Abstract:
Previous methods for the production of a hole in a component are very time-consuming and expensive, as special lasers having ultra short laser pulse lengths are used. The inventive method varies laser pulse lengths and ultra short laser pulse lengths are used exclusively in the region which is to be removed, wherein it is possible to have a noticeable influence on through flow and/or out-flow behavior. This, for example, the inner surface of a diffuser of a hole, which can be produced in a precise manner using ultra short laser pulse lengths.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is the US National Stage of International Application No. PCT/EP2004/009793, filed Sep. 2, 2004 and claims the benefit thereof. The International Application claims the benefits of European application No. 03022635.1 filed Oct. 6, 2003 and European application No.03024966.8 filed Oct. 29, 2003, all of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a process for producing a hole as described in the claims, in which a hole is produced in a component by at least one laser and pulsed laser beams, and to an apparatus for carrying out the process as described in the claims.  
       BACKGROUND OF THE INVENTION  
       [0003]     With many components, in particular castings, material has to subsequently be removed, for example to form recesses or through-holes. In particular in the case of turbine components, which have film-cooling holes for cooling purposes, holes are introduced retrospectively following production of the component.  
         [0004]     Turbine components of this type often also have layers, such as for example a metallic interlayer and/or a ceramic outer layer. The film-cooling holes then have to be produced through the layers and the substrate (casting).  
         [0005]     U.S. Pat. No. 6,172,331 and U.S. Pat. No. 6,054,673 disclose a laser drilling method for introducing holes into layer systems in which ultrashort laser pulse lengths are used. A laser pulse length is searched for within a defined laser pulse length range and used to produce the hole.  
         [0006]     DE 100 63 309 A1 discloses a process for producing a cooling air opening by means of a laser, in which the laser parameters are set in such a way that material is removed by sublimation.  
         [0007]     The use of ultrashort laser pulses of this type is expensive and very time-consuming on account of their low mean powers.  
       SUMMARY OF THE INVENTION  
       [0008]     Therefore, it is an object of the invention to overcome this problem.  
         [0009]     The object is achieved by the process as claimed in the claims, in which different laser pulse lengths are used.  
         [0010]     It is particularly advantageous if short laser pulse lengths are used only in one of the first process steps in order to produce optimum properties in an outer upper region of the cut surface, since these properties are crucial for the behaviour of a medium as it flows out of the hole and for the properties of a medium as it flows around this hole. The properties of the cut surface are less critical in the interior of the hole, and consequently longer laser pulse lengths, which can cause inhomogeneous cut surfaces, can be used there.  
         [0011]     A further object is to provide an apparatus with which the process can be carried out quickly and easily. This object is achieved by the apparatus as claimed in the claims.  
         [0012]     The subclaims list further advantageous measures of the process.  
         [0013]     The measures listed in the subclaims can be combined with one another in an advantageous way. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention is explained in more detail with reference to the figures, in which:  
         [0015]      FIG. 1  shows a hole in a substrate,  
         [0016]      FIG. 2  shows a hole in a layer system,  
         [0017]      FIGS. 3, 4 ,  5 ,  6 ,  7 ,  8 ,  9  show process steps of the process according to the invention,  
         [0018]      FIG. 10  shows an apparatus for carrying out the process,  
         [0019]      FIG. 11  shows a turbine blade or vane,  
         [0020]      FIG. 12  shows a gas turbine, and  
         [0021]      FIG. 13  shows a combustion chamber. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1  shows a component  1  with a hole  7 . The component  1  comprises a substrate  4  (for example a casting). The substrate  4  may be metallic and/or ceramic. In particular in the case of turbine components, such as for example turbine rotor blades  120  ( FIGS. 10, 11 ) or turbine guide vanes  130  ( FIG. 11 ), combustion chamber linings  155  ( FIG. 12 ) and other housing parts of a steam or gas turbine  100  ( FIG. 11 , but also aircraft turbine), the substrate  4  consists of a nickel-base, cobalt-base or iron-base superalloy.  
         [0023]     The substrate  4  has a hole  7  which is, for example, a through-hole. It may also be a blind hole.  
         [0024]     The hole  7  comprises a lower region  10  in a lower region of the hole  7 , which is, for example, symmetrical and, for example, also circular in form, and a diffusor  13  at a surface  14  of the substrate  4 . The diffusor  13  constitutes, for example, a widening in the cross section with respect to the part  10  of the hole  7 . The hole  7  is, for example, a film-cooling hole. In particular the inner surface of the diffusor  13  should be flat in order to allow a medium to flow out of the hole  7  in an optimum way.  
