Search Results (12)

This paper generalizes the geometrical rounding mechanism of regenerative centerless supports as applied to centerless grinding, shoe centerless grinding, and centerless support superfinishing. Relationships between support conditions and rounding stability are analyzed using a newly introduced parameter, the generalized center height angle. The effects of roundness errors at the support points on the depth of cut are clarified, and the rounding stability for each undulation on the workpiece is examined. Additionally, the geometrical filter effects caused by interference and the contact length with abrasive wheels are depicted, showing a significant reduction in roundness components for undulations above the cutoff threshold. The proposed rounding mechanism, based on the generalized center height angle, accurately predicts unstable undulations, a finding that is experimentally verified through tests on both centerless grinding and shoe centerless grinding setups. Full article

With growing environmental concerns and regulatory requirements, manufacturers are increasingly required to monitor and reduce the environmental impacts of their production processes. Despite increasing digitalization and data-collection capabilities, manufacturers are challenged in collecting the right data and framing process improvement targets. To address this challenge, this paper presents a bottom-up methodology based on the life cycle assessment for identifying performance indicators with the goal of monitoring and reducing the overall environmental impacts of a manufacturing process. More specifically, process performance indicators are defined as a set of controllable process parameters, and their suitability for sustainability monitoring is evaluated based on their sensitivity, measurability, actionability, reliability, timeliness, and human-centricity with respect to a chosen environmental impact category. The bottom-up formulation of process performance indicators is demonstrated through a real-world case study on an infeed centerless grinding process in a large manufacturing company. Results from the case study show that the process performance indicators with regards to climate change impacts included (i) reduction in grinding time, (ii) reduction in total grinding power, (iii) reduction in sparkout time, and (iv) increase in batch size. Full article

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 (S_nf), the speed of the workpiece (n_w), and the grinding depth (a_f), 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. Full article

Roundness is one of the most important evaluation indexes of rotary parts. The formation and change of roundness in the machining of parts is essentially the formation and genetic process of profile. Centerless positioning machining is one of the main surface finishing methods of rotary parts. The rounding mechanism of centerless positioning machining determines its unique roundness profile formation and genetic characteristics. How to eliminate the roundness error of centerless positioning machining has become one of the important issues in the research of high-precision rotary part machining. This paper explores the influence of process parameters on the roundness error from the perspective of profile evolution during centerless grinding and electrochemical mechanical machining, with the aim of providing a cross-process collaboration strategy for improving bearing raceway accuracy. Through an experiment of centerless grinding, the influence law and mechanism of process parameters on the profile are discussed. On this basis, electrochemical mechanical machining experiments are designed to explore the variation rules and mechanisms of different profile shapes in the machining process. The cross-process collaboration strategy is studied, and reasonable parameters of centerless grinding and electrochemical mechanical machining are determined. The results show that in the centerless grinding stage, increasing the support plate angle can form a multiple-lobe profile with high frequency within a wide range of process parameters. Electrochemical mechanical machining can effectively smooth the high-frequency profile and appropriately expanding the cathode coverage can improve the roundness error and reduce the requirement of initial accuracy of a multiple-lobe profile workpiece to a certain extent. Therefore, the combined machining technology of “centerless grinding + electrochemical mechanical machining” provides an efficient technical means to realize the precision machining of rotary parts such as bearing raceways. Full article

In order to improve the accuracy and batch consistency of cylindrical roller machining, in this paper, a both-sides cylindrical roller machining method based on hard ceramic plate is proposed. Traditional cast iron and stainless-steel polishing plate were replaced by ceramic materials with high hardness and good wear resistance. After processing by centerless grinding, the cylindrical roller is processed by both-sides lapping and polishing using Al₂O₃ ceramic plates. The roundness, diameter and surface quality of the roller and the wear of the ceramic plate before and after machining were compared and analyzed in order to evaluate the feasibility and effectiveness of this method. After grinding for 1 h and polishing for 8 h, the average roundness of the cylindrical rollers decreased from the initial 2.3 μm to 0.32 μm, while the roundness of each roller tended to be the same. At the same time, the batch diameter deviation of cylindrical rollers was reduced from 3 μm to 1 μm, and the batch consistency was satisfactory. The machining marks produced by centerless grinding on the roller surface were completely removed, and the surface quality was significantly improved. The surface roughness after polishing reached Ra 16 nm. The upper and lower ceramic plate had certain wear, but the amount was small, having little impact on the machining results. The shape accuracy and batch consistency of the rollers after machining were satisfactory. The ceramic plate had high hardness, good wear resistance and small wear in the machining process. Additionally, it could maintain extremely high flatness for a long time. Using hard ceramic plates to process cylindrical rollers, high precision and high consistency cylindrical rollers can be obtained after machining. Full article

In today’s engineering industry, technical diagnostics presents many advantages for improving the management of machining centers and automated production lines. As the fourth industrial revolution is currently being implemented, which includes machine diagnostics, the idea of adding information from the field of vibrodiagnostics was born. The vibration of the workpiece or machine tool negatively affects the geometric parameters of the machined surfaces of the workpiece. Through vibrodiagnostics, the influence of cutting parameters on the oscillation of a bearing steel workpiece during centerless grinding is investigated. The presented publication deals with the vibration of the mechanical parts of a centerless grinding machine. The oscillations are recorded by acceleration sensors, which are also placed on the support ruler in which the workpieces are guided, and the recorded data are input parameters for statistical processing of acceleration values in the form of statistical characteristics (minimum, lower quartile, median, upper quartile, maximum). In this paper, this procedure was applied for the selection of the optimum cutting parameters (for the speed of the support wheel), where the machining parameters at which the minimum oscillation values occur were selected based on the above-mentioned statistical characteristics. This optimization procedure revealed increased vibration values which reached the highest amplitude on the ruler, namely accelerations of 11 m/s², the origin of which was subsequently detected by STFT because the occurrence of resonance events or the excitation of natural frequencies of the machine were suspected. The STFT analysis identified a resonant region at machine start-up determined by the spindle speed which excites the resonance on the machine. The speed range between 1950 and 2150 rpm, which corresponds to the built-up resonance, was provided to the technologists to ensure that the machine was not operated around this resonance region at 400 and 760 Hz until the undesired phenomenon was eliminated. The results of the individual measurements provided information on the ideal setting of the cutting parameters and the current state of the machine. Full article

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 (S_nf), the speed of the workpiece (V_w), the cutting depth of fine grinding (a_f), and the number of ground parts (N_p), 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 (G_w), 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 G_w, N’p, and MRR and mathematical models that express the dependencies of outcome parameters G_w, 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: S_nf = 15.38 (µm/s), Vw = 6.00 (m/min), a_f = 11.76 (µm), and N_p = 20 (parts/cycle). In addition, the impact of the four process parameters (S_nf, V_w, a_f, N_p) on the wear of the grinding wheel (G_w), the oval level of parts (O_p), 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 G_w, Ra, Op, and MRR were controlled within 5% of the ranges. Full article

This paper presents the effect of grinding wheel contact stiffness on the plunge grinding cycle. First, it proposes a novel model of the generalized plunge grinding system. The model is applicable to all plunge grinding operations including cylindrical, centerless, shoe-centerless, internal, and shoe-internal grinding. The analysis of the model explicitly describes transient behaviors during the ramp infeed and the spark-out in the plunge grinding cycle. Clarification is provided regarding the premise that the system stiffness is composed of machine stiffness and wheel contact stiffness, and these stiffnesses significantly affect productivity and grinding accuracy. The elastic deflection of the grinding wheel is accurately measured and formulas for representing the deflection nature under various contact loads are derived. The deflection model allows us to find the non-linear contact stiffness with respect to the normal load. The contact stiffnesses of four kinds of grinding wheels with different grades and bond materials are presented. Both cylindrical grinding and centerless grinding tests are carried out, and it is experimentally revealed that the time constant at ramp infeed and spark-out is significantly prolonged by reducing the grinding force. It is verified that a simulation of the grinding tests using the proposed model can accurately predict critical parameters like forces and machine deflection during plunge grinding operations. Finally, this paper provides a guideline for grinding cycle design in order to achieve the required productivity and grinding accuracy. Full article

