Method and apparatus for manufacturing uhmwpe structures comprising graphene

Abstract

A method of manufacturing a UHMWPE structure comprising graphene, comprising the steps of: i. Providing a build chamber having a vertically movable platform defining a build plate on which a powder material can be sintered layer by layer in an SLS 3D printing process; ii. Preheating the building chamber; iii. Reducing the pressure within the build chamber and / or supplying an inert gas into the build chamber; iv. Depositing a layer of UHMWPE powder on the build plate to define a print bed; v. Exposing a selected region of the layer of UHMWPE powder to at least one first laser source to produce a sintered region of the layer of UHMWPE powder; vi. Exposing a selected region of the sintered region of the UHMWPE powder to at least one second laser source, thereby forming graphene derived from the UHMWPE powder; vii. Lowering the platform by an order corresponding to the thickness of the UHMWPE powder layer, and depositing a further UHMWPE powder layer thereon; and viii. Repeating the steps (v) to (vii) until the structure is completed.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for manufacturing a graphene-containing UHMWPE structure using additive manufacturing techniques, and more particularly to a method for manufacturing an improved bulletproof vest. Background Art

[0002] Ultra-high molecular weight polyethylene (UHMWPE) is a high-performance polymer with a low coefficient of friction, very good wear resistance, high toughness and impact resistance, as well as high chemical resistance and good biocompatibility. It is used in shipbuilding, the textile industry, and biomedical applications. It has also been found that, due to its light weight and good ballistic resistance, it can provide advantageous properties when used to manufacture bulletproof vests.

[0003] However, due to the extremely long polymer chains, the melt viscosity of UHMWPE parts is very high, and thus it cannot be easily produced by traditional plastic manufacturing techniques such as injection molding or extrusion.

[0004] Selective laser sintering (SLS) is an additive manufacturing technique that uses a laser as a power and heat source to sinter powder materials (usually nylon or polyamide). The laser targets points in subsequent layers of the powder material on the printing bed and bonds the materials together layer by layer at the positions defined by the 3D model to create a solid structure. Due to the transparency and highly aggregated structure of UHMWPE, it is difficult to process UHMWPE using SLS technology, resulting in finished products with high porosity and poor material consistency, and it is impossible to manufacture thin sheets for flexible circuits.

[0005] In addition, although UHMWPE has good ballistic performance, UHMWPE bulletproof vests usually cannot stop bullets from large-caliber weapons without being too thick. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a method for manufacturing a graphene-containing UHMWPE structure, comprising the steps of:

[0007] i. providing a build chamber having a vertically movable platform that defines a build plate on which powder materials can be sintered layer by layer in an SLS 3D printing process;

[0008] ii. preheating the build chamber;

[0009] iii. reducing the pressure in the build chamber and / or supplying an inert gas to the build chamber;

[0010] iv. depositing a layer of UHMWPE powder on the build plate to define a printing bed;

[0011] v. Exposing a selected area of the UHMWPE powder layer to at least one first laser source to produce a sintered area of the UHMWPE powder layer;

[0012] vi. Exposing a selected area of the sintered area of the UHMWPE powder to at least one second laser source to form graphene derived from the UHMWPE powder;

[0013] vii. Lowering the platform by one step corresponding to the thickness of the UHMWPE powder layer and depositing another UHMWPE powder layer thereon;

[0014] viii. Repeating steps (v) to (vii) until the structure is complete.

[0015] In a preferred embodiment, the at least one first laser source includes a non - focused IR laser source distributed over the selected area of the UHMWPE powder layer and one or more focused UV lasers, the focused UV lasers being adapted to sinter the contour and / or details of the selected area of the UHMWPE powder layer.

[0016] The second laser source may include one or more focused UV lasers adapted to induce the formation of graphene in a selected area of the printing bed.

[0017] The method may further include the step of pressing the UHMWPE powder layer deposited on the build plate after exposing the selected area of the layer to the at least one first laser source. A heating roller adapted to traverse across the build plate may be used to press the UHMWPE layer.

[0018] The method may further include the steps of detecting a local downward displacement of the heating roller during movement of the roller across the printing bed, and subsequently adding additional powder, and optionally repeating sintering to areas where the displacement of the heating roller indicates the presence of voids in the UHMWPE layer before repeating the step of traversing the heating roller across the printing bed.

