WO1995025003A1

WO1995025003A1 - Stereolithographic process and device for producing objects in a bath of a radiation-hardenable liquid

Info

Publication number: WO1995025003A1
Application number: PCT/DE1995/000348
Authority: WO
Inventors: Matthias Fockele; Dieter Schwarze
Original assignee: Matthias Fockele; Dieter Schwarze
Priority date: 1994-03-15
Filing date: 1995-03-14
Publication date: 1995-09-21
Also published as: DE4408754A1; AU2066495A

Abstract

A stereolithographic process and device are disclosed for producing an object (8) in a bath of a radiation-hardenable dielectric liquid (4). The layer of the object (8) most recently hardened by radiation next to the surface (22) of the bath is moved forward in the bath in order to provide a liquid layer to be subsequently radiation-hardened on the previously hardened layer. In order to produce a subsequently hardened layer having a uniform thickness on the previously hardened layer, an electric field is generated by high-voltage electrodes (28, 29) and/or an ultrasonic field is generated by ultrasonic sources and the field is made to act on the liquid that forms the layer to be subsequently hardened. Another aspect of the invention is that an electric field is made to act on the presently irradiated area while the liquid is hardened. This allows privileged directions of the liquid molecules to be set that are expressed in the hardened object (8) by anisotropies of its physical properties.

Description

STEREOLITHOGRAPHIC METHOD FOR PRODUCING A

OBJECTS IN A BATHROOM BY RADIATION

ESTABLISHABLE LIQUID AND DEVICE FOR

IMPLEMENTATION OF THE PROCEDURE

The invention relates to a stereolithographic method for producing an object in a bath of a dielectric liquid that can be solidified by the action of radiation, the object being solidified by irradiating the liquid in accordance with the desired object shape.

The invention relates in particular to a stereolithographic method for the layer-by-layer production of an object in a bath of a dielectric liquid that can be solidified by the action of radiation, wherein a layer of the object that was last solidified by irradiation near the surface of the bath continues into the bath is moved and / or the liquid level of the bath is raised relative to the surface of the last solidified layer in order to provide a liquid layer to be subsequently solidified by irradiation on the last solidified layer.

Stereolithographic methods of the type mentioned above are described, for example, in the publication "A Review of 3D Solid Object Generation", A.J. Herbert in Journal of Imaging Technology, Vol. 15, 1989, pages 186 to 190.

In one of the known process variants, the liquid photopolymer plastic is solidified under the surface of the bath in the overlap region of two laser beams which are directed into the photopolymer bath from different sides. By moving the laser beams appropriately, their overlap area in the photopolymer bath can be shifted in order to solidify coherent areas of an object.

According to another variant of the stereolithographic

Production of plastic objects such as those from the

EP 0 171 069 A2 is known, the object is solidified in layers, whereby a carrier plate is first arranged closely below the bath surface and the layer of the liquid lying above the carrier plate is irradiated in accordance with the desired cross section of the object, in order to add a base layer to the object solidify, which rests on the carrier plate. The carrier plate with the layer solidified thereon is then moved further into the plastic bath in order to provide a liquid layer to be subsequently solidified over the already solidified layer, the liquid layer thickness corresponding to the thickness of the subsequently solidified layer. By appropriate Irradiation of the liquid layer then forms the next solid object layer that adheres to the previously formed object layer. In this way, further layers are solidified until the desired object is solidified overall.

The irradiation of the liquid in the commonly used photopolymers is preferably carried out by means of electromagnetic radiation, in particular ultraviolet light. EP 0 171 069 A2 also refers to the

Use of electron beams for curing appropriate liquid plastics pointed out.

A method for the stereolithographic layer-by-layer production of a plastic object is further described in the article by Hideo Kodama, "Automatic Method for Fabricating a Three-Dimensional Plastic Model with Photohardening Polymer", Rev. Sei. Instr. 52 (11), November 1981, pages 1770 to 1773. The problem with these methods of layer-by-layer stereolithographic production of an object is that it is difficult to form a liquid layer on the last solidified layer that is sufficiently uniform for the subsequent irradiation process. In particular, after lowering the last solidified layer, areas of insufficient wetting of the last solidified layer and areas with excess liquid compared to the general level of the liquid bath were frequently observed.

