MOLD ASSEMBLY AND METHOD FOR MANUFACTURING METAL CASTINGS

Abstract

A mold assembly for manufacturing a metal alloy casting includes a cope and drag mold, a plurality of sand cores and a pressure core. The cope mold includes an upper portion of a mold cavity. The drag mold includes a gating system, a lower portion of the mold cavity, and an upper portion of a plurality of riser cavities. The gating system is in communication with the riser cavities to provide pressurized liquid metal alloy to the riser cavities. The pressure core has a plurality of protrusions that are disposed in each of the upper portion of the plurality of riser cavities.

Claims

1. A mold assembly for manufacturing a metal alloy casting, the mold assembly comprising; a cope mold including an upper portion of a mold cavity; a drag mold including a lower portion of the mold cavity and an upper portion of at least a first riser cavity, and wherein the cope mold is disposed on top of the drag mold to combine the upper portion and lower portion of the mold cavity; a plurality of sand cores disposed on the interior of the mold cavity of the cope and drag molds, and a pressure core having at least a first protrusion, and wherein the first protrusion is disposed adjacent to the first riser cavity and includes a top surface that forms a bottom portion of the first riser cavity.

2. The mold assembly of claim 1 wherein the pressure core is disposed in one of a first position and a second position, and wherein the first riser cavity has a first volume when the pressure core is in the first position, and the first riser cavity has a second volume when the pressure core is in the second position, and the second volume is less than the first volume.

3. The mold assembly of claim 1 further including a gating system and a piston core, and wherein the gating system has a runner in communication with the first riser cavity and the piston core is disposed in one of a first and a second position.

4. The mold assembly of claim 3 wherein the first position of the piston core allows for communication between the first riser cavity and the runner and the second position of the piston core inhibits communication between the first riser cavity and the runner.

5. The mold assembly of claim 1 wherein the drag mold further includes a gating system that communicates liquid metal alloy from a pressurized source of liquid metal alloy to the riser cavities.

6. The mold assembly of claim 5 wherein the pressurized source of liquid metal alloy includes one of an electromagnetic pump, a mechanical pump, and a low-pressure furnace.

7. The mold assembly of claim 5 wherein the pressurized source of liquid metal alloy includes a pouring basin and sprue.

8. The mold assembly of claim 1 wherein the cope mold and drag mold are permanent metal molds.

9. The mold assembly of claim 8 wherein the pressure core is a movable portion of the drag mold.

10. A mold assembly for manufacturing a metal alloy casting, the mold assembly comprising; a sand core assembly having a riser core and a first piston core, and wherein the riser core includes a gating system and at least a first riser cavity and the first piston core is disposed adjacent the first riser cavity; a cope mold including an upper portion of a mold cavity; a drag mold including a lower portion of the mold cavity and a first piston core actuator, and wherein the sand core assembly is disposed in the lower portion of the mold cavity, the cope mold is disposed on the drag mold, and the first piston core actuator is fixed for common movement with the piston core; wherein the first piston core is disposed in one of a first position and a second position, and wherein the first riser cavity has a first volume when the first piston core is in the first position, and the first riser cavity has a second volume when the first piston core is in the second position, and the second volume of the first riser cavity is less than the first volume of the first riser cavity.

11. The mold assembly of claim 10 wherein the first piston core has a top surface that forms a portion of the first riser cavity.

12. The mold assembly of claim 11 wherein the first piston core includes a cross section having a width that is smaller than a cross section of the first riser cavity.

13. The mold assembly of claim 10 wherein the pressurized source of liquid metal alloy includes one of an electromagnetic pump, a mechanical pump, and a low-pressure furnace.

14. The mold assembly of claim 10 wherein the pressurized source of liquid metal alloy includes a pouring basin and sprue.

15. The mold assembly of claim 10 further including a second piston core, and wherein the gating system has a runner in communication with the first riser cavity, the second piston core is disposed proximate the runner in one of a first and a second position, the first position of the second piston core allows for communication between the first riser cavity and the runner and the second position of the second piston core inhibits communication between the first riser cavity and the runner.

