Printhead unit and method for constructing molded parts in layers

Abstract

The invention relates to a system for applying a printing liquid, comprising a printhead unit (101) which comprises an assembly of printing modules (102) and a printing fluctuation compensating module (106). The invention is characterized in that the printhead and the printing fluctuation compensating module (106) are coupled. The invention also relates to a method for producing models which use the aforementioned system.

Description

[0001] Print head unit and method for layer-by-layer construction of molded parts

[0002] The invention relates to a print head unit and its use in a method for producing three-dimensional models using layer build-up technology.

[0003] European patent EP 0 431 924 B1 describes a method for producing three-dimensional objects from computer data. A thin layer of particulate material is applied to a build platform using a recoater, and the particulate material (generally a fluid) is selectively printed with a binder material using a print head. The particle area printed with the binder bonds and solidifies under the influence of the binder and, if necessary, an additional hardener. The build platform is then lowered by one layer thickness in a build cylinder and covered with a new layer of particulate material, which is also printed as described above. These steps are repeated until a certain desired object height is reached. The printed and solidified areas thus form a three-dimensional object (molded part).

[0004] This object, made from solidified particulate material, is embedded in loose particulate material after completion, and is then removed from it. This is done, for example, using a vacuum cleaner. What remains are the desired objects, which are then freed from residual powder, for example, by brushing. In conventional print heads or systems with multiple components in printing systems for the layered construction of models, the printing fluid is often not distributed evenly and uniformly. In particular, the moment of inertia during the traversing processes can cause problems, and the delivery of the printing fluid or its availability at the nozzles can be disrupted.

[0005] It was therefore an object of the present invention to reduce or completely avoid the disadvantages of the prior art.

[0006] It was therefore a further object of the present invention to provide a system in which the pressure fluid is present substantially uniformly in each subunit and / or can be present and / or dispensed at the same pressure.

[0007] Brief summary of the invention

[0008] In one aspect, the invention relates to a system for applying a printing fluid comprising a print head unit (101), comprising an arrangement of print modules (102) and a pressure fluctuation compensation module (106), characterized in that the print head and the pressure fluctuation compensation module (106) are coupled.

[0009] In one aspect, the invention relates to a

[0010] Pressure fluctuation compensation module. In one aspect, the invention relates to a method for producing 3D molded parts, in which all known steps of an additive printing process are performed and in which a system as described above is used.

[0011] Short description of the characters

[0012] Fig. 1 shows an aspect of the invention, which represents a print head unit 101, which is essentially characterized in that an arrangement of printing modules 102 are connected to a circulating pressure fluid supply by means of pressure fluid connection lines 105 via pressure homogenization elements 103 and 104.

[0013] Fig. 2a illustrates an example of an aspect of the invention, which is a pressure fluctuation compensation module.

[0014] Fig. 2b illustrates an example of an aspect of the invention, which represents a further pressure fluctuation compensation module.

[0015] Fig. 3 shows an example of an aspect of the invention, illustrating the fluid supply of the print head unit with the included print modules.

[0016] Fig. 4 shows an example of a system according to the invention in which a cleaning fluid can be used.

[0017] Detailed description of the invention According to the invention, an object underlying the application is achieved by a system according to claim 1 and / or by a pressure fluctuation compensation module according to claim 16 and / or by a printing device according to claim 20 and / or by a method according to claim 21. Further preferred aspects are described in the subclaims.

[0018] In the following, some terms of the revelation will be explained in more detail.

[0019] For the purposes of the disclosure, "layer construction processes" or "3D printing processes" or "3D processes" or "3D printing" are all processes known from the prior art that enable the construction of components in three-dimensional shapes and are compatible with the process components and devices described below.

[0020] "Binder jetting" in the sense of the disclosure means that powder is applied layer by layer to a build platform, the cross-sections of the component on this powder layer are printed with one or more liquids, the position of the build platform is changed by one layer thickness to the last position, and these steps are repeated until the component is finished. Binder jetting also includes layer-by-layer construction processes that require an additional process component, such as layer-by-layer exposure, e.g., with IR or UV radiation.

[0021] In the "high-speed sintering process" as defined in the disclosure, a thin layer of plastic granulate, such as PA12 or TPU, is applied to a preferably heated build platform (build area). An inkjet print head then moves over a large area of ​​the platform and wets the areas of the build area where the prototype is to be created with electromagnetic radiation, e.g., infrared-absorbing ink (absorber). The build platform is then irradiated with (e.g., infrared) light. The wetted areas absorb the heat, causing it to melt and bond with the underlying powder layer. However, the unprinted powder remains loose. After sintering, the build platform lowers by one layer thickness. This process is repeated until the build of a component is complete. The sintered parts are then cooled in a controlled manner in the build chamber before they can be removed and unpacked.In a variation, a so-called detailing agent can be printed in addition to the absorber, which serves to cool the printed areas. A variant of the high-speed sintering process is also known as the fusion jet process, in which the print head sprays a heat-absorbing liquid (often referred to as a "fusing agent," which corresponds to the absorber) onto a layer of the particle material. Immediately after printing, a heat source (infrared light) is applied. The areas to which the "fusing agent" has been applied are heated more than the powder without this liquid. This melts the required areas together. A further additive is then used, also called a "detailing agent," which serves as insulation. This selective imprint occurs around the areas where the "fusing agent" or absorber has been printed. This additive is intended to promote sharp edge formation.This goal is to be achieved by increasing the temperature differences between the printed and unused powder. Such processes can also include processes known as multijet fusion or selective absorption sintering.

[0022] “Laser sintering process” within the meaning of the disclosure is a 3D printing process in which the particulate material is selectively solidified by means of a laser.