The obvious measure to immerse the already completed part of the object and thus the last solidified layer further than a layer thickness into the bath and then to raise it again after sufficient wetting of the last solidified layer only gives better results to a limited extent, since it is due to adhesion adhering excess is not effectively eliminated in this way and also the control of the respective

Height adjustment of the wearing becomes more complicated. A stereolithographic method and an apparatus for carrying out the method is also described in DE 41 34 265 A1. For the preparation of a sufficiently uniformly thick layer of liquid over the last solidified layer of the object, DE 41 34 265 A1 proposes using a flexible wiper lip in order to

Brush the bathroom surface smooth after the last one

solidified layer has been lowered.

The invention is based on the object of specifying a stereolithographic method with a new type of preparation of the region of the liquid to be subsequently solidified and an apparatus for carrying out the method. According to a first aspect of the invention according to claim 1 it is proposed to achieve the object that in the stereolithographic method for the layer-by-layer production of an object an electric field is generated by means of high-voltage electrodes and the liquid to be subsequently solidified is allowed to act.

The electrical high-voltage field is used for dielectric polarization, in particular orientation polarization of molecules of the dielectric liquid, so that due to the interaction of the electrical field with the dielectric material, internal forces are generated which compensate for the unevenness of the liquid over the last solidified layer of the already solidified part of the property can be used. The high-voltage electrodes can be, for example, plate electrodes that are on opposite sides of the object being created tes are arranged and at least partially immersed in the liquid. Good results regarding the wetting of the last solidified layer with a sufficiently uniformly thick liquid layer to be subsequently solidified were achieved with an electric field which contained field components parallel to the surface of the last solidified layer, which during the lowering or after lowering the already solidified part of the The liquid flowing through onto the last solidified layer. A homogeneous or inhomogeneous static field can be used as the electric field in order to prepare the layer to be subsequently solidified. In the method according to the invention, it is in particular not necessary to move the last solidified layer further into the bath or to raise the liquid level further than the last solidified layer than the thickness of the layer subsequently to be solidified requires. Furthermore, the desired wetting and smoothing of the layer to be subsequently solidified takes place without contact and without mechanical smoothing agents. The problem of damage to the last solidified surface layer with a smoothing knife or the like, which occurs during smoothing by mechanical means, does not therefore occur.

It should be pointed out that the electrodes of the high-voltage electrode arrangement do not necessarily have to be immersed in the liquid. The desired effect can also be achieved if the electrodes are appropriately held just above the liquid surface.

The desired wetting and smoothing effect can be increased further if an electrical high-voltage alternating field is allowed to act on the liquid forming the layer to be subsequently solidified, when it flows onto the last solidified layer. By the Alternating field can be deliberately generated with appropriate selection of the alternating frequency dielectric losses in the area of the liquid penetrated by the field above the last solidified layer, which lead to local heating of the liquid and thus improve its fluidity. It will therefore both

The force of the electric field on the molecules of the dielectric liquid as well as the local improvement in fluidity are used to prepare a uniformly thick layer of liquid for the subsequent irradiation process.

According to a variant of the procedure according to the invention, the effect is exploited that dielectric liquid is drawn into the area between the electrodes when an electric field acts between two high-voltage electrodes if the electrodes are brought sufficiently close to the surface of the bath or, if appropriate, partially into the bath be immersed. The high-voltage electrodes, which are preferably in the form of sheet electrodes, are initially held to the side of the area in which the object to be produced is produced. After the respective last solidified layer has been lowered, the high-voltage electrode arrangement is moved over the last solidified layer, the lower edges of the electrodes in question preferably being kept just above or exactly at the level of the desired liquid level. The liquid electrostatically picked up between the electrodes exits through a gap between the electrodes when the electrode arrangement sweeps over the last solidified layer. It is not necessary to reduce the electrode voltage in order to dispense the liquid from the area between the electrodes in question. It has been shown that due to Adhesion effects liquid is released from the electrodes to the last solidified layer.

On the other hand, however, the electrode voltage can of course be reduced in order to control the amount of liquid to be dispensed. The electrode arrangement can be moved one or more times over the already solidified part of the object to prepare the desired layer to be subsequently solidified, if necessary,

The method according to the invention can be used beyond the purpose of producing a uniformly thick layer that is subsequently to be solidified and, independently thereof, to prepare the material to be solidified in the sense explained below.

It has been shown that anisotropic physical properties can be imparted to the solidified material if a static high-voltage electric field acts on the currently irradiated area of the liquid during the solidification by irradiation. It is assumed that due to the orientation polarization in the electric field, the liquid molecules experience a preferred orientation in accordance with the direction of the electric field and that the corresponding structure is quasi "frozen" during solidification, so that a texture-like structure is formed.

