Abstract:
A laser built up method on an object with different surfaces is provided. The object can be coated locally, which is not possible by the conventional rapid prototyping processes. The object is put into a powder bed, powder is provided on or near the object and the powder is only locally provided on the upper outer surface of the object and then densified.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of European Patent Office application No. 11156368.0 EP filed Mar. 1, 2011. All of the applications are incorporated by reference herein in their entirety. 
       FIELD OF INVENTION 
       [0002]    The invention relates to a laser build-up method using vibration for powder filling and an apparatus. 
       BACKGROUND OF INVENTION 
       [0003]    Selective Laser Melting is a relatively well known and modem method of creating parts and components from powder material. A machine used together with this method comprises a table or building platform on which the part is built. Layer by layer after the leading of a layer of powder which is molten by a laser beam. The layer thickness is created by a scraper that moves over the powder bed. One major requirement for the functionality of the machine is that the object does not contain any obstacle sticking out upwards from the powder bed. This implies that only part with a flat upper surface can be used. This is generally no problem when parts are built from “scratch” but any application including repairing of existing objects will need a preceding operation where the object is machined in such a way that the top surface is flat. 
         [0004]    The selective laser melting in its current known form is limited to planar horizontal surfaces and where the component can be retracted downward for each sintered layer. 
         [0005]    There are a number of processes available for depositing material to components by sintering metallic powder by laser. These methods varies slightly and can be divided into laser cladding, where powder is fed to the melting area and melted by a laser beam that can move in multiple axis and Laser Sintering where the powder is resident in a powder bed and the laser beam is oriented top down. 
         [0006]    Laser cladding has a low yield in terms of supplied powder and the deposit rate on the substrate is limited. 
       SUMMARY OF INVENTION 
       [0007]    Therefore it is the aim of the invention to overcome the above described problems. 
         [0008]    The problem is solved by a method according to the claims. 
         [0009]    The invention describes methods for how powder distribution and layer thickness control can be applied to objects by locally applying powder or by vibration. 
         [0010]    In the dependent claims further advantageous features are listed, which can be combined arbitrarily with each other to yield further advantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIGS. 1 to 9  show steps of the inventive method. 
       
    
    
       [0012]    The figures and the description are only examples of the invention. 
       DETAILED DESCRIPTION OF INVENTION 
       [0013]      FIG. 1  shows an exemplary apparatus  1  to perform this method. 
         [0014]    The apparatus  1  comprises especially a container  10  wherein powder  7  (as arrow) or a powder bed  8  and an object  4  to be coated is present. 
         [0015]    There is no need for having a container or powder bed (see  FIG. 3 ,  9 ). 
         [0016]    The object  4  has especially several upper surfaces  13 ,  16  on one side, wherein only the lower upper surface  16  shall preferably be coated. But the invention is not limited to non planar surfaces. 
         [0017]    The object  4  is retracted so that height of the powder bed  8  is higher than the surface  16  ( FIG. 2 ). 
         [0018]    By using vibration means  22  powder  7  is filled and distributed on the surface  16  for getting a powder layer  14  ( FIG. 4 ). 
         [0019]    The powder  7 ,  8  is supplied to the apparatus  1  and by vibration the powder flows easily over one surface  16  of the object  4 . 
         [0020]    The vibration means  22  can be attached directly to the object  4  and/or the container  10 . Even several vibration means  22  can be used at different locations (object  4 , container  10 ). 
         [0021]    An alternative is to use a powder supply  34  with supplies powder  35  on the surface  16  ( FIG. 3 ). The powder supply  34  is preferably moved over the surface  16 . The powder  35  is preferably only locally applied. In this case no powder bed or container is necessary. 
         [0022]    Also vibration means  22  can be used to densify or to homogenize the powder. 
         [0023]    Especially there is a level control that makes sure that there is enough powder in the apparatus  1 . If the powder level is too low, additional powder is fed in and the apparatus  1  is re-vibrated to let the powder flow freely and being distributed over the wanted surface  16 . 
         [0024]    There can be a tool  31  ( FIG. 5 ) which applied to  FIG. 3  or  FIG. 4  to remove or push aside excess powder from the areas where the laser beam  28  is supposed not to melt. The thickness of the powder layer  14  may reach the desired value by vibration only ( FIG. 4 ). The tool ( 31  in  FIG. 5  or  34  in  FIG. 3 ) is preferably taking care of this as it moves over the surface  16  to be coated and pushes aside all excess powder. This function resembles the scraper as it forms a layer with a predefined and controlled thickness but unlike the scraper which usually travels in one direction only the whole width of the apparatus along the X-axis this tool ( 34  or  31 ) travels along any desired path over the surface  16  in both X and Y directions and this path avoids the obstacle surface  13 . 
         [0025]    After having completed the supply of powder for one layer, in the next step ( FIG. 6 ) a laser beam  8  of a laser  25  or electron beams are used to densify especially to sinter or to melt the powder layer  14  of  FIG. 3 ,  4  or  5 . 
         [0026]    The densification can also preferably be locally ( FIG. 4 ,  5 ,  6 ,  8 ,  9 ). 
         [0027]    In the next step the object  4  can be again retracted, so that the level of powder bed  8  is higher than the desified layer  31  ( FIG. 7 ) and no powder or empty space  32  is present above the layer  31 . 
         [0028]    The object  4  or the container  10  is put into vibration and a second powder layer  14 ′ is filled on the object  4  or as described in  FIG. 3  (by powder supplier),  4  or  5 . 
         [0029]    This can be repeated to build up several layers. 
         [0030]    This method can be used to repair components and can especially be performed locally. 
         [0031]    The method requires an apparatus  1  for laser sintering or melting powder and comprises especially a horizontal powder bed  8  that especially gradually retracts especially downward as each layer is built up. Each powder layer is densified by a laser beam sweeping over the powder layer  14  and densifying the powder and attaching powder to a previous layer. The downward movement of the powder bed  8  can be programmed to increments of a millimeter and can especially correspond to the size of the powder particles. 
         [0032]    Conventional Selective Laser Sintering Machines has a scraper which for each layer must be swept over the whole upper surface (here  13 ,  16 ) pushing powder material in front of the scraper and creating a layer of powder. 
         [0033]    The invention does not use the scraper but a cylindrical tool on X and Y guides with the movement similar to a milling machine 
         [0034]      FIG. 9  shows another example of the method. 
         [0035]    The lower upper surface  16  is totally surrounded by the upper surface  13 . 
         [0036]    In this groove a powder  7  is supplied which is in most cases nonuniformly distributed. A powder supply does not have to move over the surface  16 . By vibration means  22  the powder  7  is distributed uniformly inside the groove forming a powder layer  14 . 
         [0037]    After that a laser  25  with laser beams  28  is used to densify the powder layer  14  to get a dense layer  31 , wherein the powder layer  14  can preferably only locally be densified. 
         [0038]    In  FIG. 9  the container and the powder bed is not shown or not necessary and even the vibration means are not shown all over the several steps of  FIG. 4 . 
         [0039]    A CNC program is preferably used for moving and controlling the object  4 , the laser  25  or other tools (in all figures). 
         [0040]    The invention uses a robust tool with that may get in contact with the object if the object for same reason has been deflected by heat or strain. This feature can in some cases readjust the object and remove burrs and spatters. 
         [0041]    The invention expands Selective Laser Melting to cover also non planar object found typically in all repair businesses. 
         [0042]    The advantage of the invention are that it is now possible to limit the Selective Laser Melting to an area that does not have to be plane and to selective areas of an object that does not have a planar upper surface and lead to a reduction of operating time of the apparatus  1 .