METHODS FOR USE IN PRINTING

Abstract

The invention provides a powder bed printing system and process which reduces the time period needed to complete the recoating and heating of each material layer in the process, thereby reducing process overhead and printing time.

Claims

1. A powder bed 3D printing system comprising a plurality of printing areas; a powder coating assembly; a print head assembly; and one or more heating units; wherein the plurality of printing areas are in a form of (a) a powder bed having a surface defining at least two printing areas, or (b) two or more powder beds; wherein the system is configured and operable for simultaneous printing of two or more 3D objects.

2. The system according to claim 1, comprising one or more powder beds, at least one of which having a plurality of printing areas.

3. The system according to claim 1, comprising at least two separate powder beds.

4. The system according to claim 1, wherein the powder coating assembly comprises (i) at least one powder coating and/or recoating mechanisms that is optionally heated, each comprising at least one roller or blade, (ii) at least one powder supply unit, optionally one for each of the coating or recoating mechanisms, and optionally (iii) at least one powder overflow cartridge configured for collecting left over powders.

5. The system according to claim 1, wherein the print head assembly is movable over and in proximity of each of the two or more printing areas.

6. The system according to claim 1, wherein the print head assembly comprises a print head in the form of an array of lasers, or laser mirror scanners, or one or more sources of thermal energy.

7. The system according to claim 6, wherein at least one laser in said array of lasers is selected from a quantum cascade laser (QCL), a CO.sub.2 laser, a fiber laser and a diode laser.

8. (canceled)

9. The system according to claim 1, wherein the heating unit comprises at least one infrared emitter, optionally arranged in a form of an array, configured and operable for powder preheating or heating.

10. (canceled)

11. The system according to claim 9, wherein the heating unit further comprises or is associated with one or more temperature sensors configured and operable for measuring a temperature of the powder prior to, during or after powder heating.

12. (canceled)

13. (canceled)

14. (canceled)

15. A process for constructing two or more 3D objects in a simultaneous fashion, said process utilizing a powder bed printing system comprising a printing area in a form of (i) at least two printing areas on a powder bed, or (ii) two or more different powder beds, one or more of the printing areas (i) or (ii) having been previously powder coated and thermally treated, the process comprises: powder coating one or more printing areas or powder beds and thermally treating said coated printing areas or powder beds; simultaneously therewith treating one or more of the previously powder coated and thermally treated printing areas or powder beds under conditions of selective laser sintering (SLS), SLS treating the powder coated and thermally treated printing areas or powder beds; and simultaneously therewith coating and thermally treating the SLS treated one or more previously coated and thermally treated printing areas or powder beds, and repeating the steps to construct the 3D objects.

16. The process according to claim 15, wherein the number of powder beds is between two and ten, one or more of which optionally comprising two or more printing areas.

17. (canceled)

18. (canceled)

19. The process according to claim 15, wherein the SLS comprises use of an array of lasers, or laser mirror scanners, or one or more sources of thermal energy.

20. The process according to claim 19, wherein at least one laser in said array of lasers is selected from a quantum cascade laser (QCL), a CO.sub.2 laser, a fiber laser and a diode laser.

21. The process according to claim 20, wherein the array of lasers is an array of at least two QCL lasers, at least two CO.sub.2 lasers, at least two fiber lasers, at least two diode lasers or a combination of two or more laser types.

22. A process for adjusting temperature of a powder layer comprising at least one powder material in a printing process, the process comprises: (a) heating with a heating element having a fixed (constant) thermal radiation (amount and spectra) a first powder layer to a temperature T.sub.1, being lower than the sintering temperature of the at least one powder material, over a period t.sub.1; (b) determining (by direct or indirect temperature measurement) the temperature of the first powder layer; (c) if the temperature of the first powder layer is lower than T.sub.1 or the sintering temperature, coating a second powder layer on the first powder layer and heating the second powder layer with the heating element for a period t.sub.2 being greater than t.sub.1; and (d) repeating steps (b) and (c) one or more times until the sintering temperature is achieved.

