Patent Publication Number: US-2021178666-A1

Title: Build material compaction

Description:
BACKGROUND 
     Additive manufacture systems, more commonly known as three-dimensional (3D) printing systems, may generate 3D objects by selective solidification of portions of successive layers of a build material formed on a movable build platform. Some such systems may use a powdered, or powder-like, build material comprising, for example, granular particles. Such a build material may include, for example, build materials formed from of any suitable plastic, ceramic, or metal material. 
    
    
     
       BRIEF DESCRIPTION 
       Examples will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are side views of a simplified build material supply module according to one example; 
         FIG. 2  is a block diagram illustrating a supply module controller according to one example; 
         FIG. 3  is a flow diagram outlining operation of a build material supply module according to one example; 
         FIG. 4  is a flow diagram outlining operation of the build material supply module according to one example; 
         FIG. 5  is a block diagram showing a side view of a simplified three-dimensional printing system according to one example; 
         FIG. 6  is a block diagram illustrating a 3D printing system controller according to one example; 
         FIG. 7  is a flow diagram outlining operation of a three-dimensional printing system according to one example; 
         FIG. 8  is a side view of a simplified build material supply module according to one example; and 
         FIG. 9  is a flow diagram outlining operation of a build material supply module according to one example. 
     
    
    
     DETAILED DESCRIPTION 
     A key process of powder-based 3D printing systems is the formation of a uniform thickness layer of build material on a build platform, or on a previously formed layer of build material. Having a uniform thickness layer enables high quality 3D objects to be generated. 
     The formation of a layer of build material often involves a build material supply module to provide a predetermined volume of build material on a supply platform to one side of the build platform. A recoater mechanism, such as a roller or a wiper blade, may then spread the provided volume of build material over the build platform to form the layer of build material. 
     To ensure formation of build material layers having a uniform thickness, the mechanism which supplies the predetermined volume of build material has to accurately, and repeatedly, provide the predetermined volume of build material for spreading. 
     Referring now to  FIG. 1 , there is shown a side view of a simplified build material supply module  100  for supplying a predetermined volume of build material for spreading over a build platform. The supply module  100  comprises a set of walls  102  which may, for example, form an open cuboidal structure. Within the walls  102  is positioned a supply platform  104  that has cross-section to fit within the walls  102  and may comprise sealing elements to effectively seal the build platform against the walls  102 . The supply platform  104  is movable vertically within the walls, for example through a drive mechanism  106  such as a piston, a rack and pinion configuration, a screw thread, or the like. The drive mechanism  106  may be moved, for example, using a supply platform drive module  112 . The supply platform  104  and walls  102  form an open-topped variable volume build material supply chamber  108 . As shown in  FIG. 1A , the supply chamber  108  may be filled with a build material  110  to height H 1  as measured from the top of the supply platform  104 . A controller  110  may, for example, by controlling the supply platform drive module  112 , cause the supply plafform  104  to move up or down within the supply chamber  108 . In one example, the controller may cause the supply platform  104  to move up and/or down at different speeds, as will be described below. 
     Referring now to  FIG. 2 , there is shown a block diagram illustrating the controller  110  in more detail. The controller  110  comprises a processor  202  such as a microprocessor, microcontroller, or the like. The processor  202  is coupled to memory  204 , for example via a communication bus (not shown). The memory  204  stores instructions  206  to move the supply plafform  104  to compact build material in the supply chamber  108 . The instructions  206  are machine readable instructions that, when executed by the processor  202 , cause the controller  110  to move the supply platform  104  to compact build material present in the supply chamber  108 . 
     Operation of the system  100  is described now with further reference to the flow diagram of  FIG. 3 . 
     Initially, build material  110  is received in the supply module  100  in any suitable manner. For example, the build material  110  may be poured into the supply module  110  by a user from a box or other container containing the build material  110 . In another example, the build material  110  may be supplied to the supply module  110  by a build material management system (not shown). 
