Centerless Grinding Operations Research Articles

ГРУППИРОВАНИЕ ПО ТЕХНОЛОГИЧЕСКИМ ПРИЗНАКАМ ОПЕРАЦИЙ ВРЕЗНОГО БЕСЦЕНТРОВОГО ШЛИФОВАНИЯ

Mortise, as one of the methods of centerless grinding, has high productivity and processing accuracy. However, the scope of its application in existing industries is limited to a rather narrow area. This is largely due to the lack of a fully formed methodological base for the stages of equipment setup and management of the implementation of the technological operation. The article presents proposals for the structural classification of inset centerless grinding, including their grouping according to the criterion of uniformity of design procedures of individual stages of technological support. The created formalized models ensure the consistent formation of clusters of processing schemes with the possibility of taking into account specific production conditions. The results of the grouping of processing methods for design procedures for the appointment of rational technological modes of mortise centerless grinding operations are presented.

The Effects of Process Parameters on Workpiece Roundness in the Shoe-Type Centerless Grinding Operation for Internal Raceway of Ball Bearings

One of the most important indices of bearing raceway, roundness, has an important influence on the life and performance of the bearing. Currently, shoe-type centerless grinding (STCG) is a core process for the fabrication of the raceway surface. Some researchers have carried out studies in this field; however, the reason and extent of the influence of process parameters on the workpiece roundness in the STCG operation for the internal raceway of the 6208 ball bearings are not clear up to now. In this paper, new research on the effects of process parameters on workpiece roundness in the STCG operation for the internal raceway of the 6208 ball bearings is presented. The influence of the angular placement of the two shoes, as well as the technology parameters including the offset between the rotational centers of the workpiece and the magnetic drivehead (e), the normal feed rate (Snf), the speed of the workpiece (nw), and the grinding depth (af), on the roundness of the raceway surface were investigated both theoretically and experimentally to solve the difficulties in the STCG operation to ensure the roundness of the raceway surface. Based on the research results, a guideline for selecting initial process parameters is introduced to ensure the roundness of the bearing raceway in the STCG operation for the internal raceway of 6208_ball bearings on the 3MK136B grinder.

Multistage centerless grinding setup via discrete mapping

This article introduces a multistage approach for the execution of plunge centerless grinding operations aimed at accelerating waviness cancellation from workpiece initial profile, while preventing the harmful consequences of geometrical process instability. It suggests decomposing the process into multiple phases characterized by different workpiece heights and/or blade angle. The best parameters combination is identified by computing and analyzing the transition matrix of the overall process after a discretization of the profile evolution equation. Choosing to apply a two stages process, a map is computed with the most critical amplification gain of the harmonic components on the workpiece profile, for different heights combination. The gain map can be used to identify the height combination that guarantees a given roundness reduction with the minimal process duration for any initial profile. The analysis result is demonstrated comparing the effectiveness of a 2-stages process with the usual single stage process of the same duration.

Совершенствование технологической подготовки операций бесцентрового шлифования

Совершенствование технологической подготовки операций бесцентрового шлифования

Multi-Objective Optimization of Process Parameters to Enhance Efficiency in the Shoe-Type Centerless Grinding Operation for Internal Raceway of Ball Bearings

In this article, new research on the multi-objective optimization of the process parameters applied to enhance the efficiency in the shoe-type centerless grinding operation for the inner ring raceway of the ball bearing made from SUJ2 alloy steel is presented. The four important input parameters for this process, which included the normal feed rate of fine grinding (Snf), the speed of the workpiece (Vw), the cutting depth of fine grinding (af), and the number of ground parts (Np), were investigated. The aim of the study was to find the most appropriate value set of process parameters in order to, simultaneously minimize the grindstone wear (Gw), maximize the material removal rate (MRR) and the total number of ground parts in a grinding cycle (N’p), while guaranteeing other technology requirements such as surface roughness Ra ≤ 0.5 (µm), oval level Op ≤ 3 (µm), etc. In order to solve the problem, based on the experimental data, in which the grindstone wear was measured online by a measuring system consisting of two pneumatic probes, the optimization of the target functions of Gw, N’p, and MRR and mathematical models that express the dependencies of outcome parameters Gw, Ra, Op, MRR, etc. on the process parameters were determined. Therefore, a global optimal solution of such a discrete and nonlinear multi-objective optimization problem was solved by using a genetic algorithm, presenting the most appropriate process parameters as follows: Snf = 15.38 (µm/s), Vw = 6.00 (m/min), af = 11.76 (µm), and Np = 20 (parts/cycle). In addition, the impact of the four process parameters (Snf, Vw, af, Np) on the wear of the grinding wheel (Gw), the oval level of parts (Op), and the surface roughness of parts (Ra) was evaluated. The discovered technology mode has been applied to the real machining process for the inner ring raceway of the 6208_ball bearing made from SUJ2 alloy steel, and the outcome showed a much better result in comparison with default setting modes, while still ensuring the technology requirements. The difference between the predicted values and the real values of the parameters Gw, Ra, Op, and MRR were controlled within 5% of the ranges.

