Method and system for printing a structural element

Abstract

A method of printing a structural element, comprising supplying a binding printing material to a print head mounted on a gantry, said binding printing material comprising at least a binder, water, and an aggregate with a maximum particle diameter of more than 4 millimeter, and said print head comprising an agitation unit volume of the nozzle from a nozzle inlet to a nozzle outlet following a curved travel path, which is longer than a distance measured in parallel to the transportation direction from nozzle inlet to the nozzle outlet.

Description

[0001] Title

[0002] Method and system for printing a structural element.

[0003] Field of the invention

[0004] The invention relates to the field of 3D printing of construction structures.

[0005] Background

[0006] In the field of 3D printing structural elements, such as walls of buildings, it is common to print using a mixture of water, binder, such as cement, fine aggregates with a maximum particle diameter of 4 mm or less, and optionally additives as the printing material. Within the context of 3D construction printing such materials are referred to as 'concrete', but outside the technical field they are known as mortar. Concrete outside of the field is known to comprise rocks or stone with a diameter of more than 4 mm. The reason why mortar is used instead of traditional concrete in 3D printing for construction is the advantageous properties of mortar for the 3D printing process. Amongst others this includes smooth surfaces, good adhesion between layers, and easy mixing and pumping during the printing process, and mortar has sufficient compressive strength for the relatively small scale printing done so far. However, it remains a desire to be able to utilize larger aggregates for structures needing high compressive strength.

[0007] Furthermore, a problem of printing with larger aggregates is that the larger aggregates make it difficult to surface finish the resulting structures. The larger aggregates may show in the surface of the walls, creating a heterogenous visual impression of the structure.

[0008] Additionally, in some cases larger aggregates tend to collect at the bottom of the printed layers and thus reduce the layer adhesion between the new, upper layer and the old, lower layer.

[0009] Summary

[0010] A first aspect relates to a method of printing a structural element, the method comprising:

[0011] a) supplying a binding printing material to a print head mounted on a gantry, said binding printing material comprising at least a binder, water, and an aggregate witha maximum particle diameter of more than 4 millimeter, and said print head comprising an agitation unit having an agitation unit inlet and agitation unit outlet, b) transporting the binding printing material through the agitation unit along a transportation direction to a nozzle, and

[0012] c) passing the binding printing material through an inner volume of the nozzle from a nozzle inlet to a nozzle outlet following a curved travel path, which is longer than a distance measured in parallel to the transportation direction from the nozzle inlet to the nozzle outlet.

[0013] The curved travel path causes the formation and retention of a lubrication layer, which is a layer of binder paste mostly free from larger aggregates, to form at the inside walls of the nozzle. Thus, larger aggregates will be less common at the outer surfaces of a printed layer and they show less on the outside of the printed layer, disrupting less the visual impression of the printed structure. Also, the lubrication layer advantageously reduces cracks caused by thin layers of mortar becoming loose and falling off larger aggregates close to the outer surface and thus reduce the chances of water entering the printed structure through such cracks. Thus, the structural integrity is increased.

[0014] Also, the lubrication layer that is forming and extruded at the bottom of each layer may provide a good adhesion to another layer, increasing the mechanical strength of the structure. It is understood that the curved travel path of the binding printing material within the nozzle is defined by the geometric configuration of the nozzle. The flow dynamics of the binding printing material, and the friction between the binding printing material and internal surfaces of the nozzle influences the formation of the lubrication layer.

[0015] In the hose, which delivers the printing material to the printing head, a hose lubrication layer may be formed. However, this hose lubrication layer can not be maintained and transferred to the nozzle as the agitation unit disrupts the hose lubrication layer. Therefore, the method is particular advantageous as it allows the formation of a lubrication layer in a printing head comprising an agitation unit.In a further embodiment, a radius of the curved travel path is at least 50 millimeter and not more than 10 meter.

[0016] The radius may be between 100 millimeter and 5 meter, such as 200 millimeter and 1 meter. Additionally, the travel path may comprise a further radius between 50 millimeter and 10 meter, such as 100 millimeter and 5 meter, or such as 200 millimeter and 1 meter.

