Not Applicable
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.
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.
Utilizing the two chamber casting system, one of the primary tenets is the use of a crucible in order to contain the target material during melt and prior to evacuation into the pattern mold. In order to accelerate the melting of the target material and reduce cycle times, it is necessary to preheat the crucible to higher temperatures (>500 C). This causes a faster heating and subsequent melting of the target material thus reducing the time necessary to evacuate the material from the crucible into the pattern mold. The accelerated process also reduces the potential for reaction of the target material and may allow for more complete fill of complex geometries.
One aspect of the present invention is a method for unit cell casting of titanium or titanium-alloys. The method includes positioning a mold within an internal chamber. 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 having a pressure no greater than 3×10−2 atmosphere. The method also includes injecting a pressurized gas into the evacuated external chamber to create a pressurized external chamber with a pressure in excess of 1 atm. The method also includes melting the titanium alloy ingot within the ceramic crucible utilizing induction heating generated by an induction coil, wherein a position of the induction coil begins at a upper third of the titanium alloy ingot and during the melting of the titanium alloy ingot the position of the induction coil is lowered relative to the titanium alloy ingot to terminate at a bottom of the titanium alloy ingot. The method also includes transferring the completely melted titanium alloy material into the mold from the crucible using a pressure differential created 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 PLC controls power to the induction coil to superheat the titanium alloy ingot in the ceramic crucible, and the PLC also controls the positioning of the induction coil. The placement of the induction coil first acts on the upper portion of the ingot melting the material from the top down, causing molten material to cascade around the still-solid ingot and forming a seal before the electromagnetic forces of the induction coil affect the remaining 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.
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 an upper third of the ingot within the ceramic crucible, an internal chamber positioned within the external chamber, 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 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. Placement of the induction coil first acts on the upper portion of the ingot melting the material from the top down, causing molten material to cascade around the still-solid ingot and forming a seal before the electromagnetic forces of the induction coil affect the remaining material. The external chamber is evacuated to create an evacuated external chamber wherein the ceramic crucible contains a titanium alloy ingot positioned therein. A pressurized gas is injected into the evacuated external chamber to create a pressurized external 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 power for the induction coil is commences at a first power level of 15 kiloWatts and increases to a second power level greater than 50 kiloWatts. The internal chamber is evacuated to create an evacuated internal 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.
Yet another aspect of the present invention is a method for unit cell casting of titanium or titanium-alloys. The method 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 having a pressure no greater than 3×10−2 atmosphere. The method also includes melting the titanium alloy ingot within the ceramic crucible utilizing induction heating generated by an induction coil wherein a position of the induction coil begins at a upper third of the titanium alloy ingot and during the melting of the titanium alloy ingot the position of the induction coil is lowered relative to the titanium alloy ingot to terminate at a bottom of the titanium alloy ingot. The method also includes injecting a pressurized gas into the evacuated external chamber to create a pressurized external chamber with a pressure in excess of 1 atmosphere, wherein the pressure differential is at a maximum. The method also includes utilizing a high pressure differential between the external chamber and the internal chamber to flow the completely melted titanium alloy material into the mold from the crucible.
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.
In the two chamber casting system, when utilizing Titanium as the target material to melt and fill a pattern mold or molds, there can be difficulties to fill those molds due to the relative viscosity of titanium. In order to overcome the challenge of completely filling the pattern mold, the titanium is heated to a temperature past its melt point and preferably the material is superheated. This is done in the two-chamber casting system type of equipment where the crucible is not cooled (as in typical casting practices). Heating the material past its melt point and approaching and/or exceeding the superheated state increases the fluidity of the material and allows the opportunity to fill complex and/or thin-wall pattern molds.
In the two chamber casting system, the target material (placed in the crucible, and subsequently melted through the use of an induction coil) is typically a single ingot cut from bar stock utilized at room temperature. In order to accelerate the melting of the target material and reduce cycle times, it is necessary to preheat the ingot to higher temperatures (>300 C). This causes a faster heating and subsequent melting of the target material thus reducing the time necessary to evacuate the material from the crucible into the pattern mold. The accelerated process also reduces the potential for reaction of the target material and may allow for more complete fill of complex geometries.
Utilizing the two chamber casting system, one of the primary tenets is the use of a crucible in order to contain the target material during melt and prior to evacuation into the pattern mold. In order to reduce operating costs while still allowing the electromagnetic forces from the induction coil to act upon the target material, the crucible should be formed of a molded crucible formed of >90% Yttria. This will allow for the crucible to be reused and also minimize any reaction between the crucible and the target material during melt.
Utilizing the two chamber casting system, one of the primary tenets is the use of a crucible in order to contain the target material during melt and prior to evacuation into the pattern mold. In order to reduce operating costs while still allowing the electromagnetic forces from the induction coil to act upon the target material, the crucible should be formed of a molded crucible formed of >90% Zirconia. This will allow for the crucible to be reused and reduce overall cost due to crucible usage and materials.
Utilizing the two chamber casting system, one of the primary tenets is the use of a crucible in order to contain the target material during melt and prior to evacuation into the pattern mold. In order to reduce operating costs while still allowing the electromagnetic forces from the induction coil to act upon the target material, the crucible is preferably formed of a molded crucible formed of Yttria and infused with Barium. This will provide the benefits of a molded Yttria crucible (reusable, low reactivity) with the benefit of the target material being less apt to stick to the surface thus providing better evacuation and higher chance of reuse.
As shown in
The crucible 10 is preferably composed of a ceramic material. In a most preferred embodiment, the crucible 10 is composed of a first layer 11a, a second layer 11b and a silica based third layer 11c, as shown in
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
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 10b 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
As shown in
In an alternative embodiment shown in
As shown in
A preferred thickness of the first layer 11a 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
A method 900 for unit cell casting of titanium or titanium-alloys is shown in
A method 1000 for unit cell casting of titanium or titanium-alloys is shown in
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.
The present application claims priority to U.S. Provisional Patent Application No. 62/440,223 filed on Dec. 29, 2016, and U.S. Provisional Patent Application No. 62/440,338 filed on Dec. 29, 2016, each of which is hereby incorporated by reference in its entirety.