R. A. F. Valente

On the use of EAS solid‐shell formulations in the numerical simulation of incremental forming processes

Purpose – Incremental sheet forming represents a promising process in the manufacturing of metallic components, particularly its variant known as single point incremental forming (SPIF). The purpose of this paper is to test and validate the results coming from numerical simulation of SPIF processes using the reduced enhanced solid‐shell formulation, when compared to the solid finite elements available in ABAQUS software. The use of SPIF techniques in the production of small batch components has a potential wide application in fields such as rapid prototyping and biomechanical devices.Design/methodology/approach – Incremental forming processes differ from conventional stamping by not using a press and by requiring a lower number of tools, since no dedicated punches and dies are necessary, which lowers the overall production costs. In addition, it shows relative simplicity and flexible setup for complex parts, when compared with conventional technologies. However, the low speed of production and low‐dimensi...

Numerical Simulation of Hydroforming Process Involving a Tubular Blank with Dissimilar Thickness

The research and development of innovative procedures have a vital importance to lightweight construction technology, in particular for future vehicle concepts. The implementation of modern lightweight construction concepts results in a specification emphasizing the aspects of both uniform forming of large-scale parts as well as complex local geometric details.

Single point incremental forming simulation with adaptive remeshing technique using solid-shell elements

Purpose – Numerical simulation of the single point incremental forming (SPIF) processes can be very demanding and time consuming due to the constantly changing contact conditions between the tool and the sheet surface, as well as the nonlinear material behaviour combined with non-monotonic strain paths. The purpose of this paper is to propose an adaptive remeshing technique implemented in the in-house implicit finite element code LAGAMINE, to reduce the simulation time. This remeshing technique automatically refines only a portion of the sheet mesh in vicinity of the tool, therefore following the tool motion. As a result, refined meshes are avoided and consequently the total CPU time can be drastically reduced. Design/methodology/approach – SPIF is a dieless manufacturing process in which a sheet is deformed by using a tool with a spherical tip. This dieless feature makes the process appropriate for rapid-prototyping and allows for an innovative possibility to reduce overall costs for small batches, since...

Integrated design and numerical simulation of stiffened panels including friction stir welding effects

Stiffened panels are usually the basic structural building blocks of airplanes, vessels and other structures with high requirements of strength-to-weight ratio. They typically consist of a plate with equally spaced longitudinal stiffeners on one side, often with intermediate transverse stiffeners. Large aeronautical and naval parts are primarily designed based on their longitudinal compressive strength. The structural stability of such thin-walled structures, when subjected to compressive loads, is highly dependent on the buckling strength of the structure as a whole and of each structural member. In the present work, a number of modelling and numerical calculations, based on the Finite Element Method (FEM), is carried out in order to predict the ultimate load level when stiffened panels are subjected to compressive solicitations. The simulation models account not only for the elasto-plastic nonlinear behaviour, but also for the residual stresses, material properties modifications and geometrical distortions that arise from Friction Stir Welding (FSW) operations. To construct the model considering residual stresses, their distribution in FSW butt joints are obtained by means of a numerical-experimental procedure, namely the contour method, which allows for the evaluation of the normal residual stress distribution on a specimen section. FSW samples have been sectioned orthogonally to the welding line by wire electrical discharge machining (WEDM). Displacements of the relaxed surfaces are then recorded using a Coordinate Measuring Machine and processed in a MATLAB environment. Finally, the residual stress distribution is evaluated by means of an elastic FE model of the cut sample, using the measured and digitalized out-of-plane displacements as input nodal boundary conditions. With these considerations, the main goal of the present work will then be related to the evaluation of the effect of FSW operations, in the ultimate load of stiffened panels with complex cross-section shapes, by means of realist numerical simulation models.

Numerical Simulation of a Conical Shape Made By Single Point Incremental

The Single Point Incremental Forming (SPIF) is a manufacturing process in which a sheet is deformed by using a relative small tool without the need of dies. The current work aims the application of the adaptive remeshing technique developed for shell and extended to 3D brick elements in general, and specifically to RESS (Reduced Enhanced Solid-Shell) formulation [1]. The study will be focused on NUMISHEET 2014 benchmark: a cone shape made by SPIF process. The purpose is to use the developed tools to predict the deformed shape and tool-load histories.

