IT201800010225A1 - Improved equipment and method for 3D printing articles with high mechanical and aesthetic characteristics. - Google Patents

Description

PERFECTED EQUIPMENT AND METHOD FOR 3D PRINTING OF

ARTICLES WITH HIGH MECHANICAL AND AESTHETIC CHARACTERISTICS

DESCRIPTION

The present invention relates to an improved equipment and method for the 3D printing of articles with high mechanical and aesthetic characteristics.

Background

The invention concerns the field of additive manufacturing, or more simply of 3D printing. 3D printing refers to the manufacture of three-dimensional objects through an additive manufacturing process starting from a digital 3D model, created using a CAD modeling system.

After having produced a 3D model, as is known in the branch, the related file is subjected to a processing process using particular software programs that perform the so-called "slicing" of the geometry, i.e. extrapolate a sequence of cross sections of the model itself that constitute the layers that will compose the object.

There are several technologies for 3D printing, which differ mainly in the way the layers are printed.

The present invention relates in particular to the method known as FDM® (Fused Deposition Modeling, a trademark registered by Stratasys Ltd), or also as FFF (Fused Filament Fabrication), which is based on the use of an extrusion head equipped with a nozzle from which a molten polymer emerges which is deposited in layers, according to a predetermined 3D model, in order to manufacture the article having the desired shape. The cooling of the polymer gives rise to the formation of the solid object of the desired shape.

Usually 3D printing is associated with 3-axis motion systems, in which the material extruded from the nozzle can be deposited coplanar with the printer work surface.

3D printing systems are known that use extrusion heads fed either with a continuous thread or with polymer granules that are melted and deposited through a nozzle on a support surface on which the object to be printed is formed. Such known systems use extrusion heads provided with a circular section nozzle, which therefore do not require a particular orientation in space during the deposition of the molten material. However, the formation of articles by depositing a molten jet of circular section has some disadvantages in that the contact surface between the superimposed layers is reduced, therefore the mechanical and aesthetic properties are not optimal.

Furthermore, the known systems do not provide for the possibility of using reinforcing elements such as continuous fibers or filaments, so as to obtain a composite article, i.e. comprising the polymer that is extruded and a reinforcing material consisting of continuous fibers or filaments which adhere, or they are integrated into the polymer itself.

Finally, the known systems are made for 3-axis printers of large dimensions, which are difficult to adapt to 6-axis movement systems, thus not allowing good control interfaced with anthropomorphic industrial robots, and not allowing the creation of objects with particular shapes. Such known systems are therefore unable to meet the needs of an increasingly demanding professional market in terms of quality and resistance of the printed product.

WO 2017/085649 A1 describes an equipment and a method for 3D printing of fiber-based composite materials. The apparatus and method described are based on the impregnation of a continuous fiber with a liquid consisting of a polymerizable resin, for example a thermosetting resin, and its subsequent feeding to a feeding head equipped with a nozzle sized according to the section. of the fiber, to prevent excess resin from dripping from the nozzle. The resin is then polymerized and placed on the support surface on which the object to be printed is formed. The traction of the fiber is determined by the initial point of physical anchoring on the support surface and by the acceleration given by the movement system to spread the fiber, which simply flows from a spool through a resin impregnation system up to the feeding head and to the nozzle. The amount of usable resin is low, being determined by the impregnation capacity of the fiber itself, so the molded object has a relatively low resin / fiber weight ratio. Due to the limited quantity of usable resin and the scarce availability of thermosetting resins compared to all possible thermoplastic composites, the method has limited application possibilities, being able to manufacture only bonded products with very high rigidity, with transparent or semitransparent materials. In this context, the technical task of the present invention is to make available an apparatus and a method for the three-dimensional printing of articles that eliminate or reduce the drawbacks of known systems.

In particular, an object of the present invention is to provide an apparatus and a method for the three-dimensional printing of articles of high mechanical and aesthetic qualities. Another purpose of the present invention is to provide an apparatus and a method for the three-dimensional printing of articles of high mechanical and aesthetic quality comprising one or more thermoplastic resins reinforced with continuous fibers or filaments, therefore of composite articles.

A further object of the present invention is to provide an apparatus and a method for three-dimensional printing that can be applied to handling systems having more than 3 degrees of freedom of movement, for example that can be interfaced with anthropomorphic industrial robots with 6 axes, and thus allowing the creation of objects with particular shapes and even large dimensions.

Summary of the invention

The aforesaid and other purposes and advantages of the invention, as will emerge from the following description, are achieved with an apparatus for the three-dimensional printing of articles in thermoplastic resin, comprising a print head associated with means for moving along at least 3 axes, in said printing head comprises a melting chamber provided with heating means for said thermoplastic resin, feeding means of said thermoplastic resin to said melting chamber and a nozzle, characterized in that said nozzle comprises an outlet hole with a polygonal section for called fused thermoplastic resin.

According to another aspect of the invention, said print head of said three-dimensional printing equipment is mounted inside a ball bearing which is associated with said handling means according to at least 3 axes.

