In this paper, the development of an experimental die casting setup to perform simultaneous in-situ measurements of temperatures, air-gap formation and contact pressures is presented. The derivation of the resulting heat transfer coefficients between mold and melt is also included. To take the influence of different cooling rates into account, an active die tempering is applied. For the implementation of this experimental setup, a special mold for a rotationally symmetrical test specimen is developed which incorporates the necessary measuring technique and can be adapted to different cooling conditions by means of exchangeable die inserts. Concluding, first results and the corresponding heat transfer coefficients are presented.Keywords: Heat transfer coefficient / air-gap formation / contact pressure / mold tempering / permanent mold casting Es wird die Entwicklung eines Kokillenguss-Versuchssaufbaus vorgestellt, um gleichzeitige in-situ Messungen von Temperaturen, Spaltbildung und Kontaktdrücken zu ermö glichen, genauso wie die Ermittlung der sich daraus ableitenden Wä rmeü bergangskoeffizienten zwischen Form und Gussteil. Dabei wird der Einfluss von verschiedenen Abkü hlraten durch aktive Formtemperierung berü cksichtigt. Hierfü r wird eine spezielle Form fü r ein rotationssymmetrisches Gussteil entwickelt, die die nö tige Messtechnik aufnehmen sowie durch wechselbare Formeinsä tze an verschiedene Abkü hlbedingungen angepasst werden kann. Es werden erste Ergebnisse inklusive der zugehö rigen Wä rmeü bergangskoeffizienten vorgestellt.Schlü sselwö rter: Wä rmeü bergangskoeffizient / Spaltbildung / Kontaktdruck / Formtemperierung / Dauerformguss Figure 6. Values of the air-gap related heat transfer coefficient for different die temperatures versus the corresponding cast interface temperature. On the right side for the complete solidification process and on the left side a cut out with a smaller temperature range. N. Wolff et al.
Local heat transfer in gravity die casting is of great importance for precision in terms of distortion, mechanical properties, and the quality of the castings due to its effect on solidification. Depending on contact conditions such as liquid melt to solid mold, a gap between mold and component, or contact pressure between casting and mold as a result of shrinkage, there are very large differences in heat transfer. The influences of mold material, mold coating and its influence of aging, mold temperature control, and layout on the heat transfer coefficient (HTC) were investigated experimentally for different contact cases. The experiments were carried out on a rotationally symmetrical experimental setup with modular exchangeable die inserts and cores using an AlSi7Mg0.3 alloy. From the results of the individual test series, the quantitative shares of the above-mentioned influencing variables in the respective effective heat transfer coefficients were determined by means of analysis of variance. From this, the parameters having the most significant influence on the local heat balance were derived.
The thermal mold design and the identification of a proper cooling channel design are primordial steps in the development of complex molds for injection molding. In order to find a suitable cooling channel system, a lot of effort is needed to avoid part warpage after solidification. In current research, a simulative procedure to optimize the cooling channel layout iteratively is being developed at the Institute of Plastics Processing. These algorithms are transferred to the metal gravity die casting process, which has several similar requirements to the mold. Effectively, the simulation is simplified to a heat conduction problem. Instead of water, high temperature resistant oil is deployed and the casted material is a A356 aluminum alloy instead of semi-crystalline plastics. The algorithm is adapted to these changed boundary conditions and the calculation of the optimized heat distribution is performed. Aim of this procedure is the construction of a mold producing parts with less warpage than a conventional mold. Keywords: Thermal mold design / inverse heat conduction / cooling channel layout / heat transfer / metal gravity die casting Die thermische Werkzeugauslegung und die Identifizierung eines geeigneten Kühlkanaldesigns sind grundlegende Schritte in der Konstruktion komplexer Werkzeuge für das Spritzgießen von Kunststoffen. Um ein passendes Kühlkanaldesign zu finden, das den Bauteilverzug während der Erstarrung minimiert, muss großer Aufwand betrieben werden. Aus diesem Grund wird eine simulative Prozesskette am Institut für Kunststoffverarbeitung der RWTH Aachen entwickelt, die das Kühlkanallayout des Spritzgießwerkzeuges iterativ optimiert. Diese Algorithmen werden auf den Prozess des Metalldauerformgusses übertragen, der ähnliche Anforderungen an den Formenbau hat. Die Methodik wird an diese veränderten Randbedingungen angepasst und die Berechnung der optimierten Wärmeverteilung in der Form erfolgt. Ziel dieser Optimierung ist die Konstruktion einer Gussform zur Produktion von Bauteilen mit verringertem Verzug im Vergleich zu einer konventionell gefertigten Form.
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