[0019] Preferably, the method includes the step of pre - heating the build chamber in a separate pre - heating chamber before transferring the build chamber to a printer housing that houses the first laser source and the second laser source. The method may further include the step of transferring the build chamber to a second chamber after the structure is complete and allowing the build chamber to cool within the second chamber. The pre - heating chamber, the second chamber, and the printer housing may include operable doors that work together to allow transfer of the build chamber between them while maintaining a reduced pressure and / or inert gas atmosphere within the pre - heating chamber, the second chamber, and the printer housing.

[0020] According to another aspect of the present invention, there is provided an apparatus for manufacturing a UHMWPE structure comprising graphene, comprising:

[0021] A build chamber having a vertically movable platform that defines a build plate on which powder material can be sintered layer by layer in an SLS 3D printing process;

[0022] A printer housing within which the build chamber can be enclosed;

[0023] The housing includes heating means for heating the build chamber;

[0024] Means for reducing the pressure within the housing and / or supplying an inert gas to the housing;

[0025] A powder supply system adapted to deposit a layer of UHMWPE powder on the build plate;

[0026] A first laser system adapted to sinter selected regions of the uppermost layer of UHMWPE powder that defines a print bed on the build plate in the build chamber; and

[0027] A second laser system adapted to induce the formation of graphene on the print bed.

[0028] The at least one first laser source may include a non-focused IR laser source distributed over the selected region of the UHMWPE powder layer and one or more focused UV lasers adapted to sinter the contour and / or details of the selected region of the UHMWPE powder layer.

[0029] The second laser source may include one or more focused UV lasers adapted to induce the formation of graphene on selected regions of the print bed.

[0030] The powder supply system may include a powder storage hopper mounted on a gantry within the housing and above the build plate. A metering wheel may be coupled to the outlet of the powder storage hopper at the top of the housing for metering the powder flow from the lower end of the hopper. The powder storage hopper may be adapted to move along a line parallel to the build plate while operating the metering wheel, thereby depositing a trace of powder near the build plate. Preferably, rollers are mounted in the housing to traverse across the print bed to distribute the trace of powder over the print bed. The rollers preferably include heating means for heating the outer surface of the rollers.

[0031] The roller may be adapted to press downwardly against the printing bed as it traverses the printing bed, such that the roller can pass through each new sintered layer on the printing bed and press downwardly on the layer to ensure sufficient adhesion between the layers and reduce the porosity of the sintered structure.

[0032] Preferably, the roller includes means for detecting a local downward displacement of the roller during movement of the roller on the printing bed after sintering the powder on the printing bed, the detecting means providing feedback to a control system of the apparatus, wherein the control system is adapted to add additional powder and optionally repeat sintering of areas, wherein displacement of the heated roller indicates the presence of voids and / or incomplete sintering in the UHMWPE layer prior to repeating the step of traversing the roller across the printing bed.

[0033] The control system may be programmed to scan the surface of the material on the printing bed when deflection of the roller indicates the presence of voids and / or incomplete sintering in the UHMWPE layer, thereby determining which areas have been correctly sintered and which areas have not been sintered, then disperse another layer of powder on the printing bed in the event that the build plate will not move downward to start the next layer, and repeat a further sintering process with emphasis on the identified poorly sintered areas. The control system may be programmed to scan the surface again after completion of the further sintering step to determine if any areas remain that have not been correctly sintered, in which case the control system will cause the roller to traverse across the printing bed again to apply further pressure to the structure to adhere the layers, and this process can be repeated until the feedback mechanism deems the sintering to be satisfactory.

[0034] The apparatus may also include a preheating chamber within the build chamber, the preheating chamber being capable of being preheated before being transferred to the printer housing that houses the first laser source and the second laser source. A second chamber may be provided into which the build chamber can be transferred to cool therein after the structure in the printer housing is completed. The second chamber may include a second preheating chamber. Preferably, the preheating chamber and the second chamber are adapted to be portable and movable relative to the printer housing. The preheating chamber, the second chamber and the printer housing preferably include cooperable openable doors to permit transfer of the build chamber therebetween while maintaining a reduced pressure and / or inert gas atmosphere within the preheating chamber, the second chamber and the printer housing. Description of the Drawings