According to another aspect of the invention, said apparatus for three-dimensional printing comprising the print head mounted inside a ball bearing is adapted for printing composite articles comprising one or more thermoplastic resins and a continuous reinforcing element.

In this case, the apparatus for the three-dimensional printing of composite articles with a continuous reinforcing element comprises a printing head associated with handling means along at least 3 axes, and means for feeding said continuous reinforcing element to said printing head, characterized in that said print head is mounted inside a ball bearing and comprises an extruder for a thermoplastic resin, means for feeding said thermoplastic resin to said extruder and means for guiding said continuous reinforcing element, in which:

- said extruder comprises a melting chamber, in which a rotating screw is mounted around its longitudinal axis and the longitudinal axis of the extruder, heating means for said thermoplastic resin and a nozzle; And

- said nozzle comprises an outlet hole of said thermoplastic resin melted from said melting chamber and a guide channel of said continuous reinforcing element towards said outlet hole, in which said outlet hole has a polygonal section.

A further aspect of the invention also relates to a method for the three-dimensional printing of articles comprising the steps of:

a) feeding a thermoplastic resin to a printing head rotatable around its longitudinal axis according to an angle of 360 °;

b) melting said thermoplastic resin in said printing head having a nozzle with a polygonal section hole and expelling a flow of resin having a corresponding polygonal section;

c) moving said print head according to a predefined program to form said article while maintaining a predefined spatial orientation of said resin flow of polygonal section;

d) depositing said resin flow on a printing plane or surface to form said article with overlapping or side-by-side layers along the sides of said resin flow of polygonal section, without being bound to the coplanarity between the layers and the printing surface.

Yet another aspect of the invention relates to a method for the three-dimensional printing of composite articles comprising continuous reinforcing elements comprising the following additional steps:

a1) joining a continuous reinforcing element to said fused thermoplastic resin and forming a continuous flow of composite material comprising said continuous reinforcing element and said fused thermoplastic resin;

c1) keeping fixed the position of said continuous reinforcing element with respect to said thermoplastic resin melted in said print head.

According to the present invention, the term "thermoplastic resin" indicates both a single resin and a mixture of thermoplastic resins.

According to the present invention, the term "continuous reinforcing element" indicates a continuous filament or a continuous fiber or a weave of fibers such as a rope or a ribbon, having any cross section. The material constituting this element can be a natural or synthetic resin, a metal, glass, carbon, an inorganic material, or a combination of these materials. Glass, carbon and inorganic materials (such as basalt) are particularly advantageous when they are in the form of fiber.

Detailed description

The apparatus and the method for the three-dimensional printing of articles according to the invention find application in various manufacturing sectors, especially those dealing with products and semi-finished products that require lightness, resistance and that have complex geometries, even on large volumes, with production numbers that do not justify the investment in a mold that is often even impossible to make.

Among the sectors of interest are the nautical and aeronautical sectors, and that of the production of bodies and frames, including the automotive sector. Last, but not least, the architectural sector, where the invention makes it possible to create load-bearing structures characterized by great lightness and shapes that are totally adaptable to the specific needs of each individual creation, without the need to prepare molds.

The invention is now described with reference to the attached figures, given by way of non-limiting example, in which:

- Fig. 1 is a schematic perspective view of an embodiment of an apparatus according to the invention;

- Fig.2 is a schematic sectional view of a print head of the apparatus of Fig.1 according to a first embodiment of the invention;

- Fig.2A is a schematic perspective view of a detail of the head of Fig.2; - Fig. 3 is a schematic perspective view of an article printed with the print head of Fig. 2;

- Fig. 3A is a schematic perspective view of an article molded according to the known art;

- Fig.4 is a schematic sectional view of a print head according to a second embodiment of the invention;

- Fig. 5 is a schematic sectional view of a print head according to a third embodiment of the invention;

- Fig.5A is a schematic perspective view of a detail of the head of Fig.5; - Figs. 6A and 6B are schematic perspective views of composite articles printed with the print head of Fig.5;

- Fig.7 is a schematic sectional view of a print head according to a fourth embodiment of the invention;

- Fig. 8 is an enlarged schematic view of a detail of the print head of Fig. 7; And

- Fig. 9 is an enlarged schematic view of a different embodiment of the print head of Fig.7.

With reference to Fig.1, an apparatus for the three-dimensional printing of articles has been illustrated comprising a print head 10 mounted on the arm 12 of a 6-axis robot, designated by the arrows I-VI.

A thermoplastic resin is fed to the print head 10 through a line 14 and through a nozzle 50, located at the lower end of the print head 10, a flow 18 of molten resin is expelled, which is deposited on a printing plane or surface. 20 to form an object 22.

The print head 10 is moved according to a predetermined 3D model, in order to manufacture the article 22 having the desired shape.

