Abstract:
A process for producing a hole with an asymmetrical diffuser is produced. The angular position of the laser with respect to the substrate is changed discontinuously during the processing. The production of complex holes in a substrate is simplified by using a laser in five different angular positions relative to a substrate to be processed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2009/060623, filed Aug. 17, 2009 and claims the benefit thereof. All of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a process for producing a hole with an asymmetrical diffuser, in which process the angular position of the laser with respect to the substrate is changed discontinuously during the processing. 
       BACKGROUND OF INVENTION 
       [0003]    The use of the laser for producing holes in substrates where the laser is also moved over the surface is known. 
         [0004]    Processes for producing holes with side-delimiting flanks are known in the prior art. By way of example, U.S. Pat. No. 6,420,677 describes a process for the laser-assisted formation of cooling air holes in turbine blades or vanes. In this case, provision is made to discharge a sequence of laser pulses onto the surface of the turbine blade or vane, wherein parts of the turbine material are vaporized such that a hole is formed along a Z axis. 
       SUMMARY OF INVENTION 
       [0005]    It is therefore an object of the present invention to specify a process of the type mentioned in the introduction, in which no damage to the hole flank occurs as a result of interaction with the laser beam. 
         [0006]    This object is achieved by a process as claimed in the claims. 
         [0007]    According to the invention, this object is achieved by a partial volume of the hole being formed in each of a plurality of production steps. 
         [0008]    The dependent claims list further advantageous measures which can be combined with one another, as desired, in order to achieve further advantages. 
         [0009]    The basic concept of the invention is therefore to divide the overall volume of the hole to be produced into partial volumes and to form these in individual production steps. The component material of some of the individual partial volumes is removed by a side flank of the hole being traced in each case with the laser beam. 
         [0010]    Here, the laser beam is preferably oriented such that it includes an angle of greater than 8° with the traced flank. Since, during the production of the hole, the laser beam is not directed onto the component surface close to, and parallel with, the already-formed flank of the hole, an impermissible interaction between the laser beam and the flank is prevented. Furthermore, the division of the overall volume of the hole into a plurality of partial volumes allows complex hole geometries to be formed. 
         [0011]    Instead of the laser, electron beams or the like can also be used. 
         [0012]    According to a further embodiment of the invention, the laser beam is oriented such that it includes an angle of greater than 10° and less than 90°, preferably of greater than 15° and less than 80° and particularly preferably of greater than 20° and less than 60° with the traced flank. An angle of 9° is especially preferred. 
         [0013]    In one development of the invention, provision is made for a pulsed laser beam to be directed onto the component surface in the hole. In this case, a laser beam with a variable pulse width can be used. The pulse width can lie in the range of 50 ns to 800 ns, preferably of 70 ns to 600 ns and in particular of 200 ns to 500 ns. A pulse width of 400 ns is especially preferred. With such a pulsed laser beam, the component material can be vaporized particularly quickly. This is particularly advantageous for the production of the diffuser. 
         [0014]    A laser beam with a frequency in the range of 20 kHz to 40 kHz, preferably of 25 kHz to 35 kHz and in particular of 28 kHz to 32 kHz can advantageously also be directed onto the component surface. 
         [0015]    This is particularly advantageous for the production of the diffuser. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a film-cooling hole to be produced, 
           [0017]      FIGS. 2-8  show schematic illustrations of the course of the process, 
           [0018]      FIG. 9  shows a gas turbine, 
           [0019]      FIG. 10  shows a turbine blade or vane, and 
           [0020]      FIG. 11  shows a list of superalloys. 
       
    
    
       [0021]    The description and the figures represent merely exemplary embodiments of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0022]      FIG. 1  shows a hole  1  in a substrate  4 . The hole  1  is preferably a continuous hole, not a blind hole. 
         [0023]    Particularly in the case of turbine blades or vanes  120 ,  130 , the substrate  4  has a nickel-base or cobalt-base superalloy according to  FIG. 11 . 
         [0024]    The film-cooling hole  1  has at least two differently configured sections  7 ,  10 , in particular only two sections  7 ,  10 . 
         [0025]    The first section is an inner proportion  7 , which preferably has a cylindrical or rotationally symmetrical cross section or has at least a constant cross section in an outflow direction  8 . 
         [0026]    A hot gas flows over the film-cooling hole  1  in an overflow direction  9 . The outflow direction  8  of the cooling medium and the overflow direction  9  form an acute angle with one another. 
         [0027]    From a certain depth beneath an outer surface  12  of the substrate  4  toward the surface  12 , the cross section of the film-cooling hole  1  widens compared to the inner proportion  7 . This represents the diffuser  10 . At a kink point  14  of a left-hand surface  17   a  of the film-cooling hole  1 , which represents the transition from the diffuser  10  to the inner proportion  7  opposite, a perpendicular line  19  on the inner surface  17   a  intersects an opposing section  15  in the substrate  4  at the surface  12 . 
