【作者】 史晓帆；

【导师】 高霖；

【作者基本信息】 南京航空航天大学 ， 航空宇航制造工程， 2013， 博士

【摘要】 金属板料渐进成形技术是一种适用于单件、小批量钣金产品的快速制造技术。该技术根据模型的几何信息，采用分层制造的方法将制件逐次成形。板料在成形过程中产生的局部变形使渐进成形技术的成形精度相对较低，严重制约了该技术在实际生产中的推广应用。对此，本文对渐进成形中严重影响成形精度和产品外观的成形缺陷进行了较为系统的研究，提出了一些可以提高成形精度的工艺改进措施，并通过试验证明了各种改进措施的可行性和有效性。本文主要研究工作如下：(1)成形机理研究。对材料的变形过程进行了较为细致的研究，将材料的变形分为初始变形区域、变形中间区域和变形完成区域。基于纯剪切变形的假设，研究了成形过程中应力、应变和成形力的变化。在进行应力分析时，提出了一种考虑到板料内部非均匀应力分布状态的应力计算方法，解释了制件内部残余应力的产生原因。在进行成形力分析时，根据纯剪切变形和存在刚性端的假设，提出了一种考虑到材料加工硬化且较为准确的成形力计算方法。(2)各种精度问题及其影响因素的研究。首先通过试验测试和数值计算的方法研究了成形工具头在成形过程中的变形，然后在剔除成形工具头变形影响的基础上对正、负渐进成形鼓包、平面侧壁鼓凸、回弹和牵连变形等精度问题进行了较为系统的试验研究，找出了成形参数对各种缺陷的影响关系。(3)改进工艺研究。提出了几种有利于提高成形精度的工艺改进措施，主要有：使用平头成形工具头改善负渐进成形中的鼓包和回弹；对板料托架施加预拉量配合使用平头成形工具头，改善正渐进成形制件上出现的顶部鼓包、根部压痕和边缘翘曲；使用局部加热的方法改善平面侧壁鼓凸和牵连变形，为防止过快的成形速度造成板料被电火花击穿，提出了一种在不影响成形效率的前提下避免放电现象的无干涉螺旋线成形轨迹生成方法。试验结果表明，各种改进工艺措施可以非常有效地提高制件的最终成形精度。(4)补偿成形工艺研究。提出了一种基于简单测量的补偿模型构建方法，使用该方法构建的补偿模型，可使成形精度出现明显提高，有效降低了回弹和平面侧壁鼓凸对成形精度带来的影响。在构建平面侧壁补偿模型时，提出了一种基于二次曲面的侧壁形状逼近模型，有效简化了补偿成形的实施难度。(5)切边变形研究。通过数值方法计算了简化模型的残余应力，通过试验方法研究了制件在经过切边处理后的变形，找出了各种成形参数对切边变形量的影响。提出了使用退火处理的方法来降低制件的切边变形，并确定了AA1060铝合金制件的最佳退火温度为320℃。(6)通过钣金样品的实际试制过程证明了各种改进成形工艺的有效性。使用平头成形工具头和退火处理的方法分别消除了盖板制件的底部鼓包和回弹翘曲，同时，对该模型使用正渐进成形的方法进行了工艺尝试，同样达到了避免回弹翘曲的目的。此外，还使用局部的补偿成形工艺得到了侧壁平整的复杂制件。更多还原

【Abstract】 Incremental sheet mental forming is a novel kind of sheet metal forming technology which suitsspaceman and small batches. During the process, the sheet metal part is formed layer by layeraccording to the CAD model. Because of localized deformation, parts formed by incremental formingare of low accuracy, which makes it very difficult to popularize the novel process in the actualengineering. To solve the problem, some forming defects which affect the forming accuracy and finalappearance were investigated and some optimized processes, whose feasibility and validity have beenproved in experiments, were also proposed. Main achievements are shown as followed:(1) Study on forming mechanism. The deformation process was studied with more details, andthe deformed area was divided into three different zones, namely primary deformation zone,transitional deformation zone and completed deformation zone. The disciplinarian of strain, stress andforming force was studied based on pure shear deformation hypothesis. A method of stress calculation,considering the uneven stress distribution, was proposed. In addition, a method of forming forcecalculation, considering the working hardening of the material and more similar to the hypothesis ofpure shear deformation and rigid end, was proposed(2) Study on forming defects and influencing factors. Effect of the deformation of forming toolswas investigated by experiments and numerical calculation. Some accuracy defects, namely bulge innegative and positive incremental forming, bulge of the flat wall, spring back and involvingdeformation, were experimentally studied to find out the relationship between forming defects andprocess parameters.(3) Study on optimized process. Some optimized processes which benefit forming accuracywere proposed. The optimized processes are listed as followed: employing flat end forming tools toreduce bulge height in negative incremental forming and spring back; setting displacement of theclamping frame and employing flat end forming tool to avoid bulge in positive incremental forming,groove and edge warp; employing localized heating to reduce bulge of the flat wall and involvingdeformation and proposing a helical tool path generation method without interference and formingefficiency decrease. The validity of the optimized processes was proved by experiments.(4) Study on compensation forming process. A simple-measurement based method ofestablishing compensation model was proposed. Effects of spring back and bulge of flat wall werereduced significantly by the compensation forming process. In the study of establishing the compensation model of bulge of flat wall, a second-degree surface based model was proposed to fitthe bulging shape and makes it much easier to realize compensation forming process.(5) Study on trimming deformation. Rudimental stress was caculated by numerical method, andeffect of process parameters on trmming deformation was studied experimentally. The method ofreducing triming deformation by anneal treatment was proposed. Some extra experiments werecarried out to confirm320℃as the best anneal temperature.(6) Finally, the optimized processes proposed in the thesis were tested by manufacturing twoactual spacemen. For the cover board part, bottom bulge and edge warp was avoided by employingthe flat end tool and anneal treatment respectively. Meanwhile, edge warp was deleted by negativeincremental forming. In addition, localized compensation forming process was employed to reducebulge height of flat wall of complex parts.更多还原