In Fig. 1 reference has been made to a 6-axis robot, but of course it is possible to use a robot, or another device for moving the print head, which has more or less degrees of freedom of movement, for example 3, 4 , 5, 7, 8 and 9. It is clear that the use of complex movement systems, such as robotic systems with 6 axes or more, allows you to freely vary the spatial orientation according to which the material is extruded and deposited. melted, allowing the manufacture of objects with more articulated and more performing geometries. According to an aspect of the invention, the printing head 10 is mounted inside a ball bearing 13 which is associated with the arm 12 of the robot by means of a fixing flange, so as to be able to perform a rotation of 360 ° around the longitudinal axis Y, as indicated by arrow VII of Fig.1.

In Figs. 2 and 2A show a print head 10 to which a continuous thread 11 of thermoplastic resin is fed, coming from a coil not shown.

The continuous wire 11 is introduced into a melting chamber 30 by means of a wire pusher device 25, placed upstream of the melting chamber 30. The wire pusher device 25 comprises an idle roller 29 and a motorized roller 27, driven in rotation by a non-electric motor. shown, which grasp the wire 11 and push it downwards, inside the melting chamber 30. The electric motor and the wire pusher 25 are integral with the print head 10 and move with it by rotating integrally inside the bearing 13, so as to avoid that the rotation of the head 10 causes the thermoplastic resin thread 11 to twist on itself. This is particularly useful when the fiber, or filament, does not have a circular section, but for example has a rectangular section.

The melting chamber 30 is provided with heating means constituted, for example, by resistances 38, suitable for establishing in the melting chamber 30 the temperature necessary for the melting of the thermoplastic resin. In one embodiment the resistors 38 can be for example high temperature resistors, for example high density cartridge resistors, capable of working in constant operation up to a temperature of 800 ° C, in the melting chamber 30.

The terminal part of the extruder includes a nozzle 50 for the release of the melted thermoplastic resin.

As shown in more detail in Fig.2A, the melting chamber extends into the nozzle 50, whose internal cavity has an upper part 50a which constitutes the lower extension of the melting chamber 30, and has a cylindrical shape. The internal cavity of the nozzle 50 is also formed with an intermediate part 50b of a conical shape and a lower part 50c which gradually varies until it assumes a parallelepiped shape and ends with a hole 52 through which a flow 18 of melted thermoplastic resin is expelled. . The hole 52 has a polygonal section, more particularly square.

With reference to Fig. 3, a molded article 22 was shown obtained by depositing and superimposing the flow 18 of resin expelled from the hole 52 of the nozzle 50, therefore having a square section, like the hole 52 itself. The various layers of thermoplastic material they have been laid with the sides parallel, therefore they adhere perfectly along all the surfaces in contact, increasing the mechanical resistance of the product and improving its surface quality. In fact, the surfaces of the artefact are planar and homogeneous.

Fig. 3A shows a similar article 22A obtained by means of a 3D printer according to the known technique, ie with a nozzle provided with a round expulsion hole. In this case it can be seen that the various layers 18A of deposited material adhere only along a reduced contact area, a factor which causes a limited mechanical resistance. Furthermore, the surface quality is not good, as the surface is defined by ridges and valleys that require a smoothing operation to obtain a flat and homogeneous surface.

To obtain the deposition of overlapping layers in a correct way, as shown in Fig. 3, the entire print head 10 is able to rotate on itself by 360 ° inside bearings such as the bearing 13 of Fig. 1, according to axis VII, so that the flow of deposited resin always maintains the same relative position for whatever position the robot assumes in its movement.

The orientation of the print head can be achieved either by means of an accelerometer / gyroscope that detects the movements of the robot, or by command of the robot itself, indicating the degrees of rotation that the head 10 must have.

Using these means, the material can be deposited while keeping the faces of the layer in contact with the previous one parallel, as shown in Fig. 3.

With reference to Fig. 4, a print head 10 according to a second embodiment of the invention has been illustrated, in which the thermoplastic resin is fed in the form of granules instead of a continuous thread. The elements of this second embodiment of the print head 10 which correspond to the elements of the first embodiment are indicated with the same reference number.

The print head 10 is connected to means for feeding the thermoplastic resin 11, consisting of a hopper 24 and a feeding duct 26. The thermoplastic resin is typically in the form of granules, flakes, compounds or powders. It is loaded into the hopper 24 in bulk form and transferred by gravity to the print head 10 through the duct 26.

The print head 10 comprises an extruder 28 for thermoplastic resins, provided with a melting chamber 30 in which a worm 32 is mounted, which rotates around its own longitudinal axis Y, coinciding with the longitudinal axis of the extruder and of the head. print itself. The melting chamber 30 is provided with a duct 34 for the introduction of the resin granules coming from the supply duct 26. The screw 32 is driven by a motor 35, through means known in the art. A motor 36 controls the rotation of the extruder 28 around the longitudinal axis Y, as defined by arrow VII in Fig.1. This rotation is allowed by the assembly of the entire printing head 10 inside a bearing 13, as also shown in Fig. 1. According to an aspect of the invention, the printing head 10 can perform a rotation of 360 ° around the longitudinal axis Y.

