Patent Publication Number: US-2004040361-A1

Title: Method of producing bladed components, blanks for bladed components, and use of the blanks

Description:
STATEMENT OF RELATED APPLICATIONS  
       [0001] This application is based on and claims priority on German Patent Application No. 10240942.0 filed on Sep. 2, 2002 and German Patent Application No. 10243169.8 filed on Sep. 18, 2002.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Technical Field  
       [0003] The invention relates to a method of producing bladed components for fluid-flow machines, a blank being produced by forging and the blank subsequently being machined. The invention also relates to a method of producing blanks for bladed components for fluid-flow machines, the blank being forged from a forgeable material, to the uses of such blanks, and to a die for forging blanks for bladed components for fluid-flow machines, a blank being produced by forging and the blank subsequently being machined.  
       [0004] 2. Prior Art  
       [0005] Bladed components serve to produce fluid-flow machines. In particular, bladed components are used for impellers, guide wheels or even stationary guide rings for compressors and turbochargers. However, the bladed components may also be propellers or individual blades of fluid-flow machines.  
       [0006] The said bladed components are mainly formed from forged blanks that are subsequently machined, to be precise preferably by multi-axis (e.g. five-axis) milling. The blanks are produced by hammer or drop forging and are merely given an envelope contour of the component plus the forging allowance during the forging. The blank in this case is a relatively roughly preformed blank, the volume of which has to be cut by over 60%, often up to 80%, in order to obtain the desired bladed component therefrom. Such extensive cutting of the forged blank requires long machine cycle times, for which reason the bladed components produced according to known methods are very expensive to produce. In addition, considerable material is lost during large-volume cutting. In particular in the case of components made of expensive materials, such as titanium for example, this is uneconomical. The said disadvantages of the prior art have an adverse effect in particular in the large-scale production of such bladed components of, for example, turbochargers for motor vehicles.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] Based thereon, the object of the invention is to provide a method whereby bladed components or forged blanks for producing bladed components can be produced more economically compared with known methods. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0008] A method of producing bladed components in particular for fluid-flow machines that have a blank being produced by forging and the blank subsequently being machined, characterized in that the blank is forged to near-net shape serves to achieve this object. This method is characterized in particular by the fact that the blank is forged to “near-net shape”. In this connection, the expression “near-net shape” refers to the forging which not only creates a blank which corresponds to the envelope contour of the finished component, as in the prior art, but also creates a blank which is located inside the envelope contour. As a result, individual blades or even groups of several blades can be preformed to the greatest possible extent during the forging, the forged contour still having a sufficient allowance for the final machining of the blades so that the surfaces of all the blades are completely covered by the subsequent machining. Due to such forging of the blank to near-net shape, only a fraction of the volume of the forged blank, compared with conventional methods, needs to be cut. As a result, the cutting operation can take place considerably quicker, as a result of which machine cycle times, in particular of milling machines for carrying out the machining, can be saved. But the material consumption is also reduced by the method according to the invention; this is because less raw material is lost.  
     [0009] Furthermore, provision is made for the blank to be forged to near-net shape in such a way that only the forging allowance has to be machined. Intermediate spaces are preferably at least partly produced between at least some blades during the forging. As a result, the contour of the blades is already preformed during the forging. Either the contour of each blade is preformed or, in the case of components having groups of small and large blades, the outlines of each group of a large and a small blade are preformed. In the process, the blades are already given in principle at least approximately the form of the finished blades, although a forging allowance is retained so that the forged blank still has sufficient material in order to be able to form the contour of the finished component, in particular the surfaces of the blades, over the full surface area by machining. As a result, bladed components that do not differ with regard to their precision from components produced according to known methods can be formed by the method according to the invention. However, the cutting cost can be markedly reduced by the forging of the blank having intermediate spaces between adjacent blades and/or having the requisite forging allowance.  
     [0010] A further method for achieving the object mentioned at the beginning has the features in which the blank being forged from a forgeable material, characterized in that the blank is drop-forged to near-net shape. This method relates to the production of blanks for bladed components for forming, in particular, fluid-flow machines. The forging to near-net shape, in particular drop forging, results in a blank from which bladed components or even individual blades or propellers can be produced at a relatively low cutting cost. The forging to near-net shape is effected to such an extent as has been defined in connection with the method described at the beginning.  
