Method for 3D printing a structure, 3D structure printing system and printing unit for use in a 3D structure printing system

Abstract

A method for 3D printing a structure using a printing unit 2 with a hopper 21 and a printing head 22 is disclosed. The method includes obtaining a precursor printing material including a binder, water, and sand, forming a flow of the precursor printing material toward the printing unit 2 through a material inlet pipe 23 using a material pump 61, adding a quantity of a first additive to the precursor printing material via an additive tube 9 downstream of the material pump 61 and upstream of the hopper 21, and optionally adding one or more additional additives, mixing the precursor printing material, the first additive, and the optional one or more additional additives to form a printing material, and extruding the printing material via a printing head 22. The present invention also relates to a 3D structure printing system 1 and a printing unit 2 with a hopper 21 and a printing head 22.

Description

[Technical field]

[0001] The present invention relates to a method for 3D printing a structure, a 3D structure printing system and a printing unit for use in a 3D structure printing system. [Background technology]

[0002] 3D printing of buildings and other structures using heterogeneous composite materials such as concrete as the printing material has been known for some time and is now moving to a more advanced stage of technological development, where the basic process has been improved.

[0003] It is well known that transporting a heterogeneous composite material such as concrete over long distances, for example by pumping it through pipes or tubes, can affect the quality of the material. This can result in, for example, segregation, where aggregates separate from the cement paste of the concrete or are unevenly distributed. Furthermore, a production stop can change the viscosity of the concrete waiting to be used.

[0004] Patent documents 1 and 2 each disclose a printing unit equipped with a sensor capable of transmitting information regarding the amount and condition of the printing material (concrete) in the hopper to a control unit, and an additive outlet capable of mixing water, superplasticizer, water-reducing agent and / or hardener.

[0005] This allows fine tuning of the print material, for example to correct if the print material is too hard or too soft.

[0006] However, ensuring effective mixing of the elements added to the hopper can be difficult. Ineffective mixing can lead to variations in the material properties of the printing material, which can result in defects and weaknesses in the printed structure. This problem is even more pronounced in 3D structure printing systems that do not have a hopper in the printing unit. Attempts have been made to correct for small variations in material properties by adding additives directly to the print head, but experiments have shown that proper mixing with the printing material is very difficult to achieve.

[0007] Additionally, transporting the printing material to the printing unit can be difficult, especially when constructing large structures such as multi-storage buildings.

[0008] Another problem that arises when constructing large structures is that the number of both planned and unplanned production outages is typically relatively high.

[0009] Dealing with a large 3D printing system filled with printing material during a production shutdown can be difficult - for example, it can become very problematic if the printing material starts to solidify inside the tubing and pumps used to transport the printing material to the print head. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 2019-0050509 [Patent Document 2] US Patent Application Publication No. 2021 / 146573 Summary of the Invention [Problem to be solved by the invention]

[0011] It is therefore an object of the present invention to provide an improved method and / or system for 3D printing structures. [Means for solving the problem]

[0012] According to a first aspect, the present disclosure relates to a method for 3D printing a structure using a printing unit comprising a hopper and a print head, the print head being disposed below the hopper in an operational state of the printing unit and configured to extrude a printing material through a nozzle opening. The method comprises: Obtaining a precursor printing material, the precursor printing material including a binder, water, and sand; forming a flow of precursor printing material toward the printing unit using a material pump; adding a quantity of a first additive to the precursor printing material downstream of the material pump; Optionally, adding one or more additional additives; mixing the precursor printing material, the first additive, and optionally one or more additional additives to form a printing material; and extruding the printing material through the print head. Here, a first additive is added to the precursor printing material before it reaches the hopper.

[0013] As a result, the printing material may be formed near or within the printing unit by mixing the precursor printing material and the first additive near or within the printing unit, which may further simplify the construction of larger structures.

[0014] As an example, the precursor printing material may have material properties that facilitate pumping and in some cases transport. Additionally, the precursor printing material may have material properties that facilitate cleaning of process equipment, including material pumps.

[0015] Another advantage of adding the first additive upstream of the hopper, i.e., before the precursor printing material flows into the hopper, is that the movement of the precursor printing material moving to the printing unit may contribute to the additive being at least partially mixed with the precursor printing material before it flows into the hopper.

[0016] Adding the first additive upstream of the hopper may allow further mixing of the additive depending on the amount of precursor printing material being fed to the printing unit. In this way, the material flowing into the hopper always has the same composition and there is no need to rely on an estimate of the amount of printing material present in the hopper to calculate the actual composition.

[0017] The combination of improved mixing and more precise control of the composition of the mixture has the advantage that the printing unit can not only correct unintended deviations from the intended properties of the printing material, but also actively modify the properties of the printing material for specific purposes. In particular, it is envisaged that a relatively soft precursor printing material is fed to the printing unit and the first additive is a viscosity modifier (VMA). That is, VMA can be added at the additive outlet to further harden the printing material. In 3D printing, a relatively hard material is generally required to create the desired shape, but it is difficult to move a hard material through pipes, making it difficult to feed the material to the print head. Also, as the size of the construction increases, this becomes a real problem. By using a more flexible material and hardening it in the printing unit, less and / or cheaper equipment may be required to move the printing material. Furthermore, a standard type of concrete that may be available, for example, from an external concrete manufacturer and / or used elsewhere on the construction site, may be used as the precursor printing material, thus eliminating the need for an on-site concrete manufacturing facility.

