Cycle optimization in cam-lobe grinding for high productivity

Cycle optimization in cam-lobe grinding is presented for improving productivity. It includes novel modeling of the instantaneous geometry, kinematics and temperature for any workpiece form. A technical assessment of three process-control strategies – (1) constant specific material removal rate, (2) constant power, and (3) constant temperature – is made. The constant-temperature process provides the shortest cycle time without thermal damage. A detailed analysis of this process considers the role of machine limitations, including maximum speed, acceleration, and jerk, as well as the cam-lobe geometrical effects. The optimization results are validated by grinding tests in an actual production line.     

平面磨削中工件温度场的直接测温

平面磨削中工件温度场采用红外成像的电荷偶合装置(CCD)测量。在高空问、瞬时条件下红外辐射(IR)温度测量一直是沿磨削试件一侧进行测定试件表面和次表面的温度。用斜面磨削的方法，使磨削深度持续增加，获得了随材料磨除率而改变的磨削温度的变化。这些测量结果与用传统的恒磨除率磨削试验具有良好的相关性。确定了最高温度的位置和值，包括温度梯度。讨论了确定磨削热模型测量的含意及工件的烧伤苗头的预测。     

超声振动辅助缓进给磨削温度场仿真与试验分析

目的通过对比研究磨削过程中超声振动辅助缓进给磨削工件表面的温度变化,验证超声振动对磨削热的影响,为进一步研究磨削机理提供依据。方法基于磨削温度场解析模型,建立了磨削热源平均强度。运用ANSYS软件热分析模块分别对普通缓进给磨削和超声辅助缓进给磨削进行了工件表面温度场仿真,得到了不同载荷步的温度场分布以及工件表面的温度时间变化曲线,较准确地反映了磨削工件时工件表面的温度变化。结果试验和模拟表明,缓进给磨削工件时,工件表面温度较高,对工件施加超声振动后,能够有效降低磨削力,减少磨削过程中产生的热量,降低工件表面温度20%左右。结论超声振动辅助磨削工件时,由于工件高频振动导致磨粒与工件间断性接触,使磨削过程变为有规律的脉冲状断续磨削,有利于工件散热,降低了磨削温度,为避免缓进给磨削时容易出现的磨削烧伤现象提供了技术支持。     

On the mechanics of the grinding process, Part III—thermal analysis of the abrasive cut-off operation

This is Part III of a 3 part series on the Mechanics of the Grinding Process. Part I deals with the stochastic nature of the grinding process, Part II deals with the thermal analysis of the fine grinding process and this paper (Part III) deals with the thermal analysis of the cut-off operation. Heat generated in the abrasive cut-off operation can affect the life of resin bonded grinding wheels and cause thermal damage to the workpiece. Thermal analysis of the abrasive cut-off operation can, therefore, provide guidelines for proper selection of the grinding conditions and optimization of the process parameters for improved wheel life and minimal thermal damage to the workpiece. In this investigation, a new thermal model of the abrasive cut-off operation is presented based on statistical distribution of the abrasive grains on the surface of the wheel. Both cutting and ploughing/rubbing that take place between the abrasive grains and the work material are considered, depending on the depth of indentation of the abrasives into the work material. In contrast to the previous models, where the apparent contact area between the wheel and the workpiece was taken as the heat source, this model considers the real area of contact, namely, the cumulative area of actual contacting grains present at the interface as the heat source. It may be noted that this is only a small fraction of the total contact area as only a small percentage of the abrasive grains present on the surface of the cut-off wheel are in actual contact with the workpiece at any given time and even a smaller fraction of them are actual cutting grains taking part in the cut-off operation. Since, the Peclet number, N_Pe in the case of cut-off grinding is rather high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source with the same heat liberation intensity as the circular disc heat source. However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the wheel-work interface, for a longer period of time ( milliseconds) whereas the workpiece contacts the heat source for shorter period of time ( a few microseconds). The temperature in the grinding zone is taken as the sum of the background temperature due to the distributed action of the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip-workpiece interfaces (local thermal analysis), similar to the work reported in the literature [Proc Roy Soc (London) A 453 (1997) 1083]. The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The model developed provides a better appreciation of the cut-off operation; a realistic estimation of the heat partition between the wheel, the workpiece, and the chip; thermal gradients in the workpiece due to abrasive cut-off operation, and an insight into the wear of the cut-off wheels.     

