Abstract:
A method of forming a build in a powder bed includes emitting a plurality of laser beams from selected fibers of a diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build; and simultaneously melting powder in the powder bed corresponding to the pattern of the layer of the build. An apparatus for forming a build in a powder bed includes a diode laser fiber array including a plurality of diode lasers and a plurality of optical fibers corresponding to the plurality of diode lasers, each optical fiber configured to receive a laser beam from a respective diode laser and configured to emitting the laser beam; a support configured to support a powder bed or a component configured to support the powder bed at a distance from ends of the optical fibers; and a controller configured to control the diode laser fiber array to emit a plurality of laser beams from selected fibers of the diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build and simultaneously melt the powder in the powder bed corresponding to the pattern of the layer of the build.

Description:
BACKGROUND 
       [0001]    The present technology relates generally to the use of a diode laser fiber array for Direct Metal Laser Melting (DMLM) for use in the fabrication or repair of components, more particularly components of a gas turbine engine. 
         [0002]    Additive manufacturing is a known technology that enables the “3D-printing” of components of various materials including metals, ceramics and plastics. In additive manufacturing, a part is built in a layer-by-layer manner by leveling metal powder and selectively fusing the powder using a high-power laser or electron beam. After each layer, more powder is added and the laser forms the next layer, simultaneously fusing it to the prior layers to fabricate a complete component buried in a powder bed. Additive manufacturing systems and processes are used to fabricate precision three-dimensional components from a digital model. 
         [0003]    In making a build in current powder bed systems, the laser beam or electron beam is used to scan a layer of powder to sinter and melt the desired shape in the layers of the powder bed. The typical scanning time for such systems per layer is in the range of 70-100 seconds. For some applications, the build can require days of processing time. One application of DMLM is in the fabrication and repair of airfoils for gas turbine engines for aircraft. The geometries of the airfoils are difficult to form using conventional casting technologies, thus fabrication of the airfoils using a DMLM process or an electron-beam melting process has been proposed. With the layers built upon one another and joined to one another cross-section by cross-section, an airfoil or portion thereof, such as for a repair, with the required geometries, may be produced. The airfoil may require post-processing to provide desired structural characteristics. 
         [0004]    Another problem of laser scanning Direct Metal Laser Melting (DMLM) systems is rapid cooling rates that can lead to cracking of certain alloys during the additive manufacturing build process. Rapid cooling rates also present difficulties in obtaining desirable grain growth, for example grain growth that is normal to the layer surface. 
       BRIEF DESCRIPTION 
       [0005]    In accordance with one example of the technology disclosed herein, a method of forming a build in a powder bed comprises emitting a plurality of laser beams from selected fibers of a diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build; and simultaneously melting powder in the powder bed corresponding to the pattern of the layer of the build. 
         [0006]    In accordance with another example of the technology disclosed herein, an apparatus for forming a build in a powder bed comprises a diode laser fiber array comprising a plurality of diode lasers and a plurality of optical fibers corresponding to the plurality of diode lasers, each optical fiber configured to receive a laser beam from a respective diode laser and configured to emitting the laser beam; a support configured to support a powder bed or a component configured to support the powder bed at some working distance from ends of the optical fibers; and a controller configured to control the diode laser fiber array to emit a plurality of laser beams from selected fibers of the diode laser fiber array onto the powder bed, the selected fibers of the array corresponding to a pattern of a layer of the build and simultaneously melt the powder in the powder bed corresponding to the pattern of the layer of the build. 
     
    
     
       DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present technology will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1A  schematically illustrates a diode laser fiber array for use with the present technology; 
           [0009]      FIG. 1B  schematically illustrates another diode laser fiber array for use with the present technology; 
           [0010]      FIG. 1C  schematically illustrates another diode laser fiber array for use with the present technology; 
           [0011]      FIG. 2  schematically illustrates a system for simultaneous melting of a powder bed layer by a diode laser fiber array according to an example of the present technology; 
           [0012]      FIG. 3  schematically illustrates a fiber optic construction usable in a diode laser fiber array according to an example of the present technology; 
           [0013]      FIG. 4A  schematically illustrates a fiber array usable with the system according to the present technology; and 
           [0014]      FIG. 4B  schematically illustrates another fiber array usable with the system according to the present technology. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to  FIG. 1A , a diode laser array  101  (e.g., a diode laser bar or stack) includes a plurality of diode lasers, or emitters,  103 , each emitting a beam of radiation  105 . A plurality of cylindrical lenses  107  are positioned between the diode lasers  103  and a plurality of optical fibers  109  to couple each diode laser  103  to an optical fiber  109 . The optical fibers  109  may be provided in a bundle  102  between the diode laser array and the free ends of the optical fibers, as shown for example in  FIGS. 1A-1C . However, it should be appreciated that diode fiber laser arrays that do not use coupling optics may be used with the present technology, as discussed below. 