The melting chamber 30 is provided with heating means constituted, for example, by resistances 38, suitable for establishing in the melting chamber 30 the temperature necessary for the melting of the thermoplastic resin, together with the shear force exerted by the worm 32. In one embodiment the resistors 38 are high power resistors, capable of achieving temperatures up to 450 ° C in the melting chamber 30.

The terminal part of the extruder includes a nozzle 50 for the release of the melted thermoplastic resin. The nozzle 50 has a truncated cone shape and is provided with an internal cavity as shown in Fig. 2A, ending with a polygonal hole 52, in particular with a square section.

The nozzle 50 is equipped with electrical resistances 39, for example high density cartridge resistors, capable of working in constant operation up to a temperature of 800 ° C, thus being able to further heat the resin granules for processing with special polymers. performers.

Fig. 5 shows a third embodiment of the print head according to the invention, similar to the first embodiment (Fig. 2) as regards the feeding of the resin 11 in the form of a continuous thread, but different from this form actuation due to the presence of a continuous reinforcing element, such that the molded article is a composite consisting of resin and reinforcing element.

With reference to Fig. 5, the continuous wire 11 is introduced into a melting chamber 30 by means of a wire pusher device 25, placed upstream of the melting chamber 30, similarly to what is shown in Fig. 2. The wire pusher device 25 comprises a roller idle 29 and a motorized roller 27, driven in rotation by an electric motor not shown. The electric motor and the wire pusher 25 are integral with the print head 10 and move with it by rotating integrally inside the bearing 13, so as to prevent the rotation of the head 10 from causing the resin thread to twist on itself. thermoplastic 11 or a twist of the reinforcing fiber 40. This is particularly useful when the fiber, or filament, has no circular section, but for example has a rectangular section.

The melting chamber 30 is provided with heating means constituted, for example, by resistances 38, suitable for establishing in the melting chamber 30 the temperature necessary for the melting of the thermoplastic resin. In one embodiment the resistors 38 are high density cartridge resistors, capable of working in constant operation up to a temperature of 800 ° C.

The terminal part of the extruder includes a nozzle 50 for the release of the melted thermoplastic resin.

The print head 10 also comprises means for feeding a continuous reinforcing element, consisting for example of a continuous fiber 40 wound on a reel 42. The feeding means for the fiber 40 comprise an electric motor 43, which drives a yarn pusher device 44, placed next to the melting chamber 30.

The nozzle 50 has a truncated conical shape and an upper part 51 is defined in it on which a hole 41 is provided, near the outer edge of the part 51, through which the fiber 40 enters the nozzle 50.

In one embodiment, the thread pusher device 44 of the fiber 40 is similar to the thread pusher device 25 of the synthetic resin thread.

At the output of the wire pusher 44, the fiber 40 enters the terminal part of the print head 10, consisting of the nozzle 50, through the hole 41 for communication with a channel 56, as also shown in Fig. 5A. The hole 41 is made in the upper part 51 of the nozzle 50, outside the melting chamber.

As shown in more detail in Fig.5A, the melting chamber extends into the nozzle 50, whose internal cavity has an upper part 50a which constitutes the lower extension of the melting chamber 30, and has a cylindrical shape. The internal cavity of the nozzle 50 is also formed with an intermediate part 50b of conical shape and a lower part 50c which gradually varies in shape until it assumes a parallelepiped shape and ends with a hole 52 through which a flow 18 of resin is expelled. fused thermoplastic.

The hole 52 has a polygonal section, more particularly rectangular.

The fiber 40 is joined to the flow of melted thermoplastic resin 18 so that the deposition of layers of thermoplastic resin leads to the formation of a composite molded article.

As mentioned, the fiber 40 can be made of various materials, such as carbon, glass, metal or other synthetic resin having a melting point higher than that of the thermoplastic resin 11.

With reference to Figs. 6A and 6B, some shapes of the composite material were shown at the outlet of the nozzle 50, with a rectangular section.

In Fig. 6A an extruded composite material 18A comprising a single fiber 40A was shown.

Figure 6B shows an extruded composite material 18B comprising a weave of fibers or tape 40B.

As shown in Fig. 1, and previously mentioned, the entire print head 10 is able to rotate on itself so that the flow of polygonal section material being deposited, and the reinforcing fiber 40A, or the belt 40B, combined with the thermoplastic resin, always maintain the same relative position with respect to the cast of molten resin, regardless of the position assumed by the robot or other movement system in its movement. This feature is important in making a composite material having the structure shown in Figs. 6A and 6B since it is advantageous that the tape can combine with the resin always maintaining the same relative position with respect to the cast of molten resin, and that this can be deposited superimposed or side by side in layers with parallel orientation of the faces.

The orientation of the print head can be achieved either by means of an accelerometer / gyroscope that detects the movements of the robot, or by command of the robot itself, indicating the degrees of rotation that the head 10 must have.

