WO2020002752A1

WO2020002752A1 - Stereolithography apparatus

Info

Publication number: WO2020002752A1
Application number: PCT/FI2019/050192
Authority: WO
Inventors: Samppa Dravantti; Tero Rakkolainen
Original assignee: Planmeca Oy
Priority date: 2018-06-28
Filing date: 2019-03-11
Publication date: 2020-01-02
Also published as: FI129774B; FI20185581A1

Abstract

A stereolithography apparatus, comprising: a table (3) having a horizontal first upper surface (4) on which a vat (1) is placeable for holding photosensitive light-curable polymer for use in a stereolithographic 3D printing process, the vat having a transparent bottom (2) made of flexible film material, the table having an opening (5); an exposure arrangement (6) arranged at the opening (5) of the table for providing, from below of a vat placed, in use, on the table, an electromagnetic radiation pattern of a print, layer to be printed, the exposure arrangement comprising a second upper surface (7); a build platform (8) having a lower surface (9) on which the object, to be 3D printed can be built up; an elevator mechanism (10) comprising a movable frame (11) to which the build platform (8) is connected, the frame (11) being movable in a vertical direction; and venting means (12) for allowing entry of air between the transparent bottom (2) and the second upper surface (7).

Description

STEREOLITHOGRAPHY APPARATUS

FIELD OF THE INVENTION

The invention concerns the technology of stereolitho- graphic 3D printing, also known as stereolithographic additive manufacturing. In particular the invention concerns a stereolithography apparatus for "bottom-up" fabrication of three-dimensional objects. BACKGROUND OF THE INVENTION

Stereolithography is a 3D printing or additive manu facturing technique in which optical radiation is used to photopolymerize suitable raw material to produce the desired object. The raw material comes to the pro- cess in the form of a resin. A vat is used to hold an amount of resin, and a build platform is moved in the vertical direction so that the ob ect to be produced grows layer by layer onto a build surface of the build platform. The present description concerns in particu- lar the so-called "bottom up" variant of stereolithog raphy, in which the photopolymerizing optical radia tion comes from below the vat and the build platform moves upwards away from the remaining resin as the manufacturing proceeds .

The stereolithography apparatus may comprise a table having a horizontal first upper surface on which a vat is placeable, for holding photosensitive light-curable polymer for use in a stereolithographic 3D printing process. The vat has a transparent bottom made of flexible film material.. The table may have an open ing. The apparatus further comprises an exposure arrangement arranged for providing, from below of a vat placed on the table, an electromagnetic radiation pat- tern of a print layer to be printed. The exposure arrangement comprises a second upper surface which may be flush with the first upper surface of the table. The apparatus further comprises a build platform hav ing a lower surface on which the object to be 3D printed can be built up. The apparatus further com- prises an elevator mechanism comprising a movable frame to which the build platform is connected. The frame is movable in a vertical direction between posi tions including a first position and a second posi tion. In the first position the lower surface of the build platform is raised at a distance from the bottom of the vat placed, with the apparatus in use, on the table. While using the apparatus during the printing process, the lower surface and the layers of the ob ject printed thereon are repeatedly lowered into prox- iraity with the bottom of the vat.

When the build platform is moved upwards between the printing sequences, a vacuum may be form between the transparent bottom and the second upper surface before the layer of the object being built on the lower sur face is peeled off from the transparent bottom. A a long moving distance may be necessary to secure com plete peeling off. The greater the moving distance, the more time is needed to travel said distance and the slower the overall process becomes. Thus, there is a need for advancing the peeling off.

OBJECTIVE OF THE INVENTION

The objective of the invention is to alleviate the dis dvantages mentioned above.

In particular, it is an objective of the present in vention to provide a stereolithography apparatus wherein generation of a vacuum as discussed above can be eliminated or at least diminished and the separation of the object being manufactured from the bottom of a vat advanced. SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides a stereolithography apparatus, comprising

- a table having a horizontal first upper surface on which a vat is placeable for holding photosensitive light-curable polymer for use in a stereo lithographic 3D printing process, the vat having a transparent bottom (2) made of flexible film material, the table optionally having an opening,

- am exposure arrangement for providing, from below of a vat placed on the table, thus on the hori zontal first upper surface thereof, an electromagnetic radiation pattern of a print layer to be printed, the exposure arrangement optionally comprising a second upper: surface at the opening and which is flush with the first upper surface of the table,

- a build platform having a lower surface on which the object to be 3D printed can be built up,

- an elevator mechanism comprising a movable frame to which the build platform is connected, the frame being movable in a vertical direction between positions including a first position in which the lower surface of the build platfor is raised at a dis tance from the botto of the vat placed, with the ap- paratus in use, on the table, and at second position in which, while using the apparatus, the lower surface and the layers of the object printed thereon is lowered into proximity with the bottom of the vat, and

- venting means for allowing entry of air be- tween the transparent bottom and the second upper sur face .

The technical effect of the invention is that the venting means relieves a vacuum or prevents forming of it, to advance separation of the object from the bot tom of the vat . In an embodiment of the stereolithography apparatus, the venting means comprises an air channel arranged in the table . In an embodiment of the stereolithography apparatus, the air channel comprises grooves formed to the first upper surface of the table.