         [0016]    Referring to  FIG. 1B , the diode laser fiber array  101  may include lenses  117  at the ends of the optical fibers  109 . The lenses  117  may be configured to provide collimated laser beams  120  from the optical fibers  109 . Referring to  FIG. 1C , the diode laser fiber array  101  may not include optics (e.g. a lens) between the diode lasers  103  and the optical fibers  109  and the beams of radiation  105  may be received by the optical fibers  109  in proximity to the diode lasers  103 . The optical fibers  109  may have lenses  117  at their respective ends. The lenses  117  may be configured to provide a predetermined divergence to the laser beams  120  emitted from the optical fibers  109 . It should also be appreciated that instead of providing lenses that the ends of the optical fibers  109  may be shaped to provide collimated or divergent laser beams  120 . 
         [0017]    Referring to  FIG. 2 , the diode laser fiber array  101  directs laser beams  120  from the optical fibers  109  into a powder bed  130  to simultaneously melt all of the desired powder in a layer. To generate a desired pattern, for example of a repair or a component to be fabricated, the required diode lasers  103  are turned on to affect the desired simultaneous melting from each fiber  109 . The melting process time for the desired pattern may be less than a second, which is at least two orders of magnitude faster than current scanning processes. 
         [0018]    The powder bed  130  may be provided on a component  150 , for example an airfoil of a gas turbine engine of an aircraft, which is supported on a support  170  to provide a repair to the component. Although the present technology may be applicable to the repair function on components, it should be appreciated that the present technology is applicable for the additive manufacturing build of new make components. The powder bed may be provided on the support  170  and the diode laser fiber array  101  used to build or fabricate the component layer by layer. 
         [0019]    The support  170  may be moved by an actuator or an actuator system  175  that is configured to move the support  170  in the Z direction (i.e. normal to the powder bed  130 ) as shown in  FIG. 2 . The actuator or actuator system  175  may also be configured to move the support  170  in the XY plane as shown in  FIG. 2 , although the support  170  is not moved in the XY plane during simultaneous melting of the powder bed from each fiber  109 . The actuator or actuator system  175  may be controlled by controller  135  that is configured to control the actuator or actuator system  175  and the diode laser fiber array  101 . The actuator or actuator system  175  may include, for example, a linear motor(s) and/or hydraulic and/or pneumatic piston(s) and/or a screw drive mechanism(s) and/or a conveyor. As the diode laser fiber array  101  is capable of simultaneously melting all of the required powder in the layer for a pattern, there is no need to move either the array  101  or the powder bed  130  during melting, for example as is done with current systems in which a laser beam or electron beam is used to scan a layer of powder. 
         [0020]    The distance D between the array of optical fibers  109  (i.e. the ends of the optical fibers  109 ) and the powder bed  130  may be controlled by moving the support  170  in the Z direction. The distance D may depend on the type of laser beams  120  emitted by the optical fibers  109  (e.g. whether the laser beams  120  are collimated or divergent, and the amount of divergence), the average output power of each diode laser  103 , the pulse energy of each diode laser  103 , the pulse width of each diode laser  103 , and or the beam distribution (e.g. Gaussian, top hat, etc.). The ends of the optical fibers  109  may be located at, for example, about 5 mm to about 150 mm, for example about 20 mm to about 80 mm above the powder bed  130  so that any region of a layer of the powder bed  130  can be melted at the same time by turning the required diode lasers  103  on at the same time. 
         [0021]    The controller  135  controls the turning on and turning off of each diode laser  103 . The controller may also control the rate at which the power of each diode laser  103  is reduced when turned off. The controller  135  may turn each diode laser  103  on and off within a time frame of, for example, about 5 to 15 milliseconds, or longer if needed. For a given layer of powder  130 , for example above an airfoil to be repaired, the desired laser diodes  103  are activated to melt the powder in the desired shape per a CAD design, which may be input and/or stored in the controller  135 . This process may be repeated as many times as necessary to build up the required repair region. In the case of the system being used to fabricate a component, e.g. an airfoil, the process is repeated as many times as necessary to build the component. The controller  135  controls the actuator or actuator  175  to move the support  170  downwardly as layers of powder are added and subsequently processed by the diode laser fiber array. Each layer formed may be, for example, about 1 μm to about 1 mm thick. In the case of repair of an airfoil, each layer may be formed, for example, about 100 μm thick. 
         [0022]    The controller  135  may be a computer processor or other logic-based device, software components (e.g., software applications), and/or a combination of hardware components and software components (e.g., a computer processor or other logic-based device and associated software application, a computer processor, or other logic-based device having hard-wired control instructions, or the like). 
