WO2024005630A1

WO2024005630A1 - Liquefier assembly with a cooled protective sleeve around hot-end

Info

Publication number: WO2024005630A1
Application number: PCT/NL2023/050311
Authority: WO
Inventors: Kornelis Hermanus WELLING; Johan Andreas Versteegh; Beerend GROOT
Original assignee: Ultimaker B.V
Priority date: 2022-06-30
Filing date: 2023-06-06
Publication date: 2024-01-04
Also published as: NL2032330B1

Abstract

A liquefier assembly (1) for use in a fused filament fabrication system is described. The assembly comprises a liquefier tube (2) having an inlet (21) and an outlet (22), a nozzle (9) arranged at the outlet of the liquefier tube, a cooling element (3) arranged around a first section (23) of the liquefier tube, and a heating element (4) arranged around a second section (24) of the liquefier tube, the second section being located downstream the first section. The assembly comprises a heat conductive sleeve (5) arranged around the second section of the liquefier tube, wherein an inner wall of the sleeve is distant from the liquefier tube, and wherein a first outer end (51) of the sleeve is thermally coupled to the cooling element. A shield (6) is arranged to shield a space (7) between the liquefier tube and the sleeve, the shield comprising heat conductive material and being thermally coupled to a second outer end of the sleeve.

Description

Liquefier assembly with a cooled protective sleeve around hot-end

Field of the invention

The present invention relates to a liquefier assembly for use in a fused filament fabrication system. More specifically, the invention relates to a liquefier assembly with a cooled protective sleeve around part of the liquefier tube. The invention also relates to a fused filament fabrication system comprising such a liquefier assembly.

Background art

Fused filament fabrication (FFF) is a 3D printing process that uses a continuous filament of a thermoplastic material to fabricate printed objects. The filament is fed from a filament supply through a moving, heated liquefiers, and is deposited through a print nozzle onto an upper surface of a build platform. The liquefier may be moved relative to the build platform under computer control to define a printed shape. In certain FFF devices, the liquefier moves in two dimensions to deposit one horizontal plane, or layer, at a time. The work or the liquefier 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.

Many present liquefiers are limited in the maximum printing temperature, have relatively long heat up (and cooldown) times and are restricted in the channel length of the hot-end. To obviate these problems, liquefier assemblies are produced having a relatively long but fragile liquefier tube. In some known systems, such liquefier tubes are then protected by means of a sleeve around the liquefier tubes. Since the liquefier tube is heated at the hot-end, the sleeve around the hot-end is also heated. A known disadvantage of such configurations is that in the event that print material is not correctly deposited, it may want to creep up and this may cause malfunctioning of the FFF system. Especially if the creeping up of the material is not detected on time, this may have serious consequences for the liquefier assemble, the housing in which it may be arranged, and/or the FFF system as a whole.

Summary of the invention

The aim of the present invention is to provide a liquefier assembly for use in an FFF system that solves at least some of the problems of the prior art mentioned above.

The invention also relates to a fused filament fabrication system comprising such a liquefier assembly, a liquefier assembly for use in a fused filament fabrication system. The assembly comprises a liquefier tube having an inlet and an outlet, a nozzle arranged at the outlet of the liquefier tube, a cooling element arranged around a first section of the liquefier tube, and a heating element arranged around a second section of the liquefier tube, the second section being located downstream the first section. The assembly also comprises a heat conductive sleeve arranged around the second section of the liquefier tube, wherein an inner wall of the sleeve is distant from the liquefier tube, and wherein a first outer end of the sleeve is thermally coupled to the cooling element. A shield located near the nozzle and arranged to shield a space between the liquefier tube and the sleeve, the shield comprising heat conductive material and being thermally coupled to a second outer end of the sleeve.

