AN EXPERIMENTAL EVALUATION OF CUTTING TEMPERATURES DURING HIGH SPEED MACHINING OF HARDENED D2 TOOL STEEL

This paper investigates experimentally the effects of different process parameters on the cutting edge temperature during high speed machining of D2 tool steel using polycrystalline cubic boron nitride (PCBN) tools. The cutting edge temperature is measured using thermocouples. The process parameters considered are cutting speed, feed rate, nose radius, rake angle, and tool wear. The effects of different edge preparations including sharp, honed and chamfered are also investigated. The results show that increasing cutting speed and feed rate increases the cutting temperature while increasing nose radius reduces the cutting edge temperature. In addition, there is an optimum rake angle value at which minimum cutting temperature is generated.     

端铣淬硬钢时新型陶瓷刀具热破损的强激光模拟

利用强激光热模拟实验，模拟好单齿端铣刀在铣削过程中的温度变化规律，并用有限元对刀具的温度场和热应力场进行了分析。从对热冲击后的刀片ＳＥＭ分析发现，在热源附近产生了通过热源以径向为主的网状裂纹。最后对刀具热裂的机理进行了分析。     

评价断续车削淬硬钢时硬质合金刀片抗早期破损能力的一个新参数

本文通过分析和实验,提出了用能量法来评价刀片抗早期破损能力的观点。文中分析了切削过程中的能量转换关系,指出切削过程中的各类能量可以通过实测的宏观物理量——切削力、切削温度等来加以衡量,并建立了表明各类能量之间分配关系的回归方程式。对在实际切削条件下所测得的回归诸元进行分析计算,获得了一个与刀片早期破损具有相关关系的实验参数——临界单位冲击功率e。由于e是在实际切削条件下获得的实验参数,在评价刀片抗早期破损的能力方面,可望比沿用的静态材料力学参数具有更大的优越性。     

INFLUENCE OF MACHINING PARAMETERS ON THE WHITE LAYER FORMATION PROCESS AND ITS CHARACTERISTICS IN TURNING OF HARDENED STEEL

This article contains results of experimental research activities of white layer formation (WLF) and its characteristics during a process of turning hardened steels (THS), which have been carried out in laboratories of DD Cimos TMD Ai Grada?ac. WLF. Characteristics during the THS process were analyzed from the aspects of influence caused by machining parameters as well as tool flank wear width. Experimental tests of tool wear have been performed. The tool used in experimental tool wear was ceramic cutting insert CNGA 120408T, catalogue mark IN22 Al2O3-TiCN. In accordance with achieved results, value of tool flank wear 220 µm has been set as the criterion of wear. In accordance with defined wear criterion, determination of level and type of influence that machining parameters have on WLF and its characteristics were carried out in accordance with planned experimental methodology. Experiments have shown that cutting speed and tool flank wear width (for all other machining conditions unchanged) can be used for control of WLF and its characteristics. Structural changes in surface layer of the working piece, during the cutting process of hardened material, except for the WLF are also presented through a transition zone, e.g., dark layer, which has lower hardness than the initial material. Hard WL can take over a protection role for a machined surface from abrasive actions, while softened zone (dark layer) can take over a function of WL solder with the initial material. Analysis of achieved results points to a possibility of controlling the WLF and its characteristics, and therefore a possibility of using WL in a positive context. The basis for the above mentioned is the effect of additional plastic deformation of WL (APDWL), which occurs only under certain machining conditions. The effect seen, if follows WLF, results in decrease of machined surface roughness compared to its expected value. Accordingly there is a possibility for identification of WL on a machined surface by measuring the roughness parameters without previous metallographic preparation of samples.     

AISI-01钢激光表面强化层组织与硬度分布的研究

本文研究了激光加热工艺参数及钢的原始组织对AISI-01钢激光淬火层组织及硬度的影响。对各组样品表面淬硬层及心部组织的光学显微镜、电子显微镜、X射线衍射及显微硬度分析的结果表明,在激光功率400～600W、扫描速率0.02～0.42cm/s的范围内,可获得深度0.30～0.60mm、表面硬度60～68HRC的淬硬层。然而,激光功率与扫描速度的不同组合,将改变淬硬层表面残留奥氏体及未溶解碳化物的数量。以获得较均匀的淬硬层组织及较平缓的硬度-深度曲线考虑,样品的原始组织以调质处理至硬度30～40HRC为佳。     

SURFACE INTEGRITY CHARACTERIZATION AND PREDICTION IN MACHINING OF HARDENED AND DIFFICULT-TO-MACHINE ALLOYS: A STATE-OF-ART RESEARCH REVIEW AND ANALYSIS

This paper presents a review of the state-of-art research on surface integrity characterization, especially the characteristics of residual stresses produced in machining of hardened steels, titanium and nickel-based superalloys using the geometrically defined tools. The interrelationships among residual stresses, microstructures, and tool-wear have been discussed. Current research on residual stress modeling and simulation using finite element method has been critically assessed. Also, the rationale for developing multi-scale simulation models for predicting residual stresses in machining has been presented. At the end, possible future work has been proposed.     

