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。     

基于传热反算建立磨削三维热模型的新方法

首先使用热电偶测量平面磨削时CBN砂轮与工件接触区下方处不同位置点温度;然后基于传热反问题理论,优化实际测量温度值与理论仿真温度值间的目标函数,反算出进入工件的热量,从而得出进入工件的能量比例;最后建立磨削三维热模型,计算出不同磨削时刻工件表面温度。实验结果表明,CBN砂轮进入工件的能量比例与实际值相吻合,基于传热反算方法建立磨削三维热模型具有可行性。     

General temperature rise solution for a moving plane heat source problem in surface grinding

In the present study, the general solutions for a transient state as well as for the temperature rise formed everywhere in the workpiece due to a rectangular-shaped moving plane heat source arising at the grinding zone are derived. The present analysis starts from a point heat source solution by applying the method of separation of variables to a three-dimensional heat conduction problem. Because the workpiece moving velocity is quite small, the convective term related to the workpiece velocity is first excluded from the heat conduction equation. This workpiece velocity effect will be included in the model by slightly modifying the coordinate variable in the sliding direction shown in the solution of the point heat source. Therefore, the general three-dimensional solution of the stationary temperature rise can be expressed in an integral form as a function of the product value of the unknown initial condition and the particular solution of temperature rise. The unknown initial temperature rise in the solution can be replaced by the point heat source due to frictional that multiplying the product of the Dirac delta functions defined for three directions. Using the definition of the Dirac delta function, the temperature rise solution for a point heat source can thus be obtained. This solution is further extended to obtain the moving and uniform heat sources arising in a rectangular grinding zone. A comparison among the experimental result and the theoretical results predicted by the present model and Jaeger’s model [Jaeger JC (1942) Proc Roy Soc, NSW 76:203–224.] show that the present model is quite accurate and is generally superior to Jaeger’s model; it can be applied to predict the three-dimensional temperature rise distributions in the workpiece.     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

TEMPERATURE DISTRIBUTION DURING ELECTRO-DISCHARGE ABRASIVE GRINDING

The objective of this work is to develop a finite element method (FEM) based mathematical model to simulate the hybrid machining process of grinding and electric discharge machining (EDM), named as Electro-discharge abrasive grinding (EDAG), for temperature distribution in the workpiece. Two different finite element codes have been developed to calculate the temperature distribution due to grinding heat source and EDM heat source separately. The transient temperature field within workpiece due to cut-off grinding is determined due to moving rectangular heat source. Gaussian heat distribution of power within a spark has been considered in the calculation of temperature distribution due to EDM. Temperature distribution in the workpiece due to combined process is obtained by using superposition. The simulation shows a sudden rise in temperature at the spark location. The predicted results can be used for calculation of thermal stresses, which play a major role as far as high-quality product requirements are concerned.     

Investigation of a heat pipe cooling system in high-efficiency grinding

The high grinding temperature is one of the problems restricting on the further development of high-efficiency grinding due to the workpiece burnout and excessive wheel wear. An original method about enhancing heat transfer in the contact zone based on heat pipe technology is put forward to reduce the grinding temperature in this paper. Drawing on the structure of rotation heat pipe, one heat pipe cooling system, heat pipe grinding wheel (HPGW) applied to high-efficiency grinding, is developed and its heat transfer principle is illustrated. Besides, the cooling effect in the contact zone using HPGW is simulated through a three-dimensional heat transfer model in grinding, and the influence of different parameters of the wheel speed, cooling condition, and heat flux input on the grinding temperature is analyzed. Eventually, preliminary grinding experiments with HPGW were carried out to verify the cooling effect by comparing with non-HPGW in grinding of 0.45 wt.% C steel and titanium alloy Ti-6A1-6V. Results show that using HPGW can significantly reduce the grinding temperature and prevent the burnout.     

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。     

硬质合金磨削温度场的仿真与试验研究

在硬质合金磨削中,磨削能大部分转化为热量,导致磨削区温度升高,出现磨削烧伤和磨削裂纹等磨削缺陷问题。利用ANSYS中的载荷加载法以及单元生死技术对磨削过程进行温度仿真分析,得到硬质合金磨削温度场的整体分布规律,研究了不同工况条件下磨削区和已加工表面的温度变化。将仿真结果与试验测得结果进行对比,两者结果具有很好的一致性,说明采用仿真对磨削温度进行预测是可行的,随着工件进给速度的增大,仿真温度与试验温度越相近。根据仿真温度,可以更好地减少磨削缺陷,提高工件加工质量。     

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。     

开槽砂轮缓进给深切磨削时工件表层温度场解析

采用热源法推导出开槽砂轮缓进给深切磨削时磨削弧区工件表层温度分布的理论解析式，并利用理论计算公式结合磨削实验完成了施加水射流冲击条件下工件表层温度场的推演计算，计算结果与实验结果基本吻合，证实了开槽砂轮辅以弧区定向高压水射流冲击强化换热的确具有良好的冷却效果。     

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.     

Theoretical Analysis of Thermal Stresses in Electro-discharge Diamond Grinding

Excessive heat generated at the machining zone, during Electro-discharge diamond grinding (EDDG), is the major cause of thermal stresses, untempered martensite, overtempered martensite, and cracks. Therefore, the key to achieve good surface integrity in a machined part is to prevent excessive temperature and thermal stresses generated during machining process. A finite element model has been developed to estimate thermal stresses during EDDG when the current is switched-off. First, the developed code calculates the temperature in the workpiece and then the thermal stress field is estimated using this temperature field. Computations were carried out in plane strain condition for different down feeds of the grinding wheel. The effects of time of grinding and feed on thermal stress distribution have been reported. The thermal stresses are found to be higher near top surface at initial time of grinding but shifted away towards bottom after some grinding time.     