[0017] The curved travel path may comprise a first section with a first radius and a second section with a second radius. Wherein the first radius and the second radius are different. The curved travel path may comprise a third section with a third radius and the third radius being different from the first and second radius.

[0018] It is noted that "a radius" indicates the radius of a circular segment which is forming part of the travel path.

[0019] The curvature is advantageous as it gently guides the binding printing material through the nozzle with a lesser risk of larger aggregates disrupting the lubrication layer.

[0020] In a further embodiment the curved travel path is longer than the distance measured in parallel to the transportation direction from the nozzle inlet to the nozzle outlet by at least a factor of 1.1.

[0021] In this embodiment the curved travel path that is to be travelled by the binding printing material is longer than a distance from the nozzle inlet to a nozzle outlet by at least a factor of 1.1 and thereby providing length to form a lubrication layer on the inside walls of the nozzle without increasing the overall size of the print head. Correspondingly the factor may be at least 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2. The curved travel path may have a length between 100 millimeter and 1 meter, such as for example 300 millimeter. The curved travel path may have a length between 200 millimeter and 500 millimeter. The length of the curved travel path is the distance from the nozzle inlet to the nozzle outlet following the curved travel path. Generally, the curved travel path can be defined as the path comprising all center points of cross sections of the inner volume of the nozzle which are perpendicular tothe travel direction. But under some circumstances the curved travel path may be affected by friction between the binding printing material and the inner nozzle walls and therefore deviate from the above definition. However, the principles disclosed herein still apply.

[0022] In a further embodiment the method comprises, before agitating the binding printing material, a step of mixing the binding printing material in a hopper mounted on the print head by using a stirrer located inside the hopper, and wherein the hopper is in fluid connection with the agitation unit.

[0023] In this embodiment the hopper provides a buffer in the printing process allowing to even out delays in the delivery of binding printing material to the print head and maintain a lubrication layer through out the process and thereby increase the chance of a continuous and time efficient printing process.

[0024] In a further embodiment the method comprises a step of rotating the nozzle around a rotation axis, wherein the rotation axis is parallel to the transportation direction, and the nozzle is extruding printing material in an output direction 90 to 20 degree from the transportation direction.

[0025] Thereby the orientation of the nozzle outlet and hence the output direction of the extruded material may be adjusted to conform to a desired shape of the printed structure. Also, the printing head may be compact, saving space. Furthermore, no interruption of the printing process is necessary to turn a corner and thus no interruption of the lubrication layer takes place.

[0026] In a further embodiment the rotation axis intersects the agitation unit. Thereby, the method allows to print in tight spaces, and easily turn corners.

[0027] In a further embodiment the agitation unit comprises a screw conveyor configured to rotate around a screw axis, and the nozzle outlet intersects the screw axis.

[0028] The screw conveyor advantageously compresses the binding printing material and reliably fills the nozzle with binding printing material avoiding air pockets in theprinted layer. This may contribute to strength and stability of the structure and / or reduce the risk of interruption of the lubrication layer by air bubbles.

[0029] In a further embodiment the outlet of the nozzle coincides with the rotation axis. Consequently, the nozzle can be advantageously rotated with minimal change in the location of the nozzle outlet and without having to use other actuators to compensate for a movement of the nozzle caused by the rotation. This in turn facilitates the printing process and turning of corners while maintaining a lubrication layer.

[0030] In a further embodiment the method comprises, before the step of b) transporting a binding printing material, the steps of transporting a mortar mixture in the agitation unit, the mortar mixture comprising only aggregates with a diameter of less than 4 millimeter, at least a binder, and water, and extruding from the nozzle the mortar mixture.

[0031] This additional step is desirable as it promotes an initial formation of a lubrication layer and thereby increases the chances of a desirable printing process, where larger aggregates don't form part of the outer surface and / or the lubrication layer that is forming at the bottom provides a good adhesion to a bottom layer.

[0032] In a further embodiment the method comprises the step of compacting the binding printing material by guiding it through a continuously narrowing portion of the nozzle.

