Patent Application
20240100591
The present invention relates generally to die casting, and more specifically to a method and system for the cooling and purging processes during die casting.
Die casting is the injection of molten metal under high pressure into a steel mold, interchangeably referred to as a die, for the purposes of rapid manufacturing at rapid production rates. The molten metal is most often a non-ferrous alloy, which are used because the best performance for die-cast products is gained through a blend of materials. Some typical alloys that are used for die casting are aluminum alloys, magnesium alloys and zinc alloys, which contain other elements such as silicon.
Two methods can be used to inject molten metal into a die; cold chamber and hot chamber. A schematic illustration of a typical cold chamber die casting machine 10 is shown in
The die casting machine 10 further includes a pressure chamber 20 through which molten metal from a supply 22 is delivered or injected into the mold 12 using a plunger 24. One or more shot sleeves 26 in the cover half 14 allow molten metal to enter the die and fill the part cavity 18. When the pressure chamber 20 is filled with molten metal, the plunger 24 starts traveling forward and builds up pressure, thereby forcing the metal to flow though the shot sleeve 26 to the part cavity 18. After the metal has solidified, the plunger 24 returns to its initial position, and the ejector half 16 of the die opens for the part or casting to be removed from the mold 12. Ejector pins 27 are used to push the casting out of the ejector half 16 of the mold 12. This process is referred to as a single casting cycle. Multiple casting cycles can be completed during a die casting operation.
A schematic illustration of a typical cold chamber die casting mold 12 is shown in
Cooling lines 36 run throughout the mold 12, through which coolant, such as water or oil flows to aid in the removal of heat from the mold 12. There are a number of individual cooling lines 36 that are responsible for cooling different parts of the casting or shot. The number of cooling lines 36 in a mold varies according to the size of the mold. For example, a small mold may have fifteen cooling lines, while a large mold may have over a hundred cooling lines. The cooling lines 36 are all in communication with a coolant flow system (not shown), from which coolant is delivered to the cooling lines, and to which coolant returns after it flow through the cooling lines. Many coolant flow systems for dies are part of a plant-wide water system. Other coolant flow systems are “closed-loop” systems, in which coolant is only cycled through the coolant flow system.
The casting can be divided into multiple heat flow zones that are cooled by one or more cooling lines 36. The heat flow zones are generally indicated by the dotted boxes on
There are primarily three critical die-casting process control requirements. The first requirement relates to the timing and function of the die casting machine. The timing of the opening and closing of the mold must be closely managed during the process to sequence operations such as injecting metal into the part, dealing with moving slides, making any intricate details in the casting, and extracting the part. The timing of these and other operations can be controlled to optimize the production rate and quality of the castings.
The second requirement relates to the injection processes at the shot end of the die casting machine. The injection processes, both from the standpoint of hardware and software, have been developed over time to optimize the control of injecting the liquid metal into the mold. Injection speed, injection pressure, and flow rate are all involved in the control of the injection process and can be taken into account during the design of the die casting process. Technologies have been developed to address the first two requirements in terms of machine design and shot end design to manage the first two problems that die casters have dealt with.
The third requirement relates to the thermal design, monitoring and control of the die casting process, including temperature detection and the removal of heat from the mold. Thermal design encompasses designing the cooling system of a die casting machine, which includes determining the number of cooling lines, the placement of each cooling line relative to the part cavity, the depth of each cooling line relative to the die surface, using the appropriate size, i.e. diameter, of cooling line, and determining the appropriate flow rate of each cooling line. Thermal monitoring refers to monitoring temperature and heat during the actual use of the die. Thermal control encompasses taking the information gathered from thermal monitoring and responding to that information, with respect to the intended thermal design.
Thermal design has historically been haphazard in the engineering of die casting processes. This is partly because the mathematics involved in thermally designing a die can be complex.
Thermal monitoring and control has to be almost non-existent in the die casting industry, although a few attempts have been made in the field to monitor temperatures and flow rates. Some dies employ simple flow monitoring devices that are essentially mechanical flow meters to monitor the flow rate of coolant through cooling lines.