In an embodiment of the stereolithography apparatus, the vat placeable on the table comprises a rim defining, together with the transparent bottom attached to the rim, an inner space for receiving the photosensitive light-curable polymer therein, and the transpar ent bottom has a first area which is larger than a second area of the second upper surface defining an intermediate area between the first area and the second area ,

In an embodiment of the stereolithography apparatus, the rim has an inner periphery and an outer periphery, and the grooves comprise a plurality of first grooves formed on the table, each of the first grooves having one end extending beyond the inner periphery to the intermediate area, and another end extending near to the outer periphery.

In an embodiment of the stereolithography apparatus, the grooves comprise a ring-like second groove at least partly surrounding the outer periphery, and the first cjrooves open to the second groove.

In an embodiment of the stereolithography apparatus, the venting means comprises through-channels arranged to the table at the intermediate area in proximity with the opening for providing pressurized air between the transparent bottom of the vat placed, with the ap- paratus In use, on the table, and the second upper surface of the exposure arrangement.

In an embodiment of the stereolithography apparatus, the apparatus is a 3D printer for fabrication of dental objects. It may be a 3D printer for creating den tal. splints, models, surgical guides, temporary fill ings and orthodontic models with true precision and efficiency .

It is to be understood that the aspects and embodi ments of the invention described above may be used in any combination with each other. Several of the as pects and embodiments may be combined together to form a further: embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to pro vide a further: understanding of the invention and con- stitute a part of this specification, illustrate embodiments of the invention and together with the de scription help to explain the principles of the inven- tion . In the drawings : Figure la shows a partial axonoinetric view of a stereolithography apparatus according to an embodiment of the invention, the build platform being in a first pos ion, Figure lb shows the stereolithography apparatus of

Figure la, the build platform being in a second position,

Figure le shows the stereolithography apparatus of Figure la, the vat being missing from the table where by the venting means formed to the table can be seen, Figure 2 is a schematic side view of the stereolithog raphy apparatus of Figure la,

Figure 3 is a plan view III-IXI from Figure lc, show- ing the table having the venting means,

Figure 4 is a plan view IV-IV from Figure la, the vat being placed on the table, Figure 5 is a cross-section V-V from Figure 4, and

Figure 6 corresponds to the cross-section of Figure 5, showing an alternative arrangement of the venting means .

DETAILED DESCRIPTION OF THE INVENTION

Figures la - lc and 2 show a stereolithography apparatus which can be used for "bottom-up" three- dimensional printing of three-dimensional objects.

The stereolithography apparatus comprises a vat 1, which may be releasable and replaceable, for holding photosensitive light-curable polymer for use in a ste reolithographic 3D printing process. The vat 1 has a transparent bottom 2 made of flexible film material. The film material may be a thin FEP (Fluorinated eth ylene propylene) film. The thickness of the film is of the order of 0,1 m and it is highly tensioned like "a drumhead" to a rim 15 of the vat 1 (see also Figure 5) to form the transparent bottom 2 thereof.

The stereolithography apparatus comprises a table 3 having a horizontal first upper surface 4 on which the vat 1 is placeable. In Figures la and lb can be seen the vat 1 being placed on the table 3. In Figure lc the vat 1 is removed. A stereolitography apparatus may be provided without a vat, whereby a separate vat may be placed, for use of the apparatus, on the table, such as on a horizontal first upper surface thereof.

Referring to Figures 3 and 4, the table 3 has an open ing 5. An exposure arrangement 6 is arranged at the opening 5 of the table 3. The exposure arrangement 6 provides, from below of the vat 1, an electromagnetic radiation pattern of a print layer to be printed and cured. The exposure arrangement 6 comprises a planar second upper surface 7 which is flush with the first upper surface 4 of the table 3. In an embodiment the exposure arrangement 6 may be an LCD display, the up- per surface of which being said planar second upper surface 7, In another not-shown embodiment the exposure arrangement 6, the electromagnetic radiation pat tern may be projected by a projector device on a transparent screen plate whereby the planar second up- per surface 7 is the upper surface of the screen plate .

Referring to Figure la-lc and 2, the stereolithography apparatus comprises a build platfor 8 having a planar lower surface 9 on which the object to be 3D printed can be built up.

Figure 3 shows an elevator mechanism 10 comprising a movable frame 11 to which the build platform 8 is con- nested. The elevator mechanism 10 comprises a linear actuator, such as a ball screw mechanism or like, which is able to provide precise positioning.

The frame 11 is movable in a vertical direction be- tween positions including a first position I shown: in Figure la in which the planar lower surface 9 of the build platform is raised at a distance from the bottom 2 of the vat 1, and a second position II shown in Fig ure lb in which, while using the apparatus, the planar lower surface 9 and the layers of the object printed thereon is lowered into proximity with the bottom 2 of the vat 1. In the first printing sequence the planar lower surface 9 contacts the transparent bottom 2 and presses it against the planar upper surface 7 of the exposure arrangement 6. In the next printing sequences the layer of the object being built on the planar low- er surface 9 presses the transparent bottom 2 against the planar upper surface 7. In the first and subse quent printing sequences, when the build platform 8 is moved upwards, a vacuum may form between the transparent bottom 2 and the second upper surface 7.

