Patent Application
20160361766
The present invention relates to a method for manufacturing a metallic body having a cladding according to the preamble of claim 1.
Hot Isostatic Pressing (HIP) is a conventional method for manufacturing components of metallic material. The method allows for manufacturing of complex components in near-net shape and also for integration of different materials in the same product. In HIP, a steel capsule which defines the final shape of the component is filled with metallic powder and thereafter subjected to high temperature and high pressure so that the particles of the metallic powder bond into a solid component.
Hot Isostatic Pressing may be used to apply claddings of metallic materials onto pre-manufactured cores. WO2004/030850A1 describes a method for manufacturing fuel valve nozzles. According to the method, a metallic tube section is arranged to form a space around a pre-forged nozzle core. The space is filled with metallic powder and the arrangement is enclosed in a capsule and subjected to HIP so that the metallic powder, the core and the tube section bond into a solid component.
A similar method for manufacturing a valve nozzle is described in Applicants European Patent Application EP12173411. This method comprises the steps of forming a solid blank in a metal machining operation into a hollow body which comprises a bottom wall from which a core extends and a lateral wall which encloses a space around core. The space is filled with metal cladding material and closed by an upper wall and subsequently subjected to HIP.
After HIP the solid components are typically subjected to machining in order to expose the cladding on the core. Typically, machining is performed by turning or milling.
However, often the final consolidated component is deformed during the HIP process. This causes a problem in the machining of the component since it becomes difficult to accurately clamp and center the component in the machining apparatus. As a consequence thereof, the cladding may not be machined to an accurate thickness. A further drawback with the prior art is that the machining of the components is time consuming and costly due to cumbersome manual labor and a poor yield of acceptable components.
Consequently, it is an object of the present invention to present an improved method which allows for manufacturing by HIP of metallic components having a cladding whereby the cladding on the final components has very low thickness variation. A further object of the present invention is to achieve a cost effective method for manufacturing of metallic components having a cladding. Yet a further object of the present invention is to present a method for manufacturing of metallic component having a cladding whereby the method can be performed in short time and with little effort.
According to a first aspect of the invention at least one of the above objects is achieved by a method for manufacturing a metallic body 50 having a core 5 and metallic cladding 60, comprising the following steps:
By providing the centering means in the hollow body prior to the step of Hot Isostatic Pressing it is possible to accurately center the HIP:ed solid body in a metal machining apparatus with respect to the center of core of the solid body, even if the solid body is deformed during HIP. By subsequently machining the cladding to a predetermined thickness which is determined as a distance from the center of the core, the thickness of the cladding around the core may be held within a very narrow tolerance range.
The principle of invention is further explained with reference to
It should however be appreciated that
According to the invention, the centering means 11 and 12 are applied prior to HIP in the center of the bottom and upper walls 3, 9 of the hollow body (position X1). During densification, the periphery of the capsule 10 and the solid body 20 is deformed anisotropic in radial direction as indicated in
In the case of conventional manufacturing of a cladded component (which does not comprise centering means), the end of the solid body 20 is typically gripped by a chuck and the solid body will therefore be centered with respect to the center of the chuck. However, since the circumference of the solid body is deformed anisotropic, the center of the chuck will not be aligned with the center of the core of the pre-manufactured body. Instead, the solid body will be centered along the line X2 which is offset from the center of the core. When the solid body is machined the offset centering will cause the solid body to rotate eccentrically and cause the thickness to vary on the core.
Further embodiments and advantages of the present invention are disclosed in the dependent claims and the following detailed description.
The inventive method will in the following be described in detail with reference to the manufacturing of a fuel injection nozzle blank for a diesel engine, in particular a two-stroke diesel engine. For further details it is referred to Applicants non-published European Patent Application EP12173411 which content herewith is incorporated by reference
In a first step of the method a hollow body 2 is provided.
According to a first alternative of the inventive method, the hollow body 2 is manufactured by machining of a solid blank of metal, i.e. a single piece of metal for example a solid cylindrical bar of steel. The solid steel blank is subjected to a metal machining operation, for example milling, in which metal is removed from the blank such that the core 5, the space 6 and the lateral wall 4 are formed in one end of the blank 1 and leaves the bottom wall 3 in the other end of the blank. The advantage thereof is that the position of the various parts of the hollow body, i.e. the core and the bottom- and upper wall can be made very precise in relation to each other. There is further no need for auxiliary operations such as welding for attaching the parts of the hollow body to each other.
According to a second alternative of the inventive method, see
In a second step, see
In a third step the filled hollow body 2 is closed. Thereby is a top wall 9 arranged on top of the upper end of the lateral wall 4. The top wall 9, see
According to the invention, the bottom wall 3 and the top wall 9 of the filled hollow body 2 are provided with centering means 11 and 12 for centering the final HIP:ed body in a metal machining apparatus.
