Patent Publication Number: US-2018043428-A1

Title: Unit Cell Titanium Casting

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 62/372626, filed on Aug. 9, 2016, which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to precision titanium casting. More specifically, the present invention relates to an apparatus and method for precision titanium casting utilizing induction heating. 
     Description of the Related Art 
     Various methods of titanium casting are well-known. One such method is investment casting which involves a lost wax procedure. 
     Vacuum electric arc smelting is another method in which a titanium ingot is melted by substantial heat generated by mutual discharging in a high current state by respectively using a titanium ingot crucible and a water-cooled copper crucible as a positive electrode and a negative electrode, thereby forming a molten liquid metal in the crucible and completing the casting of the titanium. 
     Another method is vacuum induction smelting in which an induction coil is wrapped outside a split-type water-cooled copper crucible. The electromagnetic force generated by the induction coil passes through a nonmetal isolation portion between splits of the copper crucible and then acts on a titanium ingot placed inside the crucible. Then the molten metal forms a molten metal liquid inside the crucible and the casting of the titanium is completed. 
     Vacuum induction smelting and vacuum electric arc smelting require the use of a water-cooled copper crucible which results in the loss of substantial heat. The actual power consumed is very little (only 20% to 30% of the power actually acts on the titanium). Furthermore, the preparation of the molding shell is very complex and time consuming, which adds to the costs. In the traditional casting technology, the operation time of a single furnace is usually 60 to 80 minutes, and the loading and discharge process requires the coordination of many people. In the traditional casting technology, the process from the preparation of the wax pattern to the clearing of the molding shell can take ten days. 
     Titanium is an extremely reactive metal. During melting via traditional casting processes, a water cooling environment is required. The molten titanium liquid will come into direct contact with water if the crucible cracks, resulting in a fierce reaction, or even explosion, which poses a great threat to production safety. 
     To solve the above problems, a new kind of titanium alloy induction melting vacuum suction casting device is urgently needed, to solve the problems with existing titanium alloy casting, such as low efficiency, high cost, complicated technology, heavy workload, difficulty with preparing high-quality molding shells, long cycle and potential hazard. 
     BRIEF SUMMARY OF THE INVENTION 
     Utilizing the two chamber casting system, one of the primary tenets is the use of a pressure differential in order to assist the evacuation of material from the crucible into the pattern mold. In order to truly optimize the filling of complex geometries, the physical properties of resulting parts, and the efficiency of the equipment, it is beneficial to vary the pressure differential utilized during the casting sequence. Optimally, the beginning of the cycle will have a minimal pressure differential between the outer chamber (containing the crucible) and the inner chamber (containing the pattern mold). This pressure differential is achieved through the use of a vacuum (to remove Oxygen and reduce pressure) and Argon (to replace any remaining Oxygen and increase pressure). Immediately prior to crucible evacuation the pressure in the inner chamber would be decreased; this will allow for additional pressure-assisted transition in order to allow the filling of complex geometries, while minimizing turbulent flow of molten Titanium, and also minimizing overall equipment cycle times. 
     One aspect of the present invention is a method for unit cell casting of titanium or titanium-alloys. The method monitoring a pressure of an internal chamber utilizing a first vacuum gauge. The method also includes monitoring a pressure of an external chamber utilizing a second vacuum gauge. The method also includes transmitting the pressure of the internal chamber and the pressure of the external chamber to a programmable logic controller (PLC. The method also includes evacuating an external chamber to create an evacuated external chamber wherein a ceramic crucible containing a titanium alloy ingot is positioned therein. The method also includes evacuating the internal chamber to create an evacuated internal chamber. The method also includes melting the titanium alloy ingot within the ceramic crucible utilizing induction heating generated by an induction coil positioned around the ceramic crucible. The method also includes injecting a pressurized gas into the evacuated external chamber to create a pressurized external chamber. The method also includes transferring the completely melted titanium alloy material into the mold from the crucible using a maximum pressure differential created between the external chamber and the internal chamber. The pressure of the internal chamber and the pressure of the external chamber are monitored and communicated to the PLC during the casting process, and wherein the PLC controls the casting process based on the pressure of the internal chamber and the pressure of the external chamber. 