         [0028]      FIG. 2  is a plan view of the surface  12  with the diffuser  10  shown in  FIG. 1 . 
         [0029]    In the overflow direction  9 , the diffuser  10  has a front edge  22 ′ and a rear edge  22 ″ on the surface  12  (these edges are preferably rectilinear here but can also be curved). 
         [0030]    The side flanks  11 ′,  11 ″ (these flanks are preferably rectilinear here but can also be curved) of the diffuser  10  are at two different angles α, β to the front edge  22 ′. 
         [0031]    The diffuser  10  is widened transversely to the overflow direction  9  and, with respect to the extension of the inner proportion  7  which is indicated by dashed lines, has flanks  11 ′,  11 ″ which are at two different angles α and β. 
         [0032]    Preferably, α&lt;β; α, β&lt;90°. 
         [0033]      FIGS. 3-8  show the schematic course of the process for producing the hole  1 . 
         [0034]    The processing is preferably effected by trepanning. 
         [0035]    The process begins with the provision of the substrate  4  ( FIG. 3 ), which is then processed using a laser  22  or electron beam source in a first angular position (I), preferably the first laser position (I) ( FIG. 4 ). 
         [0036]    In the text which follows, the laser is used by way of example as the processing machine. 
         [0037]    In this case, the inner proportion  7  is produced from the surface  12  as far as the opposing inner surface  13  of the substrate  4  (in the hollow space) ( FIG. 4 ). 
         [0038]    Here, the laser  22  preferably does not have to be moved (percussion). In the process, a remnant  16  remains in order to finish the diffuser  10  ( FIG. 4 ). The inner proportion  7  is finished. 
         [0039]      FIG. 8  shows the region  16  which is still to be removed ( FIG. 4 ) after production of the inner proportion  7 . 
         [0040]    This volume  16  to be removed is preferably removed in four partial steps. 
         [0041]      FIGS. 5 to 8  show the removal of the remnant  16 . α and β denote the orientation of the remnant  16  in terms of the angles α and β ( FIG. 2 ). 
         [0042]    The first volume  33  of the remnant  16  which is to be removed is shown in  FIG. 5 . 
         [0043]    The first partial volume  33  represents a polyhedron with a quadrangular base face  30  (at the top in the drawing), two triangular side faces  32 ′,  32 ″ and two opposing quadrangles  32 ′″,  32 ″″ as side faces. 
         [0044]      FIG. 5  also shows the overflow direction  9 , which runs over the base face  30 , i.e. the base face  30  is closest to the surface  12 . 
         [0045]    The face  32 ″″ lies on the inner surface of the diffuser  10 . This partial volume  33  is produced in the second laser position II, which differs from the first laser position I. 
         [0046]    The edge  31 ″″, which is formed by the side faces  32 ′″,  32 ″″, is oriented toward the interior of the inner proportion  7 . The partial volume  33  is a pentahedron (five-sided polyhedron). 
         [0047]    In a third step, which is shown in  FIG. 6 , a further partial volume  36  is removed. 
         [0048]    The second partial volume  36  to be removed adjoins the front quadrangle face  32 ′″ shown in  FIG. 5 , the partial volume  36  likewise representing a polyhedron with a quadrangular base face (=face  32 ′″), which represents the contact face with the polyhedron  33 , and four triangular faces  36 ′,  36 ″,  36 ′″,  36 ″″. The partial volumes  33  and  36  give a partial volume  42 , which represents a quadrangular base face  30  with  4  triangular side faces  41 ′. The partial volume  36  has a tip  35 . 
         [0049]    Both the partial volume  36  and the partial volume  42  (=33+36) represent a pentahedron. 
         [0050]    This partial volume  36  is produced in the second laser position III, which differs from the first laser position II. 
         [0051]      FIG. 7  shows how a third partial volume  39  is produced adjoining the partial volumes  33 ,  36  or partial volume  42  according to  FIGS. 5 and 6 . 
         [0052]    This gives the partial volume  48 . 
         [0053]    In this case, a partial volume  39  is removed in a fourth laser position IV, which  39  adjoins the left-hand side face  41 ′ of the polyhedron  42  ( FIG. 6 ), i.e. the side with the smaller angle α. 
         [0054]    The laser position IV differs from the laser position III and in particular also from the laser positions I, II. 
         [0055]    The base face of the partial volume  39  is triangular and adjoins the contact face  41 ′ of the polyhedron  42 , where the tip  35  of the partial volume  36  has been extended to the tip  45 , and gives a new partial volume  48 . 
         [0056]    In a new, changed fifth position V ( FIG. 8 ), a further partial volume  51  is removed, such that the region  16  to be removed has been removed completely. 
         [0057]    By virtue of the partial volume  51 , the tip  54  thereof is extended in turn with respect to the tip  45  and adjoins the flank of the diffuser with the smaller angle a. 
