METHOD FOR PROVIDING PRINTABLE MELT FOR OPERATURED A PRINT HEAD FOR A 3D PRINTER

Description

[0001] The present invention relates to a method for providing printable melt for operating 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 should be dispensed 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] The most common method is fused deposition modeling (FDM), in which a filament made from the starting material is melted in an electrically heated extruder nozzle and deposited layer by layer onto a platform. In this filament form, the starting material is very expensive.

[0005] US Patent 2016 / 082 627 A1 proposes feeding the starting material in granular form and conveying it by screw conveyor to a heated zone, from which it emerges in a plasticized form. Granules are significantly cheaper, and mixtures of different thermoplastic materials can be easily produced in this way.

[0006] Furthermore, a printhead is known from DE 102016222306 A1, in which granules are plasticized via a piston and a heated section. When the piston presses on the granules, they are compacted and conveyed to a plasticization zone in the lower part of the printhead. This generates forces that place considerable stress on the piston and a cylinder wall of the printhead, potentially leading to increased wear on the cylinder wall of the printhead housing. A complex melting geometry with a heat-conducting structure is also disclosed, wherein the heating power of a heating element is introduced into the plasticized material to bring it into a liquid phase.

[0007] EP 3 326 790 A1 discloses a manufacturing device for a three-dimensional object, including a material feed unit, which has a nozzle part configured to eject a shaping material for forming the three-dimensional object, wherein the manufacturing device has a feed part that feeds shaping material into the nozzle part.

[0008] EP 3 117 982 A1 discloses a three-dimensional printing system comprising a printhead arranged vertically above a build platform, the printhead having a variable-width nozzle with a rectangular opening, a means for moving the printhead and a means for extruding granules through the variable-width nozzle to provide a molten ribbon of ink vertically above the build platform.

[0009] DE 10 2017 205673 A1 discloses an extrusion unit for a device for extruding thermoplastic materials, wherein the extrusion unit is designed as a separate component that can be connected to a metering unit of the device and comprises a hot runner system with an inlet and an outlet, wherein the inlet can be connected to an outlet of the metering unit.

[0010] The invention is based on the objective of providing a method for supplying printable melt for operating a printhead for a 3D printer and a printhead for a 3D printer, wherein the method and the printhead provide high-quality melt in reproducible quality. Disclosure of the invention

[0011] Within the scope of the invention, a method for providing printable melt for operating a print head for a 3D printer was developed.

[0012] The process includes the following steps: Converting the material from a solid phase through a plastic phase into a liquid phase and compacting the material.

[0013] The process also includes steps that are part of a workflow from filling to opening the printhead nozzle during print preparation. This print preparation process is also called the refill process, as it is a recurring sequence that is repeated as often as necessary during the printing of a part. The refill process is the method of providing printable molten material to operate the printhead of a 3D printer.

[0014] The printhead for carrying out the method comprises an actuator device arranged in a housing of the printhead for controlling the piston, a nozzle head with one or more heating elements for converting the material from a solid phase via a plastic phase into a liquid phase, and the nozzle for dispensing the liquid phase of the material from the nozzle head, wherein, according to the invention, the nozzle is at least partially closed during the compression of the material.

[0015] The actuator for controlling the piston can be an electric motor, for example with a mechanical transmission, or a hydraulic drive with a hydraulic pressure source.

[0016] An electric motor as an actuator device has a lower weight compared to a hydraulic drive and therefore advantageously ensures high dynamics of the entire printer and the printing process, since less mass has to be accelerated.

[0017] A hydraulic drive advantageously achieves high forces when controlling the piston.

[0018] The invention comprises the compaction of the material during the compaction process, comprising the following steps: Pre-compacting the material by advancing the piston, closing the nozzle of the print head, compacting the material by advancing the piston and holding the piston in a holding position.

[0019] According to the invention, the pre-compression of the material is carried out by advancing the piston in a pressure- and / or force-controlled manner, whereby pre-compression is carried out up to a position that is reached when a material-dependent slope and / or a material-dependent slope angle of a force and / or pressure curve is reached and / or exceeded.

[0020] Pre-compression is achieved by force- or pressure-controlled actuation of the piston by the actuator device, with the piston head's target position located in the first third of the plasticizing zone, starting from the cold zone. The granules are compressed in the plasticizing zone by the piston's advance, while simultaneously molten material is present in the melt zone between the cavity and the nozzle. This forces the plasticized granules into the melt within the mixing zone.

[0021] Lowering the piston, and analogously moving the piston needle towards the nozzle, causes molten metal to emerge from the nozzle. This advantageously displaces any remaining air or air inclusions from the nozzle head, thus clearing the nozzle.

[0022] Once the target position for pre-compression is reached, the nozzle of the printhead is closed.

[0023] The nozzle can be closed, for example, by a shut-off valve, or advantageously by positioning the print head on a plate within the printer's build chamber. Alternatively, the nozzle can be closed by moving the print head to an already printed area of ​​a component.

[0024] In the next process step, the material is compacted by advancing the piston with the nozzle closed, under pressure control, and a holding position is reached until a peak pressure is achieved.

[0025] In a further training, the piston is held in the holding position, whereby the pressure and temperature of the liquid phase are measured during the holding process and the measured values ​​are checked by the evaluation unit to functionally monitor the compression process.

[0026] Furthermore, the nozzle remains closed while the piston is held in the holding position.

[0027] To compress the material, the piston is advanced by the actuator under pressure control until a defined peak pressure, and thus a peak pressure position, is reached. The nozzle is closed during this process. The piston needle can be immersed in the melt chamber to such an extent that a portion of the liquid phase from the upper part of the melt chamber is displaced through the openings of the kidney-shaped piece from the melt zone back into the mixing zone, thereby mixing this portion of the liquid phase with the plastic phase from the plasticizing zone in the mixing zone.

[0028] The so-called peak pressure position is then held for a material-dependent predefined period; therefore, the peak pressure position is also the holding position of the print head.

[0029] The nozzle is closed while the piston is held in the holding position.

[0030] During the holding process, residual air is displaced and the melt is homogenized in the mixing zone C. This advantageously results in a better energy flow and a more homogeneous material.

[0031] The holding process described here also serves advantageously for analyzing and checking the printhead system, as the following effects can occur during pressure measurement. An increase in the melt pressure would indicate that the melt is outgassing, for example, because the melt temperature is too high. Excessively high melt temperatures are undesirable, as air plasma can form, which would lead to chemical decomposition.

[0032] A significant drop in melt pressure could, for example, indicate a leak in the printhead system or that there was still too much air in the system. This effect could occur if, for instance, too much cold material was present in the cavity because the printhead's temperature management was not optimally configured.

