IT201800006331A1 - Extrusion head for 3D printers. - Google Patents

Description

Extrusion head for 3D printers.

Extrusion head for 3D printers.

The present invention refers to an extrusion head for 3D printers of the FDM type.

This 3D printing technology FDM (fused deposition modeling) is a technology in which a thermoplastic material heated by a resistance (for example at temperatures of 250 ° C) is passed through a nozzle, which layer after layer manages to give shape to the 'object. Currently, the material is fed in the form of a filament.

As part of this 3D printing with FDM technology, despite various attempts made (see patent application US2015321419A1), to date there are still no known versions of granule or powder extruder that can in fact be used reliably on common FDM 3D printers designed for wire printing, both small and large.

Among the advantages of using granules or powder over wire are: a) greater number of usable materials available on the market, b) greater flow rate (understood as the quantity of extruded material per unit of time), therefore ideal for printing of medium-large parts, c) lower cost of the material (remember that the materials are commonly found on the market in the form of granules or powders / flakes, while the yarn requires an additional processing), d) possibility of coloring the material on line.

The purpose of the present invention is to provide, in the field of 3D printing with FDM technology, an extrusion head that uses raw material in the form of granules, powder, flakes or other similar geometries, but also wanting very viscous paste or fluids (e.g. example clay, cement, etc.) hereinafter "granule extruder". The novelty consists in the possibility of using the extruder on 3D printers designed for wire printing by simply replacing the wire extrusion head with the granule one, with the obvious benefits that this entails.

The aforementioned replacement is possible not only by the printer manufacturer, but also by the end user (retrofit). The extruder according to the present invention is compatible not only with medium-large size printers, but also with small ones (eg with the common printing area 20x20 cm <2>).

The problem of compatibility with existing wire printers, even with small ones, is solved thanks to the following characteristics of the invention: a) very reduced dimensions and weight, b) simplicity of construction, assembly, use and maintenance, c) low consumption and use of the same components as the most common wire FDM printers, d) compatibility with existing electronics, software, firmware and operating logic.

From the point of view of a printer user, the operating logic of the invented granule extruder is very similar to that of a wire extruder, therefore the granule extruder is easily managed by the average user in the same way it manages wire printers.

The extruder according to the present invention is of reduced size and weight, an essential and optimized design, construction simplicity, and uses materials and parts that are easily available on the market. This allows its realization with low production costs, allowing its potential diffusion even in the mass market. Despite the simplicity of construction and the small size, thanks to the design as a whole and to some details, the extruder is flexible enough to process a wide range of materials and powerful enough to reach capacities well above (even 10 times) those achievable. with common wire printers.

An aspect of the present invention relates to an extrusion head for 3D printers having the characteristics of the attached claim 1.

Further characteristics of the present invention are contained in the dependent claims.

The features and advantages of the present invention will become more evident from the following description of an exemplary and non-limiting embodiment of the invention, referring to the attached schematic drawings, in which:

Figure 1 shows a side view of the extrusion head according to the present invention;

Figure 2 shows a longitudinal section of the head of figure 1.

With reference to the aforementioned figures, the extrusion head according to the present invention comprises an external structure 101, a feeding hopper 102, adapted to contain the material to be fed to the extruder and to facilitate its introduction into an extrusion channel 142. A screw of longitudinal extrusion 131 is inserted in this channel, substantially crosses the entire head and rotates driven by a motor 104 through a transmission mechanism 110-111-112.

The lower part of the hopper 171 typically has a funnel shape with an angle of inclination, processing and surface finish (smooth, rough or grooved) optimized for the type of material fed.

An extrusion cylinder 141 is fixed below the hopper 102 and to the structure 101 for example by means of a counter flange 161. This counter flange and this lower part of the hopper also act as the first section of the extrusion channel 142 which then continues inside the cylinder of extrusion 141.

Height, internal diameter, machining and surface finish of this counter flange (smooth, rough or grooved) are optimized for the type of material fed. It is made with different types of materials to obtain the desired surface finish, thermal conductivity, coefficient of friction, wear resistance, etc. desired.

