LU101265B1

LU101265B1 - Bead de-twisting system and method

Info

Publication number: LU101265B1
Application number: LU101265A
Authority: LU
Inventors: Paul Worms; Christoph MITNA
Original assignee: BigRep GmbH
Priority date: 2019-06-11
Filing date: 2019-06-11
Publication date: 2020-12-11
Also published as: WO2020249603A1

Abstract

The present disclosure refers to a 3D-printhead and a SD-printing method wherein a material outlet is rotated according to a direction of a printing trajectory for strand de-twisting.

Description

Title: Bead de-twisting system and method | |

FIELD

[0001] The present invention relates to additive manufacturing. In particular, the pre- sent invention relates to a bead de-twisting system and method for an additive manu- facturing apparatus.

BACKGROUND

[0002] In the field of additive manufacturing an additive manufacturing apparatus is also called a 3D-printer. In 3D-printing objects or workpieces are built/created/gener- ated by subsequent depositing layers (beads) of material onto each other. This mate- rial may be plastic material and in particular, the depositing process may be the FDM | or FFF process. The material supplied to the 3D-printer may be filament or granulated material.

[0003] The 3D-printer usually comprises a printhead that moves in three directions. Also, there are 3D-printers that comprise printhead that move in two directions and a printbed (the surface or structure on/to which the workpiece(s) are created) that moves in the third direction. Also, there are printheads that are mounted to a conventional industrial robot such that the printhead can realize complex trajectories. The printhead generally comprises an extruder to apply the material to build up the workpiece.

[0004] In the field of FDM or FFF printing, the printhead conventionally may comprise an extruder comprising a hotend and a material feed unit. The material feed unit sup- plies material (the material from which the workpiece is built) to the hotend. Said ma- terial is heated up to its melting temperature within said hotend and extruded through | a nozzle that is connected to the hotend. The extruded material forms a deposited strand that in turn forms one layer of the workpiece being built. An outlet opening of the nozzle (material outlet) has usually a circular cross section. The heated and plastic- state material leaves the printhead/the nozzle trough said outlet opening to build up the workpiece(s). The extruder may use any known technology such as screw extrud- ers, gear pumps, tube liquefiers or any combination of these. 1

[0005] In the field of concrete-printing slit nozzles or also nozzles having a nozzle | opening with a rectangular cross-section are commonly used to create increased wall thicknesses in one pass of the nozzle. However, to perform changes in the print direc- tion (e.g. printing corners or radiuses), the slit nozzle must be turned according to the nozzle or print trajectory to avoid distortion or warping of the deposited material and thus a failure in shape of the workpiece. Such a printing method for concrete was for example developed by the Eindhoven University of Technology (https:/iwww.tue.nl/en/research/research-groups/structural-engineering-and-de- sign/concrete-research-areas/3d-concrete-printing/). A slit nozzle having a nozzle opening with a rectangular cross section in the sense of this application has 90° angles in all four corners and two pairs of unequally long and straight sides.

[0006] Jordan R. Raney et al. disclosed rotational 3D printing of damage-tolerant composites with programmable mechanics (https://www.pnas.org/con- tent/115/6/1198). The aim was to achieve control over fiber alignment during direct writing of a viscoelastic fiber-filled epoxy ink. To this end a printhead system was dis- closed in which a stepper motor controls the angular velocity of a rotating nozzle. The unidirectional rotation of the nozzle serves so orientate the fibers in the fiber-filled epoxy ink during the print.

