Extrusion-based additive manufacturing method, 3D printing system, and 3D printed object

Abstract

The present invention relates to a method for reducing the additional printing time of a 3D object (1), the additional printing time being associated with the printing of an outer wall (2) of the 3D object, the outer wall having an outer surface (3) with enhanced smoothness, the outer wall being arranged to surround an inner part (8) of the 3D object, the outer wall comprising at least one region, the at least one region comprising a first outer wall portion (2a) and a second outer wall portion (2b), the first outer wall portion forming an outer surface with enhanced smoothness, the second outer wall portion being arranged between the first outer wall portion and the inner part and providing a low-resolution portion of the outer wall, the low-resolution portion having an outer surface that is less smooth than the first outer wall portion. Thus, the additional printing time associated with printing the outer wall having an outer surface with enhanced smoothness can be reduced. The present invention also relates to a 3D printing system (30) for carrying out the method according to the present invention and a 3D printed object having the outer wall as described above.

Description

[0001] Field of the Invention

[0002] The present invention relates to a method for reducing additional printing time of a 3D object, which additional printing time is related to the printing of an outer wall of the 3D object, which has an outer surface with enhanced smoothness, and the 3D object is manufactured using an extrusion-based additive manufacturing process by stacking primary and secondary layers of a track comprising an extruded raw material.

[0003] The invention further relates to a 3D printing system for manufacturing a 3D object using an extrusion-based additive manufacturing process, the system comprising a processing unit configured to perform the method according to the invention.

[0004] The present invention also relates to 3D printed objects manufactured using an extrusion-based additive manufacturing process.

[0005] Background of the Invention

[0006] In 3D printing using an extrusion-based additive manufacturing process, a 3D object is formed by layering extruded feedstock in a controlled manner so that a desired 3D object can be created. A 3D printing system is typically utilized that includes a print head that is movable in 3D space relative to a build plate while dispensing feedstock onto at least one build plate and onto a previously deposited track of feedstock supported by the build plate. However, a variety of options can be used to relatively move the print head and the build plate that prints the 3D object.

[0007] The 3D printing system includes a control system configured to control a controllable positioning system to which the print head is attached to control the movement of the print head. The pattern of the tool path can be generated by software, and the pattern is used to move the print head and the track for depositing extruded raw materials.

[0008] The 3D object is created in a reference position on the build plate relative to the movable print head, and the raw material can be fused with the previously deposited track. The modeling material can be fed into the print head in the form of, for example, filaments, particles, rods, liquids, resins or suspensions.

[0009] The raw material is dispensed from the print head by a raw material liquefaction unit and deposited on the build plate in the form of tracks that form a track layer, or when a previous layer of the 3D object to be created has been deposited, deposited on previously deposited tracks that are allowed to solidify. The raw material may be thermally fused or chemically fused or otherwise fused with the previously deposited tracks, and the molding material may be dispensed from the print head and deposited on the previously deposited tracks and solidified after deposition.

[0010] The relative movement of the build plate and the 3D object supported thereby with respect to the print head along the track and the simultaneous deposition of material from the print head allows the 3D object to be built and gradually acquire its desired shape with each successive deposition track of material.

[0011] Depending on the application of the 3D printed object obtained by extrusion-based additive manufacturing, in particular the smoothness of the outer surface of the 3D printed object is an important property. The desired smoothness of the outer surface of the 3D printed object can be achieved by choosing an appropriate thickness, as seen in a direction perpendicular to the building plate, of the tracks of the raw material used to constitute the outer surface. A person skilled in the art will understand that by reducing the thickness of the tracks of the raw material, the smoothness of the outer surface of the parts of the 3D printed object that have a non-zero angle relative to the building plate can be improved. However, this comes at the expense of increasing the printing time of the 3D printed object, due to the increased printing time, the 3D printing system used has a lower output and, therefore, the cost of the 3D printed object increases.

[0012] US 2017 / 0151714A1 discloses a 3D printing device, wherein the device is configured to use a building material to form a peripheral wall in multiple layers, the combined multiple layers having a first height, and to form a filling section within the peripheral wall, wherein the filling section is formed to include a single layer and has a second height equal to the first height of the peripheral wall.

[0013] CN106915076A discloses a layer thickness design method suitable for fused deposition modeling. The method specifically includes the following steps: 1) setting design parameters; 2) determining the height range of each surface; 3) determining the length value lj and the minimum inclination angle θj of the height interval; 4) calculating the layer thickness hj in the jth height interval; 5) calculating the layer range in the jth height interval; 6) calculating the minimum number of cycles zmin.j in the jth height interval; 7) calculating the interval coefficient kj for calculating the layer thickness in the jth height interval; 8) correcting the minimum number of cycles zmin.j and the interval coefficient kj in the jth height interval; 9) calculating the layer number Y, the number of cycles Z, and the number of cycles Z' of the inner circle to be filled in the jth height interval. The method disclosed in the present invention has the advantages of being able to relatively reduce printing time and improve molding efficiency.

[0014] Based on the above, there is a need to provide a method that allows providing a 3D object with an outer wall, the outer wall having an outer surface with enhanced smoothness, and wherein the additional printing time associated with the printing of the outer wall can be reduced. Preferably, the additional printing time associated with printing the outer wall can be limited as much as possible.

[0015] Contents of the invention

[0016] The object of the present invention is to provide a method for reducing the additional printing time of a 3D object, which additional printing time is associated with printing the outer wall of the 3D object, which has an outer surface with enhanced smoothness, and the method overcomes or at least reduces at least one of the above-mentioned and / or other disadvantages associated with the known methods in the art for printing a 3D object, which includes an outer wall with an outer surface with enhanced smoothness.

[0017] Another object of the present invention is to provide a 3D printing system comprising a processing unit configured to execute the method according to the present invention.

[0018] Another object of the present invention is to provide a 3D printed object with an outer surface with enhanced smoothness, which is manufactured using an extrusion-based additive manufacturing process. Using the method according to the present invention, the additional printing time associated with printing with an outer surface with enhanced smoothness can be reduced.

[0019] Various aspects of the invention are set out in the accompanying independent and dependent claims, features from the dependent claims may be combined with features from the independent claims as appropriate and not only as explicitly set out in the claims, and furthermore all features may be replaced by other technically equivalent features.

[0020] At least one of the above objects is achieved by providing a method for reducing additional printing time of a 3D object, the additional printing time being associated with printing of an outer wall of the 3D object, the outer wall having an outer surface with enhanced smoothness, the 3D object being manufactured by an extrusion-based additive manufacturing process by stacking a main layer and a sub-layer, the main layer and the sub-layer comprising a track of extruded feedstock, the 3D object comprising an inner portion, the outer wall being arranged to surround the inner portion, the method comprising:

[0021] Acquire a 3D model of the 3D object;

[0022] Slicing the 3D model using a predetermined slice height to determine the number of slices;

[0023] For at least one of the multiple slices:

[0024] Determining the outer boundary of the 3D model;

[0025] Determine whether an inner boundary in the outer wall can be defined to divide the outer wall into a first outer wall portion and a second outer wall portion, wherein the first outer wall portion is arranged to extend between the outer boundary and the inner boundary and is configured to have a sub-layer stacking group, the sub-layer stacking group having a total height equal to a predetermined slice height to form an outer surface with enhanced smoothness; and the second outer wall portion is arranged to extend between the inner boundary and the inner portion and is configured to have a main layer, the main layer having a predetermined main layer height equal to the predetermined slice height, wherein

[0026] In response to determining that a predetermined slice height of a corresponding slice of the plurality of slices is at least as high as a predetermined main layer height, thereby establishing that an inner boundary in the outer wall is definable:

[0027] Positioning the inner boundary at a predetermined distance from the outer boundary, at which distance, corresponding to at least one sublayer of the stack of sublayers, the minimum number of tracks of the first type of extruded material is equal to 1;

[0028] filling at least one sublayer in the first outer wall portion with a track of a first type of track having a predetermined first track height equal to the predetermined sublayer height and being a fraction of the predetermined slice height, and a track width having a minimum value equal to 50% of a nominal track width of the first type of track and a maximum value equal to 200% of the nominal track width of the first type of track, and

[0029] filling said second outer wall portion with said main layer; or

[0030] In response to determining that a predetermined slice height of a corresponding slice of the plurality of slices is less than a predetermined main layer height, thereby determining that an inner boundary in the outer wall is indefinable:

[0031] The outer wall of the corresponding slice is filled with a plurality of sub-layers, wherein each of the plurality of sub-layers has a predetermined sub-layer height that is a fraction of the predetermined slice height.

