US20070277952A1

US20070277952A1 - Rapid localized directional solidification of liquid or semi-solid material contained by media mold

Info

Publication number: US20070277952A1
Application number: US11/442,550
Authority: US
Inventors: Edward J. Le Vert; Bruce A. McMellon; Donald Young
Original assignee: Vulcan Engineering Co Inc
Current assignee: Vulcan Engineering Co Inc
Priority date: 2006-05-30
Filing date: 2006-05-30
Publication date: 2007-12-06

Abstract

An arrangement for forcing rapid localized directional solidification, or global homogenous accelerated solidification of a liquid or semi-solid parent material, which is contained by a media mold that possesses porous properties. The process produces solidified matrix structures and cast properties in the parent material otherwise not possible through conventional solidification methods under ambient conditions. The process is capable of enhancing ordinary production cycles by reducing the overall cycle time required to produce a normally solidified material in a porous media mold. Gas is introduced into the mold media through a manifold or series of manifolds transmitting the gas to spray nozzles and further controlling the physical and mechanical properties of the gas such that the gas permeates through the mold media contacting the liquid or semi solid-parent material and effectively causing rapid solidification of the parent material, primarily as a result of the temperature differential and heat transfer between the gas and the parent material.

Description

BACKGROUND AND SUMMARY

The inventions described herein relate generally to molding and casting. More specifically, they relate to molding and casting wherein a media mold is produced for the purpose of receiving a liquid poured, injected or filled by vacuum therein, and solidifying the liquid to produce a shape specified by the mold. Aspects of the inventions relate to a foundry process of producing bonded media molds whether bonded by organic or inorganic binders and filling the molds with molten metal alloys and allowing the poured molds to solidify to the mold shape. Other aspects of the inventions relate to a foundry process of lost foam casting wherein unbonded media is molded around a foam shape and molten metal is poured, injected or filled by vacuum into the mold and the molten metal displaces the foam shape and this metal solidifies to produce a specified shape or shapes.
In a media mold casting process liquefied parent material is poured or injected into a mold formed into a desired shape by media. In the mold, the liquid parent material solidifies under ambient conditions to form a solid having the shape of its mold. In a foundry sand or media casting process, liquid metals or metal alloys are poured or injected into media molds. However, metal alloys solidifying under normal ambient conditions form various microstructual constituents in the cast matrix. Many times these matrix constituents are undesirable and result in overall degradation of parent material properties. In media molding casting processes solidification is generally considered to be slower than other conventional casting. In some cases with slower solidification rates, in certain alloys, lower achievable casting properties result. When this phenomenon occurs it may hamper the enhanced development of certain castings within certain casting processes. When casting engineers' design a casting, which requires certain minimum physical and/or mechanical cast properties for a specific alloy which are greater than are achievable in the present process technology alternative forms of casting must be considered. Many times alternative forms of casting are less desirable because of limitations with casting geometries, increased environmental compliance cost, or possibly a higher production cost is required to produce the same casting from the alternative process. In particular the Lost Foam Casting Process is desirable for producing very complex cast shapes.
The inventions described herein enable the lost foam casting process, normally considered to be a slow solidification process, to achieve much greater solidification rates, which produces a casting work product having better physical and mechanical properties that can be achieved with traditional processes. This is particularly true for certain casting alloys whose mechanical properties significantly degrade with slower solidification rates. As one example, the casting of automotive aluminum engine blocks and heads according to the processes taught herein results in significantly improved finished work product alloy properties compared with those achieved as a result of conventional casting.

BRIEF DESCRIPTION OF THE DRAWINGS

Apparatus embodying features of the invention are depicted in the accompanying drawings which form a portion of this application and wherein:

FIG. 1 is side view of an arrangement for casting a six-cylinder engine block. It shows an arrangement of a gas spray manifold with nozzles located to direct localized gas spray patterns to crankshaft bearing housings only for the six-cylinder engine block casting.

FIG. 2 is sectional of the arrangement shown in FIG. 1.

