Patent Publication Number: US-2015083692-A1

Title: Laser cladding system filler material distribution apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application incorporates by reference commonly owned, co-pending United States utility patent application entitled “SUPERALLOY LASER CLADDING WITH SURFACE TOPOLOGY ENERGY TRANSFER COMPENSATION”, Attorney Docket Number 2012P09110US, filed concurrently herewith and assigned Ser. No. [to be assigned]. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to laser cladding superalloy components, such as service-degraded turbine blades and vanes. More particularly, the present invention methods relate to welding one or more filler material layers to substrates along continuous weld translation paths. Filler material, such as metal powder, is introduced in a pattern on the substrate by a filler distribution apparatus having a linear or polygonal array of dispensing apertures for uniform distribution in advance of or during a laser beam transferring optical energy to the substrate along the continuous weld translation path. 
     2. Description of the Prior Art 
     “Structural” repair of gas turbine or other superalloy components is commonly recognized as replacing damaged material with matching alloy material and achieving properties, such as strength, that are close to the original manufacture component specifications (e.g., at least seventy percent ultimate tensile strength of the original specification). For example, it is preferable to perform structural repairs on turbine blades that have experienced surface cracks, so that risk of further cracking is reduced, and the blades are restored to original material structural and dimensional specifications. 
     Repair of nickel and cobalt based superalloy material that is used to manufacture turbine components, such as turbine blades, is challenging, due to the metallurgic properties of the finished blade material. The finished turbine blade alloys are typically strengthened during post casting heat treatments, which render them difficult to perform subsequent structural welding. For example a superalloy having more than 6% aggregate aluminum or titanium content, such as CM247 alloy, is more susceptible to strain age cracking when subjected to high-temperature welding than a lower aluminum-titanium content X-750 superalloy. 
     Currently used welding processes for superalloy fabrication or repair generally involve substantial melting of the substrate adjoining the weld preparation, and complete melting of the welding rod or other filler material added. When a blade constructed of such a material is welded with filler metal of the same or similar alloy, the blade is susceptible to solidification (aka liquation) cracking within and proximate to the weld, and/or strain age (aka reheat) cracking during subsequent heat treatment processes intended to restore the superalloy original strength and other material properties comparable to a new component. 
     One known superalloy joining and repair method that attempts to melt superalloy filler material without thermally degrading the underlying superalloy substrate is laser beam welding, also known as laser beam micro cladding. Superalloy filler material (often powdered filler) compatible with or identical to the superalloy substrate material is pre-positioned on a substrate surface prior to welding or sprayed on the surface with pressurized gas through a channel during the cladding process. A “spot” area of focused laser optical energy generated by a fixed-optic laser (i.e., other than relative translation, laser and substrate have a fixed relative orientation during laser beam application) liquefies the filler material and heats the substrate surface sufficiently to facilitate good coalescence of the filler and substrate material, that subsequently solidify as a clad deposit layer on the substrate surface. Compared to other known traditional welding processes, laser beam micro-cladding is a lower heat input process, with relatively good control over melting of the substrate and rapid solidification that reduce propensity to cause previously-described solidification cracking. Lower heat input to the superalloy substrate during laser welding/cladding also minimizes residual stresses that otherwise would be susceptible to previously described post-weld heat treatment strain age cracking. While laser cladding welds have structural advantages over traditionally-formed welds, practical manufacturing and repair realities require larger cladding surface area and/or volume coverage than can be filled by any single pass applied cladding deposit. 
     To meet needs for adding volume to superalloy components, a laser-cladded deposit on a substrate can be formed from single- or two-dimensional arrays of adjoining solidified clad passes. Multiple laser-welded cladding passes and layers can be applied to build surface dimensional volume. Creating arrays of laser-clad deposits often results in microcracks and defects in the deposited material and underlying substrate in the heat affected zone material. Some defects are related to lack of fusion (LoF) that is common when there is insufficient localized laser optical energy heat input. Often a substrate, such as a turbine blade, requires structural repair filling of a missing volume of the blade substrate material with an equivalent volume of superalloy filler, in order to restore the blade&#39;s original structural dimensions. In known laser cladding techniques the missing blade substrate volume is filled with a two-dimensional filler weld array of individually-applied laser clad deposits or passes. The laser beam focus position and substrate surface are moved relative to each other after a single deposit formation to weld the next deposit, analogous to a series of abutting, overlapping bumps or dots. With known multi-dimensional filler material depositing equipment, either a layer of the filler particles (often in powder form) are prepositioned in a layer on the substrate surface or directed through a pressurized gas-fed nozzle over the laser “spot” projected location. While U.S. Patent Publication No. 2010/0078411 describes a mechanical auger-fed powder feed cylinder that distributes cladding filler powder through a single nozzle, single point distribution is not optimal for multi-dimensional filler material distribution applications. 