[0023] “3D molded part”, “molded body” or “component” within the meaning of the disclosure are all three-dimensional objects produced by means of the method according to the invention and / or the device according to the invention which have a dimensional stability.

[0024] "Build space" is the geometric location in which the particulate material bed grows during the build process through repeated coating with particulate material, or through which the bed flows in continuous principles. Generally, the build space is defined by a floor, the build platform, walls, and an open ceiling surface, the build level. Continuous principles usually include a conveyor belt and delimiting side walls. The build space can also be configured by a so-called job box, which is a unit that can be moved into and out of the fixture and allows for batch production. A job box is moved out after the process is completed, and a new job box can be immediately moved into the fixture, thus increasing the production volume and thus the fixture performance.

[0025] All flowable materials known for 3D printing can be used as "building material" or "particle material" or "powder" or "powder bulk" within the meaning of the disclosure, particularly in powder form, as a slurry, or as a liquid. These can be, for example, sand, ceramic powder, glass powder, and other powders made of inorganic or organic materials such as metal powder, plastics, wood particles, fiber materials, cellulose and / or lactose powder, as well as other types of organic, powdery materials. The particulate material is preferably a dry, free-flowing powder, but a cohesive, cut-resistant powder can also be used. This cohesiveness can also be achieved by adding a binder material or an auxiliary material such as a liquid. The addition of a liquid can result in the particulate material in the form of a slurry being freely flowable.In general, particulate material within the meaning of the disclosure can also be referred to as fluids.

[0026] In the present application, particulate material and powder are used synonymously.

[0027] Particle material deposition is the process by which a defined layer of powder is created. This can occur either on the build platform (build field) or on an inclined plane relative to a conveyor belt in continuous processes. Particle material deposition is also referred to as "coating" or "recoating."

[0028] "Selective liquid application" or "selective binder application" within the meaning of the disclosure can be carried out after each particulate material application or, depending on the requirements of the molded body and to optimize molded body production, can also be carried out irregularly, for example, multiple times with respect to one particulate material application. A cross-sectional image through the desired body is printed.

[0029] Any known 3D printing device that includes the required components can be used as a "device" for performing a method according to the disclosure. Typical components include the coater, build field, means for moving the build field or other components in continuous processes, job box, dosing devices, and heating and irradiation means, as well as other components known to those skilled in the art, which are therefore not described in detail here.

[0030] The "building material" according to the disclosure is always applied in a "defined layer" or "layer thickness," which is individually adjusted depending on the building material and process conditions. It is, for example, 0.05 to 5 mm, preferably 0.07 to 2 mm.

[0031] A "coater blade" within the meaning of the disclosure is a substantially flat metallic component or one made of another suitable material, which is located at the outlet opening of the coater and through which the fluid is dispensed onto the build platform and smoothed. A coater can have one or two or more coater blades. A coater blade can be an oscillating blade that performs oscillations in the sense of a rotary movement when excited. Furthermore, this oscillation can be switched on and off by a means for generating oscillations. Depending on the arrangement of the outlet opening, the coater blade is arranged "substantially horizontally" or "substantially vertically" within the meaning of the disclosure.

[0032] "Coolant" as used in the disclosure is a means capable of cooling a radiating unit or a fluid dosing means, for example, by means of water or another liquid or a gas blow stream.

[0033] The "heating phase" within the meaning of the disclosure characterizes heating of the device at the beginning of the method. The heating phase is completed when the actual temperature of the device reaches a steady-state value.

[0034] The "cooling phase" within the meaning of the disclosure refers to the duration necessary to cool the particulate material to such an extent that the components contained therein do not experience any noticeable plastic deformation upon removal from the build chamber, or the "cooling time" within the meaning of the disclosure is the period of time that must be waited for before molded bodies produced by the sintering process can be removed from the build chamber without being damaged. The cooling time is usually specified as the minimum time required when the outer sides of the build chamber are cooled to the maximum and is usually specified such that the hottest location in the build chamber volume safely falls below the heat distortion temperature of the material used.

[0035] The "absorber" or "IR absorber" in the context of this disclosure is a medium that can be processed with an inkjet print head or with another matrix-like device and promotes the absorption of radiation for local heating of the building material. The absorber can also be particulate, such as black toner. Absorbers can be applied uniformly or selectively in different amounts. The absorber can be applied, for example, as a mixture of absorbers with different absorption maxima, or different absorbers can be applied independently of one another, e.g., one after the other, alternately, or in a predetermined sequence. By applying different amounts, the strength in the building material can be controlled and different strengths can be selectively achieved, for example, in the molded part to be produced and the casing surrounding it.The strength ranges from the strength of the component itself to a strength only slightly higher than that of the construction material without the absorber print. This makes it possible to regulate the temperature in the build area / construction space and, if desired, to easily remove the jacket used for temperature regulation around the manufactured component.

[0036] "Absorption" in this disclosure refers to the absorption of thermal energy from radiation by the building material. Absorption depends on the absorber and / or powder type and the wavelength of the radiation.

[0037] For the purposes of this disclosure, "energy introduction means" means a source for introducing energy into the build space and / or the particulate material and / or the areas printed with absorbers. This can be, for example, an energy source for tempering or heating particulate material, even before the absorber is introduced. However, it could also be irradiation of the build area with fixed or movable radiation sources. If the radiation source is used for solidification after the absorber has been introduced, the absorber is preferably matched to the type of radiation and preferably optimized. This should result in different heating intensities of "activated" and non-"activated" powder. "Activated" means that the absorber impression increases the temperature in these areas compared to the remaining areas in the build space and the particulate material areas not printed with absorbers.

[0038] "IR heating" in the context of this disclosure specifically means irradiation of the construction area with an IR radiator. The IR radiator can be static or moved across the construction area using a traversing unit. Through the use of the absorber, the IR heating in the construction area leads to temperature increases of varying degrees.

