Patent Publication Number: US-2022219289-A1

Title: Method and apparatus for producing 3d moldings by layering technology, using a core cleaning station

Description:
CLAIM OF PRIORITY 
     This application is a national phase filing under 35 USC § 371 from PCT Application serial number PCT/DE2020/000127 filed on Jun. 11, 2020, and claims priority therefrom. This application further claims priority to German Patent Application Number DE 10 2019 004 122.4, filed on Jun. 13, 2019. The contents of PCT/DE2020/00127 and DE 10 2019 004 122.4 are each incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The invention relates to a method and an apparatus for producing three-dimensional models by layering technology using a core cleaning station. 
     BACKGROUND 
     European Patent EP 0 431 924 B1 describes a process for producing three-dimensional objects based on computer data. In the process, a thin layer of particulate material is deposited on a platform and has a binder material selectively printed thereon by means of a print head. The particulate region with the binder printed thereon bonds and solidifies under the influence of the binder and, optionally, an additional hardener. Next, the platform is lowered by one layer thickness into a construction cylinder and provided with a new layer of particulate material, the latter also being printed on as described above. These steps are repeated until a certain desired height of the object is achieved. Thus, the printed and solidified regions form a three-dimensional object. 
     Upon completion, said object made of solidified particulate material is embedded in loose particulate material, from which it subsequently has to be freed. Until now, this has been done manually and is very time-consuming and therefore very cost-intensive. The parts are freed from residual powder, for example, by means of a suction device and/or by simple brushing. 
     It was therefore an object of the present invention to provide constructional means allowing improved 3D printing process flows or at least improving or altogether avoiding the disadvantages of the prior art. 
     Another object of the present invention was to provide means for automating the cleaning step, thus helping to save labor and costs. 
     A further object of the present invention was to provide an improved 3D printing method in which various work steps are automated and assembly line production in 3D printing can be achieved at least in part. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention relates to a core cleaning station for cleaning 3D moldings, comprising a housing having an opening which is optionally closable or comprises a means for closing and means for generating a bead jet and an air jet and a deposit surface or/and a support for the 3D molding. 
     In another aspect, the invention relates to a 3D printing apparatus comprising an attached cleaning station (core cleaning station). 
     In a further aspect, the invention relates to a method for manufacturing 3D moldings, wherein at least one cleaning step is performed in an automated or semi-automated manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a configuration example of a cleaning station (core cleaning station) ( 10 ). 
         FIG. 2  shows the view into the core cleaning station ( 10 ) with adjustable air nozzles ( 4 ). 
         FIG. 3  shows a part of a handling robot ( 7 ) with a swivel arm. 
         FIGS. 4 a  and 4 b    schematically illustrate a 3D molding ( 9 ) on a core support ( 2 ) and on the swivel arm of a handling robot ( 7 ), respectively. 
         FIGS. 5 a  and 5 b    illustrate a 3D molding ( 9 ) subjected to bead blasting ( 8 ) and immersed in a bead bath in a container ( 6 ), respectively. 
         FIG. 6  shows how the 3D molding ( 9 ) on the core support ( 2 ) is exposed to an air jet by means of adjustable air nozzles ( 4 ) for further cleaning and removal of unsolidified particulate material. 
     
    
    
     DETAILED DESCRIPTION 
     According to the invention, a problem underlying the application is solved by providing a core cleaning station capable of cleaning a manufactured 3D molding substantially semi-automatically or automatically, and by a method using such a core cleaning station. 
     First of all, several terms according to the invention will be explained in more detail below. 
     A “3D molding”, “molded article” or “part” in the sense of the invention means any three-dimensional object manufactured by means of the method according to the invention or/and the apparatus according to the invention and exhibiting dimensional stability. 
