Michael Marré

Influence of Mandrel's Surface and Material on the Mechanical Properties of Joints Produced by Electromagnetic Compression

Electromagnetic compression of tubular profiles with high electrical conductivity is an innovative joining process for the manufacturing of lightweight structures. The mandrels material has an influence on the transferable loads which is affected by the Youngs modulus as well as the strength of the material. This was investigated, on the one hand, by changing the mandrels material and, on the other hand, by using the same mandrel material with differing strength. Furthermore, taking conventional interference fits into account, the contact areas influence on the joints quality seems to be of significance, as e.g. the contact area and the friction coefficient between the joining partners proportionally determine an allowed axial load or torsional momentum. Therefore, different contact area surfaces were prepared by shot peening and different machining operations and strategies. The mandrels surfaces were modified by shot peening with glass beads and Al2O3 particles. An alternative preparation was performed using simultaneous five-axis milling, because potential joining partners in lightweight frame structures within the Transregional Collaborative Research Centre SFB/TR10 would be manufactured similarly. After that, the manufactured surfaces were characterized by measuring the surface roughness and using confocal whitelight microscopy. Afterwards the modified mandrels were joined by electromagnetic compression. The influence of different mandrels surface conditions on the joints mechanical properties was analysed by tensile tests. Finally, conclusions and design rules for the manufacturing of joints by electromagnetic compression are given.

Joining by Compression and Expansion of (None-) Reinforced Profiles

One major objective of the Collaborative Research Center SFB/TR10 is the flexible and competitive production of frame structures which meet the requirements of lightweight design. The development of composite extrusion by embedding continuous reinforcing elements, like e.g. steel wires, in profiles during the extrusion process illustrates one approach to fulfill these conditions. To assemble such composite profiles, joining processes and strategies have to be developed taking into account the special composite material characteristics. In addition, the flexible production of lightweight frame structures in small quantities generates more requirements on the joining technology. The feasibility of joining by forming has been carried out investigating experimentally both conventionally extruded and reinforced profiles. Therefore, joining profiles to lightweight frame structures by both expansion and compression has been examined. The necessary forming pressure for the joining by forming processes was applied to tubular workpieces by a medium (hydroforming) and by a magnetic field (electromagnetic compression). Joints have been manufactured by these two processes to transmit axial loads either by force- or form-fit.

An Experimental Study on the Groove Design for Joints Produced by Hydraulic Expansion Considering Axial or Torque Load

This article presents research work on the influence of the design characteristics of the joint partner elements and especially of grooving and pocketing on the tensile and torsional strength of tubular joints produced by hydraulic expansion when tubes are made of aluminum EN AW-6060. In general, joining of tubular elements can be performed by different methods, but internal expansion presents an interesting alternative to other methods like welding and mechanical forming processes. Commonly, hydraulic expansion is used for the manufacturing of heat exchangers. As a result, time effective and resistant joints must be produced in particular when applying hydraulic expansion in the manufacturing of lightweight structures.

Analytic Prediction of the Process Parameters for Form-Fit Joining by Die-Less Hydroforming

The Commission of the European Communities aims for a reduction of new car CO2 emissions of 120 grams per kilometer in 2012. As a result of the omnipresent efforts of the automotive industry to hit these tighter emission standards innovative lightweight strategies, e.g. the use of lightweight materials are developed. This entails new joining techniques that are appropriated to the new lightweight materials. The die-less hydroforming process is a joining method for tubular joints which meets the new demands of lightweight strategies. Since there is no need for any additional connection elements or filling material, it is an interesting alternative to conventional welding and riveting processes. The present paper describes the basic principle of the die-less hydroforming joining technology with a special focus on form-fit connections. An analytical model, based on the membrane theory with an additional local consideration of bending stresses is developed. This analytic approach can be used to calculate the working fluid pressure, required to bulge the tube material into the groove of the outer joining partner. Taking into account the material parameters as well as the groove and tube geometry, this model allows a reliable process design. Additionally, validation of the model by experimental investigations will be provided.

Prozesskette zur flexiblen Herstellung leichter Tragwerkstrukturen: Steigerung der Qualität und Zuverlässigkeit

Kurzfassung Im Rahmen des Sonderforschungsbereich Transregio 10 (SFB/TR 10) „Integration von Umformen, Trennen und Fügen für die flexible Fertigung von leichten Tragwerkstrukturen“ wird eine Prozesskette zur produktflexiblen Kleinserienfertigung von Space-Frame-Rahmenstrukturen aufgebaut. An diesem Forschungsprojekt sind Institute der Technischen Universität Dortmund, der Technischen Universität München und der Universität Karlsruhe (TH) beteiligt. Um bereits frühzeitig die Qualität und die Zuverlässigkeit der Prozesskette zu verbessern, wurde in einem standortübergreifenden Qualitätsarbeitskreis eine System-FMEA Prozess für die einzelnen Teilprozesse durchgeführt. Mit dieser konnten projektbegleitend potenzielle Fehlerschwerpunkte ermittelt und gezielt Gegenmaßnahmen eingeleitet werden. Im folgenden Artikel werden die eingeleiteten Fehlervermeidungsmaßnahmen für die am SFB/TR 10 beteiligten Prozesse und Verfahren beschrieben. Die Prozesse sind im Einzelnen: Das mehrachsige Runden beim Strangpressen sowie das darauf folgende fliegende Abtrennen zur Herstellung der Rahmenelemente, eine flexible und intelligente Greiftechnik in Kombination mit einer Handhabungs- und Bearbeitungskinematik zur spanenden Bearbeitung sowie als letzte Schritte die Verfahren Innenhochdruckfügen, Rührreibschweißen und Laserstrahlschweißen zum Fügen der Einzelteile zu einer Rahmenstruktur.

Industrielle Anwendungen für das neue Fertigungsverfahren Runden beim Strangpressen

Beim Biegen von Profilen konnen unerwunschte Verformungen auftreten, die das Ergebnis negativ beeinflussen. Ein Grund, warum die Prozesskette Strangpressen, Recken und Biegen oft nicht den Genauigkeitsanspruchen genugt, liegt unter anderem in der fur Biegeprozesse typischen Ruckfederung. Auch konnen sich beim Verformen von Profilen mit unterschiedlichen Wandstarken bei zu kleinen Biegeradien Falten bilden. Aufgrund der genannten Nachteile innerhalb der konventionellen Prozesskette zur Herstellung gebogener Profile wurde am Institut fur Umformtechnik und Leichtbau das Verfahren Runden beim Strangpressen (RubS) entwickelt, dessen Prinzipien im Folgenden dargestellt werden.