EP3233334B1

EP3233334B1 - Steel foam and method for manufacturing steel foam

Info

Publication number: EP3233334B1
Application number: EP15871037.6A
Authority: EP
Inventors: Hathibelagal M. ROSHAN
Original assignee: Maynard Steel Casting Co
Current assignee: Maynard Steel Casting Co
Priority date: 2014-12-19
Filing date: 2015-12-17
Publication date: 2020-10-07
Anticipated expiration: 2035-12-17
Also published as: CN107206482A; EP3233334A1; WO2016100598A1; EP3233334A4

Description

BACKGROUND

The present invention relates to steel foam and, more particularly, to steel foam and methods of producing steel foam.
Metal is considered a foam if pores are distributed within the metal to take up a certain minimum percentage of the total volume of the metal. The introduction of pores or voids into a metal component typically decreases the density and weight of the metal component compared to a solid metal component. Metal foam components also frequently display a higher plate bending stiffness than solid metal components. Currently, commercial metal foam components are generally limited to aluminum, despite the fact that steel foam components would exhibit many superior properties if they could be produced in volume at reasonable cost. US 4 534 266 A discloses a method for casting a steel armor plate comprising ceramic inserts. FR 2 932 705 A1 discloses a method for producing a cellular steel component.

SUMMARY

Embodiments of the present invention provide the ability to produce steel foam components having consistent densities. In addition, embodiments of the present invention provide the ability to produce steel foam components having predictable mechanical properties. Furthermore, embodiments of the present invention provide the ability to produce steel foam components on an industrial scale.
Additional embodiments provide the ability to produce gradient density lightweight steel foam. Further embodiments provide the ability to produce selective variable density lightweight steel foam.
The present invention provides engineers working with steel a new degree of freedom: density. The design space potentially covered by steel applications can grow significantly with density as a variable. Among other things, the present invention opens new opportunities for designers to find suitable military and naval applications for not only energy absorption, but also blast resistant and ballistic applications to resist the impact of sharp objects due to their high strength and hardness.
Some embodiments of the present invention provide a method of producing a steel foam component, according to claim 1.
In some embodiments, the present invention provides a steel foam component according to claim 9.
Some embodiments of the present invention provide an insert for use with a mold for creating a steel foam component, according to claim 15.
Other aspects of the present invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic of a system for producing a steel foam component.
Fig. 2 is a perspective view of an insert for use with the system of Fig. 1.
Fig. 3 is a perspective view of another insert for use with the system of Fig. 1.
Fig. 4 is a perspective view of yet another insert for use with the system of Fig. 1.
Fig. 5 is a perspective view of a steel foam component produced using the insert of Fig. 3.
Fig. 6 is a perspective view of a steel foam component produced using the insert of Fig. 4.
Fig. 7 is a perspective view of a steel foam component produced using the insert of Fig. 5.
Fig. 8 is a flow chart depicting a method of producing a steel foam component using the system of Fig. 1.
Fig. 9 is a perspective view of another steel foam component produced using the insert of Fig. 2.
Fig. 10 is a cross-sectional view of the steel foam component of Fig. 9.

DETAILED DESCRIPTION

Before embodiments of the present invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
Fig. 1 illustrates a system 10 for producing a steel foam component. The illustrated system 10 includes a three dimensional mold 14 formed in two halves, a bottom half 18 (i.e., a drag) and a top half 22 (i.e., a cope). The mold 14 is formed from wood or metal and filled with drag sand. The bottom half 18 and the top half 22 define a cavity 34 within the drag sand of the mold 14. The cavity 34 is formed in the shape of the steel foam component being produced. At least one of the halves 18, 22 also defines a pour opening 38 (e.g., a fan gate) in communication with the cavity 34. The opening 38 allows molten steel to be poured into the cavity 34. The cavity 34 is defined by an upper inner surface 42, a lower inner surface 46, and an inner peripheral surface 50 extending between the upper inner surface 42 and the lower inner surface 46.
Positioned within the pour opening 38 is a filter 62. In some embodiments, the filter 62 may be composed of alumina. In other embodiments, the filter 62 may be composed of other materials suitable for use with molten steel. In the illustrated embodiment, the filter 62 is coupled to the top half 22 of the mold 14. The filter 62 is secured within the pour opening 38 and substantially fills a length of the pour opening 38.
The system 10 also includes at least one chaplet 66 positioned within the cavity 34 of the mold 14. Each chaplet 66 is a relatively thin shim made of metal. The chaplets 66 support an insert 78 above the lower inner surface 46 of the mold so that the insert 78 is spaced apart from (i.e., does not directly contact) the lower surface 46.
Figs. 2-4 illustrate embodiments of inserts 78a-c for use in the system 10 of Fig. 1. In the illustrated embodiments, the inserts 78a-c are 3D-printed inserts (i.e., inserts formed using a 3D printer). In other, non inventive embodiments, the inserts 78a-c may be made using other suitable means. For example, the inserts 78a-c could be extruded, blow-molded, form molded, cast, packed, machined, carved, or otherwise formed into a desired shaped. The process used to create the inserts 78a-c can be highly-repeatable (like 3D printing or extruding), can be randomized (like blow-molding), or can be a one-off-type process (e.g., hand sculpted).
In addition, the illustrated inserts 78a-c are composed of sand bonded with a chemical binder (e.g., resin), but may alternatively be composed of other suitable materials. As used herein, "sand" refers to any flowable material or media, such as small breads, grains, or granules. For example, the sand may be conventional sand, foundry sand, kinetic sand, sand-fiber mixtures, sand-clay mixtures, ceramics, silica alumina, combinations of materials, and the like. The sand is a media that can withstand high temperatures for steel casting, but is held together by a binder that burns off slowly when exposed to the high temperatures.
Although the inserts 78a-c are described below with reference to specific embodiments, it should be readily apparent that other shapes and sizes of inserts may also or alternatively be employed. For example, by creating the inserts 78a-c with a 3D printer, the geometric configuration of the inserts 78a-c may be selected and designed to create any desired pattern of pores within a steel component. Furthermore, the dimensions of the inserts78a-c may be scaled as desired to match the dimensions of any steel component. Multiple inserts may also be positioned within a single mold cavity to achieve desired geometries and sizes.
As shown in Fig. 2, the insert 78a includes a plurality of interconnected cores 82a. The illustrated cores 82a are in the form of repeating geometric shapes. By way of example only, the interconnected cores 82a are arranged in rows 84a arranged parallel to a horizontal axis H. The repeating interconnected cores 82a are further arranged in columns 88a that are parallel to a vertical axis V. The horizontal axis H and the vertical axis V are used to facilitate discussion of the inserts 78a-c with reference to the figures, and are not intended to be limiting.
Each of the interconnected cores 82a includes a central portion 86a and protrusions 90a extending from the central portion 86a. The illustrated central portions 86a are spheres. In the illustrated embodiment, four protrusions 90a extend from each of the central portions 86a in directions parallel to either the horizontal axis H or the vertical axis V. As shown, two of the protrusions 90a extend parallel to the horizontal axis H and in opposite directions. Further, two of the protrusions 90a extend parallel to the vertical axis V and in opposite directions. The protrusions 90a adjacent edges of the insert 78a further define ends that are flat surfaces 94a. Each core 82a additionally includes two secondary protrusions 98a extending in opposite directions from the central portions 86a along a third axis T. The third axis T is perpendicular to the horizontal axis H and the vertical axis V. The illustrated secondary protrusions 98a are generally smaller than the protrusions 90a. The protrusions 98a further define ends with flat surfaces 102a. The insert 78a further defines a periphery 120a, which includes the endmost rows 84a (i.e., highest and lowest along the vertical axis V) and the endmost columns 88a (i.e., leftmost and rightmost along the horizontal axis H.).