[0035] An apparatus for manufacturing a UHMWPE structure comprising graphene according to an embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0036] Figure 1Perspective view of a 3D printing device for manufacturing a graphene - incorporated UHMWPE structure according to an embodiment of the present invention;

[0037] Figure 2 is Figure 1 Cross - sectional view of the device;

[0038] Figure 3 is Figure 2 Detailed view of region A in;

[0039] Figure 4 is Figure 1 Schematic diagram of the laser assembly of the device;

[0040] Figure 5 is Figure 5 Detailed schematic diagram of the mirror system of the IR laser of the laser assembly;

[0041] Figure 6 is Figure 4 Further schematic diagram of the IR laser system of the laser assembly; and

[0042] Figure 7 is Figure 4 Schematic diagram of the UV sintering laser of the laser assembly. Detailed implementation

[0043] As shown in the figure, according to an embodiment of the present invention, a device for manufacturing a UHMWPE structure containing graphene includes a sealed printer housing 2, which is suitable for filling inert gases such as nitrogen, and a build chamber 4 can be placed inside it.

[0044] The printing bed 6 defines the top of a vertically movable platform within the build chamber 4. The vertically movable platform defines a build plate, and a structure is created layer by layer on the build plate within the build chamber through a selective laser sintering (SLS) 3D printing process. A powder supply system 10 is provided above the build chamber 4 inside the housing for transporting a layer of UHMWPE powder onto the printing bed 6 of the build chamber.

[0045] A heating device (not shown) is provided inside the printer housing 2 to heat and maintain the temperature of the build chamber 4 at a temperature just below the melting point of the powder. A liquid nitrogen storage tank 8 can be located in the lower region of the printer housing 2.

[0046] The laser assembly is mounted on the upper part of the printer housing 2, above the build chamber 4. The laser assembly includes a first laser system that is adapted to heat a selected area of the uppermost powder on the print bed 6 to below the melting point of the material or just to the melting point of the material, thereby fusing (sintering) the particles in the selected area of the uppermost powder together and fusing (sintering) with the already sintered material in the lower layer. The unfused powder supports the sintered structure during the printing process and eliminates the need for a dedicated support structure.

[0047] In a preferred embodiment, the first laser system includes an infrared (IR) laser 10, the output of which is reflected and pulsed via suitable mirrors and lenses 12 but not focused onto the uppermost powder on the print bed, so as to cover a two-dimensional area above the print bed. As Figure 5 shown, the IR laser 10 is preferably pulsed onto a first sinusoidal mirror 12A at a frequency between 1 Hz and 1 GHz, and the first sinusoidal mirror 12A is adapted to slowly move through the light beam in the same direction as the wave in the mirror. After the laser pulses are reflected by the first mirror 12A, they can be directed to a second stationary sinusoidal mirror 12B arranged at 90° to the first mirror 12A. This reflects the laser pulses into a one-dimensional line capable of scanning across the print bed 6. As Figure 6 shown, this pulse path is directed through a series of lenses 12C to a liquid crystal on silicon (LCOS) screen 12D. This screen 12D will display the pattern required for this particular printed layer and will only reflect the pulses in these areas. Then, this reflection is directed onto the print bed 6, on which a portion of the uppermost powder determined by the pattern on the LCOS screen is sintered. This process sinters the powder to define a body of the desired shape.

[0048] The IR laser 10 can include a 100w CO2 laser with a pulse frequency between 1 Hz and 1 GHz and is slightly defocused to disperse the beam size to approximately 1 mm wide through a series of glass lenses. Then, the beam is directed to a first sinusoidal holographic mirror 12A (with a wavelength of 10 microns), which moves parallel to the wave in the mirror at a constant speed of 1 mm per second. After the laser pulses are reflected by this mirror, they are directed to a second sinusoidal mirror 12B arranged at 90° to the first mirror. This arrangement can advantageously disperse the laser pulses from a fixed point of approximately 1 mm to a series of random points in an area of approximately 330 mm x 330 mm. By varying the pulse rate, the IR laser can be controlled to hit almost all of the selected areas on the print bed 6 at least once to ensure that the entire powder layer in the selected areas has been sintered. After reflection from this secondary mirror, the pulses are directed to the LCOS screen 12D, which will only display the selected areas on the print bed 6 that need to be sintered. This ensures that only the pulses in this area are reflected onto the print bed 6 and the correct areas are sintered.