NUMERICAL SIMULATION AND EXPERIMENTAL VALIDATION OF THE TEMPERATURE FIELD IN SURFACE GRINDING

Three-dimensional numerical simulations are carried out to investigate the temperature field in the contact zone due to the thermal loading of the workpiece in surface grinding. This technique considers that the thermophysical properties of the workpiece material are non-linear according to temperature, the contact zone between the wheel and the workpiece is assumed as an arc surface, and the heat flux entering the workpiece is assumed as proportional to the local undeformed chip thickness. A good agreement is found between the simulated results and the experimental observations. The high grinding temperature leads to the thermal expansion of the workpiece material, which causes the thickness of the actual material removal layer to be larger than the cutting depth. The grinding temperature at the central portion is higher than that on the side of the workpiece during the wet grinding, thus the material removal layer in the central zone is thicker than that on the side zone, and the workpiece surface is concave across the grinding width.     

Force and thermal effects in vibration-assisted grinding

Because it reduces forces and temperatures, vibration-assisted grinding has the potential to improve the feasibility of dry grinding. This paper presents an experimental study of force and temperature effects in dry and wet grinding at vibration frequencies below ultrasonic. Based on a moving line heat source model, heat flux quantities were estimated from subsurface temperature measurements. Reductions in force of up to 30 % were observed for dry grinding with 2,360 Hz vibration assistance. For the same condition, heat flux into the workpiece reduced by 42 %. The paper presents evidence that vibration assistance has a beneficial effect on the convective heat transfer rate.     

Temperature distribution in the workpiece due to plane magnetic abrasive finishing using FEM

A mathematical model is developed for the prediction of magnetic potential using Maxwell’s equations and finite element method is used to find the magnetic potential distribution within the gap between tool bottom surface and workpiece top surface. From magnetic potential model, the magnetic pressure developed and corresponding heat flux generated on workpiece surface are evaluated. Further a mathematical model is developed for heat transfer in the workpiece and again finite element method is used for the prediction of temperature rise in the workpiece. The effects of various operating input parameter on magnetic potential distribution in the gap and temperature rise in the workpiece has been studied.     

An experimental investigation of temperatures and energy partition in grinding of cemented carbide with a brazed diamond wheel

An experimental investigation is reported of the temperatures and energy partition in the grinding of cemented carbide with a vacuum brazed diamond wheel. During the experiments, the temperature distributions along the workpiece surface were measured using a sandwiched foil thermocouples and the energy partition to the workpiece estimated using a temperature matching method. The effects of the various grinding conditions, including wheel velocity, feed rate, and depth of cut, on the temperatures and the energy partition were investigated. The measured temperature responses were found to be in good relation with the analytical results of a moving heat source with a triangular distribution at the grinding zone. It was found that the grinding temperatures measured under different grinding conditions varied from 10°C to 100°C. The energy partition to the workpiece in dry grinding was found to be from 35% to 70%. Based on the energy partition values obtained from the experiments, the diamond tip temperature was calculated and found to be over the temperature necessary for the graphitization of diamond if the circular grain contact of radius is smaller than a critical value.     

A NEW TECHNOLOGY ON ENHANCING HEAT TRANSFER AT GRINDING ZONE THROUGH JET IMPINGEMENT DURING CREEP FEED GRINDING

This paper presents a jet-impingement technology to enhance heat transfer at the grinding zone. The jet-impingement technology uses a new apparatus developed to spray grinding fluid onto the workpiece surface at the grinding zone from the radial holes of an electroplated CBN wheel. Because the fluid is sprayed normally on the workpiece surface at the grinding zone, the heat transfer to the fluid is significantly improved as compared to the conventional fluid delivery methods. Experimental results, obtained under both imitated grinding tests and actual creep-feed grinding of titanium alloys, show that the jet-impingement technology lowers grinding temperature significantly. Much higher material removal rates are possible with jet-impingement without workpiece burn.     

Depth of thermal penetration in straight grinding

Unlike the usual numerical FEM approach to determine the thermally affected layer during the grinding process, we propose a simple analytical approach to estimate the depth of thermal penetration. For this purpose, the one-dimensional definition of depth of thermal penetration is applied to the two-dimensional heat transfer models of straight grinding. A method for computing the depth of thermal penetration in these two-dimensional models is derived and compared to the one-dimensional approximation. For dry grinding, it turns out that the one-dimensional approximation is quite accurate when we consider a moderate percentage in the temperature fall beneath the surface, regardless the type of heat flux profile entering into the workpiece (i.e., constant, linear, triangular, or parabolic). In wet grinding, the latter is true if we consider a constant heat flux profile and a high Peclet number, i.e., Pe >?5. Finally, the one- and two-dimensional approaches calculating analytically the depth of thermal penetration have been compared to the temperature field numerically evaluated by a three-dimensional FEM simulation given in the literature, obtaining a quite good agreement.     

Effects of the heat source profiles on the thermal distribution for ultraprecision grinding

In order to investigate the thermal effects on the workpiece during ultraprecision grinding processes, an analytical thermal model is firstly developed. Based on the established model, both the steady-state and the transient temperature distributions are obtained and the effects of the grinding parameters on the temperature distribution are analyzed. Various heat source profiles are utilized to simulate diverse ultraprecision grinding conditions, and the effects of the parameters of the heat source on the temperature distribution are investigated. The developed thermal model and analysis results provide further insights of the temperature distributions for ultraprecision grinding processes.     

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.