Quadratic curve heat flux distribution model in the grinding zone

In order to estimate temperature distribution and the influence of grinding parameters on grinding temperature in the grinding zone, a theoretical model used for calculating and simulating the grinding process must be established. Many simplified heat source models developed previously have some errors compared with the actual heat flux to the workpiece. Therefore, based on the triangular heat flux distribution model and temperature distributions measured, an inverse method for the heat transfer mechanism in the grinding zone was investigated and a quadratic curve heat flux distribution model was developed to determine the heat flux distribution and predict the surface temperature of the workpiece. From the theoretical expression of heat flux to the workpiece, it has been found that the quadratic curve heat flux is the superposition of square law heat flux, triangular heat flux, and uniform heat flux in the grinding zone. By comparison of theoretical analysis with the experimental results, it has been demonstrated that the solution using a quadratic curve heat flux can improve the grinding model by decreasing the error, although the uniform and triangular heat fluxes can explain the condition of the heat flux to the workpiece along the grinding zone.     

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.     

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.     

磨削淬硬温度场的数值模拟

根据磨削比能、传热学等理论建立了磨削淬硬温度场的有限元模型,借助有限元软件Ansys对40Cr钢磨削温度场及工件的冷却速度进行了研究,得出了工件磨削温度场。最后通过不同工艺参数下的工艺试验与Ansys计算值进行了对比。结果表明,使用Ansys和试验值是吻合的,说明使用有限元方法模拟工件表面温度场是可靠和可行的。     

Numerical and experimental studies on the temperature field in precision grinding of SiCp/Al composites

During precision machining of SiCp/Al composites, the temperature of the workpiece surface directly affects the machining quality. In this paper, a triangle heat source model was used to calculate the heat flow during grinding of SiCp/Al composites, then, a three-dimensional finite element method was employed to investigate the temperature distribution at different process parameters, i.e., grinding depth and feed speed of the worktable. In addition, the temperature measures using embedded thermocouple were applied to compare with predictions from the thermal model. The results indicate that the grinding temperature predicted by the finite element method agrees well with the experiment data, and the triangle heat source model was suitable for estimating the workpiece temperature of precision grinding.     

Force modeling of microscale grinding process incorporating thermal effects

Grinding at the microscale is an essential process in view of its competitive edge over other processes in the fabrication of micro-sized features and parts. The quality of the parts produced by the microscale grinding process can be influenced by various factors related to the mechanical forces induced. Therefore, the predictive modeling of microscale grinding in the context of forces is useful to provide guidance for further development and optimization of this process. In this study, a new model to address mechanical and thermal interactions between the workpiece and an individual single grit on a microscale grinding wheel was developed. This developed model integrates the ploughing and associated friction effects and a moving heat source on the micro-grinding zone under given machining conditions to estimate the thermal effect in microscale grinding process. The ratio of heat partition into the workpiece in the thermal model was also experimentally calibrated using embedded thermocouple measurement followed by analytical calculations. This model quantitatively predicts microscale grinding forces incorporating material properties as functions of strain, strain rate, and temperature. In order to verify this developed model, the experiments based on a surface microscale grinding setup were performed for changing depths of cut. In addition to this, the sensitivity analysis of this model behavior was conducted to identify main effective factors. A comparison between the experiment data and predictions shows that the force model captures the main trend of the microscale grinding physics within the computed range of parameters.     

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.     

Simulation of thermal stresses due to grinding

An efficient finite element procedure has been developed to calculate the temperatures and stresses arising due to a moving source of heat. The procedure is applied to calculate the thermal stresses produced in hardened steels during grinding. The thermal load during grinding is modeled as a uniformly or triangularly distributed, 2D heat source moving across the surface of a half-space, which is insulated or subjected to convective cooling. The grinding of elastic and elastic–plastic workpiece materials has been simulated. The calculated transient stresses and temperatures in an elastic solid are found to be in good agreement with prior analytical and numerical results. In an elastic–plastic workpiece material, for which no analytical solution is available for the residual stress distributions, the finite element calculations show that the near surface residual stress is predominantly tensile and that the magnitude of this stress increases with increasing heat flux values. Based on an analysis of the effects of workpiece velocity, heat flux magnitude and convective cooling, on the residual stress distributions in an elastic–plastic solid, it is seen that the calculated thermal stress distributions are consistent with experimentally measured residual stresses on ground surfaces. Furthermore, the results explain often cited observations pertaining to thermally induced grinding stresses in metals.     