[0049] The first laser system preferably further includes a separate ultraviolet laser system 14, which is provided for more precisely creating fine details (such as the edges of the desired structure) in the structure. In one embodiment, four UV lasers 14A, 14B, 14C, 14D may be provided, each UV laser emitting a focused beam, which is directed onto a corresponding pair of rotating mirrors 15A, 15B, 15C, 15D, one of each pair of rotating mirrors rotating in the x-plane and the other in the y-plane, thereby allowing the focused beams from each of the UV lasers 14A, 14B, 14C, 14D to be directed to any point in the corresponding designated quarter of the print bed 6. This allows for precise edges of the sintered structure.

[0050] The combination of pulsed sintering (IR laser 10) and cold machining (UV laser 14) enables the precise creation of complex shapes at very high speeds.

[0051] The UV lasers 14A, 14B, 14C, 14D may each include an excimer laser, namely a xenon fluoride (XeF) 351 nm laser. The reaction of ultraviolet laser with materials is very different from that of infrared laser, because it does not heat the material to make it melt. Instead, the ultraviolet laser provides very precise and local energy to break and reform the bonds in the material.

[0052] By using four such ultraviolet lasers to sinter the edges of the structure in a given powder layer, with each quadrant corresponding to a build plate, each laser can easily cover the entire area of its quadrant and effectively "draw" the edges of the shape of the structure to be created with high precision.

[0053] The device includes a second laser system for inducing the formation of graphene in a selected layer of sintered powder on the print bed 6 when it is desired to incorporate graphene material into the finished structure, the graphene being obtained from the UHMWPE powder by a laser-induced graphene (LIG) process.

[0054] The second laser system may include a further arrangement of UV lasers and mirrors, the mirrors having the same structure as the UV lasers of the first laser system. The second laser system includes four UV lasers 16, each UV laser covering a quarter of the print bed 6. Each laser is guided using x- and y-movable mirrors so that each laser beam can be directed as required. The lasers in the second laser system may include krypton fluoride (KrF) 248 nm lasers. The output of these lasers will be directed onto the already sintered material to produce graphene of the desired shape. This can cover all of the already sintered material in the layer, or can cover only a part of the sintered layer of any desired shape and any shape in between. As Figure 4As shown, the UV sintering laser 14 and the UV graphene laser 16 can be associated with a common set of optical devices and a rotating mirror for directing the generated beam onto the printing bed 6.

[0055] After sintering the topmost layer of powder and optionally forming graphene in its selected areas, the platform then lowers by one layer into the build chamber, typically by a distance between 50 and 200 microns, and deposits another layer of powder on top of the build plate, and then this process is repeated.

[0056] In the embodiment shown in the drawings, the powder supply system 10 includes a powder storage hopper disposed in the upper part of the build chamber, and the powder storage hopper is adapted to convey a thin layer of powder onto the printing bed.

[0057] Most known SLS printers feed powder onto the build plate by providing a powder storage chamber beside the build plate that is similar in size to the build chamber. A piston lifts the powder in the powder storage chamber horizontally from below to just above the level of the build plate, and a roller is used to spread a layer of this powder from the powder storage chamber onto the build plate. However, this system requires the powder storage chamber to be located near the build chamber, which greatly increases the footprint of the printer and also increases the complexity of system maintenance.

[0058] The present invention solves this problem by providing a powder storage hopper 17 in the housing and on the gantry above the build plate. A metering wheel can be coupled to the outlet of the powder storage hopper at the top of the housing for metering the powder flow from the lower end of the hopper.

[0059] Once filled, the powder storage hopper is adapted to move along a line parallel to the build plate while operating the metering wheel, thereby depositing a trace of powder near the build plate. A roller 18 can be provided for spreading this powder trace onto the printing bed 6. Although this powder supply system requires a metering wheel and an accurate control system to ensure uniform distribution of the powder on the build plate, it greatly reduces the footprint of the printer and simplifies powder storage.

[0060] In the above state, a roller 18 is provided to move the powder above the printing bed 6. The roller 18 can be formed of metal and is preferably heated internally. The roller 18 is preferably driven by a motor to move back and forth above the build plate. Additional actuators or motors can be provided, one at each end of the roller 18, to press the roller 18 down onto the build plate, thereby generating pressure on each powder layer.

