NL2030255B1 - Support printing in FFF using crystalline interface layer - Google Patents

Abstract

An FFF method (70) for generating a 3D object is described. The method comprises the printing (71) of the 3D object using a build material, wherein the 3D object comprising at least one overhang. At least one support structure is printed underneath the at least one overhang wherein the support structure is printed using the build material. The support structure comprises an interface layer (15) contacting the 3D object. This interface layer (15) has a degree of crystallinity greater than the degree of crystallinity of at least those parts of the 3D object that get into direct contact with the interface layer (15). The higher degree of crystallinity enables more easy removal ofthe support structure after printing.

Description

Support printing in FFF using crystalline interface layer

Field of the invention

The present invention relates to a fused filament fabrication method for generating a 3D object. The invention also relates to a method of generating instructions for printing three- dimensional {3D) objects with an FFF printer. The invention also relates to a computing device comprising one or more processing units 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 continuous 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.

Currently there are two main methods of printing with crystallizable materials: printing mostly amorphous and printing mostly crystalline. Both methods can be followed up with an annealing step to increase the degree of crystallinity. Typically, the state in which these materials are printed in is decided by the build volume temperature (i.e. the temperature within the build chamber of the FFF printer). If this temperature is below the glass transition temperature, the material stays amorphous. If it is above the crystallization temperature, the resulting part will end up crystalline. The degree of crystallinity can be estimated by different analytical methods and it typically ranges between 10 and 80%, with crystallized polymers often called “semi-crystalline".

Most of the current print strategies within FFF are focused on uniformity i.e. keeping the printed part properties the same over a print. Semi-crystalline materials are printed with the idea that the part is either fully amorphous or ‘fully’ crystalline, to have uniform properties and to improve printability. Some strategies revolve around annealing amorphous parts to make them crystalline. But these strategies have a big disadvantage. It is not possible to use the material properties of the crystalline and the amorphous phase at the same time. If different properties are required locally, typically this is solved by using a second material or by changing the toolpath (lower infill, higher surface roughness, etcetera).

Publication “Influence of thermal processing conditions in 3D printing on the crystallinity and mechanical properties of PEEK material”, Chuncheng Yang et al., Journal of Materials

Processing Tech. 248 (2017) 1-7, describes a temperature-control 3D printing method. The method is used to control and realize different degrees of crystallinity and mechanical properties for different PEEK (Poly-ether-ether-ketone) parts, even in different regions of the same PEEK part. It is mentioned that PEEK is a high-performance, temperature-resistant semicrystalline polymer which is frequently used as a replacement for metals in a wide variety of high- performance end-use application. Thermal processing conditions during manufacturing process for PEEK can implement a significant impact on its crystallinity and mechanical properties directly and indirectly. The researchers prepared different PEEK samples prepared for calculating crystallinity and performing tension tests, in order to investigate the relationship between various thermal processing conditions (the ambient temperature, the nozzle temperature and heat treatment methods) in FFF process and crystallinity and mechanical properties, such as tensile strength, elastic modulus and breaking elongation of pure PEEK material.

Summary of the invention

The aim of the present invention is to provide an alternative use for the controlled crystallization of material in an FFF printing process.

According to a first aspect of the present invention, there is provided an FFF method for generating a 3D object. The method comprises the printing the 3D object using a build material.

The 3D object comprises at least one overhang. The method comprises the printing at least one support structure underneath the at least one overhang wherein the support structure is printed using the build material. The support structure comprises an interface layer contacting the 3D object, the interface layer having a degree of crystallinity greater than the degree of crystallinity of at least those parts of the 3D object that get into direct contact with the interface layer.

The interface layer does adhere to the underlying layer of the support, because the interface layer is still amorphous before it cools down and becomes more crystalline. By printing the interface layer relatively hot, slow and/or with little cooling, this layer is given time to become more crystalline. It crystallizes after it is already bonded to the layer below, i.e. to the underlying layer of the support structure. When depositing a build layer on top of this interface layer, there will be not enough energy and/or time to let this (crystallized) interface layer melt again, so the layer on top does not stick to it properly. This will facilitate the removal of the support structure from the 3D object after printing.

