NL2030050B1 - A liquefier for use in an FFF system - Google Patents

Abstract

A liquefier (1) for use in an FFF system is described comprising a thermally-conductive liquefier tube (2) comprising an inlet end and an outlet end, a nozzle (5) attached to the outlet end ofthe liquefiertube, a heater assembly (60;70;80) comprising at least one PTC resistor arranged at at least part of an outer surface ofthe liquefiertube to impart heat into the liquefiertube, and a number of power lines (7,8) connected to the at least one PTC resistor. The electrical resistance ofthe PTC resistor continuously increases with temperature over a temperature work range. Using such a configuration results in a passive temperature control overthe length ofthe liquefier enabling faster flow of the molten filament and thus faster printing.

Description

A liquefier for use in an FFF system

Field of the invention

The present invention relates to a liquefier for use in an FFF system and to an FFF printing system comprising such a liquefier. The invention more particularly relates to a liquefier comprising a heater assembly for creating a multi-zone heating in the liquefier.

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 liquefier in a moving 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.

FFF material is at ambient temperature when it enters the liquefier. The liquefier contains a heating element to raise the temperature of the material to the desired printing temperature. A

FFF printer liquefier will thus have a temperature gradient over its length when it starts extruding.

The AT between liquefier wall and filament at the side where the solid material enters will be larger than at the exit when extruding, so more heater power is needed at the entry than near the exit of the liquefier. A good thermal conduction along the length of the liquefier will enable transfer of this heat from entry to exit of the liquefier, which makes liquefiers possible that can reach high flow rates. However, above a certain flow rate the molten filament will be too cold and viscous when it reaches the nozzle and cannot be pushed through by the feeding system anymore.

Furthermore, good thermal conduction typically requires more conducting material and thus also a higher thermal mass, leading to longer warmup and cooldown times of the liquefier body.

Nowadays, very often a heater cartridge is used which is mounted in a heater block. This heater block has a good thermal conductance (e.g. brass, copper or aluminum), ensuring that more heat is transported to the cold areas preventing large gradients over the liquefier. If a liquefier is made from less heat conducting materials (e.g. Stainless Steel, Titanium) or if the liquefier has a relatively thin wall, it is more challenging to transfer the heat to the colder areas.

This can particularly be challenging when using longer liquefiers. Some longer liquefier designs use a multi-zone heater design in which two or more zones from the entry to the exit of the liquefier are defined, where each zone has a separate heater element and temperature sensor that can be controlled. This prevents a large power density gradient over the liquefier.

Publication DE202014008106U1 describes a liquefier for use in an FFF system. The liquefier comprises a liquefier tube in which a filament is molten using multi-zone heater assembly. The multi-zone heater assembly is designed to reduce temperature gradients within the liquefier tube. Such a liquefier is rather complex because multiple sensors are needed to control the different zones. Both sensors and heating elements need to be connected which requires a lot of cable connections and control logic which makes the liquefier prone to malfunctioning.

Summary of the invention

The aim of the present invention is to provide a liquefier for use in an FFF printing system that provides for multi-zone heating but is less complex than the state of the art mentioned above.

According to a first aspect of the present invention, there is provided a liquefier for use in an FFF system, the liquefier comprising a thermally-conductive liquefier tube comprising an inlet end and an outlet end, a nozzle attached to the outlet end of the liquefier tube, and a heater assembly comprising at least one PTC (Positive Temperature Coefficient) resistor arranged on at least part of an outer surface of the liquefier tube to impart heat into the liquefier tube. The liquefier also comprises a number of power lines connected to the at least one PTC resistor. The electrical resistance of the at least one PTC resistor continuously increases with temperature over the temperature work range of the liquefier.

In an embodiment, multiple PTC resistors are arranged along the length of the liquefier.