     “Construction space” is the geometric location where the particulate material bed grows during the construction process by repeated coating with particulate material or through which the bed passes when applying continuous principles. The construction space is generally bounded by a bottom, i.e. the construction platform, by walls and an open top surface, i.e. the construction plane. In continuous principles, there usually are a conveyor belt and limiting side walls. The construction space can also be designed in the form of what is called a job box, which constitutes a unit that can be moved in and out of the device and allows batch production, with one job box being moved out after completion of a process to allow a new job box to be moved into the device immediately, thereby increasing both the production volume and, consequently, the performance of the device. 
     “Construction platform” or “construction field” as used in the disclosure means the surface to which the particulate material is applied and on which the particulate material is selectively solidified to build up a predetermined three-dimensional molding. 
     The “particulate materials” or “particulate construction materials” or “construction materials” of use herein may be any materials known for powder-based 3D printing, in particular polymers, ceramics and metals. The particulate material is preferably a free-flowing powder when dry, but may also be a cohesive, cut-resistant powder or a particle-charged liquid. In this specification, particulate material and powder are used synonymously. 
     The “particulate material application” is the process of generating a defined layer of powder. This may be done either on the construction platform or on an inclined plane relative to a conveyor belt in continuous principles. The particulate material application will also be referred to below as “coating” or “recoating”. 
     “Selective liquid application” in the sense of the invention may be effected after each particulate material application or irregularly, depending on the requirements for the molded article and for optimization of the molded article production, e.g. several times with respect to particulate material application. In this case, a sectional image is printed by the desired article. 
     The “device” used for carrying out the method according to the invention may be any known 3D-printing apparatus which includes the required parts. Common components include recoater, construction field, means for moving the construction field or other parts in continuous processes, metering devices and heating and/or irradiating means and other parts which are known to the person skilled in the art and will therefore not be described in detail herein. These apparatus components are combined with a core cleaning station for the cleaning step. 
     The “packing density” describes the filling of the geometric space by a solid. It depends on the nature of the particulate material and the application device and is an important initial parameter for the sintering process. 
     The construction material is always applied in a “defined layer” or “layer thickness”, which is individually adjusted according to the construction material and the process conditions. It is, for example, 0.05 to 0.5 mm, preferably 0.1 to 0.3 mm. 
     “Gap” or “gap opening” as used in the disclosure refers to the means through which particulate material is applied by the recoater or to the construction platform, respectively, and by means of which the applied amount of particulate material can be controlled. The particulate material exits the recoater through the “gap” or “gap opening” and flows onto the construction platform. The “closure” or “recoater closure” controls the amount of particulate material released. 
     A “coating blade” or “oscillating blade” in the sense of the disclosure relates to a means of a recoater device facing the construction platform, which may be combined with further means to control the application of particulate material. The “coating blade” can form a gap with another part or means of the recoater device, which gap is closed by a material cone at standstill. In the present disclosure, the “coating blade” is closed and opened by a controllable closure, e.g. a spring steel sheet, thereby controlling the application of particulate material to the construction field. 
     A “closure device” in the sense of the disclosure relates to the combination of coating blade, controllable closure and actuator in a particulate material recoater. 
     A “closure means” or “closure” or “coater closure” in the sense of the disclosure is a means that allows the gap of the recoater to be closed and opened in a controlled manner. This may be a spring steel sheet, for example. 
     An “actuating means” or “actuator” in the sense of the disclosure is used to open and close the closure means. 
     “Opening speed” in the sense of the disclosure means the length of time it takes for the closure means to be driven from its closed position to its maximum opening. 
     In the sense of the disclosure, “closure opening process” refers to the process of moving the closure means from its closed position to its open position. Accordingly, a “closure closing process” is the reverse process. 
     “Travel speed” in the sense of the disclosure refers to the speed of advancing or retracting the recoater. The travel speed and the opening speed are important variables that influence the process sequence, the production speed for 3D moldings and the control of the start-up and the printing process. Thus, these variables also influence the cost-effectiveness of a 3D printing apparatus. 
