Procedure and apparatus for additive manufacturing of a three-dimensional element

Abstract

The subject matter is a procedure for additive manufacturing of a three-dimensional element by means of an additive manufacturing apparatus, comprising the steps of: - mixing basic components inside a mixer to obtain a construction material; - introducing said construction material into a hopper of a pump; - pumping the construction material into an end effector (20) by means of the pump; - discharging the construction material from a nozzle (22) of the end effector (20). Said end effector (20) is moved during the procedure so as to deposit the construction material in predefined positions. Said procedure envisages that the end effector (20) comprises at least one further opening (24) for the introduction into a hollow body (21), upstream of the nozzle (22), of a medium suitable for reducing the density of the construction material coming from the respective generator and to be mixed with the construction material in order to alter the physical and / or mechanical and / or rheological properties thereof.

Description

[0001] PROCEDURE AND APPARATUS FOR ADDH1VE MANUFACTURING OF A THREE-DIMENS8ONAL ELEMENT

[0002] Technical field

[0003] The present invention relates to a procedure and an apparatus for additive manufacturing of a three-dimensional element, according to claims 1 and 11.

[0004] Prior art

[0005] In the field of additive manufacturing, commonly known as 3D printing, various techniques have been developed for the manufacture of objects layer by layer. An area of particular interest is additive manufacturing that uses materials such as concrete as a basis, which enables the construction of complex structures with improved structural characteristics. However, the existing processes for additive manufacturing with concrete show limitations when it comes to controlling and modifying the density of the printed material during the printing process.

[0006] The advantages connected to additive manufacturing have led the advent of this technology to be considered almost like a new industrial revolution. Thanks to this technology, it is in fact possible to achieve so-called mass customisation of industrial production: the cost of a product need no longer depend on the complexity of its shape. In recent years, such technologies are attracting an ever-growing interest in the construction and street furniture sectors, but also in the sector of interior and exterior design.

[0007] Traditional manufacturing techniques are based on pouring a material into formwork or moulds, which often entail procedures that require a great deal of time and work, as well as costs that increase significantly with increases in the complexity of the shape of the element to be produced. Additive manufacturing, by contrast, allows direct deposition of the material, layer by layer, based on a digital model, thereby reducing construction times and allowing greater freedom of design.

[0008] The systems currently used in additive manufacturing, especially in cases where the technology is applied for materials such as clay, concrete, geopolymers, etc., consist of:

[0009] 1 . a mixer for mixing the basic ingredients;

[0010] 2. a pump with a hopper that collects the material prepared in step 1 and conveys it, through a tube of an appropriate diameter and size, onto the printing system, for example a robotic arm, which moves the material in accordance with a preset path;

[0011] 3. an end effector, i.e. the device attached to the movement system, for example a robotic arm (or a numerically controlled machine or a 3D printer, ...); in less advanced cases, the end effector is substantially a funnel-shaped device to which the tube conveying the material is connected; this device, through a nozzle, deposits the material on the laying surface. In more advanced cases, in addition to the opening for the entry of the material, the end effector can also be provided with a motor, a screw extruder and further openings for the entry of other additions to be made conveniently at the end effector itself and not in the step of mixing of the material. This is the case, for example, when setting and / or hardening accelerators are added: adding them in the initial mixing step could cause a sudden hardening of material already in the pump or during the step of pumping into the tube, thus affecting the entire production process. In other cases, the end effector could be provided with further appendages, for example for depositing metal bars, metal wires, fibres or another type of material.

[0012] In the simplest case, the system allows for the production of three- dimensional elements with extreme freedom of shape by exploiting the rheological properties of the material, which is characterised by very high thixotropy. In fact, the types of material to be used in these cases must be such as to be able to be pumped without too much difficulty and, above all able to maintain their shape once they are deposited on the laying surface and able to bear the weight of the layers placed on top of them during the additive manufacturing process. Since no modification is made to the properties of the material at the end effector, the material must already possess all the required characteristics immediately after the mixing step, thus in the hopper of the pump. Although this is possible, it entails considerable difficulties in the design of the material and, above all, it strongly limits the system’s applicability to specific materials. Furthermore, a material’s self-bearing capacity is often in contrast with the ease of pumping, another characteristic that materials must possess in order that they can be applied correctly with this technology.

