This master’s thesis deals with the composite materials and especially aims on the carbon and glass fiber composites. It points out different composition types and manufacturing methods which reflect in the different mechanical properties, final quality of the manufactured part and also in the manufacturing time. The practical part includes two particular manufacturing methods using prepregs, one cured in an autoclave and one by hot compression moulding.

The development of lightweight design for automotive applications has lasted for many years and is still increasing. Vehicles with light structures use less fuel, emit less CO2, and are better for the environment. The next generation of lightweight vehicle structures will be realized using materials with a high strength-to-weight ratio, corrosion resistance, and high bending stiffness such as high-strength aluminium alloys. Increased formability, lower spring-back, and the ability to incorporate age-hardening heat treatments into the process are all advantages of the hot forming of aluminium alloys. However, because aluminium is prone to adhesion even at low temperatures, it can be difficult to avoid its transfer onto the tool. When forming aluminium, lubrication is always required to lower the interfacial shear strength and avoid direct contact between the interacting surfaces, to promote low friction and wear. However, lubricants can fail and significant issues with material transfer arise. Because of this, interruptions are needed for tool refurbishing, this issue affects process efficiency. Developing new or improved lubrication technologies to prevent adhesion and high friction, surface engineering solutions, as well as effective testing platforms related to aluminium forming, are vital. A significant challenge when studying the interaction between lubricant, aluminium, and tools often result in poor reproducibility of tests and uncertainties regarding the effect of lubricant thickness/weight on the friction behavior. Problems associated with reproducibility also affect modelling and simulations of the forming operation, as there are many uncertainties in the experimental campaigns, thus affecting the validation stages. The current study aim is to optimize the tribology test methodology used in the hot strip drawing method, with emphasis on the lubricant application methodology, to improve the reproducibility of tribological tests. Lubricant application methodology was developed by using air-brush equipment, and a consistent amount of lubricant. Different lubricant weights were characterized using two different types of lubricants (graphite-based and polymer-based lubricants), and then the tribological response was evaluated after the tribological tests. Lubricants were applied on cast iron and tool steel (CrN coated) to take into consideration the effect of the surface material and topography on the reproducibility, and consistency of the lubricant application methodology. The hot strip drawing method was used to perform tests at 350°C temperature, 10MPa pressure and 100mm sliding distance. To simulate the forming conditions encountered in hot stamping of aluminium, solubilization of a 6XXX aluminium alloy at 540°C was done before testing. An optical microscope, 3D optical profilometry, and SEM were used for the characterization of specimens after the tribological tests. With the lubricant application method, good reproducibility was obtained and it was determined that, in the case of cast iron, as the amount of both lubricants (polymer-based, graphite-based) increases the effective sliding also increases, but tool steel (CrN coated) shows slightly good results only when lubricant amounts are highest.

This thesis deals with peritectic reactions and transformations that occur during the solidification of many alloys. Peritectics are believed to be a major cause of crack-formation in many steels, thus, good knowledge of the mechanisms by which these phenomena occur is essential for preventing such defects. The thesis also handles the behaviour of metals, in particular cast structures, during hot forming. Grain size and microstructure are of most importance in determining the strength, toughness and performance of a steel. For achieving enhanced mechanical and microstructural properties, good understanding of the phenomena occurring during hot forming is required. Peritectic reactions and transformations were studied in Fe-base and steel alloys through differential thermal analysis (DTA) experiments and micrographic investigation of quenched DTA samples. The effect of the ferrite/austenite interface strain during the peritectic reaction on equilibrium conditions was thermodynamically analysed, and the results were related to temperature observations from DTA experiments conducted on Fe-base alloys and low-alloy steels. Massive transformations from ferrite to austenite