[0033] The method according to the invention can advantageously lead to the determination of a spring constant of the liquid phase, wherein the determination of a spring constant of the liquid phase can comprise the following steps: Pressure-controlled retraction from the holding position after the holding period ends to a target position, which is reached when the melt pressure reaches a target pressure, determining the pressure difference between the peak pressure and the target pressure, determining the distance between the holding position and the target position, and calculating the spring constant of the liquid phase.

[0034] The spring constant results from the compressibility of the melt and leads to a correction factor, or form factor, which is needed for the exact control of the piston by the actuator device.

[0035] Due to the compressibility of the melt, for example, 1.2 volume units of a geometric piston stroke correspond to 1.0 volume units of a discharged volume of melt. Without compressibility, the ratio would be 1:1.

[0036] By determining the spring constant of the melt, the actuator can precisely control the piston. This spring constant ensures, among other things, that the actual melt discharge matches the calculated volumetric flow rate, depending on the printhead's feed rate during printing. This means that at every printing position and at every printhead feed rate, the required amount of melt is applied to the component.

[0037] In a training course, the liquid phase preparation for printing includes the following steps: Active decompression of the liquid phase by retracting the piston depending on the spring constant and opening the nozzle.

[0038] During active decompression, the piston is retracted by approximately 1 to 2 millimeters, depending on the determined spring constant. This advantageously prevents any melt from escaping the nozzle or nozzle opening when it is opened. This would otherwise occur if the position were held further due to the influence of gravity in the open system. Simultaneously, the melt is relieved of pressure, similar to a spring.

[0039] The printing process then begins with further print preparation through compression.

[0040] The entire printhead system is compressible, as the melt, for example, can exhibit a compression of approximately 20%. Therefore, the volume displaced by the piston's movement does not correspond to the volume of the extruded material, which can result in inaccurate and irregular extrusion.

[0041] The dispensing of the liquid phase, i.e., the printing, is carried out under pressure control, whereby: the pressure in the melting chamber is constantly measured, the piston is actively controlled via the control unit, whereby the piston's feed is adjusted by a correction factor depending on the pressure, the correction factor being derived from the calculated spring constant of the liquid phase of the material.

[0042] The measured pressure corresponds to the pressure caused by the discharge of the liquid phase onto the component, and the correction factor is advantageous to compensate for the compressibility of the liquid phase.

[0043] The compression of the melt in the melt chamber at the start of printing is generated partly by friction at the nozzle opening when the melt is "squeezed out" and partly by the resistance when printing onto the component or a substrate support on which the component is built.

[0044] Uniform molten metal discharge is achieved through intelligent control of the printhead, whereby asynchronous piston movements, adjusted by the correction factor, are implemented via an electronic gearbox on the actuator. The correction factor, which is derived in particular from the determined spring constant of the melt, is essentially integrated into the system. Therefore, the method advantageously avoids the limitations of synchronous movements found in conventional NC systems.

[0045] In a further development of the process, the conversion of the material from a solid phase via a plastic phase to a liquid phase includes at least the following step: Heating the material by one or more heating elements of the nozzle head.

[0046] The processes of compression and conversion largely take place simultaneously, as heating energy is introduced into the printhead via one or more heating zones during both processes.

[0047] An electrically driven actuator proves to be dynamic and very effective in this case.

[0048] The piston of the printhead comprises a first piston section for connection to the actuator device, and a piston head for connection to the first piston section and for receiving the piston needle. The first piston section is preferably designed as a hollow aluminum piston, allowing coolant to be circulated through it and thus advantageously achieving piston cooling. The piston head has a bottom surface on the side facing the nozzle, with the piston needle protruding from the center of this underside. The area of ​​the bottom surface of the piston head, minus the virtual area of ​​the piston needle, forms a piston surface for generating pressure on the material. The underside of the piston head is cooled by the piston cooling process, thereby locally reducing the viscosity of the melt or the plastic material at the piston base.This prevents molten material from flowing towards the drive mechanism, thus advantageously preventing the piston from jamming in the piston bushing and the molten material from entering the drive mechanism. Furthermore, the material detaches more easily from the piston base or the underside of the piston head during retraction, allowing for easy refilling of solid material or granules when the piston reaches its starting or ending point, without the residual material adhering to the piston base.

[0049] A temperature sensor is preferably mounted on the underside of the piston head, or on the piston base. This arrangement of the temperature sensor enables piston-position-dependent thermal management of the printhead, resulting in faster heating of the material without the molten material coming into contact with the underside of the piston head. This advantageously accelerates the filling process of the printhead.

[0050] The piston head is designed as a cylindrical component and is preferably made of a thermally resistant material. The combination of the first piston part being made of aluminum and the piston head of, for example, steel, proves advantageous because the piston thus has an elastic upper section to absorb the mechanical stresses and a thermally resistant lower section in the area of ​​the heated material.

[0051] Depending on the piston position, the piston needle protrudes only partially into the bore of the kidney piece or completely through it, thus guiding the piston needle advantageously in the central bore of the kidney piece.

[0052] The kidney-shaped piece has concentrically arranged openings, which form a fluidic connection between a cavity located in the piston bushing and a melting chamber located in a lower part of the nozzle head.

[0053] The cavity is located inside the piston bushing and is formed by a volume whose outer surface is formed by the inside of the piston bushing, the outside of the piston needle, the top of the kidney piece and the bottom of the piston.

[0054] Within the cavity, the material, or granules, are compacted by the piston movement over the underside of the piston head, or the piston surface. During material compaction, the thermal management of the print head is set such that no liquid phase, or melt, of the material forms within the cavity, but rather the material develops into a plastic phase. This advantageously prevents any plasticized material from adhering to the underside of the piston. However, during compaction, some of the liquid phase, or melt, in the melt chamber is forced out of the melt chamber into the cavity of the piston bushing by the piston needle penetrating the melt chamber and through the concentrically arranged openings of the kidney-shaped piece. In this process, some of the melt mixes with some of the plastic phase.In this process, the melt releases energy into the plastic phase, advantageously producing a more homogeneous material. The kidney-shaped element thus acts as a mixer, or rather a static mixer, since, apart from the piston movement, no other moving parts are required to mix the plastic and liquid phases. The design of the kidney-shaped element therefore advantageously provides an aperture effect, leading to improved mixing of the material, or rather the melt, with the plasticized material.

[0055] The kidney-shaped piece directs the heating energy from the heating element in the nozzle head into both the melt and the piston needle, which advantageously ensures improved energy management when heating the melt.

[0056] The kidney piece can also be designed as a separate component or formed in one piece with the piston bushing.

[0057] Furthermore, a pressure sensor for the pressure p L , and / or a temperature sensor for the temperature TL of the liquid phase is arranged in the melting chamber.

