Considering the stiffness of the forming tools in the numerical analysis of the ironing process

Ironing can occur in cylindrical cup drawing whenever the thickness of the drawn flange is larger than the gap between the punch and the die. This is particularly relevant for materials that present r-values lower than 1.0, such as the aluminium alloys, since they tend to present more thickening of the flange. The aim of this study is to evaluate numerically the impact of the elastic deformation of the forming tools on the final cup geometry, i.e., the earing profile and the evolution of thickness along the circumferential direction, at different heights. Different contact conditions are also analysed since they strongly affect both the thickness strain and the earing profile. The process conditions considered are the ones from EXACT, the ESAFORM Benchmark 2021, enabling the comparison with experimental results. Considering the deformation of the forming tools mainly impacts the ironing stage, enabling predicting wall thickness values larger than the gap between the punch and the die.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under projects with reference 2022.08459.PTDC, UIDB/00285/2020 and LA/P/0112/2020

Study on the influence of the strain rate sensitivity on the springback of the AA5086 alloy under warm forming conditions

Warm forming processes have been successfully applied to overcome some important drawbacks of the aluminium alloys, such as poor formability and large springback. The virtual try-out of this type of processes requires the accurate prediction of springback. The process conditions considered in this work are the ones established for the benchmark 3 - Springback of an Al-Mg alloy in warm forming conditions, proposed under the Numisheet 2016 international conference. The material under analysis is the AA5086-H111 aluminium alloy. Its mechanical behaviour is described by a Hockett-Sherby hardening law and an orthotropic yield function. The numerical analysis of the warm forming process is performed considering different yield criteria, using a strain rate-dependent flow rule. Although the material presents a positive strain rate sensitivity at 240 degrees C, the influence of the punch velocity on the punch force evolution is negligible due to the impact of the punch velocity on the temperature distribution in the cup. Since the hoop stress distribution on the ring (before splitting) is only slightly influenced by the punch velocity, the impact of the punch velocity on the springback is also negligible.The authors would like to acknowledge the funding from of the Foundation for Science and Technology (FCT) under projects with reference PTDC/EME-EME/30592/2017 and PTDC/EME-EME/31657/2017 and by European Regional Development Fund through the Portugal 2020 program and the Centro 2020 Regional Operational Programme under the project MATIS and UIDB/00285/2020

Influence of the orthotropic behaviour on defects prediction in cup drawing, reverse redrawing and expansion

Finite elements analysis is commonly used in the cans tool design since it allows predicting different sheet metal defects and instabilities that significantly affect the efficient production of beverage cans. These defects include caring, due to the material orthotropic behaviour, thinning and fracture. The numerical prediction of these kind of defects is more complex when different combinations of strain paths are involved. The process conditions considered in this work involve the drawing of a cylindrical cup, the reverse redrawing and the expansion. The two materials under analysis are an AA5352 aluminium alloy and a TH330 steel. The materials orthotropic plastic behaviour is modelled with a non-quadratic yield criterion. The results show that changes in the yield surface lead to slight changes in the caring profile and in the location were strain localization occurs. Moreover, the numerical model must describe in detail the process conditions, since they may affect the formability prediction.The authors would like to acknowledge the funding from of the Foundation for Science and Technology (FCT) under projects with reference PTDC/EME-EME/30592/2017 and PTDC/EME-EME/31243/2017 and by European Regional Development Fund (ERDF) through the Portugal 2020 program and the Centro 2020 Regional Operational Programme (CENTRO-01-0145-FEDER-031657) under project MATIS (CENTRO-01-0145-FEDER-000014) and UID/EMS/00285/2020

The role of evolutive elastic properties in the performance of a sheet formed spring applied in multimedia car industry

The manufacturing process and the behavior of a sheet formed spring manufactured from an aluminum sheet is described and investigated in this work considering the specifications for the in-service conditions. The sheet formed spring is intended to be applied in car multimedia industry to replace bolted connections. Among others, are investigated the roles of the constitutive parameters and the hypothesis of evolutive elastic properties with the plastic work in the multi-step forming process and in working conditions.This research was sponsored by:a) Portugal Incentive System for Research and Technological Development. Project in co-promotion no 36265/2013 (Project HMIExcel - 2013-2015), andb) FCT with the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 - Programa Operacional Competitividade e Internacionalizacao (POCI) with the reference project POCI-01-0145-FEDER-006941.info:eu-repo/semantics/publishedVersio

