Abstract:
A filler made of glass beads is provided. The glass improves the absorption and the distribution of the energy of the beam such that an internal wall of the hollow component is not damaged. A process for producing a through-hole in a hollow component is provided. Also, an apparatus for laser drilling is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 09015077.2 EP filed Dec. 4, 2009, which is incorporated by reference herein in its entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to a filler for the drilling of hollow components, in which a through-hole is produced through an outer wall, and also to a process and an apparatus therefor. 
       BACKGROUND OF INVENTION 
       [0003]    Components such as, for example, turbine blades or vanes have film-cooling holes as through-holes which are introduced after the component has been cast. 
         [0004]    For this purpose, lasers or electron beams are used to produce the hole in an outer wall. In the case of a hollow component, the cavity is generally filled with a material in order to prevent excessive damage to an internal wall when the hole is shot through at the end of the process. This can be done by filling with UV-curable material. 
         [0005]    However, this is not always adequate, e.g. when the material evaporates and then escapes outward through the hole. 
         [0006]    In addition, the introduction and removal of the material is time-consuming. 
       SUMMARY OF INVENTION 
       [0007]    It is therefore an object of the invention to solve the above-mentioned problem. 
         [0008]    The object is achieved by a filler as claimed in the claims, a process as claimed in the claims and an apparatus as claimed in the claims. 
         [0009]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to obtain further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows an arrangement for carrying out the process with such a filler, 
           [0011]      FIG. 2  shows a turbine blade or vane, and 
           [0012]      FIG. 3  shows a list of superalloys. 
       
    
    
       [0013]    The figures and the description represent merely exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0014]      FIG. 1  shows a subregion of a component  1 ,  120 ,  130 . 
         [0015]    The component  1  is preferably an internally cooled turbine blade or vane  120 ,  130 , and so the component  1 ,  120 ,  130  has a cavity  19 . 
         [0016]    A hole  7  is produced starting from the outer surface  22  of an outer wall  4 . 
         [0017]    In its final state, the hole  7  should provide a through-hole, as shown by dotted lines in  FIG. 1 . 
         [0018]    A laser  10  which emits laser beams  13  that evaporate the material of the wall  4  is preferably used for drilling. 
         [0019]    It is likewise also possible to use electron beams or other high-energy beams. 
         [0020]    The problem during the process is that, when the last region  25  of the through-hole  7  is produced, some of the laser beams can penetrate into the cavity  19  and damage an opposite wall  28  in the cavity  19 . 
         [0021]    To counter this, a filler  16 ′,  16 ″,  16 ′ is introduced into the cavity  19  in order to protect the internal wall  28 . 
         [0022]    According to the invention, here beads  16 ′,  16 ″, . . . , in particular glass beads, are introduced into the cavity  19 . 
         [0023]    The purpose of the beads  16 ′,  16 ″, . . . is to absorb and/or reflect the energy beam (laser beam). 
         [0024]    The glass beads preferably have a diameter ≦5 mm, in particular ≦2 mm, very particularly ≦1.2 mm. It is preferably also possible to use different bead diameters, e.g. smaller beads can fill the intermediate space between relatively large beads in order to achieve a higher packing density. 
         [0025]    The diameter is preferably at least 0.1 mm, in particular 0.3 mm. 
         [0026]    In this case, use is preferably made of a silicate glass or a beryllium glass. 
         [0027]    No particularly high demands are made on the glass beads with respect to roundness or surface quality so as to avoid focusing. 
         [0028]    The absorption process of the laser energy or of the energy beams can likewise be improved by colored glass beads, preferably green or blue glass beads. 
         [0029]    If the laser or the energy beam impinges on one such glass bead or on a plurality of such glass beads, the laser energy is split up, and so the energy of the laser beam which is split up or the propagation of the laser beam no longer suffices for damage to occur on the opposite wall. The energy beam is consumed by dimensional defects and the surface quality. 
         [0030]    The energy is also absorbed if the laser beam impinges on the glass bead in solid form and the latter shatters. The cavity which thereby becomes free is filled by other glass beads, which move forward. This is done automatically owing to the dead weight of the glass beads. 
         [0031]    The beads may have a solid or porous form. 
         [0032]    The glass bead or the remainder of the glass beads can simply be removed from the interior of the component  1  or the turbine blades or vanes  120 ,  130  by simply pouring them out or by slightly shaking them mechanically. As opposed to the use of wax or other materials, renewed heating and emptying by softening the filler does not have to take place. This accelerates the removal of the filler considerably. 
