磨削淬火技术的温度场分析和材料相变研究

磨削淬火技术是利用磨削热对工件表面进行热处理 ,使工件表层发生马氏体相变 ,达到与表面强化处理一样的性能。通过对温度场的分析和材料相变的研究 ,发现利用计算机仿真磨削淬火温度场 ,不仅可以节省大量分析时间和试验费用 ,而且可以利用磨削温度场仿真技术 ,通过选择不同的工艺参数来预测和控制相变层厚度     

超声振动磨削陶瓷的温度场特性研究

采用人工热电偶法,通过普通磨削和超声振动磨削对比实验,对陶瓷材料ZrO2平面磨削的温度场进行了实验研究。并对磨削参数与磨削温度的关系,进行了理论分析及实验验证。结论表明:距磨削表面越远,其磨削温度的峰值越远离热源;增大磨削深度、提高磨削速度和工作台进给速度都会使工件表面温度升高。正交试验表明,磨削深度对温度场的影响较大。普通磨削时工件表层的温度较高,易发生磨削烧伤,采用超声复合磨削能有效降低工件表层温度。     

断续磨削时工件表层温度场解析

建立了周期变化的移动热源模型,并引进卷积概念,推导了计算断续磨削时工件表层非稳态脉动温度场的理论公式。该公式可以包容连续磨削的情况,且可计算任意时刻的瞬态温度分布。利用推得的公式对断续磨削时的温度场及其降温机理作了深入的研究,并对关于理论公式进行了实验校核。     

弧齿锥齿轮磨削表面烧伤建模仿真与实验验证

采用理论推导、数值仿真法和实验手段相结合的方法,首先以SG砂轮对20CrMnTi弧齿锥齿轮的成形磨削建立了温度场的有限元模型,选用了矩形分布热源的移动加载方法并用ANSYS软件进行了温度场的仿真分析,发现不同磨削参数对磨削温度场的影响规律,即随着径向进给量的增大,工件磨削区表面温度升高;砂轮速度越高,磨削温度升高;随着展成速度的增大,磨削温度呈现先减少后增加的趋势。然后观察弧齿锥齿轮大轮烧伤区的金相组织,检查齿部截面硬度梯度。发现当工件磨削表面出现轻微烧伤时,表面组织出现了屈氏体;当出现中度烧伤时,最外表面为二次淬火马氏体,下层为回火马氏体或索氏体;严重时,表面组织有索氏体。最后发现当齿轮发生轻微烧伤时,表面显微硬度明显低于磨削前的硬度,此时变质层深度大于0.2mm;严重烧伤时,表面发生了退火烧伤,表面显微硬度下降较多,变质层深度增大,且烧伤越严重,表面显微硬度下降越多。得出:当变质层深度大于0.2mm时,产生不同程度的磨削烧伤。     

磨削淬火技术的研究现状与展望

磨削淬火技术利用磨削热对工件表面进行热处理,使工件表层发生马氏体相变,达到与表面强化处理一样的性能。本文对磨削淬火技术的研究现状进行了总结,针对目前研究中存在的问题,提出了磨削淬火技术研究的发展方向。     

基于瑞利分布的平面磨削温度场的仿真研究

考虑磨粒在砂轮表面随机分布对接触区热流密度分布的影响,基于未变形磨屑厚度的瑞利分布理论,假定流入工件的热流密度呈瑞利分布,建立了瑞利分布热源模型。采用基于有限元法的瑞利分布热源模型对典型磨削工况进行仿真计算,将计算结果与矩形分布及三角形分布仿真结果进行对比,系统地分析了热源模型、磨削液对温度场的影响规律。结合磨削实验测量值,发现基于瑞利分布的热源模型仿真结果与实验测量值吻合较好。     

基于ANSYS的平面磨削温度场的有限元仿真

通过确定移动热源的加载方式,运用ANSYS软件的热分析模块对磨削温度场进行仿真分析,得到了不同载荷步的温度场分布以及不同深度的节点的温度变化曲线,验证了越靠近热源磨削温度越高以及工件下层材料温升显著低于工件表面。通过改变砂轮线速度、工件进给速度和磨削深度,得到了主要的磨削参数对磨削区温度场的影响状况,证明了钛合金磨削存在临界磨削速度。在临界磨削速度附近某一区间磨削温度出现回落,因此适当的磨削速度、高的工件进给速度和小的磨削深度可以有效的减小磨削温度。     

