【作者】 李毅；

【导师】 李明哲；

【作者基本信息】 吉林大学 ， 材料加工工程， 2019， 博士

【摘要】 金属三维曲面零件在航空、汽车、轮船等行业内被广泛使用。传统模具曲面成形由于具有高精度、生产周期短等优点,是大批量同样规格三维金属曲面零件生产的首选工艺。但是模具制造的周期长以及生产成本高昂,使得传统模具成形难以应对多样化、小批量金属曲面零件的生产需求。柔性轧制是一种新颖的三维曲面成形工艺,通过将传统的轧制工艺与多点理念相结合,实现柔性连续的曲面成形,并根据该工艺的特点,可以快速有效地满足市场对多样化、小批量曲面的需求。由于成形设备结构简单,造价低,成形件表面光滑等一系列的优点,使该工艺具有良好的应用发展前景。目前柔性轧制工艺仍处于发展阶段,存在很多问题需要去解决。本文以圆弧为辊缝的轮廓进行曲面成形,研究了成形区对三维曲面成形结果的影响,针对在成形大曲率曲面的过程中产生的质量问题,提出了相应的解决措施。本文研究的主要内容和结论如下:(1)探讨了柔性轧制中曲面的成形原理以及成形过程,分析了凸形件和鞍形件的辊缝分布。对成形过程中板料的接触变形区进行力学分析,研究了板料的不均匀纵向伸长量分布引起的纵向弯曲变形,且推导了凸形件与鞍形件的辊缝函数。(2)根据柔性轧制成形过程,建立了相应的有限元模型,并确定了成形过程中涉及的边界条件等相关建模参数。提出一种快速配置辊缝分布的方案,对凸形件和鞍形件的成形过程进行了数值模拟,并对成形结果进行了分析。(3)在有限元分析中,研究了板料成形区对成形曲面件的影响。结果表明:以圆弧作为辊缝轮廓得到的曲面质量较好。随着板料长度的增加,成形曲面件的稳定区长度得到显著提升;随着板料宽度的增加,成形曲面件的塑性变形增大,稳定区长度有所减小,厚向减薄精度降低,板料减薄量下降,等效弯曲变形增加。当压下量不变时,随着板料厚度的增加,塑性变形减小,厚向减薄精度下降,板料减薄量降低,等效弯曲变形减小。当板料厚度不变时,随着压下量的增加,塑性变形有所提升,厚向减薄精度下降,板料厚度值减小、等效弯曲变形降低。(4)对大曲率曲面的成形缺陷进行了研究,通过对缺陷产生的机理进行分析,提出了基于柔性轧制的异步成形工艺,并研究了该工艺对凸形件以及鞍形件成形结果的影响。实验结果表明:通过合理地调节上下辊各自与板料的摩擦,异步成形工艺可以有效地提升零件的成形均匀程度,提高有效成形区域的长度,并且实现成形曲面件纵向变形的调节,达到修正成形误差的目的。(5)针对由加工硬化导致的大曲率曲面纵向变形受限的问题,提出了渐进式多道次成形工艺,并对成形原理进行分析。通过数值模拟验证了渐进式多道次成形工艺对凸形件以及鞍形件成形结果的影响。实验表明:通过合理地设计每一道次板料的变形量,能有效地避免成形缺陷的产生,实现纵向弯曲变形的最大化。制定合理的成形次数,可以提高成形效率,缩短成形周期。(6)对柔性轧制成形实验设备以及成形过程进行详述。介绍了测量工具以及操作流程,并对成形曲面件进行测量。通过对成形件的形面、厚度以及纵向变形的误差分析,验证了数值模拟指导实验的可行性。更多还原

【Abstract】 Three-dimensional surface parts are widely used in aviation,automobile,ship and other industries.Traditional die forming has the advantages of high precision and short production cycle.It is the preferred process for manufacturing large quantities of 3D surface parts with same specification.However,as the longer manufacturing cycle and higher production cost of die,it is difficult for traditional die forming to meet the demand of 3D surface parts with diversification and small batch.Flexible rolling is a novel forming process for 3D surface parts,which combines traditional rolling process with multi-point concept to realize flexible continuous surface forming.Based on the characteristics of this process,it can quickly and effectively meet the market’s requirements for 3D surface parts with diversification and small batch.Due to the advantages of simple structure of forming equipment,low cost and smooth surface of forming parts,the process has a good prospect of application and development.At present,the flexible rolling technology is still in the developing stage,many problems need to be solved.In this paper,the influence of sheet forming zone on forming results of 3D surface part was studied by using the circular arc as roll gap contour,and the solutions to the problem of forming small curvature surface part were proposedThe main contents and conclusions in this paper are as follows:(1)The principle of flexible rolling and the forming process of 3D surface have been discussed;And the roll gap distributions of convex surface part and saddle surface part have been analyzed;In the forming process,the mechanical of sheet contact deformation area has been analyzed;The longitudinal bending deformation caused by uneven longitudinal elongation distribution of sheet metal has been studied;the roll gap functions of convex surface part and saddle surface part have been derived.(2)According to the process of flexible rolling,the corresponding finite element model has been established,and the boundary conditions and other related modeling parameters involved in this process have been determined.In this paper,a scheme for rapid configuration of roll gap distribution is presented,the forming process of convex surface part and saddle surface part have been simulated and the forming results are analyzed.(3)In the finite element analysis,the influence of the sheet forming zone on the forming results of 3D surface part has been studied,and the results showed that the quality of 3D surface part obtained by using circular arc as the contour of roll gap was better.With the increase of the longitudinal forming length,the stable area length of forming surface part increases obviously.With the increase of transverse forming length,the plastic deformation of forming surface part increases,the stable area length decreases,the thickness thinning precision decreases,the sheet thinning decreases,and the equivalent bending deformation increases.When the rolling reduction is constant,with the increase of sheet thickness,the plastic deformation decreases,the thickness thinning precision decreases,the sheet thinning decreases,and the equivalent bending deformation decreases.When the sheet thickness remains unchanged,with the increase of rolling reduction,the plastic deformation increases and the thickness thinning precision decreases,the sheet thickness decreases,and the equivalent bending deformation decreases.(4)The forming defects of small curvature surface part have been studied,and the flexible rolling asynchronous forming process is proposed by analyzing the mechanism of defects.The experimental results show that the asynchronous forming process can effectively improve the uniformity of forming surface part and increase the effective forming area length.By properly adjusting the friction between the upper,lower rolls and the sheet metal,the longitudinal deformation of forming surface part can be controlled and the forming error can be corrected.(5)For the problem of limited longitudinal deformation of small curvature surface part caused by machining hardening,the incremental multi-step forming process has been proposed,and the forming principle was analyzed.In the numerical simulation,the influence of incremental multi-step forming process on the forming results of convex surface part and saddle surface part is verified.The experiment shows that the forming defects can be avoided and the longitudinal bending deformation can be maximized by reasonably designing the deformation amount of each forming step.Making a reasonable number of forming times can improve the forming efficiency and reduce the forming period.(6)The experimental equipment and forming process of flexible rolling are described in detail.The measuring tool and operation procedure have been introduced,and the forming surface parts have been measured.By the error analysis of shape,thickness and longitudinal deformation of forming parts,the feasibility of numerical simulation in guiding experiment is verified.更多还原