On the mechanics of the grinding process, Part II—thermal analysis of fine grinding

Thermal analysis of fine grinding is conducted taking into consideration the stochastic nature of the distribution of abrasive grains and its role under fine grinding (dry) conditions to determine the grinding temperatures and the heat partition at the contacting interface. The analysis considers the grain–workpiece interactions at the local level and the wheel–workpiece interactions at the global level. The workpiece temperature in the grinding zone is taken as the sum of the background temperature due to distributed action of all the previous active grains operating in the grinding zone (global thermal analysis) and the localized temperature spikes experienced at the current abrasive grain tip–workpiece interfaces (local thermal analysis), similar to the work reported in the literature. Since the Peclet number, N_Pe, in the case of fine grinding is very high (a few hundred), the heat flow between the work and the contacting abrasive grains can be considered to be nearly one-dimensional. In this paper, we consider the interaction between an abrasive grain and the workpiece at the contact interface. Consequently, the heat source relative to the grain is stationary and relative to the workpiece is fast moving. The interface heat source on the grain side as well as on the workpiece side is equivalent to an infinitely large plane heat source (with the same heat liberation intensity as the circular disc heat source). However, it will be shown in the paper that the contacting times are different. For example, the abrasive grain contacts the heat source, as it moves over the interface, for a longer period of time (˜milliseconds) whereas the workpiece contacts the heat source for a shorter period of time (˜a few microseconds). The equivalent thermal model developed in the present investigation is simple and represents the process more realistically, especially the heat partition. The analytical results reported here are found to be in good agreement with both the analytical and experimental results reported in the literature by other researchers.     

磨削硬化深度预测

磨削硬化是利用磨削过程中产生的热、机械复合作用直接对工件进行表面淬火的新工艺。通过建立磨削温度三维分析模型和热金属效应分析,实现磨削硬化加工工件硬度的预测。基于瞬时温度分布和运动非稳定三维热传导微分方程,并考虑砂轮与工件及冷却液与工件交互作用时热传导情况和材料本身的热扩散,建立了磨削温度三维分析预测模型,结合对加工过程奥氏体相位比例的计算及珍珠岩、残余奥氏体和马氏体的转变等热冶金效应分析,得出磨削硬化加工后硬化深度,实现随加工参数变化的硬化深度分布预测。将此模型与有限元模型进行对比,并通过实验进行了验证。     

Temperatures in deep grinding of finite workpieces

This paper investigates the diverse thermal effects generated in high efficiency deep grinding (HEDG). Using a new thermal model of circular arc contact with transient analysis, the transient behaviour of the maximum contact temperature has been analysed for various grinding conditions. It is found that steady state conditions can be achieved for the conditions of sufficient workpiece length and high workspeeds. The effect is important for the understanding of the deep grinding process and for the prediction of satisfactory grinding conditions. HEDG conditions also have very apparent effects on the depth of heat penetration to the workpiece. The parameters investigated include mean contact angle, Peclet number and the heat source distribution. Experimental results are presented for specific energy, energy partition and mean temperature for high efficiency deep grinding.     

基于温度匹配法的平面磨削3D有限元仿真及试验

为了准确预测工件表面及亚表面不同深度的温度场变化,基于反热源原理,以实际测量的磨削温度为基础,采用温度匹配法建立适应真实磨削加工时接触区的热源模型。运用有限元法,仿真计算工件磨削温度场的变化,并与瑞利分布热源模型预测结果对比,对工件表面及亚表面不同深度磨削弧区的磨削温度场进行测量。结果表明:基于温度匹配法建立的热源模型模拟的表面及亚表面不同深度温度场与实测值具有很好的一致性,相对误差在3.0%～7.5%,比瑞利热源模型预测的温度场分布精度提高了近2倍。      

高效深磨中温度的理论分析

本文提出了高效深磨的热模型。该热模型中，工件与砂轮的接触用圆弧面表述。发现接触角和Peclet数对磨削区温度有很强的影响。发现材料去除率高而且无磨削烧伤。新热模型对接触区温度很准确的预测。还发现高效深磨中比磨削能很低。而磨屑带走了大部分热。同时，在磨削液被阻碍进入磨削区后，工件的温度急剧上升。     

凸轮型面摆动磨削残余应力有限元建模及分析

为分析摆动磨削工艺参数对表面残余应力的影响规律,基于热-力顺序耦合理论,建立基于温度场的凸轮残余应力有限元仿真模型,研究摆动频率、摆动幅度、砂轮线速度、磨削深度、工件转速、砂轮宽度、砂轮直径等工艺参数对凸轮型面残余应力的影响规律。结果表明：残余应力随工件转速、磨削深度、砂轮线速度的增加而增加,随砂轮宽度的增加先增加然后趋于平缓,随砂轮直径的增加而减少,随摆动频率与摆动幅度的增加而缓慢增加。     

A High Material Removal Rate Grinding Process for the Production of Automotive Crankshafts

In this paper the application of high efficiency deep grinding to cylindrical plunge grinding is demonstrated and thermal modelling used to optimise the grinding cycle for an automotive steel and cast iron. The benefits associated with the high work speed achievable in cylindrical grinding are highlighted and both thermal modelling and experimental measurements have established that low workpiece temperatures are possible even when specific material removal rates of 2000 mm³/mm.s are achieved. Surface integrity studies based on microstructural analysis and Barkhausen noise have also demonstrated the effectiveness of the process.     