Reference is made to Figures lc and 2 to 6. Venting means 12 are provided for allowing entry of air between the transparent bottom 2 and the planar second upper surface 7 for relieving said vacuum, The venting means 12 may comprise an air channel arranged in the table 3, Figures 3 and 4 show that in the illustrated embodiment the air channel comprises grooves 13, 14 formed to the first upper surface 4 of the table 3. The vat 1 comprises a rim 15 defining, together with the transparent bottom 2 attached to the rim, an inner space 16 for receiving the photosensitive light- curable polymer therein. As can be seen in Figures 4 and 5, the transparent bottom 2 has a first area which is larger than a second area of the planar second up per surface 7 defining an intermediate area .17 between the first area and the second area. The rim 15 has an inner periphery 18 and an outer periphery 19, and the grooves comprise a plurality of first grooves 13 formed on the table 3, each of the first grooves 13 having one end extending beyond the inner periphery .18 to the intermediate area 17, and another end extending near to or beyond the outer periphery 19. The grooves may comprise a ring-like second groove 14 at least partly surrounding the outer periphery 19, and the first grooves 13 open to the second groove 14. Mainly the grooves 13 provide an air path enabling entry of air to the intermediate area 17 between the transpar ent bottom 2 and the planar second upper surface 7 for relieving the vacuum to facilitate peeling off with minimum separation force .

Figure 6 shoves a further embodiment wherein the vent ing means 12 comprises through-channels 20 arranged to the table 3 at the intermediate area 17 in proximity with the opening 5 for providing pressurized air be- tween the transparent bottom 2 of the vat 1 and the planar second upper surface 7 of the exposure arrangement 6. The arrangement may comprise a separate pipe line 21 connected to the through-channels 20 or they may formed inside the table 3. to air pump 22 may be provided to generate the pressurized air. A control device 23 may be provided to control the operation of the pump 23 and/or a valve 24 arranged in the pipeline 21. It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The in vention and its embodiment are thus not limited to the examples described above, but instead may vary within the scope of the claims .

Claims

1. A stereolithography apparatus, comprising

- a table (3) having a horizontal first upper surface (4) on which a vat (1) is placeable for hold- ing photosensitive light-curable polymer for use in a stereolithographic 3D printing process, the vat having a transparent bottom (2) made of flexible film materi al ,

- an exposure arrangement (6) arranged for providing, from below of a vat placed, in use, on the table (3) , an electromagnetic radiation pattern of a print layer to be printed, the exposure arrangement comprising a second upper surface (7),

- a build platform (8) having a lower: surface (9) on which the object to be 3D printed can be built up,

- an elevator mechanism (10) comprising a movable frame (11) to which the build platform (8) is connected, the frame (11) being movable in a vertical direction between positions including a first position (1) in which the lower surface (9) of the build plat form is raised at a distance fro the bottom (2) of a vat (1) placed, in user, on the table (3) and a second position (II) in which, while using the apparatus, the lower surface (9) and the layers of the object printed thereon is lowered into proximity with the bottom (2) of the vat (1), and

- venting means (12) for allowing entry of air between the transparent bottom (2) and the second upper surface (7).

2. A stereolithography apparatus according to claim 1, wherein the venting means (12) comprises an air chan nel arranged in the table (3) .

3. A stereolithography apparatus according to claim 2, wherein the air channel comprises grooves (13, 14) formed to the first upper surface (4) of the table

4. A stereolithography apparatus according to any one of the claims 1 to 3, wherein the vat (X) comprises a rim (15) defining, together with the transparent bot tom (2) attached to the rim, an inner space (16) for receiving the photosensitive light-curable polymer therein, and the transparent bottom (2) has a first area which is larger than a second area of trie second upper surface (7) defining an intermediate area (17) between the first area and the second area.

5. A stereolithography apparatus according to claim 4, wherein the rim (15) has an inner periphery (IS) and an outer periphery (19), and the grooves comprise a plurality of first groovers (13) formed on the table (3), each of the first grooves (13) having one end extending beyond the inner periphery (18) to the inter- mediate area (17), and another end extending near to the outer periphery (19) .

6. A stereolithography apparatus according to claim 5, 'wherein the grooves comprise a ring-like second groove (14) at least partly surrounding the outer periphery

(19), and the first grooves (13) open to the second groove (14) .

7. A stereolithography apparatus according to any one of the claims 2 to 6, wherein the venting means (12) comprises through-channels (20) arranged to the table (3) at the intermediate area (17) in proximity with the opening (5) for providing pressurized air between the transparent bottom (2) of a vat (1) placed, in use, on the table (3) and the second upper surface (7) of the exposure arrangement (6) .

8. A stereolithography apparatus according to any one of the claims 1 to 7, wherein the table (3) has an opening (5) and the second upper surface (7) is flush with the first upper surface (4) of the table (3).