Analysis of damage and fracture formulations in cold extrusion

In forming processes, components generally undergo large deformations. This induces the evolution of damage, which can influence material and product properties. To capture these effects, a continuum damage mechanics (CDM) model, based on the work of Lemaitre [8] and Soyarslan [13, 14] as well as different fracture criteria according to Cockcroft and Latham [2], Freudenthal [4] and Oyane [10] are implemented and in- vestigated. While the CDM theory considers the evolution of damage and the associated softening, fracture criteria do not affect the results of the mechanical finite element (FE) analysis. However, a coupling is generally possible via element deletion, but material softening cannot be depicted in the simulation. Tensile tests with notched specimens are performed in order to obtain the material parameters associated with these models by inverse parameter identification processes. The optimized set of parameters is finally ap- plied to the damage and fracture models used for the FE simulations of a cold extrusion process, which are investigated in terms of damage evolution and material failure. It is demonstrated that the CDM model predicts the evolution of damage observed for differ- ent process parameters in cold extrusion quantitatively. The prediction of the failure by the fracture criteria does not agree well with the experiments

Interaction of process parameters, forming mechanisms, and residual stresses in single point incremental forming

The residual stress state of a sheet metal component manufactured by metal forming has a significant influence on the mechanical properties, and thus determines the time until the component fails, especially for dynamic loads. The origin of the resulting residual stress state of incrementally formed parts with regard to the forming mechanisms of shearing, bending, and the normal stress component is still under investigation. The relationship between the process parameters, the forming mechanisms, and the resulting residual stress state for a complex part geometry manufactured by single point incremental forming (SPIF) is presented in this publication. For this purpose, a validated numerical process model is used to analyze the influence of the step-down increment Δz for truncated cones on the characteristics of the forming mechanisms and the resulting residual stress state. For the first time the forming mechanisms are evaluated numerically on both sides of the formed component. A relationship between the process parameters, forming mechanisms, residual stresses, and the mechanical properties of an incrementally formed component is shown. Shearing-induced hardening is identified as a relevant influence on the residual stress state of cones

Online measurement of the radial workpiece displacement in electromagnetic forming subsequent to hot aluminum extrusion

Electromagnetic compression was integrated into the process chain of hot metal extrusion in order to reduce the cross section of the workpiece locally. To integrate both processes, a tool coil for electro-magnetic compression is positioned behind the die exit and coaxially to the extrudate. Additionally, a counter die in the shape of a mandrel can be mounted to the mandrel of a porthole extrusion die, which extends into the working area of the tool coil. Experiments were conducted on hollow profiles which were compressed by electromagnetic forming subsequent to extrusion. Due to an extremely short processing time of the high speed forming process, a compensation of the relative speed between the workpiece and the tooling can be ignored. For determine the workpiece displacement during the electromagnetic forming process, a new measuring strategy based on the Photon Doppler Velocimetry was developed

Soft Sensors for Property-Controlled Multi-Stage Press Hardening of 22MnB5

In multi-stage press hardening, the product properties are determined by the thermo-mechanical history during the sequence of heat treatment and forming steps. To measure these properties and finally to control them by feedback, two soft sensors are developed in this work. The press hardening of 22MnB5 sheet material in a progressive die, where the material is first rapidly austenitized, then pre-cooled, stretch-formed, and finally die bent, serves as the framework for the development of these sensors. To provide feedback on the temporal and spatial temperature distribution, a soft sensor based on a model derived from the Dynamic mode decomposition (DMD) is presented. The model is extended to a parametric DMD and combined with a Kalman filter to estimate the temperature (-distribution) as a function of all process-relevant control variables. The soft sensor can estimate the temperature distribution based on local thermocouple measurements with an error of less than 10 °C during the process-relevant time steps. For the online prediction of the final microstructure, an artificial neural network (ANN)-based microstructure soft sensor is developed. As part of this, a transferable framework for deriving input parameters for the ANN based on the process route in multi-stage press hardening is presented, along with a method for developing a training database using a 1-element model implemented with LS-Dyna and utilizing the material model Mat248 (PHS_BMW). The developed ANN-based microstructure soft sensor can predict the final microstructure for specific regions of the formed and hardened sheet in a time span of far less than 1 s with a maximum deviation of a phase fraction of 1.8 % to a reference simulation

Control-Oriented Characterization of Product Properties During Hot Hole-Flanging of X46Cr13 Sheet Material in a Progressive-Die

Robust and versatile production is enabled by a closed-loop control of product properties. This essentially relies on the characterization of the interaction between properties and available degrees of freedom to control the process. In particular, this work examines the setting of collar height, thinning, curvature, and hardness during hot hole-flanging of X46Cr13 sheet material with simultaneous heat treatment to identify approaches for a closed-loop property control in hot hole- flanging during multi-stage hot sheet metal forming. To scrutinize the adjustability of the hardness of X46Cr13 sheet material by heat treatment with rapid heating and short dwell times, quenching tests with austenitizing temperatures from 900 to 1100 ◦ C and dwell times from 1 to 300 s were carried out. A hardness between 317 and 680 HV10 was measured. By analyzing the force-displacement curve and the contact situation between tools and blank during hot hole-flanging, an understanding for the process was established. To determine the adjustability of geometrical collar properties and the hardness of the collar, collars were formed at punch speeds between 5 and 100 mm/s and at different temperatures. Here, a dependency of the geometry of the collar on temperature and punch speed as well as setting of the hardness was demonstrated

