Abstract:
In a method for producing a three-dimensional object wherein the object is produced layer by layer by applying a layer of a material which can be solidified by irradiation with electromagnetic radiation and subsequently solidifying the layer at the points corresponding to the object by irradiation the problem is encountered that the production process is considerably delayed by long heating and cooldown times within the apparatus used for the production. According to the invention this problem is solved by irradiating and thereby solidifying in each layer a region of the material surrounding the object so as to produce a container wall (26) for the material (21).

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for producing a three-dimensional object and to an apparatus for carrying out such a method. 
     BACKGROUND OF THE INVENTION 
     Such a method is disclosed for example in U.S. Pat. No. 4,863,538. In this case the material is a powderous solid material which is applied in layers to the upper side of a lowerable piston and which is sintered at places corresponding to the object by means of a laser. For forming the successive layers the piston is stepwise lowered within a cylinder which surrounds the powderous material. A heater maintains the material at an operating temperature of about 150° C. as required for the sintering process. 
     This known method has the drawbacks that together with the material also the cylinder must be heated up to the operating temperature which requires a preheating time of 2 to 3 hours. Moreover, before removing the object from the cylinder a slow cooling down to below 100° C. must be carried out in order to avoid the risk of dust explosion. During this cool-down period the object must remain within the cylinder. In summary, the known method results in long rigging and strip-down times and therefore long production times. This drawback shall be eliminated with the invention. 
     SUMMARY OF THE INVENTION 
     According to the invention this problem shall be solved by the features as set forth in the claims. Since according to the invention the container wall corresponding to the conventional cylinder is produced simultaneously with the object, the preheating of the cylinder and therefore the long rigging time is eliminated. After finishing the object the container wall which does not form part of the apparatus can be removed from the apparatus together with the object for a controlled cool-down, so that the long cool-down time within the apparatus and therefore the strip-down time is also eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic illustration of an apparatus in accord with one embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following the invention shall be described with an embodiment by reference to the FIGURE. The FIGURE is a schematic sectional representation of the inventive apparatus. 
     The apparatus comprises a substantially horizontal work table 1 having a hole in the form of a cutout 2. The cutout 2 is preferably circular with a cross-section which is greater than the greatest cross-sectional area of the object 3 to be produced. However, the cutout 2 may also have any other suitable shape. An irradiation device 4, for example a laser, delivering a focussed light beam 5 is arranged above the work table 1. The light beam is deflected through a deflection device 6, for example a rotating mirror, onto the plane of the work table 1 in the form of a deflected beam 7. A control device 8 controls the deflection device so that the deflected beam 7 strikes any desired point within the operational region defined by the cutout 2. 
     An as well substantially horizontal base 9 in the form of a platform is provided below the cutout 2. The base 9 is formed as a laterally guided table having a shape corresponding to the cutout 2 and is displaceable in direction of the arrow 11 by means of an as well laterally arranged level adjustment device 10 between an uppermost position in which the upper surface of the base is within the cutout 2 and substantially at the same level as the upper side of the work table 1, and a lowermost position which is indicated by dotted lines in the FIGURE and in which the base 9 is lowered to such an extent that the surface thereof is level with an adjacent receiving plate 12. The distance between the receiving plate and the work table, i.e. the level adjustment range of the base, is greater than the maximum height of the object 3. 
     Adjacent to the receiving plate 12 the apparatus comprises an opening 13 which is tightly closeable by means of a door 14. A removal container 15 is provided which can be sealingly attached or docked, resp., to the opening at the side thereof opposite to the receiving plate 12. The removal container 15 also comprises a door 16 for sealingly closing the container 15 and supply means 17 for an inert gas, for example nitrogen, and a heater 18. 
     An output or discharge device, resp., 19, for example in the form of a laterally arranged pusher or the like, is formed and disposed to displace the object resting on the base 19 in the lowermost position thereof from the base 9 onto the receiving plate 12 and through the (opened) doors 14, 16 into the removal container 15. 
     A device 20 for applying a layer of a powderous material 21 is conventionally formed as a drum which is horizontally movable along the work table 1 across the cutout 2 from a position in which the material 21 is applied from supply 22 onto the surface of the drum. A possible material 21 is low-melting plastic material such as nylon having a grain size of about 10 μm or below, but also metal powder or hybrids, i.e. plastic-coated metal or ceramic powder. Further, a radiation heater 23 directed towards the operational region is disposed above the cutout 2. 
