NL2032639B1

NL2032639B1 - Method of printing a three-dimensional (3D) object with an FFF system

Info

Publication number: NL2032639B1
Application number: NL2032639A
Authority: NL
Inventors: Kuipers Tim
Original assignee: Ultimaker Bv
Priority date: 2022-07-29
Filing date: 2022-07-29
Publication date: 2024-02-06

Abstract

A method of printing a three-dimensional (3D) object with an FFF system is described. The method comprises printing at least a part of a first layer ofthe 3D object on a build surface ofthe 5 FFF system, and purging of an amount of print material after some or all parts ofthe ﬁrst layer are printed. By performing purge actions during the printing ofthe ﬁrst layer, the risk of printing an object with the so-called elephant foot is avoided. Figure 1 10

Description

Method of printing a three-dimensional (3D) object with an FFF system

Field of the invention

The present invention relates to a method of printing a three-dimensional (3D) object with a Fused Filament Fabrication (FFF) system. The invention also relates to a method of generating instructions for printing three-dimensional (3D) objects with an FFF system. The invention also relates to a computing device arranged to perform the method of generating instructions and to a computer program product.

Background art

Fused Filament Fabrication (FFF) is a 3D printing process that uses a filament of a thermoplastic material. Filament is fed from a filament supply through a moving, heated print head, and is deposited through a print nozzle onto an upper surface of a build plate. The print head may be moved relative to the build plate under computer control to define a printed shape.

In certain FFF devices, the print head moves in two dimensions to deposit one horizontal plane, or layer, at a time. The work or the print head is then moved vertically by a small amount to begin a new layer. In this way a 3D printed object can be produced made out of a thermoplastic material.

Although very much wanted, the upper surface of the build plate of most current FFF systems is not completely flat. To avoid any printing issues during printing, the build plate surface needs to be measured before printing. The measurement can be performed using contactless or contacting bed level sensors. The measurements can be performed at a plurality of locations on the surface, so as to produce a height map. This height map will be used by the FFF system to correct the Z value of the first deposited layer.

Due to inaccuracy in the bed level measurements, the first layer can either be deposited with too much space or too little space between the nozzle and the build surface, leading to under extrusion or over extrusion respectively.

Too much under extrusion can cause printed traces to stick to the nozzle rather than staying on their place on the build plate. Moreover it could lead to adhesion issues. On the other hand, over extrusion can cause material to bulge out over the top of the first layer, which can cause subsequent layers to be too wide. Moreover, over extrusion leads to a build-up of pressure in the system, which can only be released in consecutive layers. This can cause the first couple of layers to be wider than the CAD model, which is commonly known as the elephant’s foot.

Summary of the invention

The aim of the present invention is to provide a method of printing a three-dimensional (3D) object with an FFF system that overcomes at least one of the problems of the state of the art as mentioned above.

According to a first aspect of the present invention, there is provided a method of printing a three-dimensional (3D) object with an FFF system, the method comprising:

- printing at least a part of a first layer of the 3D object on a build surface of the FFF system; - purging of an amount of print material after some or all parts of the first layer are printed.

The invention relates to a method of printing the first layer in order to mitigate the issues which arise due to over extrusion caused by inaccuracy of the Z positioning of the nozzle with reference to the build surface. The method provides for more accurate first layers, while better controlling the adhesion to, and release from, the build surface. Also the risk of the elephant’s foot, commonly experienced when having over extrusion on the first layer, is minimized.

In an embodiment, the purging is performed directly after printing the end of the first layer.

In this manner, the whole first layer of the object is printed before a possible overpressure is released by means of a purge action. In this way a next layer can be started without having any overpressure in the print head, also decreasing the risk of the elephant’s foot.

In an embodiment, the purging is performed during the printing of the traces which make up the first layer.

In an embodiment, the purging of an amount comprises printing one or more purge traces. At least one of the one or more purge traces may be printed distant from to the first layer of the 3D object. In this case, the pure lines are printed next to the object and are not part of the object. These distant purge traces are also referred to as ‘sacrificial traces’.

Alternatively, or additionally, at least one of the one or more purge traces is printed in an open reserved area not yet printed in the first layer of the 3D object. This embodiment avoids or decreases the number of sacrificial traces, reducing the amount of printed material.