[0061] The roller 18 can have multiple functions.

[0062] As described above, before sintering the powder layer, the roller 18 is first used to spread the powder layer onto the printing bed 6.

[0063] The secondary function of roller 18 can be used after sintering each powder layer. In this secondary function, the heating roller 18 can pass over each newly sintered layer on the printing bed and press down onto each newly sintered layer, preferably with a pressure between 0.5 and 6 bar. The purpose of this is to ensure sufficient adhesion between the layers and reduce the porosity of the sintered structure.

[0064] Roller 18 can also be associated with a feedback mechanism that includes means for detecting the vertical displacement of the roller towards the build plate. Such a feedback mechanism may help to determine excessive porosity in the sintered structure and / or whether the structural layers are not properly fused. When the roller traverses the printing bed, a detected local downward displacement of the roller can indicate areas of poor porosity or sintering in the layer. When such a situation is detected, roller 18 can be moved to the side of the printing bed and the surface of the material on the printing bed can be scanned, for example using lidar, to determine which areas of the part have been properly sintered and which areas have not. Once this has been determined by the said scanning step, roller 18 can be used to disperse another powder layer on the printing bed without moving the build plate downwards to start the next layer. Then, the laser sintering process can be repeated, focusing on the poorly sintered areas. After this laser sintering step is completed, the surface can be scanned again. If the problem persists, the roller will traverse the printing bed again, applying further pressure to the structure to adhere the layers, and this process may be repeated until the feedback mechanism deems the sintering to be satisfactory.

[0065] If the feedback mechanism, particularly the scanning step, determines that the sintering has been successful, it can be determined that the problem detected by the displacement is adhesion and / or porosity in deeper layers of the structure. In this case, the roller can be operated to apply greater pressure to the printing bed and complete more traverses on the printing bed until the feedback mechanism determines that the pressure applied by the roller on the structure on the build plate is uniform. At this point, the build plate can be moved down one step and then the formation of the next layer can begin.

[0066] Most SLS printers use a manual system to move the build chamber within the printer. These systems typically require the build chamber to be manually placed in the printer through a front opening, and the build chamber will remain stationary during the heating, printing, and subsequent cooling processes. The advantage of such a known system is that the manual movement simplifies the mechanism inside the printer because no moving parts are required to assist in positioning the printing bed relative to the sintering laser footprint, thus allowing accurate and repeatable printing. This lack of additional mechanism also reduces the overall footprint and cost of the entire printer.

[0067] The main drawback of this known SLS printer is that during the heating and cooling processes, the build chamber 4 needs to remain stationary within the printer to ensure uniform cooling of the produced sintered structure and thus prevent deformation of the resulting structure. Large prints can take up to twenty-four hours, which can result in a heating time of over one hour and a cooling time of over ten hours for a typical print, leading to a printer downtime of up to 50%.

[0068] Some known systems attempt to address this problem by creating a larger internal chamber within the printer to allow multiple chambers to be stored at once and thus print sequentially on multiple chambers, reducing the downtime of the machine. However, this significantly increases the footprint of the printer and the power required to heat the now larger internal volume of the machine.

[0069] This problem is solved in the device according to a preferred embodiment of the present invention by heating and cooling each build chamber in a separate portable preheating chamber 20 external to the printer housing. This preheating chamber is preferably separate from the printer housing 2 of the device and can be adapted to be coupled to the main printer housing 2, whereby the preheated build chamber 4 can be moved from the preheating chamber 20 and enter and exit the housing 2 through mating insulated doors 22 provided on one or both sides of the housing (preferably through the inlet and outlet sides) and the mating side of the preheating chamber 20, such that the printing / sintering process can start immediately.

[0070] Once the preheated build chamber 4 is transferred from the preheating chamber 20 into the printer housing 2, the corresponding door 22 can be closed and sealed. A second preheating chamber 20 can be located on the opposite side of the housing 2, near the exit door of the housing, where the same process can occur, transferring the build chamber 4 containing the complete print / structure currently within the housing 2 into the second preheating chamber, where the build chamber can be allowed to cool slowly without the need to leave it in the main printer housing during such cooling, thus significantly reducing the downtime of the machine.