[0032] Those skilled in the art will appreciate that the gist of the method according to the invention is to divide the outer wall of the 3D object at least partially into a first outer wall portion and a second outer wall portion. In order to be able to divide the outer wall into the first outer wall portion and the second outer wall portion, for each slice of a plurality of slices, it is determined whether an inner boundary in the outer wall can be defined. If the predetermined slice height allows for accommodating the main layer, i.e. if the predetermined slice height is at least as high as the predetermined main layer height, the inner boundary can be defined in the corresponding slice of the plurality of slices. In practice, the predetermined main layer height is selected to be equal to the predetermined slice height of the slice number that has been determined based on the 3D model of the 3D object. Those skilled in the art will appreciate that the corresponding inner boundary of the corresponding slice of the plurality of slices can be oriented at any suitable non-zero angle relative to the corresponding slice of the plurality of slices, as seen in a direction parallel to the corresponding slice. Therefore, it will be clear that the inner boundaries of different slices of the plurality of slices can have different orientations.

[0033] In the case where an inner boundary can be defined in a corresponding slice of a plurality of slices, the outer wall can be divided into the first outer wall portion and the second outer wall portion. The first outer wall portion of the corresponding slice can be filled with a complete sub-layer stacking group, i.e. a sub-layer stacking group having a total height that can be equal to a predetermined slice height. Each sub-layer of the sub-layer stacking group in the first outer wall portion has a predetermined sub-layer height, which is a part of the predetermined slice height. The second outer wall portion of the corresponding slice can be filled with a main layer, which has a predetermined main layer height equal to the predetermined slice height of the corresponding slice. In this way, the outer wall of the 3D object can be at least partially provided with a second outer wall portion, which has a lower smoothness than the outer surface of the 3D object with enhanced smoothness, and therefore has a higher surface roughness. Preferably, an inner boundary can be defined in all slices of the plurality of slices so as to divide the outer wall of each slice into the first outer wall portion and the second outer wall portion. Those skilled in the art will understand that by dividing the outer wall of at least one of the multiple slices into the first outer wall portion and the second outer wall portion, it is not necessary to print the entire outer wall of the 3D object with the same enhanced smoothness of the outer surface of the 3D object, and therefore, the printing time of the 3D object can be reduced.

[0034] If a slice in the plurality of slices has a slice height that is less than the predetermined main layer height, i.e. the corresponding slice cannot accommodate the main layer, then an inner boundary cannot be defined in the corresponding slice. Instead, each slice can be filled with a plurality of sub-layers, wherein each sub-layer in the plurality of sub-layers has a predetermined sub-layer height, which is a portion of the predetermined slice height. Those skilled in the art will appreciate that each sub-layer in the plurality of sub-layers and each sub-layer of the stacked group of sub-layers in the first outer wall portion typically has a predetermined sub-layer height, which is the same portion of the predetermined slice height. In this way, an outer surface with enhanced smoothness of the 3D object as a whole can still be achieved.

[0035] A person skilled in the art will appreciate that the method according to the present invention can not only reduce the additional printing time of a 3D object associated with the printing of an outer surface with enhanced smoothness, but can also be used to reduce the total printing time of a 3D object having an outer surface with a predetermined smoothness, which already meets the requirements of a specific application. The latter is achieved by providing at least one slice of a determinable number of slices for a 3D model of a 3D object having a first outer wall portion and a second outer wall portion, wherein the first outer wall portion has an enhanced smoothness compared to the second outer wall portion. Therefore, the method according to the present invention can reduce the additional printing time of a 3D object associated with the printing of an outer surface of a 3D object, wherein the outer surface has an enhanced smoothness. Alternatively, if the outer surface already has an appropriate smoothness, the method according to the present invention can reduce the printing time of the 3D object.

[0036] Those skilled in the art will appreciate that it is also possible that each of the plurality of sub-layers has a predetermined sub-layer height, which is a first portion of the predetermined slice height, and each sub-layer of the stacked group of sub-layers in the first outer wall portion has a predetermined sub-layer height, which is a second portion of the predetermined slice height, wherein the first portion and the second portion are not the same. In this case, a difference in enhanced smoothness of a portion of the outer surface of the 3D object can be achieved.

[0037] In the context of the present invention, a part is interpreted as a part of the whole. Therefore, it should be clear to those skilled in the art that a predetermined sublayer height as a part of the predetermined slice height is interpreted as being smaller than the predetermined slice height, preferably significantly smaller than the predetermined slice height.

[0038] Furthermore, it will be understood by those skilled in the art that, in the context of the present invention, the outer surface of a 3D object is interpreted as any surface that has a boundary with the environment outside the 3D object. For example, if the 3D object is a tube, the surface of the tube wall surrounding the internal passage through the tube will be interpreted as the outer surface of the tube. Of course, the same applies to the surface of the tube wall facing away from the internal passage through the tube, the latter surface being naturally considered as the outer surface.

[0039] Based on the above, an example of a method according to the present invention is a method for reducing additional printing time of a 3D object associated with printing an outer wall of the 3D object, the outer wall having an outer surface with enhanced smoothness, the 3D object being manufactured by an extrusion-based additive manufacturing process by stacking a main layer and a sub-layer comprising a track of extruded raw material, the 3D object comprising an inner part, the outer wall being arranged as an outer wall surrounding the inner part, the method comprising:

[0040] Obtaining a 3D model of the 3D object;

[0041] Slicing the 3D model using a predetermined slice height to determine the number of slices;

[0042] For each slice in the plurality of slices:

[0043] Determining the outer boundary of the 3D model;

[0044] determining whether an inner boundary in the outer wall is definable to divide the outer wall into a first outer wall portion and a second outer wall portion, wherein the first outer wall portion is arranged to extend between the outer boundary and the inner boundary and is configured to form an outer surface of the 3D object with enhanced smoothness, and the second outer wall portion is arranged to extend between the inner boundary and the inner portion, wherein

[0045] In response to determining that an inner boundary in the outer wall is definable for a corresponding slice of the plurality of slices, filling the first outer wall portion with a stacked group of sub-layers having a total height equal to the predetermined slice height, and filling the second outer wall portion with a main layer having a predetermined main layer height equal to the predetermined slice height, wherein each sub-layer of the stacked group of sub-layers has a predetermined sub-layer height, the predetermined sub-layer height being a fraction of the predetermined slice height; or

[0046] In response to determining that an inner boundary in the outer wall of a corresponding slice among the multiple slices is indefinable, the outer wall of the corresponding slice is filled with multiple sub-layers, wherein each sub-layer of the multiple sub-layers has a predetermined sub-layer height, and the predetermined sub-layer height is a portion of the predetermined slice height.

[0047] In an embodiment of the method according to the invention, in the case where the inner boundary in the outer wall is definable, for a respective sublayer, if the distance from the outer boundary to the inner boundary is smaller than the minimum value of the track width of the first type of track, the filling of the respective sublayer of the stack of sublayers is omitted. In this way, the respective sublayer cannot be filled with the first type of track of the extrusion raw material.