     With known single deposit “spot” laser cladding methods a weld array of deposits often exhibits lack of fusion (LoF) at corners of every weld pass. The LoF is caused by combinations of one or more of localized variations in the blade substrate surface topology that require corresponding variations in laser optical energy transfer in order to maintain desired fusion, including: asymmetric heat sink properties; diminished power density; and surface reflectivity of both optical energy and powder. For example, a previously applied solidified laser-clad deposit has a curved surface bounded an edge that is in contact with the substrate surface. That previously applied deposit represents additional heat sink material that must be heated along with underlying substrate when the next laser-clad deposit is formed in abutting relationship to create a continuous weld line. Additionally, the curvature of the prior deposit spreads the laser beam energy transfer of the next adjoining deposit and reduces localized power density (e.g., watts per unit area). Potentially the curved surface also changes localized laser optical reflectivity, which may be compounded by non-uniform filler powder distribution, e.g., scattering away from the curved surface, adding additional reflectivity variance. 
     When the next laser cladding deposit is applied in adjoining, overlapping relationship with the existing deposit, a common uniformly applied power and/or filler powder distribution across the new laser focus zone would not apply sufficient localized fusion energy, causing a poorer than desired weld in the overlapping region between the prior and new deposits. An overall uniform increase in applied heat energy by the laser when forming deposits, in order to compensate for “worst case” lack of fusion in the overlapping regions of prior and new deposits, is more than required for good fusion of the bare substrate abutting the prior deposit edge along the weld line. This results in over-melting, over-heating and over-stressing of the crack sensitive substrate material, which may unnecessarily instigate subsequent hot cracking and/or strain age cracking. 
     It is often desirable to build superalloy material dimensional volume in a newly fabricated or repaired service-degraded superalloy component, such as a turbine blade or vane. When known laser cladding methods are employed multiple pass layers are applied over previously deposited multiple pass layers to create the needed built up volume. Laser microcladding with fixed optics requires multiple passes to accomplish a typical repair buildup because the size of overall area to be repaired is large relative to the beam diameter at focus. Each pass overlap involves a challenge in ensuring that full fusion is achieved within each built-up layer and that full fusion is achieved with the previously-applied underlying layer. Typically in known fixed optic laser cladding processes weld solidification crystal alignment tends to shift from perpendicular to the substrate in the first few applied layers and then tends to shift at an increasingly skewed angle in subsequently applied clad layers. Microcracking often initiates upon such shifts in the inter-layer crystallographic orientation. 
     The above-referenced related U.S. patent application Ser. No. ______/File No. 2012P09110US describes a laser welding/cladding invention that solves the shortcomings of known serial deposit laser cladding processes for welding of superalloy substrates, such as a turbine blades or vanes, which clad one or more layers on the substrate for structurally building up surface area and/or volume with superalloy filler material. In the new invention of the referenced United States patent application, sufficient laser optical energy is transferred to the welding filler material and underlying substrate to assure filler melting and adequate substrate surface wetting for good fusion. However, energy transfer is maintained below a level that jeopardizes substrate thermal degradation. Optical energy transfer to the filler and substrate is maintained uniformly as the laser beam and substrate are moved relative to each other along a translation path by varying the energy transfer rate to compensate for localized substrate topology variations. In this way a continuous weld cladding layer is formed of uniform consistency—rather than the previously known technique of forming a series of aligned, overlapping individual cladding deposits. For example, the optical energy transfer rate is increased for relatively more reflective or curved zones that do not absorb the laser&#39;s optical energy as efficiently as relatively non-reflective or flat zones. Energy transfer rate can be varied, for example by oscillating the laser beam transverse to the translation movement path, varying its movement and/or oscillation velocity, changing laser beam focus to narrower or wider beam, or changing the laser beam power output. The laser beam may be rastered in one-, two- or three dimensions to build a continuous cladding layer. When multiple cladding layers are applied on each other, using the new inventive methods of the referenced United States patent application, uniaxial crystallographic orientation generally perpendicular to the substrate is maintained in the clad buildup. Uniaxial orientation reduces likelihood of microcracking that often occurs when cladding multiple multipass layers using known fixed optic laser welding techniques. 
