PULVER METALLURGICAL COMPONENT PRODUCTION The present invention is related to manufacturing components produced by means of pow- der-metallurgical manufacturing processes. More precisely, the invention relates to manu- facturing components including internal concaves and channels.

Background of the Invention It is well known in the art to produce high-class components having almost the final di- mensions by means of powder metallurgic manufacturing methods by using hot-isostatic pressing (HIP). The manufacturing method thereby comprises typically the following main steps: 1. Manufacturing a gas-atomized powder.

2. Designing and manufacturing a sheet metal capsule by means of sheet metal form- ing, cutting and welding techniques.

3. Filling the capsule with the powder.

4. Evacuation of the capsule.

5. Sealing of the capsule.

6. Hot-isostatic pressing by means of temperature and pressure (e. g. for steels typi- cally T 1100-1200°, pressure 100-120 MPa and time 1-4 h).

7. Machining, heat treatment and inspection.

In the method, the capsule die is manufactured as over-sized, in order to take into account the volumetric change of the encapsulated powder when the gas-atomized powder is con- solidated. Typically, in case of a gas-atomized powder, the density is 60-70 % of the theo- retical density, in other words, the capsule can contract significantly when the powder is consolidated into the density of 100 %. Control of the dimensional changes taking place, when the powder is consolidated, is essential for achieving the dimensional accuracy of the products and naturally it has an essential influence on the production costs due to the amount of tooling allowances and the need for machining.

A powder metallurgic method using hot isostatic pressing is also applicable for manufac- turing products having internal channels and cavities, e. g. for heating and cooling of com- ponents. Cavities and channels can be manufactured by making into the powder capsule a capsule corresponding with the desired channel and cavity structure and by filling with powder the space between the capsule surrounding the whole structure and the capsule forming the channel and cavity. The accuracy of the location of these channels is in general critical with respect to the heating or cooling of the components and, in addition, it can have influence on the mechanical reliability of the structure.

In many cases it is, however, not possible to achieve a sufficient dimensional accuracy by means of the powder metallurgic technology alone, because the contraction of the powder is not sufficiently controlled or the starting density before consolidation is not homogenous enough for the controlled consolidation. In that case an alternative is to use in the compo- nent a solid basic material, in which that part of the powder is encapsulated, into which the channels and cavities are formed. Thus, the amount of the contracting powder is minimized and, in addition, the contracting can be controlled so that a better predictability of the con- solidation can be achieved. Even in those cases the control of the dimensions in the most critical objects is not accurate enough, because for example when large surfaces are con- solidated, the dimensional changes are too big.

One alternative that has been used to some extent is to use solid basic materials, the joint surfaces of which are confronted against each other accurately. The joint surfaces are placed in the surrounding capsule so that the pressure in the hot isostatic pressing presses the surfaces against each other, thus providing a diffusion bonding. In this method the sur- faces of the solid pieces to be joined must be well finished, especially clean and even, to ensure an adequate quality of the bonding. In addition, typically, the temperature and pres- sure of the hot isostatic pressing must be increased and the time prolonged compared with a powder metallurgic bonding, in order to ensure the good quality of the bonding. On the other hand, even the smallest impurities of the joint surfaces or moving of the surfaces dur- ing the hot isostatic pressing can prevent the bonding or weaken its quality significantly.

Description of the Invention In the method in accordance with the invention the component is manufactured so, that substantially solid, preformed pieces produced by forging, casting or machining are used,

and material in powder form, in an encapsulated space, is used for the joint surfaces of the solid pieces to be joined by isostatic pressing, More precisely, the method in accordance with the invention is characterized in by what has been stated in the characterizing part of Claim 1.

The invention will be described in more detail in the following, with reference to the en- closed drawings, in which Figures la-1 c show examples of embodiments of the method in accordance with the invention.

Figure la shows one embodiment of an application of the method in accordance with the invention. In the figure, the joint area of the solid pieces 1,1'and 1"has been sealed with gas-tight welds 3 and a capsule plate 4. The area formed in that way has been filled with powder material 2. In this embodiment the welds between the joint surfaces have been partly made directly between the solid pieces. The gas tightness is a precondition for using the hot isostatic pressing. After this the powder has been consolidated by means of pres- sure and/or temperature, like for example by hot isostatic pressing. The capsule plates and welds connected thereto can remain in the component or they can be removed for example by machining and in certain cases by acid etching.

In the embodiment shown in Figure lb, the embodiment of Figure la has been improved by replacing the gas tight welds that bond the solid pieces directly with each other by cap- sule plates 4'. This is a way to improve the gas tightness of these joints.

In the embodiment of Figure lc, the amount of powder to be used in the joint has been minimized. In the figure, the area formed into the jointing point of the solid pieces 1, 1' and 1"has been filled with powder 2 and solid material 5 in order to minimize the amount of the powder material. The joint area is sealed gas tightly by means of gas tight welds 3 and a capsule plate 4. With a solution in accordance with this embodiment, the changes in the volume and dimensional accuracy caused by the consolidation of the powder can be minimized.

Due to the use of powder materials, the requirements for the dimensional accuracy of the joint surfaces are not as big as when using only solid materials. In addition, due to the strong plastic deformation caused by the consolidation of the powder, the oxide films of

the junctions of the powder and solid material are efficiently broken, thus providing a more reliable and better joint compared with the solid-solid-joint.

As the amount of the powder to be used is very much limited only at the junctions of the pieces to be joined, the dimensional changes caused by the contraction of the powder are not big, whereby more accurate dimensions are achieved after the hot isostatic pressing, than by using as basic material a capsule totally filled with powder or powder encapsulated on the surface of the solid material. For example the capsule surrounding the joint surfaces can be (1) welded to the solid materials at both sides of the joint, (II) the whole interior of the concave or the channel can be encapsulated and (III) in addition, gas-tight capsules can be manufactured between the solid materials, said capsules transmitting the isostatic gas pressure to the joint surface and consolidating the powder between the joint surfaces.

The following advantages, among others, can be achieved by the method of the invention: (a) Components having more accurate dimensions can be manufactured by means of the method in accordance with the present invention, than by using materials manufactured by means of powder only or by using powder encapsulated into the surface of the solid material for sealing the internal concaves, (b) More reliable joints can be achieved by means of the method in accordance with the present invention, than by connecting solid materials by hot isostatic pressing; in addition, the requirements for dimensional accuracy of the joint surfaces of the solid materials are not as big, (c) The joints in the components are mainly free of welding joints; welding joints can be left to the gas tight welds surrounding the joint surfaces inside the component, but they form only a small part of the load bearing cross surface, and in addition, eventual welding mistakes not opening to the surface are closed during the hot isostatic pressing.