Experimental and finite element analysis of temperature and energy partition to the workpiece while grinding with a flexible robot

Grinding processes performed with flexible robotic tool holders are very unlike conventional types of grinding because of low stiffness of the robot's structure. A special flexible robotic grinding process is used for in situ maintenance of large hydroelectric equipment for bulk material removal over large areas rather than as a finishing step, as is the case for most conventional grindings. Due to the low structural stiffness of tool holder, cutting is interrupted at each revolution of wheel during the grinding process. In this study, an investigation is carried out to determine the temperatures and energy partition to the workpiece for the above-mentioned flexible robotic grinding process by a three-dimensional finite element thermal model. Experiments were undertaken using embedded thermocouples to obtain the subsurface temperature at several points in the workpiece during the process. Then, energy partition to the workpiece was evaluated using a temperature-matching method between the experimental and numerical results. This ratio is used for predicting the temperature field at the wheel–workpiece interface with a relevant heat source function. Kinematics of cut and the flexible robot's dynamic behavior are considered in applying the heat input to the model. The energy partition to the workpiece in this specific flexible grinding process is found to be lower than for analogous conventional precision grinding processes. Two models, one from the literature and one from the power model of the process, are modified and proposed for determining the energy partition. The results showed that the energy partition ratio decreases by increasing the process power. Also, this ratio slightly decreases at higher feed speeds. In addition, lower temperatures were seen at higher powers due to the lower intensity of heat input over a larger contact area. Experimental observations show close agreement between simulated contact temperatures and measured results.     

Thermal Analysis of Grinding

Thermal damage is one of the main limitations of the grinding process, so it is important to understand the factors which affect grinding temperatures. This paper presents an overview of analytical methods to calculate grinding temperatures and their effect on thermal damage. The general analytical approach consists of modeling the grinding zone as a heat source which moves along the workpiece surface. A critical factor for calculating grinding temperatures is the energy partition, which is the fraction of the grinding energy transported as heat to the workpiece at the grinding zone. For shallow cut grinding with conventional abrasive wheels, the energy partition is typically 60%-85%. However for creep-feed grinding with slow workspeeds and large depths of cut, the energy partition is only about 5%. Such low energy partitions are attributed to cooling by the fluid at the grinding zone. Heat conduction to the grains can also reduce the energy partition especially with CBN abrasives which have high thermal conductivity. For High Efficiency Deep Grinding (HEDG) using CBN wheels with large depths of cut and fast workspeeds, preheated material ahead of the grinding zone is removed together with the chips, thereby lowering the temperature on the finished surface. Analytical models have been developed which take all of these effects into account. Much more research is needed to better understand and quantify how grinding temperatures affect the surface integrity of the finished workpiece.     

表面形貌对砂轮磨削流体压力与润滑的影响

目的从磨削液压力及润滑方面找到减少磨粒磨损、磨削热和降低工件表面粗糙度的方法。方法基于实际情况,将砂轮突出的磨粒分布函数和工件在磨削之前存在的粗糙度函数等效为余弦函数,对陶瓷结合剂CBN砂轮磨削45号钢而产生的流体压力和膜厚进行了分析。结果考虑砂轮和工件的表面粗糙度时,压力波动集中在中心区域,磨削区最大压力和最大膜厚明显增大。在考虑热效应的情况下,当两表面波长相等、幅值同时增大时,最大膜厚及平均膜厚增大,而幅值相等、波长增大时,润滑情况没有改善;当砂轮表面幅值波长相等且变大时,最大膜厚及平均膜厚增大,由此也可以得出当砂轮表面幅值波长不变,工件表面如此变化时结果相同;当两表面幅值和波长不相等且都成倍增大时,最大膜厚及平均膜厚增大。结论膜厚增大利于润滑时,能降低磨削温度,减少磨削烧伤和热变形,降低工件磨削后的表面粗糙度,减少非工作磨粒的磨损,减少砂轮修正次数,延长砂轮寿命。但是膜厚不会无限增大,因为磨削区域并不封闭,在实际工程中可依据此理论来确定最优解,优化磨削过程。     

Experimental study on grinding force and grinding temperature of Aermet 100 steel in surface grinding

