外文翻译--薄板冲压件焊装夹具设计方法

附 录附录A 英文文献On Welding-Installation Fixtures Design of Sheet StampingAbstract: Due to forming error and compliance of stamp-ing, the fixture design of sheet stamping assembly is different from the fixture design of common machining component. In recent years, the new principles and algorithms of fixture design of sheet stamping have been developed. In the paper, the concept of shape closure and force closure, screw theory were firstly introduced. Secondly, the deterministic locating and total fixturing conditions were derived. Thirdly, an “N-2-1”locating principle and optimal design method for sheet stamping were described. Finally, the varia-tional method of robust fixture configuration design for 3-D workpieces was discussed. It can be predicated that the locating error can be reduced by this method.Key Words: Fixture; Sheet Stamping; Optimal Design; Ro-Bust DesignDue to its high productivity and material utilization, stamping is widely used in automobiles, aircraft, and various household appliances manufacturing industry. The welding assembly of stamping becomes the key process of those products manufacturing, because welding fixture not only affects the performance of productivity, but also is directly related to the quality of the product. Statistics from the U.S. auto industry show that 72% of the body manufacturing errors are from the position error of welding fixture, so how to effectively reduce and control the positioning error is essential to improve the welding quality. Sheet stamping assembly is significantly different from general machining, which not only meets the common requirements of precise positioning, but also gives full consideration to the easy deformation of sheet metal parts and stamping manufacturing characteristics of large deviations to adapt the products quality requirements. Over the last decade, many scholars working in the design of sheet stamping assembly have proposed design theories and methods of some new sheet stamping assembly, and achieved remarkable results. At first, this paper introduces the research progress of fixture design, and then systematically elaborates the N-2-1 locating principle of fixture and the methods of optimal design and robust design, finally makes the conclusion.Manufacturing process (such as machining, welding, assembly and testing, etc.), the fixture is used in three-dimensional positioning and clamping device. The central problem of fixture design is to choose the optimal positioning points and determine their best position to achieve the determine constraints positioning of work piece. If the work piece can be full restriction depending on the geometry of contact area will, we called it shape closed; If it also have to be fully bound with friction, we called it force closure. Generally, shape closure stresses dynamic analysis, but force closure focuses on the work piece of static stability. In 1885, Reuleaux first studied the mechanism of two-dimensional objects shape closure, and proved that the formation of two-dimensional objects shape closure need four anchor points 2. After that Somoff proved the formation of three-dimensional objects shape closure need seven anchor points. In 1978, Lakshminarayana 3 further proved the formation of three-dimensional objects shape closure need at least seven anchor points in the perspective of static equilibrium using algebraic theory In 1988, Nguyen researched the mechanism of the machine