Abstract:
A system and method for thermal management of a die is disclosed wherein cooling of the die is controlled by controlling coolant flow to switch between laminar flow and turbulent flow as desired.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to die casting and more particularly to a system and method for thermal management of a die by controlling coolant flow.  
       BACKGROUND OF THE INVENTION  
       [0002]     In order to control part quality and minimize cycle time, it is necessary to cool a die during a die casting operation. Typically, water or oil have been used as a coolant or cooling medium inside cooling channels in the dies. The coolant extracts heat from the die and the casting material during the die casting cycle. Attempts have been made to control the amount of flow of the coolant to control the amount of heat extracted from the die. In some cases, the flow of coolant has been stopped and restarted to control heat extraction.  
         [0003]     The goal in using the coolant is an attempt to attain steady state temperatures to cool the die so the cast material cools in a desired amount of time. Controlling the amount of heat extracted by controlling the amount of flow of the coolant works satisfactorily with castings having a consistent wall thickness. However, undesirable results are obtained where the casting wall thickness varies from thick to thin, or with complex shapes. In this situation, inconsistent cooling occurs where the coolant cools the thin areas quickly and the thick areas slowly. The inconsistent cooling results in cold die casting defects such as cold flow and hot die casting defects such as soldering. Additionally, an area of the casting which is needed to feed pressure to a thicker section of the casting can be prematurely cooled. As a result, shrink porosity can be present in the thicker section of the casting.  
         [0004]     It would be desirable to produce a system for thermal management of a die wherein control of heat extracted is maximized.  
       SUMMARY OF THE INVENTION  
       [0005]     Consistent and consonant with the present invention, a system for thermal management of a die wherein control of heat extracted is maximized, has surprisingly been discovered.  
         [0006]     In one embodiment, a system for thermal management of a source of heat comprises: a source of coolant; a source of heat having an inlet and an outlet; a flow control valve having an inlet and an outlet, the inlet of the flow control valve in fluid communication with the source of coolant and the outlet of the flow control valve in fluid communication with the inlet of the source of heat, the flow control valve providing laminar flow of a coolant at the outlet thereof; and a bypass conduit providing fluid communication between the source of coolant and the inlet of the source of heat, the bypass conduit facilitating selective bypassing of the flow control valve, a flow through the bypass conduit being turbulent flow.  
         [0007]     In another embodiment, system for thermal management of a die comprises: a source of coolant; a die having an inlet and an outlet, the inlet and the outlet connected by a cooling conduit formed in the die; a flow control valve having an inlet and an outlet, the inlet of the flow control valve in fluid communication with the source of coolant and the outlet of the flow control valve in fluid communication with the inlet of the die, the flow control valve providing laminar flow of a coolant at the outlet thereof, a bypass conduit providing fluid communication between the source of coolant and the die, the bypass conduit providing a bypass around the flow control valve, a flow through the bypass conduit being turbulent flow; and a diverter valve in fluid communication with the source of coolant, the diverter valve facilitating selective bypassing of the flow control valve through the bypass conduit.  
         [0008]     The invention also provides methods for thermal management of a die.  
         [0009]     One method according to the invention comprises the steps of providing a source of coolant; providing a flow control valve having an inlet and an outlet, the inlet of the flow control valve in fluid communication with the source of coolant and the outlet of the flow control valve in fluid communication with an inlet of the source of heat, the flow control valve providing laminar flow of a coolant at the outlet thereof; providing a bypass conduit in fluid communication between the source of coolant and the source of heat, the bypass conduit providing a bypass around the flow control valve, a flow through the bypass conduit being turbulent flow; providing a diverter valve in fluid communication with the source of coolant, the diverter valve facilitating selective bypassing of the flow control valve through the bypass conduit; and causing the coolant to flow as desired through one of the flow control valve to provide laminar flow to the source of heat and the bypass conduit to provide turbulent flow to the source of heat, thus controlling a heat removal rate from the source of heat.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]     The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:  
         [0011]      FIG. 1  is a schematic flow diagram showing a system for thermal management of a die according to an embodiment of the invention and showing a diverter valve in a first position;  
         [0012]      FIG. 2  is a schematic flow diagram showing the system for thermal management of a die illustrated in  FIG. 1  showing the diverter valve in a second position; and  
         [0013]      FIG. 3  is a schematic diagram illustrating a portion of a die casting die and showing a conduit for a coolant. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]      FIG. 1  depicts a flow diagram showing a system for thermal management of a die  10  according to an embodiment of the invention. A die or source of heat  12 , is shown having a coolant inlet  14  and a coolant outlet  16 . A return conduit or pipe  17  having a pressure relief valve  18  disposed therein provides fluid communication between the outlet  16  of said die  12  and a source of coolant  20 . The pressure relief valve  18  can be any conventional type such as a mechanically operated or electrically or pneumatically operated, for example. The source of coolant  20  includes a coolant fluid  22  disposed therein. The source of coolant  20  can be a tank or reservoir, for example. Alternatively, the return conduit  17  can be in fluid communication with a discharge point (not shown) such as a sewer or waterway. The coolant  22  can be any conventional coolant such as water or oil for example.  
