This application claims priority to German Patent Application DE102008019332.1 filed Apr. 16, 2008, the entirety of which is incorporated by reference herein.
This invention relates to a method for milling blisks for gas-turbine engines, where at the periphery of a disk blank a multitude of integrally provided blisk blades is pre-shaped by rough milling and subsequently finish machined by finish milling of the pressure and suction side as well as of the annulus.
For the compressors of gas-turbine engines, as is generally known, blisks are also used, on which the rotor blades are integrally connected with the rotor disk to form a one-piece unit. Compared with rotor wheels with conventional blading, on which separately manufactured rotor blades are retained in a dovetail-shaped groove on the periphery of the rotor disk, integrally bladed rotors are characterized, besides reduced assembly costs, by less weight and reduced centrifugal loading of the supporting disk, enabling a multitude of blades to be arranged and, finally, aerodynamic efficiency to be increased.
Blisks are manufactured either by connecting separately produced blade elements to a supporting disk by friction welding, or by milling the blade contours from the solid material, starting at the periphery of a disk blank.
The rotor blades have a complex, three-dimensional shape in that they typically twist around a radial axis, taper from the blade root towards the blade tip, have a concave pressure side and a convex suction side and their blade tip is not parallel to the blade root. Cutting and machining of these blades from the solid material are usually accomplished by point-contact milling using a cutter with semi-spherical cutting head. While a channel is first produced in a rough milling operation, the pressure side and the suction side and, finally, the annulus are finish machined in a subsequent finish milling operation. Rough milling of the channel and subsequent finish milling of the side walls can also be performed sectionally in alternation, actually until the annulus is reached and can be finished. The term “annulus” hereinafter also refers to the transition area between the side faces of the blade and the annulus.
The above mentioned point-contact finishing process for shaping the side faces of the rotor blades, which, for example, is described in Specification U.S. Pat. No. 6,077,002 A, is disadvantageous in that it is time-consuming and with the long operating times and the correspondingly high tool consumption entails high tool and manufacturing costs. Due to the wear of the cutter by the long operating times during finish milling the side faces, dimensional accuracy of the blades, whose thickness increases with increasing tool operating time and corresponding tool wear, is not ensured.
A less time-consuming method for finish milling the side faces of the three-dimensionally shaped blisks is five-axis flank milling, in which a shank-type cutter, whose tool axis is routed parallelly to the blade surfaces, is used to cut areal strips along the suction side and the pressure side parallelly to the root of the blade. Flank milling enables tool wear and tool costs to be reduced and both the dimensional accuracy of the individual blades and the surface finish thereof to be improved. Nevertheless, disadvantageous aerodynamic losses are also encountered on the suction and pressure side of blisk blades whose surface finish is produced by flank milling.
A broad aspect of the present invention is to provide a method for the milling of blisks, which allows a reduction of the aerodynamic losses.
When milling three-dimensionally shaped blisk blades from the solid material of a disk blank, the side faces of the blisk blades, upon being pre-shaped by rough milling, are finished by flank milling and thereby brought to final size. The direction of movement of the cutter, or the course of the cutting strips produced in flank milling, agrees with the direction of flow of the gases at the pressure side and the suction side of the blisk blades in operation of the engine, thereby enabling aerodynamic losses at the blade surfaces to be reduced.
According to a first process variant, the—equally wide—cutting strips which the cutting edge of a cutting tool produces at the blade tip and at the annulus (transition area to the annulus) extend parallelly to these, with a length difference between the blade leading edge and the blade trailing edge due to the oblique alignment of the blade tip and the annulus, i.e. a change in blade length and an inclination between blade tip and annulus, being compensated by overlapping the cutting strips in a fan-like manner. Overlapping milling also reduces the height of the steps between the cutting strips, thereby further improving the flow conditions at the blade surfaces and reducing the polishing effort for the blades.
According to yet another characteristic of the present invention, cutting paths starting at the blade tip and the annulus and extending parallelly to these and to each other can be produced, with the cutting strips overlapping or intersecting each other in the transition area between the cutting strips disposed parallelly to the blade tip and to the annulus. Preferably, the cutting strips produced parallelly to the blade tip may in this variant extend up to the highest point of the annulus, so that cutting strips extending parallelly to the annulus are produced only close to the latter.
The present invention is more fully described in light of the accompanying drawings, showing a preferred embodiment. In the drawings,
As shown in
According to yet another variant shown
Number | Date | Country | Kind |
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10 2008 019 332.1 | Apr 2008 | DE | national |