PRINT HEAD FOR THE ADDITIVE MANUFACTURING OF FIBRE REINFORCED MATERIALS

Abstract

In a first aspect, the invention refers to a printhead for the additive manufacturing of a fibre reinforced material, comprising a fibre reinforcement in a polymer matrix, comprising an infiltration unit for mixing and/or infiltrating a fibre roving with a molten polymer; at least one feeder for a polymer and/or a fibre roving to the infiltration unit; a heating element, at least for partially melting the polymer within the infiltration unit; at least one deflecting element within the infiltration unit and an outlet for the resulting fibre reinforced material from the infiltration unit, wherein the molten polymer can be guided within the infiltration unit with a polymer flow direction, from the feeder to the outlet, along a channel between the feeder and the outlet, and the fibre roving can be guided within the channel, by means of deflection, around the deflecting element, area by area, transversely to the polymer flow direction, from the feeder to the outlet.

In another aspect, the invention refers to the use of a printhead for additive manufacturing, as well as to a process for additive manufacturing, and to a fibre reinforced material produced by the printhead.

Claims

1. A printhead for the additive manufacturing of a fibre reinforced material, comprising fibre reinforcement in a polymer matrix, comprising: an infiltration unit (1) for mixing and/or infiltrating a fibre roving with a molten polymer; at least one feeder for a polymer (7) and/or a fibre roving (5) to the infiltration unit (1); a heating element, for at least partial melting of the polymer within the infiltration unit (1); at least one deflecting element (15) within the infiltration unit (1); and an outlet (11) of the infiltration unit for the resulting fibre reinforced material from the infiltration unit (1), characterised in that the molten polymer and the fibre roving can be guided within the infiltration unit (1) along a channel (9) between the feeder (7) and the outlet (11), and the fibre roving can be deflected within the channel (9) by the deflecting element (15), area by area, transversely and/or obliquely to a straight-line movement between the feeder (5) and the outlet (11).

2. The printhead according to claim 1, characterised in that the molten polymer can be guided within the infiltration unit with a polymer flow direction, from the feeder to the outlet, along a channel between the feeder and the outlet, and the fibre roving can be guided within the channel, by means of deflection, around the deflecting element, area by area, transversely to the polymer flow direction, from the feeder to the outlet.

3. The printhead according to claim 1, characterised in that a nozzle (13) for the controlled placement of the fibre reinforced material on a printing surface is comprised, wherein the nozzle (13) is located at the outlet and wherein the nozzle (13) and the printing surface are preferably configured for a relative movement between the nozzle (13) and the printing surface, in particular in all spatial directions and/or with all possible degrees of freedom.

4. The printhead according to claim 1, characterized in that the printhead comprises at least two, preferably at least three, more preferably at least four, and, in particular, at least five deflecting elements (15).

5. The printhead according to claim 4, characterised in that 2-8 deflecting elements (15) are included.

6. The printhead according to claim 1, characterised in that at least one feeder each for the polymer (7) and the fibre roving (5) is comprised.

7. The printhead according to claim 1, characterized in that the layout and/or a radial extension of the deflecting element (15) is configured for the deflection of the fibre roving around the deflecting element (15), a change in speed of the fibre roving, an expansion of the fibre roving and/or the guiding of the fibre roving transversely and/or obliquely to the polymer flow direction and/or for the straight-line movement between the feeder (5) and the outlet (11).

8. The printhead according to claim 1, characterised in that the deflecting element (15) is cylindrical, at least area by area, and has an axial layout perpendicular to the polymer flow direction and/or to the rectilinear guide between feeder (5) and outlet (11) within the channel (9).

9. The printhead according to claim 8, characterized in that the deflecting element (15) comprises at least one rounded edge and/or pin (17) within the channel (9).

10. The printhead according to claim 1, characterized in that the deflecting element (15) has a bending transverse to the polymer flow direction and/or to the straight-line movement between the feeder (5) and the outlet (11), which can be described at least area by area, by a radius, the radius preferably being between 1-20 mm, more preferably between 2-5 mm, and, in particular, 4 mm.

11. The printhead according to claim 1, characterized in that the deflecting element (15), in particular, the rounded edge and/or the rounded pin (17) are positioned in such a manner that it crosses the centre of the channel (19), preferably in the longitudinal direction.

