Abstract:
Forming respective packets ( 20, 21, 46, 50, 52, 70, 82, 84 ) of filler metal powder ( 24 ) and flux powder ( 26 ) for adjacent placement on a working surface ( 30 ) for laser deposition of the metal. Each packet may be formed of a sacrificial sleeve ( 22 ) or adjacently seamed sheets ( 72 A-D), which may include flux fibers such as alumina, zirconia, basalt, or silica. A packet ( 56 ) of flux may be disposed centrally inside a packet ( 56 ) of metal or vice versa. A connected stack ( 70, 82, 84 ) of three packets ( 74 A-C,  86 A-C) may be formed by seaming ( 76 A-B) four stacked sheets ( 72 A-D) around common edges and filling the three resulting spaces between the sheets with a respective vertical sequence of metal/flux/metal or flux/metal/flux powders. Quilting and intermediate stitching may provide for precise control of material distribution and facilitate feeding of material.

Description:
[0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 14/282,410 filed 20 May 2014 (attorney docket number 2014P06058US) and co-pending U.S. patent application Ser. No. 14/175,525 filed on 07 Feb. 2014 (attorney docket number 2014P02381 US), both of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to additive fabrication and repair of metal components, and particularly to preplacement of metal filler powder and flux powder on a working surface for laser deposition of the metal. 
       BACKGROUND OF THE INVENTION 
       [0003]    Laser melting of filler metal is used for additive manufacturing and repair of articles including gas turbine components. Flux can be introduced via a flux core in a wire of filler metal or a flux coating on a filler wire or as granulated flux material fed in conjunction with solid filler metal in wire or strip form. Alternately, the filler metal and flux can be provided in powder form. Powder is particularly advantageous because laser energy is more readily captured by powder than by solid filler metal. A disadvantage of wire feed is that the laser beam must continually focus on the wire while simultaneously feeding and moving the wire in precise alignment with the laser. Wire cannot be moved as quickly as a laser beam scanned by pivoting mirrors. Thus, wire limits the processing speed. 
         [0004]    Filler powder delivery options include: 
         [0005]    (1) Powder sprayed to the point of processing. This results in scattering and waste of powder. Even on flat horizontal surfaces, the net capture of sprayed powder is only about 65%. Powder spray nozzles cannot move as quickly as a laser beam, so nozzles limit the processing speed. 
         [0006]    (2) Preplacement of powdered metal and powdered flux in separate layers. This controls the filler thickness distribution and the metal/flux ratio. However, it is labor intensive and time consuming. 
         [0007]    (3) Preplacement of a mixture of powdered metal and powdered flux. This reduces labor by about half over placing metal and flux in separate layers. However, it is difficult to ensure uniform mixing due to differences in size and density of the respective powders. Use of composite metal/flux powder avoids such mixing and segregation issues, but composite preparation is expensive and time consuming. 
         [0008]    (4) Capturing metal and flux powders in a sacrificial sleeve or packet that is placed in the path of processing is a good option because powder waste is minimized and precise distribution of powder is possible. This method is relatively quick and requires little labor. However, mixed metal and flux powders in a sleeve can still segregate, resulting in inconsistent metal/flux ratios across the powder volume and the working surface area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is explained in the following description in view of the drawings that show: 
           [0010]      FIG. 1  is a sectional view of a filler packet formed by a sacrificial sleeve containing metal powder. 
           [0011]      FIG. 2  is a sectional view of respective packets of metal powder and flux powder placed on a working surface and framed by laser blocking shoes for an accurate edge. 
           [0012]      FIG. 3  shows horizontal repetition of the packets of  FIG. 2  to cover a wider area. 
           [0013]      FIG. 4  illustrates a process of directing a laser beam onto the packets of  FIG. 3  forming a metal melt covered by a slag blanket. 
           [0014]      FIG. 5  shows an array of adjacent packets containing metal powder, flux powder, and a laser blocking material in respectively different portions of the array. 
           [0015]      FIG. 6  is a perspective view of a filler packet maintained in a flat shape by quilting. 
           [0016]      FIG. 7  is a sectional view of two stacked quilted packets containing metal and flux powders respectively. 
           [0017]      FIG. 8  is a perspective/sectional view of a combined two-packet embodiment with a sleeve containing flux powder centrally located within a sleeve containing metal powder. 
