Product and method for feeding powder into a powder bed 3D printer

Abstract

The present invention provides a metal powder-polymer matrix film for 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 architecture of the polymer sheet or on the surface of the polymer sheet, and wherein the thickness of the polymer sheet is at least half of the powder thickness.

Description

Field of the Invention

[0001] The present invention relates to a method for delivering powder for 3D printing (additive manufacturing - AM) such as selective laser melting (SLM) in a powder bed machine and to a tape product for providing said powder. Background Art

[0002] The earliest use of additive manufacturing (AM) was in rapid prototyping (RP) during the late 1980s and early 1990s. Prototypes allow manufacturers the opportunity to examine the design of an object in more detail and even test it before producing the finished product. RP allows manufacturers to produce these prototypes much faster than before, typically within days or sometimes hours of conceiving the design. In RP, the designer uses computer-aided design (CAD) software to create a model, and then the machine follows the software model to determine the best way to build the object. The RP concept has recently evolved into the principle of 3D printing (or AM), which has significant advantages compared to more conventional manufacturing, such as design complexity, tool-lessness, product customization, limited waste, reduced inventory.

[0003] In a conventional 3D printing powder bed machine, powder is delivered from a large hopper to the working area, where any particles are spread over a large or smaller area by using a blade or a roller. At this stage, a laser (or electron beam) will melt / consolidate a part of the layer. Thus, a new powder layer is laid and the process is repeated until the complete geometry of the part is formed. In each run, the powder layer thickness varies between approximately 40 μm and 100 μm.

[0004] When considering AM of metallic materials, there is no doubt that the powder bed fusion (PBF) process and especially selective laser melting (SLM) stand out compared to others due to the optimal combination of process flexibility, part quality (low porosity, high geometric accuracy, etc.) and material capabilities. For example, in SLM, powder is delivered from a large hopper to the working area, and the particles are spread over a large or smaller area using a blade or roller. At this stage, the laser will melt / consolidate a part of the layer. Thus, a new powder layer is laid and the process is repeated until the complete geometry of the part is formed based on the details stored in the STL file. The powder layer thickness (per layer) varies approximately between 40 μm and 100 μm. A large starting powder volume is always required, and the entire powder bed (or build plate) needs to be covered regardless of the part size (small or large). This results in screening and recycling large amounts or stockpiles of material after any print (small or large). Additionally, due to the nature of the blade spreading mechanism, the thickness of the powder bed is actually non-uniform and undergoes continuous readjustment during the laser scanning process. This results in critical process inconsistencies across the build platform and contributes to process repeatability issues. Despite the "state-of-the-art" label, the current way of feeding powder onto the bed area and keeping it in place during the laser processing has inherently strong method limitations that are challenging to solve.

[0005] US2017274595 describes involving inserting a stack of build plate sheets into a material feeder, transferring one sheet from the stack in the material feeder to a printer, depositing a fluid on a single sheet while the sheet is resting on a printer platen, transferring the sheet from the printer to a powder system, depositing powder onto the single sheet such that the powder adheres to the area of the sheet where the printer has deposited the fluid, removing any powder that has not adhered to the sheet, melting the powder on the build plate, and repeating the steps for as many additional sheets as required to fabricate a specified 3D object. US20170157841 describes a system that includes a build platform, a recoater for dispensing build powder onto the build platform, an energy source, a foil feed assembly, and a controller for controlling the actuation of these components. A method of forming a 3D article includes depositing a layer of build powder on a build platform surface, melting selected portions of the build powder layer, applying a foil sheet on the build powder layer, melting selected portions of the foil sheet onto the build powder layer, removing the foil sheet from the build powder layer, and then lowering the build platform surface to prepare for depositing the next build powder layer. However, the problems with the systems and methods described in the US patent documents are that it is not possible to achieve thin printed metal sheets, and large metal sheets are rigid and difficult to conform to the support surface during printing. Additionally, welding of metal sheets is likely to require more energy input, resulting in higher residual stresses due to enhanced thermal gradients.

[0006] US 2018 / 514946 describes a rigid pre-patterned metal powder-polymer matrix film for 3D printing. US 2016 / 101470 describes using multiple lasers and sintering steps to produce 3D objects using sintered materials (where metal powder and binder are kneaded into a sheet shape on a tabletop). Giraud et al. (Thermal Spray 202, pp. 265-270 (2012)) describe using cold spraying in the metallization of cryogenic-resistant materials such as organic composites (e.g., metallization of PA66-matrix composites with aluminum). Lupoi R. et al. (Surface and Coatings Technology, Vol. 205(7), pp. 2167-2173 (2010)) describe using cold spraying to produce metal coatings on non-metallic surfaces such as polymers and composites. WO 2018 / 143292 describes a method of manufacturing laminated 3D objects using multiple pre-patterned foils, some of which may include metal.

