Elimination of Hot Tears in Steel Castings by Means of Solidification Pattern Optimization
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TWENTY years after the introduction of simulation software for foundries into the industry, casting process simulation has become an accepted tool for process and design layout. Metal casting process simulation is used to provide detailed information about the mold filling, solidification, and solid-state cooling, and with that, also information about the local microstructure, nonuniform distribution of mechanical properties, and subsequently residual stress and distortion buildup.[1–9] Casting simulation tries to use physically realistic models without overtaxing the computer. At the same time, the simulations need to give applicable results in the shortest time possible. Because of the multitude of factors affecting the quality of castings and the complex interactions of physics, metallurgy, and casting geometry, empirical knowledge is the main source on which ‘‘optimized manufacturing engineering’’ is based. Foundry simulation can quantify experience, but unfortunately, it can test only one ‘‘state’’ or layout. It provides insights into the root causes of problems, whereas conclusions from PETR KOTAS, Postdoc, CEM CELAL TUTUM, Assistant Professor, and JESPER HENRI HATTEL, Professor, are with the Department of Mechanical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark. Contact e-mail: pkot@ mek.dtu.dk JESPER THORBORG, Software Development Engineer, is with the MAGMA GmbH, D-52072 Aachen, Germany. Manuscript submitted April 13, 2011. Article published online December 23, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
calculations or subsequent optimization still require an engineer’s interpretation and decision after each simulation run. This means that a continuous improvement involves ‘‘trial and error’’—both in reality and in simulation. In recent years, the usage of simulations software has improved and now integrates parallel processing computers. It is feasible to calculate numerous versions and layouts in almost unlimited configurations. The advantage of having such short calculation times only can be used providing that a computer can analyze calculated variants automatically with respect to predefined objectives (e.g., maximum feeding, low porosity, low air entrapment, etc.) and subsequently create new variants and analyze them in the same manner to achieve the optimal solution. By integrating such software for casting process simulation with an optimization algorithm, a computer-based optimization tool is established that can determine the optimal values of user-defined design variables, thereby optimizing a given casting process with respect to predefined objectives.[10] Autonomous optimization uses the simulation tool as a virtual test field. By modifying pouring conditions, gating designs, or process parameters, the software tries to find the optimal route to fulfill the desired objective. Several parameters can be changed at the same time and be evaluated independently from each other. Autonomous optimization tools combine the classic approach of foundry engineers to find the ‘‘bes
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