Roller Geometry Research Articles

Cold rotary forming of thin-wall component from flat-disc blank

Flow forming, one of the rotary-forming processes, is used mainly to produce thin-walled high-precision tubular components. Due to its flexibility and low tool load requirement, the process has great potential to be extended to the forming of net-shape components for thin and intricate features from bulk raw materials, such as solid bar ingot, cast and forged performs. In the work reported in this paper, a flow-forming facility was established to investigate the feasibility of forming thin-walled cups from flat-disc blanks by investigating the effects of roller geometry, degree of material reduction and roller geometry on material flow. In addition, a 3D Finite Element (FE) model was developed to simulate the ‘bending’ process, based on the experimental conditions. The results showed that it is possible to adopt a two-step forming process, ‘bending’ and flow forming to enable material flow along the mandrel in order to form a thin-wall cup component using two different profiles and adopting an axial roller movement. Quality of the cups formed depends on the diameter reduction, starting disc thickness of the blank and the number of pass in the flow-forming stage. The results predicted by the FE simulation was compared with the experimental results and showed close agreement. This work illustrates the possibility of adopting flow-forming processes for the production of thin section, which would be difficult and expensive to produce by press forming. In addition, it also showed that although FEM is an effective tool to optimize process parameters, computational time remains as the main barrier for its prevalent usage especially for incremental processes such as flow forming and spinning processes.

A Novel Method for Estimating Solid Fraction of Roller-Compacted Ribbons

A simple method has been developed to estimate solid fraction or relative density of compacts using the weight of ribbons produced during roller compaction. The method provides an alternative to the commonly used dimensional measurement, especially for formulations not amenable to forming quality ribbons. Surface texture of the compaction rolls has been taken into consideration in our mathematical treatment along with correction for ribbon relaxation. Ribbon relaxation occurring upon ribbon exiting the compaction zone is estimated using roll geometry, roll gap, and ribbon thickness. Detailed experimental runs have been carried out to confirm the validity of the proposed theory. The predicted solid fraction was found comparable to that from actual dimensional measurement by caliper. In the case of the microcrystalline cellulose/dicalcium phosphate one:one formulation, the predicted solid fraction had an error sum of squares (SSE) of 2.64E-03 when compared to the dimensional method. When relaxation was included, the SSE decreased by four folds. Similarly, for the microcrystalline cellulose/lactose monohydrate 2:1 formulation, the SSE decreased twelfth folds when relaxation was taken into consideration. These results further confirm the utility of the proposed throughput method for estimating the solid fraction of ribbons.

A Study on Throw Simulation for Baseball Pitching Machine with Rollers and Its Optimization

Pitching machine is widely used in venues ranging from professional baseball stadiums to batting centers. However, the throw performance of the pitching machines that have been developed so far for use during batting practice is not very high. Pitches such as the fastball, curveball and screwball are easily achieved by the pitching machine with three rollers which were developed by the authors. In this study, the moving behavior and contact stress state of the ball pitched with the three rollers type pitching machine is analyzed using dynamic finite element analysis software (ANSYS/LS-DYNA). The effect of the seam of a baseball to the throw accuracy is analyzed numerically. In the analysis, the finite element models of a detailed baseball with a seam and a pitching machine with three rollers are used. Additionally, convex and concave rollers are made and those are analyzed. From the analytical results, it is understood that the convex roller is higher than other rollers in throw accuracy. The convex roller geometry is optimized, and the optimum conditions (shapes and material properties) of the convex roller are decided. Moreover, the validity of the condition is confirmed by the throw experiment.

Plastic work approach for surface defect prediction in the hot bar rolling process

In this study, a numerical technique was developed to study the effect of processing parameters on instability of the steel during five passes hot bar rolling process. For this a processing map developed based on the plastic work approach was used with finite element analyses to judge occurrence of instability during the process. The effect of roll geometry and processing temperature on hot rolled bars was examined with the help of a parametric study by employing the numerical technique developed. Based on this parametric study, the improved roll pass design and initial processing temperature were determined, respectively, for reducing flow instability during the process. The laboratory rolling mill was used to validate the numerical results. It was found that with the increase of the initial temperature in the process the less flow instability was observed compared to the change of the roll geometry introduced at each pass under the present investigation condition. It was found that the current numerical technique implemented will be useful in identifying the important parameters governing the formation of surface cracks in the multi-stage hot bar rolling process.

