磨削淬硬工件热变形数值分析

磨削淬硬技术在加工过程中因高温引发了工件热变形,导致加工后工件呈凹形,影响了磨削淬硬层的分布。本文通过ANSYS热—力耦合模块对磨削淬硬中的热变形进行了模拟分析,用时变磨削热流密度加载模拟得到结果与试验测量结果吻合性好。     

Fabrication of small aspheric moulds using single point inclined axis grinding

Single point inclined axis grinding techniques, including the wheel setting, wheel–workpiece interference, error source determination and compensation approaches, were studied to fabricate small aspheric moulds of high profile accuracy. The interference of a cylindrical grinding wheel with the workpiece was analysed and the criteria for selection of wheel geometry for avoiding the interference was proposed. The grinding process was performed with compensation focused on two major error sources, wheel setting error and wheel wear. The grinding results showed that the compensation approach was efficient and the developed grinding process was capable to generate small aspheric concave surfaces on tungsten carbide material with a profile error of smaller than 200 nm in PV value after two to three compensation cycles.     

Workpiece roundness profile in the frequency domain: an application in cylindrical plunge grinding

In grinding, most control strategies are based on the spindle power measurement, but recently, acoustic emission has been widely used for wheel wear and gap elimination. This paper explores a potential use of acoustic emission (AE) to detect workpiece lobes. This was achieved by sectioning and analysing the AE signal in the frequency domain. For the first time, the profile of the ground workpiece was predicted mathematically using key frequencies extracted from the AE signals. The results were validated against actual workpiece profile measurements. The relative shift of the wave formed on the surface of the part was expressed using the wheel-workpiece frequency ratio. A comparative study showed that the workpiece roundness profile could be monitored in the frequency domain using the AE signal during grinding.     

Selections of working conditions for creep feed grinding. Part(III): avoidance of the workpiece burning by using improved BP neural network

In this study, the grinding force of the creep feed grinding are modeled and forecasted by using the improved back propagation neural (BPN) network. The results show that the grinding energy can be accurately predicted by the application of the grinding force model. Due to the previous paper, the workpiece burning occurs as the grinding energy is greater than the critical grinding. Thus, a judgment for the occurrence of the workpiece burning can be achieved. Comparing with the experimental results, the applied algorithm of the improved BPN network is proved to be effective in forecasting the working conditions of the workpiece burning. Thus, a selection scheme of working conditions in view of the avoidance of the workpiece burning is further developed. Considering the working efficiency, the working conditions are selected to maximum metal removed rate, MRR_max. The results show that a larger size of wheel is available to have a better working efficiency.     

Study of grinding tool profiling for robotic processes

In the fabrication and maintenance of hydroelectric turbines, the reconstruction by grinding of certain high-curvature surfaces such as junctions has not yet been robotized and must now be done manually. The problem is related to the very fast grinding wheel wear and the difficulty in controlling the position and orientation of the robot's grinder to adjust to changes in wheel shape. If the grinding wheel orientation is kept constant with respect to the workpiece, wheel-workpiece conformity increases, specific energy increases, the material removal rate drops and glazing of the wheel may occur. This article presents a method for controlling simultaneously the profile of both the workpiece and the grinding wheel. The orientation of the wheel is oscillated to maintain a constant wheel profile throughout its life and thus achieve better control in material removal. Research results provide the basis for robotic grinding tool profiling.     

Kinematic simulation of the uncut chip thickness and surface finish using a reduced set of 3D grinding wheel measurements

This paper combined experimentally-measured grinding wheel topography data taken around the entire circumference of the grinding wheel with a kinematic simulation of the grinding process. Several new methods were developed in order to create the resulting high-fidelity and computationally-efficient simulation. First a novel peak-removal technique was developed and applied to effectively remove erroneous peaks in the raw wheel topography data. Next a method was found to determine only the active cutting points on the wheel model by considering the kinematics of the grinding process. This new approach was able to reduce the simulation time from over twelve hours to about four seconds without losing any information about the cutting edge–workpiece interaction. The resulting predicted workpiece surface was then experimentally validated by carrying out a grinding experiment using the same grinding wheel used to develop the grinding wheel computer model and then measuring the resulting workpiece surface profile. Good agreement between simulated and experimental workpiece profiles was observed. Finally, the validated simulator was used to develop a kinematically-exact method to calculate the maximum uncut chip thickness and the simulation results were investigated for different depths of cut, wheel speeds and workpiece feeds.     

