EP2103384B1 - Method for manufacturing a welded blisk - Google Patents

Abstract

The method involves welding prefabricated blisks with each other, and subjecting a blisk spool to thermal treatment. The blisk spool as whole within flowable, pasty polishing medium is polished by a relative motion generated between the blisk spool and the medium by vibration and/or translation and/or rotation of the blisk spool or a container. Polishing movement of the medium is suppressed by guide elements in blade regions with unwanted material removal or the regions are covered or dimensioned during production of the blisks according to the material removal expected during polishing.

Description

The invention relates to a method for producing a blisk drum, in which two or more prefabricated blisks are welded together and the blisk drum thus formed is subsequently subjected to a heat treatment and the blade surfaces are polished in the last processing step.

Gas turbine rotors, and particularly the rotors of gas turbine engine compressors, are designed with a blading integrally formed on the annular outer periphery of a disk or ring for reliability, weight-saving, performance and durability. Such components are referred to as blisks, which term is a shorthand of the English language term "blade integrated disk". The production of blisks is known to be carried out by welding, in particular friction welding, separately manufactured blades with the peripheral surface of the preferably forged disc or by emanating from the outer peripheral surface of the disc material removal by means of cutting and / or chemical processes for forming the blades of the full material. Finally, a fine machining of the blades by smoothing, for example, vibratory sliding according to WO 00/29171 in that the blisk is housed in a vibrating medium-filled vibrating container in which the blades are ground or polished due to a spiraling motion of the grinding medium caused by the vibration, and thereafter substantially satisfying the aerodynamic requirements during operation of the gas turbine Have roughness (Ra) on the blade surfaces. Subsequently If necessary, the blisk disk is subjected to an etching process. The joining of the individual blisks to a blisk drum, for example in a welding process, is followed by a heat treatment of the entire blisk drum and etching processes and a solidification process, as a result of which the roughness values are markedly worsened and the blade surfaces have to be smoothed again.

The smoothing of the blades on a blisk drum is known to be controlled by robots controlled by a predetermined program and equipped with a polishing lance. The polishing of the individual blades with polishing lances is time consuming and costly. In addition, the accessibility to the blade surfaces is partially limited, so that the required aerodynamic efficiency can not be achieved.

The invention has for its object to provide a method for producing a welded blisk drum in such a way that the blisk blades meet both the roughness of the side surfaces as well as in terms of their leading and trailing edge and extending on the blade tip high aerodynamic requirements and the time and Cost is also low.

According to the invention the object is achieved by a method according to the features of patent claim 1. Advantageous developments and expedient embodiments of the invention are the subject of the dependent claims.

The basic idea of the invention is to immerse a welded and heat-treated blister drum as a whole in a pasty, flowable abrasive medium and the Bliskschaufeln by a generated between the blisk drum and the abrasive medium To grind relative movement exclusively on the pressure and the suction side, while blade edges are made in the production of the individual blisks with a certain excess according to the eroded at the blade edges on the action of the abrasive medium material, so that the blade edges are indeed treated with the abrasive medium, but ultimately have the aerodynamically most favorable form.

In addition, by arranged in the abrasive medium guide elements prevents the relative movement of the abrasive medium in the edge regions and the abrasive medium are primarily directed to the surfaces to be ground of the blades.

In this way, all blade surfaces of a blisk drum can be polished in a single operation with little time and cost, while the blade edges retain their already generated during the production of the individual blisks aerodynamically favorable shape.

The relative movement between the abrasive media and the blisk blades is achieved by a vibratory movement of the container containing the blisk drum held therein and the abrasive media. The blisk can also move in the grinding medium but translational or rotating. It is also conceivable a combination of the aforementioned movement variants, wherein both the blisk drum and the container receiving the abrasive medium can be moved. The blisk drum can be arranged vertically or horizontally in the container receiving the abrasive medium. Before being introduced into the grinding medium, the open end faces of the blisk drum are closed.

In a further embodiment of the invention, an abrasive paste with abrasive carriers bonded into it is used as the grinding medium so as to increase the pressure build-up on the blade surfaces to be ground.

According to a further feature of the invention, the surface of the blisk drum after the heat treatment is first treated with an etchant in order to reduce a surface roughness caused by the heat treatment. By subsequent to the etching treatment ball solidification of the blade surfaces, the strength of the blades is increased and reduces the risk of stress corrosion cracking. As a result of shot peening, the roughness of the blade surfaces increases. In the subsequent polishing of the entire blisk drum in the abrasive medium, however, the roughness of the blade surfaces is reduced to a value that meets the highest aerodynamic requirements.

An embodiment of the invention will be explained in more detail below.