[0058] The pressure pL measurement is the primary parameter that determines the output, or discharge, or mass flow rate of melt from the outlet. An additional measurement of the temperature λL allows the temperature dependence of the material's viscosity to be considered when determining the mass flow rate Q. The piston feed enables precise control of the metered quantity. For the quality of the manufactured component or object, temperature control λL, particularly through constant and precise regulation, is even more crucial to prevent thermal degradation of the material.

[0059] In addition, a displacement measuring system for the position s of the piston, and / or a sensor for the force F exerted by the piston on the material or for a hydraulic pressure p H exerted on the piston, is provided on the actuator device and / or on the piston.

[0060] The piston's feed rate is a measure of the amount of material to be extruded. This amount can be monitored, among other things, via the displacement measuring system. Furthermore, the force F correlates directly with the pressure in the material.

[0061] Furthermore, a temperature sensor for the temperature TK of the plastic phase of the material is arranged on the piston, in particular on the underside of the piston head of the piston.

[0062] This arrangement of the temperature sensor enables piston-position-dependent thermal management of the printhead, resulting in faster heating of the material without the molten material coming into contact with the underside of the piston head. This advantageously accelerates the printhead filling process or reduces the required filling time.

[0063] 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. Brief description of the drawing

[0064] They show: Fig. 1 a printhead for a 3D printer for carrying out the method according to the invention; Fig. 2 another illustration of the printhead; Fig. 3 a section of the printhead; Fig. 4 a schematic representation of the printhead; Fig. 5 a flowchart of a process with inventive partial steps for providing printable melt; Fig. 6 a section of the printhead showing a print gradient; Fig. 7 different positions of a piston in the printhead; Fig. 8 a flowchart of a procedure for filling a cavity of the printhead; Fig. 9 a flowchart of a procedure for closing an opening cross-section of a piston bushing of the printhead; Fig. 10 a flowchart of a process for converting a material from a solid phase through a plastic phase into a liquid phase; Fig. 11 a flowchart of a process for compacting the material; Fig. 12 a flowchart of a procedure for determining a spring constant of the liquid phase of the material and Fig. 13 a flowchart of a process for preparing the liquid phase of the material for printing. Examples of implementation

[0065] Fig. 1 Figure 1 shows a printhead 100 for a 3D printer, comprising an actuator 110 arranged in a housing 1 of the printhead 100 for controlling a piston 3, a feed device 2 for a printable material 10, a flange 5 arranged on the housing 1 and the feed device 2 with a cooling device 50, a nozzle head 6 with heating elements 61, 63 for converting the material 10 from a solid phase 10 via a plastic phase 11 into a liquid phase 12, and a nozzle 8 for dispensing the liquid phase 12 of the material 10 from the nozzle head 6. The printhead 100 includes a separate piston bushing 4 for guiding the piston 3.

[0066] The internally cooled flange 5, provided by the cooling device 50, ensures thermal separation of the lower heated area of ​​the printhead 100 from the actuator device 110, or from the drive of the piston 3.

[0067] The piston 3 comprises a first piston part 31 for connecting the piston 3 to the actuator device 110, and a piston head 34, which is attached to the first piston part 31 and accommodates a piston needle 32 in the direction of the nozzle 8. A temperature sensor 36 for measuring the temperature TK of the plastic phase 11 of the material is arranged on the piston 3, or on a lower surface 35 of the piston head 34. The lower surface 35 of the piston head 34 forms a piston base 35. The first piston part 31 is preferably designed as a hollow aluminum piston, which has an internal cavity designed as a cooling channel. A piston cooling element 33 is arranged at the lower end of the first piston part 31 and is cooled by a coolant system.

[0068] The piston cooling system 33 ensures that the material 11, 12 solidifies at the piston base 35 and thereby seals the piston 3 towards the actuator device 110, or prevents the flow of liquid melt 12 towards the actuator device 110. A cooling liquid is preferably used as the coolant, which is conveyed via connections and flexible lines through the housing 1 into a cooling connection 37 of the first piston part 31.

[0069] The cooling device 50 in the flange 5 is supplied with coolant by the same coolant system.

[0070] As the material 11, 12 cools at the piston base 35, its viscosity locally decreases, causing it to detach from the piston 3 without forming strings when the piston is retracted. This creates space for new material 10.

[0071] Fig. 1 shows the piston 3 in a starting position for filling the printhead 100 with printable material 10, which is fed into the printhead 100 via the feed device 2.

[0072] The feeding device 2 is funnel-shaped, with the material 10, preferably granules, being filled from above into an opening of the feeding device 2. The material 10 reaches the piston bushing 4 by gravity up to an opening 21, or rather, to an opening cross-section of the piston bushing 4. An air duct 20 is arranged in the lower region of the feeding device 2 above the opening 21. This air duct is supplied with air pulses by a pneumatic valve 22. The pneumatic valve 22 and the air duct 20 form an injection device that intermittently supplies the granules 10 with bursts of air such that they are propelled towards the upper region of the feeding device 2, thereby separating the individual granules 10 from one another. When the airflow is switched off, the granules 10 located in the lower region of the feeding device 2 fall into the piston bushing 4 through the open opening cross-section 21.

[0073] The blowing device of the feed unit 2 prevents the granule pieces 10 from jamming, thus preventing clogging of the feed unit 2 and ensuring the piston bushing 4 is reliably filled with granule 10. Furthermore, smaller diameters can be used in the inlet of the feed unit 2.

[0074] The refilling process requires blowing behind the granules 10, which creates a lifting effect, causing them to slide into the printhead 100. This agitation is necessary for automated operation, and the resulting gravitational impulse or impact causes the granules 10 to slide down.

[0075] The piston bushing 4 has an upper section 41 projecting into the flange 5 and a lower section 42 projecting into an upper section 60 of the nozzle head 6. A stop 43 is arranged between the upper section 41 and the lower section 42 of the piston bushing 4, separating the flange 5 and the nozzle head 6 from each other. The opening 21, or the opening cross-section, is located in the upper section 41 of the piston bushing 4 and has a gate 44 on the inner surface of the piston bushing 4. The gate 44 causes granules 10 to be sheared off between the gate 44 and the piston base 35 when the opening cross-section 21 is closed by the piston 3, until the piston base 35 reaches a position below the gate 44.

[0076] The piston bushing 4 has an obtuse angle at the chamfer 44, which is sharp-edged and hardened. Local hardening is advantageous in this case. Alternatively, the chamfer 44 can also be formed by a separate insert, similar to an indexable insert.

[0077] The design of the gate 44 advantageously reduces the forces required to shear off the granules 10, thereby saving energy and making the materials of the piston bushing 4 and the piston 3 less susceptible to wear. However, the edge of the gate 44 is extremely prone to wear.

[0078] A kidney-shaped piece 7 is arranged on the lower part 42 of the piston bushing 4, wherein the kidney-shaped piece 7 has a centrally extending bore 70 for receiving a piston needle 32 of the piston 3.

