高速外圆磨削18 CrNiMo7-6齿轮钢工艺参数优化

以18 CrNiMo7-6齿轮钢为试验材料,采用正交试验法,研究高速外圆磨削加工中砂轮线速度、工件转速、砂轮径向进给速度和砂轮粒度等工艺参数对工件三维表面粗糙度幅度参数Sa、Sku和Ssk等工艺指标的影响.运用灰色关联分析方法对试验结果进行分析研究,将多项工艺指标的优化问题转化为单一目标灰关联度优化,以正交试验极差分析...     

Precision, Stability and Productivity Increase in Throughfeed Centerless Grinding

Centerless grinding is a high precision manufacturing process commonly applied to the mass production of many industrial components. However, workpiece roundness is critically affected by geometric lobing and no practical tool has been developed to solve the problem in throughfeed working mode. Based on simulation methods previously applied to plunge grinding, a new software tool has been developed in this work. The software determines the optimal working configuration and can be used to reduce set-up time and improve three important features: 1) Precision, as the roundness error is rapidly corrected at the optimal configuration. 2) Productivity, since the workpiece stock can be significantly reduced. 3) Stability, because the process is less sensitive to the original roundness error of the workpiece.     

Experimental characterization of micro-grinding process using compressed chilly air

The objective of this research is to characterize the micro-grinding process under the condition of compressed chilly air in the meso-scale grinding machine tool system. The meso-scale grinding machine tool having the size of 210×190×220 mm is developed in a horizontal configuration. To investigate the effect of compressed chilly air on the micro-grinding performances, grinding force, tool wear patterns and surface roughness are measured and analyzed with varying depths-of-cut feed speeds and temperatures of the compressed air. A series of micro-grinding experiments are conducted by considering electroplated CBN grinding tool and stainless steel workpiece and vitrified CBN grinding tool and tool steel workpiece. The experimental results show the effectiveness of compressed chilly air and its ability to improve tool life with decreased grinding forces in the micro-grinding process.     

Temperature distribution in a workpiece during cylindrical plunge grinding

In cylindrical plunge grinding, a large amount of heat flows into the workpiece continuously, accumulates and remains even after the process, which causes dimensional error. Therefore it is necessary to investigate the temperature distribution in the workpiece during grinding and analyze the influence of grinding heat on the dimension. Such an investigation has not been done enough, because the technology to measure the temperature distribution in the rotating workpiece has not matured. Considering such background, an in-process measuring system has been developed, which makes it possible to detect the temperature distribution in a wide range from the outer surface to the inside of the rotating workpiece. The system consists of small temperature sensors which are embedded into the workpiece, a micro computer attached on the workpiece which acquires the data from the sensors and transmits to a personal computer by a wireless communication device. Furthermore the contact type thermocouple which enables to measure the rotating surface temperature is added to the system. Measurement experiments revealed that the grinding heat conducts from the workpiece surface toward the center, accumulates, and remains in the workpiece even after the process. Heat conduction simulation was also performed. Good agreement was achieved between the simulated temperatures and experimental measurements.     

An integrated model of tool grinding: challenges,chances and limits of predicting process dynamics

The objective of manufacturing technology, to reduce machining costs, increase product quality and optimize process setups, is only achievable by considering the entire manufacturing process and its interrelations. Especially in tool grinding, strong interactions exist between workpiece dynamics, grinding wheel engagement, structure deformations and cutting process conditions, which makes an integrated model necessary. This paper introduces a tool grinding model that combines time-dependent dynamical aspects of the grinding wheel and workpiece with local varying contact conditions to predict the final workpiece geometry and cutting forces with a high resolution in space and time. The model is capable to reproduce systemic effects on cutting forces and ground geometries which only occurs in the interplay of all system components. The model is also positively tested in representing influences of process parameters and in optimizing the machining. The excellent agreement of simulations and experimental data shows the model’s potential in manufacturing technology, but also in investigating grinding aspects, which are not fully understood yet.     

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.     

Comparison of numerically and analytically predicted contact temperatures in shallow and deep dry grinding with infrared measurements

Contact zone thermal models of the grinding process are an important tool for the proper selection of process parameters to minimize workpiece damage while improving process efficiency. Validating contact zone thermal models with experimental measurements is difficult due to the high-speed and stochastic nature of the grinding process. In this work an infrared imaging system is used to validate two numerical thermal models, which are then compared to an established analytical contact zone thermal model. The two numerical thermal models consist of a shallow grinding model and a deep grinding model, where the deep grinding model takes the contact angle into account while the shallow grinding model does not. The results show that at small depths of cut both the numerical models and the analytical model perform well; however, as the depth of cut is increased the numerical models’ accuracy increases as compared to the analytical model. The increase in accuracy may be a result of the 2D solution of the numerical models as compared to the 1D solution of the analytical model. Additionally, it was found that the contact angle has very little effect on the contact temperatures. This work also reinforces Rowe's analytical work, using experimental and numerical results, which indicated that the workpiece temperatures are reduced by grinding at higher Peclet numbers for a given material removal rate.     