         [0015]     A pump inlet  24  of a pump  26  is in fluid communication with the source of coolant  20 . The pump  26  may be located at the source of coolant  20  or at a point remote therefrom. It is understood that the pump  26  can be eliminated if the source of coolant  20  delivers the coolant  22  at a pressure sufficient to cause the coolant  22  to flow through the die  12  and the remainder of the system  10  at a turbulent flow rate. A pump outlet  28  is in fluid communication with a diverter valve  30 . The diverter valve  30  can be any conventional valve such as a three-way valve or a spool valve, for example, and can be controlled manually or automatically by a controller (not shown). In  FIG. 1 , the diverter valve  30  is shown in a first position to provide fluid communication between the pump  26  and a first check valve  32 . The first check valve  32  is disposed in a bypass conduit or pipe  31 . It is understood that any conventional valve or check valve can be used without departing from the scope and spirit of the invention. The first check valve  32  is in fluid communication with the coolant inlet  14  of the die  12 .  
         [0016]     The first position of the diverter valve  30  also causes an interruption in fluid communication between the pump  26  and an inlet  33  of a flow control valve  34 . The flow control valve  34  controls the flow of the coolant  22  to result in laminar flow at an outlet  36  thereof. The flow control valve  34  can be any conventional valve such as a solenoid valve, for example. Additionally, although only one flow control valve  34  is shown, it is understood that more than one valve can be used as desired to result in laminar flow without departing from the scope and spirit of the invention. The flow control valve  34  is in fluid communication with a second check valve  38 . The second check valve  38  can be any conventional valve or check valve. The second check valve  38  is in fluid communication with the coolant inlet  14  of the die  12 .  
         [0017]      FIG. 2  shows the system  10  illustrated in  FIG. 1  with the diverter valve  30  in a second position. The second position provides fluid communication between the pump  26  and the flow control valve  34 . Additionally, the second position of the diverter valve  30  causes an interruption in fluid communication between the pump  26  and the first check valve  32 .  
         [0018]      FIG. 3  schematically shows a portion of the inside of the die  12 . Molten metal such as aluminum, for example, is introduced through an injection conduit or gating system  40 . An injection cylinder (not shown) typically pressurizes the molten metal. A flow direction of the molten metal in the injection conduit  40  is indicated by the arrow. A casting  42  is formed when the molten metal is introduced into a cavity  44  of the die  12 . The casting  42  may have areas of varying thickness. In the embodiment shown, the casting  42  includes a thick portion  46  and a thin portion  48 . A cooling conduit  50  is formed in the die  12  to convey coolant  22  to areas of the die  12  where cooling is required. A direction of flow of the coolant  22  is indicated by the arrows.  
         [0019]     In operation, the system for thermal management of a die  10  circulates the coolant  22  through the die  12  to remove heat therefrom. When it is desired to maximize heat removal from the die  12 , the diverter valve  30  is placed in the first position as shown in  FIG. 1 . The coolant  22  is caused to flow through the diverter valve  30 , the bypass  31  including the first check valve  32 , the die  12 , the return conduit  17  including the pressure relief valve  18 , and to the source of coolant  20 . Resultant flow through the system  10  with the diverter valve  30  in the first position is turbulent flow. The difference in heat transfer rates from the die  12  is expected to be three to four times greater using turbulent flow versus laminar flow. Thus, heat removal from the die  12  is maximized with the diverter valve  30  in the first position.  
         [0020]     When it is desired to minimize the heat removal from the die  12 , the diverter valve  30  is placed in the second position as shown in  FIG. 2 . The coolant  22  is caused to flow through the diverter valve  30 , the flow control valve  34 , the second check valve  38 , the die  12 , the pressure relief valve  18 , and to the source of coolant  20 . The flow control valve  34  causes the flow through the system  10  to be laminar flow. Thus, with the diverter valve  30  in the second position the heat removal from the die  12  is minimized.  
         [0021]     Laminar flow can be used, for example, during an open dwell of a die casting machine cycle to reduce the heat removal from the die  12 , and retain the heat in the die  12 . A return to turbulent flow could be made just prior to the injection of molten metal into the die  12 . Turbulent flow would be maintained during the die  12  cooling operation. If it is desired to vary or slow the cooling rate of a casting  42 , the flow can be switched from turbulent flow to laminar flow and back to turbulent flow to result in the desired cooling rate.  
         [0022]     During operation of the system  10 , the pressure relief valve  18  operates to create a backpressure in the die  12  portion of the system  10 . The backpressure created militates against the undesirable formation of steam in the die  12 .  
         [0023]     One use for the system  10  as shown and described herein is where a thin portion  48  supplies a thick portion  46  of a die  12  as shown in  FIG. 3 . The coolant  22  can be switched from turbulent flow to laminar flow to militate against over cooling of the thin portion  48 .  
         [0024]     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.