Printhead for 3D printer with pressure measurement system

Abstract

The invention relates to a print head (1) for a 3D printer (50) for producing objects (6), comprising a reservoir (2) for receiving a liquid phase (32) of a starting material (3), the viscosity of which can be varied, means (4) for varying the pressure in the reservoir (2) being provided, and wherein the reservoir (2) has at least one outlet (5) through which the starting material (3) can be discharged. A liquid phase (32) of the starting material (3) can be extruded from the outlet (5) by increasing the pressure in the reservoir (2) for producing the object (6), a pressure measuring system (100) for measuring the pressure of the liquid phase (32) being arranged in the region (5a) of the outlet (5), the pressure measuring system (100) comprises an adapter device (110), a connecting element (120), a pressure sensor (130) and a liquid medium (140) for transmitting pressure in the pressure measuring system (100). The invention further relates to a 3D printer (50) having the print head (1).

Description

Background Art

[0001] A 3D printer for materials that can vary in viscosity obtains the solid phase of the material as the initial material, thereby generating a liquid phase and selectively applying the liquid phase to parts belonging to the object to be produced. Such a 3D printer includes a print head in which the initial material is prepared for printing. In addition, a device is provided for generating a relative movement between the print head and the working surface on which the object is to be formed. Here, only the print head can be moved, or only the working surface can be moved, or both the print head and the working surface can be moved simultaneously.

[0002] Generally, the liquid phase of the initial material is discharged from the outlet by applying a force or pressure, such that the liquid phase is deposited on the object to be manufactured and solidifies there. The liquid phase of the initial material can here be selectively discharged from the outlet as a continuous wire bundle or in the form of individual droplets. When the diameter of the outlet is fixed, the most important adjustment parameter during the printing process is the force applied to the liquid phase or the pressure introduced into the liquid phase. US2016 / 046 073A1 discloses that the shear force applied to the liquid phase by the outlet and the viscosity of the liquid phase can also be adjusted by pressure.

[0003] DE 10 2016 222 306 A1 discloses a print head for a 3D printer, which has a conveying device for conveying particles from a feed zone to a plasticizing zone, wherein the conveying device includes a piston that can be introduced into the feed zone.

[0004] DE 10 2016 222 315 A1 discloses a print head for a 3D printer, wherein a pressure sensor for measuring the pressure of the liquid phase of the initial material and a temperature sensor for measuring the temperature of the liquid phase of the initial material are arranged in the region of the outlet. Summary of the Invention

[0005] The object of the present invention is to provide a print head that can achieve a stable printing process at low cost.

[0006] The present invention relates to a print head for a 3D printer for manufacturing an object and a 3D printer having a print head according to the present invention.

[0007] Within the scope of the present invention, a print head for a 3D printer has been developed. The print head includes a reservoir for receiving the liquid phase of an initial material that can vary in viscosity. A device is provided for changing the pressure p in the reservoir. The reservoir has at least one outlet through which the liquid phase of the initial material can be extruded in the direction of the object to be manufactured by increasing the pressure in the reservoir. A pressure measurement system for measuring the pressure of the liquid phase is arranged in the region of the outlet.

[0008] According to the invention, the pressure measurement system comprises an adapter device, a connecting element, a pressure sensor and a liquid medium for transmitting pressure within the pressure measurement system.

[0009] It has been recognized that pressure is the main parameter determining the mass flow of the starting material flowing out of the outlet. Here, the pressure value at the outlet is crucial. The pressure present at the outlet can be significantly different from, for example, the pressure introduced into the liquid phase of the starting material at the other end of the reservoir. Most of the materials used in 3D printers are thermoplastic and thus compressible. For example, if the diameter of the outlet is on the order of 100 μm, such that structures with an accuracy of ±50 μm can be printed, a high pressure of 1500 bar is required to discharge the starting material through the outlet. At pressures of this order of magnitude, the compressibility of the starting material is so important that it is inaccurate to determine the mass flow based on the pressure introduced into the starting material away from the outlet.

[0010] Even if the pressure is no longer analyzed and evaluated in terms of mass flow at all in the simplest embodiment, the measurement or monitoring of the pressure already enables quality control. For example, if the pressure remains constant within certain limits during the printing process, this can be regarded as a signal of a high-quality printing process. Conversely, strong fluctuations in the pressure can be regarded as a signal of problems occurring during printing. Thus, the manufactured object can be marked as defective, for example. The printing process can also be interrupted below a determined minimum quality so as not to invest more time and starting material in an irreparable object.

