In several applications of casting, dendritic microstructure is not desirable as it results in poor mechanical properties. Enhancing fluid flow in the mushy zone by stirring is one of the means to suppress this dendritic growth. Strong fluid flow detaches the dendrites formed at the solid-liquid interface and carries them into the mould to form slurry. When this slurry solidifies, the microstructure is characterized by globular, non-dendritic primary phase particles, separated and enclosed by a near-eutectic lower-melting secondary phase. This property represents a great potential for further processing in semisolid forming (SSF) by various techniques such as pressure die casting and forging. Among all currently available methods, linear electromagnetic (EM) stirring is considered as one of the most suitable routes for large scale production of semisolid feed stock. One of the biggest advantages of EM stirring is that the stirring intensity and direction can be modulated externally and in a non-intrusive manner. With this viewpoint, the primary objective of the present research is to investigate rheocasting using linear electromagnetic stirring. A systematic development of a linear electromagnetic stirrer (LEMS) is the subject of the first part of the thesis. The LEMS consists of a set of six primary coils displaced in space. These coils are excited by a three-phase power supply to produce an axially travelling magnetic field. The metal to be stirred is placed in the annular space of the stirrer. The travelling field induces secondary current in the molten metal. The current and magnetic fields interact to generate a net mechanical force in the metal, commonly termed as the Lorentz force. The molten metal is stirred under the influence of this force. Two prototype stirrers, one for low melting alloys and the other for aluminium alloys are developed. The stirrers are characterized by measuring forces on low melting point alloy and on solid aluminum cylinders placed inside the annular space of the stirrer. As an outcome of these tests, a non-intrusive method of detecting stirring of liquid metal is developed. The development of a rheocasting mould for the LEMS forms the second part of the work presented in the thesis. The mould design and cooling arrangement are such that solidification in the mould is primarily unidirectional. Heat from the solidifying metal is extracted at the bottom of the mould, so that the axisymmetric EM stirring effectively shears the dendrites formed at the solid-liquid interface. The outer surface of the mould is cooled with water or air exiting from 64 jets, each of 4 mm diameter. Such an arrangement provides a high heat transfer coefficient and a wide range of cooling rate in the metal ranging from 0.01 to 10 K/s. Temperature is measured at various depths in the solidifying melt and at other key locations in the mould to assess the various heat transfer mechanisms. The results from the rheocasting experiments using the above mould and LEMS are presented in the third and final part of the thesis. Such studies are required for understanding the solidification process in presence of electromagnetic stirring and for highlighting the important issues connecting solidification, fluid flow, dendrite fragmentation and the resulting microstructure. A series of experiments are performed with A356 (Al-7Si-0.3Mg) alloy. Experiments are conducted with various combinations of operating parameters, and the resulting microstructures and cooling curves at various locations are examined. The key process parameters are stirring current, cooling rate, pouring temperature, and stirring current frequency. The parametric studies also include the case without EM stirring in which liquid aluminium is poured into the rheocast mould without powering the LEMS. It is found that stirring at high currents produces non-dendritic microstructures at all locations of the billet. For lower currents, however, dendritic microstructures are observed in regions outside the zone of active stirring. Stirring also enhances heat loss from the exposed top surface, leading to solid front advancement from the top as well. Without EM stirring, microstructures are found to be dendritic everywhere. The percentage of primary α-Al phase and its number density are found to increase with stirring intensity. With a decrease in cooling rate with air as the coolant, the average grain size of primary α-Al phase increases. Excitation frequency is found to be an important parameter, with lower frequencies generating a more uniform force field distribution, and higher frequencies enhancing induction heating. At higher frequencies, the effect of higher induction heating results in the formation of larger and coarser primary phase grains. This phenomenon has led to the development of a one-step process for rheocasting and heat treatment of billets.