         [0058]    The laser position V preferably differs from the laser position IV and preferably also from the laser positions I, II, HI. 
         [0059]    The film-cooling hole  1  can also be produced in the manner described above if a metallic bonding layer, preferably of the MCrAlY type, and/or a ceramic layer is present on said layer or the substrate  4 . 
         [0060]      FIG. 9  shows, by way of example, a partial longitudinal section through a gas turbine  100 . 
         [0061]    In the interior, the gas turbine  100  has a rotor  103  with a shaft  101  which is mounted such that it can rotate about an axis of rotation  102  and is also referred to as the turbine rotor. 
         [0062]    An intake housing  104 , a compressor  105 , a, for example, toroidal combustion chamber  110 , in particular an annular combustion chamber, with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas housing  109  follow one another along the rotor  103 . 
         [0063]    The annular combustion chamber  110  is in communication with a, for example, annular hot-gas passage  111 , where, by way of example, four successive turbine stages  112  form the turbine  108 . 
         [0064]    Each turbine stage  112  is formed, for example, from two blade or vane rings. As seen in the direction of flow of a working medium  113 , in the hot-gas passage  111  a row of guide vanes  115  is followed by a row  125  formed from rotor blades  120 . 
         [0065]    The guide vanes  130  are secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are fitted to the rotor  103  for example by means of a turbine disk  133 . 
         [0066]    A generator (not shown) is coupled to the rotor  103 . 
         [0067]    While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake housing  104  and compresses it. The compressed air provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mix is then burnt in the combustion chamber  110 , forming the working medium  113 . From there, the working medium  113  flows along the hot-gas passage  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  is expanded at the rotor blades  120 , transferring its momentum, so that the rotor blades  120  drive the rotor  103  and the latter in turn drives the generator coupled to it. 
         [0068]    While the gas turbine  100  is operating, the components which are exposed to the hot working medium  113  are subject to thermal stresses. The guide vanes  130  and rotor blades  120  of the first turbine stage  112 , as seen in the direction of flow of the working medium  113 , together with the heat shield elements which line the annular combustion chamber  110 , are subject to the highest thermal stresses. 
         [0069]    To be able to withstand the temperatures which prevail there, they may be cooled by means of a coolant. 
         [0070]    Substrates of the components may likewise have a directional structure, i.e. they are in single-crystal form (SX structure) or have only longitudinally oriented grains (DS structure). 
         [0071]    By way of example, iron-base, nickel-base or cobalt-base superalloys are used as material for the components, in particular for the turbine blade or vane  120 ,  130  and components of the combustion chamber  110 . 
         [0072]    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. 
         [0073]    The blades or vanes  120 ,  130  may likewise have coatings protecting against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron 
         [0074]    (Fe), cobalt (Co), nickel (Ni), X is an active element and stands for yttrium (Y) and/or silicon, scandium (Sc) and/or at least one rare earth element, or hafnium). 
         [0075]    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. 
         [0076]    It is also possible for a thermal barrier coating to be present on the MCrAlX, consisting 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. 
         [0077]    Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD). 
         [0078]    The guide vane  130  has a guide vane root (not shown here), which faces the inner housing  138  of the turbine  108 , and a guide vane head which is at the opposite end from the guide vane root. The guide vane head faces the rotor  103  and is fixed to a securing ring  140  of the stator  143 . 
         [0079]      FIG. 10  shows a perspective view of a rotor blade  120  or guide vane  130  of a turbomachine, which extends along a longitudinal axis  121 . 
         [0080]    The turbomachine may be a gas turbine of an aircraft or of a power plant for generating electricity, a steam turbine or a compressor. 
         [0081]    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 . 
         [0082]    As a guide vane  130 , the vane  130  may have a further platform (not shown) at its vane tip  415 . 
         [0083]    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 . 
         [0084]    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. 
         [0085]    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 . 
         [0086]    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 . 
         [0087]    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. 
         [0088]    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. 
         [0089]    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. 
         [0090]    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. 
         [0091]    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. 
         [0092]    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). 
         [0093]    Processes of this type are known from U.S. Pat. No. 6,024,792 and EP 0 892 090 A1. 
         [0094]    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 (Hf)). 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. 
         [0095]    The density is preferably 95% of the theoretical density. 
         [0096]    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). 
         [0097]    The layer preferably has a composition Co-30Ni-28Cr-8A1-0.6Y-0.7Si or Co-28Ni-24Cr-10A1-0.6Y. In addition to these cobalt- base protective coatings, it is also preferable to use nickel-base protective layers, such as Ni-10Cr-12A1-0.6Y-3Re or Ni-12Co-21Cr-11A1-0.4Y-2Re or Ni-25Co-17Cr-10A1-0.4Y-1.5Re. 
         [0098]    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. 
         [0099]    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). 
         [0100]    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. 
         [0101]    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. 
         [0102]    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).