           [0018]      FIG. 9  is a transverse sectional view of a packet embodiment formed as in  FIG. 8 , then quilted with a longitudinal stitch to control the powder distribution. 
           [0019]      FIG. 10  shows a single layer of the two-packet embodiment of  FIG. 8  placed on a working surface between laser blocking shoes. 
           [0020]      FIG. 11  shows a double layer of the two-packet embodiment of  FIG. 8  placed on a working surface between laser blocking shoes. 
           [0021]      FIG. 12  is a sectional view of apparatus and process for building squealer ridges on a gas turbine blade tip using aspects of the invention. 
           [0022]      FIG. 13  shows a connected vertical stack of three packets of metal/flux/metal formed in respective spaces between four stacked sheets seamed together around the edges. 
           [0023]      FIG. 14  shows a horizontal repetition of the 3 stacked packets of  FIG. 13  using quilting intermediate the seamed edges. 
           [0024]      FIG. 15  shows a connected vertical stack of three packets of flux/metal/flux formed in respective spaces between four stacked sheets seamed together around the edges. 
           [0025]      FIG. 16  illustrates a method of providing an elongated form of stacked filler packets on a roll, and feeding the stacked filler packets from the roll ahead of laser processing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  shows a filler packet  20  for laser deposition formed of a sleeve  22  containing metal powder  24 . The sleeve may be a sacrificial material such as cotton or synthetic fabric or a polymer film, and/or it may include flux constituents such as at least one of zirconia, alumina, basalt, and silica fabric. 
         [0027]      FIG. 2 . shows an upper filler packet  21  of flux powder  26  on a lower filler packet  20  of metal powder  24  placed on a working surface  30 , which may be a surface of a substrate for repair or fabrication or a worktable or bed of support material such as graphite or zirconia for a first layer of new fabrication. The filler packets may be abutted or framed by one or more adjacent rigid forms or shoes  32  of a laser blocking material such as graphite or zirconia that can tolerate the heat of processing. Such shoes contain and accurately define sides of the melt pool and thus define sides of the final deposition layer. Such shoes also manage heat dissipation by way of their conductive properties (e.g. graphite) or insulative properties (e.g. zirconia). 
         [0028]      FIG. 3  shows an area of a working surface  30  covered by horizontal repetitions of the stacked packets  20 ,  21  of  FIG. 2 . Alternately flat quilted packets may be used to cover relatively wide areas as later shown. 
         [0029]      FIG. 4  shows a laser emitter  34  emitting a laser beam  36  to melt the metal and flux powders, forming a melt pool  38  with a blanket of slag  40 . The slag blanket thermally insulates the melt pool, which maximizes laser energy transfer to the metal powder, makes heating more uniform, and makes solidification more gradual and consistent. Other forms of energy beams may be used such as electron beams and plasma beams. 
         [0030]      FIG. 5  shows an array  42  of adjacent filler packets including bottom layers of packets with metal powder  24 , a top layer of packets with flux powder  26 , and a side array of packets with a laser blocking material powder  44 . 
         [0031]      FIG. 6  shows a planar filler packet  46  with quilting  48  to maintain the planar shape and to maintain uniform (or alternately non-uniform but deliberate and controlled) distribution of powder over the plane of the filler packet. Such planar packet would be of particular use for applications to wide surfaces of either flat or curved configuration.  FIG. 7  shows a first planar (in this case flat) filler packet  46  containing metal powder  24 , and a second flat filler packet  50  containing flux powder  26 , placed on a working surface  30  and framed by laser blocking shoes  32 . Quilting with at least one line of intermediate stitching as shown provides a relatively thin and wide packet. For example the packet width may be at least twice the thickness to provide a given thickness of filler material over a wider area. 
         [0032]      FIG. 8  shows a combined two-packet embodiment  52  with an outer sleeve  54  containing metal powder  24  and a concentric inner sleeve  56  containing flux powder  26  and surrounded by the metal powder. The sleeves may include fabric or other flexible sacrificial tubing as previously described. Exemplary non-limiting diameters are 6 mm for the outer sleeve and 3 mm for the inner sleeve. The packets may be intermittently stitched  57  transversely along the length of this coaxial rope-like arrangement to control powder distribution. Arrangements as shown in  FIG. 6  and  FIG. 8  may be elongated as needed, and may be fed from rolls of blanket-like or rope-like packets respectively to the locations to be processed. 
