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Single point incremental forming (SPIF) is an emerging application in sheet metal prototyping and small batch production, which enables dieless production of sheet metal parts. This research area has grown in the last years, both experimentally and numerically. However, numerical investigations into SPIF process need further improvement to predict the formed shape correctly and faster than current approaches. The current work aims the use of an adaptive remeshing technique, originally developed for shell and later extended to 3D 'brick' elements, leading to a Reduced Enhanced Solid-Shell formulation. The CPU time reduction is a demanded request to perform the numerical simulations. A two-slope pyramid shape is used to carry out the numerical simulation and modelling. Its geometric difficulty on the numerical shape prediction and the through thickness stress behaviour are the main analysis targets in the present work. This work confirmed a significant CPU time reduction and an acceptable shape prediction accuracy using an adaptive remeshing method combined with the selected solid-shell element. The stress distribution in thickness direction revealed the occurrence of bending/unbending plus stretching and plastic deformation in regions far from the local deformation in the tool vicinity. [ABSTRACT FROM AUTHOR]

Single point incremental forming (SPIF), needing no dedicated tools, is the simplest variant of incremental sheet metal forming processes. In the present work, a simplified model of SPIF of a truncated cone, capable of predicting the thickness distribution, has been developed using sequential limit analysis (SLA). The obtained results were validated experimentally and compared with thickness predictions obtained from an explicit shell FE model implemented in Abaqus. It is shown that SLA is capable to solve the thickness prediction problem more accurately and efficiently than the equivalent FEA approach. As an application of the proposed model, the effect of the diameter of the hemispherical tool tip and the step down on the thickness distribution and the minimum thickness in a 50° cone is studied using SLA. By introducing bending and stretching zones in the wall of the cone, variations of the minimum thickness by changing the tool diameter and the step down are discussed. [ABSTRACT FROM AUTHOR]

Multistage forming is one of the most practical solutions to avoid severe thinning in single point incremental forming (SPIF). A successful implementation of multistage SPIF is strongly dependent on an appropriate deformation path. In this paper, firstly, a simplified modeling technique is proposed using sequential limit analysis. It is shown that sequential limit analysis can predict the thickness distribution faster than an equivalent model in a commercial finite element modeling code like Abaqus can. The reliability of the model is assessed by comparing experimental and simulated results for single-stage and multistage SPIF cones. This model is utilized to study the effect of various deformation paths on the thickness distribution. As a result, a new multistage strategy is designed and implemented to form a 70° wall angle cone in three stages. The thickness distribution of the cone is improved significantly compared to cones formed by a single-stage and a conventional three-stage strategy. Besides this improvement, the new multistage SPIF can be carried out in much less time. [ABSTRACT FROM AUTHOR]

The aim of the study was to establish practical formulae allowing to predict the forces occurring during the single point incremental forming process. This study has been based on a large set of systematic experiments on the one hand and on results of finite elements modeling simulations on the other. This led to analytical formulae allowing to compute the three main components of the force for five selected materials in function of the working conditions (sheet thickness, wall angle, tool diameter, and step down) with a good precision. Moreover, a general model has been deduced, allowing to compute an approximate value for the force for any material, based on knowledge of the tensile strength only. [ABSTRACT FROM AUTHOR]

Knowledge of the twist, induced during Single Point Incremental Forming is of importance for understanding asymmetric behaviour when using unidirectional toolpaths. In order to correctly position cut-outs and pre-formed features in the undeformed sheets, insight in the magnitude and direction of the induced twist during incremental forming is required. The resulting twist direction, reported by different research groups in both single and two point incremental forming, typically corresponds to the toolpath direction as a result of the friction between tool and work piece when using a unidirectional toolpath. However a twist in opposite direction can be observed when processing parts with high drawing angles. Detailed analysis of twist phenomena provides insight in the forming mechanics of single point incremental forming. The purpose of this paper is to study the occurrence of twist by means of strain measurements and document its influence on the thickness distribution in parts characterised by stiff semi-vertical rib features. [ABSTRACT FROM AUTHOR]

The Single Point Incremental Forming Process (SPIF) makes use of a single, small forming tool to incrementally deform a metal sheet into a complex shape. Without a need for dedicated tooling, this process meets the demand for small batch production and Rapid Prototyping of industrial shell-like structures. The sheet is formed due to a locally applied stress field on its surface, consisting of a normal and a shear component. The shear component is strongly influenced by friction with the dragging forming tool. In common practice, SPIF is performed under well lubricated conditions and with tool rotation, both designed to minimize friction. Through-Thickness Shear (TTS), which is part of the deformation mechanism in SPIF, may be intuitively linked to the friction applied during the process. In this paper, the role of friction in SPIF is experimentally investigated through the forming of an aluminium alloy sheet (AA3103-O) into a large wall angle cone with and without imposed tool rotation. It is found that only the force component along the instantaneous tool movement direction depends on the tool rotation, i.e. on the friction conditions. Finite Element (FE) simulations are also presented, which use (i) continuum elements, so that TTS can be taken into account, (ii) a sub-millimetre FE mesh, so that the small contact zone may be adequately modelled, and (iii) a mixed isotropic-kinematic hardening law that captures the anisotropic hardening until large strains. Under these three conditions, a quite accurate prediction of the forming force is obtained. Furthermore, it is shown how the validation of the FE constitutive law may be decoupled from the validation of the FE contact model. Finally, it is seen that overall TTS predictions are affected by tool rotation, which shows that the deformation mechanism in SPIF may be controlled to a certain extent by the imposed tool rotation. [ABSTRACT FROM AUTHOR]