16. A method for manufacturing a lightweight metal alloy casting, the method comprising: providing a mold assembly including an cope mold, a drag mold, and a core assembly forming a mold cavity, and wherein the drag mold includes at least a first riser cavity and a gating system, and wherein the first riser cavity is at least partially formed by a movable first piston actuator, and the runner is at least partially formed by a movable second piston actuator; initializing filling the gating system with a pressurized liquid metal alloy; completing filling the gating system, the first riser cavity, and mold cavity with the pressurized liquid metal alloy; discontinuing filling the mold assembly with the pressurized liquid metal alloy and activating the second piston actuator to close the runner; applying a force to a bottom surface of the movable piston actuator mold in the direction of the drag mold and increasing the hydraulic pressure of the liquid metal alloy in the first riser cavity.

17. The method of claim 16 further comprises extracting a solidified casting from the mold cavity and placing the casting in an oven for heat treatment.

18. The method of claim 17 further comprises ejecting a solidified casting from the casting cavity.

19. The method of claim 18 further comprises placing the casting in an oven for heat treatment.

20. The method of claim 16 applying a force to a bottom surface of the movable piston actuator mold in the direction of the drag mold to increase the hydraulic pressure of the liquid metal alloy in the first riser cavity further comprises applying a force to a bottom surface of the movable piston actuator mold in the direction of the drag mold, decreasing the volume of the first riser cavity and increasing the hydraulic pressure of the liquid metal alloy in the first riser cavity.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0027] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0028] FIG. 1 is a view of the head deck and combustion chambers of a cylinder head casting according to the principles of the present invention;

[0029] FIG. 2 is a perspective view of a cylinder head casting according to the principles of the present invention;

[0030] FIG. 3 is a partially assembled view of a mold assembly according to the principles of the present invention;

[0031] FIG. 4A is an end view of a mold assembly according to the principles of the present invention;

[0032] FIG. 4B is a side view of a mold assembly according to the principles of the present invention;

[0033] FIG. 5 is a perspective cut-away view of a portion of a mold assembly according to the principles of the principles of the present invention;

[0034] FIG. 6 is a section view of a portion of the mold assembly according to the principles of the present invention;

[0035] FIGS. 7A-7C are section views of the interior of a mold assembly in various stages of a casting method according to the principles of the present invention;

[0036] FIG. 8 is a section view of a portion of the mold assembly according to the principles of the present invention,

[0037] FIG. 9 is a section view of a portion of the mold assembly according to the principles of the present invention, and

[0038] FIG. 10 is a flowchart depicting a method of casting metal alloys according to the principles of the present invention.

DESCRIPTION

[0039] Referring to the drawings, wherein like reference numbers refer to like components, in FIGS. 1 and 2 an aluminum alloy cylinder head 10 produced using a metal alloy casting method 100 is illustrated in accordance with an example of the present invention and will now be described. In general, the cylinder head 10 includes features such as a head deck 12, combustion chambers 14, intake and exhaust ports 16, camshaft bearings 18, spark plug holes 20, water jacket openings 22, and oil passages 24, among other features. More particularly, the important features of the cylinder head 10 that are at least partially formed during the casting process include the head deck 12 and combustion chambers 14. Product specifications for the head deck 12 and combustion chambers 14 generally require higher yield and tensile strength than other areas of the cylinder head 10. Furthermore, improving cooling rates locally can be achieved with less effort than improving cooling rates in the entirety of the casting. For example, faster cooling rates of the head deck and combustion chambers produce finer microstructure; approximately 20 m dendritic arm spacing (DAS), and higher strengths. Other areas of the cylinder head 10 that cool at a slower rate may result in DAS of about 60 m. Additionally, mechanical properties can be improved by other means such as providing pressurized liquid metal to areas of the casting that solidify last. This results in improved microstructure by reducing porosity and shrinkage defects.

[0040] Turning now to FIG. 3, a mold assembly 30 used in a casting method to produce cylinder heads 10 according to the present invention is illustrated and will now be described. The particular mold assembly 30 of FIG. 3 produces two cylinder head 10 castings in a mold cavity 8 formed by a number of sand cores 32 and sand molds 34. However, certain exterior features of the cylinder head 10 casting may be formed using sand or metal molds 34. For example, the molds 34 may be made from tool steel and fitted with hydraulic actuators to provide improved mechanical properties and reusable or permanent molds 34.

