DIE-CAST BODIES WITH THERMAL CONDUCTIVE INSERTS

Abstract

A method of making an article includes placing a high thermal conductive insert in a mold. A liquid metal composition is introduced into the mold into contact with the high thermal conductive insert. The liquid metal composition in the mold is solidified to form a solid metal article with the high thermal conductive insert retained therein, and the solid metal article with the high thermal conductive insert retained therein is removed from the mold.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority to IN Application No. 201641036695, filed in the Indian Patent Office on Oct. 26, 2016.

BACKGROUND

Thermal management by conductive heat transfer is utilized in a variety of applications. For example, heat-generating electronic components can be designed to dissipate heat by conductive heat transfer through housings or other structures to a heat sink. In aerospace applications, conductive heat transfer can be used in conjunction with components disposed on an aircraft exterior such as sensor components or housings, which can be subject to ice formation during flight or during icing weather conditions on the ground.

For example, aircraft airspeed sensors typically rely on air pressure sensors that measure total pressure in a Pitot tube housing through pressure sensing ports disposed in the Pitot tube's interior walls. Ice formation can block such pressure sensing port or alter the fluid dynamic properties of the Pitot tube openings, which can cause false airspeed readings. Ice buildup on Pitot tubes is commonly addressed by conductively transferring heat from a heating element through the Pitot tube walls to icing locations. Aircraft total air temperature (TAT) sensors can measure the following four temperatures: (1) Static air temperature (SAT) or (TS), (2) total air temperature (TAT) or (Tt), (3) recovery temperature (Tr), and (4) measured temperature (Tm). Static air temperature (SAT) or (TS) is the temperature of the undisturbed air through which the aircraft is about to fly. Total air temperature (TAT) or (Tt) is the maximum air temperature that can be attained by 100% conversion of the kinetic energy of the flight. The measurement of TAT is derived from the recovery temperature (Tr), which is the adiabatic value of local air temperature on each portion of the aircraft surface due to incomplete recovery of the kinetic energy. Temperature (Tr) is in turn obtained from the measured temperature (Tm), which is the actual temperature as measured, and which differs from recovery temperature because of heat transfer effects due to imposed environments. The temperature sensor housing should protect the temperature sensing element while delivering a continuous regulated flow of outside air to the temperature sensing element that accurately represents the temperature of the outside air (i.e., avoiding recirculating eddy currents that could lead to a false temperature measurement). It is also important to avoid ice buildup that could interfere with accurate temperature measurement, which is often accomplished by providing a heating element in the housing that conductively transfers heat to icing locations.

BRIEF DESCRIPTION

According to some embodiments of the disclosure, a method of making an article comprises disposing a high thermal conductive insert in a mold. A liquid metal composition is introduced into the mold into contact with the high thermal conductive insert. The liquid metal composition in the mold is solidified to form a solid metal article comprising the high thermal conductive insert retained therein, and the solid metal article comprising the high thermal conductive insert retained therein is removed from the mold.

According to some embodiments of the disclosure, an article comprises a cast metal body and a high thermal conductive insert retained in the cast metal body.

According to some embodiments of the disclosure, a method of transferring heat comprises providing a cast metal body and a high thermal conductive insert retained in the cast metal body. Heat is provided from a heat source at a first location of the cast metal body, and is transferred from the first location of the cast metal body through the high thermal conductive insert to a second location of the cast metal body.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter of this disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic depiction of casting assembly in an example embodiment for fabricating a Pitot tube;

FIG. 2 is a schematic depiction of a cast metal body in an example embodiment of a Pitot tube;

FIG. 3A is a schematic depiction of a cast metal body in an example embodiment of a temperature sensor housing, and FIG. 3B is a magnified view of a portion of the temperature sensor housing depicting high thermal conductive inserts in a cut-out view of the housing; and

FIG. 4A is a schematic depiction of a high thermal conductive insert in a perspective view, and FIG. 4B in an example embodiment of the insert with a thermally conductive metal via.

