Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2002-10-30
2004-09-28
Dunn, Tom (Department: 1725)
Metal founding
Process
Shaping a forming surface
C164S519000, C264S135000
Reexamination Certificate
active
06796366
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
At least one aspect of this invention relates generally to producing a freeze-cast substrate and, more specifically, to methods for producing a freeze-cast substrate with minimal distortion.
2. Background Art
Spray forming techniques for producing steel prototype tooling, such as dies or molds, are commonly utilized to make steel tooling. The typical spray forming technique includes the following steps: (1) casting a ceramic substrate containing a spraying pattern about a mold containing a master pattern of the tool to be produced; (2) spraying metallic particles onto the ceramic substrate containing the spraying pattern; (3) allowing the sprayed metallic particles to form a metal deposit having the general shape of the master pattern; and (4) separating the metal deposit from the ceramic substrate.
The casting step is commonly accomplished through a freeze-casting process. One typical freeze-casting process includes the following steps: (1) pouring a slurry into the mold containing the master pattern, (2) lowering the temperature of the slurry to freeze the slurry and form a freeze-cast substrate containing the spraying pattern, (3) extracting the freeze-cast substrate from the mold, (4) thawing the freeze-cast substrate, and (5) drying the freeze-cast substrate during the firing cycle.
While the above method of freeze-casting produces acceptable freeze-cast substrates, the method may produce warping and/or distortion in the spraying pattern. Consequently, the metal deposit may not accurately reflect the master pattern. In extreme cases, the warping and/or distortion may be so pronounced that the metal deposit is rendered unusable as a steel prototype tool. Accordingly, it is an object of the present invention to provide methods of producing a freeze-cast substrate that minimize the amount of distortion the freeze-cast substrate.
SUMMARY OF INVENTION
At least one aspect of the present invention is related to methods for producing a freeze-cast substrate.
One preferred method embodiment includes introducing a slurry into a mold unit and lowering the temperature of the slurry to freeze the slurry and form a freeze-cast substrate while controlling temperature gradients within the mold unit to minimize distortion in the freeze-cast substrate. The mold unit is comprised of a mold contained within a casting receptacle.
Insulating material can be placed around at least a portion of the casting receptacle to control temperature gradients within the mold unit. The rate at which the temperature is lowered can be controlled to minimize temperature gradients in the mold unit over time. Alternatively, the lowering step can include abruptly decreasing the temperature of the mold unit from room temperature to a sub-chilling temperature.
A chilling apparatus, i.e a freezer, can be provided for the lowering step. The chilling apparatus can include a temperature controller for adjusting the temperature within the chilling apparatus.
Once the freeze-cast substrate is formed, metallic particles can be sprayed onto the spraying pattern of the freeze-cast substrate using a spray forming technique. Examples of suitable spray forming techniques include, but are not limited to, cold spraying, flame powder, flame wire, arc spraying, plasma spraying, high energy plasma spraying, vacuum plasma spraying, detonation, and high velocity oxyfuel.
Another preferred method embodiment includes introducing a slurry into a mold unit comprised of a mold contained within a casting receptacle, placing insulation around at least a portion of the casting receptacle to minimize distortion in the freeze-cast substrate by controlling temperature gradients within the mold unit and lowering the temperature of the slurry to freeze the slurry to form a freeze-cast substrate.
In accord with another preferred embodiment, a mold unit for producing a freeze-cast substrate is disclosed which comprises a mold, a substrate receptacle having a base panel having a receiving surface for receiving the mold and side panels having inner and outer surfaces and a layer of insulating material provided around at least a portion of the outer surfaces of the side panels for minimizing distortion of the freeze-cast substrate by controlling temperature gradients within the mold and slurry. The layer of insulating material can be fiberglass insulating material.
These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.
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European Patent Office, International Search Report dated Feb. 12, 2003.
Allor Richard L.
Nicholson John Michael
Roche Allen Dennis
Samir Samir
Brooks & Kushman P.C.
Dunn Tom
Ford Motor Company
Porcari Damian
Tran Len
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