Stability analysis and time domain simulation of multiple diameter parts during infeed centerless grinding

Multiple diameter part applications cope a relevant percentage of infeed centerless grinding operations. Nevertheless, general stability analysis and process optimisation has been mainly investigated for mono-diameter parts. This paper presents a time domain simulation software developed for multiple diameter parts that allows the simulation of average and particular evolution of process forces, power, machine deflections, thermal behaviour, real part diameter and roughness. First, a work rotation stability analysis is carried out. Then, with the use of both the stability analysis and the infeed cycle simulation, optimized process parameters and cycles are defined in order to increase process productivity.     

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.     

Determination of waviness decrease rate by measuring the frequency characteristics of the grinding force in centerless grinding

In centerless grinding, it is difficult to optimize the grinding conditions for minimizing the workpiece roundness error because of the high number of process parameters such as center height angle, blade angle, and stock removal rate. We had previously proposed a function for evaluating grinding conditions, i.e., the waviness decrease rate, in order to automatically select the optimum process parameters. In order to build a closed-loop control system for the process parameters, however, it is necessary to find a practical way to determine the waviness decrease rate. In this paper, the relationship between the waviness decrease rate and the dynamic components of the grinding force was investigated analytically. It was found that the frequency characteristics of the waviness decrease rate show a similar tendency to those of the grinding force. A grinding force measurement system was built and experiments for measuring the frequency characteristics of the grinding force were carried out. As a result, it was confirmed that the waviness decrease rate can be determined by measuring the frequency characteristics of the grinding force.     

Effectiveness of continuous workpiece speed variation (CWSV) for chatter avoidance in throughfeed centerless grinding

The continuous rotation speed variation is demonstrated to be an efficient method to avoid regenerative chatter in different machining processes. This paper presents a time-domain dynamic model for throughfeed centerless grinding process that can predict chatter by means of part roundness error evolution. Continuous workpiece speed variation (CWSV) has been implemented in this model to analyze the influence of this disturbing method on the dynamic instability. Experimental results have validated the model and verified the effectiveness of CWSV for chatter avoidance and surface finish and dimensional tolerances improvement. It has been demonstrated that the selection of the optimal variation parameters is an important factor not only for chatter avoidance, but also for the stability of surface finish and dimensional tolerances since workpiece speed variation has a direct influence on throughfeed rate and grinding forces.     

A new in-feed centerless grinding technique using a surface grinder

This paper deals with the development of an alternative centerless grinding technique, i.e., in-feed centerless grinding based on a surface grinder. In this new method, a compact centerless grinding unit, composed of an ultrasonic elliptic-vibration shoe, a blade and their respective holders, is installed onto the worktable of a surface grinder, and the in-feed centerless grinding operation is performed as a rotating grinding wheel is fed in downward to the cylindrical workpiece held on the shoe and the blade. During grinding, the rotational speed of the workpiece is controlled by the ultrasonic elliptic-vibration of the shoe that is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304). A simulation method is proposed for clarifying the workpiece rounding process and predicting the workpiece roundness in this new centerless grinding, and the effects of process parameters such as the eccentric angle, the wheel feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were investigated by simulation followed by experimental confirmation. The obtained results indicate that: (1) the optimum eccentric angle is around 6°; (2) higher machining accuracy can be obtained under a lower grinding wheel feed rate, larger stock removal and faster workpiece rotational speed; (3) the workpiece roundness was improved from an initial value of 19.90 μm to a final one of 0.90 μm after grinding under the optimal grinding conditions.     

A new through-feed centerless grinding technique using a surface grinder

This paper proposes an alternative centerless grinding technique, i.e., through-feed centerless grinding using a surface grinder. In the new method, a compact centerless grinding unit, composed of a guide plate, an ultrasonic shoe, a blade, and their respective holders, is installed onto the worktable of a surface grinder, and the through-feed centerless grinding operation is performed as the workpiece located on the guide plate is fed into the space between the grinding wheel and ultrasonic shoe. The ultrasonic shoe, produced by bonding a piezoelectric ceramic device onto a metal elastic body, is tilted at a small angle so as to provide sufficient force to control the workpiece rotational motion and to feed the workpiece along its axis by the ultrasonic elliptic-vibration. In this paper, the workpiece motion control tests were carried out firstly to make sure that the workpiece rotational speed and through-feed rate can be exactly controlled by the ultrasonic shoe which is essential for performing high-precision grinding operations. Then, the effects of major process parameters such as the workpiece eccentric angle, the stock removal, the ultrasonic shoe tilt angle and the applied voltage amplitude on the machining accuracy (i.e. workpiece cylindricity and workpiece roundness) were clarified experimentally. The obtained results indicate that: (1) the workpiece rotational speed can be adjusted by changing the applied voltage amplitude, whereas its through-feed rate can be adjusted by changing both the applied voltage amplitude and the ultrasonic shoe tilt angle; (2) the optimum eccentric angle is 6°, and a larger stock removal, a smaller tilt angle, or a higher applied voltage is better for higher machining accuracy; (3) the workpiece cylindricity and roundness were improved from the initial value of 16.63 μm and 14.86 μm to the final ones of 1.49 μm and 0.74 μm under the optimal grinding conditions.     

