Vibratory Finisher Research Articles

Modeling of the Vibratory Tube Finisher Container

Abstract The paper is dedicated to the problem of modeling the container of vibratory tube finisher additive manufacturing technology. The aim of the research is to develop an engineering approach of designing a rational model of deformative oscillations of a big size container. A thin-walled open cross section cylindrical beam is used as a model of bend and rotation of the vibratory tube finisher container. A method of division of all components of a strain and deformative state into the main and secondary is used to evaluate variants of a model of the vibratory tube finisher container. A ratio of the principle dimension of a cross section and changing of the stress-strain state is used as a weight parameter of components of potential and kinetic energy. A shear model of a thin-walled beam can be used to study the dynamic deformations not only in the elongated containers but in containers with commensurable quantities of its specific dimensions, too. Accuracy regarding the main natural frequency will be satisfied (with error about 1 %) when the length of the container is two times greater than a specific dimension of a cross section. Conditions of the rational models of deformation vibrations of containers are presented in a graph form that is comfortable in engineering practice.

Comparison of DEM predictions and measured wall-media contact forces and work in a vibratory finisher

Discrete element methods (DEM) have been widely used in predicting the behavior of vibrated granular media, including that in vibratory finishing (VF) processes. In VF loose abrasive particles are fluidized by a vibrating container and the particle vibration work on the surface of parts entrained in the granular bed. In the present work, DEM was used to predict the forces exerted by the container walls on the granular media and the results were compared with previous experimental measurements performed with varying frequencies of vibration and amounts of media in the container. It was found that the overall trends in the DEM simulations were comparable to the experiments results, in that wall forces increased significantly with frequency but less so with increasing media mass. This was attributed to the viscous forces of granular media deformation, which generated wall forces that tended to increase with increasing media deformation rate and with increasing media pressure, although these trends were less pronounced in the DEM models than in the experiments. The DEM predictions of the contact force magnitudes were, however, well predicted in only two of the three container locations. The DEM predictions were also characterized by much larger cycle-to-cycle variations in the wall-media contact behavior than was observed experimentally. This included the presence of apparently random vibration cycles without any wall-media contact, which were not present in the actual force measurements.

Dynamic modeling and trajectory measurement on vibratory finishing

Vibratory finishing has been widely used in advanced manufacturing industry, such as aerospace, wind power equipment, and hydraulic equipment. Although the mechanism of vibratory surface finishing has been studied for decades, the fundamental issues of vibratory finishing such as the trajectories of media and workpiece during finishing are still not solved. In this study, a four-degree-of-freedom dynamic model is developed to analyze the dynamic responses of the vibratory finisher and validated by experimental tests. Coupled RecurDyn and EDEM technique is employed to simulate the trajectories of media and workpiece in a vibratory finisher. The simulation results are validated by X-ray experimental tests. Both the simulation and X-ray images show that the global trajectories of media and workpiece are a combination of three motions, circumferential motion around the center axis of the vibrating barrel, the radial elliptical motion around the center of rotation, and the self-flip movement. The trajectories of media exhibit an annular helix motion in the vibratory barrel in general. The shape, density, and weight of a workpiece and media have a significant effect on their global trajectory and local movements. The mechanism of vibratory surface finishing is better understood, which has great importance to the improvement of existing surface finishing processing technology and development of the next generation of vibratory mass finishing.

Measurements of wall-media contact forces and work in a vibratory finisher

The bulk flow and local impact velocities of loose abrasive particles in vibratory finishing operations have been explained in the literature in terms of the forces exerted by the vibrating container walls. In the present work, these forces were measured using a force sensor embedded in the walls of a vibrating tub finisher loaded with various amounts of steel media and subject to different vibration frequencies. It was found that wall-media contact forces increased with the depth of media above the sensor and with the normal wall velocity, which explained why wall forces remained approximately unchanged with varying media mass, but increased with increasing tub frequency. The average impulse of the wall on the media increased with increasing media mass and decreased with increasing frequency of vibration. The work done by the walls was also measured and was found to increase with increasing tub frequency for a fixed media mass.

Development of technological solutions for flour production with specified quality parameters

Today, bakery and milling industry is actively developing, as well as other branches of food industry. This is due to the applying of new foreign trends to the technology and range of products of the Ukrainian market. In these conditions, the classic offering of flour is already inadequate. To meet the needs of modern bakeries, milling industry is facing a new challenge: production of flour grades with specified quality parameters.
 The article considers the technological and baking properties of flour from all systems of the technological process of a flourmill with a capacity of 300 tons per day. Studies have shown that flour from first-quality systems is whiter by 15–20 units, is by 1.0–1.8% lower in ash, by 1–3% lower in protein, by 2–4% lower in gluten with more elastic properties, has a Falling Number higher by 80–110 s, a water absorption capacity lower by 1–5%, a damaged starch value lower by 1–3 UCD as compared to flour from systems of some other quality. Technological solutions are developed for producing a special flour grade by its selection and mixing from the streams of the 1st break system (B1/B2), 1st reduction system (C1/C2), 2nd sizing system (R2), and 1st vibratory bran finisher system (V1). It has been found that the developed grade of flour – patent superior grade flour – meets the requirements and has high baking performance. It has a gluten content higher by 2%, Falling Number lower by 20 s, and Starch Damage less by 2 UCD, as compared to patent high grade flour. This makes it possible to obtain bread larger in volume by 55 cm3, with smooth, even crust, elastic white crumb, and uniform porosity (80%). According to rheological characteristics determined with a Mixolab device, patent superior grade flour has a higher Water Absorption Index, a higher Viscosity Index, a lower Gluten+ Index, and a lower Amylase Index than patent high grade flour. The developed technological solutions for producing flour with specified quality parameters have been introduced at the flourmill with an equipment package, from the company Alapala (Turkey), with a capacity of 300 tons per day.

