Patent Application
20150336172
The present invention relates to a method of producing a metallic body provided with a metallic cladding, comprising the following steps: providing a hollow body that comprises a bottom wall, a core that extends from the bottom wall and a lateral wall and that presents an inner space; filling said space with a metallic cladding material that will form said cladding; positioning the hollow body in a metallic capsule; closing the metallic capsule and evacuating air from the interior of the latter, and; applying an elevated pressure and an elevated temperature on the outside of said capsule such that said cladding material is bonded to said hollow body.
Preferably, but not necessarily, after said application of elevated pressure and elevated temperature, a final body formed by the hollow body and the cladding material is subjected to a machining operation, in which one part thereof is removed and the cladding material is exposed as a cladding on a second part thereof.
The applied elevated pressure is an isostatic pressure generated by means of pressurised gas. The elevated temperature is below the temperatures at which any of the metals used melt. The process of applying elevated pressure and elevated temperature thereby belongs to the processes commonly named Hot Isostatic Pressure processes.
The invention has been developed with regard to the production of injector nozzles for diesel engines, in which there is provided a Ni-base cladding on a tool steel body. However, it should be understood that, even though this is a preferred implementation of the inventive idea, the invention is applicable to production of all kind of metallic bodies in accordance with the preamble of claim 1 in which a metallic cladding material is to be applied on a particular body of another metallic material. The capsule is used for sealing purposes necessary for the HIP process, whereby sealing of each of a large number of the above-mentioned hollow bodies housed in said capsule can be avoided.
Injector needles for diesel engines are presently being produced by means of a method know as the Sand-HIP-Method. According to this method, hollow bodies made of a suitable steel grade and having a central core extending therein are filled with a metallic cladding material formed by a powder, typically a Ni-based powder. Thereby, the exposed part of the central core is totally covered by the powder. The powder is pre-pressed (preferably mechanically) in order to achieve a high density before an elevated pressure and temperature in accordance with the HIP process is later applied thereto. After pre-pressing of the powder, an open top part of the hollow body, through which the powder has been introduced, is closed, and remaining air is evacuated from the interior of the closed hollow body. In this way a plurality of hollow bodies are provided.
Furthermore, there is provided a capsule, in which a plurality of such hollow bodies is to be positioned during the subsequent HIP process. The reason for providing said capsule is that the individual hollow bodies are not sealed and evacuated with regard to air. Said capsule may have a cylindrical or tubular shape with a bottom wall and a lateral wall. The bottom wall is covered with sand, on which said plurality of hollow bodies are positioned side by side in a given pattern with spacing between each hollow body. After that, said spacing is filled with sand. The hollow bodies are also covered with sand on top thereof. Subsequently to the sand-filling operation, the top of the capsule is closed by provision of an upper wall, air is evacuated from the interior of the capsule (and thereby also the interior of the hollow bodies) and the capsule is finally sealed. Thereafter, the capsule is subjected to an elevated pressure and an elevated temperature in accordance with the principles of Hot Isostatic Pressing, whereby the powder of the metallic cladding material densifies further and gets bonded to the surrounding material of the hollow body, including said core. The capsule is then opened and the hollow bodies are taken out. Each (initially) hollow body is machined such that the lateral wall and the top wall are removed and the cladding material is exposed. Also the cladding is machined to such a degree that, outgoing from the given size and extension of the core, a predetermined cladding thickness is achieved on the latter. The machining is a turning operation and is based on the presumption that the geometry of the hollow body is symmetric around a central axis of the latter.
However, during the HIP process, the shape of the hollow body and the core may be somewhat deformed due to the interaction between the sand and the hollow bodies. It is believed that this deformation is due to the fact that friction within the sand results in a non-uniform pressure being applied on the hollow body. As a result of this slight deformation, the extension of the core is not exactly the same as it was initially, resulting in inexactness and an uncertainty of the actual cladding thickness as the material of the hollow body and part of the cladding material is later removed by way of machining. As long as the tolerance requirements are not too tough, this deviation from perfect symmetry can be accepted. However, as tolerance requirements are getting stricter, a way of improving the tolerances upon production of the injection nozzles is requested.