In an embodiment, a part of the support structure not being the interface layer has a degree of crystallinity that is less than the degree of the crystallinity of the interface layer. The degree of crystallinity of the part of the support structure not being the interface layer may be in a range of 0%-15%. Such degree’s result is a relatively amorphous support structure which is relatively flexible but still strong enough to support the overhang.

In an embodiment, the degree of crystallinity of the interface layer lies above 25%. Such a relative high degree of crystallinity of the interface layer significantly reduces the adhesion between the interface layer on the 3D object above, enabling easy removal of the support structures.

In an embodiment, the degree of crystallinity of the interface layer is achieved by keeping a trace of deposited material within a crystallization temperature range of the build material for an appropriate time. It is noted that the appropriate time will also depend on the type of build material.

The degree of crystallinity of the interface layer may be increased by using different techniques which may be combined as well. These techniques may comprise the controlling a fan of an FFF system during deposition, the controlling a print speed of a printhead of the FFF system, the controlling a nozzle temperature, the controlling a geometry of a trace, and suitable planning of the traces. All these techniques influence the amount of energy dissipation from the deposited traces and thus will influence the crystallization process. The specific settings for these techniques will need to be tuned by way of testing the different techniques separately or in combination.

In an embodiment, the degree of crystallinity of the interface layer is increased by means of ironing the interface layer using an ironing means such as a nozzle. This technique can be used after a complete layer has been deposited or part of the layer. If a nozzle comprises a flat under surface, this surface can be used to iron the interface layer. Alternatively a separate ironing tool could be used.

In an embodiment, the build material comprises a semi-crystalline polymer. Examples of polymers that gave good results are PEEK, PEKK, PPS, PA, PLA and PET.

In an embodiment, the complete 3D object after printing has a degree of crystallinity below 10%. Such a low degree of crystallinity results in optimal bonding of the layers of the 3D object.

In an embodiment, the support structure comprises one or more upstanding meandering thin walls, and a platform on top of the meandering walls, the platform comprising at least one support layer arranged under the interface layer, the at least one support layer having a degree of crystallinity less than that of the interface layer.

According to a further aspect, there is provided a method of generating instructions for printing three-dimensional (3D) objects with an FFF printer, the method comprising: - receiving a 3D model of a 3D object; - identifying overhangs in the 3D model; - generating models of support structures that support the overhangs during a print process; - generating instructions for the FFF printer to print the 3D object and the support structures in build material, wherein an interface layer of the support structures touching the 3D object is deposited using print settings that cause a higher degree of crystallinity of the interface layer as compared to those parts of the 3D object that get into direct contact with the interface layer.

According to a further aspect, there is provided a computing device comprising one or more processing units, the one or more processing units being arranged to perform the method of generating instructions as described above.

According to yet a further aspect, there is provided 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 of generating instructions as described above.

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 cross-section of a 3D object generated by using an FFF method according to an embodiment;

Figure 2 schematically shows a cross-section of the support structure according to an embodiment;

Figure 3 schematically shows a cross-section of the support walls in a plane parallel to the build plate;

Figure 4 schematically shows part of a cross-section of a spherical 3D object which is partly supported by a support structure;

Figure 5 is a graph of the crystallization half-time for PEEK with different molecular weights;

Figure 6 schematically shows part of a print head that can be used to deposit material onto a build plate;

Figure 7 is a flow chart of an FFF method according to an embodiment;

Figure 8 shows a flow chart of a method of generating instructions for printing three- dimensional (3D) objects with an FFF printer, according an embodiment of the invention, and

Figure 9 schematically shows a computing device 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

Figure 1 schematically shows a cross section of a 3D object generated by using an FFF method according to an embodiment. The 3D object in this example comprises a plateau 10 and two legs 11, 12. Both the plateau 10 and the legs 11, 12 extend in a direction perpendicular to the drawing plane. The 3D object is printed on a print plate 6 of a FFF printing system using a layer- by-layer deposition method. The part of the plateau 10 between the two legs 11,12 constitutes an overhang which needs support during printing to avoid printing errors and/or unwanted surface roughness at the bottom of the plateau as will be appreciated by the skilled person. Today's slicing programs are able to calculate the place and the size of the support needed for supporting such overhangs. In the example of Figure 1, it is assumed that only the middle part of the overhang needs support. A support structure 14 is created underneath the overhang.