In a first method step, the annular disks are first produced with integrally molded or shaped blades, so-called blisks, in the respectively required dimensioning for the individual stages of the compressor of a gas turbine and then welded into a multi-stage blisk drum. The roughness of the blade surfaces at this time is at a roughness value (Ra) of about 0.25. Subsequently, the blisk drum is subjected to a heat treatment to eliminate the stresses caused by the welding process. In a subsequent chemical treatment in an etching medium, by ablating a brittle surface layer formed as a result of the heat treatment, the surface roughness is reduced to a roughness value Ra of increased by about 0.4. In the next step, the blades of the blisk drum are shot-peened in a special process in which the shape of the leading and trailing edges of the blade and the blade tip edge is not affected in order to increase the strength of the blades by introducing compressive residual stresses in the mutual surface layers Minimize the risk of cracking and thus increase the life of the blades. As a result of the shot peening, however, a multiplicity of extremely small dome-shaped recesses are formed in the blade surfaces, so that the roughness value of the blade surface increases to a roughness value Ra of approximately 0.7. The shot peening process is followed by a vibratory grinding treatment of all blades of the blisk drum, as a result of which the blade surfaces have an aerodynamically advantageous roughness value of Ra ≦ 0.25 and the shape of the blade edges also satisfies the aerodynamic requirements imposed on them.

The aforementioned vibratory grinding of the blade surfaces is carried out in a filled with a pasty, flowable abrasive medium, sized according to the shape and size of the blisk drum abrasive container by a relative movement between the abrasive medium and the blade surfaces. The blisk drum, which is closed at the front, completely dips into the grinding medium. The relative movement between the abrasive medium and the blade surfaces may be effected by vibration of the abrasive container and the blisk drum mounted thereon, for example, perpendicularly, the abrasive medium performing a torodial motion due to vibration of the abrasive container. However, it is also conceivable that the blisk drum is translationally moved in the abrasive or is rotated about its axis. The movement of the blade surfaces relative to the abrasive medium can also be achieved by a rotary movement of a horizontally mounted in the abrasive container blisk drum. It is also a combination of the aforementioned Blisktrommelbewegungen conceivable, that is, vibration and / or translation and / or rotation.

The abrasive medium consists of abrasive carriers embedded in a grinding paste, the combination of compact abrasive carriers and actual abrasive providing the necessary pressure build-up on the grinding surfaces and optimum grinding action.

With the aid of guide elements arranged in the grinding medium, the grinding medium can be specifically directed to the blade surfaces to be machined in order to achieve the desired grinding effect there, while the relative movement between the blade parts not to be treated, namely the blade edges, and the grinding medium is prevented not to change the original shape of the blade edges. Alternatively, undesired material removal at the blade edges / blade tips can also be prevented by covering them.
The blade tips of the blades of the blisk remain thereby straight and sharp-edged, while maintaining a predetermined, preferred oval profile of the blade leading edges. In one embodiment variant, the grinding process can also be carried out without covering the blade edges or suppressing the relative movement at the blade edges, if already during the production of the individual blisks in the area in question, for example the leading edge of the blade, a certain amount of excess material that is involved with the Grinding abraded amount of material is identical, "held", that is, the blades during manufacture in knowledge of the unwanted during grinding material removal be dimensioned larger in the appropriate places.

As a result of the method described above by way of example, a blisk drum is provided which meets the highest aerodynamic requirements in terms of the blade edge geometry and the roughness of the blade surfaces and which can also be produced with reduced time and cost. According to the present embodiment, welded blisk drums can be produced, the blades of which have high strength and resistance to stress corrosion cracking, aerodynamically shaped leading and trailing edges and a sharp edged blade tip edge to ensure the required gap attitude and finally over blade side surfaces with an aerodynamically advantageous low roughness in the present embodiment is Ra ≤ 0.25 have.

Claims (6)

1. Method for the manufacture of a blisk drum in which two or several pre-manufactured blisks are joined together by welding or other processes, and the blisk drum so produced is subsequently subject to heat treatment and the blade surfaces are polished in the final processing step, characterized in that the blisk drum is polished as a whole within a flowable, pasty abrasive medium by a relative movement between the blisk drum and the abrasive medium, this movement being generated by vibration and/or translation and/or rotation of the blisk drum and a tub containing the abrasive medium, where the blades in blade areas, where no material removal is desired, are overdimensioned during manufacture of the blisks to take account of the material removal expected during polishing.
2. Method in accordance with Claim 1, characterized in that a certain amount of material, which exceeds the final shape, is provided on the blade edges, with this surplus stock being removed during the polishing operation or by other processes.
3. Method in accordance with Claim 1 or 2, characterized in that the open end faces of the blisk drum are closed prior to being immersed in the abrasive medium.
4. Method in accordance with one of the Claims 1 to 3, characterized in that the abrasive medium is an abrasive paste with abrasive carriers embedded therein, to build-up pressure on the surfaces to be ground.
5. Method in accordance with one of the Claims 1 to 4, characterized in that the surface of the blisk drum is treated with an etchant upon heat treatment.
6. Method in accordance with Claim 5, characterized in that the blades of the blisk drum are shot-peened after etching or subject to other surface-strengthening processes.