Incremental volumetric and Dual Kriging remapping methods

The transfer of variables between distinct spatial domains is a problem shared by many research fields. Among other applications, it may be required for visualization purposes or for intermediate analysis of a process. In any case, two important factors must be considered: accuracy and computational performance. The accuracy becomes more important when the results have an impact on the subsequent stages of the process' analysis, as it could lead to incorrect results. The computational performance is a permanent requirement due to the ever-increasing complexity of the analysed processes. The aim of this work is to present a new remapping method, based on Dual Kriging interpolation, developed to enable accurate and efficient variable transfer operations between two different domains, discretized with hexahedral finite elements. Two strategies are proposed, which take into account different selections of interpolation points and are based on specific Finite Element Method features. They are compared with the Incremental Volumetric Remapping method in two remapping examples, one of which includes a trimming operation, highlighting their advantages and limitations. The results show that the Dual Kriging remapping method, combined with a 2D selection strategy for the donor points, can contribute to increase the accuracy of the state variables remapping operation, particularly when they present a strong gradient along the stacking direction.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under projects P2020-PTDC/EMS-TEC/0702/2014 (POCI-01-0145-FEDER-016779) and P2020-PTDC/EMS-TEC/6400/2014 (POCI-01-0145-FEDER-016876) by UE/FEDER through the program COMPETE 2020. The second author is also grateful to the FCT for the Postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

Desafíos para tributación de la economía creativa y de colaboración en Brasil

El propósito del trabajo es analizar la tributación de la economía social en Brasil, con especial énfasis en la economía creativa y la economía de colaboración, que recientemente están a un ritmo acelerado de crecimiento y carecen de tratamiento legal adecuado. En Brasil y en otros países no existe una definición teórica clara de lo que es creativo y Economía de Colaboración que dificulta adecuado gestión de los instrumentos legales, especialmente las relacionadas con los impuestos. El artículo se abordará el sistema tributario brasileño complejo y cómo puede ser aplicado en la economía creativa .La metodología será la literatura y revisión legislativa.--------------------------------------------------------------------------The purpose of the paper is to analyze the taxation of the social economy in Brazil, with special emphasis on the creative economy and the collaborative economy, which are recently at an accelerated pace of growth and lack adequate legal treatment. In Brazil and in other countries there is no clear theoretical definition of what is creative and Economics of Collaboration that makes it difficult to manage the legal instruments, especially those related to taxes. The article will address the complex Brazilian tax system and how it can be applied in the creative economy. The methodology will be literature and legislative revision.Artículo revisado por pare

Numerical analysis on the elastic deformation of the tools in sheet metal forming processes

The forming tools are commonly assumed as rigid in the finite element simulation of sheet metal forming processes. This assumption allows to simplify the numerical model and, subsequently, reduce the required computational cost. Nevertheless, the elastic deformation of the tools can influence considerably the material flow, specifically the distribution of the blank-holder pressure over the flange area. This study presents the finite element analysis of the reverse deep drawing of a cylindrical cup, where the forming tools are modelled either as rigid or as deformable bodies. Additionally, the numerical results are compared with the experimental ones, in order to assess the accuracy of the proposed finite element model. Considering the elastic deformation of the tools, the numerical results are in better agreement with the experimental measurements, namely the cup wall thickness distribution. On the other hand, the computational time of the simulation increases significantly in comparison with the classical approach (rigid tools).The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) under projects with reference UID/EMS/00285/2013, P2020- PTDC/EMS-TEC/0702/2014 (POCI-01-0145-FEDER-016779) and P2020-PTDC/EMS-TEC/6400/2014 (POCI-01-0145-FEDER-016876) by UE/FEDER through the program COMPETE2020. The first author is also grateful to the FCT for the Postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

Study on the influence of orthotropy and tension–compression asymmetry of metal sheets in springback and formability predictions

Most yield criteria possess a point-symmetry with respect to its center, meaning that a stress state and its reverse state have the same absolute value. However, this can be an unrealistic approximation, even for cubic metals (both face-centered cubic and body center cubic)), which can present a small asymmetry between the yield stress in tension and compression, i.e. a strength differential (SD) effect. This work analyzes the influence of taking or not into account the SD effect in the modeling of the sheet orthotropic behavior in the numerical simulation of a cylindrical cup drawing process. The yield criterion adopted is the CPB06 [1], including its version with two linear transformations [2], allowing a better fitting of the experimental data available. The material analyzed presents a quite small tension-compression ratio of 0.963. However, this small SD effect leads to a slightly higher punch force during the bending dominated stage, resulting in a very small influence on the springback prediction. The influence on the thickness evolution during the process is negligible.Fundação para a Ciência e a Tecnologia(SFRH/BPD/101334/2014

Study of the frictional contact conditions in the hole expansion test

The adoption of advanced high-strength steels is growing in the automotive industry due to their good strength-to-weight ratio. However, the frictional contact conditions differ from the ones arising in mild steels due to the high values of contact pressure. The objective of this study is the detailed numerical analysis of the frictional contact conditions in the hole expansion test. The Coulomb friction law is adopted in the finite element model, using different values for the (constant) friction coefficient, as well as a pressure dependent friction coefficient. The increase of the friction coefficient leads to an increase of the punch force and a slight decrease of the hole expansion. The results show that increasing the friction coefficient postpones the onset of necking, but the localization does not change.Fundação para a Ciência e a Tecnologia(SFRH/BPD/101334/2014