LU101897B1

LU101897B1 - 3D-printing system and method

Info

Publication number: LU101897B1
Application number: LU101897A
Authority: LU
Inventors: Christoph MITNA
Original assignee: BigRep GmbH
Priority date: 2020-06-27
Filing date: 2020-06-27
Publication date: 2022-01-10
Also published as: WO2021260228A1

Abstract

The application refers to a 3D-printing system comprising a nozzle and a dispensing unit, wherein the nozzle is configured to deposit build material and the dispensing unit is configured to controllably dispense a reactive agent at least partially onto the build material and/or onto deposited material in or before an intersection area in which a nozzle axis intersects with a build plane.

Description

LU101897 | Title: 3D-printing system and method |

[0001] The present application relates to additive manufacturing. In particular, the pre- | sent application relates to a 3D-printing system and method. |

[0002] In the field of additive manufacturing an additive manufacturing apparatus is | also called a 3D-printer. In 3D-printing parts or workpieces are built/created/generated | by subsequent depositing layers of build material (comprising at least one individual | bead or strand of said build material) onto each other. This build material may be plastic È material, and in particular, the depositing process may be the FDM or FFF or FLM process or any other polymer melt dispensing process. The build material supplied to . the 3D-printer may be filament or granulated thermoplastic material. |

[0003] The 3D-printer usually comprises a printhead that moves in three directions © along a printing trajectory or tool path. Also, there are 3D-printers that comprise print- . head that move in two directions (commonly the X- and Y-direction or axis) and a print- | bed (the surface or structure on/to which the workpiece(s) are created) that moves in | the third direction (commonly the Z-direction or axis). Also, there are printheads that | are mounted to a conventional industrial robot such that the printhead can realize com- | plex printing trajectories. The printhead generally comprises an extruder to apply the | material to build up the workpiece. |

[0004] In the field of FDM or FFF/FLM -printing, the printhead conventionally com- . prises a material supply system (e.g. at least one of a liquefier, a melt pump, a material | feed unit) that supplies build material to a nozzle. The build material exits said nozzle . and hence said printhead and forms the subsequent deposited layers. Conventionally, | said build material is heated up prior to leaving the nozzle. The extruded material forms | a deposited strand that in turn forms one layer of the workpiece being built. An outlet | opening of the nozzle (material outlet) has usually a circular cross section. |

LU101897 |

[0005] A decisive property of any printed part is the interlayer bonding. The interlayer | bonding refers to the mechanical strength or stability between the individual deposited | layers of build material that set up the workpiece. It is desirable to have a strong inter- | layer bonding in order to achieve workpieces having increased stability. The interlayer | bonding is mainly influenced by the interdiffusion of the polymer chains between the || layers. In FLM usually an interlayer strength between subsequent layers is weaker than | the strength within the layer. In other words, parts printed with FLM usually exhibit a | higher level of strength in the x/y- direction than in the z-direction. Conventional work- | pieces printed with FLM therefore exhibit anisotropic properties. |

[0006] The interlayer bonding is also influenced by wetting. In terms of conventional | FLM-3D-printing, wetting does not have a significant influence on the interlayer bond- | ing because of the high cooling rates of the molten material exiting the nozzle and A therefore a direct increasing of the material's viscosity. The present application also | increases the wetting of the previously printed layer and thus activates an additional : bonding mechanism. |

[0007] The interlayer bonding is also influenced by the number, size and shape of | voids. These voids are created during the deposition of the build material and essen- | tially are empty spaces between adjacent strands of deposited build material (see fig. | attached). The size, shape and number of voids are dependent on various factors | among which there are the shape (of a cross section) of the material opening, the . viscosity of the build material being deposited, etc. .

[0008] The application of a liquid ink alternating with the application of build material | is known from US 2014 162 033 A1. |

[0009] It is the object of the present application to improve said interlayer bonding. Ê Selected embodiments are comprised in the dependent claims. Each of which, alone | or in any combination with the other dependent claims, can represent an embodiment ; of the present application. |

LU101897 |

[0010] According to one aspect of the present application a 3D-printing system com- | prises a nozzle and a dispensing unit. The nozzle is configured to deposit build material | and the dispensing unit is configured to controllably dispense a reactive agent at least | partially onto the build material and/or onto deposited material in an intersection area | in which a nozzle axis intersects with a build plane. This may have the advantage that | the different layers of build material have an increased interlayer bonding due to a | reaction of the reactive agent and the build material. This may also have the advantage | that there are less voids. Further, this may also have the advantage that a surface of | the workpiece is smoother, i.e. the individual deposited strands of build material are | less distinguishable from each other. .