[0018] Although reference is made primarily to concrete as an example of a printing material, i.e., the binder is cement, it should be understood that the issues associated with printing with concrete may also apply to other types of printing materials that include binders, water and sand. Examples of alternative binders include clay, lime and polymers.

[0019] "Sand" means an inert granular material having a particle size less than 4 mm, and includes geological materials and recycled materials such as glass. The particle size may be obtained by grinding, and / or the material may be washed, sieved, or otherwise selected to achieve the desired particle size distribution.

[0020] In addition to sand, the precursor printing material may include other aggregates, including, for example, rocks of geological origin and recycled materials such as crushed concrete. It may further include fibers, such as steel or natural fibers, and / or additives, such as air entrainers or plasticizers.

[0021] The binder, water and sand can be mixed to form the precursor printing material on-site, such as, for example, at a construction site or a remote location.

[0022] It should be understood that the method can be used to construct building walls, but can also be used to produce other structures not traditionally thought of as buildings, such as building foundations, wind turbine bases, bridges, etc.

[0023] In some embodiments, at least a portion of the mixing is performed using rotating elements.

[0024] The rotating element can be located in the printing unit or any other unit of the system downstream of the material pump. Mixing immediately after adding the additives can result in a homogenous mixture.

[0025] The rotating element can be wholly or partially disposed within a hopper of the printing unit such that the printing material can be formed in the hopper by mixing the precursor printing material, the first additive, and optionally one or more additional additives.

[0026] As a result, finished print material can be delivered to only a small portion of the system, making it easier to handle both planned and unplanned production outages.

[0027] Additionally or alternatively, the placement of a rotating element within the hopper may help prevent degradation of the print material, for example by premature setting or separation.

[0028] A rotating element within the hopper may include a mixing arm and a motor that rotates the mixing arm within the hopper to assist in mixing the precursor printing material and the first additive, as well as any additional additives.

[0029] The rotating element can be configured to advance the printing material during printing, for example by using a rotating screw extending from a hopper into the print head, to create a continuous flow of printing material through the print head.

[0030] The printing unit may include multiple rotating elements, for example a rotating element with a mixing arm in a hopper and a rotating screw in a print head.

[0031] In some embodiments, the first additive is a viscosity modifier configured to increase the viscosity of the precursor printing material, a VMA, or an accelerator configured to promote setting and / or hardening of the printing material.

[0032] The use of a precursor printing material that has a lower viscosity than the printing material makes the printing material easier to pump, which allows for the use of simpler pumping equipment and / or the construction of larger structures. Additionally, the lower viscosity of the precursor printing material allows for easier cleaning of process equipment, including material pumps, and easier transportation in, for example, mixer trucks.

[0033] The precursor printing material may be purposely selected to have a viscosity that is too low for the precursor printing material to be used as a printing material.

[0034] Using a precursor printing material for the printing material that sets and / or hardens at a slower rate than desired reduces the risk of the material setting or hardening within the system, which can be particularly advantageous in the event of a production shutdown and can also facilitate easier cleaning.

[0035] Adding the first additive close to the printing unit may also have advantages in terms of additive consumption and may allow the use of additives that would not be suitable otherwise, such as accelerators that cause rapid setting and / or hardening.

[0036] If the two additive outlets are arranged at a distance from each other in the material conveying direction, the two additives can be added at different times, one before the other. This is advantageous, for example, if one additive has a higher viscosity than the other, or if one additive would interfere with the effect of the other if added together. In addition, it may be advantageous to provide three or more outlets. This may allow, for example, to use different outlets at different times for different additives, depending on the required printing material properties.

[0037] It is currently believed to be advantageous to add the accelerator as the first additive, followed by VMA in the form of a reinforcing agent.

[0038] In some embodiments, the volume per mille of the first additive in the printed material is at least 0.2‰, at least 0.5‰, or at least 1.2‰.

[0039] As a result, by adding the first additive, the properties of the printing material may be significantly different from the precursor printing material, for example, the viscosity of the printing material may be significantly higher than the viscosity of the precursor printing material.

[0040] The amount per mille by volume of the first additive in the printed material is given by the following formula:

number

[0041] In some embodiments, the volume per mille of the first additive in the printed material is less than 10‰, less than 5‰, or less than 2.5‰.

[0042] In some embodiments, a structure is constructed at a construction site, but the binder, water and sand are mixed at a location away from the construction site to form the precursor printing material and transported to the construction site by one or more delivery vehicles.

[0043] As a result, construction costs may be reduced because more processes may be performed off-site, for example in a central manufacturing facility dedicated to the production of precursor printing materials.

[0044] The transport vehicle may be any transport vehicle, such as a truck or a ship.

[0045] The additive or additives may be added using one or more additive pumps.

[0046] In some embodiments, the material pump generates a pulsating flow of the precursor printing material toward the hopper, and the first additive is added to the precursor printing material before it reaches the hopper.

[0047] When the material pump generates a pulsating flow of the precursor printing material, the additive pump can generate a pulsating flow of the first additive synchronized with the pulsating flow of the precursor printing material.