SUMMARY

[0007] It was observed that in the FDM/FFF process and especially during direction changes in the trajectory of the printhead (a change in the print trajectory) having a large change angle and/or small radius, that there is the effect that the deposited or extracted material strand twists. This twisting of the extracted material strand can for example be seen on the markings made by the nozzle on the surface of the deposited material strand (see Figure 1). The twisting of the deposited material or strand may create a vertical shrink component within the deposited material. This can lead to warp- ing of the strand at the corners or narrow radiuses and/or a reduced interlayer bond between the layers of deposited material. Materials with a high crystallization content or high shrinkage are in particular prone to warping and/or a reduced interlayer bond due to the twisting of the deposited material. 2

BL

[0008] It is thus the object of the present application to provide 3D-printhead, a 3D- printer and a 3D-printing method according to the appended independent claims to overcome the above inconveniences. Selected embodiments are comprised in the de- pendent claims. Each of which, alone or in any combination with the other dependent claims, can represent an embodiment of the present application. The advantage ofan - apparatus and/or 3D-printing method according to the appended independent claims is the untwisting of the extracted material. This means that the flow direction of the extracted material in the corners or curves of the print trajectory is identical to a flow direction obtained with extracted material along a straight print trajectory. As a result, flow lines of the extracted material remain parallel to each other even in different layers of the workpiece.

[0009] According to one aspect of the present application an 3D-printhead for strand de-twisting comprises a material outlet, a support and a motor. The motor is fixed to the support and the material outlet is rotatable by means of the motor with respect to the support. Thus, the motor is operatively coupled to the material outlet. This coupling may be direct or indirect. This may have the advantage that the material outlet may be controllably and/or alternating rotated while the 3D-printhead is moving along a print trajectory and consequently influences the flow lines of the deposited material.

[0010] According to another aspect of the present application a 3D-printhead for strand de-twisting comprises an extruder, a support and a motor. The extruder is ro- tatable with respect to the support by means of the motor. This may have the ad- vantage that the printhead and its nozzle opening may be rotated while a 3D-printer comprising such printhead is printing along a print trajectory. The extruder may com- prise a hotend.

[0011] According to another aspect of the present application a 3D-printhead has a nozzle with a nozzle opening, wherein the nozzle opening has one of the following cross-sections: rotationally symmetric cross-section, an elliptic cross-section, a cross- shaped cross-section, a symmetrical polygon shaped cross-section, rhomboid, a sym- metrical polygon shaped cross-section with concave sides, a symmetrical polygon shaped cross-section with convex sides. This may have the advantage, that for each 3 material and/or printing trajectory the suitable cross-section may be chosen while avoiding a twisting of the deposited material strand.

[0012] According to another aspect of the present application a 3D-printer comprises a 3D-printhead of the above aspects or a 3D-printhead being controllably rotatable with | respect to a fixing point of the 3D-printhead on the printer. The fixing point is a point | on the 3D-printer where the assembly representing the 3D-printhead is fixed to the rest of the 3D-printer, e.g. the motion system causing the 3D-printhead to move along the X, y, Z axes. This motion system may be a gantry system or an industrial robot. The above support may be fixedly connected to the fixing point.

[0013] According to another aspect of the present application the 3D-printhead may be for FFF/FDM printing.

[0014] According to another aspect of the present application the 3D-printhead may | deposit one another complementing strands of deposited material by means of a cor- respondingly shaped material outlet. This may have the advantage that void spaces between the deposited strands of material may be reduced or even avoided, resulting in improved mechanical properties of the workpiece created. Void spaces between the deposited strands reduce the interlayer bond.

[0015] According to another aspect of the present application a 3D-printing method for strand de-twisting is disclosed. According to the method a material outlet having a non-rectangular cross-section is moved along a printing trajectory and the material outlet is rotated with respect to the printing trajectory. This may have the advantage that the deposited strand or material has a homogeneous strand orientation. This re- duces shrinkage and warping in an advantageous manner.

