锯切加工中金刚石节块的热磨损及Ti—Cr涂层对热磨损的抑制作用

在锯切花岗石过程中,用三明治薄膜热电偶监测接触界面的温度响应,研究了节块式金刚石工具与花岗石接触界面的温度特征,通过将试验结果与解析结果拟合得到热量传入节块的比例,并在此基础上求解出金刚石磨粒的表面温度.结果表明,在干摩擦下的花岗石锯切过程中,工具与工件接触弧区内90%以上的热量传入金刚石节块,节块表面部分金刚石磨粒的表面温度超过1000℃,金刚石的3种典型失效方式均受到锯切热的直接影响.在金刚石表面镀覆Ti-Cr合金可以有效抑制锯切热引起的磨粒脱落.     

锯切过程中花岗石与金刚石间的摩擦效应

通过测量锯切力和计算锯切比能,获得了多种条件下的比能与单颗磨粒平均载荷的试验,从能量角度探讨了花岗石的锯石的锯切机理,并建立了单颗磨粒平均载荷与磨粒纵向切削面积平均值之间,单位宽度功率消耗与滑擦面积之间的对应关系。结果表明,锯切过程中能量主要消耗于花岗石与金刚石间的摩擦,由于单颗磨粒向切削面积平均值同时包含了磨粒切削深度与弧长的影响,更适用于描述锯切过程。锯切中锯切深度和材料去除率等因素的影响均可     

摩擦学学报第21卷(2001年第1～6期总第81～86期)总目次

研究论文金刚石砂轮与花岗石摩擦界面能量传输特征的实验研究徐西鹏 ,MAL KIN S　 1(1)………………………离子注入对 Si O2 表面非晶碳薄膜的化学状态及摩擦学性能的影响　　　……………………………………　徐　洮 ,杨生荣 ,齐尚奎 ,吕晋军 ,薛群基　 1(6 )……………………………………………………………氮及钛等离子体基离子注入铝合金表面改性层的摩擦磨损性能研究廖家轩 ,夏立芳　 1(10 )………………多弧离子镀硬质膜的抗空蚀性能研究潘国顺 ,杨文言 ,邵天敏 ,王义民　 1(15 )………………………………外加极化电位对 316 L不…     

单颗金刚石磨削花岗石中力的离散单元分析及试验验证

对花岗石进行了单颗粒金刚石磨削试验.通过测量磨削力对单颗金刚石磨粒所承受的平均法向力和切向力进行了研究,讨论了主轴转速和单颗磨粒最大切削厚度与磨削力的关系.利用离散单元方法(DEM)构造了2种不同的花岗石数字模型,在此基础上对单颗磨粒磨削进行了模拟分析,分析结果与试验结果基本吻合.     

磨削花岗石过程中钎焊金刚石磨损特征分析

通过跟踪测量金刚石磨粒出露高度及其磨损状态比例,分析钎焊金刚石在磨削花岗石过程中的磨损特征,利用三明治热电偶法测量工具-工件接触区的工件表面温度.结果表明,在所试验的钎焊工具中,金刚石磨粒主要以破碎磨损为主,约有44%的磨粒直接从完整状态产生台阶式宏观破碎,磨粒的宏观破碎均发生于磨粒与结合剂的结合部.磨削过程中工具-工件接触区的表面温度约为480 ℃,该温度不足以使金刚石磨粒产生石墨化.钎焊金刚石磨粒的出露高度越高,磨粒所承受的弯矩越大,弯矩增加以及工件对磨粒的剪切力是导致金刚石磨粒产生结合部破碎的主要原因.     