Dynamic model of a centerless grinding machine based on an updated FE model

Centerless grinding operations present some characteristic features that make the process especially susceptible to regenerative chatter instabilities. Theoretical study of these vibrations present some difficulties due to the large amount of parameters involved in the process and, in addition, such a study requires a precise determination of dynamic properties of the particular machine under study. Taking into account the important role of the dynamic characteristics in the process, in this paper both analytic and experimental approaches are used with the aim of studying precisely the vibration modes participating in the response. Using as reference results obtained from an experimental modal analysis (EMA) performed in the machine, the finite element (FE) model was validated and improved using correlation and updating techniques. This updated model was used to obtain a state space reduced order model with which several simulations were carried out. The simulations were compared with results obtained in machining tests and it was demonstrated that the model predicts accurately the dynamic behavior of the centerless grinding machine, especially concerning on chatter.     

Optimization of Set-up Conditions for Stability of The Centerless Grinding Process

The stability of the centerless grinding process is very sensitive to the set-up conditions due to the uniqueness of the work-holding system. Centerless grinding produces precision components with high productivity only when the set-up condition is optimally chosen. This paper describes the effect of set-up conditions on three stability criteria of the centerless grinding system. It also presents guidelines for determining proper set-up conditions to avoid spinners, chatter vibration and roundness problems. Finally, an algorithm for providing the optimum set-up condition based on process aims is proposed and the simulation results are discussed.     

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.     

An active system of reduction of vibrations in a centerless grinding machine using piezoelectric actuators

Centerless grinding has been extensively used in production engineering to produce accurate cylindrical parts together with high productivities. On the other hand, regenerative chatter vibrations are one of the major problems that limit the ability to produce round workpieces. This constraint can be solved selecting proper machine setup conditions, which still largely relies on a trial and error method, and sometimes this approach is not optimum in a productivity sense. This paper shows a novel method to reduce chatter vibrations in a centerless grinding machine using actively controlled piezoelectric actuators. A simplified model of the machine is used to simulate the behavior of several commercially available piezoelectric actuators in two different locations of the machine. Based on these simulations, a selection of proper actuators and their optimal location is obtained and the control system is implemented experimentally. Experimental results show that the control strategy provides a stabilizing effect on chatter. Thus, the viability of using piezoelectric actuators as active components is demonstrated, providing an important advance in the knowledge of chatter control in centerless grinding machines.     

Simulation investigation of through-feed centerless grinding process performed on a surface grinder

This paper proposes a simulation method for investigating the through-feed centerless grinding process performed on a surface grinder, where a compact centerless grinding unit, composed of a guide plate, an ultrasonic elliptic-vibration shoe, a blade, and their respective holders, is installed onto the worktable of a surface grinder, and the through-feed centerless grinding operation is performed as the workpiece located on the guide plate is fed into the space between the grinding wheel and ultrasonic shoe. The geometrical arrangement of the grinding apparatus including the contact lines on the grinding wheel, ultrasonic shoe, and blade are analyzed firstly for building a 3-D simulation model. Then, the workpiece forming process and the effects of major process parameters such as the workpiece eccentric angle, the stock removal, the ultrasonic shoe tilt angle and the applied voltage amplitude on the machining accuracy (i.e. workpiece cylindricity and roundness) are clarified by simulation and experiments. The obtained results indicate that higher machining accuracy can be achieved under the conditions of larger workpiece stock removal, smaller ultrasonic shoe tilt angle and higher applied voltage amplitude, while the workpiece eccentric angle is at 6°.     

Simulation based optimization of the NC-shape grinding process with toroid grinding wheels

For achieving high material removal rates while grinding free formed surfaces, shape grinding with toroid grinding wheels is favored. The material removal is carried out line by line. The contact area between grinding wheel and workpiece is therefore complex and varying. Without detailed knowledge about the contact area, which is influenced by many factors, the shape grinding process can only be performed sub-optimally. To improve this flexible production process and in order to ensure a suitable process strategy a simulation-tool is being developed. The simulation comprises a geometric-kinematic process simulation and a finite elements simulation. This paper presents basic parts of the investigation, modelling and simulation of the NC-shape grinding process with toroid grinding wheels.     