A practical approach for simulation and manufacturing of a ball-end mill using a 5-axis CNC grinding machine

This paper presents a detailed manufacturing model that can be used for grinding a ball-end mill using 5-axis CNC (computer numerical controlled) grinding machine. The profile of the helical groove can be calculated exactly using the given wheel profile and relative movements between the workpiece and the grinding wheel. The proposed model is related to some analytical, differential geometry and kinematics to control the motions of the workpiece and grinding wheels in grinding processes. The manufacturing model presented in this paper provides a practical and efficient method for developing the simulation software for the design and the manufacture of a ball-end mill.     

Selections of working conditions for creep feed grinding. Part(II): workpiece temperature and critical grinding energy for burning

In this study, the workpiece temperature is predicted by the thermal model presented in the previous paper. Also, the grinding energy when the fluid begins to cause boiling is defined as the critical grinding energy for the workpiece burning. Thus, a sequence of experiments are performed. The results show that the predicted workpiece temperatures have great agreement with experimental and published data. Hence, the validity of the thermal model is proved. From the measured signals of grinding force and workpiece temperature, the occurrence of workpiece burning is accompanied with the abrupt rise of both signals. At the moment, the experimental grinding energy is also greater than the critical grinding energy. Thus, the workpiece burning can be predicted or evaluated so as to avoid the working conditions of burning occurrence.     

Online dressing of profile grinding wheels

Improving the dressing accuracy and efficiency of profile grinding wheels has been increasingly demanded. The significance is addressed in the practical application of precision engineering. In this study, an online dressing system of profile grinding wheels is introduced. A special feature of the system is the application of the non-contact image measuring method used to evaluate deviation of the grinding wheel’s edge in determining the timing and amount of dressing. Diamond form rollers were selected to generate the profile grinding wheels with steep profile flanks by taking advantage of their high flexibility, short dressing times, and low wear rate. A series of grinding and dressing tests were carried out to investigate the dressing accuracy and surface quality for the profile grinding wheels with the proposed system. Through repeated experimental investigations, it was found that the dressing force is a key parameter in determining the number of passes needed in achieving high efficiency dressing. This is to assure that the length of the dressing time, and waste of the dresser and grinding wheel can be minimized. Other main dressing conditions that influence the grinding wheel and workpiece roughness include speed ratio, cross feed and roller profile radius.     

The effects of dynamic characteristics on the surface texture in mirror grinding

In order to make clear the effects of mirror grinding conditions on the ground surfaces in the surface mirror grinding of sintered carbide adopting an in-process electrolytic dressing method, experiments are conducted to measure the vibration signals of the workpiece during grinding and the profile of the ground surface. It is found that components with low frequency vibration signals have a very close relation to the undulation of a ground surface and components with high frequencies to the surface roughness .     

单晶刚玉砂轮磨削GH4169合金磨削能传入工件比例研究

指出了确定磨削能传入工件比例对研究GH4169合金磨削机理的必要性,分析了已有理论计算公式确定磨削GH4169合金过程中磨削能传入工件比例的局限性。设计和实施了试验与有限元分析相结合的方法,对单晶刚玉砂轮磨削GH4169合金过程中磨削能传入工件的比例进行了确定,并进一步对该比例与磨削工艺参数之间的关系进行了研究,拟合了关系方程。结果表明,在试验工艺条件下,磨削能传入工件比例在25%~62%之间,且该比例与工艺参数之间的关系可用指数函数形式的方程描述。     