[0079] The kidney-shaped piece 7 further comprises concentrically arranged openings 71, which form a fluidic connection between a cavity 40 located in the piston bushing 4 and a melting chamber 81 located in a lower part 62 of the nozzle head 6. The cavity 40 is located within the piston bushing 4 and is formed by the inner surface of the piston bushing 4, the outer surface of the piston needle 32, the upper surface of the kidney-shaped piece 7, and the lower surface 35 of the piston 3.

[0080] A preferred function of the kidney-shaped piece 7 is the heat conduction, or energy transfer, from the heating elements 61, 63 of the nozzle head 6 into the liquid phase 12 of the material, or the melt 12. This is achieved in particular by increasing the contact area to the cavity 40 and thus to the plastic phase 11 of the material.

[0081] Another function is to guide the piston needle 32, whereby the contact of the piston needle 32 within the bore 70 additionally ensures that the piston needle 32 is heated to the required process temperature. The final process temperature is only reached in the nozzle head 6 towards the nozzle 8.

[0082] During a filling process of the printhead 100, the nozzle 8 is closed, particularly during compression 630, and when the piston 3 is actuated by the actuator device 110, the material 10, 11, 12 arranged in the cavity 40 and melting chamber 81 is compressed by the piston feed.

[0083] The nozzle head 6 comprises the heating elements 61 and 63 of the print head 100, with a first heating element 61 arranged in the upper nozzle head 60 and a second heating element 63 arranged in the lower nozzle head 62. The upper nozzle head 60 has a section 64 located between the upper nozzle head 60 and the lower nozzle head 62, against which the kidney-shaped piece 7 rests. A cooling ring 84 is arranged on the nozzle head 6 in the area of ​​the nozzle 8. This cools the component to be printed and thermally insulates the component from the print head 100.

[0084] The heating elements 61, 63 in the nozzle head 6 heat the material 10, 11, 12 within the cavity 40, the kidney-shaped section 7, and the melting chamber 82 until the liquid phase 12 of the material reaches its process temperature and can be discharged from the nozzle 8. The melting chamber 82 is designed such that it tapers from the section 64 of the upper nozzle head 60 to the nozzle 8. The conical inlet of the melting chamber 81 allows for an increase in the volume flow and prevents material deposits on the inner wall of the nozzle head 6. Because there is less material 12, or volume, in a conically tapered melting chamber 81 compared to a cylindrical one, the mixing process is further optimized. The piston needle 32 therefore has to displace less volume in order to force parts of the melt 12 back through the openings 71 of the kidney piece 7 from the melt chamber 81 into the cavity 40 during compression.

[0085] Furthermore, the printhead 100 comprises additional sensors, with a pressure sensor 83 for the pressure pL and a temperature sensor 82 for the temperature TL of the liquid phase 12 of the material being arranged in the melting chamber 81. Additional sensors are arranged on the actuator device 110, including a displacement measuring system 111 for the position s of the piston 3 and a sensor 112 for the force F exerted by the piston 3 on the material 10, 11 or for a hydraulic pressure pH exerted on the piston 3. In an alternative embodiment, the sensors 111, 112 can also be arranged on the piston 3 of the printhead 100.

[0086] Fig. 2 Figure 1 shows another representation of the printhead 100, wherein the solid phase 10 of the material comprises the granule pieces 10 and the feed device 2 includes the injection device 25 for separating the granule pieces 10 from one another. The injection device 25 comprises the pneumatic valve 22 and the air duct 20, wherein the air duct 20 is arranged in a housing part 27 of the feed device 2 and opens into a lower region 24 of the feed device 2 above the opening cross-section 21 of the flange 5.

[0087] The air channel 20 can be supplied with air pulses 26 via the pneumatic valve 22, whereby the air pulses 26 act on the granule pieces 10 in the lower area 24 in such a way that they separate from each other.

[0088] The feed device 2 is funnel-shaped, with the granules 10 being filled from above into an opening 23 of the feed device 2. The material 10 reaches the opening cross-section 21 of the flange 5 by gravity, up to the piston bushing 4, or to the opening cross-section 21 of the piston bushing 4. In the lower region 24 of the feed device 2, above the opening cross-section 21 of the flange 5, an air duct 20 of the injection device 25 is arranged. The air duct 20 is supplied with air pulses 26 by the pneumatic valve 22. The injection device 25 comprises the pneumatic valve 22 and the air duct 20, whereby the granules 10 are supplied with air pulses at intervals such that they are propelled towards the upper region of the feed device 2, thereby separating the individual granules 10 from one another.When the injection device 25 is switched off, the granules 10 located in the lower section 24 of the feeder 2 fall into a cavity 40 of the piston bushing 4 through the open opening cross-section 21. The injection device 25 of the feeder 2 thus prevents the granules 10 from jamming, thereby preventing clogging of the feeder 2 and ensuring the piston bushing 4 is reliably filled with granules 10. The refilling process requires blowing air behind the granules 10, which creates a lifting effect, causing them to slide into the printhead 100. This agitation is necessary for automated operation, and the resulting gravitational impulse or impact causes the granules 10 to slide down.

[0089] Fig. 3 Figure 1 shows a section of the printhead 100 in a view rotated by 90°, showing state zones A, B, C, D, E of the printhead 100 filled with material 10, 11, 12 during operation, starting from the upper part 41 of the piston bushing 4, via the kidney-shaped piece 7, to the nozzle 8. State zones A, B, C, D, E represent a state of matter of the material 10 as a function of its temperature Ts, whereby the state of matter of the material 10 can change across state zones A, B, C, D, E from a solid phase 10 through a plastic phase 11 to a liquid phase 12.

[0090] The temperature TS, or the temperature profile of the material 10, 11, 12 within the printhead 100, is shown in a diagram above the printhead 100, where it is represented over the path s, or the length of a working area 120 of the printhead 100.

[0091] The state zones A, B, C, D, E of the printhead 100 comprise a cold zone A with material in solid phase 10, a plasticizing zone B with material in plastic phase 11, a melting zone D and a process zone E, each with material in liquid phase 12. Furthermore, the state zones comprise a mixing zone C with material in plastic 11 and liquid 12 phases.

[0092] The cooling device 50 in the flange 5 and the piston cooling 33 integrated in the piston 3 are designed to keep the temperature TS of the plastic phase 11 of the material in the plasticization zone B below a glass transition temperature Tg, even after the material 11 plasticizes and transitions into a liquid phase 12. In the embodiments shown here, the plasticization zone B, with the material in plastic phase 11, describes a state of the material, or rather the granules, in which the viscosity of the granules is already changing, thereby optimizing a compaction and a mixing process, but the plastic phase 11 of the granules has not yet transitioned into the liquid phase 12.