23. The process according to claim 22, the process comprising: (a) thermally treating a preformed first powder layer comprising at least one powder material with a heating element having a fixed thermal radiation for a period of time t.sub.1 sufficient to increase the temperature of the first powder layer to a predetermined set-point temperature T.sub.1; (b) determining the temperature of the thermally treated first powder layer, such that: (b1) if the temperature determined is T.sub.1, the period of time required to heat the first powder layer is t.sub.1; (b2) if the temperature determined is lower than T.sub.1, determining a period of time t.sub.2 that is greater than t.sub.1; or (b3) if the temperature determined is greater than T.sub.1, determining a period of time t.sub.2 that is smaller than t.sub.1; (c) forming a further powder layer comprising the at least one powder material on said thermally treated first powder layer; (d) thermally treating said further powder layer with the heating element for a period of time t.sub.2 that is greater than or smaller than t.sub.1; (e) determining the temperature of the thermally treated further powder layer, such that: (e1) if the temperature determined is T.sub.1, the period of time required to heat the powder layer is t.sub.2; (e2) if the temperature determined is lower than T.sub.1, determining a period of time t.sub.3 that is greater than t.sub.2; or (e3) if the temperature determined is greater than T.sub.1, determining a period of time t.sub.3 that is smaller than t.sub.2; and repeating steps (c)-(e) one or more times until the period of time required to achieve a temperature T.sub.1, when using the heating element having a fixed (constant) thermal radiation (amount and spectra), is determined.

24. The process according to claim 23, wherein each powder layer is heated once over a period being equal to t.sub.1 or greater than t.sub.1, wherein t.sub.1 is the length of the initial heating session.

25. The process according to claim 23, wherein the preformed first powder layer comprising at least one powder material is a single material layer.

26. (canceled)

27. (canceled)

28. (canceled)

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. (canceled)

34. A heating module for use in an additive material manufacturing apparatus/printer, the heating module comprising: a heating element adjustable to provide heat of a constant energy; a means for determining temperature of a layered material, at one or more regions thereof; a control unit adapted to control on/off function of the heating element and optionally further comprising a processor programmed with a set-point temperature that the layered material is to reach.

35. The process according to claim 15, comprising a step of adjusting temperature of the powder coating.

36. The process according to claim 35, wherein the step of adjusting the temperature of the powder coating comprises: (a) heating with a heating element having a fixed (constant) thermal radiation (amount and spectra) a first powder layer to a temperature T.sub.1, being lower than the sintering temperature of the at least one powder material, over a period t.sub.1; (b) determining (by direct or indirect temperature measurements) the temperature of the first powder layer; (c) if the temperature of the first powder layer is lower than the sintering temperature, coating a second powder layer on the first powder layer and heating the second powder layer with the heating element for a period t.sub.2 being greater than t.sub.1; and (d) repeating steps (b) and (c) one or more times until the sintering temperature is achieved.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0100] FIG. 1 provides a plot of a layer temperature. Initial temperature stabilization takes about 15 layers (initial temperature step). Printing starts at layer 20. It is evident that the temperature of the printed layers is maintained in a narrow range of +/−1 degree. Thus, demonstrating the effectiveness of the heating profile.

[0101] FIG. 2 presents the IR Lamp time ON vs layer number. A plot of the time required to heat each layer (heating profile). It can be seen that until about the 15th layer, the system is on a learning curve to determine the time required for heating the layer. The IR on time then fluctuates slightly within a range to maintain the required process set point to compensate for temperature changes.

[0102] FIG. 3 presents the results of a mechanical stress strain test on dog bones manufactured on a commercially available SLS system. Values x, y and z represent printing orientation in the printer. Samples were tested per ASTM D-638 Type V standard at a speed of 5 mm per min. X direction: Young Modulus 2000 MPa (2%) Stress at max load of 50 N/mm.sup.2 and elongation fracture point of less than 20%. Y direction: Young Modulus 1900 MPa (2%) Stress at max load of 48 N/mm.sup.2 and elongation fracture point of less than 20%. Z direction: Young Modulus 2000 MPa (2%) Stress at max load of 43 N/mm.sup.2 and elongation fracture point of less than 5%.