Finite element analysis of incrementally formed parts

Single point incremental forming (SPIF) processes represent a breakpoint from traditional forming processes, and possibly a new era in small batches production, customised parts or rapid prototyping. n nGiven its easy implementation, SPIF is being currently a subject of intensive experimental and numerical research. Consequently, dimensional inaccuracy in formed parts is still a real problem to tackle, demanding a correct prediction of forming forces, springback defects and strain path effects. n nThis work concerns a first step of a detailed numerical study, validated with available experimental results in the literature raised about simulation of SPIF processes. To this end, it is proposed a general simulation framework of SPIF processes using the finite element method with implicit solution schemes, along with innovative solid-shell elements for 3D analysis. n nFinally, the use of solid-shell elements provides several advantages compared to shell elements, as considering automatically full 3D stress states and constitutive laws, thickness variations, double sided contact and normal stresses.

Numerical Study of Hydroforming with Tailor-Welded Tubular Blanks

The hydroforming process represents an alternative production method when complex geometry components are required. Considering the cost per unit as a critical value, hydroforming shows up as a competitive production method. In this work a case study is presented where the initial part, two tubes with different thicknesses and a butt‐weld, is hydroformed. Simulation analyses are presented based on the Finite Element Method. A particular focus will be carried out on the characterization of the Heat Affected Zone (HAZ), namely geometry and mechanical properties.

Finite Element Method in Machining Processes: A Review

An ecological production and low cost is the target of several industries. Increasingly, the product development is critical stage to obtain a great quality and fair price. This stage will define shapes and parameters that will able to reduce wastes and improve the product. However, the expense of prototypes also should be reduced, because, in general, the prototypes are more expensive that final product. The use of finite element method (FEM) can avoid much tests that reduce number of prototypes, and consequently the project cost. In the machining processes simulation, several cutting conditions can be reproduced to define the best tool and parameters in function of analyzed forces, stress, damages and others. This paper debates the use of FEM in the machining processes, shows some researches and indicates the main attributes to develop simulation studies for conventional machining and micromachining.

Influence of friction stir welding effects on the compressive strength of aluminium alloy thin-walled structures

The main objective of the present work is to investigate the effect of the residual stresses originated by the friction stir welding (FSW) process in the compressive strength of aluminium alloy plates. The finite element method (FEM) is used to simulate the welding process and calculate the distribution of the residual stresses. The model is validated using a residual stress map obtained by means of the contour method from a friction stir welded AA2024-24 plate. The results from the welding simulation were then used to numerically assess the influence of the residual stresses on the collapse load of the plate.

On the Development and Computational Implementation of Complex Constitutive Models and Parameters’ Identification Procedures

Nowadays, the automotive industry has focused its attention to weight reduction of the vehicles to overcome environmental restrictions. For this purpose, new materials, namely, advanced high strength steels and aluminum alloys have emerged. These materials combine good formability and ductility, with a high tensile strength due to a multi-phase structure (for the steel alloys) and reduced weight (for the aluminum alloys). As a consequence of their advanced performances, complex constitutive models are required in order to describe the various mechanical features involved. In this work, the anisotropic plastic behavior of dual-phase steels and high strength aluminum alloys is described by the non-quadratic Yld2004-18p yield criterion, combined with a mixed isotropic-nonlinear kinematic hardening law. This phenomenological model allows for an accurate description of complex anisotropy and Bauschinger effects of the materials, which are essential for a reliable prediction of deep drawing and springback results using numerical simulations. To this end, an efficient computational implementation is needed, altogether with an inverse methodology to properly identify the constitutive parameters to be used as numerical simulation input. The constitutive model is implemented in the commercial finite element code ABAQUS as a user-defined material subroutine (UMAT). A multi-stage return mapping procedure, which utilizes the control of the potential residual, is implemented to integrate the constitutive equations at any instant of time (pseudo-time), during a deformation process. Additionally, an inverse methodology is developed to identify the constitutive model parameters of the studied alloys. The identification framework is based on an interface program that links an optimization software and the commercial finite element code. This methodology compares experimental data with the respective results numerically obtained. The implemented optimization process aims to minimize an objective function, which defines the difference between experimental and numerical results using the Levenberg-Marquardt gradient-based optimization method. The proposed integrated approach is validated in a number of benchmarks in sheet metal forming, including monotonic and cyclic loading, with the goal to infer about the modelling of anisotropic effects.