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.     

Tool wear and profile development in contour grinding of optical components

Wear induced changes in grinding tool profile have been studied for a CNC contour grinding process designed for the fabrication of precision optical components. Tool profile was measured experimentally by examining the “footprint” left by the tool when subsequently fed into a prepared surface. A numerical model was developed to predict detailed tool profiles as a function of the process parameters and total removal. Wear caused the development of approximately flat bevels on tools initially trued to a spherical shape, changing both the height and position of the lowest cutting point on the tool, with the potential to produce significant profile errors on the workpiece surface. The observation of approximately flat tool bevels was also used to develop an analytic solution for the tool shape evolution. With this analytic approximation contact height and width can be readily estimated and could be incorporated into an algorithm to adjust the tool path.     

Grinding of PCBN cutting inserts

PCBN cutting inserts have been more often used in order to attend to the demands of an economically viable process and to lead to a proper workpiece surface quality. A proper application of this cutting material requires its adequate processing. Plunge-face grinding is used for finishing the inserts after sintering. To choose a suitable grinding tool and process parameters, the properties of the ground cutting inserts must be taken into account. Therefore, the influence of PCBN grain size and composition on the insert cutting edge and surface quality has to be investigated. This work aims to give an overview of material removal mechanisms, process forces and abrasive grain wear during grinding different PCBN inserts. It was found that the insert quality depends mainly on the material removal mechanism, which in the studied case is defined by the PCBN grain size.     

基于自动检测与机械手的全自动锯片磨削数控系统

文章详细介绍了在数控锯片磨削加工系统中,采用毛坯供给机械手和电感式位移传感器,实现对毛坯上下料,毛坯与成品尺寸检测以及锯片磨削加工等磨削全过程的自动控制方法.其特点在于将磨削过程、毛坯供给与检测三个过程独立开采,使得本文开发的全自动锯片磨削系统,实现在锯片磨削加工同时,一边用机械手来上下料和锯片尺寸的检测,不仅提高了自动化水平,而且有效地重叠了磨削加工时间和毛坯准备时间,显著提高了生产效率.     

Modelling and simulation of process: machine interaction in grinding

This article presents an overview of current simulation methods describing the interaction of grinding process and grinding machine structure, e.g., vibrations, deflections, or thermal deformations. Innovative process models which describe the effects of the grinding wheel–workpiece interaction inside the contact zone are shown in detail. Furthermore, simulation models representing the static and dynamic behaviour of a grinding machine and its components are discussed. Machine tool components with a high influence on the process results are modelled more detailed than those with low influence. The key issue of the paper is the coupling of process and machine tool models for predicting the interactions of process and machine. Several coupling methods are introduced and the improvements of the simulation results are documented. On the basis of the presented simulation approaches, grinding processes and machines can be designed more effectively resulting in higher workpiece quality and process stability.     

Tool wear monitoring for micro-end grinding of ceramic materials

As grinding process usually is a final step of a machining procedure, excessive grinding tool wear could deteriorate both workpiece surface quality and its dimensional accuracy. This becomes more severe in the case of microgrinding than in conventional grinding because microgrinding wheels are more sensitive to tool wear. An effective tool wear monitoring technique is, therefore, crucial for maintaining consistent machining quality and high efficiency in microgrinding. In this paper, the influence of tool wear and tool stiffness on microgrinding process signals such as grinding force, grinding system vibration, acoustic emission signal and spindle load, are analyzed during end grinding of ceramic materials. To indicate the actual wear status of a microgrinding wheel, this study proposed a new monitoring parameter by fusing grinding force and system vibration signals, based on the concept of varying cutting stiffness. This new monitoring parameter is then experimentally tested in microgrinding a series of ceramic miniature features with consistent and inconsistent geometry.     

