【作者】 赵德颖；

【导师】 孙惠学；

【作者基本信息】 燕山大学 ， 材料加工工程， 2009， 博士

【摘要】 转向节是汽车转向系统的关键零件,对其机械性能和表面质量要求非常严格。目前国内枝杈类转向节锻件生产工艺落后,成为其提高生产效率、改善产品质量的瓶颈。因此如何高效、节能地生产出优质的枝杈类转向节锻件,已成为汽车行业亟待解决的技术问题。本文以复杂锻件的精密成形为指导思想,根据闭塞挤压成形理论,以捷达轿车转向节为研究对象,在深入分析该类锻件成形特点的基础上,首次提出采用闭塞挤压成形的方法成形转向节锻件。为了验证闭塞挤压成形枝杈类转向节锻件的可行性,对捷达轿车转向节成形过程进行了实验研究,拟定了成形工艺,设计了成形模具,获得了尺寸精确、表面质量良好的铅和40Cr转向节1:2试件。通过对40Cr试件进行金相组织分析,发现该锻件的晶粒组织明显细化,说明闭塞挤压成形工艺可明显提高锻件的机械性能。在此基础上分析了锻件产生缩孔缺陷的主要因素,并提出了相应的解决方案。在实验研究和数值分析的基础上,提出了“一火两锻”的成形新工艺,即首先采用闭塞挤压技术生产预锻件,然后进行开式终锻。该工艺的关键是预锻成形工序的设计。通过在DEFORMTM环境下对“一火两锻”成形过程中的应力、应变、速度和温度场等的分布规律的模拟,研究了枝杈类锻件闭塞挤压塑性成形规律。模拟结果表明,“一火两锻”工艺能显著改善变形金属流动、降低锻压设备公称压力和提高模具寿命。为进一步降低预锻成形力、提高模具和冲头的使用寿命,将挤压带式闭塞挤压引入“一火两锻”成形工艺。通过热力耦合分析,获得了挤压带长度、摩擦条件、模具工作温度、冲头挤压速度等主要工艺参数对金属流动规律、挤压力和张模力的影响,揭示了挤压带式闭塞挤压成形机理,为该工艺的实际应用提供了重要参考。利用上限法推导了挤压带式闭塞挤压成形具有空间角度枝杈的复杂锻件的挤压力计算公式。运用该公式计算了捷达轿车转向节锻件挤压力,计算结果与模拟结果较好吻合,说明该公式具有较高的计算精度。本文通过数值模拟,证明了以挤压带式闭塞挤压成形为基础的“一火两锻”成形工艺,在成形复杂枝杈类转向节锻件的可行性。该工艺不仅拓宽了闭塞挤压工艺的应用范围,而且大大简化复杂枝杈类锻件的生产过程,可降低生产成本,为复杂枝杈类锻件精密成形提供了一条行之有效的途径。更多还原

【Abstract】 Steering knuckle is the key part of vehicle steering system, so the requirements of its mechanical properties and surface qualities are very strict. The current production technologies of branch-like steering knuckle are obsolete, which become the restriction of increasing productivity and improving the quality. It becomes urgent technical matters for automotive industry to produce the parts efficiently and economically.In this dissertation, with the guidelines of precision forming complex forging pieces, basing on the forming theory of closed die extrusion, choosing the Jetta steering knuckle to be investigated, analyzing its forming characteristics deeply, the closed die extrusion technology is proposed to form steering knuckle forging piece firstly.To verify the feasibility of closed die extrusion technology forming branch-like steering knuckle forging piece, experimental researches are carried on the forming process of Jetta steering knuckle, forming technology has been drawn up, and dies have been designed. Precise and qualified 1:2 lead and 40Cr specimens have been obtained. With the metallurgical analysis of 40Cr forging pieces, it is presented that the crystal grain has been refined and the mechanical property can be improved with the technology. The mechanism and influencing factors of shrinkage cavity defect are analyzed on this basis.Based on experimental researches and numerical analysis, the technology of two forging steps in one heat is presented, which consist of closed die extrusion preforging and open die finish forging, whose critical step is preforging process. By utilizing DEFORMTM software, the stress, strain, velocity and temperature fields during forming process are obtained, and then the plastic forming law of branch-like forging pieces in closed die extrusion has been studied. Simulation results show that with the technology of two forging steps in one heat, the metal flow can be improved evidently, the nominal pressure of forging press equipments can be reduced, and die life can be prolonged.To further reduce the shaping force of preforging and increase the service life of dies and punches, closed die extrusion with extrusion-belt is introduced to the technology of two forging steps in one heat. By the thermo-mechanical coupling simulation, the influence of main technological parameters to metal flow, extrusion force and opening force are studied and determined, such as extrusion-belt length, friction conditions, die work temperature and punch extrusion speed, then the mechanism of closed die extrusion with extrusion-belt is acquired, which are very important to the actual application of the technology.By using upper bound method, the extrusion force formula is deduced, which is appropriate for closed die extrusion with extrusion-belt forming complicated forging pieces with space angle branches. By using the formula, the extrusion forces in closed die extrusion forming Jetta steering knuckle are calculated. The calculation results agreed with simulation results, which indicate that the formula has high calculation accuracy.By using numerical simulation, it is approved that the technology of two forging steps in one heat is feasible, whose core is closed die extrusion with extrusion belt. The new technology enlarges the applying range of closed die extrusion, greatly simplifies the production technology of complicated branch-like forging pieces, reduces the production cost, and provides effective method for the precision forming of the complicated branch-like forging parts.更多还原