[0039] An "IR emitter" within the meaning of this disclosure is a source of infrared radiation. Glowing wires in quartz or ceramic housings are usually used to generate the radiation. Depending on the materials used, different wavelengths of radiation result. The wavelength of this type of emitter also depends on the power.

[0040] An "overhead lamp" or "overhead spotlight" or "spotlight unit" or "spotlight unit" or "spotlight unit" or "spotlight heater" or "build field heater" within the meaning of the disclosure is a radiation source mounted above the build field. The wavelength of the emitted electromagnetic radiation is stationary and its radiant power can be regulated. It is a unit that emits electromagnetic radiation of a specific spectrum. It can contain individual spotlights or a number of spotlights. It can optionally cover substantially the entire build field and be mounted at one position in the device, or it can be smaller than the build field and be movable across the build field.

[0041] "Sintering" or "melting" in the context of this disclosure refers to the partial coalescence of the particles in the powder. In this system, sintering is associated with the buildup of strength.

[0042] For the purposes of this disclosure, the term "sintering window" refers to the difference between the melting point occurring during the initial heating of the powder and the solidification point occurring during subsequent cooling.

[0043] For the purposes of this disclosure, the "sintering temperature" is the temperature at which the powder first melts and bonds.

[0044] "Edge area" within the meaning of the disclosure is the area of ​​a radiator unit that is located at the edge of the radiator unit and can be separated from the interior area. The edge area and interior area form the total area of ​​the radiator unit with respect to its surface on which the radiator units are mounted.

[0045] "Interior area" within the meaning of the disclosure is the area of ​​a radiator unit that is located inside the radiator unit and can be demarcated from the peripheral area.

[0046] "3D printer" or "printer" or "3D printing machine" within the meaning of the disclosure refers to the device in which a 3D printing process can take place. A 3D printer within the meaning of the disclosure comprises a means for applying build material, e.g., a fluid such as a particulate material, and a solidification unit, e.g., a print head or an energy input means such as a laser or a heat lamp. Other machine components known to those skilled in the art and components known in 3D printing are combined with the above-mentioned machine components depending on the specific requirements of the individual case. Alternatively, the term "device" can be chosen.

[0047] "Construction site" is the level or, in a broader sense, the geometric location on or in which a particulate material bed grows during the construction process by repeated coating with particulate material. The construction site is often bounded by a floor, the "construction platform," by walls, and an open ceiling area, the construction level.

[0048] The process "printing" or "3D printing" within the meaning of the disclosure refers to the combination of the processes of material application, selective solidification or printing and adjustment of the working height and takes place in an open or closed process or construction space.

[0049] A "receiving plane" within the meaning of the disclosure is the plane onto which building material is applied. According to the disclosure, the receiving plane is always freely accessible in one spatial direction by a linear movement.

[0050] "Spreading" or "applying" or "depositing" within the meaning of the disclosure means any manner by which the particulate material is distributed. For example, a larger quantity of powder may be placed at the starting position of a coating run and distributed or spread into the coating volume by a blade or a rotating roller.

[0051] "Coater" or "recoater" or "material application means" within the meaning of the disclosure is the unit by means of which a fluid is applied to the build area. This can consist of a fluid reservoir and a fluid application unit, wherein according to the present invention, the fluid application unit comprises a fluid outlet and a "squeegee device." This squeegee device could be a coater blade. However, any other conceivable suitable squeegee device could also be used. Rotating rollers or a nozzle, for example, are also conceivable. The material can be supplied freely via reservoirs or extruder screws, pressurization, or other material conveying devices.

[0052] The "print head" or "means for selective solidification" within the meaning of the disclosure is typically composed of various components. These can include, among others, printing modules. The printing modules have a plurality of nozzles from which the "binder" is ejected in droplet form onto the build area in a controlled manner. The printing modules are aligned relative to the print head. The print head is aligned relative to the machine. This allows the position of a nozzle to be assigned to the machine coordinate system. The plane in which the nozzles are located is usually referred to as a nozzle plate. Another means for selective solidification can also be one or more lasers or other radiation sources, or a heat lamp. Arrays of such radiation sources, such as laser diode arrays, are also contemplated. Within the meaning of the disclosure, it is permissible for the introduction of selectivity to occur separately from the solidification reaction.For example, a print head or one or more lasers can be used to selectively treat the layer, and other layer treatment agents can initiate solidification. In one embodiment, the particulate material is printed with an IR absorber and then solidified with an infrared source. One or more printing modules can be mounted in a special arrangement within a "print head" assembly. The assembly as a whole serves to wet a surface—here, a particulate material on the build area—with liquid (printing fluid) according to the DOD principle.

[0053] "Printing module" or "fluid dosing means" within the meaning of the disclosure refers to a unit for applying a liquid to a surface by means of the so-called ink-jet process according to the DOD principle.

[0054] "Layer treatment means" within the meaning of the disclosure are all means suitable for achieving a specific effect in the layer. These can be the aforementioned units such as the print head or laser, but also heat sources in the form of IR radiators or other radiation sources such as UV radiators. Means for de- or ionization of the layer are also conceivable. What all layer treatment means have in common is that their effective zone is distributed linearly across the layer and that, like the other layer units such as the print head or coater, they must be guided across the build field in order to reach the entire layer.

[0055] "Drop-On-Demand" or "DOD" or "DOD principle" as used herein refers to a method of applying a liquid to a surface, which is active only at the locations where the application is desired.

