Method of making a capsule for hot isostatic pressing

Abstract

A method of making a capsule 2 for hot isostatic pressing (HIPing) comprises: (i) selecting a first sheet of metal; (ii) subjecting the first sheet to a forming process, for example die forming, thereby to define a first member 4a of the capsule; (iii) securing said first member to one or more other members thereby to define at least part of a capsule for HIPing.

Claims

1. A method of making a capsule for hot isostatic pressing (HIPing), the method comprising: (i) selecting a first sheet of metal; (ii) subjecting the first sheet to a forming process thereby to define a first member of the capsule; (iii) selecting a second sheet of metal; (iv) subjecting the second sheet to a forming process thereby to define a second member of the capsule comprising first and second elongate edges; (v) securing said first member to the second member thereby to define at least part of a capsule for HIPing, by abutting the first and second elongate edges of the first member against the first and second elongate edges of the second member and securing the abutting edges together by welding.

2. A method according to claim 1, wherein said first sheet of metal selected in step (i) has a thickness of at least 1 mm and a face having an area of at least 0.25 m.sup.2 and less than 4 m.sup.2; wherein, in step (ii), said first sheet is subjected to a forming process using a die; and wherein the method comprises using the same die to produce a plurality of substantially identical first members.

3. The method according to claim 1, wherein said first member includes no weld lines or welded areas and/or said first member has a substantially constant thickness across its extent.

4. The method according to claim 3, wherein said first member includes at least three, outwardly facing curved areas, and wherein one or a plurality of said curved areas is semi-circular in shape.

5. The method according to claim 4, wherein said first member includes a component (A) which is semi-cylindrical; and a component (B) which is semi-cylindrical; and a component (C) which is semi-cylindrical.

6. The method according to claim 5, wherein said first member includes a component (D) which is semi-frusto conical; and, optionally, includes a component (E) which is semi-frusto conical; and a component (F) which is semi-frusto conical.

7. The method according to claim 6, wherein said first member includes an outwardly facing convex curve defined between a pair of adjacent components selected from components (A), (B), (C), (D), (E) and (F).

8. The method according to claim 7, wherein said first member includes an outwardly facing concave curve defined between a pair of adjacent components selected from components (A), (B), (C), (D), (E) and (F).

9. The method according to claim 1, wherein said first member includes a plurality of concave curves and a plurality of convex curves and wherein said first member includes at least three bends, wherein each of said bends is the result of bending said first sheet through an angle in the range of 5 to 90°.

10. The method according to claim 1, wherein: said second member includes no weld lines or welded areas and has a substantially constant thickness across its extent; and/or said second member includes at least three outwardly facing curved areas; and/or said second member includes one or a plurality of curved areas which are semi-circular in shape; and/or said second member include a component (A) which is semi-cylindrical; and a component (B) which is semi-cylindrical; and a component (C) which is semi-cylindrical.

11. The method according to claim 10, wherein said second member includes a component (D) which is semi-frusto conical; and/or a component (E) which is semi-frusto conical; and/or a component (F) which is semi-frusto conical; and said second member includes a plurality of concave curves and a plurality of convex curves.

12. A method according to any of claim 10, wherein the first and second sheets are subjected to substantially identical processes to produce a first member and second member which are substantially identical.

13. The method according to claim 10, wherein said first member and said second member each define shells which are secured to one another to define at least part of the capsule, wherein said first member includes a first elongate edge which is non-linear and which extends substantially within a single plane, said first member including a second elongate edge which is diametrically opposed to said first elongate edge, wherein said second elongate edge is non-linear and extends in a single plane which is the same plane in which the first elongate edge extends; wherein said first elongate edge of the second member is non-linear and which extends substantially within a single plane, said second elongate edge of said second member, is diametrically opposed to said first elongate edge, wherein said second elongate edge is non-linear and extends in a single plane which is the same plane in which the first elongate edge extends.

14. The method according to claim 1, wherein the capsule defines a substantially closed container which has fewer than ten weld lines which are externally visible on viewing the closed container, excluding any weld lines associated with any orifice(s) which is/are arranged to allow access into a void of the container.

15. The method according to claim 1, the method including arranging a structure within a void defined within the assembly comprising said first member and a or said second member, wherein the structure includes a cylindrical component and/or a frusto-conical component.

16. A capsule made as described in claim 1, wherein: the capsule comprises a first member secured to one or more other members thereby to define at least part of a capsule for HIPing, wherein said first member includes no weld lines or welded areas, has a substantially constant thickness across its extent and includes at least three outwardly facing curved areas, wherein one or a plurality of said curved areas is part circular in shape; the capsule comprises a second member wherein said second member includes no weld lines or welded areas, has a substantially constant thickness across its extent and includes at least three outwardly facing curved areas, wherein one or a plurality of said curved areas is part circular in shape; in said capsule said first and second members are welded so that a gas tight seal is defined between the two members; and wherein said capsule is gas tight.

17. A method of producing a component (herein a “HIPed component”), the method comprising: (i) selecting a capsule as claimed in claim 16; (ii) subjecting the capsule to HIP.