[0048] In one example of the method according to the invention, filling a first outer wall portion with a sub-layer stacking group having a total height equal to a predetermined slice height comprises filling at least one sub-layer of the sub-layer stacking group with a minimum number of tracks of the first type of tracks of the extruded raw material, wherein the tracks of the first type of tracks have a predetermined first track height equal to the predetermined sub-layer height.

[0049] In this way, the distance from the outer boundary to the inner boundary of the first outer wall portion of at least one slice in the plurality of slices seen in a direction parallel to the slice can be reduced. Therefore, the inner boundary of the at least one slice can be arranged at a preferred distance from the outer boundary of the 3D model. It will be appreciated by those skilled in the art that, preferably, each sublayer of the sublayer stacking group is provided with a minimum number of tracks of the first type of track of the extruded raw material. As a result, the corresponding length of the first outer wall portion of the corresponding slice in the plurality of slices can be reduced. It will be appreciated by those skilled in the art that if the inner boundary of the corresponding slice in the plurality of slices is at a preferred distance from the corresponding outer boundary of the corresponding slice, the predetermined smoothness of the outer surface of the 3D object that should be achieved can be reduced. Therefore, by positioning the corresponding inner boundary of the corresponding slice in the plurality of slices at a corresponding preferred distance relative to the corresponding outer boundary of the corresponding slice, the additional printing time associated with printing the outer wall of the 3D object with enhanced smoothness (i.e., enhanced resolution or reduced roughness) can be reduced.

[0050] In an embodiment of the method according to the invention, in the case where the inner boundary in the outer wall is definable, for a corresponding sublayer, the distance from the outer boundary to the inner boundary is greater than the maximum value of the track width of the first type of track, then the corresponding sublayer of the sublayer stacking group is filled with at least two tracks of the first type of track, wherein the total width of the at least two tracks is equal to the distance. A person skilled in the art will understand that each of the at least two tracks of the first type of track has a corresponding track width ranging from a minimum value of the track width of the first type of track to a maximum value of the track width of the first type of track.

[0051] In one example of the method according to the invention, filling the first outer wall portion with a stack of sub-layers having a total height equal to the predetermined slice height further comprises: positioning the inner boundary at a predetermined distance from the outer boundary, at which distance, for at least one sub-layer of the stack of sub-layers, a minimum number of tracks of the first type of extruded feedstock is equal to 1. Wherein each track of the first type of tracks has a track width within a range, the range having a lower boundary and an upper boundary, the lower boundary being defined as a minimum percentage of a nominal track width of the first type of tracks, and the upper boundary being defined as a maximum percentage of a nominal track width of the first type of tracks.

[0052] It will be appreciated by those skilled in the art that in this manner, when viewed in a direction parallel to the slice, the distance from the outer boundary to the inner boundary of the first outer wall portion of at least one slice of the plurality of slices can be kept as small as possible. Therefore, the inner boundary of the at least one slice can be arranged at an optimal distance from the outer boundary of the 3D model. It will be appreciated by those skilled in the art that, preferably, each sublayer of the sublayer stacking group is provided with a track of the first type of track of the extruded raw material. As a result, the corresponding distance from the outer boundary to the inner boundary of the corresponding first outer wall portion of all slices of the plurality of slices can be kept as small as possible. It will be appreciated by those skilled in the art that the respective inner boundaries of the respective slices of the plurality of slices are at their optimal distances, because the smoothness enhancement of the outer surface of the 3D object should be achieved, and the first outer wall portion of each enhanced resolution is arranged to be as small as possible. Therefore, by positioning the respective inner boundaries of the respective slices of the plurality of slices at their respective optimal distances relative to the respective outer boundaries of the respective slices, the additional printing time associated with printing the outer wall of the 3D object with enhanced smoothness (i.e., enhanced resolution or reduced roughness) can be reduced as much as possible.

[0053] A person skilled in the art will appreciate that the distance between the outer boundary and the inner boundary may be different for each track of the first type of track of the extruded stock in the first outer wall portion, depending on the shape of the outer boundary of the corresponding slice. It is possible to fill each sublayer of the sublayer stacking group between the outer boundary and the inner boundary with one track of the first type of track, as long as the required track width remains within the above-mentioned range with an upper boundary and a lower boundary, wherein the lower boundary is defined as a minimum percentage of the rated track width of the first type of track, and the upper boundary is defined as a maximum percentage of the rated track width of the first type of track. A person skilled in the art will appreciate that the number of first type of tracks may vary at different positions along the circumference of the first outer wall portion.

[0054] In case the inner boundary in a corresponding slice of the plurality of slices is positioned at a distance closer to the outer boundary than the aforementioned optimal distance of the inner boundary, at least one sublayer of the stacked group of sublayers cannot be provided with a track of the first type of track of the extruded raw material, because such a track must be printed to be smaller than the track width observed in a direction parallel to the slices, i.e. the track width is equal to a minimum percentage of the nominal track width of the first type of track. In case at least one sublayer of the stacked group of sublayers cannot be provided with a track of the first type of track of the extruded raw material, the outer surface of the 3D object cannot have a predetermined smoothness, because the aforementioned type of sublayer cannot be provided with the first type of track of the extruded raw material. Such lack of extruded raw material will make the smoothness of the outer surface of the 3D object less enhanced than desired.

[0055] Furthermore, in the case where the inner boundary in a corresponding slice of the plurality of slices is positioned at a distance further away from the outer boundary than the above-mentioned optimal distance of the inner boundary, a sublayer of the stacked group of sublayers arranged in the first outer wall portion will be provided with a plurality of first type tracks of extruded raw material, because the track width of such tracks observed in a direction parallel to the slices is greater than or equal to the track width of the maximum percentage of the nominal track width of the first type track that can be achieved. A person skilled in the art will understand that in the case where the sublayer of the stacked group of sublayers arranged in the first outer wall portion will be provided with a plurality of first type tracks of extruded raw material, it will be possible to achieve enhanced smoothness of the outer surface of the 3D object. However, the additional printing time associated with printing the first outer wall portion with smoothness enhancement, i.e. enhanced resolution or reduced roughness, will be suboptimal because a track with at least one higher resolution than required and necessary must be printed in the first outer wall portion. Therefore, the cost involved in printing the 3D object will be higher than at least one of the required costs.

[0056] In an embodiment of the method according to the invention, in the case where the inner boundary in the outer wall is definable, the distance from the outer boundary to the inner boundary has a minimum value equal to 50% of the nominal track width of the first type of track and a maximum value equal to 200% of the nominal track width of the first type of track to allow each sublayer of the sublayer stacking group to be filled with one track of the first type of track. In this way, the distance from the outer boundary to the inner boundary through the first outer wall portion, seen in a direction parallel to each sublayer, can be kept as small as possible. Therefore, the additional printing time of the first outer wall portion can be reduced as much as possible, while improving the surface smoothness of the first outer wall portion.

[0057] In an example of the method according to the invention, the minimum percentage of the nominal track width of the first type of track is 50% and the maximum percentage of the nominal track width of the first type of track is 200%.

[0058] A person skilled in the art will appreciate that the minimum percentage of the nominal track width of the first type of track that can be achieved depends, among other things, on the extrusion-based additive manufacturing process used, the geometry of the nozzles of the print head used, and the type of raw material used. The same applies to the maximum percentage of the nominal track width of the first type of track that can be achieved.

[0059] In an embodiment of the method according to the present invention, filling the outer wall of the respective slice with the plurality of sub-layers further comprises:

[0060] filling at least one of the plurality of sub-layers with a minimum number of tracks of a first type of tracks of the extruded stock;

[0061] The minimum number of tracks is one of the following:

[0062] if the outer wall of the at least one sublayer has a width less than a minimum value of the track width of the first type of track, the minimum number of tracks is zero to prevent filling of the at least one sublayer;

[0063] If the width of the outer wall of the at least one sublayer is within the range between a minimum value and a maximum value of the track width of the first type of track, the minimum number of tracks is 1; and

[0064] If the width of the outer wall is larger than the maximum value of the track width of the first type of track, the minimum number of tracks is at least two, wherein the at least two tracks have a total width equal to the width of the outer wall.

