Influences of Tool Wear on Residual Stress and Fatigue Life of Workpiece in Hard Cutting Process

Tool wear has an important influence on the residual stress distribution on the machined surface.Also,it will influence the fatigue life of finished workpiece. In this research,the hard turning process of hardened die steel Cr12 MoV was studied by using PCBN tool with considering tool wear. Based on the numerical treatment of residual stress,the dispersion and distribution curves of different tool wear were fitted,and the influence mechanism of tool wear on the residual stress distribution of machined surface was analyzed.Based on the theory of fatigue mechanics and mathematical statistics,the mathematical model for difference of stress dispersion and fatigue life was established. The rotating and bending tests were carried out on the standard parts after cutting process for the workpiece. The influence of tool wear on fatigue life was revealed by fracture surface morphology and fatigue life study. The results provide theoretical support for control of residual stress and the fatigue property of the machined surface under the actual working conditions.

Stress Field Analyses of Functionally Gradient Ceramic Tool by FEM

The cutting properties of the functionally gradient ceramic cutting tools relate closely to the gradient distribution. A cutting model of the functionally gradient ceramic tool is firstly designed in the present paper. The optimum of gradient distribution is obtained by way of the FEM analyses.

FLOW STRESS MODEL FOR HARD MACHINING OF AISI H13 WORK TOOL STEEL

An approach is presented to characterize the stress response of workpiece in hard machining, accounted for the effect of the initial workpiece hardness, temperature, strain and strain rate on flow stress. AISI H13 work tool steel was chosen to verify this methodology. The proposed flow stress model demonstrates a good agreement with data collected from published experiments. Therefore, the proposed model can be used to predict the corresponding flow stress-strain response of AISI H13 work tool steel with variation of the initial workpiece hardness in hard machining.

Dynamic Reliability Sensitivity of Cemented Carbide Cutting Tool

Influence of geometric and cutting parameters of cemented carbide cutting tool on reliability of cutting tool has become more and more mature, yet influence of its physical and material parameters on reliability is still blank. In view of this, cutting test and fatigue crack growth test of YT05 cemented carbide cutting tool are conducted to measure such data as the original crack size, growth size, times of impact loading, number and time of cutting tool in failure, and stress distribution of cutting tool is also obtained by simulating cutting process of tools. Mathematical models on dynamic reliability and dynamic reliability sensitivity of cutting tool are derived respectively by taking machining time and times of impact loading into account, thus change rules of dynamic reliability sensitivity to physical and material parameters can be obtained. Theoretical and experimental results show that sensitive degree on each parameter of tools increases gradually with the increase of machining time and times of impact loading, especially for parameters such as fracture toughness, shape parameter, and cutting stress. This proposed model solves such problems as how to determine the most sensitive parameter and influence degree of physical parameters and material parameters to reliability, which is sensitivity, and can provide theoretical foundation for improving reliability of cutting tool system.

Relationship Between Thermal Shock Behavior and Cutting Performance of a Functionally Gradient Ceramic Tool

Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.

Effects of tool flank wear on orthogonal cutting process of aluminum alloy

The tool flank begins to wear out as soon as cutting process proceeds. Cutting parameters such as cutting forces and cutting temperature will vary with increasing degree of flank wear. In order to reveal the relationship between them, the theoretical situations of cutting process were analyzed considering the tool flank wear effect. The variation rules of cutting force, residual stress and temperature distributions along with the tool flank wear were analyzed comparing with the sharp tool tip. Through FEM simulation method, affections of the tool flank wear value VB on cutting forces, residual stress and temperature distributions were analyzed. A special result in this simulation is that the thrust force is more sensitive to tool flank wear, which can be used as a recognition method of tool condition monitoring. The FEM simulation analysis result agrees well with the experimental measuring data in public literatures and some experiments made also by the authors.

体外受精-胚胎移植患者生育压力评估工具的研究进展

本文对体外受精-胚胎移植患者生育压力的普适性、特异性评估工具的主要内容、特征及应用现状进行综述,提出未来研究者应进一步进行相关量表的开发和汉化工作,有效识别和管理体外受精-胚胎移植患者的生育压力。

