【作者】 陈喜娣；

【导师】 蔡中义；

【作者基本信息】 吉林大学 ， 材料加工工程， 2004， 硕士

【摘要】 多点成形技术是金属板材三维自由曲面成形的一种柔性加工方法，其基本思想是将传统的整体模具离散化，由一系列规则排列的基本体（或称冲头）组成的“柔性多点模具”来代替，由基本体球头的包络曲面来完成板材成形。多点成形技术作为一种新兴的技术已在飞机、船舶、汽车等诸多制造领域有着广泛的应用前景。无压边多点成形通常用于变形量不大的曲面成形，是板材多点成形过程中使用频率很高的一种成形方法。多点成形在成形变形量不大的曲面时，通常不压边，这样既可省去切边工序又可以节省材料，另一方面又能简化多点压机结构，降低其造价。由于没有压边圈，板材面内变形力较小，主要以面外弯曲变形为主，导致在多点成形中起皱缺陷更容易出现，特别是在薄板多点成形中，起皱是工艺上必须克服的成形缺陷。由于没有压边圈的作用，板材成形过程中，回弹对成形件最终形状的影响要比有压边时大。影响回弹的因素很多，如板材厚度，板材的材质以及成形件变形量的大小等。本文采用数值模拟技术对多点成形过程的回弹进行了分析，另外还探讨了典型零件在多点成形时，通过控制基本体群成形面形状消除回弹的方法。1. 板材无压边多点成形的起皱数值模拟采用显式算法进形起皱数值模拟时，板材必须离散成足够小的有限元单元，使皱纹能够已相当小的波长正确的模拟出来。通过不同尺寸有限元单元的数值结果比较，建立了板材无压边起皱分析的有限元模型。对双向曲率曲面—球面和马鞍面进行了详细的数值模拟，研究了板材厚度、曲率半径以及材质等对起皱的影响。板厚与变形程度是影响起皱的重要因素，增大板材厚 71<WP=76>吉林大学硕士研究生学位论文度，减小成形件曲率半径均可有效的抑制起皱的产生；文中对 08AL 和 L2Y2铝两种不同材料的板材成形球面和马鞍面的起皱现象进行了有限元分析。结果表明选用具有较大的弹性模量的 08AL较具有较小弹性模量的 L2Y2 不容易产生起皱缺陷。 通过对多点成形过程中的起皱产生过程的分析，发现在无压边多点成形中，起皱主要产生于基本体对板材的不完全约束，在成形后期起皱出现最大值，在成形结束时，部分皱纹被压平。基于对多种不同板厚、不同曲率半径的球面和马鞍面成形件的数值分析，得到了球面与马鞍面无压边、不起皱多点成形极限图。在本文之前，还没有多点成形不起皱极限图方面的结果。 2. 板材无压边多点成形的回弹数值模拟。 完整的板材成形包括加载和卸载两个过程。本文建立了采用显-隐式算法模拟回弹问题的有限元模型。即采用动态显式算法模拟板材成形过程，采用隐式算法模拟卸载回弹过程。这种方法克服了显式算法耗时大，难以收敛的缺点，解决了隐式算法不能处理好接触问题的缺点，极大的提高了回弹数值的计算效率，具有实用性和高效性的特点。 主要分析了板材厚度、成形件变形量以及材质等对柱面、球面及马鞍面的无压边多点成形的回弹影响，并且利用中心插分法，拟合出成形件回弹前、后曲面形状，计算出回弹量的大小。由数值模拟结果可以看出，在多点成形中，板材厚度越小，变形量越小，卸载后回弹越大，反之，厚度越大，变形量越大则回弹越小。 3. 多点成形过程中成形面的修正与回弹控制的研究 利用数值模拟技术，在回弹分析的基础上，给出了基于回弹数值计算的柱面、球面多点成形基本体群成形面的修正方法。对于目标曲率半径为的圆柱面，但板厚为 1.0mm时，经过三次修正，形状总体误差只有 0.0044m；板厚为 1.5mm时，经过五次修正，形状误差达到 0.00083m；对于目标曲率半径为 1200mm，板厚为 1.5mm时，经过两次修正形状误差达到 0.0962m；依据最后一次修正的成形面调整基本体群的形状进形多点成形，可以有效的补偿板回弹影响。实现板材的一次精确成形，提高产品的成形精度。这些结果对多点成形技术的进一步工程应用具有一定的参考价值和实际意义更多还原

【Abstract】 Multi-point forming(MPF) is a flexible manufacturing technology for threedimensional sheet metal forming. In multi-point forming, the conventional solid dieis replaced by “flexible Multi-point die” composed by a series of discrete elements(or punches). The forming process of sheet metal is implemented by the envelopesurface of punches. Multi-point Forming can be applied extensively in a lot offields such as aircraft, stream and navel ships, vehicle, large sculpture and modernarchitecture etc. Sheet metal forming in MPF without blank holder, which is a commonprocess method, is usually applied in processing those kinds of surface parts whichhave not big deformation amount. In this process condition, the original materialconsuming and the press cost can be reduced to a low level as well as simplifyingthe press structure and leaving out trimming procedure in metal sheet formingprocess. without blank holder, the deformation inside the surface is distinctlysmaller than the bending outside the surface. Wrinkle is a key factor to determinewhether the part could be formed and become one of primary forming defectsespecially for thin metal sheet in MPF. On the other hand, in this condition, springback was more serious than thoseforming with blank holder. Springback was affected by numerous factors, such asthickness of metal sheet, material property and deformation amount and so on. Andthe last content of this paper was to research the springback eleminating methodthrough controlling the forming surface of the elements group for metal sheet inmulti-point forming process.1.Numerical simulation of wrinkling in multi-point forming formetal sheet without blank holder As view from mechanics, wrinkle is a kind of plastic ?in metal sheet surface.It is more difficult with static implicit algorithm than dynamic explicit in analyzing 73<WP=78>吉林大学硕士研究生学位论文wrinkling problem. Based on the explicit algorithm, there must be offered as fineelement as to make the wrinkle to simulate with adequate small wavelength. Obtained the numerical simulation results of wrinkle with different size offinite element, establishing the finite element model for wrinkling numericalanalysis. The Multi-point forming process of sphere, saddle surface of differentmaterials with different thickness and deformations were simulated, and thoseresults show that metal sheet thickness, deformation and material property haveeffect on wrinkle defect. With metal sheet thickness increasing, deformationdiminishing, wrinkle can be gradually weakened. Simultaneously, wrinkle wasaffected by material property too. In this paper, two material, 08Al steel and L2Y2pure aluminum are simulated, and found L2Y2 pure aluminum are more sensitiveto wrinkling than 08AL steel because the Elastic modulus of 08AL is greater thanthat of L2Y2. In this paper, the wrinkling growing up process was also analyzed, anddiscovered that wrinkling in multi-point forming for metal sheet without blankholder, derives from metal sheet under an half-baked restraining which comes fromthe elements group. The maximal of wrinkle depth appear in the anaphase of theforming processing, and some wrinkle can be planished at the end of forming. Inaddition, the non-wrinkling limit of sphere and saddle surface were obtained.2. Numerical simulation of springback in multi-point forming formetal sheet without blank holder There were included loading and unloading course in an intact metal sheetforming. Based on explicit-implicit algorithm, the finite element model fornumerical simulation of springback was established. Dynamic-explicit formulationwas employed to analyze the loading process and implicit formulation to unloadingprocess. This method not only overcomes the time consuming and convergenceproblem in explicit algorithm but also avoids the contact difficult in implicitalgorithm, with go更多还原