[0048] As a result, by synchronizing the material pump and the additive pump, efficient mixing of the precursor printing material and the first additive can be achieved even in a hopper where the printing material flows continuously toward the print head, i.e., where the material is continuously consumed.

[0049] The material pump that delivers the precursor printing material may be any pump configured to generate a pulsating flow. As an example, the material pump may be a piston pump.

[0050] The material pump and the additive pump can be synchronized so that the ratio of the volumetric flow rates of the two pumps at any given time is substantially constant.

[0051] According to a second aspect, the present disclosure relates to a 3D construction printing system configured to print using a printing material. The 3D construction printing system comprises a printing unit, a gantry system, a material pump, flexible tubing, and an additive system. The printing unit comprises a hopper, a print head, and a rotating element. The additive system comprises a control mechanism, an additive outlet, and a control unit. wherein the gantry system is configured to move the printing units in three-dimensional space; the material pump is configured to receive a precursor printing material including a binder, water, and sand, and to pump the precursor printing material through the flexible tube toward the printing units to form a flow of the precursor printing material in a material transport direction; the hopper is disposed downstream of the material pump and upstream of the print head in a material conveying direction; a control unit operably connected to the control mechanism of the additive system for controlling the amount of additive added to the precursor printing material; An additive outlet of the additive system is positioned upstream of the hopper in the material conveying direction and provides a fluid connection between the control mechanism and the flow of precursor printing material downstream of the material pump, and the control unit is configured to control the control mechanism to form a flow of a first additive in the flow of precursor printing material, thereby forming a flow of printing material that is extruded through the nozzle opening of the print head.

[0052] By mixing the precursor printing material with a first additive near or within the printing unit, it may be easier to build larger structures, as described above with reference to the first aspect of the invention. To avoid excessive repetition, some embodiments and advantages of the invention are described with reference to only one aspect of the invention. It is understood that such embodiments and advantages also apply to other aspects.

[0053] In some embodiments, the hopper has a rotating element configured to advance the printing material and generate a continuous flow of printing material toward the print head during printing.

[0054] The control mechanism for the additive system may be a control valve and / or an additive pump, for example a high precision pump capable of precisely dosing the first additive.

[0055] In some embodiments, an additive outlet for additional additives is located within the printing unit.

[0056] In some embodiments, the system includes an additive container having an outlet fluidly connected to a control mechanism of the additive system, the additive container containing a quantity of a first additive.

[0057] In some embodiments, the additive container is a replaceable container, eg, a container that can be replaced with a new additive container when it is exhausted.

[0058] In some embodiments, the additive container is a single-use, disposable container.

[0059] In some embodiments, the additive container contains at least 0.25 liters of the first additive, at least 0.5 liters of the first additive, or at least 2 liters of the first additive when full.

[0060] In some embodiments, the control unit of the additive system is configured to control the control mechanism to add a certain amount of additive to the stream of precursor printing material such that the first additive is present in the printing material at a volumetric concentration of at least 0.2‰, at least 0.5‰, or at least 1.2‰ per mille.

[0061] In some embodiments, the control unit of the additive system is configured to control the control mechanism to add a certain amount of additive to the stream of precursor printing material such that the first additive has a volumetric percentage per mille in the printing material of less than 10‰, less than 5‰, or less than 2.5‰.

[0062] In some embodiments, the system further comprises at least one additive pump for supplying the additive.

[0063] In some embodiments, the material pump is configured to generate a pulsating flow of the precursor printing material toward the hopper, and the additive system is configured to add the first additive to the precursor printing material before the precursor printing material reaches the hopper, optionally via the additive pump configured to generate a pulsating flow of the first additive synchronized with the pulsating flow of the precursor printing material.

[0064] As a result, by synchronizing the material pump and the additive pump, effective mixing of the precursor printing material and the first additive can be achieved in the hopper even when there is a continuous flow of printing material toward the print head.

[0065] The material pump that delivers the precursor printing material may be any pump configured to generate a pulsating flow. As an example, the material pump may be a piston pump.

[0066] The material pump and additive pump can be synchronized so that the ratio of the volumetric flow rates of the two pumps at any given time is substantially constant.

[0067] The system can be configured to mix the precursor printing material and the first additive in a hopper, where the hopper is provided with a rotating element including a motor and a mixing arm to assist in mixing the precursor printing material and the first additive.

[0068] In one embodiment, the additive system includes an adapter disposed on the extension of the flexible tubing between the material pump and the hopper such that the flow of precursor printing material passes through the adapter, where the adapter is provided with at least one additive outlet, which may allow for adaptation of an existing 3D building printing system without the additive system or for adapting the 3D building printing system to a different application.

[0069] The adapter may include one or more side branches, such as pipe stubs extending from a main portion of the adapter, configured to connect to an additive storage unit or to receive an additive tube having an additive outlet.

[0070] In one embodiment, at least one additive tube having an additive outlet extends into the adapter such that the additive outlet is positioned at a centerline of the adapter, the centerline extending parallel to the material transport direction, which may contribute to achieving a well-mixed printed material, as described in more detail below.

[0071] In one embodiment, the additive reservoir is located above the additive outlet in use and is provided with a valve or additive pump to control the amount of additive added.

[0072] In one embodiment, the material inlet valve is positioned upstream of the additive outlet in the material conveying direction.