12. The printhead according to claim 1, characterised in that a melting of the polymer is carried out before the feeding (7).

13. The printhead according to claim 1, characterized in that the heating element is configured at least for an area by area heating of the polymer and/or the fibre roving to a temperature above the melting temperature of the polymer.

14. (canceled)

15. The printhead according to claim 1, characterised in that the material overflow (3) is configured for discharging the polymer in and/or opposite to the direction of fibre movement.

16. The printhead according to claim 15, characterised in that the polymer is fed in the form of granulates and/or filaments.

17. The printhead according to claim 16, characterized in that the filament is fed directly and/or through a Bowden extruder.

18. A printhead according to claim 16, characterized in that the granulate is fed through a screw extruder.

19. The printhead according to claim 1, comprising a material conveying unit (27) after the infiltration unit (1), configured for conveying the fibre reinforced material towards the nozzle (13, 23).

20. The printhead according to claim 1, comprising a cutting tool (21) for cutting the fibre reinforced material.

21. The printhead according to claim 1, characterized in that the cutting tool (21) is disposed in front of the nozzle (13, 23), between the nozzle (13, 23) and the infiltration unit (1).

22. The printhead according to claim 1, characterized in that a hotend comprising a nozzle (13, 23) and a heating element for heating the nozzle (13, 23).

23. The printhead according to claim 1, characterized in that a cooling element is comprised between the infiltration unit (1) and cutting tool (21) and/or hotend.

24. The printhead according to claim 19, characterized in that the cutting tool (21) is disposed behind the nozzle (13, 23) and the printhead is preferably configured for a distance change between the nozzle (13, 23) and the printing surface for cutting the fibre reinforced material by the cutting tool (21).

25. The printhead according to claim 1, further comprising a feeding element, comprising a first conveying unit for the polymer and a second conveying unit for the fibre roving, and preferably a cooling element (25) between the infiltration unit (1) and the feeding element.

26. The printhead according to claim 1, characterized in that a Bowden system (29) is included, whereby the Bowden system (29), comprises a Bowden tube (31) between the infiltration unit (1) and the hotend, and a cutting tool (21), which is disposed in front of the Bowden tube (31) or behind the Bowden tube (31), in front of or behind the hotend.

27. The printhead according to claim 1, characterised in that several nozzles (13, 23) and/or infiltration units (1) are included.

28. The printhead according to claim 1, characterized in that an infiltration unit (1) comprises several feeders for the polymer (7) and/or the fibre roving (5), whereby different materials and/or fibre roving strengths are fed.

29. The printhead according to claim 1, characterised in that an element for a pre-treatment of the fibre roving is comprised, wherein the pre-treatment is selected from the group comprising sizing, removing an epoxy sizing and/or plasma treatment.

30. A process comprising using the printhead of claim 1 to carry out an additive process.

31. A process comprising using the printhead of claim 1 for the production of pre-pregs and/or organic sheets.

32. A process for additively manufacturing a fibre reinforced material, comprising a fibre reinforcement in a polymer matrix using the printhead according to claim 1, comprising the following steps: feeding the polymer and the fibre roving to the infiltration unit (1) via at least one feeder (5, 7); heating the infiltration unit (1) by the heating element; guiding the polymer melted by heating inside the infiltration unit (1) along a channel (9) between the feeder (5, 7) and the outlet (11), preferably with the polymer flow direction from the feeder (5, 7) to the outlet (11); guiding the fibre roving along the channel (9) via the deflecting element (15), the fibre roving undergoing a change in speed, being guided and/or widened, area by area, transversely and/or obliquely to the polymer flow direction from the feeder (7) to the outlet and/or being guided in a straight-line movement between the feeder (5) and the outlet (11).

33. The process according to claim 32 for an additive process, further comprising the steps of: controlled relative movement between the nozzle (13, 23) and the printing surface, and printing a fibre reinforced material on the printing surface, according to an object to be printed; preferably cutting the fibre reinforced material with the cutting tool (21) during and/or after completion of a printing operation.

