某曲轴热模锻成形工艺设计及优化

Design and optimization on hot die forging process for a crankshaft

为控制某曲轴的模锻成形质量、避免锻造缺陷的产生。首先,通过热压缩实验获取了40Cr钢在不同温度和应变速率下的流变数据,并用Hansel-Spittel方程进行了拟合,获得了40Cr钢的本构关系,为模锻成形工艺仿真提供了精确的材料数据。等温压缩实验表明:应变速率和温度对40Cr钢的应力水平有显著性影响;当应变速率和应变相同时,应力随着温度的增加而降低;当温度和应变相同时,应力随着应变速率的增加而增加。在低应变速率、高温条件下,材料具有显著的应力峰值;这是由于温度越高、应变速率越低,材料在变形过程中具有足够的能量和时间进行动态再结晶软化。随后,基于金属稳定热加工理论建立了40Cr钢的热加工图,并对压缩试样进行微观组织分析,验证了热加工图的合理性。基于热加工图得到了某曲轴的成形温度推荐范围为900~1000℃、应变速率为0.01~0.1 s^(-1)。最后,为了解决某曲轴平衡块填充不满的问题,提出了基于拉丁超立方抽样、数值仿真获取样本、克里金模型构建响应面、遗传算法优化的策略,数值仿真和生产试制结果验证了该策略能够得到充填完整、无锻造缺陷的曲轴锻件,可提升成形质量、减少试错成本。此外,实验试制也验证了选取的成形温度和应变速率能够得到组织细小且均匀的锻件。

To control the die forging quality of a crankshaft and avoid forging defects,the rheological data of 40Cr steel at different temperatures and strain rates were obtained by hot compression experiments,and the constitutive relationship of 40Cr steel was obtained by fitting with Hansel-Spittel equation to provide accurate material data for die forging process simulation.Isothermal compression experiment shows that the strain rate and temperature have significant effects on the stress level of 40Cr steel.When the strain rate and strain are the same,the stress decreases with the increasing of temperature,and when the temperature and strain are the same,the stress increases with the increasing of strain rate.Under the condition of low strain rate and high temperature,the material has a significant stress peak.This is because that the higher the temperature is,the lower the strain rate is,the material has enough energy and time for dynamic recrystallization softening during the deformation.Subsequently,the hot processing map of 40Cr steel was established based on the metal stable hot processing theory,and the rationality of the hot processing map was verified by microstructure analysis of compressed samples.Based on the hot processing map,the recommended forming temperature range of a certain crankshaft is 900-1000℃,and the strain rate is 0.01-0.1 s-1.Finally,in order to solve the problem of insufficient filling for a certain crankshaft balance block,a strategy based on Latin hypercube sampling,numerical simulation for sample obtainment,Kriging model for response surface construction and genetic algorithm optimization was proposed.The results of numerical simulation and production trial production verify that the strategy can obtain crankshaft forgings with complete filling and no forging defects,improve the forming quality,and reduce the cost of trial and error.In addition,the trial production also verifies that the selected forming temperature and strain rate can obtain the forgings with fine and uniform structure.