Using these means, the fiber 40 - in the form for example of the ribbon 40B - can be deposited in a uniform manner and well incorporated or joined to the resin, in various relative spatial arrangements. For example, the fiber 40 can be deposited keeping the longest side of the rectangle always oriented correctly, so as to achieve an optimal deposition of the layers, as previously mentioned.

At the end of the processing, or if it is necessary to have one or more points of discontinuity in the fiber within the processing, a pneumatic cutter placed on the side of the head 10 cuts the fiber. This pneumatic cutter, not shown, is brought into position under the outlet of the head 10 by means of a servomechanism that lowers and raises it so as not to create collisions with the workpiece when not in use.

The equipment of the invention allows you to insert or join any type of fiber, ribbon or rope, including copper conductors, to the thermoplastic resin, thus allowing you to insert electrical connections, including structural ones, inside the printed object.

The print head 10, as mentioned, is able to rotate on itself for an extension of 360 °, in order to be able to direct both the fiber 40 well and to correctly orient the nozzle 50. This movement is made possible by the fact that the head 10 is supported by a ball bearing 13 of large dimensions, fixed to the connection flange with the arm 12 of the robot (Fig. 1). The stepping motor which rotates the entire head 10 is connected to the same flange, thanks to the commands given by a control system, not shown. This can use both direct signals from the robot and a gyroscope-accelerometer placed on the head itself, which detects its movements in space.

The motion is transmitted from the motor to the head 10 by means of a crown gear, not shown, to ensure its accuracy.

The use of all the aforementioned methods on a robot with 6 or more axes allows you to overcome the shape constraints imposed by the classic 3-axis printing, allowing you to create real lattices of fiber and thermoplastic resin for a very high structural resistance compared to that obtained with normal 3D printing, in addition to the fact of being able to create even more complex shapes due to the absence of constraints in terms of undercut.

With reference to Figs. 7 and 8, a fourth embodiment of the invention has been shown, similar to the second embodiment of Fig. 4 as regards the feeding of the resin in the form of granules, but different from this embodiment due to the presence of a continuous reinforcing element, such that the molded article is a composite consisting of resin and a reinforcing element.

In this embodiment, the print head 10 is connected to means for feeding the thermoplastic resin 11, consisting of a hopper 24 and a feeding duct 26. The thermoplastic resin is typically in the form of granules, compound flakes and powders. It is loaded into the hopper 24 in bulk form and transferred by gravity to the print head 10 through the duct 26.

The print head 10 comprises an extruder 28 for thermoplastic resins, provided with a melting chamber 30 in which a worm 32 is mounted, rotating around its longitudinal axis Y, coinciding with the longitudinal axis of the extruder. The melting chamber 30 is provided with a duct 34 for the introduction of the resin granules coming from the supply duct 26. The screw 32 is driven by a motor 35, through means known in the art. A motor 36 controls the rotation of the extruder 28 around the longitudinal axis Y, as defined by arrow VII in Fig.1. Even the entire print head 10 can rotate 360 ° being mounted inside a bearing 13, as also shown in Fig.1.

The melting chamber 30 is provided with heating means consisting, for example, of resistances 38, suitable for establishing in the melting chamber 30 the temperature necessary for the melting of the thermoplastic resin, together with the shear force exerted by the worm 32. In one embodiment the resistors 38 are high power resistors, capable of achieving temperatures up to 450 ° C in the melting chamber 30.

The terminal part of the extruder includes a nozzle 50 for the release of the melted thermoplastic resin.

The print head 10 also comprises means for feeding a continuous reinforcing element, consisting for example of a continuous fiber 40 wound on a reel 42. The feeding means for the fiber 40 comprise an electric motor 43, which drives a yarn pusher device 44, placed next to the melting chamber 30 of the extruder 28, but outside the extruder 28. The fiber is then unwound from the reel 42 to enter a tube 46, which protects it and guides it up to the wire pusher 44, mounted on the tube 46, outside the extruder.

The nozzle 50 has a truncated conical shape and an upper part 51 is defined in it on which a hole 41 is provided, near the outer edge. More particularly, the wire pusher 44 is mounted on the tube 46 at the hole 41, through which the fiber 40 enters the nozzle 50.

In one embodiment, the wire pusher device 44 comprises a knurled pinion driven by a belt connected to the motor 43 in a way that is not illustrated as it is known. The fiber 40 is pushed against the pinion by a pressure roller urged by a spring. The rotation of the knurled pinion advances the fiber 40 by dragging it downwards, in the direction of the arrow A.

The electric motor 43 and the wire pusher 44 are integral with the print head 10 and move with it, so as to prevent the rotation of the head 10 from causing the fiber 40 to twist on itself. This is particularly useful when the fiber, or filament, has no circular section, but for example has a polygonal section.

At the outlet of the wire pusher 44, the fiber 40 enters the terminal part of the print head 10, consisting of the nozzle 50, through the hole 41 for communication with a channel 56, as will be explained later.