At least one of the one or more purge traces may be printed as part of an infill of the first layer of the 3D object, without performing any travel moves of the nozzle. By avoiding travel moves for the purge actions, the print time is reduced.

In an embodiment, the purging of an amount comprises purging a blob on the build surface. It is noted that this blob is purged during the printing of the first layer or just after having finished the first layer. This purge blob is different from the blob normally printed before a print is started, which could be regarded as a ‘prime blob’.

In an embodiment, the purging of an amount comprises printing at least a part of a skirt around the first layer of the 3D object.

In an embodiment, the purging of an amount is executed every time after a predetermined amount of material in the first layer of the 3D object has been extruded. So for example, every time after extruding X amount of material in the first layer of the object, the print head is moved over to a purging location and extrudes one or more purges traces.

In an embodiment, the purging of an amount is executed every time after a predetermined amount of material in the first layer of the 3D object has been extruded, but only when certain traces are completed. In this way, the actual amount of material extruded can be slightly different from the setting value X, when we require that print traces such as walls, should be fully finished before doing a purge action. Such a requirement would lead to better visual quality because interrupting a wall line in the middle would lead to defects, commonly known as the seam.

In an embodiment, the part of the first layer of the 3D object is printed on the build surface of the FFF system using over extrusion. By willingly using over extrusion we will ensure that the initial layer is not under extruded. Such under extrusion could cause bad build surface adhesion, increasing the risk of release of the layer from the build surface.

The invention also relates to a method of generating instructions for an FFF system, the method comprising: - receiving a 3D model of a 3D object; - generating instructions for the FFF system to print at least a part of first layer of the 3D object on a build surface of the FFF system, and to purge of an amount of print material after some or all parts of the first layer are printed.

The invention also relates to a computing device comprising one or more processing units, the one or more processing units being arranged to perform the method as described above.

The invention also relates to a computer program product comprising code embodied on computer-readable storage and configured so as when run on one or more processing units to perform the described method of generating instructions.

Brief description of the drawings

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings,

Figure 1 schematically shows a flow chart for a method of printing a three-dimensional (3D) object with an FFF system according to an embodiment of the invention;

Figure 2 shows a part of slicer preview made by a software program according to an embodiment of the invention;

Figure 3 shows a part of slicer preview made by a slicing software program according to another embodiment of the invention;

Figure 4 shows a part of a slicer preview which is produced using a method according to a further embodiment;

Figure 5 schematically shows a computing device according to an embodiment;

Figure 6 schematically shows an example of an FFF device, also referred to as the 3D printer, and

Figure 7 is a flow chart of a method of generating instructions for an additive manufacturing system to print a 3D object, according to an embodiment.

It should be noted that items which have the same reference numbers in different Figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

Detailed description of embodiments

In the description below the word ‘line’ is used to refer to a planned toolpath calculated by a slicing software program, whereas the word ‘trace’ is used to refer to a printed trace actually printed by an FFF system.

Figure 1 schematically shows a flow chart for a method 100 of printing a three- dimensional (3D) object with an FFF system according to an embodiment of the invention. The method 100 comprises printing 101 at least a part of a first layer of the 3D object on a build surface of the FFF system, and purging 102 of an amount of print material after some or all parts of the first layer are printed.

The purging may be performed directly after printing the end of the first layer. During the printing of the first layer, a pressure may be built up in the liquefier of the printing system. This pressure is released due to the purging of material. Instead of purging at the end of the first layer, the purging can be performed during the printing of the traces which make up the first layer.

In an embodiment, the purging comprises printing one or more purge traces. The one or more purge traces may be printed distant from to the first layer of the 3D object.

Figure 2 shows a part 1 of slicer preview made by a software program according to an embodiment of the invention. In this example, the slicing software prepares for a print of the well known ‘3DBenchy’, designed and licensed under a Creative Commons License by the company

Creative Tools Sweden AB. Figure 2 is a top view of a first layer comprising a number of print lines that are calculated by the slicing software program.

The first layer 2 of the object comprises a shell line 21 (also referred to as outer wall line) and two inner wall lines 22, 23. In this example, the first layer comprises a number of cavities, see for example cavities 25 and 26, which cavities result in a certain sign visible from the bottom side once the object is finished and removed from the build surface. Cavity 25 is enclosed by a shell line 27 and two inner wall lines 28, 29. The area between the inner lines 23 and the inner lines 29 is filled by a number of infill lines 24 (see white lines).