[0041] The sand cores 32 form part of the exterior features and all the interior features of the cylinder head 10 casting and include, for example, two end cores 36, two side cores 38, two center cores 40, two head cover cores 42, two exhaust port cores 44, two intake port cores 46, two water jacket cores 48, and two oil drain cores 50. The molds 34 include a lower or drag mold 62, an upper or cope mold 64, and a pressure core or mold 76. During assembly of the mold assembly 30, the sand cores 32 are inserted in a specified order into the drag mold 62 or the cope mold 64. In the example shown in FIGS. 3, 4A, and 4B, the sand cores 32 are placed in the drag mold 62 with the cope mold 64 placed on top of the assembled sand cores 32 thus securing the sand cores 32 in place. In some embodiments, the sand cores 32 are assembled into a core package prior to placing the core package into the drag mold 62. In other embodiments, the sand cores 32 may require adhesive, screws, and other retention mechanisms to hold the sand cores 32 in place. However, such practices are within the scope of the present invention. Details regarding the pressure core or mold 76 are explained in more detail below.

[0042] In the present invention, the included features of the drag mold 62 are of particular interest. The drag mold 62 includes a gating system 66 formed for receiving liquid metal from a pressurized liquid metal alloy source and directing the liquid metal alloy to the cavities formed therein by the sand cores 32 and sand molds 34 of the mold assembly 30. While a portion of the gating system 66 is viewable in FIG. 3, the gating system 66 is shown in more detail in FIGS. 4A, 4B, 5, and 6. The gating system 66 of the drag mold 62 includes an inlet 68, a plurality of runners or runners 70, and a plurality of riser cavities 72. More specifically, the inlet 68 receives the liquid metal alloy from a pressurized liquid metal alloy source such as an electromagnetic or mechanical pump. Another mechanism that may be used to provide pressurized liquid metal alloy to the inlet 68 includes a feature formed in the mold assembly 30 having a pouring basin 86 and a sprue 88, as shown in FIG. 4B. Independent of the means of providing pressurized liquid metal alloy to the inlet 68, the inlet 68 transfers the liquid metal to the runners 70. The runners 70 are in communication with and feed liquid metal to the plurality of riser cavities 72. The runners 70 control the flow rate and turbulence of the liquid metal by controlling the diameter and shape of the runners 70. The riser cavities 72 are filled with the liquid metal starting at the bottom of the riser cavities 72 and in turn fill the mold cavity 8 of the mold assembly 30 as the liquid metal rises into the casting cavities formed by the space between the sand cores 32 and the molds 34.

[0043] Referring now to FIG. 6, the core structure used in the formation of the riser cavities 72 is illustrated and will now be described. The riser cavity includes an upper portion 82 and a lower portion 83. The upper portion 82 of the riser cavity 72 is formed in the drag mold 62 while the lower portion 83 of the riser cavity is formed by the pressure core 76. The upper and lower portions 82, 83 of the riser cavities 72 form the cavity that produces the risers 72 when the liquid metal alloy is introduced into the mold assembly 10. The pressure core 76 includes a plurality of protrusions 78 each extending into the cavity 82 of the drag mold 62. In other embodiments, multiple pressure cores having a single protrusion may be incorporated into the mold assembly 10. Regardless of the configuration of the pressure core 76, what is necessary is for the protrusions 78 to move relative to the drag mold 62. As shown in FIG. 6, the upper portion 82 of the riser cavity 72 is shaped like a bullet, however, other shapes or configurations of the riser cavity may be contemplated without departing from the scope of the invention. For example, a riser cavity 72 may be a continuous cavity shape that extends from a cover rail of a cylinder head. In the present embodiment, the protrusions 78 of the pressure core 76 have a cylindrical shape with a smaller diameter D than that of the upper portion 82 of the riser cavity 76. In other embodiments, multiple pressure cores having a single protrusion may be incorporated into the mold assembly 10. Regardless of the configuration of the pressure core 76, the constant among all embodiments is that the protrusions 78 are capable of relative movement to the drag mold 62.