In this embodiment, the degree of crystallinity of a top layer 15 of the support structure is increased during, or after, printing that layer. The rest of the support structure 14 as well as the 3D object is printed with a lower degree of crystallinity, and may even be amorphous. The top layer 15 of the support structure is referred to as the interface layer 15 forming an interface between the 3D object and the more amorphous part of the support structure 14 below.

The advantage of creating a more crystallized interface 15 is that it adheres very well to the more amorphous support structure 14, but it adheres poorly to the more amorphous object 5 printed on top. This makes it easy to break off the entire support from the 3D object and leave a nice surface of the print.

It is noted that parts of the 3D object may have a higher degree of crystallinity as well. For example the plateau 10 may comprise an elongated semi-crystalline part to make the plateau 10 more strong. Also in such an embodiment, the rest of the 3D object is more or less amorphous, at least at those parts that get into contact with the interface layer 15.

Figure 2 schematically shows a cross section of the support structure 14 according to an embodiment. The support structure comprises a support roof 14A and support walls 14B. The top layer 15 of the support structure has a high degree of crystallinity while the rest of the structure is more amorphous (i.e. having a lower degree of crystallinity). In an embodiment, the degree of crystallinity of the part of the support structure not being the interface layer lies in a range of 0%- 15%.

Figure 3 schematically shows a cross section of the support walls 14B in a plane parallel to the build plate 6 (see also Figure 1). The walls 14B follow a meandering pattern. Such a pattern creates sufficient support while using relatively little print material. The support roof 14A preferably supports the whole interface layer 15. In an embodiment, the support roof 14A comprises a number of layers of printing material, extending over the same area as the crystalline interface layer 15.

It is noted that the invention is not limited to the support of horizontal overhangs. The invention can be used in all situations where support is needed. Figure 4 schematically shows part of a cross section of a spherical 3D object 20 which is partly supported by a support structure 30. A typical layer of the spherical 3D object 20 comprises a number of wall traces 22, 23 and infill traces 24. The wall traces 22, 23 may be circular traces forming the outer wall of the 3D object 20.

The infill may be optional. The infill may have different structures as will be appreciated by the skilled person. The infill may be a 100% infill, or it may be a partly open infill, such as a 20% infill.

The support structure 30 may comprise a number of amorphous traces 31 wherein traces contacting the 3D object 20 are crystallized forming the interface layer, see dashed traces 32 in

Figure 4. The crystallized traces 32 may be circular traces similar to the wall traces 22, 23 of the 3D object. It is noted that the track of the traces 32 will depend on the local needs for support and the slicing strategies used.

The crystalline interface layer may be created by depositing build material and keeping a trace of deposited material near the optimal crystallization temperature of the build material for an appropriate time. The appropriate time may depend on the materials used, the nozzle temperature, the build volume temperature, the air flow rate and the print speed.

Figure 5 is a graph of the crystallization half-time for PEEK with different molecular weights. The graph was published in “Isothermal crystallization of poly (ether ether ketone) with different molecular weights over a wide temperature range”, Seo, J, Gohn, AM, Dubin, O, et al. in

Polymer Crystallization 2.1 (2019):e10055. Figure 5 shows a curve 52 for PEEK 650G, a curve 53 for PEEK 450G and a curve 54 for PEEK 150G.

From the graph of Figure 5 it can be seen that crystallization rates are the highest at an optimal crystallization temperature range. Optimal crystallization rates for these types of PEEK lie in a temperature range between 200 — 250 °C. It is noted that crystallization is also possible outside this range, but that more time is needed at those temperatures. It is clear from Figure 5 that temperatures below 175 °C and above 325 °C will not be appropriate.

The temperature range in which crystallization of a material takes place, is also referred to as the crystallization temperature window. According to an embodiment of the invention, a print process is provided in which the time the deposited material spends in the crystallization temperature window is controlled by means of a nozzle temperature, a print speed and/or local reheating, in order to control the crystallization degree of individual traces of the interface layer.

The proposed method can be performed using a known print head, but using different printing settings and/or instructions as compared to the state of the art.

Figure 6 schematically shows part of a print head 60 that can be used to deposit material onto a build plate 6. The print head 60 comprises a liquefier having an inlet 81 for letting in a filament 5, a cold end 62 and a hot-end 63. Between the hot-end 63 and the cold-end 62, a heat break 64 is present. The hot-end 63 comprises a heating element 65 arranged to heat the hot-end 63 so as to melt the filament 5, see molten filament 6 in the hot-end 63. The print head 60 further comprises a nozzle 66 and two fans 67 arranged to blow air onto the deposited material, i.e. onto the deposited traces in order to cool the traces. In this figure a simplified print is shown comprising a first layer 41, a second layer 42 and a third layer 43. The nozzle 66 of the print head 2 comprises an orifice and an ironing surface around the orifice. The ironing surface can be used to iron the traces during deposition or iron the traces later on in order to reheat the traces so that they are crystallized.

In an embodiment, the deposited traces are kept in a crystallization temperature range (i.e. window) for a sufficient long time in order to enable crystallization of those traces. Cooling down the traces quickly {and keeping them cool) will result in material having a lower degree of crystallinity.

The wanted crystallization of the interface traces can for example be achieved by controlling the speed of the fans 67. By introducing increased airflow to the trace, the trace cools faster and will spend less time in crystallization temperature window resulting in a lower degree of crystallinity. Turning the fan off has the opposite effect resulting in a higher degree of crystallinity.

Alternatively or additionally, the print head 64 can be moved relative to the build plate 6 with adapted speed in order to create crystalline traces. By moving the printhead 60 faster, less heat is conducted from the nozzle into the traces. So the just printed trace cools down faster and surrounded traces are heated up less. This reduces time spend near the optimal crystallization temperature so that the material is less crystalline or even amorphous. Decreasing speed has the opposite effect, creating a more crystalline material.

Alternatively or additionally, the nozzle temperature can be tuned so that the interface traces become crystalline. Increasing the nozzle temperature is the easiest way to pump more heat into the current trace and its surrounding traces. This will keep the trace near the optimal crystallization temperature for a longer time, while reheating the surrounding traces back towards the optimal crystallization temperature. This way, higher nozzle temperatures increase the local crystallization, lower nozzle temperatures have the opposite effect.

Alternatively or additionally, the geometry of a traces can be controlled. For example, thicker traces will cool down slower and thus will have a higher degree of crystallinity under the same environmental circumstances. Another option is to appropriately plan tracks (i.e. paths) of the traces. New traces may heat up neighbouring traces which will result in increased crystallinity of those neighbouring traces.

In an embodiment, the degree of crystallinity of the interface layer is increased by means of ironing the interface layer using an ironing means such as the nozzle 886. Ironing specific parts of the print, reheats the traces. By inputting the right amount of thermal energy (by balancing nozzle/tool temperature and speed), the degree of crystallization can be increased locally. It is noted that the nozzle geometry effects the thermal energy input into the printed layers: a larger contact surface and more radiation will both increase the thermal input. This has effect on how print speed, nozzle temperature and ironing introduce crystallinity.

The invention provides for a wider application range with a single material. It provides for a higher print quality, a higher production rate, lower costs, especially since separate support material is no longer required.

In an embodiment, the 3D object and the support are printed using polymers like PEEK (Polyetheretherketone), PEKK (Polyetherketoneketone), PPS (Polyphenylene sulfide), PA (Polyamide), PLA (Polylactic acid) and PET (Polyethylene terephthalate), taking full advantage of both the amorphous and crystalline properties of these polymers.