18. The method according to claim 6, wherein: said second member includes no weld lines or welded areas and has a substantially constant thickness across its extent; said second member includes at least three outwardly facing curved areas; said second member includes one or a plurality of curved areas which is semi-circular in shape; said second member includes a component (A) which is semi-cylindrical; and a component (B) which is semi-cylindrical; and a component (C) which is semi-cylindrical.

19. The method according to claim 6, wherein said first member and said second member each define shells which are secured to one another to define at least part of the capsule, wherein said first member includes a first elongate edge which is non-linear and which extends substantially within a single plane, said first member including a second elongate edge which is diametrically opposed to said first elongate edge, wherein said second elongate edge is non-linear and extends in a single plane which is the same plane in which the first elongate edge extends; wherein said a first elongate edge of the first member is non-linear and extends substantially within a single plane, said second elongate edge of the second member, is diametrically opposed to said first elongate edge, wherein said second elongate edge is non-linear and extends in a single plane which is the same plane in which the first elongate edge extends.

20. The method according to claim 19, wherein the capsule defines a substantially closed container which has fewer than four weld lines which are externally visible on viewing the closed container, excluding any weld lines associated with any orifice(s) which is/are arranged to allow access into a void of the container; and wherein the first and second sheets are subjected to substantially identical processes to produce a first member and second member which are substantially identical.

Description

(1) Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

(2) FIG. 1 is an end view of a capsule for HIP;

(3) FIG. 2 is a cross-section along line II-II of FIG. 1;

(4) FIG. 3 is a perspective view of the capsule of FIGS. 1 and 2;

(5) FIG. 4a is a side view of one half of an outer part of a capsule which is similar to the capsule of FIGS. 1 and 2;

(6) FIG. 4b is a side view of one half of an inner tube of the capsule; and

(7) FIG. 4c is a side view of one half of an inner cone of the capsule which is arranged to cooperate with the tube of FIG. 4b (although FIG. 4c is presented on a larger scale compared to FIG. 4b).

(8) In the figures, the same of similar parts have the same reference numerals.

(9) A capsule 2 for producing a relatively complex shaped final component comprises an identical pair of outer members 4a, 4b (FIG. 3) within which are secured an inner cylinder 6 and an inner cone 8. The capsule is closed by first end disc 10 at one end and second end disc 12 at an opposite end and shown in FIG. 3. The half capsule shown in FIG. 4a is similar to that shown in FIG. 3, except the FIG. 4a capsule does not include first and second end discs (10, 12) but, instead, includes preformed semi-circular ends 121, 123. Referring again to FIG. 3 respective tubes 13, 15, 17, 19, 21 extend through end disc 10 for introducing powdered metal into the capsule and/or for evacuating the capsule prior to hot isostatic pressing (HIP). The design of the capsule 2 may be produced with the help of Finite Element Analysis (FEA) so that the final component produced using the capsule is optimised.

(10) Features of the capsule and its use are described in further detail below.

(11) Outer member 4a is made from a single cold rolled steel sheet. The member is unitary and includes no weld lines. The member 4a is made by die forming methods. Hydroforming is a type of die forming which uses a high pressure hydraulic fluid to press the steel sheet, at ambient temperature (e.g. about 23° C.), into a die. Flexforming is similar except it uses a bladder containing a fluid which is used to urge the sheet steel into the die so the steel assumes the shape of the die.

(12) Outer member 4a has a relatively complex shape which is defined in a single sheet of steel. At its end adjacent end disc 12 (or preformed end 121), the member 4a includes a wall section 20 which is substantially semi-cylindrical in shape. Moving leftwardly in the representation of FIG. 2, a semi-frusto conical section 22 is contiguous with wall section 20 and its outer surface is angled inwardly, relative to the outer surface of wall section 20, at an obtuse angle of about 225°. There is a smooth outwardly-facing convex curve 23 between respective sections 20, 22. Next, there is a wall section 24 which is substantially semi-cylindrical in shape and which has an outer surface which defines an angle of about 135° to conical section 22, there being a smooth, outwardly-facing concave curve 25 between respective sections.

(13) Wall section 24 is contiguous with a semi-frusto conical section 28, the outer surface of which is angled at an angle of about 135° to the outer surface of wall section 24. A smooth, outwardly-facing concave curve 29 is defined between sections 24, 28.

(14) Wall section 28 is contiguous with wall section 30 which is substantially semi-cylindrical in shape and which has an outer surface which defines an angle of about 225° to section 28, there being a smooth, outwardly-facing convex curve 32 between respective sections.

(15) Between front end disc 10 (or preformed end 123) and wall section 30, outer member 4a is relatively more complex in shape. It includes a semi-frusto conical section 34 which is contiguous with section 30 at one end. At its opposite end, it is contiguous with a radially extending semi-annular section 36 which, in turn, is continuous with a semi-frusto conical section 38. Section 38 is contiguous with a semi-cylindrical section 40.

(16) It will be appreciated that, between section 30 and disc 10 (or preformed end 123) of member 4a, there is a series of short sections which include both convex and concave curves between the sections.