MODELING OF WHITE AND DARK LAYER FORMATION IN HARD MACHINING OF AISI 52100 BEARING STEEL

In machining of hardened materials, maintaining surface integrity is one of the most critical requirements. Often, the major indicators of surface integrity of machined parts are surface roughness and residual stresses. However, the material microstructure also changes on the surface of machined hardened steels and this must be taken into account for process modeling. Therefore, in order for manufacturers to maximize their gains from utilizing hard finish turning, accurate predictive models for surface integrity are needed, which are capable of predicting both white and dark layer formation as a function of the machining conditions. In this paper, a detailed approach to develop such a finite element (FE) model is presented. In particular, a hardness-based flow stress model was implemented in the FE code and an empirical model was developed for describing the phase transformations that create white and dark layers in AISI 52100 steel. An iterative procedure was utilized for calibrating the proposed empirical model for the microstructural changes associated with white and dark layers in AISI 52100 steel. Finally, the proposed FE model was validated by comparing the predicted results with the experimental evidence found in the published literature.     

机床功率监控系统的数学模型及其应用

从机床能量传输数学模型出发,首次建立了机床功率信息传感型监控系统（简称机床功率监控系统）的数学模型,提出了些模型在研究机床功率信息动态响应特性,提示功率住处随切削负载率和在外界干扰信息作用下的变化规律,识别刀具磨损、破损状态,诊断机械加工故障,测试机械加工过程中的某些机械量或电量等方面有着多种功能和用途,并列举了应用此模型提示机床功率监控系统中功率信息的迟滞响应特性的实例。     

高速加工热缩加长刀杆与刀具配合径向夹持刚度分析

建立热缩加长刀杆与刀具配合的有限元模型,给出一种合理确定模型中接触刚度系数的有效方法.随后对不同过盈量、夹持长度及主轴转速对热缩加长刀杆与刀具配合的径向夹持刚度的影响进行分析.最后在建立径向夹持刚度测量方法的基础上,对有限元分析结果进行验证.结果表明,合理的接触刚度系数是正确建立热缩加长刀杆与刀具配合有限元模型的关键;热缩加长刀杆与刀具配合间存在有合理的配合过盈量与夹持长度,以保证配合间夹持均衡而具有很好的夹持刚度,又不至使刀杆强度超过其屈服条件而降低刀杆的使用寿命和精度;当转速超过一定范围时,应考虑离心力对热缩加长刀杆与刀具配合径向夹持刚度的削弱作用.     

INVESTIGATION OF THE TOOL WEAR AND SURFACE FINISH IN LOW-SPEED MILLING OF STAINLESS STEEL UNDER FLOOD AND MIST LUBRICATION

This paper examines the performance of AlN/TiN coated carbide tool during milling of STAVAX® (modified AISI 420 stainless steel) at a low speed of 50 m/min under conventional flood and mist lubrication. Abrasion, chipping, fracture resulting in the formation of crater and catastrophic failure are the wear mechanisms encountered during machining under flood lubrication. The flank wear, and the likeliness of the cutting tool to fracture, chip and fail prematurely increased with an increase in the hardness of the workpiece and a reduction in the helix angle of the tool. Small quantity of mineral oil sprayed in mist form was effective in reducing the flank wear and severity of abrasion wear, and preventing the formation of crater and the occurrence of catastrophic failure. In milling 35 and 55 HRC-STAVAX® using a feed rate of 0.4 mm/tooth and a depth of cut of 0.2 mm under mist lubrication, the cutting edge of the 25° and 40° helix angle tools only suffered small-scale edge chipping and abrasive wear throughout the entire duration of testing. The influence of the ductility of the workpiece on the surface finish and the effectiveness of mist lubricant in improving the surface finish are also discussed.     

机床沿曲线高速加工时的运动学与动力学特性分析

详细分析了刀具沿曲线加工时，刀具路径几何特性（位置、切向矢量、曲率）与机床的运动学特性（进给速度、加速度）以及动力学特性（伺服电动机驱动力、切削负载、摩擦力）之间的关系。并采用解析的方法，计算了在各轴加速度和伺服电动机驱动力约束条件下，机床沿曲线加工时的最大安全进给速度。分析结果表明刀具路径几何特性对机床的运动学和动力学特性有很大的影响。     

耐热钢持久强度的统计特性及其在寿命评估中的应用

采用统计方法对12CrMo1V和2．25Cr-Mo钢的持久强度数据进行统计分析，确定其分布类型和分布参数，并运用蒙特卡罗模拟法评定电站管道等高温承压部件的可靠寿命：研究结果表明，12Cr1MoV和2．25Cr-Mo钢的持久强度σ10^4^540均服从对数正态分布，利用持久强度的统计特性预测高温承压部件的寿命，合理考虑持久强度的分散性对结构寿命的影响，可提高寿命预测的可靠度。     

