Abstract:
The present disclosure relates to methods of preparing a material for welding. The material is prepared by utilizing a laser to obliterate contaminants from the material surface.

Description:
BACKGROUND 
     Present embodiments relate generally to gas turbine engines. More particularly, but not by way of limitation, present embodiments relate to methods of preparing a material with a laser for welding. 
     In turbine engines, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gas which flow downstream through turbine stages. These turbine stages extract energy from the combustion gas. A high pressure turbine includes a first stage nozzle and a rotor assembly including a disk and a plurality of turbine blades. The high pressure turbine first receives the hot combustion gas from the combustor and includes a first stage stator nozzle that directs the combustion gas downstream through a row of high pressure turbine rotor blades extending radially outwardly from a first rotor disk. In a two stage turbine, a second stage stator nozzle is positioned downstream of the first stage blades followed in turn by a row of second stage turbine blades extending radially outwardly from a second rotor disk. The stator nozzles direct the hot combustion gas in a manner to maximize extraction at the adjacent downstream turbine blades. 
     The first and second rotor disks are joined to the compressor by a corresponding rotor shaft for powering the compressor during operation. These are typically referred to as the high pressure turbine. The turbine engine may include a number of stages of static airfoils, commonly referred to as vanes, interspaced in the engine axial direction between rotating airfoils commonly referred to as blades. A multi-stage low pressure turbine follows the two stage high pressure turbine and is typically joined by a second shaft to a fan disposed upstream from the compressor in a typical turbofan aircraft engine configuration for powering an aircraft in flight. 
     As the combustion gas flows downstream through the turbine stages, energy is extracted therefrom and the pressure of the combustion gas is reduced. The combustion gas is used to power the compressor as well as a turbine output shaft for power and marine use or provide thrust in aviation usage. In this manner, fuel energy is converted to mechanical energy of the rotating shaft to power the compressor and supply compressed air needed to continue the process. 
     During the operation of the gas turbine engine, it is necessary to obtain temperature readings at different locations in the engine. This data is utilized by the engine control logic to properly operate the engine and provide maximum performance at the highest efficiency. One such temperature probe which is utilized at the exhaust area of the combustor, it is known as an Exhaust Gas Temperature probe or EGT probe. These probes utilize thermocouples, typically having a dissimilar metal to create a differential which may be then related to a temperature which is provided to the engine control logic. The thermocouple wires are disposed in a sheath with an insulating magnesium oxide. To prepare the thermocouple wires for installation and welding, the thermocouple sheath is stripped away from the portion of the thermocouple wire or lead which is to be welded. The magnesium oxide powder must also be cleaned away. 
     Various methods have been attempted in order to perform this cleaning. The magnesium oxide powder has been cleaned with alcohol in an attempt to remove such from the wire. Additionally, rotating blades have been utilized in an attempt to mechanically remove the magnesium oxide. As a further alternative, abrasive pads have been utilized in an attempt to manually remove the magnesium oxide powder. Unfortunately, the thermocouple leads are extremely costly and mechanical and other means of cleaning have resulted in damage and discarding of an unacceptable percentage of the thermocouples. 
     Of the remaining thermocouples which are not damaged in the mechanical cleaning process, various of these structures have problems with the weld bond due to remaining contaminants on the surface of the thermocouple lead or wire. Specifically, for example, magnesium oxide powder may not be thoroughly cleaned from the surface and therefore results in welds which have high porosity in the weld, low percentage of weld fusion across the wire diameter and low percentage of weld fusion. The fractures of a poor weld bond are depicted in  FIG. 8  across the terminal. 
     As may be seen from the foregoing, there is a need to optimize the cleaning procedure of materials which will be welded while limiting damage during the process so that the optimal bond may occur when the weld process occurs. 
     SUMMARY 
     Some embodiments of the present disclosure relate to a method of preparing a material for welding. The material is prepared by utilizing a laser to obliterate contaminants from the material surface. The laser provides an improved cleaning as opposed to other methods of cleaning. The method also inhibits damage to the wires or leads which occurs with mechanical cleaning processes. 