(17) Outer member 4b of the capsule is identical to member 4a. Together, outer members 4a and 4b represent identical halves which are arranged to define the majority and/or substantially the whole of a radially outwardly facing surface of a final component which is made using the capsule 2 in a HIP process.

(18) In capsule 2, inner cylinder 6 and inner cone 8 are welded in position. Then, the two outer members 4a and 4b are abutted and welded to one another so that substantially straight, axially extending, diametrically-opposed weld seams 42a, 42b (FIG. 3) are defined on the outside of the capsule 2. Discs 10, 12 and associated tubes 13, 15, 17, 19, 21 (if provided) are also welded in position to define the completed capsule 2.

(19) It should be appreciated that the capsule 2 can be assembled significantly more rapidly than an equivalent capsule which may comprise individual sections which are welded to define, for example, sections 20, 24, 28, 30, 34, 36, 38, 40. Furthermore, the number and/or total length of weld seams used to assemble capsule 2 will advantageously be significantly less than in an equivalent capsule which includes multiple individual sections to define, for example, sections 20, 24, 28, 30, 34, 36, 38, 40.

(20) Minimising the number of weld seams may also help to minimise the amount of heat the capsule is subjected to during its manufacture. Welding subjects the capsule to heat which may distort the geometry of any weld and/or any part being welded. Thus, using outer members 4a, 4b (which incorporate complex geometry) may help to improve tolerances within the capsule and, consequently, in a final component formed using the capsule.

(21) Furthermore, minimising the number of welds may minimise the overall error introduced into the capsule by virtue of the degree of error associated with each weld and may therefore reduce the number of capsules which are rejected for being outside design parameters upon post-welding inspection.

(22) It is also found that, by reducing the complexity of weld seams required, a capsule produced is less susceptible to weakness and potential failure. For example, as described, between front end disc 10 (or preformed end 123) and wall section 30, outer member 4a (and identical outer member 4b) are relatively complex. Welding individual sections to define such complexity would be time-consuming and any defective weld would, in turn, lead to a defective capsule. Thus, by avoiding complex weld seams (or at least reducing their number/length) and providing outer members 4a, 4b as described, advantages may arise.

(23) After construction of the capsule 2, it is evacuated by connecting a vacuum line to one or more of tubes 13, 15, 17, 19, 21 and then is subjected to helium leak testing to ensure it is gas-tight. Next, it is filled with powdered metal via one or more of the tubes.

(24) The powdered metal may be selected from, but is not limited to, stainless steels including austenitic, ferritic and martensitic grades, duplex and super duplex stainless steels, Ni, Ti and CoCr alloys together with metal matrix composite alloys. The metal powder may be filled up to 100% volume of the void defined in capsule 2. The powder fill weight is calculated based on the capsule design and the particle size distribution of the metal powder. The metal powder is filled into the capsule to achieve a known powder fill weight and an optimum powder packing density.

(25) After filling of the capsule 2, it is evacuated of entrapped air by connecting a vacuum line to one of the tubes and pulling a vacuum. Then, tubes are crimped to seal the assembly.

(26) Next, the capsule 2 is subjected to HIP by placing it in a HIP system and subjecting it to a predetermined temperature and pressure for a predetermined time.

(27) After HIP, the capsule is placed in a heat treatment furnace at a predetermined temperature for a predetermined time in order to achieve optimum material properties for the final component.

(28) After HIP, parts of the capsule which are not to be included in the final component are removed. This may be done by immersion of the post-HIPed assembly in various acids and stages for a suitable time to dissolve away the sheet steel which encases the component. In particular, outer members 4a, 4b are dissolved away. After being HIPed, the powdered metal is fully dense and has a fine homogenous grain size.

(29) In addition to advantages associated with the capsule itself, a final component made using outer members 4a, 4b may also exhibit advantages. In this regard, since the final component is made using a capsule which may have very tight tolerances, the final component made may likewise have tight tolerances. Furthermore, the amount of machining required, post-HIP, may be reduced, compared to the situation when known methods are used to make components. This may arise by virtue, for example, of being able to define rounded edges and/or corners of predetermined radii, as described.

(30) Use of outer members 4a, 4b may also help to reduce weld imprints on the final component. For example, in known methods wherein some welds in a capsule are joined by parallel flanges, weld imprints may be clearly visible in the final component, because the flanges inevitably include some space which may fill with powder during manufacture. Such weld imprints may be minimised by use of the process described herein.

(31) It may be possible, by inspection of a final component made using the process described, to confirm the final component has been made using a capsule including identical outer members 4a, 4b because the final component may include two parallel, axially extending, diametrically spaced apart lines or areas defined (or apparent) in the outer surface of the component.

(32) Advantageously, once a die has been produced to enable formation of parts of a capsule, for example outer members 4a, 4b, the die may be used numerous times to produce a multiplicity of identical members for capsules which may, in turn, be used to produce a multiplicity of identical final components. Thus, the method described enables more consistent production of capsules and final components than hitherto.

(33) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.