[0044] Each of the plurality of protrusions 78 includes a top surface 84 that forms the bottom portion 83 of the riser cavities 72. The protrusions 78 are fitted into the upper portion 82 of the riser cavities 72 and are capable of movement within the cavities 82 in an upward direction Y. More particularly, the pressure core 76 is capable of being manipulated into at least two positions. In a first position, detailed in FIGS. 7A and 7B, the pressure core 76 is disposed such that the riser cavities 72 have a first volume. In a second position, detailed in FIG. 7C, a force Y is applied to the pressure core 76 so that the pressure core 76 is disposed such that the riser cavities 72 have a second volume which is less than the first volume. The reduction in volume between the first and the second positions translates to an increase in pressure of the liquid metal alloy in the casting cavity, explained in more detail below. Furthermore, it is preferable that the protrusions 78 are being forced into a volume of the riser cavity 72 that is still mostly liquid so as to increase the pressure of the liquid in the riser cavity 72 and subsequently in the mold cavity 8.

[0045] With continuing reference to FIGS. 7A, 7B, and 7C, a series of figures depicting progressive stages of the manufacturing of cast alloy cylinder heads 10 are illustrated and will now be described. After the mold assembly 30 is inspected and assembled, the mold assembly 30 is inserted into a machine and secured by hydraulic clamping mechanisms such that the drag mold 62 of the mold assembly 30, and therefore the gating system 66, is the lower portion of the mold assembly 30. A pressurized source of liquid metal alloy (not shown) is provided to the inlet 68 of the gating system 66. As the liquid metal alloy is introduced to the gating system 66, the liquid metal alloy first fills the runner 70 and risers 72 before reaching the mold cavity 8, as in FIG. 7A. As the liquid metal alloy continues to enter the gating system 66, the level of the liquid metal alloy rises through the risers 72 and begins to fill the mold cavity 8, as in FIG. 7B. In FIG. 7C, the liquid metal alloy completely fills the mold cavity 8 and the machine applies a force to the pressure cores 76 in the upward direction Y while holding the mold assembly 30 as a whole in the same position. At this point in the process, the metal alloy in the top portion of the mold cavity 8 is starting to solidify while the last liquid metal alloy that enters the mold assembly 30 is hottest and remains liquid. As the metal in the mold cavity 8 solidifies, additional liquid metal is required to inhibit porosity or shrinkage defects. Thus, the application of pressure in the risers 72 by the pressure core 76 promotes the feeding of additional liquid metal alloy to the mold cavity 8 as the first metal in the mold cavity 8 solidifies. The additional liquid metal feeds the voids formed by the contracting solidification of the first metal in the mold cavity 8.

[0046] With reference to FIG. 8, another embodiment of the present invention including an alternative core and mold assembly 100 is illustrated and will now be described. In this particular example, a riser cavity 102 is formed by a metal mold 104 and several sand cores, including, a riser core 106, a base core 108, and a piston core 110. More specifically, the riser core 106, base core 108 and piston core 110 are assembled to form a riser cavity 112 and placed within the metal mold 104. In one embodiment, the piston core 110 may be made as a breakaway portion of the base core 108. Furthermore, the metal mold 104 may be a mold for a semi-permanent mold machine or any one of several mold machines or processes utilizing a metal mold 104 without departing from the scope of the invention.

[0047] The riser cavity 112 includes an upper portion 114 and a lower portion 116. The upper portion 114 of the riser cavity 112 is formed in the riser core 106 while the lower portion 116 of the riser cavity is formed partially by the base core 108 and the piston core 110. The riser core 106 also includes a portion of the gating system 118 that provides a path for the liquid metal alloy to communicate between the source of the pressurized liquid metal alloy and the riser cavity 112. The upper and lower portions 114, 116 of the riser cavity 112 form to cast the risers 72 when the pressurized liquid metal alloy is introduced into the core and mold assembly 100.

