Abstract:
The present invention relates to a method and a device for manufacturing a three-dimensional object, wherein the object is generated by successively solidifying single layers of fluid or powdery solidifiable building material by the action of electromagnetic radiation. The method comprises steps for emitting a first pulsed electromagnetic radiation onto a first area of a layer of the building material, and for emitting a second continuous electromagnetic radiation onto a second area of the layer of the building material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of copending application U.S. Ser. No. 13/032,283, filed on Feb. 22, 2011, which claims under 35 U.S.C. §119(a) the benefit of German Application No. 10 2010 008 960.5, filed Feb. 23, 2010, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a method and a device for manufacturing a three-dimensional object. The manufactured object is in particular suitable for application in the field of microtechnology. 
         [0004]    (b) Description of the Related Art 
         [0005]    EP 0 758 952 B1 describes a known method and device for manufacturing a three-dimensional object, where the object is generated by successive solidification of single layers of a liquid or powdery solidifiable building material by action of electromagnetic radiation. Here, the electromagnetic radiation is preferably a pulsed laser radiation. DE 100 28 063 A1 and DE 100 65 960 A1 show a similar device, where the electromagnetic radiation is a pulsed laser radiation. 
         [0006]    DE 102 58 934 A1 describes a method and a device for selectively connecting bodies with supports by means of laser beams. A pulsed laser radiation is applied and the radiation pressure is used for compacting and additionally heating the powder layer. As described, the method is applicable to the generation of microstructures. The parts producible by the known method, in particular metal parts, however, have a residual porosity, for which reason they are not suitable for certain applications in the microtechnology field. 
       SUMMARY 
       [0007]    An object of the present invention is therefore to provide a method and a device for manufacturing a three-dimensional object that may, in turn, be utilized in the field of microtechnology. 
         [0008]    This object is solved by a method for manufacturing a three-dimensional object and by a device for manufacturing the three-dimensional object. 
         [0009]    The method and device according to the present invention may be used suitably and advantageously in a micro laser sintering (micro-LS) process, by which three-dimensional objects, with a resolution in the range of micrometers, are built-up. 
         [0010]    By such a method and device, three-dimensional components with enhanced density may be produced, and the mechanical properties of the manufactured component may be improved correspondingly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0011]    Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. In the drawings: 
           [0012]      FIG. 1  shows a schematic view of a device for manufacturing a three-dimensional object according to one or more embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    Referring now to  FIG. 1 , a laser sintering device comprises a frame  1 , which is open towards the top and has a platform  2  arranged therein that is movable in a vertical direction. The platform  2  is adapted to carry the three-dimensional object  3  to be manufactured. The frame  1  and the platform  2  define inside a building space. The platform  2  is connected to a lifting mechanism  12  that moves the platform  2  in a vertical direction so that the layer of the object  3  that is to be solidified is arranged in a working plane  4 , respectively. 
         [0014]    Furthermore, a coating device  5  for applying a layer of a powdery building material  3   a  is provided. Regarding the building material  3   a,  any laser-sinterable powder or powders may be used, such as polymers, for example, polyamide and/or polystyrene, metals, ceramics, compound materials and in particular high temperature plastics such as for example PAEK (polyaryletherketone). Regarding metal-containing powder material, any metals and their alloys, as well as blends with metallic components or with non-metallic components may be utilized. At first, the building material  3   a  is fed from a reservoir  6  to the frame  1 . The coating device  5  is then moved to a predetermined height in the working plane  4 , so that the layer of the powdery building material  3   a  lies with a defined height above the previously solidified layer. The device further comprises a laser  7  to generate a laser beam  7   a,  focused by means of a deflection device  8  to any points in the working plane  4 . In so doing, the laser beam  7   a  can selectively solidify the powdery building material  3   a  at positions corresponding to the cross-section of the object  3  to be manufactured. Regarding lasers, any laser or lasers may be used that are suitable for laser sintering or laser melting of the corresponding building material, respectively, for example, CO 2 -lasers, solid state lasers and others. 
         [0015]    Reference numeral  10  refers to a process chamber, in which the frame  1 , the platform  2 , the lifting mechanism  12 , and the coating device  5  can be arranged. Reference numeral  9  refers to an opening in the process chamber  10  for introducing the laser beam  7   a.  Preferably, a protective gas is introduced into the process chamber  10 . Further, a control unit  11  is provided, through which the device is controlled in a coordinated manner for carrying out the building process. 