hands force closure 4, and in 1989 Asada and Kitagawa 5 researched the machine hands shape closure which used for convex and concave parts Generally six positioning principles requires clamping force to make work piece fully constrained, so usually it is force closure.Over the last decade, the spiral theory” widely used in fixture design, which describes the three-dimensional motion as translating along one direction and rotating around this axis. Originally spiral theory proposed by Ball 6, and developed by literature 7 and 8. According to spiral theory, literature 9 studied seven different types of finger contact, and suggested using finger-like shape to completely fix objects. Literature 10 using the extended spiral theory analyzed that rigid bodys full or part restriction exist frictional clamp. Literature 11 proposed mathematical theory of fixtures automatic layout for prismatic work pieces. Literature 12 discussed the ability of different fixtures position contact preventing work pieces from spiral movement, and proposed a restrict method of work piece movement for the fixture design. Using small spiral model literature 13 discussed the positioning errors of fixture impact work pieces geometry accuracy. Literature 14 researched surface contact and friction problems in the analysis of fixture restriction. Considering dynamic constraints, completely clamping, and tool path errors, literature 15 developed fixture design and analysis software. It can be said that spiral theory of fixture design has been used for determining position, full clamping, contact type, and friction problems and achieved remarkable results.Lots of literatures focus on the fixture design of rigid pieces, but the fixture design of flexible sheet pieces is rarely involved, especially considering the deformation of the work piece under processing loads is almost none. In fact, as in the aviation industry and the automotive industry, the deformation of sheet may result in serious bias. For easily deformed sheet, positioning fixture not only has basic functions that limiting rigid body motion, but also must be able to limit excessive deformation of the work piece. The research that earlier considering the rigidity of work pieces or fixture positing cell will be found in the literature 16 based on the experimental results they studied fixture stiffness and wears effects on the size accuracy. Literature 17 proposed a finite element model of the fixture system for flexible positioning fixture, and the power in process of processing can be seen as the force acting on the node. Based on this model, you can calculate the deformation of the work piece, the clamping force, stress distribution and friction between the work piece and fixture positioning units contact points can be calculated by Coulombs law. Although by considering the deformation of the work piece and the finite element analysis this area have been promoted, but it has neither proposed any specific positing principle, nor proposed positioning scheme for flexible sheet. In addition, this model does not combine the finite element analysis results of the work piece with the fixture design; it is more than the analysis of the work piece other than fixture design. Literature 18 proposed a analysis method of sheet fixture positing, they studied the fixture positioning system using the case and flat three-point and four-point to posit, so the fixture layout must make the stress in the work