WO20047030850 describes a method for manufacturing fuel nozzles for diesel engines by applying a corrosion resistant cladding onto a preformed core member. Page 16, lines 12-30 and FIG. 3 describes an embodiment for manufacturing of a nozzle by providing a preformed core member 12, placing the core member 12 in a tubular capsule 15, placing a filler pipe 21 around the core member 12 and filling the space between core member and filler pipe with a powder of a cladding material. The arrangement is thereafter subjected to HIP.
U.S. Pat. No. 6,168,871 B1 shows a method of manufacturing blades or vanes for gas turbines. According to one embodiment a vane is manufactured by arranging a jacket 14 around a mandrel 12 and filling the cavity 18 there between with powder. Subsequently, the jacket 12 and/or the mandrel 18 are removed (col 3, line 65-col 4, line 1 and lines 21-24. According to a second embodiment the mandrel 12 may be provided with a cross-sectional configuration to form spars 26 in the interior of the blade (col 4, line 41-51).
A further method for manufacturing a fuel injection nozzle is described in EP2450557.
It is an object of the present invention to present a method of producing a metallic body provided with a metallic cladding which remedies at least some of the above-mentioned deficiencies of prior art.
In particular, it is an object to improve the exactness of the thickness of the cladding, and thereby to enable higher tolerance requirements.
The object of the invention is achieved by means of the initially defined method, wherein said capsule is coaxial with the hollow body and has a lateral inner periphery that has a shape and dimension that corresponds to the shape and dimension of the outer lateral periphery of said hollow body, characterised in that said hollow body with the core therein is formed in a machining operation in which material is removed from a blank of a solid piece of material, wherein after said application of elevated pressure and elevated temperature, a final body comprised by the hollow body and the cladding material attached thereto is subjected to a machining operation, in which one first part of said hollow body is removed and the cladding material is exposed as a cladding on a second part of said hollow body wherein said first part comprises the lateral wall of the hollow body and said second part of the hollow body comprises the core that extends from the bottom wall of the hollow body.
Since the hollow body is formed in a machining operation in which material is removed from a blank of a solid piece of the positions of the respective parts of the hollow body, i.e. the core and the hollow wall, are very precise in relation to each other. This in turn provides the advantage that the final body that results after HIP is very symmetric and can be machined such that a high degree of dimensional accuracy of the metallic cladding is achieved.
There is a tight fit, i.e. only a small spacing, between the outer periphery of the hollow body and the inner periphery of the capsule. If said spacing is too large, the capsule may be unevenly (non-uniformly) deformed, and as a result thereof, the pressure applied to the hollow body may non-uniform, and, as result thereof, the hollow body may become deformed, which will affect the exactness of the thickness of the cladding negatively as the latter is exposed by means of a machining operation such as a turning operation.
It is therefore preferred that, at least for the case in which the hollow body has a circular outer periphery, the ratio between an inner diameter (or cross-section measure, for geometries other than circular) of the capsule and an outer diameter (corresponding cross-section measure) of said hollow body, defined as Dcapsule/Dhollow body is in the range of 1-1.15, or even more restricted, preferably in the range of 1-1.10, or even 1-1.05.
According to a preferred embodiment of the invention, the capsule is elongated and has a length which is a plurality of the length of the hollow body, wherein the method includes that a plurality of hollow bodies are stapled on each other inside the capsule before the latter is closed. Thereby, efficient production of large numbers of the coated body is promoted.
According to a preferred embodiment, said first part comprises the lateral wall of the hollow body and said second part of the hollow body comprises a core that extends from the bottom wall of the hollow body, wherein there is a spacing between the lateral outer periphery of said core and the inner periphery of the lateral wall of hollow body, and wherein said spacing is filled with said metallic cladding material. Typically, the hollow body, with the core therein, is produced by a machining operation in which material is removed from a solid piece of metal material, such as a rod or bar, such that the core is exposed and a tubular shape of the body is generated. Thus, preferably, the hollow body is a tubular body which is closed in one end thereof by a bottom wall and presents a core extending from said bottom wall, leaving a space between the core and an inner periphery of a lateral wall thereof.
According to one embodiment, the metallic cladding material with which said space is filled is a metallic powder. The use of powder makes it possible to fill also spaces of more complicated shape, and to use different powders for different parts of said space. After filling of the hollow body with powder, the latter is closed, but not sealed.