This aspect of the invention makes it possible for the first time not only to preselect the shape of an object to be produced stereolithographically, but also physical, in particular mechanical, properties that are dependent on location and direction. to produce more complicated anisotropies, the

Direction and possibly the intensity of the electrical see field depending on the currently irradiated location.

It should be pointed out that the latter aspect of the invention can be used both in a method with layer-wise solidification of the object according to claim 1 and in a stereolithographic method in which the solidification takes place in the volume of the bath, for example in the intersection area of two intersecting laser beams .

A device for performing the method according to the invention is specified in claim 9. Further developments of the device for implementing different method variants are specified in claims 10 to 24.

The invention furthermore relates to a stereolithographic method for the layer-by-layer production of an object in a bath of a liquid that can be solidified by the action of radiation, a layer of the object that was last solidified by irradiation near the surface of the bath being moved further into the bath and / or the liquid level of the bath is raised relative to the surface of the last solidified layer in order to provide a liquid layer to be subsequently solidified by irradiation on the last solidified layer, the method being characterized in that sound waves, in particular ultrasound waves, act on the liquid forming the layer to be subsequently solidified leaves.

According to the above-mentioned first aspect of the invention, this method is also based on the idea of allowing a field to act on the liquid in order to ensure that the wetting layer is as uniformly thick as possible on the surface to provide the last solidified layer.

In this case, however, a sound field is used instead of an electrical field in order to exert non-contact forces on the material to form the layer to be subsequently solidified.

Within the scope of the invention, a combination of the method according to claim 1 and the method according to claim 8 can also be realized by using both an electric field and a sound field in order to bring about a uniform wetting of the last solidified layer.

A device for performing the method according to claim 8 is specified in claims 25 to 27.

The invention is explained in more detail below on the basis of preferred exemplary embodiments with reference to the figures.

FIG. 1 a shows a device according to the invention for stereolithographic production of an object in a schematic side view, partly in section. FIG. 1 b shows a top view of the container shown in FIG. 1 a.

2 shows components of a second exemplary embodiment of the invention in a schematic sectional side view.

FIG. 3 shows a variant of the high-voltage electrode arrangement shown in FIG. 2. The device for stereolithographic production of an object shown in FIG. 1 a comprises a container 2 to take up a liquid under normal conditions

Plastic 4, which can be solidified under the action of radiation. Suitable plastic materials which can be crosslinked or hardened by the action of electromagnetic radiation are mentioned, for example, in DE 41 38 309 A1.

A support plate 6 for holding the object 8 to be produced is provided in the container 2. The carrier plate 6 is fastened to a rod 10 which extends out of the container 2 through a sealing arrangement in the container base 14. The rod 10 is axially movable by means of a drive, not shown, so that the carrier plate 6 and the part of the object 8 supported thereon and already solidified can be moved deeper into the plastic bath 4.

In FIG. 1a, 16 denotes a UV radiation source, in particular a laser, which provides the UV light required to solidify the photopolymer plastic 4.

A deflection mirror 18 is arranged approximately in the middle above the carrier plate 6 and deflects the bundled light beam 20 towards the surface 22 of the plastic bath 4. The

Deflecting mirror 18 can be pivoted by means of a schematically indicated pivoting device 24, so that the UV beam 25 reflected by the mirror 18 can be directed in a controlled manner to any desired location on the surface 22 of the plastic bath 4.

At the start of the production of an object, the carrier plate 6 is located at a short distance from the surface 22 in the plastic bath 4. The swiveling device 24 of the deflecting mirror 18 is then controlled by a computer (not shown) in such a way that the UV beam 25 is at the Surface 22 scans a surface area which corresponds to the desired cross section of the first layer of object 8 to be solidified, namely the layer directly adjacent to the carrier plate 6.

After this first layer by the action of the

Radiation has been solidified, the carrier plate 6 is moved a certain amount substantially into the plastic bath 4 under the control of the control computer, in accordance with the thickness of the layer to be subsequently hardened, in order to form a new layer of liquid plastic 4 on the already solidified layer.

In principle, the liquid layer could now pass through

Scanning with the UV beam 25 corresponding to the cross section of the next layer of the object 8 to be hardened. However, it has been shown that the liquid level above the last solidified layer was often not even due to adhesion effects and the like, and the liquid layer subsequently to be solidified was therefore not uniformly thick. In the case of more complicated cross-sections, it was also the case that surface areas were wetted extremely inadequately at the usual lowering depths.

