PRODUCT INNOVATIONS
BMW’s Inorganic Core Drying Simulated with Flow-3D Te BMW metalcasting facility in
Landshut, Germany, uses an inorganic coremaking process that is environ- mentally friendly and healthier for the workers on the shop floor because it uses water based binders. The inorganic process also offers potential improved casting quality due to reduced core gas production and lower tool temperatures. In the process, the molding sand is shot into a mold, which is heated during shooting and drying. As a conse- quence, the core dries and hardens first in a thin layer adjacent to the wall. After the shooting process, the core is vented with hot pressurized air. The water in the core is vapor- ized by the hot air, and the air-vapor mixture leaves the core through the bottom venting nozzles. Removal of the water results in the hardening of the core by a chemical reaction of the binder. Flow Science Inc., Santa Fe, N.M.,
developed a simulation of the inorgan- ic core drying process to help predict and correct some core defects that were occurring in production. The new core drying model con- siders porous sand cores of arbitrary
A core for an upcoming production part was exhibiting imperfections due to residual moisture.
shapes with variable properties, such as moisture content, temperature and vapor concentration. By simu- lating transient conditions through- out a core, engineers can make de- tailed investigations of non-uniform initial conditions, as well as a
variety of drying techniques. Flow Science first conducted a set of experiments on a simple, ge- neric core to validate its core drying simulation model before testing it on a core for a production part. The core, which had not yet been finalized, was exhibiting two minor imperfections as a consequence of excess residual moisture. Te geometry of the core and the
nozzles by which the core is vented were set up in a CAD system and imported into the Flow-3D simula- tion program in .STL format. Te simulated residual moisture detected corresponded with the areas that had been producing the imperfections. Based on the simulation results, BMW modified the number and position of the venting nozzles and performed a second simulation. Te results showed a complete removal of the critical areas of high residual moisture. Subsequent production of cores based on the simulation confirmed the results.
The simulated residual moisture detected in the Flow Science model matched the affected areas in the real core.
44 | MODERN CASTING December 2011
Tis article is based on the paper “Core Dry- ing Simulation and Validation,” presented at the 115th
Metalcasting Congress. Visit
www.flow3d.com for more information.
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