Patent Publication Number: US-11654476-B2

Title: Hybrid core for manufacturing of castings

Description:
INTRODUCTION 
     The present disclosure relates to a hybrid core for manufacturing of cast components. 
     Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process. Casting is most often used for making complex shapes that would be otherwise difficult or uneconomical to make by other methods. Sand casting, also known as sand mold casting, is a metal casting process characterized by using sand as the mold material. The term “sand casting” may also refer to an object produced via the sand-casting process. 
     Certain bulky equipment like machine tool beds, ship propellers, combustion engine components (such as cylinder heads, engine blocks, and exhaust manifolds), etc., may be cast more easily in the required size, rather than be fabricated by joining several small pieces. The mold cavity and gating system are typically created by compacting the sand around models called patterns, by carving directly into the sand, or by  3 D printing. The mold includes runners and risers that enable the molten metal to fill the mold cavity by acting as reservoirs to feed the shrinkage of the casting as it solidifies. During the casting process, metal is first heated until it becomes liquid and is then poured into the mold after certain melt treatment such as degassing, adding grain refiner, and adjusting alloy element contents. The mold gradually heats up after absorbing the heat from liquid metal. Consequently, the molten metal is continuously cooled until it solidifies. After the solidified part (the casting) is taken out of the mold and following a shake out, excess material in the casting (such as the runners and risers) is removed. 
     Cores are frequently used for sand casting components with internal cavities and reentrant angles, i.e., interior angles greater than 180 degrees. For example, cores are used to define multiple passages in engine blocks, cylinder heads, and exhaust manifolds. Cores are typically disposable items constructed from materials such as sand, clay, coal, and resin. Core materials generally have sufficient strength for handling in the green state, and, especially in compression, to withstand the forces, e.g., material weight, of casting, sufficient permeability to allow escape of gases, good refractoriness to withstand casting temperatures. Because cores are normally destroyed during removal from the solidified casting, core materials are generally selected to permit core break-up during shake out. The core material is typically recycled. 
     SUMMARY 
     A hybrid core for manufacturing a cast component, the hybrid core including a sand core portion having an exterior shape configured to define an interior feature of the cast component. The hybrid core also includes a metal chill element embedded within the sand core portion. The metal chill element is configured to locally absorb heat energy from the cast component during its cooling and solidification thereof. The metal chill element is constructed and arranged within the sand core portion to be removed during shake out from the cast component subsequent to the solidification thereof. 
     The metal chill element may have a solid cross-section. 
     Alternatively, the metal chill element may have a hollow cross-section, or have a varying cross-section where one section is hollow and another is solid. 
     The metal chill element may have a unitary or single-piece construction. 
     Alternatively, the metal chill element may include a multi-piece construction configured to facilitate removal of the metal chill element during shake out from the cast component. 
     The metal chill element having multi-piece construction may include a first piece of the metal chill element interconnected with a second piece of the metal chill element. 
     The metal chill element may be defined by an exterior surface. In such an embodiment, the metal chill element may include a coating on the exterior surface positioned to contact the cast component and configured to minimize sticking of the metal chill element to the interior feature of the cast component. The coating is intended to not restrict heat transfer from the cast component to the metal element. 
     The coating may include at least one of ceramic, nitride, silicon, and titanium. 
     The coating may have a thickness in a range of 50 nanometers to 5 microns. 
     The metal chill element may have an exterior shape configured to follow a shape or geometry of the interior feature of the cast component. 
     A system and a method for manufacturing a cast component using such a hybrid core are also disclosed. 
     The above features and advantages, and other features and advantages of the present disclosure, will be readily apparent from the following detailed description of the embodiment(s) and best mode(s) for carrying out the described disclosure when taken in connection with the accompanying drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic partial view of an embodiment of a cast component having an interior feature generally formed with the aid of a casting core, according to the disclosure. 
         FIG.  2    is a schematic top perspective partial cutaway view of an embodiment of a hybrid casting core having a metal chill element embedded within a sand core portion used to manufacture the interior feature of the cast component shown in  FIG.  1   , according to the disclosure. 
         FIG.  3    is a schematic top perspective partial cutaway view of another embodiment of the hybrid casting core having a metal chill element embedded within a sand core portion, according to the disclosure. 
         FIG.  4    is a schematic top perspective partial view of the hybrid core shown in  FIG.  2   . 
         FIG.  5    is a schematic cross-sectional front view of an embodiment of the metal chill element having a coating, according to the disclosure. 
         FIG.  6    is a schematic cross-sectional front view of another embodiment of the metal chill element, according to the disclosure. 
         FIG.  7    is a schematic cross-sectional longitudinal view of another embodiment of the metal chill element, according to the disclosure. 
         FIG.  8    is a schematic cross-sectional longitudinal view of another embodiment of the metal chill element, according to the disclosure. 
         FIG.  9    is a schematic cross-sectional front view of an interconnected multi-piece embodiment of the metal chill element, according to the disclosure. 
         FIG.  10    is a flow diagram of a method of preparing the hybrid core, shown in  FIGS.  2 - 9   , for generation of the cast component, according to the disclosure. 
         FIG.  11    is a schematic illustration of a system for manufacturing the cast component shown in  FIG.  1   , the system including the hybrid core shown in  FIGS.  2 - 9   , according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Terms such as “above”, “below”, “upward”, “downward”, “top”, “bottom”, etc., are used in the present disclosure descriptively for the figures, and do not represent limitations on the scope of the disclosure, as defined by the appended claims. 
     Referring to  FIG.  1   , a cast component  10  is depicted. The cast component  10  is specifically a “sand casting”, also known as sand mold casting. Generally, a sand casting is a metal casting produced by using sand as the mold material. The cast component  10  may be a cylinder head (shown in  FIG.  1   ) having an integrated exhaust manifold, such as for an internal combustion gasoline engine or a diesel engine (not shown). A separate embodiment of the cast component  10  may be configured as another part for a piece of machinery, industrial equipment, etc. 
     As shown in each of  FIG.  1   , the cast component  10  includes an interior feature  12 , such as internal cavity, a reentrant angle (an interior angle greater than 180 degrees), or a passage formed by using a core during the casting process. In the particular cylinder head embodiment of the cast component  10 , the interior feature  12  is specifically depicted as exhaust passages or runners of the integrated exhaust manifold converging into an exhaust collector. Generally, a core is a disposable item constructed from materials specifically selected to permit the subject core be removed from the cast component  10  after its solidification in the mold. During the casting process, the molten metal generally solidifies at a rate that depends on the design of the mold and the thermal conductivity of the core. 
     In general, the faster the solidification rate, the finer the cast material microstructure and thus the higher the mechanical properties of the casting. Typically, a sand core has low thermal conductivity and affects coarse material microstructure and low material properties in the finished casting. For example, low cooling rate during solidification of the cast component  10  around an exhaust manifold wall  14  with the use of a sand core may result in a crack  16  (shown in  FIG.  1   ) when the cast component like the cylinder head is subject to engine durability testing or road use, as the particular area experiences high thermal and mechanical stresses. As described in detail below, a hybrid core of various configurations is envisioned to increase local solidification rate of the liquid metal and enhance local material properties of the cast component  10 . 
     Sand cores are typically produced by introducing core sand into specifically configured core boxes, for example half core, dump core, split core, and gang core boxes. Binders may be added to core sands to enhance the core strength. Dry-sand cores are frequently produced in dump core boxes, in which sand is packed into the box and scraped level with the top of the box. A plate, typically constructed from wood or metal, is placed over the box, and then the box with the plate in place is flipped over such that the formed core segment may drop out of the core box. The formed core segment is then baked or otherwise hardened. For complex shape cores, multiple core segments may be hot glued together or joined using other attachment methods. 
     Simple shape one-piece sand cores may also be produced in split core boxes. A typical split core box is made of two halves and has at least one hole for introduction of sand for the core. Cores with constant cross-sections may be created using specifically configured core-producing extruders. The resultant extrusions are then cut to proper length and hardened. Single-piece cores with more complex shapes may be made in a manner similar to injection moldings and die castings. Following extraction and, if required, assembly of the core segments, rough spots on the surface of the resultant core may be filed or sanded down. Finally, the core is lightly coated with graphite, silica, or mica to give the core a smoother surface finish and greater resistance to heat. 
