ABSTRACT Forming, cutting and welding of metal by impulse has significant advantages, in that sho... more ABSTRACT Forming, cutting and welding of metal by impulse has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can enable much lighter and more agile equipment because large static forces do not need to be resisted. Impulse forming is most commonly executed using electromagnetic forming. However, the application of electromagnetic forming is limited at high energies and large numbers of operations by the availability of long-lived electromagnetic coils (or actuators, as they are sometimes referred to). Low-cost, disposable actuators have been suggested as one method to counteract this issue. Here we propose the use of low-cost foils or wires that are intentionally vaporized by a pulsed electric current, in order to create an intense mechanical impulse. Applications including cutting, forming, and dimensional calibration are demonstrated and discussed. The available literature that could provide design guidance is reviewed. A simple cutting and welding experiment using a vaporizing aluminum foil is demonstrated. Further experiments study the expansion of simple copper tubes using the impulse developed from copper and aluminum wires that are vaporized using capacitor bank discharge with nominal charged voltages between 3.4 and 6.7 kV, and peak currents between 60 and 150 kA delivered with rise times on the order of 20 μs. This gives some guidance on how forming operations may be designed and, opens possible areas for further research.
ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2008
Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, n... more Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, namely central bursts, in direct forward extrusion process is presented. Accordingly, in a thermodynamically consistent setting, a local Lemaitre variant damage model with ...
ABSTRACT Forming tasks in Sheet Metal Prototyping are currently a balancing act between part flex... more ABSTRACT Forming tasks in Sheet Metal Prototyping are currently a balancing act between part flexibility and accuracy. In view of Asymmetric Incremental Sheet Forming (AISF), the part support is the decisive factor: Die-based processes such as TPIF are restricted to the given geometry of the part. On the other hand, the die-less variant (SPIF) is prone to a much more complex process-layout – once a similar accuracy needs to be obtained. Consequently, this requires a flexible die concept, supporting the part in the critical zones only. Within this article we meet this challenge by introducing the configurable tooling concept "FlexDie". This support tool comprises a construction kit for skeleton dies allowing for an adjustment of its geometry to almost any desired shape. Based on the solar cooker benchmark by Jeswiet et al., we show both the tooling-concept and the feasibility. The latter we discuss, based on the quality features geometric accuracy as well as surface quality. Both features are assessed with respect to the forming results obtained by use of a full-die. The accuracy resulting by applying the FlexDie is only slightly inferior to the parts formed by use of a full-die. However, the FlexDie allows for simple optimization of both, die and part geometry. In addition, compensation strategies by adapting the toolpath are still possible. In summary, the results show the feasibility of the FlexDie concept for industrial ISF tasks - even at very low production volumes.
The work presented aims to provide a time-efficient solution strategy for Asymmetric Incremental ... more The work presented aims to provide a time-efficient solution strategy for Asymmetric Incremental Sheet Forming (AISF). Denoted strategy comprises a decoupling algorithm focusing on the small elastic-plastic forming zone, while reducing the elastic partition to a few elements only. The latter is achieved by applying static condensation, thus entailing the need for a frequent update of the Superelements due to large displacements. Within the scope of this work the implementation of an updating scheme for the use of Superelements in AISF-Simulations is presented. The article presents the algorithm and the speed increase as well as the error obtained by the mentioned scheme.
Mit der Prototypenfertigung ist eine nicht zu unterschätzende Kostenfrage verbunden. Auch die ink... more Mit der Prototypenfertigung ist eine nicht zu unterschätzende Kostenfrage verbunden. Auch die inkrementellen Umformverfahren, die bereits ein hohes Einsparpotential bieten, sind prozesstechnisch durch die Faktoren Qualität, Flexibilität und Maschinenkosten begrenzt. Entwickelt wurde ein neuartiges Werkzeugkonzept, mit dem sich einfache Blechbauteile ohne hohe Investitionskosten vollkinematisch herstellen lassen. Link: http://www.vdi-z.de/vdi-z/currentarticle.php?data[article_id]=48209
ABSTRACT The design of porthole dies for aluminum extrusion processes is very complex. For the ac... more ABSTRACT The design of porthole dies for aluminum extrusion processes is very complex. For the accurate design, fundamental knowledge about material flow is of major importance. To gain these information, numerical methods are increasingly utilized. The accuracy of the simulation results depends mainly on the precision of the used boundary conditions in the model. Therefore, visioplastic analyses of the material flow inside a porthole die are presented in this paper. A special modular tool concept was developed to prepare and visualize the material flow inside the process. The results of the experimental analysis were used for the verification of numerical results which were calculated with the commercial software codes Deform3D and HyperXtrude.
ABSTRACT In the field of sheet metal forming traditional forming processes are used. However, a q... more ABSTRACT In the field of sheet metal forming traditional forming processes are used. However, a quasi-static forming process combined with a high speed forming process can enhance the forming limits of a single one. In this paper, the investigation of the process chain quasi-static deep drawing – electromagnetic forming by means of a new coupled damage-viscoplasticity model for large deformations is performed. The finite strain constitutive model, used in the finite element simulation combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. The anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. Hill-type plastic anisotropy is modelled by expressing the yield surface as a function of second-order structure tensors as additional tensor-valued arguments. The coupling of damage and plasticity is carried out in a constitutive manner according to the effective stress concept. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package of LS-Dyna with the electromagnetical modul. Aim of the work is to show the increasing formability of the sheet by combining quasi-static deep drawing processes with high speed electromagnetic forming process.
