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.     

神经外科颅骨磨削温度场预测新模型

基于恒定热流密度的温度场理论计算值与实际温度值的误差较大,是当前磨削温度场理论研究的瓶颈。建立了不同冷却条件下的对流换热系数及材料内部的热传导模型,通过实时采集动态磨削力,利用高次高斯函数拟合建立了动态热流密度模型,并以此为基础建立了神经外科骨磨削温度场预测新模型。在干式磨削、喷雾式及纳米粒子射流喷雾式冷却条件下对骨磨削温度场进行了数值分析,并采用与人体颅骨力学性能最相近的新鲜牛股骨密质骨,采用羟基磷灰石纳米粒子及生理盐水进行了试验验证。结果表明,与试验测得温度值相比,采用基于恒定热流密度的温度场模型计算的温度值误差为18.8%,而采用新模型计算的温度值误差为6.6%,理论分析与试验结果吻合,即骨磨削温度场预测新模型更符合实际工况。     

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。     

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.     

Determination of the Partition Coefficient for the Grinding of a Hard WC-Co-Cr Coating with a Diamond Wheel

□ Determination of the partition ratio is fundamental to a thermo-mechanical approach to the grinding process. To establish the energy balance, accurate measurements and numerical modelling must be combined. In this work, such a method is applied to the grinding of a HVOF WC-Cr-Co hard coating. A double pole grindable thermocouple was developed to measure the temperature in the arc of cut, and its effective length. The heat flux absorbed by the workpiece is found by fitting the numerical solution to the temperature profile measured during the cooling phase, behind the contact. Identical results for the heat flux may be obtained by fitting the results to the analytical solution from moving heat source theory, but the maximum interface temperature is underestimated. A finite element solution, using MSC Marc software allows a closer approach to the maximum temperature measured at the interface during grinding, provided that the thickness of the coating is correctly modelled.     

基于FLUENT的热管砂轮换热能力仿真分析

采用CFD软件FLUENT建立了热管砂轮的三维有限体积传热模型,通过改变砂轮外圆面热流密度和砂轮转速,得出对应参数条件下热管砂轮的温度场分布,并分析各参数对砂轮换热能力的影响.仿真实验结果表明:随着热源面热流密度的增大,砂轮外圆面温度越高;在冷端条件一定的情况下,提高砂轮转速能降低砂轮外圆面温度.     

磨削温度信号的测量与分析

在磨削力的研究和磨削加工过程监控中都需要测量磨削温度。通过试验和理论计算,研究了磨削区的最高磨削温度及热电偶测温技术。试验采用对合金钢38MnSiVS6进行平面磨削加工,使用人工热电偶测量磨削接触区的最高温度。通过对测量温度值与理论计算值进行比对分析研究,发现试验结果与采用热模型理论的计算结果基本一致。研究结果还表明,热电偶结的大小对信号的可靠性和准确性有很大的影响。影响测量精度的其他因素还包括热电偶时间常数,高速流动的冷却液,信噪比的改善等。     

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.     

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.     

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.     

高效深磨中磨削温度和表面烧伤研究

介绍了一种高效深磨的磨削热模型——圆弧热源模型，该模型和直线倾斜平面模型相比改进了温度的预测；给出了圆弧热源磨削温度的积分公式和量纲一温度计算式；详细分析了热流量，推导了工件、砂轮、磨削液和磨屑的对流因子计算公式，在此基础上给出了最大接触温度的计算公式；使用J形热电偶测量了磨削接触面接近磨削烧伤时的最高磨削温度和磨削液沸腾的温度。实验结果与理论计算值对比表明，测量温度与理论计算温度有极好的一致性。     

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.     

Analysis of temperature distributions in surface grinding with intermittent wheels

An analytical model was established to calculate the curve of temperature distributions in surface grinding with intermittent wheels. In order to predict the numbers of the pulses imposed on the fluctuating temperature profile, a new quantity, the dynamic number of wheel segments in the grinding zone, was defined. The temperatures at the grinding zone were measured by using a foil thermocouple. It is found that the new quantity, the dynamic number of wheel segments, can be used to accurately predict the pulses on the measured temperature curves in the grinding zone. Through matching the calculated temperature curves with the measured results, it is found that the temperature profile is greatly dependent on the wheel segment-engaging states even at identical grinding parameters. However, the wheel segment-engaging states have little influence on the values of peak and valley temperatures.     