FIG. 3 is a depiction of the spray manifold oriented within a lost foam V-6 engine block cluster assembly contained in a molding flask.

FIGS. 4, 5 and 6 depict various arrangements to fixture the gas supply to the spray manifold inside the molding flask. FIG. 4 shows an arrangement wherein gas supply is from the bottom and a detail of the gas distribution region. FIG. 5 shows an arrangement wherein gas supply from the side. FIG. 6 shows an arrangement wherein gas supply is from the top.

FIG. 7 depicts a gas spray manifold with nozzles located to direct localized gas spray patterns to selected regions of a six-cylinder engine head casting.

FIGS. 8 (front view) and 9 (side view) are depictions of the spray manifold oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask with gas supply through the base of the flask

FIGS. 10 (front view) and 11 (side view) are depictions of the spray manifold oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask with gas supply through the side of the flask.

FIGS. 12 (front view) and 13 (side view) are depictions of the spray manifold oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask with gas supply through the top of the flask

FIG. 14 is a simplified flow chart depicting a typical process of gas quenching or gas forced cooling according to the inventions.

FIG. 15 shows an example of a process according to the inventions utilizing lost foam casting for gas quenching or gas forced cooling. It depicts a reusable-molding flask with a gas manifold configured through its base. It will be understood that the process does not necessarily require the use of a reusable-molding flask. The mold may be flask-less and the process can still be carried out.

FIG. 16 shows an example of a process according to the inventions utilizing lost foam casting for gas quenching or gas forced cooling. It depicts a lost foam-casting cluster inserted into a flask and situated or located in a repeatable manner with respect to the gas manifold and nozzles. The use of a lost foam cluster in this figure is an example only. Any casting replica material or a casting mold void is adequate for the process.

FIG. 17 shows an example of a process according to the inventions utilizing lost foam casting for gas quenching or gas forced cooling. The mold is depicted as filled with a mold media surrounding the casting replica and the mold has been compacted to support the desired shape of the final cast product.

FIG. 18 shows an example of a step sequence utilizing lost foam casting for gas quenching or gas forced cooling. It depicts the filled and compacted mold poured with liquid or semi-solid parent material, which has replaced the foam replica and the parent material has taken the shape of the desired final cast product.

FIG. 19 shows an example of a step sequence utilizing lost foam casting for gas quenching or gas forced cooling. The gas source has been initialized and gas is depicted permeating through the mold media and contacting the parent casting material. It will be understood that the act of gassing the parent casting material may also occur during the process of mold filling (FIG. 18) as well as occurring intermittently in a local region, sequentially along a local region or globally throughout the mold to produce the desired results.

FIG. 20 (PRIOR ART) is a copy in its entirety of “Table 6” of Metals Handbook, Ninth Edition, Volume 2, Properties and Selection: Nonferrous Alloys and Pure metals. pp 150-151 (1979).

FIG. 21 (PRIOR ART) is a copy of FIGS. 4-9 of Aluminum Casting Technology, 2^ndEdition, The American Foundrymen's Society, p 55, (1993). In that publication, FIGS. 4-9 is labeld: “General Structure of Alloy 390.0 (100X).”

DETAILED DESCRIPTION

Referring to the figures for a clearer understanding of the process it will be understood that certain components depicted and discussed herein are conventional foundry or manufacturing components that may be replaced by equivalent structures for performing the same operation without departing from the scope of this invention.
FIGS. 1 and 2 depict an example of a gassing manifold for a six (6) cylinder engine block. In order to provide gas quenching, there is provided a gas spray manifold 120 with nozzles 124. Nozzles 124 are located in such a manner as to direct localized gas spray patterns only to the crankshaft bearing housings of a six-cylinder engine block casting.
FIG. 2 is a cross section taken along line 2-2 of FIG. 1. In this cross section it is possible to see more of the structural arrangement of manifold and nozzles, more specifically, outside manifold pipe wall 122 and inside manifold pipe wall 123 and nozzles 124.
FIG. 3 shows another structural arrangement for gas quenching. This arrangement includes a gas spray manifold 120 oriented within a lost foam V-6 engine block cluster assembly contained in a molding flask 140. Gas spray manifold 120 is provided with gas through a bottom feed supply gas manifold 132. A cast block 134 is visible in side view. A down sprue 138 provides the pathway for molten metal to the mold through gating 136.
Various structural arrangements can be utilized for feeding gas into a gas spray manifold 120. FIGS. 4, 5 and 6 depict three of the many possible such arrangements for supplying gas to a gas spray manifold 120 inside the molding flask.
FIG. 4 shows an arrangement in which gas is supplied from the bottom. The figure includes an enlarged portion showing a casting bore 142 and a spray manifold 120 with its gas spray pattern 144. This figure shows one example of a structural arrangement in which spray manifold 120 distributes gas through the manifold and spray nozzles 124 and how gas permeates through the porous molding media to contact the cast metal surface in a desired localized region of the casting bore area.
FIG. 5 shows a structural arrangement in which gas is fed from the side. A side feed supply gas manifold 146 provides gas to gas spray manifold 120.
FIG. 6 shows an arrangement in which gas is fed from the top. A top feed supply gas manifold 148 provides gas to gas spray manifold 120.
FIG. 7 depicts another structural arrangement for gas quenching. Gas spray manifold 130 has nozzles 124 located so as to direct localized gas spray patterns to selected regions of six-cylinder engine head castings. A gas supply 154 provides gas to manifold 130 which releases it into material in the mold via nozzles 124.
FIGS. 8 and 9 depict a spray manifold 130 oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask 140 with a bottom supply gas manifold 132 providing gas through the base of the molding flask. FIG. 8 shows a front view of molding flask 140 and FIG. 9 shows a side view of molding flask 140. In FIG. 8 opposing side views of cylinder head 150 and cylinder head 152 are visible. Cylinder head 150 is shown in bottom view in FIG. 9.
FIGS. 10 and 11 depict a spray manifold 130 oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask 140 with a side feed gas supply manifold 146 FIG. 10 shows cylinder heads 150 and 152 in side view and molding flask 140 in front view. FIG. 11 shows cylinder head 150 in bottom view and molding flask 140 in side view. The arrangement shown in FIGS. 10 and 11 utilizes a side feed gas supply manifold 146.
FIGS. 12 and 13 depict a spray manifold 130 oriented within a lost foam V-6 engine head cluster assembly contained in a molding flask 140 with a top feed supply gas manifold 148. FIG. 12 shows side views of cylinder heads 150 and 152. and FIG. 13 shows a bottom view of cylinder head 152. FIG. 12 shows a front view of molding flask 140 and FIG. 13 shows a side view of the molding flask.
FIG. 14 is a simplified flow chart depicting a gas quench or gas forced cooling process. Mold media is prepared at step 160. The mold media for a lost foam process is an unbonded free flowing substance. In preparing the media for molding it is typically staged into a storage hopper situated directly above molding flask 140. At step 162 the mold itself is prepared. The foam cluster (foam pattern, down sprue and gating system fully assembled) are placed into the molding flask and situated about the gas spray manifold using structures (not shown) that permit repeatable placement mold after mold.
Energy is then applied to the molding flask by an external source and the staged media in the hopper above the flask is released and allowed to rain into the flask at a desired rate. As the flask fills with mold media the energy applied to the flask causes the media to fully compact or densify and therefore to fully contain and maintain the shape of the casting cluster. Casting material is prepared at step 164. Selecting the metal alloy desired and making elemental adjustments to the alloy chemistry during melting to achieve the final desired composition accomplish preparing casting material. The mold is filled at step 166 with the casting material prepared at step 164.
During the gas quenching process at step 170 gas is released into the spray manifold and is allowed to flow into the mold through various nozzles 124 (not shown in FIG. 8). The gas quenching or forced gas cooling process may be initialized at any time upon or during mold filling, after mold fill is complete and even allowed to continue for accelerated mold cooling after casting solidification and desired cast microstructures are completed. Upon contact with the molten parent material the gas medium produces cooling in the parent material at a rate much above (or increased to) normal conventional cooling.
This ability to directly effect or change the cooling rate in a desired manner allows the gas quenching or forced gas cooling process to produce different parent metal alloy solidified cast structures with correspondingly different parent alloy physical and mechanical properties. The mold and its contents are cooled at step 172. This cooling may take place naturally over time or continuing the gas flow globally throughout the mold may induce further cooling. At step 174 the mold and cast product are separated. Reference numerals 170 a, 170 b and 170 c indicate that the gas quenching can occur at different times (it may indeed be more desirable to have it occur at different times during the process to produce varying or different results. For example, at 170 a the gas quenching process is started ‘after’ the metal filling process is complete and is continued until the metal is completely solidified.
At 170 b the gas quenching process begins ‘during’ the process of filling the mold with metal and is allowed to continue until the metal is completely solidified and ‘further’ until some mold super cooling has taken place. At 170 c the gas quenching process begins ‘during’ the process of filling the mold with metal and is allowed to continue until the metal is completely solidified and ‘further’ until complete mold super cooling has taken place. These are only three examples; derivations can occur anywhere in-between and overlapping these.
Referring to FIGS. 1, 3, 7, 8, 9, 10 and 11 it will be understood that the inventions utilize pipes, nozzles and manifolds, surrounded by mold media to direct a flow or multiple individual flows of a gaseous medium either globally or to a specified area of a casting after or during the process of the casting mold being filled with liquid or semi-solid parent material. However, conventional bonded sand or ceramic cores may also be used for the purpose of directing the gaseous medium. Not shown in the drawings, but relating to these figures is an external source or container for the gas, which may contain a gas in its liquid state. Further, along with this source are the means to valve and control the properties of a gas to enable flow and flow properties to be adjusted as well as initiate and to terminate gas flow and further for these variables to be stored and recalled numerically via a programmable logic controller as a recipe for use in serial production.
FIGS. 15-19 show examples of a step sequence utilizing lost foam casting for the gas quenching process. These figures depict a typical, but not the only possible, process sequence. The lost foam casting process includes the following steps:

providing an empty molding flask;
positioning a foam cluster about a gas manifold
filling the flask with mold media and compacting the mold;
filling the mold with molten parent material; and
initiating a gassing sequence in which gas is caused to permeate through the mold media contacting molten and solidified metal.

FIG. 15 depicts a reusable-molding flask with a gas manifold configured through its base. The inventions described herein apply to both reusable and non-reusable molding flasks. Also, the mold may be flask-less and the process can still be carried out. The gas quenching process begins with an empty molding flask 140 as shown in FIG. 15.
FIG. 16 depicts the next step of the gas quenching process. In FIG. 16 a lost foam-casting cluster is inserted into the molding flask 140 and is positioned by structures (not shown) in a repeatable manner with respect to a gas spray manifold 120 and nozzles 124. The use of a lost foam cluster in this figure is an example only. The inventions described herein are adaptable to various casting replica materials and various types of casting molds. Times, temperatures, types of gas, etc. are determined by many factors including mold materials, size of mold, parent materials, temperature, etc. In FIG. 16 foam cluster 176 has been properly positioned about the gas spray manifold 120.
The next step of the gas quenching process is filling molding flask 140 with mold media and compacting the mold. FIG. 17 depicts a state in which the mold has been filled with a mold media surrounding the casting replica. The mold has been compacted to support the desired shape of the final cast product, referred to generally by reference numeral 178.
FIG. 18 depicts the next step of the gas quenching process in which molten material (liquid or semi-solid parent material) 180 is poured into the mold. Molten parent material poured into the mold replaces the foam replica and this molten parent material takes the shape of the desired final cast product.
The final step of the gas quenching process is illustrated in FIG. 19. A gassing process is carried out. This gassing process may have one or more steps of flowing gas through a gas spray manifold 120 and further through spray nozzles 124. Gas spraying from nozzles 124 permeates through the porus mold media and contacts the parent material in a global or localized manner. The gassing process and the configuration of nozzles 124 are arranged so as to accomplish the desired result. FIG. 19 represents a state in which the gassing process is underway. Gas is depicted permeating through the mold media and contacting the parent casting material. The gassing process can include steps carried out at various times in the molding process. For example, gassing the parent casting material may also occur during the filling of parent material into the mold (see FIG. 14) as well as occurring intermittently in a local region, sequentially along a local region or globally throughout the mold to produce the desired results. (i.e. 170 a, b, c)
The following are two examples of specific processes in accordance with the inventions.

