Casting Processes

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Simulation of Centrifugal Casting via STAR-Cast

In centrifugal casting processes the casting domain is rotated during the casting process. Consequently, for this type of casting process simulation, STAR-Cast solves the governing equations in a rotating coordinate system. In other words, the terms arising due to rotation, such as rotation rate, coriolis force and centrifugal force are directly modeled in the governing equations, thus solving these equations according to a coordinate system which rotates with the casting domain.

Enhanced simulation of mold filling and solidification in centrifugal casting processes relies on STAR-Cast’s multiphase approach, taking into account a pressure-dependent gas atmosphere in the mold cavity. For accurate and sharp capturing of the filling front, STAR-Cast provides the HRIC algorithm (High Resolution Interface Capturing). A so-called porous baffle boundary condition allows simulation of the pressure-dependent outflow of gas through porous mold materials.

In centrifugal casting processes, mold-filling is determined by the rotation speed of the casting mold and the movement of the crucible relative to the mold:

Case 1: The crucible with liquid melt rotates with the mold. Due to the accelerating crucible, the melt experiences centrifugal and coriolis force and therefore flows out of the crucible into the mold cavity. This mold-filling or inlet-condition is exactly defined by the rotation speed and thus allows accurate modeling of mold-filling.

Left: Simulation model for centrifugal casting of a cluster of 8 turbocharger wheels, including the ceramic shell mold. The melt crucible rotates with the mold.

Right: Temperature-coupled mold-filling simulation based on an accelerated rotation.

 

Case 2: The crucible is stationary relative to the rotating mold. The melt experiences an angular momentum via a boundary condition imposed on the walls of the cavity.

This involves simultaneous pouring of melt from the crucible and filling of the rotating mould. Unless both are simulated simultaneously inaccuracy in the modelling can occur especially the inlet flow conditions into the rotating mould. STAR-Cast uses state-of-the-art overset meshes for modelling the tilting of the crucible. Here two different mesh regions belonging to the crucible and the funnel are generated and can overlap in an arbitrary manner. Using the overset meshes does not require any mesh modification after generating the initial mesh, thus offering greater flexibility over the standard meshing techniques.

Rotation of the shell mould is performed by movement of the mesh vertices of the mould during the transient analysis. This method is useful for simulating non axis-symmetric of the shell mould and overcomes the disadvantages of the rotating frame of references. For the rotation motion, it is possible to superpose rigid rotations on the top of the original rigid motion, which can permit rotations around multiple axis at the same time.