Temperature estimation and slip-line force analytical models for the estimation of the radial forming force in the RARR process of flat rings

open2noIn this study, a mathematical model for the prediction of the temperature evolution in the ring during the radial-axial ring rolling process is developed and used, together with the authors’ previous results, to determine analytically the flow stress of the material during process. These results, combined with Hill's slip-line field solution adapted to the RARR process, allow a fast and reasonably precise calculation of the radial forming force, a key parameter at the preliminary stage of the process design. The approach is validated by applying the proposed model to a case available in the literature and comparing the analytical results with those of the laboratory experiment and FEM simulation. Following the successful comparison, the models were applied to a large variety of flat rings, comparing analytical predictions with the results of FEM simulations. The accuracy of the analytical calculation and the reliability of the proposed models, for different ring configuration and process parameters, are presented and discussed.embargoed_20190501Quagliato, Luca; Berti, GuidoQuagliato, Luca; Berti, Guid

Analytic temperature evaluation and process forces estimation for the RARR process of flat rings

Two different analytical models are derived for the estimation of the temperature drop in the two deformation stages of radial-axial ring rolling process of flat rings. The temperature estimation, along with previous results regarding geometry, strain and strain rate, is used to calculate the variation of the flow stress of the material during the process and accordingly to derive the process forces, utilizing different forces estimation models already available in the literature

Change of the yield stress in roll formed ERW pipes considering the Bauschinger effect

ERW pipes formed with the roll forming process show a yield stress distribution along the circumferential direction and their quality is strongly influenced by the magnitude and by the distributions of the yield stress. In addition to that, strips are subjected to cyclic loading during roll forming process. Since ERW pipes are firstly roll formed, welded and then sized, in order to develop an enhanced predicting method for the calculation of the ERW pipe yield stress, the same process flow has been also applied to authors\u2019 numerical simulations. The Yoshida-Uemori kinematic hardening model has been applied considering several subdivision of the strain range, and different parameters, aiming to find the best correlation between the estimated Bauschinger effect and the one measured in the relevant cyclic loading experiment. The comparisons between estimated and experimentally-measured values of the thickness distribution, and of the locally-measured yield stress, prove both reliability and accuracy of the adopted process chain analysis. The growth of the sizing effect ratio has shown to cause the increase of the yield stress, which becomes more uniform along the circumferential direction

material property of metal skin sheet molding compound laminate structures for the production of lightweight vehicles body frame

Abstract The present research work focusses on both the material characterization and the preliminary test applications for hybrid structures made of high strength steel skin and sheet molding compound (SMC) core, aimed for the production of lightweight automotive body frames. A full material characterization has been carried out in order to determine the properties of the single materials, high strength steel and sheet molding compound. In addition, laminate specimens made of steel skin and SMC core have been manufactured utilizing the compression molding process and the relevant stress-strain behavior have been tested. By means of shear test, the shear strength resistance of the adhesive, utilized for the cohesion between these two materials, have been also characterized. In order to test the proposed hybrid material for the application in the automotive industry, the case of a commercial vehicle B-pillar component have been considered and tested by means of FEM analysis. By simulating the severe load conditions to which the B-pillar has to stand, the numerical analysis implemented in ANSYS will show how the developed material is able to withstand the same load conditions of the original full-steel one while granting a considerable reduction of weight

radial forging of aluminum to steel preform for the production of light weighted wheel bearing outer race

Abstract In this research work an innovative procedure through which to manufacture the outer race of vehicles wheels bearing, aiming to reduce their total weight, is proposed. Utilizing the radial forging process, an aluminum workpiece is forged on a steel core, resulting in the same geometry for the wheel bearing outer race but allowing to achieve a considerable weight reduction. By considering the most burdensome load conditions the outer race has to stand, a stress analysis is implemented in ABAQUS/Standard by applying both bolts and bearing ball forces. Based on the stress distribution, the portion of the cross-section where the load is bearable by the aluminum 6061 alloy is identified and a new steel workpiece, realized by removing the above-mentioned volume, is created. The aluminum workpiece is then hot-forged on the steel part, replacing the removed steel volume and recreating the original shape of the bearing outer race, afterwards tested with the same load conditions to verify that the combined forged part is able to withstand the same loads. To optimize the interface behavior between hot-forged Al6061 and 45Cr steel, simple tension test specimens, realized by forging an aluminum workpiece on a steel plate, have been manufactured realizing different surface knurling on the steel plate and by pre-heating the aluminum part at different temperatures. With the proposed approach, the weight of the bearing outer race has been reduced of 35.8% while granting the same mechanical performances of the original component

steel skin smc laminate structures for lightweight automotive manufacturing

In the present research work an innovative material, made of steel skin and sheet molding compound core, is presented and is aimed to be utilized for the production of automotive body frames. For a precise description of the laminate structure, the material properties of all the components, including the adhesive utilized as an interlayer, have been carried out, along with the simple tension test of the composite material. The result have shown that the proposed laminate structure has a specific yield strength 114% higher than 6061 T6 aluminum, 34% higher than 7075 T6 aluminum, 186% higher than AISI 304 stainless steel (30HRC) and 42% than SK5 high-strength steel (52HRC), showing its reliability and convenience for the realization of automotive components. After calibrating the material properties of the laminate structure, and utilizing as reference the simple tension results of the laminate structure, the derived material properties have been utilized for the simulation of the mechanical behavior of an automotive B-pillar. The results have been compared with those of a standard B-pillar made of steel, showing that the MS-SMC laminate structure manifests load and impact carry capacity comparable with those of high strength steel, while granting, at least, an 11% weight reduction

FEASIBLE SETUP DEFINITION AND ANALYTICAL STRAIN ESTIMATION FOR RADIAL-AXIAL RING ROLLING PROCESSES

In recent years, the radial-axial ring rolling process has assumed a growing importance in bulk deformation processes due to its low costs and high efficiency. Based on literature studies, and applying innovative concepts about feeding speed ranges, the paper details an efficient way to define feasible process parameters, both for FE simulations and real processes. Using a discretized representation of the ring by subdividing it into slices, the mathematical model estimates the geometry evolution of each slice during the whole ring rolling process, su-perseding previous averaged calculations and opening the way to a more detailed estimation of diameters, contact arc lengths, strains, stresses and forces. Based on the ring\u2019s estimated dimensions, the mathematical frame, suitable for cold, warm and hot processes, allows to derive the three strain components of the strain tensor, while filling the incompleteness of the literature where only the equivalent plastic strain was considered, and to estimate process forces, founded on the calculation of the flow stress of the material. The proposed analytical models have been applied to a wide range of rings with different ex-pansion profiles and dimensions ratio, and the relevant predictions have been compared with the results of FE simulations, showing a good reliability of the proposed approach

Mathematical definition of the 3D strain field of the ring in the radial-axial ring rolling process

Received 29 March 2016 Received in revised form 4 July 2016 Accepted 7 July 2016 Available online 15 July 2016 Keywords: Metal forming Ring rolling Strain analysis Analytic functions FE analysis 1. Introduction Radial-axial ring rolling (RARR) is widely used in the produc- tion of seamless rings for the automotive and aerospace industries, where a ring work-piece is drawn into the mandrel-main roll gap and the axial rolls gap, causing expansion of the diameter as well as reduction in the thickness and height [1,2]. In the literature, many efforts have been spent in the in- vestigation of the radial-axial ring rolling process considering different points of view, generally aiming to improve the knowl- edge of the interactions among the ring, the tools, the process set up and the production environment. As concerns the process de- sign, Hua et al. [3] defined useful rules for the estimation of the ring stiffness, which is an important factor to avoid collapses or unexpected deformations during the forming process. Zhou et al. [4], utilizing ABAQUS/Explicit solver, studied the influence of the tools dimensions, providing rules to optimize their choice. Zhou et al. [5] also analyzed the influence of the axial rolls motion laws n Corresponding author. E-mail address: [email protected] (L. Quagliato). http://dx.doi.org/10.1016/j.ijmecsci.2016.07.009 0020-7403/& 2016 Elsevier Ltd. All rights reserved. abstract The paper focuses on the radial-axial ring rolling process and details a new mathematical approach for the determination of the evolution of the ring geometry during the deformation process, taking into account separately the sequence of incremental deformations occurring when the ring passes through the mandrel-main roll gap and through the axial rolls gap. Based on the determined geometry of the ring, the three strain components of the strain tensor are estimated and the equivalent plastic strain is computed. The proposed approach, taking into account a third strain in each deformation gap, allows an estimation of the equivalent plastic strain, which is a required parameter for the analytical estimation of the flow stress of the material, needed to compute the forming force. Since a direct validation of the strain components is not possible in the industrial RARR process, authors\u2019 models for the determination of geometry and strain, together with preliminary authors\u2019 models for the estimation of strain rate and temperature drop along the process, have been applied to a literature case for the estimation of the radial forming force in order to obtain a validation of the proposed models. Prediction of radial forming force utilizes a literature model based on slip line theory adapted to the ring rolling process. To extend the validation of the approach and to explore the quality of its predictions to other process configurations, different geometry of the ring have been considered and compared with FEM predictions. These com- parisons resulted in good agreement between analytical and FEM results as concerns ring geometry evolution, strain tensor prediction and effective strain estimation

A new kinematic approach for process set-up and ring evolution prediction in RARR Process

Within Radial Axial Ring Rolling process, a new methodology has been developed in order to minimize the amount of required FE simulations to reach the final set of optimal parameters for the set-up of the process. Through a kinematic approach, a mathematic model has been developed with the aim of predicting the evolution of ring expansion. Based on volume constancy principle, Keeton’s correlation and assuming an initial value for the inner diameter of the blank, which minimizes the scrapped material, the proposed algorithm allows also to determinate blank initial geometry. Optimal ranges for mandrel and axial rolls motion laws are calculated for both speeds in order to reach the final desired geometry of the ring, respecting the conditions that ensure process stability and ring uniform expansion. Moreover, mandrel feeding speed is assumed to be linear and upper axial roll feeding speed is accordingly derived through Keeton’s correlation which ensures process stability. Ring geometry is estimated for each ring portion (slice) and not in terms of average value for the considered round. The mathematical model has been tested through FE simulations applied to three different ring shapes resulting in a reasonable error (<1%) between FE simulations and model estimations, confirming the reliability of the proposed approach