微型管件轴向补料液压成形工艺研究

发布时间：2018-10-22 17:55

【摘要】：在微机电、医疗器械等领域,对微型异形管件的需求正逐渐上升。液压成形能够高效生产微型异形管件,成为研究的重点。由于零件尺寸与晶粒大小接近,微型管件产生了尺度效应问题,成形能力降低,制约了其发展。轴向补料工艺能够提高管件成形能力,已在常规异形管件生产中广泛应用。为了提高微型管件成形能力,本文将轴向补料工艺引入微型管件液压成形中,进行了相关研究。首先,对微型管件液压成形导向区内的摩擦特性进行了研究。采用自行开发的实验装置,通过测定初始摩擦力与总推力,并根据内压大小以及其它尺寸参数,即可计算出摩擦系数。分别对外径2mm与1mm的304不锈钢微型管件进行实验,结果发现随着尺寸缩小,摩擦系数显著上升。造成微型管件摩擦尺度效应的主要原因在于管件外表面为曲面,曲率半径的缩小导致模具表面相对凹凸不平程度减低,使液体润滑剂存储困难,摩擦力增大。其次,对轴向补料工艺进行了数值与实验分析。利用GTN细观损伤模型,直接将外径2mm,壁厚0.15mm的304不锈钢微型管件的流动应力引入到材料属性当中,对微型管件进行建模;同时,基于大量的轴向补料自由胀形实验,通过在线性加载路径条件下获得的破裂点压力值,考察补料量对成形能力的影响。模拟与实验结果表明,轴向补料工艺能够提高微型管件液压成形能力,但由于尺度效应问题,实际成形能力受到多种因素影响,从而表现出显著的工艺分散性。最后,为了考察微型管件实际成形能力,对不同尺寸的304不锈钢微型管件,在不同补料量的条件下,进行了 30%胀形率的成形实验以及等径T形三通管液压成形实验。成形实验的结果发现,两种管件在不同补料量条件下都能实现成形。T形管液压成形实验发现,两种管件成形后支管最大高度过低,不足以形成完整的支管,这是由于尺度效应使材料的应变延伸率下降。数值模拟的结果则表明,增大补料量能够改善壁厚减薄,提高成形能力,但由于摩擦力的影响,导致管件两端壁厚显著增厚。
[Abstract]:In the field of micro-electromechanical, medical devices, the demand for micro-shaped pipe fittings is increasing gradually. Hydroforming has become the focus of research because it can efficiently produce miniature special-shaped pipe fittings. Because the size of the parts is close to the grain size, the miniature pipe fittings have the problem of scale effect, and the forming ability is reduced, which restricts their development. Axial feeding technology can improve the forming ability of pipe fittings and has been widely used in the production of conventional special-shaped pipe fittings. In order to improve the forming ability of micro tube fittings, this paper introduces the axial feeding technology into hydroforming of micro pipe fittings. Firstly, the friction characteristics in the hydroforming guide zone of micro tube fittings are studied. The friction coefficient can be calculated by measuring the initial friction force and the total thrust force and according to the internal pressure and other dimension parameters. The experimental results show that the friction coefficient of 304 stainless steel pipes with external diameters 2mm and 1mm increases significantly with the reduction of size. The main reason for the friction scale effect of micro pipe fittings is that the outer surface of the pipe fittings is curved surface. The reduction of curvature radius leads to the reduction of the relative uneven degree of the die surface, which makes the storage of liquid lubricant difficult and the friction force increase. Secondly, the numerical and experimental analysis of axial feeding process is carried out. Using the GTN damage model, the flow stress of 304 stainless steel tube fittings with external diameter of 2 mm and wall thickness of 0.15mm is directly introduced into the material properties to model the micro tube fittings. At the same time, based on a large number of free bulging experiments of axial feeding, the flow stress of 304 stainless steel micro-tube fittings with external diameter of 2 mm and wall thickness of 0.15mm is directly introduced into the material properties. The influence of feeding amount on the forming capacity was investigated by the fracture point pressure value obtained under the linear loading path condition. The simulation and experimental results show that the axial feeding process can improve the hydroforming ability of micro pipe fittings, but due to the scale effect, the actual forming ability is affected by many factors, thus showing a remarkable process dispersion. Finally, in order to investigate the actual forming ability of micro tube fittings, the forming experiments of 30% bulging rate and equal diameter T-shaped three-way tube hydroforming experiments were carried out for 304 stainless steel micro-tubes with different sizes under different feeding quantities. The results of forming experiments show that the two kinds of pipe fittings can be formed under the condition of different recharge amount, and the hydroforming experiment of T-shaped tube shows that the maximum height of the branch pipe is too low to form a complete branch tube after the forming of the two kinds of pipe fittings. This is due to the reduction of the strain elongation of the material due to the scale effect. The results of numerical simulation show that the wall thickness can be improved and the forming ability can be improved by increasing the amount of feedstock, but due to the influence of friction, the wall thickness at both ends of the pipe is significantly increased.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG306

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