FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION
A method of 3D printing.
APPLICANTS
Aditya Birla Science and Technology Company Pvt Ltd, Plot number 1 and 1-A/1, Taloja, MIDC, Taluka-Panvel, District- Raigad- 410208, Maharashtra, India.
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes this invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
[001] The present invention relates to a method of 3D printing. More particularly, the present invention relates to a method of 3D printing to build taller and more robust structures.
BACKGROUND OF THE INVENTION
[002] 3D printing is a technique for building a concrete structure with the help of a 3D printer. In this technique, concrete mix is extruded through a circular nozzle of the 3D printer to print parallel layers of concrete which are bound in a layer-wise approach.
[003] There are a few problems associated with the current method of 3D printing of concrete to form a structure. One of the challenges is the ‘buildability’ of the structure. As one continues to print, the dead load of the structure keeps on increasing and beyond a point, the first few layers start to crumble due to high dead load. This puts a restriction on the number of layers that can be printed on the top of each other. Attempts have been made to solve this problem by either modifying the mix design or increasing the thickness of the printed filament. However, both attempts have led to an increase in thickness that additionally reduces the carpet area of the structure.
[004] Secondly, as 3D printing technique involves printing of parallel layers, structures up to a certain height can only be printed. Beyond a certain height, the parallel layers start to lose stability. It has also been noticed that after a certain height, due to loss of stability, the layers begin to slide thereby leading to tilting of taller structures. Therefore, it is difficult to build stable taller structures by the existing method of 3D printing.

[005] Hence, there is a need of a method of 3D printing that solves some of the problems present in the prior art.
SUMMARY OF THE INVENTION
[006] According to an embodiments of the present invention, there is provided a method of 3D printing wherein:
(a) extruding a first layer of concrete in a pre-determined direction by a 3D printer;
(b) extruding a second layer of concrete on top of the first layer in a direction perpendicular to the direction in which the first layer is extruded; and
(c) repeating steps (a) and (b) alternately until a desired 3D printed structure is obtained,
wherein the second layer and every alternate layer to the second layer has at least one sublayer.
BRIEF DESCRIPTION OF THE DRAWINGS
[007] Figure 1 shows a perspective view of the direction of extrusion of concrete in first as well as second layer, in accordance with an embodiment of the present invention;
[008] Figure 2 shows a perspective view of 3D printed structure made up of multiple layers with each deposited layer being perpendicular to each other and alternate layers from the second layer onwards comprising sublayers, in accordance with the embodiment of the present invention; and
[009] Figure 3 provides a comparison between the stability of a structures printed with layers that are (a) parallel and (b) perpendicular, to each other, according to the embodiments of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS
[010] Accordingly, the embodiments of the present invention provide a method of 3D printing of concrete by using a 3D printer to build taller and more robust structures.
[011] According to the embodiments of the present invention, there is provided a method of 3D printing wherein in the first step, a first layer of concrete is extruded by a 3D printer in a pre-determined direction and in the second step, a second layer of concrete is extruded on top of the first layer in a direction perpendicular to the direction in which the first layer is extruded. Both the first and second steps are repeated alternately until a desired 3D printed structure is obtained.
[012] Moreover, the second layer and every alternate layer to the second layer has at least one sublayer. The number of sublayers can be decided based on the length of the preceding layer. Also, the sublayers are extruded in a manner such that the number of joints between the sublayer are minimum. Preferably, all the sublayers forming the second layer are in contact with each other so as to form a continuous second layer.
[013] In an embodiment, as shown in Figure 1, the length of each sublayer of the second layer is equal to the width of the first layer. After the second layer is extruded covering the full length of the first layer, a third layer is extruded in a direction perpendicular to the second layer and parallel to the first layer and subsequently a fourth layer is extruded on top of the third layer in a direction perpendicular to the third layer and parallel to the second layer. This method of perpendicular printing of alternate layers is repeated until the required height of the structure is obtained. This technique helps not only to increase the height of the structure but also improves the overall stability of the structure.