Obviously, the centering means should be provided in a position of the hollow body which is not covered by cladding material, thus free of cladding material.
Preferably, the centering means 11 and 12 are located in the center of the bottom and top wall so that they are aligned along a straight line 13 running through longitudinally through the center of the core 5 and through the both centering means 11, 12.
The centering means in both the bottom wall and the top wall of the hollow body are preferably designed to be engaged by corresponding centers in conventional metal machining apparatuses. According to the present invention, a “metal machining apparatus” also known as “metal machine tool” or “machine tool” may be a metal cutting machine such as a lathe or milling cutter. The metal machining apparatus may also be an Electrical Discharge Machining device.
Preferably, the metal machining apparatus is a lathe, i.e. an apparatus for machining steel by turning. As will be described further below the centers for lathes are so called “male centers” in form of cones or truncated cones. Alternatively, the centers in lathes are so called “female centers” in the form of a sleeve with a conically shaped opening a.k.a “tapered sleeve”. Such centers are commercially available, for example from the company Röhm (RÖHM GmbH, Heinrich-Röhm-Straβe 50, 89567 Sontheim/Brenz, Germany).
Consequently, the centering means in the hollow body are in the form of “male centering means” or “female centering means” The male centering means is a protruding element, for example in the form of a cone or a truncated cone. The female centering means is a recess i.e. a bore. For example the female centering means is in the form of a recess or a bore with the shape of a cone or a truncated cone. It is preferred that the centering means in the hollow body are complementary with commercially available centers in lathes. However, the male centering means could be a protruding element of any shape and the female centering means could be a recess of any shape.
In
It is obvious that either a male centering means or a female centering means could be provided in the upper wall or in the bottom wall of the hollow body 2. For example, a male centering means could be provided in the bottom wall 3 and a female centering means in the upper wall 9 or vice versa. It is also possible to provide male centering means in both the bottom wall 3 and the upper wall 9. Or to provide female centering means in both the bottom wall 3 and the upper wall 9 of the hollow body 2.
Female centering means, e.g. recesses or bores, may be achieved by drilling or milling. Male centering means, for example cones, or truncated cones, may be achieved by machining of the end surface of the bottom wall or the top wall of the hollow body. It is also possible to pre-manufacture cones or truncated cones, by machining and subsequently attaching the cones by welding to the top or the bottom walls of the hollow body.
The hollow body is then placed in a capsule 10, see
With reference to
There is a possibility that female centering means in the hollow bodies deforms or even closes during HIP. To avoid this, a cover piece 40 may be placed in the bottom of the capsule, prior to inserting the hollow bodies into the capsule. The cover piece 40 comprises one surface 40a which is supported on the bottom of the capsule and one surface 40b which comprises a protruding element 40c which is adopted to fit into a female centering means. In this case the protruding element 40c is truncated cone. The protruding element 40c of the cover piece 40 fills out the female centering means 11 of the first hollow body 2 in the capsule 10 and prevents the centering means 11 from deforming during HIP. Obviously, the cover piece is also provided with a boron nitride coating to prevent bonding. Further filled and closed hollow bodies are subsequently inserted into the capsule and stapled on top of each other. Thereby is the male centering means 12 of one hollow body 2 received in the female centering means 11 of the next hollow body 2. On top of the uppermost hollow body 2, a second cover piece 40 is placed. The second end piece comprises one surface 40b which comprises a recess 40d which is adopted to receive the male centering 12 means of the uppermost hollow body. The opposite surface 40a is flat and directed towards the opening of the capsule. The arrangement of the second cover piece 40 prevents that the male centering means of the uppermost hollow body from damaging the capsule during HIP. It is obvious that the design of the cover pieces may be adapted to the centering means in the hollow bodies.
The described arrangement of placing several hollow bodies in a capsule is of course a cost effective way of manufacturing large amounts of injection nozzles. However, the described arrangement of hollow bodies with female centering means in bottom and male centering means in the top provides additional advantages. Firstly, this arrangement locks individual hollow bodies in the staple to each other and causes the staple of hollow bodies to remain relatively stable during HIP. Secondly, by the described arrangement the female centering means in one hollow body is protected from deformation during HIP by the male centering means in another hollow body. Therefore only one cover piece is needed to protect the female centering means in the lower most hollow body. This reduces cost further.
Preferably, the male centering means have the form of a truncated cone with an inclination angle of maximum 60°, preferably 40-60°. Preferably, the female centering means is a bore with the same shape of truncated cone, i.e. an inclination angle of maximum 60°, preferably 40-60°. Tests has shown that mating centering means with theses dimensions results in little or no deformation of the female centering means during HIP. Tests have also shown these dimensions prevents that the male centering means to get stuck in the female centering means during HIP. Thereby the hollow bodies may be easily separated from each other after HIP.