With reference to Fig. 8, the nozzle 50 includes a hole 52 for the outlet of the molten resin from the extruder 28, with a polygonal section, in particular rectangular.

The nozzle 50 also comprises a channel 56 for containing and guiding the fiber 40, which accesses it through the hole 41. The channel 56 is oriented obliquely starting from the peripheral hole 41 towards the Y axis of the extruder, so to guide the fiber 40 towards the hole 52 for the outlet of the molten resin from the extruder. In the area immediately downstream of the hole 52, the fiber 40 comes into contact with the molten resin so as to form a continuous flow of composite material 18.

The feeding speed of the fiber 40 is adjusted to correspond to the extrusion speed of the thermoplastic resin, with extrusion speed meaning the length of the extruded filament in the unit of time, for example mm / minute.

In a different embodiment, shown in Fig. 9, the fiber 40 is incorporated in the cast of molten resin that comes out of the extruder. In this embodiment, the terminal part of the channel 56 is located coaxially with respect to the hole 52 of the extruder, so that the fiber 40 is incorporated into the flow of the molten resin before it comes out of the hole 52.

The nozzle 50 is equipped with electrical resistances 39, for example high density cartridge resistors, capable of working in constant operation up to a temperature of 800 ° C, thus being able to further heat the resin granules for processing with special polymers. performers.

As mentioned, the fiber 40 can be made of various materials, such as carbon, glass, metal or other synthetic resin having a melting point higher than that of the thermoplastic resin 11.

The shapes of the composite material at the outlet of the nozzle 50 have been shown in Figs.

6A and 6B.

As shown in Fig. 1, and previously mentioned, the whole print head 10 is able to rotate on itself for 360 °, so that the flow of polygonal section material that is deposited, and the fiber 40A of reinforcement, or the belt 40B, combined with the thermoplastic resin, always maintain the same relative position with respect to the cast of molten resin, regardless of the position the robot assumes in its movement. This feature is important in making a composite material having the structure shown in Figs. 6A and 6B since it is advantageous that the tape can combine with the resin always maintaining the same relative position with respect to the cast of molten resin, and that this can be deposited superimposed or side by side in layers with programmed orientation of the faces.

The orientation of the print head can be achieved either by means of an accelerometer / gyroscope that detects the movements of the robot, or by command of the robot itself, indicating the degrees of rotation that the head 10 must have.

Using these means, the fiber 40 - in the form for example of the ribbon 40B - can be deposited in a uniform manner and well incorporated or joined to the resin, in various relative spatial arrangements. For example, the fiber 40 can be deposited keeping the longest side of the rectangle always oriented correctly, so as to achieve an optimal deposition of the layers, as previously mentioned.

At the end of the processing, or if it is necessary to have one or more points of discontinuity in the fiber within the processing, a pneumatic cutter placed on the side of the head 10 cuts the fiber. This pneumatic cutter, not shown, is brought into position under the outlet of the head 10 by means of a servomechanism, which lowers and raises it so as not to create collisions with the workpiece when not in use.

The equipment of the invention allows you to insert or join any type of fiber, ribbon or rope, including copper conductors, to the thermoplastic resin, thus allowing you to insert electrical connections, including structural ones, inside the printed object.

As mentioned, the movement of the head 10 is made possible by the fact that the head is mounted inside a large-sized ball bearing 13, fixed to the connection flange with the arm 12 of the robot. The stepping motor 36 is connected to the same flange, which rotates the entire head 10, thanks to the commands given by a control system, not shown. This can use both direct signals from the robot and a gyroscope-accelerometer placed on the head itself, which detects its movements in space.

The motion is transmitted from the motor to the head 10 by means of a crown gear, not shown, to ensure its accuracy.

The use of all the aforementioned methods on a robot with 6 or more axes allows to overcome the shape constraints imposed by the classic 3-axis printing, allowing the creation of real fiber and thermoplastic resin networks for a very high structural resistance compared to that obtained with normal 3D printing, in addition to the fact of being able to create even more complex shapes due to the absence of constraints in terms of undercut.

However, it is understood that the head 10 is structured to be used on any movement system, such as a large 3-axis support on a numerically controlled machine, or on an overhead crane with a vertical axis having a rigid and non-rigid movement. hanging hook.

The equipment according to the invention, and the related systems, are controlled by a combined system of electronics and software.

In one embodiment, the electronics comprises a multiprocessor card that controls all the operation, from an interface card with the robot, which allows uniform management of the two, from a control panel where, in addition to the two cards, they are housed all power components, power supplies, motor drives and the like, and a control console for the human-machine interface.

The equipment includes a cooling system divided into two distinct parts, not shown.

One part has the function of cooling the functional parts of the print head such as the motors and the parts inlet of the material that must not be heated. This type of cooling is accomplished using a coolant.

Another part has the function of cooling the printed object to make it harden. This type of cooling is achieved by means of compressed air.

