T. Matthias

Numerical Investigations of the Strain-Adaptive Bone Remodeling in the Prosthetic Pelvis

Bone remodeling due to stress shielding is a major cause of hip implants aseptic loosening. Previously, investigations on this phenomenon were based mainly on clinical observations. Currently, the finite element method (FEM) has been established as a reliable and efficient computing method to examine stress shielding after total hip arthroplasty and the related bone remodeling in the prosthetic Femur.

Numerical analysis of draw bending of load-adapted sheet metal profiles

In comparison to traditional roll forming processes, draw bending process represents a flexible and inexpensive production of open sheet metal profiles. Draw bending technologies allow the fabrication of load-adapted parts for applications in lightweight design. It enables the fabrication for predominantly bearing-like parts with adjustable cross sections along the longitudinal axis. This paper introduces the draw bending process with its functional principle and specifies the most important characteristics. It includes the key results of some research projects dealing with draw bending, which prove the applicability of this technique to produce load-adapted profiles. The fabrication of u-shaped profiles with various dimensions and adjusted cross sections as well as the fabrication of hat-shaped profiles with various widths of flange and adjusted longitudinal warping was investigated. The profiling is, in contrast to deep drawing processes, not bound to the form of the tools. The control of the draw bending process defines the contour of the profile during its production. Thereby an increased flexibility is achieved which is particularly useful for small series. Moreover numerical results are presented. The production of load adapted profiles and the buckling of the bottom area, as a result of a cross-sectional variation along the longitudinal axis are in the focus of the numerical and experimental investigations.

New Strategies in Finite Element Analysis of Material Processing

Under the supervision of Professor Bernd-Arno Behrens, the head of the Institute of Metal Forming and Metal-Forming Machines (IFUM), three PhD projects were carried out during the span of the Research Training Group 615 (GRK 615). All the projects originated in the Department of Numerical Methods, which is headed by Dr. Anas Bouguecha, and were related to finite element modeling and simulation of materials processing. Thus, Kanwar Bir Sidhu developed and implemented remeshing and rezoning algorithms to cope with severe plastic deformation and crack propagation in thin sheet blanking. The subject of Ilya Peshekhodov was a multiscale approach in modeling of forming processes of metal sheets coated with thin polymer composite coatings. With the help of the fluid mechanics approach, Thorsten Matthias modeled bulk forming processes of aluminum alloys in a semi-solid state. These projects are presented below along with some exemplary results.

Characterisation of the joining zone of serially arranged hybrid semi-finished components

Forming of already joined semi-finished products is an innovative approach to manufacture components which are well-adapted to external loads. This approach results in an economically and ecologically improved production by the targeted use of high-quality materials in component areas, which undergo high stresses. One possible production method for hybrid semi-finished products is friction welding. This welding method allows for the production of hybrid semi-finished products made of aluminium and steel as well as steel and steel. In this paper, the thermomechanical tensile and shear stresses causing a failure of the joined zone are experimentally determined through tension tests. These tests are performed with specimens whose joint zones are aligned with different angles to the load direction.

Importance of material and friction characterisation for FE-aided process design of hybrid bevel gears

Solid-forming components are often used in areas where they are subjected to very high loads. For most solid components locally divergent and sometimes contradictory requirements exist. Despite these contradictory requirements, almost exclusively monomaterials are nowadays used for the production of solid components. These components often reach their material-specific limits because of increasing demands on the products. Thus a significant increase in product quality and profitability would result from combining different materials in order to create tailored properties. In the Collaborative Research Center (CRC) 1153 “Tailored Forming” at the Leibniz Universitat Hannover, this topic is investigated. The primary objective of the CRC 1153 is to develop and investigate new tailored manufacturing processes to produce reliable hybrid solid semi-finished components. In contrast to existing production processes of hybrid solid components, semi-finished workpieces in the CRC 1153 are joined before the forming p...