     Another aspect of the present invention is a system method for unit cell casting of titanium or titanium-alloys. The system comprises an external chamber, a ceramic crucible positioned within the external chamber, an induction coil positioned around a bottom section of the ceramic crucible, an internal chamber positioned within the external chamber, and a mold positioned within the internal chamber. A first vacuum gauge positioned within the internal chamber. A second vacuum gauge positioned within the external chamber. A PLC in communication with the first vacuum gauge, the second vacuum gauge, and the induction coil. The external chamber is evacuated to create an evacuated external chamber wherein the ceramic crucible contains a titanium alloy ingot positioned therein. The internal chamber is evacuated to create an evacuated internal chamber. The titanium alloy ingot is melted within the ceramic crucible utilizing induction heating generated by the induction coil positioned around the ceramic crucible, wherein a pressure differential between the external chamber and the internal chamber is at a minimum. A pressurized gas is injected into the evacuated external chamber to create a pressurized external chamber. The titanium alloy material is completely transferred into the mold from the crucible using a maximum pressure differential created between the external chamber and the internal chamber. The pressure of the internal chamber and the pressure of the external chamber are monitored and communicated to the PLC during the casting process, and wherein the PLC controls the casting process based on the pressure of the internal chamber and the pressure of the external chamber. 
     The pressurized gas is preferably argon. The mold is preferably covered in a kaolin wool insulating material. The mold is preferably for a thin-walled golf club head. The mold is alternatively for an article having a wall thickness less than 0.250 inch. The induction melting time preferably ranges from 30 seconds to 90 seconds. The ceramic crucible is preferably composed of two yttria-based primary crucible layers, wherein a first primary crucible layer has a thickness ranging from 0.010 inch to 0.060 inch, and a second primary crucible layer has a thickness ranging from 0.001 inch to 0.020 inch. The ceramic crucible further comprises a silica based backup layer. The induction coil is preferably positioned around a bottom section of the ceramic crucible. The induction coil is alternatively positioned around an upper section of the ceramic crucible. 
     Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an illustration of a unit-cell casting system. 
         FIG. 2  is an isolated view of an interior chamber, crucible, induction coils and mold of the unit-cell casting system, showing placement of the induction coils at a lower section of the crucible. 
         FIG. 2A  is an isolated view of an interior chamber, crucible, induction coils and mold of the unit-cell casting system, showing placement of the induction coils at an upper section of the crucible. 
         FIG. 2B  is an isolated view of an interior chamber, crucible, induction coils and mold of the unit-cell casting system, showing an insulation material wrapped around the mold. 
         FIG. 3A  is an illustration of a technician pre-heating a mold in an oven. 
         FIG. 3B  is an illustration of a technician attaching the pre-heated mold to a lid of the internal container. 
         FIG. 3C  is an illustration of a technician attaching the lid to the internal container. 
         FIG. 3D  is an isolated view of the internal container. 
         FIG. 3E  is an isolated view of the lid of the internal container. 
         FIG. 3F  is an isolated view of the internal chamber of the internal container showing infrared heaters. 
         FIG. 4  is an illustration of a unit-cell casting system during an external chamber evacuation step. 
         FIG. 4A  is an illustration of a unit-cell casting system during an external chamber pressurization step. 
         FIG. 4B  is an illustration of a unit-cell casting system during an ingot melting step. 
         FIG. 5  is an illustration of a PLC unit and computer for a unit cell casting system. 
         FIG. 6  is a block diagram of a unit cell casting method. 
         FIG. 7  is an isolated view of a crucible for a unit cell casting system. 
         FIG. 8  is a flow chart of a method for unit cell titanium casting. 
         FIG. 9  is a flow chart of a method for unit cell titanium casting. 
         FIG. 10  is a flow chart of a method for unit cell titanium casting. 
         FIG. 11  is an illustration of a PLC unit, an operator&#39;s computer for a unit cell casting system, an internal chamber with monitoring connections. 
         FIG. 12  is an illustration of a PLC unit, an operator&#39;s computer for a unit cell casting system, an internal chamber with monitoring connections. 
         FIG. 13  is an isolated bottom plan view of an iris gate between the crucible and the mold. 
         FIG. 14  is an isolated bottom plan view of a scissor gate between the crucible and the mold, with the scissor gate partially closed. 
         FIG. 15  is an isolated bottom plan view of a gate with two doors between the crucible and the mold. 
         FIG. 16  is an isolated bottom plan view of a sliding gate between the crucible and the mold. 
         FIG. 17  is an illustration of a PLC unit, an operator&#39;s computer for a unit cell casting system, and a crucible over a connection with a gate that is operated by the PLC. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     During the casting process it is critical to ensure that the material be heated sufficiently and consistently in order to ensure proper flow into the pattern mold. Especially with the use of a bottom-fed/gravity flow system, having the ability to control the pour time will allow for optimum material properties in the finished part. In order to achieve this, a mechanical door or gate is utilized to evacuate the melting crucible at precisely the correct (and repeatable) moment during the cycle. The mechanics of the door itself are designed in various embodiments; sliding, scissor, iris, etc. as long as it is able to retain the material and provide a vacuum seal. This door is controlled through the use of a Programmable Logic Controller (PLC) and is preferably actuated based on time, temperature, or pressure of the system. The use of this feature allows for precise evacuation times providing consistent and optimum part quality. 