[0071] The preheating chamber 20 is preferably adapted to preheat the build chamber 4 and fill it with an inert gas, preferably nitrogen. This can allow the preheated build chamber to be ready to move into the main housing and start printing / sintering immediately after the previous print is completed and removed from the main housing into another portable preheating chamber, greatly accelerating the manufacturing time by reducing downtime. All these processes are repeated until the printing is complete, at which point the door in the exit area will open and the build chamber will move to its own section for cooling and depressurization. Then, a new empty build chamber will be moved into the build area.

[0072] The powder used in the device will include ultra-high molecular weight polyethylene (UHMWPE) as its base polymer. This is an uncommon material for SLS printing as it is colorless and has a low melting point. Most polymers used in SLS printing are dark or black, such as Nylon 11. This is because it absorbs the laser better, making the sintering process easier. Since UHMWPE is colorless, this may make it difficult to sinter. Due to its very low melting point (130°C to 136°C), it is difficult to sinter without completely melting the material. These factors make it a poor choice for SLS 3D printing and it is therefore usually overlooked as a polymer for this process.

[0073] The present invention overcomes these problems by defocusing the infrared laser beam used for sintering. This uses the same amount of energy but covers a much wider area, preventing the material from completely melting. This laser is used for most of the parts. The process gently pushes the material so that bonds are formed between the powder particles. Due to the heated environment in the build chamber, the material is close to its melting point and only a small amount of additional energy is required to start bonding between the powder particles.

[0074] If desired, after layer sintering, it can be processed to form graphene. This process involves scribing a second laser system over the desired area to remove hydrogen atoms from the UHMWPE, leaving only carbon. The energy of the laser forces these carbon atoms to bond together to form a sheet of graphene covering all the desired areas of the print bed.

[0075] The above device can be advantageously used to manufacture bulletproof vests, where the graphene sheets can be integrated into the UHMWPE structure to improve the bulletproof performance of the bulletproof vest. It is also envisaged that the device can be used to manufacture many other UHMWPE products that may benefit from the incorporation of graphene in the structure to provide enhanced mechanical and / or electrical properties.

[0076] The present invention is not limited to the embodiments described herein, but can be amended or modified without departing from the scope of the invention as defined by the appended claims.

Claims

1. A method of manufacturing a UHMWPE structure comprising graphene, comprising the steps of: i. providing a build chamber having a vertically movable platform that defines a build plate on which powder material can be sintered layer by layer in an SLS 3D printing process; ii. preheating the build chamber; iii. reducing the pressure in the build chamber and / or supplying an inert gas to the build chamber; iv. depositing a layer of UHMWPE powder on the build plate to define a print bed; v. exposing a selected area of the UHMWPE powder layer to at least one first laser source to create a sintered area of the UHMWPE powder layer; vi. exposing a selected area of the sintered area of the UHMWPE powder to at least one second laser source, thereby forming graphene derived from the UHMWPE powder; vii. lowering the platform by one order corresponding to the thickness of the UHMWPE powder layer and depositing another layer of UHMWPE powder thereon; viii. repeating steps (v) to (vii) until the structure is complete.

2. The method according to claim 1, wherein the at least one first laser source comprises a non-focused IR laser source distributed over the selected area of the UHMWPE powder layer and one or more focused UV lasers adapted to sinter the contour and / or details of the selected area of the UHMWPE powder layer.

3. The method according to claim 1 or claim 2, wherein the second laser source comprises one or more focused UV lasers adapted to induce the formation of graphene on a selected area of the print bed.

4. The method according to any one of the preceding claims, comprising a further step of pressing the UHMWPE powder layer deposited on the build plate after exposing the selected area of the layer to the at least one first laser source.

5. The method according to claim 4, wherein a heating roller adapted to traverse across the build plate is used to press the UHMWPE layer.

6. The method according to claim 5, comprising the following steps: Detecting a local downward displacement of the heating roller during movement of the roller across the print bed and subsequently adding additional powder and optionally repeating sintering to an area where the displacement of the heating roller indicates the presence of voids in the UHMWPE layer before repeating the step of traversing the heating roller across the print bed.

7. The method according to any one of the preceding claims, comprising the following steps: Preheating the build chamber in a separate preheating chamber before transferring the build chamber to a printer housing accommodating the first laser source and the second laser source.