The preview of Figure 2 also shows a number of purge lines 3. During the printing of the first layer 2 of the object, these purge lines are printed. For example, after the standard print preparation and purging procedure, the nozzle will first move to a location 50 where deposition starts to print the shell line 21. Once the nozzle arrives back at location 50, it will temporarily stop with printing the first layer of the object, and will move to a location 51 to print a purge line 31 first.

Once the purge line 31 is finished, the nozzle will move to a location 52 to continue printing, in this case a shell line 27 enclosing a letter ‘C’ in the bottom of the object. Due to the intermediate purging operation, a possible overpressure in the print head will be released, and the next shell line will not be over extruded.

It is noted that most of the print lines (e.g. 21, 22, 23, 24) in the preview of Figure 2 do not touch each other. However, the resulting printed traces will touch each other so as to form a continuous bottom surface of the object (except for the cavities 25, 26). It is noted that the purge lines 3 do not touch each other, also not after printing. The reason is that freely printed purge lines will better enable the release of the pressure build up in the system.

In order to limit the number of purge lines that could affect the quality of the final object, the order of the initial layer of the 3D object can be optimized. By intermitting purge lines with standard lines in the first layer we can create spaces where the lines being laid down have room for the over extrudate to flow into. Figures 3 and 4 show two such ordering methods for the 5 bottom skin and the walls respectively.

Figure 3 shows a part 1 of slicer preview made by a slicing software program according to another embodiment of the invention. In this example, the slicing software designs additional purge areas 60, 61 in the first layer of the object 2. In this example, the reserved areas 60, 61 are located within the infill pattern 24. In this embodiment, the purge traces are printed in the reserved areas 60, 61 during the first layer of the 3D object. The purge traces are printed each time a certain pressure build up in the system is achieved and are planned accordingly. For each material the moment of purging can depend on printing time, on the amount of printed material, the length of the printed traces, the presence of neighbouring traces or a combination of the aforementioned. To keep the shell trace dimensionally accurate, purge lines will preferably not be planned in the shell. If a purge is needed before the shell is finished it may be planned in an area not designated as shell. In this case a shell trace will be interrupted to purge in an aera planned by the slicer for example an inner wall or as part of the infill.

Figure 4 shows a part 1 of a slicer preview which is produced using a method according to a further embodiment. In the example of Figure 4, the first layer of the object 2 only has one inner wall line, see lines 22 and 28. The preview shows an open area 70 which substantially follows the inner wall lines 22, 28. This results in an open area between the infill pattern 24 and the inner lines 22, 28. The width of the area 70 is such that a purge line can be printed without any limitations for the printed material. So, during the purging, the over pressure in the system can be released. It is noted that preferably, the purge traces are printed in such a way that overpressure is released while the purge traces also contact the neighbouring lines. This will result in a smooth bottom surface of the object, having no unwanted recesses or holes.

The slicing software may plan the order of the different lines in such a way that outer walls are always printed first and with minimal touching/adjacent lines, so that there is minimal chance of pressure build up caused by flow restrictions due to already present traces.

The purging of an amount of print material can alternatively or additionally be achieved by printing at least a part of a skirt around the first layer of the 3D object 2. In the example of Figure 4, the preview also shows three skin lines 80. Part or all of these skirt lines 80 may be designed to function as purge lines to perform a purging action so as to release pressure from the system.

In an embodiment, the purging of an amount comprises purging a blob on the build surface. Figure 6 shows a side view of a purge blob 1021 on a build surface of a build plate 1018.

The purging of the amount of print material may be executed every time after a predetermined amount of material in the first layer of the 3D object has been extruded. By using a filament sensor or a feed rate sensor in a feeder of the system, the amount of filament fed to the nozzle can be measured and compared with the predetermined amount of material. Alternatively,

the slicing software may be arranged to calculate the location in the first layer at which the predetermined amount of print material is expected to be deposited.

The purging may be executed after a predetermined amount of material in the first layer of the 3D object has been extruded, but only when certain traces are completed. In this way, the lines, for example, a shell trace (see corresponding shell line 21 in Figure 2) is finished completely without an unwanted travel move in between the printing of that trace.

In order to increase the adhesion on the first layer with a given uncertainty of the bed position, according to an embodiment, the part of the first layer of the 3D object is printed on the build surface of the FFF system using over extrusion. In that way, even if the bed is farther from the nozzle than the system thinks it is, there will not be under extrusion.

Figure 5 schematically shows a computing device 500 according to an embodiment. The device 500 comprises one or more processing units 511, an I/O interface 512 and a memory 513.

The processing unit 511 is arranged to read and write data and computer instructions from the memory 513. The processing units 511 may also be arranged to communicate with sensors and other equipment via the I/O interface 512. The computing device 500 may also comprise an interface 514 arranged to communicate with other devices via a LAN or WAN (not shown). Figure 5 also shows a display 515 which may be connected to the interface 512 so as to show information regarding a slicing process of a 3D object. The memory 513 may comprise a volatile memory such as RAM, or a non-volatile memory such as a ROM memory, or any other type of computer-readable storage. The memory 513 may comprise a computer program product comprising code configured to make the processing units 511 perform one or more of the embodiments of the method as described above.

Figure 6 schematically shows an example of an FFF device 1000, also referred to as the 3D printer 1000. The 3D printer 1000 comprises a print head 1002 also referred to a deposition head 1002. At its outer end the deposition head 1002 comprises a nozzle 1004 where molten filament can leave the deposition head 1002. A filament 1005 is fed into the print head 1002 by means of a feeder 1003. Part of the filament 1005 is stored in a filament storage which could be a spool 1008 rotatably arranged onto a housing (not shown) of the 3D printer, or rotatably arranged within a container (not shown) containing one or more spools. The 3D printer 1000 comprises a controller 1007 arranged to control the feeder 1003 and the movement of the print head 1002, and thus of the nozzle 1004. The controller 1007 may comprise one or more processing units 1070.

By executing suitable instructions on the processing units 1070, the FFF device 1000 may be arranged to perform the method as described with reference to Figure 7. The instructions may comprise G-code produced by the computing device 210 shown in Figure 5.

In this embodiment, the 3D printer further comprises a Bowden tube 1009 arranged to guide the filament 1005 from the feeder 1003 to the print head 1002. The 3D printer 1000 also comprises a gantry arranged to move the print head 1002 at least in one direction, indicated as the X-direction. In this embodiment, the print head 1002 is also movable in a Y-direction perpendicular to the X-direction and the Z-direction. The gantry comprises at least one mechanical driver 1014 and one or more axles 1015 and a print head docking unit 1016. The print head docking unit 1018 holds the print head 1002 and for that reason is also called the print head mount 1016. It is noted that the print head docking unit 1016 may be arranged to hold more than one print head, such as for example two print heads each receiving its own filament. The feeder 1003 is arranged to feed and retract the filament 1005 to and from the print head 1002. The feeder 1003 may be arranged to feed and retract filament at different speeds to be determined by the controller 1007.

A build plate 1018 may be arranged in or under the 3D printer 1000 depending on the type of 3D printer. The build plate 1018 may comprise a glass plate or any other object suitable as a substrate. In the example of Figure 8, the build plate 1018 is movably arranged relative to the print head 1002 in a Z-direction. It is noted that instead of a build plate, other build surfaces may be used such as surfaces of movable belts. Figure 6 also shows a side view of a first layer of a 3D object to be printed. In this example a purge blob 1021 is printed during the printing of the first layer 2. It is noted that more than one purge blob can be printed during the printing of the first layer. Alternatively, purge lines can be printed as was described with reference to Figure 2, 3 and 4.

Figure 7 is a flow chart of a method of generating instructions for an additive manufacturing system to print a 3D object, according to an embodiment. The method 700 comprises receiving 701 a 3D model of a 3D object. The method also comprises generating 702 instructions for the FFF system to print at least a part of first layer of the 3D object on a build surface of the FFF system, and to purge of an amount of print material after some or all parts of the first layer are printed.

In view of the above, the present invention can now be summarized by the following embodiments:

Embodiment 1. A method of printing a three-dimensional (3D) object with an FFF system, the method comprising: - printing at least a part of a first layer of the 3D object on a build surface of the FFF system; - purging of an amount of print material after some or all parts of the first layer are printed.

Embodiment 2. The method according to embodiment 1, wherein the purging is performed directly after printing the end of the first layer.

Embodiment 3. The method according to embodiment 1 or 2, wherein the purging is performed during the printing of the traces which make up the first layer.

Embodiment 4. The method according to any one of the preceding embodiments, wherein the purging of an amount comprises printing one or more purge traces.

Embodiment 5. The method according to embodiment 4, wherein at least one of the one or more purge traces is printed distant from to the first layer of the 3D object.

Embodiment 6. The method according to embodiment 4 or 5, wherein at least one of the one or more purge traces is printed in an open reserved area not yet printed in the first layer of the 3D object.

Embodiment 7. The method according to embodiment 4, 5 or 6, wherein at least one of the one or more purge traces is printed as part of an infill of the first layer of the 3D object, without performing any travel moves of the nozzle.

Embodiment 8. The method according to any one of the preceding embodiments, wherein the purging of an amount comprises purging a blob on the build surface.

Embodiment 9. The method according to any one of the preceding embodiments, wherein the purging of an amount comprises printing at least a part of a skirt around the first layer of the 3D object.

Embodiment 10. The method according to any one of the preceding embodiments, wherein the purging of an amount is executed every time after a predetermined amount of material in the first layer of the 3D object has been extruded.

Embodiment 11. The method according to embodiment 10, wherein the purging of an amount is executed every time after a predetermined amount of material in the first layer of the 3D object has been extruded, but only when certain traces are completed.

Embodiment 12. The method according to any one of the preceding embodiments, wherein the part of the first layer of the 3D object is printed on the build surface of the FFF system using over extrusion.

Embodiment 13. A method of generating instructions for an FFF system, the method comprising: - receiving a 3D model of a 3D object; - generating instructions for the FFF system to print at least a part of first layer of the 3D object on a build surface of the FFF system, and to purge of an amount of print material after some or all parts of the first layer are printed.

Embodiment 14. A computing device comprising one or more processing units, the one or more processing units being arranged to perform the method according to the preceding embodiment.

Embodiment 15. A computer program product comprising code embodied on computer-readable storage and configured so as when run on one or more processing units to perform the method according to embodiment 13.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible and are included in the scope of protection as defined in the appended claims. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CONCLUSIONS

1. Method for printing a three-dimensional (3D) object with an FFF system, the method comprising: - printing (101) at least part of a first layer of the 3D object on a building surface of the FFF -system; - purging (102) an amount of printing material after some or all parts of the first layer have been printed.

Method according to claim 1, characterized in that the purging is carried out immediately after printing the end of the first layer.

Method according to claim 1 or 2, wherein the purging is carried out during printing of the tracks forming the first layer.

4. Method according to any of the preceding claims, wherein purging a quantity comprises printing one or more purging tracks.

Method according to claim 4, wherein at least one of the one or more purgation tracks is printed at a distance from the first layer of the 3D object.

Method according to claim 4 or 5, wherein at least one of the one or more purgation tracks is printed in an open reserved area that has not yet been printed in the first layer of the 3D object.

A method according to claim 4, 5 or 8, wherein at least one of the one or more purgation tracks is printed as part of an infill of the first layer of the 3D object, without performing any non-printing displacement movements of the nozzle feed.

A method according to any one of the preceding claims, wherein purging an amount comprises purging a blob on the build surface.

A method according to any one of the preceding claims, wherein purging an amount comprises printing at least part of a skirt around the first layer of the 3D object.

10. Method according to any one of the preceding claims, wherein the purging of an amount is carried out each time after a predetermined amount of material has been extruded into the first layer of the 3D object.

A method according to claim 10, wherein the purging of an amount is performed every time after a predetermined amount of material has been extruded into the first layer of the 3D object, but only when certain tracks have already been completed.

Method according to any of the preceding claims, wherein the part of the first layer of the 3D object is printed on the building surface of the FFF system by means of over-extrusion.

13. A method for generating instructions for an FFF system, the method comprising: - receiving a 3D model of a 3D object; - generating instructions for the FFF system to print at least part of the first layer of the 3D object on a build surface of the FFF system, and to purge an amount of printing material after some or all parts of the first are printed low.

14. Computing device comprising one or more processing units, wherein the one or more processing units are designed to carry out the method according to the preceding claim.

A computer program product comprising code embodied in computer-readable storage and configured so that, when executed on one or more processing units (511), it performs the method of claim 13.