Print head for a 3D printer

Abstract

The invention relates to a print head (10) for a 3D printer (1), comprising a feed (12) for a starting material (21) with variable viscosity, a plasticizing zone (14), a melting zone (18) and an outlet opening (16) for the liquid phase (22) of the starting material (21) as well as a conveying device (30) for conveying the starting material (21) from the feed (12) into the melting zone (18), wherein the conveying device (30) comprises a piston (31) that can be inserted into the plasticizing zone (14), wherein the piston (31) has a first piston section (50) facing the melting zone (18). It is characterized by the fact that the first piston section (50) is arranged between the plasticizing zone (14) and the melting zone (18).

Description

[0001] The present invention relates to a print head for a 3D printer. State of the art

[0002] A 3D printer for a material with variable viscosity receives a solid phase of this material as its starting material, converts it into a liquid phase, and selectively applies this liquid phase to the areas belonging to the object to be produced. Such a 3D printer includes a print head in which the starting material is prepared for printing. Furthermore, it incorporates means for generating relative movement between the print head and the build platform on which the object is to be created. This movement can be limited to either the print head alone, the build platform alone, or both.

[0003] The printhead has a first operating state in which liquid material is extruded, and a second operating state in which no liquid material is extruded. The second operating state is used, for example, when moving to a different position on the work surface and no material is to be deposited along the way. Switching between the two operating states of the printhead can be achieved, for example, by turning the extrusion of the solid feed material on or off.

[0004] From DE 10 2016 222 306 A1, it is known to plasticize granules via a piston and a heated section. When the piston presses on the granules, they are compacted and conveyed to a plasticization zone.

[0005] German patent application DE 10 2021 202 649 A1 discloses a method for providing a pressable melt. In particular, the method comprises converting a material from a solid phase through a plastic phase to a liquid phase, wherein the material is compressed by moving a piston and a spring constant of the liquid phase is determined for pressure preparation. The phase transition takes place during the printing process.

[0006] The invention is based on the objective of providing a printhead that optimizes the phase transition from solid material to liquid material and enables a stable printing process. Disclosure of the invention

[0007] Within the scope of the invention, a printhead for a 3D printer was developed. This printhead comprises a feed for a starting material with variable viscosity, a plasticizing zone, a melting zone, and an outlet for the liquid phase of the starting material, as well as a conveying device for conveying the starting material from the feed into the melting zone. The conveying device includes a piston that can be inserted into the plasticizing zone, the piston having a first piston section facing the melting zone. The feed can, in particular, be provided for a starting material in the form of granules. The starting material can, in particular, be a thermoplastic material.

[0008] According to the invention, the first piston section is arranged between the plasticizing zone and the melt zone. This arrangement allows for easy separation of the granules and the melt, advantageously ensuring that the piston, or rather the first piston section, only presses on pure melt during extrusion. Furthermore, costs are reduced because no additional actuator is required for melting outside the printhead. The separation of granules and the melt also reduces material adhesion to the piston, or rather the first piston section, allowing for more precise piston control. This advantageously reduces the number of parameters required for refilling and printing, saving computing resources and accelerating the printing process. Additionally, the printhead has a compact design.

[0009] In a particularly advantageous embodiment of the invention, the first piston section comprises a piston core element and a piston sleeve, wherein the piston core element is attached to a piston rod of the piston and the piston sleeve is guided axially displaceably to the piston core element on a guide surface in a recess of the print head.

[0010] In a further development, the first piston section forms a fluidic connection between the plasticizing zone and the melt zone.

[0011] In a further development, the first piston section forms a fluid-tight connection when moving in towards the outlet opening and a fluid-open connection between the plasticizing zone and the melt zone when moving back.

[0012] The first piston section of the piston thus forms a backflow preventer, thereby separating the plasticizing and extrusion processes of the material and advantageously shortening the filling process, or so-called refill. In particular, a homogeneous starting material is provided for printing, and the piston, or rather the first piston section, presses directly onto the melt. An advantageous result of the printhead according to the invention is a reduction in the material's residence time in the printhead. This also reduces the waiting time for a printable melt to be provided, thereby increasing the quality of the dispensed material. As a result, for example, the component's appearance and properties are improved.

[0013] In a further development, the fluidic connection between the plasticizing zone and the melting zone is formed between the piston sleeve and the piston core element.

[0014] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to figures. Examples of implementation

[0015] They show: Fig. 1. a state-of-the-art printhead; Fig. 2 a printhead according to the invention in a first embodiment and Fig. 3 the printhead in a second version.

[0016] Fig. Figure 1 shows a printhead 10 according to the prior art. The illustrated printhead 10 for a 3D printer 1 comprises a feed zone 11 with a feeder 12 for a starting material 20, 21 with variable viscosity, a plasticizing zone 14 with a heater 15 and an outlet 16 for the liquid phase 22 of the starting material 21, and a conveying device 30 for conveying the starting material 21 from the feed zone 11 into the plasticizing zone 14, wherein the conveying device 30 includes a piston 31 that can be inserted into the feed zone 11. The piston 31 has a first piston section 5 facing the plasticizing zone 14 with a guide surface 9, through which the piston 31 is guided in a recess 7 of the printhead 10.

[0017] Furthermore, the printhead 10 comprises a housing 19 with the piston 31 guided therein. The piston 31 consists of the first piston section 5 and a second piston section 6. The first piston section 5 is guided in the central recess 7 of the housing 19, sealing against the starting material 20, 21. It prevents the solid phase 21 of the starting material 20 from escaping and forces this solid phase 21 from the intake zone 11 into the compression zone 11a, where a boundary layer 11b forms with the liquid phase 22 of the starting material 20. The second piston section 6 is located above the first piston section 5 and is moved, for example, by a spindle of a motor (not shown) in the vertical direction 38. Electric motors are preferably used. When the piston 31 moves towards the outlet opening 16 of the print head 10, the liquid phase 22 of the starting material 20 is expelled from the outlet opening 16. Fig. Figure 1 is a snapshot of the state in which this is possible, i.e., the printhead 10 is ready to print. In this state, the working volume 17 within the central recess 7 in the housing 19 of the printhead 10 is comparatively small.

[0018] In the Fig. In the embodiment shown in Figure 1, the solid phase 21 of the starting material 20 is fed via a funnel 12 and trickles into the feed zone 11 in the print head 10 as soon as the piston 31 is retracted behind this feed zone 11. The starting material 20 is preferably a granulate. For this trickle to be possible, only the solid phase 21 of the starting material may be present in the feed zone 11. This solid phase 21 must not melt or clump together. Therefore, the feed zone 11 is cooled externally by a coolant 13. The coolant 13 comprises active cooling 13a with a cooling medium and passive cooling 13b with cooling fins. This helps to ensure that the temperature TS in the feed zone remains below the temperature TP at which the solid phase 21 of the starting material 20 plasticizes.

[0019] Furthermore, an air injection nozzle (not shown) can be arranged on the feeder 12, preferably located near an opening surface 8 of the feeder 12 leading to the recess 7. The air injection nozzle ensures that, by means of pressurized air, any granules that have not completely trickled into the feeder zone 11 are either blown into the feeder zone 11 or blown from the area of ​​the opening surface 8 up the hopper 12, so that the piston 31 can easily close the opening surface 8.

[0020] The solid phase 21 of the starting material 20 is heated in the plasticization zone 14 by means of the heater 15 and thereby transformed into the liquid phase 22, which is able to escape from the outlet opening 16 when pressurized.

[0021] The temperature T curve along axis 19b of housing 19 is shown on the right. Fig. 1 outlined.