[0093] Furthermore, the nozzle head 6 comprises two heating zones 65, 66. The method according to the invention can also be carried out with one or more heating zones. In the first heating zone 65, a partial region of the plasticizing zone B, the mixing zone C, and a partial region of the melting zone D are arranged, wherein a first heating element 61 is arranged in the upper nozzle head 60 such that the heating energy from the first heating element 61 can be introduced into the material 10, 11, 12 via the lower partial region of the piston bushing 42, the kidney-shaped section 7, and a partial section 64 of the upper nozzle head.

[0094] In the second heating zone 66, a part of the melt zone D and the process zone E are arranged, wherein a second heating element 63 is arranged in the lower nozzle head 62 such that the heating energy from the second heating element 63 can be introduced into the liquid phase 12 of the material via the lower nozzle head 62.

[0095] The diagram shows that the temperature TS of material 10, 11, 12 increases steadily along the path s of the working area 120 of the printhead 100. In the cold zone A, the effect of the cooling device 50 of the flange 5 is predominant, causing the granules 10 to heat up only slowly along path s. From the plasticizing zone B onwards, the influence of the first heating zone 65 with the first heating element 61 begins to increase, with the temperature curve rising sharply until the glass transition temperature Tg is reached, at which point the mixing zone C begins. The temperature Ts continues to rise in the mixing zone C at a lower rate until the melting zone D is reached. There, the influence of the second heating zone 66 with the second heating element 63 begins, causing the temperature Ts of the melt 12 to rise sharply until the process temperature of the melt 12 is reached in the process zone E, and printable melt 12 has been formed.

[0096] The temperature Ts must be set so that the granules 10 can trickle into the cavity 40 during filling without clumping, but are also preheated sufficiently to allow shearing of the material 10, 11 at the gate 44 with minimal force. The temperature management of the printhead 100 is set such that the cooling device 50 in the flange 5 introduces a cooling temperature of approximately 40°C into the piston bushing 4 and thus into the material 10, 11, and the first heating element 61 of the first heating zone 65 introduces a heating temperature of approximately 30°C below the glass transition temperature Tg, or the melting temperature of the material 10, 11, 12.

[0097] This effect is supported by piston cooling 33. The cooling of material 11, 12 at the piston base 35 locally reduces its viscosity, causing it to detach from the piston 3 without forming strings when the piston is retracted. This creates space for new material 10 when the piston 3 releases the opening cross-section 21 to the feed device 2.

[0098] The temperature sensor 36 on the piston base 35 measures the temperature TK at the contact point between the piston 3 and the material 10, 11. This allows the cooling and heating power of the printhead 100 to be calculated so that the glass transition temperature Tg of the material 10 is not exceeded. Due to the arrangement of the temperature sensor 36 on the piston base 35, the heating elements 61, 63 can be controlled based on the piston position, thus enabling temperature TS to be set. This results in faster heating of the material 11, 12. The thermal management of the printhead 100 therefore also allows the processing of plastics with low melting points of less than 60 to 80°C.

[0099] During a compression process to produce the liquid phase 12 of the material in process zone E, the nozzle 8 is closed. The nozzle 8 can be closed, for example, by a shut-off valve (not shown) or by positioning the print head 100 on a plate in the printer's build chamber. Alternatively, a previously printed area of ​​a component 9 can be approached, thereby closing the nozzle 8. In this example, during the compression process, the piston needle 32 is immersed in the melt chamber 81 and moves further into it, displacing portions of the liquid phase 12 from the melt zone D back into the mixing zone C. This causes the liquid phase 12 to mix with the plastic phase 11 from the plasticization zone B in the mixing zone C.

[0100] The liquid phase 12 from the melt zone D is thereby displaced from the upper area of ​​the melt chamber 81 through the openings 71 of the kidney piece 7 back into the cavity 40 of the piston bushing 4 into the mixing zone C.

[0101] Fig. 4 Figure 1 shows a schematic representation of the printhead 100 with a control and regulation unit 113 for active control of the actuator device 110 for moving the piston 3 and an evaluation unit 114, which is designed to evaluate the measured values ​​of the sensors 36, 82, 83, 111, 112 and to transmit the results to the control and regulation unit 113 for active control of the actuator device 110 and for active control of the heating elements 61, 63.

[0102] The control and regulation unit 113 is provided for active control of the actuator device 110 for moving the piston 3 according to an operating strategy to be executed for filling and printing and for active control of the temperatures of the first 61 and second 63 heating element.

[0103] The active control of the actuator device 110 is determined by the sensor signals received by the evaluation unit 114 and the results calculated from the respective values.

[0104] The pressure sensor 83 for the pressure pL and the temperature sensor 82 for the temperature TL of the liquid phase 12 are arranged in the melting chamber 81. The displacement measuring system 111 for the position s of the piston 3 and the sensor 112 for the force F exerted by the piston 3 on the material 10, 11 or for a hydraulic pressure pH exerted on the piston 3 are arranged on the actuator device 110 or on the piston 3.

[0105] Furthermore, the temperature sensor 36 for the temperature TK of the plastic phase 11 of the material is arranged on the piston 3.

[0106] The signals s, F, p H , TK , TL , p L of sensors 111, 112, 36, 82, 83, represented by dashed arrows, are transmitted to the evaluation unit 114, subsequently evaluated in this unit or in a cloud, and the results are transmitted as control variable i to the control unit 113 according to an operating strategy, and the actuator device 110, as well as the heating elements 61, 63 are controlled accordingly.

[0107] Fig. 5 shows a flowchart of a process 200 for providing printable melt 12 for operating the printhead 100, wherein the process 200 comprises the following steps: Filling 210 of a cavity 40 with printable material 10 by means of a feeding device 2, closing 220 of an opening cross-section 21 of a piston bushing 4 by advancing a piston 3 from a starting position 3a in the direction of a nozzle 8 of the print head 100, converting 230 of the material from a solid phase 10 via a plastic phase 11 into a liquid phase 12, compacting 240 of the material 10, 11, 12, determining 250 a spring constant of the liquid phase 12 and preparing 260 the liquid phase 12 for printing.

[0108] At least the closing 220, the conversion 230, the compression 240, the determination 250 of the spring constant and the pressure preparation 260 of the process 200 are carried out by an active control of the actuator device 110 by the control unit 113, wherein the results of the evaluation unit 114 from the measured values ​​of the sensors 36, 82, 83, 111, 112 are passed on to the control unit 113.

[0109] The procedural steps will be explained in more detail below.

[0110] Fig. 6 Figure 1 shows a section of a possible embodiment of the printhead 100 according to the invention and two diagrams 6a, 6b, which show a pressure or pressure force profile during the provision of printable melt 12 or various process steps of the process 200 for providing printable melt. Fig. 7 shows the different positions of piston 3 for the various process steps or states. Fig. 6 starting at the starting position 3a to the end position 3z of the piston base 35. During the execution of the process steps, the cooling devices 50, 33 in the flange 5 and piston 3, as well as the heating elements 61, 63 are active and the melting chamber 81, as well as the kidney piece 7 are filled with melt 12 and in the lower part of the cavity 40 there is still granules in plastic phase 11.

