Method for producing matched fluid contact surfaces

Details Method for producing matched fluid contact surfaces Method for producing matched fluid contact surfaces

2000-04-28

2003-04-01

Barlow, John (Department: 2863)

Data processing: measuring, calibrating, or testing

Testing system

Of mechanical system

Reexamination Certificate

active

06542843

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method for producing matched fluid contact surfaces on rotor units with integral blades.
BACKGROUND OF THE INVENTION
As a rule, rotor units with integral blades whose blades are integrally connected to the hub, free from backlash, by means of welding, forging, soldering or bonding, provide advantages concerning strength, weight and design volume. They are therefore increasingly incorporated in advanced turbomachinery constructions. In this context, the primary object is the replacement of the generally used positive-fit rotating blade attachment (e.g. with pine tree or dovetail profiles) in rotors with essentially axial through flow. Both blade attachment/installation and blade repair/exchange, are admittedly more expensive and difficult in rotors with integral blades than in positive fit constructions. Modified or novel production and repair methods are required of which linear friction welding is a particularly striking and important example. In spite of its name, this joining process by friction welding is metallurgically closer to forging than to welding. Induction welding is another currently used joining process in which after electroinductive heating by joining pressure, a fine-grain “forging microstructure” is generated too.
Soldering and bonding processes are in principle also possible, but most of the time, the joining zone thermally/mechanically forms a “weak point”.
Without exception, currently used joining methods require overmeasure in the area of the joining zone, in at least one of the components to be joined. This requirement may result from the type of component clamping and introduction of force (such as in linear friction welding) or it may result from the criterion that the joining zone should be able to be reworked on all sides, in particular so as to compensate for geometric joining errors. During the joining process itself, as a rule, there is an issue of material (e.g. flash during friction welding) which subsequently also needs to be removed. In any case at least the area of the joining zone is reworked and optimized by removing material from its surface shape, with aspects of fluidic behavior and strength having to be taken into account. The surfaces to be constructed must in addition be matched to existing actual surfaces, with the latter having to be acquired by measuring methods. With modern, efficient production, the measured values are electronically stored, the three dimensions of the surfaces to be produced are calculated, and shaped by means of removal by machine, with all three steps of “measuring”, “calculating” and “producing” being based on linked data processing.
From the European published application EP 0 837 220 A2 a method for repair of worn blade tips of compressor blades and turbine blades is known in which the worn blade tip is cut off at a defined radial height h and replaced by a repair profile whose contour is exactly matched; with attachment of said repair profile occurring by soldering or welding. After separating the worn region, the actual geometry of the remaining rotor blade is measured in the area of the separation plane and thus the plane which will later become the joining plane, and according to these measurement data an exactly matching repair profile is produced, preferably by laser beam cutting with three-dimensional cut guidance. In this process, the surface of the remaining rotor blade from the separation/joining plane with the repair profile, is continued in radial direction to the blade tip so as to be tangentially straight on all sides. Any rework is only required at the soldering joint or at the weld seam, if at all. Apart from the advantage of minimal rework, this method also provides the advantage that, after local repair, the blade can be reused rather than having to be replaced. This method which represents a special form of patching is also suitable for rotor units with integral blades, but only for repairs in the area of the blade tips. Due to the nature of the method, only those surfaces can be produced whose surface lines—in horizontal direction—are straight (cutting with straight laser beam), i.e. no curved surfaces according to requirements, for example as required at the transition from the rotor blade to the hub. The repair component's surface finish by means of laser to finished dimensions must take place before the repair component is attached to the remaining rotor blade. Consequently, it is almost impossible to compensate for geometric joining errors at this stage, as there is no removable overmeasure. Working the repair component/patch to finished dimensions is no longer possible after joining because the laser beam, which essentially cuts radially inward from the blade tip, would at least in places penetrate the remaining rotor blade, thus damaging said rotor blade.
The German published application DE 40 14 808 A1 describes a machine vision system for automating a machine processing method. Specifically, the system is to be used for repairing worn turbine blade tips, by laser powder build-up welding. The blade tips are of a special geometry in which the thin blade wall describing the profile projects radially beyond the actual face. If the projecting blade wall touches the turbine housing or a housing coating, it experiences wear which can be repaired by build-up welding. First, the worn face edge of the blade wall is ground down, i.e. made plane and smooth. The profiled ring surface described by the face edge is optoelectronically recorded by a camera and converted into a mathematical ring curve with locally defined thickness (width). The data is used directly for controlling the weld process, with the local material build up (powder flow, laser intensity) being matched to the respective thickness of the remaining wall. In this way there is a de facto continuation of an exterior and an interior actual contour with at least approximately plane face, by means of material build up, which certainly requires some rework.
The article “Kompressor- und Turbinenschaufeln automatisch reparieren” [Repairing compressor blades and turbine blades automatically] on pages 672-674 of the German journal Werkstatt und Betrieb 129 (1996) [Workshop and Factory], describes repair of blade tips and blade edges by build-up welding. The spatial actual contour of the respective blade is scanned in several sections near the weld bead and is stored. The actual contour is mathematically continued into the build-up weld area and produced by means of NC processing. It is possible to take into account special geometries at the blade tips, e.g. curved or kinked surface lines. Such a special geometry is for example scanned on a master blade and stored. There is also a reference to an intelligent equalization between the faulty actual geometries and the master geometries. Nevertheless, the expert is not provided with any concrete pointers as to how such equalization should take place.
In the case of rotor units with integral blades, the geometric area for producing matched surfaces can extend along the entire height of the ring volume, i.e. from the hub to the blade tips. The first application case is the production of new components in the context of which the blades, which preferably are largely in their finished state, are joined to the hub and where at least in the area of the joining zones close to the hub, the blades are formed by metal removing.
During operation of the rotors, wear and damage can occur which require repair. In the worst case, entire blades need to be replaced, but more frequently, more or less sizeable blade parts or areas need to be replaced. Naturally this concerns mostly the inlet edges and outlet edges as well as the tips of the blades. The damaged areas are separated, e.g. by means of laser beam cutting, and replaced by components/patches with oversize. If the damage extends only a little into the blade material, a simple build up of material with overmeasure, e.g. by means of laser powder build-up welding may be

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