Simulation of workpiece forming and centre displacement in plunge centreless grinding

By reducing the set-up time of centreless grinding system, higher process flexibility and productivity can be obtained. This goal is approached by developing a simulation model that assists in efficient centreless grinding system set-up. In this paper, an analytical modelling of plunge centreless grinding is described. The developed model incorporates the workpiece forming mechanism along with workpiece dynamics and facilitates the simulation of workpiece form and its centre displacement. The prototype simulation model has been embedded within a spreadsheet environment and experimentally verified.     

圆柱零件无心磨削时导轮廓形研究

通过对砂轮、导轮、工件、托板坐标系相互位置的分析，建立了导轮廓形的数学模型，得到圆柱零件无心磨削时导轮廓形的表面特征。经过实验得出了导轮廓形面与工件半径的关系曲线。理论分析和计算表明：位移量h存在时，导轮表面是准双曲面的一部分。导轮廓形的曲率随着工件半径r的增大而减少。提出了用金刚石笔修整导轮廓形时的机床调整参数。通过数值模拟，建立了目标函数。应用参数化法获得最优参数值，提高了无心磨削圆柱零件的加工精度。     

Generalized practical models of cylindrical plunge grinding processes

This paper presents generalized grinding process models developed for cylindrical grinding processes based on the systematic analysis and experiments. The generalized model forms are established to maintain the same model structures with a minimal number of parameters so that the model coefficients can be determined through a small number of experiments when applied to different grinding workpiece materials and wheels. The relationships for power, surface roughness, G-ratio and surface burning are established for various steel alloys and alumina grinding wheels. It is shown that the established models provide good predictive capabilities while maintaining simple structures.     

A study of the corner wear in cylindrical plunge grinding

The tolerance on the corner radius is quite important in a number of cylindrical grinding operations and hence the corner wear is critical. Preliminary investigations have shown that the corner wears off in increasing arcs of radii and could be simulated by dressing the corner to specific radii. A possible method of in-process monitoring of corner wear is by monitoring of the grinding forces during the process. This paper briefly discusses the nature of corner wear and the force fluctuations encountered in plunge grinding due to corner wear, as also the possibilities of using this data for in-process monitoring of corner wear. Another possible method of in-process monitoring of corner wear by using air-flow technique is also discussed briefly.     

Correlating surface roughness and vibration on plunge cylindrical grinding of steel

Since the wear of a grinding wheel has a direct effect on the workpiece vibration and both have effect on the workpiece quality, the main goal of this work is to study the relation between the process vibration signals and the workpiece quality (mean roughness, circularity and burning) as the grinding wheel gets worn, in an attempt to use these signals to decide the exact moment to dress the wheel. In order to reach this goal, several experiments were carried out in a plunge cylindrical grinding operation of an AISI 52100 quenched and tempered steel, having as input variables the dressing overlap ratio, the spark out time and the workpiece velocity. The output variables were the workpiece surface roughness and circularity and also the process vibration during both, the cutting phase and the spark out phase of the grinding cycle. The main conclusions were: (1) it is possible to have good workpiece quality even with a vibration level much higher than that obtained with a recently dressed wheel; (2) vibration during cutting phase and at the end of complete spark out can be used to monitor the wheel condition at least when high dressing overlap ratio is used; and (3) the decrease in the spark out time makes the vibration at the end of spark out increase a lot, but does not cause such a damage in surface roughness. This fact makes the use of partial spark out feasible in some situations.     

A study on chatter boundaries of cylindrical plunge grinding with process condition-dependent dynamics

This paper presents a systematic study on the chatter characteristics of cylindrical plunge grinding processes. Chatter occurrence under a wide range of operating conditions is experimentally identified. The unique transient chatter behaviors during spark-in and spark-out of plunge grinding are also studied; and the transient chatter occurrence is separated from the steady-state chatter occurrence, which is used to define the chatter boundaries.It is shown that the measured structure dynamics of the wheel/workpiece exhibit strong dependency on grinding conditions. The dynamic/chatter model of cylindrical plunge grinding [H. Li, Y.C. Shin, A time-domain dynamic model for chatter prediction of cylindrical plunge grinding processes, ASME Journal of Manufacturing Science and Engineering 128(2) (2006) 404–415] is improved to handle the grinding force-dependent structure dynamics, and the modified model is validated by comparing the predicted chatter boundaries with experimental chatter conditions.     

Effect of grinding-induced cyclic heating on the hardened layer generation in the plunge grinding of a cylindrical component

This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness.     