     The act of filling the supply module  100  with build material  110  may cause build material particles to mix with air as the build material is being introduced into the supply module  100 . As a result, the build material  110  may, upon filling, have a first density or compaction level. If left for a sufficient period of time, for example, the build material particles may (depending on the build material characteristics) naturally compact under gravity to a have a second density or compaction level higher than the first density or compaction level. If build material from the supply module  100  is used to form layers of build material for processing by a 3D printing system before the density or level of compaction has stabilized, over the course of a 3D printing print job (which may last for several hours), the density or compaction level of build material used to form the layers may change over time. This may lead to layers of build material used in a 3D print job being formed from build material have different densities or compactions levels, which may in turn lead to generated 3D objects having non-intended properties. 
     At block  302 , the controller  110  controls the supply plafform  104  to move within the supply module  100  in a predetermined manner to cause compaction of the build material  110 . In one example, the controller  110  causes the supply plafform to move up by a first distance, and then down by the first distance over a predetermined number of compaction cycles. For example, the first distance may be a distance in the range of about 10 to 20 mm, or about 10 to 30 mm, or about 10 to 40 mm, or about 5 to 10 mm, or about 5 to 20 mm, or about 5 to 30 mm. In other examples the first distance may be in a lower range, or a higher range. In another example, the first distance may be in a range having a lower end between about 2 to 10 mm, or a having a higher end between about 20 to 50 mm. In one example, the amplitude of supply plafform movement may be asymmetrical, or aperiodic, such that different ones of the up and down movements of the supply platform move the supply platform by a different distance. 
     In one example, the speed at which the supply platform  104  is moved by the first distance may be higher than a speed at which the supply platform  104  is moved when supplying a predetermined volume of build material for spreading. For example, the supply platform  104  may be moved at a speed of about 10 cm/s, or about 5 cm/s, or about 15 cm/s. In other examples, the supply plafform  104  may be moved at other speeds. 
     In one example, the number of repeated raising and lowering cycles of the supply plafform may be about 5 cycles, about 10 cycles, about 15 cycles, about 20 cycles, about 25 cycles, about 30 cycles, about 40 cycles, about 50 cycles, or any other suitable number of cycles. 
     In one example, during the compaction cycles, the upper level of the build material within the supply module  100  is not moved above the upper level of the supply module  100  such that the build material  100  is contained completely within the supply module  100  during compaction. This may help prevent build material from becoming airborne during the compaction process. 
     In one example, moving of the supply platform in the manner described above may impart small shocks or impacts to build material within the supply module  100 , which in turn causes the build material  110  to compact, as illustrated in  FIG. 1B . As shown in  FIG. 1B , the build material  110  has a height of H 2 , which is less than the original height H 1 . 
     Depending on the height of the supply module  100 , the amount of build material therein, and the method used to supply material to the supply module  100 , the build material  100  may compact, for example, by between about 5 to 10% of its original height H 1 . In other examples the build material  100  may compact by a greater or a lesser amount. 
     In one example, the number and nature of the compaction cycles may be predetermined based on the type of build material  110  being used. For example, through experimentation it may be determined that a given type of plastic build material should undergo  30  compaction cycles of an amplitude and a particular speed, whereas a different kind of build material should undergo  20  compaction cycles. 
     After completion of the compaction cycles, the controller  110  may control the supply platform  104  to raise the supply platform to supply compacted build material for spreading over a build platform. This is illustrated at block  402  in  FIG. 4 . For example, the controller  110  may raise the supply platform  104  such that a predetermined height of compacted build material  110  is positioned above the upper level of the supply module such that this build material may be used to form a layer of build material on a build platform. 
     In one example, the supply platform  104  may be raised manually by a user, for example through a user interface provided on a 3D printing system, until the top surface of the compacted build material  110  is positioned at the top of the supply module  100 . In another example, the supply platform  104  may be raised until a build material height detector indicates that the top surface of the compacted build material  110  is positioned at the top of the supply module  100 . In a further example, supply platform  104  may be progressively raised, and a layering module may operate to form layers of build material on a build plafform until a layer forming detection module (not shown) detects that a complete and acceptable layer of build material has been formed on the build platform. This may use, for example, a vision system or one or multiple height sensors. In yet another example, the supply platform  104  may be progressively raised, and a layering module may operate to form layers of build material on a build plafform until it is detected that excess build material remaining after a layer forming process is received in an excess build material overflow receiver. 