[0065] As described above, if a slice of the plurality of slices has a slice height that is less than the predetermined main layer height, i.e., the respective slice cannot accommodate the main layer, then an inner boundary cannot be defined in the respective slice. Instead of dividing the outer wall into the first outer wall portion and the second outer wall portion, the respective slice can be filled with a plurality of sub-layers. Each of the plurality of sub-layers has a predetermined sub-layer height that is a fraction of the predetermined slice height. Those skilled in the art will appreciate that the predetermined main layer height may be different for individual layers. The same considerations apply to the layers having their respective predetermined main layer heights.

[0066] Those skilled in the art will appreciate that by filling at least one of the plurality of sub-layers with a minimum number of tracks of the first type of tracks of the extruded material, the printing time of the corresponding sub-layer can be reduced. As a result, the additional printing time associated with printing an outer surface with enhanced smoothness can be reduced.

[0067] Those skilled in the art will appreciate that preferably each of the plurality of sub-layers is filled with a minimum number of tracks of the first type of tracks of extruded stock as this allows for further reduction of additional printing time associated with printing the smoothness enhanced outer surface.

[0068] In one example of the method according to the invention, filling the outer wall of the respective slice with a plurality of sub-layers further comprises filling at least one of the plurality of sub-layers with a minimum number of tracks of the first type of tracks of the extruded feedstock.

[0069] In an embodiment of the method according to the invention, filling the second outer wall portion with a main layer having a predetermined main layer height equal to the predetermined slice height comprises: providing a second type of track of the extruded feedstock, wherein the second type of track has a predetermined second track height equal to the predetermined main layer height. As mentioned above, a person skilled in the art will understand that the predetermined main layer height may be different for individual layers.

[0070] In addition, those skilled in the art will appreciate that in this manner, it is not necessary to print the entire outer wall of the 3D object with the same enhanced smoothness of the outer surface of the 3D object. Therefore, the additional printing time associated with printing an outer surface with enhanced smoothness can be reduced.

[0071] In one embodiment of the method according to the invention, the inner part is provided with a filling structure comprising a mesh of a main layer comprising tracks of the second type of extruded stock.

[0072] Those skilled in the art will appreciate that in this way the printing time of the inner part can be reduced. This allows reducing the overall printing time of a 3D object having an outer surface with enhanced smoothness.

[0073] In an embodiment of the method according to the invention, the predetermined slice height depends on a desired printing time of the 3D object.

[0074] Those skilled in the art will appreciate that, with a higher predetermined slice height, the printing time of the 3D object will be reduced, as less print head movement is required. Obviously, with a lower predetermined slice height, the printing time of the 3D object will increase, as more print head movement is required.

[0075] In an embodiment of the method according to the invention, the predetermined slice height depends on a desired enhancement value of the smoothness of the outer surface of the 3D object.

[0076] A person skilled in the art will understand that in the case where a higher enhancement value of the smoothness of the outer surface of the 3D object is desired, i.e., the outer surface of the 3D object has a higher resolution and therefore has a lower roughness, a lower predetermined slice height is required. As a result, the printing time of the 3D object will increase as more print head movements are required. Obviously, in the case where a lower enhancement value of the smoothness of the outer surface of the 3D object is desired, i.e., the outer surface of the 3D object has a lower resolution and therefore has a higher roughness, a higher predetermined slice height can be used. Therefore, the printing time of the 3D object will be reduced as fewer print head movements are required.

[0077] In an embodiment of the method according to the invention, the stacked group of sub-layers of the first outer wall portion is arranged in contact with the main layer of the second outer wall portion at said inner boundary.

[0078] Those skilled in the art will appreciate that in this way the stability and integrity of the outer wall as a whole can be ensured.

[0079] In an embodiment of the method according to the invention, the contact at the inner border is free of gaps.

[0080] It should be noted that in the context of the present invention, contact at the inner boundary without voids should be interpreted as contact between the first type of track of the extruded material and the second type of track of the extruded material, wherein the contact does not include any voids. Those skilled in the art will understand that such contact at the inner boundary can improve the stability and integrity of the outer wall as a whole.

[0081] According to another aspect of the present invention, a 3D printing system for manufacturing a 3D object using an extrusion-based additive manufacturing process is provided, the system comprising a processing unit for executing the method according to the present invention.

[0082] Those skilled in the art will appreciate that the processing unit of the 3D printing system according to the present invention is operably connected to all relevant components of the 3D printing system required for printing a 3D object using an extrusion-based additive manufacturing process. Thus, the 3D printing system according to the present invention is used to provide a 3D object with an outer surface having enhanced smoothness while allowing for a reduction in additional printing time associated with printing an outer surface having enhanced smoothness.

[0083] According to another aspect of the present invention, a 3D printed object manufactured using a method according to the present invention is provided. In one example, the 3D printed object includes an outer wall having an outer surface with enhanced smoothness. The 3D printed object is manufactured using an extrusion-based additive manufacturing process, the 3D printed object includes an inner portion, the outer wall is arranged to surround the inner portion, the outer wall includes at least one area, wherein the outer wall includes a first outer wall portion and a second outer wall portion, wherein in at least one area of ​​the outer wall:

[0084] The first outer wall portion is configured to form an outer surface of the 3D printed object having enhanced smoothness;

[0085] The first outer wall portion includes at least one track of a first type of tracks for extruding feedstock, the at least one track of the first type of tracks having a predetermined first track height;

[0086] the second outer wall portion being disposed between the first outer wall portion and the inner portion;

[0087] the second outer wall portion includes at least one track of a second type of tracks for extruding feedstock, the at least one track of the second type of tracks having a predetermined second track height; and

[0088] The predetermined first track height of at least one track of the first type of track is a fraction of the predetermined second track height of at least one track of the second type of track.

[0089] Those skilled in the art will appreciate that by providing a 3D printed object having an outer wall, the outer wall comprising at least one region, wherein the outer wall comprises a first outer wall portion and a second outer wall portion, a 3D printed object having an outer surface with enhanced smoothness can be obtained while allowing for a reduction in the additional printing time associated with printing an outer surface with enhanced smoothness. The first outer wall portion and the second outer wall portion can be observed after forming an appropriate cross section through the 3D printed object. In this way, it can be determined whether the 3D printed object is printed according to the teachings of the present invention.

[0090] In an example of a 3D printed object according to the present invention, in at least one area of ​​the outer wall located at the inner boundary between the first outer wall portion and the second outer wall portion, at least one of the first type of tracks of the extruded raw material of the first outer wall portion and at least one of the second type of tracks of the extruded raw material of the second outer wall portion are in contact with each other without gaps.

[0091] As described above, in the context of the present invention, contact at the inner boundary without voids is interpreted as contact between at least one track of the first type of track of the extruded material and at least one track of the second type of track of the extruded material, wherein the contact does not include any voids. A person skilled in the art will appreciate that such contact at the inner boundary can improve the stability and integrity of the outer wall as a whole.

[0092] In one example of a 3D printed object according to the invention, the inner portion is provided with a filling structure comprising a grid of second type tracks of extruded feedstock.

[0093] A person skilled in the art will appreciate that in this way the printing time of the inner part may be reduced, which allows reducing the overall printing time of a 3D object having an outer surface with enhanced smoothness. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Further features and advantages of the invention will become apparent from the description of the invention by means of exemplary and non-limiting embodiments of a method, a 3D printing system and a 3D printed object according to the invention.

[0095] Those skilled in the art will appreciate that the described embodiments of the method, 3D printing system, and 3D printed object according to the present invention are merely exemplary in nature and are not to be construed as limiting the scope of protection in any way. Those skilled in the art will recognize that alternative and equivalent embodiments of the method, 3D printing system, and 3D printed object may be conceived and reduced to practice without departing from the scope of protection of the present invention.