[0011] This is particularly important when using 3D printing in industrial production, where quality assurance strategies are usually mandatory in order for the production process to be certified.

[0012] The structure of the pressure measurement system according to the invention enables a flexible and modular design advantageously, such that the structural space of the print head can be reduced. The modular structure of the pressure measurement system advantageously reduces the costs for the pressure measurement of the melt, since a high-temperature pressure sensor that needs to be installed directly in the reservoir is not required. Thus, the system advantageously constitutes an economical and technically valuable solution, which can be used at high operating temperatures.

[0013] Omitting the direct installation of the pressure sensor on the print head advantageously contributes to reducing the weight and structural space of the print head, since neither the sensor nor the additional evaluation electronics have to be arranged in the vicinity of the print head. In addition, the structure according to the invention enables the necessary evaluation electronics not to have to be arranged in the vicinity of the thermal measurement zone, which results in better measurement results, since the influence of temperature on the measurement is reduced.

[0014] In an extended embodiment, the adapter device is arranged on the reservoir of the print head.

[0015] In a preferred embodiment, the adapter device has a diaphragm facing the reservoir and a cavity for receiving the medium between the diaphragm and the connecting element. This advantageously enables a pressure transmission between the diaphragm and the pressure sensor.

[0016] The use of a diaphragm in the adapter device for receiving the pressure in the reservoir advantageously enables a robust structure and thus has advantages over, for example, optical waveguides or piezoresistive elements. In a particularly advantageous embodiment, the diaphragm, in particular the pressure diaphragm, is made of spring steel.

[0017] The connecting element is arranged between the adapter device heated by the melt and the possibly temperature-sensitive pressure sensor, and advantageously fulfills the function of passively conducting heat from the medium and releasing it to the surroundings, thereby preventing the pressure sensor from overheating. The connecting element thus advantageously brings about passive cooling of the medium.

[0018] The cavity formed by the adapter device and the connecting element is filled with a medium, for example oil, which can be used at temperatures up to 380° C. or more. In a particularly advantageous embodiment, the medium is a hydraulic cylinder oil with an operating temperature of approximately 380° C. The print head has a constant temperature profile during operation with respect to melt preparation, whereby the viscosity of the medium for receiving the pressure remains constant during the printing operation. In another embodiment, the medium can be a low-melting-point metal.

[0019] In one embodiment, the adapter device is designed in multiple parts, wherein the adapter device comprises at least one core, which comprises a cavity for accommodating the medium, and an adapter for fastening the adapter device to the reservoir.

[0020] In an extension, a gap is formed between the core of the adapter device and the adapter, and the adapter has an exhaust device for exhausting the gap. The air present in the cavity can be advantageously flushed out by the exhaust device, especially the exhaust screw, when filling and replacing the medium.

[0021] In one embodiment, the pressure sensor is connected to the connecting element via a receiving device. Due to the modular design, the pressure sensor is so far away from the heated melt that a standard sensor can be used. In an advantageous embodiment, the pressure measuring sensor has an operating temperature of approximately 130° C.

[0022] In one embodiment, the receiving device has a calibration device for regulating the pressure of the medium in the pressure measuring system.

[0023] In one embodiment, the calibration device has an adjustable piston.

[0024] In an extended embodiment, a temperature sensor for measuring the temperature of the medium can be used.

[0025] Furthermore, in an extended embodiment, a regulating system can be used, the task of which is to detect all process parameters during operation in order to regulate the pressure measuring system such that the measurement result is not affected. Here, possible influencing factors are the thermal expansion of the medium, excessive pre-pressure in the measuring system, and residual air present in the system.

[0026] Furthermore, the invention includes a 3D printer having a print head according to the invention. Description of the Drawings

[0027] Further measures for improving the invention will be shown in detail below together with the description of the preferred embodiments of the invention according to the drawings.

