DIRECT SQUEEZE CASTING

Abstract

A casting system includes a pour cup, a plurality of runners that receive molten metal from the pouring cup, a top mold and a bottom mold that receive the molten metal from the plurality of runners, and a plurality of slides positioned within the top mold and the bottom mold. The positioning of the plurality of slides applies direct pressure on the molten metal in the top mold and the bottom mold to form a cast structural component.

Claims

1. A casting system comprising: a pour cup; a plurality of runners that receive molten metal from the pouring cup; a top mold and a bottom mold that receive the molten metal from the plurality of runners; and a plurality of slides positioned within the top mold and the bottom mold, wherein positioning of the plurality of slides applies direct pressure on the molten metal in the top mold and the bottom mold to form a structural component.

2. The casting system of claim 1 wherein the pour cup is a gravity pour cup.

3. The casting system of claim 1 wherein the pour cup is a tilt pour cup.

4. The casting system of claim 1 wherein interior surfaces of the top mold and the bottom mold have a pressure sensitive coating.

5. The casting system of claim 1 wherein the pour cup introduces the molten metal to the plurality of runners with a pour velocity of less than 100 cm/sec.

6. The casting system of claim 1 wherein the plurality of slides is four slides.

7. The casting system of claim 7 wherein each slide is an insert that reciprocates along a respective channel.

8. The casting system of claim 1 wherein the pour cup introduces molten metal to the runners so that the molten metal flows into the mold quiescently without turbulence.

9. The casting system of claim 1 wherein the applied pressure is between about 60 psi and about 3000 psi.

10. An apparatus to form a mechanical component comprising: a first mold; a second mold, the first mold and the second mold being configured to receive molten metal; a plurality of slides positioned within the top mold and the bottom mold, wherein positioning of the plurality of slides applies direct pressure on the molten metal in the top mold and the bottom mold to form a mechanical component.

11. The apparatus of claim 10 wherein interior surfaces of the first mold and the second mold have a pressure sensitive coating.

12. The apparatus of claim 10 wherein the plurality of slides is four slides.

13. The apparatus of claim 12 wherein each slide is an insert that reciprocates along a respective channel.

14. The apparatus of claim 10 wherein the applied pressure is between about 60 psi and about 3000 psi.

15. A method of casting a mechanical component, the method comprising: pouring molten metal into an interior cavity defined by a first mold and a second mold; and exerting pressure on the molten metal to form a structural cast component.

16. The method of claim 15 wherein interior surfaces of the first mold and the second mold are have a pressure sensitive coating.

17. The method of claim 15 wherein the molten metal pours into the interior cavity with a velocity of less than 100 cm/sec.

18. The method of claim 15 wherein the molten metal flows into the interior cavity quiescently without turbulence.

19. The method of claim 15 wherein the applied pressure is between about 60 psi and about 3000 psi.

20. The method of claim 15 wherein the applied pressure is produced by a plurality of slides positioned in the first mold and the second mold.

21. The method of claim 20 wherein the slides move outwards along respective channels to accommodate an overfill volume, and wherein the slides move inward to compensate for metal shrinkage as the molten metal transitions to a solid, while the positioning of the slides maintain the desired pressure on the solidifying casting.

22. The method of claim 20 wherein the slides are configured to move to apply direct pressure to the molten metal as it solidifies, and wherein pressure is applied and controlled with use of one or more pressure punches applied to regions of interest of the solidifying casting, the slides and the one or more pressure punches operating simultaneously or independently of each other.

Description

DRAWINGS

[0012] 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 components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the drawings:

[0013] FIG. 1 illustrates a system for direct squeeze casting in accordance with the principles of the present invention;

[0014] FIG. 2 is cut-away view of the system;

[0015] FIG. 3 is a cut-away view of another direct squeeze casting system in accordance with the principles of the present invention;

[0016] FIG. 4 is a perspective view of a top mold and bottom mold for the direct squeeze casting system shown in FIG. 1;

[0017] FIG. 5 is an interior view of the top and bottom molds;

[0018] FIG. 6 illustrates the top and bottom molds separately;

[0019] FIG. 7 is a schematic view of the system shown in FIG. 1 in use molding a component.

DETAILED DESCRIPTION

[0020] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.

[0021] Referring now to the drawings, a direct squeeze system to cast structural components embodying the principles of the present invention is illustrated therein and designated at 10. Turning in particular to FIGS. 1 and 2, the system 10 includes a pour cup 12 that communicates with a downsprue or downgate 14, which, in turn, communicates with a runner 20. The runner communicates with a set of molds 16 and 18 through a plurality of ingates 22.

[0022] Referring to FIG. 4, there is shown the direct squeeze casting system 10 in use. Molten metal 11 is poured into the pour cup 12. The molten metal flows down the downgate 12 through the runner 20 into the ingates 22. Note that the runner 20 is not shown and only one ingate 22 is shown in FIG. 4 for the sake of simplicity. It should be understood, that only one ingate 22 may be employed or any number of ingates that communicate with the runner 20 may be employed. For example, FIGS. 1 and 2 show the system 10 with seven ingates 22. Accordingly, the molten metal 11 flows through the one or more ingates 22 into the bottom mold 18. The bottom mold 18 and the top mold 16 define a mold cavity or an interior region 28. Hence, as the molten metal flows into the bottom mold 18, the molten metal fills the interior region 28. As the molten metal in the interior region 28 cools, it forms a structural component 30. The top mold 16 includes a vent 29 to flush air from the mold cavity thereby relieving pressure within the interior regions 28. Further, a direct pressure punch may be associated with the vent. That is, the punch may be controlled to vary the hydrostatic pressure in the molten metal as the component 30 solidifies. Note that more than one pressure punch may be employed to apply pressure to regions of interest of the solidifying casting,

[0023] Turning to FIG. 3, there is shown an alternative direct squeeze casting system 100. Most of the components of the system 100 are the same as those of the system 10. The system 100, however, has a tilt cup 112 rather than the pour cup 12 and the downgate 14 arrangement. Accordingly, after the tilt cup 112 is filled with molten metal, the tilt cup, or entire cup and mold package 112 is tilted in the direction of the arrow 114 to pour the molten metal into the runner 20 such that that the molten metal fills the interior region 28 as described previously. Mold cavity fill can also be accomplished with other fill systems including; Electromagnetic pump, Low Pressure pumps and dosing systems.