[0011] The dispensing unit controllably dispenses the reactive agent. This may be a | simple on/off control or a flow rate-controlled dispensing to achieve a variable flow rate . of the dispensed reactive agent. The control of the dispensing may inter alia be de- | pendent at least on one of a position in the printing trajectory, the type of build material, | a feeding rate, a cross section of a material opening of the nozzle, a feed rate of the | build material, ambient temperature. Also, the temperature of the reactive agent may | be controlled and/or detected. Further, the reactive agent is conveyed through the 3D- | printing system to the dispensing unit and may serve as a cooling to sections of the , 3D-printing system like heat sinks or a cold end on the way there. |

[0012] The nozzle and/or the material opening have a nozzle axis that passes through | the nozzle and material opening essentially in what is commonly known as the Z-di- | rection of 3D-printers. The nozzle axis intersects with the build plane. That is the top | surface of the already deposited strands of build material. Hence, with each layer that | is deposited or printed, the build plane moves up in the Z-direction. Commonly, the . build plane is parallel to a plane spanned by the X- and Y-direction of the 3D-printer. | Of course, this only is true if one is to regard a very small detail of a printed workpiece | as these on a macro level of course exhibit surfaces that are not only parallel to the | coordinate system of the 3D printer. The deposited material is build material that was . earlier deposited through the material opening. .

LU101897 |

[0013] The reactive agent is to be selected dependent on the build materials that is to | be printed. The reactive agent or solvent allows an improved interdiffusion of polymer | chains and thus causing an increased interlayer bonding. The reactive agent also im- | proves wetting. For example in the case of PVA (PVOH) being the build material, the | reactive agent can be water. Examples of other plastic materials and their possible | solvents are listed and separately disclosed in fig. 1, of course the present application | is not limited thereto. As a general rule, polymers dissolve most readily in solvents with | similar polarity — polar polymers in polar solvents and nonpolar polymers in nonpolar | solvents. |

[0014] The reactive agent aides in increasing the wetting/wettability of the dispensed | build material by keeping the disposed built material longer in a flowable state and thus | increase the wetting and thus the interlayer bonding. The ratio between adhesive and A cohesive forces increases. The increased wettability results in an increased interdiffu- | sion and hence an increased interlayer bonding. |

[0015] According to another aspect of the present application the dispensing unit |! comprises a peripheral nozzle that may at least partially surround the material opening | and/or the nozzle. This may have the advantage that build material leaving the nozzle . (being deposited) is at least partially coated with the reactive agent while being depos- | ited. |

[0016] According to another aspect of the present application the dispensing unit is | configured to rotate with respect to at least a section of the 3D-printing system. Said | section may be a part of the 3D-printing system like a fixture attaching the 3D-printing | system to a commonly known gantry system. In other words, in an initial system in | which the 3D-printing system is considered static, the dispensing unit rotates with re- | spect to the 3D-printing system. This may have the advantage that the dispensing unit | can be placed in the best possible position regarding the 3D-printing system and/or the | printing trajectory. The dispensing unit may rotate together with the nozzle having the | material opening or independently from the nozzle. In other words, the dispensing unit | and the nozzle are rotating together, the dispensing unit and the nozzle are both sep- . arately rotatable or only the dispensing unit is rotatable. :

LU101897 |

[0017] According to another aspect of the present application the dispensing unit | comprises a diffuser nozzle. This may have the advantage that a reduced amount of | the reactive agent is needed to sufficiently cover a given area of the build material. | Further, this may have the advantage that the reactive agent may easier reach difficult | geometries in the workpiece. Also, the reactive agent may be applied to a larger area. | Further, the deposition of the reactive agent is more uniform. |

[0018] According to another aspect of the present application the 3D-printing system | comprises an FLM-3D-printhead. This may have the advantage that the 3D-printing | system may be used to efficiently produce workpieces. |