The invention shows ways in which the preparation of the liquid layer to be subsequently solidified can be carried out quickly and reliably. For this purpose, a high-voltage electrode arrangement 26 is proposed, by means of which an electric field is generated in the region of the layer to be subsequently solidified in order to exert non-contact force effects on the dielectric photopolymerization liquid 4 by dielectric polarization, in particular orientation polarization. Although numerous variations are possible in the number, shape and arrangement of the electrodes of the high-voltage electrode arrangements, the exemplary embodiment shown in FIG 1b, take the resulting object 8 between them. The plate electrodes 28 to 31 are aligned essentially transversely to the surface 22 of the plastic bath 4 and dip slightly into the bath with their lower edges 32, 33. In this connection, it should be pointed out that it is not absolutely necessary for the electrodes 28 to 31 to be immersed, since the intended purpose of applying an electric field to the uppermost layer of liquid can also be achieved if the electrode edges 32, 33 are held just above the surface 22 of the plastic bath 4. The device according to the invention shown schematically in Fig. 1a can be operated according to an operating mode such that after lowering the last solidified layer of the object 8 at least two electrodes of different polarity, in particular electrodes opposite each other, are supplied with an electrical high voltage in order to To generate an area of the layer to be subsequently solidified, which due to the dielectric polarization interacts with the liquid here. It has been shown that due to the action of the electric field, better wetting of the last solidified surface of the object 8 takes place and unevenness on the surface 22 of the plastic bath 4 in the area between the electrodes 28 to 31 tends to be compensated, so that a

subsequent exposure by means of the UV beam 25 according to the desired cross section of the following consolidating layer can take place.

The electric field generated by the electrodes 28 to 31 can be a static electric field.

However, very good results have also been achieved with alternating electrical fields. Here, in particular, the frequency of the alternating electric field can be set such that dielectric losses in the liquid in the region of the layer to be subsequently solidified, which lead to local heating of the plastic 4 in the region of the layer, occur quite deliberately. In this way, the flowability of the plastic in the heated area is increased, which also contributes to the better and faster setting of a largely uniform liquid layer over the last solidified layer.

In the operating modes of the high-voltage electrode arrangement discussed so far, the electrical field is switched off before the exposure process begins.

It should be pointed out that the switching on and off and the entire control of the high-voltage electrode arrangement 26 are controlled by the control computer (not shown). It should also be pointed out that means which are not shown and are known per se are provided, which ensure that the liquid level of the plastic bath 4 remains essentially constant during the manufacture of the object 8.

The electrode plates 28 to 31 are arranged on a mounting mechanism 34, which is only partially and schematically shown, which makes it possible to move the electrodes 28 to 31 and thus the distances between the

Adjust electrode plates as required. The holding tion mechanism 34 also enables the height of the electrode arrangement 26 to be adjusted.

An extremely interesting possible use which is independent of the described function of the electrode arrangement 26 will be discussed below.

A further possibility is explained beforehand of achieving a better and more uniform wetting of the last solidified layer of the object 8 by the action of a field. This is a sound field, in particular an ultrasound field, which is generated by means of one or more ultrasound sources and is coupled to the liquid for wetting the last solidified layer of the object 8.

In the embodiment shown in Fig. 1a, two ultrasonic RF modulators 38 are attached to the side walls 40 of the container 2 approximately at the level of the surface 22 of the plastic bath 4 in order to generate ultrasonic waves which are in the liquid, in particular in the surface area of interest Liquid 4, reproduce. The ultrasonic transmitters 38 can be designed and arranged such that they set the container walls 40 in vibration in order to feed ultrasonic energy into the liquid 4 via the container walls 40. Alternatively, the ultrasonic transmitters 38 can, however, also be set up to couple the sound energy generated by them directly into the liquid 4.

It has been shown that the action of such an ultrasound field on the liquid can largely eliminate undesirable unevenness in the region of the layer to be subsequently solidified, and wetting that is sufficiently uniform for the subsequent exposure process is thus achieved. Although both the high-voltage electrode arrangement 26 and the ultrasound sources 38 are shown in FIG. 1 a, each of these devices can nevertheless be used independently of the other, in particular also with the omission of the other, in order to provide a sufficiently uniform liquid layer during or after the lowering the last solidified

Prepare layer of object 8. Of course, both devices 26 and 38 can also be used simultaneously in order to achieve the goal pursued. In this context, reference is made to the possibility of designing one or more of the electrode plates 28 to 31 as ultrasonic vibrators or to couple them to an ultrasonic transmitter.