ABSTRACT Forming, cutting and welding of metal by impulse has significant advantages, in that sho... more ABSTRACT Forming, cutting and welding of metal by impulse has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can enable much lighter and more agile equipment because large static forces do not need to be resisted. Impulse forming is most commonly executed using electromagnetic forming. However, the application of electromagnetic forming is limited at high energies and large numbers of operations by the availability of long-lived electromagnetic coils (or actuators, as they are sometimes referred to). Low-cost, disposable actuators have been suggested as one method to counteract this issue. Here we propose the use of low-cost foils or wires that are intentionally vaporized by a pulsed electric current, in order to create an intense mechanical impulse. Applications including cutting, forming, and dimensional calibration are demonstrated and discussed. The available literature that could provide design guidance is reviewed. A simple cutting and welding experiment using a vaporizing aluminum foil is demonstrated. Further experiments study the expansion of simple copper tubes using the impulse developed from copper and aluminum wires that are vaporized using capacitor bank discharge with nominal charged voltages between 3.4 and 6.7 kV, and peak currents between 60 and 150 kA delivered with rise times on the order of 20 μs. This gives some guidance on how forming operations may be designed and, opens possible areas for further research.
ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2008
Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, n... more Materializing Continuum Damage Mechanics (CDM), numerical modeling of discrete internal cracks, namely central bursts, in direct forward extrusion process is presented. Accordingly, in a thermodynamically consistent setting, a local Lemaitre variant damage model with ...
ABSTRACT Forming tasks in Sheet Metal Prototyping are currently a balancing act between part flex... more ABSTRACT Forming tasks in Sheet Metal Prototyping are currently a balancing act between part flexibility and accuracy. In view of Asymmetric Incremental Sheet Forming (AISF), the part support is the decisive factor: Die-based processes such as TPIF are restricted to the given geometry of the part. On the other hand, the die-less variant (SPIF) is prone to a much more complex process-layout – once a similar accuracy needs to be obtained. Consequently, this requires a flexible die concept, supporting the part in the critical zones only. Within this article we meet this challenge by introducing the configurable tooling concept "FlexDie". This support tool comprises a construction kit for skeleton dies allowing for an adjustment of its geometry to almost any desired shape. Based on the solar cooker benchmark by Jeswiet et al., we show both the tooling-concept and the feasibility. The latter we discuss, based on the quality features geometric accuracy as well as surface quality. Both features are assessed with respect to the forming results obtained by use of a full-die. The accuracy resulting by applying the FlexDie is only slightly inferior to the parts formed by use of a full-die. However, the FlexDie allows for simple optimization of both, die and part geometry. In addition, compensation strategies by adapting the toolpath are still possible. In summary, the results show the feasibility of the FlexDie concept for industrial ISF tasks - even at very low production volumes.
The work presented aims to provide a time-efficient solution strategy for Asymmetric Incremental ... more The work presented aims to provide a time-efficient solution strategy for Asymmetric Incremental Sheet Forming (AISF). Denoted strategy comprises a decoupling algorithm focusing on the small elastic-plastic forming zone, while reducing the elastic partition to a few elements only. The latter is achieved by applying static condensation, thus entailing the need for a frequent update of the Superelements due to large displacements. Within the scope of this work the implementation of an updating scheme for the use of Superelements in AISF-Simulations is presented. The article presents the algorithm and the speed increase as well as the error obtained by the mentioned scheme.
Mit der Prototypenfertigung ist eine nicht zu unterschätzende Kostenfrage verbunden. Auch die ink... more Mit der Prototypenfertigung ist eine nicht zu unterschätzende Kostenfrage verbunden. Auch die inkrementellen Umformverfahren, die bereits ein hohes Einsparpotential bieten, sind prozesstechnisch durch die Faktoren Qualität, Flexibilität und Maschinenkosten begrenzt. Entwickelt wurde ein neuartiges Werkzeugkonzept, mit dem sich einfache Blechbauteile ohne hohe Investitionskosten vollkinematisch herstellen lassen. Link: http://www.vdi-z.de/vdi-z/currentarticle.php?data[article_id]=48209
ABSTRACT The design of porthole dies for aluminum extrusion processes is very complex. For the ac... more ABSTRACT The design of porthole dies for aluminum extrusion processes is very complex. For the accurate design, fundamental knowledge about material flow is of major importance. To gain these information, numerical methods are increasingly utilized. The accuracy of the simulation results depends mainly on the precision of the used boundary conditions in the model. Therefore, visioplastic analyses of the material flow inside a porthole die are presented in this paper. A special modular tool concept was developed to prepare and visualize the material flow inside the process. The results of the experimental analysis were used for the verification of numerical results which were calculated with the commercial software codes Deform3D and HyperXtrude.
ABSTRACT In the field of sheet metal forming traditional forming processes are used. However, a q... more ABSTRACT In the field of sheet metal forming traditional forming processes are used. However, a quasi-static forming process combined with a high speed forming process can enhance the forming limits of a single one. In this paper, the investigation of the process chain quasi-static deep drawing – electromagnetic forming by means of a new coupled damage-viscoplasticity model for large deformations is performed. The finite strain constitutive model, used in the finite element simulation combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. The anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. Hill-type plastic anisotropy is modelled by expressing the yield surface as a function of second-order structure tensors as additional tensor-valued arguments. The coupling of damage and plasticity is carried out in a constitutive manner according to the effective stress concept. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package of LS-Dyna with the electromagnetical modul. Aim of the work is to show the increasing formability of the sheet by combining quasi-static deep drawing processes with high speed electromagnetic forming process.
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