HHT相对谱熵及其在轴承退化状态识别中的应用

为有效地对轴承退化状态进行识别,对轴承退化特征提取方法进行了研究。基于HHT变换的非平稳信号分析能力和相对熵可以较好表征振动信号概率分布差异的特性,提出基于HHT相对谱熵的轴承退化特征提取方法。通过仿真信号对定义的HHT相对能谱熵(HREE)和HHT相对奇异谱熵(HRQE)的合理性和有效性进行了验证。将这两个特征指标组成退化特征,对实测轴承内圈和外圈故障模式下的不同程度故障振动信号进行了进一步分析,并通过相关向量机对轴承退化状态进行了识别,结果验证了所提方法的有效性。     

高温316L钢非线性疲劳蠕变损伤演化模型及其应用

为了研究高温两级和多级疲劳蠕变载荷作用下计及载荷历程效应的寿命预测方法,文中首先基于韧性耗竭理论提出一种非线性疲劳蠕变损伤演化模型,并通过316L不锈钢高温单级应力、温度疲劳蠕变试验,确定模型中的损伤指数,以该损伤模型结合多级加载的损伤破坏准则对高温两级应力、温度疲劳蠕变载荷作用下316L钢的寿命进行预测,得出与试验较...     

钢中最大夹杂尺寸的评估与疲劳强度的预测

采用两种极值统计方法(statistics of extrem values,SEV;generalized Pareto distribution,GPD)对某一商用42CrMo钢的最大夹杂尺寸进行评估,并且预测其对应的疲劳强度.与实验结果比较发现,两种方法预测的夹杂大小及疲劳强度和超声疲劳实验的结果接近,且在一定的小体积范围内SEV方法预测的最大夹杂尺寸与实验结果更相近.     

高速工具钢的超长寿命S-N曲线特征和内部裂纹萌生行为

为了研究高速工具钢超长寿命S-N曲线特征和内部裂纹萌生行为,使用沙漏形状试样在室温空气环境下进行旋转弯曲的疲劳试验。结果表明,材料的S-N曲线均由表面裂纹萌生型和内部裂纹萌生型组成。表面裂纹萌生型的S-N曲线位于高应力幅短寿命区,内部裂纹萌生型的S-N曲线位于低应力幅长寿命区。前者的S-N曲线向后者的转移几乎是连续的,回火温度对疲劳强度和寿命没有明显的影响。分别使用扫描电子显微镜、扫描探针显微镜和电子探针X射线微区分析仪对内部裂纹萌生位置和材料组织进行对比观察,在萌生内部裂纹的夹杂物周围存在一个颗粒区域,该区域内凸起的颗粒是组织中的球形碳化物。颗粒区是在内部裂纹扩展的应力强度因子门槛值范围以下形成的,对超长寿命疲劳起着重要的作用。     

车轮应变疲劳性能及损伤演变规律研究

通过试验分析了Φ９１５喂线车轮的低周疲劳行为，测定了循环稳定和单调拉伸应力－应变曲线，给出了应变－寿命及应力－寿命关系，讨论了循环软化、循环硬化特性，导出应变疲劳损伤演变方程和寿命估算方程。列表给出车轮钢的全部应变疲劳参数和与之对应的静态参数，可供设计选材、寿命估算时使用。     

基于高强钢与材料填充的白车身耐撞性轻量化设计

车身结构在碰撞中承担着变形吸能、传递碰撞力以及维持生存空间的作用,基于耐撞性前提下的白车身轻量化设计,有助于提高车辆动力性与燃油经济性,降低排放。将车身结构碰撞形式分解为轴向压溃与横向弯曲两种工况,通过研究不同等级高强钢板与不同类型材料填充组合结构在两种工况下的吸能与抗弯性能,得到针对安全部件与模块的优化结论。将这些结论应用于某量产SUV车身,仿真分析表明该方法不仅提升了车身耐撞性能,同时降低了白车身质量,实现了车身的耐撞性与轻量化设计。     

反求工程中二维对称几何模型的约束重构理论及其应用

为提高二维对称几何模型重构的整体品质,反映其初始的设计意图,提出二维对称几何模型的约束重构理论及方法.首先构建参数化点,反射对称以对称轴为中心将对称部分的点集作镜像变换映射到基本点集的一边,旋转对称以旋转中心点为中心将对称部分的点集作旋转变换映射到基本点集的一边,形成参数化的点集.其次识别并处理二维曲线间的约束以及对称模型的边界约束.最后将参数化的点集与基本点集一起作为曲线拟合的目标点集,建立带约束的目标拟合函数,将其转化成无约束优化问题,采用L-M方法迭代求解.实例表明反求结果在满足初始几何约束的同时,能够保证几何模型严格的对称.     

最优超松弛因子的一种确定方法及其在裂纹计算中的应用

结合黄金分割法，提出一种最优松弛因子的优选法。该方法区别于常用的直接计算求取的方法和试错法，具有明显的优点。给出的断裂力学应用实例表明计算机确定最优松弛因子的方法是明显有效的。文中给出的松弛因子值可供工程直接应用。