This paper investigates grinding force and grinding temperature of ultra-high strength steel Aermet 100 in conventional surface grinding using a single alumina wheel, a white alumina wheel and a cubic boron nitride wheel. First, mathematical models of grinding force and grinding temperature for three wheels were established. Then, the role of chip formation force and friction force in grinding force was investigated and thermal distribution in contact zone between workpiece and wheel was analyzed based on the mathematical model. The experimental result indicated that the minimum grinding force and the maximum grinding force ratio under the same grinding parameters can be achieved when using a CBN wheel and a single alumina wheel, respectively. When the phenomenon of large grinding force and high grinding temperature appeared, the workpiece material would adhere locally to the single alumina wheel. Grinding temperature was in a high state under the effect of two main aspects: poor thermal properties of grinding wheel and low coolant efficiency. The predicted value of grinding force and grinding temperature were compared with those experimentally obtained and the results show a reasonable agreement.     

Geometric,kinematical and thermal analyses of non-round cylindrical grinding

This paper is concerned with the analyses of grinding geometry and kinematics in the grinding zone and develops a thermal model, along with a chip-thickness-dependent value of specific grinding energy into the workpiece. The grinding geometry and kinematics are modeled for arbitrary non-round workpiece forms. Unlike other models, which are based on a fixed, constant geometry, the model presented here is based on first principles using a fundamental, transient, non-constant geometry and thus constitutes a much-needed advancement in grinding technology. A novel experimental approach is also taken, which uses the specific grinding energy into the workpiece, rather than the total specific grinding energy coupled with an estimate of the energy partition, an estimate which previously has proven difficult to achieve accurately. The model is verified with experimental work and predicted temperatures are in reasonable agreement with temperatures associated with the onset of thermal damage, determined via metallographic examination and Barkhausen noise. Finally, some of the challenges of using Barkhausen noise to evaluate thermal damage are investigated, namely the differing response characteristics of stressed and overtempered material vs. rehardened material, and how these can be overcome in practice.     

Modelling of cutting induced workpiece temperatures for dry milling

A thermal model has been developed that predicts machining induced workpiece temperatures for peripheral milling. The model was developed to determine the magnitude and distribution of workpiece temperatures for dry milling of aerospace aluminium alloys. The analytical model incorporates elements of the physical nature of the metal cutting process with analytical approaches developed for grinding to produce a peripheral milling thermal model that is directly applicable to industry. Test and model results show that cutting induced workpiece heating reduces significantly as cutting speed and feedrates are increased. The research suggests that dry machining of aluminium should be carried out at high cutting speeds and feeds to minimise temperature rise in the workpiece.     

基于视觉技术的铸件打磨机器人设计

通过分析铸件毛坯现有打磨技术的劣势,提出自动扫描三维重构铸件模型,获取工件3D点云数据,然后根据打磨工艺自动规划路径并进行离线编程,获得机器人运动程序,最后按照工艺路径自动完成铸件打磨的工艺方案。在综合考虑成本、功能、力学及干涉等各方面因素的基础上,确定打磨装备的整体布局形式,并对专用恒力打磨机构、视觉系统等关键部件作了详细设计与阐述。利用现有的机械设备、工业相机及线激光组成的视觉系统对实验工件进行三维模型重构,结果显示:模型尺寸精度在±0.1 mm以内,扫描速度为1 000 mm/min。打磨实验显示:打磨后工件表面粗糙度值小于Ra6.3μm,整个打磨表面平整度也满足检测需要,单台设备打磨效率达到人工的10倍左右。     

Analysis of workpiece thermal behaviour in cut-off grinding of high-strength steel bars to control quality and efficiency

Cut-off grinding is a machining process for separating various components and materials. The application of this trimming technology for high-strength steel bars leads to thermally induced defects such as grinding burrs and residual stresses. By means of a developed and empirically validated FE model it is possible to control the temperature distribution in the workpiece. The implementation of a CBN grinding wheel along with the optimization of the cutting parameters allows a significant decrease of the thermal load in the machined bar. As a consequence, thermal defects are reduced, thus leading to a high-quality trimming process.     

THERMAL STUDY ON THE GRINDING OF GRANITE WITH SUPERABRASIVE TOOLS

Diamondabrasivetoolsareextensivelyusedintheprocessingofstone ,frominitialsawingtofinalfinishing .Infact,abrasiveprocessingofgraniteandmarbleforconstructionisthemostimportantfactorintheconsumptionofindustrialdiamond .Duringgrinding ,diamondabrasivegritsonthewheelsurfaceinteractwiththeworkpieceanddothecutting .Theenergyexpendedbythegrindingprocesscanleadtoelevatedtemperaturesatthegrindingzone ,whichmaycausethermaldamagetotheworkpieceandpromotewheelwear.Accordinglyextensivepastresearchhasbeenconc…