pieces below the yield stress. However, this method does not solve the essential problem of sheet fixture, because reducing deformation is the key to the positioning of sheet. Based on literature 17, literature 19 continued further study, that using the finite element modeling to choose fixture layout makes the deformation minimum in the first base-level. To determine the optimal fixture layout, using quasi-Newton optimization algorithm makes the deformation squares on the finite element mesh of the key nodes minimum. Design variables are the three anchor points on the first base required by 3-2-1 principle.Sheet stamping assembly fixtures are widely used in automobiles, aircraft and household appliances industries, whose design quality directly affects the entire product manufacturing deviations. Due to sheet metal stampings characteristic of flexibility and manufacturing variations, the principle of traditional fixture design can not meet the design requirements, although the research of fixture design is already quite mature and the positioning principle of rigid part and the spiral theory has been in-depth study. N-2-1 Location principle, for the characteristic of easy deformation on the horizontal of Sheet Metal Stamping, presents that when the number of anchor points is more than 3 in the first base surface, position effect depends not only on the number of anchor points, but also on the arrangement of the anchor points. Apart from that, it proposes the finite element analysis and the design of nonlinear programming method of the anchor, which provides theoretical basis and design methods for the design of sheet welding fixture. Because of the larger manufacture size deviation of sheet metal parts and the remarkable effect of the choice of anchor position for position deviation, robust fixture design can significantly improve the positioning error. Therefore, during the design of sheet welding fixture, implementing the N-2-1 location principle and robust design method is extremely important. It has been proved to have a multiplier effect.References1Li B, Tang H, Yang X,et al.Quality Design of Fixture Planning for Sheet Metal Assembly J .International Journal of Advanced Manufacturing Technology,2007,32 (7-8):690-697.2Ceglarek D, Shi J. Dimensional Variation Reduction for Automotive Body Assembly J.Manufacturing Review, 1995,8(2):139-154.3Ceglarek D, Shi J. Fixture Failure Diagnosis for Autobody Assembly Using Pattern RecognitionJ.ASME Journal of Engineering Industry,1996,118(1):55-66.4Apley D, Shi J. Diagnosis of Multiple Fixture Faults in Panel AssemblyJ.ASME Journal of Manufacturing Science and Engineering,1998,120(4):793-801.5Chang M, Gossard D C. Computational Method forDiagnosis of Variation-related Assembly Problems J . International Journal of Production Research,1998,36 (11):2985-2995.6Liu Y, Hu S. Assembly Fixture Fault Diagnosis Using Designated Component Analysis J.ASME Journal of Manufacturing Science and Engine ering,2005,127(2): 358-368.7Khan A, Ceglarek D, Shi J,et al.Sensor Optimization for Fault Diagnosis in Single Fixture Systems: a Methodology J .ASME Journal of Manufacturing Science and Engineering,1999,121(1):109-117.8Djurdjanovic D, Ni J. Stream of Variation Based Analysis and Synthesis of Measurement Schemes in Multi-station Machining Systems C . Proceedings of the ASME International Mechamical Engineering Congress and Exposition, New York,2001,12:297-304.9Ding Y, Kim P, Ceglarek