The sleeve has two functions. The sleeve acts as a bumper protecting the liquefier tube from getting damaged in case of collision, or external forces. Since a first outer end of the sleeve is thermally coupled to the cooling element, the sleeve is cooled. At its turn the sleeve will cool the shield. Since the shield is near the nozzle, it will be heated by the nozzle but cooled by the sleeve. In the event that print material is not correctly deposited, it may want to creep up and may cause malfunctioning of the FFF system. However, due to the cooled shield and the cooled sleeve, the molten print materials will solidify, and will no longer creep up but can only find a way down away from the assembly. In this way, an unwanted flooding of the print material into the sleeve or around the sleeve is avoided.

In an embodiment, the outlet of the liquefier tube and/or the nozzle is mechanically coupled to the heat conductive sleeve. Due to this mechanical coupling, the liquefier is mechanically supported by the shield. Due to this the liquefier tube can be designed relatively long and thin, which provides for higher flow rates during printing and shorter heat up and cool down times. The mechanical coupling can be achieved e.g. by designing a proper shield contacting the nozzle. Alternatively or additionally the coupling may comprise one or more bars arranged between the tube/nozzle and the sleeve.

In an embodiment, the heat conductive sleeve comprises one or more cylindrical shaped sections. Alternatively the sleeve may have a rectangular section and a cylindrical section, depending on the design of the cooling element and the shield.

In an embodiment, the cooling element comprises a cylindrical extension, wherein an outer end of a cylindrical section of the sleeve is arranged around the cylindrical extension. This design provides for an easy and firm coupling between the cooling element and the sleeve.

In an embodiment, the heating element comprises an electrical resistive coating arranged on part of an outer surface of the liquefier tube. Since this coating can be made relatively thin, it requires little space, as compared to heater block. As a result the sleeve can be made relatively thin giving more design freedom for the receiving element receiving the liquefier assembly, such as the liquefier assembly mount.

In an embodiment, the liquefier tube and the nozzle are completely made out of a metal, meaning that no Teflon or another temperature limiting material is present in the hot end. Such a hot-end design enables printing with high temperatures (up to 500 °C) and using a large range of FDM materials including ABS, PC and Nylon.

In an embodiment, a body of the nozzle comprises steel and the inner surface is coated using electroless nickel coating. These materials provide for a very wear resistant nozzle.

In an embodiment, the liquefier tube extends out of the cooling element with a length of at least 10 mm. In another embodiment, the extension is at least 40 mm. These length will result is long hot ends which will enable a high flow rate. Longer liquefiers, means more time to head up the filament. Such relatively long hot-ends will also match better with bigger nozzle die holes, up to 1 .2 mm.

In an embodiment, the liquefier tube extends from an upstream side of the cooling element to the nozzle. This provides for one single filament guiding tube, transporting filament from the cold zone to nozzle, without any edges where the filament and/or meniscus could get trapped during de priming.

In an embodiment, the shield comprises a curved sheet metal having an opening for receiving a tip of the nozzle. Such a curved shield can be made very thin but still be rigid. Furthermore, such a curved shield can be arranged really close to the orifice of the nozzle. In this way, the nozzle tip will not be cooled too much by object cooling fans blowing along the liquefier towards the build platform.

In an embodiment, the assembly comprises a first circuit board comprising a number of connectors for electrical connection to connectors of the filament fabrication system. The assembly may also comprise a second circuit board, the second circuit board (also referred to as connector PCB) being connected to the first circuit board by first wiring and connected to the heating element via second wiring. The second wiring can be very thin for connection to the heating element. Thin wiring is preferred in case of connecting a heat coating.

In an embodiment, the assembly comprises an interface plate (e.g. outer ‘ring’ around the sleeve) arranged at an outer surface of the sleeve, wherein the second circuit board is fixed onto the interface plate. In this way the second circuit board is coupled to liquefier assembly. So if the liquefier assembly is lifted relative to the liquefier support system, the second circuit board is lifted too, and the second wiring is not bended and wear or damage to the second wiring is minimized.