Structure 101, made of material with good thermal conductivity (eg aluminum), acts both as a load-bearing structure to which the main components are fixed, and as a heat sink. Heat dissipation can be improved by making fins and / or by using one or more cooling fans or other means to remove heat.

The head also comprises a heating body 181 placed in the end part of the extrusion cylinder 141, advantageously provided with an insulation coating 103. This head ends at the bottom with a die 121 which is connected to the end of the extrusion channel 142. According to the present invention, the the lower part of the hopper 171 is made by means of a piece separated from the rest of the hopper, to allow its simple replacement according to the material fed. This also allows the realization of the same with different types of materials to obtain the desired surface finish, thermal conductivity, coefficient of friction, wear resistance, etc. desired.

Another aspect of the present invention relates to the realization, on the walls of the hopper 102, of holes and / or gratings which allow air cooling, with the possible help of one or more cooling fans, both of the granule contained therein and of a first section 135 of the extrusion screw 131, preventing the material from softening or melting prematurely, preventing the regular flow of the material itself along the extrusion channel 142.

The lower part of the hopper 171, or the possible counter flange 161 or the first section of the extrusion cylinder 141 may have a lateral hole for the feeding, by means of a special dispenser, of colored grains (or grains of color masterbatch, i.e. grains containing concentrated pigments) directly at the entrance of the extrusion channel 142. The possibility of dosing grains of different colors, in random or determined order, with random or determined times, for the printing of multicolored objects is an innovative aspect in the field of extrusion from granule for 3D printing.

The extrusion screw 131 can have different shapes, but it is typically made up of a smooth section 132 and a helical section 133. On the basis of well-known criteria in the world of extrusion of thermoplastic materials, the helical section is normally designed according to the material to be extruded and typically consists of a feed / transport section, a compression / melting section and a metering section. Typically, the diameter of the core (and therefore the depth of the slot) and / or the pitch of the screw are variable.

According to the present invention, the extrusion screw 131 has an extremely simplified geometry which allows considerable savings in the construction of the screw or even the use, after appropriate modification, of common and even less expensive drill bits. In particular, the drill bit for wood auger, also called bit for wooden beams, in addition to the lower cost also offers the advantage of having, for the same external diameter, a much smaller core than the typical extrusion screws and therefore a deeper cavity, which allows the use of larger granules. This deviation / simplification with respect to the canonical construction criteria is almost always allowed thanks to the fewer criticalities that the extrusion process for 3D printing presents compared to that for the other more common uses.

This screw preferably has a length / diameter ratio L / D (length of the helical section 133 inside the extrusion channel 142, therefore effectively used for the transport and melting of the material / diameter) of the extrusion screw 131 of less than 10, typically 6, from which the extreme compactness of the extruder. The L / D ratio used differs considerably from the recommended values of 20-30, necessary and in fact used in the vast majority of granule extruders on the market. Such a low L / D ratio is sufficient thanks to the fewer criticalities that the extrusion process for 3D printing presents. It also has the great benefit of degrading the material less thanks to the lower friction (shear stress) of the material and the shorter residence time of the same inside the extrusion channel 142.

The extrusion cylinder 141 comprises a metal block, typically cylindrical, with a cylindrical cavity (which forms this extrusion channel 142) and a flange 149 for fixing to the structure 101, for example by means of screws or bolts. The surface of the extrusion channel 142 can be smooth, rough or grooved, in its entire length or only in one or more segments.

According to the present invention, the diameter of the extrusion channel 142 is variable and preferably has a first upper longitudinal section 147 whose diameters 144A / 144B are wider than the diameter 143 of a second lower longitudinal section 148. This variation in diameter can also be progressive , that is, the extrusion channel 142, or a portion thereof, can have a conical shape. This aspect solves many of the problems related to the transport and melting of the material.

Another innovative aspect is the use of a material with a thermal conductivity lower than 40 W / (m K) (e.g. stainless steel) for the construction of the extrusion cylinder 141.