Stahl wird heutzutage fast ausschließlich im kontinuierlichen Stranggussprozess zu Halbzeugen verschiedener Geometrien verarbeitet. Flüssiger Stahl wird dabei über ein Tauchrohr in eine wassergekühlte, nach unten offene Kokille gefüllt und erstarrt an deren Wänden. Der innen noch flüssige Strang wird kontinuierlich nach unten aus der Kokille abgezogen und ist erst nach mehreren Metern komplett erstarrt. Die Qualität des Halbzeugs wird vorwiegend durch die Strömung in der Kokille beeinflusst. In der Industrie werden seit langer Zeit verschiedene elektromagnetische Aktuatoren eingesetzt, um die Strömungsstruktur in der Kokille mithilfe von Lorentzkräften zu beeinflussen. Bedingt durch die hohe Temperatur des flüssigen Stahls und dessen Undurchsichtigkeit lässt sich die Strömungsstruktur im realen Prozess jedoch kaum untersuchen. Zur Optimierung sowie zum besseren Verständnis der Vorgänge in der Kokille sind daher numerische Simulationen und Modellexperimente notwendig. In dieser Arbeit werden die Ergebnisse experimenteller Untersuchungen zum kontinuierlichen Stranggießen von Stahl unter dem Einfluss verschiedener elektromagnetischer Aktuatoren präsentiert. Die Experimente wurden an der Mini-LIMMCAST-Anlage des Helmholtz-Zentrum Dresden-Rossendorf (HZDR) durchgeführt. Mini-LIMMCAST ist ein Modell einer Strangguss-Anlage, welches isotherm mit der bei Raumtemperatur flüssigen Metalllegierung GaInSn betrieben wird. Durch die Verwendung von flüssigem Metall als Modellfluid können die Auswirkungen elektromagnetischer Aktuatoren untersucht werden, jedoch kann aufgrund der Undurchsichtigkeit des Modellfluids die Geschwindigkeitsverteilung in der Kokille nicht mittels optischer Verfahren erfasst werden. Daher wird zur Messung der Geschwindigkeitsverteilung in der Kokille die Ultraschall-Doppler-Velocimetrie eingesetzt. Die Ergebnisse von Messungen an zwei verschiedenen Kokillen-Geometrien werden vorgestellt: zum Einen solche an einer zylindrischen Kokille, bei welcher auf verschiedene Arten eine Drehströmung erzeugt wurde. Dies erfolgte durch elektromagnetisches Rühren in der Kokille sowie durch ein Tauchrohr mit spiralförmigen Auslässen. Zum Anderen wird eine Kokille mit rechteckigem Querschnitt, wie sie in Brammen-Anlagen verwendet wird, betrachtet. In dieser wird die Strömung sowohl durch ein statisches Magnetfeld, einer sogenannten elektromagnetischen Bremse, als auch durch elektromagnetische Wechselfelder beeinflusst. Die Ergebnisse dieser Arbeit zeigen eine Reihe zuvor nicht beschriebener Phänomene, wie das zeitliche Verhalten des Jets in der Rundkokille mit elektromagnetischem Rührer oder den Mechanismus der in der Brammen-Geometrie mit elektromagnetischer Bremse für eine Veränderung der Geschwindigkeit an der freien Oberfläche der Kokille sorgt. Umfassende experimentelle Parameterstudien erlauben detaillierte Einblicke in die beim Stranggießen auftretenden Strömungsstrukturen, wie sie mit numerischen Simulationsmodellen nur unter einem immensen Einsatz von Rechenleistung zu erzielen wären. / Today, steel is almost exclusively processed into semi-finished products of various geometries by the continuous casting process. Liquid steel is filled through a submerged entry nozzle into a water-cooled, downwardly open mould and solidifies on its walls. The strand, which is still liquid on the inside, is continuously drawn downwards out of the mould and is then completely solidified after several metres. The quality of the semi-finished product is mainly influenced by the flow in the mould. For many years, various electromagnetic actuators have been used in industry to influence the flow structure in the mould by the application of Lorentz forces. Due to the high temperature of the liquid steel and its opacity, however, the flow structure can hardly be investigated in the real process. Therefore, numerical simulations and model experiments are necessary to optimise and better understand the processes in the mould. In this dissertation the results of experimental investigations on continuous casting of steel under the influence of different electromagnetic actuators are presented. The experiments were performed at the Mini-LIMMCAST facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Mini-LIMMCAST is a model of a continuous casting machine which is operated isothermally with the metal alloy GaInSn, which is liquid at room temperature. By using liquid metal as model fluid, the effects of electromagnetic actuators can be investigated, but due to the opacity of the model fluid, the velocity distribution in the mould cannot be determined by optical methods. Therefore, ultrasonic Doppler velocimetry is used to measure the velocity distribution in the mould. The results of measurements using two different mould geometries are presented. One is a cylindrical mould in which a rotational flow was generated in different ways. This was achieved by electromagnetic stirring in the mould and by an submerged entry nozzle with spiral-shaped outlets. On the other hand, a mould with a rectangular cross-section, as used for slab casting, is considered. Here the flow is influenced by a static magnetic field, a so-called electromagnetic brake, as well as by alternating electromagnetic fields. The results of this work show a number of previously undescribed phenomena, such as the temporal behaviour of the jet in the round mould with an electromagnetic stirrer or the mechanism that causes a change in the speed at the free surface of the mould in the slab geometry with an electromagnetic brake. Comprehensive experimental parameter studies allow detailed insights into the flow structures occurring during continuous casting, which could only be achieved with numerical simulation models with an immense input of computing power.