     When practicing the new inventive multi-dimensional continuous laser cladding methods of the referenced United States patent application, a challenge remains how to predeposit or feed filler material in advance of or in conjunction with the continuous laser beam path over a multi-dimensional surface area. As previously noted, known multi-dimensional cladding filler material depositing methods include prepositioning a layer of filler over the entire substrate surface prior to the welding/cladding laser exposure or transfer of filler material through a channel under gas pressure before and/or during the laser exposure. In both known multi-dimensional filler material distribution methods inert gas is separately applied to the substrate surface to prevent oxidation of the filler material and/or substrate during the cladding process. In channel-applied material distribution apparatus the inert gas also transports filler material through the channel Inert gas flow tends to disrupt pre-deposited filler material (often powder) thickness on the substrate. Pressurized inert gas applied filler material does not distribute evenly on the substrate surface and is of limited efficiency—with powder wastage of 40% or more. When practicing the known serial individual deposit cladding methods, variations in filler material layer thickness could be corrected prior to applying the laser beam to generate the next cladding deposit. 
     While either of these known depositing methods were adequate for previously known serial deposit cladding, neither is optimal for the new multi-dimensional continuous laser cladding methods of the referenced United States patent application. Both of the known filler material depositing methods risk non-uniform application—and possibly disruption—of the cladding material layer uniform distribution on the substrate surface by the time the continuously moving laser beam travels along the welding path. In the case of pre-deposited filler powder, inert gas and atmospheric currents can disrupt the filler material layer thickness. Pressurized gas channel application of filler does not lead to uniform filler thickness over a wide area. Deviations in cladding material layer thickness create localized topology changes for application of the laser beam power. While laser power variation feedback mechanisms may be employed by the cladding apparatus, it is preferable to start with a relatively uniform filler material application layer that remains unchanged during the laser welding operation. 
     The less than optimal ability of known pressurized gas delivery filler material distribution method and apparatus to deliver uniform layers of filler material is often attributable to their uniaxial delivery limitations. Most known pressurized gas delivery systems are uniaxial, i.e., deliver material as a point source spray pattern that is customarily oriented coaxial with the laser beam or on an axis that delivers material sideways relative to the beam. Uniaxial delivery does not provide for spreading of filler material (often powder) uniformly across a wide area. Gas-assisted delivery often scatters filler powder indiscriminately outside of the intended welding area. The expensive superalloy scattered filler powder is wasted and is not effectively reclaimed for future welding. 
     Some known pressurized filler material powder delivery systems are capable of delivering a linear pattern of filler. An exemplary known prior art pressurized linear pattern delivery system  20  is shown in  FIGS. 1-3 . The delivery system  20  delivers filler material that is entrained in a pressurized gas stream  P  via a linear array of channels  22 . The array width of channels  22  is fixed and therefore the filler material distribution width is also fixed. Each individual channel  22  has a fixed cross-sectional area, having dimensions a×b, which limits the system  20  maximum feed rate. The delivery  P  feed rate is a function of the channel  22  cross-section and the delivery gas pressure. Usually the gas delivery pressure is fixed. To the extent that gas pressure can be adjusted, increases in pressure to increase feed rate can result in turbulent gas flow that disrupts powder distribution and in extreme cases lead to powder clumping during delivery. 
     Thus, a need exists in the art for a laser cladding filler material distribution apparatus that is capable of applying a relatively uniform filler material thickness over a multi-dimensional surface area of a substrate prior to or during application of a cladding deposit: whether a series of individual deposits using known laser cladding techniques or whether a continuous multi-dimensional deposit weld over a weld path of the new inventive laser cladding methods of the cited United States patent application. 
     Another need exists in the art for a laser cladding filler material distribution apparatus, with operational flexibility for varied applications, that is capable of applying a selectively varied, relatively uniform filler material thickness over a selectively varied multi-dimensional surface area of a substrate prior to or during application of a cladding deposit, with selectively variable feed rates, so that the distribution apparatus can accommodate different weld path dimensions. 