         [0025]      FIG. 2  shows a component  1  which is designed as a layer system. At least one layer  16  is present on the substrate  4 . This may, for example, be a metallic alloy of type MCrAlX, where M stands for at least one element selected from the group consisting of iron, cobalt and nickel. X stands for yttrium and/or at least one rare earth element. The layer  16  may also be ceramic.  
         [0026]     A further layer (not shown), for example a ceramic layer, in particular a thermal barrier coating, may also be present on the layer  16 . The thermal barrier coating is, for example, a completely or partially stabilized zirconium oxide layer, in particular an EB-PVD layer or a plasma-sprayed (APS, LPPS, VPS) layer.  
         [0027]     A hole  7  comprising the two subregions  10  and  13  is likewise introduced into this layer system.  
         [0028]     The statements which have been made in connection with the production of the hole  7  apply to substrates  4  both with and without layer or layers.  
         [0029]      FIGS. 3 and 4  show process steps of the process according to the invention. According to the invention, different laser pulse lengths are used during the process, in particular very short laser pulse lengths of less than 100 ns (nanoseconds), in particular less than 50 ns, are used in one of the first process steps. It is also possible to use laser pulse lengths of less than picoseconds or femtoseconds.  
         [0030]     If very short laser pulse lengths of less than 100 ns, in particular less than 50 ns, are used, virtually no fusion occurs in the region of the cut surface. Therefore, no cracks are formed there and consequently accurate geometries can be produced.  
         [0031]     In one of the first process steps, a first subregion of the hole  7  is produced in the component  1 . This can at least partially or completely correspond to the diffusor  13  ( FIGS. 4, 7 ,  8 ).  
         [0032]     In particular, although not necessarily, when a metallic interlayer or the metallic substrate  4  is reached, laser pulse lengths of greater than 50 ns, in particular greater than 100 ns and in particular up to 10 ms are used to produce the remaining (second) subregion  10  of the hole  7 , as illustrated in  FIG. 1  or  2 .  
         [0033]     The laser pulse lengths of a single laser  19  can be altered continuously, for example from the start of the process to the end of the process. The start of the process begins with the removal of material at the outer surface  14 , and the end of the process concludes at the depth of the hole  7 . The material is, for example, removed in layers in a plane  11  ( FIG. 6 ) and in an axial direction  15 .  
         [0034]     The process can be applied to newly produced components  1  which have been cast for the first time.  
         [0035]     The process can also be used with components  1  which are to be refurbished. Refurbishment means that components  1  which have been used by way of example have layers removed and, after repair, such as for example filling of cracks and removal of oxidation and corrosion products, are newly coated again. In this case, by way of example, impurities or coating material which has been reapplied ( FIG. 7 ) and has entered the holes  7  is removed using a laser  19 ,  19 ′.  
         [0036]     In the process, it is possible to use at least two or more lasers  19 ,  19 ′, which by way of example are deployed in succession. The various lasers  19 ,  19 ′ have different ranges of laser pulse lengths. For example, a first laser  19  may generate laser pulse lengths of less than 100 ns, in particular less than 50 ns, and a second laser  19 ′ may generate laser pulse lengths of greater than 50 ns, in particular greater than 100 ns. To produce a hole  7 , the first laser  19  is deployed first of all. Then, the second laser  19 ′ is used for the further processing.  
         [0037]      FIG. 5  shows a cross section through a hole  7 . In this case too, the process involves first of all rough machining with laser pulse lengths of greater than 50 ns, in particular greater than 100 ns, and precision machining with laser pulse lengths of less than 100 ns, in particular less than 50 ns.  
         [0038]     The lower subregion  10  of the hole  7  is machined completely, and the region of the diffusor  13  almost completely, using a laser which has laser pulse lengths of greater than 50 ns, in particular greater than 100 ns. To complete the hole  7  or the diffusor  13 , all that is then required is for a thin upper region  28  in the region of the diffusor  13  to be machined by means of a laser  19 ,  19 ′ which can generate laser pulse lengths of less than  100  ns, in particular less than 50 ns.  
         [0039]      FIG. 6  shows a plan view of a hole  7  in the component  1 . The different lasers  19 ,  19 ′ or the different laser pulse lengths of these lasers  19 ,  19 ′ are used in different process steps.  