[0016] According to another aspect of the present application the material outlet is rotated while following a curved printing trajectory according to the disclosed 3D-print- ing method. This may have the advantage that the strand de-twisting can be controlled with respect to the curvature or course of the printing trajectory. The rotation of the material outlet may be incremental or continuous along the printing trajectory. 4 a

[0017] According to another aspect of the present application a material outlet is | moved along a printing trajectory with the 3D-printing method for strand de-twisting | and the material outlet is rotated depending on changes of the direction of a printing trajectory. This may have the advantage that the strand de-twisting can be controlled with respect to the curvature or course of the printing trajectory all along the printing trajectory. This may also have the advantage that flow lines of a deposited strand of materials may be kept in a continuous orientation without changes in direction in the deposited strand.

[0018] According to another aspect of the present application any of the above meth- ods may be carried out using any of the above printheads.

[0019] According to another aspect of the present application any of the above meth- ods is carried out using a symmetrical material outlet or nozzle opening.

[0020] According to another aspect of the present application the material outlet is continuously rotated while following a curved printing trajectory. The term "continu- ously" in this context also comprises an incremental rotation wherein there is a number of increments along the curved printing trajectory.

[0021] According to another aspect of the present application the material outlet starts rotating prior to a change in the printing trajectory and stops rotating after the change in the printing trajectory is already passed according to the disclosed 3D-printing method. This may have the advantage that the material has the correct orientation when it leaves the material outlet. This is due to the fact that the material has a certain inertia and if the material outlet is rotated prior to a change in the printing direction, the material leaves the material outlet already in the correct orientation. Further, there is more time to rotate or orientate or de-twist the material.

[0022] According to another aspect of the present application the material outlet ro- tates at a precise point of change in the printing trajectory according to the disclosed 3D-printing method. This may have the advantage that the controlling of the 3D-print- ing-method is simple since there is no superposition of the rotation with the printing a trajectory. Or in other words, the rotation does not happen at the same time or simul- taneously as the change in direction of the printing trajectory.

[0023] According to another aspect of the present application the nozzle opening or material outlet oscillates according to the disclosed 3D-printing method. This may have | the advantage that the material is deposited more evenly and smoothly. Further, a molecule orientation in the material can be reduced.

[0024] According to another aspect of the present application the 3D-printing method is an FFF-3D-printing method.

[0025] According to another aspect of the present application the material outlet or nozzle opening is rotated in the same orientation as the printing trajectory changes its orientation. This may have the advantage that an orientation of the material outlet can be kept aligned with the printing trajectory.

[0026] According to another aspect of the present application the material outlet is shaped such that it creates one another complementing deposited strands of material to avoid void spaces between the deposited strands.

[0027] Each of the above aspects is to be considered an invention on its own. The aspects can be combined freely with each other and each feature not described as being dependent on another feature may also be freely combined with each other. The features of the disclosed method may be incorporated into the apparatus and vice versa.

BRIEF DESCRIPTION OF THE FIGURES

[0028] Further advantages and features of the present disclosure will be apparent from the appended figure. The figure is of merely informing purpose and not of limiting character. The figure schematically describes an embodiment of the present applica- tion. Hence, the appended figures cannot be considered limiting for e.g. the dimen- sions of the present disclosure.

| 6

[0029] Figure 1 shows a schematic view of a 3D-printhead.

[0030] Figure 2 shows a perspective view of a rotatable material outlet or nozzle open- ing and a deposited strand.

[0031] Figure 3 shows a schematic view of multiple deposited strands with their flow lines and force components (no de-twisting applied).

[0032] Figure 4 shows a schematic view of a print trajectory.

[0033] Figure 5 shows a schematic view of another print trajectory with points of a rotation of a nozzle opening.

[0034] Figure 6 shows a schematic view of another print trajectory with points of a rotation of a nozzle opening.

[0035] Figure 7 shows different cross sections of the material outlet.