齿根过渡圆弧对全齿槽成形磨削温度和残余应力影响的研究

在齿轮全齿槽成形磨削过程中,考虑相邻三个热源（齿底热源、过渡圆弧热源、齿廓热源）的耦合效应,建立了磨削温度场的三维有限元仿真模型,计算了全齿槽成形磨削温度,并在此基础上,采用基于热-结构耦合的有限元方法计算了磨削引起的残余应力,分析了磨削温度场和残余应力场的分布特征,以及齿根过渡圆弧的大小对磨削温度和磨削后齿根处残余应力分布的影响。结果表明,过渡圆弧半径对磨削温度的影响相对较小,但对齿根处残余应力的影响较大;与没有过渡圆弧的齿槽相比,当过渡圆弧半径超过2 mm时,磨削后齿根最大残余应力降低20%以上。实验测量结果与有限元仿真结果一致,证明了模拟结果的正确性。     

微量润滑平面磨削接触区换热机理的研究

磨削接触区材料去除厚度是不一致的,同时,在微量润滑过程中,雾滴之间的运动特征存在差异且易受其他因素的影响,致使整个接触区的磨削温度分布呈现出非线性,换热机理也异常复杂。从雾化机理出发,对影响换热效果的两个关键因素--雾滴直径和雾滴速度进行了分析。依据雾滴在不同壁温处表现出的不同换热特性,将磨削区划分为无沸腾换热、核态沸腾换热、过渡沸腾换热和稳定膜态沸腾换热四个不同的换热区域,建立了微量润滑磨削区的换热系数数学模型。在此基础上,运用有限元技术对微量润滑磨削表面的温度场进行了仿真分析,采用单级热电偶技术测量了磨削温度,发现磨削区仿真温度值与实验测量值吻合较好,表明通过该理论获得的微量润滑磨削表面换热系数是可信的。     

板坯结晶器传热与变形的非均匀性

结晶器的传热和变形是导致连铸坯表面缺陷及裂纹的重要因素。基于宽厚板连铸结晶器在线监控系统实测数据,建立针对实测温度的结晶器传热反问题模型,反算迭代结晶器铜板的热流与温度分布,以此为基础,将反算热流和温度施加于热-弹塑性力学模型,模拟和分析实际浇注过程中铜板传热与变形的分布特征。结果表明,结晶器温度分布呈现出明显的非均匀性,传热沿浇注方向体现出继承倾向。铜板的最大变形在宽面中心附近,变形沿中心向两侧角部逐渐减小。浇注过程中,铜板宽度方向上的变形与温度分布趋势接近,并随着电偶实测温度的波动而变化。将实测与模拟相结合的数值分析方法,能够如实反映结晶器过程的非均匀特征,为预测裂纹、优化工艺等提供借鉴和参考。     

Cutting heat dissipation in high-speed machining of carbon steel based on the calorimetric method

The cutting heat dissipation in chips, workpiece, tool and surroundings during the high-speed machining of carbon steel is quantitatively investigated based on the calorimetric method. Water is used as the medium to absorb the cutting heat; a self-designed container suitable for the high-speed lathe is used to collect the chips, and two other containers are adopted to absorb the cutting heat dissipated in the workpiece and tool, respectively. The temperature variations of the water, chips, workpiece, tool and surroundings during the closed high-speed machining are then measured. Thus, the cutting heat dissipated in each component of the cutting system, total cutting heat and heat flux are calculated. Moreover, the power resulting from the main cutting force is obtained according to the measured cutting force and predetermined cutting speed. The accuracy of cutting heat measurement by the calorimetric method is finally evaluated by comparing the total cutting heat flux with the power resulting from the main cutting force.     

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。     

Evaluation of heat partition in machining CFRP using inverse method

An inverse heat conduction method was used to determine the energy balance at the cutting zone in edge trimming of carbon fiber-reinforced polymer composites. Three-dimensional transient heat conduction problem was modeled and solved independently in Abaqus for both the workpiece and cutting tool. Temperatures at specific locations were also measured during cutting using thermocouples and infrared thermography. Minimizing the difference between measured and calculated temperatures allowed the estimation of the heat flux applied in each problem. The total electric power consumed in machining was also measured. The heat partition was determined from the measured and calculated energies to be 0.07, 0.56 and 0.37 for the workpiece, tool and chips, respectively. The temperature distribution in the workpiece indicated that heat penetration is shallow due to poor thermal conductivity. It was also found that the extent of estimated machining thermal damage in the workpiece is within 0.35?mm below the machined surface.