[0019] According to another aspect of the present application the 3D-printing system . comprises a material opening of the nozzle that has a slit or rhomboid cross section. | This may have the advantage that the reactive agent more efficiently covers the de- . posited build material. Further, this may have the advantage that voids between de- | posited strands of the build material are further reduced. Further, this may have the | advantage that the deposited strand of build material has a larger surface on which the : reactive agent is applied. In other words, more reactive agent may react with more | surface and thus increasing the interlayer bonding. |

[0020] According to another aspect of the present application the nozzle is configured . to rotate with respect to at least a section of the 3D-printing system. Said section may | be a part of the 3D-printing system like a fixture attaching the 3D-printing system to a ' commonly known gantry system. In other words, in an initial system in which the 3D- ‘ printing system is considered static, the nozzle rotates with respect to the 3D-printing | system. This may have the advantage that the build material being deposited by the | nozzle may be orientated in e.g. a favourable orientation along the respective printing | trajectory and/or the 3D-printing system. |

[0021] According to another aspect of the present application the dispensing unit . comprises capillary and/or sponge material. This may have the advantage that the re- | active agent may be applied in a precise area. The capillary material may be any type | of liquid guiding material. .

LU101897 |

[0022] According to another aspect of the present application the dispensing unit | and/or the diffuser nozzle may be arranged angled or tilted with respect to the nozzle | axis. In other words, the dispensing unit and/or the diffuser nozzle may be not parallel | to the nozzle axis. This may have the advantage that the reactive agent may be di- | rected towards the nozzle axis and thus the intersection area. The angle of the dis- | pensing unit and/or the diffuser nozzle may be controllable. |

[0023] According to another aspect of the present application a 3D-Printer comprises | any of the aforementioned 3D-printing systems. This may have the advantage that a | 3D printer is obtained that produces work pieces with increased stability. |

[0024] According to another aspect of the present application a 3D-printing method is | disclosed. According to said method a nozzle is moved along a printing trajectory and | a reactive agent is applied to already deposited build material and/or build material | being deposited (leaving the nozzle). This may have the advantage that the bond be- | tween deposited strands of build material is increased. |

[0025] According to another aspect of the present application a 3D-printing method is | disclosed wherein a dispensing unit is controlled to follow the printing trajectory. This | may have the advantage that the dispersion of a reactive agent by means of the dis- . pensing unit might be controlled in a favourable manner. .

[0026] According to another aspect of the present application a 3D-printing method is | disclosed wherein said dispensing unit is controlled to precede the nozzle on the print- . ing trajectory. This may have the advantage that the dispensing unit can be positioned . in an optimal position with respect to the position of the nozzle and the printing trajec- |

[0027] According to another aspect of the present application a 3D-printing method is | disclosed wherein the reactive agent is at least partially enwrapping the build material | deposited by the nozzle. This may have the advantage that the coating of the build | material with the reactive agent may be improved. |

LU101897 |

[0028] According to another aspect of the present application a 3D-printing method is | disclosed wherein the nozzle is rotated depending on a position of the nozzle on the Ë printing trajectory. This may have the advantage that the nozzle can be positioned in | an optimal position with respect to the position of the nozzle on the printing trajectory. |

[0029] Each of the above aspects is to be considered an invention on its own. The | aspects may be freely combined with each other and each feature not described as | being dependent on another feature may also be freely combined with each other. The | features of the disclosed method may be incorporated into the apparatus and vice A versa. |

[0030] Further advantages and features of the present disclosure will be apparent . from the appended figure. The figure is of merely informing purpose and not of limiting | character. The figure schematically describes an embodiment of the present applica- . tion. Hence, the appended figures cannot be considered limiting for e.g. the dimen- | sions of the present disclosure. |

[0031] Figure 1 shows a table with plastic materials and possible solvents or reactive | agents. |

[0032] Figure 2 schematically shows a first embodiment. |

[0033] Figure 3 schematically shows a second embodiment. |

[0034] Figure 4 schematically shows a third embodiment. :

[0035] Figures 5A to 5C show different examples of cross sections of a material open- |

[0036] Figures 6A and 6B show different situations regarding voids. Î

LU101897 |

[0037] It is to be noted that in the different embodiments described herein same | parts/elements are numbered with same reference signs, however, the disclosure in | the detailed description may be applied to all parts/elements having the regarding ref- | erence signs. Also, the directional terms / position indicating terms chosen in this de- | scription like up, upper, down, lower downwards, lateral, sideward are referring to the | directly described figure and may correspondingly be applied to the new position after | a change in position or another depicted position in another figure. |

[0038] Initially referring to figure 1 a table of plastic materials and possible solvents or | reactive agents is listed. Whenever the solvent is suitable for the material, there is a | grey square in the pairing. The 3D-printing system and method disclosed here is con- | figured to work with all possible pairings in figure 1, however, is not limited thereto. Any | thermoplastic material and respective suitable solvent may be used. Ë

[0039] Referring to figure 2 a first embodiment of the present application is depicted. | A 3D-printing system 10 comprises a nozzle 20 having a material opening 21, a dis- | pensing unit 30 configured to controllably dispense a reactive agent 40. The build ma- | terial 50 is extruded, or more generally, exits the nozzle 20 via the material opening |

21. The build material 50 is deposited onto a build surface or already deposited | strand(s) of build material 130. The 3D-printing system 10 moves along a print trajec- ; tory PT to form the layers of a workpiece as this is commonly known. The nozzle 20 | has a nozzle axis A. The nozzle axis A usually is the middle axis or symmetric axis of | a cross section of the material opening 21. The nozzle axis A passes perpendicular | trough the material opening 21 and intersects with a build plane B. The build plane B . is conventionally the top surface plane of the already deposited strands of material |

130. That is, with each deposited layer the build plane moves up (commonly the Z- . direction on a 3D-printer). |

[0040] The dispensing unit 30 moves ahead of the nozzle 20 on the print trajectory | PT and dispenses the reactive agent 40. The reactive agent 40 is depicted as droplets ) but the present disclosure Is not limited thereto. The reactive agent 40 may also be à 8 .

LU101897 | deposited in a thin jet or a spray. The reactive agent 40 at least partially covers the | deposited strands 130 ahead of the build material 50 that exits the material opening | 21 before an area where the nozzle axis A intersects with the build plane B. If the | dispensing unit 30 is moved closer to the nozzle 20 and/or the dispensed reactive | agent 40 is directed towards the nozzle 20, the reactive agent 40 is applied in an area | in which the nozzle axis A intersects with the build plane B. |

[0041] The build material 50 is deposited onto the reactive agent 40 at least partially | covering the deposited strands 130. The deposited build material 50 reacts with the | reactive agent 50 and the deposited strands 130 in the reaction zone 110. This forms | the bond (interlayer bonding) between the build material 50 and the deposited strands | 130 in the bonded area 120. The build material 50 turns in the reaction zone 110 into | a further deposited strand 130. |

[0042] Referring to figure 3 a second embodiment of the present application is de- | picted. The depicted 3D-printing system 11 corresponds to the 3D-printing system 10 a of figure 2 but for the dispensing unit. Here, the 3D-printing system 11 comprises a | dispensing unit 30 having a diffuser nozzle 31. |

[0043] The diffuser nozzle 31 defuses or sprays the reactive agent 40 as a reactive . agent spray 41 onto the deposited strands 130. There, the reactive agent 40 at least | partially covers the deposited strands 130 and may also accumulate there. Corre- | sponding to the first embodiment, the build material 50 is deposited onto the deposited | strands 130 at least partially covered with the reactive agent 40, reacts in the reaction | zone 110 and turns into also a deposited strand 130 in and after the bonding zone 130. ‘ The reactive agent spray 41 may not only be applied to the deposited strands 130 but . also to the build material 50 exiting the nozzle 20. The reactive agent spray 41 is ap- . plied before (in the sense of the printing trajectory PT) the nozzle axis A and an inter- ; section area of the nozzle axis À and the build plane B. |

[0044] Referring to figure 4 a third embodiment of the present application is depicted. / The depicted 3D-printing system 12 comprises, corresponding to the prior embodi- ; ments, a nozzle 20 having a material opening 21 through which the build material 50 ‘ is deposited and a nozzle axis A. The 3D-printing system 12 moves along a printing |

LU101897 | trajectory PT. Here however, a dispensing unit 30 comprising a peripheral nozzle 31 | at least partially surrounding the nozzle 20 and the material opening 21. Accordingly, | the reactive agent 40 covers at least partially the build material 50 exiting the material | opening 21 and thus is applied in an intersection area between the nozzle axis À and | the build plane B. In the depicted embodiment of fig. 4 the reactive agent 40 completely | surrounds the build material 50 exiting the material opening 21. |

[0045] Corresponding to the prior embodiments, there is a reaction area 110 that is | followed by the bonding area 120. Here also, the deposited build material 50 covered | in the reactive agent 40 turns into a deposited strand 130. However, the reactive agent | 40 in the reaction area 110, in particular on the upper surface 110a of the reaction area | 110, the deposited build material 50 may at least partially remain covered in reactive , agent 40 since the build material 50 is entirely covered. This may have the advantage, | that at a subsequent pass of the 3D-printing system 12 there may be still a rest of the | reactive agent 40 that aides in increasing the interlayer bonding of this subsequent | pass or layer of build material. Also, in the previous both embodiments, there may be | reactive agent 40 that is applicated to deposited strands 130 that are not yet in the | printing trajectory since there may be deposited strands 130 horizontally parallel to À each other. |

[0046] The diffuser nozzle may be applied to the third embodiment as well. In this | alternative the build material 50 is covered in reactive agent spray. This also has the | advantage, that the build material 50 exiting the material opening 21 is at least partially | covered with the reactive agent 40 but also the deposited strand(s) 130. °

[0047] Figs. 5A to 5C show different possible shapes of the material opening 21 of | the nozzle 20. Each shape is depicted in a bottom view in the respective upper part of | the figure and in a perspective view in the respective lower part of the figure. Fig. 5A ' depicts a nozzle 20 having a round or circular material opening 21. The material open- | ing 21 of fig. 5A may also be elliptic. Fig. 5B depicts a nozzle 20 having a rhomboid | material opening 21. Fig. 5C depicts a nozzle 20 having a rectangular or slit material Ë opening 21. The material openings 21 of figs. 5B and 5C are depicted having sharp ; corners, however, at least one corner may be rounded. | ;

LU101897 |

[0048] Figs. GA and 6B schematically depict different situations regarding voids 140 | between the deposited strands 130 and also different sizes of bonded areas. In fig. 6A À conventional deposited strands 130 with their respective bonding zones 120 there- | between are depicted. À conventional deposition in this case means that a conven- | tional nozzle having circular material opening was used to deposit the strands of ma- | terial 130. Consequently, the deposited strands 130 exhibit on the one hand a relatively | small bonding or contact zone 120 between the individual strands and on the other | hand a relatively large void 140 between the deposited strands 130 since the deposited | material essentially does not spread from its deposited form due to a low wetting. The | low wetting is also a reason for the relatively small bonding zone 120. |

[0049] Fig. 6B depicts deposited strands 130 that where deposited using the applica- | tion of reactive agent. The use of the reactive agent increases the wettability and thus | the size of the bonded areas 120. Also, the void 120 between the deposited strands | 130 is considerably smaller compared to Fig. 6A. Consequently, the interlayer bonding 2 between the deposited strands in Fig. 6B is considerably higher than in Fig. 6A. The | deposited strands in Figs 6A and 6B result from the same circular cross section of the | material opening. The more rectangular shape and the reduction of voids in fig. 6B È results from the increased wettability and thus interdiffusion. .

[0050] In all figures like reference sings are used for like or similar parts/elements as | in the other figures. Thus, a detailed explanation of such part/element will only be given | one for the sake of brevity. The extraction openings and nozzle openings may have . any shape that is desired and/or needed. The nozzle openings throughout the entire | disclosure may be configured to have a variable emitting characteristic. In figs. 2 and . 3 the diffuser nozzle 31 and dispensing unit 30 are depicted to be parallel to the nozzle : axis A. However, the diffuser nozzle 31 and/or dispensing unit 30 may be angled or . tilted towards the nozzle axis A. Hence, the reactive agent is directed towards the noz- | Zle axis A. An angled diffuser nozzle and/or an angled dispensing unit may help to ; better direct the reactive agent. ;

[0051] The embodiments depict possible variations of carrying out the subject matter , of the application, however, it is to be noted that the subject matter of the application :

LU101897 | is not limited to the depicted embodiments/variations but numerous combinations of | the here described embodiments/variations are possible and these combinations lie in | the field of the skills of the person skilled in the art being motivated by this description. |

[0052] The scope of protection is determined by the appended claims. The description | and drawings, however, are to be considered when interpreting the claims. Single fea- | tures or feature combinations of the described and/or depicted features may represent | independent inventive solutions. The object of the independent solutions may be found | in the description. |

[0053] All notations of ranges of values in the present description are to be understood | as to also comprise and disclose all arbitrary sub-ranges therein, e.g. the disclosure 1 | to 10 is to be understood that all sub-ranges starting from the lower limit 1up to the | upper limit 10 are also comprised and disclosed, i.e. all sub-ranges starting with a lower | limit of 1 or bigger and end with an upper limit of 10 or smaller, e.g. 1 to 1,7, or 3,2 to | 8,1, or 5,5 to 10. Only one digit after the comma is described, however the same ap- . plies mutates mutandis to any given number of digits after the comma. .

[0054] It is further to be noted that for a better understanding parts/elements are de- . picted to some extend not to scale and/or enlarged and/or down scaled. ë

Claims

| A2020/09011-LU-00 | LU101897 | 1. 3D-printing system (10, 11, 12) comprising a nozzle (20) and a dispensing unit | (30), wherein the nozzle is configured to deposit build material (50) and the dispens- | 5 ing unit is configured to controllably dispense a reactive agent (40) at least partially | onto the build material (30) and/or onto deposited material (130) in or before an inter- | section area in which a nozzle axis (A) intersects with a build plane (B).
| 2. 3D-printing system (12) according to claim 1, wherein the dispensing unit (30) | 10 comprises a peripheral nozzle (32) at least partially surrounding the material opening | (21) and/or nozzle 20, | 3. 3D-printing system (10, 11, 12) according to one of claims 1 and 2, wherein the dispensing unit (30) is configured to rotate with respect to at least a section of the | 15 3D-printing system.
| 4. 3D-printing system (11, 12) according to the preceding claims, wherein the | dispensing unit (30) comprises a diffuser nozzle (31).
| 20 5. 3D-printing system (11, 12) according to the preceding claims, wherein the | dispensing unit (30) and/or the diffuser nozzle (31) are arranged angled with respect | to the nozzle axis (A).
| 6. 3D-printing system (10, 11, 12) according to any of the preceding claims, | 25 wherein the 3D-printing system (10) comprises an FLM-3D-printhead.
| 7. 3D-printing system (10, 11, 12) according to any of the preceding claims, wherein a material opening (21) of the nozzle (20) has a slit or rhomboid cross sec- | tion.
| 30 | 8. 3D-printing system (10, 11, 12) according to any of the preceding claims, | wherein the nozzle (20) is configured to rotate with respect to at least a section of the | 3D-printing system.
A2020/09011-LU-00 LU101897
9. 3D-printing system (10, 11, 12) according to any of the preceding claims, wherein the dispensing unit (30) comprises capillary and/or sponge material.
10. 3D-Printer comprising a 3D-printing system (10, 11, 12) according the preced- ing claims.
11. 3D-printing method, wherein a nozzle (20) is moved along a printing trajectory (PT) and a reactive agent (40) is controllably applied to deposited material (130) and/or build material (50) being deposited.
12. 3D-printing method according to claim 10, wherein a dispensing unit (30) is controlled to follow the printing trajectory (PT).
13. 3D-printing method according to claim 11, wherein the dispensing unit (30) is | controlled to precede the nozzle (20) on the printing trajectory (PT). |
14. 3D-printing method according to claim 10, wherein the build material (50) de- | posited by the nozzle (20) is at least partially enwrapped with the reactive agent (40). |
15. 3D-printing method according to any of claims 10 to 12, wherein the nozzle | (20) is rotated depending on a position of the nozzle on the printing trajectory (PT). | 15