US20180056384A1

US20180056384A1 - Displacement-pressure regulator for a casting system

Info

Publication number: US20180056384A1
Application number: US15/245,658
Authority: US
Inventors: Richard J. Osborne; Herbert W. Doty; Frank Sant
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2016-08-24
Filing date: 2016-08-24
Publication date: 2018-03-01

Abstract

A casting system includes a first mold, a second mold, the first mold and the second mold being configured to receive molten metal, the first mold and the second mold exerting pressure on the molten metal to form a mechanical component as the molten metal cools, and a sensor that measures the pressure exerted on the molten metal to provide feedback information to regulate the pressure exerted on the molten metal.

Description

FIELD

The present disclosure relates to a pressure regulator. More specifically, the present disclosure relates to a displacement-pressure regulator for a casting system.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Current manufacturing processes for producing engine components of a motor vehicle, for example, cylinder blocks include high pressure die cast (HPDC) processes. Typically, as molten metal is directed to a mold, HPDC high velocity fill processes entrain air, generate oxides and have difficulty addressing metal shrinkage from certain regions within the mold. Other processes include precision sand casting which employs a bonded sand core pack mold with a large thermal bulk head chill and head deck risers to achieve desired material properties. Precision sand casting, however, is a costly process reserved for components requiring high integrity and enhanced material properties.
Accordingly, there is a need in the art for a cost efficient casting process for producing high quality and performance cast components.

SUMMARY

The present invention provides a system to cast mechanical components. Accordingly, in one aspect of the present invention, a casting system includes a first mold, a second mold, the first mold and the second mold being configured to receive molten metal, the first mold and the second mold exerting pressure on the molten metal to form a mechanical component as the molten metal cools, and a sensor that measures the pressure exerted on the molten metal to provide feedback information to regulate the pressure exerted on the molten metal.
The foregoing aspect can be further characterized by one or any combination of the features described herein, such as: the system further includes a pressure punch that receives the feedback information, the pressure punch varying the exerted pressure on the molten metal; the exerted pressure is varied according to a desired time-pressure profile; the sensor is a hydraulic pressure sensor; the sensor is a stack of Belleville washers; the system further includes a plurality of slides positioned within the first mold and the second mold, the positioning of the plurality of slides exerting the direct pressure on the molten metal; the plurality of slides is four slides; and each slide is an insert that reciprocates along a respective channel.
Accordingly, pursuant to another aspect of the present invention, an apparatus to form a mechanical component includes a first mold, a second mold, the first mold and the second mold being configured to receive molten metal, the first mold and the second mold exerting pressure on the molten metal to form a mechanical component as the molten metal cools, and a feedback mechanism that measures the exerted pressure and varies the exerted pressure to a desired time-pressure profile.
The foregoing aspect can be further characterized by one or any combination of the features described herein, such as: the feedback mechanism includes a sensor that measures the exerted pressure; the feedback mechanism includes a pressure punch that receives feedback information from the sensor, the pressure punch varying the exerted pressure on the molten metal; the sensor is a hydraulic pressure sensor; the sensor is a stack of Belleville washers; the apparatus further includes a plurality of slides positioned within the first mold and the second mold, the positioning of the plurality of slides exerting the direct pressure on the molten metal; the plurality of slides is four slides; and each slide is an insert that reciprocates along a respective channel.
Accordingly, pursuant to yet another aspect of the present invention, a method to control a casting process to form a mechanical component includes one or more of the following steps: pouring molten metal into an interior cavity defined by a first mold and a second mold, exerting pressure on the molten metal to form a mechanical component, and measuring the exerted pressure and regulating the exerted pressure according to a desired time-pressure profile.
The method to control the casting process may be further characterized by one or any combination of the following features: measuring and regulating the exerted pressure includes measuring and regulating with a hydraulic pressure sensor; measuring and regulating the exerted pressure includes measuring and regulating with a stack of Belleville washers; and exerting pressure includes exerting pressure with a plurality of slides positioned within the first mold and the second mold.
Further features, advantages, and 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.