[0111] The sections of the depicted printhead 100 correspond to that of the one in the Figuren 1 , 3 and 4 illustrated printhead 100, so that the reference numerals of the previous figures for the description of the Figuren 6 and 7 new features and references, for example the respective position of the piston 3 in relation to the piston base 35, are used, whereby new features and references, such as the respective position of the piston 3 in relation to the piston base 35, are incorporated into the Figuren 6 and 7 is marked.

[0112] Fig. 6 Diagram 6a shows two curves plotted against the distance s traveled by piston 3. The distance s is measured by the displacement measuring system 111, or displacement sensor 111, at the actuator device 110 or at piston 3.

[0113] The upper curve represents a force and pressure profile for the force F exerted by the piston 3 on the material 10, 11 or for the hydraulic pressure p H exerted on the piston 3 during the advance of the piston 3 through the actuator device 110 during closing 220 and compression 240, wherein the force or pressure sensor 112 is arranged on the actuator device 110 or on the piston 3.

[0114] The lower curve in diagram 6a represents a pressure profile of the melt pressure pL in the melting chamber 81 as a function of the piston's travel s during compression 240. The pressure sensor 83 for the pressure pL of the liquid phase 12, or the melt 12, is located in the melting chamber 81.

[0115] In the second diagram 6b, a section of the lower curve of the first diagram 6a is shown, where here too the pressure profile of the melt pressure p L in the melt chamber 81 over the path s of the piston 3 during compression 240 is shown (curve profile from pc to pd ).

[0116] Fig. 7a Figure 3 shows a starting position 3a of the piston 3 during the filling process 210 of the print head 100, with the piston base 35 positioned at the top of the opening 21 of the piston bushing 4. The entire process sequence from filling 210 to opening 820 of the nozzle during print preparation 260 is also called the refill process, as it is a recurring sequence that is repeated as often as necessary during the printing of a component 9. The refill process is the method for providing printable melt 12 to operate the print head 100 for a 3D printer. The in Fig. 7a The position of piston 3 shown is analogous to the position of piston 3 from Fig. 1 The opening 21, or rather the opening cross-section 21 of the piston bushing 4, is open and the granules 10 can be introduced into the cavity 40 of the piston bushing 4 via the feed device 2. Subsequently, the piston 3 is moved by the actuator device 110 into the Fig. 7b Position 3b shown is controlled. The piston head 35 slides past the gate 44 of the piston bushing 4, and the granules 10 projecting from the opening 21 into the cavity 40 are sheared off between the piston head 35 and the gate 44. This position is therefore called shear position 3b. After shearing 420, the opening cross-section 21 is closed 220.

[0117] The force-pressure curve F, p H increases from the starting position 3a to the shearing position 3b, with the force exerted by the actuator 110 being highest at the gate 44, i.e., at the shearing position 3b, since the actuator 110 must provide the force to shear the granules 10. This force can be reduced by suitable measures such as optimizing the gate geometry in conjunction with the design of the piston head 35 and preheating the granules 10. In contrast, the pressure curve p L of the melt 12 changes only slightly, or hardly increases at all, since the nozzle 8 is still open and no pressure build-up occurs in the melt chamber 81.

[0118] The compaction process 240 then begins, and the piston 3 is moved to position 3c by the actuator 110 under force or pressure control. During the movement of the piston 3, the force F exerted on the material or granules 10, 11, or the hydraulic pressure pH exerted on the piston 3, as well as the pressure pL in the melt 12, are measured. The movement of the piston 3 pre-compacts the material 10, 11, 12.

[0119] Position 3c is defined by the increase in force or pressure; that is, position 3c is targeted not by a direct point, but by a flank of the curves shown in diagram 6a. The flank arises at a transition point pLc, Fc, pHc, respectively, from the straight line with little or no slope (the area from position 3a to position 3c) to the point where the curve rises (at position 3c), at which a predefined slope or angle of inclination is reached and / or exceeded. Position 3c is located in the first third of plasticizing zone B. The granules 10, 11 are compressed in plasticizing zone B by the advance of the piston 3, while simultaneously, melt 12 is present in the melt zone D between the cavity 40 and the nozzle 8. The plasticized granules 11 are thereby pressed into the melt 12 in the mixing zone C.

[0120] By lowering the piston 3 and, analogously, the piston needle 32 towards the nozzle 8, molten metal 12 emerges from the nozzle 8, thereby displacing any remaining air or air inclusions from the nozzle head 6. This clears the nozzle 8.

[0121] Position 3c is subject to a tolerance due to the process and material properties, which means that the position 3c of piston 3 may vary slightly during different, successive refilling operations of the printhead 100. Position 3c is therefore not a fixed point. If position 3c is within the specified tolerance, it is ensured that the filling process 210 was successful, meaning that enough granules 10 were filled into the cavity 40 and that the melt chamber 81 is already filled with melt 12. If, for example, the flank begins too far before position 3c, there is too much highly viscous or hard material 10, 11 in the area from the piston base 35 to the nozzle 8, and the mixing process in the mixing zone C may not have been successful. If, for example, the flank begins far behind position 3c, too little material 10 may have been added.

[0122] After reaching position 3c, the pre-compression 610 is completed and the nozzle 8 of the printhead 100 is closed 620.

[0123] For compression 630, the piston 3 is advanced from position 3c under pressure control until a predefined peak pressure pd is reached and the piston head 35 rests on the in Fig. 7c The position shown was 3D. The peak pressure (pd) can vary between approximately 100 and 300 bar, depending on the material and requirements.

[0124] The so-called peak pressure position 3d is then held for a material-dependent, predefined period. The piston base 35 protrudes into the first heating zone 65, and the piston needle 32 into the melting chamber 81. During this holding period, a portion of the melt 12 flows from the melting chamber 81 of the nozzle head 6 through the openings 71 of the kidney-shaped piece 7 back into the mixing zone C and into the plastic granules 10 located there. This displaces residual air and homogenizes the melt 12 in the mixing zone C. This results in improved energy flow and the production of a more homogeneous material 11, 12. The returning melt 12 becomes plastic, and the granules 11, which are pushed into the kidney-shaped piece 7, become molten. This results in the mixing of the material 11, 12.

[0125] The holding process 640 described here also serves for the analysis and system check of the printhead 100, as the following effects can occur during the pressure measurement of the pressure p L. An increase in the pressure p L in the melt 12 would mean that the melt 12 is outgassing, for example, because the temperature TL is too high. Excessively high melt temperatures TL are undesirable, as air plasma can form, which would lead to chemical decomposition.