Enhanced granular medium-based tube press hardening

Active and passive control strategies of internal pressure for hot forming of tubes and profiles with granular media are described. Force transmission and plastic deformation of granular medium is experimentally investigated. Friction between tube, granular medium and die as also the external stress field are shown to be essential for the process understanding. Wrinkling, thinning and insufficient forming of the tube establishes the process window for the active pressure process. By improving the punch geometry and controlling tribological conditions, the process limits are extended. Examples for the passive pressure process reveal new opportunities for hot forming of tubes and profiles.Comment: 4 pages, 11 figure

Control-Oriented Characterization of Product Properties during Hot Hole-Flanging of X46Cr13 Sheet Material in a Progressive-Die

Robust and versatile production is enabled by a closed-loop control of product properties. This essentially relies on the characterization of the interaction between properties and available degrees of freedom to control the process. In particular, this work examines the setting of collar height, thinning, curvature, and hardness during hot hole-flanging of X46Cr13 sheet material with simultaneous heat treatment to identify approaches for a closed-loop property control in hot hole-flanging during multi-stage hot sheet metal forming. To scrutinize the adjustability of the hardness of X46Cr13 sheet material by heat treatment with rapid heating and short dwell times, quenching tests with austenitizing temperatures from 900 to 1100 °C and dwell times from 1 to 300 s were carried out. A hardness between 317 and 680 HV10 was measured. By analyzing the force-displacement curve and the contact situation between tools and blank during hot hole-flanging, an understanding for the process was established. To determine the adjustability of geometrical collar properties and the hardness of the collar, collars were formed at punch speeds between 5 and 100 mm/s and at different temperatures. Here, a dependency of the geometry of the collar on temperature and punch speed as well as setting of the hardness was demonstrated

Aufbereitung von optischen Messdaten zur Analyse der asymmetrischen inkrementellen Blechumformung (AIBU)

Ziel unseres Projektes ist die statistische Analyse der bisher wenig erforschten asymmetrischen inkrementellen Blechumformung (AIBU). Ein elementares Problem hierbei ist die Quanti zierung der Qualität eines gefertigten Bauteils. Da der AIBU-Prozess ein inkrementeller Prozess ist, spielt die Qualität der gesamten dreidimensionalen Geometrie des Fertigteils eine Rolle. Nur wenn sie gänzlich quanti ziert werden kann, ist eine Untersuchung der Prozessdynamik möglich. Die dreidimensionale Vermessung des Fertigteils ist jedoch mit den herkömmlichen (taktilen) Messmethoden nur schwer möglich, daher stellen wir in diesem Diskussionspapier ein Verfahren zur Aufbereitung von optischen Messdaten vor, welches eine solche Analyse ermöglicht. Hierbei wird die Geometrie der Bauteile zunächst optisch komplett vermessen. Aufbauend auf diesen Messungen werden in einem mehrstu figen Ansatz die Messdaten mittels statistischer Methoden aufbereitet, um Artefakte heraus zu filtern, Ober- und Unterseiten zu trennen und schließlich auch die Wandstärken zu bestimmen. Kennt man die exakte Geometrie des Fertigteils und dessen Wandstärke über die gesamte Oberfläche, können hieraus leicht Qualitätskennzahlen errechnet werden. In Kapitel 2 werden zunächst die prozesstechnischen Grundlagen der AIBU und deren Prozessparameter und Einflussfaktoren eingeführt. In Kapitel 3 wird das in diesem Papier verwendete Experiment und die Messmethodik erklärt. Das Kapitel 4 befasst sich dann detailliert mit den einzelnen Schritten der Messdatenaufbereitung. Das letzte Kapitel diskutiert die Reproduzierbarkeit und Verlässlichkeit der vorgestellten Methode

Internationalization and Digitalization in Engineering Education

[EN] Digital, virtual and E-learning elements have increasingly become a part in higher education and, most recently, the high potential of digitalization for processes of strategic internationalization of higher education institutions is coming into focus. The collaborative project of three German universities, XYZ, is working on strategies for the internationalization and virtualization of engineering education. While these topics used to be different key areas of the project, a combination of both distinguished itself as a potential new working field. This paper introduces two pilot concepts that were implemented and evaluated at the universities Y and Z which both aim at the complementation of incoming students’ experiences in Germany by digital means. At Y, a transnational online class explores means of preparing degree-mobile engineering students from all over the world for their master’s studies in Germany. At Z, an online course was designed to accompany a summer school research exchange for US-American engineering students in order to prolong their short-term mobility by digital elements. These pilot projects were well-accepted by students and faculty at both universities and their evaluations between 2014 and 2017 have revealed valuable results for further optimization. This paper presents the results and discusses future potential.Strenger, N.; May, D.; Ortelt, T.; Kruse, D.; Frerich, S.; Tekkaya, AE. (2017). Internationalization and Digitalization in Engineering Education. En Proceedings of the 3rd International Conference on Higher Education Advances. Editorial Universitat Politècnica de València. 558-565. https://doi.org/10.4995/HEAD17.2017.528955856

Investigations of ductile damage in DP600 and DC04 deep drawing steel sheets during punching

The paper presents numerical and microstructural investigations on a punching process of 2 mm thick steel sheets. The dual phase steel DP600 and the mild steel DC04 exhibit different damage and fracture characteristics. To distinguish the void development and crack initiation for both materials, interrupted tests at varied punch displacements are analyzed. The void volume fractions in the shearing zone are identified by scanning electron microscopy (SEM). The Gurson model family, which is recently extended for shear fracture, is utilized to model the elastoplastic behavior with ductile damage. The effect of the shear governing void growth parameter, introduced by Nahshon and Hutchinson (2008), is discussed