Bulk mass flow in a vibratory finisher: mechanisms and effect of process parameters

Vibratory finishing is a widely-used manufacturing process in which a vibrating container filled with granular media becomes fluidized. The resulting bulk flow entrains workpieces and exposes their surfaces to the impacts resulting from the small-scale media vibrations. The bulk flow is responsible for entrainment and mixing, while the media vibration does work on the surfaces. The selection of machine vibration parameters is commonly based on experience due to the difficulty in predicting the fluidized bed behavior. In this work, a discrete element method was used to investigate how the bulk flow in an actual tub finisher filled with steel balls depends on the tub motion parameters through a parametric study. The underlying mechanisms that create and drive the bulk flow were identified by examining the relationships between the bulk flow rates and the wall forces. Finally, the connection between the wall motion and the wall forces was investigated. The tub frequency was the most effective control parameter and there was an optimal phase difference between the horizontal and vertical vibrations to maximize bulk flow. The relationship between the media packing at the walls and the tangential forces between the walls and the media explained the formation and speed of the bulk flow. Lastly, it was shown that the tangential wall forces, unlike the normal forces, cannot be obtained from the known wall motion alone since they also depend on the media velocities relative to the walls.

Finite element continuum modeling of vibrationally-fluidized granular flows

Discrete element modeling of granular flows is effective, but requires large numerical models. In an effort to reduce computational effort, this paper presents a finite element (FE) continuum model of the vibrationally fluidized granular flow produced by a tub vibratory finisher. The constitutive equations governing the continuum model were calibrated using the discrete element method (DEM). A constant stiffness was used for the normal contact of the polyurethane tub wall and the spherical steel media, and an effective coefficient of Coulomb friction was obtained by studying the variation of the shear and normal forces at different points along the tub wall using DEM simulations. The DEM predictions of the ratio of the tangential to normal contact forces showed that rolling of the media on the tub wall was much more common than sliding, and the average effective coefficient of friction was relatively uniform over the wall. Average values of the equivalent elastic and plastic properties of the media were used in the continuum model, neglecting the small local variations that existed within the vibrationally-fluidized bed. The bulk flow behavior of the equivalent continuum media was then studied using both Lagrangian and Eulerian FE formulations. The bulk flow velocities predicted by the Lagrangian approach were in good agreement with those obtained using DEM simulations over a wide range of tub wall amplitudes. The qualitative trend of the local impact velocity distribution at various locations in the tub predicted by the DEM agreed with the trend predicted by the continuum model using the shear rate as a measure of the granular temperature and hence local velocity. The FE simulations required approximately 8 times less computing time than the equivalent DEM.

Particle impact velocities in a vibrationally fluidized granular flow: Measurements and discrete element predictions

Both the local impact and bulk flow velocities within a tub vibratory finisher were predicted using discrete element modeling (DEM) and compared to the measured values for spherical steel media. The sensitivities of the predicted impact velocities to uncertainties in the contact coefficients (friction, restitution and rolling friction) were studied, beginning with an analytical model of two-body collision. The sensitivity analysis was then extended to a simplified DE model of the flow within the vibratory finisher consisting of a single-layer of particles moving between parallel sheets of glass. It was observed that the impact and bulk flow velocities were relatively insensitive to uncertainties in the coefficients of friction and restitution. These coefficients were measured for the particle–particle and the particle–wall interactions for the steel media and tub wall using a linear tribometer and a laser displacement sensor. Several DE models with different numbers of particle layers between the glass partitions were compared, and it was concluded that the predicted impact and bulk flow velocities were dependent on the number of layers in the model. Consequently, the final DE model mimicked the key aspects of the experimental setup, including the submerged laser displacement sensor used to make the measurements of bulk flow and impact velocity. Another investigation showed that a reduced shear modulus could be used in the model to decrease run times without significantly affecting either the bulk flow or impact velocities. The DE method predictions of both impact velocity and bulk flow velocity were in reasonable agreement with the experimental measurements at points within the vibrationally-fluidized bed, with maximum differences of 20% and 30%, respectively.