[0033] This advantageously compacts the binding printing material in order to remove air pockets in the binding printing material and thus increases the mechanical integrity of the printed structure. It may also press the larger aggregates towards a center of the nozzle.

[0034] In a further embodiment the binding printing material is concrete and the binder is cement. This is advantageous as concrete and cement provide good physical properties of the printed structure and are readily available. Alternatively, thebinder may be lime, gypsum, bitumen, or clay. Thereby the material with desired properties may be chosen, for example taking local availability or climate impact into consideration.

[0035] A second aspect relates to a system for printing binding printing material. The system comprising, a gantry, a print head mounted on the gantry, an agitation unit comprised by the print head, the agitation unit configured to transport material along a transportation direction, and a nozzle being in fluid connection with the agitation unit, the nozzle comprised by the print head, wherein the nozzle is configured to guide the binding printing material through an inner volume of the nozzle from a nozzle inlet to a nozzle outlet following a curved travel path, which is longer than a distance measured in parallel to the transportation direction from the nozzle inlet to the nozzle outlet.

[0036] Thereby the system is suitable to create a lubrication layer at the inside walls of the nozzle. Thus, less larger aggregates will form part of an outer surface of a printed layer and will be less likely to show on the outside of the printed layer disturbing the visual impression of the printed structure.

[0037] Also, the lubrication layer that is forming and extruded at the bottom, which is the side of the extruded material that is facing the ground, provides a good adhesion to a below layer.

[0038] In a further embodiment the system further comprises a hopper in fluid connection with the agitation unit, and a stirrer located inside the hopper configured to mix a binding printing material.

[0039] In this embodiment the hopper provides a buffer in the printing process allowing to even out delays in the delivery of binding printing material to the print head and thereby increase the chance of a continuous and time efficient printing process. Also, the stirrer allows to alter the printing material by adding additives, for example accelerators, to obtain a printing material which hardens faster.In a further embodiment the nozzle is configured to rotate around a rotation axis, the rotation axis being parallel to the transportation direction. Thereby the orientation of the nozzle outlet and the extruded material may be adjusted to conform to a desired shape of the printed structure. Also, the printing head may be compact, saving space.

[0040] In a further embodiment the rotation axis intersects the agitation unit. Thereby the width dimension of the print head may be kept to a minimum.

[0041] In a further embodiment the nozzle comprises a section that continuously narrows towards the nozzle outlet. This advantageously allows to compact the binding printing material in order to remove air pockets in the binding printing material and thus increases the mechanical strength of the printed structure. The nozzle may continuously change it's cross section for example from a round shape to a rectangular shape along the travel path of the binding printing material. Thereby, the binding printing material may be gently transformed into a desired rectangular shape for extrusion without damaging the lubrication layer. The advantage of a rectangular shape would be a structure with shallow or no ridges.

[0042] However, also other shapes at the nozzle outlet are suitable such as for example an elliptical shape, for a structure that has deeper ridges, for example to offer more surface area for post processing if so desired.

[0043] In a further embodiment the inner volume is being delimited by at least one curved inner nozzle wall defining the curved travel path.

[0044] The curved travel path may be horizontal, which is any direction that is perpendicular to the gravitational force of the earth while the system is in use or within 10 degree of being horizontal at the nozzle outlet. This may be achieved by the nozzle walls guiding the binding printing material accordingly.

[0045] The system may further be configured for guiding the binding printing material close to a height of a below layer, on which a new layer is to printed, this may be achieved by a bevel on a nozzle wall at the nozzle outlet. Thereby the printing layer is carefullylaid down onto the below layer without disrupting it, or the lubrication layer of the new layer.

[0046] Additionally, or alternatively, the curved travel path may be vertical, which is the direction of the gravitational force of the earth while the system is in use, or within 10 degree of being vertical at the nozzle inlet. This in turn contributes to a low necessary output power of the agitation unit as the printing material follows the gravitational force.

[0047] As horizontal may be understood any direction that is perpendicular to the gravitational force of the earth while the system is in use. Vertical may be understood as any direction parallel with the gravitational force of the earth.