Furthermore, the first longitudinal section 147 has a very small thickness (intended as the difference between internal diameter 144A and external diameter 146 divided by two) (the minimum possible compatible with the mechanical properties required, typically 1 mm) smaller than the thickness of the second section 148 which corresponds to the section subject to the action of the heater body 181.

This allows to create a thermal break between the heated section 148 and the feed hopper 102, which is necessary for the good operation of the extruder (in particular to prevent softening or premature melting of the material in the hopper 102 or in the first section of the feeding channel. extrusion 142). This also entails the further benefit of a lower heat dispersion and therefore a lower energy consumption, hence the smaller size, weight and cost of the electrical resistances 191 of the heater 181.

Compared to other solutions adopted (e.g. use of a ring of insulating material, often fragile or with poor resistance to high temperatures), the proposed solution allows to obtain excellent mechanical and thermal performance of the extruder (which can potentially reach temperatures up to 480 ° C), as well as reducing the construction complexity and cost.

If the aforementioned thermal break is not sufficient for the good functioning of the extruder, it is possible to provide for the creation of fins along the first section 147 (as added parts or as a single piece) and a cooling by air or other refrigerant fluid, with possible control of the temperature by acting on the flow rate of the refrigerant fluid. It is also possible to provide for the insertion of a dissipator 159, placed between the hopper 102 and the extrusion cylinder 141. This dissipator can be made of a material with high thermal conductivity (eg aluminum), with air cooling or other refrigerant fluid. , with possible temperature control by acting on the flow rate of the refrigerant fluid. The heating body 181 has the function of heating the extrusion cylinder 141 to melt the material to be extruded. In the illustrated version it consists of a metal block, preferably made of a material with high thermal conductivity (e.g. aluminum), which houses electrical resistances 191, but can be made up of any other element capable of supplying thermal energy to the extrusion cylinder 141 . The electric resistors 191, of suitable diameter, length, voltage and power, are housed in holes 192. They are not rigidly fixed or stuck there, but simply suspended (held by their power cable 198) or blocked in the potential downward fall. screw / grain 197, with the consequent benefit of eliminating the tensions (both in the resistor body and in the power cable) due to rigid fixing, thermal expansion and / or movement / vibration of the power cable. A further peculiar aspect of the invention is the possibility of positioning the electrical resistances 191 at a variable distance 193 according to the temperature profile to be obtained along the extrusion cylinder 141. This results in the advantages of maximum constructive simplicity, flexibility in configuring the extruder for different needs and the possibility of modifying it during life as needs change.

Furthermore, the extrusion cylinder 141 and the heating body 181 can be made in a single body, made of a material with a thermal conductivity lower than 40 W / (m K) (eg stainless steel). The advantages of this solution are the possibility of having the electrical resistances 191 as close as possible to the extrusion channel 142, hence more effective and efficient heating, as well as better control of the temperature of the extrusion cylinder 141.

In the illustrated version, the heater body has one or more holes 195 at different distances 196 for housing at least one temperature sensor used to control the temperature of the extrusion cylinder 141.

The insulation 103 serves to limit heat losses, with the benefit of lower energy consumption, hence the smaller size, weight and cost of the electric resistances 191 or other heating element. The temperature control of the extrusion cylinder 141 also benefits from the insulation 103, which is not affected by any external disturbances (changes in ambient temperature, air currents, etc.).

The spinneret 121 has the function of conveying, through its internal channel 122 and a nozzle 125, the molten material towards the extruder outlet and of allowing it to be deposited on the printing surface for the production of three-dimensional pieces.

In the illustrated version, the die 121 is threaded as a male and can be easily unscrewed and removed to allow cleaning / maintenance or replacement with one of different characteristics, or to purge / clean the extrusion channel 142. The designer / builder also benefits from this solution, which allows him to easily modify the characteristics of the last section of the extruder by simply replacing the die 121, without having to modify the extrusion cylinder 141.