Large area rolling of functional metallic micro structures

The reliable fabrication of functional surface structures has become an important factor in modern production processes. With regard to the field of large area micro patterning, particular applications demand for economical manufacturing processes to gain advantageous surfaces. The process-integrated rolling of these structures is a promising approach if suitable roll geometries can be manufactured. This paper focuses on the large area rolling of so called riblet structures. Both experimental test series and related numerical forming simulations are taken into account. Furthermore, demands and potentials from the roll manufacturing point of view are highlighted. Above all, the feasibility of a new winding concept for the continuous patterning of rolls with small negative riblet structures is pointed out. By this means, challenging requirements in connection with riblet rolls—the realization of finest structures with sharp ground radii—can be matched.

Coating flows of non-Newtonian fluids: weakly and strongly elastic limits

This paper presents an asymptotic analysis of the thickness of the liquid film that coats a smooth solid substrate when it is withdrawn from a bath of non-Newtonian fluid, and compares the results with experimental measurements. The film thickness is, to a good approximation, uniform above the point where the film is withdrawn from the fluid bath, and depends on the rotation rate, the fluid properties and the substrate geometry. Theoretical predictions of the film thickness for a number of different substrate geometries (an inclined plate, roller and fiber) are presented, and are compared with experimental measurements in a single roller geometry. Results are obtained for two different limits of the Criminale–Ericksen–Filbey constitutive equation in which the fluid rheology is either weakly elastic and dominated by shear thinning, or strongly elastic and dominated by elastic stresses. A lubrication analysis yields a thin-film equation which characterizes the film thickness as a function of spatial position. The rheological properties of the test fluids are measured independently using steady and oscillatory shearing deformations. The viscometric parameters are then used, in conjunction with the governing thin-film equation, which is solved using matched asymptotics, to give a quantitative prediction of the thickness of the fluid coating. The onset of an instability which causes the film thickness to vary with axial position along the roller is also observed experimentally.

Numerical Analysis of Force and Power Parameters in Cold Ring Rolling

During cold ring rolling process, the accurate prediction and analysis of force and power parameters, including roll force (RF) and roll moment (RM), is important in selecting, designing and developing the forming rolls and cold ring rolling mills. In this paper, a three-dimensional elastic-plastic dynamic explicit FE model of cold ring rolling process has been presented and validated in terms of roll force and geometry development. Based on the model, the variation laws of force and power parameters under different sizes of forming rolls (including driver roll and idle roll) and forming parameters (including the rotational speed of driver roll 1 n and the feed rate of idle roll v ) have been revealed by comprehensive numerical simulations.

FEM analysis for V–H rolling process by updating geometric method

Three passes of slab rolling during vertical–horizontal rolling process were simulated with explicit dynamic FEM by updating geometric method. Simulation model of the next pass was built when the rolling geometry model was updated after previous pass was finished, changing roll gap, material attribution and boundary conditions. The calculated results of the slab shape are in good agreement with the experimental ones. It is shown that the explicit dynamic FEM and updating geometric method can be used effectively to analyze the multi-passes of V–H rolling process.

The effect of roll and clad sheet geometry on the necking instability during rolling of clad sheet metals

Experimental evidence is presented showing that the rolling strain required to produce internal necking in clad sheet depends both on the volume fraction of each constituent in the clad and the geometry of the rolls. This result was not predicted by earlier localization analysis that approximates the stress/strain field in rolling with that of plane strain compression. The evolution of hardness during rolling and complementary finite element results point to redundant shearing of the soft phase as the reason for this behavior. Such redundant shear differentially strengthens the softer component of the clad and reduces the induced tensile stress in the harder component, delaying the localization. Therefore, unwanted strain localization in rolling of clad sheets can be delayed significantly by the use of small radius rolls in configurations such as a Sendzimir mill.