[0048] In a further embodiment a radius of the curved inner nozzle wall is at least 50 millimeter and not more than 10 meter. The radius may be between 100 millimeter and 5 meter, such as 200 millimeter and 1 meter, such as 100 millimeter and 500 millimeter. Additionally, the travel path may comprise a further radius between 50 millimeter and 10 meter, such as 100 millimeter and 5 meter, such as 200 millimeter and 1 meter, such as 100 millimeter and 500 millimeter.

[0049] In this embodiment the curvature is advantageous as it gently guides the binding printing material through the nozzle with a low risk of larger aggregates disrupting the lubrication layer as the radius is not too small, all while without increasing too much the overall size of the nozzle while still changing the direction of travel of the printing material at the nozzle inlet to a different, essentially horizontal (+- 20 degree) direction of travel at the nozzle outlet.

[0050] It should be understood that the embodiments and features described herein are not intended to be limiting. Although particular embodiments are discussed with specific features, those skilled in the art will understand that any combination of features from different embodiments may be combined, unless otherwise noted. These combinations are considered to be within the scope of the invention, and the examples provided are merely illustrative and not exhaustive.

[0051] Brief description of drawingsFig. 1 shows a concrete printer as it may be used on-site.

[0052] Fig. 2 shows a cross section of a printing head.

[0053] Fig. 3 shows an orthographic view of a nozzle.

[0054] Fig. 4 shows a top view of a nozzle.

[0055] Fig. 5 shows a side view of a nozzle.

[0056] Fig. 6 shows a cross sectional view of a nozzle.

[0057] Fig. 7 shows an orthographic view of a nozzle.

[0058] Fig. 8 shows a front view of a nozzle.

[0059] Fig. 9 shows a cross sectional view of a nozzle.

[0060] Fig. 10 shows an orthographic view of a nozzle.

[0061] Fig. 11 shows a side view of a nozzle.

[0062] Fig. 12 shows a cross section view of a nozzle.

[0063] Fig. 13 shows a top view of a nozzle.

[0064] Fig. 14 shows a cross section view of a nozzle with lubrication layer.

[0065] Detailed Description

[0066] In Fig. 1 a printer 1 is shown comprising a gantry 3 and a printing head 2. The printing head 2 is connected to a pump 5 via a hose 7. The pump 5 is configured to pump 5 a printing material towards the printing head 2. The printing head 2 is moved by the gantry 3 in order to extrude printing material at various locations to form a structural element 4, such as for example a part of a building.

[0067] In Fig. 2 the printing head 2 comprises a hopper 8 for receiving and storing printing material. One end of the hose 7 may end above the hopper 8 and adds printing material to the hopper. The hopper 8 has a stirrer 14 to mix the printing material. This may be especially desirable when additives are added to the printing material at the printing head 2.

[0068] The printing head 2 further comprises an agitation unit 13 which agitates the printing material and moves it forward towards a nozzle inlet 6.1 following a transportation direction 11. The agitation unit 13 comprises a screw conveyor. In the embodiment shown in Fig. 2 the screw conveyor and the stirrer 14 are mounted onone axle. The axle may be powered via an axle motor which is not shown in the figure. However, the use of separate axles and driving means for the stirrer and the agitation unit is also possible.

[0069] As the printing material is moved towards the nozzle it enters the nozzle at the nozzle inlet 6.1 and is pushed through the nozzle 6 to the nozzle outlet 6.2. While travelling down the nozzle 6 the printing material follows a curved travel path 9 until it reaches the nozzle outlet 6.2. Whereas the transportation direction 11 is also the direct direction from the nozzle inlet to the nozzle outlet, the curved travel path 9 is longer, here 1.75 times longer than the distance from the nozzle inlet to the nozzle outlet.

[0070] Also shown in Fig. 2 is a rotation axis 10 about which the nozzle 6 may be rotated during operation to facilitate printing. Here, the rotation axis 10 coincides with the nozzle outlet 6.2 easing the rotation of the nozzle outlet 6.2 without displacing the nozzle 6, or vice versa. For example, to turn a corner of the structural element being printed. A nozzle motor, not shown, may be configured to control the rotation of the nozzle 6 along the rotation axis 10. Rotation of the nozzle may also be achieved by rotating the entire printing head. This also applies to the other embodiments shown in the drawings. The printing material is here extruded in a direction which is closer to being parallel to the horizontal direction than to the vertical direction.

