Papers by Keyword: Forming

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Authors: Jean Guillaume Orliac, Adrien Charmetant, Fabrice Morestin, Philippe Boisse, Stephane Otin
Abstract: In order to simulate 3D interlock composite reinforcement behavior in forming processes like Resin Transfer Molding (RTM), it is necessary to predict yarns positions in the fabric during the preforming stage of the process. The present paper deals about thick 3D interlock fabric forming simulation using a specific hexahedral semi-discrete finite elements simulation tool : Plast4. Using the virtual work principle, we distinguish the virtual internal work due to tensions in yarns from other internal virtual works. The part of material stiffness relative to yarns tension is described as "first order stiffness" by a 3D discrete beam model. The rest of the rigidities - like transverse compression, shear strains or friction between yarns - are depicted by a continuous quad-based discretization designated in our work as "second order stiffness". A combination of this "first order" discrete model and a continuous orthotropic hyperelastic "second order" material formulation will enables us to simulate interlock preforming process. Jointly to the simulation work, we also had to specify and perform experimental testing identification of material's parameters. Thoses parameters concern both parts of the model. A bilinear tension approach for the yarns discrete modelization and an orthotropic continuous material for the "second order" part.
Authors: Ge Yan Fu, Shi Hong Shi
Abstract: Coating samples prepared by laser cladding were subjected to repeated impact fatigue experiment. It is observed through phenomenological analysis that most coating cracks are original from the surface. And then, the cracks extend by the combined action of coating inner stress and repeated impact compression stress. The formation of crack is close related to performance of coating material. It can be divided to traversed crack and reticular crack from surface side; it also can be divided to vertical extend crack and reticular extend crack from the cross section side. Rigid and brickle coating has a shorter repeated impact life because a kind of linear crack is formed easily in it. On the other hand, tougher coating has a long life. Mechanics of nucleation and expansion of crack was explained by using stress concentration theory and vacancy concentration theory. The anti-repeated impact fatigue performance of laser cladding part could be improved by increasing toughness and reducing hardness of the coating material. Furthermore, suitable dispersion strengthening and fine-crystal strengthening can obtain the same purpose.
Authors: Bernd Engel, Christopher Kuhnhen, Christian Mathes, Christopher Heftrich, Peter Frohn, Sebastian Groth
Abstract: During the bending of tubes, specific geometric deviations from the desired shape geometry occur. These deformations comprise cross-sectional deformation, wall-thinning of the outer arc and wall-thickening of the inner arc. During the bending of parts with small bend factors, geometric deviations on the inner arc in form of waves and wrinkles may arise as other typical quality criteria. A quantitative evaluation of those deviations has yet to be defined. Currently, only an instruction for measuring the height of the wrinkles at the inner arc according to DIN EN 13480-4 is known. In this standard, only the two highest wrinkles and the valley in between are included. The characteristics of the wrinkle, especially the flank angle and the rise of deformation are disregarded, although they are responsible for the failure of the bent part. Tool damages can also occur. A development of an evaluation factor to assess deformations in the bow area for bent parts is presented in this paper. In addition, it will be possible to quantify geometric deviations in the bow area. By using the newly developed evaluation factor for geometrical deformations in the bow area, the determination of the quality of the bent part should become more reproducible.
Authors: Horst Meier, O. Dewald, Jian Zhang
Abstract: This paper describes a new sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes. The kinematic based generation of the shape is implemented by means of a new forming machine comprising of two industrial robots. Compared to conventional sheet metal forming machines this newly developed sheet metal forming process offers a high geometrical form flexibility and also shows comparatively small deformation forces for high deformation degrees. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of the two robots. The sheet metal components manufactured in first attempts are simple geometries like truncated pyramids and cones as well as spherical cups. Among other things the forming results could be improved by an adjustment of the movement strategy, a variation of individual process parameters and geometric modifications of the tools. Apart from a measurement of the form deviations of the sheet metal with a Coordinate Measurement Machine rasterised and deformed sheet metals were used for deformation analyses. In order to be able to use the potential of this process, a goal-oriented process design is as necessary as specific process knowledge. In order to achieve process stability and safety the essential process parameters and the process boundaries have to be determined.
Authors: Philipp Hildenbrand, Michael Lechner, Marion Merklein
Abstract: Applying bulk forming processes on sheet metals enables the manufacturing of functional components with local wall thickness distributions. Using tailored blanks improves the forming of the functional components and increases the material efficiency. One process for manufacturing tailored blanks with defined sheet thickness distributions is a flexible rolling process. However, this process requires a complex process strategy. Additionally, tailored blanks out of high-strength steels from this process have failed in subsequent forming. Thus, a new rolling concept with a defined shaping of the material into a die cavity has been developed. This new concept requires the development of a new process strategy. In this paper, the general qualification and first results of the new concept are presented.
Authors: Walid Najjar, Xavier Legrand, Cedric Pupin, Philippe Dal Santo, Serge Boude
Abstract: In this paper, a discrete approach for the simulation of the preforming of dry woven reinforcement is proposed. A “unit cell” is built using elastic isotropic shells and axial connectors instead of bars and beams used in previous studies. Shell elements are used to take into account the in-plane shear stiffness and to manage contact phenomenon with the punch and die. Connectors reinforce the structure in the yarn directions and naturally capture the specific behavior of the fabric. To identify the material parameters, uniaxial tensile tests and bias tests have been employed. A numerical algorithm, coupling Matlab and Abaqus/Explicit, is used to determine the shear parameters by an inverse method. The model has been implemented in Abaqus to simulate hemispherical stamping. Experimental results are compared to numerical simulations, good agreement between both results is shown.
Authors: L. Mosse, Wesley J. Cantwell, M.J. Cardew-Hall, Paul Compston, Shankar Kalyanasundaram
Abstract: The quality of the part and the robustness of the process in stamp-forming of sheet materials are determined by a number of variables. This study looks at the application of the stamping process to a Fibre-Metal Laminate (FML) material system and the effect of the process variables on the formability characteristics of these material systems. The effect of pre-heating temperature on the splitting and wrinkling behaviour has been investigated for two different FML systems. It has been found that different FML systems exhibit different failure modes.
Authors: Nazim Baluch, Nordin Norani, Shahimi Mohtar
Abstract: To improve crash worthiness and fuel economy, the automotive industry is, increasingly, using Advanced High Strength Steel (AHSS). However, in recent years, stampers, particularly those serving the automotive industry, have begun to face new challenges related to the increased use of AHSS. Stamping AHSS can push the capability limits of some lubricants and often cause lubricant film break down and galling thereby increasing scrap rate and tool maintenance cost. This paper discusses the advantages of AHSS in auto metal stampings, highlights the new challenges faced by stampers, and delineates the exigency of draw lubricant in producing high quality auto stampings from AHSS.
Authors: Roland Ritt, Martín Machado, Michael Fischlschweiger, Zoltan Major, Thomas Antretter
Abstract: A methodology to calculate surface strains from a rectangular grid placed on a forming blank is introduced. This method consists of treating the grid points as nodes of a finite element (FE) model and assigning elements to the grid. The strains are then computed following FE analysis. If higher order elements are used, also more information within the element can be obtained which allows a coarser grid without loss of accuracy. This is the major advantage of the approach presented herein.
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