In this study, the Single Point Incremental Forming process (SPIF) is applied on a specific aluminium alloy used in the aerospace industry since this technique and material combine a low specific weight, high strength and stiffness properties and high strain levels. To be able to optimize the process, a model and its material parameters are required. It was noticed that a simple isotropic hardening model was not sufficient to provide an accurate tool force prediction []. Therefore an elasto-plastic law with a mixed isotropic-kinematic hardening is investigated. The inverse method coupled with the Finite Element (FE) code: “Lagamine” [] is used to fit the material data of this complex law. In order to validate the model and the material data, a Line test and a Cone test are used. [ABSTRACT FROM AUTHOR]

The aim of the study was to establish practical formulas allowing to predict the forces occurring during the process of Single Point Incremental Forming (SPIF). This study has been based on a large set of systematic experiments on one hand and on results of FEM simulations on the other hand. This led to analytical formulas allowing to compute the three main components of the force for five selected materials in function of the working conditions (sheet thickness, wall angle, tool diameter and step down) with a good precision. Moreover a general model has been deduced allowing to compute an approximate value for the force for any material, based on knowledge of the tensile strength only. [ABSTRACT FROM AUTHOR]

In this paper, the Finite Element submodelling technique is applied to model the small plastic zone in the Incremental Forming process with an adequately fine (sub-millimetre) mesh at a computationally acceptable cost. The focus lies on the distribution of the contact pressure between sheet and forming tool. Different forming conditions of truncated cones are considered. Results show that the contact consists of two distinguishable parts. The obtained insights can be applied in the physical modelling of forming forces, which allows improving part accuracy through compensation for the mechanical stiffness of the forming machine. [ABSTRACT FROM AUTHOR]

Although Incremental Forming offers distinct advantages over traditional forming processes, such as short lead times and low setup costs, the process still has some drawbacks. Besides the obtainable accuracy, one of the main challenges of the process are the process limits. Many workpiece geometries cannot be manufactured due to the fact that the maximum wall angle that can be formed is limited for a certain sheet material and thickness to a given angle. Different solutions to this approach have been proposed and this paper further investigates one of those solutions, the multi step approach for single point incremental forming. Experiments were performed and compared with simulations to better understand the phenomena underlying the improved process performance. [ABSTRACT FROM AUTHOR]

The purpose of this article is to develop an inverse method for adjusting the material parameters for single point incremental forming (SPIF). The main idea consists in FEM simulations of simple tests involving the SPIF specificities (the “line test”) performed on the machine used for the process itself. This approach decreases the equipment cost. It has the advantage that the material parameters are fitted for heterogeneous stress and strain fields close to the ones occurring during the actual process. A first set of material parameters, adjusted for the aluminum alloy AA3103 with classical tests (tensile and cyclic shear tests), is compared with parameters adjusted by the line test. It is shown that the chosen tests and the strain state level have an important impact on the adjusted material data and on the accuracy of the tool force prediction reached during the SPIF process. [ABSTRACT FROM AUTHOR]

Laser cutting is nowadays a well-established sheet metal processing method. The cutting of thick plates (>15 mm) is, however, still characterized by more narrow process windows compared to those for thin sheets. Therefore good cutting quality cannot always be guaranteed. The development of a monitoring system that can measure the cut quality on-line could form a solution to this problem. In this study, the determination of an appropriate monitoring system is dealt with. The applicability for monitoring purposes of two types of sensors is investigated: the microphone and the photodiode. For both types, correlation between the sensor output and the cut quality is investigated. Besides contour cutting, piercing is also covered in the study. The full break-through of the piercing can be monitored by both sensors. Furthermore quantitative relations between cut quality parameters and photodiode signal parameters could be determined. [ABSTRACT FROM AUTHOR]

As part of a multidisciplinary study of brain damage in children fatally injured in motor vehicle accidents, a simple method to quantify and visualise the distribution and extent of injury has been developed. Vascular and axonal injury were assessed using coronal brain sections stained for haematoxylin and eosin, or reacted immunohistochemically for β-amyloid precursor protein. Subsequent analysis was carried out using NIH Image software, and the resulting information is displayed in schematic diagrams. These summary diagrams simply and clearly show the distribution of injury in both the coronal and horizontal planes. This technique offers an advantage over previous scoring methods in that it provides both a quantitative and a visual summary of the distribution and extent of brain injury. This information can then be used to compare the injury distribution and severity with estimated impact points and acceleration data. [ABSTRACT FROM AUTHOR]