     As shown in  FIG. 1 , a unit cell titanium casting system  5  comprises an external container  44 , an internal container  39 , a vacuum mechanism  60 , a crucible  10 , an induction coil  15 , a coil electrical generation mechanism  25 , and a mold  30 . The external container  44  defines an external chamber  45 . The internal container  39  defines an internal chamber  40 . The vacuum mechanism  60  includes a vacuum line  71 , a vacuum connector  70  and pressure gauges  75   a  and  75   b . The vacuum mechanism  60  is utilized to evacuate and pressurize the external chamber  45  and the internal chamber  40  in order to create a pressure differential between the internal chamber  40  and the external chamber  45 . 
     The crucible  10  is preferably composed of a ceramic material. In a most preferred embodiment, the crucible  10  is composed of a first layer  11   a , a second layer  11   b  and a silica based third layer  11   c , as shown in  FIG. 7 . A metal ingot  20  is placed within the interior of the crucible  10 . The metal ingot  20  is preferably a titanium alloy material. The volume of the crucible  10  preferably corresponds to the amount of metal necessary for forming the article. The interior of the crucible  10  preferably has a diameter ranging from 15 centimeters (“cm”) to  90   c  m, more preferably from 35 cm to 60 cm. A height of the crucible  10  preferably ranges 30 cm to 200 cm, and more preferably from 60 cm to 100 cm. 
     A connection nozzle  27  is connected between a bottom opening (not shown) of the crucible  10  and an opening to the mold  30 . The connection nozzle  27  allows the melted metal material from the ingot  20  to flow into the mold  30  for casting of the article. Specifically, the size of connection nozzle  27  is determined based on the size and shape of the cavity of the mold  30 , and is preferably from 5 cm to 100 cm, and more preferably from 15 cm to 50 cm. 
     The induction coil  15  is wrapped around the crucible  10 . The induction coil  15  is energized to generate an electromagnetic force to melt the metal ingot  20  (e.g., titanium alloy ingot) within the crucible  10 . The coil electrical generation mechanism  25  provides the electricity to the induction coil  15 . As shown in  FIG. 2 , the induction coil  15  is wrapped around a bottom section  10   b  of the crucible  10 . This melts the bottom of the ingot  20  first. As shown in  FIG. 2A , the induction coil  15  is wrapped around an upper section  10   a  of the crucible  10 . This melts the top of the ingot  20  first. 
     In order to optimize the ability of the target material to seal around the port of a ceramic crucible  10 , the induction coil  15 is preferably centered on the upper third of the ingot  20 . This positioning allows the induction coil  15  to first act on the upper portion of the ingot  20  (melting the material from the top down), causing molten material to cascade around the still-solid ingot  20  and forming a seal before the electromagnetic forces of the induction coil  15  affect the remaining material. 
     Alternatively, in order to fully utilize the electromagnetic forces of the induction coil  15 , to include the electromagnetic stirring of the melt, the induction coil  15  is positioned towards the bottom  10   b  of the ceramic crucible  10 . This positioning allows for a uniform melt as molten material cascades onto itself and also increased homogeneity of the pour as the electromagnetic forces can better act on the molten material prior to it being evacuated from the crucible  10 . 
     Melting of the ingot  20  of titanium alloy is carried out in a vacuum condition for induction melting. The induction coil  15  is connected to the coil electrical generation mechanism  25 . 
     The ceramic crucible  10  is utilized for vacuum induction melting of the titanium alloy. The ceramic material does not interfere with the fielding effect of the electromagnetic force, and the electro-magnetic induction energy generated by the induction coil  15  is fully focused on melting the ingot of titanium alloy. 
     In an embodiment shown in  FIG. 2B , an insulating material  31  is wrapped around the mold  30 . During casting pattern molds are preheated prior to use in order to improve the flow of material into the mold itself and to better allow the mold  30  to fill completely. Due to the nature of titanium materials, and the melting process itself, the more that heat loss is minimized, the greater time the material has to flow and fill the mold  30  prior to solidification. To this end, pattern mold heat is retained through the use of an insulating material  31  (e.g.: Kaolin wool) thereby extending the useful period of the mold  30  prior to the pour and allowing for better fill, including filling of more difficult molds (e.g., thin walled castings). 