From a theoretical standpoint, the thermocouples can be used to determine the die surface temperature. Typically, a thermocouple is placed by drilling a hole to a location between the die surface and the cooling line surface, usually approximately halfway between the die surface and the cooling line surface. In use, the die surface temperature may be as high as 700 to 800 degrees Fahrenheit, while the cooling line surface temperature may be 100 degrees, and there may be less than one inch between the die surface and the water line surface. Therefore, a steep thermal gradient exists between the die surface and the water line surface, and the thermocouple is located within this steep thermal gradient. The location of the thermocouple within the temperature gradient, i.e. the distance of the thermocouple from the die surface, is used to determine the temperature at the die surface.
One problem with using thermocouples to monitor temperature lies in accurately placing the thermocouple at a desired location. Thus far, thermocouples have proved unreliable in determining the die surface temperature. Because it is difficult to drill in a straight line though the mold, it is almost impossible to know the exact location of the thermocouple within the temperature gradient. This is highly undesired, since even small deviations from the planned location of the thermocouple can result in large inaccuracies in temperature. For example, if the end of the drilled hole is off by 1/10 inch in either direction, the location of the thermocouple within the temperature gradient may cause a +/−25 to 50 degree Fahrenheit variation in the temperature measured.
Another problem associated with using thermocouples to monitor temperature are in their physical functionality. Thermocouples require adequate contact with the mold for accurate thermal measurement, but thermocouples are often difficult to seat properly within the drilled hole. J- and K-type thermocouples, the type of thermocouples used in die casting processes, do not have a high level of accuracy when it comes to die casting process, because they have a read error from 1 to 2.5%. Thermocouples often can break and must be replaced. Thermocouples have wires that come out of the die that must be plugged into a box to measure the temperature from the thermocouple, and these wires can be easily cut or otherwise damaged. Die setup can vary from 30 minutes to eight hours, and the list of items that must be completed in the setup is on the order of 30 to 100 different specific things that must be done to remove a mold and put a new mold into the die. Adding to that process by having to connect and verify the function of thermocouples is not very desirable.
Yet another problem associated with using thermocouples to monitor temperature is that thermocouples can only be used in select areas within the mold. Areas such as the biscuit, the runner system, the overflows, and slides cannot be fitted with thermocouples, and so the temperature of these areas of the mold are not monitored.
Thermal control using information supplied by thermocouples in past die casting systems has been rudimentary at best. The data supplied by thermocouples can be tracked and used for correlation with product quality. Some die casting systems are configured to turn coolant flow on or off based upon thermocouple readings, in which case there is no respect for the heat removed from the mold. One issue with this practice is that it can induce some thermal variation into the die casting process because there is a lag between the temperature the thermocouples are detecting and the temperature at the surface of the mold. Turning coolant flow on and off creates a sinusoidal temperature variation at the mold surface.
Another problem with current die casting thermal monitoring, and control is that little emphasis has been given to dimensional accuracy and precision in relation to gas porosity defects. The die casting process has long been considered a net shape process, but not an accurate one. The reason behind the poor dimensional accuracy and precision is that the injection temperature of the liquid metal varies in different sections of the casting, and the casting is ejected at an inconsistent temperature, the shrinkage that the casting undergoes will be inconsistent as well since the entire casting has to cool down to ambient temperature. For example, if one section of the casting is at a temperature of 800 degrees Fahrenheit at ejection, and another section of the casting is at 300 degrees Fahrenheit at ejection, the section at 800 degrees Fahrenheit will undergo more shrinkage than the section at 300 degrees Fahrenheit. This inconsistent shrinkage will create distortion and dimensional inaccuracy in the casting, which will force the utilization of machining operations to achieve reasonable dimensional control.
Another problem associated with poor thermal monitoring and control occurs during the process of ejecting the casting from the mold. If there is a “hot spot” in the die, i.e. a portion of the die that retains more heat than the rest of the die, ejection is delayed because that areas of the casting must cool longer than the rest of the casting, which means that the remainder of the casting will be cooler than it needs to be for ejection. When the casting cools too long within the mold, it can contract around details in the die, and may then require significant force to eject the casting, which can cause distortion or leaking of the casting. Waiting for the portions of the casting near the “hot spots” to cool also results in longer cycle times.