非最小相位法向电磁应力驱动快速刀具伺服系统轨迹跟踪控制

基于快速刀具伺服(FTS)的金刚石车削是复杂光学表面超精密制造的一种高效手段。为进一步提高具有非最小相位特征的电磁法应力驱动FTS的控制性能,将系统逆动力学补偿嵌入主控制回路中以改善被控对象动力学特征。对改善后的被控系统以比例微分积分(PID)和前馈补偿作为主控制器,并以基于内模原理的并联谐振控制器实现周期性轨迹的超高精度跟踪。考虑系统非最小相位特征,结合因子分解和镜像极点配置方法获得了系统稳定逆动力学模型。实验测试结果表明:该文所设计的控制方法,获得了1070 Hz(-3 dB)闭环带宽;100 Hz正弦轨迹实际跟踪误差小于±0.375%,并可对5 nm台阶轨迹进行稳定闭环跟踪,证明所设计的FTS控制系统可有效实现nm精度切削。

高速切削GH2132涂层刀具表面及次表面性能演变研究

高速切削过程中,涂层刀具表面性能及次表面残余应力的变化会直接影响刀具的切削性能。采用PVD-TiAlN硬质合金涂层刀具进行高速车削GH2132高温合金试验,研究刀具表面性能在切削过程中的变化规律,并用拉曼光谱法测量了刀具不同磨损阶段的涂层次表面残余应力分布。结果表明,刀具在完整寿命期间内,表面残余压应力和表面显微硬度均呈先增大后减小的趋势。刀具从未磨损到稳定磨损阶段中期,涂层截面残余应力均为残余压应力占主体且沿深度方向逐渐增大,但切削至稳定磨损阶段后期时,涂层在靠近基体位置出现残余压应力减小的现象。在稳定磨损阶段前期,刀具有最佳的表面性能及最大的次表面压应力,此时刀具切削性能最佳,刀具磨损缓慢。

刀具刀尖结构对高速硬车削GCr15轴承套圈表面质量的影响研究

高速硬车削是目前实现轴承套圈高效精密加工的关键技术之一。由于轴承套圈具有硬度高、强度大及薄壁等难加工特点,高速硬车削该类材料零件往往存在刀具失效快、表面质量不易保证等难题。为此,以PCBN刀具高速硬车削GCr15薄壁轴承套圈为研究对象,通过单因素基础切削试验探究修光刃宽度和刀尖圆弧半径等刀具刀尖结构对切削力和切削温度的影响,并在此基础上进行正交试验,对比分析刀具刀尖结构和切削速度、进给量等切削用量对已加工表面粗糙度和残余应力的影响,优选工艺参数,从而为高效高质量加工轴承套圈提供关键技术与数据支撑。

热处理变形控制工艺优化装置设计与研究

热处理工装是保持和提高复杂结构铸件精度的关键技术装备。为消除长度大、壁厚小、型面结构复杂的铸件在机械加工过程中带来的应力,本文结合计算机辅助方法,分析典型零件热处理变形的影响因素,设计和制造热处理工艺优化专用装置。同时,结合实际热处理形变程度,不断完善设计方案。通过测试热处理前后铸件型面变形量的大小,最终确定了适用铸件的热处理变形控制工艺优化装置,极大程度地消除了零件的残余应力,减小了热处理过程中的变形量。

某钻井工具探管开裂原因

某钻井工具探管发生横向开裂现象,采用宏观观察、化学成分分析、硬度测试、金相检验、扫描电镜和能谱分析等方法对探管的开裂原因进行分析。结果表明:探管材料为奥氏体不锈钢,服役环境中的氯离子为其应力腐蚀提供了腐蚀环境,探管在钻进过程中承受轴向应力,加上制造过程中探管产生的残余应力,这些因素均为探管发生应力腐蚀开裂提供了力学条件,最终导致其发生氯化物应力腐蚀开裂。

基于轴向应力波理论的冲击能量测量方法及应用

研究一种基于轴向应力波理论的冲击能量测量方法,将冲击能量的测量转换为对应力波的测量,进一步开发了电锤冲击能量的计算机辅助测量系统。系统采用定制长度与直径以及对杨氏模量和质量密度进行标定的测试杆,使用精确的应变片和惠斯顿电桥、微信号放大电路、高速ADC数据采集卡和相应的冲击能量测量软件进行实验。实验结果表明:测量方法与应用提升了电动工具冲击能量的智能化测量水平,测量数据准确可靠。