     As shown in  FIGS. 3A, 3B, 3C, 3D and 3E , the mold  30  is preheated in an oven  80 . During unit cell casting, pattern molds  30  are preheated prior to use in order to improve the flow of material into the mold  30  itself and to better allow the mold  30  to fill completely. Due to the nature of titanium materials, and the melting process itself, there is a likely correlation between the temperature of the mold  30  and the ability to fill complex and/or thin walled pattern molds  30 . Temperatures testing include 1050° C., 1060° C., 1100° C., 1150° C.,  1200  ° C., 1250° C. and 1260° C. The pre-heated mold is removed from the 80 and attached to a lid  35  of the internal container  39 . 
     In an alternative embodiment shown in  FIG. 3F , infrared heaters  50   a  and  50   b  are used to maintain the heat of the mold  30  within the internal chamber  40 . Due to the nature of titanium materials, and the melting process itself, the more that heat loss is minimized, the greater time the material can flow and fill the mold  30  prior to solidification. To this end, pattern mold heat is retained through the use of infrared heaters  50   a  and  50   b  placed within the internal walls of the internal chamber  40  of the internal container  39  in order to minimize pattern mold cool down and improve the ability to cast complex and/or thin-walled parts. 
       FIGS. 4, 4A and 4B  illustrate the casting process using a pressure differential between the external chamber  45  and the internal chamber  40  to assist in the flow of melted titanium alloy materials into a mold  30 . 
       FIG. 5  illustrates a programmable logic computer (“PLC”) and operator computer  91  utilized with the unit cell casting system  5 . 
       FIG. 6  is a block diagram of a unit cell casting method  600 . At step  601 , an ingot  20  is prepared for casting. The single ingot  20  is utilized to manufacture a single article such as a golf club head  29 . As opposed to manufacturing multiple articles in a single process, which results in the loss of material, the present invention manufactures only a single article in each process. At step  602 , the mold  30  is preheated in an oven. At step  603 , the external chamber  45  is evacuated. At step  604 , the external chamber  45  is pressurized with an argon gas. At step  605 , the internal chamber  40  is evacuated. At step  606 , the induction coil  15  is energized and at step  607  the ingot  20  is melted within the crucible  10 . At the step  608 , the melted material flows into mold  30 . At step  609 , the de-molding process occurs. At step  610 , the article (golf club head)  29  is finished. A frequency generated in the induction coil ranges from 1 kilo-Hertz to 50 kilo-Hertz, and a power ranges from 15 kilo-Watts to 50 kilo-Watts. An atmospheric pressure of the evacuated internal chamber ranges from 3×10 −2  atmosphere to 9.87×10 −7  atmosphere. An atmospheric pressure of the evacuated internal chamber ranges from 9.87×10 −7  atmosphere to 9.87×10 −13  atmosphere. 
     As shown in  FIG. 7 , the first layer  11   a  and the second layer  11   b  are preferably composed of yttrium oxide and other materials. Yttrium oxide is highly inert to titanium in a high-temperature environment resulting in no chemical reaction between the two materials. Yttrium oxide also isolates the ceramic material from the titanium during the melting process to prevent reaction between them to ensure the smooth melting of the titanium-alloy. The third layer  11   c  of the crucible  10  is preferably composed of silicon dioxide and other materials. The silicon dioxide resists the metallic expansion and thermal stress during the melting process to ensure strength of the crucible. 
     A preferred thickness of the first layer  11   a  is from 0.5 mm to 1.5 mm and the preferred thickness range of the crucible  10  is from 5 mm to 15 mm. 
     A method  800  for unit cell casting of titanium or titanium-alloys is shown in  FIG. 8 . At block  801 , a pressure of an internal chamber is monitored utilizing a first vacuum gauge. At block  802 , a pressure of an external chamber is monitored utilizing a second vacuum gauge. At block  803 , the pressure of the internal chamber and the pressure of the external chamber are transmitted to a programmable logic controller (PLC). At block  804 , a mold is positioned within the internal chamber. At block  805 , an external chamber is evacuated to create an evacuated external chamber having a pressure no greater than 3×10 −2  atmosphere, wherein a ceramic crucible containing a titanium alloy ingot is positioned therein. At block  806 , the internal chamber is evacuated to create an evacuated internal chamber having a pressure no greater than 3×10 −2  atmosphere, wherein the external chamber and the internal chamber have an equal pressurization. At block  807 , the titanium alloy ingot is melted within the ceramic crucible utilizing induction heating generated by an induction coil positioned around the ceramic crucible. At block  808 , the completely melted titanium alloy material is transferred into the mold from the crucible using a pressure equalization between the external chamber and the internal chamber. A pressure equalization is maintained between the external chamber and the internal chamber during the melting of the titanium alloy ingot. The pressure of the internal chamber and the pressure of the external chamber are monitored and communicated to the PLC during the casting process, and wherein the PLC controls the casting process based on the pressure of the internal chamber and the pressure of the external chamber. 