The powering of these PTC resistors creates a multiple zone heating. Due to the continuous increase of the electrical resistance in the work range, the heat dissipation of each resistor, or in case of one resistor in each zone of the resistor, will depend on the local temperature of the liquefier tube: if the temperature in the liquefier tube at some zone decreases, the resistance of the PTC resistor at that zone decreases and that PTC resistor will supply more heat and will correct the temperature in the liquefier tube at that zone. Similarly, if the temperature in the liquefier tube at some zone increases, the resistance of the PTC resistor at that zone increases and that PTC resistor will supply less heat and will correct the temperature in the liquefier tube at that zone. In this way a passive temperature control system is created by the PTC resistor(s). The only control needed is the control of the mean temperature which can be executed by a power supply having a particular setting depending on a temperature measured at or near the outlet end of the liquefier tube. By applying more power where it is needed, this liquefier assembly is less dependent on axial heat flow to distribute heat; thus allowing for thinner walls and, hence, lower thermal mass than a conventional liquefier.

An additional benefit of the PTC is that it has a self-limiting end temperature, which prevents overheating in case malfunctioning of the electronic circuit. The invented resistance layout will allow high flow rates with a low thermal mass liquefier, enabling fast heat up and cool down times.

In an embodiment the at least one PTC resistor, at least in use, is connected to a power supply via the power lines in such a way that electric current through the PTC resistor runs perpendicular to a main axis of the liquefier tube. Such a design enables the placement of many resistors on the outer surface of the liquefier where each resistor is defining one temperature zone. No intermediate power lines between the PTC resistors are needed, and thus an optimal coverage of the outer surface is possible. In an alternative embodiment, the resistors are connected in such a way that the current through the resistors runs parallel to the main axis of the liquefier. Such a configuration requires more connection lines and thus less area can be used to place the resistors.

In an embodiment, the temperature work range is at least 200 °C wide, for example 300 °C. In an embodiment, PTC resistors are used that can properly operate in a range between 200 °C and 500 °C. This is the practical range for all the thermoplastics used for FFF printers, so many different types of thermoplastics can be liquified using such a liquefier. In an embodiment, the at least one PTC resistor comprises multiple PTC resistors which, at least in use, are electrically connected in parallel by the power lines. The PTC resistors may be separate positive temperature resistance (PTC) heater strips that are arranged perpendicular to the liquefier filament flow direction. The PTC heater strips are arranged to create a parallel resistor layout.

This layout will automatically increase the power in colder areas of the liquefier (the inlet end) when needed.

In an embodiment, the liquefier tube comprises a wall having a thickness of between 0.5 — 1.5 mm. Such a relatively thin wall results in a low thermal mass so that the heaters have almost immediate effect on the printing material in the liquefier tube.

In an embodiment, the liquefier further comprises a temperature sensor, such as a PT100 sensor, arranged to measure a temperature of part of the liquefier tube.

The measured temperature measured by the sensor can be used by a controller. The controller receiving the signals from the sensor can control the temperature of the liquefier at the location of the sensor by providing a specific amount of power to the heating elements (i.e. the

PTC resistors).

In an embodiment, one or more of the resistive elements are made by screen printing a paste on the outer surface of the liquefier tube, which is then fired in an oven, creating a thick-film heater.

By screen printing a paste on the outer surface a thin layer of resistive material can easily be applied. The layer may comprise e.g. a binding material and an alloy containing elements such as palladium and ruthenium. In an embodiment, heater strips are screen printed thick film tracks.

Alternatively, a thin conductive metal film (CVD) may be applied in which a pattern is trimmed with a laser.

In an embodiment, the power connections (i.e. the power lines) are made by Chemical

Vapour Deposition of a metal strip on the outer surface of the liquefier tube. This will result in a relatively smooth surface of the resistors and the power lines, which surface can be coated with e.g. enamel, after which the coated liquefier is fired in an oven.

In an embodiment, the number of power lines is two, wherein each of the power lines extend longitudinal along the liquefier tube and the power lines are located at opposing sides of the tube.

This results in a symmetrical configuration of PTC resistors, wherein each zone is heated by two PTC resistors. In case of screen-printed PTC resistors, the two opposing power lines will enable a maximum use of the surface of the liquefier as compared to two power lines being arranged next to each other. The latter will always require some surface in between the power lines which surface cannot be used for a screen-printed resistor.

