A PRODUCT AND METHOD FOR POWDER FEEDING IN POWDER BED 3D PRINTERS

Abstract

The present invention provides a metal powder-polymer matrix film for use in delivering metal powder to a three-dimensional printing process, the matrix comprising at least one metal powder and a polymer sheet, wherein the metal powder is incorporated within the polymer sheet architecture or on the polymer sheet surface, and wherein the polymer sheet has a thickness that is at least half that of the powder thickness.

Claims

1. A metal powder-polymer matrix flexible film for use in delivering metal powder to a three-dimensional printing process, the matrix comprising at least one metal powder and a polymer sheet, wherein the metal powder is incorporated within the polymer sheet architecture or on the polymer sheet surface; and wherein the flexible film comprises at least 90 wt % of the metal powder.

2. The metal powder-matrix film of claim 1, wherein the thickness of the matrix is between about 1 μm to about 150 μm.

3. The metal powder-matrix film of claim 2, wherein the thickness of the matrix is between about 5 μm to about 100 μm.

4. The metal powder-polymer matrix film according to any one of claims 1 to 3, wherein the polymer is selected from the group comprising a thermoplastic, epoxy, silicone, vulcanised rubber, polyester, polyurethane, polyethylene, polypropylene, polyamide, polyetheramide, polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), a fluoroplastic, polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

5. The metal powder-polymer matrix film according to any one of claims 1 to 4, wherein the metal is selected from the group comprising stainless steel, tungsten, titanium, titanium alloys, aluminium, aluminium alloys, copper, nickel, nickel alloys, super alloys, high entropy alloys, cobalt-chrome, barium, molybdenum, NiTi (nitilon), NiTi alloys, ceramic materials, metal-ceramic composites, metal-diamond composites, tantalum, tantalum carbide, and combinations thereof.

6. The metal powder-polymer matrix film according to any one of the preceding claims, wherein the metal powder is embedded within the polymer sheet architecture.

7. The metal powder-polymer matrix film according to any one of claims 1 to 5, wherein when the metal powder particles are closely packed and attached to one side of the polymer sheet.

8. A method of manufacturing the metal powder-polymer matrix flexible film of claim 1, the method comprising the steps of: mixing the metal powder with the polymer in a ratio of about 4:1 to form a metal powder and polymer mixture; and forming the metal powder-polymer matrix flexible film.

9. The method of claim 8 for manufacturing the metal powder-polymer matrix flexible claim 1, wherein when the metal powder is incorporated within the polymer sheet architecture, the metal powder-polymer flexible film is formed by solvent casting, thermal hot pressing, extrusion techniques or by joining a number of thin layers of metal-containing polymer sheet together.

10. The method of claim 8 for manufacturing the metal powder-polymer matrix flexible claim 1, wherein when the metal powder is on the surface of the metal powder-polymer matrix flexible film, the metal powder is attached to one side of flexible film by an adhesive, by extrusion, by hot pressing, by electro-spraying or by cold spraying.

11. The method of any one of claims 8 to 10 for manufacturing the metal powder-polymer matrix flexible film of claim 1, wherein the metal powder-polymer matrix film is formed by extruding the metal powder and polymer mixture.

12. The method of claim 11 for manufacturing the metal powder-polymer matrix flexible claim 1, wherein the metal powder-polymer matrix flexible film is extruded by the process selected from film extrusion, and other similar processes.

13. The method of any one of claims 8 to 12 for manufacturing the metal powder-polymer matrix flexible film of claim 1, wherein the metal powder-polymer matrix flexible film is extruded as a continuous roll.

14. A method of producing a 3D product using the metal powder-polymer matrix flexible claim 1, the method comprising applying the metal powder-polymer matrix flexible film to a build plate; irradiating the metal powder-polymer matrix flexible film to vaporise the polymer and melt the metal particles together to form a 2D layer; placing the same or a new layer of metal powder-polymer matrix flexible film on top of the previous 2D layer, and repeating the application of the heat source for a number of cycles to produce the desired 3D product.