Figure 7 is a flow chart of an FFF method 70 according to an embodiment. The FFF method for generating a 3D object comprises the printing the 3D object using a build material, the 3D object comprising at least one overhang, see step 71. The method also comprises the printing of at least one support structure underneath the at least one overhang wherein the support structure is printed using the build material, see step 72, wherein the support structure is amorphous except for a crystalline interface layer contacting the 3D object, the 3D object being amorphous at least at a parts/layers that get into contact with the interface layer. It is noted that the support and the 3D object are created simultaneously in a layer-by-layer building process. So sometimes after steps 71, step 72 may follow, and visa versa.

Figure 8 shows a flow chart of a method 130 of generating instructions for printing three- dimensional (3D) objects with an FFF printer, according an embodiment of the invention. The method comprises receiving 131 a 3D model of a 3D object, and identifying 132 overhangs in the 3D model. The method 130 further comprises generating 133 models of support structures that support the overhangs during a print process. The method 130 also comprises generating 134 instructions for the FFF printer to print the 3D object and the support structures in build material,

wherein an interface layer of the support structures touching the 3D object is deposited using print settings that cause the interface layer to crystallize.

Figure 9 schematically shows a computing device 100 according to an embodiment. The device 100 comprises a processing unit 111, an VO interface 112 and a memory 113. The processing unit 111 is arranged to read and write data and computer instructions from the memory 113. The processing unit 111 may also be arranged to communicate with sensors and other equipment via the I/O interface 112. The computing device 100 may also comprise an interface 114 arranged to communicate with other devices via a LAN or WAN (not shown). Figure 12 also shows a display 115 which may be connected to the interface 112 so as to show information regarding a slicing process of a 3D object. The memory 113 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 113 may comprise a computer program product comprising code configured to make the processing unit 111 perform one or more of the embodiments of the method as described above.

In the above the following embodiments were described.

Embodiment 1. An FFF method (70) for generating a 3D object, the method comprising: - printing (71) the 3D object using a build material, the 3D object comprising at least one overhang; - printing (72) at least one support structure underneath the at least one overhang wherein the support structure is printed using the build material, wherein the support structure comprises an interface layer (15) contacting the 3D object, the interface layer (15) having a degree of crystallinity greater than the degree of crystallinity of at least those parts of the 3D object that get into direct contact with the interface layer (15).

Embodiment 2. The FFF method according to embodiment 1, wherein a part (14A,14B) of the support structure not being the interface layer has a degree of crystallinity that is less than the degree of the crystallinity of the interface layer.

Embodiment 3. The FFF method according to embodiment 2, wherein the degree of crystallinity of the part of the support structure not being the interface layer lies in a range of 0%-15%.

Embodiment 4. The FFF method according to any one of the preceding embodiments, wherein the degree of crystallinity of the interface layer lies above 25%.

Embodiment 5. The FFF method according to any one of the preceding embodiments, wherein the degree of crystallinity of the interface layer is achieved by keeping a trace of deposited material within a crystallization temperature range of the build material for an appropriate time.

Embodiment 6. The FFF method according to embodiment 5, wherein the degree of crystallinity of the interface layer (15) is increased by way of at least one of: - controlling a fan of an FFF system during deposition; - controlling a print speed of a printhead of the FFF system; - controlling a nozzle temperature; - controlling a geometry of a trace, and - suitable planning of the traces.

Embodiment 7. The FFF method according to any one of the preceding embodiments, wherein the degree of crystallinity of the interface layer is increased by means of ironing the interface layer using an ironing means such as a nozzle.

Embodiment 8. The FFF method according to any one of the preceding embodiments, wherein the build material comprises a semi-crystalline polymer.

Embodiment 9. The FFF method according to embodiment 8, wherein the build material comprises one of the set comprising PEEK, PEKK, PPS, PA, PLA and PET.

Embodiment 10. The FFF method according to any one of the preceding embodiments, wherein the complete 3D object after printing has a degree of crystallinity below 10%.

Embodiment 11. The FFF method according to any one of the preceding embodiments, wherein the support structure comprises one or more upstanding meandering thin walls, and a platform on top of the meandering walls, the platform comprising at least one support layer arranged under the interface layer, the at least one support layer having a degree of crystallinity less than that of the interface layer.