“Hot spots” in the die may also cause soldering to occur, which is when the temperature of a portion of the die is so high that the die spray burns off and the casting sticks inside the part cavity. The casting may still be ejected, but some of the casting material may stick to the die and oxidize.
In the drawings:
Aspects of this disclosure are related to a method and system of detecting a leak and performing an air purge of a mold used during a casting process. At least aspects of the detection of the leak and the air purge methods and systems can be utilized in tandem with or independently from one another. As a non-limiting example, the casting process can be the casting process shown and described in
As used herein, the term “upstream” refers to a direction that is opposite the fluid flow direction, and the term “downstream” refers to a direction that is in the same direction as the fluid flow. The term “fore” or “forward” means in front of something and “aft” or “rearward” means behind something. For example, when used in terms of fluid flow, fore/forward can mean upstream and aft/rearward can mean downstream.
Furthermore, as used herein, the term “set” or a “set” of elements can be any number of elements, including only one.
Further yet, as used herein, the term “fluid” or iterations thereof can refer to any suitable fluid that is used during the casting process such as, but not limited to, a liquid (e.g., water or a molten metal) or a gas (e.g., air).
Connection references (e.g., attached, coupled, secured, fastened, connected, and joined) are to be construed broadly and can include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to one another. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto can vary.
The casting system 100 includes a gas inlet 104, a water inlet 106 and a fluid outlet 130. The gas inlet 104 is any suitable inlet configured to supply a fluid in gaseous form to the casting system 100. As a non-limiting example, the gas inlet 104 can be an air inlet that supplies air (e.g., ambient pressurized air) to the casting system. The water inlet 106 and the gas inlet 104 are each selectively and independently fluidly coupled to the mold 102 via a first valve 110 and a second valve 108, respectively. A first check valve 112 is provided downstream of the second valve 108 to ensure a fluid within the casting system 100 downstream of the first check valve 112 does not flow backwards and into the second valve 108. The first valve 110 is directly fluidly coupled to a first branch 134 and a second branch 136. A second check valve 114 is provided downstream of the first valve 110 along the first branch 134 to ensure a fluid within the casting system 100 downstream of the second check valve 114 does not flow backwards and into the first valve 110. A third check valve 116 is provided downstream of the first valve 110 along the second branch 136 to ensure a fluid within the casting system 100 downstream of the third check valve 116 does not flow backwards and into the first valve 110. While illustrated as including the first check valve 112, the second check valve 114 and the third check valve 116, it will be appreciated that the casting system 100 can include any number of check valves provided along any suitable portion of the casting system 100. It will be further appreciated that the casting system 100 can be formed without any check valve.
A switch 118 can be provided along the second branch 136 downstream of the second check valve 114. The switch 118 is a normally-off switch that can be latched or otherwise closed when water flows through the second branch 136 and through the third check valve 116.
The first branch 134 and the second branch 136 meet at a water junction 138 downstream the second check valve 114 and the third check valve 116. A third valve 120 is provided downstream of and directly fluidly coupled to the water junction 138. Alternatively, the first branch 134 and the second branch 136 can each be separately fluidly coupled to the third valve 120 such that the third valve 120 defines the water junction 138.
A fluid junction 140 is provided downstream the first check valve 112 and the third valve 120 and defines a location where the fluid from the gas inlet 104 can meet the fluid from the water inlet 106. As such, the portion of the casting system 100 downstream the fluid junction 140 can be defined by the presence of only water, only a gaseous fluid, or a mixture of water and gaseous fluid depending on which of the second valve 108, the first valve 110 or the third valves 120 are open.
A mold fluid inlet 122 can fluidly couple the fluid junction 140 to the mold 102. Alternatively, the fluid junction 140 can be formed at or within the mold 102 such that that the fluid junction 140 defines the mold fluid inlet 122. A mold fluid outlet 124 fluidly couples the mold to an outlet valve 126, which is ultimately fluidly coupled to the fluid outlet 130. A sensor 128 can be provided downstream of the outlet valve 126. The sensor 128 can be used for a multitude of reasons. As a non-limiting example, the sensor 128 can be used to measure the heat of the fluid exiting the casting system 100. As a non-limiting example, the sensor 128 can be used to determine the presence of or non-presence of a fluid (e.g., water and/or gaseous fluid).