磨削过程中砂轮耐用度的试验研究

当砂轮磨钝时,磨削力、力比、磨削振动振幅、磨削噪声声压、磨削表面粗糙度以及工件不圆度均会发生急剧变化,因此可把它发生急变以前的某一时间作为砂轮的耐用度。本文根据所建立的砂轮耐用度判定标准,研究了外圆磨削300M超高强度钢时磨削参数对砂轮耐用度的影响。     

Effects of process parameters on workpiece roundness in tangential-feed centerless grinding using a surface grinder

The present authors proposed a new centerless grinding method using a surface grinder in their previous study [Wu, Y., Kondo, T., Kato, M., 2005. A new centerless grinding technique using a surface grinder. J. Mater. Process. Technol. 162–163, 709–717]. In this method, a compact centerless grinding unit composed mainly of an ultrasonic elliptic-vibration shoe is installed onto the worktable of a multipurpose surface grinder to perform tangential-feed centerless grinding operations. However, for the complete establishment of the new method it is crucial to clarify the workpiece rounding process and the effects of process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the machining accuracy, i.e., workpiece roundness, so that the optimum grinding conditions can be determined. In this paper, the effects of the process parameters on workpiece roundness are investigated by simulation and experiments. For the simulation analysis, a grinding model taking into account the elastic deformation of the machine is created. Then, a practical way to determine the machining-elasticity parameter is developed. Further, simulation analysis is carried out to predict the variation of workpiece roundness during grinding and to discover how the process parameters affect the roundness. Finally, actual grinding operations are performed by installing the previously constructed unit onto a CNC surface grinder to confirm the simulation results. The obtained results indicate that: (1) a slower worktable feed rate and higher workpiece rotational speed give better roundness; (2) better roundness can be also obtained when the stock removal is set at a larger value; (3) the workpiece roundness was improved from an initial value of 23.9 μm to a final value of 0.84 μm after grinding.     

细长轴车削与磨削参数优化研究

针对细长轴车削和磨削加工参数的选择问题,建立以工件刚度、刀片强度、刀杆刚度、机床进给机构强度、机床功率、机床参数、加工表面粗糙度、加工余量等作为约束条件,以切削速度、进给量、背吃刀量、工件转速、磨削余量、径向进给量等参数为优化变量,以车、磨多工序成本最低为目标的切削参数优化模型。以某型号电机轴为案例,运用MATLAB模式搜索工具箱对其车削和磨削参数进行寻优,与切削参数的传统选择方法比较表明,工序成本可降低35%以上,从而验证了优化模型的有效性。     

随机网格结构固结磨料磨盘平面磨削性能研究

针对超精密磨削加工过程对工件材料去除效率、表面质量、亚表面损伤等指标的复合需求,提出一种基于泰勒多边形设计的随机网格结构固结磨料磨盘（textured-fixed abrasive plate, T-FAP）,并以光固化树脂作为结合剂基体材料混合微米级氧化铝磨料制备磨盘,使用MATLAB图像分析和磨抛轨迹仿真方法研究磨盘磨削过程中表面磨损时变图案特征对其加工性能的影响,并通过铝制工件的平面磨削实验对磨盘磨削过程中的材料去除率及工件表面粗糙度进行分析。实验结果表明：相比传统固结磨料磨盘,采用随机网格结构磨盘加工的工件表面粗糙度为0.84μm,材料去除率为3.21μm/min,能够在保证材料去除率的同时获得较高的表面精度。     

研磨机研磨运动轨迹分析

研磨是一种利用磨具通过磨料作用于工件表面,进行微量加工的工艺方法.针对某端面研磨机的设计,提出两自由度差动轮系机构的主传动方案,分析工件与研具之间的相对运动.采用Matlab软件进行运动轨迹仿真,结果表明:研磨机中行星齿轮公转转速与自转转速的比值与研磨运动轨迹及研磨质量密切相关,从而为研磨机的产品设计及工况选择提供了理论依据.     

Modeling and measurement of active parameters and workpiece home position of a multi-axis machine tool

The complex structures of a multi-axis machine tool may produce inaccuracies at the tool tip caused by dimensional errors in the machine's link parameters. This paper addresses two important issues for precision machining: (1) which link parameters (denoted as active parameters) of a machine tool can affect the machining accuracy of a workpiece and (2) how to measure the active parameters by using a grinding wheel as a measuring probe. To achieve this, a modified Denavit–Hartenberg (D–H) notation is introduced to model a multi-axis machine tool. The NC data equations are then derived in terms of the machine's link parameters. It is found that the link parameters of a machine tool can be divided into two types: active and nonactive parameters. The prerequisite for obtaining an accurately machined workpiece is to have correct values of the active parameters and the workpiece home position. Based on the developed NC data equations of a multi-axis machine tool, this paper also addresses the technique of using a grinding wheel as a measuring probe to determine the active parameters and the workpiece home position. Experimental results are also given with illustrative examples.     

CNC磨削加工中砂轮几何工艺参数自动检测的建模

为了确保CNC工具磨床上用金刚石砂轮磨削工件的精度，金刚石砂轮的几何形状和其相对工件的位置要有严格的要求，为此本文系统地给出了应用电感式位移传感器对砂轮动态几何形状、砂轮与工件相对位置等工艺参数的自动检测建模方法，运用此方法检测砂轮动态几何参数，可以改善被加工工件的精度。