A METHOD OF 3D PRINTING

Abstract

A method of 3D printing an item, wherein a spray material comprising a powder entrained in an oxygen comprising carrier gas is emitted from a spray nozzle 8. The nozzle 8 comprises a constricted throat 11 that has a thermal conductivity of at least 10 W/mk and a hardness of at least 10 Rockwell C (HRC). The temperature of the throat does not exceed 250° C., and preferably does not exceed 200° C.

Claims

1-19. (canceled)

20. A method of 3D printing an item, wherein: a) a spray material comprising a powder entrained in an oxygen comprising carrier gas is emitted from a spray nozzle; b) the spray nozzle comprises a constricted throat that has: i. a thermal conductivity of at least 10 W/mk; ii. a hardness of at least 10 Rockwell C (HRC); and c) a temperature of the constricted throat does not exceed 250° C.

21. A method according to claim 20, wherein the hardness is at least 20 Rockwell C (HRC).

22. A method according to claim 20, wherein at c) the temperature of the constricted throat does not exceed 200° C.

23. A method according to claim 20, wherein the constricted throat has an electrical conductivity greater than 1 S/m.

24. A method according to claim 20, wherein the carrier gas comprises at least 1% oxygen.

25. A method according to claim 20, wherein the carrier gas comprises compressed air.)

26. A method according to claim 20, wherein the constricted throat comprises between 5% and 30% by volume of: a) chromium carbide; b) iron carbide; c) vanadium carbide; or d) any combination of these.

27. A method according to claim 20, wherein the constricted throat comprises iron-nickel alloy.

28. A method according to claim 20, wherein the constricted throat comprises Ni-hard.

29. A method according to claim 20, wherein the constricted throat comprises one or more of: a) Cold Work steel(s); b) Plastic mould steel(s); c) Oil Hardening steel; d) Shock Resistant steel; e) High Speed steel(s); and f) White Cast iron(s).

30. A method according to claim 29, wherein the Cold Work steel(s) comprise(s) cold work powder steel(s).

31. A method according to claim 29, wherein the steel at items a)-e) of claim 29 comprises one or more of: i. D2 or a commercial equivalent; ii. A2, A6 or a commercial equivalent; iii. P20 or a commercial equivalent; iv. O1, O2 or a commercial equivalent; v. S2, S6 or S7, or a commercial equivalent; and vi. M2, M42 or a commercial equivalent.

32. A method according to claim 29, wherein: a) the Cold Work steel comprises a composition with greater than 1% carbon and greater than 5% chromium; or b) the Cold Work steel comprises a composition with greater than 2% carbon and greater than 6% vanadium; or c) the Plastic Mould Steel comprises a composition with at least 0.35% carbon, at least 2% chromium and at least than 1% nickel; or d) the High Speed Steel comprises a composition greater than 0.8% carbon, greater than 3.5% chromium, greater than 4% molybdenum, and greater than 1% vanadium; or e) the White Cast Iron comprises EN-JN2049.

33. A method according to claim 20, comprising a cooling system employed to control the temperature of the constricted throat.

34. A method according to claim 20, wherein: a) the hardness is at least 20 Rockwell C (HRC); b) at c) the temperature of the constricted throat does not exceed 200° C.; c) the throat has an electrical conductivity greater than 1 S/m; and d) the carrier gas comprises at least 1% oxygen.

35. A method according to claim 34, wherein the constricted throat comprises between 5% and 30% by volume of: a) chromium carbide; b) iron carbide; c) vanadium carbide; or d) any combination of these.

36. A method according to claim 34, wherein the constricted throat comprises iron-nickel alloy.

37. A method according to claim 34, wherein the constricted throat comprises one or more of: a) Cold Work steel(s); b) Plastic mould steel(s); c) Oil Hardening steel; d) Shock Resistant steel; e) High Speed steel(s); and f) White Cast iron(s).

38. A 3D printer suitable for and arranged to print according to the method of claim 20.

39. A 3D printer suitable for and arranged to print according to the method of claim 34.

Description

DRAWINGS

[0048] Some preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings of which:

[0049] FIG. 1 is an isometric view of a 3D printer;

[0050] FIG. 2 is a schematic side view of an item which has been 3D printed by the printer; and

[0051] FIG. 3 is a schematic side view of a spray nozzle forming part of the printer.

DETAILED DESCRIPTION

[0052] Referring to FIG. 1, a 3D printer has a grip 1 which incorporates a robotic arm 2 by which at least part of the grip can move. The printer also has a cold spray head 3. The grip 1 holds a substrate and exposes it to print material sprayed from the spray head 3 to build a 3D item on the substrate.