     “Core cleaning station” or “cleaning station” as used in the disclosure means a container or housing or partitioned space into which 3D moldings may be introduced and which are partially or substantially completely freed of particulate material by various means. The cleaning station may have a closable opening or means to substantially prevent particulate materials escaping from the interior, such as a curtain or rows of brushes. The cleaning station as defined in the disclosure may include further means useful for cleaning such as recycling means, reservoirs, holding means, fastening means, controllable or/and movable air or material nozzles. 
     “Beads” in the sense of the disclosure are particulate parts which may be round or/and rounded or/and structured and which are brought into contact with the 3D molding to be cleaned or wherein the 3D molding is introduced or immersed therein. The “beads” can also advantageously penetrate a complex geometry by means of an air flow and thus detach non-solidified particulate material from the 3D molding, thereby freeing the latter from such material. The beads can be made of different materials or mixtures of materials. For example, zeolites, orange gel, silica gel, one or more clay minerals, one or more diatomites or/and one or more sepiolites can be used. 
     A “container for receiving beads” as defined in the disclosure is any means in which beads can be provided or returned and which has a volume of between 10 liters and 1,000 liters in volume. 
     “Means for recycling beads” as defined in the disclosure refers to any means used to collect, transport or/and vacuum beads and to guide or return them to a container for receiving beads. 
     A “depositing means” in the sense of the disclosure is any suitable means, such as a receiving unit, a surface for depositing, a surface for depositing 3D moldings, which preferably has a fixing means for fixing one or more 3D moldings and which is preferably movable or/and pivotable in its X, Y, Z axis. 
     “Gripping means” in the sense of the disclosure can be any device that can pick up a 3D molding in a controlled manner and transport it to another location in space or simply fix it in place; it may be, for example, a robotic device that can be moved and controlled three-dimensionally. 
     The various aspects of the invention will be described in more detail below. 
     In one aspect, the invention relates to a cleaning station suitable for cleaning 3D moldings, comprising a housing with an opening, optionally closable, means suitable to generate a bead jet or/and means suitable to generate an air jet, or/and a container for receiving beads, means for recycling beads, optionally a depositing means, which is preferably movable in its X, Y, Z axis or/and is pivotable, or/and wherein the depositing means has a depositing surface for the 3D molding or/and the depositing surface has a fixing means for the 3D molding. 
     In another aspect, the disclosure relates to a 3D printing apparatus comprising a cleaning station as described above and other components common in 3D printing. 
     With the cleaning station according to the invention and the 3D printing apparatus, a particularly advantageous solution has been provided to solve the problem underlying the application. 
     Surprisingly, using the above apparatus components in the combination shown, very advantageous time and cost savings were achieved. 
     Furthermore, with the apparatus according to the invention, the above-described problems or disadvantages are at least reduced or avoided completely. 
     The cleaning station described herein may further include or comprise means for recycling beads, wherein the means for recycling may be a tube chain conveyor. 
     The cleaning station as disclosed herein uses beads which, by means of a bead jet, partially or substantially completely free the 3D molding from non-solidified particulate material and thus clean it; the beads of the bead jet or in the container in the cleaning station consist of or comprise zeolites, orange gel, silica gel, one or more clay minerals, one or more diatomites or/and one or more sepiolites. 
     In another aspect, the disclosure relates to a cleaning station as described herein, wherein the beads are cleaned by means of a cleaning means, the cleaning means preferably being disposed inside or outside the cleaning station. For example, the cleaning means may be located outside of and above or below the cleaning station and it may include, for example, a contaminant separation means. 
     In another aspect, the disclosure relates to a 3D printing apparatus coupled to the cleaning station described above. Such 3D printing apparatuses are known to the skilled person and therefore need not be described in further detail here. Well-known manufacturers of such systems include 3D-Systems Inc, voxeljet AG or Stratasys. The 3D printing apparatus is coupled to the cleaning station via a robot with gripping means or/and swiveling means such as a swiveling gripper arm or with other suitable conveying means. It is thus possible to achieve semi-automation or automation of 3D molding production using known 3D printing processes, such as powder-based 3D printing processes with selective binder impression or laser sintering or high-speed sintering, etc., and of the cleaning of the parts and, if necessary, of the further processing of the 3D moldings. As a result, very advantageous time benefits, cost benefits and work quality benefits can be achieved for the operating personnel. 