[0028] The drawings show:

[0029] Figure 1 : a print head (1) of a 3D printer (50) according to the prior art;

[0030] Figure 2 : a print head (1) having a pressure measuring system (100) according to the invention;

[0031] Figure 3 : a part of the pressure measuring system (100). Detailed Description

[0032] Figure 1 A 3D printer 50 according to the prior art is shown, which includes a piston extruder having a movable piston 21. The solid phase 31 of the starting material 3 is present in particulate form and is supplied through a feed hopper 11. If the piston 21 is pulled back or moved upward in the print head 1, the solid starting material 31 flows down from the feed hopper 11. If the piston 21 is then pushed forward or moved downward, the solid starting material 31 is pressed into a plasticizing zone 12 provided with a heater 13. In the plasticizing zone 12, a liquid phase 32 of the starting material 3 is formed.

[0033] The reservoir 2 tapers nozzle-like in the region 5a of the outlet 5. The material 33 extruded through the outlet is output in the direction of the object 6 to be manufactured, which is constructed on a substrate 61 that is movable in three spatial directions x, y, and z by means of a positioning device 62 in this example. It is also known that the positioning device 62 is located below the print head 1 and can only move in the z direction, in which case the print head moves in the x-y direction. The extruded material 33 transfers a mass flow Q and an energy flow E.

[0034] In the region 5 a of the outlet 5 a is arranged a pressure sensor for measuring the pressure p of the liquid phase 32 of the starting material 3 . L The pressure sensor 7 and the temperature T of the liquid phase 32 of the starting material 3 are L The pressure sensor 7 is composed of a rod 71 introduced into the reservoir 2 through the thermal insulation 15 and a force sensor 72 on which the rod 71 acts. The measured pressure p L and the measured temperature T L is transmitted to the analysis and evaluation unit 9. The analysis and evaluation unit 9 calculates the volume increase ΔV + , volume shrinkage ΔV - , mass flow Q and energy flow E. The pressure p in the reservoir 2 is generated by the advancement of the piston 21 . The drive source of the piston 21 thus forms the means 4 for generating the pressure p in the reservoir 2 .

[0035] Additionally, in this example, a displacement measuring system 22 for measuring the position s of the piston 21 in the print head 1 and a displacement measuring system 23 for measuring the force F exerted by the piston 21 are provided. F The force sensor 23. Therefore, the evaluation unit 9 not only measures the pressure p of the liquid phase 32 of the starting material 3, but also measures the pressure p of the liquid phase 32 of the starting material 3. L and temperature T L In addition, we also get the position s and the force F F . p L and T L is also directly transmitted to the regulator 10, which acts on the drive source 4 of the piston 21 with the adjustment variable 14. The regulator 10 is thus able to adjust p L and / or T L Adjust to a predefined target value.

[0036] In addition, the controller 10 also receives the parameter ΔV determined by the evaluation unit 9 + , ΔV - , Q and E. Therefore, the regulator 10 can also regulate one or more of these parameters to a predefined target value.

[0037] Figure 2 The print head 1 of the 3D printer 50 for manufacturing an object 6 according to the present invention is shown, wherein the basic structure of the print head 1 is Figure 1 In the region of the outlet 5 a pressure gauge for measuring the pressure p of the liquid phase 32 is arranged. LThe pressure measurement system 100. The liquid phase 32 is a melt, and the pressure is the melt pressure. The pressure measurement system 100 includes an adapter device 110, a connection element 120, a pressure sensor 130, and a liquid medium 140 for transmitting pressure within the pressure measurement system 100. The adapter device 110 is arranged on the reservoir 2 of the print head 1. The reservoir 2 forms the nozzle prechamber of the print head 1. The adapter device 110 has a diaphragm 115 in the direction towards the reservoir 2 and has a cavity 150 for receiving the medium 140 between the diaphragm 115 and the connection element 120. The adapter device 110 is constructed in multiple parts, wherein the adapter device includes at least one core 111 and an adapter 112 for fastening the adapter device 110 to the reservoir 2, and the core includes a cavity 150 for receiving the medium 140.

[0038] A sensor assembly 130 is arranged on the part of the connection element 120 opposite to the adapter device 110. On this sensor assembly, a pressure sensor 135 is connected to the connection element 120 through a receiving device 131. The receiving device 131 has a calibration device 132 for adjusting the pressure of the medium 140 in the pressure measurement system 100. The calibration device 132 has an adjustable piston 133.