The second valve 108, the first valve 110, the third valve 120, and the outlet valve 126 can be any suitable valve such as, but not limited to, a solenoid valve.
The casting system 100 can include a control system including a controller module 142 having a processor 144 and a memory 156 can be communicatively coupled to respective portions of the casting system 100 The memory 146 can be defined as an internal storage for various aspects of the casting system 100. For example, the memory 146 can store code, executable instructions, commands, instructions, authorization keys, specialized data keys, passwords, or the like. The memory 146 can be RAM, ROM, flash memory, or one or more different types of portable electronic memory, such as discs, DVDs, CD-ROMs, etc., or any suitable combination of these types of memory. The processor 144 can be defined as a portion of the controller module 142 which can receive an input, perform calculations, and output executable data. The processor 144 can be a microprocessor. The control system can be communicatively coupled to and control at least a portion of the casting system 100. As a non-limiting example, the second valve 108, the first valve 110, the third valve 120 and the outlet valve 126 can be selectively controlled via the control system. As a non-limiting example, the switch 118 can be monitored via the control system and determine if the switch 118 is opened or closed. As a non-limiting example, the control system can monitor the sensor 128 and send a communication to an exterior system to alert a user to the presence of or non-presence of the leak 132. As a non-limiting example, the exterior system can be an alarm, a light, a computer, a printer, a smartphone, or any other suitable system that can alert or otherwise inform a user of the casting system 100 to the presence of or non-presence of the leak 132.
During operation, the casting system 100 can be used to detect the presence of or non-presence of the leak 132 by performing the following operations.
To detect the presence of or non-presence of the leak 132 (e.g., a leak) the third valve 120 opens and the first valve 110 opens and directs the water from the water inlet 106 and through the second branch 136. The second valve 108, the first valve 110 leading to the first branch 134 and the outlet valve 126 are both closed. Meaning that the only way for the water to exit the casting system 100 would be through the leak 132. If there is the leak 132, the water will flow past the switch 118 (thus closing the switch 118), through the mold fluid inlet 122 and out the leak 132. If there is not a leak 132, the water will not flow through the casting system 100 and thus not close the switch 118. The switch 118 being closed indicates the leak 132 is present, while the switch 118 being open indicates the non-presence of the leak 132. As the engagement of the switch 118 is used to determine the presence of or non-presence of the leak 132, the switch 118 can be defined as a leak detector.
If the switch 118 is closed (e.g., the leak 132 is present), the casting system 100 can proceed with the casting process. However, the water that flowed through the casting system 100 to detect the leak 132 must first be purged from the casting system 100. This is done by opening the second valve 108 and closing the outlet valve 126, the first valve 110 and the third valve 120. The pressurized gaseous fluid will then flow through the casting system 100 and eject any residual water through the leak 132.
Once the residual water is removed, the casting process can resume by further opening the outlet valve 126 and allowing the pressurized gaseous fluid to flow through the mold fluid outlet 124 and out of the fluid outlet 130. The first, second, third, and outlet valves 110, 108, 120, 126 can then all be closed. During the metal injection, the first valve 110 is opened to allow water to flow through the first branch 134. The second valve 120 is further opened to allow for water, and only water, to flow into the mold fluid inlet 122. The outlet valve 126 is opened to allow for the water within the mold 102 to flow out the fluid outlet 130. This process is used as a method to cool the mold 102 and the molten metal during the casting process. The cooling of the mold 102 can be done for a period of time determined by the feedback or measurements from the sensor 128. As a non-limiting example, the sensor 128 can measure the heat leaving the casting system 100 through the mold fluid outlet 124. Once the temperature has heat removal reaches a predetermined threshold value, the cooling can stop and the process can resume as appropriate.
The method 150 includes a series of normal casting procedures or is otherwise defined as the casting process. The casting process can include the pouring of a molten metal, at 152, injection of the metal into the mold 102, at 154, the impact of the mold 102, at 156, the opening of the die holding the mold 102, at 158, the extraction of the part formed by the mold 102, at 160, the spraying (e.g., with water) of the part, at 162, the blowoff of part, at 164, and the closing of the die, at 166.