DRAWINGS

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:

FIG. 1 is a perspective view of a top mold and bottom mold for the direct squeeze casting system in accordance with the principles of the present invention;

FIG. 2 is an interior view of the top and bottom molds;

FIG. 3 illustrates the top and bottom molds separately;

FIG. 4 is a schematic view of the system shown in FIG. 1 in use molding a component;

FIG. 5 is a schematic view of a displacement-pressure regulator system incorporated into the casting system in accordance with the principles of the present invention;

FIG. 6 is a graph of a pressure-time plot for the casting system;

FIG. 7 illustrates a Belleville washer stack displacement-pressure sensor for the casting system; and

FIG. 8 illustrates a hydraulic displacement-pressure sensor for the casting system; and

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
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 FIG. 1, the system 10 includes a pour cup 12 that communicates with a downsprue or downgate 14, which, in turn, communicates a set of molds 16 and 18 through one or more ingates 22. When the system 10 is in use, molten metal 11 is poured into the pour cup 12. The molten metal flows down the downgate 14 into the gates 22. Note that in certain arrangements the downgate 14 communicates with a runner that distributes the molten metal to a plurality of ingates 22. Although no runner and only one gate 22 is shown in FIG. 1 for the sake of simplicity, it should be understood that more than one ingate 22 may be employed with a runner. Accordingly, the molten metal 11 flows through the one or more gates 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 incudes a vent 29 to relieve pressure within the interior region 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. Other processes to fill the molds include tilt pour, low pressure, and electromagnetic pumps.
In the system 10, the molten metal is poured into the respective system with a slow pour velocity. For example, in some arrangements, the pour velocity through the gates 22 is less than 100 cm/sec, preferably less than 50 cm/sec. 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 system 10 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.
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. 2 and 3, 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 configure 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. 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 metal component 30 (shown as a block for the sake of simplicity).
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. 4 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. Further, the applied pressure can be controlled with the use of the aforementioned pressure punch and the vent 29.
Referring to FIG. 5, there is shown the casting system 10 with a pressure sensor/regulator system 71 incorporated into the top mold 16. Specifically, the pressure sensor/regulator system includes one or more pressure sensors 70 and 72 that measures the pressure in the molten metal 30 as the molten metal cools and solidifies. The die material surrounding sensors 70 and 72 can either be insulated or externally heated. Insulating or heating the sensors keeps metal in them molten longer so they maintain the ability to sense hydrostatic pressure and act as a kinetic riser, thereby feeding the local regions in the casting process. This pressure information is fed back to a pressure punch 82 positioned in the vent 29 as indicated by the feedback arrows 84 and 85. The sensors 70 and 72 can be associated with displacement regulators as the molten metal expands and contracts as indicated by the movement (double arrows 78 and 80) of respective pistons 74 and 76.
Hence, when the system 10 is in use, molten metal 30 is poured into the interior cavity 28 defined by the molds 16 and 18. The pressure punch 82 is pressed into the molten metal 30 to apply a desired pressure 100 (FIG. 6) while the vent 29 allows gas to escape from the interior cavity 28. The pistons 74 and 76 initially move outwards to accommodate the molten metal 30. The pistons 74 and 76 then move inwards to account for contraction of the molten metal 30 as it cools. In the meantime, the pressure sensors 70 and 72 measure the cavity pressure, which is transmitted back to the pressure punch 82. Accordingly, the applied pressure is adjusted with the piston punch 82 and the regulators 74 and 76 so that the applied pressure 100 provides a desired cavity pressure 102.
In sum, the molds 16 and 18 are closed and mechanically locked except for a direct pressure punch detail. Molten metal, such as, for example, 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 mechanical component 30 solidifies. The molds 16 and 18 are opened and the mechanical component is removed.
The displacement-pressure regulator can provide basic functions during the castings process, including providing measurement of internal hydrostatic molten metal pressure for feedback control of pressure applied by pressure punch(s), and providing repository for excess molten metal added to compensate the approximately 6% metal shrinkage when aluminum alloy transitions from liquid to solid. Note that 6 to 10% excess molten metal is added to the mold cavity to offset the 6% metal shrinkage, and pressure punch(s) and other moving mold slides are able to move to their dimensional set points and excess metal not used to offset liquid to solid shrinkage such that casting dimensions are met. Further, excess repository metal can be removed by machining. Moreover, the displacement-pressure regulator enables molten metal displacement repositories to act as kinetic risers with the ability to feed metal shrinkage in regions with desirable feed-paths to repositories. Kinetic risers are kept active through insulating or externally heating them to allow molten metal in repositories to remain liquid for an extended period of time.
One or both the sensors 70 and 72 can be a stack of Bellville washers 90 (FIG. 7) made of individual washers 91 that are configured to enable movement of the pistons 74 and 76. In other arrangements, one or both sensors 70 and 72 can be hydraulic pressure sensor 92 (FIG. 8) with a cylinder 94 filled with a hydraulic fluid that interacts with a piston 96. The piston 96 in turn abuts against the respective pistons 74 and 76. In some arrangements, the mold cavity or interior region 28 is coated with a high thermal resistant-pressure activated coating. 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 casting 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.
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.

