Patent Application
20170001238
The present disclosure relates to metal foams, more particularly, to a dual investment method to manufacture metal foam.
Reticulated metal foams are porous, low-density solid foams that includes few, if any, intact bubbles or windows. Reticulated metal foams have a wide range of application and may be utilized in many aerospace applications.
Numerous existing manufacturing technologies for producing reticulated metal foams have been attempted, however, automated production of such reticulated structures may be rather difficult to implement as the ceramic investment often proves difficult to remove without damage to the resultant relatively delicate metallic foam structure. Further, the existing manufacturing technologies lack the capability to efficiently manufacturer relatively large sheets of metal foam as the weight of the ceramic investment is sufficient to crush and convolute the shape of the polyurethane foam precursors. This may result in castability complications, polymer burnout, and reduced dimensional tolerances.
Current standard practice for the flask investment of patterns for investment casting involves use regular geometric solids as the flask. This results in a mold with a consistent cross section that will tend to naturally cooled from the exterior surfaces inward. This inward cooling leads to an outside-inward solidification of cast metal which may result in shrinkage porosity in the last area to solidify.
A method to manufacture reticulated metal foam via a dual investment solid mold according to one disclosed non-limiting embodiment of the present disclosure can include pre-investing a precursor with a diluted pre-investment ceramic plaster to encapsulate the precursor; and investing the encapsulated precursor with a ceramic plaster within a varied cross-section mold.
A further embodiment of the present disclosure may include, wherein the varied cross-section mold is of a trapezoidal prism shape.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold forms a mold thickness between an outer periphery of the encapsulated precursor at a top of the encapsulated precursor is between 200-500% a thickness between the outer periphery of the encapsulated precursor at a base of the encapsulated precursor.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold forms a ratio between a top to a base thereof that is about 3:1.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold is of a trapezoidal prism shape.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the precursor is a reticulated foam.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the precursor is a polyurethane foam.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the precursor is completely encapsulated with the diluted pre-investment ceramic plaster.
A further embodiment of any of the embodiments of the present disclosure may include, further comprising, coating the precursor in a molten wax to increase ligament thickness.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the ceramic plaster is more rigid than the diluted pre-investment ceramic plaster.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the diluted pre-investment ceramic plaster is about 55:100 water to powder ratio.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the ceramic plaster is about 28:100 water to powder ratio.
A varied cross-section mold according to another disclosed non-limiting embodiment of the present disclosure can include a mold thickness adjacent to an outer periphery of a pattern at a top of the varied cross-section mold is between 200-500% a thickness between the outer periphery of the pattern at a base of the varied cross-section mold.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold is of a trapezoidal prism shape.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold forms a mold with a ratio between a top to a base thereof that is about 3:1.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold is of a trapezoidal prism shape that forms a mold with a ratio between a top to a base thereof that is about 3:1.
A varied cross-section mold according to another disclosed non-limiting embodiment of the present disclosure can include a trapezoidal prism shape with a pour cone in a top, the top larger than the base.
A further embodiment of any of the embodiments of the present disclosure may include, wherein a mold thickness adjacent to an outer periphery of a pattern at a top of the varied cross-section mold is between 200-500% a thickness between the outer periphery of the pattern at a base of the varied cross-section mold.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold forms a mold with a ratio between the top to the base thereof that is about 3:1.
A further embodiment of any of the embodiments of the present disclosure may include, wherein the varied cross-section mold contains a rectangular pattern.
The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting.
Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiments. The drawings that accompany the detailed description can be briefly described as follows:
Initially, a precursor 20 (
Next, the precursor 20 is heated, then dipped or otherwise coated in a molten wax 22 to increase ligament thickness (Step 104;
It should be appreciated that various processes may be utilized to facilitate the wax coating such as location of the precursor 20 into the oven for few minutes to re-melt the wax on the precursor 20; utilization of an air gun used to blow out and/or to even out the wax coating; and/or repeat the re-heat/air gun process as necessary to produce an even coating of wax. Alternatively, or in addition, the precursor 20 may be controlled a CMC machine to assure that the way coating is consistently and equivalently applied. The precursor 20 is then a coated precursor 30 that is then allowed to cool (
Next, a wax gating 40 is attached to each end 42, 44 of the coated precursor 30 (step 106;
Next, a container 50 is formed to support the wax gating 40 and attached coated precursor 30 therein (step 108;
Next, the wax gating 40 and attached coated precursor 30 is pre-invested by pouring a slurry of diluted pre-investment ceramic plaster into the container 50 to form a pre-investment block 60 (step 110;
The ceramic plaster may be otherwise mixed per manufacturer's recommendations, but, the ceramic plaster is highly diluted, e.g., water to powder ratio of 55:100 used for Ultra-Vest as compared to manufacturer recommended 39-42:100 to provide the diluted pre-investment ceramic plaster. It should be appreciated that various processes may be utilized to facilitate pouring such as a vibration plate to facilitate slurry infiltration into the coated precursor 30; location in a vacuum chamber to remove trapped air, etc. The vacuum may be released once bubbles stop breaching the surface, or slurry starts setting up. The container 50 may then be topped off with excess slurry if necessary.
The heavily water-diluted ceramic plaster reduces the strength of the ceramic, which facilitates post cast removal. The heavily water-diluted ceramic plaster also readily flows into the polymer reticulated foam structure, ensuring 100% investment. This is significant in the production of very dense, fine pore, metal foams. This pre-invested may thus take the form of a block, panel, brick, sheets, etc. Once pre-invested, they are essentially a rectangular prism of the diluted investment plaster with the foam encapsulated inside.
The pre-investment block 60 is then allowed to harden for about 10 minutes then, once set, transferred to humidity controlled drying room. The final pre-investment block 60, when solidified, is only slightly larger than the original poly foam precursor 20 shape. This step allows maintenance and support of the precursor 20 structural integrity that may be otherwise compromised. That is, the shape of the precursor 20 is protected. The wax assembly procedure (step 112) can then begin after about 2 hours drying time.
The wax assembly procedure (step 112) may include attachment of gates 70, 72, and a pour cone 74, to the pre-investment block 60 to form a gated pre-investment block 80 (
The gated pre-investment block 80 is then located within an outer mold assembly 82 with wax rods 84 as vents placed inside a wax-coated tube 86 (
Next, the outer mold assembly 82 is invested with a ceramic plaster for final investment (step 114). The ceramic plaster may be mixed per manufacturer's recommendations, e.g., water to powder ratio of 28:100 of Glass-Cast 910 product. The final investment of the mold 90 is thereby significantly more rigid and robust than the pre-investment ceramic plaster.
The mold 90 is then allowed to set up and dry in a humidity-controlled room for minimum of about 2 hours (step 116) before de-wax (step 118). The final mold 90 may be de-waxed for about minimum 3-4 hours at about 250° F. (preferably overnight).
Once, de-waxed, the mold 90 is inspected (step 120). Various inspection regimes may be provided.
Next, the final mold 90 is placed in a gas burnout furnace to burnout the original precursor 20 (step 122). The burnout may, for example, follow the schedule: 300 F to 1350 F (732C) in 10.5 hrs (100 F/hour); fast ramp, e.g., ramp rate of 100-200 F/hr max, to 1000 F (538 C) if all water driven out of mold; soak at 1350 F (732 C) until burnout complete which may require up to about 12-24 hours depending on mold size.
Next, the mold 90 receives the molten metal material (step 124;
The mold 90 may then be pressurized (step 126). The pressure may be between about 5-10 psi or until aluminum exits the mold 90 via the vents formed by the wax rods 84. It should be appreciated that various pressurization and non-pressurization schemes may be alternatively utilized.
The mold 90 is then air cooled at room temperature for about 4-5 hours (step 128). It should be appreciated various time periods may be alternatively required.
The reticulated metal foam may then be removed via various mechanical and/or water sprays (step 130). For example, water may be sprayed to remove the internal investment and mechanical vibration may alternatively or additionally be utilized to facilitate material break up. Repeated rotation between water spray and mechanical facilitates clean metal foam formation. Alternatively, or in addition, a dental plaster remover such as a citric-based solution may be utilized to dissolve the internal investment.
The method 100 to manufacture reticulated metal foam via the dual investment solid mold with diluted pre-investment ceramic plaster is very fluid and fills even dense, fine pore size foams with ease, compared to current technology. The fluidity of the pre-investment reduces likelihood of entrapped bubbles in the foam structure to ensure 100% investment of the foam precursor. Pre-investment of the foam shapes also facilitates relatively larger foam sheets to be cast than existing technologies. This is, because the pre-investment surrounds and completely encapsulates the delicate foam structure, once solidification occurs, the foam structure and shape is protected from distortion during the final solid mold investment step. When trying to cast larger foam sheets without the pre-investment, the weight of the final, heavier, and stronger ceramic investment can move and compress the polyurethane foam.
The pre-investment also maintains or increases dimensional tolerance as the foam is encapsulated in the light ceramic plaster. The relatively heavier, stronger ceramic, which is poured over the pre-investment, cannot exert pressure, move, or stress the delicate foam structure that has already been encapsulated in the diluted pre-investment ceramic plaster. The pre-investment step also eliminates the possibility of foam distortion or contamination during the wax assembly mold process. The pre-investment, which was heavily diluted with water over the manufacturer's recommendation, is very weak. After casting, the pre-invested block is removed and can be easily washed away using regular water hose pressure, reducing time and potential for damage to the reticulated metal foam structure.
With reference to
The varied cross-section mold 200 includes a relatively narrow cross-section 202 at a base 204 that flares to a relatively wide cross-section 206 at a top 208 that includes a pour cone 210. In one example, a thickness 212 between an outer periphery 214 of the pattern 216 at a top 218 of the pattern 216 is between 200-500% a thickness 220 between the outer periphery 214 of the pattern 216 at a base 222 of the pattern 216. That is, the thickness 212 of varied cross-section mold 200 adjacent to the pour cone 210 is thicker than the thickness 220 adjacent to the base 222 of the pattern 216.
With reference to
Due to the insulating properties of varied cross-section mold 200, heat will more rapidly dissipate through the areas with a small cross section and more slowly through areas with a large cross section. This will establish a gradient in the cast metal during solidification and lead to solidification that begins in the area with the smallest flask cross-section 230 (relatively cool) and progress towards the areas with the largest flask cross section 240 (relatively hot). In this manner, the solidification can be controlled and shrinkage porosity can be readily minimized and directed toward non-damaging areas (such as the pour cone).
The varied cross-section mold 200 may be readily utilized in various randomly oriented grain structure castings such as equiax investment and sand casting including automotive and other ferrous casting industries.
The use of the terms “a,” “an,” “the,” and similar references in the context of description (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. It should be appreciated that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to normal operational attitude and should not be considered otherwise limiting.
Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.
It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.
Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.
The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.