[0007] An object of the present invention is to overcome at least one of the above problems. Summary of the Invention

[0008] The present invention describes a novel way of delivering powder for 3D printing in a powder bed machine, which is fundamentally different from the conventional way of implementing this. The metal powder is closely packed and embedded or attached within a thin polymer sheet, the thickness of which is slightly greater than the diameter of the metal powder particles. This thin sheet forms a single '2D layer'. Then a laser beam emitted from above the 2D layer is used to evaporate the polymer binder and then the metal particles are melted (sintered) together. After sintering, the metal particles solidify instantaneously. Then a new 2D layer or the unused portion of a used 2D layer is placed directly on top of the previously printed layer, and then this new layer or the unused portion of the used 2D layer is also melted. After melting, this layer consolidates with the previously melted layer below. This process is repeated multiple times until a 3D part is fabricated from multiple 2D sheets (if required). The first 2D layer is built on a metal build plate or the like, which can be removed after construction. The method is suitable for retrofitting existing PBF machines that can print both large and small parts simultaneously, can process a variety of materials, and has minimal powder handling.

[0009] The 3D part is produced from a metal powder-polymer matrix film, which is flexible and adapted to be mounted on a roller and delivered to a 3D printer as a continuous roll of film. The claimed films of the present invention are cost-effective, flexible and recyclable. In some cases, they are bio-based and biodegradable. The fact that the film is formed as a continuous flexible sheet means that when printing a 3D part by moving the build plate relative to the flexible film or moving the flexible film relative to the build plate, the user can utilize all areas of the sheet.

[0010] According to the present invention, there is provided a metal powder-polymer matrix film for 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 architecture of the polymer sheet or on the surface of the polymer sheet, and wherein the thickness of the polymer sheet is at least half the thickness of the powder thickness.

[0011] According to the present invention, as listed in the appended claims, there is provided a metal powder-polymer matrix flexible film for 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 architecture of the polymer sheet or on the surface of the polymer sheet; and wherein the flexible film comprises at least 90 wt% of the metal powder.

[0012] In one aspect, the thickness of the matrix is between about 1 μm and about 150 μm. Preferably, the thickness of the matrix is between about 5 μm and about 100 μm.

[0013] In one aspect, the polymer is selected from the group consisting of: thermoplastics, epoxy resins, silicones, vulcanized rubbers, polyesters, polyurethanes, polyethylene, polypropylene, polyamides, polyetheramides, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), fluoroplastics, polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polyhydroxyalkanoates (PHA), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and combinations thereof.

[0014] In one aspect, the metal is selected from the group consisting of: stainless steel, tungsten, titanium, titanium alloys, aluminum, aluminum alloys, copper, nickel, nickel alloys, superalloys, high entropy alloys, cobalt-chromium alloys, barium, molybdenum, NiTi (nitinol), NiTi alloys, ceramic materials, metal-ceramic composites, metal-diamond composites, tantalum, tantalum carbide, and combinations thereof.

[0015] In one aspect, the metal powder is embedded within the architecture of the polymer sheet.

[0016] In one aspect, the metal powder particles are closely packed and attached to one side of the polymer sheet. In this aspect, the thickness of the polymer sheet together with the attached metal powder particles is greater than the diameter of the metal powder particles.

[0017] In one aspect, a method of manufacturing the above-described metal powder-polymer matrix film is provided, the method further comprising mixing the metal powder and the polymer in a ratio of about 4:1 to form a mixture, and forming a metal-powder matrix film. Typically, the method includes extruding the mixture to form a metal powder-polymer matrix film.

[0018] In one aspect, when the metal powder is incorporated within the architecture of the polymer sheet, the metal powder-polymer flexible film is formed by solvent casting, thermocompression, extrusion techniques, or by joining together thin layers of multiple metal-containing polymer sheets.

[0019] Preferably, 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 the flexible film by an adhesive, by extrusion, by thermocompression, by electrospraying, or by cold spraying.

[0020] In one aspect, a metal powder-polymer matrix film is formed by extruding a metal powder and polymer mixture. Preferably, the extrusion method is selected from film extrusion and other methods known to those skilled in the art. Desirably, the metal powder-polymer matrix flexible film is extruded as a continuous roll.

[0021] In one aspect, a method of producing a 3D product using the above-described metal powder-polymer matrix flexible film is provided, the method comprising applying the metal powder-polymer matrix film to a build plate; irradiating the matrix flexible film to evaporate the polymer and fuse the metal particles together to form a 2D layer; placing a new metal powder-polymer matrix flexible film layer on top of the previous 2D layer; and repeating the application of a heat source for a plurality of cycles to produce the desired 3D product. Preferably, the new metal powder-polymer matrix flexible film layer is an unused area of the flexible film layer used or a new metal powder-polymer matrix flexible film layer. Preferably, the flexible film is delivered to the printing process via a roller system. Desirably, the flexible film is extruded as a continuous roll. By extruding the metal powder-polymer matrix flexible film as a continuous roll, the continuous roll can be placed on a continuous roller of a 3D printer. When printing a 3D product, the roller delivering the flexible film can move relative to the bed on which the build plate is mounted, or when printing a 3D product, the build plate can move relative to the flexible film.

[0022] In one aspect, the metal powder-polymer flexible film is recyclable. When the flexible film roll or sheet is used up, the remaining scrap of the unused material can be recycled and recast or re-extruded into a complete metal powder-polymer matrix flexible film roll or sheet for printing 3D products.

[0023] In one aspect, the metal powder-polymer flexible film is degradable, biodegradable, and / or compostable.

[0024] In one aspect, the metal powder-polymer flexible film is a single thick layer (used as a coating) or multiple layers stacked on top of each other (e.g., to form a 3D product or part).

[0025] In one aspect, the build plate is weldable metal or weldable plastic.

[0026] In one aspect, the substrate film is irradiated by an infrared radiation device, a laser, an electron beam, an arc, a heating plate in contact with the material, or a plasma. Preferably, the laser is selected from CO2 lasers, 1064 nm infrared Nd:YAG lasers, infrared fiber lasers, diode lasers, argon lasers, krypton lasers, argon / krypton lasers, helium-cadmium lasers, copper vapor lasers, xenon lasers, iodine lasers, oxygen lasers, and excimer lasers. Ideally, in embodiments of aspects of the present invention, the substrate film is irradiated by an ion laser and preferably an argon laser.

[0027] In one aspect, the method for producing a 3D product is selected from the group consisting of: laser cladding, selective laser melting, selective laser sintering, wire cladding, cold spraying, power spraying, high velocity oxygen fuel (HVOF) spray coating, high velocity air fuel (HVAF) spray coating, plasma spraying, arc spraying, direct energy deposition (DED), and combinations thereof.

[0028] In one aspect, the method for producing a 3D product is carried out by multi-directional printing, wherein the substrate film and the heat source for welding or sintering the film are configured to rotate 360° in all dimensions.

[0029] In one aspect, a 3D product produced by the above method is provided.

[0030] It should also be understood that the above-described substrate film and method can be used to modify the surface of an existing preformed (3D) product or part. In one aspect, a method of printing on an existing preformed product or part using the above-described metal powder-polymer matrix flexible film is provided, the method comprising applying the metal powder-polymer matrix flexible film to the preformed product or part; irradiating the metal powder-polymer matrix flexible film to evaporate the polymer and fuse the metal particles together to form a 2D layer on the preformed product or part; optionally, placing the same or a new layer of the metal powder-polymer matrix flexible film on top of the previous 2D layer or on another surface of the preformed product or part; and repeating the application of the heat source for a plurality of cycles to produce the desired effect on the preformed product or part.

[0031] The method of printing on an existing preformed product or part is typically carried out by omnidirectional printing, i.e., printing from all directions and angles. The printing involved can be used as spot welding, for repairing preformed products or parts, for coating preformed products or parts, for building features on preformed products or parts, for adding different metal features on preformed products or parts, etc. The omnidirectional method means that the metal powder-polymer matrix flexible film can be applied from various angles and not just from above the build plate.

[0032] The claimed substrate film of the present invention can be used as a feedstock material for a direct energy deposition (DED) process. This will allow the user to build (potentially different materials) structures on existing components of products produced using more conventional manufacturing routes such as casting, extrusion, forging, machining, etc. This will also allow the user to print objects from multiple directions, potentially reducing the final residual stresses on the finished product. The advantage of using this method compared to the state-of-the-art powder blowing and wire feeding DED is the ability to achieve much higher geometric accuracy, the same as that achievable using an SLM process.

[0033] The claimed polymer-metal matrix of the present invention can be rolled into sheets, thus significantly reducing storage complexity and cost and eliminating the need to store reactive metals under argon. The polymer-metal matrix allows the use of multiple metals, which can be used simultaneously and quickly in the same build, so that if new materials are required from build to build and part to part, there is no need to completely clean the machine. This eliminates the 'rogue particle' problem that plagues PBF-based processes. This is a significant step-change improvement over current technological capabilities, as this is not possible currently in the case of other powder bed manufacturing methods such as SLM. The method disclosed herein allows for the rapid manufacture of multi-metal parts, which are used for 3D printing metals for the first time. There is no need for post-processing of the polymer and metal via debinding and sintering furnaces, as the parts are fully sintered in the build chamber.

[0034] Definition

[0035] In this specification, the term "sintering" shall be understood to mean coalescing into a solid or porous material by heating without liquefaction. The terms "sintering" or "sintered" are also respectively understood to mean "welding" or "welded", and these terms may be used interchangeably.

[0036] In this specification, in the context of a metal-polymer film matrix, the term "matrix" shall be understood to mean a metal-polymer film strip formed by melt-processing a polymer and metal particles together and hot-pressing.

[0037] In this specification, the term "flexible" shall be understood to mean that a metal powder-polymer matrix film can be easily bent or flexed without breaking.

[0038] In this specification, the term "complex structure" shall be understood to mean a three-dimensional part geometry that cannot be easily manufactured using conventional methods such as casting, machining, forging, and the like.

[0039] In this specification, the term "weldable metal" or "weldable thermoplastic (or weldable plastic)" shall be understood to mean materials that can be joined together by applying heat input at the contact interface (which can also be achieved by including fillers to facilitate the joining action). In the case of not adding filler materials (resistance, electron beam, laser, and some autogenous arc welding), the welded metal / thermoplastic has the same composition as the parent material. In the case of adding filler materials to the weld pool, the composition of the welded metal / thermoplastic (plastic) is usually different from that of the parent material. Examples of weldable metals are steel, stainless steel, titanium, titanium alloys (such as Ti64 or grades 5 and 23 Ti), aluminum, aluminum alloys (such as Al 6061 and Al 7075), copper, nickel, nickel alloys, superalloys (such as Inconel 625 and 718), high-entropy alloys (such as FeCoNiCrMn), cobalt-chromium alloys, barium, and molybdenum. Examples of weldable plastics are epoxy resins, silicones, vulcanized rubbers, polyesters, polyurethanes, polyethylene, polypropylene, polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), fluoroplastics, polyetheramide (PEBA), polyetheramide 2533, polylactic acid (PLA), polycaprolactone (PCL), polybutylene succinate (PBS), polyhydroxyalkanoates (PHA), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Other examples include ceramic-metal composites such as WC-Co and metal-diamond combinations, metal-alumina combinations.

[0040] In this specification, the term "build plate" or "metal build plate" shall be understood to mean the surface on which the metal-impregnated polymer sheet / composite material is placed. The build plate preferably has the same metal as the powder material, as this will maximize the weldability of the metal-polymer composite. However, the present invention is also used for multi-material printing, so combinations of different metals are also possible.

[0041] In this specification, the term "architecture of the polymer sheet" shall be understood to mean the structural features of the polymer sheet that accommodate the insertion of metal particles within the polymer sheet itself.

[0042] In this specification, the term "integrate" or "embed" shall be understood to mean in the case of integrating or embedding metal particles with the architecture of the polymer sheet therein.

[0043] In this specification, the term "extrusion" shall be understood to mean the process for manufacturing an article having a fixed cross-sectional profile, where the material constituting the article is pushed through a die having the desired cross-section. The process can be done with hot or cold materials.

[0044] Materials and Methods

[0045] In the experiments described herein, a steel substrate was selected as the build substrate material. On top of it, a commercial tape layer was attached only on one side (see Figure 1 a and Figure 1 b). At this stage, stainless steel powder (SS 316 was used in the experiment) was manually laid on one side of the tape. Any portion of the powder that was not adhered to the tape was removed from the area. At this stage, the area was irradiated with a laser. Laser irradiation exposure resulted in two outcomes: (i) removal or partial removal of the polymer layer, and (ii) welding of the powder to the underlying layer. In this experiment, the process was systematically repeated up to 4 layers of tape, thereby producing a sintered metal block at the end of the process (see Figure 3 a). Typically, the substrate is removed after printing, so it does not play a major role in the actual printing process.

[0046] Production of Metal / Polymer Matrix Composites

[0047] To reduce the moisture content to the recommended level before processing, the polymer material (in this case, PEBAX) and metal particles (in this case, tungsten particles) were dried in a vacuum oven at 60 °C. Using a Brabender 50EHT twin-screw internal mixer, 40 cm 3Blended 20% PEBAX 2533 and 80% tungsten nanoparticles. After the complete polymer melt has formed, the metal particle additive is slowly added. The mixer temperature is set at 145 °C, the mixing time is 10 minutes, and the screw speed is 50 RPM. The resulting material is formed into a film by hot compression at 145 °C using a hydraulic press. The polymer is placed between a release film (DuPont TM ) and a metal frame to control the film thickness. Once the polymer has melted, the hydraulic press is closed with a force of 90 kN and the force is maintained for 2 minutes. Cooling is achieved by circulating cold water through the platen while the polymer is kept under pressure.

[0048] The metal powder layer is laid on a flat surface. Then, the adhesive polymer is rolled onto the powder layer until it appears that nothing else adheres to it, thus forming a composite material.

[0049] Preparation of Metal Binder Sheets for 3D Printing

[0050] A metal powder-polymer matrix flexible film (sheet) is fabricated by the solvent casting method using a doctor blade coating technique, which produces a flexible sheet (film) with uniform thickness and smooth surface characteristics. The coating paste is prepared by dispersing metal particles into a stock polymer solution and casting the viscous solution onto a selected substrate. A fixed 90° angled razor blade is placed on the substrate, and the metal powder-polymer solution is dispensed along the sidewall of the blade onto the substrate. The substrate is dragged at a controlled speed by a pump, and then the blade can spread the metal powder-polymer solution evenly on the substrate. After coating, the sample is placed in a fume hood and dried at atmospheric pressure for 2 hours. By adjusting the gap between the casting knife and the substrate, the thickness of the film can be easily controlled from microns to millimeters. Figure 5 Depicts the processing flow for the fabrication of a metal powder-polymer matrix film (sheet).

[0051] Printing 3D Products

[0052] The printing of 3D products can be carried out in a manner similar to the previously described experiment. 1) First, a 3D part is generated in computer-aided design (CAD) format. 2) The software will generate a stereolithography (STL) (or equivalent) file of the part, which contains information for the printing machine to process. The STL file also has information related to the multiple layers into which the 3D part is subdivided. The metal-impregnated polymer sheets will have been fabricated separately and be ready for use. 3) After placing the first polymer layer on the build plate, a laser (or electron beam) is used to debind the polymer matrix and sinter and / or melt the metal powder onto the underlying layer. 4) Then the unused sheet is removed from the area. 5) The procedure is repeated for the desired number of layers to form the 3D part.

[0053] Automation of the process is envisioned by moving polymer sheets or multiple polymer sheets with multiple materials using, for example, rollers and by moving with a robotic arm. The build direction can be vertical, horizontal, or both. In conventional selective laser melting (SLM) and metal 3D printing, the build direction is vertical, but in the present invention, the vertical direction is not limited thereto. In fact, it will be possible to selectively determine the build direction by positioning the polymer sheet along the part in a specific orientation or along a desired face and build another / multiple layers therefrom. Relative to the prior art level, the present invention is also applicable to 3D printing features onto existing non-3D printed parts.

[0054] 6) Once printing is complete, the part is mechanically removed from the build plate and finished with additional machining (if required). Description of the Drawings

[0055] With reference to the drawings, the present invention will be more clearly understood from the following description of embodiments of the present invention given by way of example only, wherein:

[0056] Figure 1 Shows (a) a 2D polymer layer before metal impregnation; and (b) a 2D polymer layer after metal impregnation;

[0057] Figure 2 Shows (a) a polymer-metal matrix and a metal build plate under a laser scanning head; and (b) sintered and unsintered metal powders after laser exposure;

[0058] Figure 3 Shows (a) an optical microscope view of 4 consolidated layers and a metal build plate; and (b) a scanning electron microscope (SEM) surface image of a single laser scan, showing the locations where powder particles are welded together;

[0059] Figure 4 Shows the incorporation of tungsten in a thermoplastic resin produced using the claimed method of the present invention;

[0060] Figure 5 Is a schematic diagram of the solvent casting method for manufacturing the metal powder-polymer flexible film of the present invention;

[0061] Figure 6 Shows by Figure 5 The titanium-polymer flexible film (sheet) produced by the method depicted in;

[0062] Figure 7 Shows the thermogravimetric analysis of the stainless steel / PCL metal flexible film (sheet) produced by the claimed method;

[0063] Figure 8 (a) andFigure 8 (b) shows the scanning electron microscope (SEM) analysis of (a) metal nanoparticles and (b) the claimed metal powder-polymer flexible film (sheet) of the present invention;

[0064] Figure 9 (a) and Figure 9 (b) shows the energy-dispersive X-ray (EDAX) analysis of the claimed metal powder-polymer flexible film (sheet) of the present invention having (a) stainless steel and (b) Ti64 metal particles;

[0065] Figure 10 Shows the SEM image of laser scanning on a build plate without any metal powder or any metal powder-polymer flexible film of the present invention claimed;

[0066] Figure 11 Shows the SEM image of sintered powder manually laid on an unheated build plate (top row) and the SEM image of the sintered metal powder-polymer flexible film of the present invention claimed on the build plate (bottom row). An argon laser was used at 90 W, where the scanning rates were 100, 400, and 700 mm / s;

[0067] Figure 12 Shows the SEM image of sintered powder manually laid on an unheated build plate (top row) and the SEM image of the sintered metal powder-polymer flexible film of the present invention claimed on the build plate (bottom row). An argon laser was used at 65 W, where the scanning rates were 100, 400, and 700 mm / s;

[0068] Figure 13 Shows the SEM image of sintered powder manually laid on an unheated build plate (top row) and the SEM image of the sintered metal powder-polymer flexible film of the present invention claimed on the build plate (bottom row). An argon laser was used at 40 W, where the scanning rates were 100, 400, and 700 mm / s. Detailed Description

[0069] The present invention includes a novel method for delivering powder in a powder bed machine (e.g., SLM) for 3D printing. The metal powder is tightly packed and embedded or attached within a thin polymer sheet having a thickness slightly greater than the metal powder particles. This thin sheet forms a single '2D layer'.

[0070] Figure 1 (a) and Figure 1(b) shows the 2D polymer layer before and after metal (316L stainless steel) impregnation, respectively. First, stainless steel particles (d50 = 30 μm) are tightly packed and bonded in an adhesive polymer sheet about 30 - 40 μm thick, resulting in a metal / polymer matrix composite (see Figure 1 (b)). After impregnation, the polymer layer (in this example, polyetheramide (PEBA) 2533) is placed on top of the metal build plate (see Figure 2 (a)). Then the polymer - metal matrix is exposed to a laser beam with a small cross - sectional area (in this case, a 150W CO2 laser with a spot diameter of 100 μm; a 1064nm infrared Nd:YAG or fiber laser can also be used) (see Figure 2 (b)). This can be a single - pass or multi - pass laser scanning strategy. When exposed to the laser beam, both the polymer and the metal are irradiated. This causes the polymer to rapidly thermally degrade and evaporate, and the metal particles to quickly reach the melting temperature and weld or sinter together (see Figure 3 (a) and Figure 3 (b)). The laser path determines the shape of the 2D layer being built.

[0071] Specifically, within the thickness of the first irradiated layer, a metal melt pool is formed between the molten powder and the thin section of the build plate. Once the laser exposure is removed, these layers cool and solidify almost instantaneously, resulting in a metal bond between the first layer molten layer and the metal build plate. Then the next polymer - metal matrix layer is placed on top of the first 2D layer. This new layer is also irradiated using the same parameters by the laser, again causing the new layer and several underlying layers (depending on the energy density of the laser exposure) to melt. This consolidates the new layer to the underlying layers. In this example, the process is repeated 4 times, resulting in a total printed thickness of approximately 121 μm, as shown in Figure 3 (a). No polymer traces from the sheet can be observed in the printed layer and line cross - section, concluding that it has evaporated. If any residual polymer remains on the 2D layer after a single laser pass, the user can apply one or more additional irradiation steps to the formed 2D layer to evaporate the residual polymer remaining from the initial irradiation step. One or more such additional irradiation steps can be considered a cleaning weld to remove any remaining polymer from the formed 2D layer.

[0072] Figure 3 (b) shows the result of multiple single laser scans at the same location starting from a fresh tape powder sheet. It is possible to completely evaporate the adhesive polymer and form a powder "line" (in Figure 3Adjust the processing parameters in such a way that the (between the black dashed lines in (b)) is welded to the build plate. As explained, this process can be repeated until the 3D geometry is fully formed, where each new polymer-metal matrix layer defines a new 2D layer. This process can be used for all weldable metals, just as it can be used in the case of conventional PBF.

[0073] Figure 4 It is shown that it is possible to incorporate micron-sized tungsten (W) powder into a thermoplastic resin using an extruder to produce a metal incorporation of 80%. In this case, the resulting sheet thickness is 80 μm, and despite the high W incorporation, a high level of flexibility is maintained. Although a proof of concept was carried out using commercial tape and powder adhered to it, Figure 3 the results in represent a stronger alternative with a greater level of impregnation control and material selection. The sheet thickness can also be reduced.

[0074] Examples

[0075] 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 with continuous stirring for 12 h at room temperature. 7.5 g of stainless steel particles (316L) were mixed with 5 ml of the PCL solution to produce a homogeneous solution, and the solution was spread on the substrate using a doctor blade set as described above. After drying for 2 h, the flexible metal powder-polymer matrix film was peeled off the substrate, and the samples were analyzed for mechanical properties, thermogravimetric analysis, scanning electron microscopy, and EDAX analysis.

[0076] Example 2: In another example, to study the role of the polymer, a stock solution containing a blend of polylactic acid (PLA) / PCL in chloroform and dimethylformamide (DMF) solvents was prepared by dissolving 14 g of PLA / PCL (80:20 ratio) in 100 ml of a chloroform / DMF (80:20 ratio) mixture with continuous stirring for 12 h at room temperature. 7.5 g of stainless steel particles (316L) were mixed with 5 ml of the PLA / PCL solution to produce a homogeneous solution, and the solution was spread on the substrate using a doctor blade set as described above. After drying for 2 h, the flexible metal powder-polymer film was peeled off the substrate, and the samples were analyzed for mechanical properties, thermogravimetric analysis, scanning electron microscopy (SEM), and EDAX analysis.

[0077] Figure 6Shows a typical metal powder-polymer flexible film (sheet) produced by the claimed method. Various compositions of stainless steel and titanium particulate metal powder-polymer flexible films are prepared, where the metal particles are >90 wt%. Table 1 shows the composition of the film, the conditions for production, and the thickness of the flexible film. A metal powder-polymer flexible film thickness from 1 μm to 300 μm can be achieved using the claimed method of the present invention.

[0078] Table 1. Summary of metal-polymer composition, doctor blade coating conditions, and thickness of metal-adhesive sheet

[0079]

[0080] Thermogravimetric analysis (TGA) is performed on the metal powder-polymer flexible film to find the exact metal content in the produced film. Figure 7 Shows the TGA thermogram of a metal sheet prepared with 316L stainless steel particles and PCL as the binder solution. It is evident from the TGA analysis that the amount of metal remaining at the end of the TGA analysis is approximately 96 wt%, indicating that the film contains >90 wt% metal.

[0081] Table 2 shows the amounts of metal content in the various films produced. It is evident that all films have a metal content of more than 90 wt%. The original TGA graphs of the produced metal powder-polymer matrix flexible films are present in the supporting information. Prior art sheets claim a maximum of 80% metal by volume. This is a significantly lower metal content compared to the claimed matrix film of the present invention. For example, as Figure 7 and shown in Table 2, the metal content is 96 wt% and the polymer is only 4 wt%. This is a significantly increased metal content compared to the metal content obtained previously with prior art metal sheets.

[0082] Table 2. Metal content in metal powder-polymer matrix flexible films

[0083]

[0084] The metal and the claimed metal powder-polymer flexible film of the present invention are characterized by SEM analysis to evaluate the morphology of the produced film. Figure 8 Shows the SEM analysis of the produced metal nanoparticles and metal powder-polymer flexible film. It is evident from the SEM micrographs that the metal particles are uniformly coated with the polymer (binder). This is important for maintaining the strength of the film. If the metal particles are not coated with the polymer, this could be a weakness and the film pads could break during the process. We do not want regions with more or less polymer, which could lead to inconsistent welding and non-uniformity at the layer level.

[0085] The metal sheet is further analyzed by EDAX analysis to confirm the types of metals present in the film. Figure 9 The EDAX analysis of the sheet made of 316L stainless steel and Ti64 metal particles is shown. It is evident from the EDAX spectra that iron is dominant in the stainless steel metal powder-polymer flexible film and Ti is dominant in the Ti64 metal powder-polymer flexible film. The EDAX analysis of the claimed film of the present invention clearly demonstrates that the metal particles are dominant in the film and there is no contamination.

[0086] Figures 10 to 13 It is shown that the claimed matrix film and method of the present invention provide a sintered polymer-metal matrix film that produces a standard sintered layer at least comparable to the sintered layers of the prior art powder bed methods and materials. This is clearly shown in the examples in the figures. As opposed to using a laser without powder Figure 10 on the contrary, layer welding can be clearly observed from Figures 11 - 13 which shows a completely different surface morphology. In all cases, it is possible to identify the sintering lines from the welding and observe the laser scan pattern (for both the manually laid powder and the claimed matrix film of the present invention). It can be concluded that even though the processing parameters are different, the mechanism of welding the powder bed material and the claimed polymer-metal matrix film of the present invention does not change. This means that the polymer-metal matrix film is not an inhibitor of welding. Figure 10

[0087] The polymer-metal matrix can be rolled into sheets, thereby significantly reducing storage complexity and cost and eliminating the need to store reactive metals under argon. The polymer-metal matrix allows the use of multiple metals, which can be used simultaneously in the same build, thus eliminating the need to completely clean the machine, for example, for 3D printing of multi-material functionally graded components. This is a significant step-change improvement over the current state of the art capabilities, as this is not possible in the case of other powder bed technologies such as SLM at present.

[0088] ​The use of the polymer-metal matrix of the present invention in the 3D printing process eliminates the need for a PBF-based 3D printing system, thus eliminating a significant number of both safety and technical issues associated with powder storage and the manufacturing process. Compared with the current PBF process, the build time can be significantly reduced by using an automated polymer sheet feeder, thus eliminating the need to recoat the powder layer. Using this technology, the layer thickness will be extremely consistent, thus improving the stability of the current metal 3D printing process. Bonding the metal powder in the polymer matrix prevents the formation of an oxygen layer on the surface of the metal powder, thus improving the chemical stability of the metal, which is of great concern in industries where the oxygen inclusions in the final alloy must be kept to a minimum, such as biomedical and aerospace. Additionally:

[0089] · It may ultimately be possible to use nanoparticles in the SLM process, which are now prohibited due to the harmful hazards when present in large quantities and the possible oxygen exposure. Using nanoparticles will significantly reduce the necessary laser power required for welding, thus minimizing the residual stress in the final part (the main issue at the time of writing).

[0090] · As the layer thickness decreases, it may be possible to achieve powder consolidation with customized laser pulses by emulating the principle of laser shock peening. This will significantly reduce the working temperature, which has obvious benefits for the part quality.

[0091] · This concept can also help process materials that are reflective and thus difficult to process by SLM (such as copper and aluminum). It is conceivable that the polymer sheet is dark and thus an absorber for radiation. Heat will conduct to the pre-heated powder, thus resulting in a higher absorption coefficient.

[0092] The embodiments of the present invention described with reference to the accompanying drawings include computer devices and / or processes executed in computer devices. However, the present invention also extends to computer programs, particularly computer programs stored on or in a carrier, the carrier being adapted to control a process and put the process into practice. The program may be in the form of source code, object code, or code intermediate between source and object code, such as in a partially compiled form or in any other form suitable for implementing the method according to the present invention. The carrier may include a storage medium, such as a ROM, for example a CD ROM, or a magnetic recording medium, such as a floppy disk or a hard disk. The carrier may be an electrical or optical signal, which may be transmitted via a cable or an optical fiber or by radio or other means.

[0093] In this 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 fully interchangeable and they shall all be given the broadest possible interpretation and vice versa.

[0094] The invention is not limited to the embodiments described above, but may vary in construction and detail.

Claims

1. A recyclable metal powder-polymer matrix flexible film for delivering metal powder to a three-dimensional printing process, said matrix comprising at least one metal powder and a polymer selected from the group consisting of polyester, polyethylene, polypropylene, polyamide, polyvinyl chloride, polylactic acid, and polycaprolactone, wherein said metal powder is incorporated within the architecture of said polymer or on the surface of said polymer; wherein said recyclable metal powder-polymer matrix flexible film comprises at least 90 wt% of said metal powder; and wherein when the flexible film roll or sheet is used up, the remaining waste of the unused material is recycled and recast or re-extruded into a complete metal powder-polymer matrix flexible film roll or sheet for printing 3D products.

2. The recyclable metal powder-polymer matrix flexible film according to claim 1, wherein the thickness of the matrix is between 1 μm and 150 μm.

3. The recyclable metal powder-polymer matrix flexible film according to claim 1, wherein the metal is selected from the group consisting of stainless steel, tungsten, titanium, titanium alloy, aluminum, aluminum alloy, copper, nickel, nickel alloy, superalloy, high entropy alloy, cobalt-chromium alloy, barium, molybdenum, nitinol, ceramic material, metal-ceramic composite, metal-diamond composite, tantalum, tantalum carbide, and combinations thereof.

4. The recyclable metal powder-polymer matrix flexible film according to any one of claims 1 to 3, wherein the metal powder is embedded within the architecture of the polymer.

5. The recyclable metal powder-polymer matrix flexible film according to any one of claims 1 to 3, wherein the particles of the metal powder are closely packed and attached to one side of the polymer.

6. A method of manufacturing the recyclable metal powder-polymer matrix flexible film according to claim 1, said method comprising the steps of: Mixing the metal powder and the polymer in a ratio of 4:1 to form a metal powder and polymer mixture; and Forming the recyclable metal powder-polymer matrix flexible film.

7. The method of manufacturing the recyclable metal powder-polymer matrix flexible film according to claim 1 according to claim 6, wherein when the metal powder is incorporated within the architecture of the polymer, the recyclable metal powder-polymer flexible film is formed by solvent casting, thermothermal pressing, extrusion techniques, or by joining together thin layers of multiple metal-containing polymer sheets.

8. The method of manufacturing the recyclable metal powder-polymer matrix flexible film according to claim 1 according to claim 6, wherein when the metal powder is on the surface of the recyclable metal powder-polymer matrix flexible film, the metal powder is attached to one side of the flexible film by an adhesive, by extrusion, by hot pressing, by electrospraying, or by cold spraying.

9. The method of manufacturing a recyclable metal powder-polymer matrix flexible film according to claim 1, as claimed in claim 6, wherein the recyclable metal powder-polymer matrix flexible film is formed by extruding the metal powder and polymer mixture.

10. The method of manufacturing a recyclable metal powder-polymer matrix flexible film according to claim 1, as claimed in claim 6, wherein the recyclable metal powder-polymer matrix flexible film is extruded by a method selected from film extrusion.

11. The method of manufacturing a recyclable metal powder-polymer matrix flexible film according to claim 1, as claimed in any one of claims 6 to 10, wherein the recyclable metal powder-polymer matrix flexible film is extruded as a continuous roll.

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

13. The method according to claim 12, wherein the build plate is a weldable metal or a weldable plastic.

14. A method of printing on an existing preformed product or part using the recyclable metal powder-polymer matrix flexible film according to claim 1, the method comprising applying the recyclable metal powder-polymer matrix flexible film to the preformed product or part; heating the recyclable metal powder-polymer matrix flexible film to evaporate the polymer and fuse the metal particles together to form a 2D layer on the preformed product or part; and repeating the application of a heat source for a plurality of cycles to produce the desired effect on the preformed product or part.

15. A method of printing on an existing preformed product or part using the recyclable metal powder-polymer matrix flexible film according to claim 1, the method comprising applying the recyclable metal powder-polymer matrix flexible film to the preformed product or part; heating the recyclable metal powder-polymer matrix flexible film to evaporate the polymer and fuse the metal particles together to form a 2D layer on the preformed product or part; placing the same or a new layer of recyclable metal powder-polymer matrix flexible film on top of the previous 2D layer or on another surface of the preformed product or part; and repeating the application of a heat source for a plurality of cycles to produce the desired effect on the preformed product or part.

16. The method according to any one of claims 12 to 15, wherein the recyclable metal powder-polymer matrix flexible film is heated by an infrared radiation device, a laser, an electron beam, a heating plate in contact with the material, or a plasma.

17. The method according to claim 16, wherein the laser is selected from a CO2 laser, a 1064 nm infrared Nd:YAG laser, an infrared fiber 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.

18. The method according to any one of claims 12 to 15, wherein the heating step is carried out by laser cladding, selective laser melting, selective laser sintering, and combinations thereof.

19. The method according to any one of claims 12 to 15, wherein the method is carried out at atmospheric pressure.

20. The method according to any one of claims 12 to 15, wherein the method further comprises the additional step of heating the formed 2D layer at least once to evaporate any residual polymer that may remain from the initial heating step.

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