[0048] The metal mold 104 includes a piston core actuator 120 having a top surface 122 on which is disposed the piston core 110. The piston core actuator 120 and the piston core 110 are capable of relative movement with the metal mold 104 and the base core 108. In one embodiment, the piston core 110 and the base core 108 may be made as a connected single core with the piston core 110 being designed as a breakaway portion of the base core 108. The piston core actuator 120 is further fixed to a hydraulic slide (not shown) or other force inducing mechanism that applies a force P to the piston core actuator 120.

[0049] In one example of the present invention, multiple piston cores 110 and riser cavities 112 are included in the core and mold assembly 100 as is required by the design of the casting. Regardless of the configuration and number of piston cores 110 and riser cavities 112, what is necessary is for the piston cores 110 to move relative to the riser cavities 112. The piston core 110, as shown in FIG. 8, has a cross section X that is significantly smaller than the cross section Y of the riser cavity 112. This allows for the piston core 112 to move into the riser cavity 112 without contacting metal alloy closer to the core surfaces that might be already solidified.

[0050] Turning now to FIG. 9, another embodiment of the present invention including an alternative core and mold assembly 100 is illustrated and will now be described. Some features of FIG. 9 include carryover reference numbers of similar features from previous FIGS. In this example, the gating system 118 includes a runner 124 that communicates pressurized liquid metal alloy through the gating system 118 from the inlet 68 to the riser cavities 112. The runner 124 is formed by the metal mold 104 and several sand cores, including, a riser or cope core 106, a base or drag core 108, and a piston core 110. More specifically, the cope core 106, drag core 108 and piston core 110 are assembled to form a runner 112 and placed within the metal mold 104. In one embodiment, the piston core 110 may be made as a breakaway portion of the drag core 108. Furthermore, the metal mold 104 may be a mold for a semi-permanent mold machine or any one of several mold machines or processes utilizing a metal mold 104 without departing from the scope of the invention.

[0051] The metal mold 104 includes a piston core actuator 126 having a top surface 128 on which is disposed the piston core 110. This embodiment may be included in several of the gating systems 118 runners 124 throughout the mold assembly 100. The piston core actuator 126 and the piston core 110 are capable of relative movement with the metal mold 104 and the drag core 108. In one embodiment, the piston core 110 and the base core 108 may be made as a connected single core with the piston core 110 being designed as a breakaway portion of the base core 108. The piston core actuator 120 is further fixed to a hydraulic slide (not shown) or other force inducing mechanism that applies a force F to the piston core actuator 120. The piston core 110, when engaged by the piston core actuator 120, moves into the runner 124 effectively blocking the runner 124 and preventing any additional flow of liquid metal alloy from flowing in either direction in the runner 124. The piston core actuator 120 in this embodiment may operate independently form the piston core actuator 120 of the embodiment shown in FIG. 8.

[0052] Referring now to FIG. 10, a flowchart depicting a method 200 for manufacturing cast alloy cylinder heads 10 is illustrated and will now be described. The method 200 begins with a first step 202 of providing a mold assembly 30. The mold assembly 30 includes a drag or lower mold 62 having a gating system 66 formed therein and a pressure core 76, a cope or upper mold 64, and a plurality of sand cores 32. A second step 204 begins to fill the gating system 66 and mold cavity 8 with pressurized liquid metal alloy. A third step 206 completes filling the mold cavity 8 or partially fills the mold cavity 8. A fourth step 208 discontinues filling the system with pressurized liquid metal alloy and engages the piston core actuator 120 effectively closing the runner 118 leading to the riser cavities 112. Alternatively, the runner 118 freezes to prevent backflow of liquid metal alloy from the riser cavity 72. A fifth step 210 applies a force to the bottom surface of the pressure core 76 in the upward direction Y to pressurize the liquid metal alloy in the riser cavity 72 thus forcing liquid metal alloy into any voids formed in the solidification of the metal alloy in the mold cavity 8. A sixth step 212 places the mold assembly 30 in an oven for sand removal and heat treatment. Alternatively, a seventh step 214 ejects the casting from the mold cavity 8, removes the gating system and risers from the casting, cleans sand cores from the internal passages of the casting, and heat treats the casting.

[0053] While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and examples for practicing the invention within the scope of the appended claims.