Embodiment 12. A method of generating instructions for printing three-dimensional (3D) objects with an FFF printer, the method comprising: - receiving a 3D model of a 3D object; - identifying overhangs in the 3D model; - generating models of support structures (14A,14B) that support the overhangs during a print process; - generating instructions for the FFF printer to print the 3D object and the support structures in build material, wherein an interface layer (15) of the support structures touching the 3D object is deposited using print settings that cause a higher degree of crystallinity of the interface layer (15) as compared to those parts of the 3D object that get into direct contact with the interface layer (15).

Embodiment 13. A computing device comprising one or more processing units, the one or more processing units being arranged to perform the method according to embadiment 12.

Embodiment 14. A computer program product comprising code embodied on computer-readable storage and configured so as when run on one or more processing units (111) to perform the method according to embodiment 12.

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 (14)

CONCLUSIESCONCLUSIONS 1. Een FFF- werkwijze (70) voor het genereren van een 3D-object, waarbij de werkwijze omvat: - het printen (71) van het 3D-object met behulp van een bouwmateriaal, waarbij het 3D-object ten minste één overhang omvat; - het printen (72) van ten minste één draagstructuur onder de ten minste ene overhang waarbij de draagstructuur wordt geprint met gebruikmaking van het bouwmateriaal, waarbij de draagstructuur een interface laag (15) omvat die contact maakt met het 3D-object, waarbij de interface laag (15) een kristalliniteitsgraad heeft die groter is dan de kristalliniteitsgraad van ten minste die delen van het 3D-object die in direct contact komen met de interface laag (15).An FFF method (70) for generating a 3D object, the method comprising: - printing (71) the 3D object using a building material, the 3D object comprising at least one overhang ; - printing (72) at least one support structure under the at least one overhang, the support structure being printed using the building material, the support structure comprising an interface layer (15) contacting the 3D object, the interface layer (15) has a degree of crystallinity greater than the degree of crystallinity of at least those parts of the 3D object that come into direct contact with the interface layer (15). 2. De FFF-werkwijze volgens conclusie 1, waarbij een deel (14A, 14B) van de draagstructuur dat niet de interface laag is, een kristalliniteitsgraad heeft die kleiner is dan de kristalliniteitsgraad van de interface laag.The FFF method of claim 1, wherein a portion (14A, 14B) of the support structure other than the interface layer has a degree of crystallinity less than the degree of crystallinity of the interface layer. 3. FFF-werkwijze volgens conclusie 2, waarbij de kristalliniteitsgraad van het deel van de dragerstructuur dat niet de interface laag is, in een bereik ligt van 0%-15%.The FFF method according to claim 2, wherein the degree of crystallinity of the portion of the support structure other than the interface layer is in a range of 0%-15%. 4. FFF-werkwijze volgens één van de voorgaande conclusies, waarbij de kristalliniteitsgraad van de interface laag boven 25% ligt.The FFF method according to any one of the preceding claims, wherein the crystallinity degree of the interface layer is above 25%. 5. FFF-werkwijze volgens één van de voorgaande conclusies, waarbij de kristalliniteitsgraad van de interface laag wordt bereikt door een spoor van afgezet materiaal gedurende een geschikte tijd binnen een kristallisatietemperatuurbereik van het bouwmateriaal te houden.The FFF method according to any one of the preceding claims, wherein the degree of crystallinity of the interface layer is achieved by keeping a trace of deposited material within a crystallization temperature range of the build material for a suitable time. 6. FFF-werkwijze volgens conclusie 5, waarbij de kristalliniteitsgraad van de interface laag (15) wordt verhoogd door middel van ten minste één van: - aansturen van een ventilator van een FFF-systeem tijdens depositie; - het regelen van een printsnelheid van een printkop van het FFF-systeem; - het regelen van een mondstuktemperatuur; - het aanpassen van een geometrie van een spoor, en - een geschikte planning van de sporen.The FFF method according to claim 5, wherein the degree of crystallinity of the interface layer (15) is increased by means of at least one of: - driving a fan of an FFF system during deposition; - controlling a print speed of a print head of the FFF system; - controlling a nozzle temperature; - adjusting a geometry of a track, and - a suitable planning of the tracks. 