The method 150, further includes a branch to detect the presence of or non-presence of the leak 192 along the mold 102. This detection branch occurs between spraying, at 162, and closing the die, at 166. As a non-limiting example, a leak test start can occur at 168 in tandem with, directly before or directly after the spray, at 162. The leak test (e.g., the detection of the leak described above) is performed, at 168, and ends, at 170. A decision is performed, at 172, to determine whether or not a leak was detected (e.g., whether or not the switch 118 is opened or closed). If the leak 132 has not formed, the process proceeds to the die closing, at 166. If, however, the leak 132 has formed the process moves to purge the residual water from the casting system 100 as described above, at 174. It is contemplated that an additional step of communicating the presence of the leak to a user of the casting system 100 can be performed after the leak 132 has been detected. Communicating the presence of the leak 132 can include alerting or otherwise informing the user of the leak 132. The user can further be presented with an option to proceed with the casting process (e.g., proceed to the die closing, at 166) or ending the process to fix the leak 132 and/or replace the mold 102.
The casting system 200 includes a gas inlet 204 and a water inlet 206 that meet at a junction 240 defining or fluidly coupled to a mold fluid inlet 222 of the mold 202. A mold fluid outlet 224 is fluidly coupled to a fluid outlet 230 defining a fluid outlet of the casting system 200. A sensor 228 is provided along the mold fluid outlet 224. A first valve 210 selectively fluidly couples the water inlet 206 to the mold 202. A second valve 208 selectively fluidly couples the gas inlet 204 to the mold 202. A first check valve 212 is provided downstream the second valve 208. A second check valve 214 is provided downstream the first valve 210. The casting system 200 can include any number of check valves including no check valves. The mold 202 an include or not include a leak 232. The casting system 200 can be used to at least detect the presence of or non-presence of the leak 232. The casting system 200 can include a control system including a controller module 242 with a processor 244 and a memory 246.
The casting system 200 is similar to the casting system 100, except that the casting system 200, however, the casting system 200 does not detect the presence of or non-presence of the leak 232 but instead assumes that the leak 232 is always present. As such, during operation, a purge of residual water is always performed by opening the second valve 208 and closing the first valve 210. This is done so that if there is the leak 232, any residual water will be purged from the leak 232. Otherwise, if there is not the leak 232 the residual water within the casting system 200 is ejected through the fluid outlet 230. The residual water can come from the cooling water that is used when pouring the molten metal into the mold 202.
The method 250 can include a series of normal casting procedures or otherwise defined as the casting process. The casting process can include the pouring of a molten metal, at 252, injection of the metal into the mold 202, at 254, the impact of the mold 202, at 256, the opening of the die holding the mold 202, at 258, the extraction of the part formed by the mold 202, at 260, the spraying (e.g., with water) of the part, at 262, the blowoff of part, at 264, and the closing of the die, at 266.
The method 250 further includes purging the casting system 200 of any residual water from the casting system 200 and removing the heat from the casting system 200 associated with pouring the metal, at 254. During, after, or before impact, at 256, the first valve 210 is opened, at 276, to begin the cooling of the molten metal that was just poured, at 254. A check can be performed, at 278, to see whether or not a gaseous fluid purge is desired. The desire of the gaseous fluid purge can be set by a user or otherwise automatically assumed to be desired or not desired by the casting system 200. If the gaseous fluid purge is not desired, the standard logic of the second valve 208 and the first valve 210 (e.g., the second valve 208 is closed and the first valve 210 is opened) is performed, at 280, and the method 250 proceeds with opening the die, at 258. If the gaseous fluid purge is desired, however, another check is performed, at 282, to determine the heat exiting the system. This is done by measuring the heat of the fluid flowing across the sensor 228. If the heat exceeds a threshold value (e.g., the mold 202 needs further cooling), the flow of water continues through the casting system 200, at 286 until the heat is below the threshold value. If, however, the heat does not exceed the threshold value (e.g., the mold 202 does not need further cooling), the water stops being fed through the system by closing the first valve 210, at 284. In either case, once the heat drops below the threshold value, the gaseous fluid purge can begin, at 288, by performing the steps outlined previously. The gaseous fluid purge can end, at 290, and the method 250 can proceed back to the impact, at 256.