8. The method according to claim 7, comprising the following steps: After the structure is complete, transferring the build chamber to a second chamber and allowing the build chamber to cool within the second chamber.

9. The method according to claims 7 and 8, wherein the preheating chamber, the second chamber and the printer housing comprise cooperable openable doors to allow transfer of the build chamber therebetween while maintaining a reduced pressure and / or an inert gas atmosphere within the preheating chamber, the second chamber and the printer housing.

10. An apparatus for manufacturing a graphene-containing UHMWPE structure, comprising: A build chamber having a vertically movable platform that defines a build plate on which powder material can be sintered layer by layer in an SLS 3D printing process; A housing within which the build chamber can be enclosed; The housing includes heating means for heating the build chamber; Means for reducing the pressure within the housing and / or supplying an inert gas to the housing; A powder supply system adapted to deposit a layer of UHMWPE powder on the build plate; A first laser system adapted to sinter selected regions of the uppermost layer of UHMWPE powder that defines a print bed on the build plate of the build chamber; And A second laser system adapted to induce the formation of graphene on the print bed.

11. The apparatus according to claim 10, wherein the at least one first laser source includes a non-focused IR laser source distributed over the selected regions of the UHMWPE powder layer and one or more focused UV lasers adapted to sinter the contours and / or details of the selected regions of the UHMWPE powder layer.

12. The apparatus according to claim 10 or claim 11, wherein the second laser source includes one or more focused UV lasers adapted to induce the formation of graphene on selected regions of the print bed.

13. The apparatus according to any one of claims 10 to 12, wherein the powder supply system includes a powder storage hopper mounted on a gantry within the housing and above the build plate.

14. The apparatus according to claim 13, wherein a metering wheel is coupled to the outlet of the powder storage hopper at the top of the housing for metering the powder flow from the lower end of the hopper.

15. The apparatus according to claim 14, wherein the powder storage hopper is adapted to move along a line parallel to the build plate while operating the metering wheel, thereby depositing a trace of powder near the build plate.

16. The apparatus according to claim 15, wherein rollers are mounted in the housing to traverse across the print bed to distribute the trace of powder across the print bed.

17. The apparatus according to claim 16, wherein the rollers include heating means for heating the outer surface of the rollers.

18. The apparatus according to claim 17, wherein the rollers are adapted to press down against the print bed as they traverse across the print bed such that the rollers can pass through each newly sintered layer on the print bed and press down on the layer to ensure sufficient adhesion between layers and reduce the porosity of the sintered structure.

19. The apparatus according to claim 18, wherein the roller comprises means for detecting a local downward displacement of the roller during movement of the roller across the print bed after sintering the powder on the print bed, the detecting means providing feedback to a control system of the apparatus, wherein the control system is adapted to add additional powder and optionally repeat sintering of areas, wherein displacement of the heated roller indicates the presence of voids and / or incomplete sintering in the UHMWPE layer before repeating the step of traversing the roller across the print bed.

20. The apparatus according to claim 19, wherein the control system is programmed to scan the surface of the material on the print bed when deflection of the roller indicates the presence of voids and / or incomplete sintering in the UHMWPE layer, so as to determine which areas have been correctly sintered and which areas have not been sintered, and then to disperse another layer of powder on the print bed without the build plate moving down to start the next layer, and repeat a further sintering process, focusing on the identified areas of poor sintering.

21. The apparatus according to claim 20, wherein the control system is programmed to scan the surface again after completion of the further sintering step, so as to determine whether any areas that have not been correctly sintered remain, in which case the control system will cause the roller to traverse across the print bed again, applying further pressure to the structure to adhere the layer, and this process can be repeated until the feedback mechanism deems the sintering to be satisfactory.

22. The apparatus according to any one of claims 10 to 21, further comprising a preheating chamber in the build chamber, the preheating chamber being capable of being preheated before being transferred to the printer housing accommodating the first laser source and the second laser source.

23. The apparatus according to claim 22, further comprising a second chamber into which the build chamber can be transferred to cool therein after completion of the structure in the printer housing.

24. The method according to claim 23, wherein the preheating chamber, the second chamber and the printer housing comprise cooperable openable doors to allow transfer of the build chamber therebetween while maintaining a reduced pressure and / or an inert gas atmosphere within the preheating chamber, the second chamber and the printer housing.

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