Due to the fact that the sleeve is cooled (i.e. by the cooling element), the connector PCB could be mounted on this sleeve very close to the hot end without getting too hot. As a result, the second wiring (i.e. between the connector PCB and the heater on the hot-end) could be made relative short. The first wiring (between the connector PCB and the first circuit board) can be thicker wires, which is preferred since this wiring will be bent frequently due to the lifting of the assembly. The first wiring may comprise a flex-PCB designed for small movements and bending. The combination of a moving connector PCB and a static firs circuit board together with suitable wiring in between will result in a strong overall design. Due to intermediate connector PCB, less and smaller components can be used in the assembly, as compared to the relatively big connectors used in the prior art.

According to a further aspect, there is provided a fused filament fabrication system comprising a liquefier assembly 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 part of a liquefier assembly according to an embodiment;

Figure 2 schematically shows a cut-out view of a lower part of the liquefier assembly according to a further embodiment;

Figure 3 schematically shows a cross section of part of a liquefier assembly according to a further embodiment of the invention;

Figure 4 schematically shows a cross section of part of a liquefier assembly according to a further embodiment of the invention;

Figure 5 shows a cut out view of a further embodiment of the liquefier assembly;

Figure 6 schematically shows a cross section of a liquefier assembly according to an embodiment of the invention;

Figure 7 schematically shows a cut out view of a liquefier assembly according to another embodiment;

Figure 8 shows a perspective view of a lower part of the liquefier assembly according to an embodiment, and

Figure 9 schematically shows a front view of an FFF system according to an embodiment of the invention.

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 part of a liquefier assembly 1 according to an embodiment of the invention. The liquefier assembly 1 comprises a liquefier tube 2 having an inlet 21 and an outlet 22. The liquefier assembly 1 further comprises a nozzle 9 arranged at the outlet 22 of the liquefier tube 2. A cooling element 3 is arranged around a first section 23 of the liquefier tube 2. In this example, the cooling element 3 comprises a cylindrical shaped main body 31 and a number of cooling fins 32 arranged around the main body 31 . The main body 31 comprises a through hole through which the liquefier tube 2 is inserted.

A heating element 4 is arranged around a second section 24 of the liquefier tube 2. This second section 24 is located downstream the first section 23. In this embodiment, the heating element 4 comprises a heating block arranged to heat a part of the liquefier tube 2 so as to make thermoplastic filament fed into the liquefier tube, melt.

The liquefier assembly 1 further comprises a heat conductive sleeve 5 arranged around the second section 24 of the liquefier tube 2. The inner wall of the sleeve 5 is distant from the liquefier tube 2. At a first outer end 51 the sleeve 5 is thermally coupled to the cooling element 3.

The liquefier assembly 1 further comprises a shield 6 located near the nozzle 9 and arranged to shield a space 7 between the liquefier tube 2 and the sleeve 5. The shield 6 comprises a heat conductive material and is thermally coupled to a second outer end 52 of the sleeve 5.

In the example of Figure 1 , the liquefier tube 2 extends through the cooling element 3 and the heating element 4 onto the nozzle 9. An advantage of using one continuous tube transporting filament from the cold zone to nozzle, is that are no edges in the liquefier channel, so the risk of getting filament trapped during filament feeding or retracting is minimized.

Optionally, the assembly 1 comprises a sleeve cooling element 8, which is arranged around the sleeve 5 at the first outer end 51 of the sleeve 5. The sleeve cooling element 8 is arranged to cool at least part of the sleeve 5. The sleeve cooling element 8 is not in contact with the liquefier tube 2. Both the cooling element 3 and the sleeve cooling element 8 may be cooled by way of using one or more fans (not shown in Figure 1) arranged to generate an air flow to and/or from the cooling elements.

The liquefier tube 2 may be a cylindrical tube having a diameter d1 . The value of d1 will depend on the thickness of filament to be used for manufacturing a part. For example, in case a filament with a thickness of 2.85 mm is used, the diameter d1 may be approximately 3 mm. The sleeve 5 may comprise a cylindrical tube having a diameter d2. In an embodiment, the diameter d2 of the sleeve 5 lies in a range of 15-40 mm.

