Prediction of hot distortion of sand cores – a further step toward the digitization of core production

Prediction of hot distortion of sand cores – a further step toward the digitization of core production

Magma GmbH and HA have joined forces in a long-term cooperation to quantitatively describe the hot distortion of sand cores.

Together, Magma as a specialist for the virtual optimization of foundry processes and HA as a supplier of foundry chemicals intend to develop and provide digital core data for foundries. Visitors at Gifa 2019 have the chance to see the concrete steps being taken at the stands of the two cooperation partners.

Increasing demands on the dimensional tolerances of castings are especially critical for thin-walled sections, where even small deformations of sand cores can be critical for maintaining the required wall thicknesses and component geometry. The deformation of a sand core is dependent on its thermal expansion and the position of the corresponding core marks. For long thin-walled cores, buoyancy forces of the metal on the core play an additional important role. In the case of organic binders, even low buoyancy forces can lead to time-dependent deformation of the core due to creep effects in the binder resin (Fig. 1).

Fig. 2: Core distortion of thin-walled, filigree cores is a major cause of deviations in the required wall thickness of the casting

In order minimize the deformation of sand cores, their thermal and mechanical behavior during casting must be understood. With this knowledge, simulation programs can be used to predict how the core sand will behave during the casting process, particularly at high temperatures (Fig. 2).

Magma has implemented a numerical model in Magmasoft in which the core sand is treated as a porous medium, and both the pressure and temperature dependence of the core strength is considered. Time-dependent core deformation due to binder softening and decomposition are additionally taken into account through creep models. The effects on the core of e.g. buoyancy forces during casting are also calculated.

The cooperation between HA and Magma is aimed at quantifying the thermo-mechanical behavior of different molding materials during casting for the primary HA binder systems. Magma has developed a methodology to characterize the material behavior of cores using standard samples. HA is using this systematic approach in carrying out extensive investigations at its Centre of Competence for both organic and inorganic HA binder systems and different sand types. These data will be used to generate product-dependent data sets, to make both the time and temperature dependent behavior of core distortion quantitatively predictable in Magmasoft. The results are being validated through in-situ measurements at the HA technical centre in Baddeckenstedt, Germany, using optical measurement methods to quantify the deformation of sand cores as a function of time during solidification (Fig. 3).

Fig. 3: Casting tests to characterize core distortion. Close-up photos of warped cores, (a) and (b), and comparative simulation to predict core distortion (c). Source: Magma, Nemak and Foundry Institute of the RWTH Aachen University.

“The aim of our cooperation is to provide users of Magmasoft with validated data for the quantitative prediction of core distortion for HA products. With this new database, our joint customers will be supported even better in the layout of their core and casting designs,” says Jörg C. Sturm, a managing director of Magma. And Amine Serghini, responsible for Sales and Marketing and member of HA’s Executive Board, says: “We have a great interest in quantifying the behavior of our binder systems during casting. The cooperation with Magma in this area will enable us to offer our customers another important added benefit.”

At Gifa, both partners will present the first results of the joint development project, which is planned as a long-term cooperation.

Magma will be exhibiting at Gifa and Metec in Hall 12, Stand A19/20, and in Hall 4, Stand E29
HA will be exhibiting at Gifa in Hall 12, Stand C50

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