were observed in the micrographs of a number of quenched low-alloy steel samples and it was proposed that these transformations are uncontrolled by diffusion, and occur in the solid state as a visco-plastic stress relief process. DTA study of an austenitic stainless steel indicated that the alloy can exhibit primary precipitations to either ferrite or austenite. A continuously-cast breakout shell of the steel was analyzed and it was suggested that the observed irregularities in growth were due to alternating precipitations of ferrite and austenite; parts of the shell with higher ratios of primary-precipitated ferrite shrink in volume at the peritectic temperature and experience reduced growths. An experimental method for studying the behaviour of metals during hot forming developed, and hot compression tests were conducted on cast copper and ball-bearing steel samples. Flow stress curves were obtained at varying temperatures and strain rates, and the results showed good agreement with earlier observations reported in literature. Micrographic analysis of quenched samples revealed variations in grain size and a model was fitted to describe the grain size as a function of deformation temperature and strain. Solidification growth during continuous casting of stainless steel and copper was numerically modelled. A varying heat transfer coefficient was proposed to approximate the experimentally measured growth irregularities in the continuously-cast stainless steel breakout shell. Solidification growth of pure copper was also modelled in the Southwire continuous casting process. Temperature measurements from the chill mould were used to approximate the temperature gradient and the heat extraction from the solidifying strand, and the results were used in a two-dimensional model of solidification. / QC 20100803

Bauteilkonstruktionen mit integrierten Kunststoffnietverbindungen nehmen aufgrund der steigenden Anzahl artfremder Werkstoffkombinationen im Rahmen von Hybridbauweisen kontinuierlich zu. Als nicht lösbare und punktuell wirkende Verbindung wird das Kunststoffnieten insbesondere aufgrund seiner kosteneffizienten und einfach anmutenden Prozessführung u. a. für die Herstellung von Elektronik- und Sensorelementen sowie für das Verbinden von Bauteilen im Interieur- bzw. Exterieur-Bereich eingesetzt. Aufgrund der hohen Anwendungs- und Werkstoffvielfalt unterliegt der Kunststoffnietprozess jedoch komplexen Anforderungen, die für eine sichere Prozessanwendung durch ein hinreichendes Prozessverständnis sowie eine zielführende Qualitätssicherung kompensiert werden müssen. Die vorliegende Dissertation befasst sich mit der wissenschaftlichen Analyse der thermischen Nietprozesse Warmumformen und Heißluftnieten. Im Mittelpunkt der Betrachtungen steht die systematische Ausarbeitung der Zusammenhänge zwischen dem Verfahrensablauf, den mechanischen Eigenschaften sowie dem resultierenden Versagensverhalten der Nietverbindung. Die Ergebnisse zeigen, dass bei einer optimierten Prozessführung für beide thermischen Nietverfahren hohe mechanische Eigenschaften erreicht werden können. Als dominierender Faktor offenbarte sich die Anbindungsqualität des Nietkopfes an den Nietzapfen, welche in einem direkten Zusammenhang zum Erwärmungs- und Umformverhalten des Nietzapfens steht. Zudem sind die Verarbeitungseigenschaften und die erreichbare Verbindungsqualität vom eingesetzten Werkstoff abhängig. / Due to the rising number of dissimilar material combinations in the field of hybrid design, components with integrated plastic rivet joints are steadily increasing. Among other things, staking is primary used as a non-detachable and point-acting joint for the production of electronic and sensor elements as well as for the joining of components in the automotive interior and exterior by reason of its cost-efficient and seemingly simple process control. However, due to the high diversity of applications and materials, the staking process is subject to complex requirements, which must be compensated by a sufficient understanding of the process as well as a perfected quality assurance in order to ensure reliable process application. The present dissertation deals with the scientific analysis of the thermal staking processes hot forming staking and hot air staking. The investigations focus on the systematic analysis of the relationships between the procedure itself, the mechanical properties and the resulting failure behavior of the riveted joint. The results show that high mechanical properties can be achieved for both thermal staking processes by having an optimized process control. The most dominant factor revealed to be the bond quality of the rivet head to the rivet pin, which is directly related to the heating and forming behavior of the rivet pin. In addition, the processing properties and the achievable joint quality depend on the material which is used.