The sleeve 5 acts as a bumper protecting the liquefier tube 2 from getting damaged in case of collision with a printed part or by other external forces. The sleeve 5 may comprise a metal like aluminium, or another heat conductive material like conductive ceramics. Since the sleeve 5 is thermally connected to the cooling element 3, the sleeve 5 is cooled by the cooling element 3.

Figure 2 schematically shows a cut-out view of a lower part of the liquefier assembly 1 according to a further embodiment. In this embodiment, the sleeve 5 comprises a tapered sections 54 which outer end is in contact with a disk 6 acting as the shield mentioned above. In this embodiment, the disk 6 is in thermal and mechanical contact with the nozzle 9. Since the disk 6 is made out of a heat conductive material, like metal or ceramics, it will be relatively hot at the side of the nozzle 9, but colder at the side of the sleeve 5.

The advantage of the shield 6 being cooled by the cooled sleeve 5 is that in case the molten print material coming out of the nozzle 9 is not correctly deposited onto a build surface or onto a previously printed layer, it will not creep up into or onto the sleeve 5, since it will solidify due to the lower temperature. In this way flooding of the print material into the sleeve or around the sleeve and further into other parts of the system is avoided or at least considerably reduced.

Figure 3 schematically shows a cross section of part of a liquefier assembly 1 according to a further embodiment of the invention. Similar to the previous embodiment, the liquefier assembly 1 of Figure 3 comprises a cooling element 3 for cooling a first section 23 of the tube 2 and a heating element 4 arranged around the second section 24 of the liquefier tube 2 so as to heat up that second section 24. In this embodiment the cooling element 3 is extended by means of an additional cooling element 3’. The additional cooling element is coupled to the sleeve 5. In this embodiment the sleeve 5 comprises four walls 56 made out of a metal such as aluminum, which is a good thermal conductor. The inner surface 57 of these walls of the sleeve 5 are distant from the liquefier tube 2, resulting in an inner space 7. In an embodiment, the walls 56 are connected to the additional cooling element 3’. The liquefier assembly 1 further comprises a shield 6 located near the nozzle 9 and arranged to shield the inner space 7 between the liquefier tube 2 and the sleeve 5. In this embodiment, the shield 6 is curved in the plane of view, and is rectangular shaped in a perpendicular cross section. The shield 6 comprises a heat conductive material (e.g. a metal) and is thermally coupled to a second outer end 52 of the sleeve 5. The shield 6 may be part of a sheet metal with a hole for the nozzle, and arranged around two of the walls 56, extending up to the additional cooling element 3’.

It is noted that the curved shield 6 in Figure 3 is in contact with nozzle 9 close to the orifice. This is preferred to make sure ambient air and object cooling do not cool down the nozzle 9.

Figure 4 schematically shows a cross section of part of a liquefier assembly 1 according to a further embodiment of the invention. In this embodiment, the heating element comprises an electrical resistive coating 40 arranged on part of an outer surface of the liquefier tube 2. The coating 40 heats up due to an electrical current. An example of such a coating is electrical resistance ceramic heater paste. The heating element 40 is arranged around the second section 24 of the liquefier tube 2 so as to heat up that second section 24.

Similar to the embodiment of Figure 1 , the liquefier assembly 1 of Figure 4 comprises a heat conductive sleeve 5 arranged around the second section 24 of the liquefier tube 2. The inner wall of the sleeve 5 is distant from the liquefier tube 2. At a first outer end 51 the sleeve 5 is thermally coupled to the cooling element 3. The liquefier assembly 1 further comprises a shield 6 located near the nozzle 9 and arranged to shield a space 7 between the liquefier tube 2 and the sleeve 5. The shield 6 comprises a heat conductive material and is thermally coupled to a second outer end 52 of the sleeve 5.

It is noted that the coating 40 requires relatively little space, as compared to heater block 4 present in the embodiment of Figure 1 . So the sleeve 5 can be made relatively thin giving more design freedom. Furthermore, due to the relatively low thermal mass of the liquefier tube 2 and the coating 40, this liquefier assembly is able to change temperature very quickly. This will have positive effects on speed changes during printing and will also reduce heating up and cooling down times.

The liquefier tube 2 and/or the nozzle 9 may be mechanically coupled to the heat conductive sleeve 5. In one embodiment, this mechanical coupling is achieved by the shield 6 as shown in Figure 2. Alternatively, the mechanical coupling may be embodied by one or more support bars extending from the liquefier end 22 or the nozzle 9 to the shield 5. An advantage of supporting, at least in horizontal plane, the liquefier 2 near the nozzle is that the liquefier tube 2 can be designed relatively long and thin, which provides for higher flow rates during printing.

In embodiment, the liquefier tube 2 extends out of the cooling element with a length L1 of at least 10 mm. A relatively long liquefier means more time to heat up the filament, enabling higher flow rates. This longer liquefier tube will also enable the use of bigger nozzle die holes, up to 1 .2 mm in case of a liquefier diameter d1 of 3 mm.

It is noted that in the embodiment of Figure 1 and 3, the liquefier assembly 1 comprises a liquefier tube that extends from an upstream side of the cooling element 3 to the nozzle 9. So the filament is guided from the inlet to the nozzle 9 via one tube. There are no transitions where filament could get trapper during printing or retracting, resulting in less errors.

Figure 4 shows a cut out view of a further embodiment of the liquefier assembly 1 . The liquefier assembly 1 comprises a liquefier tube 20, a cooling element 3 and a heating element 40 arranged around part of the liquefier tube 40. A nozzle 9 is arranged at the outlet of the liquefier tube 40. In this embodiment, the cooling element 3 comprises a main body 31 and a number of cooling fins 32. The cooling element 3 also comprises a tube-shaped extension 34 extending towards the nozzle 9.

In this embodiment the heat conductive sleeve 5 comprises two cylindrical shaped sections, see 51 and 52. The second section 52 has a larger diameter than the first section 51 . The second section 52 is arranged around the extension 34 of the cooling element 3. An advantage of the configuration shown in Figure 4 is that the sleeve 5 is in good thermal contact with the cooling element 3 while at the same time having a relatively thin shape towards the nozzle 9.

The liquefier assembly 1 of Figure 4 further comprises a disc 55 also referred to as interface plate 55. The interface plate 55 may be fully or partly made out of a heat conductive material like metal or aluminium. The function of the plate 55 will be explained in more detail below.

It is noted that while the sections (i.e. 51 and 52) of the heat conductive sleeve 5 have circular cross sections, alternatively they may have oval, triangular or rectangular cross sections. A cylindrical cross section is preferred since this will result in the most robust design.

The liquefier tube 2 and the nozzle 9 may be completely made out of a metal with no Teflon or another temperature limiting material in the hot-end. In an embodiment, the heating element 4, 40 is arranged to heat up the hot-end to a temperature between 100 - 500 °C. This temperature range enables the use of a very wide range of printing materials, like PPS and PEI and also PEEK.

In an embodiment, a body of the nozzle 9 comprises steel and the inner surface is coated using an electroless nickel coating. This configuration makes the nozzle 9 very wear resistant.

Figure 6 schematically shows a cross section of a liquefier assembly 1 according to an embodiment of the invention. In this example, the liquefier assembly 1 comprises all the elements shown in Figure 4 assembled into a support system 60. The support system 60 comprises a main body 61 (see shaded part), a slide 62 and a spring 63. The support system 60 is arranged to support all the elements shown in Figure 4 and to mount the liquefier assembly 1 into an FFF system (see also Figure 9).

The slide 62 is slidably arranged into the main body 61 . The spring 63 is arranged to push down the slide 62 together with the liquefier tube 20, the cooling element 3 and the nozzle 9. Once mounted into a printing system, like an Ultimaker S5 printer, the nozzle 9 can be lifted up by means of a lifting mechanism as was disclosed in patent publication EP 3 199 326 B1 in the name of Ultimaker BV.

If the liquefier assembly 1 is mounted into the printing system, a user can push up the slide 62 to lift the nozzle 9 and the liquefier tube 20, so as to conveniently remove the assembly.

Figure 7 schematically shows a cut out view of a liquefier assembly according to another embodiment. As compared to the embodiment of Figure 6, the liquefier assembly of Figure 7 also comprises a sleeve cooling element 8 already described with reference to Figure 4. The sleeve cooling element 8 is arranged around the sleeve 5 near the first cooling element 3.

Figure 7 further shows that the liquefier assembly 1 comprises a first circuit board 70 comprising a number of connectors 71 for electrical connection to connectors of a filament fabrication system 100 (see also Figure 9). The assembly 1 also comprises a second circuit board 72, the second circuit board being connected to the first circuit board 50 by first wiring 81 and connected to the heating element 40 via second wiring (not shown in Figure 7). The liquefier assembly 1 also comprises an interface plate 55 arranged at an outer surface of the sleeve 5, wherein the second circuit board 72 is fixed onto the interface plate 55.

Figure 8 shows a perspective view of a lower part of the liquefier assembly 1 according to an embodiment. This embodiment is quite similar to the one of Figure 7 except that the sleeve cooling element 8 is absent and the interface plate 55 is disc shaped and not oval as was shown in Figure 7. The liquefier assembly 1 of Figure 8 comprises a heat element 40 made out of a coating arranged on the outer surface of the liquefier tube (not visible in Figure 8). The heat element 40 may be manufactured by applying a thick film heater paste pattern on the liquefier tube 2 by means of e.g. screen printing and then curing this in an oven. The heater paste pattern may be connected by way of connecters that are connected to the second circuit board 72 via relatively thin (second) wiring 82, see Figure 8. The sleeve 5 may comprises an opening for passing through of the second wiring 82. In an embodiment, the second circuit board 72 is a printed circuit board also referred to as connector PCB since the main function is to connect the first wiring 81 to the second wiring 82.

It is noted that the electrically connecting a heater paste pattern on a thin liquefier tube requires relatively thin wires (e.g. having a diameter less than 0.5 mm). Such thin wires may break easily if they are made too long. Furthermore, since the nozzle and liquefier tube will frequently be lifted relative to the support 61 , the second wiring will experience a lot of bending if it would have been connected to the first circuit board 70, which is fixed to the support 61 . By adding an additional (intermediate) circuit board (i.e. circuit board 72) the wiring toward the heating element 40 can be designed relatively thin, and the wiring towards the first circuit board 70 can be made thicker. Since the second circuit board is fixed onto the sleeve 5 via the interface plate 55, it will move up and down together with the nozzle and the liquefier tube. So the thin second wiring 82 will not get bended nor stretched. On the other hand, the first wiring 81 will get bended during lifting of the nozzle and liquefier tube, but since it is thicker (e.g. diameter larger than 1 mm) it is more robust and will withstand bending for many times. In the embodiment of Figure 8, the first wiring 81 comprises a flex cable comprising several coper wires arranged in parallel. The flex cable is designed for small movements. This will result in a strong overall design.

It is noted that part of the first and second wiring may be used to deliver power to the heating element, while another part may be used to transfer sensing date. The heating element may comprise a temperature sensor which generates a sensing signal that is communicated to the first circuit board 70 and via the connectors 71 to a control system of the FFF system.

As was described above, the sleeve 5 is cooled by the cooling element 3, 3’ (and optionally also by sleeve cooling element 8) and transfers the cold towards the interface plate 55. Due to this cooled bumper design, the connector PCB 72 can be mounted on this bumper very close to the hot end. So the fragile wires (i.e. wiring 81) can be relative short and will also not move when the nozzle is lifted.

Figure 9 schematically shows a front view of an FFF system 100 according to an embodiment of the invention. The FFF system 100 comprises a housing 102 and a build platform

104 arranged in the housing 102. In this embodiment, the build platform 104 is movably arranged in the housing 102 and can move up and down in a Z-direction. The FFF system 100 comprises a mount 105 arranged to hold one or more liquefier assemblies 1 as described above. The mount

105 is movably arranged in the housing 102 and can be moved in an X and Y direction by a gantry 106 as will be clear to the skilled reader. In this example, two fans 110, 112 are arranged in the housing of the mount 105 to provide air flows for cooling the cooling elements and/or other parts of the liquefier assemblies 1 . Other fans, not shown, may be provided to blow air towards the build platform 104 in order to cool printed traces, as is appreciated by the skilled person. It is noted that the housing 102 may be absent and that the gantry 106 is supported by a frame instead of the housing 102.

The FFF system 100 further comprises a controller 120 arranged to control the movement of the mount 105 and the movement of the build platform 104. The controller 120 may also be arranged to control the heating 4;40 of the liquefier assemblies 1 and to control one or more filament feeders (not shown in Figure 9).

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 as long as they 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 within the scope of the appended claims. 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

1 . A liquefier assembly for use in a fused filament fabrication system, the assembly comprising:

- a liquefier tube having an inlet and an outlet;

- a nozzle arranged at the outlet of the liquefier tube;

- a cooling element arranged around a first section of the liquefier tube;

- a heating element arranged around a second section of the liquefier tube, the second section being located downstream the first section;

- a heat conductive sleeve arranged around the second section of the liquefier tube, wherein an inner wall of the sleeve is distant from the liquefier tube, and wherein a first outer end of the sleeve is thermally coupled to the cooling element;

- a shield located near the nozzle and arranged to shield a space between the liquefier tube and the sleeve, the shield comprising heat conductive material and being thermally coupled to a second outer end of the sleeve.

2. The liquefier assembly according to claim 1 , wherein the outlet of the liquefier tube and/or the nozzle is mechanically coupled to the heat conductive sleeve.

3. The liquefier assembly according to claim 1 or 2, wherein the heat conductive sleeve comprises one or more cylindrical shaped sections.

4. The liquefier assembly according to claim 3, wherein the cooling element comprises a cylindrical extension, wherein an outer end of a cylindrical section of the sleeve is arranged around the cylindrical extension.

5. The liquefier assembly according to any one of the preceding claims, wherein the heating element comprises an electrical resistive coating arranged on part of an outer surface of the liquefier tube.

6. The liquefier assembly according to any one of the preceding claims, wherein the liquefier tube and the nozzle are completely made out of a metal.

7. The liquefier assembly according to any one of the preceding claims, wherein a body of the nozzle comprises steel and the inner surface is coated using electroless nickel coating.

8. The liquefier assembly according to any one of the preceding claims, wherein the liquefier tube extends out of the cooling element with a length of at least 10 mm.

9. The liquefier assembly according to any one of the preceding claims, wherein the liquefier tube extends from an upstream side of the cooling element to the nozzle.

10. The liquefier assembly according to any one of the preceding claims, wherein the shield comprises a curved sheet metal having an opening for receiving a tip of the nozzle.

11 . The liquefier assembly according to any one of the preceding claims, wherein the assembly comprises a first circuit board comprising a number of connectors for electrical connection to connectors of the filament fabrication system.

12. The liquefier assembly according to claim 11 , wherein the assembly comprises a second circuit board, the second circuit board being connected to the first circuit board by first wiring and connected to the heating element via second wiring.

13. The liquefier assembly according to claim 12, wherein the assembly comprises an interface plate arranged at an outer surface of the sleeve, wherein the second circuit board is fixed onto the interface plate.

14. Fused filament fabrication system comprising a liquefier assembly according to any one of the preceding claims.