[0073] According to a third aspect, the present disclosure relates to a printing unit for use in a 3D structure printing system and configured to print using a printing material comprising a precursor printing material and a first additive. The precursor printing material comprises a binder, water and sand. The printing unit includes a material inlet, a hopper configured to accommodate a quantity of the printing material, a print head configured to extrude the printing material, the print head being disposed downstream of the hopper in a material conveying direction, a rotating element configured to move the printing material from the hopper to the print head in the material conveying direction, and an additive outlet, the additive outlet being positioned upstream of the hopper in the material conveying direction.

[0074] Providing an additive outlet upstream of the hopper means that the additives can be mixed depending on the amount of precursor printing material being fed to the printing units. In this way, the material flowing into the hopper can have a constant composition and there is no need to rely on estimates of the amount of printing material present in the hopper to calculate the actual composition.

[0075] By providing an additive outlet upstream of the material hopper, i.e., before the precursor printing material flows into the hopper, movement of the precursor printing material moving toward the material inlet can contribute to the additive being at least partially mixed with the precursor printing material before it flows into the hopper.

[0076] Particularly in large printing units designed to receive and extrude large volumes of printing material per unit of time, it may be advantageous for the printing unit to further comprise a rotating element disposed within the hopper.

[0077] In one embodiment, the material inlet comprises at least one inlet pipe protruding from the body of the hopper, the material inlet pipe being provided with an additive outlet.

[0078] If the material inlet is provided with multiple additive outlets, the additive outlets may be spaced apart from one another in the material conveying direction, and different additives may be added at different times as described above. Approximately the same effect may be achieved by adding a first additive in or at the inlet pipe and another additive directly in the hopper.

[0079] In one embodiment, the additive outlet is provided on the side of the material inlet pipe that faces upwards in use of the printing unit, in this way gravity can assist in mixing the additive, which may also be applied to the adapters mentioned above.

[0080] Additional or alternative methods of facilitating mixing include forming an additive outlet in the additive tube and having the additive tube protrude into the material inlet pipe.

[0081] As a result, the additive may be added to the center portion of the precursor printing material stream, which may result in faster and more efficient mixing of the additive with the precursor printing material.

[0082] The additive outlet is located at the centerline of the material inlet pipe, the centerline extending parallel to the material conveying direction. This may be achieved by having at least a distal portion of the additive tube have an additive outlet extending substantially parallel to the centerline of the material inlet pipe. Experiments have shown that when pumping concrete, there may be a high concentration of aggregate at the centerline of the pipe conveying the concrete. Locating the additive outlet at the centerline may help reduce this effect, thereby contributing to achieving a well-mixed printed material.

[0083] Additionally, it may be advantageous to position the additive outlet between the centerline and the inside of the material inlet pipe, for example halfway between the centerline and the inside of the material inlet pipe, to reduce resistance to the flow of material in the material inlet pipe and / or to reduce the risk of clogging the material inlet pipe. This also applies to the adapter.

[0084] Which embodiment and location of the additive outlet is better will depend on factors such as the diameter of the material inlet pipe, the viscosity of the additive, the viscosity of the precursor printing material, whether the additive is water soluble, etc., and can be determined by experimentation.

[0085] In one embodiment, the printing unit further comprises an additive storage unit connected to the additive outlet. The additive reservoir may be arranged above the additive outlet in the use state of the printing unit, so that the additive is fed under the influence of gravity, in which case a valve may be provided to make it possible to control the amount of additive added. Alternatively, an additive pump may be provided to pump the additive to the additive outlet.

[0086] In one embodiment, the printing unit further comprises a material inlet valve positioned upstream of the additive outlet in the material transport direction. This allows precise control of the amount of precursor printing material flowing from the material inlet, so that even the first precursor printing material flowing into the print head at the start of the printing process or after a production stop has an intended and well-defined composition. Furthermore, the valve allows for quick and precise shut-off of the supply of precursor printing material in case of a production stop and at the end of the printing process, thereby reducing waste of precursor printing material and / or cleaning the hopper and rotating elements (if present).

[0087] The various aspects of the present invention can be implemented in various ways, such as the method for 3D printing a structure, the 3D structure printing system and the printing unit for use in the 3D structure printing system described above and below, each providing one or more of the benefits and advantages described in relation to at least one of the aspects described above, and each comprising one or more preferred embodiments corresponding to the preferred embodiments described in relation to at least one of the aspects described above and / or the preferred embodiments disclosed in the dependent claims. Furthermore, it will be understood that an embodiment described in relation to one of the aspects described herein may be equally applicable to the other aspects. [Brief description of the drawings]

[0088] In the following description, embodiments of the present invention are explained with reference to schematic diagrams. [Figure 1] FIG. 1 is a flow chart illustrating an embodiment of a method for 3D printing a structure. [Diagram 2] FIG. 2 is a schematic perspective view of one embodiment of a 3D structure printing system. [Diagram 3] FIG. 3 is a schematic cross-sectional view of a first embodiment of a printing unit. [Figure 4] FIG. 4 is a schematic cross-sectional view of a second embodiment of a printing unit. [Diagram 5] FIG. 5 is a schematic cross-sectional view of a third embodiment of a printing unit. [Figure 6] FIG. 6 is a schematic cross-sectional view of a fourth embodiment of a printing unit. [Figure 7] FIG. 7 is a schematic cross-sectional view of a fifth embodiment of a printing unit. [Figure 8] FIG. 8 is a schematic cross-sectional view of a sixth embodiment of a printing unit. [Figure 9] FIG. 9 is an exploded perspective view of parts of a seventh embodiment of a printing unit. [Figure 10] FIG. 10 is an exploded view of the additive tube. [Figure 11] FIG. 11 is a perspective view of the additive tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0089] Referring first to FIG. 1, a flow diagram of one embodiment of a method for 3D printing a structure is shown.