     An additional need exists in the art for a laser cladding filler material distribution apparatus that can be integrated with or whose filler material distribution pattern can be coordinated with a laser cladding apparatus, so that a uniform layer of filler material is applied to a desired surface area of a substrate prior to or during arrival of a cladding laser beam along a serial deposit or a continuous welding path. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is to create a laser cladding filler material distribution apparatus that is capable of applying a relatively uniform filler material thickness over a multi-dimensional surface area of a substrate prior to or during application of a cladding deposit. 
     Another object of the invention is to create a laser cladding filler material distribution apparatus that has operational flexibility for varied application, that more specifically is capable of applying a selectively varied, relatively uniform filler material thickness over a selectively varied multi-dimensional surface area of a substrate prior to or during application of a cladding deposit, and with selectively variable feed rates, so that the distribution apparatus can accommodate different weld path dimensions. 
     An additional object of the invention is to create a laser cladding filler material distribution apparatus that can be integrated with, or whose filler material distribution pattern can be coordinated with a laser cladding apparatus, so that a uniform layer of filler material is applied to a desired multi-dimensional surface area of substrate prior to or during arrival of a cladding laser beam along a serial deposit or a continuous welding path. 
     These and other objects are achieved in accordance with an embodiment of the present invention by a laser cladding filler distribution system. Filler material, such as metal powder, is introduced in a pattern on a substrate by the filler distribution apparatus, which has a linear or polygonal array of dispensing distribution apertures for uniform distribution in advance of or during a laser beam transferring optical energy to the substrate. The distribution apparatus includes a housing (or assembly of coupled housings) that defines the distribution aperture array and an internal chamber in communication with the distribution apertures that is adapted for retention of filler material. A mechanical feed mechanism, such as an auger, is adapted for feeding filler material from the internal chamber through the distribution apertures without (or with limited amounts of) pressurized gas that might otherwise cause filler clumping and other non-uniform material distribution. A feed mechanism drive system, preferably under supervision by a control system, is coupled to the mechanical feed mechanism, adapted for selectively varying filler material feed rate. The distribution aperture array may be selectively reconfigured to vary selectively the filler material multi-dimensional distribution pattern. 
     Embodiments of the present invention feature apparatus for laser cladding filler material distribution, including a modular housing having an external surface defining a distribution aperture and an internal chamber in communication with the distribution aperture adapted for retention of filler material in the chamber. The modular housing is adapted for selective combination with other modular housings for selective assembly of varying distribution aperture arrays. A mechanical feed mechanism feeds filler material from the internal chamber through the distribution aperture without (or with limited amounts of) pressurized gas. A drive system is coupled to the mechanical feed mechanism, adapted for selectively varying filler material feed rate. A plurality of modular housings is oriented in a distribution aperture array, with a mounting structure coupling the modular housings into the distribution aperture arrays to meet the needs of different filler distribution patterns (e.g., linear or polygonal filler distribution patterns on substrates). Aperture isolation mechanisms can be provided for selectively isolating one or more distribution apertures from source filler material in the internal chamber(s). Aperture adjustment mechanisms may be provided for selectively varying distribution aperture dimensions in order to vary filler material distribution. The mechanical feed mechanism may be an auger driven by a motorized drive system. The drive system may be coupled to a controller for controlling filler material feed rate through one or more of the distribution apertures. 
     Other embodiments of the present invention feature apparatus for laser cladding filler material distribution, comprising a housing having an external surface defining an array of at least two distribution apertures for controlled distribution of filler material on a cladding substrate, and an internal chamber in communication with the distribution apertures adapted for retention of filler material in the chamber. A mechanical feed mechanism feeds filler material from the internal chamber through the apertures in the distribution aperture array without (or with limited amounts of) pressurized gas. The feed mechanism may be an auger. A feed mechanism drive system, such as for example an electric motor drive, is coupled to the mechanical feed mechanism, for selectively varying filler material feed rate. 
     Additional embodiments of the present invention feature a laser cladding system comprising an apparatus for laser cladding filler material distribution, having a housing with an external surface defining an array of at least two distribution apertures for controlled distribution of filler material on a cladding substrate, and an internal chamber in communication with the distribution apertures adapted for retention of filler material therein; a mechanical feed mechanism adapted for feeding filler material from the internal chamber through the distribution apertures in the aperture array without (or with limited amounts of) pressurized gas; and a feed mechanism drive system, coupled to the mechanical feed mechanism, for selectively varying filler material feed rate. The laser cladding system also has a laser generating a laser beam for transferring optical energy to the substrate and filler material on the substrate that fuses the filler material to the substrate as a filler layer; a movable mirror intercepting the laser beam, for orienting the laser beam on the substrate; and a laser drive system coupled to each of the respective movable mirror and the laser for causing relative motion between the laser beam and substrate. 
     The objects and features of the present invention may be applied jointly or severally in any combination or sub-combination by those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front elevational schematic view of a known gas assisted filler material powder distribution system; 
         FIG. 2  is a side elevational view of the known distribution system of  FIG. 1 ; 
         FIG. 3  is a cross sectional view of the known distribution system of  FIG. 2 , taken along  3 - 3 ; 
         FIG. 4  is a schematic view of an exemplary embodiment of a filler material distribution apparatus of the present invention incorporated in a laser beam welding system; 
         FIG. 5  shows is a schematic view of an exemplary multi-layer laser weld rastering pattern of the laser beam welding system of  FIG. 4 ; 
         FIG. 6  is a schematic end elevational view of the filler material distribution apparatus of  FIG. 4  distributing filler material on a substrate in advance of the laser beam rastering pattern welding path; 
         FIG. 7  is a schematic top plan view of the filler material distribution apparatus of  FIG. 4  distributing filler material on a substrate in advance of the laser beam rastering pattern welding path; 
         FIG. 8  is an axial cross sectional view of the filler material distribution apparatus of  FIG. 4  distributing filler material across a substrate surface area in advance of the laser beam rastering pattern welding path first width; 
         FIG. 9  is an axial cross sectional view of the filler material distribution apparatus of  FIG. 4  distributing filler material across a substrate surface area in advance of the laser beam rastering pattern welding path second narrower width than the width shown in  FIG. 8 ; 
         FIG. 10  is a partial cross sectional view of another exemplary embodiment of a filler material distribution apparatus of the present invention, having selectively variable-sized distribution apertures; 
         FIG. 11  is a partial cross sectional front elevational view of another exemplary embodiment of a filler material distribution apparatus of the present invention, having reconfigurable modules for selectively varying the distribution aperture array; and 
         FIG. 12  is a partial cross sectional side elevational view of the filler material distribution apparatus of  FIG. 11 . 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
     DETAILED DESCRIPTION 
     After considering the following description, those skilled in the art will clearly realize that the teachings of the present invention can be readily utilized for laser cladding filler material distribution systems that are capable of selectively varying multi-dimensional distribution patterns to accommodate multi-dimensional laser welding paths. The distribution system of the present invention facilitates uniform distribution of filler material across a welding pattern path: whether a series of serially deposited welds generated by known cladding systems and methods or multi-dimensional rastered continuous weld patterns that are performed by the new invention welding system and methods in U.S. patent application Ser. No. ______/File No. 2012P09110US. In exemplary embodiments of the present invention filler material (often in powder form) is introduced in a pattern on a substrate by a filler distribution apparatus having a linear or polygonal array of dispensing distribution apertures for uniform distribution in advance of or in conjunction with a laser beam transferring optical energy to the substrate. The distribution apparatus includes a housing (or assembly of coupled housings) that defines the distribution aperture array and an internal chamber in communication with the apertures that is adapted for retention of filler material. A mechanical feed mechanism, such as an auger, is adapted for feeding filler material from the internal chamber through the distribution apertures without (or with limited amounts of) pressurized gas that might otherwise cause filler clumping and other non-uniform material distribution. A feed mechanism drive system is coupled to the mechanical feed mechanism, adapted for selectively varying filler material feed rate. The aperture array may be selectively reconfigured to vary selectively the filler material distribution pattern. 