     A hybrid core  20 , shown in various configurations in  FIGS.  2 - 4   , is configured to address the thermal stress related cracking  16  of the cast component  10 , such as in the proximity to the wall  14 . Specifically, the hybrid core  20  is intended to increase local solidification rate and enhance local material properties of the finished cast component  10 , as needed. The hybrid core  20  is particularly configured for manufacturing the cast component  10 , and more particularly for forming the interior feature  12 . The hybrid core  20  includes a sand core portion  22 . The sand core portion  22  has an exterior shape  24  configured to define the interior feature  12  of the cast component  10 . The hybrid core  20  also includes a metal chill element  26  embedded within the sand core portion  22 . The metal chill element  26  is configured to locally absorb heat energy from the molten metal during cooling of the cast component  10  and solidification thereof. The hybrid core  20  may be generated by having the sand core portion  22  formed in a core box around one of the embodiments of the metal chill element  26  that are disclosed below. 
     In general, the metal chill element  26  material should have higher melting temperature than the material used for the actual casting. For cast components manufactured from aluminum, for instance, material selected for the metal chill element  26  may be copper, bronze, cast iron, or tool (stainless) steel. Such metal chill element materials may be employed primarily because of their high thermal conductivity and durability. However, for aluminum castings, when used with a ceramic coating, aluminum (whose melting point is around 660 degrees C.) may also be used as the material for the metal chill element. Another option for the coating is spray-on alcohol-based graphite coating. Such a spray-on coating may include graphite flakes/particles (60˜70%), organic bentonite (2-3%), organic binder (1-2%), inorganic binder (1.5-2.5%), polyvinyl butyral (PVB, 0.2-0.5%), additives (2-5%), and remaining mixture based on anhydrous ethanol with other alcohol solvent(s). 
     The metal chill element  26  is shaped such that it may be either fully embedded within the sand core portion  22  and covered thereby or partially embedded within the sand core portion, thus being partially exposed. The metal chill element  26  is arranged within the mold as part of the hybrid core  20  for cooling the molten metal and thus controlling the solidification rate of the cast component  10  proximate the interior feature  12  during the casting process. By absorbing heat energy from the molten metal, the metal chill element  26  is intended to yield refined microstructure of the casting material and improved mechanical properties of the cast component  10  under operation. Such improved mechanical properties will in turn minimize the likelihood of cracking of the cast component  10 . For example, in manufacturing aluminum castings, the metal chill element  26  is intended to enhance localized cooling of the casting, and thereby decrease the cast aluminum material&#39;s dendrite arm spacing (DAS), which would improve the strength of the cast component  10  in the region around the interior feature  12 . 
     The metal chill element  26  is additionally shaped such that it may be removed during shake out from the cast component  10  subsequent to the solidification thereof. Of particular importance is the removal of the hybrid core  20  without damaging or otherwise disrupting the structure of the formed cast component  10 , which is facilitated by the arrangement of the metal chill element  26  within the sand core portion  22 . Specifically, the sand core portion  22  may be initially broken up inside the solidified cast component  10 , which will in turn permit the metal chill element  26  to be pulled out of the cast component during the shake out. 
     As shown in  FIG.  5    in a cross-sectional view  5 - 5 , the metal chill element  26  may have a solid cross-section  28 A. Alternatively, as shown in a cross-sectional view  6 - 6  in  FIG.  6   , the metal chill element  26  may have a hollow cross-section  28 B. The hollow cross-section  28 B may have a varying thickness along an axis X of the metal chill element  26  (as shown in a cross-sectional view  7 - 7  in  FIG.  7   ). Additionally, the metal chill element  26  may have a combined or mixed configuration, where the cross-section of one portion  28 A is solid and the cross-section of another portion  28 B is hollow (as shown in a cross-sectional view  8 - 8  in  FIG.  8   ). As shown in  FIGS.  2  and  4   , the metal chill element  26  may have a unitary or single-piece construction. The configuration of the metal chill element  26  shown in  FIG.  4    may be generated, for example, by being cast or machined from solid. In general, the metal chill element  26  may be generated by machining, casting, using a specifically configured core-producing extruder, or via a  3 D printing process. 
     Alternatively, as shown in  FIG.  3   , the metal chill element  26  may include a multi-piece construction, e.g., having separate, unlinked and non-contacting respective first and second segments  26 - 1 ,  26 - 2 . The metal chill element  26  depicted in  FIG.  3    specifically includes non-contacting first and second segments  26 - 1 ,  26 - 2  to facilitate removal of the metal chill element during shake out from the cast component  10 . As shown in a cross-sectional view  9 - 9  in  FIG.  9   , the metal chill element  26  may have the first segment  26 - 1  interconnected with the second segment  26 - 2 , i.e., the two pieces being in contact with each other. For example, the first segment  26 - 1  and the second segment  26 - 2  may be interconnected or interlocked by fitting together via complementary projections and recesses. Such a configuration of the metal chill element  26  may be used to accurately establish and maintain spacing between the respective individual first and second segments  26 - 1 ,  26 - 2  when the chill element is positioned within the sand core portion  22 . 
     As shown in  FIG.  4   , the metal chill element  26  may be defined by an exterior surface  30 . The exterior surface  30  of the metal chill element  26  may be generally formed such that an exterior shape  30 A defined thereby is configured to internally follow an external shape  22 A of the sand core portion  22 , which is used to form a shape  12 A defined by the interior feature  12  of the cast component  10 . However, some portions of the metal chill element  26  may protrude beyond the sand core portion  22 . During the casting process, such protruding portions of the metal chill element  26  may come in direct contact with the interior feature  12  or other areas of the cast component  10 . To address such an eventuality, the metal chill element  26  may include a coating  32  (as shown in the cross-sectional view  5 - 5  in  FIG.  5   ) applied to the exterior surface  30  thereof. 
     The coating  32  is specifically intended to minimize possible sticking of the metal chill element  26  to the sand core portion  22  and minimize its sticking to the cast component  10  in areas of direct contact between the metal chill element and the interior feature  12 . The coating  32  would be additionally selected to have the least effect on, i.e., not restrict, transfer of heat energy from the cast component  10  to the metal chill element  26 . The coating  32  may be applied as a sprayable mold wash. Specific compositions of the mold washes may be: ˜30% water, ˜10% soluble mineral oil, ˜10% Kerosene, ˜40% silica flour, and ˜10% ceramic powders. To limit the effect of the coating  32  on heat transfer, the composition of the coating may include at least one of ceramic, nitride, silicon, and titanium, for example, according to a non-limiting list, ceramic-aluminide, nitride-aluminide, and titanium-aluminide, silicon-nitride, silicon-carbide, a diamond-like coating, boron nitride, and cerium oxide. To further limit its effect on heat transfer, the coating  32  may have a thickness in a range of 50 nanometers (nm) to 5 micrometers or microns (μm), depending on the sizes of silica flour and ceramic powders used in the wash. 
     A method  100  of preparing the hybrid core  20  for generation of the cast component  10  is shown in  FIG.  10    and described below with reference to the structure of the hybrid core shown in  FIGS.  2 - 9   . Method  100  commences in frame  102  with generating an embodiment of the metal chill element  26  by one of the above-disclosed approaches. Following frame  102 , the method may advance to frame  104 . In frame  104 , the method includes applying the coating  32  to the exterior surface  30  of the metal chill element  26 . After frame  102  or frame  104  the method will move on to frame  106 . In frame  106 , the method includes arranging the formed metal chill element  26  in a core box. In frame  106 , the method may specifically include arrangement or assembly of individual first and second segments  26 - 1 ,  26 - 2  of the metal chill element  26 , if appropriate for the specific embodiment of the hybrid core  20 . 