[0090] In step I) a precursor printing material is obtained. The precursor printing material is produced in an on-site mixing unit or is supplied from an external manufacturing site. The precursor printing material may be, for example, concrete or another heterogeneous composite material comprising a binder, water and sand.

[0091] In step II) a material pump is used to create a flow of precursor printing material towards the printing unit. The flow can be continuous or pulsating, for example when using a piston pump, but the flow rate needs to be well defined and accurately controlled.

[0092] In step III) a constant amount of a first additive is added to the precursor printing material. The mixing of the additive occurs downstream of the material pump in the material conveying direction and upstream of the hopper of the printing unit, i.e. between the material pump and the printing unit. The first additive may be added using an additive pump, which may be synchronized with the material pump used to form the flow of the precursor printing material so that the ratio of the volumetric flow rates of the material pump and the additive pump at any point in time is substantially constant. In other words, the amount of additive to a given amount of precursor printing material is always the same, as required.

[0093] Step IV) is optional and consists of mixing one or more additional additives. One example of such an additive is an air entrainment agent.

[0094] In step V), the precursor printing material is mixed with the additives added in steps III) and IV) to form the printing material, at least a portion of the mixing being performed using a rotating element disposed within the printing unit, for example, a rotating element disposed within a hopper.

[0095] In step VI), the printing material is extruded through a print head that includes a nozzle that imparts the desired shape to the extruded material, the speed of extrusion being controlled by the action of a rotating element.

[0096] Referring now to FIG. 2, a 3D building printing system 1 is shown. The system comprises a printing unit 2 mounted on a gantry system 3 configured to move the printing unit in a three-dimensional space defined by the X-axis, the Y-axis and the Z-axis. The printing unit 2 is mounted for movement along a first cross beam 31 in a horizontal direction along the X-axis, the first cross beam is mounted for movement along a set of second cross beams 32 in a horizontal direction along the Y-axis, and the second set of cross beams is mounted for movement along four vertical columns 33 in a vertical direction along the Z-axis. Thus, the position and length of the four vertical columns 33 limits the space in which the printing unit 2 can move. The movement of the beams 31, 32 is realized here using motors integrated into the mounting blocks 310, 320, and the printing unit 2 moves by a chain drive (not shown) driven by a motor integrated into the mounting block of the first cross beam 310.

[0097] Each of the four vertical columns 33 of the gantry system 3 rests on a foundation 34 provided on a surface 4 on which the structure will be printed, printing a first wall 5 of the building. The surface 4 can be, for example, the ground, a foundation or the top surface of an existing structure.

[0098] Next to the gantry system 3 a precursor printing material supply facility 6 is shown, with a piping system 7 connecting the precursor printing material supply facility to the printing units 2 and acting as a precursor printing material supply line.

[0099] The precursor printing material supply facility 6 may comprise a rotating element and / or a buffer unit for receiving precursor printing material produced elsewhere. The precursor printing material may be, for example, concrete and may be produced in the precursor printing material supply facility or may be supplied from an external production site. Additionally, material supplied from an external production site may be modified in the precursor printing material supply facility, for example by mixing with one or more additives, aggregates or fibers.

[0100] A material pump 61 is used to push precursor printing material from the precursor printing material supply facility 6 through the piping system 7 to the printing units. In the illustrated embodiment, the material pump is integrated into the precursor printing material supply facility 6, but could be a separate unit. It should be understood that in the same way, the material pump 61 could replace or supplement a material pump located within or on the gantry system 3, and that such a material pump could be a suction pump. It is currently considered advantageous to use a piston pump that is well suited to moving high viscosity materials. This is true regardless of how other parts of the 3D structure printing system are embodied.

[0101] The piping system 7 here consists of flexible tubes, which allows it to follow the movements of the gantry system 3 and the printing units and ensure a continuous and reliable supply of precursor printing material. The piping system may also include pipes.

[0102] One or more additive supply lines (not shown) may be integrated into the piping system 7 .

[0103] In the embodiment shown, the precursor printing material supply arrangement incorporates a control unit 8 for controlling the supply of precursor printing material to the printing unit 2. Alternatively, the control unit 8 could be located elsewhere, such as on or within the printing unit 2, or on the gantry system 3 or within the printing unit 2.

[0104] One embodiment of the printing unit 2 is shown in Figure 3. The printing unit 2 comprises a hopper 21 and a print head 22 which is arranged below the hopper in the use state of the printing unit. A material inlet pipe 23 extends from the side wall of the hopper 21 and a rotating element in the form of a rotating screw 24 extends from the hopper into the print head. Printing material (not shown) is fed into the hopper, the screw serving to convey the printing material into the print head. For this purpose, the hopper is arranged in front of the print head in the material transport direction T.

