【作者】 刘晨；

【导师】 张乐乐；

【作者基本信息】 北京交通大学 ， 安全技术及工程， 2010， 硕士

【摘要】 电火花切槽是连杆裂解加工的关键核心工序之一,切槽之后结构的力学状态、裂纹的分布区域、裂纹状态、数量及残余应力等因素直接影响后续工艺,因此,分析连杆电火花切槽过程的受力状态,讨论裂纹对工艺过程的影响对于优化、控制与改进工艺和设备具有重要的理论意义与工程价值。本文采用仿真与试验分析相结合的方法,分析了在外载荷(切削)耦合多物理场(温度场与残余应力场)条件下结构的受力过程与响应,并分析了裂纹产生的过程和机理,进而建立工艺参数与裂纹状态之间的关系。论文主要工作包括：(1)温度场分析时热载荷和边界条件的确定。采用仿真的方法比较了各种热源模型的适用特点和情况,选择了适合于电火花切槽仿真计算的热源模型,并考虑了加工电流振荡对放电通道的影响,通过修正热源的热流量集中程度系数对热源进行了改进,并将改进的热源实现了仿真应用。(2)建立了连杆局部结构的有限元模型,采用热-结构顺序耦合的方法,实现了基于单元生死的电火花切槽过程工件温度场及应力场的分析。结果表明,在热载荷和残余应力共同作用下,在蚀除材料的同时裂解槽边缘薄弱区域产生的热应力将超过材料的抗拉强度而产生裂纹。(3)将局部结构的应力状态作为启裂过程仿真的边界条件,进行裂纹分布状态的模拟,并进一步进行了基于残余应力的启裂过程的仿真,计算了含有残余应力场的结构的启裂阈值。同时,将启裂载荷的阈值作为后续工艺参数对比的一个关键因素。(4)对多工况的切槽过程的数值模拟仿真结果进行对比分析,研究了不同峰值电流或脉宽对电火花切槽的应力与裂纹分布状态以及裂解工艺的影响,建立了电火花放电的工艺参数与裂解工艺之间的关系。更多还原

【Abstract】 Electrical discharge wire-cutting notching is one of the core processes of fracture splitting of connecting rod, and after cutting notching, many factors such as structural mechanical state, crack distribution region, crack condition and amount and residual stress, directly impact on the following process. Therefore, several activities such as analyzing the strained condition in the process of electrical discharge wire-cutting notching of connecting rod, discussing how the crack has influenced the technological process, have shown the essential theoretical significance and construction value in terms of optimizing, controlling and improving technological process and equipments.The method of combining simulation and experimental analysis was primarily adopted. Firstly, in the condition of external load (cutting) multi-physics coupling (temperature field and residual stress field), the structural force and response was analyzed, and the process and mechanism of cracks was analyzed as well. Furthermore, the relationship between the technological process parameters and crack state was established. The paper mainly includes.1. Establishment of heat load and boundary conditions in the analysis of temperature field. Simulation method was adopted to compare the applying characteristics and circumstances of various heat source models, the heat resources model which was suitable for electrical discharge wire-cutting notching simulation calculation, was chosen and then improved, therefore, a better three dimensional cylindrical heat source, which demonstrated the specific process of electrical discharge wire-cutting notching, was improved and finally achieved the simulation application.2. The finite element model of connecting rod local structure was built up, and the thermal-structure sequential coupling method was used, so as to achieved the analysis of temperature field and stress field of workpiece in the process of electrical discharge wire-cutting notching which based on element birth and death. The results show that under the heat load and residual stress, along with material corrosion, the heat stress in the edge weak region of splitter exceeded the tensile strength of materials, which end up in cracks.3. The stress of local structure act as boundary conditions in the process of splitting simulation, the crack distribution was simulated and then the splitting process simulation which based on residual stress was conducted, subsequently the structural crack initiation with residual stress field was calculated, at the same time, the stress state of local structure was used as initial condition of following micro-simulation.4. The numerical simulation results of multiple condition splitting process were compared and analyzed, then the impacts that different peak current or impulse duration had imposed on stress of electrical discharge wire-cutting notching, crack distribution and cracking process were studied, and at last the relationship between technological parameters of spark discharge and cracking process were established.更多还原