         [0033]      FIG. 2  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0034]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0035]    The blade or vane  120 ,  130  has, in succession along the longitudinal axis  121 , a securing region  400 , an adjoining blade or vane platform  403  and a main blade or vane part  406  and a blade or vane tip  415 . 
         [0036]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0037]    A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to a shaft or a disk (not shown), is formed in the securing region  400 . 
         [0038]    The blade or vane root  183  is designed, for example, in hammerhead form. Other configurations, such as a fir-tree or dovetail root, are possible. 
         [0039]    The blade or vane  120 ,  130  has a leading edge  409  and a trailing edge  412  for a medium which flows past the main blade or vane part  406 . 
         [0040]    In the case of conventional blades or vanes  120 ,  130 , by way of example solid metallic materials, in particular superalloys, are used in all regions  400 ,  403 ,  406  of the blade or vane  120 ,  130 . 
         [0041]    Superalloys of this type are known, for example, from EP 1 204 776 B1, EP 1 306 454, EP 1 319 729 A1, WO 99/67435 or WO 00/44949. 
         [0042]    The blade or vane  120 ,  130  may in this case be produced by a casting process, by means of directional solidification, by a forging process, by a milling process or combinations thereof. 
         [0043]    Workpieces with a single-crystal structure or structures are used as components for machines which, in operation, are exposed to high mechanical, thermal and/or chemical stresses. 
         [0044]    Single-crystal workpieces of this type are produced, for example, by directional solidification from the melt. This involves casting processes in which the liquid metallic alloy solidifies to form the single-crystal structure, i.e. the single-crystal workpiece, or solidifies directionally. 
         [0045]    In this case, dendritic crystals are oriented along the direction of heat flow and form either a columnar crystalline grain structure (i.e. grains which run over the entire length of the workpiece and are referred to here, in accordance with the language customarily used, as directionally solidified) or a single-crystal structure, i.e. the entire workpiece consists of one single crystal. In these processes, a transition to globular (polycrystalline) solidification needs to be avoided, since non-directional growth inevitably forms transverse and longitudinal grain boundaries, which negate the favorable properties of the directionally solidified or single-crystal component. 
         [0046]    Where the text refers in general terms to directionally solidified microstructures, this is to be understood as meaning both single crystals, which do not have any grain boundaries or at most have small-angle grain boundaries, and columnar crystal structures, which do have grain boundaries running in the longitudinal direction but do not have any transverse grain boundaries. This second form of crystalline structures is also described as directionally solidified microstructures (directionally solidified structures). 
         [0047]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0048]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion or oxidation e.g. (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon and/or at least one rare earth element, or hafnium (HO). Alloys of this type are known from EP 0 486 489 B1, EP 0 786 017 B1, EP 0 412 397 B1 or EP 1 306 454 A1. 
         [0049]    The density is preferably 95% of the theoretical density. 
         [0050]    A protective aluminum oxide layer (TGO=thermally grown oxide layer) is formed on the MCrAlX layer (as an intermediate layer or as the outermost layer). 
         [0051]    The layer preferably has a composition Co-30Ni-28Cr-8Al-0.6Y-0.7Si or Co-28Ni-24Cr-10Al-0.6Y. In addition to these cobalt-based protective coatings, it is also preferable to use nickel-based protective layers, such as Ni-10Cr-12Al-0.6Y-3Re or Ni-12Co-21Cr-11Al-0.4Y-2Re or Ni-25Co-17Cr-10Al-0.4Y-1.5Re. 
         [0052]    It is also possible for a thermal barrier coating, which is preferably the outermost layer and consists for example of ZrO 2 , Y 2 O 3 —ZrO 2 , i.e. unstabilized, partially stabilized or fully stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide, to be present on the MCrAlX. 
         [0053]    The thermal barrier coating covers the entire MCrAlX layer. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0054]    Other coating processes are possible, for example atmospheric plasma spraying (APS), LPPS, VPS or CVD. The thermal barrier coating may include grains that are porous or have micro-cracks or macro-cracks, in order to improve the resistance to thermal shocks. The thermal barrier coating is therefore preferably more porous than the MCrAlX layer. 
         [0055]    Refurbishment means that after they have been used, protective layers may have to be removed from components  120 ,  130  (e.g. by sand-blasting). Then, the corrosion and/or oxidation layers and products are removed. If appropriate, cracks in the component  120 ,  130  are also repaired. This is followed by recoating of the component  120 ,  130 , after which the component  120 ,  130  can be reused. 
         [0056]    The blade or vane  120 ,  130  may be hollow or solid in form. If the blade or vane  120 ,  130  is to be cooled, it is hollow and may also have film-cooling holes  418  (indicated by dashed lines).