The sequence depicted in the method 150, 250 for illustrative purposes only and is not meant to limit the method 150, 250 in any way as it is understood that the portions of the method 150, 250 can proceed in a different logical order, additional or intervening portions can be included, or described portions of the method can be divided into multiple portions, or described portions of the method can be omitted without detracting from the described method. For example, the method 150, 250 can include various other steps such as alerting a user to the presence or non-presence of the leak.
As a non-limiting example, the method 150, 250 can include a method of automatically detecting the presence of or non-presence of a leak. The automatic performance of the method 150, 250 or parts of the method 150, 250 can be done through use of the control system, specifically the controller module 142, 242.
As a non-limiting example, the method 150 can include a branch to detect the presence of or non-presence of the leak 192 along the mold 102, via the controller module 142. The leak test (e.g., the detection of the leak described above) is performed, via opening and closing of valves via the controller module 142 or measurement or detection of values (e.g., of the switch 118) via the controller module 142, at 168, and ends, at 170. A decision can be performed, via the controller module 142, at 172, to determine whether or not a leak was detected (e.g., whether or not the switch 118 is opened or closed). If the leak 132 has not formed, the process proceeds to the die closing, via a command from the controller module 142, at 166. If, however, the leak 132 has formed the process moves to purge the residual water from the casting system 100 as described above, via a command from the controller module 142, at 174. It is contemplated that an additional step of communicating, via the controller module 142, the presence of the leak to a user of the casting system 100 can be performed after the leak 132 has been detected.
As a non-limiting example, the method 250 can include after, or before impact, at 256, the first valve 210 is opened, at 276, via the controller module 242, to begin the cooling of the molten metal that was just poured, at 254. A check can be performed, via the controller module 242, at 278, to see whether or not a gaseous fluid purge is desired. If the gaseous fluid purge is not desired, the standard logic of the second valve 208 and the first valve 210 (e.g., the second valve 208 is closed and the first valve 210 is opened) is performed, via the controller module 242, at 280, and the method 250 proceeds with opening the die, via the controller module 242, at 258. If the gaseous fluid purge is desired, however, another check is performed, via the controller module 242, at 282, to determine the heat exiting the system. This is done by measuring, via the controller module 242, the heat of the fluid flowing across the sensor 228. If it is determined, via the controller module 242, the heat exceeds a threshold value (e.g., the mold 202 needs further cooling), the flow of water continues through the casting system 200, at 286 until the heat is below the threshold value, via a command from the controller module 242. If, however, the heat does not exceed the threshold value (e.g., the mold 202 does not need further cooling), the water stops being fed through the system by closing the first valve 210, via a command from the controller module 242, at 284. In either case, once the heat drops below the threshold value, the gaseous fluid purge can begin, via the controller module 242, at 288, by performing the steps, via the controller module 242, outlined previously. The gaseous fluid purge can end, via the controller module 242, at 290, and the method 250 can proceed back to the impact, at 256.
Benefits of the present disclosure include a method and system for a casting process better suited for mitigating and detecting the presence of a leak when compared to a conventional casting process. For example, the conventional casting process relies on physical inspection of the mold or a failed casting in order to determine if a leak has formed. If the leak has occurred, the mold must be repaired or otherwise not used any more. During the conventional casting process, water or other fluid are used to cool the molten metal. If there is any residual water within the system that is not purged out (e.g., within the leak), then failure of the casting can occur when the molten metal comes into contact with the residual fluid that was used to cool the molten metal. The method and system, as described herein, however, is able to purge any residual fluid from the mold to ensure that even if there is a leak, there will not be any residual fluid within the leak or any other part of the mold such that the pouring of the molten metal can occur even if there is a leak. Using a mold with a leak formed within the mold is not feasible with the conventional casting process. Further, the method and system, as described herein, allows for the detection of the leak without the need for physical inspection of the mold and prior to the mold breaking, as would happen if a mold were used in the conventional casting process. The detection of the leak and the purging of the residual water, in turn, results in a method and system for a casting process better suited for mitigating and detecting the presence of a leak when compared to the conventional casting process.
This application claims the benefit of U.S. Provisional Application No. 63/410,801, filed Sep. 28, 2022, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63410801 | Sep 2022 | US |