FE-Based Design of a Forging Tool System for a Hybrid Bevel Gear

Multi-material solutions offer numerous benefits producing tailored-made hybrid components with enhanced application-optimized properties contrary to conventional monolithic parts. However, designing of corresponding manufacturing processes is often challenging due to various technical aspects. This paper represents a process route for the manufacturing of a hybrid bevel gear by means of tailored forming technology with a focus on die forging and describes the main challenges within the forming stage. Due to local material-specific properties, uncommon material flow and complex geometry of the final part, an individual forming tool system with a geared die was accurately designed. Besides the forming tool system, the FE-based design of the forging process as well as the necessary material characterisation will be presented. Finally, the initial results of the experimental forging investigations are shown.

Numerische Berechnung des Verschleißes an der Dornwalze eines Ringwalzprozesses in Abhängigkeit prozessrelevanter Parameter

Ringwalzen ist ein Umformprozess zur Herstellung nahtloser Ringe. Der Prozess kennzeichnet sich durch eine komplexe Kinematik der formgebenden Walzen und der Zentrierwalzen. Bei der Auslegung eines Ringwalzprozesses ist es erforderlich, die Vorringgeometrie und die Walzstrategie, d.xa0h. die Vorschube und Drehzahlen der einzelnen Walzen, so aufeinander abzustimmen, dass die geforderte Endkontur moglichst optimal erreicht wird. Mit Hilfe der FE-Simulation konnen bereits vor dem Produktionsstart gezielt Optimierungen, wie z.xa0B. die Optimierung von Walzstrategien durchgefuhrt und dadurch die Anzahl kostspieliger Probewalzungen auf ein Minimum beschrankt werden. Ein weiterer wichtiger Faktor ist der Verschleis an den Walzen. n n n nIm Vordergrund der Arbeit stehen die FE-Modellierung eines Ringwalzprozesses und die numerische Berechnung des Verschleises an der Dornwalze unter Variation prozessbedingter Parameter. n n n nRing rolling is a forming process for the production of seamless rings. The process is characterized by a complex interaction of the shaping rollers and the centering rollers. In the design of a ring rolling process, it is necessary that the rolling and pre-ring geometry strategy, i.e. the speeds and feeds of the individual rollers to align such that the required final shape is achieved optimally. Using the finite element simulation before starting the production optimizations concerning the process can be performed and thereby the number of costly rolling samples be kept to a minimum. n n n nThe objective of the work focuses on the finite element modeling of a ring rolling process and the numerical calculation of the wear at the mandrel caused of the variation of process-related parameters.

Numerische Berechnung einer integrierten Wärmebehandlung für das Gleitziehbiegen von Profilen und die experimentelle Umsetzung

Kurzfassung Mithilfe des Umformverfahrens Gleitziehbiegen lässt sich eine sehr große Bandbreite von Profilbauteilen mit variablen Querschnitten unter Nutzung einer Umformanlage und eines Werkzeugsatzes herstellen. Eine lokale Wärmebehandlung kann bei gleichbleibendem Bauteilgewicht zu einer partiellen Erhöhung der Festigkeit in den entsprechenden Bauteilbereichen genutzt werden. Im Rahmen dieser Untersuchungen wird die prinzipielle Machbarkeit der Festigkeitssteigerung von Profilen experimentell und numerisch aufgezeigt. Nach der simulationsgestützten Auslegung des Gleitziehbiegeprozesses mit einer integrierten Wärmebehandlung wird die Versuchseinrichtung vorgestellt. Mithilfe der Finite-Element (FE)-Berechnungen des gesamten Verfahrensablaufs konnten Informationen bezüglich der Prozessparameter und geeigneter Erwärm- und Abkühlstrategien geliefert werden. Diese wurden in der Auslegungs- und Konstruktionsphase des Versuchsaufbaus genutzt. Abschließend wurde der numerisch ausgelegte Prozess umgesetzt und so die Ergebnisse der Simulation validiert.

Consideration of the Machine Influence on Multistage Sheet Metal Forming Processes

Metal forming processes are highly affected by the properties of the forming machine. In multistage processes, the force path curve of each stage is influenced by the surrounding stages. This research focuses on the interaction between the forming machine and multistage processes with respect to the quality of the workpiece. The accuracy of the numerical results could be increased by coupling the process simulation with the machine simulation. Further influencing factors, such as different friction conditions during forming and the elasticity of the tool, were considered in the simulation. In addition, the thermal properties of the press were investigated and considered in the machine simulation. Hence, a better correlation between the numerical results and the experiment could be achieved.