Simulation of plunge centerless grinding processes

Workpiece out-of-roundness is one of the most important problems in centerless grinding. Besides geometrical and kinematical effects, the dynamical behavior of the machine structure, the grinding and regulating wheel together with the support blade fundamentally influence the process stability and the workpiece accuracy. The paper presents a method for a numerical simulation of plunge centerless grinding processes in time domain. Under consideration of the geometrical conditions of the grinding gap and the dynamical compliance behavior of the grinding system the developed algorithm enables a quantitative determination of the workpiece out-of-roundness, the progression of grinding and reaction forces as well as the calculation of dynamical displacements.     

感应加热过程中工件表层温度分布及机理分析

采用热模拟试验研究了大截面圆柱工件在感应加热过程中的磁场和温度场分布,探讨了工件内的温度分布以及温度随时间的变化规律.试验结果表明:感应线圈中工件侧的磁场分布受丁件内的涡流影响较大,由于磁场的叠加作用,工件表面磁场分布在相对于线圈的中部位置出现最大值.根据圆柱工件表面的温度变化规律得出3个阶段,第一阶段由于热量损失工件次表面温度最高;第二阶段工件温度达到居里点,工件的物性参数发生变化导致表面温度最高;第三阶段温度波峰依次波动向内传递.     

Analysis of the different forms of application and types of cutting fluid used in plunge cylindrical grinding using conventional and superabrasive CBN grinding wheels

The work reported here involved an investigation into the grinding process, one of the last finishing processes carried out on a production line. Although several input parameters are involved in this process, attention today focuses strongly on the form and amount of cutting fluid employed, since these substances may be seriously pernicious to human health and to the environment, and involve high purchasing and maintenance costs when utilized and stored incorrectly. The type and amount of cutting fluid used directly affect some of the main output variables of the grinding process which are analyzed here, such as tangential cutting force, specific grinding energy, acoustic emission, diametrical wear, roughness, residual stress and scanning electron microscopy. To analyze the influence of these variables, an optimised fluid application methodology was developed (involving rounded 5, 4 and 3 mm diameter nozzles and high fluid application pressures) to reduce the amount of fluid used in the grinding process and improve its performance in comparison with the conventional fluid application method (of diffuser nozzles and lower fluid application pressure). To this end, two types of cutting fluid (a 5% synthetic emulsion and neat oil) and two abrasive tools (an aluminium oxide and a superabrasive CBN grinding wheel) were used. The results revealed that, in every situation, the optimised application of cutting fluid significantly improved the efficiency of the process, particularly the combined use of neat oil and CBN grinding wheel.     

Modelling of grinding gap macro geometry and workpiece kinematics in throughfeed centreless grinding

The paper discusses the simulation of a throughfeed centreless grinding process in a virtual environment (VE). The developed simulations are based on an analytical grinding gap model describing the grinding gap macro geometry and workpiece kinematics. First of all, the model is embedded in a desktop application (Cegris), which facilitates regulating wheel truing and the determination of set-up variables, both of which yield an optimal grinding gap macro geometry in a reduced set-up time. Finally, the Cegris is ported to a CAVE (CAVE Automatic Virtual Environment) for an interactive visualisation of the process, an application used to train machine tool operators.     

Time-domain dynamic modelling of the external plunge grinding process

This paper presents a time-domain dynamic model of the external plunge grinding process. The model consists of a block-based simulation tool that substantially simplifies the inclusion of different effects, the variation of process or machine parameters, and the study of the parameters which influence the process. Since it is a time-domain model, non-linear effects can be considered. Particular attention is paid to the inclusion in the model of the interference phenomenon between two consecutive workpiece revolutions. The inclusion of this phenomenon is particularly important when trying to explain why process parameters which cause unstable conditions during stability analyses can, however, lead to acceptable workpiece results. The model permits the visualisation of this lobe destruction effect between consecutive workpiece revolutions.The actual infeed constitutes the model input, i.e. different infeed rates and spark-out time. The importance of the different model parameters is discussed within the paper, with special attention being given to the application of this model to the grinding with CBN wheels.     