[0071] Figs. 3 - 6 show the same nozzle in different views. In Fig. 3 teeth 15 are shown at the nozzle outlet 6.2. These teeth may be helping to observe the rate with which printing material is extruded based of the resulting shape of the imprint of the teeth 15 in the structural element 4. Furthermore, the lasting pattern left by the teeth in the printed layer may help to take up shearing forces between the layers when a new layer is set into the pattern, and thus increase the integrity of the structural element 4.

[0072] Fig. 4 shows a top view of the nozzle inlet 6.1, from where the printing material is entering the nozzle. A nozzle motor, not shown, may be configured to contact thenozzle at the engaging element 20 to control the rotation of the nozzle 6 along the rotation axis 10.

[0073] Fig. 5 is a sideview of the same nozzle showing the rotational axis 10, which is centered on the nozzle inlet 6.1.

[0074] Fig. 6 shows a sectional view of the nozzle and the curved travel path 9 of the printing material through the nozzle. The curved travel path 9 is shown as the dashed line and defined by the nozzle wall 6.3. The inner side of the nozzle wall is curved to cause the printing material to follow the curved travel path 9. The inner side of the nozzle wall gradually changes shape along the curved travel path from the nozzle inlet, which is circular, to the nozzle outlet, which is rectangular.

[0075] Figs. 7 to 9 show a nozzle comprising flaps 16, which interact with the printing material after the printing material has left the nozzle and help to flatten the structural element 4. The nozzle has teeth 15 which are smoothly transitioning into the inner nozzle wall 6.3 and thereby leaving an imprint on the printing material with a reduced risk of trapping larger aggregates. Fig. 8 and 9 also show the rotation axis 10 which is centered on the nozzle inlet 6.1. Furthermore, in Fig. 9 it can be seen that the inner cross sectional area of the nozzle decreases from the nozzle inlet 6.1 to the nozzle outlet 6.2.

[0076] Figs. 10 to 13 depict another embodiment which in comparison to the embodiment shown in Figs. 3 to 6 has a less wide nozzle outlet 6.2. Also, the extrusion direction here varies only slightly from the vertical direction (+- 20 degree). The length of the curved travel path is longer than the distance of the nozzle inlet to the nozzle outlet along the transportation direction, for example here by a factor of approximately 1.1. Here the transportation direction is parallel to the rotation axis 10. It is noted that "a radius" indicates the radius of a circular segment which is forming part of the travel path.

[0077] Fig. 12 shows radii 21 of circular segments that are forming part of the travel path 9. The radii have sizes large enough to avoid disturbance in the lubrication layer 17.Fig. 14 shows a nozzle in use with printing material comprising large and small aggregates 19 travelling down from the nozzle inlet 6.1 to the nozzle outlet 6.2 with an established lubrication layer 17. As the printing material moves smoothly, i.e. without sharp turns, towards the nozzle outlet 6.2 a lubrication layer 17 is formed and maintained, which maintains a distance between the inner side of the nozzle wall 6.3 and large aggregates 18. This lubrication layer 17 is mostly free from larger aggregates and contains mostly small aggregates 19 and the remaining components of the printing material (not shown). The lubrication layer 17 is formed while the material is travelling along the curved travel path 9 and extruded in a continuous manner together with the rest of the printing material comprising larger aggregates. Alternatively, and / or additionally the lubrication layer 17 may be initially actively created by first printing with a printing material free from larger aggregates. Even though the lubrication layer is depicted as a discrete area, it will fade and have a gradual nature. The same applies to the size of aggregates which may have a wide variation and are simplified for drawing purposes.