单点修整工具磨损对砂轮磨削表面的影响

在磨削加工过程中,砂轮表面的切削刃分布情况与磨削工件表面特征直接相关,而砂轮表面特征又与修整过程相联系,为研究单点金刚石笔的磨损和修整参数对磨削工件表面的影响,利用数值模拟和试验测量的方法揭示了砂轮修整及磨削过程,在修整重叠率为3时,讨论了修整参数与工件表面形貌特征的关系,并获得金刚石笔的磨损对磨削表面的影响.结果表明:金刚石笔初期修整阶段,磨削工件表面的峰谷分布明显具有规律性,其0.12 mm的变化周期完全为修整导程的复映;金刚石笔磨损后,工件截面曲线特征的规律性减弱,测量的表面粗糙度由0.52μm减小到0.38μm,最后导致工件表面烧伤;若调整修整导程保持原重叠率,则表面粗糙度增大为0.81μm.     

界面调控对类金刚石碳基薄膜/铜摩擦副摩擦学行为的影响

无氢DLC/金属铜摩擦副体系摩擦系数高且不易调控，调整DLC/金属铜摩擦界面从而降低其摩擦系数是亟待解决的问题. 本研究中通过制备含氢与无氢类金刚石碳基薄膜，采用试验分析与模拟计算结合的方法研究了不同氢含量碳基薄膜与铜配副的摩擦学特性并讨论了氢原子在摩擦界面对改善摩擦学性能所起的作用. 结果表明:摩擦界面的结构特性对于类金刚石碳基薄膜/铜配副体系摩擦学性能有非常重要的影响，氢原子可以通过减小摩擦副之间的黏着从而起到调节摩擦界面的作用. 通过向DLC中掺杂氢等钝化元素可有效调控界面处的相互作用从而调控体系摩擦学性能. 本研究方法为降低DLC/铜摩擦副体系摩擦系数提供参考.      

用人工神经网络计算机技术进行金刚石工具的摩擦学设计

在分析讨论了金刚石工具的摩擦学性能及其磨损机理之后，采用人工神经网络计算机技术编制了金刚石工具磨擦学设计的计算机程序，并且依据这种程序设计制造了一组铣磨轮，进而将其装机作了大理石材的磨削加工现场应用考察，结果表明，通过本程序设计可以使铣磨轮的平均消耗数减少１１％，磨削数率提高２８％，这是在采用人工神经网络计算机程序进行设计时，将实际工作数据作为神经元程序的学习和检查样本，它充分引入了现场使用状况对     

锯切花岗石过程中金刚石节块磨损特征及影响因素分析

在已有的节块磨损规律的基础上，对锯切花岗石过程中的金刚石及其固位载体－粘合剂的磨损规律进行了研究。通过实验，跟踪观察了不同金刚石节块在各种加工条件下的磨损状态。结果表明；金刚石的工作状态与节块的使用性能有良好的对应关系，金刚石的微破碎和完善晶型比例越高节块耐磨性越好；宏观破碎和脱落比例越高节块耐磨性越差。金刚石的粒度，含量，品级，粘合剂和金刚石的匹配以及锯切用量组合等均明显影响锯切效果。     

不同粗糙度煤岩界面超低摩擦效应与声发射特征试验研究

为了揭示动载扰动作用下煤岩界面粗糙度对超低摩擦型冲击地压影响机制,采用自行研制的煤岩界面超低摩擦试验装置,以沈阳红阳三矿1082 m采深煤岩体为研究对象,通过改变煤块与砂岩块体表面粗糙度来模拟煤岩界面不同粗糙特性,以粗糙度系数表征煤岩界面粗糙程度,工作块体水平位移表征冲击过程中超低摩擦效应强度,声发射能量为工作块体摩擦滑动过程中的信号参数,进行应力波扰动下不同粗糙度煤岩界面超低摩擦试验.研究结果表明:(1)超低摩擦滑动过程中,工作块体水平位移、声发射能量计数以及累计能量曲线呈现出孕育阶段、激发阶段、稳定阶段变化特征;(2)煤岩界面粗糙度越小,工作块体水平位移和声发射能量峰值越大,煤岩界面越易发生超低摩擦效应;(3)不同煤岩界面粗糙度下,相比于其他扰动频率, 2 Hz时更易发生超低摩擦效应;(4)给出了声发射能量峰值与煤岩界面粗糙度系数对应关系.声发射能量峰值可以有效表征超低摩擦效应强度,可以用声发射能量峰值预测超低摩擦效应强度.     