[0013] In the most complex case, i.e. of an end effector equipped with a motor, screw extruder, and openings for the entry of further additions shortly before the deposition of the material, it is possible to implement solutions that facilitate the production of objects with this technology. In fact, for example, by providing the end effector with an opening from which an accelerating admixture is introduced (a tube will thus be connected to the end effector, through which the admixture, usually in liquid form, is introduced by means of an appropriate pumping system), it is possible to design a mix characterised by excellent pumping properties by introducing the accelerator and, consequently, modifying its rheological properties, at the end effector, immediately before the deposition thereof. This makes it possible to have the system work at its best and to have greater flexibility in the design of the initial mix. The same consideration applies in the event that a viscosity modifying admixture is injected.

[0014] The emphasis placed on exploiting the properties of an engineerable material such as foamed or cellular concrete, whose density can be varied by suitably modifying the mix design, suggests the idea of being able to design and produce a three-dimensional element that is not characterised by a preset density determined a priori, as can be done with the technologies existing today, and rather of being able to vary the density during the step of laying the material itself. Today, any variation of the mix design of a construction material takes place in the initial mixer, an operation that can require stopping the additive manufacturing apparatus at every change in the mix design and precludes continuously varying the density during the printing process. In other known solutions, in cases where one desires a precise control of density, other approaches provide for the use of internal structures or voids inside the printed object. These structures are generally obtained by pausing the printing process, manually positioning or inserting lightweight materials or foams and then resuming the printing operation. Such procedures interrupt the continuity and speed of the printing process and also introduce potential weak points and lack of uniformity within the structure, thus possibly compromising its strength and overall stability, if not duly taken into consideration at the design stage.

[0015] A rapid change in the mix design and density of the construction material would allow significant progress in the design of elements produced by additive manufacturing, since it would enable not only the topological optimisation of the sections through the deposition of material according to a predetermined path, but also an optimisation, without discontinuity, of the properties that the material must possess (physical and mechanical) along the path itself.

[0016] The control of density is of fundamental importance in various applications in which structural requirements, thermal properties or weight considerations make it necessary to be able to modify the density of the printed material during the manufacturing process.

[0017] Considering the disadvantages of the current state of the art, there is an evident need for an improved additive manufacturing process which offers a dynamic control over the density of the printed material without compromising the efficiency, structural integrity and quality of the printed objects.

[0018] Object of the invention

[0019] The object of the present invention is to provide an innovative solution that allows rapid, precise modifications of density during the additive manufacturing process. Brief description of the drawings

[0020] Further advantages and features of the invention will become more apparent from the description of a possible embodiment thereof, provided solely by way of non-limiting example, with the aid of the appended drawings, in which:

[0021] - figs. 1 - 4 represent different embodiments of an end effector as per the invention;

[0022] - fig. 2a specifies some features of the solution in figure 2;

[0023] - fig. 5 represents a particular embodiment of an end effector as per the invention connected to a second end effector;

[0024] - figs. 6-7 represent two schematic configurations of an additive manufacturing apparatus as per the invention;

[0025] - fig. 8 represents a block diagram illustrating a procedure for additive manufacturing as per the invention;

[0026] Detailed description of preferred embodiments of the invention

[0027] An apparatus for additive manufacturing of a three-dimensional element comprises:

[0028] - a mixer for mixing basic components to obtain a construction material; the term “mixer” is understood also to include turbo mixers;

[0029] - a pump provided with a hopper adapted to receive the construction material from the mixer;

[0030] - an end effector 20 connected to the pump, the end effector 20 comprising a hollow body 21 provided with a nozzle 22 for emitting the construction material and an opening 23 for receiving the construction material from the pump;

[0031] - a generator of a medium suitable for reducing the density of the construction material; in the present description the term “generator” means, for example, generators, pumps, air compressors, and the like. Some possible configurations of a generator may comprise, for example, a foam generator, a tank connected to a pump for conveying an airentraining admixture, or an air compressor connected to a system for conveying compressed air.

[0032] - a movement system for moving the end effector 20.

[0033] An end effector 20 as per the invention further comprises at least one further opening 24 for introducing into the hollow body 21 , upstream of the nozzle 22, a medium suitable for reducing the density of the construction material coming from the respective generator and to be mixed with the construction material.

[0034] For the purposes of the present invention, the expression “medium suitable for reducing the density of the construction material” refers to any material / substance / mixture capable of altering the density of the construction material. Advantageously this medium can consist in a foam, compressed air, or compressed air mixed with an air-entraining agent. The foam may be obtained, for example, by dispersion of a gas in a liquid, obtained by turbulent mixing and favoured by the presence of substances that lower the surface tension.