Working range for sequences and series of two-symmetrical grooves in wire rod rolling

A calculation procedure has been developed to determine the working range for series of grooves including “oval”, “round”, “false round”, “square” and “diamond” shapes. The minimum and maximum roll-gap setting and corresponding bar areas are calculated for all grooves. Flatter ovals increase the flexibility in false round–oval series and low rolling geometry factors reduce the working range. The working range is smaller for pass sequences designed for high reductions. To evaluate the model, laboratory tests for passes in “round”–“oval”–“false round”–“oval” sequences were carried out. Samples from a square–oval series were examined and it was shown that this series was insufficient for stainless steel wire rod rolling. The fitting factors were too high and the square grooves were slightly overfilled. It is shown that “false round”–“oval” series give the largest working range and thus enable the rolling of a wide range of different stainless steel grades.

Numerical Study of the 10 January 1998 Lake-Effect Bands Observed during Lake-ICE

Abstract This paper presents the results of a series of idealized cloud resolving simulations of the evolution of moist roll convection observed as part of the Lake-Induced Convection Experiment (Lake-ICE) that took place during the 1997/98 winter over central Lake Michigan. Satellite and radar observations of the roll convection depict striking linear rolls stretching from 10 km off the western shore of the lake, across to the eastern shore, and then continuing across Michigan. The spacing of the primary rolls was observed to be 6 km, giving a ratio of spacing to depth of about 5:1, which is consistent with theory. In addition, a longer wavelength (13 km) of stationary banding was observed parallel to the shoreline. In an earlier study of this case, multiply nested simulations of the convective rolls based on real data variable initialization were successful in producing banded structures with similar spacing and location over the water to those observed using fine grid resolution of about 500 m. Unfortunately, the initial locations of simulated bands were organized primarily by numerical effects of grid interpolation. This suggested that the spacing of the bands was robust, but that their initial location was highly sensitive to subtle systematic forcings. In this paper, a set of idealized model experiments, designed to isolate the role that physically realistic local forcing plays in the organization of the rolls, was performed. Because externally generated upstream turbulence was suppressed in these tests so as not to bias the result, the generation of rolls was delayed until 20–30 km downwind of the observed location and the location simulated in the previous grid nesting experiments. It was shown that the subtle effects of the shoreline geometry were sufficient to spawn a near-surface streamwise vorticity that became the primary seed for roll development at the most efficient mode of roll convection. These results suggest that previous structures evolved in the upstream shear-driven land-based mixed layer were likely also important in determining where the nonlocal overturning was first triggered. It is not clear from these results whether the shear-driven structures that evolved over the land also played a significant role in organizing the structural geometry of the lake rolls. Results also suggested that the shore parallel bands were a robust feature of the atmospheric structure resulting from resonant gravity wave trapping in the frontal layer.

Effects of roller path and geometry on the flow forming of solid cylindrical components

Flow forming is used mainly to produce thin walled high precision tubular components. Due to the flexibility and low tool load requirement, the process is capable of being extended to the manufacture of shapes from bulk raw material, such as solid bar ingot, cast and forged preforms. In the work reported in this paper, a simple flow forming facility was established to enable the effects of roller path and geometry, on the flow of metal, to be examined. An FE model has been developed to simulate the process, based on experimental conditions. The results show that, for a cylindrical roller moving axially along a work-piece, metal moves predominantly in a radial direction, forming a flange. When a roller with a rounded contact region, ‘nosed’, is used, the metal flow is predominantly axial. Radial roller movement results in the formation of a ‘cup’ or a ‘boss’ on the end of the work-piece. The dimensions of the feature depend on the roller geometry, feed rate and amount of deformation. The results illustrate the ability of flow forming to be used for production of shapes of thin section, which would be difficult and expensive to be made by press forming.