DETAILED DESCRIPTION

With reference now to the Figures, FIG. 1 schematically depicts a casting assembly 10 for an example embodiment of fabricating a Pitot tube body. As shown in FIG. 1, cast assembly 10 includes a mold 12 having an inner cavity wall 13 configured in the shape of an outer surface of the Pitot tube body (42, FIG. 2). The mold can be any type of mold, including but not limited to a metal die that can be used for die casting, ceramic molds prepared from a wax pattern as in investment or lost wax casting, etc. A removable molding core 14 having an outer wall 15 configured in the shape of an inner surface of the Pitot tube body 42 (FIG. 2) is disposed is disposed in the mold inner cavity, forming a void space 17 corresponding to the shape of the Pitot tube body 42 (FIG. 2).

As further shown in FIG. 1, high thermal conductive inserts 16, 18, 20, 22, 24, 16, 28, and 30 are disposed in the casting assembly 10 between the die inner cavity wall 13 and the core outer wall 15. The high thermal conductive inserts can be formed from any material having higher thermal conductivity than, and compatible melting points and thermal expansion coefficients with the metal composition out of which the cast metal is to be fabricated. Examples of materials for the high thermal conductive inserts include, but are not limited to thermally-conductive carbon materials such as pyrolytic carbon, pyrolytic graphite, compression annealed pyrolytic graphite (APG), highly oriented pyrolytic graphite, and compatible metals having higher thermal conductivity and higher melting point than the metal of the cast body. The above and various other types and grades of pyrolytic graphite are commercially available, typically in flat sheet format. In some embodiments, any of the above pyrolytic graphite materials can be formed in arcuate sheets (e.g., to match the arc of the Pitot tube) by chemical vapor deposition of carbon onto an arcuate temporary support during fabrication of the inserts.

The number and positioning of the inserts depicted in FIG. 1 is an example embodiment, and other arrangements can be utilized. For example, the inserts 28 and 30 positioned near the opening of Pitot tube 40 (FIG. 2) could be omitted from the casting process, and optionally attached in a post-casting fabrication of a Pitot tube nose assembly as described in Indian patent application 201641003314 filed 29 Jan. 2016 (U.S. patent application Ser. No. 15/090,804 filed Apr. 5, 2016), the disclosure of which is incorporated herein by reference in its entirety. The high thermal conductive inserts are depicted in FIG. 1 positioned to be fully encapsulated by the metal composition of the cast body, and can be held in position during fabrication by various cast techniques or components such as pins (not shown) that can be removed after casting or left in and integrated into the cast body. Details of other cast techniques such as die casting, investment casting and components such as sprue holes, gates, die runners, etc., are not explicitly depicted in FIG. 1, but it is understood that these and other known components and techniques can be employed by the skilled person. In other example embodiments, the high thermal conductive inserts can be positioned adjacent one of the mold surfaces such as mold inner cavity wall 13 or core outer wall 15 so that it forms part of the outer surface of the cast body.

In some embodiments, a retention feature can be included by at least partially surrounding (including fully encapsulating) the high conductive thermal insert with the cast metal. In embodiments where an insert is embedded at the surface of the cast body, a retention feature can be incorporated by configuring a sheet- or panel-shaped insert to have a smaller perimeter facing the mold wall than a perimeter of the insert at a position remote from the mold wall so that cast metal can form a retention feature between the mold wall and the insert portion with the larger perimeter. Other retention features can be utilized, including but not limited to notches or recesses in the insert that accept infiltration of liquid metal during casting, surface roughening of the insert, chemical surface treatments such as etching, or coatings applied to the surface of the insert (e.g., physical vapor deposition of a metal that is compatible with metal composition of the cast body).