冷作磨具钢Cr12MoV磨削温度场解析模型的建立

磨削温度的研究一直是磨削领域的重点课题,磨削热可能导致零件表面出现热损伤。针对冷作磨具钢Cr12MoV磨削接触区的温度场进行了理论分析,利用热源法建立了磨削温度场的数学模型,并对此温度场的计算机仿真模型进行分析。     

平面磨削温度场有限元仿真及实验

在考虑不同磨削参数对温度场的影响的情况下,根据三角形热源模型对磨削工件进行了有限元仿真,获得了工件的温度分布。采用热电偶法测量了工件的磨削温度,发现有限元仿真值与实验测量值相当吻合,仿真结果能够真实反映工件的温度场。该有限元仿真方法对磨削过程中工件温度场的研究具有实际意义,为避免磨削烧伤提供了技术支持。     

球面磨削温度场数值仿真的研究

根据杯形砂轮磨削球面的特点,采用绕球面旋转加载的半圆弧热源模型对磨削过程进行有限元仿真,研究球面磨削时工件表面的温度场分布.将仿真结果与实验结果进行比较,发现有限元仿真值与实验测得量相当接近.     

Experiment research on grind-hardening of AISI5140 steel based on thermal compensation

The grind-hardening process utilizes the heat generated to induce martensitic phase transformation. However, the maximum achievable harden layer depth is limited due to high grinding forces, and the tensile residual stress appears on the ground surface in the grind-hardening process. This paper proposes a new grind-hardening technology using thermal compensation. The workpiece of AISI5140 steel is preheated by electric resistance heating, and ground under the condition of the workpiece temperature 25°C, 120°C, 180°C and 240°C. The grinding force, harden layer depth and surface quality including residual stress on ground surface, surface roughness and micro-hardness are investigated. The experimental results show that a deep harden layer with a fine grain martensite can be obtained with the thermal compensation. The ground workpiece surface produces a certain compressive residual stress, and the residual compressive stress value increases with preheating temperature. As the preheating temperature increases, grinding force slightly decreases, while there is slightly increment of surface roughness. Compared with the conventional grind-hardening process, both the harden layer depth and residual stress distribution are significantly improved.

     

Grinding wheel effect in the grind-hardening process

The grind-hardening process is based on the utilization of the generated heat in the grinding zone for inducing a metallurgical transformation on the surface of the ground workpiece. The workpiece surface is locally heated above the austenitization temperature and subsequently is quenched to increase surface hardness. A theoretical model was developed for the prediction of the heat-generation rate as a function of the process parameters and the grinding wheel characteristics. The model combined with a database of relationships among the heat entering the workpiece, the process parameters, and the hardness penetration depth (HPD), which was presented by the authors in an earlier publication, allows the assessment of the grinding wheel’s effect characteristics on the hardening output of the process. The experimental results have verified the predictions of the theoretical model and served for its calibration.     

基于分段变磨削力的磨削强化层仿真

分析了磨削强化工艺过程中实际磨削时间以及磨削过程中磨削力的变化规律,提出了分段变磨削力磨削温度仿真方法来预测磨削强化层深度分布。首先对磨削力进行离散,计算相应的热流密度;然后将热流密度按砂轮与工件实际接触长度依次施加到工件的磨削表面,对工件磨削过程中的温度场进行仿真分析,得到了磨削强化层的分布;最后将所提出仿真方法与实验和传统仿真方法进行了比较分析。结果表明,基于分段变磨削力仿真可以更准确地预测工件沿磨削方向的磨削强化层分布。     

磨削淬硬技术研究现状及其展望

磨削淬硬技术是一种绿色表面淬火技术,该技术视磨削热为积极因素,主动利用磨削热对工件表面进行热处理,使工件表层发生马氏体相变,达到与表面强化处理一样的性能.对磨削淬硬技术的研究现状进行总结,指出存在的问题.提出磨削淬硬技术的发展方向和展望.     