产妇分娩创伤评估工具的研究进展

对国内外分娩创伤评估工具的内容、特点及应用情况进行综述,以期促进我国分娩创伤研究,为准确评估分娩创伤水平提供参考。

718镍基合金切削加工过程刀具磨损影响研究

为分析不同的刀具磨损形式和磨损量对于718镍基合金切削过程和切削结果的影响,基于有限元工具和正交模型对刀具在刀尖圆磨损、后刀面磨损以及月牙洼磨损3种不同磨损形式和不同磨损量条件下对718镍基合金的切削过程进行了相应的仿真。通过建立多个路径对切削过程温度分布和加工后的表面残余应力分布进行提取、求平均值。结果表明,不管何种形式的刀具磨损,都会对切削结果产生明显的影响,随着刀具磨损量的增大,切削力和切削温度都会呈现增大趋势,同时表面残余应力也基本上呈现不断恶化的趋势,不过前期切削温度未能使得材料产生更多的热塑性变形时,切削力占主导作用,此时残余应力的变化呈现相应的反常现象。

基于有限元的顶驱下套管装置密封胶筒设计

密封胶筒是顶驱下套管装置实现套管密封、泥浆循环等作业功能的关键部件。为探究密封胶筒工作原理并为其研发提供理论依据,通过有限元分析软件建立了数值仿真模型,采用自适应网格技术模拟了密封胶筒插入套管及密封高压泥浆的动态过程。分析了密封胶筒的密封原理,研究了动态过程中密封胶筒几何形态及应力状态的变化特性。并对密封胶筒进行了力学分析和强度校核,结果表明:当密封最大泥浆压力时,胶杯最大应力为15.77 MPa,骨架最大应力为370.3 MPa,表明密封胶筒强度满足设计要求。最后通过应用试验检验密封胶筒的密封效果,验证了仿真计算各项数据的准确性,表明此密封胶筒性能满足现场使用要求。

测试工装引起的单板FPGA失效分析及改进方案

针对某直流输电工程单板出现的FPGA失效故障,以故障FPGA失效表现为出发点,分析单板FPGA失效背景与原因,审视单板测试工装原理及测试方案,并针对问题提出整改措施。

基于Inconel 718车削过程有限元仿真的刀具刃口几何参数优化

基于Third Wave Advant Edge建立二维有限元模型,对镍基高温合金Inconel 718的车削过程进行数值仿真分析,并通过直角车削试验验证仿真模型的精准度;提出了刃口几何参数的优化流程,获得了不同刃口几何参数下的切削温度和应力分布,研究了刀具刃口几何参数对刀具应力及刀具温度的影响,进而对加工镍基合金的刀具刃口参数进行优化。仿真结果表明:在选定后角7°时,粗加工镍基合金Inconel 718的最优前角为6°,最优刃口钝圆半径为60μm;随着刀具前角的增加(0°~10°),切削温度逐渐增加,刀具应力先减小后增加,切屑的高温区逐渐减小,刀具的高应力区逐渐向后刀面扩展;随着刃口钝圆半径的增加(30μm^80μm),刀具温度逐渐增加,温度分布无明显变化,刀具应力先减小后增加,切削刃附近应力集中现象减弱。

基于最小切块应力的西兰花切块加工刀具参数优化研究

为了给西兰花切块机的设计提供理论依据,获得最佳切块效果,该文以收获期的西兰花作为切块对象,选择西兰花切块位置、刀具刃角、刀具结构以及入切角为影响因素,在万能材料试验机上进行了单因素与多因素的切应力试验,单因素试验结果表明:切块位置为距离花蕾顶端40 mm、光刀、入切角为60?、刀具刃角为5?~10?之间时切应力最小。多因素试验结果表明:影响切应力的因素主次次序依次是切块位置、刀具结构、刀具刃角、入切角;切块位置为距离花蕾顶端40mm、刀具结构为球形刀、刀具刃角为8?、入切角为90?时切块效果最佳。根据试验优化结果设计了西兰花切块刀具,并在自制的切块样机上进行了切块试验,切块效果良好,切块成功率达到91%,验证了刀具参数优化的合理性。研究结果可为后续西兰花切块机切块刀具的设计提供参考。

基于CAE/CFD技术的套管防磨工具优化设计

在深井和大位移井钻进中,常常由于钻井周期长及狗腿度严重等问题导致套管和钻杆接头严重磨损甚至磨穿,带来安全隐患和巨大的经济损失。针对现有套管防磨工具使用寿命短和压耗大的问题,应用CAE和CFD技术分析了其过流压耗及间歇碰撞滚滑状态下的工作应力,提出了有针对性的改进措施,改进后结构的峰值工作应力和压耗分别减小20.8%和17.3%,可磨损体积增大14.0%;对挡圈及锁紧结构进行了优化设计,降低了其拆装难度。优化后的防磨工具压耗更小,可以有效减小套管和钻杆的磨损。