     The control device 8, the level adjustment device 10 and the discharge device 19 are each connected with a central control device 24 for a coordinated control of those devices in the manner described in the following. 
     In operation the base 9 is first moved by means of the level adjustment device 10 into the uppermost position in which the surface of the base 9 is level with the surface of the work table 1, and thereafter lowered by an amount corresponding to the intended thickness of the first material layer so as to form within the cutout 2 a lowered region which is defined laterally by the walls of the cutout 2 and at the bottom by the surface of the base 9. Thereupon a first layer of the material 21 having the intended layer thickness is charged into the space formed by the cutout 2 and the base 9 or into the lowered region, resp., by means of the drum 20 and heated up to a suitable working temperature, for example 140° C. to 160° C., by means of the heater 23. Thereafter the control device 24 drives the deflection device 6 through the control 8 thereof in such a manner that the deflected beam 7 subsequently strikes all points of the layer and solidifies the material 21 thereat by sintering. In this manner first a solid bottom layer 25 is formed. 
     In a second step the base 9 is lowered by the amount of one layer thickness by the control device 24 through the level adjustment device 10 and a second material layer is charged into the thus generated lowered region within the cutout 2 by means of the drum 20 and again heated up by the heater 23. This time the deflection device 6 is driven by the control device 24 in such a manner that the deflected beam 7 strikes only the region of the material layer adjacent to the inner surface of the cutout 2 and solidifies the material layer thereat by sintering, whereby a first annular wall layer having a wall thickness of about 2 to 10 mm is produced which completely surrounds the remaining powderous material of the layer. 
     After lowering the base 9 by the amount of the layer thickness of the next layer, charging material 21 and heating in the same manner as above described the production of the object 3 proper can start. To this end the control device 24 drives the deflection device 6 in such a manner that the deflected beam 7 strikes those points of the layer which are to be solidified corresponding to the coordinates of the object 3 as stored in the control device 24. Before or after the production of this object layer a second annular wall layer of equal wall thickness is sintered onto the first annular wall layer in the same manner as described above. 
     The procedure is repeated in analogous manner for the further layers. By sintering an annular wall layer onto the underlying annular wall layer when producing each object layer an annular wall portion 26 in the form of a container wall is generated which surrounds the object 3 together with the remaining unsintered material 21 and prevents material 21 from escaping when lowering the base 9 to below the work table 1. 
     After finishing the final object layer only an annular wall layer is solidified in a manner corresponding to the above-described second step and thereafter a cover layer 27 is solidified in the same manner as when producing the bottom layer 25, the cover layer 27 cooperating with the bottom layer 25 and the wall portion 26 to form a container 28 which sealingly surrounds the object 3 and the remaining unsintered material. 
     Thereafter the base is lowered in the manner indicated by dotted lines in the FIGURE to the level of the receiving plate 12 by means of the level adjustment device 10 and a removal container 15 which was previously heated to a temperature of as well about 140°-160° C. under a nitrogen atmosphere is attached to the discharge opening 13. After opening the doors 14, 16 the discharge device is operated to push the container 28 through the opening 13 into the removal container 15. After closing the doors 14 and 16 the removal container 15 can be removed and a new object can be produced without further waiting delay. The required slow cool-down of the object 3 occurs within the removal container 15 by corresponding control of the heater 18 independently of the production of the next object. 
     During the production of the object 3 an inert gas atmosphere, preferably a nitrogen atmosphere, is also produced within the working region by per se known (not shown) means. Owing to the lockage-type form of the doors 14, 16 an escape of this atmosphere when discharging the finished object 3 and therefore an interruption of the production is avoided. 
     Modifications of the invention are possible. The production of the bottom layer 25 can be omitted; also the cover layer 27 is not required if a safe cool-down of the then bare remaining powder within the removal container 15 under inert gas atmosphere is possible; on the other hand, when producing both layers 25, 27 and thus the sealed container 28, the cool-down can possibly be carried out without removal container 15 or without inert gas atmosphere, resp. Apart from a drum the layer applying device 20 may also be designed as a dispensing or scraping device, pusher, brush, blade or any other device which is suitable for applying a uniform layer of a powderous material; the heaters 18, 23 may be formed as a radiation or circulating air heater and any other source of electromagnetic radiation outputting a focussed beam or sufficient energy for sintering, such as a light source or a cathode ray source, may be used for the irradiation device. Further, liquid material can be used in place of powderous material. Finally, the solidified wall layer forming the container wall is not necessarily circular, but may have any suitable form of a substantially closed line. However, preferably this form corresponds to the shape of the cutout 2.