Development of a laser displacement probe to measure particle impact velocities in vibrationally fluidized granular flows

Abstract A new laser displacement probe was developed to measure the impact velocities of particles within vibrationally fluidized beds. Key features of the displacement signals were interpreted using an analysis of the motion of a vibrating particle contacting the vibrating sensor window. The sensor output was also used to measure bulk flow velocity along the probe window and to provide a measure of the media packing. The probe was demonstrated in a tub vibratory finisher containing either steel or porcelain spheres. Sample measurements were made at several fixed locations in the vibratory tub, in three orthogonal directions. The displacement signals from the laser sensors were analyzed to obtain the probability distribution functions of the impact velocity of the particles. The impact velocity was affected by the orientation of the laser probe relative to the bulk flow velocity, and the density and elastic properties of the granular media. The average impact velocity of the porcelain balls was greater than that of the steel balls. The impact velocities of the particles were largely independent of their bulk flow speed and packing density. The present laser sensor impact velocity measurements are compared with those obtained in a previous study using an impact force sensor.

Edge rounding of brittle materials by low velocity erosive wear

The finishing of sharp brittle edges frequently has the objective of achieving uniform edge rounding with low roughness, while avoiding the formation of relatively large chips. In the present work, detailed observations were made on the edge chipping and rounding of borosilicate glass and silicon nitride due to the low velocity erosive wear generated in a vibratory tub and a vibratory bowl finisher. Large-scale chipping was measured as function of the included angle of the edge and of the width of edge chamfers. Given the observed strengthening effect of edge blunting against chip formation, a processing approach was developed to achieve smooth edges in the vibratory finishing of brittle materials. In addition to the observations made on the large-scale edge chipping in vibratory finishing, it was found that all the processed glass and ceramic specimens exhibited a narrow wear band of abraded material on the curved edges of the specimens, and that the adjacent flat surfaces were unaffected or minimally affected by the erosive wear process. A fracture-based erosive wear mechanism is presented in which edge wear is attributed to micro-scale edge chipping, caused by the indentation of abrasive particles protruding from the finishing media. The rate of edge wear was found to be closely related to the evolving microtopography of the edge as reflected by measurements of a roughness parameter that is proportional to the density of peaks and the average included angle of the peaks. The suggested erosion mechanism is compared with the observed trends and rates of edge rounding.

Modeling the development of Almen strip curvature in vibratory finishing

The paper presents a model of the process by which Almen strips are plastically deformed by media impacts in vibratory finishing. The motivation behind this was to extend the use of Almen strip measurements as a means of characterizing the effect of media impact velocity on residual stress formation during vibratory finishing. Two impact velocity distributions measured in a vibratory finisher were used in the model to simulate the deformations of the surface of an Almen strip. Two thicknesses of Almen strips were considered. The quantitative agreement between the model saturation curves and the experimental curves describing the Almen strip deflection as a function of finishing time was fair, though the overall trends regarding deflection were predicted well.

Characterization of vibratory finishing using the Almen system

The Almen system was adapted to a vibratory finishing process to characterize the effect of varying process parameters for the purposes of process development and control. Saturation curves for two types of aluminum Almen strips were obtained by finishing at two distinct conditions using a tub type vibratory finisher and steel spherical media. Comparison with the normal contact forces and effective impact velocities, measured for both these conditions in a previous study [D. Ciampini, M. Papini, J.K. Spelt, Impact velocity measurement of media in a vibratory finisher, J. Mater. Process. Technol., 183 (2007) 347–357], provided insight into the mechanics of the vibratory finishing process. An electromagnetic apparatus was constructed to simulate the normal impacts in the vibratory finisher. It was found that surface-normal impacts at velocities comparable to the higher range in the vibratory finisher produced Almen saturation curves similar to those created in the vibratory finisher. This provided support for the modeling approximation of treating all contact events in a vibratory finisher as effective surface-normal impacts, and the accuracy of the effective impact velocity measurement employed in [D. Ciampini, M. Papini, J.K. Spelt, Impact velocity measurement of media in a vibratory finisher, J. Mater. Process. Technol., 183 (2007) 347–357].

Impact velocity measurement of media in a vibratory finisher

The surface-normal impact velocity distributions, impact frequencies and impact power per unit area were measured using a force sensor in a vibratory finisher for two types of spherical media. These parameters control the degree, rate and character of plastic deformation and erosion of a workpiece surface in vibratory finishing. The force sensor was also used to quantify the effect of media type, finisher amplitude, and location within the finisher on the probability distribution of the particle impact velocity normal to the workpiece. It was found that reducing the total media mass in the finisher and moving closer to the wall resulted in a more aggressive process; i.e. the contact frequency, total energy flux and the average and maximum effective impact velocities were all increased with less total media mass. It was also found that contacts occur periodically within time periods that correspond to the finisher's driving frequency.

Contact forces and mechanisms in a vibratory finisher

The normal and tangential contact forces in a vibratory finishing machine were measured using a newly developed force sensor. A video system was used to record the motion of the finishing media as it collided with the test surface. Media contact occurred in three different modes. The ratio of the normal and tangential forces was compared with the measured friction coefficient under dry and water-wet conditions. This confirmed that media sliding occurred under water-wet conditions.