     [0011] The blank is preferably drop-forged in such a way that mainly only the forging allowance has to be machined. In this case, intermediate spaces are expediently formed at least for the most part between adjacent blades or groups of several blades. These intermediate spaces are dimensioned in such a way that, compared with the finished bladed component, they are smaller essentially by only the forging dimension and as a result, in the region of the forged intermediate spaces, only the forging dimension has to machined from the blank during the final machining.  
     [0012] According to a preferred development of the method, which may also be a development of the method described above, the blank—if required by the finished component—is provided with undercuts, to be precise either all the undercuts or only some undercuts. The undercuts come about by the contour, to be forged, of the bladed component being set back in the longitudinal direction of the same or in the pressing direction, in particular by being negatively inclined. Owing to the fact that the blank is already given undercuts during the drop forging, forging to near-net shape is also possible in the case of components having a complex contour, for example impellers having inclined blades. In particular, intermediate spaces between adjacent inclined blades can be brought closer to the contour of the finished component to such an extent that there is only such an oversize which corresponds essentially to the forging dimension. As a result, the material quantity to be cut can be reduced to below 40% of the blank volume.  
     [0013] According to a preferred development of the method, the blank can be provided with undercuts during the drop forging by at least part of the die, preferably the top die, being rotated. In particular in the case of rotationally symmetrical components, such as impellers, guide wheels or propellers for example, the top die and/or the bottom die is/are rotated about an axis of rotation running in the pressing direction. The top die or the bottom die is rotated during the forging by the size of the undercut. Accordingly, the top die or the bottom die is turned back when the die is opened after the forging. However, it would also be conceivable to rotate both the top die and the bottom die simultaneously or one after the other, only each die part then having to be rotated by half the size of the undercut. The rotation of the top die and/or of the bottom die is preferably effected after the die has been completely closed, but may also be effected continuously when the die is being closed.  
     [0014] Furthermore, the invention relates to the use of a forging, produced by at least partial drop forging to near-net shape, as a blank to be machined for impellers, guide wheels or guide rings, having blades, of fluid-flow machines, in particular compressors, turbochargers or pumps or also for propellers or individual blades. The said bladed components, on account of their complex and often arched contour, require complicated, costly machining. By the use of blanks forged to near-net shape for producing the said bladed components, the subsequent machining of these blanks can be carried out with a smaller cutting volume, as a result of which considerable costs for the cutting operation can be saved without the forging operation becoming correspondingly more expensive as a result, since the forging to near-net shape, apart from slightly higher die costs, which only arise once, causes no appreciable extra costs compared with the forging of blanks having a rough contour.  
     [0015] The use of a blank drop-forged to near-net shape for producing the said bladed components by machining, such as, in particular compressors, turbochargers, pumps or propellers, is especially economical because the said components mainly have a multiplicity of blades.  
     [0016] A die for achieving the object mentioned at the beginning has at least a bottom die and a top die, at least the top die being movable in the pressing direction towards the bottom die, characterized in that at least parts of the die can be rotated about an axis running in the pressing direction. Owing to the fact that at least parts of the top die and/or of the bottom die are rotatable, undercuts of the blank to be forged can be produced in a simple manner. In particular, the undercuts can be formed by relatively simple means without the die becoming more complex or requiring additional parts as a result.  
     [0017] The top die and/or the bottom die can preferably be rotated in each case about an axis running in the pressing direction. Alternatively, it is also conceivable to rotate the top die and the bottom die relative to one another or displace them on a path running at an angle or perpendicularly to the pressing direction.  
     [0018] With the method according to the invention and the die according to the invention, all the current materials for bladed components can be machined, to be precise in particular all forgeable metals, in particular titanium, aluminum and nickel-base alloys.  
     [0019] A preferred exemplary embodiment of the invention, to be precise the production of a bladed component which is designed as a rotationally symmetrical impeller, is described in more detail below.  
     [0020] A section of a bar or a billet of a forgeable material serves as initial material for the impeller to be produced. The bar or the billet is rough-forged, continuously cast, extruded and/or rolled. A blank for the impeller to be produced is forged from such a bar or the billet.  