[0105] The screw 24 may also be used to agitate the printing material contained in the hopper, for example, to prevent the printing material contained in the hopper from hardening more quickly than usual during production stoppages.

[0106] The print head 22 comprises a nozzle 221 through which the printing material is extruded, and a barrel 222 configured to direct the printing material to the nozzle. Such print heads are well known to those skilled in the art and will not be described in further detail here.

[0107] An additive outlet in the form of an additive tube 9 projects into the material inlet pipe 23 so that additives such as viscosity modifiers can be added to the precursor printing material before it flows into the hopper 21. For this reason, it is sometimes thought that the upstream end of the material inlet pipe 23 as viewed from the material conveying direction T constitutes the precursor printing material inlet, and the downstream end of the material inlet pipe 23 constitutes the printing material outlet.

[0108] It should be understood that in this embodiment, the additive tube protrudes into the centerline C of the material inlet pipe, thereby causing the additive to be added to the center of the flow of precursor printing material, while in other embodiments the additive tube does not protrude as far into the material inlet pipe.

[0109] In the embodiment shown in Figure 3, both the material inlet pipe 23 and the additive tube 9 are provided with pinch valves 231, 91 which can be used to stop the flow of precursor printing material and additive respectively, allowing a fast and well-controlled stop of supply in the event of a production stoppage.

[0110] The precursor printing material flows into the hopper 21 through the material inlet pipe 23 and as the screw 24 rotates, the additives are mixed with the precursor printing material, thereby creating the printing material for use with the printhead.

[0111] Turning now to the second embodiment of the printing unit shown in Figure 4, the same reference numerals are used as in Figure 3 and only the differences between the two embodiments are described, and such reference numerals are used in the remaining figures for elements having substantially the same function.

[0112] In Figure 4, the additive tube 9 is disposed on the upwardly facing side of the material inlet pipe 23 in the in-use state of the printing unit 2 and is substantially vertical, whereas the additive tube 9 in Figure 3 extends substantially perpendicular to the centerline C of the material inlet pipe. This positioning of the additive tube 9 may facilitate the feeding of the additive through the additive tube by gravity. Additionally, the angle between the additive tube 9 and the material inlet pipe 23 may improve mixing of the additive with the precursor printing material.

[0113] It will be appreciated that although the additive tube 9 is shown here with straight ends, it may be angled so that one side of the pipe extends further into the material inlet pipe than the other, as shown in Figure 8. It will further be appreciated that the additive tube 9 need not protrude into the material inlet pipe, but rather an additive outlet (not shown) in the form of a simple opening in the material inlet pipe may be used in place of the additive tube 9.

[0114] Turning now to a third embodiment of a printing unit shown in Figure 5, the same reference numerals as in Figures 3 and 4 are used and only the differences between the embodiments will be described.

[0115] In this embodiment, the material inlet pipe 23 includes a curve and has a first portion 230 that extends from the side wall of the hopper 21, as well as a second portion 232 that extends upwardly substantially parallel to the side wall of the hopper 21. This causes the additive tube 9 to protrude into the material inlet pipe 23 at the curve and extend along the centerline C of the first portion 230 of the material inlet pipe 23. This means that the additive entering the material inlet pipe flows in the same direction as the precursor printing material, potentially facilitating mixing.

[0116] Referring now to a fourth embodiment of a printing unit shown in FIG. 6, the same reference numerals as in FIGS. 3 to 5 are used and only the differences between the embodiments are described.

[0117] In this embodiment, the hopper 21 is provided with a rotating element 25 including a motor 251 and two mixer arms 252 configured to rotate within the hopper and constituting a rotating element. The screw 24 is here relatively short and extends only into the barrel 222 of the print head 22. This embodiment is preferred here as the movement of the screw may not be sufficient to achieve sufficient mixing of the precursor printing material with the additives.

[0118] In the embodiment of Figures 3 to 6, the material inlet pipe 23 extends at an angle of about 30 degrees to the horizontal in the in-use state of the printing unit, although it should be understood that other angles are possible. An angle of 20 degrees to 50 degrees to the vertical in the in-use state of the printing unit is considered advantageous here, and an additional printing unit is shown in Figure 7 at an angle of 45 degrees. This embodiment further differs from the embodiment of Figure 6 in that it includes two additive tubes 9a, 9b mounted on an adapter 70 separate from the material inlet pipe 23. The material inlet pipe 23 of the hopper 21 is now provided with a connector 27, such as a thread, for interconnection with the adapter 70 or piping system 7.

[0119] In FIG. 7, each of the two additive tubes 9a, 9b extends in the material conveying direction T, substantially similar to FIG. 4, but also at an angle of 45 degrees to the center line C of the pipe unit, as described above.

[0120] Two separate additive tubes 9a, 9b spaced apart in the material conveying direction T allow one additive to be added before the other. This may be advantageous, for example, if one additive has a higher viscosity than the other, or if adding two additives together would cause one additive to interfere with the effect of the other. Although only two additive tubes are shown, it should be understood that there may be more.

[0121] The embodiment shown in FIG. 8 corresponds to the embodiment of FIG. 7, except for the design of the rotating element 25 and the design of the additive tubes 9a, 9b.