双程切入磨削表面硬化层的研究

采用缓进给磨削方式和不同的磨削行程对40Cr钢进行了磨削淬硬,对单程和双程磨削表面硬化层的组织与性能进行了比较。结果表明,尽管单程和双程磨削时的原始组织不同,但两者的表面硬化层组织及其变化趋势完全相同。双程磨削淬硬可使表面硬化层深度及其均匀性、显微硬度及耐磨性得到进一步提高;但其最大残余压应力值及应力影响深度有所降低。双程磨削硬化层组织的形成机制同样适用于多程磨削淬硬或淬硬钢的磨削淬硬等场合。     

Fast time constant estimation for plunge grinding process control

The time constant of a grinding control system indicates the speed of response to a control command and reflects variations of the wheel condition. In order to allow correct and continuous control adjustment, fast in-process estimation of the parameter is necessary. The significance of the grinding system time constant is discussed and the control system for the plunge grinding process described. An algorithm for fast time constant estimation is presented for adaptive control of the grinding process. The algorithm is useful for geometry-based grinding control systems where a workpiece size sensor is used and multiple control tasks are implemented. Experimental testing of the algorithm is explained and comparison between results from grinding and those from analysis shows that the proposed algorithm is sufficiently accurate and effective for adaptive control of the plunge grinding process.     

Stability analysis of chatter vibration for a thin-wall cylindrical workpiece

The vibration characteristics and the vibration direction angle between the beam mode and shell mode of the three-jaw clamped thin-wall cylindrical workpiece will change according to the relative position of the cutting tool to the chucking jaws. This will induce parametric vibration and cause the chatter characteristics of a thin-wall cylindrical workpiece to become more complicated than those of a solid workpiece. In this study, the three-jaw clamped thin-wall cylindrical workpiece was considered as a parametrically excited vibration system. Initially, the relationship between the parametric vibration and the workpiece system structure was investigated, and then the equivalent stability cutting depth of the thin-wall cylindrical workpiece was analyzed by a numerical calculation method. When the three-jaw clamped thin-wall cylindrical workpiece was considered as a parametric vibration system, the analytical results were consistent with the experimental results.     

High-efficiency internal cylindrical grinding with a new kinematic

Based on a new kinematic, a prototype internal grinding machine was developed in KSF. The main target to design such machine was to defeat some problems of internal grinding such as poor enrichment of coolant lubricant, deflection of grinding tool and the resulting inaccuracy, low material removal and high heat generation because of long contact length. This new concept could not only overcome the a/m problems, but should also create different topography on the workpiece surface which is appropriate for some functional applications.     

Experimental analysis of wheel/workpiece dynamic interactions in grinding

The aim of this work is to study the wheel/workpiece dynamic interactions in high-speed grinding using vitrified CBN wheel and DTG (difficult to grind) work materials. This problem is typical in the grinding of engine valve heads. The influence of tangential force per abrasive grain was investigated as an important control variable for the determination of G ratio. Experiments were carried out to observe the influence of vibrations in the wheel wear. The measurements of acoustic emission (AE) and vibration signals helped in identifying the correlation between the dynamic interactions (produced by forced random excitation) and the wheel wear. The wheel regenerative chatter phenomenon was observed by using the wheel mapping technique.     

Dynamic modeling of a novel workpiece table for active surface grinding control

In order to implement active control during surface grinding, a workpiece micro-positioning table utilizing a piezoelectric translator has been developed. The workpiece table has a working area of 100×100 mm and a nominal working range of 45 μm. The resolution of the workpiece table is less than 20 nm and the natural frequency is 579.2 Hz. The rigidity of the workpiece table under the open loop condition is approximately 17 N/μm. Under the closed loop condition, the rigidity is better than 400 N/μm. The design of the workpiece table is presented together with considerations to achieve the high dynamic characteristics, where the maximum acceleration is up to 33g (g is the acceleration of gravity). The dynamic models of the piezoelectric translator and the workpiece table have been established. Experimental testing has been carried out, verifying the performance of the workpiece table and the established dynamic models for the workpiece micro-positioning table.     

切入式磨削烧伤仿真预测与控制方法研究

基于磨削热传递模型和磨削去除率模型,提出了一种基于监控功率信号的切入式磨削烧伤仿真预测与控制方法,对砂轮在粗磨、半精磨、精磨、光磨各阶段的磨削功率信号进行监测,再利用计算机对机床数控系统各加工工艺参数进行控制,使砂轮实际磨削功率信号始终低于磨削烧伤最大功率边界的5%～15%,来避免出现工件磨削烧伤现象;同时,用轴承套圈内圆磨削试验验证了该方法的有效性和实用性。      

三辊行星轧制中轧辊与轧件接触区分布

三辊行星轧制中,轧辊轧件接触区的分布是轧制力和轧制功率计算的基础,是轧辊外轮廓设计的重要依据.研究结合了实际轧制过程中轧辊和轧件的运动特点,引入相应的约束条件,给出接触区分布的解析表达式;在给定轧制工艺参数下,数值分析计算出接触区具体的分布情况.该方法避开了轧辊轧件线接触的假设,可给出接触区分布情况.结果显示,该分布不...