     [0021] Depending on the type of material used, the forging is effected in the hot state or even in the cold state. The forging is carried out, to be precise to near-net shape according to the invention, in a die described in more detail below. That is to say that the blank produced during the forging is not merely put into a die which corresponds to the envelope contour of the impeller to be produced plus the forging dimension, but rather the blank, during the forging to near-net shape according to the invention, is given a contour which to a very large extent is brought close to the finished impeller to be produced. This contour has recesses that extend into the envelope contour of the impeller. Intermediate spaces between adjacent blades or groups of several blades are already at least partly produced by the recesses during the forging. The recesses have such dimensions that a forging allowance is retained so that the blades can be finish-machined over the full surface area.  
     [0022] In impellers having identical blades, a forged intermediate space is located between all the adjacent blades, the intermediate space extending at least partly between adjacent blades. In impellers having groups of large or small blades, the intermediate spaces are designed in such a way that they extend in each case between a blade pair consisting of a large and a small blade, but not between a large blade and the small blade assigned to it.  
     [0023] The impellers mainly have blades that are inclined slightly in the direction of their longitudinal center axis. This results in undercuts on the rear side of the blades. These undercuts are also partly formed during the drop forging, to be precise by the rotation of a die part, in particular of a die half, or by relative rotation of both die halves relative to one another. The respective die half is preferably rotated about an axis running in the pressing direction. In the case of rotationally symmetrical impellers, this axis at the same time runs along the center longitudinal axis of the impellers. The rotation of at least one die half, for example the top die, may be effected after the closing of the die, that is to say when both die halves are moved together. When the die halves are moved apart, the top die is rotated in the opposite direction. However, it is also conceivable to rotate at least the top die continuously when the die halves are being moved together.  
     [0024] By the rotation of at least parts of the die during the drop forging, the intermediate spaces between adjacent blades, following the angled direction of the blades, may likewise run at an angle, as a result of which undercut drop forging, to very-near-net shape, of the blank is possible.  
     [0025] Once the blank has been drop-forged, the finished impeller is machined therefrom, to be precise preferably by milling. The milling is preferably effected with a 5-axis CNC milling machine. In the process, at least the surfaces of all the blades are completely machined. Due to the drop forging to near-net shape according to the invention, essentially only the forging allowance needs to be removed by machining. Consequently, due to the machining operation, only half the volume of the blank at most, preferably markedly less, is to be removed by a cutting action. The cycle times of the machines for machining the blank and the quantity of the blank volume that is to be cut and is therefore unused can thus be reduced compared with the prior art.  
     [0026] The blank produced according to the described method and made, for example, of titanium, aluminum and nickel-base alloys, but also of other wrought alloys, is especially suitable for the finish machining of bladed components for compressors, specifically compressors for aircraft engine construction, as well as stationary compressors and compressors for gas and steam turbines or other turbines. However, the blank produced by the method according to the invention may also serve for the production by machining of impellers for turbochargers, for pump impellers, for propellers and individual blades.  
     [0027] A die for producing the blank for a preferably rotationally symmetrical impeller has a bottom die and a top die. The top die can be moved up and down relative to the bottom die, to be precise in the pressing direction. The pressing direction in this case corresponds to the longitudinal center axis, that is to say the axis of rotation of the impeller. The impression in the top die also has projections that serve during the drop forging to produce intermediate spaces between adjacent blades or adjacent groups of small and large blades.  
     [0028] In impellers having inclined blades, the intermediate space has an undercut at the rear side of the respective blade. The intermediate space, at the rear side of the respective blade, then runs such as to be directed inwards at an angle, that is to say it is set back. In order to be able to produce such undercuts during the drop forging, the top die is rotated about an axis that runs in the pressing direction and preferably lies on the longitudinal center axis of the blade wheel. Consequently, the top die can not only be moved up and down in the pressing direction relative to the fixed bottom die, it can also be rotated about the longitudinal center axis of the blade wheel or impeller. An appropriate drive is assigned to the top die for this purpose. This drive can either rotate the top die after the closing of the die, that is to say after complete lowering of the top die onto the bottom die, or the top die is rotated when it is being lowered.  
     [0029] The method described and the die described are suitable not only for producing an impeller, mentioned by way of example in the above description, but also for producing other bladed components for compressors, turbochargers, pumps or even propellers.