[0035] The presence of the opening 24 directly in the end effector 20 allows the density of the construction material to be altered in proximity to the nozzle 22. In this manner, the amount of material present between the opening 24 and the nozzle 22 is much less than that present in systems in which the density is controlled in the initial mixer and there is thus a reduced time delay between the modification of the mix design to vary the density and the emission, from the nozzle 22, of the material with the desired density. In this manner one avoids stopping and emptying the system and enables a dynamic delivery of a construction material with variable density. The apparatus 1 comprises an adjustable valve 92 which regulates the introduction, into the hollow body 21 , of the medium suitable for reducing the density of the material. The adjustable valve 92 can take on a configuration in which it prevents the introduction, a configuration of maximum introduction, and optionally at least one intermediate configuration. The valve 92 is adjustable in a continuous or discrete manner. The adjustable valve 92 is located at said opening 24 or along a conduit leading to said opening 24. Conveniently, the adjustable valve 92, in a configuration in which it prevents said introduction, directs said medium suitable for reducing the density of the material towards a discharge outlet. In this manner one avoids stagnation in the valve 92 and / or in a section of tubing upstream of the valve 92. Therefore, upon the opening of the valve 92 it will be possible to use material that has not remained standing for a long time in the valve 92 and / or in the section of tubing upstream of the valve 92.

[0036] Conveniently, a corresponding valve can also be present to regulate the introduction into the hollow body 21 of one or more fluids described in the present description.

[0037] Conveniently, one or more of the characteristics described with reference to the valve 92 that regulates the introduction into the hollow body 21 of the medium suitable for reducing the density of the material can be repeated for each corresponding valve that regulates the introduction of another fluid into the hollow body 21 .

[0038] Advantageously, in the event that the medium suitable for reducing the density of the construction material requires the presence of an airentraining agent, at least one opening will be further comprised in the end effector 20 of the additive manufacturing apparatus to allow the introduction into the hollow body 21 of an air-entraining agent through a suitable pumping and dosing system thereof. Conveniently, a valve can be present which regulates the introduction of the air-entraining agent into the end effector 20.

[0039] Advantageously, it can be envisaged that the end effector 20 of the additive manufacturing apparatus further comprises at least one opening 25 for the introduction of at least one accelerator into the hollow body 21 through a suitable pumping and dosing system thereof, to enable rapid hardening of the construction material.

[0040] Advantageously, it can be envisaged that the end effector 20 of the additive manufacturing apparatus further comprises at least one opening 26 for the introduction of at least one admixture into the hollow body 21 . This admixture will have different purposes from the previously mentioned ones.

[0041] In order to facilitate the homogenisation of the construction material with the medium suitable for reducing the density of the construction material, it can be envisaged that the end effector 20 of the additive manufacturing apparatus further comprises mixing means 28 inside the hollow body 21 thereof. These means usually consist of propellers, whose shape varies based on the characteristics of the construction material to be mixed and which are disposed inside the hollow body 21 along the vertical axis thereof. A movement means, such as an electric motor, is usually installed at the end effector in order to drive these propellers. Conveniently, the mixing means 28 comprise dynamic mixing means. The dynamic mixing means can be activated at an adjustable speed. The activation of the mixing means 28 takes place by means of an adjustable-speed actuator 91.

[0042] The apparatus 1 comprises, in fact, an actuator 91 for activating the mixing means 28.

[0043] The apparatus 1 comprises control means 9.

[0044] For example, the control means 9 dynamically regulate the activation of the dynamic mixing means (for example the actuator 91 ).

[0045] In an alternative or additional solution, the control means 9 dynamically regulate the activation of the valve 92; this advantageously takes place according to the desired variation of the density of the construction material. The valve 92 could also be absent and the control means 9 could activate said generator (of the medium suitable for reducing the density of the construction material) which sends the medium suitable for reducing the density of the material to the end effector. In this manner, one could enable a dynamic delivery of a construction material with variable density. In order to improve the mixing and homogenisation effect, it can be envisaged that the end effector 20 of the additive manufacturing apparatus further comprises, on the inner wall of the hollow body 21 , protuberances 29 for mixing which can consist of inserts insertable into the hollow body 21 via through openings 50 present on the wall thereof. In addition, therefore, mixing means of a static type may also be present.

[0046] The control means 9 could also regulate the introduction into the end effector of one or more substances / admixtures (indicated in the present description). In an embodiment illustrated in fig. 5, the nozzle 22 of the end effector 20 is connected to an opening 30 of the hollow body 2T of a second end effector 20’ to allow for the introduction of the construction material coming out of the first end effector 20 into said second end effector 20’; said second end effector comprising at least one opening 40 for the introduction, into the hollow body 2T, of at least one further medium suitable for reducing the density of the construction material and a nozzle 22’ for emitting the construction material coming from the first end effector 20 mixed with said further medium suitable for reducing the density of the construction material.

[0047] Advantageously, a further opening (not illustrated) can be provided for the introduction of at least one admixture into the hollow body 21 ’.

[0048] In this case as well, the second end effector 20’ can further comprise mixing means 28’ inside the hollow body 2T thereof and also protuberances for mixing on the inner wall of the hollow body 21 ’.

[0049] Advantageously, in this case as well, the protuberances may consist of inserts insertable into the hollow body 2T via through openings present on the wall thereof.

[0050] Considering the above, the present invention discloses a procedure for additive manufacturing of a three-dimensional element by means of an additive manufacturing apparatus comprising:

[0051] - a mixer for mixing basic components to obtain a construction material;

[0052] - a pump provided with a hopper adapted to receive the construction material from the mixer;

[0053] - an end effector 20 connected to the pump, the end effector 20 comprising a hollow body 21 provided with a nozzle 22 for emitting the construction material and an opening 23 for receiving the construction material from the pump;

[0054] - a generator of a medium suitable for reducing the density of the construction material;

[0055] - a movement system for moving the end effector 20; the procedure comprising the steps of:

[0056] - mixing basic components inside the mixer to obtain a construction material;

[0057] - introducing the construction material into the hopper of the pump;

[0058] - pumping the construction material into the end effector by means of the pump 20;

[0059] - discharging the construction material from the nozzle 22 of the end effector 20; it being envisaged that the end effector 20 is moved by the movement system during the procedure so as to deposit the construction material in predefined positions;

[0060] The end effector 20 comprises at least one further opening 24 for the introduction into the hollow body 21 , upstream of the nozzle 22, of a medium suitable for reducing the density of the construction material coming from the respective generator and to be mixed with the construction material in order to alter the physical and / or mechanical and / or rheological properties thereof; and the procedure comprises at least the following steps:

[0061] - introducing a medium suitable for reducing the density of the construction material coming from the respective generator directly into the hollow body 21 of the end effector 20 via the opening 24. The step of introducing the medium suitable for reducing the density of the material into the hollow body 21 is controlled by an adjustable valve 92. The adjustable valve 92 can take on a configuration in which it prevents the introduction, a configuration of maximum introduction and optionally at least one intermediate configuration.

[0062] The procedure as per the invention, in the event that the end effector 20 of the additive manufacturing apparatus further comprises at least one opening for the introduction of an air-entraining agent into the hollow body 21 , comprises a step of introducing an air-entraining agent directly into the hollow body 21 of the end effector 20 via said opening.

[0063] The procedure as per the invention, in the event that the end effector 20 of the additive manufacturing apparatus further comprises at least one opening 25 for the introduction of at least one accelerator into the hollow body 21 , comprises a step of: introducing at least one accelerator directly into the hollow body 21 of the end effector 20 via the opening 25.

[0064] The procedure as per the invention, in the event that the end effector 20 of the additive manufacturing apparatus further comprises at least one opening 26 for the introduction of at least one admixture into the hollow body 21 , comprises a step of introducing at least one admixture directly into the hollow body 21 of the end effector 20 via the opening 26.

[0065] The procedure as per the invention, in the event that the end effector 20 of the additive manufacturing apparatus further comprises mixing means 28 inside the hollow body 21 thereof, comprises a step of activating the mixing means 28 so that the construction material mixed with the medium suitable for reducing the density thereof is rendered homogeneous. The activation of the mixing means 28 takes place at an adjustable speed (for example by means of an adjustable-speed actuator 91 ).

[0066] The control means 9 dynamically regulate said actuator 91 and / or said adjustable valve 92. This takes place, for example, based on the desired reduction in the density of the construction material. The valve 92 could also be absent and the control means 9 could activate said generator (of the medium suitable for reducing the density of the construction material) which sends the medium suitable for reducing the density of the material to the end effector. In this manner, one could enable a dynamic delivery of a construction material with variable density. The control means 9 may also correspond to the control system described in the course of the present description.

[0067] The procedure as per the invention, in the event that the nozzle 22 of the end effector 20 is connected to an opening 30 of the hollow body 2T of a second end effector 20’ to allow for the introduction of the construction material coming out of the first end effector 20 into said second end effector 20’, envisages that said second end effector comprises at least one opening 40 for the introduction of at least one admixture into the hollow body 2T and a nozzle 22’ for emitting the construction material coming from the first end effector 20 mixed with said further admixture, and further comprises the steps of:

[0068] - introducing the construction material coming out of the nozzle 22 of the end effector 20 into the hollow body 2T of the second end effector 20’ via the opening 30;

[0069] - introducing at least one admixture into the hollow body 2T of the second end effector 20’ via the opening 40

[0070] - emitting, through the nozzle 23’, the construction material obtained by mixing the construction material coming from the first end effector 20 and at least one admixture.

[0071] The procedure as per the invention, in the event that the second end effector 20’ further comprises mixing means 28’ inside the hollow body 2T thereof, comprises a step of activating the mixing means 28 so that the construction material coming from the first end effector 20 with the admixture added into the hollow body 2T is rendered homogeneous.

[0072] In an apparatus as per the invention, in order to modify in real time the amount of medium suitable for reducing the density of the construction material or of any admixture to be mixed with the construction material, suitable dosing systems can be present.

[0073] Advantageously, all the elements of the system can be managed remotely by means of a control system which enables a continuous variation of the doses of the admixtures and construction material output by the pump. Though the inventive concept has been described with reference to example embodiments, it will be evident to the person skilled in the art that various changes and modifications can be introduced without going outside the scope of the inventive concept. Therefore, it should be understood that the aforesaid embodiments are not limiting, but rather illustrative. The invention is defined by the following claims.

Claims

CLAIMS1. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT by means of an additive manufacturing apparatus comprising:- a mixer for mixing basic components inside the mixer to obtain a construction material;- a pump provided with a hopper adapted to receive the construction material from the mixer;- an end effector (20) connected to the pump, the end effector (20) comprising a hollow body (21 ) provided with a nozzle (22) for emitting the construction material and an opening (23) for receiving the construction material from the pump;- a generator of a medium suitable for reducing the density of the construction material;- a movement system for moving the end effector (20); the procedure comprising the steps of:- mixing basic components inside the mixer to obtain a construction material;- introducing the construction material into the hopper of the pump;- pumping the construction material into the end effector by means of the pump (20);- discharging the construction material from the nozzle (22) of the end effector (20); it being envisaged that the end effector (20) is moved by the movement system during the procedure so as to deposit the construction material in predefined positions; the end effector (20) of the additive manufacturing apparatus further comprising mixing means (28) inside the hollow body (21 ) thereof; said procedure being characterised in that the end effector (20) comprises at least one further opening (24) for the introduction into the hollow body (21 ), upstream of the nozzle (22), of a medium suitable forreducing the density of the construction material coming from the respective generator and to be mixed with the construction material in order to alter the physical and / or mechanical and / or rheological properties thereof; and in that it comprises at least the following steps:- introducing a medium suitable for reducing the density of the construction material coming from the respective generator directly into the hollow body (21 ) of the end effector (20) via the opening (24) to enable a dynamic delivery of a construction material with variable density;- activating the mixing means (28) so that the construction material mixed with the medium suitable for reducing the density thereof is rendered homogeneous.

2. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 1 , wherein the activation of the mixing means (28) takes place by means of an adjustable-speed actuator (91 ); the step of introducing the medium suitable for reducing the density of the material into the hollow body (21 ) being controlled by an adjustable valve (92); said adjustable valve (92) being able to take on a configuration in which it prevents said introduction, a configuration of maximum introduction and at least one intermediate configuration; according to the desired reduction in the density of the construction material, said control means (9) dynamically regulating said actuator (91 ) and / or said adjustable valve (92).

3. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 2, wherein said adjustable valve (92), in a configuration wherein it prevents said introduction, directs said medium suitable for reducing the density of the material towards a discharge outlet.

4. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 1 or 2 or 3, wherein the medium suitable for reducing the density of the construction material is afoam.

5. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 1 or 2 or 3, wherein the medium suitable for reducing the density of the construction material is compressed air.

6. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 5, wherein the end effector(20) of the additive manufacturing apparatus further comprises at least one opening for the introduction of an air-entraining agent into the hollow body(21 ) through a suitable pumping and dosing system thereof; and wherein the procedure further comprises a step of:- introducing an air-entraining agent directly into the hollow body (21 ) of the end effector (20) via said opening.

7. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of the preceding claims, wherein the step of introducing a medium suitable for reducing the density of the construction material comprises modifying in real time the amount of said medium suitable for reducing the density of the construction material by means of dosing systems.

8. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of the preceding claims, which comprises remotely managing a continuous variation of the dosages of admixtures and construction material output by the pump by means of a control system.

9. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of the preceding claims, wherein the end effector (20) of the additive manufacturing apparatus further comprises at least one opening (25) for the introduction of at least one accelerator into the hollow body (21 ), through a suitable pumping and dosing system thereof; and wherein the procedure further comprises a step of:- introducing at least one accelerator directly into the hollow body (21 ) of the end effector (20) via the opening (25).

10. PROCEDURE FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of the preceding claims, wherein the end effector (20) of the additive manufacturing apparatus further comprises at least one opening (26) for the introduction of at least one admixture into the hollow body (21 ); and wherein the procedure further comprises a step of:- introducing at least one admixture directly into the hollow body (21 ) of the end effector (20) via the opening (26).

11. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT comprising:- a mixer for mixing basic components to obtain a construction material;- a pump provided with a hopper adapted to receive the construction material from the mixer;- an end effector (20) connected to the pump, the end effector (20) comprising a hollow body (21 ) provided with a nozzle (22) for emitting the construction material and an opening (23) for receiving the construction material from the pump;- a generator of a medium suitable for reducing the density of the construction material;- a movement system for moving the end effector (20); characterised in that the end effector (20) comprises at least one further opening (24) for the introduction into the hollow body (21 ), upstream of the nozzle (22), of a medium suitable for reducing the density of the construction material coming from the respective generator and to be mixed with the construction material to enable a dynamic delivery of a construction material with variable density; the end effector (20) of the additive manufacturing apparatus further comprising, inside the hollow body (21 ) thereof, mixing means (28)activatable so that the construction material mixed with the medium suitable for reducing the density thereof is rendered homogeneous.

12. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 11 , wherein said apparatus comprises:- an adjustable valve (92) which regulates the introduction of the medium suitable for reducing the density of the material into the hollow body (21 ); said adjustable valve (92) being able to take on a configuration in which it prevents said introduction, a configuration of maximum introduction and at least one intermediate configuration;- control means (9) which dynamically regulate the activation of the mixing means (28) and / or of the adjustable valve (92) based on the desired reduction in the density of the construction material.

13. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 11 or 12, wherein the medium suitable for reducing the density of the construction material is a foam.

14. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 11 or 12, wherein the medium suitable for reducing the density of the construction material is compressed air.

15. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to claim 14, wherein the end effector(20) of the additive manufacturing apparatus further comprises at least one opening for the introduction of an air-entraining agent into the hollow body(21 ).

16. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 15, wherein the end effector (20) of the additive manufacturing apparatus further comprises at least one opening (25) for the introduction of at least one accelerator into the hollow body (21 ).

17. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 16, wherein the end effector (20) of the additive manufacturing apparatus further comprises at least one opening (26) for the introduction of at least one admixture into the hollow body (21 ).

18. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 17, wherein said mixing means (28) consist of propellers which are disposed inside the hollow body (21 ) along the vertical axis thereof; a movement means for activating said propellers being installed at the end effector.

19. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 18, wherein the end effector (20) of the additive manufacturing apparatus further comprises protuberances (29) for mixing on the inner wall of the hollow body (21 ).

20. APPARATUS FOR ADDITIVE MANUFACTURING of A THREE- DIMENSIONAL ELEMENT according to the claim 19, wherein the protuberances consist of inserts insertable into the hollow body (21 ) via through openings (50) present on the wall thereof.

21. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 20, wherein said apparatus comprises dosing systems capable of modifying in real time the amount of medium suitable for reducing the density of the construction material.

22. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE- DIMENSIONAL ELEMENT according to any one of claims 11 to 21 , wherein said apparatus comprises a control system for controlling the elements of the apparatus and capable of remotely managing a continuous variation of the dosages of admixtures and construction material output by the pump.

23. APPARATUS FOR ADDITIVE MANUFACTURING OF A THREE-DIMENSIONAL ELEMENT according to any one of claims 11 to 21 , wherein it further comprises a control system configured to remotely control the elements of the apparatus.

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