     According to some embodiments, a method of preparing a thermocouple for welding, comprises exposing a lead, positioning the lead adjacent a laser, passing the laser over the lead at least once and obliterating surface contaminants from the lead with the laser. 
     All of the above outlined features are to be understood as exemplary only and many more features and objectives of the method may be gleaned from the disclosure herein. Therefore, no limiting interpretation of this summary is to be understood without further reading of the entire specification, claims, and drawings included herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE ILLUSTRATIONS 
       The above-mentioned and other features and advantages of this disclosure, and the manner of attaining them, will become more apparent and the process sensor will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a side section schematic view of an exemplary turbine engine. 
         FIG. 2  is an side elevation view of an exemplary process sensor assembly. 
         FIG. 3  is a side elevation view of a thermocouple. 
         FIG. 4  is a schematic view of a method of preparing the leads of a thermocouple with a laser. 
         FIG. 5  is a detail section view of the process sensor assembly. 
         FIG. 6  is a section view of an exemplary weld following the process of laser cleaning. 
         FIG. 7  is a flow chart setting for the exemplary steps of the method. 
         FIG. 8  is an section view of an exemplary weld depicting poor bond due to inadequate cleaning. 
     
    
    
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments provided, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation, not limitation of the disclosed embodiments. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present embodiments without departing from the scope or spirit of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to still yield further embodiments. Thus it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Present embodiments provide a method of laser prepping a thermocouple wire or lead prior to welding. The prepping process provides laser removal of contaminants on the material, such as a wire surface, which would otherwise preclude an appropriate weld. Additionally, the laser prepping method results in less damage to the thermocouple wires or leads. 
     The terms fore and aft are used with respect to the engine axis and generally mean toward the front of the turbine engine or the rear of the turbine engine in the direction of the engine axis, respectively. 
     Referring now to  FIGS. 1-7 , various embodiments of methods of cleaning or prepping a thermocouple lead which provides improved welding characteristics. 
     Referring initially to  FIG. 1 , a schematic side section view of a gas turbine engine  10  is shown having an engine inlet end  12 , a compressor  14 , a combustor  16  and a multi-stage high pressure turbine  20 . The gas turbine  10  may be used for aviation, power generation, industrial, marine or the like. Depending on the usage, the engine inlet end  12  may alternatively contain multi-stage compressors rather than a fan. The gas turbine  10  is axis-symmetrical about engine axis  26  or shaft  24  so that various engine components rotate thereabout. In operation air enters through the air inlet end  12  of the engine  10  and moves through at least one stage of compression where the air pressure is increased and directed to the combustor  16 . The compressed air is mixed with fuel and burned providing the hot combustion gas which exits the combustor  16  toward the high pressure turbine  20 . At the high pressure turbine  20 , energy is extracted from the hot combustion gas causing rotation of turbine blades which in turn cause rotation of the shaft  24 . The shaft  24  passes toward the front of the engine to continue rotation of the one or more compressor stages  14 , a turbofan  18  or inlet fan blades, depending on the turbine design. 
     The axis-symmetrical shaft  24  extends through the through the turbine engine  10 , from the forward end to an aft end. The shaft  24  is supported by bearings along its length. The shaft  24  may be hollow to allow rotation of a low pressure turbine shaft  28  therein. Both shafts  24 ,  28  may rotate about a centerline  26  of the engine. During operation the shafts  24 ,  28  rotate along with other structures connected to the shafts such as the rotor assemblies of the turbine  20  and compressor  14  in order to create power or thrust depending on the area of use, for example power, industrial or aviation. 
     Referring still to  FIG. 1 , the inlet  12  includes a turbofan  18  which has a plurality of blades. The turbofan  18  is connected by shaft  28  to the low pressure turbine  19  and creates thrust for the turbine engine  10 . Aft of the combustor  16  is one exemplary location for a temperature probe  30 . Although an exhaust gas temperature is discussed herein, sensors may be initialized at various locations such as the compressor  14  turbines  20 ,  19  and other locations. Additionally, the method of preparing is not limited to temperature sensors but may be utilized with any type of sensor requiring leads to be cleaned prior to an subsequent manufacturing process. 
     Referring now to  FIG. 2 , a temperature probe  30  which is defined by elongate housing  32  having a probe portion  34  extending from the lower end thereof. Along some portion of the housing  32  is a flange  36  which is utilized to mount the probe  30  in a location of the gas turbine engine  10 . 
     The upper portion of the housing includes two terminals  38 ,  40  extending from opposite sides thereof. The terminals of the exemplary embodiment are “KN” and “KP” type leads or wires. One skilled in the art will understand that KN and KP are negatively polarized nickel-aluminum-silicon type K thermoelement and positively polarized nickel-chromium type K thermoelement, respectively. The terminals  38 ,  40  are each formed by two wires or leads which extend outwardly from the housing structure and which are welded together. Each pair of wires must be cleaned at ends in order to provide a proper weld and form terminals. 
     Referring now to  FIG. 3 , an elevation view of an exemplary thermocouple  50  is depicted. The thermocouple  50  includes a sheath  52  which according to one exemplary embodiment may be formed of an inconel material. However, various materials may be utilized to form this sheath. Within the sheath  52  are the thermocouple leads  54 ,  58 , which are each formed of a pair of wires and which are welded together at ends to define the terminals  38 ,  40 . The sheath  52  is also filled with an insulation  60 , for example magnesium oxide, in powder form to insulate leads  54 ,  58 . The magnesium oxide  60  is depicted in the figure with stippling along the leads  54 ,  58 . The magnesium oxide  60  must be removed near the end of the leads  54 ,  58  so that the pairs of wires may be welded together to define the terminals  38 ,  40 . 
     The problem as described previously with thermocouple leads occur when cleaning the ends of the leads  54 ,  58  to form suitable areas for welding to form the terminal  38 ,  40 . The magnesium oxide removal process can be difficult and lead to damaged leads or weak bonds due to the contaminant material not being thoroughly removed from the leads  54 ,  58 . This poor weld bond is shown at  FIG. 8  which fractures extending through the welded material. 
     Referring now to  FIG. 4 , an exemplary schematic view of the laser which prepares the thermocouple  50 , is depicted schematically. The laser  70  may be utilized to prepare the leads  54 ,  58  by obliterating contaminants  60  at the ends of the wire pairs that define the terminals  38 ,  40  ( FIG. 3 ). The laser  70  is depicted with a plurality of linkages  72  so that the laser  70  may be movable relative to the thermocouple  50 . Any means of movement may be utilized and the depiction of linkages should not be considered limiting. For example, linear motion may be used. Similarly, the laser may be rotatable. Additionally, the thermocouple  50  may be movable which allows for movement of the thermocouple  50  relative to the laser  70 . Thus either or both of the structures may be movable to aid in the cleaning procedure. According to at least one exemplary embodiment, the laser  70  may pass the thermocouple leads  54 ,  58  in one pass. Next the leads are rotated 180° so that the opposite side of the leads may also be cleaned as desirable. This method may be used due to the circular cross-section of the wires defining leads  54 ,  58 . 
     The exemplary method exposes the leads  54 ,  58  for subsequent welding. First, the leads  54 ,  58  are positioned adjacent the laser  70  as depicted in one exemplary embodiment of  FIG. 4 . Next the laser  70  passes over the leads  54 ,  58 , each of which are defined by a pair of wires. This may require movement of one or more of the wires, laser or retaining structures. With the laser  70  operating, the surface contaminants are obliterated from the ends of leads  54 ,  58  to expose clean wire or lead material. This renders the leads  54 ,  58  suitable for welding. 
     When moving the laser  70 , the speed of the movement varies the energy which is imparted to the thermocouple leads  54 ,  58 . For example, when the laser is moved faster relative to the leads  54 ,  58  the energy imparted decreases. To the contrary when the laser  70  is moved slower, the energy imparted on the leads  54 ,  58  increases. According to some exemplary embodiments, the laser  70  may move at a velocity of about 30 inches per second according to one preferable but exemplary embodiment. Other velocities may utilize to impart a desired amount of energy for obliteration of contaminants  60 . 
     The laser  70  may have a pulse frequency of between 100,000 and 150,000 cycles per second (Hz). More preferably, the laser  70  may have a pulse frequency ranging between 30,000 and 60,000 cycles per second. The laser  70  may have a beam width or tracking width of between 0.001 inches and 0.005 inches. More preferably, the laser  70  may have a beam width or track width of about 0.002 inches. 
     Referring now to  FIG. 5 , a side section view of the exemplary probe  30  is depicted in part with the housing  32  shown and terminals  38 ,  40  extending therefrom. The thermocouple  50  is shown with the leads  54 ,  58  extending from opposite sides of a housing  32  and forming the terminal  38 ,  40 . Each of the terminals  38 ,  40 , as previously described, is formed of a pair of wires which are welded together. Although a single wire is shown, a pair of wires is utilized and the unseen wire is disposed behind the wire that is depicted. This manufacturing step occurs after the cleaning or preparation process of the leads  54 ,  58  and with the wires extending from terminal walls  62 , the wire pairs are welded to define the terminal  38 ,  40 . 
     Referring now to  FIG. 6 , a side section view of an exemplary terminal  38  is depicted and thus a detailed section view, two thermocouple wires  54  are shown extending through an exemplary terminal wall area  62 . Due to the preparation process previously described, the weld bond of the wires  54  is clean with appropriate bonding. The wires  54  do not depict any broken or cracked areas which would create bonding problems. Additionally, the clean thermocouple leads  54  allow for such appropriate weld to occur when the subsequent welding of these leads happens during the manufacture process. 
     According to one example, the following criteria are desirable and may be met by use of the laser cleaning process described herein. It is desirable that the weld fusion across the wire diameter exposed be greater than 80%. It is also desirable that the weld fusion across the terminal post walls be greater than 80%. It is further desirable that individual porosity diameter should not be greater than 0.015 inches. Finally, it is desirable as well that the total area of accumulated porosity shall not exceed 30% of the total weld area exposed. These goals are capable by cleaning the thermocouple leads or wires  54 ,  58  which the laser process described herein. Whereas in the alternative, prior art methods of cleaning the thermocouple leads or wires  54 ,  58  did not result in such favorable results in the welding process. 
     The laser  70  according to one exemplary embodiment is a Trumark 6020 laser with a wave length of 1,064 nm. The beam quality M 2  is 1.2 and has a pulse repetition rate of between 1,000 and 120,000 hz or cycles per second. The focus diameter of the laser is about 45 micrometers and has a scanner calibration accuracy of plus or minus 50 micrometers. The power setting of the laser according to one embodiment may be set to 100% to achieve the results described. However, this power setting may vary by varying the velocity of which the laser  70  moves. 
     Referring now to  FIG. 7 , exemplary steps of the method are shown in a flowchart. For example, the lead or other material is exposed for cleaning at step  110 . Next, the material is positioned adjacent the laser at step  120 . This may also or alternatively require movement of the laser  70  to a preselected position. In a third exemplary step  130 , one of the laser or the material is moved relative to the other of the laser or material so that the contaminants may be obliterated at step  140 . If required, an additional step of moving one of the laser or material for a second pass may be utilized at step  150  for further cleaning. Various adjustments may be made to the laser  70  during these steps such as power, focus, beam width, and speed of movement all in accordance with the goal of obtaining a desirable removal of surface contaminants from the lead or material. 
     While multiple inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the invent of embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure. 
     Examples are used to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the apparatus and/or method, including making and using any devices or systems and performing any incorporated methods. These examples are not intended to be exhaustive or to limit the disclosure to the precise steps and/or forms disclosed, and many modifications and variations are possible in light of the above teaching. Features described herein may be combined in any combination. Steps of a method described herein may be performed in any sequence that is physically possible. 
     All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Furthermore, references to one embodiment are not intended to be interpreted as excluding the existence of additional embodiments that may also incorporate the recited feature. 
     It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited. 
     In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures.