中空薄壁件温冷复合精密锻挤工艺研究及成形质量控制

发布时间：2018-11-17 16:44

【摘要】：在精密锻造技术中,温冷复合成形工艺结合了温锻和冷锻的优点,具有显著的成形优势,被广泛应用于机械制造行业中。中空薄壁类零件种类繁多,壁薄,结构复杂,尺寸精度及力学性能要求较高,在汽车变速器系统、底盘系统及发动机系统中需求量极大。目前此类零件多采用温冷复合精密锻挤工艺进行生产,但是在工艺设计的合理性、制造精度和成形质量的控制方面还存在许多问题。因此,研究中空薄壁类零件的成形工艺特点并通过工艺改进消除典型的成形缺陷,对此类零件生产质量的提高具有重要的指导意义。本文根据零件形状,将中空薄壁类结构件分为杯类、杯杆类、带法兰及带齿类。并分别对各类零件进行结构分析,提出了各类零件的主要成形工艺。总结了中空薄壁类零件在实际生产中容易出现的质量问题,对零件成形时的填充不足、尺寸精度低、组织不均匀和开裂问题进行了研究,并提出了工艺解决方法。对齿类零件和杯类零件的填充问题进行了研究分析,以法兰外齿圈和薄壁钢筒零件为例,为改善其成形质量提出了工艺优化方案。针对法兰外齿圈生产中齿形填充不足和成形力大的问题,采用孔分流改进工艺及温挤齿形工艺,提高了齿形填充性并降低了变形力,并获得了温挤齿后最佳的齿形冷精整量。模拟结果表明采用两种温挤齿方案成形后的锻件齿形轮廓填充饱满,且成形力低,不仅缩短了生产时长也提高了成形质量。针对目前薄壁钢筒零件冷精整工序中产生的筒底间隙问题,在冷锻前增加一道切削肩部斜角工序可以显著降低间隙值。本文以某钢筒为例对冷精整工序中的金属流动过程进行了分析,获得了筒底间隙值的变化规律,并提出了合理的肩部斜角取值范围。通过对多组设计方案进行模拟,获得了肩部斜角和凹模入模半角对筒底间隙和筒底厚度的影响规律,确定了最优的肩部斜角和凹模入模半角。最后对反挤凹模结构进行改进,直接反挤出肩部斜角,模拟结果表明此方案不仅可以省去机加工工序,而且最终锻件的形状和尺寸精度都符合生产要求。对成形过程中出现的裂纹问题进行了研究。以蓄能器壳体零件为例,针对其冷成形中出现的开裂问题,提出了预成形设计方案和热处理改进方案来消除成形裂纹。其中对两种预成形形状进行了模拟分析,确定了最优的预成形结构;并将原成形方案中的去应力退火工艺改为等温退火工艺,结果表明显著改善了冷成形中的锻件组织消除了底部裂纹,且此方案已投入实际生产。
[Abstract]:In the precision forging technology, the warm and cold compound forming process combines the advantages of warm forging and cold forging, and has obvious forming advantages, and is widely used in the mechanical manufacturing industry. There are many kinds of hollow thin-walled parts, thin wall, complex structure, high dimensional precision and mechanical performance requirements, which is in great demand in automobile transmission system, chassis system and engine system. At present, this kind of parts is produced by temperature and cold compound precision forging and extrusion process, but there are still many problems in the aspects of the rationality of process design, the control of manufacturing precision and forming quality. Therefore, it is of great significance to study the forming process characteristics of hollow thin-walled parts and eliminate the typical forming defects through process improvement, which has an important guiding significance for the improvement of production quality of such parts. According to the shape of the parts, the hollow thin-walled structural parts are divided into cup type, cup rod type, flange and toothed type. The main forming process of each kind of parts is put forward by analyzing the structure of each kind of parts. The quality problems of hollow thin-walled parts in practical production are summarized. The problems of insufficient filling, low dimensional precision, uneven structure and cracking in forming are studied, and the technological solutions are put forward. The filling problem of tooth parts and cup parts is studied and analyzed. Taking the flange outer gear ring and thin-walled steel cylinder as examples, the process optimization scheme is put forward to improve the forming quality of tooth parts and cup parts. Aiming at the problems of insufficient filling and large forming force in the production of flange outer gear ring, the improved technology of split hole and warm extrusion was adopted to improve the filling property of tooth shape and reduce the deformation force, and the optimum cold finishing quantity of tooth profile after warm extrusion was obtained. The simulation results show that the profile of the forgings formed by two warm extrusion schemes is full and the forming force is low which not only shortens the production time but also improves the forming quality. In view of the gap problem in the cold finishing process of thin-walled steel cylinder parts, the gap value can be significantly reduced by adding a cutting shoulder bevel before cold forging. In this paper, taking a steel cylinder as an example, the metal flow process in the cold finishing process is analyzed, and the variation law of the gap value in the bottom of the cylinder is obtained, and a reasonable range of shoulder angle values is put forward. Through the simulation of many groups of design schemes, the effects of shoulder angle and die half angle on the bottom clearance and the thickness of the cylinder bottom are obtained, and the optimal shoulder angle and die entry half angle are determined. Finally, the structure of the reverse extrusion die is improved, and the angle of the shoulder is directly reversed. The simulation results show that this scheme can not only save the machining process, but also meet the requirements of the final forging shape and dimension accuracy. The crack problem in forming process is studied. Taking the accumulator shell as an example, the pre-forming design scheme and the heat treatment improvement scheme are proposed to eliminate the forming crack in view of the cracking problem in cold forming. Among them, two kinds of preformed shapes are simulated and analyzed, and the optimal preforming structure is determined. The results show that the structure of forging in cold forming has been greatly improved and the bottom crack has been eliminated, and the scheme has been put into practice.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG316

【相似文献】