An alternative method is devised for calculating dynamic stability maps in cylindrical and centerless infeed grinding processes. The method is based on the application of the Floquet theorem by repeated time integrations. Without the need of building the transition matrix, this is the most efficient calculation in terms of computation effort compared to previously presented time-domain stability analysis methods (semi-discretization or time-domain simulations). In the analyzed cases, subspace iteration has been up to 130 times faster. One of the advantages of these time-domain methods to the detriment of frequency domain ones is that they can analyze the stability of regenerative chatter with the application of variable workpiece speed, a well-known technique to avoid chatter vibrations in grinding processes so the optimal combination of amplitude and frequency can be selected. Subspace iteration methods also deal with this analysis, providing an efficient solution between 27 and 47 times faster than the abovementioned methods. Validation of this method has been carried out by comparing its accuracy with previous published methods such as semi-discretization, frequency and time-domain simulations, obtaining good correlation in the results of the dynamic stability maps and the instability reduction ratio maps due to the application of variable speed. Full article

This paper synthesizes the design of an infeed cylindrical grinding system into a total system composed of the grinding mechanism and the grinding machine characteristics. The causalities between the grinding parameters and the machine structures are discussed, and the infeed grinding processes are analyzed as outputs that represent responses to the inputs. These relationships are integrated into a block diagram with closed-loop feedback. A novel model exhibiting practical parameters such as grinding speed, infeed rate and MRR (Material Removal Rate) is proposed. The analysis of the grinding system derived a critical factor, the “grinding time contact,” which governs the transient behaviors of process parameters such as forces and machine deflection. The process parameters during the infeed cycle including spark-out grinding were investigated, and the formulas required for the cycle design are presented. Furthermore, to improve accuracy and productivity, the features of the cycle design are described and procedures for controlling size error and roundness are discussed. Finally, the model was verified with infeed grinding tests applied to both the chuck-type cylindrical and centerless grinding methods. Full article

The through-feed method in centerless grinding allows manufacturers to produce cylindrical parts at much higher levels of productivity than can be achieved with in-feed grinding, so it has been extensively employed in industry. However, its rounding mechanism is not yet well understood due to the complexity of the through-feed process. This paper presents the fundamental parameters, such as material removal rates, forces, and so on in the through-feed grinding, and analyses on the grinding system with feedback loops, including regenerative functions and the machine dynamic functions. Further, the characteristic roots of the system, representing the number of waves and the growth rates of the harmonics in roundness, are identified at each grinding position from entry to exit. To evaluate the grinding process stability, a rounding stability index (RSI) was proposed. It was demonstrated that the analytical tool modeled in this paper can identify the optimum operational conditions by the RSI for achieving desired grinding productivity and accuracy. Finally, the model is verified with grinding tests, and the nm-order roundness obtained by the tests is shown. Full article

The centerless grinding process demonstrates superior grinding accuracy with extremely high productivity, but only if the setup conditions are properly set up. Otherwise, various unfavorable phenomena manifest during the grinding processes and become serious obstacles to achieving that high quality and productivity. These phenomena are associated with the fundamental stabilities of the centerless grinding system, so it is essential to keep the system stable by setting up the appropriate grinding conditions. This paper describes the development of a model for finding the setup conditions that simultaneously satisfy the three stability criteria of centerless grinding systems: (1) work rotation stability for safe operations; (2) geometrical rounding stability for better roundness; and (3) dynamic system stability for chatter-free grinding. The objective of the model development is to produce combinations of optimal setup conditions as the outputs of the model, and to rank the priority of the outputs using PI (performance index) functions based on the process aims (productivity or accuracy). The paper demonstrates that the developed model, named Opt-Setup Master, can generate the optimum setup conditions to ensure safe operations, better roundness and chatter-free grinding. It provides practical setup conditions as well as scientific parameters and fundamental grinding parameters. Finally, the paper verifies that the Opt-Setup Master provides the setup conditions that simultaneously satisfy all three stability criteria of the centerless grinding system. Full article