[0122] Here, one mixing arm 252a is shorter than in Figure 8 so that it operates higher in the hopper 21, which may help reduce the risk of creating dead zones where the print material is not properly processed. Providing an additional arm or using a different type of mixer may achieve much the same effect.

[0123] Here, the ends of the additive tubes 9a, 9b are beveled, so that the additive outlets point downwards in the material flow direction T. This reduces the risk of the additive tubes being blocked by concrete and may facilitate mixing of the additive.

[0124] A further embodiment of a printing unit of the same general structure as in Figures 3 to 8, but without the printhead, is shown in Figure 9. Here a separate adapter 70 with two pipe stubs 71a, 71b is provided for receiving two additive tubes 9a, 9b. Each additive tube here consists of a pipe section 91 and a set of connector fittings 92, 93 for attachment respectively to the pipe stub and to an additive supply line (not shown).

[0125] All of the illustrated embodiments including two additive tubes include an adapter, however it will be appreciated that more than one additive tube may be provided in the material inlet pipe 23 of Figures 3 to 6 and that even in embodiments without additive tubes it may be advantageous to provide more than one outlet opening spaced apart from one another.

[0126] Although each of the adapters 70 shown in the drawings has a curved portion, it should be understood that the adapter may be straight or have multiple curves. Similarly, the adapters may vary in size.

[0127] An exploded view of the additive tubes 9a, 9b shown in Figure 9 is shown in Figure 10. At one end of the pipe section 91 a connector fitting 92 for attachment to the pipe stubs 71a, 71b is shown with a threaded fitting 921 and a gasket member 922, and at the other end a connector fitting 93 for attachment to the pipe stub is shown with a second fitting 931 and a pair of valve members 932, 933.

[0128] The pipe section 91 and connector fitting 92 are shown in more detail in Figure 11. As shown, the pipe section 91 has an angled cut at its end which serves as the end 94 which forms the actual outlet, as described above with reference to Figure 8.

[0129] The insertion depth of the pipe section 91 in the adapter 70 may be adjusted by adjusting the position of the connector fitting 92 on the pipe section 91 .

[0130] The embodiments illustrated in the drawings and described above are intended as examples only and are not intended to limit the scope of the invention as defined by the appended claims.

Claims

1. 1. A method for 3D printing a structure using a printing unit including a hopper and a print head, the print head being positioned below the hopper when the printing unit is in use and configured to extrude printing material through a nozzle opening, the method comprising: obtaining a precursor printing material, the precursor printing material including a binder, water, and sand; forming a flow of the precursor printing material toward the printing unit using a material pump; adding a quantity of a first additive to the precursor printing material downstream of the material pump; Optionally adding one or more additional additives; mixing the precursor printing material, the first additive, and the optional one or more additional additives to form the printing material; extruding the printing material through the print head; Including, The method, wherein the first additive is added to the precursor printing material before the precursor printing material reaches the hopper.

2. The method of claim 1 , wherein at least a portion of said mixing is performed using a rotating element.

3. 3. The method of claim 1 or claim 2, wherein a rotating element is used to advance the printing material during printing and to create a continuous flow of the printing material past the print head.

4. 10. The method of claim 1, wherein at least a portion of the mixing of the precursor printing material, the first additive, and the optional one or more additional additives occurs in the hopper.

5. The method of claim 1 , wherein the optional one or more additional additives are added to the precursor printing material in the printing unit.

6. The method of claim 1 , wherein the first additive and / or the optional one or more additional additives are added to the precursor printing material using one or more additive pumps.

7. 7. The method of claim 6, wherein the material pump generates a pulsating flow of the precursor printing material toward the hopper, and the additive pump generates a pulsating flow of the first additive synchronized with the pulsating flow of the precursor printing material.

8. 8. The method of claim 7, wherein the material pump and the additive pump are synchronized so that the ratio of volumetric flow rates of the pumps at any one time is substantially constant.

9. The method of claim 1 , wherein the first additive is a viscosity modifier (VMA) configured to increase the viscosity of the precursor printing material.

10. 10. The method of claim 1, wherein the first additive in the printing material has a volume per mille of at least 0.2%; at least 0.5%; or at least 1.2%.

11. 10. The method of claim 1, wherein the first additive in the printing material has a volume per mille of less than 10%; less than 5%; or less than 2.5%.

12. 10. The method of claim 1, wherein the structure is constructed at a construction site and binder, water, and sand are mixed away from the construction site by one or more transport vehicles that are transported to the construction site to form the precursor printing material.

13. The method of claim 1 , wherein the binder is cement.

14. The method of claim 1 , wherein the structure is a building foundation, a wind turbine base, or a building wall.

15. 1. A 3D structure printing system configured to print using a printing material, the 3D structure printing system comprising: a printing unit, a gantry system, a material pump, flexible tubing, and an additive system, the printing unit comprising a hopper, a print head, and a rotating element, the additive system comprising a control mechanism, an additive outlet, and a control unit; the gantry system is configured to move the printing unit in three-dimensional space; the material pump is configured to receive a precursor printing material including a binder, water, and sand, and to pump the precursor printing material through the flexible tube toward the printing unit to form a material transport direction flow of the precursor printing material; the hopper is disposed downstream of the material pump and upstream of the print head in the material conveying direction; the control unit is operably connected to the control mechanism of the additive system to control an amount of a first additive added to the precursor printing material; a control unit configured to control the control mechanism to form a flow of the first additive into the flow of precursor printing material, thereby forming a flow of the printing material for extrusion through a nozzle opening of the print head;

16. 16. The 3D structure printing system of claim 15, wherein the additive system is configured to add the first additive to the precursor printing material before the precursor printing material reaches the hopper.