[0096] Reference will be made to the accompanying drawings in the accompanying drawings. The accompanying drawings are schematic in nature and are not necessarily drawn to scale. In addition, the same reference numerals indicate the same or similar components. In the accompanying drawings,

[0097] Figure 1A shows a schematic cross-sectional view of a first exemplary non-limiting embodiment of a 3D printed object according to the invention, the 3D printed object being obtained by the method according to the invention, wherein a first outer wall portion of an outer wall of the 3D object is provided with a first type of rail with a variable rail width;

[0098] Figure 1B shows a schematic cross-sectional view of a second exemplary non-limiting embodiment of a 3D printed object according to the invention, the 3D printed object being obtained by the method according to the invention, wherein a first outer wall portion of an outer wall of the 3D object is provided with a first type of rail having a predetermined rail width;

[0099] Figure 2 A flow chart showing an exemplary non-limiting embodiment of a method according to the present invention for determining an inner boundary in a slice of a 3D model of a 3D object to divide an outer wall into a first outer wall portion and a second outer wall portion and providing a first type of track with a minimum amount of raw material for each sub-layer of a stacking group of sub-layers in the first outer wall portion;

[0100] Figure 3A , Figure 3B and Figure 3C Schematically shows how to Figure 1A A second exemplary non-limiting embodiment of determining an optimal distance between an inner boundary and an outer boundary of a 3D model of a 3D object is shown;

[0101] Figure 4A and Figure 4B Schematically illustrated are exemplary and non-limiting embodiments, wherein the respective inner boundaries in the respective slices are oriented at different non-zero angles relative to the respective slices as seen in a direction parallel to the respective slices, i.e. as seen in a main direction in which the respective slices extend, and wherein no gaps are present between the stacked group of sublayers of the first outer wall portion and the main layer of the second outer wall portion;

[0102] Figure 4C An exemplary and non-limiting embodiment is schematically shown, wherein the inner boundary has Figure 4B and wherein a gap exists between the stacked group of sublayers of the first outer wall portion and the main layer of the second outer wall portion;

[0103] Figure 5The results of a comparative study for printing different hemispheres with different sizes and structural properties are shown, wherein the different hemispheres were printed using a method according to the invention, a method known in the art for printing with a coarse, i.e. low, resolution, and a method known in the art for printing with a fine, or high, resolution. The time penalty for the method using a coarse, or low, resolution and the method according to the invention are shown, with the total printing time for the method using a coarse, or low, resolution as a reference;

[0104] Fig. 6A shows a first version of another exemplary non-limiting 3D printed object obtained using methods known in the art for printing at a coarse or low resolution;

[0105] Figure 6B The method according to the present invention obtains Fig. 6A A second version of the exemplary, non-limiting 3D printed object shown in FIG. ; and

[0106] Figure 7 A schematic representation of a 3D printing system according to the invention is shown, the 3D printing system comprising an exemplary non-limiting embodiment of a processing unit for printing a 3D object according to the method of the invention. DETAILED DESCRIPTION

[0107] The present invention will be further illustrated in the exemplary embodiments of the present invention as shown below.

[0108] Figure 1A A schematic cross-sectional view of an exemplary non-limiting embodiment of a 3D printed object 1 according to the present invention is shown. A person skilled in the art will appreciate that a 3D printed object may be any object that can be printed using an extrusion-based additive manufacturing process. Figure 1A The 3D printed object 1 is shown to include an outer wall 2, which includes at least one area, wherein the outer wall 2 includes a first outer wall portion 2a and a second outer wall portion 2b. In this area, the first outer wall portion 2a forms an outer surface 3 with enhanced smoothness. Figure 1AAs shown, enhanced smoothness of the outer surface 3 is achieved by filling the first outer wall portion 2a with a first type track 6 having a variable track width 20 and a predetermined first track height 22, the predetermined first track height 22 being a portion of a predetermined second track height 23 of a second type track 7 filling the second outer wall portion 2b. Those skilled in the art will appreciate that in this way, an outer surface with enhanced smoothness can be achieved by printing the first type track 6 only in the first outer wall portion 2a. Filling the second outer wall portion 2b with the second type track 7 having the predetermined second track height 23 provides a low-resolution portion of the outer wall having an outer surface that is less smooth than the first outer wall portion. Therefore, the additional printing time of the 3D object 1 associated with the printing of the outer wall 2 can be reduced compared to a case where the entire outer wall 2 is provided with the first type track 6.

[0109] In a region of the 3D object 1 where the outer wall 2 does not include the first outer wall portion 2a and the second outer wall portion 2b, the outer wall 2 includes a plurality of sub-layers 18. A sub-layer of the plurality of sub-layers is provided with a first type track 6 of an extruded raw material having a predetermined first track height 22. In this way, the outer surface 3 of the 3D object 1 has the same enhancement of smoothness in this region of the outer wall 2 as in a region of the outer wall including the first outer wall portion 2a and the second outer wall portion 2b.

[0110] Those skilled in the art will appreciate that the first outer wall portion 2a and the second outer wall portion 2b may be observed after forming an appropriate cross section through the 3D printed object 1. In this way, it may be determined whether the 3D printed object 1 is printed according to the teachings of the present invention.

[0111] The second outer wall portion 2b is arranged between the first outer wall portion 2a and the inner portion 8 of the 3D printed object 1. The inner portion 8 is provided with a filling structure 21, which includes a track network of the second type of tracks 7 of the extruded raw material. Those skilled in the art will understand that by providing the inner portion 8 with a filling structure 21, the printing time of the inner portion and thus the total printing time of the 3D object 1 can be reduced.

[0112] Figure 1B A schematic cross-sectional view of a second exemplary non-limiting embodiment of a 3D printed object 1 according to the invention is shown, the 3D printed object 1 being obtained by the method according to the invention, wherein a first outer wall portion 2a of an outer wall 2 of the 3D object 1 is provided with a first type of rail 6 having a predetermined rail width 20. By comparison Figure 1A and Figure 1B, a person skilled in the art will appreciate that, for the first type of track 6 in the first outer wall portion 2a, by adopting a predetermined track width 20 instead of a variable track width 20, there can be a gap 24 between the track stack of the first type of track 6 in the first outer wall portion 2a and the track stack of the second type of track 7 in the second outer wall portion 2b. Therefore, the variable track width 20 can be used to reduce and ultimately avoid any gap between the track stack of the first type of track 6 in the first outer wall portion 2a and the track stack of the second type of track 7 in the second outer wall portion 2b.

[0113] Figure 2 A flowchart 200 is shown of an exemplary non-limiting embodiment of a method according to the present invention for determining an inner boundary in a slice of a 3D model of a 3D object to divide an outer wall into a first outer wall portion and a second outer wall portion, and providing a first type track with a minimum amount of raw material for each sublayer of a sublayer stacking group in the first outer wall portion.

[0114] As Figure 2 In step one 201 of flowchart 200 of , it is assumed that all sublayers of the stacking group of sublayers arranged in the first outer wall portion are printed with a single track having the minimum possible track width, i.e. a track width equal to a minimum percentage of the rated track width of the first type of track of the raw material. A person skilled in the art will appreciate that the minimum percentage of the rated track width of the first type of track that can be achieved depends, inter alia, on the extrusion-based additive manufacturing process used, the geometry of the nozzles of the print head used and the type of raw material used, and the same applies to the maximum percentage of the rated track width of the first type of track that can be achieved. The track width of a single track can be adjusted between a minimum percentage of the rated track width of the first type of track and a maximum percentage of the rated track width of the first type of track. If the desired track width is less than the minimum percentage of the rated track width of the first type of track, the track cannot be printed. If the desired track width is greater than the maximum track width, an additional track needs to be printed.

