Centreless Grinding Process Research Articles

An application of artificial neural network and particle swarm optimisation technique for modelling and optimisation of centreless grinding process

Centreless grinding operation is widely used in manufacturing industry for its high level of accuracy and micro-finishing of shaft, pin material. This paper presents an application of artificial neural network and particle swarm optimisation techniques for modelling and optimisation of centreless grinding operation for machining of C40 steel crane-hook-pin. Full factorial design is used taking three factors at three levels each and a total 33 or 27 number of experiments are done in all possible combination of factors. The performance of this particular trained neural network has been tested with the experimental data and found satisfactory. Thus the proposed ANN model is efficiently used for predicting surface roughness in centreless grinding operation. Particle swarm optimisation technique combining with response surface modelling are used to find optimal parameter settings. The optimal parameter corresponds to 12 rpm regulating wheel speed, 1/3rd opening of coolant valve opening and 20.002 µm depth of cut.

An application of artificial neural network and particle swarm optimisation technique for modelling and optimisation of centreless grinding process

An application of artificial neural network and particle swarm optimisation technique for modelling and optimisation of centreless grinding process

Monitoring of through-feed centreless grinding processes with acoustic emission signals

Abstract Grinding is a mechanical removal process applied mainly in finishing operations of hardened workpieces to produce small tolerances with high-quality. Especially, centreless grinding is broadly used in serial production due to the requirement of high accuracy in process. Centreless grinding is used to produce several mechanical components such as, bushings, needles, ball bearings, valves, and stems for shock absorbers. However, the setup of machine tools is very complex and needs long time due to the great number of input variables that should be checked and configured. The acoustic emission monitoring can be used to help the first setup or during the grinding process becoming a on-line detection system. Considering the importance of obtaining an efficient methodology to predict and detect the surface quality and the dimensional errors, a monitoring of the frequency on the spectrum of acoustic emission (EA) was conducted, related to surface roughness Rz, cylindricity, and roundness. The FFT and Wavelet were applied aiming to help the analysis of data and provide the best understanding of the signal and generating an intelligent information in the automation in grinding process. Thus, in this work the results showed that the analysis of the harmonic content of acoustic emission signal is a powerful tool to monitoring the centreless grinding process.

Selection of optimal condition for finishing of centreless-cylindrical ground parts using grey relational and principal component analyses

In this paper, an attempt has been made to determine optimal setting of the centreless grinding process parameters. Three process parameters, i.e., grinding speed, grinding feed and dressing feed each at three levels were considered. The multi-performance characteristics of the process were measured in terms of diameteral deviation, out-of-roundness and surface roughness of the workpiece. Twenty-seven experiments, as per Taguchi’s L27 orthogonal array, were performed on EN52 steel. Grey relational analysis combined with principal component analysis was used to determine grey relational grade. Subsequently, Taguchi response table method and ANOVA were used for data analysis. Confirmation experiment was conducted to determine the gain over the initial design. Results revealed that the grinding speed of 3,500 m/min, grinding feed of 3 mm/min and dressing feed of 100 mm/min yielded the optimum multi-performance characteristics. It was also found that the dressing feed had more effect on responses followed by grinding speed and grinding feed.

Design of an active control of vibration in a centreless grinding machine: theoretical study and experimental implementation

The appearance of vibrations during centreless grinding process is one of the main factors limiting the current requirements of precision and productivity. This paper presents a novel procedure for the design of an active vibration reduction system in a centreless grinding machine using piezoelectric actuators. The different phases involved in the modelling procedure of the machine tool are explained, together with the followed approach to locate the actuators. Taking as reference the finite element model of the machine, the most important mode shapes affecting the chatter behaviour have been considered to obtain a low order state space model. This reduced model has been used to simulate the effectiveness of the control strategy and the results have been compared with those obtained experimentally after the system implementation. A good agreement has been obtained demonstrating that the modelling procedure followed is useful to predict the effectiveness of control systems.

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.

Design of grinding factors based on response surface methodology

The presented paper describes a systematic methodology for empirical modelling and optimization of the plunge centreless grinding process. The assessment of microgeometric quality defining quantity is supported by post-process surface roughness measurements. The design of grinding factors is based on response surface methodology, which integrates a design of experiment, regression modelling technique for fitting a model to experimental data and basic optimization. Central composite response surface design has been employed to develop a second-order surface roughness model. The model has been fully constructed by determination of its structure and regression coefficients. The final goal of experimental study focuses on determination of optimum centreless grinding system set-up and operating conditions for minimization of surface roughness. The computer-aided single-objective optimization, solved by non-linear programming and genetic algorithm, is applied. The results of two different optimization approaches for determination of optimal operating conditions are compared. Finally, further research directions are presented.