基于正交试验-遗传神经网络的陶瓷球面精密磨削参数优化

针对陶瓷等难加工材料的精密加工要求与特点以及球面磨削传统加工模式,分析了氮化硅陶瓷材料球面廓形工件砂轮法向跟踪精密磨削的方法。采用正交试验法设计试验,运用极差法和方差法综合分析相关磨削工艺参数对工件加工质量与效率的影响规律。考虑到当前磨削加工工艺方案选择与优选的难点,利用遗传神经网络算法建立了工件加工质量与效率和相关磨削工艺参数之间的非线性映射关系,并基于正交试验法的分析结果对遗传神经网络算法进行了改进,实现了相关磨削工艺参数的优化,缩短了氮化硅陶瓷材料球面廓形工件数控磨削工艺制定与操作的时间,提高了磨削加工质量和效率。     

Some observations on profile wear in creep-feed grinding

Tests were performed to investigate the effect of various parameters on the wear of a profiled grinding wheel when creep-feed grinding a nickel-base alloy. The wear of a number of different radii, angles and profile heights was monitored. It was found that this wear was strongly influenced by the total distance travelled by an individual grit while in contact with the workpiece and by the workpiece feed rate. In addition, using a neat oil grinding fluid resulted in less wear than a water-based fluid and a 120 grit wheel wore less than a 60–80 grit wheel. A simple theoretical model was developed for predicting the effect of stock removal rate on profile wear in the creep-feed grinding of a “difficult-to-grind” material and this gave good correlation with the experimental trends.     

Grinding of high-lead and gothic-arc profile ball-nuts with free quill-inclination

A method for gothic-arc ball-nut grinding is presented. The gothic-arc is a combined curve of two arcs with the same radius and shifted centers. Generally, gothic-arcs are manufactured by form grinding; the grinding wheel is formed into the gothic-arc and is tilted at the lead angle of the thread. In ball-nut grinding, which is internal grinding, interference between quill (wheel shaft) and internal surface of a workpiece limits the length of the ball-nut. In the presented method, the quill is tilted independently of the lead angle so as not to contact the internal surface of the workpiece. Instead, the wheel is formed into an optimum profile with which the nut obtains a gothic-arc profile. The procedure of finding the optimum wheel profile is presented. Grinding simulation showed that the gothic-arc thread is obtained accurately by the method, though a part of the thread surface is not a perfect gothic-arc. This method allows the use of large-diameter wheels to manufacture high-lead ball-nuts.     

TEMPERATURE AND ENERGY PARTITION IN HIGH-SPEED GRINDING OF ALUMINA WITH A BRAZED DIAMOND WHEEL

An investigation is reported on the temperatures and energy partitions for high speed grinding of alumina with a brazed diamond wheel. The grinding temperature at the wheel-workpiece interface was measured using a pair of grindable foil thermocouples. The energy partition to the workpiece was evaluated by matching the analytical temperatures to the measured results. The influences of the grinding conditions, including wheel speed, the depth of cut, workpiece velocity, and material removal rate, on the temperatures and energy partitions were investigated. In all tests, the maximum grinding zone temperature rise was below 260°C. The energy partitions to the workpiece obtained under different grinding conditions varied from 30% to 75%. The calculated diamond tip temperature might be over 1000°C if the circular grain contact radius of contact was less than a critical value.     

Critical success factors for Kaizen implementation in manufacturing industries in Mexico

To machine a noncoaxial nonaxisymmetric aspheric lens, a new parallel grinding method that employs a fixture with an adjustable gradient (AGF) is proposed. The AGF is developed for a three-axis computer numerically controlled grinding machine. The grinding method is presented according to the proposed grinding system. To ensure the machining accuracy, the main machining errors and the compensation algorithm are discussed for the grinding method using the AGF. Simulation results show that the AGF rotation errors are crucial factors affecting the profile error of the machined workpiece. Experimental results show that employing the compensation algorithm increases machining accuracy.     