[0036] Figure 8 shows an example of different layers of deposited strands.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Referring to figure 1 a schematic view of a 3D-print head 10 comprising a noz- zle 20, having a nozzle opening 25 is depicted. The 3D-printhead 10 further comprises an extruder 50, a support 30 and a motor 40. The 3D-printhead is adapted to be fixed by means of the support to a 3D-printer (not shown). The motor 40 is fixedly connected to the support 30. The extruder 50 is fixed to the nozzle 20 with the nozzle opening 25. The motor 40 is further adapted to rotate the extruder 50 with the nozzle 20 and nozzle opening 25 with respect to the support 30. Thus, the motor 40 is operatively coupled to the nozzle 20 by any suitable means or arrangement. The 3D-printhead 10 may be a FFF-3D-printhead in which plastic material is heated up (e.g. by extruder 50) and then deposited into a deposited strand of material through nozzle opening 25.

[0038] Fig. 2 depicts a deposited strand 60 of material with flow lines FL1 and FL2. Further, a schematic nozzle 20 is shown with the nozzle opening 25. In fig. 2 the nozzle 7 -YYYY aaa 0000]

opening has the same shape or cross section (circular) on the bottom (towards the deposited strand 60 and thus not visible in fig. 2) as on the visible top. In this example the center point of the nozzle opening 25 follows the print trajectory PT that is controlled by the control unit (not shown) of a 3D-printer (not shown) the nozzle 20 is fixed to. Flow line FI1 indicates the flow line of the depicted deposited strand 60 of material if the deposited strand 60 is printed or deposited in a conventional way (no de-twisting applied). Because of the angle and thus change of direction in the print trajectory PT, the flow line FL1 changes its position within the deposited strand 60. Only one flow line is depicted exemplary for a number of flow lines within the deposited strand 60.

[0039] If the nozzle opening 25 is rotated (depicted arrow on nozzle 20) to rotate in the same direction as the printing trajectory PT changes its direction, then flow line FL2 is the result. By rotating the nozzle opening 25 in the same direction or orientation as the change of direction in the print trajectory PT, the flow line FL2 remains unchanged, in the depicted example in the middie of the deposited strand 60.

[0040] Fig. 3 depicts multiple deposited strands 60 with the flow line FL1 according to fig. 2. In case of an FFF-3D-printing method the deposited strand(s) 60 are subject to shrinkage S due to the cooling of the material and thus a contraction. The shrinkage S is essentially parallel to the flow line within the deposited strand 60. Due to the bend in the flow line FL1 there is a horizontal component H and vertical component V. This results in a shrinkage S in the area of the bend of flow line FL1 that is not parallel to the shrinkage S in the left side of fig. 3. The different orientations of shrinkage S in the same deposited strand 60 and together with the other deposited strands 60 above and below may result in a deformation of the workpiece being built up by the deposited strands 60. In particular, the area of the bend(s) of flow line FL1 are likely to follow the shrinkage S that is unparallel to the overall orientation of the deposited strand 60. In the depicted example the right part of the deposited strands 60 is prone to bend up- wards in fig. 3 due to the resulting orientation of the shrinkage S because of the hori- zontal component H and vertical component V.

[0041] Fig. 4 depicts a print trajectory PT that changes its direction or orientation in point P. In this example the change in direction is 90° and thus essentially corresponds 8 -— "7 to the situation depicted in fig. 2 (if viewed from above). In the example of fig. 4 the material outlet 25 or nozzle opening is rotated in the sense of the depicted arrow in the same direction as the print trajectory PT changes its direction or orientation. In other words, the print trajectory PT changes its direction with a 90° corner to the left in fig. 4, | so the material outlet 25 or nozzle opening is also rotated to the left or in this case | counter clockwise when the material outlet 25 reaches point P. A flow line correspond- ing to flow line FL2 depicted in fig. 2 is the result.

[0042] The material outlet 25 is rotated by an angle of rotation a. In the example of fig. 4 the angle of rotation a is 90° and thus corresponds to a change angle of the direction of the printing trajectory PT (here 90°). However, a may be more or less than the change angle of the direction of the printing trajectory PT.

