Abstract:
The invention relates to a powder build unit ( 4 ) for a device for the additive manufacture of components, having at least one electric lead ( 22 ) and having at least one power source ( 38 ) that is connected to the electric lead. The electric lead ( 22 ) functions as a powder distributor and as a heating element. In addition, the invention comprises a device that contains this powder build unit, as well as a corresponding method.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a powder build unit, a corresponding device that comprises this powder unit, and a method that employs the powder build unit according to the invention. 
         [0002]    Additive or generative manufacture is known under various names, most of which are trade names of machine manufacturers or research institutions. These names include selective laser melting (SLM), direct metal laser sintering (DMLS), laser powder bed (LPB), and laser cusing (laser beam melting). 
         [0003]    The method includes the selective melting of a powder layer deposited on a platform by means of a laser or electron beam. Afterward, the platform is lowered and another powder layer is deposited. The method is repeated until an adequate number of layers have been formed in order to generate a complete three-dimensional object. 
         [0004]    For deposition of the powder on the platform, a coater is moved transversely across the platform and pushes a mound of powder in front of it. The coater is at a certain distance from the preceding powder layer. Typically, doctor blades or brushes are employed as coaters. In these methods of manufacture based on powder beds, the surface roughness depends on, among other factors, the particle diameters. The smaller the particle size is, the lesser is the surface roughness of the manufactured component. However, a metal powder with smaller particle diameters is hygroscopic; that is, moisture, in particular water, from the surroundings is bound on the surfaces of the particles. As a result, the powder forms clumps and can no longer be distributed with a uniform thickness. Furthermore, additional energy is needed for the water present in the powder in order to melt the powder. However, this additional energy depends on the amount of bound water. This can lead to the fact that the powder completely melts in a locally dry region of a layer and the powder only partially melts in a locally moist region of the same layer. As a result of this, the layer is bonded to the preceding layer only in some regions. In the worst case, the partially manufactured component must be discarded. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, the present invention is based on the object of presenting a powder build unit that deposits dry powder. 
         [0006]    The invention relates to a powder build unit for a device for the additive manufacture of components, the powder build unit having at least one electric lead and at least one power source that is connected to the electric lead. The electric lead functions in this case as a powder distributor and as a heating element. This has the advantage that a so-called doctor blade is not required for the distribution of powder. Furthermore, the electric lead functioning as a heat source is in direct contact with the powder. In this way, the heat can be better introduced into the powder. As a result of the local introduction of heat, the temperature, for example, in a powder bed of an SLM, SLS, or EBM unit (EBM—electron beam melting) is raised. In the process, the residual moisture contained in the powder and due to water, in particular, evaporates before the powder particles are fused. 
         [0007]    In an advantageous embodiment of the invention, the electric lead has a cavity. Preferably, the cavity of the electric lead can be filled with a cooling fluid. This offers the advantage that it is possible to regulate the temperature of the electric lead. 
         [0008]    In another advantageous embodiment of the invention, the powder build unit has a cooling pump for circulating cooling fluid through the cavity, said cooling pump being in fluid communication with the cavity. This offers the advantage of being better able to dissipate the heat that is present in the lead. Furthermore, the electric lead can thereby be cooled very rapidly to room temperature. In an advantageous way, this offers the possibility of heating only certain regions of the powder bed. 
         [0009]    In another advantageous embodiment of the invention, the electric lead is formed from a solid wire. This has the advantage that it is possible to apply high currents without melting the electric lead. 
         [0010]    In another advantageous embodiment of the invention, the electric lead is rigid and/or flexible. Depending on its application, the electric lead can be designed to be flexible at the edges and rigid in the center, for example. 
         [0011]    In another advantageous embodiment of the invention, the electric lead is coiled, with an insulation being arranged between two adjacent windings. Such a coil has the advantage of being able to operate as a roller mechanically and being able to generate more heat electrically. The insulation can be constituted of air, a ceramic, or a plastic. 
         [0012]    In another advantageous embodiment of the invention, the power source generates a direct current and/or an alternating current. By means of the direct current, the electric lead is operated as a pure heating wire. In this way, everything in immediate proximity is heated. Therefore, when the powder is being distributed, if the electric lead is situated in the vicinity of the component that has already been built up, the mound of powder being pushed in front of the electric lead and the already built-up region of the component are heated. If, in contrast, an alternating current is applied to the electric lead, a magnetic alternating field is generated, so that an alternating current can be created by induction in the component that has already been built up. As a result of this, only the region of the component that has already been built up is heated. In the process, the powder remains uninfluenced, because its electrical resistance is too high. Therefore, no eddy current can build up in the powder. If, for example, two separated electric leads are used, it is possible to apply a direct current to one electric lead and an alternating current to the other electric lead. This offers the advantage of being able to heat the mound of powder via the direct current lead. The direct current lead can preheat the component somewhat when it passes it. The alternating current lead can then additionally introduce thermal energy into the component, without the mound of powder being heated too strongly. In general, the individual particles of powder require less thermal energy for melting than does the upper region of the component. As a result, it is possible to prevent the particles from melting already in the mound of powder. The moist powder need only be dried in order to ensure the flowability of the powder in the mound of powder. 
         [0013]    In another advantageous embodiment of the invention, the electric lead is coiled around, in particular, a soft magnetic core. This has the advantage that the induction produced by the alternating current is greater. Soft magnetic materials are ferromagnetic materials that can be readily magnetized in a magnetic field. Such materials include, among others, iron, cobalt, and nickel. 