         [0033]      FIG. 9  is a sectional view of a packet embodiment  53  formed as in  FIG. 8 , and then quilted with at least one line of longitudinal stitching  58  to form and maintain a relatively thin and wide packet that provides a given thickness of filler material over a wider area. For example the packet width W may be at least twice the thickness T. 
         [0034]      FIG. 10  shows combined filler packets  52  placed on a working surface and surrounded by laser blocking boots  32 .  FIG. 11  shows multiple layers of such filler packets placed on the working surface for thicker deposition in a single process. Alternately, a first deposition can be made with a single layer of packets. After solidification, the slag is removed, and the process is repeated with further layer(s) of packets as needed. 
         [0035]      FIG. 12  shows a gas turbine blade tip  59  with a pressure side PS and a suction side SS in a chamber or fixture  60  that holds laser blocking shoes  62  against sides of the blade tip. A further laser blocking shoe  64  is positioned on the blade tip cap  66 . This provides channels  68  for building a squealer ridge on the blade tip. Packets of metal powder  24  and flux powder  26  as described herein are placed in the channels for laser deposition. After a first deposition layer is formed and solidified, the slag is removed. The first deposition layer then provides a new working surface on which additional layer(s) (if required) may be deposited to build-up the squealer ridge to a desired height. 
         [0036]      FIG. 13  shows a connected stack  70  of three packets  74 A-C formed by seaming  76 A-B four stacked sacrificial sheets  72 A-D around common edges thereof, and filling the three resulting spaces between the sheets with a sequence of metal/flux/metal (shown) or flux/metal/flux ( FIG. 15 ). The seams  76 A-B may be stitches, adhesive, or melts. In this embodiment, the flux packet  74 B cannot rise or sink in the surrounding metal powder, since the metal powder cannot flow between the upper and lower packets  74 A,  74 C. 
         [0037]      FIG. 14  shows a connected stack  82  of four sacrificial sheets  72 A-D that are seamed  76 A-B around common edges thereof, and are quilted  48 , forming a planar (in this case flat) combination of vertically adjacent packets  74 A-C as in  FIG. 13  that are repeated horizontally, providing a distribution of filler material over an area of the working surface. Quilting provides a relatively thin and wide packet. For example the packet width W may be at least twice the thickness T to provide a desired thickness of filler material over a wider area. 
         [0038]      FIG. 15  shows a connected stack  84  of three adjacent packets  86 A-C formed by seaming  76 A-B four stacked sacrificial sheets  72 A-D around common edges thereof, and filling the three resulting spaces between the sheets with a sequence of flux/metal/flux. The ratios of the packet sizes in embodiments  70 ,  82 , and  84  can be adjusted as desired.  FIG. 15  illustrates sizing the bottom, middle, and top packets respectively smallest, largest, and intermediate. Thus the central metal packet is largest, the lower flux packet is thinnest, but is sufficient to facilitate fusion and to provide flux rising through the melt to scavenge contaminants, and the top flux packet is intermediate in size to form a slag blanket on the melt pool. 
         [0039]      FIG. 16  illustrates a method of providing an elongated form  87  of stacked filler packets  88 ,  89 ,  90  on a roll  92 . The elongated form may comprise one or more sequences of filler packets attached end-to-end, or it may comprise stacked filler packets formed as in one of  FIG. 8 ,  9 , or  13 - 15 . The roll  92  may feed the elongated form of stacked filler packets onto a substrate  99  ahead of a laser beam  34  that melts the metal and flux filler powders on the substrate, forming a metal layer  95  fused to the substrate and a slag blanket  96  on the metal layer. Optionally, an adhesive  97  may be applied to the elongated form of filler packets as it unrolls before it contacts the surface  30  of the substrate, or the adhesive may be applied directly to the working surface  30  ahead of the roll  92 . 
         [0040]    Whether stacked or assembled coaxially, the dual packet system and method allows for simple preplacement of powders, and avoids segregation issues. Packets may be automatically fed ahead of laser processing by feeders pulling elongated packet(s) or a series of connected packets from spools. The packets may be used on non-horizontal surfaces by gluing the packets in position with adhesives or cements designed for use with silica or other ceramic-like materials. 
         [0041]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.