In a preferred mode of operation of the ultrasound transmitters 38, these are switched off by the control computer before the layer to be subsequently hardened is exposed.

The further use of the high-voltage electrode arrangement 26 which has already been indicated is explained below. This use also relates to the preparation of the material of the layer of the object 8 to be subsequently solidified, but the focus is not on the formation of a liquid layer that is as uniformly thick as possible, but on the electrical influencing of the material during the solidification process. The corresponding operating mode of the high-voltage electrode arrangement 26 determines

Electrode combinations are supplied with corresponding DC voltages in order to form a static electric field in the desired direction in the liquid layer to be solidified and to maintain it during the exposure of this layer, possibly depending on the point currently exposed. It has It has been shown that layers hardened in this way with specifically anisotropic physical properties can be produced. In this way, in particular mechanical and optical properties, such as light transmission, strength, elasticity, dimensional stability and. Like., Depending on the relevant position of the material in the object 8 and in particular directional influence. In order to be able to set as many different field directions as possible, it is proposed that the high-voltage electrode arrangement 26 be around 42 in FIG. 1a

Train axis to be rotatable. The respective rotational position of the high-voltage electrode arrangement 26 can be set by the control computer as a function of the currently exposed point of the layer to be solidified, in order to determine the desired anisotropic effects in a program-controlled manner when the corresponding points are exposed. This creates for the first time the possibility of not only defining the shape of the stereolithographically manufactured object, but also to a certain extent the anisotropy of physical properties of the object 8 prior to the manufacture of the object 8, or corresponding data for controlling the pivoting device 24 of the deflecting mirror 18 and the electrode arrangement 26 for the purpose of determining the respective direction and, if appropriate, strength of the electric field as a function of the currently exposed location in a memory of the control computer, which can be called up for the later control process of the invention

Save device.

A possible physical explanation of the effect of the selectively producible anisotropy of the solidified material could be that the molecules of the liquid, which usually have a permanent dipole moment Because of the orientation polarization, photopolymers in the high-voltage electrical field experience a preferred orientation corresponding to the electrical field profile and that this preferred orientation is "frozen", so to speak, during solidification.

Further tests have shown that the effect can be increased if the light from the UV light source used for curing is polarized, in particular linearly polarized. The anisotropy effect is increased if the direction of polarization of the E-field vector of the curing light in the region of the liquid layer to be cured is essentially parallel to the E-field vector of the field generated by the high-voltage electrodes 28 to 31. To take advantage of this effect, the device according to FIG. 1 a comprises a polarization device 46 in the beam path of the beam 25 in order to adjust the polarization direction of the light used for curing in a controlled manner, in particular depending on the direction of the high-voltage field of the electrode arrangement 26 at the location of the currently exposed point.

It should be emphasized that the influencing of the currently solidified liquid plastic 4 by an electric field of a high-voltage electrode arrangement can be an aspect of the invention that is independent of the described exemplary embodiments. In particular, the underlying idea can be generally realized in any form of stereolithographic production of objects, even if the

Liquid is not cured in the area of the surface of a photopolymer bath, but the curing takes place inside a photopolymer bath, as described, for example, in Journal of Imaging Technology, Vol. 4, August 1989, pp. 186-190, in the article "A Review of 3D Solid

Object Generation ", AJ Herbert Any field direction in three-dimensional space can be set by appropriate arrangement of high-voltage electrodes in order to achieve corresponding anisotropic effects.

Moreover, the invention is in no way limited to the fact that electromagnetic radiation is used for curing. It works in all its forms even when a polymer material that can be solidified by particle radiation, such as electron radiation, is used and irradiated accordingly.

The possibility of manufacturing in terms of physical properties of anisotropic plastic bodies can also be exploited in the context of the invention to initially only produce solidified or semi-finished material by stereolithographic means, which is brought into a desired shape by later mechanical processing or the like. For example, cylindrical or cuboid bodies with anisotropic properties can easily be produced for further processing,

In particular in the case of such simply shaped bodies, it may be expedient to use a flat area instead of the individual beam scanning of the layer to be hardened

To choose exposure, the electrical field applied by means of the high-voltage electrodes being able to be kept constant with respect to the field direction during the exposure of the layer in question.