Micro-hole Maching of Copper Using the Electro-discharge Machining Process with a Tungsten Carbide Electrode Compared with a Copper Electrode

This paper describes micro-hole machining of a copper plate using the electro-discharge machining (EDM) process. Tungsten carbide was selected as the material for the electrode and compared with a copper-electrode. A precision centreless grinding process was employed to grind the electrode down to the desired diameter. A series of experiments were performed on a traditional EDM machine to investigate the effects of electrode material polarity setting and of a rotating electrode. Results have shown that electrode wear and hole enlargement are both smaller when positive polarity machining is selected; whereas electrode wear is larger and machining speed is higher when negative polarity machining is selected. High-quality micro-hole machining in copper can be achieved by the proposed method.

Influence of contact loss between workpiece and grinding wheel on the roundness errors in centreless grinding

The objective of this paper is the study of certain non-linear phenomena in the centreless grinding process and their effect on roundness quality. These phenomena arise as a consequence of contact loss between workpiece and grinding wheel. A simplified analysis of the problem is carried out to determine the main parameters involved. A qualitative assessment of the effect of these parameters is undertaken by means of a time simulation based on a non-linear bi-dimensional model of the centreless grinding process. Two situations are analysed: the steady process, and the transient spark-out process. The results, which are generalised in graphics form provide an estimation of roundness errors resulting from working under linearly unstable conditions. Finally, a correlation between theoretical and experimental results is presented.

Computer simulation of the plunge centreless grinding process

This paper reports the kinematic analysis of the plunge centreless grinding process considering a uniform mode of infeed. Computer simulation was carried out initially for an ideally round workpiece and regulating wheel, and the optimum set-up and process parameters such as the workpiece surface speed, the work-blade angle, the included tangent angle, etc, to minimise the out-of-roundness error on the workpiece were obtained. Further using these optimum parameters, the effect of regulating wheel and workpiece profile errors such as steps, lobes and randomness, etc., in governing the roundness error produced on the workpiece were studied. In addition, harmonic analysis of the profile produced on the workpiece was carried out to study in details the profile characteristics such as the amplitude spectrum, the dominant harmonic and the average undulation number. The results reported herein will aid manufacturing shop engineers to select set-up and process parameters properly to improve product accuracy in the plunge centreless grinding process.

Experimental investigation of the through-feed centreless-grinding process

This paper reports the results of an experimental programme to study the effects of process parameters on the surface roughness and out-of-roundness error on components produced by the through-feed centreless-grinding process. Experiments have been planned based on the statistical response surface methodology (RSM) technique. Mathematical models correlating the process parameters to the process responses have been obtained. In conclusion, optimal process conditions to minimize the surface roughness and the out-of-roundness error of components are reported.

Some investigations on plunge feed centreless grinding process

This paper reports the results of an experimental programme to study the effects of process parameters on the surface roughness and out-of-roundness error on components produced by the plunge feed centreless grinding process. Experiments have been planned based on the statistical response surface methodology (RSM) technique. Mathematical models correlating the process parameters to the process responses are obtained. In conclusion, optimal process conditions to minimize the out-of-roundness error and the surface roughness on the components are reported

Simulation for the manufacture of rollers for bearings

A model that simulates the rounding up action of rollers for bearings using the centreless grinding process is presented. The basic model can be visualised by representing a centreless grinding machine in which the grinding wheel advances towards the control wheel and the work blade during the infeed cycle. Incorporated in the model is an oscillatory motion of the grinding wheel about its axis, the amplitude of which depends on the magnitude of unbalance of the grinding wheel. Workpiece speed, geometric configuration and grinding wheel speed were varied whilst other process variables were held constant. The criteria for assessing the roundness profiles of the rollers were computed roundness traces. Data obtained revealed that the geometric configuration was more influencial than grinding wheel unbalance in governing the number of waves on the workpiece. For a given set of parameters, it is possible to predict the final roundness profiles of rollers using the model. A more sophisticated model based on the dynamic properties of the process has also been developed.

Vibration Monitoring of the Internal Centreless Grinding Process Part 2: Experimental Results

Experimental results of grinding tests are presented showing how both forced and self-excited vibration occurring during the internal centreless grinding process can be associated with deterioration in workpiece finish and form. Mechanical vibration from rotating machine elements and wear of the dressing diamond and grinding wheel are all investigated. It is shown how a deterioration in these parameters can be associated with characteristic vibration signatures, and a good correlation obtained with the models proposed in Part 1 of this paper.

Vibration Monitoring of the Internal Centreless Grinding Process Part 1: Mathematical Models

The grinding process is complex with many interrelated parameters, and an initially stable process can become unstable as grinding conditions naturally deteriorate. Forced vibration from machine rotating elements and self-excited vibration produce a relative radial movement between the wheel and workpiece during grinding and the wheel and diamond during dressing, causing errors in workpiece finish and form. By monitoring vibration produced during the grinding and wheel dressing operations a measure of expected workpiece quality can be obtained. In order to use vibration monitoring effectively as a means of detecting adverse grinding and dressing conditions it is necessary to gain an insight into the dynamics of the process so that relevant parameters for monitoring are identified. In Part 1 of this paper, with the aid of simple models, the different types of vibration that can occur during the grinding and dressing operations are identified, along with their likely effect on workpiece quality.

Investigations on the through-feed centreless grinding process

SUMMARY This paper reports the results of an experimental programme to study the effect of process parameters on the surface finish and out-of-roundness error on parts produced by the through-feed centreless grinding process. Experiments have been planned based on the statistical response surface methodology (RSM) technique. Mathematical models correlating the process parameters to the process responses are obtained. In conclusion, optimal process conditions to minimize the out-of-roundness error and to improve the surface finish on parts are reported.

Coping with Compliance in the Control of Grinding Processes

This research examines the effects of system compliance on the achievement of size in the centreless grinding process. Work has been carried out on incorporating a compliance model into an adaptive control strategy. A prime objective was to optimise the process in order to reduce cycle time. The strategy takes account of the machine compliance, the variable nature of the grinding forces and of compliance due to thin wall components.

Three-Dimensional Geometric Analysis of the Plunge Centreless Grinding Process

The grinding action and the rounding mechanism are highly complex in centreless grinding. The axis of the workpiece not only moves laterally but also tilts during the grinding process. Rowe and Barash have developed a two-dimensional model for an infeed centreless grinding neglecting the tilt of the workpiece. In this paper, an attempt has been made to develop a simulation model which incorporates the tilt of the workpiece. The theoretical and experimental investigations have been carried out with workpieces having specific geometries and the results are discussed.

Improvements in Centreless Grinding Machine Design

In order to investigate the effects of a high mount frequency and the stiffness requirements in the centreless grinding process, a now research oriented machine tool has been designed and developed. Compared with a conventional machine of comparable size it has a very much higher static stiffness and a first resonant frequency of 500 Hz. The grinding results suggest that future centreless grinding machines should be designed to achieve a high first resonant frequency to minimise forced vibrations. However, for some grinding operations it may be beneficial to continue to utilise a compliant rubber bonded control wheel to provide adequate static compliance and hence avoid exaggeration of the geometric regenerative effect. A combination of a moderate degree of static compliance and a high first resonant frequency was found to jive the best overall results. It was also shown that there is an optimal range of rotational work-speeds for minimum roundness errors. This range was related to the grinding wheel rotational speed by the ratio Ng/Hw. The optimal speed ratio range for the new stiff machine was 2 to 13 whereas for a conventional machine the range was 6 to 9 for otherwise similar grinding conditions.

A technique for simulation of cylindrical grinding processes by hybrid computation

Whereas analogue computers may be used to simulate simple models of machining processes, the construction of more realistic models with long time delays is not easily achieved with sufficient phase accuracy. For this situation a digital computer has been used and has the additional benefit that logical statements may be built in to a program if required for computation of limiting conditions. This paper shows how a hybrid analogue/digital model provides an economical and realistic solution to simulation of cylindrical grinding processes. The model described is applied to a simple situation but serves to demonstrate the importance of the following considerations in grinding processes. 1. (1) Realistic time delays. 2. (2) The importance of large static compliance. 3. (3) Transient behaviour. The model may be applied to various grinding processes with little modification. The centreless grinding process is particularly interesting because there are three basic time delays involved.