Cooling in grind-hardening operations

The grind hardening process utilizes the heat dissipation in the grinding area for inducing metallurgical transformation on the surface of the ground workpiece. The workpiece surface is selectively heated above the austenitisation temperature and subsequently is self-quenched so as to achieve the anticipated surface hardening. In order for self-quenching to occur sufficient material mass must be present to conduct the heat away from the surface. However, in the case of grind-hardening of thin workpieces or cylindrical workpieces of small diameter, the quenching has to be assisted with the application of coolant fluid. In this paper, the utilization of the coolant fluid for the grind-hardening of small diameter cylindrical parts is investigated. The rapid heating of the workpiece and the short austenitising time are taken into consideration both for the estimation of the hardness profile and the hardness penetration depth (HPD). A finite element analysis (FEA) model is developed for this specific case and its predictions are verified experimentally.     

A hybrid of theory and numerical simulation research for virtual rolling of double-groove ball rings

The analytical thermal model of the grinding process is an important tool for predicting temperature to minimize workpiece thermal damage while improving process efficiency. As more and more numerical models are developed for the grinding temperature research, the established analytical model can be validated with numerical method. A new analytical thermal model of arc moving heat source for rectangular workpiece is deduced, and the temperature distribution results of this analytical model are compared with a validated numerical model. A principle based on the influences of parameters on the analytical and numerical results is proposed for comparing the analytical and numerical model. The comparison result shows that the temperature distribution results agree well on the contact surface, and there are few errors on the finished surface; the significant errors only appear at the boundary between different areas. The established analytical model is validated by the comparison result and can be used for further research about the heat transfer in surface grinding by cup wheel.     

一维斜向超声振动辅助磨削滚动轴承钢工艺及试验研究

针对目前只有一维轴向、一维切向等振动方向不变的一维超声振动辅助磨削的情况,首次提出了一维斜向超声振动辅助磨削工艺方法。利用MATLAB对一维斜向超声振动辅助磨削磨粒的运动轨迹进行了模拟分析。建立了超声振动试验系统的动力学模型。通过对超声振动工作台的模态分析,研制了一维斜向超声振动辅助磨削试验系统,对不同角度下超声振动辅助磨削滚动轴承钢的磨削力及表面粗糙度值进行了研究,探究了磨削力及表面粗糙度值随超声振动方向的变化规律。多次试验结果表明,超声振动角度为67.5°附近的表面粗糙度值明显优于其他角度的表面粗糙度值,磨削力也有减小。对正交试验结果的极差分析得出：当超声振动角度为67.5°、砂轮速度为20m/s、工件速度为0.5m/min以及磨削深度为4μm时,加工后的工件表面粗糙度达到最低值,其中工件速度是影响表面粗糙度的最重要工艺参数。     

Residual stresses due to a moving heat source

An analytical model based on finite element method is presented for determination of the residual stresses of thermal and mechanical origin due to surface grinding process. The temperature field within the workpiece is determined as the quasi-steady state temperature distribution due to the moving heat source. An iterative procedure is employed for evaluation of the step-by-step movement of the temperature field and the force, in order to simulate the movement of the grinding wheel over the workpiece. Computation of the elastic-plastic stress history culminates in the residual stress state of the workpiece. Influence of the magnitude of mechanical force, the rate of heat input and the speed of movement of workpiece on the residual stress distribution, are discussed.     

Selections of working conditions for creep feed grinding. Part(I)–thermal partition ratios

A thermal model focused on the heat transfer to the fluid, workpiece and grain is developed for creep feed grinding. In this model, the conduction effect in the moving direction of the workpiece is considered which is found to be very significant especially for creep feed grinding. Moreover, the thermal partition ratios to the workpiece, fluid and grain are well defined and discussed. The results reveal that the cooling effect of the fluid is more crucial especially at larger grinding depth and smaller workpiece speed. Furthermore, the promotion of the wheel speed is helpful to reduce the fraction of heat entering the workpiece. Also, the workpiece thermal partition ratio is greatly influenced by the workpiece speed. Its value is even less than 5% as the workpiece speed is smaller than 4 mm/s. Comparing the thermal partition of wet grinding to that of dry grinding, the abrupt increase of heat entering the wheel and workpiece due to the occurrence of boiling in the fluid is verified.