[0115] Step two 202 in the flowchart 200 indicates determining the inner area of ​​a single track of each sub-layer, and then determining the maximum area of ​​a single track of each sub-layer. Step three 203 in the flowchart 200 indicates defining the maximum area applicable to all areas of all sub-layers as the inner boundary, that is, dividing the outer wall into the inner boundary of the first outer wall portion and the second outer wall portion. After defining the inner boundary, step four 204 in the flowchart 200 indicates starting from the first sub-layer of the sub-layer stacking group in the first outer wall portion, which will be provided with the minimum number of tracks of the first type of raw material track. Step five 205 in the flowchart 200 indicates starting from the beginning of the track. The first determination step 206 in the flowchart 200 indicates determining whether the inside of the track touches the inner boundary. If this is the case, step six 207 in the flowchart 200 indicates going to the next position of the track. If this is not the case, the second determination step 208 indicates determining whether the track width can be increased to touch the inner boundary. If this is possible, the seventh step 209 in the flowchart 200 indicates balancing, that is, adjusting the track width to touch the inner boundary. As described above, the track width can be adjusted between a minimum percentage of the nominal track width of the first type of track and a maximum percentage of the nominal track width of the first type of track. If the width of the track cannot be adjusted so that the track can touch the inner boundary, i.e., when the track width required to touch the boundary is greater than the maximum track width, then step eight 210 in flowchart 200 indicates adding an additional track within another track. Those skilled in the art will appreciate that the number of adjacent tracks in the first outer wall portion can vary along the length of the track, depending on the slope of the outer surface.

[0116] After going to the next position of the track according to step six 207 in flowchart 200, the third decision step 211 in flowchart 200 indicates whether the track is completed. If this is not the case, at least steps 206 and 207 of the above steps 206-210 are repeated until it is determined in the third decision step 211 that the track has been completed. After the tracking is completed, step nine 212 in flowchart 200 indicates increasing the number of sublayers. The fourth decision step 213 indicates whether all sublayers are completed. If this is not the case, at least steps 205, 206, 207, 211 and 212 of the above steps 205-212 are repeated until it is determined in the fourth decision step 213 that all sublayers have been completed. If all sublayers have been completed, the last step 214 in the flowchart indicates that the layer has been completed, that is, according to the method of the present invention, the minimum number of tracks of the first type of raw material track is provided to all sublayers of the sublayer stacking group of the corresponding slice of the 3D model of the 3D object.

[0117] Figure 3A , Figure 3B and Figure 3C Schematically shows how to Figure 1AThe illustrated slice 10 of the 3D model 9 of the 3D object 1 is an exemplary, non-limiting embodiment of determining an optimal distance between an inner boundary 13 and an outer boundary 12 of the 3D model 9 .

[0118] A person skilled in the art will appreciate that the distance 19 between the outer boundary 12 and the inner boundary 13 may be different for each sub-layer 5 of the stack of sub-layers 14 in the first outer wall portion 2a, depending on the shape of the outer boundary 12 of the respective slice 10. It is possible to fill each sub-layer 5 of the stack of sub-layers 14 between the outer boundary 12 and the inner boundary 13 with a single track of the first type of track of the raw material, as long as the desired track width remains within the range of a lower boundary defined as a minimum percentage of the nominal track width of the first type of track and an upper boundary defined as a maximum percentage of the nominal track width of the first type of track.

[0119] Figure 3A The distance 19 between the inner boundary 13 and the outer boundary 12 of the 3D model 9 is shown, which is considered to be optimal in the context of the present invention. Because the first outer wall portion 2a is filled with a stack of sublayers 14, the total height of the stack of sublayers 14 is equal to the predetermined slice height 11, and each sublayer 5 of the stack of sublayers 14 can be equipped with a single track of the first type of track of extruded raw material. A person skilled in the art will understand that in this way, the distance 19 between the outer boundary 12 and the inner boundary 13 and therefore the length of the first outer wall portion 2a as seen in a direction parallel to the slice 10 can be kept as small as possible. The second outer wall portion 2b can be provided with a main layer 4 having a predetermined main layer height 16 equal to the predetermined slice height 11, and the main layer 4 can be provided with a second type of raw material track. Due to the determination of the optimal distance between the outer boundary 12 and the inner boundary 13, the additional printing time associated with printing the outer wall of the 3D object with enhanced smoothness (i.e. enhanced resolution or reduced roughness) can be reduced as much as possible.

[0120] Figure 3B The inner boundary 13 is shown to be located at a position such as Figure 3AIn the case where the optimal distance of the inner boundary 13 shown is closer to the distance 19 of the outer boundary 12, one sublayer of the sublayer stacking group cannot be arranged in the first outer wall portion 2a because it cannot provide a single track of the first type of track of the extruded raw material because such a track must be printed as a minimum percentage of the rated track width of the first type of track observed in a direction parallel to the slice 10 and less than the track width. In the case where the first outer wall portion 2a cannot provide a complete sublayer stacking group 14, i.e., a sublayer stacking group 14 having a total height 15 equal to the predetermined slice height 11, the outer surface of the 3D object cannot have the predetermined smoothness because the extruded raw material will be lost. This lack of extruded raw material will make the smoothness of the outer surface of the 3D object less than the desired enhancement. Therefore, a person skilled in the art will understand that the inner boundary 13 should be moved to Figure 3A Optimal distance shown.

[0121] Figure 3C It is shown that the inner boundary 13 is located at a distance from the outer boundary 12 such as Figure 3A In the case where the optimal distance 19 of the inner boundary 13 is shown to be further away, the sublayer 5 of the sublayer stacking group 14 arranged in the first outer wall portion 2a will have to be provided with a plurality of first type tracks of extruded raw material, because the track width of such tracks seen in a direction parallel to the slice 10 is greater than or equal to the track width of the maximum percentage of the rated track width of the first type track. Those skilled in the art will understand that in the case where the sublayer 5 of the sublayer stacking group 14 arranged in the first outer wall portion 2a will be provided with a plurality of first type tracks of extruded raw material, it will be possible to achieve enhanced smoothness of the outer surface of the 3D object. However, the additional printing time associated with printing the first outer wall portion 2a with enhanced smoothness (i.e. enhanced resolution or reduced roughness) will be excessively long because tracks with at least one higher resolution than desired and necessary must be printed in the first outer wall portion. Therefore, the costs involved in printing the 3D object will be higher than at least one of the required costs. Therefore, those skilled in the art will understand that the inner boundary 13 should be moved to Figure 3A Optimal distance shown.

[0122] Based on the above, those skilled in the art will understand that the main point of the method according to the present invention is to find the optimal distance between the inner boundary 13 and the outer boundary 12 to divide the outer wall 2 into a high-resolution first outer wall portion 2a and a low-resolution second outer wall portion 2b, wherein each sublayer 5 of the sublayer stacking group 14 in the high-resolution first outer wall portion 2a is provided with a minimum number of first type raw material tracks.

[0123] As mentioned above, a person skilled in the art will appreciate that a respective inner boundary of a respective slice of the plurality of slices may be oriented at any suitable non-zero angle relative to the respective slice of the plurality of slices, as seen in a direction parallel to the respective slice, i.e., in a main direction in which the respective slice extends. Thus, it will be clear that the inner boundaries of different slices of the plurality of slices may have different orientations, ranging from FIG. 3A to FIG. 3C As can be seen in FIG, the inner boundary 13 in the slice 10 can be oriented vertically, i.e., at a non-zero angle of 90° relative to the slice 10 as seen in a direction parallel to the slice 10. FIG. 3A to FIG. 3C In the specific embodiment shown, the direction parallel to the slice 10 is interpreted as the horizontal direction. In this case, the non-zero angle between the inner boundary 13 and the horizontal direction is 90°. FIG. 3A to FIG. 3C It can be seen that there is no gap between the partial layer stack 14 of the first outer wall part 2a and the main layer 4 of the second outer wall part 2b.