Roll compaction of maize powder

This paper presents a study of a roll compaction process as a dry granulation method for typical food materials such as maize powder. This process is widely applied in industry as it can continuously produce large quantities of granular product at comparatively low cost. The objectives of this work were to predict the roll compaction performance from a simple measurement involving uniaxial die compaction using the classical Johanson model. This involved determination of the optimum operating conditions for the production of granules as evaluated by apparent density. In the current work, a smooth counter-rotating rolling mill with a roller diameter of 0.08 m and a roller width of 0.20 m was used. The operating conditions for the rolling mill are shown to be influenced by parameters such as the roll gap, the roll speed, the feed powder amount, and the friction ratio. Material properties such as the compressibility factor and the angle of wall friction were investigated using uniaxial die compaction. The angle of wall friction was analysed using both contact mechanical and continuum mechanical approaches. The results indicated that this simplified approach can be used to provide a quantitative prediction of the extent of the roll compaction performance, and can be used to design optimal roller geometries and operating conditions.

The effect of roll gap geometry on microstructure in cold-rolled aluminum

Microstructure and texture are analyzed through the thickness of two aluminum plates cold-rolled 40% with different roll gap geometries. It is found that both texture and microstructure are strongly affected by the rolling geometry. After rolling with intermediate-size draughts a rolling-type texture is developed throughout the plate thickness. In this case, grains are subdivided by extended planar dislocation boundaries preferentially aligned at an angle of 40 ± 15° to the rolling direction. In the plate rolled with small draughts, shear texture components appear in the intermediate layers. In these layers, extended planar dislocation boundaries are frequently found to be inclined closely to the rolling direction. The subsurface and central layers of this plate exhibit microstructures similar to those in the plate rolled with intermediate draughts. It is suggested that the development of different textures and microstructures at different depths is related to the activation of different slip systems due to through-thickness strain gradients.

Incremental forming of solid cylindrical components using flow forming principles

The flow forming process has been used to produce a range of engineering components, with reduced forming loads and enhanced mechanical and surface quality for a finished part, compared with press formed parts. However, studies on the flow forming of solid cylindrical components have not been documented. In this paper, test facilities were established in order to study the effects of roller geometry and feed rate on forming load and material flow when flow forming a simple solid cylindrical component with uniform diameter, using lead as the material. Experiments are carried out to study the effects of feed rates and roller geometry on material flow. A finite element (FE) model is proposed to simulate the process using ABAQUS implicit and explicit. The difficulties in simulating flow forming are outlined and the model using different formulations are compared for their efficiency in analysing the process.

On the nature of phases in Al 2O 3 and Al 2O 3–SiC thermal spray coatings

Nature of alumina phases in thermal sprayed Al 2O 3 and nanocomposite Al 2O 3–SiC coatings is investigated. The coatings were prepared using high velocity oxy fuel spraying (HVOF) and air plasma spraying (APS) techniques on mild steel substrates either with Ni5Al or Ni20Cr bond layer. Coating top layer thickness was 250 μm and 1 mm. The amount of SiC was varied from 2 to 8 mass%. Flat and roller geometries were used for substrates. While coatings on flat specimens were used for low temperature heat treatments (100 and 700 °C); peels (free forms) of roller specimens were used for high temperature (≥1000 °C) heat treatments. X-ray diffraction technique was used for phase characterisation. The coatings showed the presence of varied amounts of well-known alumina phases and the relatively new U phase. It was observed that depending upon the thermal energy of the spray process even smaller particles <20 μm, gave rise to (contrary to the earlier hypothesis) unmelted α-seeds (nuclei) and α-alumina nucleated in preference to γ-alumina. Presence of SiC (mostly inside alumina grains) in alumina nanocomposite coatings increased the amount of α-phase formation in the coatings. The transformation temperatures, of alumina polymorphs, of the thermally sprayed alumina coatings, are found to be in accordance with the dehydration of boehmite. The discrepancies (higher transformation temperatures) in the earlier literature on alumina sprayed coatings were due to the presence of impurities in the coating. SiC increased the transformation of metastable alumina polymorphs to stable α-phase by 200 °C. The alumina phases in HVOF Al 2O 3–SiC coatings undergo γ→δ→θ→α phase transformations on heating (1000–1400 °C) as observed during dehydration of boehmite. However, the transformation temperatures of metastable alumina phases in SiC containing nanocomposite coatings were 100–200 °C higher than the pure alumina coatings.