After set-up of the casting components (e.g., mold 12, core 14, and inserts 16, 18, 20, 22, 24, 26, 28, and 30), a liquid (e.g., molten) metal composition is introduced into the mold cavity 17, filling the mold cavity 17. Any metal composition suitable for casting can be used. In some embodiments, the metal composition comprises components for an aluminum alloy. In some embodiments, the metal composition comprises components for a nickel alloy. The casting assembly and the liquid metal composition in the mold cavity 17 are allowed to cool to a solidification temperature of the metal composition, thus forming the Pitot tube body 42 (FIG. 2) within the casting assembly 10. The mold 12 is opened along a parting line (not shown) running parallel with axial length of the Pitot tube body 42, and the core 17 is separated axially from the Pitot tube body 42 and removed from the Pitot tube internal cavity. Separation of the mold 12 and the core 17 from the Pitot tube body 42 can be promoted with mold component materials (e.g., mold surface morphology, surface treatments), design configuration (e.g., positioning of mold or die parting line, positioning and design of ejection pins and ejection pin receivers), and other techniques known to the skilled person. The Pitot tube body 42 with integrated high thermal conductive inserts, having been separated from the mold 12 and the core 17, is subjected to additional fabrication operations to form the Pitot tube 40 depicted in FIG. 2. Post-casting fabrication operations can include smoothing and removal of burrs from the cast surfaces of the Pitot tube body 42, filling of any holes left by the molds or mold tooling that are not part of the Pitot tube design, machining of new holes or channels (e.g., pressure sensing ports, drain holes, wire channels) (not shown), installation of a heating assembly 46, containing heating element(s) 44, can be installed and held in place with brazing. An end cap 48 and other components (not shown) such as a strut for mounting the Pitot tube to an aircraft body can be attached by brazing or other bonding techniques.

Some embodiments of integrated high thermal conductive inserts in cast metal bodies can provide various technical effects. In some embodiments, the use of inserts can provide a robust bond between the insert and the surrounding metal. In some embodiments, complex shapes and configurations can be achieved with inserts that would be difficult to achieve with other fabrication techniques such as machining a recess for an insert and embedding it into the opening with brazing. In some embodiments, the higher thermal conductivity of the inserts compared to the thermal conductivity of the cast metal body can promote more effective heat transfer throughout the metal body (e.g., more effective heat transfer for cooling electronic components, or more effective heat transfer for heating ice-forming metal surfaces on sensitive aircraft exterior components). In some embodiments, a high thermal conductive insert is positioned along a thermal flow path between a heat source (e.g., a heating element or an electronic component) and a heat sink (e.g., an exterior surface exposed to ambient air). In the example embodiment Pitot tube 40 depicted in FIG. 2, inserts 28 and 30 are positioned along a thermal flow path between the forward-most heater elements 44 and the front tip of the Pitot tube 40 where icing can occur. Inserts 16, 18, 20, 24, and 26 are disposed along a thermal flow path between various heater elements 44 and a heat sink at the external surface of the Pitot tube body 42. Additionally, the heat transfer effect provided by the inserts can allow for fewer or more widely spaced heater elements 44, resulting in any one or combination of: reduced power requirements, reduced need for added brazing, reduced payload, reduced susceptibility to icing, or broader design options for avoiding hot or cold spots. Similar technical effects can be achieved for the air temperature sensor housing depicted in FIGS. 3A and 3B, where a temperature sensor housing assembly 50 suitable for housing an air temperature such as a TAT sensor includes a cast housing body 72 having integrated high thermal conductive inserts 74 embedded inside the body (shown through imaginary cut-out window 76). Other embodiments or configurations, such as a housing box for electronic components (not shown) or electronic support or heat sink structures can be readily utilized as well.

