Method and apparatus for particle injection moulding

Abstract

A die for moulding a core by a PIM process, the core having at least one internal feature, the die including; a first die part defining a first portion of an outer surface of the core; a second die part defining a second portion of the outer surface of the core; and an internal feature forming element for defining the surface of an internal feature of the core; wherein the internal feature forming element incorporates a temperature control circuit.

Claims

1. A die for moulding a core by a particle injection moulding (PIM) process, the core having at least one internal feature, the die comprising: a first die part defining a first portion of a cavity of the die, which is configured to form an outer surface of the core; a second die part defining a second portion of the cavity of the die, which is also configured to form the outer surface of the core; and an internal feature forming sacrificial insert configured to define an outer surface of the at least one internal feature of the core, the sacrificial insert being inserted into a respective recess of each of the first die part and the second die part and extending between the first die part and the second die part, the sacrificial insert including a temperature control circuit formed by at least a plurality of micro-channels extending through an interior of the sacrificial insert between the first die part and the second die part.

2. The die as claimed in claim 1, wherein the plurality of micro-channels connect with a supply of coolant fluid that flows through the plurality of micro-channels during the PIM process.

3. The die as claimed in claim 1, wherein the plurality of micro-channels contain a substance that, upon undergoing a phase change, uses a latent heat energy associated with the phase change to cool surrounding surfaces.

4. The die as claimed in claim 3, wherein the substance is solid gallium.

5. The die as claimed in claim 3, wherein the temperature control circuit is connected to an expansion chamber, and the plurality of micro-channels contain a hydrocarbon.

6. The die as claimed in claim 2, wherein the coolant fluid is water.

7. The die as claimed in claim 1, wherein the temperature control circuit includes an embedded heat conductor.

8. The die as claimed in claim 7, wherein the embedded heat conductor is a wire that is elongate and convoluted, and snakes through the sacrificial insert from a first end to a second end.

9. The die as claimed in claim 1, wherein the temperature control circuit is configured such that temperature and heat transfer is variable as a function of position on the sacrificial insert.

10. The die as claimed in claim 1, wherein the plurality of micro-channels are any one or more of: straight, spiral, contoured, or serpentine.

11. The die as claimed in claim 1, wherein the plurality of micro-channels contain one or more of: turbulators, pin fins or pedestal features configured to increase cooling effectiveness in the plurality of micro-channels.

12. The die as claimed in claim 10, wherein the plurality of micro-channels contain one or more of: turbulators, pin fins, or pedestal features configured to increase cooling effectiveness in the plurality of micro-channels.

13. The die as claimed in claim 1, wherein the plurality of micro-channels are coated in a substance that improves a heat transfer coefficient.

14. The die as claimed in claim 10, wherein the plurality of micro-channels are coated in a substance that improves a heat transfer coefficient.

15. The die as claimed in claim 11, wherein the plurality of micro-channels are coated in a substance that improves a heat transfer coefficient.

16. The die as claimed in claim 1, wherein the sacrificial insert is formed integrally with one or both of the first die part and the second die part.

17. The die as claimed in claim 1, wherein the sacrificial insert includes an element that is separate from and receivable into one or both of the first die part and the second die part to assemble the die.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described with reference to the accompanying Figures in which;

(2) FIG. 1 shows a ceramic core for a turbine blade of a design known from the prior art;

(3) FIG. 2 shows a die for moulding the ceramic core of FIG. 1 in a PIM process as is known from the prior art;

(4) FIG. 3 shows a cutaway view of the die of FIG. 2;

(5) FIG. 4 is a reproduction of FIG. 2 from the applicant's prior published patent application U.S. Pat. No. 4,384,607 which illustrates the use of a sacrificial insert to form an internal feature of a core in a die similar to that of FIG. 2.