The invention also relates to a FFF printing system comprising a controller and a liquefier as described above, wherein the controller is arranged to control the power to the heater assembly. It is noted that the controller may comprise one or more modules, each being arranged on the liquefier, in the print head or on the main board of the printing system.

In an embodiment, the controller is arranged to measure the current through the PTC resistors and to control an average temperature of the liquefier depending on the measured current. This will obviate the need for a temperature sensor, which is a relatively expensive component, and installing such a sensor on the liquefier is rather cumbersome making manufacturing expensive.

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 side view of a liquefier for use in an FFF system according to an embodiment of the invention;

Figure 2 schematically shows a perspective view of the heater assembly of the liquefier of the embodiment of Figure 1 and a 2D projection of the PTC resistors and the power lines;

Figure 3 schematically shows an electronic schematic diagram of the PTC resistors and a power supply;

Figure 4 schematically shows an electronic schematic diagram of the PTC resistors and a power supply according to another embodiment;

Figure 5 schematically shows a perspective view of the heater assembly of the liquefier and a 2D projection of the PTC resistors and the power lines according to a further embodiment;

Figure 6 schematically shows an electronic schematic diagram of the PTC resistors and a power supply of the embodiment of Figure 5;

Figure 7 schematically shows a perspective view of a heater assembly of the liquefier and a 2D projection of the PTC resistors and the power lines according to a further embodiment;

Figure 8 schematically shows a perspective view of a heater assembly of the liquefier and a 2D projection of the PTC resistors and the power lines according to a further embodiment;

Figure 9 shows a graph of a possible relationship between the electrical resistance and the temperature of the PTC resistor over a temperature work range, and

Figure 10 schematically shows an FFF printing 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 side view of a liquefier 1 for use in an FFF system according to an embodiment of the invention. The liquefier 1 comprises a thermally-conductive 5 liquefier tube 2 comprising an inlet end 3 and an outlet end 4. The liquefier tube 2 may be made out of aluminium oxide or any other material that is heat conductive and not electrically conductive, such as Aluminium Nitride, Boron Nitride, Silicon Carbide, Beryllium Oxide and

Zirconia. It can also be made out of an electrical conduction element (e.g. steel pipe) coated with an electrical insulating (ceramic) to be able to apply the heater elements. In Figure 1 a filament 11 enters the liquefier 1 through the inlet end 3. The liquefier 1 comprises a nozzle 5 attached to the outlet end 4 of the liquefier tube 2. The liquefier 1 also comprises a heater assembly comprising eight PTC resistors arranged at at least part of an outer surface of the liquefier tube 2 to impart heat into the liquefier tube 2 so as to melt the filament 11. Please note that only four, ref. numbers 61, 62, 63, 64, of the eight PTC resistors are shown in Figure 1. The liquefier 1 further comprises a number of power lines 7, 8 electrically connected to the PTC resistors 61, 62, 63 64. The power lines 7, 8 may be manufactured using copper, silver or any other sufficiently conductive material.

The PTC resistors can be connected to a power supply (not shown in Figure 1) via the power lines 7, 8. Due to the configuration shown in Figure 1, the electric current through the PTC resistor runs perpendicular to a main axis of the liquefier tube 1, see the dashed line 9.

In the embodiment of Figure 1 a temperature sensor 10 is arranged on the liquefier 1 to measure the temperature at a location near the nozzle 5. The sensor 10 can be connected to a controller {see Figure 3) in order to control the temperature of the liquefier 1 using measurements received from the sensor 10. The sensor 10 may be e.g. a PT100 element or any other suitable temperature sensing device.

In the embodiment of Figure 1, the PTC resistors are relatively thin and curved around the circumference of the tube 2. In an embodiment the PTC resistors are screen printed onto the liquefier tube 2. This technique results in very thin layer of PTC resistors. Typical values for the thickness of such resistors lie in a range of 1 um — 100 um. With thick film screen printing or metal

CVD followed by laser trimming a resistive track pattern can be created directly on a liquefier outer surface.