         [0040]     First of all, for example, rough machining is carried out using long laser pulse lengths (&gt;50 ns, in particular &gt;100 ns). This produces the majority of the hole  7 . This inner region is denoted by reference numeral  25 . Only an outer upper region  28  of the hole  7  or the diffusor  13  then has to be removed in order to achieve the final dimensions of the hole  7  ( FIG. 8 , the outer upper region  28  is indicated by dashed lines). Only when the outer upper region  28  has been machined by means of a laser  19 ,  19 ′ with very short laser pulse lengths (&lt;100 ns, in particular &lt;50 ns) is the hole  7  or the diffusor  13  complete. The contour  29  of the diffusor  13  is therefore produced using very short laser pulse lengths, i.e. with the result that the outer upper region  28  is removed and is therefore free of cracks and fusion. The material is, for example, removed in a plane  11  (perpendicular to the axial direction  15 ).  
         [0041]     One alternative for the production of the hole  7  consists in first of all producing the outer upper region  28  using short laser pulse lengths (&lt;100 ns) down to a depth in the axial direction  15  which partially or completely corresponds to the extent of the diffusor  13  of the hole  7  in this direction  15  ( FIG. 7 , the inner region  25  is indicated by dashed lines). As a result, virtually no fusion is produced in the region of the cut surface of the diffusor  13 , and no cracks are formed there, with the result that accurate geometries can be produced. Only then is the inner region  25  removed using longer laser pulse lengths (&gt;50 ns, in particular &gt;100 ns).  
         [0042]      FIG. 9  shows the remachining (refurbishment) of a hole  7 , in which case, during coating of the substrate  4  with the material of the layer  16 , material has penetrated into the existing hole  7 . By way of example, the deeper regions in the region  10  of the hole  7  can be machined using a laser which has laser pulse lengths of greater than  50  ns, in particular greater than  100  ns. These regions are denoted by  25 . The more critical upper region  28 , for example in the region of the diffusor  13 , on which contamination is present, is machined using a laser  19 ′ which has laser pulse lengths of less than 100 ns, in particular less than 50 ns.  
         [0043]      FIG. 10  shows, by way of example, an apparatus  40  according to the invention for carrying out the process according to the invention. The apparatus  40  comprises, for example, at least one optical system  35 , in this case one optical system  35 , in particular a lens, which diverts a laser beam  22  onto the substrate  4  in order to produce the through-hole  10 .  
         [0044]     At least two lasers  19 ,  19 ′ are used. The laser beams  22 ′,  22 ″ can be passed via mirrors  31 ,  33  to the optical system  35 . The mirrors  31 ,  33  are displaceable or rotatable, so that in each case only one laser  19 ,  19 ′ emits its laser beams  22 ′ or  22 ″ via the mirrors  31  or  33  and the lens  35  onto the component  1 .  
         [0045]     It is also possible for the laser beams  22 ′ or  22 ″ to be simultaneously guided onto the component via one optical system or two or more optical systems if different regions are being removed in one plane. By way of example, the outer region  28  can be produced using short laser pulse lengths and the inner region  25  using longer laser pulse lengths at the same time.  
         [0046]     The lasers  19 ,  19 ′ may have wavelengths of  1064  nm or  532  nm. The lasers  19 ,  19 ′ may have different wavelengths. Likewise, by way of example, the laser  19  has pulse lengths of 0.05-5 ms; by contrast, the laser  19 ′ has pulse lengths of 50-500 ns.  
         [0047]     Therefore, by displacing the mirrors  31 ,  33 , it is possible for the respective laser  19 ,  19 ′ with its corresponding laser pulse lengths which are required in order for example to produce the outer upper region  28  or the inner region  25  to be introduced onto the component  1  via the optical system  35 .  
         [0048]     Both the mirrors  31 ,  33 , the optical system or the substrate  4  can be displaced in such a way that material is removed from the surface of the substrate  4  as shown in FIGS.  3  to  9 . If, for example, the outer upper region  28  is produced first of all, as shown in  FIG. 6 , the laser with the short laser pulse lengths  19 ′ is introduced. If the inner region  25  is then produced, the laser  19 ′ is decoupled by movement of the mirror  33 , and the laser  19  with its longer laser pulse lengths  10  is introduced by movement of the mirror  31 .  
         [0049]      FIG. 11  shows a perspective view of a blade or vane  120 ,  130 , which extends along a longitudinal axis  121  into which, for example, film-cooling holes, for example having a diffusor  13 , are to be introduced.  
         [0050]     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 region  406 . A blade or vane root  183 , which is used to secure the rotor blades  120 ,  130  to the shaft, is formed in the securing region  400 . The blade or vane root  183  is configured as a hammer head. Other configurations, for example as a fir-tree root or dovetail root are also possible. In the case of conventional blades or vanes  120 ,  130 , solid metallic materials are used in all regions  400 ,  403 ,  406  of the rotor blade  120 ,  130 . The rotor blade  120 ,  130  may in this case be produced by a casting process, by a forging process, by a milling process or by combinations thereof.  