According to the invention, largely homogeneous electric fields or inhomogeneous electric fields can be used according to the invention. Here, the person skilled in the art remains within the scope of the invention - the greatest possible freedom of design with regard to the geometry, the number, the combination of live electrical the and the respective direction setting of the electrodes in order to provide a desired electric field at the location cfer currently solidified. 2 shows a further exemplary embodiment of the invention with a high-voltage electrode arrangement for smoothing a layer of liquid photopolymer to be subsequently solidified over the last solidified one

Layer of an object to be produced stereolithographically.

Elements in FIG. 2, which functionally correspond to elements of the exemplary embodiment shown in FIG. 1a, are identified by the same reference numerals plus 100, so that reference can be made to the description of the exemplary embodiment according to FIGS. 1a and 1b.

In a departure from the first exemplary embodiment, the exemplary embodiment according to FIG. 2 comprises two high-voltage electrodes 128, 129 which are arranged at an angle to one another and which are arranged electrically insulated from one another on a carriage 134 which is guided on a frame, not shown, in accordance with the directions of the arrows labeled 170. The electrodes 128, 129 are sheet electrodes, which extend essentially over the entire inner dimension of the container 102 in the direction perpendicular to the drawing plane of FIG. 2. The sheet electrodes 128, 129 are located essentially above the liquid level 122 and are essentially arranged such that they run towards one another in the direction of the interior of the container, so that the electrode edges 132, 133 facing the liquid have the smallest distance between the electrodes 128, 129 define. The selectable height adjustment of the slide is adjusted so that the electrode edges 132, 133 at the desired level of the Plastic bath 104 ends. The electrodes 128, 129 or at least one of the electrodes 128, 129 can then additionally act as a doctor blade. However, the desired success is also achieved if the electrode edges 132, 133 end slightly above the liquid level 122 or slightly below the liquid level 122. The clear distance between the electrodes 128, 129 between the edges 132, 133 is preferably in the range from 1 mm to 5 mm and serves to provide a receiving and dispensing gap for receiving liquid 104 between the electrodes 132, 133 and for dispensing this liquid .

During the exposure of a layer of the object 108 to be solidified and during the lowering of the carrier plate 106 by the measure of the layer thickness of the layer to be subsequently solidified, the high-voltage electrode arrangement 126 is in an inoperative position near one of the container walls 140. After the already completed part of the object has been lowered 108 is then applied to the high voltage electrodes 128, 129 high voltage, with the result that the electrical photopolymer liquid 104 is drawn into the space between the two high voltage electrodes. The carriage 134 is then set to move

Moving the electrode arrangement 126 over the last solidified layer of the object 104, the high voltage at the electrodes 128, 129 remaining switched on. It has been found that liquid emerges from the gap between the electrodes 128, 129 through the gap 172 when the electrode arrangement subsequently moves over surface areas that have already solidified, which can be attributed to adhesion effects. In this way, the wetting of the surface areas in question is improved and overall a more uniform liquid layer of that in FIG leave electrode arrangement 126 drawn right to left over the last solidified layer. If necessary, the electrode arrangement 126 can also be repeatedly moved over the already solidified part of the object 108, but this is not normally necessary. Liquid delivery through gap 172 can also be controlled by varying the electrode voltage. With a lower electrode voltage, more liquid escapes from the relevant space per unit time than with a higher electrode voltage.

After the electrode arrangement 126 has been moved back into its non-operating position, the next exposure process can be carried out in order to solidify the liquid layer in question in accordance with the desired cross section of the object. The carrier plate 106 is then lowered further and the electrode arrangement 126 is used repeatedly in order to prepare the next layer to be solidified.

Of course, an ultrasound device supporting the wetting and smoothing process can also be provided in the exemplary embodiment according to FIG. 2 in order to allow ultrasound waves to act on the liquid in the region of the liquid layer to be solidified.

FIG. 3 shows a variant of the electrode arrangement 126 shown in FIG. 2. In deviation from the electrode arrangement 126 in FIG. 2, the electrode arrangement 226 has two further corresponding leaf electrodes 274, 276 between corresponding outer electrodes 228 and 229, which are also in FIG 3 substantially along the inside dimension of a corresponding container (not shown) for the photopolymer 204. As shown in Fig. 3, can the two inner electrodes 274, 276 may also be inclined. In the electrode arrangement 226 shown in FIG. 3, adjacent electrodes each have different voltage polarities. The advantage of an arrangement according to FIG. 3 is that, with comparable high voltage electrodes, a larger amount of liquid can be taken up in the space between the two outer electrodes 228, 229. In order to achieve better wetting of the last solidified layer of the object, this amount of liquid is then released in whole or in part again when the electrode arrangement is moved over the already solidified part of the object in question. As indicated at 280, mechanical wipers can be provided within the scope of the invention, which contribute to smoothing the liquid surface 222. The mechanical wipers 280 are preferably elastic

Lips are formed which, for example, extend over the entire length of the electrodes 228, 229 in the direction perpendicular to the plane of the drawing and are arranged on the outer electrodes 228, 229 on their outer sides.