[0056] "Sintering lamp unit" or "sintering unit" or "sintering lamp" within the meaning of the disclosure refers to the device by means of which particulate material surfaces wetted with IR acceptors are specifically heated above the melting temperature using electromagnetic radiation. A "sintering unit" within the meaning of this disclosure is the energy input means that can heat the process powder (particulate build material) above its sintering temperature. It can be stationary. In preferred embodiments, it is moved across the build area.

[0057] "Radiation converters" within the meaning of the disclosure are elements which, when exposed to electromagnetic radiation of a specific spectrum, change this spectrum in essential properties of the distribution of wavelength intensities.

[0058] The "peak wavelength" within the meaning of the disclosure refers to the wavelength of electromagnetic radiation in an approximately Planckian spectrum that exhibits the highest intensity and obeys Wien's displacement law. For emitters that do not follow the Planckian distribution, the peak wavelength can also refer to the wavelength exhibiting the highest intensity. "Overflow" within the meaning of the disclosure refers to the additional space required when an aggregate is moved completely across the build area on a linear axis from one end to the other without creating shadows on the build area.

[0059] The "coupling" of cooling circuits or of a cooling circuit with a cooling part within the meaning of the disclosure is when two functionally different parts have a coupling point or connection point at which heat exchange can take place. For example, according to the disclosure, a closed air cooling circuit is coupled with a liquid-based cooling circuit and thus the air cooling circuit, which can absorb heat from, for example, a radiation converter, transfers this heat to the liquid-based cooling circuit and then transports it directly or possibly via another coolant to the environment, whereby, when using a control circuit, the temperature at, for example, the radiation converter can be set or maintained at a target temperature.

[0060] A "closed" air cooling circuit within the meaning of the disclosure means that the air in this circuit is essentially circulated within this circuit and no supply air is supplied from outside. In a particular embodiment, this circuit is sealed so that no contaminants, such as particles of the building material, can penetrate into this circuit, thus eliminating the need for maintenance of this circuit. An "air cooling circuit" within the meaning of the disclosure is an air circulation in a tube system of the sintering unit, wherein the air or gas is circulated, for example, by means of additional means such as fans.

[0061] A "liquid-based cooling circuit" as defined in the disclosure is a closed circuit whose coolant is a liquid, such as water, oil or other known liquid coolants.

[0062] "Surface enlargement" as defined in the disclosure is any means that increases a surface area for cooling purposes, such as fins, ribs, etc., to increase cooling performance.

[0063] “Cooling part” in the sense of the disclosure is a heat exchanger.

[0064] An "arrangement of printing modules" within the meaning of the disclosure is a plurality of print heads, e.g. at least two or 3 to a plurality or 4 to 20 print heads, which may be arranged in an articulated or unarticulated manner and connected to one another.

[0065] A "pressure fluctuation compensation module" within the meaning of the disclosure is a means suitable for compensating pressure fluctuations and is directly or indirectly connected to the printing fluid or to the line system of the print heads and / or the print heads and / or is coupled to them and can effect pressure compensation. A pressure fluctuation compensation module can be designed as a 3-chamber module. Further details are described in the figures. A "pressure sensor" within the meaning of the disclosure is a means that can register pressure differences or a pressure change and can transmit them to another unit, such as a control system or a controlled system.

[0066] A "system for applying a printing fluid" within the meaning of the disclosure is an arrangement of means suitable for applying printing fluids and may include print heads, piping systems, sensors, actuators, etc.

[0067] A "pressure homogenization element" within the meaning of the disclosure serves to compensate for pressure differences and to connect pressure modules.

[0068] A "pressurized fluid supply system" within the meaning of the invention is a device that supplies pressurized fluid to an array of printing modules. Its task may be to maintain this supply at a temporally and / or spatially constant level in terms of volume flow and / or temperature during a printing process.

[0069] A "circulating pressure fluid supply" refers to a system for supplying an array of pressure modules with pressure fluid, which is conveyed in a circuit.

[0070] A "printing fluid" within the meaning of the invention is a liquid that serves to wet a surface to be printed, preferably by means of an arrangement of printing modules. The invention and its disclosure are described below.

[0071] In one aspect, the invention relates to a system for applying a printing fluid comprising a print head unit (101) comprising an arrangement of print modules (102) and a pressure fluctuation compensation module (106), characterized in that the print head and the pressure fluctuation compensation module (106) are coupled.

[0072] In a preferred system, the pressure fluctuation compensation module (106) is a 3-chamber module.

[0073] The system according to the disclosure may comprise pressure sensors and control circuits at suitable locations in the system, wherein the system preferably comprises at least two pressure sensors.

[0074] Furthermore, the system according to the disclosure may comprise pumps, control circuits, regulating circuits and pressure sensors in a coupled manner, wherein in a preferred embodiment in the system the two pressure sensors on the pressure fluctuation compensation module (106) are connected to two controlled, preferably speed-controlled pumps in the pressure fluid supply system (301).

[0075] In a preferred embodiment, the system according to the disclosure may comprise a temperature control unit having a cooling and / or heating element and at least two temperature sensors, preferably three temperature sensors. In a preferred system, the two pressure sensors on the pressure fluctuation compensation module (106) are connected to two speed-controlled pumps in the pressure fluid supply system (301).

[0076] In a further preferred system, the arrangement of pressure modules (102) are connected to a circulating pressure fluid supply by means of pressure fluid connection lines (105) via pressure homogenization elements (103) and (104).

[0077] In a further preferred system, the pressure fluid is distributed evenly across all pressure modules (102), preferably the pressure differences occurring between the pressure modules (102) will not exceed a value of ± 2 mBar, preferably 1 mBar.

[0078] A preferred system is characterized in that the pressure fluid connection lines (105) to the individual pressure fluid metering means (102) are designed to be substantially identical and / or the connection elements on the pressure homogenization elements (103) and (104) are designed to be substantially identical, preferably in length and diameter.