     A method  900  for unit cell casting of titanium or titanium-alloys is shown in  FIG. 9 . At block  901 , a pressure of an internal chamber is monitored utilizing a first vacuum gauge. At block  902 , a pressure of an external chamber is monitored utilizing a second vacuum gauge. At block  903 , the pressure of the internal chamber and the pressure of the external chamber are transmitted to a programmable logic controller (PLC). At block  904 , a mold is positioned within the internal chamber. At block  905 , an external chamber is evacuated to create an evacuated external chamber having a pressure no greater than 3×10 −2  atmosphere, wherein a ceramic crucible containing a titanium alloy ingot is positioned therein. At block  906 , the internal chamber is evacuated to create an evacuated internal chamber having a pressure no greater than 3×10 −2  atmosphere, wherein the external chamber and the internal chamber have an equal pressurization. At block  907 , the titanium alloy ingot is melted within the ceramic crucible utilizing induction heating generated by an induction coil positioned around the ceramic crucible. At block  908 , a pressurized gas is injected into the evacuated external chamber to create a pressurized external chamber with a pressure in excess of 1 atm, wherein the pressure differential between the external chamber and the internal chamber is maximized. At block  909 , the completely melted titanium alloy material is transferred into the mold from the crucible using a pressure equalization between the external chamber and the internal chamber. A high pressure differential in maintained between the external chamber and the internal chamber during the transfer of the melted titanium alloy material. The pressure of the internal chamber and the pressure of the external chamber are monitored and communicated to the PLC during the casting process, and wherein the PLC controls the casting process based on the pressure of the internal chamber and the pressure of the external chamber. 
     A method  1000  for unit cell casting of titanium or titanium-alloys is shown in  FIG. 10 . At block  1001 , a mold is positioned within an internal chamber of a casting chamber. At block  1002 , an external chamber is evacuated to create an evacuated external chamber wherein a ceramic crucible containing a titanium alloy ingot is positioned therein. At block  1003 , the internal chamber is evacuated to create an evacuated internal chamber having a pressure no greater than 3×10 −2  atmosphere. At block  1004 , the titanium alloy ingot is melted within the ceramic crucible utilizing induction heating generated by an induction coil positioned around the ceramic crucible, wherein the external chamber and the internal chamber are at an equal pressurization. At block  1005 , a pressurized gas is injected into the evacuated external chamber to create a pressurized external chamber with a pressure in excess of  1  atmosphere. At block  1006 , a high pressure differential is utilized between the external chamber and the internal chamber to flow the completely melted titanium alloy material into the mold from the crucible. 
       FIG. 11  illustrates a PLC  90 , an operator&#39;s computer  91  and an apparatus  5  for a system for unit cell titanium casting. 
       FIG. 12  illustrates a PLC  90 , an operator&#39;s computer  91  and an internal chamber with an optical pyrometer for a system for unit cell titanium casting. The optical pyrometer monitors the temperature of the internal chamber. 
       FIG. 13  is an isolated bottom plan view of an iris gate  185  between the bottom of the crucible  10   d  and the mold. The iris gate  185  is attached to the connection nozzle  27 . Two hinges  185   a  and  185   b  allow for the swing opening of the iris gate body  185   c  to permit the flow of the melted titanium into the mold. 
       FIG. 14  is an isolated bottom plan view of a scissor gate  186  between the bottom of the crucible  10   d  and the mold, with the scissor gate partially closed. The scissor gate  186  is attached to the connection nozzle  27 . The scissor gate  186  compresses inward to permit the flow of the melted titanium into the mold. 
       FIG. 15  is an isolated bottom plan view of a gate  187  between the bottom of the crucible  10   d  and the mold. The gate  187  is attached to the connection nozzle  27  by hinges  187   a - d . Two doors  187   e  and  187   f  swing open to permit the flow of the melted titanium into the mold. 
       FIG. 16  is an isolated bottom plan view of a sliding gate  188  between the bottom of the crucible  10   d  and the mold. The sliding door  188   a  is in an open position. 
       FIG. 17  is an illustration of a PLC unit, an operator&#39;s computer for a unit cell casting system, and a crucible over a connection with a gate  185  that is operated by the 
     PLC  90 . 
     Those skilled in the pertinent art will recognize that materials other than titanium and titanium alloy may be cast in the unit cell casting system without departing from the scope and spirit of the present invention. 
     From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes, modifications and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claims. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claims.