[0126] A significant drop in the melt pressure pL could, for example, indicate that the printhead 100 system is leaking or that there was still too much air in the system. This effect could occur, for instance, if too much cold material 10, 11 was present in cavity 40 because the temperature management of the printhead 100 was not optimally configured.

[0127] After the predefined period has elapsed, the piston 3 is retracted from the peak pressure position 3d by the actuator device 110 under pressure control until a target pressure pe of approximately 0 bar is reached. The system is then depressurized. This ensures that the melt 12 is depressurized and vented, resulting in a pure melt 12, particularly in process zone E, which is now of high quality and capable of being printed. Upon reaching the target pressure pe, the Fig. 7d The target pressure position 3e shown is reached, with the piston base 35 positioned outside the first heating zone 65 in the area of ​​the stop 43 of the piston bushing 4.

[0128] The pressure difference now measured between the pressure pd of the peak pressure position 3d and the pressure pe of the target pressure position 3e and the distance s traveled between the two points 3d, 3e results in a spring constant 740 of the liquid phase 12 of the material, or the melt 12.

[0129] The spring constant results from the compressibility of the melt 12 and leads to a correction factor, or form factor, which is required for the exact control of the piston 3 by the actuator device 110.

[0130] Due to the compressibility of the melt 12, for example, 1.2 volume units of a geometric piston travel s by the piston 3 correspond to 1.0 volume units of a discharged volume of the melt 12. Without compressibility, the ratio would be 1:1.

[0131] This ensures that the actuator 110 can control the piston 3 in a controlled manner, whereby the spring constant, among other things, enables the actual discharge of the melt 12 to achieve the correct, calculated volumetric flow rate of the melt 12 as a function of a web speed v B of the moving printhead 100 during printing. This means that at each printing position and at each web speed v B of the printhead 100, the required quantity of melt 12 is applied to the component 9.

[0132] Subsequently, the process of dispensing 270 of the melt 12, or the pressure process 270, is prepared via active decompression 810 by retracting the piston 3 260.

[0133] Depending on the determined spring constant, the piston 3 is retracted by approximately 1 to 2 millimeters, thus preventing any melt 12 from exiting the nozzle 8 or nozzle opening when it is subsequently opened 820. This would occur if the position 3e were held further due to the influence of gravity in the existing open system. Simultaneously, the melt 12 is relieved of pressure, similar to a spring.

[0134] The next stage of the printing process involves preparation through compression.

[0135] As already described, the entire printhead 100 system is a compressible system, since the melt 12, for example, can exhibit a compression of approximately 20%. Therefore, the volume displaced by the advance of the piston 3 does not correspond to the volume of the dispensed material 12, which can result in inaccurate and irregular dispensing. The possible volume of the melt 12 for one advance of the printing process is defined by the target position 3e and the path to the Fig. 7e shown end position 3z.

[0136] Due to the effect described above, the melt 12 is compressed during the start of printing. The compression of the melt 12 in the melt chamber 81 at the start of printing is generated partly by friction at the nozzle opening of the nozzle 8 during the "extrusion" of the melt 12, and partly by the resistance during printing onto the component 9 or a substrate support on which the component 9 is built.

[0137] Uniform discharge of the melt 12 is achieved through intelligent control of the printhead 100, whereby asynchronous movements of the piston 3, adjusted by a correction factor, are effected by the use of an electronic gearbox on the actuator device 110. The correction factor, which results in particular from the determined spring constant 740 of the melt 12, is, so to speak, mixed into the system. Therefore, the printhead 100 according to the invention is not limited to synchronous movements analogous to conventional NC systems.

[0138] The printing process is pressure-controlled, with the pressure pL of the melt 12 being continuously measured by the pressure sensor 83 in the nozzle head 6. The measured pressure pL is the pressure generated by the extrusion of the melt 12 onto the component 9, or onto the substrate carrier (if no component is yet present). Without this effect of printing onto an object, there would be no counter-pressure at the nozzle 8, apart from frictional pressure, which would result in excessive material / melt 12 being extruded from the nozzle 8.

[0139] The printing process is initiated by actively mixing in melt 12 via the intelligent control and actuation of the piston 3. This involves executing a larger stroke to compensate for the compressibility of the melt 12. While this may initially result in too much melt 12 being expelled from the nozzle 8, the pressure sensor 83 is read in parallel with the mixing of the melt 12, allowing for pressure-dependent counter-regulation.

[0140] An electrically driven actuator device 110 proves to be dynamic and very effective in this case.

[0141] During the printing process 270, the melt temperature Ts is continuously measured and in the heating zone 2 the melt 12 is regulated via the heating elements 63 in the nozzle head 6 to the required setpoint of the process temperature in the area of ​​the process zone E.

[0142] The piston 3 is controlled by the actuator device 110 according to a web speed of the print head 100 at the start of printing, whereby melt 12 is discharged from the nozzle 8.

[0143] During the printing process, the control unit 113 of the printhead 100 is activated and actively intervenes in the control of the actuator 110, for example, to add an additive setpoint or an additional quantity of material 12 as needed. If, for example, an additive setpoint is added and more material 12 is extruded from the nozzle 8 than would be the case with continuous control, the pressure p L at the nozzle head 6 also increases as a result. The additive setpoint is the added value, or the additional piston travel that must be undertaken to extrude the desired volume of melt 12 according to the correction value determined from the spring constant 740. This achieves a steady state, ensuring that the quantity of melt 12 extruded onto the component 9 remains constant.

[0144] The use of the piston needle 32 provides the advantageous effect of enabling direct volume displacement within the melt 12 in the melt chamber 81, resulting in a lower spring constant. This lower spring constant, in turn, allows for high dynamics of the print head 100. This effect arises from the more direct pressure transmission to the melt 12 via the piston needle 32. Thus, when the piston 3 advances, not only the piston base 35 transmits a pressure impulse to expel the melt 12 from the nozzle 8, but also the piston needle 32, which is positioned closer to the nozzle 8.

[0145] The printing process can be carried out until the piston base 35 reaches position 3z, where position 3z is defined such that the piston base 35 just does not reach a mechanical stop, but as in Fig. 7e The process is shown to stop shortly before reaching kidney section 7. After this point, no more material 12 can be discharged and the refill process described above is restarted.

[0146] In the Figuren 8 bis 13 Individual flowcharts of the process steps of process 200 are shown in addition to the embodiments of the invention described in the preceding figures.

[0147] Fig. 8 Figure 2 shows a flowchart of a process for filling the cavity 40 with printable material 10 by means of the feeding device 2, wherein the process 210 comprises at least the following steps: Filling 310 of the material 10 through the opening 23 of the feed device 2 into the print head 100 and generating 320 air pulses 26 to loosen the material 10, in particular the granule pieces 10 from each other.

