Metal founding – Process – With measuring – testing – inspecting – or condition determination
Reexamination Certificate
1999-07-06
2001-10-09
Dunn, Tom (Department: 1722)
Metal founding
Process
With measuring, testing, inspecting, or condition determination
C700S147000
Reexamination Certificate
active
06298898
ABSTRACT:
TECHNICAL FIELD
This invention relates to the technology of optimizing the design of casting molds by using computer models to obtain improved productivity and/or casting quality, and more particularly, to the use of computer models that focus on the thermal characteristics of the mold to predict optimum location of chills, cooling circuits and insulation.
DISCUSSION OF THE PRIOR ART
Design strategies for casting processes have ranged from experimental trial and error on the plant floor (including manual computational trials) to avoid casting cracks from cooling to automated optimization die design methods, the latter being the current state of the art. Traditionally, foundry die design is finalized when experimental trials in the foundry yield a good casting; such strategy typically involves large design lead times, high scrap rates, and less than optimum production rates. The flow diagram for the current commercial state of the art in this technology is illustrated in FIG.
1
. As shown, the casting product is first designed and redesigned as per finite element analysis with regard to stress, noise-vibration-handling, and fatigue. Tooling (dies) is then designed based on the designer's accumulated knowledge and then tried out experimentally, resulting in redesign by trial and error.
Apart from the current state of the art, others have calculated the cooling requirements for the mold using computational models with estimated material and boundary properties to roughly predict the effects of cooling variations which again require trials to optimize. Computer optimization of die design has incorporated features to consider shape and process parameters, but thermal characteristics of the die were not considered or focused upon.
SUMMARY OF THE INVENTION
What is needed is an improved method for the overall casting process that uses a structural design approach for determining optimum location of chills, cooling circuits and insulation in the die or mold to reduce cycle time and thereby increase production capacity along with an increase in casting quality. An aspect of this invention that fully meets such need draws together certain unique steps which in combination create a unique design method by: (i) using experimental data to calibrate a casting process simulation model, (ii) creating a computer solidification model of the casting process simulation model for the mold or die, and (iii) numerically optimizing the computer solidification model to tune the model for locating heat sinks, chill, cooling circuits and insulation.
In more particularity, the invention is a method of optimizing cycle time and/or casting quality in the making of a cast metal product which has been defined by a CAD product model, comprising the steps of (a) providing a computer casting model using objective functions that simulate the filling and solidification of the CAD product model within dies, the casting model being subdivided into contiguous regions with each region having terms in at least one of the objective functions for thermal conductivity, heat capacity and cooling time period, (b) populating the objective function terms with experimental data to calibrate the casting model, derive matching heat transfer coefficients for each region, and simulate filling and solidification of the product within the dies, and (c) constraining the objective functions to ensure directional solidification along the series of contiguous sections while optimizing thermal conductivity and heat capacity and iteratively evaluating the constrained objective functions to indicate at least certain regions of the casting model whereby chills and cooling channels may be added, or insulation added to effect improved cycle time and/or casting quality.
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Article in “Fonderie”,vol. 35, No. 401 (1980) p. 279-295 “Development of Thermal Steady States in Naturally-Cooled Chills: A Theoretical and Experimental Study”.
Mahadeva Shivantha
Martin Geoff
Muller Doug
Renwick Philip
Singh Darius Pradhir Kumar
Dunn Tom
Ford Global Technologies Inc.
Malleck Joseph W.
Tran Len
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