[0079] Another preferred system is designed so that the ratio of the total flow resistance of the parallel connected pressure modules to the flow resistance of the

[0080] Pressure homogenization element is greater than 50: 1.

[0081] In a preferred system, the pressure module(s) are operated with a pressure difference of the volume flow of 50-150 mbar. Another preferred system is designed such that the pressure homogenization elements (103) and (104) are connected via a check valve (114).

[0082] In a further preferred system, a pressure fluctuation compensation module (106) is attached to the pressure homogenizing elements (103) and (104).

[0083] In a further preferred system according to the disclosure, the pressure in the system and the temperature of the pressure fluid flowing through it are measured by means of measuring instruments (107) and (108).

[0084] Another preferred system is characterized in that the print head unit (101) has a print head unit coolant (115), preferably the volume flow of the coolant is monitored by means of measuring instruments such as temperature and volume flow sensors (110) and controlled by means of a control valve (111).

[0085] In a further aspect, the disclosure relates to a pressure fluctuation compensation module (106) through which a pressure fluid is guided on the way to the print head unit (101), characterized by substantially mutually coupled chambers (203) and (204) which are separated from one another by movable membranes (206) and (207), preferably comprising a third chamber (205).

[0086] A preferred pressure fluctuation compensation module (106) according to the disclosure is characterized in that the third chamber (205) is filled with a medium (208) different from the pressure fluid, preferably this medium is a gas such as air, preferably the third chamber (205) is subjected to overpressure or underpressure.

[0087] In a preferred pressure fluctuation compensation module (106) according to the disclosure, sensors (107) and (108) for measuring pressure and temperature are attached to the pressure fluctuation compensation module in the compensation chambers containing pressure fluid.

[0088] Another preferred pressure fluctuation compensation module (106) according to the disclosure is characterized in that chambers (203) and (204) each have a gas-filled intermediate chamber (205) which is connected to a third chamber (210) which has a compensation membrane (211) and the compensation membrane (211) is not in direct contact with the pressure fluid.

[0089] In a further aspect, the disclosure relates to a printing device for an additive manufacturing process comprising a system as described above and / or a pressure fluctuation compensation module as described above.

[0090] In a further aspect, the disclosure relates to a method for producing 3D molded parts in which all known steps of an additive printing process are carried out and in which a system as described above and / or a pressure fluctuation compensation module as described above is used.

[0091] It was advantageously achieved that a uniform release of pressure fluid could be achieved by using a pressure fluctuation compensation module, even at high travel speeds. This ensures that a printing device can be operated at high process speeds, while simultaneously ensuring that the pressure fluid is available at each pressure module in the desired manner in a predetermined volume and can be released essentially in the desired quantity, thus ensuring the quality of the manufactured molded part.

[0092] Further description of the revelation and further examples:

[0093] Fig. 1 illustrates a preferred system with a print head unit according to the disclosure. Fig. 1 shows a print head unit 101, which is essentially characterized in that an arrangement of print modules 102 are connected to a circulating print fluid supply by means of print fluid connection lines 105 via pressure homogenization elements 103 and 104. The pressure homogenization elements have the task of supplying print modules 102 located along one or more dimensional extensions with a print fluid, wherein their arrangement and design ensure that the print fluid is evenly distributed across all print modules by keeping the flow resistances of the individual print modules with their respective connection elements as equal as possible and as large as possible compared to the flow resistance of the pressure homogenization elements.

[0094] Differences in volume flow must under no circumstances lead to pressure differences between the printing modules exceeding a value of ± 1 mbar, as this would result in variations in the masses of the ejected droplets and thus in fluctuations in the absorption of the surface to be exposed. This would result in a different amount of energy being applied to the surface to be sintered, resulting in variations within the molded body being created.

[0095] In order to achieve this, the pressure homogenization element is designed in such a way that the cross-section through which the fluid flows is in any case large in relation to the pressure fluid connection line 105 to the pressure modules.

[0096] The lengths of the various pressure fluid connection lines 105 to the individual pressure fluid dosing means 102 should continue to be as identical as possible, as should the connection elements to the pressure homogenizing elements 103 and 104.

[0097] These relationships are evident from the following equations:

[0098] According to the Hagen-Poiseuille law, pressure losses occur due to friction losses between the flowing fluid and the inner wall of the pipe (Wolfgang Kümmel, Technical Fluid Mechanics, 2007, p. 98)

[0099] With the volume flow through the pipe V, the inner radius of the pipe r, length of the pipe I, dynamic viscosity q and the pressures p.

[0100] The pipe resistance Rpipe is the pressure difference Apv divided by the volume flow V:

[0101] The pipe resistance and the resulting pressure differences are thus dependent on the pipe's inner diameter to the fourth power. Thus, by selecting the appropriate pipe diameter, a favorable pressure distribution in the device can be achieved.

[0102] The resistance using a standard pressure module as an example when using a pressure fluid with a typical viscosity of approximately 12 mPas is approximately:

[0103] Using the electro-hydraulic analogy (Horst-W. Grollius, Fundamentals of Hydraulics, 2012, pp. 39-40), a simulation of the fluid system can be generated using electrical equivalent circuits. Here, the voltage corresponds to the pressure difference Ap and the current to the volume flow Q=V. Using this analogy, a relationship between electrical and hydraulic resistance R in a pipe with radius r and length I can be defined.

[0104] The ratio of the total flow resistance of the parallel connected pressure modules to the flow resistance of the pressure homogenization element must be better than (greater than) 50: 1.

[0105] State-of-the-art pressure modules are operated with a volume flow corresponding to a pressure difference of 50 to 150 mBar.

[0106] In an exemplary design with 5 pressure modules on a pipe with a length of approximately 1 meter, the simulation shows that this results in a minimum pipe diameter of > 10 mm if the pressure difference across all pressure modules is to be < 1 mBar.

[0107] The pressure homogenization elements can be connected via a shut-off valve 114. This can facilitate the commissioning of the print head unit as well as the replacement of individual pressure modules by reducing the differential pressure across the pressure modules when the valve is opened. This makes it easier to replace the pressure fluid in the pressure fluid lines and the pressure homogenization elements with another fluid, which can also be a gas or ambient air.

[0108] The print head unit is further characterized by the fact that a pressure fluctuation compensation module 106 is attached to the pressure homogenization elements, through which the pressure fluid is directed in both the supply line 112 and the return line 113. Furthermore, the applied pressure and the temperature of the flowing pressure fluid are measured by means of measuring instruments 107 and 108 attached to the main pressure fluid supply of the print head unit.

[0109] The printhead unit can have a printhead unit coolant 115, which can provide thermal shielding of the printhead unit from the environment. This also ensures a uniform temperature distribution across the dimensional extent of the printhead unit. The coolant can be a network or tubes through which the cooling fluid flows. The volume flow of the coolant can then be monitored using measuring instruments such as temperature and volume flow sensors 110 and controlled using a control valve 111.

[0110] An exemplary pressure fluctuation compensation module is shown in Fig. 2a.

[0111] The pressure fluctuation compensation module 106, through which the pressure fluid is conducted on its way to the print head unit 101, essentially consists of interconnected chambers 203 and 204, which are separated from each other by movable membranes 206 and 207. If necessary, a third chamber 205, filled with a different medium, can be inserted between the two chambers filled with pressure fluid. This different medium 208 can also be a gas such as air. The intermediate chamber can be subjected to an overpressure or underpressure, which can be controlled by the inlet valve 209. Thus, the restoring force acting on the membranes can be specifically controlled.The damping constant of the pressure fluctuation compensation module can thus be adjusted to the requirements and can be adapted depending on the viscosity and compressibility of the pressure fluid, as well as the number of pressure modules and the arrangement of the units in the device.

[0112] The module's task is to minimize pressure fluctuations in the pressure fluid supply system, which can occur due to pump pulsations, supply line vibrations or pressure fluid metering by the print modules. Above all, however, the coupling enables them to compensate for pressure fluctuations caused by accelerations caused by translational movements of the printing system. To ensure this to the best extent possible, the pressure compensation module is located next to the print head, which represents a new aspect, among others. If acceleration occurs in the direction of the line, the inertia of the pressure fluid in the lines and the print head unit leads to pressure fluctuations within the pressure fluid supply and thus in the connected print modules. This would result in an uncontrolled escape of pressure fluid from the print modules. However, since these are intended to release pressure fluid in a controlled manner, this would entail a loss of quality.

[0113] Only minimizing the forces involved, for example, by significantly flattening the acceleration curve, could prevent this unhindered escape. However, this would result in an undesirable, significant reduction in the speed of the translational movement of the printing system and a significant increase in the required travel distances. Reducing the number of printing modules, which would reduce the printing performance of the device, and thus reduce the printing fluid volume in the device, would also contribute to minimizing fluctuations.

[0114] Preferably, sensors 107 and 108 are mounted on the pressure fluctuation compensation module in the compensation chambers containing the pressure fluid for measuring pressure and temperature, with which the pressure fluid supply can be regulated.

[0115] Fig. 2b describes an alternative, advantageous embodiment of a pressure fluctuation compensation module 106. Essentially, the gas-filled intermediate chamber 205 from Fig. 2a is modified in that it is divided into two chambers 203 and 204, which are partially filled with gas for this purpose. The gas content can be varied by means of valves 209. The two chambers are fluidically connected by a third chamber 210. A compensating membrane 211 is located in the third chamber. The membranes 206 and 207 are thus replaced by a membrane 211, which separates not the liquids from the gas, but the two gas volumes above the liquids. Thus, only one membrane is required, and the device can be manufactured more cost-effectively and is less prone to failure.

[0116] Furthermore, the new compensating diaphragm 211 is no longer in direct contact with the pressure fluid. This eliminates the need for a diaphragm material that is chemically resistant to the pressure fluid, significantly expanding the range of materials available. This allows for advantageous adaptation to the vibration behavior and a more cost-effective design.

[0117] A further advantage is the ability to simplify access to membrane 211 thanks to the external design of chamber 210. Due to the lack of fluid contact, it can be replaced without protective equipment and in significantly less time. Since the membrane is generally a wear part, this also significantly reduces maintenance costs.

[0118] Fig. 3 shows an example of a fluid supply for the print head unit 101 with the included print modules 102. The print head unit is mounted on a linear axis, for example, so that it can move in one direction. The supply lines can be guided by a supply chain 303 as shown. The position change does not have to be limited to one dimension. The pressure fluid supply is provided by the device 301. It consists of two speed-controlled pumps for each supply direction, a fluid heater, and a filter. A reservoir with a fill level indicator contains the supply of pressure fluid, from which a quantity can be withdrawn by the feed pump. The measured values ​​of the sensors 107 and 108 in the supply and return chambers of the pressure fluctuation compensation module 106 are used to generate temporally constant pressure states at the print modules 102 by controlling the speed of the pumps via a control loop.

[0119] The temperature of the printing fluid is also regulated to a constant value by means of a fluid heater based on the measured values ​​of the temperature sensors. The temperature control device 302, which is used to control the temperature of the print head unit, is implemented here, for example, using a feed pump and a recooler.

[0120] High-frequency control of the units ensures that the pressure of the pressurized fluid at the pressure modules remains constant over time during operation, even when subjected to accelerated movement. To enable high-frequency control, the measuring instruments for the pressure in the pressurized fluid supply and return lines 107 and 108 should have a high sampling rate. Measurement frequencies of > 50 values ​​per second should be used, especially for pressure measurement recording. Furthermore, the measurement accuracy should be sufficiently high. A measurement tolerance of < ± 1 mbar appears reasonable in practice.

[0121] Experiments have shown that conventional ink circulation systems, even with higher expenditure, due to, among other things, a too sluggish control, cannot cope with accelerations of the ink dosing system mounted on a linear axis of > 0.5 m / s 2 However, limiting the acceleration to lower values ​​means that acceleration ramps must be provided for the axis movements. Furthermore, a longer settling time is required for the pressure control during the movement before reliable fluid dosing can begin.

[0122] In conventional, state-of-the-art systems, it is therefore necessary to reduce the stable working area of ​​the fixture or to use longer axis systems. This increases the fixture's dimensions, contrary to economic considerations, as the fixture's production capacity per unit area is significantly smaller. The printing process is also slowed down because the linear axes require a longer travel distance per produced layer. Thermal processes also increase energy consumption, as a larger process volume must be heated for a longer time relative to the production volume. This is significantly reflected in the cost per unit produced.

[0123] For temperature measurement, it is also important to ensure that the temperature sensors are primarily in thermal contact with the pressure fluid and not with the device itself. To achieve this, it is advantageous to insulate them from the support using a material with poor thermal conductivity. More accurate temperature measurement also enables improved control of the heating or cooling systems.

[0124] Preferably, the temperature sensors are mounted in the pressure fluctuation compensation module or in the print head unit itself, which shortens the control path and thus contributes to greater accuracy of the printing fluid temperature during dispensing. The temperature sensors can also be integrated into the pressure sensors. Furthermore, the temperature of the nozzle plate of a print module can also be used as the control temperature, which is possible, for example, with the Seiko RCA-1536M in combination with the AEWA APMB3 dispensing controller.

[0125] In one aspect, a closed-loop control system may also be provided. In one embodiment, the two pressure sensors on the pressure fluctuation compensation module are connected to two speed-controlled pumps in the pressure fluid supply system 301. The speed of both pumps is controlled via two PID controllers, with the two sensor values ​​P SU ppi y , the pressure on the supply line and Pretum , the pressure on the return line serve:

[0126] Pmeniscus = | Psuppiy — Preturn | Pdifferential = | Psuppiy | + | Preturn | Pmeniscus refers to the negative pressure applied to the fluid dosing medium, and Pdifferential refers to the differential pressure within the fluid supply system, which is followed by the circulation velocity of the pressurized fluid. These two parameters also represent the controlled variable.

[0127] The speed control of the feed pump is thus based on the input value Pdifferential, while the control of the return pump uses Pmeniscus as the input value. Both control systems operate in parallel.

[0128] The situation is similar with temperature control devices: Most pressure fluids have an optimal operating point, which is usually above the ambient temperature, e.g., between 20-50°C, preferably 35°C. At this temperature, the viscosity of the pressure fluid corresponds to the manufacturer's specifications for the pressure fluid dosing device. The heating element in 301 is used for this purpose. The sensor value of the temperature sensor T acts as the input value for the control system. SU ppiy in the inlet of the pressure fluctuation compensation module.

[0129] A second temperature sensor (Tretum) is located in the return line of the fluid system, which can be used to determine the temperature of the printing fluid flowing back from the print head unit. A third temperature sensor (Tcooling) is located in the coolant circuit and serves to regulate the cooling capacity of the print head unit cooling system to a preset value, which preferably corresponds to the printing fluid temperature control.

[0130] The cooling circuit is thermally coupled to the pressure fluid circuit via the contact between the print head unit coolant and the pressure fluid metering medium, which must be taken into account when controlling both the heating element in 301 and the cooling element 302. Preferably, the coolant is switched off as long as the heating element preheats the pressure fluid. A further sensor Qcooling, preferably integrated in 110 in the coolant circuit, can be used to limit the volume flow of the coolant by means of a further control loop if T e tum < T sup p i y . As long as the return temperature of the pressure fluid is lower than the inlet temperature, the cooling capacity can be reduced. This prevents the heating and cooling elements from working against each other or, in the worst case, from oscillating.

[0131] Fig. 4 describes a further preferred aspect of the disclosure in which a cleaning fluid can be used to clean various sections or components of the device; this cleaning can be carried out at least partially during operation. In Fig. 4, reference numerals 402 and 403 respectively denote three-way ball valves, manually or externally operated (rotary actuator). Three-way / two-way valves or coupled two-way / two-way valves can be used, which can be switched electromagnetically, pneumatically, or externally operated. If these are manually switched, they are actuated via locking couplers. A circuit is installed between the pressure fluctuation compensation device and

[0132] Pressure equalization device, whereby this is possible in both the forward and return flow.

[0133] A first functionality with a simplified process can be implemented as follows:

[0134] Both valves 402, 403 are switched almost simultaneously, thus decouple the circulating fluid system. This connects a flushing system 401 to the pressure modules. A positive pressure is applied to the inlet by pump 406 (50-500 mbar = maximum flow resistance in the pressure module). A cleaning fluid can then flow from the pressure nozzles of the pressure fluid dosing means 102, cleaning them. The majority of the cleaning fluid flows back via a return line into the cleaning fluid waste container 405. Both valves 402, 403 are then switched back to the circulating fluid system. The pressure fluid dosing means 102 and the pressure homogenization means 103 and 104 are now cleaned.