[0148] The filling of 310 of the granule pieces 10 is carried out manually or automatically, whereby the granule pieces 10 slide into the lower area 24 of the feeding device 2 due to the influence of gravity.

[0149] The generation of 320 air pulses 26 is carried out in intervals and the granule pieces 10 are flung up in the area of ​​the air pulses 26 in such a way that, as they fall, they exert an impulse on the granule pieces 10 below and cause them to slide into the heated cavity 40 of the printhead 100.

[0150] Fig. 9 Figure 2 shows a flowchart of a method for closing the opening cross-section 21 of the piston bushing 4 by the piston 3, wherein the method 220 comprises the following steps: Advance 410 of the piston 3, starting from the starting position 3a of the piston base 35 of the piston 3 in the direction of the nozzle 8 until reaching position 3b below the gate 44 of the piston bushing 4, whereby a shearing 420 of the granules 10 is achieved by the piston base 35 sliding past the gate 44.

[0151] Fig. 10 Figure 230 shows a flowchart of a process for converting the material from a solid phase 10 via a plastic phase 11 into a liquid phase 12, wherein the process 230 comprises the following steps: Heating 510 of the material 10, 11, 12 by one or more heating elements 61, 63 of the nozzle head 6.

[0152] Heating can be carried out across state zones A, B, C, D, E of the printhead 100, wherein state zones A, B, C, D, E represent a state of matter of the material 10 depending on its temperature Ts, and the state of matter of the material 10, 11, 12 is changed across state zones A, B, C, D, E from a solid phase 10 through a plastic phase 11 to a liquid phase 12 by introducing heating energy from the heating elements 61, 63. A further step can include mixing 520 of the material 11, 12 during compaction 240.

[0153] Fig. 11 Figure 240 shows a flowchart of a process for compacting material 10, 11, 12. This compaction process 240 comprises the following steps: Pre-compacting 610 of the material 10, 11, 12 by advancing the piston 3, closing 620 of the nozzle 8, compacting 630 of the material 10, 11, 12 by advancing the piston 3 and holding 640 of the piston 3 in the holding position 3d.

[0154] The pre-compression 610 of the material 10, 11, 12 is carried out by advancing the piston 3 under pressure and / or force control, whereby pre-compression is carried out up to position 3c and this position is reached when a material-dependent slope and / or a material-dependent slope angle of a force and / or pressure curve is reached and / or exceeded.

[0155] After pre-compression 610, the nozzle 8 of the printhead 100 is closed 620.

[0156] The compaction 630 of the material 10, 11, 12 is carried out by advancing the piston 3 with the nozzle 8 closed under pressure control, and the holding position 3d is approached until a peak pressure pd is reached, or is defined by the peak pressure pd.

[0157] During compression 630, the nozzle 8 is closed and the piston needle 32 dips into the melting chamber 81 of the nozzle head 6 in such a way that a part of the liquid phase 12 from an upper area of ​​the melting chamber 81 is displaced through openings 71 of the kidney piece 7 from the melting zone D back into the mixing zone C, whereby the part of the liquid phase 12 mixes with the plastic phase 11 from the plasticizing zone B in the mixing zone C.

[0158] The piston 3 is held in the holding position 3d, whereby during the holding process 640 the pressure p L and the temperature TL of the liquid phase 12 are measured and the measured values ​​are checked by the evaluation unit 114 for functional control of the compression process 240.

[0159] During the holding position 3d of piston 640, the nozzle 8 is closed and the piston needle 32 is immersed in the melting chamber 81 in such a way that a part of the liquid phase 12 from the upper area of ​​the melting chamber 81 is displaced back into the mixing zone C through the openings 71 of the kidney piece 7 from the melting zone D, causing the part of the liquid phase 12 to mix with the plastic phase 11 from the plasticizing zone B in the mixing zone C.

[0160] Fig. 12 shows a flowchart of a procedure for an example to determine the spring constant of the liquid phase 12, wherein the procedure 250 comprises the following steps: pressure-controlled retraction 710 from the holding position 3d after completion of the holding 640 to the target position 3e, which is reached when the melt pressure p L reaches a target pressure pe, determining the pressure difference 720 between the peak pressure pd and the target pressure pe, determining the distance 730 between the holding position 3d and the target position 3e and calculating the spring constant 740 of the liquid phase 12.

[0161] Fig. 13 Figure 260 shows a flowchart of a process for preparing the liquid phase 12 for printing, wherein the process 260 comprises the following steps: active decompression 810 of the liquid phase 12 by retracting the piston 3 depending on the spring constant and opening 820 of the nozzle 8.

Claims

1. Method (200) for providing a printable melt (12) for the operation of a printhead (100) for a 3D printer, wherein the method (200) comprises the following steps: - transforming (230) the material from a solid phase (10) to a liquid phase (12) via a plastic phase (11), and - compacting (240) the material (10, 11, 12), wherein the compacting (240) of the material (10, 11, 12), in particular the compaction process (240), comprises the following steps: - pre-compacting (610) the material (10, 11, 12) by advancing a piston (3) of the printhead (100), - closing (620) a nozzle (8) of the printhead (100), - compacting (630) the material (10, 11, 12) by advancing the piston (3), and - holding (640) the piston (3) in a holding position (3d), characterized in that the pre-compacting (610) of the material (10, 11, 12) is carried out in pressure- and / or force-controlled fashion by advancing the piston (3), wherein the pre-compacting is carried out as far as a position (3c) which is achieved when a material-dependent gradient and / or a material-dependent gradient angle of a force curve and / or pressure curve is reached and / or exceeded.

2. Method (200) according to Claim 1, characterized in that the nozzle (8) is closed (620) after the pre-compacting (610).

3. Method (200) according to either of Claims 1 and 2, characterized in that the compacting (630) of the material (10, 11, 12) is carried out in pressure-controlled fashion by advancing the piston (3) with the nozzle (8) closed and in the process the piston is brought closer to a holding position (3d), until a peak pressure (pd) is reached.

4. Method (200) according to Claim 3, characterized in that the piston (3) is held in the holding position (3d), wherein, during the holding operation (640), a pressure (pL) and / or a temperature (TL) of the liquid phase (12) are / is measured and the measured values are checked by an evaluation unit (114) to test the functioning of the compaction process (240).

5. Method (200) according to one of the preceding claims, characterized in that, after the compacting (240) of the material (10, 11, 12), the liquid phase (12) is prepared for printing (260), wherein the preparation for printing (260) comprises the following steps: - actively decompressing (810) the liquid phase (12) by retracting the piston (3) and - opening (820) the nozzle (8).

6. Method (200) according to Claim 1, characterized in that the transforming (230) of the material from a solid phase (10) to a liquid phase (12) via a plastic phase (11) comprises at least the following steps: - heating (510) the material (10, 11, 12) by means of one or more heating elements (61, 63) of a nozzle head (6).