         [0051]      FIG. 12  shows, by way of example, a gas turbine  100  in longitudinal part section. In the interior, the gas turbine  100  has a rotor  103  which is mounted so as to rotate about an axis of rotation  102  and is also referred to as the turbine rotor. An intake casing  104 , a compressor  105 , a, for example, torroidal combustion chamber  110 , in particular an annular combustion chamber  106 , with a plurality of coaxially arranged burners  107 , a turbine  108  and the exhaust-gas casing  109  follow one another along the rotor  103 . The annular combustion chamber  106  is in communication with a, for example, annular hot-gas duct  111 . There, by way of example, four turbine stages  112  connected in series form the turbine  108 . Each turbine stage  112  is formed from two blade or vane rings. As seen in the direction of flow of a working medium  113 , a row  125  of rotor blades  120  follows a row  115  of guide vanes in the hot-gas duct  111 .  
         [0052]     The guide vanes  130  are in this case secured to an inner housing  138  of a stator  143 , whereas the rotor blades  120  of a row  125  are arranged on the rotor  103  by means of a turbine disk  133 . A generator (not shown) is coupled to the rotor  103 .  
         [0053]     While the gas turbine  100  is operating, the compressor  105  sucks in air  135  through the intake casing  104  and compresses it. The compressed air which is provided at the turbine-side end of the compressor  105  is passed to the burners  107 , where it is mixed with a fuel. The mixture is then burnt, forming the working medium  113  in the combustion chamber  110 . From there, the working medium  113  flows along the hot-gas duct  111  past the guide vanes  130  and the rotor blades  120 . The working medium  113  expands at the rotor blades  120  in such a manner as to transfer its momentum, so that the rotor blades  120  drive the rotor  103  and the latter drives the generator coupled to it.  
         [0054]     When the gas turbine  100  is operating, the components 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 bricks which line the annular combustion chamber  106 , are subject to the highest thermal stresses. To be able to withstand the temperatures prevailing there, these components are cooled by means of a cooling medium.  
         [0055]     The substrates may also have a directional structure, i.e. they are single-crystalline (SX structure) or have only longitudinally oriented grains (DS structure). Iron-base, nickel-base or cobalt-base superalloys are used as the material.  
         [0056]     The blades or vanes  120 ,  130  may also have coatings to protect against corrosion (MCrAlX; M is at least one element selected from the group consisting of iron (Fe), cobalt (Co), Nickel (Ni), X stands for yttrium (Y) and/or at least one rare earth element) and to protect against heat by means of a thermal barrier coating. The thermal barrier coating consists, for example, of Zr,O2, Y2O4-ZrO2, i.e. it is unstabilized, partially stabilized or completely stabilized by yttrium oxide and/or calcium oxide and/or magnesium oxide. Columnar grains are produced in the thermal barrier coating by suitable coating processes, such as for example electron beam physical vapor deposition (EB-PVD).  
         [0057]     The guide vane  130  has a guide vane root (not shown here) facing the inner casing  138  of the turbine  108  and a guide vane head 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 .  
         [0058]      FIG. 13  shows a combustion chamber  110  of a gas turbine  100 . The combustion chamber  110  is configured, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners  102 , which are arranged around the turbine shaft  103  in the circumferential direction, open out into a common combustion chamber space. For this purpose, the combustion chamber  110  as a whole is configured as an annular structure which is positioned around the turbine shaft  103 .  
         [0059]     To achieve a relatively high efficiency, the combustion chamber  110  is designed for a relatively high temperature of the working medium M of approximately 1000° C. to  1600 ° C. To allow a relatively long operating time even under these operating parameters, which are unfavorable for the materials, the combustion chamber wall  153  is provided, on its side which faces the working medium M, with an inner lining formed from heat shield elements  155 . On the working medium size, each heat shield element  155  is equipped with a particularly heat-resistant protective layer or is made from material that is able to withstand high temperatures. Moreover, on account of the high temperatures in the interior of the combustion chamber  110 , a cooling system is provided for the heat shield elements  155  and/or for their holding elements. The heat shield elements  155  may also have holes  7 , for example also including a diffusor  13 , in order to cool the heat shield element  155  or to allow combustible gas to flow out.  
         [0060]     The materials of the combustion chamber wall and the coatings thereof may be similar to those of the turbine blades or vanes.  
         [0061]     The combustion chamber  110  is designed in particular to detect losses of the heat shield elements  155 . For this purpose, a number of temperature sensors  158  are positioned between the combustion chamber wall  153  and the heat shield elements  155 .