Rounding and stability in centreless grinding

The paper presents a method for selecting grinding conditions and assists researchers to understand the complex dynamics of centreless grinding. It overcomes the problem of deriving dynamic stability charts for particular geometries and difficulty of interpreting such charts to adjust work speed to overcome lobing problems. Classic dynamic stability charts cannot assess stability levels in proximity to integer lobes, a particular problem for centreless grinding. The paper overcomes these problems employing a simply calculated new dynamic stability parameter A_dyn. The new parameter A_dyn simplifies the optimisation of grinding variables including set-up geometry and work speed in relation to resonant frequency. It is difficult to interpret relative dynamic stability of centreless grinding by classical methods for different set-ups, work speeds and numbers of lobes. A new method is employed in this paper based on the well-established Nyquist stability criterion. The dynamic stability parameter A_dyn is based on the real part of the characteristic equation. It is easily computed and presented on a single chart for particular work speed, resonant frequency and for a wide range of numbers of lobes. The method clearly shows the effect on rounding strength both for stable and unstable conditions. Most authors computing dynamic stability charts have ignored positive down boundaries and negative up boundaries showing a lack of a comprehensive treatment for a situation that conflicts with recommendations for conventional positive up boundaries. The new method simplifies this problem.Small differences in set-up geometry and work speed selection can be easily assessed. The new method can be used as a diagnostic tool for adjusting grinding conditions to overcome roundness problems. The user is not constrained by a historic set-up range since there are practical situations where other set-ups are preferred such as small tangent angles for large and heavy work-pieces, and even negative tangent angle for some types of centreless machine.Previous research is reviewed to provide an understanding of the need for a new approach to stability. Practical implications are explained for selection of grinding conditions. The method is supported by reference to experimental results.     

A multi-objective genetic algorithm (GA) approach for optimization of surface grinding operations

A genetic algorithm (GA) based optimization procedure has been developed to optimize grinding conditions, viz. wheel speed, workpiece speed, depth of dressing and lead of dressing, using multi-objective function model with a weighted approach for surface grinding process. The procedure evaluates the production cost and production rate for the optimum grinding condition, subjected to constraints such as thermal damage, wheel wear parameters, machine tool stiffness and surface finish. New GA procedure is illustrated with an example and optimum results such as production cost, surface finish, metal removal rate are compared with quadratic programming techniques.     

无心磨削中影响工件形状精度的因素分析

无心磨削中，工件的磨削面就是工件的定位基准面。无心磨削后并不都能将工件的形状精度进一步改善，故要得到较高的工件形状精度就要合理地选择磨削参数。影响工件几何形状的因素很多，但影响工件某项几何要素的因素是特定的．如果将这种特定的因素进行总结，可以对实际生产过程进行指导。本文通过对各种影响工件几何要素的因素如：原始误差、工件中心高、托板顶高、磨削区域形状、侧导板位置等归类总结，分析了这些因素分别对“棱圆度”和“椭圆度”的影响，并找出了在这些因素综合作用时，找寻最佳效果的方法。工件中心高对其“棱圆度”和“椭圆度”的影响不一致，选择不同的托板顶角可以在降低中心高的同时，保证对工件“椭圆度”的影响程度，以使中心高度值较低时，满足工件“棱圆度”和“椭圆度”的要求。     

Simulation of the local kinematics in rotational grinding

The rotational grinding process enables production of substrates for the semiconductor industry by a singular capacity to meet planarity and total thickness variation (TTV) requirements. However, the simple configuration is characterised by varying local kinematics. An upper-bound simulation of the meso-scale engagement kinematics has been developed with analysis algorithms that provide estimates of local kinematical parameters. These have been correlated with local measurements for typical brittle-mode microgrinding parameters including measurements of the local normal force. The results generally correlated for surface roughness but not for local normal force where ‘equilibration’ was attributed to system local and bending stiffness components.     

A local process model for simulation of robotic belt grinding

A local process model to estimate the material removal rate in robotic belt grinding is presented and applied to the process simulation system. It calculate the acting force by incorporating the local geometry information of the workpiece instead of the cutting depth parameter with only one certain value as in a global grinding model. The simulation accuracy can be improved to below 5% even for a non-uniform contact under stable cutting conditions.     

Intelligent Centerless Grinding: Global Solution for Process Instabilities and Optimal Cycle Design

Centerless grinding productivity is largely limited by three types of instabilities: chatter, geometric lobing and workpiece rotation problems. Regardless of its negative effect in manufacturing plants, no functional tool has been developed to set up the process, because it involves the simultaneous resolution of several coupled problems. In this paper, new simulation techniques are described to determine instability-free configurations, making it possible to guarantee that the final workpiece profile is round. With this information and taking into account other process restrictions, like system static stiffness and workpiece tolerance, the optimal grinding cycle is designed. These results have been implemented into an intelligent tool to assist the application of this research in industrial environments.     

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.     

轧辊磨削原理简析

通过对轧辊磨削的数学公式模型的定性分析,深入理解磨削理论,掌握磨削规律,从分析中得出优化轧辊磨削表面质量的思路和方法,介绍了优化铝箔轧辊磨削工艺参数的实例。