Although the illustrated central portions 86a are spherical, in other embodiments, the central portions 86a may be non-spherical. For example, the central portions 86a may be square, hexagonal, octagonal, rotund, bulbous, oblong, footballs, and the like. According to a non inventive alternative, the central portions 86a may essentially be omitted such that the protrusions 90a, 98a are directly connected together as a series of pipes. In some embodiments, the shapes of the central portions 86a may vary throughout the insert 78a.
The illustrated interconnected cores 82a in Fig. 2 are connected together using 3D-printing techniques. For example, the interconnected cores 82a along the periphery 120a are coupled to two other interconnected cores 82a if located at the corners of the insert 78a, and are coupled to three other interconnected cores 82a if located elsewhere along the periphery 120a of the insert 78a. In addition, each core 82a located within the periphery 120a is connected to four other cores 82a. In other embodiments, other geometric and non-geometric shapes may be created by interconnecting the cores 82a in other manners (e.g., the cores 82a can be connected diagonally, in a honeycomb pattern, as a double helix, in a web, etc.).
As shown in Fig. 3, interconnected cores 82b of the illustrated insert 78b include central portions 86b that are substantially spherical. Further, each interconnected core 82b includes six similarly-sized protrusions 106b extending from the central portions 86b. The protrusions 106b are oriented such that two of the protrusions 106b extend along the vertical axis V in opposite directions, two of the protrusions 106b extend along the horizontal axis H in opposite directions, and two of the protrusions 106b extend along the third axis T in opposite directions. Each protrusion 106b defines a flat end surface 112b.
The interconnected cores 82b form a plurality of rows 84b parallel to the horizontal axis H. The interconnected cores 82b also form a plurality of columns 88b arranged parallel to the vertical axis V. In the illustrated embodiment, the insert 78b includes sixteen rows 84b and sixteen columns 88b of cores 82b. Further, the interconnected cores 82b form a plurality of layers 92b, each formed of sixteen rows and sixteen columns of interconnected cores 82b. The layers 92b are arranged along the third axis T, which is perpendicular to the vertical axis V and the horizontal axis H. In the illustrated embodiment, the insert 78b includes two layers 92b of cores 82b, but may alternatively include three or more layers 92b of cores 82b.
The interconnected cores 82b in Fig. 3 are connected together using 3D-printing techniques. For example, the interconnected cores 82b along a periphery 120b of the insert 78b are coupled to three other interconnected cores 82b if located at the corners of the insert 78b, or four other interconnected cores 82b if located elsewhere along a periphery 120b of the insert 78b. In addition, each core 82b located within the periphery 120b is connected to five other cores 82b. The periphery 120b is defined by the endmost rows 84b and the endmost columns 88b of the insert 78b.
As shown in Fig. 4, interconnected cores 82c of the insert 78c include central portions 86c and similarly-sized protrusions 106c having flat end surfaces 112c, similar to the interconnected cores 82b shown in Fig. 3. The insert 78c of Fig. 4, however, includes eight rows 84c of cores 82c that are parallel to the horizontal axis H, and eight columns 88c of cores 82c that are parallel to the vertical axis V. Further, the interconnected cores 82c form eight layers 92c of cores 82b, each layer 92c formed of eight rows and eight columns of interconnected cores 82c. The layers 92c are arranged along the third axis T, which is perpendicular to the vertical axis V and the horizontal axis H. The illustrated insert 78c is, thereby, substantially cube-shaped.
Fig. 5 illustrates a steel foam component 140a made using the insert 78a of Fig. 2 and the system 10 of Fig. 1. The illustrated steel foam component 140a has a body 144a in the shape of a rectangular prism. The component 140a includes a first face 148a that is generally square in shape, a second face 152a that is generally square in shape and located opposite the first face 148, and a peripheral edge 156a extending between the first face 148a and the second face 152a. As shown, the peripheral edge 156a is four-sided. The body 144a also includes a plurality of pores 174a that can form a generally uniform pattern along the peripheral edge 156a. The pores 174a are empty voids in the steel foam component 140a.
The pores 174a in Fig. 5 each have a similar geometric shape. The similar geometric shape generally matches the shape of the interconnected cores 82a of the insert 78a of Fig. 2. Similar to the arrangement of the plurality of interconnected cores 82a, each of the plurality of pores 174a is connected to at least one other of the plurality of pores 174a. The pores 174a are also arranged in a series of pore rows 176a and pore columns 180a, corresponding to the number of rows 84a and columns 88a of the insert 78a. As shown in Fig. 5, the pore rows 176a are parallel to the horizontal axis H. The pore columns 180a are parallel to the vertical axis V. Although uniformity of the pores 174a has advantages, it will be appreciated that in other embodiments the core size, shape, and/or arrangement can vary across one or more of these directions as desired for the particular application and component characteristics. For example, the core sizes and/or shapes can increase along at least one of the axes H, V, T. The shapes and/or sizes of the pores 174a can be varied by changing the shape and/or size of the corresponding insert 78a.
As illustrated in Fig. 5, the pores 174a communicate through the peripheral edge 156a of the steel foam component 140a. The openings 178a of the plurality of pores 174a that communicate through the peripheral edge 156a of the steel component are generally the size of the protrusions 90a of the insert 78a of Fig. 2.
In other embodiments, the plurality of pores 174a may not communicate with the peripheral edge 156a and/or may communicate with the first and second faces 148a, 152a. For example, the embodiment shown in Fig. 5 may be modified such that there are openings 178a on the first face 148a and/or the second face 152a. In such embodiments, the openings 178a of the plurality of pores 174a that communicate through the first and/or second faces 148a, 152a are generally the size of the small protrusions 98a of the insert 78a of Fig. 2. As another example, the embodiment shown in Fig. 5 may be modified such that there are no openings on one or more of the faces of the peripheral edge 156a, such as by eliminating the protrusions 90a on such edges of the insert 78a shown in Fig. 2.
Further, the embodiment shown in Fig. 4 may be modified such that there are only openings 178a along one side of the peripheral edge 156a, or only a portion of the openings 178a may be on a side of one or more peripheral edges 156a. In any case, at least one pore 174a of the plurality of pores 174a is configured to communicate through either the peripheral edge 156a or the first and/or second faces 148a, 152a of the steel foam component 140a.
Figs. 6-7 illustrate steel foam components 140b-c that are produced using the system 10 of Fig. 1 and the inserts 78b-c of Figs. 3-4, respectively. Similar to the uniform arrangement of interconnected cores 82b-c in Figs. 3-4, respectively, each steel foam component 140b-c includes a body 144b-c having a plurality of pores 174b-c arranged in a uniform manner, with rows 176b-c of pores 174b-c being arranged parallel to the horizontal axis H and columns 180b-c of pores 174b-c being arranged parallel to the vertical axis V. The pores 174b-c are further arranged in pore layers 182b-c along the third axis T. The illustrated embodiments show openings 178b-c of the pores 174b-c on the peripheries 120b-c of the steel foam components 140b-c. The openings 178b-c may also or alternatively be located elsewhere on the components 140b-c. The illustrated openings 178b-c are generally the same size as the similarly-sized protrusions 106b-c of the inserts 78b-c.
As discussed above in reference to Fig. 5, other arrangements of pores 174b-c are possible on the peripheral edges 156b-c and/or the first and second faces 148b-c, 152b-c of the embodiments shown in Figs. 6-7. Further, the pores 174a-c in the embodiments shown in Figs. 5-7 occupy at least 20% of the volumes of the respective bodies. In some embodiments, the pores 174a-c occupy between about 20% and about 60% of the volumes of the bodies 144a-c. Also, in some embodiments the pores 174a-c occupy between about 40% and about 60% of the volumes of the bodies 144a-c. In the illustrated embodiment, the pores 174a-c occupy approximately 50% of the volumes of the bodies 144a-c. In further embodiments, the pores 174a-c may occupy more than 60% of the volumes of the bodies 144a-c, depending at least in part upon the geometry of the inserts 78a-c and the desired structural properties of the steel foam components 140a-c.
Fig. 8 is a flow chart depicting a method of producing (e.g., casting) a steel foam component 140. References below to the steel foam component 140 generally refer to the steel foam components 140a-140c from Figs. 2-4, which are formed using the casting method with the inserts 78a-c, respectively, from Figs. 5-7, although it will be appreciated that the method discussed below is equally applicable to inserts made of any other core shapes, core sizes, and core arrangements as discussed herein.
At Step 200, the mold 14 (Fig. 1) is provided. As discussed above, the mold 14 is made of the bottom half 18 and the top half 22, which together define the cavity 34. The cavity 34 is formed to have the shape and dimensions of the desired component 140. Further, the mold 14 defines the pour opening 38. At first, the bottom half 18 and the top half 22 are separated until an insert 78 is positioned within the cavity 34.
Next, at Step 204, the insert 78 is positioned within the bottom half 18 of the mold 14. The insert 78 can be one of the 3D-printed inserts 78a-c illustrated in Figs. 2-4. Alternatively, the insert 78 can be another 3D-printed insert having a different size, shape, and/or geometrical configuration than the inserts 78a-c discussed above, and/or can be an insert produced in any of the other manners described herein. After the insert 78 is positioned in the cavity 34, the top half 22 of the mold 14 is coupled to (e.g., positioned on top of) the bottom half 18. The insert 78 fills a desired volume of the cavity 34 with a generally uniform pattern. The volume filled by the insert 78 ultimately forms pores 174 (i.e., voids) within the steel foam component 140, as shown in Figs. 5-7. As noted above, the insert 78 occupies at least 20% of the volume of the cavity 34. In other embodiments, the insert 78 occupies between about 20% and about 60% of the volume of the cavity 34. In other embodiments, the insert 78 occupies no less than about 60% of the volume of the cavity 34.
In some embodiments, the insert 78 is positioned in the cavity 34 such that the insert 78 is spaced apart from the lower inner surface 46 of the mold 14 and/or from the upper inner surface 42 of the mold 14. The one or more chaplets 66, as shown in Fig. 1, may be used to space the insert 78 from the lower inner surface 46 of the mold 14. Spacing the insert 78 from the upper and/or lower inner surfaces 42, 46 leaves an empty volume in the cavity 34 adjacent the upper and/or lower inner surfaces 42, 46 that may be completely filled with steel. Furthermore, the insert 78 may be positioned within the cavity 34 such that at least a portion of the insert 78 (e.g., the periphery 120) abuts the inner peripheral surface 50. Having the insert 78 abut the inner peripheral surface 50 inhibits steel from completely filling the volume adjacent the surface 50.
Positioning the insert 78 so it is spaced from the lower inner surface 46 of the mold 14 provides the steel foam component 140, after casting, with a continuous first face (i.e., a solid surface without any openings 178 within the first face 148). Positioning the insert 78 so it is spaced from the upper inner surface 42 of the mold 14 provides the steel foam component 140, after casting, with a continuous second face (i.e., a solid surface without any openings 178 within the second face 152). Positioning the insert 78 so that it abuts the inner peripheral surface 50 of the mold 14 creates the openings 178 in the peripheral edges 156 of the steel foam component 140. In some embodiments, the insert 78 may also or alternatively be spaced apart from the inner peripheral surface 50 of the mold 14 so that one or more of the peripheral edges 156 of the steel foam component 140 are continuous.
At Step 208, the alumina filter 62 is positioned within the pour opening 38 of the mold 14. The filter 62 can be positioned within the opening 38 when the mold 14 is first created, or when the mold 14 is assembled after the insert 78 is in position. In some embodiments, this step may be omitted if a filter is not needed.
At Step 212, molten steel is poured into the cavity 34 of the mold 14 through the pour opening 38. As the molten steel is poured into the cavity 34, the molten steel fills the cavity 34 between the insert 78 and the lower inner surface 46, the upper inner surface 42, and the inner peripheral surface 50. The alumina filter 62 (if present) helps control the velocity of the molten steel being poured into the cavity 34, and inhibits the molten steel from deforming or crushing the insert 78 before the steel has cooled.
At Step 216, the molten steel can be cooled using known techniques (e.g., waiting a period of time).
After the steel has cooled, the steel foam component 140 can then be removed from the mold 14, at Step 220. At this stage, the insert 78, which may be a 3D-printed sand insert 78, has broken down into a powder or other flowable form. The powder still remains within the steel foam component 140. As such, the insert 78 is removed from the mold 14 with the steel foam component 140.