[0103] FIG. 4 presents the results of a mechanical stress test on dog bones manufactured on a SLS system according to the invention, utilizing thermal adjustment protocols recited herein. Values x, y and z represent printing orientation in the printer. Samples were tested per ASTM D-638 Type V standard at a speed of 5 mm per min. X direction: Young Modulus 2200 MPa (2%) Stress at max load of 52 N/mm.sup.2 and elongation fracture point of 45%. Y direction: Young Modulus 2300 MPa (2%) Stress at max load of 52 N/mm.sup.2 and elongation fracture point of 42%. Z direction: Young Modulus 2100 MPa (2%) Stress at max load of 50 N/mm.sup.2 and elongation fracture point of 35%. Test results are better in all orientations x y and z. Most notably the results of fracture point are much better in the 3DM scheme X: 45% vs. 18%. Y: 43% vs. 18% and Z: 35% vs. 4%. This shows the mechanical properties of PA12 printed in the protocol described here are significantly improved compared to state of the art of SLS technology.

[0104] FIG. 5 provides an exemplary 2-powder bed system according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Exemplary Two-Powder-Bed System According to the Invention:

[0105] 1) Optionally, at least one heating element engineered to heat the whole inside of the printer environment. [0106] 2) An optional ventilator for enhanced temperature uniformity. [0107] 3) Two powder beds. [0108] 4) Two powder recoating mechanisms, each including at least one roller or blade. [0109] 5) A powder supply unit—optionally two such units per recoating mechanism to allow back and forth operation. [0110] 6) At least one powder overflow cartridge for collecting left over powder at both ends of the recoater movement. [0111] 7) A movable print head consisting of an array of laser scanners or an array of lasers without scanners. [0112] 8) One or two optionally movable IR emitter arrays for powder preheating. [0113] 9) One or more IR cameras or pyrometers to measure powder temperatures. [0114] 10) One or more cameras for process control especially for active digital alignment of multiple scanners.
Exemplary Operation of a Two-Powder-Bed System or a Powder Bed with a Two-Printing Area According to the Invention: [0115] 1) Heat environment (air and powder beds etc.) to a 1.sup.st temperature, e.g., for PA12 (Polyamide 12 aka Nylon 12) 140° C. [0116] 2) Dispense on each of the powder beds a powder layer—typically to a total thickness of 10-20 mm in total. [0117] 3) Initialize IR heaters stabilization process (same for both powder beds): [0118] i. Temperature Set point (T set)+range. Typical for PA12 170° C. +/−1° C. [0119] ii. Recoat powder (typical 100 μm layer thickness) [0120] iii. Heat using IR heaters for a given time with constant energy and spectrum [0121] iv. Read T of powder (T read) after IR heaters are off. [0122] v. Adjust IR heaters time—increase time if T read is less than T set. Decrease time if T read is more than T set. [0123] vi. Delta time can be a constant or a constant multiplying the difference between T set and T read for faster convergence. [0124] vii. Repeat until T read is stable in T set +/− range. Typically takes 5-20 layers to get there. [0125] 4) Initialize alignment procedure [0126] i. For each powder bed [0127] ii. Recoat powder layer [0128] iii. Heat with IR heaters [0129] iv. Melt or sinter powder using a digital alignment mark/fiducial mask for each scanner in the print head (4×4 in example). [0130] v. Take high resolution picture of entire print bed (melted parts look different than unmelted parts). [0131] vi. Determine all possible sintering inaccuracies (rotation, x and y movement, x and y distortion, misalignment between scan fields of all 16 scan heads). [0132] vii. Adjust said digital alignment mark/fiducial mask to correct for all inaccuracies. [0133] viii. Repeat i.-vi. Until within desired specification. [0134] 5) Printing [0135] i. Recoat 1.sup.st powder bed [0136] ii. Heat with IR heaters. [0137] iii. Measure powder temperature in at least one area. Preferably in a non-sintered area due to emissivity changes between melted and un-melted powder. [0138] iv. Move print head to 1.sup.st print head. Optional move IR heaters out of the way or to 2.sup.nd powder bed. [0139] v. Melt or sinter per powder bed 1 3D object design per layer with optional addition of alignment marks outside object area. [0140] vi. Take a picture of 1.sup.st print bed to calculate alignment changes. [0141] While iv.-vi. takes place: [0142] vii. Recoat 2.sup.nd powder bed [0143] viii. Heat with IR heaters. [0144] ix. Measure powder temperature in at least one area. Preferably in a non-sintered area due to emissivity changes between melted and un-melted powder. [0145] x. Move print head to powder bed 2 [0146] xi. Melt or sinter powder bed 2 per 3D object design per layer with optional addition of alignment marks outside object area. [0147] xii. Take a picture of 2.sup.nd print bed to calculate alignment changes. [0148] xiii. Repeat until both print beds finish printing. [0149] For each layer in each powder bed [0150] xiv. Adjust IR exposure time to keep powder temperature in range [0151] xv. Adjust object slice file to keep distortion and alignment of printed areas in spec. per camera input.