[0135] In a second mode of operation, the nozzles of the pressure fluid dosing means 102 can be cleaned as follows:

[0136] The control of the pump speeds of the pressure fluid feed and return pumps is suspended, inlet valve 402 is set to cleaning fluid, and return valve 403 is left on the ink circulation system. The cleaning fluid feed pump 406 then pumps the cleaning fluid through the pressure homogenizing agent and pressure fluid dosing agent. Due to the deactivated return pump, an overpressure is created in the system that must not exceed 150 mbar in commercially available pressure fluid dosing agents. This forces the cleaning fluid, including any contaminants, through the nozzles of the pressure fluid dosing agents, thus freeing them of dirt. Return valve 403 is then switched to the cleaning fluid circuit, and excess cleaning fluid is conveyed into the designated cleaning fluid waste container 405. Finally, the pressure fluid feed system, including the control system, can be reactivated. The nozzles of the pressure fluid dosing agents 102 are now cleaned.

[0137] In a third mode of operation, cleaning of the pressure homogenizing elements 103, 104 and

[0138] Pressure fluid dosing means 102 as follows:

[0139] During controlled operation, inlet valve 402 is switched from the pressure fluid inlet to the cleaning fluid inlet. The valve in the return line 403 initially remains in its initial position and connected to the pressure fluid circuit. Cleaning fluid pump 406 is now activated. It begins to pump the cleaning fluid through the pressure homogenization element 103, through which the cleaning fluid also reaches the pressure fluid dosing means 102, flows through it, and cleans it. By means of the still active control on the fluid return pump in the return line, the cleaning fluid is conveyed through the pressure homogenization element 104 from the pressure fluid dosing means 102 into the return line of the fluid system. Here, return valve 403 is also activated with a time delay, allowing the cleaning fluid to escape from the system and enter the cleaning fluid waste container 405. At the same time, valve 402 switches back to the pressure fluid circuit.Thus, pressure fluid is again supplied to the pressure homogenization elements 103 and 104, as well as to the pressure fluid metering device 102. Once the pressure fluid has completely flowed through all connected elements after a certain time, the return valve 403 is also switched back to the pressure fluid system, so that the system returns to its initial state. During the entire process, all controls remain active, ensuring only minimal pressure fluctuations in the system and thus ensuring that no fluid escapes unintentionally from the pressure fluid metering devices 102.

[0140] List of reference symbols

Claims

Patent claims 1. System for applying a printing fluid comprising a print head unit (101) comprising an arrangement of print modules (102) and a pressure fluctuation compensation module (106), characterized in that the print head and the pressure fluctuation compensation module (106) are coupled.

2. System according to claim 1, wherein the pressure fluctuation compensation module (106) is a 3-chamber module, preferably wherein the system has at least two pressure sensors, and / or wherein the two pressure sensors on the pressure fluctuation compensation module (106) are connected to two speed-controlled pumps in the pressure fluid supply system (301), and / or wherein the system has a temperature control unit which has a cooling and / or a heating element and which has at least two temperature sensors, preferably three temperature sensors, and / or wherein the two pressure sensors on the Pressure fluctuation compensation module (106) are connected to two speed-controlled pumps in the pressure fluid supply system (301), or / and wherein the arrangement of pressure modules (102) are connected to a circulating pressure fluid supply by means of pressure fluid connection lines (105) via pressure homogenization elements (103) and (104), preferably wherein the pressure fluid is distributed evenly across all pressure modules (102), preferably the pressure differences that occur between the pressure modules (102) do not exceed a value of ± 2 mbar, preferably 1 mBar, or / and wherein the pressure fluid connection lines (105) to the individual pressure fluid metering means (102) are designed to be substantially identical and / or the connection elements on the pressure homogenization elements (103) and (104) are designed to be substantially identical, preferably in length and diameter.

3. System according to one of the preceding claims, wherein the Ratio of the total flow resistance of the parallel connected pressure modules to the flow resistance of the Pressure homogenization element is greater than 50:

1.

4. System according to one of claims 1 - 3, wherein the pressure module(s) are operated with a pressure difference of the volume flow of 50 - 150m bar, preferably wherein the pressure homogenization elements (103) and (104) have a connection via a shut-off valve (114), and / or wherein a pressure fluctuation compensation module (106) is attached to the pressure homogenization elements (103) and (104).

5. System according to one of the preceding claims, wherein the pressure in the system and the temperature of the pressure fluid flowing through it are measured by means of measuring instruments (107) and (108).

6. System according to one of the preceding claims, wherein the print head unit (101) has a print head unit coolant (115), preferably the volume flow of the coolant is monitored by means of measuring instruments such as temperature and volume flow sensors (110) and controlled by means of a control valve (111).

7. Pressure fluctuation compensation module (106) through which a pressure fluid is passed on the way to the print head unit (101), characterized by substantially mutually coupled chambers (203) and (204) which are separated from one another by movable membranes (206) and (207), preferably comprising a third chamber (205).

8. Pressure fluctuation compensation module (106) according to claim 7, wherein the third chamber (205) is filled with a medium (208) different from the pressure fluid, preferably this medium is a gas such as air, preferably the third chamber (205) is subjected to overpressure or underpressure, preferably wherein sensors (107) and (108) are attached to the pressure fluctuation compensation module in the compensation chambers containing the pressure fluid for measuring pressure and temperature, and / or wherein chambers (203) and (204) each have a gas-filled intermediate chamber (205) which is connected to a third chamber (210) which has a compensation membrane (211) and the compensation membrane (211) is not in direct contact with the pressure fluid.

9. A printing device for an additive manufacturing process comprising a system according to any one of claims 1-6 and / or a pressure fluctuation compensation module according to any one of claims 7-8.

10. A method for producing 3D molded parts, in which all known steps of an additive printing process are carried out and in which a system according to one of claims 1 - 6 and / or a pressure fluctuation compensation module according to one of claims 7 - 8 is used.

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