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。
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.
引文
[1]杨慎华,寇淑清.发动机连杆的裂解制造工艺及设备[J].吉林大学辊锻研究所.2005(2)：1-4.
[2]寇淑清,金文明.内燃机连杆制造最新技术与发展趋势[J].长春.吉林大学辊锻研究所.2006
[3]寇淑清,杨慎华,邓春萍.裂解工艺与发动机连杆制造最新技术[J].中国机械工程.2001.12：839-841
[4]谷诤巍.发动机连杆裂解工艺新技术[J].吉林大学.2003(7)：22-23
[5]李文静,马天军.基于ANSYS对连杆的有限元分析[J].安徽理工大学.2006：1-3
[6]王亮,刘志东,黄因慧.硅片线切割有限元热分析[J].南京航空航天大学.2008：1-4
[7]黄志刚,郭钟宁.单脉冲电火花加工温度场的有限元分析[J].广东工业大学学报.2002.19(4)：38-43.
[8]张志强,赵勇.锻造工艺对发动机连杆裂解加工质量的影响.[J].2007：57-59
[9]赵万生.先进电火花加工技术[M].北京：国防工业出版社.2003
[10]张朝晖,范群波,贵大勇.ANSYS8.0热分析教程与实例分析[M].北京.中国铁道出版社.2005：62-74.
[11]高阳,刘林,郭常宁.电火花放电蚀坑的有限元热分析[J].电加工与模具.2008(2)：8-11.
[12]周晖.数控电火花加工工艺与技巧[M].北京.化学工业出版社.2008：140-151
[13]H.K.Kansal, Kunieda, Nishiwaki. Measurement of energy distribution into electrode in EDM process[J]. Advancement of Intelligent Production.1994(5):601-606
[14]VinodYadav, VijayKJain, PrakashM Dixit.Thermal stresses due to electrical discharge machining[J].International Journal of Machine Tools&Mnaufacture[J].2002(42):877-888.
[15]苏树朋.基于气体介质的电火花铣削加工技术及机理研究[D].山东大学.2008
[16]Antoine Descoeudres, Christoph Hollenstein, ReneDemellayer, Georg Walder, Optical emission spectroscopy of electrical discharge machining plasma. Journal of Materials Processing Technology[J].2004,(149) 184-190
[17]于学文,黄涤非,金玉惠.电火花加工放电通道的探讨[J].电加工.1984.(03)：8-13
[18]井上洁著.帅元伦,于学文译.放电加工的原理—模具加工技术[M].北京.国防工业出版社.1983
[19]元利伟,楼乐明,李明辉.放电通道的波动性与电火花加工机理[J].上海交通大学学报.2001.35(7)：989-997
[20]崔景芝.微细电火花加工的基本规律及其仿真研究[D].哈尔滨工业大学.2007：1-4
[21]武传松等.热过程与熔池形态[M].北京.机械工业出版社2007(2).206-209.
[22]刘兴龙,李晓燕.转向架构架焊接残余应力与变形的研究[J].研究开发,2006.2(1).9-11.
[23]Philip T. Eubank, Mukund R. PateL, Maria A. Barrufet, Bedri Bozkurt. Theoretical Models of the Electrical Discharge Maching Process. Ⅲ. The Variable Mass, Cylindrical Plasma Model. Texas A&M University[J]. J. Appl. Phys.1993,73(11):7900-7909
[24]胡宝林,张勤河.基于单元生死的气中火花放电的有限元热分析[J].山东大学.2009
[25]吴会超.基于ANSYS的焊接接头疲劳分析[J].铁道机车车辆工人.2006.6(6).1-4；10
[26]Zingerman. Regarding the Problem of the Volume of Molten Metal During Electrical Erosion[J]. Sov. Phys. Solid State,1959.(25):25-29
[27]胡庆贤.穿孔等离子弧焊接温度场的有限元分析[D].山东大学.2007
[28]秦国梁,王绪友.激光GMAW复合热源焊焊缝成形的数值模拟[J].机械科学研究院.2008
[29]阚前华,谭长建,张娟.ANSYS高级工程应用实例分析与二次开发[M].北京.电子工业出版社.2006
[30]程国柱,刘志东.基于ANSYS电火花线切割加工的温度场分析[J].南京航天航空大学.2008：24-30
[31]赵立新,刘志民等.C70S6连杆材料的研究[J].河北.河北工程学院机械系.2005
[32]Kyungmi Lee, Vladimir Estivill-Castro. Feature extraction and gating techniques for ultrasonic shaft signal classification [J]. Applied Soft Computing.2007,7
[33]张乐乐,谭南林,焦凤川.ANSYS辅助分析应用基础教程[M].北京：清华大学出版社.北京交通大学出版社.2006
[34]李亚江.切割技术及应用[M].北京.化学工业出版社.2004：238-251
[35]周勇,刘正埙.电火花加工中工具电极损耗理论研究[J].电加工与模具.1998(4)：1-3
[36]Schoichi Shimada, Hiroaki Tanaka. Molecular Dynamics Analysis of Self-sharpening Phenomenon of Thin Electrode in Single Discharge. Journal of Materials Processing Technology[J]. 2004.(149):358-362
[37]邵蕴秋.ANSYS8.0有限元分析实例导航[M].北京：中国铁路出版社.2004
[38]Jennes etc. Computer of various approaches to model the thermal load on the EDM-Wire electrode, Annals of CIRP[J].1984.33(1):245-248
[39]许华宇,李明辉,彭颖红.电火花加工理论研究现状与展望[J].电加工.1997.(3)：8-12
[40]聂毓琴,孟广伟.材料力学[M].北京.机械工业出版社.2004：25-45
[41]D拉达伊.焊接热效应·温度场·残余应力·变形[M].熊第京等译.北京.机械工业出版社.1997：189-205
[42]孟广喆,贾安东.焊接结构强度和断裂[M].北京.机械工业出版社.1986：145-202
[43]切列帕诺夫著.黄克智译.脆性断裂力学[M].北京.科学出版社.1990
[44]Kojima H., Kunieda M., Nishiwaki N. Understanding Discharge Location Movements During EDM[J].10th International Symposium for Electromachining (ISEM-10), Magdeburg, Germany,1992:144-149
[45]迟恩田.电火花成型加工技术现状[J].机械科学与技术.1996.25(2)：5-112
[46]N.Mohri, N.Saito, Y.Tsunekawa. Metal Surface Modification by Electrical Discharge Machining with Composite Electrode[J].Annals of the CIRP.1993,42(1):219-