高速精密磨削9CrWMn冷作模具钢的磨削力和比磨削能

分析了高速精密磨削9CrWMn冷作模具钢的机理,采用DEFORM软件对高速磨削模具钢9CrWMn过程进行了磨削力仿真。使用高精密高速平面磨床对模具钢9CrWMn进行了高速精密磨削试验,并在线测量了多种工况下的磨削力。结果表明:在其他两组工艺参数不变时,随着工件进给速度增加,磨削力特别是法向磨削力会增大近45%;法向磨削力和切向磨削力随着砂轮的线速度上升而下降,法向磨削力下降近33%;磨削深度对磨削力影响较大,大的磨削深度对法向磨削力的影响尤其显著,可使法向磨削力增大近100%。分析了磨削工艺参数对比磨削能的影响规律,结果显示:随着磨削深度和工件进给速度的增大,比磨削能呈比较明显的下降趋势,符合磨削加工中的尺寸效应;随着砂轮线速度的增大,比磨削能呈上升趋势。最后,对高速磨削前后工件表面的微观形貌进行了对比分析,磨削力试验结果和仿真理论分析相一致。     

基于动态轮廓采样法的轴向超声振动辅助磨削工件表面形貌预测与试验验证

提出了一种基于动态轮廓采样法的轴向超声振动辅助磨削的工件表面形貌预测方法。假设磨粒直径服从正态分布,磨粒位置服从随机分布,生成砂轮表面形貌的模型,从运动学角度建立了轴向超声振动辅助磨削过程中任意磨粒的轨迹方程,针对磨粒运动轨迹的特点,提出了动态轮廓采样方法。通过建立磨削沟槽变宽模型,引入了磨削弹性变形模型和塑性堆积模型,对动态轮廓采样方法进行了修正,最终得出工件表面形貌的预测结果。对预测结果进行了试验验证,对比分析了工件表面形貌的预测结果和实测结果,两者特征相似,且比较工件表面粗糙度的预测值和实测值平均误差为5.3%,从而验证了该预测方法的准确性。     

Form-truing error compensation of diamond grinding wheel in CNC envelope grinding of free-form surface

In computer numerical control (CNC) grinding of free-form surface, an ideal arc profile of trued diamond grinding wheel is generally employed to plan 3D tool paths, whereas its form-truing errors greatly influence the ground form accuracy. A form-truing error compensation approach is proposed by using an approached wheel arc profile to replace the previously designed ideal one. The objective is to directly compensate the trued wheel arc-profile errors. It may avoid the time consumption of traditional approach that compensates the measured coordinate point errors of workpiece to an iterative grinding operation. First, the 3D tool path surface was constructed to plan the 3D tool paths. Second, the CNC arc truing of grinding wheel was conducted to analyze the form-truing error distribution relative to the applied wheel arc profile. Then, the form-truing error compensation was carried out in CNC envelope grinding. Finally, the iterative closest point (ICP) algorithm was used to match the measured coordinate points of workpiece to ideal free-form surface. It is shown that the 3D tool path surface constructed is practicable to plan arbitrary 3D tool paths for the form-truing error compensation. The ICP matching may be used to investigate 3D ground form error distribution. It is confirmed that the form-truing error compensation can directly improve the 3D ground form accuracy. It may decrease the 3D ground form error by about 20% when the 2D form-truing error is reduced by about 58% using the same truing conditions for CNC grinding.     

Investigation into the performance of eco-friendly graphite nanofluid as lubricant in MQL grinding

In this study, the lubrication and cooling properties of eco-friendly graphite nanofluids in MQL grinding were investigated. Grinding forces, subsurface temperature of workpiece, surface roughness, micro-hardness and metallographic observations of ground surfaces were employed to evaluate the performance of synthesized nanofluids as lubricant under different grinding parameters. The results were also compared with grinding in dry, pure MQL and flood cooling conditions. The results showed that the tangential forces and force ratios in grinding using graphite nanofluid MQL are lower than that of other lubricating methods especially at extreme cutting parameters. Also, application of graphite nanofluid MQL reduced the grinding temperature at high velocities of workpiece. These reductions could be attributed to the formation of a tribofilm on the ground surface by the present of graphite nanoparticles in the wheel-workpiece interface. Additionally, the presence of this tribofilm in the contact area generated a smooth surface even at high depth of cut and velocity of workpiece. Furthermore, the micro-hardness of ground surfaces increased in graphite nanofluid MQL grinding because of infiltration of graphite nanoparticles in the grinding surface and the plastic deformation of subsurface of workpiece.