       FIG. 4  shows application an exemplary embodiment of a filler material distribution apparatus of the present invention that is incorporated in a continuous path weld laser cladding system of the type disclosed in U.S. patent application Ser. No. ______/File No. 2012P09110US. The cladding system  100  includes a work table  120  to which is affixed a work piece substrate  200 , such as a superalloy material turbine blade or vane. Optional work table motion control system  125  is used to move the work table  120  in the X, Y and Z coordinates shown or in any other single- or multi-axis coordinate system. A filler material distribution system  300  of the present invention introduces powdered filler material that is suitable for welding the substrate  200  surface  200 A in a multi-dimensional (here two-dimensional) pattern to match the raster pattern of the welding apparatus  100 . For example, if the substrate is a superalloy the filler material is often a powder of the same or compatible alloy. The distribution system  300  filler material feed rate is controlled by a filler drive system  135  that may be an electric motor drive. The distribution system  300  may have its own independent motion control system  136  for moving the poured filler material powder application zones relative to the substrate  200 . Construction of the filler material distribution system apparatus  300  will be described in greater detail following the laser cladding system  100  general system description. 
     The system  100  has a laser  140  with optional variable focus dF or power output dP that provides the laser beam optical energy source for heating the substrate  200  surface  200 A and filler material F. The system  100  also has a moveable mirror system  150  with mirror  160  that is capable of single- or multi-axis movement, shown as tilt T, pan P and rotate R axes under control of respective drives  162 ,  164  and  166 . The drives  162 ,  164  and  166  may be part of a known construction motorized motion control system or incorporated in a known galvanometer, that are under control of known controller  170 . Alternately the beam may be intercepted by multiple mirrors with single (or multiple) axes of motion to achieve each of the afore-described axes movements. 
     The controller  170  may be a stand-alone controller, programmable logic controller or personal computer. The controller  170  may also control one or more of the work table motion control system  125 , the powdered filler material distribution system drive  135  and/or the optional powdered filler material distribution system drive motion control system  136 , and/or the laser  140  variable focus dF and/or power output dP. Known open and/or closed feedback loops with the controller  170  may be associated with one or more of the drives  125 ,  135 ,  136 ,  162 - 166 , dF, dP. Laser beam optical energy transfer to the substrate and filler can also be monitored in a closed feedback loop so that the controller can vary the energy transfer rate based on the monitored energy transfer rate. A human machine interface (HMI) may be coupled to the controller  170  for monitoring welding operations and/or providing instructions for performing a welding operation. 
     When operating the welding system  100  the output beam  180  of the laser  140  is reflected off mirror  160  (or multiple mirrors) and in turn on to the turbine blade work piece, which transfers optical energy to the substrate  200  and filler material. Both the substrate  200  and filler material absorb the transferred optical energy, to melt the filler material, wet the substrate surface  200 A and fuse the melted filler and substrate surface to each other. Referring to  FIGS. 4 and 5 , the substrate  200  and laser beam  180  are moved relative to each other along a translation path by the control system engagement of the work table drive system  125  and/or the moveable mirror system  150  drives  162 ,  164 ,  166  to form a continuous welded cladding layer  200 ′. When the movable mirror system  150  is incorporated in a commercially available laser galvanometer system, relative motion between the substrate  200  and the laser beam  180  as well as the laser optical energy transfer rate can be varied by moving the galvanometer mirror  160  (or multiple mirrors) for both relative translation and oscillation. Relative motion between the laser beam  180  and the substrate  200 /filler material maintains a continuous melted weld line at the leading edge of translation motion (e.g., the right leading edge of the weld line  210  in  FIGS. 4 and 5 ) for fusion uniformity that is not possible with known unoscillated laser cladding systems. 
     As previously noted the laser optical energy absorbed at any beam focus area varies proportionately with focus time duration. By non-limiting example laser beam  180  focus time duration and proportional absorbed energy can be varied in the following ways: (i) the laser beam  180  can be oscillated parallel to or side-to-side transverse (e.g.,  211 ) the weld translation path  210 ; (ii) the oscillation or translation speed can be varied; and (iii) the laser power intensity dP or focus dF can be varied continuously or by pulse modulation. Thus by dynamically changing the rate of laser beam focus time duration the energy transfer rate to the substrate and filler is varied along the weld line translation path, so that uniform energy transfer is maintained within the entire weld, regardless of local topography variations. 