Simulation of formation waviness on working surfaces rings of roller bearings during centerless grinding operations

In the article was investigated the formation of waviness on working surfaces rings of roller bearings, which causes the appearance of noise and vibration in the bearing units of machines and mechanisms. To establish patterns of appearance of waviness were used some principles of systems theory and mathematic simulation; in particular the establishments of transfer functions, finding the equation of dynamics, usage of Laplace transformations to solve differential equations, building locus diagrams and others.For the purpose of analysis, centerless grinding system, with some simplifications was considered as a linear, continuous, closed dynamic system. On the basis of this was compiled flow-chart of plunge centerless grinding model on rigid shoes, and was found the transfer function. The solution of the system’s characteristic equation revealed influence of waviness on the ground surface and the regeneration process of this waviness on the locus diagram of displacement vector of the workpiece’s center.As the investigation, result established a regularity of change of waviness harmonics depending on the geometry of rigid shoes setting. Management of waviness surface bodies of revolution on centerless grinding operations is an important prerequisite for getting optimum quality parameters of working surfaces of the roller bearing rings and as a result effect on exploitation properties of the bearing, such as noise, durability, and reliability. Using the results of this research will allow choosing such geometry of setting grinding on rigid shoes, which predictably increases or decreases the parameters of a particular harmonic of waviness.

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°.

Ceramic Balls Machining by Centerless Grinding Using a Surface Grinder

This paper proposes a novel method for machining ceramic balls by centerless grinding technique performed on a surface grinder. In this method, a compact unit consisting mainly of an ultrasonic shoe, an ultrasonic regulator, a relay controller, a blade, a stopper and their respective holders is installed on the worktable of a surface grinder to conduct centerless grinding operations of ceramic balls. The ultrasonic shoe and regulator are produced by bonding a piezoelectric ceramic device (PZT) onto a metal elastic body, and when two phases of AC voltage are applied to the PZT an elliptic motion occurs on their end-faces which can be used to control the ball rotational motion in the radial and axial direction of the wheel, respectively. The function of the relay controller is to regulate the alternating current “on” and “off” time which is applied on the regulator for achieving the whole spherical surface grinding process. A grinding unit was actually constructed and it was experimentally confirmed that the ball rotational speed can be controlled well by the shoe or regulator. Grinding tests were subsequently carried out and the obtained results indicated that the constructed grinding unit performed well on actual ball centerless grinding operations.

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.

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.

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.

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.

Experimental Study of Tangential-Feed Centerless Grinding Process Performed on Surface Grinder

In our previous study, a new centerless grinding method using surface grinder was proposed. In this method, a compact unit consisting mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders is installed on the worktable of a multipurpose surface grinder to conduct tangential-feed centerless grinding operations. For the complete establishment of this new method, firstly in this paper workpiece rotational speed control tests were carried out to make sure that the workpiece rotational speed is exactly controlled by the elliptic vibration of shoe to achieve high-precision centerless grinding. Then, the effects of the process parameters such as the worktable feed rate, the stock removal and the workpiece rotational speed on the workpiece roundness were clarified experimentally. The obtained results showed that (1) The workpiece rotational speed can be controlled exactly by the shoe ultrasonic vibration, (2) The roundness is improved with the increases in the voltage applied and the stock removal, but the decrease in the worktable feed rate; The best roundness obtained was 0.84m.

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.