     In another aspect, the disclosure relates to a method of manufacturing 3D moldings using any known 3D printing machine and 3D printing method that can be used according to the disclosure coupled with a cleaning station as described herein. In a further aspect of such a method, there can also be further coupling after the cleaning station via conveying means to further processing stations and process steps, and thus further semi-automation or automation can be achieved. 
     A method according to the disclosure for cleaning 3D moldings comprises the following steps: a 3D molding is introduced into the cleaning station, preferably the cleaning station is substantially closed and the 3D molding is exposed to beads or a bead jet, the 3D molding being optionally exposed to an air jet in a further step. 
     In such a method, the 3D molding can be exposed to the beads from one side or from multiple sides. It is also possible to move the 3D molding in a jet of beads, or the beads circulate in a container and flow around the 3D molding and/or through the cavities of the 3D molding. For example, in one step the 3D molding can be exposed to a bead jet or a horizontal bead shower or can be introduced into a container with beads, the beads preferably being introduced into the container only after the 3D molding has been introduced, preferably wherein the container can be pivoted or/and moved in the X, Y or/and Z direction. Furthermore, the container itself may also have means suitable to achieve a movement of the beads and thus to cause or promote a movement through cavities of the 3D molding. 
     In another aspect, the 3D molding is moved in the X, Y, and/or Z directions while exposed to the bead jet or while in the container with the beads. 
     It can be advantageous if the beads of the bead jet are recycled in a circuit, preferably by means of tube chain conveyors, preferably returned to a bead storage container, the bead storage container being positioned in the vicinity of the cleaning station or, for example, being positioned at the top of the cleaning station, or/and a bead collection tray being fitted at the bottom of the cleaning station, which tray returns the beads to the bead storage container after irradiation of the 3D molding. 
     In a further process step, the 3D molding can be exposed to an air jet, preferably by means of air nozzles, the air nozzles and/or the air jet being adjustable in their jet directions. Furthermore, one or more air nozzles may be attached to or constitute an air nozzle holder, and this air nozzle holder may itself also be movable or/and pivotable in various directions. 
     In the method according to the disclosure, the bead jet may be combined with an air jet. 
     The 3D molding can be introduced into the cleaning station by gripping means or manually, preferably wherein the gripping means is a robotic device that is controllable three-dimensionally or another suitable conveying means that can effect the transfer of the 3D molding produced by the 3D printing process from the printing apparatus to the cleaning station. 
     A method as described herein, wherein the 3D molding is removed directly from the 3D printing apparatus by gripping means and is introduced into the cleaning station by gripping means, preferably wherein the 3D molding is positioned in a holding frame. 
     Furthermore, the 3D molding can be held on the gripping means in the cleaning station or positioned on a depositing means. 
     In the disclosed method, the 3D molding can be positioned on a depositing means and fixed thereon, wherein the depositing means can be moved or/and pivoted in its X, Y, Z axis or/and has a depositing surface for the 3D molding or/and the depositing surface has a fixing means for the 3D molding. The cleaning station can also simply have a depositing surface for the 3D molding, which may optionally have holding means for the 3D molding. 
     LIST OF REFERENCE NUMERALS 
     
         
         
           
               1  automatic vertical platform guidance 
               2  core support (support) for 3D molding (molding) 
               3  automatic bead circulation, e.g. with tube chain conveyor 
               4  adjustable and/or swiveling air nozzles 
               5  cabinet opening with closing means (door(s) or curtain or row of brushes) 
               6  container with beads in which the 3D molding can be immersed 
               7  handling robot with swivel arm and gripping device or holder for 3D molding 
               8  beads, e.g. silicate beads 
               9  3D molding (part) 
               10  core cleaning station