EXAMPLE 1

We can Enhance the Mechanical Properties in Aluminum Castings through Controlled Solidification by the Introduction of a Cooling Gas Medium

Mechanical properties in castings are directly related to solidification rate; in general terms, the more rapid the solidification rate, the greater the mechanical properties. The solidification rate of an aluminum casting can be determined using a metallographic technique which measures dendrite-arm spacing. FIG. 20 (PRIOR ART) is a copy in its entirety of “Table 6” of Metals Handbook, Ninth Edition, Volume 2, Properties and Selection: Nonferrous Alloys and Pure metals. pp 150-151 (1979). It shows that fine dendrite-arm spacing is accompanied by high mechanical properties. Using our claimed gas quench or gas forced cooling processes it is possible to increase the solidification rate of an aluminum casting locally and or globally in order to produce a fine dendritic-arm spacing and correspondingly enhanced mechanical properties. By the application of a gas permeating through a mold media, which is cooler than the parent casting metal temperature, a sufficiently steep thermal temperature gradient is set up, which through the normal thermal conductivity of the parent metal, allows heat to be transferred through and out of the metal at a rate great enough to increase the rate of solidification of the metal and therefore to produce a solidified cast structure with a fine dendrite-arm spacing. The solidification rate is determined by how fast or slow heat can be removed from the casting. For the casting to solidify (freeze), heat transfer has to take place. The speed at which the heat is transferred is a function of the thermal gradient. The steeper (greater) the thermal gradient, the faster heat transfer will take place and the faster the molten metal will solidify. In this regard, see Aluminum Casting Technology, 2^ndEdition, The American Foundrymen's Society, p 280, (1993).

EXAMPLE 2

We can Control an Aluminum Casting Microstructure and Resultant Casting Wear Face Properties by the Application of a Gaseous Cooling Media During Solidification

FIG. 21 (PRIOR ART) is a copy of FIGS. 4-9 of Aluminum Casting Technology, 2^ndEdition, The American Foundrymen's Society, p 55, (1993). In that publication, FIGS. 4-9 is labeld: “General Structure of Alloy 390.0 (100×).” An outstanding feature of the hypereutectic aluminum-silicon alloy microstructure is the primary silicon phase. It is this phase that gives these alloys their desirable wear characteristics. Control of primary silicon microstructures rests in two areas: solidification rate and artificial nucleation (refinement). Without the benefit of an artificial nucleation treatment, primary silicon crystals grow quite large and irregular in shape, generally forming in a somewhat segregated spatial pattern. Faster solidification rates result in smaller sizes. See the Aluminum Casting Technology publication described above. By the application of a cooled gaseous media to the mold media casting interface it is possible to increase the solidification rate of the casting and therefore enhance the silicon particulate size.
The above are merely examples of the practical application of the principles of the inventions described herein. It is possible to apply the principles of the inventions to a variety of mold materials, mold shapes, and parent nonferrous or ferrous materials.

Claims

1. A method of rapidly localized and directional solidifying a liquid or semi-solid parent material in a media mold, comprising:

introducing onto the parent material in a controlled and localized manner a gas having a temperature that is different from that of the parent material, the gas being introduced in such a manner to locally solidify the parent material in a manner and to a degree that certain microstructual constituents will not form.

2. A method of rapidly localized and directional solidifying a liquid or semi-solid parent material in a media mold, comprising:

introducing onto the parent material in a controlled localized manner a gas having a temperature that is different from the parent material, the gas being introduced in such a manner to locally solidify the parent material in a manner and to a degree that certain microstructual constituents can be made to form in a controlled manner thereby causing the resultant physical and mechanical properties of the parent material to change in an advantageous manner.

3. A method of rapidly localized and directional solidifying a liquid or semi-solid parent material in a media mold, comprising:

introducing onto the parent material in a controlled localized manner a gas having a temperature that is different from the parent material, the gas being introduced in such a manner to locally solidify the parent material in a manner that decreases the time required to solidify a parent material.

4. A method of rapidly localized and directional solidifying a liquid or semi-solid parent material in a media mold, comprising:

cooling a predetermined portion of the parent material.

5. A method according to claim 4 wherein the cooling step comprises forcing gas onto a localized portion of the parent material.

6. A method according to claim 4 further comprising:

introducing the gas through one or more nozzles in a controlled and localized manner.

7. A method according to claim 4 wherein the step of cooling comprises varying a cooling rate of the parent material by introducing gas thereto and varying contact time of the gas with the parent material and controlling its temperature to cause a variable range of properties to be developed throughout the base material structure.

8. A lost foam casting process, comprising:

providing an empty molding flask;

positioning a foam cluster about a gas manifold

filling the flask with mold media and compacting the mold;

filling the mold with molten parent material; and

carrying out a gassing sequence in which gas is caused to permeate through the mold media contacting molten metal and effectively forcing a solidification rate or rates which inherently change the structure of the solidified parent material and therefore the resultant properties of the material/metal.

9. A casting arrangement, comprising:

a mold made from a porous material;

a gas manifold for supplying gas to the mold during a casting process; and

nozzles for causing gas from the manifold to be dispersed in a localized manner so as to affect portions of the mold during a molding process.

10. A casting arrangement according to claim 9 wherein the gas manifold supplies gas from above the mold.

11. A casting arrangement according to claim 9 wherein the gas manifold supplies gas from below the mold.

12. A casting arrangement according to claim 9 wherein the gas manifold supplies gas from the side of the mold.

13. A lost foam gas quench process, comprising:

preparing a mold media of an unbonded free flowing substance;

staging the mold media in a storage hopper situated above a molding flask;

preparing a mold;

preparing a foam cluster including a foam pattern, down sprue and gating system;

placing the foam cluster into the molding flask and positioning it about a gas spray manifold using structures that permit repeatable placement mold after mold;

applying energy to the molding flask by an external source;

releasing the staged media from the hopper and allowing it to rain into the flask at a desired rate, whereby as the flask fills with mold media energy applied to the flask causes the media to compact and fully contain and maintain the shape of the casting cluster;

preparing casting material;

selecting a metal alloy desired and making elemental adjustments to the alloy chemistry during melting to achieve the final desired composition accomplish preparing casting material;

filling the mold with the casting material previously prepared; and

releasing gas into the spray manifold and allowing it to flow into the mold through nozzles;

14. A lost foam gas quench process according to claim 13 further comprising:

initializing the gas quenching process upon mold filling.

15. A lost foam gas quench process according to claim 13 further comprising:

initializing the gas quenching process after mold filling has been completed.

16. A lost foam gas quench process according to claim 13 further comprising:

initializing the gas quenching process and allowing it to continue for accelerated mold cooling after casting solidification and desired cast microstructures are completed.

17. A lost foam gas quench process according to claim 13 wherein upon contact with the molten parent material the gas medium produces cooling in the parent material at a rate much above (or increased to) normal conventional cooling.

18. A lost foam gas quench process according to claim 13 further comprising cooling naturally over a predetermined period of time.

19. A lost foam gas quench process according to claim 13 further comprising continuing gas flow globally throughout the mold to induce further cooling.

20. A lost foam gas quench process according to claim 13 further comprising separating the mold and cast product.

21. A lost foam gas quench process according to claim 13 wherein gas quenching is started after the metal filling process is complete and is continued until the metal is completely solidified.

22. A lost foam gas quench process according to claim 13 wherein gas quenching is started during the process of filling the mold with metal and is allowed to continue until the metal is completely solidified and further until some mold super cooling has taken place.