Claims

1. A casting system comprising:

a first mold;

a second mold, the first mold and the second mold being configured to receive molten metal, the first mold and the second mold exerting pressure on the molten metal to form a mechanical component as the molten metal cools; and

a sensor that measures the pressure exerted on the molten metal to provide feedback information to regulate the pressure exerted on the molten metal.

2. The system of claim 1 further comprising a pressure punch that receives the feedback information, the pressure punch varying the exerted pressure on the molten metal.

3. The system of claim 2 wherein the exerted pressure is varied according to a desired time-pressure profile.

4. The system of claim 1 wherein the sensor is a hydraulic pressure sensor.

5. The system of claim 1 wherein the sensor is a stack of Belleville washers.

6. The system of claim 1 wherein mold regions around pressure sensors are thermally insulated or externally heated to maintain molten metal in them, the molten metal in pressure repositories being the last regions to solidify so they can sense pressure and act as pressurized kinetic risers from the sensor, and wherein a change in a casting program sequence causes the sensor to initiate pressure instead of sensing pressure.

7. The system of claim 1 wherein the sensor is part of a displacement-pressure regulator that provides pressure measurement and feedback control for repository of any excess metal not consumed during compensation of the metal shrinkage during transition from liquid to solid phase transformation, the repositories being passive or kinetic risers to assist in feeding metal shrinkage.

8. The system of claim 1 further comprising a plurality of slides positioned within the first mold and the second mold, the positioning of the plurality of slides exerting the direct pressure on the molten metal.

9. The system of claim 8 wherein the plurality of slides is four slides.

10. The casting system of claim 9 wherein each slide is an insert that reciprocates along a respective channel.

11. An apparatus to form a mechanical component comprising:

a first mold;

a feedback mechanism that measures the exerted pressure and varies the exerted pressure to a desired time-pressure profile.

12. The apparatus of claim 11 wherein the feedback mechanism includes a sensor that measures the exerted pressure.

13. The apparatus of claim 12 wherein the feedback mechanism includes a pressure punch that receives feedback information from the sensor, the pressure punch varying the exerted pressure on the molten metal.

14. The apparatus of claim 12 wherein the sensor is a hydraulic pressure sensor.

15. The apparatus of claim 12 wherein the sensor is a stack of Belleville washers.

16. The apparatus of claim 11 further comprising a plurality of slides positioned within the first mold and the second mold, the positioning of the plurality of slides exerting the direct pressure on the molten metal.

17. The apparatus of claim 16 wherein the plurality of slides is four slides.

18. The apparatus of claim 17 wherein each slide is an insert that reciprocates along a respective channel.

19. A method to control a casting process to form a mechanical component, the method comprising:

pouring molten metal into an interior cavity defined by a first mold and a second mold;

exerting pressure on the molten metal to form a mechanical component; and

measuring the exerted pressure and regulating the exerted pressure according to a desired time-pressure profile.

20. The method of claim 19 wherein measuring and regulating the exerted pressure includes measuring and regulating with a hydraulic pressure sensor.

21. The method of claim 19 wherein measuring and regulating the exerted pressure includes measuring and regulating with a stack of Belleville washers.

22. The method of claim 19 wherein exerting pressure includes exerting pressure with a plurality of slides positioned within the first mold and the second mold.