[0053] The printer has two feeders 4, 5 for feeding one or more types of print material (e.g. powder) to the spray head 3. This enables a 3D item to be built up from a blend of different print materials, or for different parts of the item to be formed from different print materials. In other embodiments of the printer there may only be one of the feeders 4, 5, and in still others there may be more than two of the feeders.

[0054] The printer incorporates an internal computerised controller (not depicted) that regulates movement of the robotic arm 2 and/or the spray head 3 so that the print material is always at the correct angle of attack for forming the 3D item. The controller also controls the temperature of the print material and the speed at which it leaves the spray head 3. The controller is guided by information in CAD files to give the 3D item the desired geometry and composition. The same or a separate controller means can be used to control the temperature of the throat.

[0055] Referring to FIG. 2, the substrate 6 supports the 3D item 7 when built up from incremental layers 7a-e of print material. The robotic arm 2 adjusts the position and orientation of the substrate 6 as the item builds so that the print material is applied at the correct angle and to the right part of the substrate, or to the partially formed item, as the item builds.

[0056] The print material preferably leaves the print head as a spray. Examples of the sort of material that can be used for this are powdered alloys of non-ferrous metals such as aluminium 7075 or manganese bronze or powdered steels such as 316 stainless steel.

[0057] A particularly preferred material is Valimet 6061 applied as a cold spray at a temperature of 500° C. and a velocity of 700 m/s. In other embodiments of the invention the print material may be applied as a molten plastic filament, such as used in Fused Deposition Melding (FDM). In such cases the print material may be ABS polymer.

[0058] FIG. 3 illustrates a cold spray nozzle 8 forming part of the print head 3. The nozzle 8 may be notionally divided into four zones; A, B, C and D. Zone A is a ‘stagnation region’ that has an injector 9 for emitting print material in the form of a powder 10 into a train of high temperature high pressure carrier gas. The powder and gas together provide a ‘spray material’. Zone B is a “converging region” where the nozzle walls taper down to provide a supersonic throat 11. Zone C is a “throat and diverging region” where the nozzle walls gradually diverge. Zone D is a “straight barrel” region where the nozzle diameter is more or less constant. In some embodiments the barrel region may be omitted in favour of an elongated Zone C.

[0059] Preferably the 3D printer is such that [0060] a) the throat has a thermal conductivity greater than 10 W/mk; [0061] b) the throat has a hardness greater than 10 (and optionally greater than 20) Rockwell C (HRC); [0062] c) the throat has an electrical conductivity of at least 1 S/m; [0063] d) the throat comprises about 5%, preferably about 10% and more preferably about 20% by volume of: [0064] i) chromium carbide; [0065] ii) iron carbide; [0066] iii) vanadium carbide; or [0067] iv) any combination of the these; [0068] e) the temperature of the throat is from 50 ° C. to 250 ° C.; and [0069] f) the carrier gas has 0.5 to 24% oxygen by volume.

[0070] More preferably the 3D printer is such that— [0071] a) the throat has a thermal conductivity of from 10 W/mk; [0072] b) the throat has a hardness greater than 20 Rockwell C (HRC); [0073] c) the throat has an electrical conductivity of at least 5,000 S/m; [0074] d) the throat is formed from Ni-Hard (cast iron, alloyed with nickel and chromium); [0075] e) the temperature of the throat is 100 to 200 ° C.; and [0076] f) the carrier gas is compressed air.

[0077] Optional materials for forming the throat 11 are any one or any combination of— [0078] a) Cold work steels, for example— [0079] i) D2 and its commercial equivalents; [0080] ii) A2 and its commercial equivalents; [0081] iii) O2 and its commercial equivalents; [0082] iv) S2 and its commercial equivalents; or [0083] v) Cold work powder steels such as Bohler K390; [0084] b) Plastic mould steels, for example P20; [0085] c) High Speed Steels, for example M2 or M42; and [0086] d) White Cast irons, for example EN-JN2049.

[0087] Preferably at least the throat 11 is formed by electro-discharge machining.

[0088] It has been found that the above materials work particularly well when the print material comprises oxygen or an oxygen containing gas. While the reason for this has yet to be confirmed, it is believed that when the throat has oxide forming surfaces the gas allows for the continuous regeneration of an ablating “skin” at the throat. It is further hypothesised that the skin resists bonding/clogging by passing powder particles and, in the event that such bonding occurs, it provides a shear layer that allows powder particles to easily detach from the throat upon contact with further passing powder particles.

[0089] In terms of disclosure, this document hereby envisages and discloses each item, step or other feature mentioned herein in combination with one or more of any of the other items, steps or other features disclosed herein, in each case regardless of whether such combination is claimed.

[0090] While some preferred forms of the invention have been described by way of example, it should be understood that modifications and improvements can occur without departing from the following claims.