     As shown in  FIGS. 4 and 5 , a cladding layer may comprise a single raster linear weld  210  or a two-dimensional weld array of multiple adjoining linear welds  210 - 230 . Translation directions for each pass may be sequentially reversed as shown. Oscillation directions for each pass may be purely transverse to the translation direction as  211 ,  221  and  231  for each pass  210 ,  220  and  230  respectively. Duration of oscillation against the side of previous passes may be increased to ensure fusion. Multiple cladding layers  200 ′,  500 ,  600  may be applied on each other by sequentially alternating layers in directions in and out of  FIG. 5 , or even changing directions of translation to other than left to right e.g. to 90 degrees from left to right. All of these multi-dimensional rastering patterns require uniform distribution of filler material on the substrate surface in advance of or in conjunction with the laser beam focusing on the filler material and substrate. The present invention distribution system  300  facilitates uniform distribution of filler material on whatever variable size, multi-dimensional welding pattern “footprint” required for a specific cladding operation. 
     In  FIGS. 6 and 7 , the filler material distribution system  300  is distributing powdered filler material F in advance of the laser beam  180  rastering pattern translation path  210  direction and the oscillation path  211  directional arrows of  FIG. 5 . In this embodiment the filler distribution system  300  is moving in tandem with the laser beam  180  in the direction of travel W. Alternatively the laser beam  180  and filler material distribution system  300  can be held in fixed position relative to each other while the substrate  200  is moved in an opposite direction relative to the arrow W. 
     Exemplary embodiments of the filler material distribution system  300  are shown in  FIGS. 8-12 . The system  300  has a housing  310  (here tubular) that defines an internal cavity  320  and a plurality of filler material distribution apertures  331 - 336  (hereafter referred to as “apertures”) through which the filler material is discharged. While six apertures are shown in this exemplary embodiment, their array pattern and size may be selectively varied in order to provide a desired filler material distribution pattern. The aperture array pattern, for example may be a linear pattern, as shown in  FIGS. 8-12  or any desired polygonal pattern, e.g. rectangular, trapezoidal, etc. A rotating auger  340  mechanical feed mechanism is mounted in the housing  310  and has front seal  342  and rear seal  344  that set limits for filler material axial flow. Thus filler distribution flow width is bounded by the maximum spread of the apertures  331  and  336 . The auger  340  is rotated by distribution drive system  135  under control of the controller  170 , and transfers filler material from the supply hopper  350  to the aperture array  331 - 336  without assistance of pressurized gas, or alternatively with assistance of a limited amount of pressurized gas that does not disrupt the desired or acceptable filler material distribution pattern. While inert gas may still be needed for oxidation isolation during the welding process, that gas can be supplied independently, for example within a welding isolation chamber. Lack of pressurized gas-assisted filler feed eliminates the potential for gas flow eddy currents to disrupt the filler material distribution uniformity or to cause filler clumping. Filler material feed rate may be varied by varying the auger  340  rotational speed. Gross feed rates can be varied by changing the distribution aperture  331 - 336  dimensions (to be described later herein) or the dimensions of the auger thread pattern. 
     Filler distribution feed width is selectively varied by changing auger  340  axial position within the housing  310 . Comparing  FIGS. 8 and 9 , the feed width is narrowed by isolating one or more apertures  331 ,  332  from the auger  340 . The filler material distribution may also be varied by changing distribution aperture size, as shown in  FIG. 10 . Here an orifice plate  360 , having apertures  361 ,  362 , etc., covers the larger corresponding apertures  331 ,  332 , etc., in the housing  310 . Other aperture size-varying known mechanisms may be substituted for the orifice plate  360 , including by way of non-limiting example individually threaded orifices and adjustable shutters. 
       FIGS. 11 and 12  show an alternate embodiment filler material distribution system  300 ′, which has a modular housing  310 ′ that facilitates selective assembly of varying distribution aperture arrays by coupling multiple housing modules to each other. In this exemplary embodiment, each module  310 ′ has its own dedicated auger  340 ′ that may be driven by individual drives  135  or multiple module augers can be driven by a single drive system  135 . An advantage of individual auger  340 ′ drive is the ability to vary filler distribution across a distribution width by varying drive speeds of individual augers, if for example it is desirable to apply a different filler powder thickness across the distribution width in apertures  331 ′- 334 ′. A common filler material hopper  350 ′ can be utilized to feed all augers  340 ′ or alternatively multiple hoppers may be employed. Other forms of conduits for filler material supply may be substituted for the hoppers. 
     The module housings  310 ′ can be coupled to each other selectively by any known mounting structure  400 , such as the exemplary clamps  412  and elongated threaded fasteners  414 . Alternatively the mounting structure may be formed within the housings  310 ′. 
     Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.