Method for optimizing casting conditions using permeable mold by computer simulation

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a method of evaluating and optimizing the flow of the molten metal into the mold cavity without the need of physically modifying the mold.
More particularly, the present invention seeks to provide a method for selecting optimum combinations of metal flow rates, vacuum degree, mold materials and runner designs in order to reduce the volume of gas trapped within the cast article.
In order to achieve the above-stated object, the present invention provides a mathematical simulation method, whereby the flow patterns of a melt during cavity filling are predicted by the calculus of finite elements.
The simulation requires input data in the form of discrete elements which define the geometry of the mold cavity and the mold, along with material constants and process variables.
The results of the simulation indicate the flow patterns of the molten metal and are interpreted to calculate the total volume of gas regions which have been sealed off from the permeable sand mold, and thereby remain in the melt.
This volume can subsequently be minimized in additional simulations by modifying one or more of the following parameters: a melt flow rate into the runner system, a magnitude of the vacuum applied to the mold, material property constants such as mold or coating permeability and the geometry of the runner system and mold cavity.
Thus, the method of optimizing the conditions of vacuum casting with a permeable mold having a cavity and a runner by computer simulation according to the present invention comprises the steps of: (1) dividing the mold and a cavity thereof into a plurality of elements; (2) providing mold properties, a vacuum degree and a velocity of a melt flowing into the runner as initial data with respect to each element; (3) performing computations in a step-wise manner to determine the movement of a free surface of the melt and a rate of gas flowing through the mold until the cavity is filled with the melt; (4) calculating a total volume of any regions of gas which have been separated from the permeable mold and sealed into the melt; (5) examining whether or not the total volume of any regions of gas is substantially zero; and (6) if the total volume of any regions of gas is not substantially zero, repeating the computations with at least one of the initial data modified until the total volume of any regions of gas becomes substantially zero