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.     

磨削温度场的有限元模拟及仿真

金刚石砂轮磨削结构陶瓷过程中,所产生的磨削热是影响工件表面质量的关键因素之一,而磨削参数对工件表层温度分布有重要影响。本文采用有限元法,通过两种陶瓷材料对比分析,运用ANSYS软件对磨削温度场进行了仿真研究,利用仿真模型对影响因素作了分析。     

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。     

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.     

加压内冷却砂轮的研制及磨削性能研究

针对高温合金材料在磨削加工过程中存在磨削烧伤问题,为避免气障效应并强化冷却液在磨削弧区的换热效果,提出采用加压式内冷却断续磨削方法。利用数值模拟方法和3D打印技术对砂轮基体、加压内冷却系统和密封结构等进行设计和验证,制备了用于平面磨削的加压内冷却开槽CBN砂轮。在相同的磨削加工参数条件下,使用加压内冷却方法与外部喷射冷却方法进行镍基高温合金磨削对比试验,分析了砂轮速度、磨削深度和工件进给速度等加工参数对磨削温度、加工表面粗糙度和表面形貌的影响规律,验证了加压内冷却断续磨削方法对磨削弧区的强化换热效果。结果表明：在相同试验参数条件下磨削镍基高温合金,加压内冷却法比外部喷射冷却法的换热效率更高,得到的磨削温度更低,表面粗糙度更小,加工表面更为光滑细腻。     

Study on the convection heat transfer coefficient of coolant and the maximum temperature in the grinding process

Grinding fluid is typically applied in order to achieve reduced surface grinding temperatures, improved workpiece surface integrity, and extended wheel life compared to that which can be achieved in the dry situation. This paper presents the results of an investigation concerned with methods to determine the value of the convection heat transfer coefficient. The work is based on the theory of fluid dynamics and heat transfer that are used to describe the heat transfers within the grinding zone under different grinding conditions. The simulation research is made by means of the FEM for the wet grinding temperature distribution, and the three-dimensional topology map of the temperature distribution is obtained. Temperature is measured with the clamped thermocouple in different grinding conditions. The experimental result is approximately suitable to the simulated result. The simplicity and accuracy of the method allow the application to a wide range of grinding regimes from shallow-cut to high-efficiency deep grinding.     

叶序排布磨粒对砂轮的磨削温度场效应

在砂轮磨削过程中,磨削热影响工件表面完整性,而磨粒排布是影响磨削温度场的重要因素之一。针对磨粒叶序排布的砂轮,采用有限元法对磨削温度场进行了计算模拟分析,获得了叶序系数对工件磨削温度场的影响规律。研究结果表明,随着叶序排布系数的增大,被磨工件的表面温度和温度梯度减低。     

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.

     

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.     

Analytical modeling of grinding wheel loading phenomena

Wheel surface condition plays an important role in the grinding operation. Grinding wheel loading, meaning chip accumulation in the space between grains, leads to deteriorating wheel cutting ability and causes excessive force and temperature. This paper presents an analytical model of wheel loading phenomena as a function of cutting parameters, wheel structure, and material properties. The model is based on the adhesion of workpiece material to abrasive grain surface. It is validated by experimental results from grinding nickel-based superalloy with cubic boron nitride vitrified wheel. This model considers wheel specifications including abrasive grains size and the number of cutting edges. Cutting parameters and process temperature are the other determinant factors. On the basis of this model and empirical results, the effects of the various process parameters are presented.     

磨削淬火技术中温度场的理论研究

磨削淬火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。本文采用倾斜移动热源模型对工件温度场进行了理论计算并与Jeager移动热源模型进行了比较;分析了各加工参数对工件表面最高温度的影响;利用实验研究验证了理论分析结果。研究结果表明,在磨削淬火技术中,采用倾斜移动热源模型,可提高磨削淬火技术温度场的预测精度。