15. The method of claim 14, wherein the build plate is a weldable metal or weldable plastic.

16. A method of printing on an existing pre-formed product or part using the metal powder-polymer matrix flexible film of claim 1, the method comprising applying the metal powder-polymer matrix flexible film to the pre-formed product or part; irradiating the metal powder-polymer matrix flexible film to vaporise the polymer and melt the metal particles together to form a 2D layer on the pre-formed product or part; optionally placing the same or a new layer of metal powder-polymer matrix flexible film on top of the previous 2D layer, or on another aspect of the pre-formed product or part, and repeating the application of the heat source for a number of cycles to produce the desired effect on the pre-formed product or part.

17. The method of claim 14, claim 15 or claim 16, wherein the metal powder-polymer matrix film is irradiated by an infrared radiation device, a laser, an ion laser, an electron beam, an arc, a heated plate in contact with the material, or plasma.

18. The method of claim 17, wherein the laser is selected from a CO.sub.2 laser, a 1064 nm infrared Nd:YAG laser, an infrared fibre laser, a diode laser, an argon laser, a krypton laser, an argon/krypton laser, a helium-cadmium laser, a copper vapor laser, a xenon laser, an iodine laser, an oxygen laser, and an excimer laser.

19. The method of any one of claims 14 to 18, wherein the method is selected from the group comprising laser cladding, selective laser melting, selective laser sintering, wire cladding, cold spray, kinetic spray, High-Velocity Oxygen Fuel (HVOF) spray coating, High Velocity Air-Fuel (HVAF) spray coating, plasma spray, arc spray, Direct Energy Deposition (DED), and combinations thereof.

20. The method of any one of claims 14 to 19, wherein the process is performed at atmospheric pressure.

21. The method of any one of claims 14 to 20, wherein the process further comprises an additional step of irradiating the formed 2D layer at least once to vaporise any residual polymer that may be left over from the initial irradiation step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:—

[0051] FIG. 1 illustrates (a) a 2D polymer layer before metal impregnation; and (b) 2D polymer layer after metal impregnation.

[0052] FIG. 2 illustrates (a) a polymer-metal matrix and metal build plate underneath laser scanning head; and (b) a sintered and non-sintered metal powder post laser exposure.

[0053] FIG. 3 illustrates (a) an optical microscope view of 4 consolidated layers and metal build plate; and (b) a scanning electron microscope (SEM) surface image of a single laser scan showing where powder granules were welded together.

[0054] FIG. 4 illustrates tungsten incorporation within a thermoplastic resin produced using the method of the claimed invention.

[0055] FIG. 5 is a schematic representation of the solvent casting method of fabricating the metal powder-polymer flexible film of the invention.

[0056] FIG. 6 illustrates a titanium-polymer flexible film (sheet) produced by the method depicted in FIG. 5.

[0057] FIG. 7 illustrates a thermogravimetric analysis of a stainless steel/PCL metal flexible film (sheet) produced by the claimed method.

[0058] FIGS. 8(a) and 8(b) illustrate a scanning electron microscope (SEM) analysis of (a) metal nanoparticles and (b) a metal powder-polymer flexible film (sheet) of the claimed invention.

[0059] FIGS. 9(a) and 9(b) illustrate Energy Dispersive X-Ray (EDAX) analysis of a metal powder-polymer flexible film (sheet) of the claimed invention with (a) stainless steel and (b) Ti64 metal particles.

[0060] FIG. 10 illustrates SEM images of laser scans over the build plate without any metal powder or any metal powder-polymer flexible film of the claimed invention.

[0061] FIG. 11 illustrates SEM images of sintered powder manually laid over a non-heated build plate (top row), and SEM images of sintered metal powder-polymer flexible film of the claimed invention on a build plate (bottom row). An argon laser was used at 90W, with a scan rate of 100, 400 and 700 mm/s.

[0062] FIG. 12 illustrates SEM images of sintered powder manually laid over a non-heated build plate (top row), and SEM images of sintered metal powder-polymer flexible film of the claimed invention on a build plate (bottom row). An argon laser was used at 65W, with a scan rate of 100, 400 and 700 mm/s.

[0063] FIG. 13 illustrates SEM images of sintered powder manually laid over a non-heated build plate (top row), and SEM images of sintered metal powder-polymer flexible film of the claimed invention on a build plate (bottom row). An argon laser was used at 40W, with a scan rate of 100, 400 and 700 mm/s.

DETAILED DESCRIPTION OF THE DRAWINGS

[0064] The present invention incorporates a novel method of delivering powder in powder bed machines (such as SLM) for use in 3D printing. Metal powder is closely packed and embedded or attached within a thin polymer sheet, whose thickness is slightly larger than the metal powder particles. This thin sheet forms a single ‘2D layer’.

[0065] In FIG. 1(a) and FIG. 1(b) demonstrate a 2D polymer layer prior to metal (316L stainless steel) impregnation and after metal impregnation, respectively. Stainless steel particles (d50=30 μm) were first tightly packed and bound within an adhesive polymer sheet, approximately 30-40 μm thick, creating a metal/polymer matrix composite (see FIG. 1(b)). The polymer layer (in this example, polyether amide (PEBA) 2533), after being impregnated, was placed on top of a metallic build plate (see FIG. 2(a)). The polymer-metal matrix was then exposed to a laser beam (in this case a 150W CO.sub.2 laser, with 100 μm spot diameter; a 1064 nm infrared Nd:YAG or fibre laser could also be used) over a small section area (see FIG. 2(b)). This can be a single or multi-pass laser scanning strategy. Upon exposure to the laser beam, the polymer and metal are both irradiated. This causes the polymer to rapidly thermally degrade and vaporise, and the metal particles to rapidly reach melting temperature and weld or sinter together (see FIG. 3(a) and FIG. 3(b)). The laser path determines the shape of the 2D layer that is being built.

[0066] Specifically, within the thickness of the first layer that is irradiated, a metal melt pool is formed between the melted powder and a thin section of build plate. Once the laser exposure is removed, these layers cool and solidify almost instantaneously, causing a metallic bonding between the first melted layer and the metal build plate. The next layer of polymer-metal matrix is then placed on top of the first 2D layer. This new layer is also irradiated by the laser using the same parameters, again causing melting of the new layer and several layers underneath (depending on energy density of the laser exposure). This consolidates the new layer to the layers underneath. In this example, the process was repeated 4 times, generating a total printed thickness of approximately 121 μm, as shown in FIG. 3(a). No polymer trace from the sheet was observable in the printed layer and line cross-sections, concluding it had evaporated. If any residual polymer remains on the 2D layer following the single laser pass, the user can apply one or more additional irradiating steps on the formed 2D layer so as to vaporise the residual polymer that remained over from the initial irradiation step. This additional irradiating step(s) may be considered to be a cleaning weld to get rid of any remaining polymer from the formed 2D layer.

[0067] FIG. 3(b) shows the results of a number of single laser scans over a same location, starting from a fresh taped powder sheet. It was possible to adjust processing parameters in such a way to completely evaporate the adhesive polymer and weld a “line” of powder (between the dotted black lines in the FIG. 3(b)) onto the build plate. As explained, this process can be repeated until a 3D geometry is fully formed, with each new polymer-metal matrix layer defining a new 2D layer. This process can be used for all weldable metals just as it can be used with conventional PBF.

[0068] FIG. 4 shows that it was possible to incorporate micron-sized Tungsten (W) powder within a thermoplastic resin using an extruder to produce a metal incorporation of 80%. The resulting sheet was in this case 80 μm thick, and despite the large W incorporation, kept a high level of flexibility. Whilst the proof of concept was carried out using commercial tape and powder glued onto it, results in FIG. 3 represent a stronger alternative with a greater level of impregnation control and materials choice. The sheet thickness can be also reduced.

Examples

[0069] Example 1: In a typical process, a stock solution of 14 wt. % polycaprolactone (PCL) in chloroform was prepared by dissolving 14 g of PCL in 100 ml of chloroform at room temperature under continuous stirring for 12 hrs. 7.5 g of stainless steel particles (316L) was mixed with 5 ml of PCL solution to create a uniform solution and the solution was spread on a Teflon® substrate using a doctor blade set up as described above. After 2 hrs of drying, the flexible metal powder-polymer matrix film was peeled from the substrate and samples were analysed for mechanical properties, thermogravimetric analysis, scanning electron microscopy and EDAX analysis.

[0070] Example 2: In another example, to study the effect of polymer, a stock solution containing a blend of Polylactic acid (PLA)/PCL in chloroform and dimethyl formamide (DMF) solvent prepared by dissolving 14 g of PLA/PCL (80:20 ratio) in 100 ml of a chloroform/DMF (80:20 ratio) mixture at room temperature under continuous stirring for 12 hrs. 7.5 g of stainless steel particles (316L) was mixed with 5 ml of PLA/PCL solution to create a uniform solution and the solution was spread on a Teflon® substrate using the doctor blade set up as described above. After 2 hrs of drying, the flexible metal powder-polymer film was peeled from the substrate and samples were analysed for mechanical properties, thermogravimetric analysis, scanning electron microscopy (SEM) and EDAX analysis.

[0071] FIG. 6 shows the typical metal powder-polymer flexible film (sheet) produced by the claimed method. Various compositions of stainless steel and titanium particle metal powder-polymer flexible films were prepared with >90 wt % of metal particles. Table 1 shows the composition of films, conditions used to produce and the thickness of the flexible films. Metal powder-polymer flexible film thicknesses from 1 to 300 μm are achievable using the method of the claimed invention.

TABLE-US-00001 TABLE 1 Summary of metal-polymer composition, doctor blade coating conditions and thickness of metal-binder sheet PCL Average polymer Coating sheet Sample Metal, solution, speed, thickness, Coating code g ml cm/s μm substrate 316L S241019 7.5 5 5 100 Teflon ® S251019 8 5 5 90 S041119 4 5 5 50 S061119 5 5 4 40 S071119 5 3 4 48 Ti64 T241019 7.5 5 5 80 Teflon ® T211119 7.5 4 4 58 T221119 7.5 3 4 58 T271119 15 5 4 90 T281119 30 10 4 95

[0072] Thermogravimetric analysis (TGA) was performed on the metal powder-polymer flexible films to find the exact metal content in the films that are produced. FIG. 7 shows the TGA thermogram for metal sheet prepared with 316L stainless steel particles with PCL as binder solution. From the TGA analysis, it is evident that the amount of metal remained at the end of TGA analysis was about 96 wt %, indicating that the films contain >90 wt % of metal.

[0073] Table 2 shows the amount of metal content in the various films that are produced. It is evident that all the films have more than 90 wt % of metal content. Raw TGA plots of produced metal powder-polymer matrix flexible films are present in the supporting information. The sheets of the prior art claim a maximum of 80% metal by volume. This is a significantly much lower metal content than the matrix films of the claimed invention. For example, as shown in FIG. 7 and Table 2, the metal content is 96 wt % and polymer is only 4 wt %. This is a significantly increased metal content than that previously obtained by the prior art metal sheets.

TABLE-US-00002 TABLE 2 Metal content in the metal powder- polymer matrix flexible film Sample Metal content, Polymer content, code wt % wt % 316L S241019 95.3 4.7 S071119 94.3 5.7 S121119 96.0 4.0 S131119 97.5 2.5 S181119 95.3 4.7 Ti64 T241019 91.0 9.0 T211119 94.4 5.6

[0074] The metals and metal powder-polymer flexible films of the claimed invention were characterised by SEM analysis to evaluate the morphology of the films produced. FIG. 8 shows the SEM analysis of metal nanoparticles and metal powder-polymer flexible films produced. From SEM micrographs it is evident that the metal particles are uniformly coated with polymer (binder). This is important to retain the strength of the film. If polymer is not coated on metal particles this could be weak point and the film mat break during the process. We do not want to have area where there is more or less polymer, this could lead to weld inconsistencies and not uniformity at layers level.

[0075] The metal sheets were further analysed by EDAX analysis to confirm the type of metal present in the films. FIG. 9 shows the EDAX analysis of the sheet made with 316L stainless steel and Ti64 metal particles. From the EDAX spectra it is evident that iron is predominant in stainless steel metal powder-polymer flexible film and Ti in Ti64 metal powder-polymer flexible films. The use of EDAX analysis of the film of the claimed invention illustrates, quite clearly, that the metal particles predominate in the film and there is no contamination.

[0076] FIGS. 10 to 13 demonstrates that the matrix films and methods of the claimed invention are providing sintered polymer-metal matrix films that produce sintered layers of a standard that is at least comparable to the sintered layers of powder-bed methods and materials of the prior art. The examples in said figures clearly show this. It is clearly possible to observe the layer weld from FIGS. 11-13, as opposed to FIG. 10 where the laser was used without powder, which shows a completely different surface morphology. In all cases, it is possible to recognize the sintered lines from the welding and observe the laser scan patterns (for both manually laid powders and the matrix films of the claimed invention). It can be concluded the mechanism of welding the powder-bed materials and the polymer-metal matrix films of the claimed invention does not change even if the processing parameters are different. This means that the polymer-metal matrix film is not an inhibitor for the weld to take place.

[0077] The polymer-metal matrix can be rolled into sheets, drastically reducing storage complexity and cost, and removing the need for storage of reactive metals under argon. The polymer-metal matrix allows the use of multiple metals which can be used simultaneously in the same build, removing the need to fully clean the machine, for example, for the 3D printing of multi-material functional graded components. This is a significant step-change improvement on current technology capability, as this is currently not possible with other powder bed technologies such as in SLM.

[0078] The use of the polymer-metal matrix of the invention in a 3D printing process removes the need for PBF-based 3D printing systems, thereby removing a multitude of both safety and technical issues related to powder storage and manufacturing processes. Building time could be greatly reduced in comparison to current PBF processes by using an automated polymer sheet feeder, removing the need for powder layer recoating. Using this technology, each layer thickness will be extremely consistent, improving the stability of current metal 3D printing processes. Binding metal powders in a polymer matrix halts oxygen layer formation on the metal powder surface, improving the chemical stability of the metals, an issue extremely pertinent in safety-critical industries (such as biomedical and aerospace) where oxygen inclusion in the final alloy must be kept to a minimum. In addition: [0079] It could be finally possible to use nano-particles in an SLM process, now prohibitive due to the hazardous danger when large amounts are present and in possible oxygen exposure. Using nano-particles would dramatically reduce the necessary laser power necessary for the weld, hence minimizing residual stresses in the final part (a major problem at the time of writing). [0080] As the layer thickness reduces, it might be possible to achieve powder consolidation with a tailored laser pulse, by emulating the principles of laser shock peening. This would dramatically reduce the working temperatures with clear benefits towards the part quality. [0081] This concept can also help to process materials that are reflective, hence suitable with difficulty for SLM processing (such as copper and aluminium). The polymer sheet can be envisaged to be dark, hence an absorbent with respect to radiation. The heat would be conducted to the powder that is now pre-heated, resulting in a higher absorption coefficient.

[0082] The embodiments in the invention described with reference to the drawings comprise a computer apparatus and/or processes performed in a computer apparatus. However, the invention also extends to computer programs, particularly computer programs stored on or in a carrier adapted to control the process and effect the process into practice. The program may be in the form of source code, object code, or a code intermediate source and object code, such as in partially compiled form or in any other form suitable for use in the implementation of the method according to the invention. The carrier may comprise a storage medium such as ROM, e.g. CD ROM, or magnetic recording medium, e.g. a floppy disk or hard disk. The carrier may be an electrical or optical signal which may be transmitted via an electrical or an optical cable or by radio or other means.

[0083] In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

[0084] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.