A new centerless grinding technique using a surface grinder

This paper proposes a new centerless grinding technique using a surface grinder. By this technique centerless grinding operations can be performed at low cost by installing a compact centerless grinding unit on the worktable of a multipurpose surface grinder and without the employment of a costly centerless grinder. The unit consists mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders. The shoe is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304), and an elliptic motion occurs on its end-face when two phases of AC voltage are applied to the PZT. The function of the shoe is to hold the cylindrical workpiece in conjunction with the blade, and to control the workpiece rotational speed with the elliptic motion on its end-face during grinding. The detailed structure of the unit was designed by Finite Element Method (FEM) analysis, and an actually constructed unit was installed on the worktable of a CNC surface grinder to perform tangential centerless grinding operations after its fundamental performance such as elliptic motion generation and capacity to control workpiece rotational speed had been investigated. As a result, it was clarified that the workpiece rotational speed changes linearly with variation in the applied voltage. This indicates that the workpiece rotational motion can be precisely controlled by the elliptic motion of the shoe. In addition, the workpiece roundness was clearly improved from an initial value of 23 μm to a final value of 2.6 μm after grinding, indicating that the constructed unit performed well in actual grinding operations.

Controlling the Workpiece Rotation Speed with an Ultrasonic Regulator in Microscale Centerless Grinding(M^4 processes and micro-manufacturing for science (continued))

This paper describes the design, construction, and performance confirmation of an ultrasonic regulator used for controlling the workpiece rotation speed in microscale centerless grinding. The ultrasonic regulator is constructed by bonding a plate-shaped piezoceramic device on an I-shaped metal body (SUS304), on the end face of which microscale elliptic vibration is generated. The structure and dimensions of an ultrasonic regulator capable of controlling the workpiece rotation speed in microscale centerless grinding was designed by FEM analysis. Following workpiece rotation control tests under grinding-like configuration, an ultrasonic regulator produced was installed on an existing centerless grinder to perform actual microscale centerless grinding operations involving a tungsten carbide pin-shaped workpiece 0.6mm in diameter and 15mm in length. The experimental result gave a microscale workpiece 60μm in diameter and 15mm in length.

106 平面研削盤を用いたセンタレス研削法の開発 : 実験装置の試作と二,三の研削テスト(OS3 最新工作機械)

This paper proposes a new centerless grinding technique using surface grinder. It is a technique that centerless grinding operations are performed in low cost by installing a compact centerless grinding unit consisting mainly of an ultrasonic elliptic-vibration shoe, a blade, and their respective holders on the worktable of a multipurpose surface grinder without the employment of a costly centerless grinder. The function of the shoe is to hold the cylindrical workpiece together with the blade, and to control the workpiece rotational speed with the elliptic motion on its end face during grinding. In this report, the design and manufacture of a centerless grinding unit, and several grinding operations on the produced unit using a surface grinder are described.

Combined Taguchi and dual response method for optimization of a centerless grinding operation

Offline quality control has been widely accepted as a key to high quality products at low price. The concept of robust design using Taguchi methodology is versatile and its application is not limited to any specific area. However, Taguchi techniques have their own shortcomings. Other methodologies like dual response methodology for process optimization have also been used with success. This paper presents a successful application of combined Taguchi and dual response methodology to determine robust condition for minimization of out of roundness error of workpieces for centerless grinding operation. From the confirmation runs, it was observed that this approach led to successful identification of optimum process parameter values.

Studies on Centerless Grinding. Influeuce of Grinding Wheel Irregularity on Workpiece Roundness.

The workpiece rounding mechanism in centerless grinding is very much complicated compared to that in cylindrical grinding. Even a very small disturbance such as irregularity on the grinding wheel or the regulating wheel circumference, which makes the depth of cut at grinding point to change, may causes significant workpiece roundness deterioration in a centerless grinding operation. To minimize the effect of disturbance on the roundness, this paper investigates the mechanism of roundness deteriorating action analytically and determines the roundness error caused by disturbance quantitatively. It is found that the roundness deterioration can be avoided by controlling the ratio of grinding wheel and workpiece rotational speed.

自励振動発達の抑制機構

The chatter vibration in grinding differs from that in cutting on the points that the wavinesses are formed on both wheel and work peripheries, which makes it more difficult to solve the grinding chatter behavior. In most centerless grinding operations, however, the waviness is formed only on the work circumference and the theoretically analyzed result can well explain the experimented one. But some cares must be taken here because the special arrangement to support the work in centerless grinding has much affect on the occurrence of chatter. Under the consideration of above features, the present paper states analytically the relation between the growing up speed of self-excited chatter amplitude and the work revoluting speed in centerless grinding, and it is made clear that the amplitude of chatter can be suppressed to build up if the work speed is reduced adaptively in accordance with the occurrence of self-excited chatter vibration.