 82-86 (in Chinese).6 Li Shuo-ben. Stamping process theory and new tech-nology M. Beijing: Machinery Industry Press, 2002(in Chinese).7 Daniel F W, Jean F H, John M P. Using recon-figurable tooling and surface heating for incremen-tal forming of composite aircraft parts J. Journal ofManufacturing Science and Engineering, 2003, 125(3):333-343.8 Song Ai-ping, Yi Hong, Tang Wen-cheng, et al. 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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一种可重构的冲压模具和冲压工艺压工艺 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: A 1 1介绍介绍 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 杆系柔性成杆系柔性成形模具形模具 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8 1 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 图图1 1. .杆系柔性模的结构杆系柔性模的结构 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 图图2，柔性杆的原理图，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 图图3 3柔性杆柔性杆 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 图图4 4球形表面的上模球形表面的上模 3多点冲压和板料成型的冲压过程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 图图5 5. .模内多点压板与成形的冲压过程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 图图6 6板上弹性压力和屈曲临界应力的关系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, Fe1Fe2.。 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 4测试测试 “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。 图图7 7板料成形的应力状态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”。 图图8球形板件球形板件 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。在板料成形时,在不受支撑的区域容易起皱,因为金属板受到不平衡冲压力。 为了确保无故障成形,因此有必要增加板上压力,防止板料起皱。 图图9 半球形板件的半球形板件的3D模型模型 通过撤掉球形冲压模具的一半杆,它可以用来成形半球形板件。 现
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