         [0023]    The diode laser fiber array  101  may be controlled by the controller  135  to control the heat of powder near or adjacent to the melted region to control the cooling rate of the melted region. The controller  135  may also control the diode laser fiber array  101  to preheat the powder bed  130  and/or the component  150 . The pre-heating power densities of the diode lasers  103  may be from about 100-100,000 watts/cm 2 . By pre-heating the powder bed  130  and/or the component  150  and/or heating the region near or adjacent to the melt region, the thermal gradient may be controlled to be substantially only in the direction normal to the powder bed (i.e. in the Z direction in  FIG. 2 ). This may help with materials that are crack sensitive to fast solidification cooling rates. Desirable grain growth that&#39;s normal to the layer surface may be achievable with planar cooling of a powder bed layer. This allows formation of a directionally solidified (DS) type grain structure and a single crystal structure with the build repair of an airfoil type structure. It should also be appreciated that the diode lasers  103  may be controlled to superheat the powder bed  130  to control the viscosity of the melted region. Controlling the viscosity of the melted region allows control over, for example, evaporation of the powder, the grain structure of the solidified layer, and/or the surface finish of the repair or component. 
         [0024]    The material in the powder bed  130  may be metal powder, for example, CoCrMo powder. It should be appreciated that other materials, for example plastic, ceramic, or glass, may be used for the powder bed. Depending on the material in the powder bed, the power of each diode laser  103  may be from about 10 to about 60 watts. The power of the diode lasers  103  that are used may be related to the diameter of the optical fibers  109  used. The power density of the diode lasers  103  may be up to about 1,000,000 watts/cm 2  for melting the powder within a layer from each fiber. 
         [0025]    The fiber centering position in the fiber array (e.g. as shown in  FIGS. 4A and 4B ) is set by the diameter of a buffer, or coating  115  of the optical fiber  109 . Referring to  FIG. 3 , the optical fiber  109  comprises a core  111 , formed of for example silica, and cladding  113 , formed for example of silica, around the core  111 . In order to create a numerical aperture and provide total internal reflection within the fiber  109 , the refractory index of the silica core may be larger than the refractory index of the silica cladding. For example, the silica core may have a refractive index of about 1.45 and the silica cladding may have a refractive index of about 1.43. The cladding  113  may have a thickness of about 10 μm. 
         [0026]    The buffer, or coating,  115  surrounds the cladding  113  and may be formed of, for example, acrylate. To reduce the center spacing between the optical fibers  109 , the buffer (acrylate coating)  115  may be replaced by a thinner acrylate coating to reduce the overall fiber diameter. The thickness of the buffer, or coating  115  may be about 62 μm. The total diameter of the fiber  109  may be about 200 μm to about 250 μm. 
         [0027]    The diameter of the fiber core  111  may be about 105 μm. It should be appreciated that fiber core diameters of about 60 μm may be used. In addition, it should be appreciated that optical fibers  109  of various cross sections, may be used. For example, square fibers may be used to increase fiber packing. The melt pool size produced by the laser beam(s)  120  from each optical fiber  109  corresponds to the effective laser spot size produced by the laser beam(s)  120 . In the case of collimated laser beams  120 , the melt pool size corresponds generally to the diameter of the fiber core  111 . However, the laser beams  120  from the fibers  109  may be controlled to produce a melt pool size that is, for example, two to four times as large as the diameter of the fiber core  111 . The laser beams  120  may be controlled to have a divergence to provide a melt pool size larger than the diameter of the fiber core  111 . In the case of divergent laser beams  120 , the distance D from the ends of the fibers  109  of the array  101  to the powder bed  130  will also influence the melt pool size of each fiber. The pulse width of the laser beams and the laser beam profiles may also be controlled to adjust the melt pool size provided by each fiber. 
         [0028]    Referring to  FIGS. 4A and 4B , the array of fibers  109  may be linear as shown in  FIG. 4A  or closed packed arrangement as shown in  FIG. 4B . Other arrays, for example hexagonal, may be used. It should also be appreciated that the array may be in a shape corresponding to the shape of a component to be fabricated. The spacing between the fibers  109  may be equal to the diameter of the buffer, or coating,  115 . 
         [0029]    The diode laser fiber array of the present technology may be used to process a powder bed layer by exposing the layer with simultaneous laser energy from required diode laser beam sources. The present technology also allows melting the complete pattern in the layer in one time frame that could be less than a second and, when required, control the heat of the powder near and/or adjacent to the melted region to control the cooling rate of the melted region. The diode laser fiber array allows permits grain structure control. The commercial advantages for diode laser fiber array systems include fewer required systems to produce the same amount of parts as current systems and tailoring power bed systems to the size of the parts of interest. The technology disclosed herein may also be used to perform sintering, for example direct metal laser sintering. 
         [0030]    It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular example. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
         [0031]    While only certain features of the present technology have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes.