Patent Application
20140271341
This disclosure relates generally to manufacturing a casting. More specifically, this disclosure relates to casting against gravity and quenching castings.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Casting against gravity or counter-gravity casing can be a mold filling technique in which a pressure difference is created between a metallic melt and within a mold. The mold is held above the metallic melt, and cavity within the mold positioned to be in fluid communication with the metallic melt. The pressure within the mold is lowered relative to that around the metallic melt which causes the metallic melt to move against gravity and into the mold. The metallic melt can be solidified within the mold cavity prior to removing the pressure difference. Since the solidification of the cast components occurs while under pressure, the solidification rate may be limited by being air cooled.
According to one aspect of the present disclosure, a method of manufacturing a casting is provided. The method can include heating a ceramic mold comprising a gate inlet, and melting a metallic composition. The method can also include presenting the ceramic mold to a casting station such that the gate inlet is in fluid communication with the molten metallic composition, and casting against gravity the molten metallic composition into the heated mold through the gate inlet. Furthermore, the method can include rotating the mold to position with the gate inlet in an upward direction while the metallic composition is at least partially molten within the mold, and quenching the molten metallic composition in a liquid quench medium to solidify the molten metallic composition within the mold.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. It should be understood that throughout the description, corresponding reference numerals indicate like or corresponding parts and features.
The present disclosure generally relates to methods of manufacturing castings and castings manufactured by such methods. The methods and castings made and used according to the teachings contained herein are described through the present disclosure in conjunction with investment casting aluminum in order to more fully illustrate the concept. The use of the methods in conjunction with other types of castings and components is contemplated to be within the scope of the disclosure.
According to certain aspects of the present disclosure, a method of manufacturing a casting is provided.
Referring to
The ceramic mold 202 can be at least partially porous to gas (e.g., gas permeable). The ceramic mold 202 can be produced by an investment process. For example, the ceramic mold 202 can be formed from lost wax process where a wax pattern assembly is dipped in a ceramic slurry, coated with refractory particles, dried, and repeated to build up a ceramic shell. The ceramic slurry can be, for example, a suspension of refractory powder such as zircon, alumina, or silica in a liquid binder. The refractory particles that are coated onto the ceramic slurry can be, for example, zircon, alumina, or silica. The wax pattern can then be thermally removed, and the ceramic shell can be fired to form the ceramic mold 202. The walls of the ceramic mold 202 can include porosity and can be permeable to gas while being impermeable to molten metal. Furthermore, as further described below, the ceramic mold 202 can have relatively good thermal conduction/convection in order to control heat removal from a metallic composition cast into the ceramic mold 202.
In operational block 104 of
The metallic composition can include various elements that form an alloy. For example, a largest constituent of the metallic composition can be aluminum. Exemplary aluminum alloys include 201/A201, 203, 355/C355, A206, A356, A357, D357, E357 and F357. Other alloys that include a different largest constituent such as iron, titanium, nickel, etc. can be cast with the methods described herein. For example, melting method, atmospheric control, quenching media, etc. can be modified or adjusted depending on the metallic composition.
In operational block 106 of
The casting station 304 can include a mold chamber 210. The mold chamber 210 can be configured to be capable of maintaining a vacuum atmosphere (e.g., subambient pressure) within the mold chamber 210. A vacuum pump can be in gaseous communication with the mold chamber 210 configured to create a vacuum in the mold chamber 210. For example, the mold chamber 210 can include a vacuum inlet 211 that is in gaseous communication with a vacuum. Furthermore, the robot arm 306 can include a vacuum port that removably couples to the vacuum inlet 211. As describe below, the mold chamber 210 can be configured to be rotatable. For example, mold chamber 201 may be a separate component. The robot arm 306 can be used to rotate the mold chamber 210. Thus, the robot arm 306 can be used to move the mold chamber 210 and provide a vacuum to the mold chamber 210.
The ceramic mold 202, after being pre-heated, can be loaded into the mold chamber 210. The mold chamber 210 can be configured to be opened and closed so that the mold 202 can be loaded and removed from the mold chamber 210. The mold 202 can be loaded into the mold chamber 210 so that the gate inlet 204 can be in fluid communication with an opening 212 of the mold chamber 210 such as on a side or a bottom of the mold chamber 210. The opening 212 can include a seal to provide an air tight seal where the gate inlet 204 and the mold chamber 210 engage. As shown in
In operational block 108 of
In order to cast the molten metallic composition 214 into the mold 202, the gate inlet 204 and/or the filling tube 213 can be placed into fluid communication with the molten metallic composition 214. For example, the filling tube 213 can be inserted into the molten metallic composition 214. While the filling tube 213 is in the molten metallic composition 214, the gate inlet 204 can be pointed in a non-upward direction. For example, the gate inlet 204 can be at or near a bottom of the mold 202 to reduce turbulence during casting. The filling tube 213 can be inserted into the molten metallic composition 214 with the robot arm 306. For example, the robot arm 306 can move and position the mold chamber 210 so that the filling tube 213 is in a downward direction, and the robot arm 306 can insert the filling tube 213 into the molten metallic composition 214. After the gate inlet 204 is in fluid communication with the molten metallic composition 214, the melting chamber 217 can be gaseously isolated from the mold chamber 210. For example, the molten metallic composition 214 in the gate inlet 204 and/or the filling tube 213 can prevent gas from the melting chamber 217 from entering the gate inlet 204 and/or the filling tube 213. Furthermore, the gate inlet 204 and/or the filling tube 213 can be impermeable to gas.
As described above, a vacuum pump can be in gaseous communication with the mold chamber 210. After the gate inlet 204 is in fluid communication with the molten metallic composition 214, a vacuum can be created around the heated mold 202 to pull the molten metallic composition 214 into the gate inlet 204. The pressure in the mold chamber 210 can be decreased relative to pressure in the melting chamber 217 and around the molten metallic composition 214. Thus, a pressure differential can be created between a mold chamber 210 containing the heated mold 202 and the melting chamber 217 containing the molten metallic composition 214 such that the melting chamber 217 comprises a pressure greater than a pressure in the mold chamber 210 that results in the molten metallic composition 214 flowing against gravity and into the heated mold 202. For example, the pressure difference can cause the molten metallic composition 214 to flow into the gate inlet 204 and into the mold cavities 208. The pressure within the mold chamber 210 can be, for example, decreased to between about 20 kPa and about 70 kPa. When the pressure within the mold chamber 210 is decreases, the melting chamber 217 can maintain a pressure of about 80 kPa to about atmospheric. The pressure difference between the mold chamber 210 and the melting chamber 217 can be about 20 kPa to about 80 kPa. Furthermore, the pressure within the melting chamber 217 can be increased when the pressure within the mold chamber 210 is decreased to further increase the pressure difference. For example, the pressure in the melting chamber 217 can be increased to above atmospheric pressure. Casting against gravity can result in lower turbulent flow of the molten metallic composition which can result in reduced oxide content compared to gravity filled processes.
Described above is one example method of casting against gravity. Other methods of casting against gravity are also compatible with the present disclosure. For example, casting against gravity can include pumping the molten metallic composition against gravity into the heated mold. In a further example, casting against gravity can include injecting (e.g., upward injecting) the molten metallic composition against gravity into the heated mold.
After the molten metallic composition 214 has filled the cavities 208, the gate inlet 204 and/or the filling tube 213 can be removed from being in fluid communication with the molten metallic composition 214 that is in the crucible 216 while the pressure within the mold chamber 210 remains under vacuum to keep the molten metallic composition 214 within the cavities 208. Some molten metallic composition 214 may flow out of the gate inlet 204 and/or the filing tube 213. The gate inlet 204 can be exposed to air and cool more rapidly than the rest of the ceramic mold 202 that is within the mold chamber 210. Thus, the metallic composition 214 in the gate inlet 204 solidify while the remaining metallic composition 214 in the ceramic mold 202 remains molten which can prevent the molten metallic composition 214 from flowing out the gate inlet 204.
In operational block 110 of
In operational block 112, the method 100 can include quenching the molten metallic composition 214 in a liquid quench medium to solidify the molten metallic composition 214 within the mold 202. For example, the robot 306 can move the ceramic mold 202 to a solidification station 308. The ceramic mold 202 may be moved to the solidification station 308 while the mold 202 is still within the mold chamber 210. The mold chamber 210 may then be completely removed or partially removed from the mold 202. For example, portions of the mold chamber 210 may be separated from other portions of the mold chamber 210 so that some portions of the mold chamber 210 may remain with the mold 202 out of convenience. For example, a portion of the mold chamber 210 that mold 202 rests on may remain. Thus, at least a portion of the mold chamber 210 may go through the quenching process with the mold 202.
Although, the molten metallic composition 214 may partially solidify, the metallic composition 214 can remain at least partially molten until the metallic composition 214 is quenched. For example, as described above, the metallic composition 214 in the gate inlet 204 may solidify before quenching while the metallic composition 214 in the mold cavity 208 may remain molten. In addition, the ceramic mold 202 may be rapped or covered with a thermally insulating material prior to being placed into the mold chamber 210 to reduce the cooling rate of the ceramic mold 202 and the molten metallic composition 214 while the mold transitions from casting station 304 to the solidification station 308. The thermally insulating material can then be removed prior to quenching the molten metallic composition 214.
Referring to
The solidification rate of the metallic composition can be substantially the same as the submersion rate or the solidification rate may be different from the submersion rate. For example, if the mold 202 is submerged at a relatively low rate, the solidification rate may be substantially the same as the submersion rate. If the mold 202 is inserted at a relatively high rate, the solidification rate may be less than the submersion rate. The mold 202 may be submerged into the quench medium 502 at a rate such that the quench medium 502 remains behind a solidification front of the metallic composition. For example, the metallic composition can be cooled at a rate of at least about 10° C./s or cooled at a rate of between about 10° C./s and about 50° C./s until solidification completes during the quenching. Furthermore, the mold 202 can be maintained within the quench medium 502 after solidification in order to maintain a cooling rate higher than that of air cooling. For example, a desired microstructure may be able to be obtained with a higher cooling rate after solidification such as ensuring that dissolved constituents of an alloy remain in solution. For example, aluminum alloys may be quenched until the alloy reaches a temperature below 300° C. Using the liquid quench medium 502 to quench the casting can provide additional control of the solidification rate and less variation between castings compared to air cooling.
The liquid quench medium 502 can comprise a polymer. For example, the polymer can include polyalkylene glycol, sodium polyacrylate, polyvinyl pyrolidone, polyethyl oxazoline, poly-oxyethylene glycol or a combination thereof. Such polymers can be aqueous polymers and the quench medium 502 can also include water. For example, the liquid quench medium 502 may comprise about 5 weight percent to about 30 weight percent of the polymer. The remainder of the liquid quench medium 502 can be water. The composition of the liquid quench medium 502 can be selected to provide a desired quench rate. In one example, the liquid quench medium 502 is or includes Aqua-Quench® C polymer quenchant from Houghton™ (Norristown, Pa.). In addition, the liquid quench medium 502 can be agitated during quenching to increase the quench rate. Furthermore, other liquid quench mediums 502 can be used such as non-polymer quenchants such as oil. Furthermore, the material of the ceramic mold 202 can be selected to have a thermal conductivity to provide a desired cooling rate of the metallic composition. For example, a ceramic mold 202 that has a relatively higher thermal conductivity can result in a higher cooling rate of the metallic composition.
After the metallic composition has solidified, the mold 202 can be removed from the quench medium 502. The mold 202 can then be removed from the metallic composition, and the cast components can be removed from the gating and cleaned. The cast components may then go through various post-casting processes such as inspection and heat treatment.
The foregoing description of various forms of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications or variations are possible in light of the above teachings. The forms discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various forms and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