[0022] Fig. 2 and Fig. Figure 3 shows a printhead 10 according to the invention in sectional drawings of vertical sections through the printhead 10 in two positions. The basic structure of the printhead 10 and the control of the conveying device 30 are shown in Figure 3. Fig. The process described in Section 1 also applies largely to the printhead 10 according to the invention. The printhead 10 for a 3D printer 1 comprises a feed 12 for a starting material 21 with variable viscosity, a plasticizing zone 14, a melting zone 18, and an outlet opening 16 (not shown) for the liquid phase 22 of the starting material 21, as well as a conveying device 30 for conveying the starting material 21 from the feed 12 into the melting zone 18. The conveying device 30 comprises a piston 31 that can be inserted into the plasticizing zone 14, and the piston 31 has a first piston section 50 facing the melting zone 18. According to the invention, the first piston section 50 is arranged between the plasticizing zone 14 and the melting zone 18. Within the housing 19, heating elements 15 are arranged, which introduce energy into the plasticizing zone 14 and into the melting zone 18 in order to melt the granules 21, respectively.to keep the melt 22 in a largely homogeneous state.

[0023] The first piston section 50 comprises a piston core element 51 and a piston sleeve 52, wherein the piston core element 51 is attached to a piston rod 32 of the piston 31 and the piston sleeve 52 is guided axially displaceably to the piston core element 51 on a guide surface 9 in a recess 7 of the print head 10.

[0024] The first piston section 50 forms a fluidic connection between the plasticizing zone 14 and the melting zone 18, wherein the first piston section 50 forms a fluid-tight connection when retracting towards the outlet opening 16 (see Fig. 3) and during reversing a fluid-open connection (see Fig. 2) forms between the plasticization zone 14 and the melting zone 18.

[0025] The fluidic connection between the plasticizing zone 14 and the melting zone 18 is formed between the piston sleeve 52 and the piston core element 51.

[0026] The first piston section 50, which forms the piston head, is designed as a non-return valve, connected to the piston 31 via the piston rod 32 and a piston shaft 33. The non-return valve ensures that the unmelted granules 21 do not come into contact with the melt 22 to be printed. This prevents a potential spring-damper effect during the movement of the piston 31, which could negatively affect the subsequent printing result. When the piston 31 moves backward with the first piston section 50, i.e., the non-return valve (see arrow in Fig. 2) When the piston is moved towards the opening surface 8, or inlet opening, friction between the guide surface 9 of the recess 7, or the inner wall of the piston chamber, and the piston sleeve 52, or the outer ring of the non-return valve, opens the non-return valve, allowing the melt 22 located above the first piston section 50, or the non-return valve, to flow through the piston section 50 (dashed arrow). Simultaneously, unmelted granules 21 are retained.

[0027] At the in Fig. In the forward movement shown in 3 in the direction of the outlet opening 16, or the nozzle, the piston sleeve 52, or the outer ring of the backflow preventer, is closed again by the friction that occurs.

[0028] The print head 10 can be integrated into any 3D printer. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 222 306 A1

[0004] DE 10 2021 202 649 A1

[0005]

Claims

[1] Print head (10) for a 3D printer (1), comprising a feed (12) for a starting material (21) with variable viscosity, a plasticizing zone (14), a melting zone (18) and an outlet (16) for the liquid phase (22) of the starting material (21) and a conveying device (30) for conveying the starting material (21) from the feed (12) into the melting zone (18), wherein the conveying device (30) comprises a piston (31) that can be inserted into the plasticizing zone (14), wherein the piston (31) has a first piston section (50) facing the melting zone (18), characterized by , that the first piston section (50) is arranged between the plasticizing zone (14) and the melting zone (18). [2] Printhead (10) according to claim 1, characterized by, that the first piston section (50) comprises a piston core element (51) and a piston sleeve (52), wherein the piston core element (51) is attached to a piston rod (32) of the piston (31) and the piston sleeve (52) is guided axially displaceably to the piston core element (51) on a guide surface (9) in a recess (7) of the print head (10). [3] Printhead (10) according to claim 2, characterized by , that the first piston section (50) forms a fluidic connection between the plasticizing zone (14) and the melting zone (18). [4] Printhead (10) according to claim 3, characterized by , that the first piston section (50) forms a fluid-tight connection between the plasticizing zone (14) and the melting zone (18) when retracting towards the outlet opening (16) and a fluid-open connection when retracting. [5] Printhead (10) according to one of claims 3 or 4, characterized by, that the fluidic connection between the plasticizing zone (14) and the melting zone (18) is formed between the piston sleeve (52) and the piston core element (51).

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