[0078] Reference numbers

[0079] 1 printer

[0080] 2 printing head

[0081] 3 gantry

[0082] 4 structural element

[0083] 5 pump

[0084] 6 nozzle

[0085] 6.1 nozzle inlet

[0086] 6.2 nozzle outlet

[0087] 6.3 nozzle wall

[0088] 7 hose

[0089] 8 hopper

[0090] 9 curved travel path

[0091] 10 rotation axis11 transportation direction

[0092] 12 radius of curved inner nozzle wall

[0093] 13 agitation unit

[0094] 14 stirrer

[0095] 15 teeth

[0096] 16 flap

[0097] 17 lubrication layer

[0098] 18 large aggregates

[0099] 19 small aggregates

[0100] 20 engaging element

Claims

PATENT CLAIMS1. A method of printing a structural element, the method comprising:a) supplying a binding printing material to a print head mounted on a gantry, said binding printing material comprising at least a binder, water, and an aggregate with a maximum particle diameter of more than 4 millimeter, and said print head comprising an agitation unit having an agitation unit inlet and agitation unit outlet,b) transporting the binding printing material through the agitation unit along a transportation direction to a nozzle, and c) passing the binding printing material through an inner volume of the nozzle from a nozzle inlet to a nozzle outlet following a curved travel path, which is longer than a distance measured in parallel to the transportation direction from nozzle inlet to the nozzle outlet.

2. A method according to claim 1, wherein a radius of the curved travel path is at least 50 millimeter and not more than 10 meter.

3. A method according to any previous claim, wherein the curved travel path is longer than the distance measured in parallel to the transportation direction from the nozzle inlet to the nozzle outlet by at least a factor of 1.1.

4. A method according to any previous claim, wherein the method further comprises, before agitating the binding printing material, a step of mixing the binding printing material in a hopper mounted on the print head by using a stirrer located inside the hopper, and wherein the hopper is in fluid connection with the agitation unit.

5. A method according to claim 1, wherein the method further comprises a step of rotating the nozzle around a rotation axis, and wherein the rotation axis is parallel to the transportation direction.

6. A method according to the previous claim, wherein the rotation axis intersects the agitation unit.

7. A method according to any previous claims, wherein the agitation unit comprises a screw conveyor configured to rotate around a screw axis, and the nozzle outlet intersects the screw axis.

8. A method according to any one of claim 3 - 4, wherein the outlet of the nozzle coincides with the rotation axis.

9. A method according to any one of the previous claims, wherein the method comprises before the step of agitating a binding printing material, the steps of agitating a mortar mixture in the agitation unit, the mortar mixture comprising only aggregates with a diameter of less than 3 millimeter, at least a binder, and water, and extruding from the nozzle the mortar mixture.

10. A method according to any one of the previous claims, wherein the method comprises the step of compacting the binding printing material by guiding it through a continuously narrowing portion of the nozzle.

11. A method according to any one of the previous claims, wherein the method comprises the step of forming a lubrication layer inside the nozzle and extruding the lubrication layer.

12. A method according to any one of the previous claims, wherein the binding printing material is concrete and the binder is cement.

13. A system for printing binding printing material, the system comprising, a gantry,a print head mounted on the gantry,an agitation unit mounted on the print head, the agitation unit configured to transport material along a transportation direction, a nozzle being in fluid connection to the agitation unit, the nozzle mounted on the print head and the nozzle comprising an outlet, wherein the nozzle is configured to guide the binding printing material through an inner volume of the nozzle from a nozzle inlet to a nozzle outlet following a curved travel path, which is longer than a distance measured in parallel to the transportation direction from the nozzle inlet to the nozzle outlet.1614. A system according to claim 13, wherein the system further comprises a hopper in fluid connection with the agitation unit, and a stirrer located inside the hopper configured to mix a binding printing material.

15. A system according to any one of claims 13 - 14, wherein the nozzle is configured to rotate around a rotation axis, the rotation axis being parallel to the transportation direction.

16. A system according to claim 15, wherein the rotation axis intersects the agitation unit.

17. A system according to claim 13 - 16, wherein the nozzle comprises a section that continuously narrows towards the outlet of the nozzle.

18. A system according to any one of claim 13 - 17, wherein the inner volume is being delimited by at least one curved inner nozzle wall and defining the curved travel path.

19. A system according to claim 18, wherein a radius of the curved inner nozzle wall is at least 50 millimeter and not more than 10 meter.

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