Friction and wear of the rotary compressor vane–roller surfaces for several sliding conditions

One of the serious challenges in developing a rotary compressor with HFC refrigerant is the prediction of friction forces and wear amounts between vane and roller surfaces. In this study, the tribological characteristics of sliding surfaces using vane–roller geometry of a rotary compressor were investigated. The sliding tests were carried out under various sliding speeds, normal loads, and surface roughness. During the test, friction force, wear depth, and surface temperature were monitored. Because severe wear occurred on the vane surface, TiN coating was applied on sliding surfaces to prolong the wear life. The sliding tests indicates that there was an optimum initial surface roughness to break in and to prolong the wear life of sliding surfaces. Depending on load and speed, the protective layers, which were composed of metallic oxide and organic compound, were formed on sliding surfaces. Those would play an important role in the amounts of friction and wear between vane and roller surfaces.

Video‐imaged surf zone wave and roller structures and flow fields

The measurement of mean water levels, roller geometries, and phase ensemble‐averaged velocity and turbulence intensity fields under spilling and plunging waves breaking in a two‐dimensional laboratory surf zone is presented. The velocities were measured using digital correlation image velocimetry, while water levels and roller geometries were determined through gray scale filtering of video images. The phase ensemble‐averaged horizontal and vertical components of velocity and turbulence intensities are measured throughout the entire flow domain, including the wave roller area, by utilizing the aerated areas as part of the flow structure. The time‐averaged horizontal velocities (undertow), turbulence intensities, and turbulent kinetic energies are determined by averaging across the wave phase. Turbulence magnitudes are found to compare favorably with existing laser Doppler anemometry measurements below the wave trough level, where such measurements have generally been confined because of aeration contamination effects. The significantly higher velocity and turbulence intensity magnitudes measured above the trough level in the present experiments highlight the novel nature of the present investigation for describing flow regimes in the surf zone.

A suspension system with a variable roll centre for the improvement of vehicle handling characteristics

In this paper, the improvement of vehicle handling characteristics using variable roll centre suspension (VRCS) is investigated. A vehicle with VRCS can improve stability and ride comfort by automatically controlling suspension geometry in accordance with the running conditions of the vehicle. To achieve this, a variable roll centre concept in the McPherson strut suspension system is suggested, while the two parts most sensitive for controlling the roll centre are suggested. One is between the vehicle body-side connecting portion of the lower arm and the vehicle body (control input, LCZ), and the other is between the vehicle body-side connecting portion of the strut and the vehicle body (control input, STY). Kinematic roll centre analysis, based on the analytic half-car model, shows that the use of two control inputs, LCZ and STY, can decrease migration of the roll centre and centre of gravity according to the side force. In order to quantify the relationship between roll centre and geometry control input and evaluate handling performance, a full vehicle model of 15 degrees of freedom (DOF) is constructed using multi-body dynamic analysis software, ADAMS. In step steering and double lane change manoeuvres, simulation results demonstrate that a vehicle with VRCS adjusts roll centre migration, and handling characteristics such as roll angle, lateral acceleration and yaw rate are much improved.

Optimization of the irregular shape rolling process with an artificial neural network

This paper presents a design method for a shape roller that combines the numerical analysis and optimization of process parameters with an artificial neural network. Rolling processes are to reduce the cross-section of the incoming material while improving its properties and to obtain the desired section at the exit from the rolls. Shape rolling is one of the most complex deformation processes in comparison with that of the plates, the sheets, and the bars because the workpiece is non-uniformly reduced by grooved rolls. In the case of a product that has an irregular cross-section, the rolled product is severely bent because of the non-uniform deformation of the material in the cross-section. The product analyzed in this study is a steel cutter to cut the desired shape of leather or rubber. A neural network was used to optimize the process parameter. Finite element analyses are done by the pre-defined process parameter which represents the roller geometry. The optimization of the neural network and experimental results of shape rolling are compared. The proposed scheme has successfully optimized the process parameters.