Figure 2 schematically shows a perspective view of a heater assembly 60 of the liquefier 1 of the embodiment of Figure 1. At the bottom of Figure 2 a 2D projection of the PTC resistors 61-68 and the power lines 7,8 is shown. In this example the first power line 7 has a positive voltage and the second power line 8 has a negative voltage. The arrows in Figure 2 show the direction of the currents in the PTC resistors. The current is perpendicular to the power lines 7, 8 and thus perpendicular to the main axis 9 of the liquefier tube 2.

Figure 3 schematically shows an electronic scheme of the PTC resistors and a power supply 30. The power supply 30 applies a DC current to the PTC resistors. In an embodiment the

PTC resistors 61-65 are identical. This can for example be achieved by screen printing the resistors wherein the resistors have equal thickness, width and height.

As can be seen in Figure 3, the resistors 61, 62, 63 and 64 are arranged in parallel. Also the resistors 65, 66, 67 and 68 are arranged in parallel. A voltage V is applied over both parallel circuits. The resistors 61 and 65 are located at the same location on the liquefier tube 2 and thus heat up the same zone. This zone is referred to as ‘zone_1'. The resistors 62 and 66 heat up zone 2, etcetera. So in total four zones are created by arranging the eight resistors in this way.

The power supply 30 can be controlled by a controller 31 which receives input from the sensor 10. The controller 31 may be arranged to receive a temperature setting and will convert this temperature setting to a certain voltage. By applying this voltage to the PTC resistors, the four zones will be heated, and the sensor as well. The controller 31 is arranged to adapt the voltage so that a target temperature is equal, or almost equal, to the measured temperature.

The controller 31 is arranged such that it actively controls the total power in the heater assembly 60 to regulate the temperature of the liquefier 1 at the location of the sensor 10. When there is no flow or low flow of filament 11, this can be achieved by applying equal power to the heating elements along the length of the liquefier 1. However, at higher filament flow speeds, the filament 11 may not have reached the intended target temperature when it reaches the die (i.e. the nozzle). This is the fundamental limitation of all FFF liquefiers. One approach to increase the maximum flow rate is to increase the length of the liquefier 1 and the heated zone. There is, however, limited space available in a print head. To maximise the flow for a liquefier of a given length, more heating power could be applied. This power is most effective at the inlet end of the liquefier. While it is possible to design a liquefier with separately connected and controlled heating elements, this requires more wires and electronics. The present invention allows the heater to direct more thermal energy to the coolest end of the heater, which will be the inlet end at higher flow rates. This is done by choosing a PTC material for the heater elements, such that as the inlet end cools down when solid material enters the liquefier, the resistance of the heater element at the inlet end drops and more power is dissipated locally due to the constant supply voltage. In this way the proposed arrangement responds dynamically to a changing temperature gradient along the length of the liquefier, attempting to counteract a temperature difference between the inlet end and the outlet end. No active controller is required to control each of the zones separately as is done in the known systems.

The resistance of the PTC resistor 61, 62, 63, 84 increases when their temperature increases. So if the filament 11 flowing through the inlet end 3 cools zone_1, the PTC resistors 61 and 65 will cool down and their resistance will decrease. A decrease of resistance will cause more current through these resistors (i.e. 61, 65) at a constant voltage. Such an increase of current T will result in an increased power supply to zone_1, (Power = I?xR). In other words, the power in cooler areas of the liquefier 1 (i.e. near the inlet end) will automatically increase when needed.

This is achieved in a passive way without the need to use sensors in each zone and without the need of a controller controlling each zone actively.

