【作者】 段春争；

【导师】 王敏杰；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2005， 博士

【摘要】 近年来,高速切削加工技术在制造业中得到了广泛应用,高速切削条件下产生的锯齿形切屑可能会影响到工件的加工精度、表面粗糙度和刀具寿命。绝热剪切带的产生和发展对于锯齿形切屑形成起到了关键作用,研究锯齿形切屑形成过程中绝热剪切行为的微观机理有助于进一步认识高速切削过程中的切屑形成。本文采用材料显微观察和微观理论分析相结合的方法,对正交切削30CrNi₃MoV高强度合金钢绝热剪切行为的微观机理进行了研究,主要研究内容如下: 1.正交切削高强度钢切屑形态演变过程的实验研究。随着切削速度的提高,当切削速度达到某一临界切削速度时,带状屑转变为锯齿形切屑。锯齿形切屑产生的原因是第一变形区内因热软化超过应变和应变率强化而发生了绝热剪切局部化。对于带状屑和锯齿形切屑的切削力和切屑变形参数的测量和分析表明,锯齿形切屑与带状屑在形成机理上存在明显区别。 2.锯齿形切屑内绝热剪切带变形和温度的计算。通过对锯齿形切屑形成过程中绝热剪切各个阶段的分析,提出了一种计算绝热剪切带内材料变形和温度的方法。 3.通过对高应变速率一维剪切变形理论模型的分析,提出了绝热剪切带宽度和间距与切削速度的关系式。随着绝热剪切带的产生和发展,切屑形态发生了一系列转变,切削速度和工件材料回火硬度是影响这一转变过程的主要因素。随着切削速度的提高,绝热剪切带的显微组织发生了由形变带向转变带的演变。形变带硬度与加工硬化有关,而转变带的硬度则受到相变硬化的影响。 4.使用电子探针对绝热剪切带附近微区进行的成分分析表明,绝热剪切带内发生了C原子的短程扩散和碳化物析出。使用一种新的制样方法,获得了可用于观察锯齿形切屑内绝热剪切带及其附近区域的微细组织形貌的TEM薄膜试样。通过使用TEM对钢中转变带微细组织的观察和分析,确认绝热剪切带中心区的等轴晶粒为再结晶组织,提出了高强度钢锯齿形切屑内绝热剪切带微结构演化过程的微观模型。通过对再结晶机制的探讨,确定了高强度钢锯齿形切屑绝热剪切带内材料的再结晶机制为旋转式动态再结晶。 5.基于对锯齿形切屑断裂面的显微观察和微观断裂机理分析,提出了一种锯齿形切屑形成过程中由微孔洞形核、长大和聚合机制控制的绝热剪切韧性断裂的微观模型。更多还原

【Abstract】 In recent years, the technology for high speed machining is applied widely in manufacture companies. The formation of sawtooth chips in high speed machining can influence on machining precision, surface roughness and tool life. The occurrence and development of adiabatic shear bands of materials may play a key role during sawtooth chip formation. To investigate the microcosmic mechanism of adiabatic shear during sawtooth chip formation have important meaning to more know chip formation during high speed machining. In this paper, by microstructure observation and microcosmic theoretic analysis, the microcosmic mechanism of adiabatic shear behavior during orthogonal cutting of 30CrNi3MoV high strength alloy steel is investigated, the main investigation contents are listed as following:1. Experimental investigation of evolvement process for chip morphology during orthogonal cutting of high strength alloy steel. As the cutting speed increases, the ribbon chips transform into the sawtooth chips when a critical cutting speed is reached. The reason for the sawtooth chips is that the adiabatic shear localization occurs in the primary deformation zones when thermal softening exceeds strain and strain rate hardening. For the ribbon and sawtooth chips, the measurement and analysis results of the cutting forces and parameters of chip deformation indicate that the formation mechanism of sawtooth chips is distinctly differ from ribbon chips.2. Calculation of deformation and temperature in the adiabatic shear bands within the sawtooth chips. Based on analyzing various stages of adiabatic shear during sawtooth chip formation, a calculational method of the deformation and temperature in adiabatic shear bands is proposed.3. Based on the theoretic model of one-dimensional shear deformation under high rate loading, a relation of width and spacing for adiabatic shear band to cutting speed is proposed. As the adiabatic shear bands form and develop, a series of changes in chip morphology occur which is mainly influenced by the cutting speed and the tempering hardness of workpiece material. The deformation bands change into the transformation bands in microstructure as the cutting speed increases. The microhardness deformation bands results from work hardening, but the microhardness in the transformation bands is influenced by phase transition hardening.4. The results of composition analysis near the adiabatic shear bands by electron probe indicate that the short distance diffusion of carbon and the precipitation of carbide may occur within the adiabatic shear bands. The TEM film samples used to observe the microstructure of the adiabatic shear bands in the sawtooth chips are attained by a new sample preparation method. The observation and analysis of microstructure of transformed band by TEM indicate that the equiaxed grains in the band center are considered to be a recrystallization structure, a microstructure evolvement model in the adiabatic shear bands of high strength alloy steel is proposed,. The rotational dynamic recrystallization model based on mechanical mechanism is analyzed, the results indicate that the rotational dynamic recrystallization mechanism may rationally explain the recrystallization process occurred in the adiabatic shear bands within the sawtooth chips.5. Based on the observations of the surface of adiabatic shear fracture and the analysis of microcosmic fracture mechanism, a microcosmic model of adiabatic shear ductile fracture controlled by nucleation, growth and coalescence of microvoids during sawtooth chip formation is proposed.更多还原