17. 17. The 3D structure printing system of claim 15 or claim 16, wherein the 3D structure printing system is configured to at least partially mix the precursor printing material and the first additive in the hopper.

18. 16. The 3D structure printing system of claim 15, wherein the control mechanism of the additive system is a control valve and / or an additive pump.

19. 20. The 3D structure printing system of claim 18, wherein the material pump is configured to generate a pulsating flow of the precursor printing material toward the hopper, and the additive pump is configured to generate a pulsating flow of the first additive synchronized with the pulsating flow of the precursor printing material.

20. A 3D structure printing system as described in claim 15, wherein the additive outlet is located within the printing unit.

21. 16. The 3D structure printing system of claim 15, wherein the first additive is a viscosity modifier (VMA) configured to increase the viscosity of the precursor printing material.

22. 16. The 3D structure printing system of claim 15, further comprising an additive container comprising an outlet fluidly connected to the control mechanism of the additive system, the additive container containing a quantity of the first additive.

23. 23. The 3D structure printing system of claim 22, wherein the additive container is a replaceable container, optionally a disposable container.

24. 16. The 3D structure printing system of claim 15, wherein the control unit of the additive system is configured to control the control mechanism to add an amount of additive to the stream of precursor printing material such that the first additive is present in the printing material at a per mille by volume ratio of at least 0.2%; at least 0.5%; or at least 1.2%.

25. 16. The 3D structure printing system of claim 15, wherein the control unit of the additive system is configured to control the control mechanism to add an amount of the additive to the stream of precursor printing material such that the first additive has a per mille by volume ratio in the printing material of less than 10%; less than 5%; or less than 2.5%.

26. 16. The 3D structure printing system of claim 15, wherein the printing unit comprises a rotating element configured to advance the printing material and create a continuous stream of the printing material toward the nozzle opening.

27. 16. The 3D structure printing system of claim 15, wherein the material pump is a piston pump.

28. 16. The 3D structure printing system of claim 15, wherein the hopper is provided with a rotating element comprising a motor and a mixing arm.

29. 16. The 3D structure printing system of claim 15, wherein the additive system comprises an adapter positioned on an extension of the flexible tubing between the material pump and the hopper so that the flow of the precursor printing material passes through the adapter, and wherein at least one of the additive outlets is provided on the adapter.

30. 30. The 3D structure printing system of claim 29, wherein at least one of the additive outlets is located on a side of the adapter, the side facing upward in use.

31. 31. The 3D structure printing system of claim 30, wherein the adapter comprises one or more side branches configured to connect to an additive storage unit or to receive an additive tube comprising the additive outlet.

32. A 3D structure printing system as described in claim 31, wherein at least one additive tube with the additive outlet extends within the adapter so that the additive outlet is positioned at the center line of the adapter and the center line extends parallel to the material conveying direction.

33. 32. The 3D structure printing system of claim 31 , wherein the additive storage unit is positioned above the additive outlet in use, and a valve or additive pump is provided to control the amount of additive added.

34. 30. The 3D structure printing system of claim 29, further comprising a material inlet valve positioned upstream of the additive outlet in the material transport direction.

35. A printing unit for use in the 3D structure printing system of claim 15, configured to print using the printing material comprising the precursor printing material and the first additive, the precursor printing material comprising a binder, water and sand, the printing unit comprising: a material inlet; a hopper configured to contain a quantity of the printing material; a print head configured to extrude the printing material, the print head being positioned downstream of the hopper in the material conveying direction; a rotating element configured to move the printing material from the hopper to the print head in the material conveying direction; and an additive outlet, the additive outlet being positioned upstream of the hopper in the material conveying direction.

36. 36. The printing unit of claim 35, further comprising a rotating element disposed within the hopper.

37. 36. The printing unit of claim 35, wherein the material inlet comprises an inlet pipe protruding from a body of the hopper, the inlet pipe being provided with one or more of the additive outlets.

38. 38. A printing unit according to claim 37, wherein at least one of the additive outlets is provided on a side of the inlet pipe, the side facing upwards in an in-use state of the printing unit.

39. 38. A printing unit according to claim 37, wherein at least one of the additive outlets is formed in an additive tube, the additive tube projecting into the inlet pipe.

40. 38. The printing unit of claim 37, wherein at least one of the additive outlets is positioned at a centerline of the inlet pipe, the centerline extending parallel to the material transport direction.

41. A printing unit as described in claim 37, wherein at least a distal portion of the additive tube having the additive outlet extends substantially parallel to a center line of the inlet pipe, the center line extending parallel to the material conveying direction.

42. A printing unit as described in claim 35, further comprising an additive storage unit connected to the additive outlet.

43. 43. The printing unit of claim 42, wherein the additive storage unit is positioned above the additive outlet when the printing unit is in use, and a valve or additive pump is provided to control the amount of additive added.

44. 36. The printing unit of claim 35, further comprising a material inlet valve positioned upstream of the additive outlet in the material transport direction.

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