         [0016]    The laser sintering device, in a preferred embodiment, may be a micro laser sintering device. Micro laser sintering is characterized in that very fine powders are used and very thin layers are applied. By means of micro laser sintering, a resolution in the range of 10-20 μm or less may be reached. The powders that are used have a grain size in the range of approximately 1 nm to approximately 100 nm. The grain size is measured using laser diffraction according to DIN ISO 13320-1. The layer thickness of the applied powder layers is approximately 1 μm up to a approximately 100 μm. Generally, for the micro laser sintering the grain size and the layer thickness are sized such that the surface forces are greater than the gravitational forces. The beam diameter used may be between approximately 1 μm up to approximately 20 μm. The laser may preferably be a fiber laser or a YAG-laser. Any suitable powder from materials that can be applied in the field of microtechnology may be used. In a preferred embodiment, a metal powder is used 
         [0017]    In operation of the device in a first step the platform  2  is moved by means of the lifting mechanism  12  until its uppermost side is located one layer thickness beneath the working surface  7 . Then a first layer of the building material  3   a  is applied to the platform  2  via the reservoir  6  and the coating device  5  , and the building material  3   a  is then leveled or evened-out. Thereafter, the control unit  11  controls the deflection device  8  so that the deflected laser beam  7   a  selectively hits the positions of the layer of the building material  3   a  to be solidified. Thereby, at these positions the building material  3   a  is solidified or sintered such that the three-dimensional object  3  is generated. 
         [0018]    In a subsequent step the platform  2  is lowered by the lifting mechanism  12  by one layer thickness (the thickness of one layer of building material  3   a  to be sequentially sintered). By means of the reservoir  6  and the coating device  5 , a second layer of building material is applied, evened and selectively solidified by means of the laser beam  7   a.  These steps are repeated until the desired object  3  is manufactured. 
         [0019]    By means of the method and device according to the embodiments of the present invention, the laser  7  is controlled by means of the control unit  11  in two different operating modes. The first operating mode causes a first pulsed radiation  7   a  of the laser  7  with a first frequency. The second mode of operation causes a second radiation, that is a pulsed radiation with a higher frequency compared to the first pulsed radiation, or is a continuous radiation. The frequency of the first pulsed radiation may be, for example between 60 kHz and 450 kHz, preferably approximately 60 kHz to 300 kHz. The frequency of the second pulse radiation may be, for example, between 200 kHz and 450 kHz. 
         [0020]    The pulsed laser radiation  7   a  can be generated by pulsed excitation or also by measures within the laser  7  itself (Q-switching or mode coupling). With the pulsed laser radiation the laser beam  7   a  is not emitted continuously as with a CW-laser (continuous wave laser), but is emitted in a pulsed manner, i.e. in timely limited pulses. 
         [0021]    Preferably, a laser  7  is used that can emit both, a pulsed radiation  7   a  as well as a continuous radiation  7   a.  For the latter, a CW-laser is operated in a pulsed manner by switching on and off the “pumping power” in short cycles. Carbon dioxide laser can be operated in this way, and can be pushed up to more than 1 kHz. In another embodiment, is the generation of the pulses is by a combination of a CW-laser and a modulator, such as, for example, a simple chopper. 
         [0022]    After the coating device  5  has applied and evened a layer of the building material  3   a,  the irradiation of the layer of the building material  3   a  is effected in two steps. First, a first pulsed electromagnetic radiation  7   a  is irradiated onto a first area of a layer of the building material, and subsequently a second pulsed radiation or a continuous electromagnetic radiation  7   a  is irradiated onto a second area of the layer of the building material  3   a.    
         [0023]    Preferably, the first and the second area of the layer overlap at least partially. The areas may also fully overlap and can represent partial areas of one layer or the whole layer. Further preferably, a time period is provided between the irradiation of the first pulsed electromagnetic radiation  7   a  onto the building material  3   a  and the irradiation of the second pulsed or continuous electromagnetic radiation  7   a  onto the building material  3   a,  during which the building material  3   a  irradiated with the first pulsed electromagnetic radiation  7   a  solidifies. 
         [0024]    The combination of the first pulsed radiation and the second pulsed radiation or the continuous radiation  7   a  has a synergistic effect. First, the first pulsed radiation  7   a  causes the break-up of the surface tensions of the powder particles in the building material  3   a  and the bonding of the powder grains. Second, the second pulsed or continuous radiation  7   a  causes a further compaction of porous sintering structures in the building material  3   a  that has already been irradiated with the first pulsed electromagnetic radiation  7   a.  Thus, with the second radiation the forming of melting beads is prevented. 
         [0025]    In a an alternate embodiment, through a timely alternation, a first area of a layer can be irradiated with the first pulsed radiation and subsequently a second area of the layer that does not overlap the first area can be irradiated with the second continuous radiation. A plurality of first and second areas may thus be provided. 
         [0026]    By the division of the layers in first and second areas that are irradiated in a pulsed manner or continuously and that overlap fully, partially or don&#39;t overlap at all, the energy or heat input into the layer can be controlled and harmonized advantageously so that stresses in the layer can be reduced. 
         [0027]    The method according to the embodiments of the present invention, and the corresponding device, are advantageously suitable for micro laser sintering (micro-LS), wherein three-dimensional objects having details in the range of micrometers, are built-up. 
         [0028]    The scope of the invention is not limited to the embodiments described herein but includes other equivalents and modifications as far as they fall into the scope defined by the attached claims. 
         [0029]    The present invention is not only suitable for a laser sintering method, but also for a laser melting method, as well as stereolithography. 
         [0030]    Additionally, as an alternative to using laser radiation as electromagnetic radiation, a particle radiation, such as for example, electron radiation, may be used. 
         [0031]    Furthermore, instead of a single laser, two or more laser light sources may be used.