At Step 224, the powder remains of the insert 78 are decored (i.e., removed) from the steel foam component 140. In some embodiments, the powder remains may exit the steel foam component 140 through the openings 178 by, for example, shaking the component 140. In other embodiments, a new hole may be drilled or cut into the steel foam component 140 to facilitate removal of the powder from the component 140, such as when the steel foam component is provided with no exterior holes through which the powder can exit, or whether an insufficient number of such holes exist. Once the insert 78 is removed from the component 140, the plurality of pores 174 are exposed (i.e., left as empty voids within the steel foam component 140). Further, the steel foam component 140 may be processed to remove excess parts from the steel foam component 140 that are byproducts of the casting process. For example, the pour opening 38 may have retained cooled steel that remains attached to the desired component. This excess cooled steel can be cut off of the component 140 using known techniques.
At Step 228, the steel foam component 140 may be treated to achieve desired physical properties. For example, the component 140 may be heated treated to a desired hardness (e.g., between 100 BHN and 400 BHN). Additionally, the component may be welded by conventional welding techniques to other steel foam components 140 to form a desired structure. The steel foam components 140 are also machinable by common metalworking techniques. The resulting steel foam components 140 can comprise plain carbon and low alloy steels of matrix strengths varying, for example, from 50 ksi to 150 ksi.
Although the steel foam components shown in Figs. 5-7 are rectangular prisms, other shapes are possible. For example, steel foam components that are cylindrical, spherical, or that have other geometric and non-geometric shapes are also contemplated. Further, the steel foam components may be formed as combinations of geometric shapes, or may include any combination of geometric and non-geometric shapes. The inserts and molds in such instances would be altered accordingly to create the desired shapes and densities of the steel foam components.
The above techniques allow for the creation of steel foam components with ballistic resistant applications for military structures (e.g., ballistic plates), civilian structures (e.g., buildings and bridges), naval applications, and the like. The steel foam components also have applications in energy absorption and blast resistance. The steel foam components also have controllable and uniform densities. Steel foam components manufactured according to the processes described herein can be produced relatively inexpensively and on an industrial scale. Compared to aluminum foams, steel foams have higher specific stiffness, higher hardness, and higher strength. Structural advantages of steel foam compared to solid steel include minimization of weight, maximization of flexural strength, increased energy dissipation, and increased mechanical damping. Further applications for steel foam components include, among other things, pistons and propellers. In particular, in a vehicle equipped with a steel foam component for crash protection, the steel foam component decelerates over a longer distance and a longer period of time, thereby limiting changes in speed experienced by vehicle occupants. Further, non-structural benefits of the steel foam components include lower thermal conductivities, improved acoustic performances, allowance of air and fluid transport within the steel foam component, and better electromagnetic and radiation shielding properties.
Figs. 9 and 10 illustrate another steel foam component 140d that is produced using the system 10 of Fig. 1 and, for example, the insert 78a of Fig. 2. The steel foam component 140d is similar to the component 140a described with respect to Fig. 5. The illustrated component 140d, however, has a gradient density. That is, the component 140d includes a first section 186d that is solid, followed a second section 190d that has pores 174d. In the illustrated embodiment, the gradient density is realized along the thickness t of the component (i.e., along the axis T). In other embodiments, the gradient density may also or instead be realized along another dimension of the component (e.g., height and/or width along the axes V and H). Any gradient density in any single dimension or any combination of dimensions is possible, and falls within the spirit and scope of the present invention. With continued reference to the embodiment of Figs. 9 and 10, the volume of the sections 186d, 190d may be generally unequal or equal. In the illustrated embodiment, the volume of the second section 190d is greater than the volume of the first section 186d, by way of example only.
In some embodiments, the gradient density may be formed over more than two sections, or layers, of the component 140d. For example, the component 140d may include a first section that is solid, followed by a second section that has pores, followed by a third section having a greater density of pores of the same or different size. In such embodiments, the component 140d may have solid steel on either or both sides of a porous central section. Alternatively, the component 140d may include a first section that is solid, followed by a second section that has a plurality of pores occupying a first volume (e.g., 20%) of the section, followed by a third section that has a plurality of pores occupying a second volume (e.g., 40%) of the section, etc. The volume occupied by the pores (and, thereby, the density of the sections) may increase, decrease, alternate, or otherwise vary in any manner along any one or more dimensions of the component 140d. For example, gradient densities can exist across the thickness of a plate as shown in Fig. 9, and/or across the width or length of the plate. As other examples, gradient densities can exist in various elements with pores located on one side or end of a plate and pores of different density located across the rest of the plate, pores located in a middle of a plate with pores of different density located on opposite width-wise sides of the plate and/or opposite length-wise ends of the plate, pores located about a periphery of a rectangular or round plate or in a central portion of a rectangular or round plate with the balance of the plate having pores of different density, pores located along a portion (e.g., center or end) of a rod, shaft, strut, or other elongated element and pores of different density along the rest of such a member, pores located proximate an external surface of a rod, shaft, strut, or other elongated element and with pores of different density located further in the interior of such a member (or vice versa), and the like. Alternatively, steel foam components with selective variable densities could have a first pattern of pores formed in a first section to form a first density, and a second pattern of pores formed in a second section to form a second density that is different than the first density. Selective variable densities could also be formed in three or more distinct sections of a steel foam component.
Steel foam components having gradient densities are usable as, among other things, armor plating in military vehicles. For example, the steel foam components can be made in accordance with military spec MIL-PRF-32269 for perforated homogeneous steel armor. By way of example, a solid steel plate of 12 inches by 12 inches by 1 inch may have a weight of 40 pounds and a pounds per square foot (PSF) value of 40. In contrast, by providing a gradient density, the steel foam component 140d illustrated in Figs. 9-10 has a PSF value of 28. Other PSF values are also achievable by varying the gradient density of the component 140d, depending on the desired application and performance characteristics for the component 140d.
In further embodiments, steel foam components may be manufactured with selective variable densities. That is, the components may have pores only in certain, predetermined sections of the components, and the remainder of the components may be solid steel. For example, selective variable densities can exist in various elements with pores located on one side or end of a plate with no pores located across the rest of the plate, pores located in a middle of a plate with no pores located on opposite width-wise sides of the plate and/or opposite length-wise ends of the plate, pores located about a periphery of a rectangular or round plate or in a central portion of a rectangular or round plate with no pores in the balance of the plate, pores located along a portion (e.g., center or end) of a rod, shaft, strut, or other elongated element and no pores along the rest of such a member, pores located proximate an external surface of a rod, shaft, strut, or other elongated element and no pores of different density located further in the interior of such a member (or vice versa), and the like.
In some embodiments, a component with distinct "parts" could have one "part" that is porous and another "part" that is solid steel. For example, a piston typically includes a crown portion (i.e., a first "part") and a skirt portion (i.e., a second "part"). If the piston was formed as a selectively variable steel foam component, the crown portion could have pores, while the skirt portion could be solid steel. Other multi-"part" components are also possible (e.g., a propeller with porous blades and a solid steel hub).
Steel foam produced in accordance with the present invention is usable in manners similar to standard (i.e., non-foamed) steel. For example, steel foam components are weldable using conventional welding techniques. In addition, steel foam is machinable using conventional machine tools.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope of the appended claims.
Various features and advantages of the invention are set forth in the following claims.

Claims

A method of producing a steel foam component (140), the method comprising:
providing a mold (30), the mold (30) defining a cavity (34);

positioning a 3D-printed insert (78) within the cavity (34) of the mold (30), the insert (78) configured to form a generally uniform pattern of pores (174) within at least a portion of the steel foam component (140) and occupying at least 20 percent of the cavity (34), wherein the insert (78) includes a plurality of interconnected cores (82), each of the interconnected cores (82) including a central portion (86) and protrusions (90) extending from the central portion (86);

pouring molten steel into the cavity (34);

cooling the molten steel into the steel foam component (140);

removing the steel foam component (140) and the insert (78) from the mold (30); and

removing the insert (78) from the steel foam component (140).
The method of claim 1, further comprising draining the insert (78) out of the steel foam component (140).
The method of claim 1, wherein the insert (78) is composed of sand and a chemical binder.
The method of claim 1, wherein the insert (78) occupies between about 20 percent and about 60 percent of the volume of the cavity (34).
The method of claim 1, wherein the mold (30) includes an upper inner surface (42) and a lower inner surface (46) that define the cavity (34), and wherein positioning the insert (78) within the cavity (34) includes spacing the insert (78) apart from at least one of the upper inner surface (42) and the lower inner surface (46), in particular positioning the insert (78) within the cavity (34) by spacing the insert (78) apart from both of the upper inner surface (42) and the lower inner surface (46), in particular further comprising positioning a chaplet (66) on the lower inner surface (46) of the mold (30), wherein positioning the insert (78) within the cavity (34) includes positioning the insert (78) on the chaplet (66) to space the insert (78) apart from the lower inner surface (46).
The method of claim 5, wherein the mold (30) also includes an inner peripheral surface (50) extending between the upper inner surface (42) and the lower inner surface (46), and wherein positioning the insert (78) within the cavity (34) includes positioning the insert (78) within the cavity (34) to abut at least a portion of the inner peripheral surface (50).
The method of claim 1, wherein providing the mold (30) includes providing the mold (30) with an opening (38) in communication with the cavity (34), and wherein pouring the molten steel into the cavity (34) includes pouring the molten steel into the cavity (34) through the opening (38).
The method of claim 7, further comprising positioning a filter (62) within the opening (38), and wherein pouring the molten steel includes pouring the molten steel through the filter (62), in particular positioning an alumina filter within the opening (62).
A steel foam component (140) manufactured according to the method of claim 1, the steel foam component (140) comprising:
a steel body (144) having a plurality of pores (174), the plurality of pores (174) forming a generally uniform pattern throughout the body (144) and occupying at least 20 percent of a volume of the body (144).
The steel foam component (140) of claim 9, wherein each of the plurality of pores (174) has a similar geometric shape.
The steel foam component (140) of claim 9, wherein each of the plurality of pores (174) is in fluid communication with at least one other pore of the plurality of pores (174).
The steel foam component (140) of claim 9, wherein the plurality of pores (174) occupies between about 20 percent and about 60 percent of the volume of the body (144).
The steel foam component (140) of claim 9, wherein the body (144) includes a first face (148) and a second face (152) spaced apart from the first face (148), and wherein the first face (148) and the second face (152) are continuous steel, with the body (144) particularly also including a peripheral edge (156) extending between the first face (148) and the second face (152), and wherein particularly at least one of the plurality of pores (174) communicates through the peripheral edge (156).
The steel foam component (140) of claim 9, wherein the plurality of pores (174) is arranged in a series of rows (84) and columns (88) within the body (144).
An insert (78) for use with a mold (30) for creating a steel foam component (140), the insert (78) comprising:
a 3D-printed body (144) including a plurality of interconnected cores (82), the 3D-printed body (144) being configured to be positioned within the mold (30) to form the steel foam component (140) having a desired density that is less than a solid steel component, wherein each of the interconnected cores (82) includes a central portion (86) and protrusions (90) extending from the central portion (86).
A steel foam component (140) manufactured according to the method of claim 1, the steel foam component (140) comprising:
a steel body (144) including a first section (186) and a second section (190), the first section (186) having a first density, the second section (190) having a plurality of pores forming a pattern within the body (144), the second section (190) having a second density that is less than the first density.