     From frame  106 , the method moves on to frame  108 , where the method includes introducing and compacting core sand into the core box until the core box is full, e.g., the sand is level with the top of the core box. Following frame  108 , the method proceeds to frame  110 . In frame  110  the method includes extracting the formed hybrid core  20  from the core box. After frame  110  the method may proceed to frame  112 . In frame  112  the method may include hardening the formed hybrid core  20 , such as by baking in a furnace at temperatures in the range of 200 to 250 degrees C. Alternatively, if self-hardening sand is used (where typically two or more binder components are mixed with sand), the sand will cure and self-harden at room temperature. 
     Following frame  112 , the method may advance to frame  114 . In frame  114  the method includes assembly of individual hybrid core  20  segments, if appropriate for the specific embodiment of the core, and smoothing out, e.g., filing or sanding down, the outer surface of the hybrid core. Additionally, in frame  114  the method may include coating the outer surface of the hybrid core  20  with a suitable compound, such as graphite, silica, or mica to give the hybrid core a smoother surface finish and greater resistance to heat. The method may conclude in frame  116  following one of the frames  110 - 114 , with packaging or storing the hybrid core  20  in preparation for placing thereof in a mold for subsequent generation of the cast component  10 . 
     A system  200  for manufacturing the cast component  10  is shown in  FIG.  11    and described with reference to method  100  shown in  FIG.  10    and the structure of hybrid core  20  shown in  FIGS.  2 - 9   . As shown for exemplary purposes, the cast component  10  may be an aluminum cylinder head defining a cast-in integrated exhaust manifold. The system  200  specifically includes a mold  202  having a first or top half  202 - 1  and a second or bottom half  202 - 2  and a gating system (not shown). The first half  202 - 1  and the second half  202 - 2  of the mold  202  together define an inner cavity  204 . The inner cavity  204  is configured to form an exterior shape  10 A of the cast component  10 . The inner cavity  204  and the gating system may be created by compacting green sand or chemically bonded sand around a pattern, by carving directly into the sand, or by  3 D printing. 
     The system  200  also includes the hybrid core  20 , as described above with respect to  FIGS.  2 - 9   . The hybrid core  20  is arranged within the inner cavity  204  and configured to define the interior feature  12  of the cast component  10 , such as exhaust gas passages of an integrated exhaust manifold. The system  200  further employs a mechanism  206  for introducing a molten metal  208 , such as aluminum, into the cavity  204 , to thereby form the cast component  10 . The mechanism  206  may include a flow valve  210  and a system of runners and risers (not shown), with the valve operatively connected to the mold  202  for supplying the molten metal  208 . Operation of the flow valve  210  may be regulated via an electronic controller (not shown). The electronic controller may be programmed to dispense a specific amount of molten metal  208  into the mold  202  at a predetermined material flow rate to ensure appropriate fill of the cavity  204 . 
     When introduced via the mechanism  206 , the molten metal  208  flows into the cavity  204  and around the hybrid core  20  to form the exterior shape  10 A and the interior feature  12  of the cast component  10 . The hybrid core  20 , and specifically the metal chill element  26 , controls solidification of the molten metal  208  around the interior feature  12  to enhance mechanical properties of the manufactured cast component  10  in the region around the interior feature. The molten metal  208  is permitted to cool and solidify, after which the cast component  10  is removed from the mold. As described above, the hybrid core  20  is removed from the solidified cast component  10  during the core shakeout process, with the brake-up of the sand core portion  22  facilitating extraction of the metal chill element  26  from the casting. 
     The detailed description and the drawings or figures are supportive and descriptive of the disclosure, but the scope of the disclosure is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed disclosure have been described in detail, various alternative designs and embodiments exist for practicing the disclosure defined in the appended claims. Furthermore, the embodiments shown in the drawings or the characteristics of various embodiments mentioned in the present description are not necessarily to be understood as embodiments independent of each other. Rather, it is possible that each of the characteristics described in one of the examples of an embodiment may be combined with one or a plurality of other desired characteristics from other embodiments, resulting in other embodiments not described in words or by reference to the drawings. Accordingly, such other embodiments fall within the framework of the scope of the appended claims.