The liquid system includes a series of special cavities inside the components of the head 10 and external heat sinks mounted on the motors. The coolant is circulated by a pump. The system also includes a series of resistance thermometers mounted on the components to be cooled to monitor the temperature.

The cooling of the molded piece, on the other hand, uses the same compressed air, generated by a compressor, whose output flow is controlled by a solenoid valve with flow control to allow the right amount of air to flow onto the piece to be cooled.

To obtain a high-performance and quality print, it is advantageous to be able to stop the composite from leaking, and to be able to resume it quickly without human operations and without smudging.

According to one aspect of the invention, the lower end 32 'of the extrusion worm 32 has a conical shape (Figs. 8 and 9) and is threaded along the entire length of the cone. Furthermore, the extrusion hole 52 has internal walls sized to leave only the space indispensable for the passage of the outgoing material without creating accumulations. In this way, the mere stop of the rotation motion of the screw, or a very short rotation in the opposite direction to that of extrusion, allows to stop the outflow, which can be resumed by reactivating the rotation of the screw 32 in the extrusion direction. Alternatively, the outflow can be regulated and interrupted by a special shutter, not shown, provided in the terminal part of the nozzle 50.

An aspect of the invention also relates to a method for the three-dimensional printing of composite articles comprising continuous reinforcing elements, comprising the steps of:

a) feeding a thermoplastic resin and a continuous reinforcing element to a printing head rotatable about its longitudinal axis according to an angle of 360 °;

b) melting said thermoplastic resin in said printing head and expelling a flow of resin having a corresponding polygonal section;

c) moving said print head according to a predefined program to form said article while maintaining a predefined spatial orientation of said resin flow of polygonal section;

d) depositing said resin flow on a printing plane or surface to form said article with overlapping layers along the sides of said resin flow of polygonal section.

Yet another aspect of the invention relates to a method for the three-dimensional printing of composite articles comprising continuous reinforcing elements comprising the following additional steps:

a1) joining a continuous reinforcing element to said fused thermoplastic resin and forming a continuous flow of composite material comprising said continuous reinforcing element and said fused thermoplastic resin;

c1) keeping fixed the position of said continuous reinforcing element with respect to said thermoplastic resin melted in said print head.

With reference to the figures, and to step a), the thermoplastic resin 11 is a natural or synthetic polymer capable of being brought to the molten state by heating and subjected to shear stresses in an extruder without being substantially degraded, so as to be processed in the desired shapes which are maintained after cooling. Examples of thermoplastic resins are polyethylene, polypropylene, polyamides, polyesters.

With reference to the figures, and to step a1), as defined above, the term "continuous reinforcing element" indicates a continuous filament or a continuous fiber or a weave of fibers such as a rope or a ribbon, generally indicated with 40, having any cross section, consisting of a natural or synthetic resin, a metal, glass, carbon, an inorganic material, or a combination of such materials. In the case of a synthetic resin, it has a higher melting point than that of thermoplastic resin. Some possible cross sections are shown in Fig. 4.

With reference to step b), the method provides for the fusion in an extruder 28 contained in the print head 10 and the extrusion of a flow of molten resin of polygonal section at a speed equal to the feeding speed of the fiber or continuous filament 40. By extrusion speed we mean the length of the extrudate per unit of time, for example the length in millimeters of the filament emitted by the extruder per minute. For example, if the extrusion speed is 2600 mm / min, the feeding speed of the fiber 40 is also set at 2600 mm / min.

With reference to step c), the method provides for maintaining a predefined spatial orientation of the resin flow with a polygonal section, so as to determine the overlap of the layers in the desired way.

With reference to step c1), the method involves joining the continuous reinforcing element, for example a ribbon 40B, to the resin melted in the print head 10 before it comes out. The union may consist in the incorporation of the 40B tape in the molten resin or the adhesion to part of the same.

According to one aspect of the method according to the invention, the amount of extruded resin is variable so as to vary the ratio between the resin 11 and the fiber 40 in the composite material 18.

After the resin has cooled, the fiber 40 is stably and permanently bonded to the resin to form a composite.

With reference to step d), the print head is set in motion by handling means, such as an industrial robot having at least three degrees of freedom of movement, according to a predetermined program made according to the object to be printed.

According to one aspect of the method according to the invention, the entire print head 10 is able to rotate on itself for 360 °, so that the fiber 40, or the ribbon 40B, always maintain the same relative position with respect to the jet of molten resin, for any position the robot assumes in its handling.

As it appears from the previous description, the possibility of keeping the relative position of the fiber 40 fixed with respect to the cast of molten resin, the possibility of adjusting the quantity of resin with respect to the fiber 40 in the final composite 18 and the possibility of incorporating reinforcing elements of various shapes and materials, makes the printing method particularly flexible and advantageous.

With reference to step d), the flow of composite material 18 extruded from the print head is deposited on a printing plane or surface 20 according to successive layers of material which overlap and adhere to each other in an optimal way and form an object with smooth surfaces and improved mechanical properties.

Finally, the formed object can be forcibly cooled to stabilize its shape.

The creation of polygonal layers, preferably square or rectangular, reinforces the structure of the object and eliminates or simplifies the final finishing stages.

It should be emphasized that the possibility of using nozzles with 52 holes of non-circular but polygonal shape, for example square and rectangular, allows to obtain printed objects with smoother and more precise surfaces, even with very thick deposition layers, as well as increasing the surface of effective contact between the layers, thus also improving the mechanical properties of the printed object. In fact, since the shape of the flow of composite material 18 that deposits the layers of the object 22 is given by the shape of the hole 52 of the nozzle, by using nozzles with square and rectangular holes 52, layers are created which have a better adherence between them, improving the mechanical resistance of the whole object. In addition, the surface of the printed piece will remain smoother, avoiding that the large size of the layer requires further processing to make it smoother.

With the polygonal shape of the hole 52, for example rectangular, and by adjusting the relative size of the long and short sides, it is also possible to vary the quantity of resin with respect to that of continuous fiber present in the composite material at the outlet, to have a structural resistance even better adjustable and manageable.

Claims (13)

CLAIMS 1. Apparatus for three-dimensional printing of articles in thermoplastic resin, comprising a print head (10) associated with handling means along at least 3 axes, in which said print head comprises a melting chamber (30) equipped with heating means (38) for said thermoplastic resin, means feeding said thermoplastic resin to said melting chamber (30) and a nozzle (50), characterized in that said nozzle (50) comprises an outlet hole (52) with a polygonal section for called thermoplastic resin. 2. Apparatus according to claim 1, characterized by the fact that said print head (10) is mounted on said movement means in a rotatable way for 360 ° around the longitudinal axis Y. 3. Apparatus according to claim 2, characterized by the fact that said print head (10) is mounted inside a ball bearing (13) fixed to said handling means. 4. Apparatus according to any one of claims 1 to 3, characterized in that said means for feeding said thermoplastic resin to said melting chamber (30) of said printing head (10) consist of a reel of continuous thread or a hopper for containing granules of said thermoplastic resin. 5. Apparatus according to any one of claims 1 to 4, characterized in that said print head (10) comprises means for feeding a continuous reinforcing element and feeding said continuous reinforcing element to said outlet (52) of said nozzle (59). 6. Apparatus according to any one of claims 1 to 5, characterized in that said print head (10) comprises an extruder (28) for a thermoplastic resin (11), feeding means (24, 26) for said thermoplastic resin ( 11) to said extruder (28) and guide means (46, 56) of said continuous reinforcing element (40), in which: - said extruder (28) comprises a melting chamber (30), in which a screw (32) is mounted that can rotate around its longitudinal axis and the longitudinal axis of the extruder (Y), heating means (38, 39) of said thermoplastic resin and a nozzle (50) - said nozzle (50) comprises a polygonal hole (52) for the outlet of said thermoplastic resin melted from said melting chamber (30), a guide channel (56) of said continuous reinforcing element (40) towards said polygonal hole ( 52) at the outlet of said melted thermoplastic resin. 7. Apparatus according to any one of claims 5 and 6, characterized in that said feeding means (43, 44) of said continuous reinforcing element (40) to said printing head (10) are integral with the movements of said head of printing. 8. Apparatus according to any one of the preceding claims, characterized in that said nozzle has a frusto-conical shape, and that said guide channel (56) of said reinforcing element (40) is oriented obliquely starting from a hole (41) of access located near the outer edge of said nozzle (50) up to said outlet hole (52) of said melted thermoplastic resin. 9. Apparatus according to any one of the preceding claims, characterized in that said continuous reinforcing element (40) has the shape of a fiber, filament, weave or tape. 10. Method for the three-dimensional printing of articles comprising the steps of: a) feeding a thermoplastic resin to a printing head rotatable about its longitudinal axis according to an angle of 360 °; b) melting said thermoplastic resin in said printing head having a nozzle with a hole of polygonal section and expelling a flow of resin of corresponding polygonal section; c) moving said print head according to a predefined program to form said article while maintaining a predefined spatial orientation of said resin flow of polygonal section; d) depositing said resin flow on a printing plane or surface to form said article with overlapping or side by side layers along the sides of said resin flow of polygonal section, without coplanarity constraints between said layers and said printing surface. Method according to claim 10, for the three-dimensional printing of composite articles comprising continuous reinforcing elements comprising the following additional steps: a1) joining a continuous reinforcing element to said fused thermoplastic resin and forming a continuous flow of composite material comprising said continuous reinforcing element and said fused thermoplastic resin; c1) keeping fixed the position of said continuous reinforcing element with respect to said thermoplastic resin melted in said print head. 12. Method according to the previous claim, characterized in that the extrusion of said molten resin (11) from said extruder (28) is carried out at a speed equal to the feeding speed of said continuous reinforcing element (40). 13. Method according to any one of claims 10 or 11, characterized in that the quantity of said melted thermoplastic resin is adjustable with respect to said continuous reinforcing element.