[0039] The pressure measurement system 100 arranged on the print head 1 satisfies the function of measuring the melt pressure of the melt 32 present in the reservoir 2 or the melt reservoir and in the nozzle prechamber. Here, there is a diaphragm 115 on the wall of the reservoir 2, and this diaphragm closes the reservoir 2. On the other side of the diaphragm 115 is the cavity 150, and this cavity extends from the core 111 of the adapter device 110 through the connection element 120 into the sensor assembly 130. In this embodiment, the core 111 of the adapter device is formed by a hollow screw, and this hollow screw is inserted or screwed into the adapter 112. Therefore, the hollow screw 111 is connected to the pressure sensor 135 through the connection element 120 or a connecting tube. The cavity 150 formed by the hollow screw 111 and the connecting tube 120 is filled with the medium 150.

[0040] Now, if the melt pressure in the region of the melt reservoir 2 changes, the diaphragm 115 deforms elastically relative to the pressure. In this way, the pressure change is transmitted from the diaphragm 115 to the medium 140 in the cavity 150 and thus the pressure change is detected by the pressure sensor 135. For calibrating the pressure measurement system 100, a calibration piston 133 is installed in the receiving device 131 of the sensor assembly 130, and this calibration piston is connected to the cavity 150. Thereby, the pre-pressure in the pressure measurement system 100 can be adjusted. In addition, the connection element 120 has the function of passively conducting heat away from the medium 140 and releasing this heat to the surrounding environment, so as to avoid overheating of the pressure sensor 135. Therefore, the connection element constitutes passive cooling of the medium 140.

[0041] Figure 3 It is shown in detail that a gap 113 is formed between the core 111 and the adapter 112 of the adapter device 110, and the adapter 112 has an exhaust device 114 for exhausting the gap 113. The gap 113 formed between the adapter 112 and the hollow screw 111 extends in the axial direction of the hollow screw 111 to the diaphragm 115 and is closed outward through the exhaust device 114 or the exhaust screw. The air present in the cavity 150 can be flushed out through the exhaust screw 114 when filling and replacing the medium 140.

Claims

1. A print head (1) for a 3D printer (50) for manufacturing an object (6), the print head comprising a reservoir (2) for receiving a liquid phase (32) of an initial material (3) that is variable in its viscosity, wherein, A device (4) is provided for changing the pressure in the reservoir (2), and wherein the reservoir (2) has at least one outlet (5), and the liquid phase (32) of the starting material (3) can be extruded from the outlet by increasing the pressure in the reservoir (2) for manufacturing the object (6), wherein a pressure measurement system (100) for measuring the pressure of the liquid phase (32) is arranged in the region (5a) of the outlet (5). It is characterized in that the pressure measurement system (100) comprises an adapter device (110), a connecting element (120), a pressure sensor (130) and a liquid medium (140) for transmitting pressure within the pressure measurement system (100).

2. The print head (1) according to claim 1, characterized in that, The adapter device (110) is arranged on the reservoir (2) of the print head (1).

3. The print head (1) according to claim 2, characterized in that, The adapter device (110) has a diaphragm (115) in the direction of the reservoir (2) and has a cavity (150) for receiving the medium (140) between the diaphragm (115) and the connecting element (120).

4. The print head (1) according to claim 3, characterized in that, The adapter device (110) is constructed in a multi-piece manner, wherein the adapter device comprises at least one core (111) and an adapter (112), the core comprises a cavity (150) for receiving the medium (140), and the adapter is for fastening the adapter device (110) to the reservoir (2).

5. The print head (1) according to claim 4, characterized in that, A gap (113) is formed between the core (111) and the adapter (112) of the adapter device (110), and the adapter (112) has an exhaust device (114) for exhausting the gap (113).

6. The printhead (1) according to any one of the preceding claims, characterized in that, The pressure sensor (135) is connected to the connecting element (120) by a receiving device (131).

7. The print head (1) according to claim 6, characterized in that, The receiving device (131) has a calibration device (132) for adjusting the pressure of the medium (140) in the pressure measurement system (100).

8. The printhead (1) according to claim 6, characterized in that, The calibration device (132) has an adjustable piston (133).

9. A 3D printer (50) having a print head (1) according to any one of claims 1 to 8.

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