Simultaneous Transient Temperature Sensing of Impacted Polymers Using Infrared Detectors and Thermocouples

Infrared detectors are probably the most popular device used for transient temperature monitoring of materials deformed in the high strain-rate regime. Embedded thermocouples have also been shown to be suitable for that purpose, especially with poor thermal conductors such as polymers [Rittel, Exp Mech 38(2), 73–79, 1998b]. However, there is no direct comparison between these two techniques. This paper presents experiments during which commercial polycarbonate specimens were deformed dynamically, while the surface and core temperatures were monitored using an infrared detector and embedded thermocouple respectively. An excellent agreement was obtained between the two techniques, confirming the suitability of thermocouples for transient temperature sensing.     

SUS304钢表面粗糙度对红外图像的影响

为提高红外热像仪图像及测温精度,根据红外热像仪的测温原理和红外辐射原理,通过使用红外热像仪、CCD相机以及激光表面形状测量显微镜,研究了SUS304钢在单轴拉伸塑性变形过程中表面粗糙度与目标发射率的关系;并用热电偶和红外热像仪对塑性变形过程中的温度分布进行了测量。研究结果表明,目标发射率随表面粗糙度成比例增大,造成红外热像仪测定的塑性变形区域比实际变形区域大;通过预先设定材料的表面粗糙度,以提高有效目标发射率,能得到较好的红外图像和测温精度。     

Modeling and research of temperature distribution in surface layer of titanium alloy workpiece during AEDG and conventional grinding

Titanium and its alloys are widely recognized as the hardly machinable materials, especially due to their relatively high hardness, low thermal conductivity and possible subcritical superplasticity. Then, a thorough control of the machining process parameters shall be maintained. In this paper, we have concentrated on the grinding of the Ti6Al4V titanium alloy using cBN (boron nitride) grinding wheel combined with the AEDG (abrasive electrodischarge grinding) process. The mathematical model we have dealt with has been based mainly on Jaeger model of the heat taking over between sliding bodies with substantial upgrades related to:

• estimation of the frictional heat generating based on friction forces distribution,
• spatial, not only planar, shape of the contact area,
• generated heat partition between different parties of the grinding process,
• heat transfer in the multilayered environment.

The experimental verification of the theoretical predictions has been carried out. Fundamental difficulty in such a research is placing temperature probes sufficiently close to the ground surface with possibly low space devoted for probes due to the temperature field deformation with relation to the real conditions of grinding. The temperature field in the machined workpiece has been investigated using electronic data logging and DSP methods. Obtained results exhibit clearly that distribution of heat generation in the contact zone could be of the relatively complicated shape due to the external cooling and the very specific heat transfer and accumulation in the titanium workpiece surface layer.

     

Analytical solution of the overdetermined inverse heat conduction problem with an application to monitoring thermal stresses

The paper presents a technique for determining the transient temperature distribution, when input data as thermocouple responses are known at several interior locations. If the temperature field is known, then the thermal stresses can be calculated. The problem is overdetermined and is solved using a least squares method that minimizes the error between the computed and measured thermocouple temperatures. The present method incorporates the advantages of simplicity and accuracy of analytical solutions. Several numerical examples and measurements are presented as an indication of the accuracy of the presented method. Received on 10 January 1997     

冲击载荷下瞬态温度的实时测量方法

将红外瞬态测温装置引入SHPB冲击实验,确定了不同材料试件的温度标定曲线,并实时测量了冲击下Al合金和伪弹性TiNi合金试样的表面温度。结果表明,2种试样温度变化都经历了加载过程的温度升高,主要不同在于卸载过程,Al合金卸载过程中温度保持最大加载温度不变,而TiNi合金试样卸载过程中温度降低,这反映了2种材料不同的物理变形过程和温度变化机制。直接红外测温的实验结果与根据能量守恒理论计算的温度较好吻合,说明采用的红外测温方法实时测量冲击瞬态温度是可行的。     

Temperature determination in a transient free fuel jet with equilibrium temperature of the local molar mixture fraction