D,et al.Optimal Sensor Distribution for Variation Diagnosis for Multi-station Assembly ProcessesJ.IEEE Transactions of Robotics andAutomation,2003,19(4):543-556.10Camelio J A, Hu S. Sensor Placement for Effective Diagnosis of Multiple Faults in Fixturing of Compliant Parts J.ASME Journal of Manufacturing Science andEngineering,2005,127(1):68-74.11Li B, Yang J, Ding H. A Rapid Location and State Memory Fixture System for Arbitrarily PartJ.Journal of Donghua University,2000,17(3):27-31.12Wang Q, Yang J, Li B. Application and Realization of Rapid Searching Technology in the RL&SM Universal Fixture SystemJ.Journal of Donghua University,2002, 19(3):19-22.13Wang Y, Li B, Yang J. Investigation on Dimensional Error Compensation for Single Sheet Metal Assembly StationC. Proceedings of ICMEM, Wuxi, China,2007:699-703.14Cai W, Hu S, Yuan J. Deformable Sheet Metal Fixturing: Principles, Algorithms, and SimulationsJ.ASME Journalof Manufacturing Science and Engineering,1996,118(3): 318-324. 367Journal of Donghua University (Eng. Ed.) Vol.26, No.4(2009)附录B 文献翻译薄板冲压件焊装夹具设计方法摘要:由于薄板冲压件的易变形性和制造误差特征,薄板焊装夹具设计显著区别于普通机械加工工件定位夹具。本文首先介绍了夹具设计的形闭合与力闭合概念、螺旋理论的发展,给出了确切定位和完全夹紧条件;然后,重点阐述了面向薄板冲压件焊装夹具设计的“N-2-1”定位原理和夹具的优化设计方法;最后分析了夹具的稳健性设计方法。可以预料,采用该方法可有效地减少和控制定位误差的影响。关键词:夹具;薄板冲压件;优化设计;稳健设计冲压加工以其较高的生产率和材料利用率,广泛应用于汽车、飞机和各种家用电器制造工业,冲压件的焊接装配成为上述产品制造的关键工序,焊装夹具的性能不仅影响到生产率,而且直接关系到产品的质量。美国汽车工业的统计表明1,72%的车身制造误差源于焊装夹具定位误差,因此如何有效地减少和控制定位误差的影响,对提高焊装质量至关重要。薄板焊装夹具与通用的机加工夹具存在显著的差别,它不仅要满足精确定位的共性要求,还要充分考虑薄板冲压件的易变形性和冲压制造偏差较大的特征,以适应于产品的高质量要求。近十几年来,许多学者在薄板焊装夹具的设计上开展了大量工作,提出了一些新型的薄板冲压件焊装夹具的设计理论和方法,取得了显著效果。本文首先介绍夹具设计方法的研究进展,然后系统地阐述夹具的N-2-1定位原理、优化设计及鲁棒性设计方法,最后给出本文的结论。制造过程(如加工、焊接、装配和检测等)中,夹具是用于在三维空间定位和夹紧工件的设备。夹具设计的中心问题就是选择最优定位点数并确定它们的最佳位置,以实现工件的确定约束定位。如果工件依靠接触区域几何形状便可完全约束,称为“形闭合”;如果还必须借助摩擦才能完全约束,则称为“力闭合”。通常形状闭合强调动态分析,而力闭合则研究工件的静态稳定。1885年,Reuleaux首先研究了二维工件的形闭合机制,证明了形成二维物体的形闭合必需四个定位点2。之后,Somoff证明三维物体的形闭合需要七个定位点,1978年,Lakshminarayana3从静态平衡角度利用代数理论进一步证明了三维工件的形闭合至少需要七个点。1988年,Nguyen研究了机器手力闭合机制4,而Asada和Kitagawa5于1989年研究了用于凸形和凹形工件的机器手的形闭合。通常的六点定位原理一般地需要夹紧力将工件完全约束,因此常常是力闭合。近十几年来,“螺旋理论”广泛流行于夹具设计中,螺旋理论将三维工件的三维空间运动描述为沿某一方向的平移和绕这一轴线的转动。最初由Ball6提出,并得到文献7和文献8的发展。根据螺旋理论,文献9研究了七种不同类型的指状接触,并建议用指状外形去完全固定夹紧物体。文献10利用扩展的螺旋理论就刚体的全部或局部约束分析了有摩擦夹紧。文献11提出了用于棱柱形工件的加工夹具自动布置的数学理论。文献12讨论了各夹具定位接触阻止工件相互螺旋运动的能力,提出了一种用于夹具设计的工件运动约束方法。文献13利用小螺旋模型考虑了夹具定位误差对工件几何精度的影响。文献14在夹具约束分析中研究了表面接触和摩擦问题。文献15开发出了考虑动态约束、完全夹紧和刀具路径偏差的夹具设计和分析软件。可以说,夹具设计的螺旋理论已经用于处理确定定位和完全夹紧问题、定位质量、接触类型和摩擦等问题,并取得了明显成绩。大量的文献集中论述了刚性件的夹具设计,但关于薄板柔性件的夹具设计研究很少涉及,特别是考虑加工载荷作用下工件变形的夹具设计的研究几乎没有。实际上,象在航空工业和汽车工业,薄板变形可能导致严重的尺寸偏差。对于易变形薄板,定位夹具除了具备限制零件刚体运动的基本功能外,还必须能够限制过多的工件变形。较早考虑工件或夹具定位单元刚性的研究见于文献 16,他们根据实验结果研究了夹具刚度和磨损对尺寸精度的影响。文献17提出了一种用于柔性定位夹具的夹具系统分析的有限元模型,加工过程中的加工力可看作是作用于节点的力。基于该模型,可以计算出工件变形、夹紧力和应力分布,可运用库仑摩擦定律去计算工件与夹具定位单元间接触处的摩擦力。虽然通过考虑工件变形和有限元分析推动了这一领域,但它既没有提出任何一种具体的定位原理,也没有为具有柔性的薄板提出一种定位方案。此外,这种模型并没有将工件的有限元分析结果同夹具设计规范联系起来,它更多的是工件的分析而不是夹具设计。文献18提出了一种薄板夹具定位分析的方法,他们研究了用于平板和壳体的三点和四点夹具定位系统,夹具布置必须使得工件中的应力低于材料的屈服应力。然而,这种方法并没有解决薄板夹具的本质问题,因为减小变形是薄板件定位的关键所在。文献19在文献 17的基础上进行了更深入的研究,利用有限元建模选择使得工件在第一基准面法向的变形最小的夹具定位布置。为确定最佳夹具定位布置,利用拟牛顿优化算法使有限元网格上的关键节点的变形的平方和最小。设计变量是“3-2-1”定位原理所要求的第一基准面上的三个定位点。薄板冲压件焊装夹具广泛应用于汽车、飞机及家用电器等工业,焊装夹具的设计质量直接影响到整个产品的制造偏差。由于薄板冲压件的柔性和制造偏差特征,传统的夹具设计原理不能满足薄板冲压件的设计要求,尽管夹具设计研究已经相当成熟,刚性零件的定位原理和“螺旋理论”得到了深入研究。“N-2-1”定位原理针对薄板冲压件在横向上的易变形特征,提出了在第一基面上的定位点数目大于3,定位效果不仅取决于定位点的数目,而且取决于定位点的布置形式,并提出了采用有限元分析与非线性规划的定位点设计方法。为薄板冲压件焊装夹具的设计提供了理论基础和设计方法。由于薄板冲压件的制造尺寸偏差较大,定位点位置的选择对定位偏差的影响更明显,夹具的稳健设计可显著地改善定位误差。因此,在薄板焊装夹具设计过程中,贯彻“N-2-1”定位原理和稳健性设计方法是极为重要的,实践证明,可以收到事半功倍的效果。7