[0024] In either system 10 or 100, the molten metal is poured into the respective system with a slow pour velocity. For example, in some arrangements, the pour velocity through the ingates 22 is less than 100 cm/sec, preferably less than 50 cm/s. In contrast, in high pressure die cast (HPDC) systems, the pour velocity exceeds 2000 cm/sec, and, in some arrangements, approaches 3800 cm/sec. A particular benefit of the low speed pour velocity for the systems 10 or 100 is the quiescent flow of the molten metal as it flows into the molds 16 and 18, which thereby reduces or eliminates turbulence in the flowing molten metal. In comparison to HPDC systems, the non-turbulent flow of the molten metal reduces the entrainment of air in the molten metal, which reduces the creation of structural voids in the structural component 30. In some arrangements, the surface of the interior cavity 28 is coated with a pressure sensitive coating, which enhances heat transfer and directional solidification, since the coating has a high thermal resistance with no pressure and low or no thermal resistance with high pressure. An example of such a coating is Trabo available from REL, Inc.

[0025] Generally, molten metal shrinks as it cools. For example, aluminum shrinks about 6% as it solidifies. Another feature of the systems 10 and 100, is the ability to compensate for the shrinkage of the molten metal as it cools and solidifies. Specifically, as shown in FIGS. 5 and 6, a set of inserts or slides 32, 34, 36 and 38 are positioned in the top and bottom molds 16 and 18. The slides 32, 34, 36 and 38 are configured to reciprocate along channels 50, 52, 54 and 56 in the top mold 16 and corresponding channels 68, 70, 72 and 74 in the bottom mold 18 to accommodate material geometries of the component 30. As such, as the molten metal flows into the interior region 28 defined by a cavity 60 of the top mold 16 and a cavity 62 of the bottom mold 18, the slides 32, 34, 36 and 38 slide outwardly along their respective channels 50, 52, 54, 56 and 68, 70, 72, 74, as indicated by the arrows 40, 42, 44 and 46 to accommodate an overfill volume of for example, 10%. As the molten metal cools and shrinks, the slides 32, 34, 36 and 38 slide inwardly to compensate for shrinkage of the molten metal as is cools and solidifies to form the quality metal component 30 (shown as a block for the sake of simplicity), while the positioning of the slides maintain the desired pressure on the solidifying casting.

[0026] Note also, that the positioning of the top mold 16 and the bottom mold 18 exerts or applies controlled direct pressure on the cooling molten metal as well. For example, FIG. 7 schematically illustrates pressure being directly applied in a controlled manner from six directions (top and bottom and from the sides) to mold the mechanical component 30. Specifically, the top mold 16 can be moved up and down as indicated by the arrow 66 and the bottom mold 18 can be moved up and down as indicated by the arrow 64, in addition to the direct pressure applied by the slides 32, 34, 36 and 38 along the lines 40, 42, 44 and 46 to accommodate an overfill Further, the applied pressure can be controlled with the use of the aforementioned one or more pressure punches and the vent 29 to apply and control the pressure to regions of interest of the solidifying casting. The slides and the one or more pressure punches can operate simultaneously or independently of each other.

[0027] In sum, the mold cavity or interior region 28 is coated with a high thermal resistant-pressure activated coating. The molds 16 and 18 are closed and mechanically locked except for a direct pressure punch detail. Molten metal, such as, aluminum alloy quietly fills the mold cavity with approximately 10% overfill. The mold cavity is vented around the pressure punch or other locations. The direct pressure punch sequences shutting off the flow of molten metal through the downgate 14 and the ingates 22. The desired pressure is set and held until the cast component 30 solidifies. The molds 16 and 18 are opened and the mechanical component is removed.

[0028] In various arrangements, the direct squeeze pressure applied to the metal by the system 10 or 100 as it forms the component 30 can vary between about 60 psi to 3000 psi. It should be understood, that the inserts 32, 34, 36 and 38 arrangement can be modified for creating different component geometries. The pressure can be applied directly to a strategic region of the mechanical component 30, for example, the bulk head region of an engine block. As such, high integrity cylinder block castings can be heat treated to optimum tensile and fatigue strengths. Tensile and fatigue strengths of components produced with the system 10 or 100 can be at least double as compared to components produced with HPDC systems. Quiescent mold fill combined with low to medium squeeze pressure allows for the use of strong sand cores for internal passages and closed deck designs. Low to medium squeeze pressures can be used to drive molten metal infiltration of ceramic or metal reinforcement of local high stress regions of the component. Significantly lower casting pressures reduce tooling and press ruggedness requirements, which enables the use of simpler castings machines, hydraulic systems and controls compared to HPDC machinery. As such, simpler casting machines, hydraulics and controls and improved tool life lowers the cost per component compared to components made with HPDC systems.

[0029] The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.