[0124] Figure 4A and Figure 4B An exemplary and non-limiting embodiment is schematically shown, in which the respective inner border 13 is oriented at a different non-zero angle relative to the respective slice 10 as seen in a direction parallel to the respective slice 10, i.e. in the main direction in which the respective slice 10 extends. FIG. 4A to FIG. 4C In the particular embodiment shown, the direction parallel to each slice 10 is also interpreted as the horizontal direction. Figure 4A The inner boundary 13 in the slice 10 shown is inclined toward the outer boundary 12, while Figure 4B The inner boundary 13 in the slice 10 shown is inclined away from the outer boundary 12 .

[0125] like Figure 4A and Figure 4B As shown, the inner surface of the partial layer stack 14 of the first outer wall portion 2a has a rough shape. Figure 4C The inner boundary 13 in the slice 10 shown has a Figure 4B The inner boundary 13 is shown in the same orientation. Figure 4C In the exemplary and non-limiting embodiment shown, the stack of sublayers 14 of the first outer wall portion 2a and the main layer 4 of the second outer wall portion 2b are only partially in contact. Thus, there is a gap 24 between the bottom two sublayers of the stack of sublayers 14 of the first outer wall portion 2a and the main layer 4 of the second outer wall portion 2b. Figure 4C It can be seen that there may be gaps 24 even between the top sub-layer of the sub-layer stack 14 and the main layer 4. A person skilled in the art will appreciate that in Figure 4A and Figure 4BThere are no gaps between the individual sub-layer stacks 14 shown in FIG. 1 and the corresponding main layer 4. A person skilled in the art will appreciate that these gaps can be eliminated, for example, by pressure-controlled printing of the main layer 4 using the second outer wall portion 2b.

[0126] Figure 5 The results of a comparative study for printing different hemispheres with different sizes and structural properties using a method according to the invention, a method known in the art for printing with a coarse or low resolution, and a method known in the art for printing with a fine or high resolution are shown. The time loss using the method with a fine or high resolution and the method according to the invention is shown, taking as reference the total printing time using the method with a coarse or low resolution.

[0127] Those skilled in the art will appreciate that any 3D object may be selected for this comparative study and that a hemisphere is only a non-limiting example of a 3D object.

[0128] According to methods known in the art with coarse or low resolution, the tracks of the extruded raw material have a so-called coarse track height. According to methods known in the art with fine or high resolution, the tracks of the extruded raw material have a so-called fine track height. In order to compare the results of the total printing time of different hemispheres, the coarse track height was selected to be three times the fine track height. It will be understood by those skilled in the art that the selection of a coarse track height three times higher than the fine track height is arbitrary and any other suitable ratio can be used. According to the method of the present invention, the first outer wall portion 2a with high resolution is filled with a track of the extruded raw material with a track height equal to the fine track height, and the second outer wall portion 2b with low resolution is filled with a track of the extruded raw material with a track height equal to the coarse track height. In the case where the outer wall of the hemisphere cannot be completely divided in the first outer wall portion with high resolution and the second outer wall portion with low resolution, the corresponding area of ​​the outer wall of the hemisphere is provided with a raw material track having a height equal to the fine track height. The inner part of the hemisphere printed by the method according to the present invention also has a raw material track with a track height equal to the coarse track height.

[0129] Furthermore, in a comparative study, the printing time of hemispheres with radii of 25 mm, 50 mm, and 75 mm using the above method was compared. In addition, each hemisphere was sliced ​​with three different wall thickness settings, namely 2 mm, 5 mm wall thickness, and using a solid structure.

[0130] Based on the above, a person skilled in the art will appreciate that a total of 27 different hemispheres were printed. The time loss using the method with fine or high resolution and the method according to the present invention can be calculated by taking the total printing time using the method with coarse or low resolution as a reference.

[0131] from Figure 5 It can be clearly seen that when using the method with fine or high resolution, according to which the track height of the extruded raw material is three times lower than the track height of the track using the raw material in the method with coarse or low resolution, the total printing time for all hemispheres is roughly increased by three times as expected. When using the method according to the invention, the outer surface smoothness is equal to the smoothness produced by the method with fine or high resolution, however, the total printing time of the different hemispheres increases only by 1.1 to 1.6 times. The observed spread of this factor is mainly caused by the thickness of the outer wall. Those skilled in the art will understand that by using the method according to the invention, the additional printing time of the 3D object associated with printing the outer wall with an outer surface with enhanced smoothness can be reduced, and therefore, the total printing time of the 3D object with an outer surface with enhanced smoothness can be reduced.

[0132] Fig. 6A A first version of another exemplary non-limiting 3D printed object 1 is shown, obtained using methods known in the art for printing at a coarse or low resolution. Figure 6B The method according to the present invention obtains Fig. 6A A second version of the exemplary non-limiting 3D printed object 1 is shown. By comparison Fig. 6A and Figure 6B It can be clearly seen that the second version of the 3D printed object 1 has an outer surface 3 with enhanced smoothness compared to the outer surface 3 of the first version of the 3D printed object 1. In addition, based on Figure 5 The results of the comparative study shown, those skilled in the art will understand that Figure 6B The second version of the 3D printed object 1 shown can be printed with limited time cost. Based on the results of the above comparative study, printing Figure 6B The total time required to 3D print the second version of the object 1 shown will be longer than printing Fig. 6A The total time required for the first version of the 3D printed object 1 shown is approximately 1.1-1.6 times longer.Thus, a person skilled in the art will appreciate the above-mentioned advantages of the method according to the present invention.

[0133] Figure 7 A schematic diagram of a 3D printing system 30 according to the present invention is shown. The 3D printing system 30 comprises a processing unit 31 adapted to print a further exemplary non-limiting embodiment of a 3D object 1 using the method according to the present invention.

[0134] Those skilled in the art will appreciate that the processing unit 31 of the 3D printing system 30 according to the present invention is operably connected to all relevant components of the 3D printing system 30, which are required for printing the 3D object 1 using an extrusion-based additive manufacturing process. Therefore, the 3D printing system 30 according to the present invention is suitable for providing the 3D object 1 with an outer surface having enhanced smoothness, while allowing for a reduction in the additional printing time associated with printing the outer surface having enhanced smoothness.

[0135] The present invention can be summarized as relating to a method for reducing additional printing time of a 3D object 1 associated with printing of an outer wall 2 of the 3D object, the outer wall having an outer surface 3 with enhanced smoothness. The outer wall is arranged to surround an inner part 8 of the 3D object, the outer wall comprising at least one region, the region comprising a first outer wall portion 2a and a second outer wall portion 2b, the first outer wall portion forming an outer surface with enhanced smoothness, the second outer wall portion being arranged between the first outer wall portion and the inner part and providing a low-resolution portion of the outer wall having an outer surface that is less smooth than the first outer wall portion. Thus, the additional printing time associated with printing the outer wall having an outer surface with enhanced smoothness can be reduced. The present invention also relates to a 3D printing system 30 suitable for performing the method according to the present invention and a 3D printed object having an outer wall as described above.

[0136] It will be clear to those skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several modifications and variations thereof are possible without departing from the scope of the invention as defined by the appended claims. In particular, combinations of specific features of various aspects of the present invention may be made, and one aspect of the present invention may be further advantageously enhanced by adding features described with respect to another aspect of the present invention. Although the present invention has been described and described in detail in the drawings and specification, such illustration and description are to be considered merely illustrative or exemplary, and not restrictive.

[0137] The invention is not limited to the disclosed embodiments. Variations of the disclosed embodiments may be understood and effected by a person skilled in the art in practicing the claimed invention by studying the drawings, the description and the appended claims. In the claims, the word "comprising" does not exclude other steps or elements, and the indefinite article "a" or "an" does not exclude a plurality. The fact that certain measures are cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

[0138] Reference numerals

[0139] 1 3D (printed) objects

[0140] 2 The outer wall of a 3D (printed) object

[0141] 2a First outer wall portion

[0142] 2b Second outer wall portion

[0143] 3 External surface of the outer wall

[0144] 4 Main Floor

[0145] 5 Sublayer

[0146] 6. The first type of track for extruding raw materials

[0147] 7 Second type of track for extrusion of raw materials

[0148] 8 Internal part

[0149] 9 3D Models

[0150] 10 Number of slices of the 3D model

[0151] 11 Predetermined slice height

[0152] 12 Outer Boundary

[0153] 13 Inner Boundary

[0154] 14 Sublayer stacking groups

[0155] 15 Total height of the stack of sublayers

[0156] 16 Predetermined main floor height

[0157] 17 Predetermined sub-layer height

[0158] 18 Multiple sub-layers

[0159] 19 Distance between inner and outer boundaries

[0160] 20 Track width of the first type of track

[0161] 21 Filling structure

[0162] 22 Predetermined first track height

[0163] 23 Predetermined second track height

[0164] 24 Gap

[0165] 30 3D Printing System

[0166] 31 Processing Units

[0167] 200 Flowchart

[0168] Step 1 in the 201 flowchart

[0169] 202 Step 2 in the flowchart

[0170] 203 Step 3 in the flowchart

[0171] 204 Step 4 in the flowchart

[0172] 205 Step 5 in the flowchart

[0173] 206 The first determination step in the flowchart

[0174] 207 Step 6 in the flowchart

[0175] 208 The second determination step in the flowchart

[0176] 209 Step 7 in the flowchart

[0177] 210 Step 8 in the flowchart

[0178] 211 The third determination step in the flowchart

[0179] 212 Step 9 in the flowchart

[0180] 213 The fourth determination step in the flowchart

[0181] 214 Final step in the flowchart

Claims

1. A method for reducing the additional printing time of a 3D object (1), the additional printing time being associated with printing an outer wall (2) of the 3D object (1), the outer wall (2) having an outer surface (3) with enhanced smoothness, the 3D object (1) being manufactured by an extrusion-based additive manufacturing process by stacking a main layer (4) and a sublayer (5), the main layer (4) and the sublayer (5) comprising tracks (6, 7) of extruded raw material, the 3D object (1) comprising an inner part (8), the outer wall (2) being arranged to surround the inner part (8), the method comprising: - obtaining a 3D model (9) of the 3D object (1); - Slicing the 3D model (9) using a predetermined slice height (11) to determine the number of slices; - for at least one slice (10) of the plurality of slices: Determining the outer boundary (12) of the 3D model (9); Determining whether an inner boundary (13) in the outer wall (2) is definable to divide the outer wall into a first outer wall portion (2a) and a second outer wall portion (2b), wherein the first outer wall portion (2a) is arranged to extend between the outer boundary (12) and the inner boundary (13) and is configured to be provided with a sub-layer stacking group (14), the sub-layer stacking group (14) having a total height (15) equal to a predetermined slice height (11) to form an outer surface (3) with enhanced smoothness; and the second outer wall portion (2b) is arranged to extend between the inner boundary (13) and the inner portion (8) and is configured to be provided with a main layer (4), the main layer (4) having a predetermined main layer height (16) equal to the predetermined slice height (11), wherein In response to determining that a predetermined slice height (11) of a corresponding slice (10) of the plurality of slices is at least as high as the predetermined major layer height (16), thereby establishing that an inner boundary (13) in the outer wall (2) is definable: Positioning the inner boundary (13) at a predetermined distance (19) from the outer boundary (12), at which distance the minimum number of tracks of the first type (6) of the extruded material for at least one sublayer (5) of the stacked group (14) of sublayers is one; filling at least one sublayer (5) of the first outer wall portion (2a) with a track of a first type of track (6) having a predetermined first track height (22) equal to a predetermined sublayer height (17) and being a fraction of a predetermined slice height (11), and a track width (20) having a minimum value equal to 50% of a nominal track width of the first type of track (6) and a maximum value equal to 200% of the nominal track width of the first type of track (6), and filling said second outer wall portion (2b) with said main layer (4); or In response to determining that a predetermined slice height (11) of a corresponding slice (10) of the plurality of slices is less than a predetermined major layer height (16), thereby establishing that an inner boundary (13) in the outer wall (2) is undefinable: The outer wall (2) of the corresponding slice is filled with a plurality of sub-layers (18), wherein each sub-layer (5) of the plurality of sub-layers (18) has a predetermined sub-layer height (17) which is a fraction of the predetermined slice height (11).

2. The method according to claim 1, wherein: In the case where the inner boundary (13) in the outer wall (2) can be defined, for the corresponding sublayer, if the distance (19) from the outer boundary (12) to the inner boundary (13) is less than the minimum value of the track width (20) of the first type of track (6), the filling of the corresponding sublayer of the sublayer stacking group (14) is omitted.

3. The method according to claim 1 or 2, wherein: In the case where the inner boundary (13) in the outer wall (2) is undefinable, for the corresponding sublayer, if the distance (19) from the outer boundary (12) to the inner boundary (13) is greater than the maximum value of the track width (20) of the first type of track (6), the corresponding sublayer of the sublayer stacking group (14) is filled with at least two tracks of the first type of track (6), wherein the total width of the at least two tracks is the distance (19).

4. The method according to claim 1, wherein: In the case where the inner boundary (13) in the outer wall (2) can be defined, the distance (19) from the outer boundary (12) to the inner boundary (13) has a minimum value equal to 50% of the rated track width of the first type of track (6) and a maximum value equal to 200% of the rated track width of the first type of track (6), allowing each sublayer of the sublayer stacking group to be filled with one track of the first type of track (6).

5. The method according to claim 1, wherein: Filling the outer wall (2) of the corresponding slice with a plurality of sub-layers (18) also includes: filling at least one sub-layer (5) of the plurality of sub-layers (18) with a minimum number of tracks of the first type (6) of the extruded material; The minimum number of tracks is one of the following: If the outer wall (2) of the at least one sublayer (5) has a width that is less than the minimum value of the track width (20) of the first type of track (6), the minimum number of tracks is zero to prevent filling of the at least one sublayer (5); If the width of the outer wall (2) of the at least one sublayer (5) is within the range between the minimum value and the maximum value of the track width (20) of the first type of track (6), the minimum number of tracks is 1; and If the width of the outer wall (2) is greater than the maximum value of the track width (20) of the first type of track (6), the minimum number of tracks is at least two, wherein the at least two tracks have a total width equal to the width of the outer wall (2).

6. The method according to claim 1, wherein: Filling the second outer wall portion (2b) with a main layer (4) having a predetermined main layer height (16) equal to a predetermined slice height (11) comprises: A track of a second type of track (7) of extruded stock is provided, wherein the track of the second type of track has a predetermined second track height (23) equal to a predetermined main layer height (16).

7. The method according to claim 6, wherein: The inner part (8) is provided with a filling structure (21), the filling structure (21) comprising a grid portion of a main layer (4), the main layer of the grid portion comprising a second type of track (7) of extruded material.

8. The method according to claim 1, wherein: The predetermined slice height (11) depends on the desired printing time of the 3D object.

9. The method according to claim 1, wherein: The predetermined slice height (11) depends on a desired enhancement value of the smoothness of the outer surface (3) of the 3D object (1).

10. The method according to claim 1, wherein: The stacked group (14) of sub-layers of the first outer wall portion (2a) is arranged in contact with the main layer (4) of the second outer wall portion (2b) at the inner boundary (13).

11. A 3D printing system (30) for manufacturing a 3D object (1) using an extrusion-based additive manufacturing process, the system (30) comprising a processing unit (31) for executing the method according to any one of the preceding claims.

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