Figure 4 schematically shows an electronic diagram of the PTC resistors and a power supply 30 according to another embodiment. In this embodiment the temperature sensor 10 of

Figure 3 is absent. Instead a current sensor 32 is arranged in the circuit between the power supply 30 and a node between resistor 64 and resistor 68. The current measured by the current sensor 32 is an indication of the total power supplied by all the resistors. This total power depends on the average temperature of the liquefier 1. If the average temperature of the liquefier 1 decreases, the current through the resistors decreases, and vice versa. In this way, the controller can control the power of the heater assembly using the input of the current sensor 32.

Alternatively, the power or resistance of only the bottom most resistor could be measured to be able to measure the temperature near the nozzle. This embodiment however would require an addition wire to the system.

Figure 5 schematically shows a perspective view of a part of the liquefier 1 according to a further embodiment. At the bottom of Figure 5 a 2D projection of the PTC resistors 61-64 and the power lines 7,8 is shown. In this embodiment each zone is heated by only one PTC resistor. This is achieved by a configuration wherein the power lines 7, 8 are arranged next to each other and wherein the PTC resistors are arranged on the outer surface of the liquefier tube 2 between the two power lines. In this example the first power line 7 has a positive voltage and the second power line 8 has a negative voltage. The arrows in Figure 5 show the direction of the currents in the PTC resistors. As in the embodiment described above, the current is perpendicular to the power lines 7, 8 and thus perpendicular to the main axis 9 of the liquefier tube 2.

Figure 6 schematically shows an electronic schematic diagram of the PTC resistors 61, 62, 63, 64 and a power supply 30 of the embodiment of Figure 5. As in the embodiment of Figure 3, the power supply 30 applies a DC or AC current to the PTC resistors 61, 62, 63, 64. As can be seen in Figure 6, the PTC resistors 61, 62, 63 and 64 are arranged in parallel. A voltage V is applied over both parallel circuits. The resistor 81 is located at the same location on the liquefier tube 2 and thus heat up the same zone. This zone is referred to as ‘zone_1'. The resistor 62 heats up zone 2, etcetera. So in total four zones are created by arranging the four resistors in this way. The other components shown in Figure 6 resemble the components already described above.

Figure 7 schematically shows a perspective view of a heater assembly 70 of the liquefier 1 according to a further embodiment. In this embodiment two resistors 71, 72 are arranged at the outer surface of the liquefier tube 2, e.g. by using screen-printing techniques. At the bottom of

Figure 7 a 2D projection of the PTC resistors 71, 72 and the power lines 7, 8 is shown. In this example the first power line 7 has a positive voltage and the second power line 8 has a negative voltage. The arrows in Figure 7 show the direction of the currents in the PTC resistors. Also in this embodiment the current is perpendicular to the power lines 7, 8 and thus perpendicular to the main axis 9 of the liquefier tube 2. By using two resistors that cover all area to be heated, a multi zone heating is achieved wherein the number of heating-zones is theoretically unlimited. It should be clear to the skilled reader that the local resistance of the resistors 71, 72 will act the same way as the multi-resistor embodiments described above. It is also possible to design an embodiment with only one PTC resistor using the power line configuration of Figure 5.

Figure 8 schematically shows a perspective view of a heater assembly 80 of the liquefier 1 according to a further embodiment. In this example the heater assembly 80 comprises four PTC resistors 81, 82, 83, 84 which may be screen printed onto the liquefier tube 2 (see Figure 1). At the bottom of Figure 8, a 2D projection of the PTC resistors 81, 82, 83, 84 (see dashed items) and the power lines 7, 8 is shown. In this example the first power line 7 has a positive voltage and the second power line 8 has a negative voltage. Both of the power lines 7, 8 are branched into several branches, see e.g. branches 76, 86, which make the actual contact with the resistors. The arrows in Figure 8 show the direction of the currents in the PTC resistors when powered. In this embodiment the current through the resistors runs parallel to the main axis 9 (see also figure 1) of the liquefier tube 2. Also in this embodiment, the PTC resistors 81, 82, 83, 84 will create a mulii- zones hester assembly wherein each resistor heats one zone.

Figure 9 shows a graph of a possible the relationship 40 between the electrical resistance and the temperature of the PTC resistor over a temperature work range. In an embodiment, each of the PTC resistors 61-68 has the relationship 40 shown in the graph. Figure 9 shows a work range of 150-350 degrees Celsius as an example. If the liquefier is active, all the resistors of the heater assembly will work in this range. The electrical resistance R as a function of the temperature T is continuously increasing in the working range. In this particular example, the relation between the resistance and the temperature is linear, but also non-linear increasing functions will give the intended effect. It is further noted that the graph of the electrical resistance outside the work range is not shown since it is not relevant for the invention.

The ratio between a change of temperature and the corresponding change in resistance is referred to as the TCR (temperature coefficient of resistance). All heater elements in the above embodiments may have the same TCR. In an alternative embodiment, the heater elements near the inlet end of the liquefier have a higher TCR than the heater elements near the outlet end, to maximise the PTC effect.

According to another embodiment, the power density of the top elements is increased relative to the bottom elements (e.g. by changing the track width, thickness, or material composition) of the liquefier 1 in such a way that it would be balanced (no temperature gradient) for the average flow rate of the system. It has been shown in tests that a 20% higher power at the top relative to the bottom could for instance result in a flow at 2.5mm3s without a temperature gradient over the liquefier. in an alternative embodiment, NTC resistor elements running along the length of the liquefier 1 are used. In this embodiment two contact rings could be arranged on the lop and bottom of the liquefier 1 and vertical {Le. axial} NTC strips {or ong complete strip). Then the current flows axially, which flow could be controlled by means of a current control instead of a constant voltage. In this embodiment a series NTC configuration forms the electrical dual of the parallel PTC configuration presented before, as will be recognized by the skilled reader.

Figure 10 schematically shows an FFF printing system 100 according to an embodiment of the invention. The FFF printing system 100 comprises a liquefier 1 mounted in a print head 116. As was described above, at its outer end the liquefier 1 comprises a nozzle 5 where molten filament can leave the liquefier 1. A filament 11 is fed into the liquefier 1 by means of a feeder 103. Part of the filament 11 is stored in a filament storage which could be a spool 108 rotatably arranged onto a housing (not shown) of the FFF printing system, or rotatably arranged within a container (not shown) containing one or more spools. The FFF printing system 100 comprises a controller 31 arranged to control the feeder 103 and the movement of print head 116 and thus of the liquefier 1 and the nozzle 5. The controller 31 may comprise one or more processing units 170. The controller 31 is arranged to control the power to the heater assembly of the liquefier 1.

In this embodiment, the FFF printing system 100 further comprises a Bowden tube 109 arranged to guide the filament 11 from the feeder 103 to the liquefier 1. The FFF printing system 100 also comprises a gantry arranged to move the print head 116 at least in one direction, indicated as the X-direction. In an embodiment, the print head 116 is also movable in a Y-direction perpendicular to the X-direction. The gantry comprises at least one mechanical driver 114 and one or more axles 115. The liquefier 1 is mounted into the print head 116. It is noted that the print head 116 may be arranged to hold more than one liquefier, such as for example two liquefiers each receiving their own filament. The feeder 103 is arranged to feed and retract the filament 11 to and from the liquefier 1. The feeder 103 may be arranged to feed and retract filament at different speeds to be determined by the controller 31. Due to the heating elements (i.e. the resistors) arranged on the liquefier 1 as described above, the feeding speed of the filament can be relatively high.

Furthermore, a build plate 118 may be arranged in or under the FFF printing system 100 depending on the type of system. The build plate 118 may comprise a glass plate or any other object suitable as a substrate to print on. In the example of Figure 10, the build plate 118 is movably arranged relative to the liquefier 1 in a Z-direction, see Figure 10. It is noted that instead of a build plate, other build surfaces may be used such as surfaces of movable belts. in the above the following embodiments were described.

Embodiment 1. A liquefier (1) for use in an FFF system, the liguefier comprising: - a thermaliy-conductive liqueidier tube (2) comprising an inlet end and an outlet end; - a nozzle {5) attached to the outlel end of the liguefier tube; - a heater assembly {80:70:50} comprising al least one PTC resistor arranged al at least pari of an outer surface of the liquefier be to impan heal into the liquefier tube; - a number of power lines (7,8) connected to the at least one PTC resistor, wherein the electrical resistance of the PTC resistor continuously increases with iemperature over a temperalure work range.

Embodiment 2. The liguelier according to embodiment 1, wherein the at least one PTC resislor, at least in use, is connected to a power supply via the power lines (7.8) in such a way that electric current through the PTC resistor runs perpendicular to a main axis of the liquefier tube.

Embodiment 3. The liguefier according to embodiment 1 or 2, wherein the temperature work range is at least 200 degrees C wide.

Embodiment 4. The hquefier according lo any one of the above ambadiments, wherein the at least one PTC resistor comprises multiple PTC resistors which, at least in use, are electrically connected in parallel by the power lines.

Embodiment 5. The liquefier according to embodiment 4, wherein a power density of the PTC resisiors increases in a direction towards the inlet end of the ligusfier.

Embodiment 8. The liguefier according to any one of the above embodiments, wherein the liquefier tube comprises a wall having a thickness of between 0.5 — 1.5 mm.

Embodiment 7. The liguefier according to any one of the above embodiments, further comprising a temperature sensor arranged to measure a temperature of pari of the liquefier tube.

Embodiment 8. The liquefier according to any one of the above embodiments, wherein the at least one PTC resistor is made by screen printing a paste on the outer surface of the liquefier tube.

Embodiment S. The liquefier according to any one of the above embodiments, wherein the power lines are made by Chemical Vapour Deposition (CVD) of a metal on the outer surface of the liquefier tube.

Embodiment 10. The liquefier according to any one of the above embodiments, wherein the number of power lings is two, wherein each of the power lines extend longitudinal along the liquefier tube and the power lines are located at opposing sides of the tube.

Embodiment 11. A FFF printing system comprising a controller (31) and a liquefier according to any one of the above embodiments, wherein the controller (31) is arranged to control the power to the heater assembly.

Embodiment 12. The FFF printing system according to embodiment 11, wherein the controller {31} is arranged to measure the current through the PTC resistors and to control an average temperature of the liguefier depending on the measured current.

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 (12)

CONCLUSIESCONCLUSIONS 1. Een vloeibaarmaker (1) voor gebruik in een FFF-systeem, waarbij de vloeibaarmaker omvat: - een thermisch geleidende vloeibaarmakerbuis (2) die een inlaatuiteinde en een uitlaatuiteinde omvat; - een mondstuk (5) bevestigd aan het uitlaatuiteinde van de vloeibaarmakerbuis; - een verwarmingssamenstel (60;70;80) omvattende ten minste één PTC-weerstand die is aangebracht op ten minste een deel van een buitenoppervlak van de vloeibaarmakerbuis om warmte in de vloeibaarmakerbuis te brengen; - een aantal voedingslijnen (7,8) aangesloten op de minstens ene PTC-weerstand, waarbij de elektrische weerstand van de PTC-weerstand continu toeneemt met de temperatuur over een temperatuurwerkbereik.A liquifier (1) for use in an FFF system, the liquifier comprising: - a thermally conductive liquifier tube (2) comprising an inlet end and an outlet end; - a nozzle (5) attached to the outlet end of the liquefaction tube; - a heater assembly (60;70;80) comprising at least one PTC resistor disposed on at least a portion of an outer surface of the liquefier tube for introducing heat into the liquefier tube; - a number of supply lines (7,8) connected to the at least one PTC resistor, the electrical resistance of the PTC resistor continuously increasing with temperature over a temperature operating range. 2. Vloeibaarmaker volgens conclusie 1, waarbij de ten minste ene PTC-weerstand, althans in gebruik, via de voedingsleidingen (7,8) zodanig is aangesloten op een voeding dat de elektrische stroom door de PTC-weerstand loodrecht loopt naar een hoofdas van de vloeibaarmakerbuis.A liquefier according to claim 1, wherein the at least one PTC resistor is, at least in use, connected via the supply lines (7,8) to a power supply such that the electric current through the PTC resistor runs perpendicular to a main axis of the liquefier tube. 3. Vloeibaarmaker volgens conclusie 1 of 2, waarbij het temperatuurwerkbereik ten minste 200°C breed is.The liquefier according to claim 1 or 2, wherein the temperature operating range is at least 200°C wide. 4. Vloeibaarmaker volgens één van de voorgaande conclusies, waarbij de ten minste ene PTC- weerstand meerdere PTC-weerstanden omvat die, althans in gebruik, elektrisch parallel zijn geschakeld door de stroomleidingen.4. Liquefier as claimed in any of the foregoing claims, wherein the at least one PTC resistor comprises a plurality of PTC resistors which, at least in use, are electrically connected in parallel by the power lines. 5. Vloeibaarmaker volgens conclusie 4, met het kenmerk, dat de vermogensdichtheid van de PTC-weerstanden toeneemt in een richting naar het inlaateinde van de vloeibaarmaker.5. A liquifier according to claim 4, wherein the power density of the PTC resistors increases in a direction toward the inlet end of the liquifier. 6. De vloeibaarmaker volgens één der voorgaande conclusies, waarbij de vloeibaarmakerbuis een wand omvat met een dikte tussen 0,5 - 1,5 mm.The liquifier according to any one of the preceding claims, wherein the liquifier tube comprises a wall with a thickness between 0.5 - 1.5 mm. 7. De vloeibaarmaker volgens één van de voorgaande conclusies, verder omvattende een temperatuursensor die is ingericht om een temperatuur van een deel van de vloeibaarmakerbuis te meten.The liquifier according to any of the preceding claims, further comprising a temperature sensor adapted to sense a temperature of a portion of the liquifier tube. 8. Vloeibaarmaker volgens één van de voorgaande conclusies, waarbij de ten minste ene PTC weerstand is gemaakt door een pasta op het buitenoppervlak van de buis van de vloeibaarmaker te zeefdrukken.The liquefier according to any of the preceding claims, wherein the at least one PTC resistor is made by screen printing a paste onto the outer surface of the liquefier tube. 9. De vloeibaarmaker volgens één van de voorgaande conclusies, waarbij de elektrische leidingen zijn gemaakt door middel van Chemical Vapour Deposition (CVD) van een metaal op het buitenoppervlak van de vloeibaarmakerbuis.The liquefier according to any of the preceding claims, wherein the electrical leads are made by Chemical Vapor Deposition (CVD) of a metal on the outer surface of the liquefier tube. 10. Vloeibaarmaker volgens één van de voorgaande conclusies, waarbij het aantal voedingslijnen twee is, waarbij elk van de voedingslijnen zich longitudinaal langs de vloeibaarmakingsbuis uitstrekt en de voedingslijnen zich aan weerszijden van de buis bevinden.A liquefier as claimed in any preceding claim wherein the number of feed lines is two, each of the feed lines extending longitudinally along the liquefaction tube and the feed lines being on opposite sides of the tube. 11. FFF-afdruksysteem omvattende een regelaar (31) en een vloeibaarmaker volgens één van de voorgaande conclusies, waarbij de regelaar (31) is ingericht om het vermogen naar het verwarmingssamenstel te regelen.An FFF printing system comprising a controller (31) and a fluidizer according to any preceding claim, wherein the controller (31) is arranged to control power to the heater assembly. 12. FFF-printsysteem volgens conclusie 11, waarbij de controller (31) is ingericht om de stroom door de PTC-weerstanden te meten en om een gemiddelde temperatuur van de vloeibaarmaker te regelen, afhankelijk van de gemeten stroom.The FFF printing system according to claim 11, wherein the controller (31) is arranged to measure the current through the PTC resistors and to control an average temperature of the fluidizer depending on the measured current.