Another technical effect provided in some embodiments relates to the anisotropic nature of the thermal conductivity of some high thermal conductive materials such as pyrolytic carbon and the various forms of pyrolytic graphite. Such materials are typically prepared by chemical vapor deposition (CVD) of carbon onto a temporary substrate. CVD-deposited carbon exhibits a certain degree of ordering, which can be increased during subsequent graphitization processing. The anisotropic thermal conductivity resulting from such ordering is depicted in FIG. 4A, where a sheet 60 of high thermal conductive insert material has three axes, labeled as x/y/z, or alternatively as a/b/c. Typically, for sheets of pyrolytic carbon and the various forms of pyrolytic graphite, thermal conductivity is typically high in the x and y (or a and b) directions, and is low in the z or c direction (although materials are available with other orientations such as high thermal conductivity in the z or c direction and low thermal conductivity in the x and y directions). In any case, regardless of the direction of ordering, thermally conductive metal vias can be readily provided by machining or laser-opening of a hole through the insert in the direction of low thermal conductivity, which is then filled with liquid metal during the cast process without the need for any additional via-forming steps. An example embodiment of the high thermal conductive insert 60 having a cast-filled conductive metal via 62 is shown in FIG. 4B. The conductive metal via 62 allows for transport of heat (represented by arrows 64) through the via 62.

While the present disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the present disclosure is not limited to such disclosed embodiments. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

1. A method of making an article, comprising:

disposing a high thermal conductive insert in a mold;

introducing a liquid metal composition into the mold in contact with the high thermal conductive insert;

solidifying the liquid metal composition to form a solid metal article comprising the high thermal conductive insert retained therein; and

removing the solid metal article comprising the high thermal conductive insert retained therein from the mold.

2. The method of claim 1, wherein introduction of the liquid metal composition at least partially surrounds the high thermal conductive insert with the liquid metal composition.

3. The method of claim 1, wherein the high thermal conductive insert has anisotropic thermal conductivity and comprises an axis of thermal conductivity that is relatively low with respect to at least one other axis, and further wherein the high thermal conductive insert comprises a through-hole along the axis of relatively low thermal conductivity that is filled with the liquid metal composition to form a thermally-conductive metal via comprising solidified metal composition.

4. The method of claim 1, further comprising applying a surface treatment to the high thermal conductive insert before introducing the liquid metal composition to promote bonding of the solidified metal composition to the high thermal conductive insert.

5. The method of claim 1, wherein the high thermal conductive insert comprises pyrolytic graphite or pyrolytic carbon.

6. The method of claim 1, wherein the liquid metal composition comprises components of an aluminum alloy or nickel alloy.

7. The method of claim 1, further comprising disposing a heating element in the solid metal article.

8. The method of claim 7, wherein the high thermal conductive insert is disposed along a thermal flow path between the heating element and a heated portion of the solidified metal composition.

9. An article, comprising a cast metal body and a high thermal conductive insert retained in the cast metal body.

10. The article of claim 9, wherein the cast metal body at least partially surrounds the high thermal conductive insert with the liquid metal composition.

11. The article of claim 9, wherein the high thermal conductive insert has anisotropic thermal conductivity and comprises an axis of thermal conductivity that is relatively low with respect to at least one other axis, and further wherein the high thermal conductive insert comprises a thermally-conductive metal via comprising cast metal.

12. The article of claim 9, wherein the high thermal conductive insert comprises pyrolytic graphite or pyrolytic carbon.

13. The article of claim 9, wherein the cast metal body comprises components of an aluminum alloy or nickel alloy.

14. The article of claim 9, wherein the cast metal body comprises a heating element.

15. The article of claim 14, wherein the high thermal conductive insert is disposed along a thermal flow path between the heating element and a heated portion of the cast metal body.

16. The article of claim 15, wherein the article comprises an aircraft sensor housing, and said heated portion of the cast metal body comprises an ice forming portion of the cast metal body.

17. The article of claim 16, wherein the aircraft sensor housing comprises a Pitot tube.

18. The article of claim 16, wherein the aircraft sensor housing comprises a total air temperature sensor housing.

19. A method for transferring heat, comprising

providing a cast metal body and a high thermal conductive insert retained in the cast metal body;

providing heat from a heat source at a first location of the cast metal body; and

transferring heat from the heat source from the first location of the cast metal body through the high thermal conductive insert to a second location of the cast metal body.

20. The method of claim 19, wherein the cast metal body is an aircraft sensor housing, the heat source is a heating element disposed in or on the cast metal body, and the second location of the cast metal body is an ice-forming location.

21. An article made by the method of claim 1.