Der Forschungsgegenstand der vorliegenden Arbeit ist die kontinuierliche Herstellung eines profilförmigen Bauteils aus dem Bor-Mangan-Stahl 22MnB5 mit lokal bzw. global definierten mechanischen Eigenschaften. Dabei laufen die Formgebung und Wärmebehandlung (WBH) parallel ab. Die Hauptformgebung erfolgt zunächst im Lieferzustand, an die sich die Wärmbehandlung und die finale Formgebung anschließen. Während der WBH wird das ferritische Anfangsgefüge beim Erwärmen in Austenitgefüge und anschließend durch eine rasche Abkühlung größer 30 K/s in Martensitgefüge umgewandelt. Die Induktorform, -frequenz und die -leistung beeinflussen hierbei maßgeblich die Aufheizrate und das Erwärmungsbild. Durch kontinuierliche Formgebung und die gezielte WBH sind Profilbauteile mit Bauteilfestigkeiten bis 1500 MPa effizient herstellbar. Im Anschluss an eine Machbarkeitsstudie werden experimentelle und simulative Untersuchungen durchgeführt und die gewonnenen Ergebnisse miteinander verglichen. Dadurch kann die prinzipielle Eignung des FE-Modells nachgewiesen werden. Im Weiteren erfolgt der Vergleich von drei verschiedenen Fertigungsrouten, wobei das Hauptaugenmerk auf der erforderlichen Umformkraft und der erreichbaren Formgenauigkeit liegt. Auf Basis der Simulationsergebnisse kann festgehalten werden, dass mittels der untersuchten Technologie höchstfeste und formgenaue Profilbauteile mit definierten mechanischen Eigenschaften herstellbar sind. Der Einsatz der Technologie birgt somit ein enormes Leichtbaupotenzial. Dennoch gibt es Hemmnisse die Technologie einzusetzen, da „Wärme“ in den traditionell kalt ablaufenden Umformprozess eingebracht wird. Die Arbeit soll dazu beitragen, diese Barriere abzubauen.:1 EINLEITUNG 2 STAND DER FORSCHUNG UND ENTWICKLUNG 3 HANDLUNGSBEDARF, ZIELSETZUNG UND LÖSUNGSWEG 4 VERSUCHSPLANUNG 5 VERWENDETE WERKSTOFFE SOWIE ANLAGEN- UND WERKZEUGTECHNIK ZUR ENTWICKLUNG EINER TECHNOLOGIE ZUR HERSTELLUNG EINTEILIGER, EIGENSCHAFTSSKALIERTER PROFILBAUTEILE 6 REFERENZVERSUCHE V-GESENKBIEGEN UND KALTWALZPROFILIEREN EINES HUTPROFILS AUS 22MNB5 7 STATIONÄRES AUFHEIZVERHALTEN EINES RINGINDUKTORS UND ABSCHRECKEN MITTELS UNTERSCHIEDLICHER KÜHLMEDIEN 8 INTEGRATION EINER WÄRMEBEHANDLUNG IN DEN KONTINUIERLICHEN WALZPROFILIERPROZESS 9 ZUSAMMENFASSUNG 10 AUSBLICK / The research object of the present work is the continuous production of an open profile component made of the manganese-boron steel 22MnB5 with locally or globally defined mechanical properties. The shaping and heat treatment (SHT) take place in one process. The main shaping is first carried out in the as-delivered condition, followed by heat treatment and final shaping. During the heat treatment, the initial ferritic microstructure is transformed into an austenitic state during heating and then into a martensitic microstructure by rapid cooling at a rate of more than 30 K/s. The geometry of the induction coil, the frequency and the heating power have a significant influence on the heating rate and the heating effect. Through continuous shaping and controlled SHT, profile components with strengths of up to 1500 MPa can be produced efficiently. Following a feasibility study, experimental and simulative investigations were carried out and the results obtained were compared with each other. In this way, the principle suitability of the FE model could be demonstrated. In further steps, three different production routes were com-pared, whereby the main focus was on the required forming force and the achievable forming accuracy. Based on the obtained results, it can be stated that the investigated technology can be used to produce high-strength and dimensionally accurate profile components and defined mechanical properties with high output rate. The use of this technology thus offers a huge lightweight potential. However, as additional heat is introduced into the traditionally cold forming process, the process is more complexity and this constitutes a barrier to the use of the technology. This work is intended to overcome this barrier.:1 EINLEITUNG 2 STAND DER FORSCHUNG UND ENTWICKLUNG 3 HANDLUNGSBEDARF, ZIELSETZUNG UND LÖSUNGSWEG 4 VERSUCHSPLANUNG 5 VERWENDETE WERKSTOFFE SOWIE ANLAGEN- UND WERKZEUGTECHNIK ZUR ENTWICKLUNG EINER TECHNOLOGIE ZUR HERSTELLUNG EINTEILIGER, EIGENSCHAFTSSKALIERTER PROFILBAUTEILE 6 REFERENZVERSUCHE V-GESENKBIEGEN UND KALTWALZPROFILIEREN EINES HUTPROFILS AUS 22MNB5 7 STATIONÄRES AUFHEIZVERHALTEN EINES RINGINDUKTORS UND ABSCHRECKEN MITTELS UNTERSCHIEDLICHER KÜHLMEDIEN 8 INTEGRATION EINER WÄRMEBEHANDLUNG IN DEN KONTINUIERLICHEN WALZPROFILIERPROZESS 9 ZUSAMMENFASSUNG 10 AUSBLICK