In all of the exemplary embodiments of the invention, the high-voltage electrodes are preferably operated from a relevant high-voltage source which has a current limitation to a comparatively small current value, in particular below 1 mA, and a safety circuit so that if the electrodes are accidentally touched by a person, no life-threatening currents flow and in the event of current flow an emergency shutdown of the voltage source takes place immediately. The electrode high voltage set in successful tests was in the range of about 5-10 kV.

The high voltage electrodes are preferably blocked, ie provided with a thin insulating, in particular material-repellent layer.

As far as there has been talk of sound waves, it should be noted that the term sound waves includes mechanical waves of any suitable wavelength. A continuous sound field is preferably used to produce a uniform liquid layer on the last solidified layer, the sound wavelength being adjustable such that resonance effects are used to trigger sufficiently strong liquid movements.

However, there is also the possibility of intermittently generating mechanical shock waves in the photopolymer liquid in order to cause liquid movement.

According to the invention, the solidified object or partial object can be subjected to an ultrasound aftertreatment in any suitable liquid, but preferably in the photopolymer liquid in the container. This occurs at least in the case of thermally curable

Polymers a post-hardening of the solidified object.

Claims

PATENT CLAIMS 1. Stereolithographic method for the layer-by-layer production of an object (8; 108) in a bath of a dielectric liquid (4; 104; 204) which can be solidified by the action of radiation, one of which is last by irradiation near the surface (22; 122; 222) of the Bath solidified layer of the object (8; 108) is moved further into the bath and / or the liquid level of the bath is raised relative to the surface of the last solidified layer in order to provide a subsequent liquid layer to be solidified by irradiation on the last solidified layer,

that is, that an electric field is generated by means of high-voltage electrodes (26; 126; 226) and is allowed to act on the liquid to be subsequently solidified.

2. The method according to claim 1, characterized in that the electric field is a static electric field.

3. The method according to claim 1, characterized in that the electric field is an alternating field.

4. The method according to any one of the preceding claims, characterized in that the electric field is allowed to act on the liquid at least temporarily during the irradiation of the liquid (4) of the layer to be solidified.

5. The method according to claim 4, wherein the respective layer to be solidified is irradiated in regions, in particular by scanning, with bundled electromagnetic radiation, in accordance with the relevant cross section of the object (8) to be produced,

that is, that the electric field is allowed to act on the currently irradiated area of the layer to be solidified and that the direction of the electric field is set depending on the currently irradiated area.

6. The method according to claim 4 or 5, characterized in that polarized light, in particular linearly polarized light, is used for the irradiation and that the direction of polarization is dependent on the currently irradiated area and / or on the direction of the electric field of the high-voltage electrodes in the irradiated area sets.

7. The method according to any one of the preceding claims,

characterized in that sound waves, in particular ultrasonic waves, are allowed to act on the liquid forming the layer to be subsequently solidified in order to prepare the layer to be subsequently solidified.

8. Stereolithographic process for layers

Production of an object (8) in a bath (4) of a liquid that can be solidified by the action of radiation, a layer of the object (8) last solidified by irradiation near the surface of the bath (4) being moved further into the bath (4) and / or the liquid level of the bath is raised relative to the surface of the last solidified layer in order to in each case a liquid layer subsequently to be solidified by radiation on the last solidified to provide a constant layer,

That means that sound waves, especially ultrasonic waves, are allowed to act on the layer to be subsequently solidified.

9. Device for the stereolithographic layer-by-layer production of an object according to the method of claim 1, comprising

a container (2; 102) for receiving a bath of a dielectric liquid (4; 104; 204) that can be solidified by the action of radiation,

- An irradiation device (16, 18, 46) for

Irradiation of a layer of the liquid (4;

104; 204),

- a carrier (6; 106) for holding the part of the object (8; 108) that has already solidified by irradiation of the liquid (4; 104; 204), and

- A device (6, 10; 106, 110) for wetting the last solidified layer with a layer of liquid (4; 104) to be subsequently solidified, in particular a device for moving the carrier (6; 106) relative to the surface (22; 122; 222) of the bath, in order to move the layer of the object (8; 108) that was last solidified further into the bath and to provide a liquid layer to be subsequently solidified on the last solidified layer,

marked by

an electrical high-voltage electrode arrangement (26; 126; 226) which is set up to generate an electrical high-voltage field which penetrates the bath at least near the bath surface in the region of the layer to be subsequently solidified.

