LAITINEN ARTTU (FI)
| WO1993017820A1 | 1993-09-16 |
| DE3726259C1 | 1988-12-08 |
| 1. | Method for manufacturing a component made of powder by a hot isostatic pressing, which component is equipped with inner channels or with other inner cavities, which method comprises the following steps: manufacturing of a cavity mould with a desired size and shape ; placing the cavity mould inside a capsule in a way required by the desired cav ity ; filling the capsule with a powder around the cavity mould ; vacuuming the capsule and closing gas tightly ; performing a hot isostatic pressing, where the powder around the cavity mould densifies ; removing the cavity mould after the hot isostatic pressing, characterised in that a second hot isostatic pressing is performed where the powder outside the cavity mould densifies further. |
| 2. | Method according to claim 1, characterised in that in the manufacturing phase of the cavity mould the cavity mould with desired size and shape is filled with a first powder which differs from the powder out side the cavity mould, and the cavity mould is either closed powder tightly or it is vacuumed and closed gas tightly ; in the removing phase of the cavity mould the first powder is removed from the cavity mould. |
| 3. | Method according to claim 1, characterised in that the cavity mould is a mould made of a solid material and shaped like the cavity, that is a mould core. |
| 4. | Method according to claim 2, characterised in that the first powder is still in a pow der form when it is removed. |
| 5. | Method according to claim 1, characterised in that the first powder or the solid mould core is removed using means which comprise chemical, mechanical and/or thermal means. |
| 6. | Method according to any of the preceding claims, characterised in that the first and the second powder differ from each other by their sintrating temperature. |
| 7. | Method according to any of the preceding claims, characterised in that the material of the solid mould core and the second powder differ from each other by their melting temperature. |
| 8. | Method according to any of the preceding claims, characterised in that after the first isostatic pressing the density of the second powder is at least 90 %. |
| 9. | Method according to claim 5, characterised in that after the first isostatic pressing the density of the second powder is 9095 %. |
| 10. | Method according to any of the preceding claims, characterised in that the first pow der is a ceramic powder and the second powder is a metal powder. |
| 11. | Method according to any of the preceding claims, characterised in that the compo nent is a valve. |
The hot isostatic pressing (HIP) can be used to compress powder, usually a metal powder, into a solid component. The compression is usually carried out by using a mould made of thin metal plate, that is a so called capsule, which is filled with powder, vacuumed and placed into an autoclave in a high temperature and pressure. The capsule can be so formed that it resem- bles the actual object, then it is a so called near net shape (NNS) manufacturing.
It is previously known to make the inner channels using hot isostatic pressing so that the pres- sure enters into the channels inside the object. The defects in this technique are that the cross section dimensions of the channel change during the compression and that several welding joints cause risks during manufacturing.
Although the gas, typically argon, which is used in the compression enters during the hot isostatic pressing into the channels, the pressure of the gas is not necessarily enough to pre- vent the effects shaping the cross section profile of the material surrounding the channel. The risks of the manufacturing are linked to that in the method in question the inner channels must be in connection to the outer side of the capsule and making of welds of the gas tight connec- tion tubes is difficult.
Also a previously known methdod is disclosed in publication US3996048, where there is used tubes filled with a ceramic to build up inner channels. The difference to the present invention is that in the mentioned patent only one comperssion with the hot isostatic pressing is used and that the ceramic is removed after the compression by leaching with acid or alkali solution.
The aim of this invention is to produce a method for manufacturing a powder made compo- nent, where the effects caused by the hot isostatic pressing to the cross section profile of the inner channels are minimized and to minimize the risks relating to the manufacturing of an object, such as the difficult welding joints.
In a method according to the invention the inner channels are made so that a) the moulds used to form the inner channels of a component are filled with a first powder, preferably a ceramic powder and placed inside of the actual capsule, or b) a piece is made which is formed like the cavity and made of a solid material, preferably a copper-nickel alloy and placed inside the actual capsule. The actual capsule in turn is filled with a second powder, that is a mould pow- der, which typically is a metal powder. According to the invention it is essential that these materials, the first powder or the solid material and the second powder, differ from each other, preferably the difference is either in the different sintrating temperatures of the powder or in the different melting temperatures of the materials.
When the actual capsule is filled with a mould powder, vacuumed and closed gas tightly, a first hot isostatic pressing is performed to the capsule in the autoclave.
After the first compression through the openings which are left to the capsule either a) the first powder is removed mechanically from the inner channels or b) the solid mould core ma- terial is melt from the inner channels. After this, a second hot isostatic pressing is performed, where the mould powder densifies further.
In the following the invention is disclosed in more detail while referring to the attached draw- ings, where Figure 1 depicts the ceramic filled inner channels which are used for making inner channels and placed inside the actual capsule, and Figure 2 depicts a component to be produced after the hot isostatic pressing, and where there is depicted the openings which are used for removing the ceramic powder after the first hot isostatic pressing.
In Fig. 1 inside the actual manufacturing capsule 1, which is used for manufacturing a com- ponent from powder, a mould 2 of the desired inner channel is placed, which is manufactured preferably from a metal plate. These moulds of the inner channels are filled with a powder, preferably a ceramic powder, e. g. aluminium oxide (AL203) which differs from the actual mould powder.
When the powders are placed the article is vacuumed. The inner channel parts, which are filled with ceramic, can be either separately vacuumed and closed or a hole can be left to them, when they get vacuumed during vacuuming of the actual article. In the later case care must be taken that the ceramic powder of the inner channels and the mould powder used to fill the actual capsule, typically a metal powder, do not mix.
After this a first hot isostatic pressing is performed. The parameters for the first compression, that is the temperature (e. g. 1000-1300 °C), the pressure (e. g. 100-150 Mpa) and the time are so chosen that the mould powder in the capsule compresses almost to a full density (typically >92%, which is a typical bound density of a powder, after which the porosity through the structure is removed) but the ceramic powder used for the inner channels stays loose.
Because the ceramic powder remains loose it can be easily removed by making holes to the capsule, through which the ceramic powder is removed from the inner channels. In Fig. 2 is depicted the component to be manufatured after a hot isostatic pressing, and there is also de- picted the openings 3 which are used to remove the ceramic powder after a first hot isostatic pressing.
After this the capsule is taken again to the hot isostatic pressing, where the used parameters, i. e temperature, pressure and time are so chosen that the desired density in the mould powder is achieved. After the second compression the article, which can be e. g. a valve, is ready for follow-up processing that is typically thermal processing and machining.
If instead of a first powder is used a mould made of solid material, the main features of the processing are the same as in the above mentioned example but the parameters of the first hot isostatic pressing are so chosen that the solid mould does not melt during the processing. Af- ter the first hot isostatic pressing holes are made to the capsule and the solid moulds are re- moved by melting in an oven whose temperature is higher than the melting temperature of the solid moulds but lower than melting temperatures of the second powder and the capsule mate- rial. After removing the moulds a second hot isostatic pressing is performed, whose parame- ters are so chosen that the second powder achieves a full density.