7. FFF-werkwijze volgens één der voorgaande conclusies, waarbij de kristalliniteitsgraad van de interface laag wordt verhoogd door middel van het strijken van de interface laag met behulp van een strijkmiddel zoals een mondstuk.The FFF method according to any one of the preceding claims, wherein the degree of crystallinity of the interface layer is increased by smoothing the interface layer using a smoothing means such as a nozzle. 8. FFF-werkwijze volgens één van de voorgaande conclusies, waarbij het bouwmateriaal een semi-kristallijn polymeer omvat.The FFF method according to any of the preceding claims, wherein the building material comprises a semi-crystalline polymer. 9. FFF-werkwijze volgens conclusie 8, waarbij het bouwmateriaal is geselecteerd uit de set van PEEK, PEKK, PPS, PA, PLA en PET.The FFF method according to claim 8, wherein the building material is selected from the set of PEEK, PEKK, PPS, PA, PLA and PET. 10. FFF-werkwijze volgens één van de voorgaande conclusies, waarbij het volledige 3D-object na het printen een kristalliniteitsgraad heeft van minder dan 10%.The FFF method according to any one of the preceding claims, wherein the complete 3D object has a crystallinity degree of less than 10% after printing. 11. FFF-werkwijze volgens één van de voorgaande conclusies, waarbij de draagstructuur één of meer opstaande meanderende dunne wanden omvat, en een platform boven op de meanderende wanden, waarbij het platform ten minste één onder de interface laag aangebrachte draaglaag omvat, waarbij de ten minste ene draaglaag een kristalliniteitsgraad heeft die lager is dan die van de interface laag.The FFF method according to any one of the preceding claims, wherein the support structure comprises one or more upstanding meandering thin walls, and a platform on top of the meandering walls, the platform comprising at least one support layer disposed below the interface layer, the at least at least one carrier layer has a degree of crystallinity lower than that of the interface layer. 12. Een werkwijze voor het genereren van instructies voor het printen van driedimensionale (3D) objecten met een FFF-printer, waarbij de werkwijze omvat: - het ontvangen van een 3D-model van een 3D-object; - identificeren van overhangen in het 3D-model; - het genereren van modellen van draagconstructies (14A,14B) die de overhangen ondersteunen tijdens een printproces; - het genereren van instructies voor de FFF-printer om het 3D-object en de draagconstructies in bouwmateriaal te printen, waarbij een interface laag (15) van de draagconstructies die het 3D- object raken, wordt gedeponeerd met behulp van printinstellingen die een hogere kristalliniteitsgraad van de interface laag (15) veroorzaken in vergelijking met die delen van het 3D-object die in direct contact komen met de interface laag (15).A method for generating instructions for printing three-dimensional (3D) objects with an FFF printer, the method comprising: - receiving a 3D model of a 3D object; - identify overhangs in the 3D model; - generating models of support structures (14A,14B) that support the overhangs during a printing process; - generating instructions for the FFF printer to print the 3D object and support structures in building material, depositing an interface layer (15) of the support structures touching the 3D object using print settings that have a higher degree of crystallinity of the interface layer (15) compared to those parts of the 3D object that come in direct contact with the interface layer (15). 13. Rekeninrichting omvattende één of meerdere verwerkingseenheden, waarbij de één of meerdere verwerkingseenheden zijn ingericht om de werkwijze volgens conclusie 12 uit te voeren.A computing device comprising one or more processing units, wherein the one or more processing units are adapted to perform the method according to claim 12. 14. Een computerprogrammaproduct dat code omvat die is belichaamd in een computerleesbare opslag en die zodanig is geconfigureerd om, indien deze wordt uitgevoerd op één of meerdere verwerkingseenheden (111), de werkwijze volgens conclusie 12 uit te voeren.A computer program product comprising code embodied in computer readable storage and configured to, when executed on one or more processing units (111), perform the method of claim 12.