10. The device according to claim 9, characterized in that the high-voltage electrode arrangement (26; 126; 226) is set up to generate a static electric field.

11. The device according to claim 9, characterized in that the high-voltage electrode arrangement is set up to provide an inhomogeneous electric field.

12. The apparatus of claim 9 or 11, characterized in that the high-voltage electrode arrangement (26) is set up to generate an alternating electric field.

13. Device according to one of the preceding claims, characterized in that the high-voltage electrode arrangement (126; 226) two spaced-apart electrode elements (128, 129; 228, 229) with substantially parallel, elongated electrode edges (132, 133; 232 ; 233), in particular surface electrodes, and that the electrode elements (128, 129; 228, 229) are movably guided so that they can be moved essentially parallel to the desired bath surface over the last solidified layer of the object (8; 108)

14. The apparatus according to claim 13, characterized in that the electrode elements can be moved relative to the container by means of a drive device, in particular a carriage arrangement.

15. Device according to one of claims 13 to 14, characterized in that the electrode elements (128, 129; 228, 229) are obliquely arranged surface electrodes which have a reserve between them voir of liquid (104; 204) can accommodate.

16. The device according to one of claims 13 to 15, characterized in that between the two electrode elements (228, 229) at least two more

Electrode elements (274, 276) are arranged, all of the electrode elements being arranged at a distance from one another and immediately adjacent electrode elements having different polarities.

17. The device according to one of claims 14 to 16, characterized by a control device for controlling the drive device of the electrode arrangement (126; 226), such that the electrodes are moved over this layer at a particularly predetermined distance from the last solidified layer.

18. Device according to one of claims 13 to 17, characterized by mechanical stripper elements (280) movable with the electrode arrangement (226) for

Smoothing the bath surface covered.

19. The apparatus according to claim 18, characterized in that the stripping elements from the electrodes (128,

129; 228, 229) - or are connected to them.

20. The apparatus according to claim 9, characterized in that the high voltage electrode arrangement (26)

A pair of substantially parallel surface electrodes (28, 29) arranged to receive between them the area to be solidified of the layer to be subsequently solidified transversely to the layer plane.

21. The apparatus according to claim 20, characterized in that the high-voltage electrode arrangement (26) has a plurality of pairs of substantially parallel opposite surface electrodes (28, 29 and 30, 31) which are set up to jointly consolidate the area of the following solidifying layer transverse to the layer plane between them.

22. The apparatus according to claim 21, characterized in that the voltages of the respective electrode pairs (28, 29 or 30, 31) are adjustable independently of one another.

23. The device according to one of claims 20 to 22,

characterized in that the distance between the electrodes of a pair of electrodes is operationally adjustable.

24. The device according to one of claims 20 to 23,

characterized in that the surface electrodes (28, 29, 30, 31) are rotatably held in a controlled manner about an axis of rotation (42) which extends transversely to the surface (22) of the bath.

25. Device for the stereolithographic layer-by-layer production of an object according to the method of claim 8, comprising

a container for receiving a bath from a liquid that can be solidified by the action of radiation,

- an irradiation device for irradiating a layer of liquid (4) which is subsequently to be solidified near the surface of the bath, - a carrier (6) for holding the already

Irradiation of the liquid (4) solidified part of the object (8) and

- A device (6, 10) for wetting the last solidified layer with a layer of liquid (4) to be subsequently solidified, in particular a device for moving the carrier (6) relative to the surface (22) of the bath by the respective to move the last solidified layer of the object (8) further into the bath and to provide a subsequent liquid layer to be solidified on the last solidified layer, characterized by

a device (38) for generating sound waves, in particular ultrasound waves, in the region of the layer to be subsequently solidified.

26. The apparatus according to claim 25, characterized in that the device (38) for generating sound waves has at least one wall (40) of the container (2) vibrating sound transmitter (38).

27. The apparatus according to claim 25 or 26, characterized in that the sound frequency of the sound generating device (38) can be changed.

28. Process for producing an object in a bath from a plastic material that is liquid under normal conditions, the object being solidified by irradiating the plastic in accordance with the desired object shape,

That is, that an electric field generated by high-voltage electrodes is allowed to act on the currently irradiated area during the irradiation.