Preferably, the powder that has been introduced into the space is pre-pressed, preferably by means of a mechanically applied force, before the hollow body is closed and evacuated from air. The pre-pressed powder preferably fills the hollow body up to the upper end thereof, i.e. the end thereof at which an upper wall (hat), is attached in connection to the closure of the hollow body. The hollow body is closed such that there is communication between the inner space filled with powder and the surrounding. In other words, the hollow body is not sealed.
According to an alternative embodiment, the metallic cladding material with which said space is filled is a solid body that has a shape and size corresponding to the shape and size of said space. Thereby, the risk of having voids or the like that might be caused by a defect powder or due inexact filling of said space or erroneous pressing of the powder, is avoided, as well as the measures that have to be taken when handling a powder. An upper wall is not necessitated for the closure of the hollow body. Closure of the hollow body is achieved as the solid body of cladding material is set in place.
According to a preferred embodiment, the metallic body produced by means of said method is a nozzle, in particular an injector nozzle for diesel engines.
An embodiment of the present invention will now be described more in detail with reference to the annexed drawing, on which
The hollow body 2 comprises a first part formed by a bottom wall 3 and a lateral wall 4. It also comprises a second part formed by a core 5 that extends from the bottom wall 3 of the hollow body 2, wherein there is a space 6 (formed by a circumferential spacing) between the lateral outer periphery of said core 5 and the inner periphery of the lateral wall 4 of the hollow body 2. The lateral wall 4 extends beyond the core 5 in the longitudinal direction of the latter. In the preferred embodiment described here, the bottom wall 3, the lateral wall 4 and the core 5 are thus all formed by one and the same piece of material. Thereby, the positions of the respective parts in relation to each other can be very precise, and there is no need of any welding operation or the like in order to attach one part to the other.
The cladding material 7 has a different microstructure and/or composition than the part of the hollow body 2 on which it is to form a cladding. In this specific case, the part on which the cladding material is to form a cladding is the core 5. However, it is also conceivable that, in a different application, the cladding material could be provided for the purpose of forming a cladding on the inside of, for example, the lateral wall of a hollow body. In the present embodiment (injection nozzle for a diesel engine), the cladding material 7 has a different composition than the hollow body 2. Preferably the cladding material 7 comprises a metallic alloy that results in an improved corrosion resistance of the final product at the region or regions in which it forms a cladding on said part, here the core 5, of the hollow body 2. Preferably, when the final product is to be an injection nozzle for a diesel engine, the cladding material consists of a Nickel-based material, preferably any of NiCr49Nb1, NiCr22Al6, or NiCr22Mo8Nb4Ti.
Subsequent to the filling of the space 6 with the cladding material 7, the latter is subjected to a compression step, in which a unidirectional compressive mechanical force F is applied to the cladding material 7. In
When a compressed and relatively dense cladding material 7 is provided inside the hollow body 2, the latter is closed.
According to the invention, and as shown in
When the hollow body 2 is inserted into the capsule 10, the spacing between the outer periphery thereof and the inner periphery of the capsule 10 is only large enough to enable said insertion. Too large a difference between the diameter of the hollow body 2 and the inner diameter of the capsule 10 will result in less uniform compression transferred to the hollow body through the capsule during subsequent HIP. Preferably, the ratio between an inner diameter of the capsule 10 and an outer diameter of said hollow body 2, defined as Dcapsule/Dhollow body is in the range of 1-1,10.
The wall thickness of the capsule 10 as well as the wall thickness of the lateral wall 4 of the hollow body 2 is small enough to permit deformation thereof caused by the isostatic pressure that said walls are subjected to during the following HIP process. Subsequent to the positioning of the hollow bodies 2 in the capsule 10, the latter is closed in its opposite ends, as indicated in
As a result of the HIP process the cladding material is densified (when the initial material is in the state of a powder) and bonded to the lateral wall 3, the upper wall 9 and the core 5 of the hollow body 2. Due to the densification of the cladding material and a corresponding deformation of the lateral wall 4 of the hollow bodies 2 and the capsule 10, the latter will present waists at locations corresponding to where the cladding material is present in the capsule. This can be more clearly seen in
After separation of the individual hollow bodies 2 from each other final bodies 11 with the shape shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 12173411.5 | Jun 2012 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/062789 | 6/19/2013 | WO | 00 |