34. The process according to claim 32, characterised in that the fibre roving comprises fibres selected from the group comprising carbon fibre, aramid fibre and/or glass fibre and/or fibres and/or the polymer is selected from the group comprising polyamides (in particular PA6, PA66, PA12), polyetheretherketone, polyetherketoneketone, polyphenylene sulphide, polysulphone, polyetherimide, polytetrafluoroethene, polycarbonate, Polyethylene terephthalate (unmodified and modified with glycol), polylactide, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene-acrylate copolymer, styrene-acrylonitrile copolymer, polybutylene terephthalate polystyrene, epoxy resin, unsaturated polyester resin, vinyl ester resin, phenol-formaldehyde resin, diallyl phthalate resin, methacrylate resin, polyurethane, melamine resin and/or urea resin, preferably additionally mixtures and compounds, consisting of the individual substances with additives, to increase the fibre-matrix bonding.

35. A process comprising using the printhead of claim 1 for producing an orthosis and/or prosthesis.

36. A fibre reinforced material, comprising a fibre reinforcement in a polymer matrix, produced by the printhead, of claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0140] FIG. 1 shows a schematic representation of the printhead with infiltration unit and overflow.

[0141] FIG. 2 shows a schematic representation of the printhead, together with an infiltration unit, containing a cutting unit and a second nozzle.

[0142] FIG. 3 shows a schematic representation of the printhead, including an infiltration unit with a Bowden system.

[0143] FIG. 4 shows a schematic representation of the printhead with several feeders each for polymer and fibre roving.

[0144] FIG. 5 shows a bending stress-strain diagram of a 3-point bending test with printed composite sample of a printhead without an infiltration unit.

DETAILED DESCRIPTION OF THE FIGURES

[0145] FIG. 1 shows a schematic representation of the printhead with infiltration unit 1 and overflow 3. At the upper end of the infiltration unit, one can see the feeders for the fibre roving 5 and for the polymer 7 in the form of a filament, melt and/or granulate. These flow into a channel 9 down to the lower outlet 11, which passes directly into a nozzle 13 with a narrowing outlet cross-section for the fibre reinforced material to be printed. Three deflecting elements 15, which are designed differently, are visible in the channel 9. On the left side, two deflecting elements disposed one above the other are visible in the form of rounded edges, which are designed in the form of a cylinder segment projecting into the channel 9. On the right-hand side, there is a single deflecting element 15 in the form of a cylindrical pin 17, which is inserted in the side wall of the channel 9. One can see that the deflecting elements protrude beyond the centre of the channel in longitudinal direction 19 (dashed line) and thusly form a deflection, especially for the fibre roving (arrows in channel 9). At the lower end of the channel 9, before the outlet 11, an overflow 3 for residual polymer melt is shown pointing to the right.

[0146] FIG. 2 shows a schematic representation of the printhead including an infiltration unit 1 with a cutting unit 21 and a second nozzle 23. The fibre reinforced material exiting the outlet 11 and the first nozzle 13 of the printhead is cooled (by a cooling element 25), in order to cool down and partially harden, so that the subsequent haul-off unit 27 in the form of two counter-rotating rollers can easily transport the material. Likewise, the material is now suitable for trimming by a cutting unit 21, which is disposed directly in front of a second nozzle 23, which is designed to lay the material on the printing surface. Preferably, this second nozzle 23 is a hotend, so that the material is melted again for printing.

[0147] FIG. 3 shows, in addition to FIG. 2, a Bowden system 29 with a Bowden tube 31, which is disposed between two haul-off units 27, in order to transport the cooled fibre reinforced material through the tube 31. Thus, a very light and mobile printing unit can be provided in the form of a nozzle 23 (hotend) and a cutting tool 21, which can move independently of the infiltration unit 1.

[0148] FIG. 4 shows a printhead with two feeders each for the polymer 7 and one 5 for the preferably several fibre rovings, whereby several openings for the fibre rovings are also preferably possible here. In this manner, different materials can be fed simultaneously and/or one after the other. The feeders for the fibre rovings are preferably conducted through the same physical opening.

[0149] FIG. 5 shows a bending stress-force-deformation diagram of a 3-point bending test, with printed composite sample of a printhead, without an infiltration unit. Mechanical tests were also carried out, for the time being, with a state-of-the-art printhead that does not allow deflection via pins. During the tensile loading of manufactured strands, it was recognised that the polymeric sheath ruptures under load and the fibres are pulled out. The determined strengths of the composite material are below the pure matrix material. In addition to the tensile tests, 3-point bending tests were also carried out. Based on a micrograph analysis, it was also determined that only a coating was possible and, as such, pressing the material in via the nozzle is not possible. The mechanical properties of the composite result from the missing transfer of forces between the fibres, which results in low bending strengths of <100 MPa and high plastic stretching >5%. The high plastic stretching can be seen in the bending load-deformation diagram; in the case of fibre reinforced materials this is typically around 1-3%, see FIG. 5.

[0150] FIG. 6:

Structure of the printhead
State of the art: Publications with melt infiltration will only coat fibre rovings.
Research objective: Development of a printhead with infiltration effect.
Improved infiltration by: [0151] Widening of the fibre roving.fwdarw.Smaller infiltration distance [0152] Pressure field at the pins.fwdarw.Injection of the polymer melt
6 a) Coated roving
6 b) Infiltrated roving

[0153] FIG. 7:

Printhead with an infiltration unit

[0154] FIG. 8:

Printer configuration and materials
Open-source printing system for machine/firmware customisation
Printhead design open for other fibres (type, thread size) and matrix materials (thermoplastics)
8a) Printing configuration: Graber 13/Toolson MK2 print parts (print area 200×200×100 mm.sup.3)
8b) Carbon fibres: Torayca T300 & Tenax HTA40; matrix polymer: PA6 filament (self-extruded).

[0155] FIG. 9:

Extrusion of the PA6 filament
9a) Filament extruder Next Advance 3devo

Process Steps:

[0156] Drying of the PA6 granulate (70° C. for 16 h) [0157] Filament extrusion and winding [0158] Diameter check with 3 mm gauge
9b) Mechanical analysis:
Tensile test, according to DIN EN ISO 527-2; specimen: 1BA.
Tensile strength 0°=68 MPa
Tensile strength 90°=57 MPa
Tensile strength Z=45 MPa

[0159] FIG. 10:

10a)/10b) Slicer: Simplify 3d v4.01; slicer parameters: t.sub.hotend=295° C., t.sub.bed=60° C., cooling off, top-bottom layer 0, filling 1000%, printing speed 5 mm/s, speed of first layer 50%.

FIG. 11:

[0160] 3-point bending test according to

DIN EN ISO 14125:

[0161] 5 specimens [0162] Fibre in loading direction

[0163] FIG. 12:

Influence of layer height LH and width W [0164] Layer height LH influences the optical resolution of the FDM print and the build-up rate [0165] In multi-material printing, the layer height of the composite and thermoplastic must be the same [0166] Specimen geometry depends on the number of layers L and the number of webs per layer N

[0167] FIG. 13:

Result of the 3-point bending test.
Correlation between fibre volume content and flexural modulus
Higher bending strength with smaller layer height

[0168] FIG. 14:

Preparation: embedding agent with UV additive, micrograph near fracture surface.
Light microscope Leica DM4000 M: 14a) Dark field mode with normal light 14b) Fluorescence mode with UV light

[0169] FIG. 15:

see FIG. 8a)

[0170] At the Department of Ceramic Materials at the Technical University of Berlin, a novel process for the additive manufacturing of composites with continuous carbon fibres was investigated. A new printhead design, which infiltrates the carbon fibres in the printhead with a PA6 melt was researched. Investigations resulted in bending strengths of up to 550 MPa, a bending modulus of about 40 GPa and a fibre volume content of 30-35%. Additive manufacturing provides great advantages for the automated production of fibre reinforced materials. For example, the component is built up on a printing platform without moulds with supporting structures. A multi-material approach is possible with additional printheads, whereby the fibre reinforcement is mainly used where high strengths are required. Sustainability is very high, as there is no offcut when using carbon fibres, as it is common, for example, in the processing of organic sheets.

REFERENCE LIST

[0171] 1 Infiltration unit [0172] 3 Overflow [0173] 5 Feeder for fibre roving [0174] 7 Feeder for the polymer [0175] 9 Channel [0176] 11 Outlet [0177] 13 Nozzle [0178] 15 Deflecting element [0179] 17 Cylindrical pin [0180] 19 Centre of the duct [0181] 21 Cutting unit [0182] 23 Second nozzle [0183] 25 Cooling element [0184] 27 Haul-off unit [0185] 29 Bowden system [0186] 31 Bowden tube