Once the spinneret 121 has been removed, the molten material is free to flow out of the extrusion channel 142, the only restriction being the housing of the spinneret 121, typically with a diameter greater than 5 mm. The resulting advantage is the ease with which the user can purge the molten material out of the extrusion channel 142.

The motor 104 serves to impart the rotational motion to the screw 131, by means of a transmission and reduction mechanism 110-111-112 with gears or pulleys. The motor is at variable speed, electronically controlled, typically of the step-by-step type, to allow synchronization of the rotation motion of the screw with that of the movement of the extrusion head along the X, Y and Z axes during the 3D printing process. The reduction ratio can be easily modified according to the needs, even by the end user, by replacing gears or pulleys with others of different sizes.

During the operation of the extruder a force is generated which pushes the screw 131 upwards, with the tendency of the same to come out of the extrusion cylinder 141 where it is housed. It is therefore necessary to provide a thrust bearing or other system to prevent this upward movement. In the illustrated version, the screw 131 is locked by a thrust system comprising ring 151 screw / nut 152 groove 153 thrust bearing 155. The innovative aspect of this locking system is the extreme simplicity of construction and assembly of the same, as well as the ease with which the end user can disassemble the screw 131 for cleaning (when it becomes clogged or material is changed), maintenance or replacement. The easy disassembly of the screw 131 is also allowed by the fact that the motor 104 is placed beside the screw 131, and not above it.

Another innovative aspect of the aforesaid locking system is the possibility of making several grooves 153 at different heights, with the aim of being able to easily position the extrusion screw 131 at different heights (i.e. in a more or less backward position with respect to the die 121). This in turn makes it possible to obtain different residence times, degrees of mixing, etc. of the molten material inside the extrusion cylinder 141.

Claims (5)

In the extrusion process, the material is brought to fusion by adding both mechanical energy (through the screw 131 and therefore friction and compression of the material) and thermal energy (through electrical resistances or other system to heat the extrusion cylinder 141). An innovative aspect of the invention is the extremely low ratio between mechanical and thermal energy provided for the transport and melting of the material to be extruded, in such a way as to have a very low mechanical energy input, with the advantage of being able to use a small and light motor. . The ratio between mechanical and thermal energy used differs considerably from the recommended values, necessary and in fact used in the vast majority of granule extruders on the market. A low ratio is sufficient in our case thanks to some precautions in the design of the screw 131 and thanks to the variable diameter of the extrusion channel 142, as well as to the minor criticalities that the extrusion process for 3D printing presents. Furthermore, it is possible to dose grains of different colors, in random or determined order, with random or determined times, for printing multicolored objects. This is done by means of this dispenser which introduces the dyes into suitable lateral holes made in the lower part of the hopper 171, or in the possible counter flange 161 or in the first section of the extrusion cylinder 141. CLAIMS 1. Extrusion head for 3D printers comprising • an external structure (101), • a feed hopper (102), designed to contain the material to be fed to the extruder and to facilitate its introduction into an extrusion channel (142), • a longitudinal extrusion screw (131) inserted in this channel which substantially crosses the entire head and rotates driven by a motor (104) through a transmission mechanism (110-111-112), • the lower part of the hopper (171) being substantially funnel-shaped, • an extrusion cylinder (141) fixed below the hopper and to the structure (101) inside which the extrusion channel (142) continues, • a heating body (181) placed in the terminal part of the extrusion cylinder (141), • a spinneret (121) connected to the termination of the extrusion channel (142), characterized in that the diameter of the extrusion channel (142), where this channel also includes the counter flange (161) and the lower part of the hopper (171), is variable and has a first upper longitudinal section (147) whose diameter or diameters (144A / 144B) are larger than the diameter (143) of a second lower longitudinal section (148). 2. Head according to claim 1, in which said variation in diameter is progressive. 3. Head according to claim 2, wherein at least a portion of said channel (142) has a conical shape. 4. Head according to claim 1, in which the first longitudinal section (147) has a thickness smaller than the thickness of the second section (148) which corresponds to the section subject to the action of the heater body (181). Head according to claim 1, wherein the lower part of the hopper (171) is separated from the hopper body (102).