When all the hollow bodies have been positioned in the capsule, a lid 10b with an opening 10c is welded over the upper end of the capsule. The capsule may comprise air which is has a negative impact on the bonding of the cladding to the core. Therefore the air is evacuated from the capsule 10 by drawing a vacuum in the capsule. The vacuum is drawn through the opening in the lid and subsequently the opening in the lid is welded shut so that the capsule is sealed.
Thereafter, the hollow body 2 is subjected to Hot Isostatic Pressing (HIP), see
In the final step of the method, the solid body resulting from the HIP process is subjected to a metal machining operation in which at least a portion of lateral wall 4 is removed and the exposed cladding material 8 is machined to a cladding 60 of a predetermined thickness. Typically the machining operation is performed by turning in a lathe.
The tailstock 35 of the lathe comprises a female center 36 which consists of a tapered sleeve 37 with an inner shape in the form of a truncated cone. The sleeve is adopted to receive the male centering means 12 in the top wall 9 of the solid body 20. The center further comprises a shaft (not shown) by which it is attached to the tail stock of the lathe. In this case the center is a live center which is rotatable arranged in the tailstock. However, it could also be a so called dead center. A metal cutting tool 38, i.e. a lathe tool or lathe steel is provided to remove metal from the solid body.
In operation the male center 34 of the face drive is inserted into the female centering means 11 in the first end surface 3a of the solid body and the female center 37 of the tailstock of the lathe receives the male centering means 12 in the second end surface 4a of the solid body 20. The face driver presses the solid body towards the female center in the tailstock of the lathe and simultaneously the drive pins 33 are forced into the end surface 3a of the solid body. The solid body is centered in the lathe when both the male and female centers of the lathe are in engagement with the male and female centering means of the solid body.
If necessary, the centring means 11, 12 in the solid body 20 may be exposed prior to centring the solid body in the lathe. For example, by removing a portion of the capsule by grinding with a hand held tool.
After centering of the solid body, turning is performed until a cladding of desired thickness is achieved. This is achieved in that the control system of the lathe is programmed with a pre-determined distance between the center of the pre-manufactured body and the lathe tool. During turning at least a portion of lateral wall is 4 is removed by the lathe cutting tool 38. Typically the entire lateral wall is removed. The exposed cladding material is then also removed by the lathe tool until the pre-determined distance is reached and a cladding of a predetermined thickness is obtained.
The injection nozzle blank may thereafter be subjected to further machining into a final injection nozzle, for example drilling of holes and further machining of the cladding.
The invention will in the following be described with reference to a comparative example.
Six injection nozzles blanks were manufactured according to the inventive method. The injection nozzles comprised a hollow body of the steel AISI H13/SS2242 filled with a cladding material of NiCr22MoNbTi in powder form. The nozzles blanks had the following dimensions, see
The pre-manufactured bodies that were used in the manufacturing of the nozzle blanks were provided with a male centering means in the form of a truncated cone in the top and female centering means also in the form of a truncated cone in the bottom. The male centering means had a base diameter of 11 mm, a height of 5.5 mm and an inclination angle of 60°.
The six pre-manufactured bodies were place in a capsule and HIP:ed for 1 hour at a pressure of 970 bar and a temperature of 1150° C. Subsequently the solid bodies were machined in a lathe of the type Okuma Space Turn LB3000EX. The lathe was provided with centers in face driver and tail stock which corresponded to the centering means in the top and bottom walls of the solid bodies.
After turning the nozzles were cut at a position of 14-16 mm from the top and the cut surfaces were investigated in a light microscope to determine the thickness of the cladding layer. The dashed line in
As comparison, six further nozzles were manufactured and subjected to measurement as described above. However, the pre-manufactured bodies for these nozzles were not provided with centering means. The comparative nozzles were also turned in a lathe as described above but were clamped by a chuck in one end of the solid body.
The results from the measurements are shown in table 1:
The results show that, in comparison with the conventionally manufactured nozzles, a much narrower tolerance of the thickness of the cladding is achieved in the nozzles manufactured by the inventive method. The targeted cladding thickness of the inventive nozzles is 3 mm and the measured variation in thickness around the core is in the range of 0.03-0.12 mm. In comparison the comparative nozzles have cladding thickness which varies in the range of 0.16-0.95 mm around the core.
| Number | Date | Country | Kind |
|---|---|---|---|
| 13199002.0 | Dec 2013 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/075109 | 11/20/2013 | WO | 00 |