This paper presents the space-resolved temperature determination in the mixing zone of a transient free dimethyl ether jet flowing into a non-moving atmosphere via the time-resolved local molar mixture fraction, obtained with tracer added Laser-induced Fluorescence. The temperature of the mixture is calculated with an approach of an adiabatic mixing temperature. To validate the obtained temperatures a high-speed thermocouple measures the local temperature with high temporal resolution. The thermocouple data is corrected using a detailed model that includes all relevant effects of radiation, convection and conduction. The corrected thermocouple temperature is compared with the temperature data obtained via the local molar mixture fraction. Comparison of the corrected thermocouple data with the mixture-derived data shows excellent agreement for pressure and temperature conditions sufficiently far from the critical point of dimethyl ether.     

Prediction of transient heat transfer coefficients in thick-walled pressure components of cylindrical geometry

This paper presents a procedure for determining the transient heat transfer coefficient in cylindrical, thick-walled pressure parts. From theoretical considerations, the temperatures can be predicted at discrete locations throughout the wall, when input data such as thermocouple responses are known at one or several interior locations.Special emphasis is placed on the dynamic response of the thermometer, which measures the temperature of the inside fluid, to enable exact determination of both heat transfer coefficient and fluid temperature. The transient response of a thermocouple in a convectional thermowell (pocket) is described by the first-order convective heat transfer model in which the rate of thermoelement temperature change is proportional to the instantaneous difference between the thermoelement and fluid temperatures.     

Nonlinear chatter with large amplitude in a cylindrical plunge grinding process

The phenomenon that the stable smooth grinding process coexists with chatter vibrations with large amplitudes in a cylindrical plunge grinding process is investigated in this paper. In the analyzed dynamic model, the workpiece and the grinding wheel involved in the grinding process are regarded as a slender hinged-hinged Euler?CBernoulli beam and a damped spring mass system, respectively, and the contact force between the two is treated as the main factor that affects the dynamic behaviors of the process. Called regenerative force, the contact force represents the interaction with regenerative effects between the workpiece and the wheel. To clarify the relation between the force and the dynamical behaviors in the grinding process, all the effects of the system parameters related to the interaction, such as the grinding stiffness, the rotation speeds of the workpiece and the wheel, on the dynamic motions of the process are studied. To this end, the eigenvalues analysis is firstly carried out to find the chatter-free-region, in which the smooth grinding process is stable and the chatter vibration may be absent. And then the nonlinear chatter vibrations when the values of concerned parameter leave the chatter-free region are predicted numerically. It is interesting that both the supercritical and subcritical Hopf bifurcations are found on the same boundary of the chatter-free region. As we know, there must be a zone in the chatter-free region where the stable smooth grinding process coexists with the chatter vibration when the subcritical one arises and the switching point between the supercritical and the subcritical ones is a Bautin bifurcation point mathematically. Thus, the Bautin bifurcation analysis is performed to scan the subregion in which the smooth grinding process is not unconditional stable anymore.     

Nonlinear analysis of chatter vibration in a cylindrical transverse grinding process with two time delays using?a?nonlinear time transformation method

A nonlinear dynamic system of cylindrical transverse grinding process is studied in this paper. The system consists of a grinding wheel and a workpiece, which are connected to the base by spring-damper elements, interacting with nonlinear normal forces. This two DOF model includes two time delays originated from the regenerative effects of the workpiece and the grinding wheel. Bifurcation points are located using a numerical algorithm by which we can find all the eigenvalues in a given rectangular region on the complex plane for the delayed differential equations. Supercritical bifurcation has been found for some sets of system parameter values. The amplitudes of the limit cycles are predicted using a nonlinear time transformation method, which is similar to the harmonic balance approach in that a periodic solution is approximated by a Fourier series. However, the main difference is that a nonlinear time ? is introduced in the Fourier series rather than the physical time t. The analytical solutions of stable limit cycles up to the third harmonics are compared with numerical simulations for the retarded system. It is shown that the proposed method gives accurate approximate solutions.