[014] A third layer is then deposited over the second layer in a direction perpendicular to that of the second layer. Preferably, the third layer is deposited in such a manner such that the length of the third layer is equal to the width of the second layer. The method is repeated to deposit a fourth layer over the third layer in a direction perpendicular to that of the third layer. Preferably, the fourth layer is divided into sublayers having length equal to the width of the third layer.
[015] In an embodiment, this method of depositing layers over each other, with every layer being deposited in a perpendicular direction to each other, is repeated a predetermined number of times, so that a number of successive layers forms a shaped structure. The present method of 3D printing of cementitious material wherein the layers are deposited in a perpendicular direction to each other does not lead to sliding of layers thus leading to building of taller and sturdier structures at one go.
[016] The technique of depositing layers in a perpendicular direction provides buildability and does not lead to crumbling of lower layers. The embodiments of the present invention thus eliminate the restriction on the number of layers that can be printed on the top of each other. Figure 2 shows a perspective view of 3D printed structure made up of multiple layers with each deposited layer being perpendicular to each other.
[017] In an embodiment of the present invention, the layers of concrete are extruded using a 3D printer having a circular extruding nozzle. As illustrated in Figure 3, the stability of a structure with perpendicular layers is more than a structure with parallel layers as the center of gravity of all the layers for parallel printing has to be perfectly aligned for the structure to remain stable. If there is slight misalignment, as in case of parallel layers, the configuration tends to tumble. In perpendicular printing, as shown in Figure 3(b), the third layer on top has distance AB to traverse

before it falls off. In other words, there is a flat surface AB in which the third circular layer can move whereas in the Figure 3(a) no such support is available at all. Therefore, the present perpendicular 3D printing method is useful for layers with circular cross sections and not for square or rectangular cross sections.
[018] In another embodiment, one 3D printer is used to print the first layer and every alternate layer thereafter and a separate 3D printer is used to print the second layer and every alternate layer thereafter.
[019] Experimental Data:
Advantages and benefits of the embodiments of the present invention would become more apparent from the below experimental details to a person skilled in the art.
Example 1
[020] A first layer of concrete was extruded and the subsequent layers were extruded on top of the first layer in a direction parallel to the first layer. In the first trial, the structure could be printed up to 6 layers only, beyond which the prototype started to lose stability and tilt. It was observed that the structure tilted by 12.5° from the base. Another structure was printed by extruding parallel layers. This time only 8 layers could be extruded after which a tilt of 11° was seen.
[021] In another trial, a structure was printed with layers being alternately perpendicular to each other in accordance with the present invention. The second layer and every alternate layer thereafter had three sublayers per layer. It was observed that there was no inclination even till 10 layers and that the structure was stable.

[022] Therefore, from the experimental trials, it was observed that the present method of perpendicular printing in alternate layers provides stable and taller structures.
[023] The foregoing description of specific embodiments of the present invention has been presented for purposes of description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obvious modifications and variations are possible in light of the above teaching.

We Claim:
1. A method of 3D printing wherein:
(a) extruding a first layer of concrete in a pre-determined direction by a 3D printer;
(b) extruding a second layer of concrete on top of the first layer in a direction perpendicular to the direction in which the first layer is extruded; and
(c) repeating steps (a) and (b) alternately until a desired 3D printed structure is obtained,
wherein the second layer and every alternate layer to the second layer has at least one
sublayer.
2. The method as claimed in claim 1, wherein layers of concrete are extruded using a 3D printer having a circular extruding nozzle.
3. The method as claimed in claim 1, wherein the length of each sublayer of the second layer and every alternate layer after the second layer is equal to the width of the first layer and every alternate layer after the first layer.
4. The method as claimed in claim 1, wherein one 3D printer is used to print the first layer and every alternate layer thereafter and a separate 3D printer is used to print the second layer and every alternate layer thereafter.