     In one example, the speed at which the supply platform  104  is raised to supply build material for spreading is lower than the speed at which the supply plafform  104  is moved to compact build material. For example, moving the supply plafform  104  at a slower speed when supplying build material  110  for spreading enables the supply plafform  104  to be moved more precisely, and thus enables a more accurate volume of build material to be provided. 
     Referring now to  FIG. 5 , which shows a side view of a simplified three-dimensional printing system  500 , according to one example. The 3D printing system  500  incorporates the supply module  100  as described above. 
     The supply module  100  is positioned within the 3D printing system  500  adjacent to a build chamber  502 , or adjacent to a build chamber receiving interface (not shown). The build chamber  502  is formed from a set of walls  502  which may, for example, form an open cuboidal structure. Within the walls  502  is positioned a build platform  506  that has cross-section to fit within the walls  502  and may comprise sealing elements to effectively seal the build plafform against the walls  502 . The build platform  506  is movable vertically within the walls, for example through a drive mechanism  508  such as a piston, a rack and pinion configuration, a screw thread, or the like. The drive mechanism  508  may be moved, for example, using a supply platform drive module  510 . The build plafform  506  and walls  504  form an open-topped variable volume build chamber. 
     In one example the build chamber  502  may be part of a removably installable build unit that may be present in the 3D printing system  500  during a printing operation and that may be removed after completion of a printing operation. In one example the supply module  100  and build chamber  502  may be part of a removably installable module that may be present in the 3D printing system  500  during a printing operation and that may be removed after completion of a printing operation. The may allow, for example, non-solidified build material in the build chamber  502  to be removed by a build material management station (not shown) and further allowing 3D printed objects to be removed. This may further allow the supply chamber  100  to be refilled with build material ready for use in a further 3D printing operation. 
     The supply module  100  may, as previously described, operate to initially compact build material  110  therein, and may then raise a portion of the build material  110  a predetermined height above the upper level of the supply module  100  to provide a volume of build material for spreading over the build plafform  506 . In the example shown, a layer module  512 , such as a roller or wiper blade, is provided on a movable carriage (not shown) such that the layering module  512  may be translated over the supply module  110  to spread a volume of build material over the build platform  506 , or over a previously formed layer of build material. The layering module  512  may be controlled using a layering module drive module  514 . 
     A selective solidification module  516  may then process the formed layer of build material to selectively solidify a portion or portions of the formed layer, for example based on a 3D object model of an object to be generated. In one example, the selectively solidification module comprises a laser, to directly melt or sinter portions of each formed layer of build material. Such a system may be referred to as a selective laser sintering (SLS) system. 
     In another example, the selective solidification module  516  may comprise a printhead to selectively apply a binding agent to portions of each formed layer of build material. The selective solidification module  516  may additionally comprise an energy source, such as an ultra-violet or infra-red energy source, to cause the applied binding agent to cure, thereby solidifying a portion of the build material. Such a system may be referred to as a binder jet system. 
     In another example, the selective solidification module  516  may comprise a printhead to selectively deliver an energy absorbing fusing agent onto portions of each formed layer of build material. The selective solidification module  516  may additionally comprise an energy source, such as an infra-red energy source, to generally apply energy to the whole of each formed layer of build material. Those portions of the build material on which fusing agent was applied heat up and up melt, sinter, or otherwise coalesce, whereas portions of the build material on which no fusing agent was applied will heat up sufficiently to melt, and therefore remove non-solidified. Such a system may be referred to a fusing agent and fusing energy system. 
     After each layer of formed build material is processed by the selective solidification module  516 , the build platform is lowered by a predetermined amount, and the supply platform  104  is raised by a predetermined amount. A 3D dimensional object  518  may thus be formed within the build chamber on a layer-by-layer basis 
     The overall operation of the 3D printing system  500  is controlled by a controller  520 , further details of which are shown in  FIG. 6 . The controller  520  comprises a processor  602  such as a microprocessor, microcontroller, or the like. The processor  602  is coupled to memory  604 , for example via a communication bus (not shown). The memory  604  stores instructions  606  to control the supply platform  104  to initially compact build material in the supply chamber  108  and to subsequently provide build material for spreading over the build platform  506 . The memory  604  also stores instructions  608  to control the layer module  512  to form successive layers of build material on the build plafform  506  by spreading build material provided by the supply module  100 . The memory  604  also stores instructions  610  to control the selective solidification module  516  to selectively solidify build material of each formed layer of build material. The memory  604  also stores instructions  612  to control the build platform  506  to lower after each formed layer of build material has been processed by the selective solidification module  516 . 
     These instructions are machine readable instructions that, when executed by the processor  202 , cause the controller  520  to control the 3D printing system  500  in accordance with the flow diagram shown in  FIG. 7 . 
     Operation of the system  500  is described now with further reference to the flow diagram of  FIG. 7 . 
     At block  702 , the controller  520  moves the supply platform  104  to move, for example, to raise and lower, in a manner as described herein, to compact build material that has been provided in the supply module  100 . 
     At block  704 , the controller  520  controls the supply plafform  104  to raise to provide a predetermined volume of compacted build material above the upper surface of the supply module  100 . 
     At block  706 , the controller  520  controls the layering module  512  to spread the build material provided by the supply module  100  over the build plafform  506 , or over a previously formed layer of build material. 
     At block  708 , the controller  520  controls the selective solidification module  516  to selectively solidify, for example based on a 3D object model, portions of the formed layer of build material. 
     Blocks  704 ,  706 , and  708 , may be repeatedly performed by the controller  520  to generate a 3D object in the build chamber  502  on a layer-by-layer basis. 
     A further example of a supply module is shown in  FIG. 8 . The supply module  800  is similar to the supply module  100  of  FIG. 1 , but additionally comprises a build material height sensor  802 . The sensor  802  measures, or detects, the top surface of build material  110  within the build module  800 . For example, the sensor  802  may be a light sensor that transmits a light beam to the top surface of build material  110  and receives a reflected light beam. In another example, the sensor  802  may be an ultrasonic height detector, or any other suitable kind of sensor. A controller  804 , similar to controller  110  comprises machine readable instructions to control the supply platform  104  to compact the build material  110  until the sensor  802  indicates that the build material is compacted. Operation of the build module  800  is described below, with additional reference to the flow diagram of  FIG. 9 . 
     At block  902 , the controller  804  measures, or detects, the height of the top surface of build material  110  provided in the supply module  800 . 
     At  904 , the controller  804  moves the supply platform  104  up and down, for example as described above, for example for a predetermined number of compaction cycles. 
     At  906 , the controller  804  again measures, or detects, the height of the top surface of build material  110  in the supply module  800 . 
     At  908 , the controller  804  determines, based on the measure height, whether the build material  110  in the supply module has been compacted sufficiently. In one example, the controller  804  may determine that the build material  110  has been sufficiently compacted when the height of the build material  110  in the supply chamber has changed by a predetermined amount, for example, when the height of the powder has changed by 5%, 10%, 15%, or any other suitable amount. In another example, the controller  804  may determine that the build material  110  has been sufficiently compacted when the height of the build material  110  remains constant between compaction cycles. changed. If the controller  804  determines that the build material  110  has not compacted sufficient it performs another set of compaction cycles. If the controller  804  determines that the build material has sufficiently compacted this indicates that the build material  110  has compacted. 
     It should be noted, however, that a sufficient level of compaction may not be a maximum amount of compression attainable by the build material  110 , but rather may be an acceptable amount of compression achievable through the performance of one or multiple compaction cycles. 
     The controller  804  may then supply a volume of compacted build material for spreading over a build platform. 
     The supply module  800  may be incorporated into a 3D printing system, such as the 3D printing system shown in  FIG. 5 . 
     It will be appreciated that example described herein can be realized in the form of hardware, software or a combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape. It will be appreciated that the storage devices and storage media are examples of machine-readable storage that are suitable for storing a program or programs that, when executed, implement examples described herein. Accordingly, some examples provide a program comprising code for implementing a system or method as claimed in any preceding claim and a machine-readable storage storing such a program. 
     All the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.