         [0014]    The invention further relates to a device for the additive manufacture of components, the device having at least one component platform that can be lowered, at least one powder build unit according to the present invention for the deposition of at least one powder layer of a component material on at least one build-up zone of the component platform, with the powder build unit being movable in relation to the component platform. The device further comprises at least one radiation source for generating a high-energy beam, by means of which the powder layer can be melted and/or sintered locally in the region of the build-up zone to form a component layer. 
         [0015]    In addition, the invention comprises a method for the additive manufacture of components, in particular by using the device according to the invention, with the powder deposition or build occurring in such a way that a powder build unit has an electric lead ( 22 ) and functions as a powder distributor and as a heating element. 
         [0016]    In addition, the invention comprises the use of the powder build unit according to the invention or of the device according to the invention in a method for the additive manufacture of components. 
         [0017]    Further advantageous embodiments of the invention are discussed in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0018]    Preferred exemplary embodiments of the invention are described in detail below on the basis of the schematic drawings. Shown are: 
           [0019]      FIG. 1  is a side view of an additive manufacturing device with a powder build unit according to the invention, 
           [0020]      FIG. 2  is a side view of an additive manufacturing device with a powder build unit according to the invention, 
           [0021]      FIG. 3  is a section along line III-III in  FIG. 2 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  shows a side view of an additive manufacturing device  2  with a powder build unit  4  of the invention according to a first embodiment.  FIG. 2  shows a side view of an additive manufacturing device with a powder build unit  4 ′ of the invention according to a second embodiment. The device  2  has, on its bottom left side, a component platform  6  on which a partially manufactured component  8  is arranged and is embedded in a powder bed  10  of old powder  14 . In this context, old means that the powder is already present in the powder bed  10 . In this case, the word “old” gives no information about the age or about the quality of the powder. The device  2  has, on its bottom right side, a powder platform  12 , on which new or fresh powder  16  is arranged. In this context, new means that the powder is not yet present in the powder bed  10 . The two platforms  6  and  12  are separated from each other by a vertical intervening wall  18 . For deposition of a new powder layer  20 , the powder platform  12  is pushed a little upward first of all, so that the fresh powder  16  surmounts the intervening wall  18 . The powder build unit  4  moves from right to left over the fresh powder  16 , over the intervening wall  18 , and over the powder bed  10 . The powder build unit  4  has an electric lead  22 . In the process, the electric lead  22  operates as a coater and pushes a mound of powder  24  in front of it and thereby distributes a new powder layer  20  uniformly on the component  8 . In the first embodiment, the powder build unit  4  additionally has a doctor blade  26 , which is arranged around the electric lead  22  (see  FIG. 1 ). Or else, as depicted in  FIG. 2 , the electric lead  22  can come into direct contact with the mound of powder  24 . Once a new powder layer  20  has been deposited on the component  8 , this new powder layer  20  can be melted via a radiation source  28  arranged above the powder bed  10 . In the process, a high-energy beam  30 , such as, for example, a laser beam or an electron beam, impinges in a build-up zone  31  on the new powder layer  20 . This powder layer  20  is caused to melt or to sinter and a new component layer  32  is formed. Once the manufacture of the new component layer  32  is finished, fresh powder  16  is deposited on the component  8 , as mentioned above. The steps listed above are repeated until the component has been completely manufactured. 
         [0023]    The electric lead  22  can be formed from a solid wire or else, as in this case, can have a cavity  34 . This cavity  34  can be filled with a cooling fluid, such as, for example, water, helium, argon, and/or hydrogen. 
         [0024]      FIG. 3  shows a section along the line III-III in  FIG. 2 . The component platform  6 , on which the semifinished component  8  is arranged and is situated in the powder bed  10 , can be seen at the bottom in  FIG. 3 . The powder build unit  4  or  4 ′ is arranged directly above the powder bed  10 . The powder build unit  4  or  4 ′ has the electric lead  22 , which is wound around a core  37  with six windings. The core  37  and the six windings form a coil  36 . Thus, in  FIG. 3 , only the first winding  40 , the second winding  42 , and the third winding  44  are provided with reference numbers. Insulation  46  can be arranged between two adjacent windings. Here, air is used as insulation material. However, it needs to be pointed out that the bottom face of the coil  36  is closed, so that the powder in the mound of powder  24  can be distributed uniformly and smoothly. This coil  36  is connected to a power source  38 . This power source  38  can generate both direct current and alternating current. If the electric lead  22  is hollow, then it can be connected additionally to a cooling pump  48 . This pump  48  allows cooling fluid to flow through the hollow electric lead  22 . 
         [0025]    The functional operation of the powder build unit  4  or  4 ′ according to the invention will now be explained in detail on the basis of  FIGS. 1 and 2 . 
         [0026]    In  FIG. 1 , a direct current can be applied to the electric lead  22 . In the process, the electric lead  22  becomes hot. This thermal energy of the electric lead  22  is delivered both to the mound of powder  24  and to the upper part of the component  8 . The powder in the mound of powder  24  is dried in the process. The water present in the powder is evaporated. The temperature of the electric lead  22  can be regulated additionally by means of the cooling pump  48 . 
         [0027]    If, by contrast, the component  8  is only to be preheated, then an alternating current, which is supplied by the power source  38 , can be applied to the electric lead  22 . As soon as the powder build unit  4  or  4 ′ is situated in the vicinity of the component  8 , an alternating current is generated in the component  8  and the component  8  is correspondingly heated. The powder in the powder bed  10  has an electrical resistance that is too high for any alternating current to flow in it.