[0043] In fig. 5 another method of controlling the material outlet 25 or 3D-printing method is depicted. Here, the change angle of the direction of the printing trajectory PT is also 90° and the change in the direction of the printing trajectory PT is in point P. However, here the rotation of the material outlet 25 or nozzle opening starts in point PS and is stopped in point PE. The rotation or rotational speed of the material outlet can be constant or time variant from PS to PT. Alternatively the rotational speed or ration of rotational angle per distance increment of printing trajectory PT or time may be variable. For example, the rotational speed of the material outlet 25 may start slowly and then increases as the material outlet approaches point P and then slows down as the material outlet 25 passes point P and approaches point PE and stops at PE.

[0044] Fig. 6 depicts a bend or curve in the printing trajectory PT and thus not a rather abrupt change in the direction of the printing trajectory PT as for example depicted in figs. 4 and 5 but a gradual change in the direction of the printing trajectory PT. The multiple points with the arrows depicted in fig. 6 along the printing trajectory PT visual- ize a continuous rotation of the material outlet 25 or nozzle opening. Also, if the curva- ture of the bend in the direction of the printing trajectory PT is not continuous (e.g. slight in the beginning and then steep and then slight again), the material outlet may be rotated accordingly, or the rotational speed of the material outlet may be corre- sponding to the amount of change in the direction of the printing trajectory PT.

9 a —"" "1

[0045] In fig. 6 an oscillating movement O of the material outlet 25 or nozzle opening is depicted. Oscillating movement refers to the fact that a rotation movement in clock- wise and counter clockwise direction of the material outlet 25 in a small degree of rotational angle is superimposed to the rotation of the material outlet 25 in order to follow or align with the direction of the printing trajectory PT with one of the orientations 70 or 75 (see below). In other words, while the overall rotational sense of the material outlet 25 is kept and follows the direction of the printing trajectory PT, the material outlet 25 also moves a little clockwise and counterclockwise.

[0046] Fig. 7 depicts shapes of the cross section of the material outlet 25 or nozzle opening. A depicts a circular cross section. B depicts an ellipsoid cross section. C de- picts a quadratic cross section. This may also be a rectangular cross section with two pairs of unequally long sides. D depicts a quadratic (also rectangular is possible) cross section wherein the sides are concave. E depicts a quadratic (also rectangular is pos- sible) cross section wherein the sides are convex. F depicts a quadratic (also rectan- gular is possible) cross section wherein only two opposing sides are concave (same is | possible with a pair of opposing convex sides). G depicts a wave shaped cross section. | H depicts a cross shaped cross section. In general, all sorts of symmetric polygons are possible.

[0047] Also, there are different orientations of the material outlet 25 with respect to the printing trajectory PT possible. As an example, two possible orientations 70 and 75 are depicted in fig.7 C. The first orientation 70 originates at a central point of the square and passes through the middle of one of the sides. The second orientation 75 also originates at a central point and passes through one of the corners of the square. The orientations 70 and 75 are then aligned with the printing trajectory PT by rotating the material outlet 25 or nozzle opening. Both orientations in C of fig.7 are exemplary and can be applied to all other shapes of cross section as well.

[0048] Fig. 8 schematically depicts deposited strands 60 or different cross sections of material outlets. On the left side (indicated with A) deposited strands 60 are depicted that originate e.g. from a conventional circular shaped cross section of material outlet. Here the single deposited strands 60 have void spaces V in between the deposited

EN strands 60 due to the shape of the material outlet or nozzle opening. If a force F is applied in the indicated directions, then the resistance of the depicted strands 60 is rather weak because of the void spaces and thus reduced contact surfaces between the deposited strands 60.

[0049] On the right in fig. 8 (indicated with B) deposited strands 60 are schematically depicted that originate or are formed by a cross section of the material outlet corre- sponding to C in fig. 7 having the second orientation 75. As can be seen, the overall contact surfaces between the individual deposited strands 60 are considerably larger than on the left side of fig. 8. Consequently, the deposited strands 60 on the right side of fig. 8 can withstand a much greater force F than on the left side of fig. 8. This is due to reduced voids between the deposited strand 60 in Fig. 8B. This effect may be achieved by using a complementing form of the material outlet. In other words, the material outlet or nozzle opening has a form such that subsequent deposited strands complement each other in their shape to reduce or even avoid void spaces V between these subsequent deposited strands. The rotation of the material outlet or nozzle open- ing helps to suppress the void spaces V and de-twists the deposited strand simultane- ously and thus also aides in suppressing the void spaces V that may occur after the warping (see above, fig. 3). | 11 |

List of reference signs 3D-Printhead nozzle material outlet or nozzle opening support 40 motor 50 extruder 60 deposited strand 70 first orientation 75 second orientation FL1 flow line 1 FL2 flow line 2 S shrinkage H horizontal component V vertical component PT printing trajectory V void spaces O oscillation movement 12

A

Claims

1. 3D-printhead for strand de-twisting comprising a material outlet (25), a support (30) and a motor (40), wherein the motor is fixed to the support and wherein the ma- terial outlet (25) is rotatable with respect to the support by means of the motor.

2. 3D-printhead for strand de-twisting comprising an extruder (50), a support (30) and a motor (40), wherein the motor is fixed to the support and the extruder com- prises a nozzle (20) having a nozzle opening (25) and wherein the extruder is rotata- ble with respect to the support by means of the motor (40).

3. 3D-printhead according to claims 1 or 2, wherein the nozzle opening or mate- rial outlet (25) has one of the following cross-sections: a rotationally symmetric cross- section, an elliptic cross-section, a cross-shaped cross-section, a symmetrical poly- gon shaped cross-section, a rhomboid shaped cross-section, a symmetrical polygon shaped cross-section with concave sides, a symmetrical polygon shaped cross-sec- tion with convex sides.

4, 3D-printhead according to any of claims 1 to 3, wherein the 3D-printhead is an FFF-3D-printhead.

5. 3D-printhead according to any of claims 1 to 4, wherein the 3D-printhead de- posits one another complementing strands of deposited material (60) by means of a correspondingly shaped material outlet (25).

6. 3D-Printer comprising a 3D-printhead of the preceding claims or a 3D-print- head being controllably rotatable with respect to a fixing point of the printhead on the 3D-printer.

7. 3D-printing method for strand de-twisting, wherein a material outlet (25) is moved along a printing trajectory (PT) and the material outlet is rotated depending on changes of the direction of the printing trajectory.

13 YY — — — — — TTT

8. 3D-printing method according to claim 7 using a 3D-printhead of any of claims | 1 to 5.

9. 3D-printing method according to claim 7 or 8, wherein the material outlet (25) has a symmetric cross section. |

10. 3D-printing method according to any of claims 7 to 9, wherein the material out- let (25) is continuously rotated while the material outlet (25) follows a curved printing | trajectory.

11. 3D-printing method according to any of claims 7 to 10, wherein the material : outlet (25) starts to rotate prior to a change in the direction of the printing trajectory | and stops to rotate after the change in the direction of the printing trajectory (PT) is : passed by the material outlet (25). :

12. 3D-printing method according to claim 7 or 8, wherein the material outlet (25) | is rotated at a precise point (P) of change of the direction of the printing trajectory ; (PT). i

13. 3D-printing method according to any of claims 7 to 12, wherein the material ; outlet (25) oscillates. | :

14. 3D-printing method according to any of claims 7 to 13, wherein the 3D-printing | method is an FFF-3D-printing method.

15. 3D-printing method according to any of claims 7 to 14, wherein the material outlet (25) is rotated in the same orientation as the printing trajectory (PT) changes its orientation. |

16. 3D-printing method according to any of claims 7 to 15, wherein the material | outlet (25) deposits one another complementing deposited strands of material (60) to ; avoid void spaces (V) between the deposited strands.

: