DE102015115231B4 - Method and device for producing 3-dimensional models with a radiation-curing plastic - Google Patents

Abstract

Method for producing a 3-dimensional model (5) by applying a photopolymer layer by layer, comprising the steps of:- continuously dispensing a photopolymer by means of a movable print head (3),- curing the dispensed photopolymer by means of a movable local radiation source (4), wherein during printing a flow measurement is carried out by means of a sensor (19) in a closed control loop to adjust the intensity by the local radiation source.

Description

There are numerous state-of-the-art technologies for 3D printing. Many of these technologies are based on a liquid printing medium being solidified during the printing process, thereby forming the desired 3-dimensional object.

Fused Filament Fabrication (FFF), for example, is known from the state of the art. In this process, a plastic that is solid under room conditions is liquefied by means of a heater in a print head and then applied layer by layer by moving the print head, so that the 3-dimensional object is created. The document US 2014 / 0 061 974 A1 discloses a print head with a radiation source that varies in intensity. Document US 5 204 124 A discloses a print head with radiation source.

At room temperature, the previously liquefied plastic solidifies, creating the 3-dimensional object layer by layer. The disadvantage of this process is the hardening process. Due to the temperature differences between the liquid and solid polymer, tensions can arise in the 3-dimensional model and deformations can occur. In addition, it is a solidification process that takes time.

Stereolithography is the process of forming a 3-dimensional object in a bath of liquid, light-curing polymer. A laser or UV radiation is usually used to cure the photopolymer layer by layer. Document US 5 143 663 A discloses such a device with a separate post-curing unit.

One of the disadvantages is that the photopolymer is limited to transparent, low-viscosity materials.

Printing 3-dimensional objects using photopolymers is also carried out using inkjet technology. This involves using a low-viscosity solution of a photopolymer, which is applied in thin layers and immediately hardened using UV radiation. The disadvantage of this process is that the photopolymers used in inkjet technology are also limited to low-viscosity materials.

The object of the invention is to eliminate or at least reduce the disadvantages resulting from the prior art.

This object is achieved with a 3D printing method according to claim 1 and a 3D printing device according to claim 8. The subclaims represent preferred embodiments of the invention.

The method according to the invention is used to produce a 3-dimensional model by applying a photopolymer layer by layer, whereby the photopolymer is dispensed continuously and not drop by drop as in the inkjet method. In contrast to the inkjet method, this also allows a highly viscous material to be used for printing. This enables faster printing as more material can be deposited per layer due to the greater layer thickness. Through continuous dispensing, more material can generally be deposited than with drop by drop dispensing of photopolymers.

Continuous in the sense of this invention serves as a distinction from drop-by-drop dispensing. Intermittent (continuous) dispensing or continuous dispensing in a short time interval is continuous dispensing in the sense of the present invention.

However, the invention is not limited to highly viscous liquids, even if these are preferred. Since printing takes place at room temperature, temperature-sensitive substances can also be used as filler materials. According to the invention, in a first step the photopolymer is continuously dispensed using a movable print head.

In a second step, the dispensed photopolymer is cured using a movable local radiation source.

The combination of continuous dispensing with the principle of radiation curing has considerable advantages over the inkjet process, stereolithography and fused deposition modeling.

If a high viscosity is chosen for the photopolymer, which is possible according to the invention, the layers can be particularly thick during printing, which leads to an increased printing speed. Printing at ambient temperature prevents temperature differences in the printed model, which can lead to stresses and deformations.

According to the invention, immediately after dispensing and depositing the photopolymer, a (pre)curing of the polymer is effected by a local and movable radiation source.

Preferably, according to one embodiment, the entire model is post-cured by means of a large-area radiation source. Local or large-area radiation sources within the meaning of this invention can be a UV source, an IR source, heat radiators, in particular infrared radiators, LEDs, lasers, microwave radiators, an ultrasound source, magnetic resonance or other radiation sources.

Infrared radiators are particularly suitable in the absence of metallic particles in the dispensed material, while microwave radiators are particularly suitable in the presence of metallic particles in the dispensed material.

UV radiation sources or radiation sources for visible photons are particularly suitable for transparent filling materials.

By dividing the radiation source into a local and a large-scale source, it is particularly easy to apply a new layer of the model before the previous one has completely hardened. This enables faster printing.

It is also possible to use the local radiation source to cure only a portion of the dispensed material and remove the rest before complete curing.

It has been shown that the continuous dispensing of photopolymers is particularly suitable for the introduction of dyes or fillers.

According to one embodiment, the photopolymer is mixed with the filler or dye prior to dispensing.

According to another particularly preferred embodiment, a filler or dye is dispensed only into the outer layer of the photopolymer and is not mixed with the entire extrudate.

According to a further embodiment, fillers are arranged inside the dispensed material and surrounded by a layer of the photopolymer.

Overall, it has been shown that the application range of the printing process is significantly broadened by a non-homogeneous distribution of fillers and/or dyes in relation to the cross-section of the dispensed material (the fillers and/or dyes are only arranged in partial areas of the dispensed material).

According to a further preferred embodiment, fillers or dyes can additionally be embedded in the outer layer of the photopolymer.

According to a further embodiment, several layers of fillers or dyes are introduced into the dispensed material.

Metals, such as electrically conductive metals, can also be used as cables, fibers or particles as fillers. In this way, it is possible to print 3-dimensional circuits or cable harnesses, possibly including insulation material. It is also possible to add fillers that greatly increase the load-bearing capacity of the printed object, such as glass fibers, steel cables, aligned nanoparticles, carbon fibers, metal particles. Liquids that are not photopolymers can also be used as fillers.

Depending on the different processes, coaxial or triaxial dispensing can be provided. Coaxial drawing of a structural fiber (e.g. carbon, glass or steel fiber) into the polymer matrix during printing can offer optimized mechanical properties while at the same time providing high flexibility in shaping and can be used, for example, for the construction of individualized prostheses.

In a triaxial or quadruple-axial variant, the structure of a conductive fiber core, insulator polymer, conductive polymer and a final, insulating polymer is provided in order to print electrically shielded cables for signal routing, for example. With the present invention, cable harnesses including connectors can be printed.

Analogously, when using glass fibers, waveguides can be printed based on a central glass fiber.

Preferably, the fillers or dyes are introduced into the nozzle before dispensing.

A printhead designed to produce such dispensed materials is part of the present invention.

According to a further embodiment, fillers or dyes are introduced into the photopolymer after dispensing. This can be done, for example, by spraying on a dye or by injecting a filler or dye.

In any case, the filler or dye (if desired) is introduced using the local radiation source before curing.

A particularly fast printing process can be achieved by printing another layer onto the previous layer using a second print head while a layer is still being printed by a print head. Before the second layer is applied, however, the previous layer is (pre)hardened using the local radiation source. The local radiation source preferably follows the same path that the print head followed when printing the previous layer.

Preferably, the local radiation source has means for limiting the light beam or for focusing. According to one embodiment, the radiation source has one or more apertures. According to a further embodiment, the local radiation source has an imaging optics, such as a lens.

According to a particularly preferred embodiment, the print head is controlled using polar coordinates. This makes it technically easier to have a second print head start printing a further layer before the first print head has completed the previous layer.

According to another method, after curing using the local radiation source and before applying another layer, the unevenness of the surface on which the next layer is to be printed is detected by means of a sensor. This value or these values are then passed on to control the dispersion speed or to control the nozzle cross-section of the dispensing nozzle so that the unevenness can be compensated accordingly when printing the following layer.

According to a further embodiment, the optical measuring method can also be used to measure the lateral offset between subsequent layers and to record a comparison between the target and actual structure and calculate a correction for adjustment layer by layer. In this way, good positioning accuracy is achieved even for a low-design and therefore more cost-effective axis performance.

Preferably, the nozzle flow is measured in a closed control loop.

According to a further embodiment, the values of the sensor are passed on to the control for moving the print head, which accordingly accelerates or slows down the movement at a constant nozzle throughput in order to compensate for the unevenness.

According to a further embodiment of the invention, the printing process is carried out under an oxygen-reduced atmosphere, such as a nitrogen atmosphere or “in vacuo”. This enables particularly complete curing, since oxygen-related termination of the polymerization, which is caused by UV radiation through radical formation, is prevented.

According to the invention, a 3D printing device is also proposed for carrying out the described methods.

Accordingly, a 3D printing device according to the invention has a print head which is intended to continuously dispense photopolymers. The 3D printing device according to the invention also has a movable local radiation source which is designed and arranged in such a way that it locally at least partially hardens the extruded photopolymer. Depending on the photopolymer used, the dispensed mass must be exposed to a stronger or weaker radiation source for a shorter or longer time in order to at least pre-harden it.

The 3D printing device according to the invention therefore preferably has a control which enables a corresponding adjustment of the irradiation duration and/or intensity. According to one embodiment, an automatic adjustment of the irradiation duration and/or intensity to the polymer and/or the current hardness state is provided.

In a specific embodiment of the invention, sections of the dispensed material are not irradiated with the local radiation source, only very slightly, only very briefly or only selectively. This makes it possible to form support structures for a 3D model from the photopolymer and to remove them again before hardening using the large-scale radiation source. In this case, a laser can preferably also be provided as a local, movable radiation source or in addition to the local, movable radiation source. In contrast to laser sintering, a support structure that can later be easily removed can be formed by means of a slight pre-hardening.

According to a further embodiment, a switchable UV LED matrix is provided, which is guided so close to the print that curing takes place directly "in proximity". Different numbers of LEDs are switched on for the different print widths.

Preferably, the 3D printing device has at least one supply unit for fillers or Dyes. According to one embodiment, the fillers or dyes are introduced into the nozzle before extrusion and mixed with the photopolymer. According to another embodiment, however, the fillers or dyes are introduced into the nozzle in such a way and the nozzle is designed accordingly that the fillers or dyes are arranged locally in the extrudate.

For example, the feed unit and the nozzle of the printing device can be designed to arrange a filler inside the dispensed material, which is surrounded by the photopolymer, wherein the printing device is simultaneously designed to introduce a dye near the outer surface of the extruded material. The filler material can be a continuous fiber or particles. In the case of particles, according to one embodiment, these are to be aligned and arranged.

The non-homogeneous distribution of fillers and/or dyes in the photopolymer makes it possible to save materials such as dyes or fillers. At the same time, the range of possible material properties of the dispensed material is significantly increased by the non-homogeneous distribution of fillers and/or dyes in the dispensed material. This is also one of the main advantages over inkjet technology.

According to a further embodiment, cavities are introduced into the dispensed material. This can be done with the help of one or more fixed or controlled or variable mandrels which are arranged in the nozzle. For example, a mandrel can be provided which is designed to be foldable in and out and/or can change its shape.

By creating cavities in a 3-dimensional model, optical effects can be achieved, mechanical properties improved and capillary properties created for subsequent filling with liquids and gases.

According to another embodiment, hollow spaces are created by introducing gases. The introduction of gases is also preferably designed to be controllable.

According to a further embodiment, the feed device is arranged and designed such that it applies the fillers and/or dyes to the dispensed material after dispensing or injects them into it. In any case, however, the feed device is designed such that the fillers or dyes are introduced or applied before (pre)curing by means of the local radiation source.

According to a preferred embodiment, the 3D printing device has at least two print heads, wherein the second print head is arranged and controlled such that it prints a new layer of the photopolymer on the previous layer while the first print head is still printing the previous layer. This can be achieved particularly well with a 3D printing device in which the print heads are controlled by means of polar coordinates.

In this case, the 3D printing device preferably has a base plate on which the 3-dimensional models are printed, at least one print head, at least two drive units for changing the position of the print head in a plane running parallel to the base plate, wherein the at least one drive unit drives a support structure that can be rotated parallel to the base plate and on which at least one print head is arranged, which can be moved in the rotation plane of the support structure with the aid of a further drive unit.

A support structure according to this application is a device that supports a print head and can, for example, be designed as an arm or disk which is arranged on a shaft running orthogonally to the base plate.

Preferably, at least two print heads are provided, which can preferably be moved separately from one another.

The at least one movable local radiation source is preferably arranged and controlled in such a way that it locally hardens the preceding layer before the application of a further layer, e.g. by a second print head. According to one embodiment, the local radiation source can be firmly connected to the print head or the local print heads can be firmly connected to the local radiation sources.

According to a further embodiment, the at least one local radiation source can also be arranged to be movable independently of the print head or the print heads.

According to a further embodiment of the 3D printing device according to the invention, it has a sensor which is arranged and designed such that after the curing of the photopolymer with the at least one local movable radiation source and before the application of a further layer by means of the same or a second print head, it measures the unevenness of the surface. The distance of the layer on which another layer is to be applied from the print head is determined. Such a sensor can, for example, be firmly connected to the print head and move ahead of the nozzle of the print head in the direction of movement. In this way, the results of the measurements can be used to adjust the dispensing speed and/or the mass flow and/or the duration and/or intensity of the pre-curing by the local moving radiation source.

According to a further embodiment, the 3D printing device has a large-scale radiation source which is designed to cause the entire model to harden. In one embodiment, large-scale hardening using a radiation source can take place simultaneously during printing. In a second embodiment, hardening takes place by intermittent hardening in certain sections (interruption of printing). According to a further variant, hardening takes place after the printing process (post-curing).

Further advantageous embodiments can be seen from the figures and the following figure description.

• 1 eine seitliche Querschnittsdarstellung der erfindungsgemäßen 3D-Druckvorrichtung,
• 2 eine Draufsicht auf ein Tragwerk, welches einen oder mehrere Druckköpfe trägt,
• 3 eine schematische Ansicht einer Druckkopf-Düse mit Zufuhrvorrichtungen Für Farb- und Füllstoffe,
• 4 eine schematische Darstellung der Regelung des Druckkopfes,
• 5 eine Draufsicht auf eine Ausführungsform der Erfindung mit einem in das rotierbare Tragwerk integrierten rotierbaren Tragwerk,
• 6 eine Draufsicht auf eine Ausführungsform der Erfindung mit zwei in das rotierbare Tragwerk integrierte rotierbare Tragwerke.

Showing:

• 1 a side cross-sectional view of the 3D printing device according to the invention,
• 2 a plan view of a supporting structure carrying one or more print heads,
• 3 a schematic view of a print head nozzle with supply devices for dyes and fillers,
• 4 a schematic representation of the print head control,
• 5 a plan view of an embodiment of the invention with a rotatable support structure integrated into the rotatable support structure,
• 6 a plan view of an embodiment of the invention with two rotatable supporting structures integrated into the rotatable supporting structure.

1 shows a preferred embodiment of the 3D printing device 1 according to the invention. The 3D printing device 1 has a base plate 6 on which the 3-dimensional model 5 is printed.

The print head 3 is attached to a rotatable support structure 2. This rotatable support structure 2 is driven via a shaft 7 by a drive unit not shown here. With the help of the shaft 7, the rotatable support structure is designed to be displaceable relative to the base plate 6.

The print head is formed by a slot 8 in the radial direction (see 2 ) in the rotating supporting structure.

A drive unit (not shown) is arranged on the supporting structure, by means of which the print head 3 can be moved in the radial direction R.

At the beginning of the printing process, the support structure approaches the base plate 6 so that the tip of the print head 3 almost touches the base plate 6 of the 3D printing device 1. The print head is now moved along a predetermined path in the plane parallel to the base plate 6 and mass is dispensed.

In this embodiment, the path is output in polar coordinates. This means that with the help of the angle by which the shaft 7 is rotated and with the help of the distance of the print head from the shaft 7 in the radial direction, any desired point on the base plate can be controlled. The material dispensed and deposited on the base plate is immediately (pre)hardened by the local, movable UV radiation source 15.

With each new printed layer, the rotatable support structure 2, the print head, and the shaft 7 are moved a little away from the base plate 6. This causes the model 5 to grow. At the end of the printing process at the latest, but according to other embodiments also during periods of the printing process or during the entire printing process, the large-scale radiation sources 14 are switched on. They are designed to completely harden the model. A control of the large-scale radiation source (not shown here) controls the intensity and/or duration of the radiation depending on the model 5 or depending on the material selected for the model and/or depending on the thickness of the material in the model 5.

According to an embodiment not shown here, the printing table is additionally designed to rotate during large-scale irradiation, or the "radiation cage" can also be designed to rotate the object. According to a further embodiment, the large-scale radiation source is designed to be able to carry out a scanning (vertical) movement.

2 shows a top view of the rotatable support structure 2. A radially aligned slot 8 is arranged in the rotatable support structure 2, through which the print head 3 is guided. The drive The mechanism for moving the print head 3 in a radial direction is arranged on the supporting structure 2.

3 shows individual details of a particularly preferred print head 3. This particularly preferred print head 3 is connected to a reservoir 9 for a photopolymer, a reservoir 10 for a filler and a reservoir 16 for a dye.

The colorants and fillers come together with the photopolymer via the feed units 15 and are dispensed together with the photopolymer. A local, movable radiation source is arranged around the tip of the print head 3. In order to prevent the dispensed material from hardening as it leaves the tip of the print head and before it has been deposited on the base surface 6 or on the previous layer of the model 5, direct irradiation of the photopolymer exit from the print head 3 is prevented by a diaphragm 20.

According to this embodiment, the print head 3 is designed such that the fillers are enclosed inside the dispensed material without completely mixing with the photopolymer. With this arrangement of the print head, the dyes are introduced into the photopolymer in such a way that mixing occurs and the dispensed material has a uniform color.

The print head also has control devices (not shown here) with which the mass or volume flows of the photopolymer and the fillers and dyes can be controlled separately from one another. Preferably, sensors are also provided for detecting the mass flow of the photopolymer and/or the fillers and/or dyes.

4 shows a schematic representation of the control of the print head according to one embodiment. From the reservoir 9 for the photopolymer, the photopolymer passes through a feed device 15 to a print head 3. This print head has a sensor 19 for detecting the mass or volume flow. The data determined here are transmitted to a PC 17, which compares the actual volume flow with a target volume flow and sends control signals to an actuator 18 for adjusting the nozzle cross-section. The mass or volume flow is adjusted by adjusting the nozzle cross-section. The values determined via the volume flow sensor 19 are also used in the computer to adjust the intensity and/or duration of the local, moving UV radiation source.

A sensor (not shown here) can also be provided to detect the unevenness of the base plate and/or the layer on which printing is to take place. In this case, the results of the distance between the print head and the surface to be printed are used to control the nozzle cross-section and/or to control the intensity and/or irradiation duration by the local radiation source.

5 shows a plan view of an embodiment of the invention with a rotatable support structure 2. A second support structure (here designed as a disk) 12 is rotatably mounted (azimuth) in the support structure 2. According to one embodiment, both supports are connected to drive units and are freely movable. At the edge of the second support structure 12 or near the edge there is a recess 13 through which the print head 3 of the 3D printing device 1 (not shown here) is guided.

In this embodiment, the distance between the base plate 6 (not shown here) and the print head 3 can also be achieved by moving the base plate 6 in a direction orthogonal to the base plate 6. A local radiation source 4 is arranged around the print head. Two large-area radiation sources 14 are arranged to the side of the base plate, which can cause the entire model 5 to harden.

6 shows a plan view of a further embodiment of the invention with two rotatable support structures 12 integrated in the rotatable support structure 2. The rotatable support structure 2 shown here is preferably attached to a shaft 7 (not shown here), which in turn is moved by a drive unit. Two drive units (not shown here) are arranged on the support structure 2, which are designed to move the two support structures 12 independently of one another. A print head 3 is arranged on each of the rotatable support structures 12, which is guided through a recess 13 through the support structures 12. With the help of this arrangement, the two print heads 3 can be controlled and positioned in a plane running parallel to a base plate 6.

The distance between the base plate 6 and the print heads 3 can be varied using the described shaft 7. Since the radii of the supporting structures 12 (here designed as disks) do not reach the axis of rotation of the supporting structure 2, an S-shaped print head nozzle or a print head attachment is necessary in this embodiment in order to be able to apply material directly below the axis of rotation of the supporting structure 2. After the material has been applied, the photopolymer is (pre)cured using the local, movable radiation sources 13. After completion During the production of model 5, the three large-area radiation sources 14 are switched on and cause complete curing of the photopolymer.

Claims (14)

Method for producing a 3-dimensional model (5) by applying a photopolymer layer by layer, comprising the steps of: - continuously dispensing a photopolymer by means of a movable print head (3), - curing the dispensed photopolymer by means of a movable local radiation source (4), wherein during printing a flow measurement is carried out by means of a sensor (19) in a closed control loop to adjust the intensity by the local radiation source. Method for producing 3-dimensional models (5) according to Claim 1 , characterized in that a post-curing of the entire model (5) takes place by means of a large-capacity radiation source (14). Method for producing 3-dimensional models (5) according to Claim 1 or 2 , characterized in that fillers and/or dyes are introduced into the photopolymer before or after extrusion but before curing by means of the movable local radiation source (4). Method for producing 3-dimensional models (5) according to Claim 3 , characterized in that the fillers and/or dyes are distributed only in partial areas of the dispensed material with respect to the cross-section of the dispensed material and not homogeneously over the entire cross-section of the dispensed material. Method for producing 3-dimensional models according to one of the preceding claims, characterized in that the local radiation source (4) has means for limiting the light beam (20) or for focusing. Method for producing 3-dimensional models (5) according to one of the preceding claims, characterized in that after curing by means of the local radiation source (4) and before applying a further layer, the unevenness of the surface on which the next layer is to be printed is detected by means of a sensor and this value is used to control the extrusion speed when applying the next layer or to control the movement of the print head (3). Method for producing 3-dimensional models (5) according to one of the preceding claims, characterized in that the printing process is carried out under an oxygen-reduced atmosphere. 3D printing device (1) with at least one print head (3) which is intended to continuously dispense photopolymers, a movable local radiation source (4) which is designed and arranged to at least partially cure the dispensed photopolymer locally, wherein the print head further comprises a sensor (19) for detecting the mass or volume flow, and wherein an intensity of the movable local radiation source is adjusted by means of the values of the sensor. 3D printing device (1) according to Claim 8 , characterized in that the 3D printing device has a supply unit (15) for fillers and/or dyes, which introduces fillers and/or dyes into the photopolymer before or after dispensing but before local curing by means of the movable radiation source (4). Pressure device (1) according to Claim 9 , characterized in that the printing device (1) is designed to introduce the fillers and/or dyes, based on the cross-section of the dispensed material, only in partial areas of the dispensed material and not homogeneously distributed over the entire cross-section of the dispensed material. 3D printing device (1) according to Claim 9 or 10 , characterized in that the printing device has at least two print heads (3), the second print head being arranged and controlled so that it prints a new layer of the photopolymer on the preceding layer while the first print head is still printing the preceding layer. 3D printing device (1) according to Claim 11 , characterized in that the movable local radiation source (4) is arranged and controlled so that it locally hardens the preceding layer before the application of a layer by the second print head (3). 3D printing device (1) according to one of the Claims 9 until 12 , characterized in that the 3D printing device has a sensor which is arranged and designed to measure the unevenness of the surface after the curing of the photopolymer with the local movable radiation source (4) and before application of a further layer by means of the same or a second print head (3). on which another layer is to be applied. 3D printing device (1) according to one of the Claims 9 until 13 , characterized in that the 3D printing device has a large-capacity radiation source (14) which is designed to cause hardening of the entire model (5).

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