(6) FIG. 5 shows a first embodiment of a die in accordance with the present invention;

(7) FIG. 6(a) shows a first view of a second embodiment of a die in accordance with the present invention;

(8) FIG. 6(b) shows a second view of a second embodiment of a die in accordance with the present invention;

(9) FIG. 6(c) shows a first view of a core produced using the die of FIGS. 6(a) and 6(b);

(10) FIG. 6(d) shows a second view of a core produced using the die of FIGS. 6(a) and 6(b);

(11) FIG. 7 shows in further detail a sacrificial insert similar to that of the embodiment of FIG. 6.

(12) FIG. 8(a) shows in further detail a sacrificial insert including turbulators;

(13) FIG. 8(b) shows in further detail a sacrificial insert including pin fins; and

(14) FIG. 8(c) shows in further detail a sacrificial insert including pedestal features.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

(15) As can be seen from FIG. 5, elements forming the surfaces of an internal feature of the ceramic core are provided with a plurality of micro-channels that permit cooling by passing a cooling medium through the micro-channels. This serves to reduce the temperature of the surfaces of an internal feature during cooling of a ceramic core in the die. As can be seen, a pressure side ceramic core forming a pressure side die half 111, has a cooling fluid inlet 118, which supplies cooling fluid to a plurality of cooling micro-channels 119, contained within the internal feature forming element 114. The cooling fluid proceeds to flow through additional micro-channels 120, that are contained within a suction side core die half 110 within the internal ceramic core feature forming element 113. The cooling fluid proceeds to flow to an exit 121 within the suction side forming die half 110.

(16) FIGS. 6 (a) and (b) shows an alternative embodiment of the invention wherein rather than from two parts, the die is formed from an assembly of three parts. These parts comprise a suction side core die half 210, a pressure side core die half 211 and an internal feature forming die part 222. The internal feature forming die part 222 may comprise a different material from the other die parts 210 and 211. In the Figure, the internal feature forming die part 222 comprises a sacrificial insert. The sacrificial insert contains a plurality of micro-channels, and is located in a pocket 223 that also contains a series of micro-channels, designed to line up with the micro-channels of the insert 222. By means of the aligned channels, a cooling fluid may flow between the suction side core die half 210 and the pressure side core die half 211 through the insert 222, thereby allowing temperature at the surface of the insert 222 to be controlled. This has the effect of eliminating the previously mentioned temperature created defects associated with the prior art of U.S. Pat. No. 4,384,607.

(17) In FIG. 6(a) the suction side core die part 210 and pressure side core die part 211 are arranged in alignment. In FIG. 6(b) ends of the sacrificial internal feature forming die part 222 is received in a recess of the suction side core die part 210. Subsequently the pressure side core die part 211 can be added with an opposite end of the sacrificial internal feature forming the die part 222 being received in a recess 229 of the pressure side core die part 211. The core 201 is then moulded in the assembled die. FIG. 6 (c) shows core 201 after the suction side core die part 210 and pressure side core die part 211 have been removed. In FIG. 6(d), the sacrificial internal feature forming the die part 222 has been removed.

(18) FIG. 7 shows a more detailed view of a sacrificial insert 222 for use in the die of FIG. 6. In this embodiment, the insert is made from two plates 222a and 222b. Each plate is provided on one surface with an array of micro-channels 226. When the plates 222a, 222b are aligned, the micro-channels 226 on opposing faces together define an array of micro-tubes passing through the assembled insert 222. The plates 222a, 222b may be fastened together by means of tongue 224 and groove 225 components on oppositely facing surfaces of the plates 222a and 222b. On a second surface (that is no the surface in which the channels 226 are provided) each plate 222a, 222b is provided with lips 227 and 228 which, in pairs, form ribs which are proportioned to be securely received in recesses 229 of the suction side core die part 210 and pressure side core die part 211. Further, as shown in FIGS. 8(a)-(c), the micro-channels 226 contain one or more of: turbulators 301, pin fins 302, or pedestal features 303.

(19) The two halves of the insert are manufactured by, for example, a moulding process. In an alternative method, the insert may be formed as a single plate and holes drilled to form the micro-channels using conventional or laser drilling. The micro-channels within the metal die are best placed to be formed by using laser drilling or electro discharge machining.

(20) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.