Examensarbetet inom produktutveckling – konstruktion utfördes under perioden februari till juni 2013 och omfattar 15 högskolepoäng (C-nivå), och är den slutliga kursen inom högskoleingenjörsprogrammet Innovation och produktdesign. Examensarbetet behandlade problematiken kring produktionsanpassning och kostnadsoptimering av två stycken elektromagnetiska omrörare vid företaget ABB, Process Automation, Metallurgy i Västerås. Efter kontakt med handledaren från ABB, Jan-Erik Eriksson, påbörjades projektarbetet med att tillverkningsanpassa konstruktionen av produkterna ORD 43P och EM Stabilizer. För att åstadkomma kostnadsoptimerad och produktionsanpassad konstruktion tillämpade författarna följande produktutvecklingsverktyg: Design for Cost, Design for Manufacture och Design for Assembly. För att kontrollera att konstruktionen blev optimal, men också att den inte brister under belastning använde examensarbetarna det datorbaserade hållfasthetsverktyget finita elementmetoden i CAD-programmet SolidWorks. Val av komponenter baserades på komponenternas pris per kilo. För att välja det optimala materialet, det vill säga högsta hållfasthet till lägsta pris använde författarna materialdatabasprogrammet CES EduPack. De utvalda materialen från programmet kunde inte författarna påfinna som standard på marknaden, varför författarna ändrade strategi till att jämföra och välja material utifrån marknadsundersökning av standardmaterial hos leverantörer.   ORD 43Ps komponenter optimerades konstruktionsmässigt gentemot befintliga komponenter och härvstag och isolerplattor kostnadsreducerades markant. Komponenten stomme grundutförande undersöktes översiktligt.  Genom att produktutveckla komponenterna härvstag, isolerplattor och stomme grundutförande minskade kostnaderna för ORD 43P med 2,47 %.  Författarna ansåg att ORD 43Ps totala kostnader kan minska mellan 10-25 % eftersom många av dess komponenter är överdimensionerade och består av dyrare material än vad som krävs.  EM Stabilizer’s komponenter, lock och tryckluftsslang, utformades med optimal konstruktion och kostnadsreducerades.  Genom att produktutveckla komponenterna lock och tryckluftsslang minskade kostnaderna för EM Stabilizer med 1,3 %.  Författarna förmodar att EM Stabilizer’s kostnader kan minska, eftersom den är relativt ny på marknaden. ABB vill säkerställa att produkten uppnår sin garanterade livslängd genom att överdimensionera många av produktens komponenter och använda dyrare material än vad som är nödvändigt. / The thesis in product development – design was carried out between February and June 2013 and includes 15 credits (C-level), and is the final course of the Bachelor Program in Engineering, Innovation and Product Design.  The thesis dealt with the problem of adaptation to production and cost optimization of two pieces of electromagnetic stirrers at the company ABB, Process Automation, Metallurgy in Västerås. After contact with the supervisor from ABB, Jan-Erik Eriksson, the project work commenced to adapt the manufacturing design of the product ORD 43P and EM Stabilizer. To achieve cost-optimized production and production adapted design, the authors applied the following product development tools: Design for Cost, Design for Manufacture and Design for Assembly. To verify that the design was optimal, but also that it did not break during stress, the authors used the computer based module finite element method of the CAD program SolidWorks.  The selection of components was based on the component’s price per kilo.  To select the optimum material, that is high strength and affordable, the authors used the material database software CES EduPack. The materials selected from CES EduPack could not be found by the authors as standard material at the market. Therefore, the authors changed strategy to compare and select materials based on market research of standard materials with suppliers. The components of ORD 43P were optimized in terms of design in comparison with existing components coil bracket and insulation boards. They were also cost reduced significantly. The component frame base was examined briefly.  Through product development the components coil bracket, insulating boards and frame base the total cost of ORD 43P was reduced by 2,47 %.  The authors found that the total cost of ORD 43P could be reduced between 10-25 % as many of its components are oversized and made ​​of more expensive materials than needed.  The components of EM Stabilizer, cover and pneumatic hose, were designed with optimum design and was cost reduced.Through product development the components cover and pneumatic hose the costs of EM stabilizer were reduced by 1,3 %.  The authors assume that the costs of the EM Stabilizer can be reduced, because it is relatively new at the market. ABB want to ensure that the product reach its guaranteed life by over-sizing many of the components of the product and use more expensive material than necessary. / Kostnadssänkningsprojekt