[0152] FIG. 1 and FIG. 2 demonstrate the effectiveness of a process of thermal adjustment according to the invention. As depicted in FIG. 1, initial temperature stabilization takes about 15 layers (initial temperature step). Printing starts at layer 20. It is evident that the temperature of the printed layers is maintained at a narrow range of +/−1 degree. In FIG. 2 the presented plot of time required to heat each layer (heating profile) demonstrates that until about the 15th layer, the system is on a learning curve to determine the time required for heating the layer. The IR on time then fluctuates slightly within a range to maintain the required process set point to compensate for temperature changes.

[0153] Dog bones were printed using a process of the invention. The dog bones were tested for their mechanical stability and compared to dog bones manufactured on a commercial SLS system. As shown in FIG. 3 and FIG. 4, dog bones formed according to the invention where of higher mechanical stability.

[0154] In FIG. 3, mechanical strain of dog bones manufactured on a commercial SLS system is demonstrated. Values x, y and z represent printing orientation in the printer. Samples were tested per ASTM D-638 Type V standard at a speed of 5 mm per min. X direction: Young Modulus 2000 MPa (2%) Stress at max load of 50 N/mm.sup.2 and elongation fracture point of less than 20%. Y direction: Young Modulus 1900 MPa (2%) Stress at max load of 48 N/mm.sup.2 and elongation fracture point of less than 20%. Z direction: Young Modulus 2000 MPa (2%) Stress at max load of 43 N/mm.sup.2 and elongation fracture point of less than 5%.

[0155] FIG. 4 presents the results of a mechanical stress test on dog bones manufactured on a system according to the invention, utilizing thermal adjustment protocols recited herein. Values x, y and z represent printing orientation in the printer. Samples were tested per ASTM D-638 Type V standard at a speed of 5 mm per min. X direction: Young Modulus 2200 MPa (2%) Stress at max load of 52 N/mm.sup.2 and elongation fracture point of 45%. Y direction: Young Modulus 2300 MPa (2%) Stress at max load of 52 N/mm.sup.2 and elongation fracture point of 42%. Z direction: Young Modulus 2100 MPa (2%) Stress at max load of 50 N/mm.sup.2 and elongation fracture point of 35%.

[0156] Test results for dog bones manufactured according to the invention were better in all orientations x y and z, as compared to those measure for bones manufactured on a commercial SLS system. Most notably the results of fracture point were much better in the scheme X: 45% vs. 18%. Y: 43% vs. 18% and Z: 35% vs. 4%.

[0157] These results demonstrate that the mechanical properties of PA12 printed in the protocol described herein were significantly improved compared to state of the art of SLS technology.

[0158] A two-powder bed system 100 is exemplified in FIG. 5. The system 100 comprises two printing areas (20) and (30)—in this specific embodiment being in the form of two spaced apart or separated powder beds; a distinct powder coating assembly comprises of two rollers (40) and (50) for each separate bed; a print head assembly (70) that is positioned in proximity and over the beds; and one or more heating units (not shown in the figure). The print head assembly is movable relative to the beds, or the beds are movable relative to the assembly, or both are movable relative to each other.

[0159] In the embodiment depicted in FIG. 5, the two beds are simultaneously operated to produce two or more 3D objects. In the depicted case, each powder bed defines a plurality of printing regions, each permitting construction of a 3D object. A higher number of beds may be used in the same fashion.

[0160] As shown in FIG. 5, simultaneously with the recoating of coated and patterned bed (20), comprising a plurality of printing areas (60B), on powder bed (30) a plurality of printing areas (60A) are patterned with laser beams (80) from a print head assembly positioned over the bed (30) by moving the bed or by moving the print head assembly into position over the printing areas, namely in proximity to (or at an effective distance from). Once the thermally treated printing areas (60B) are coated with a further layer, the print head assembly (70) is moved over and into proximity with the recoated printing areas (60B) or bed (20) which are scanned with the laser (80) or any thermal source to affect patterning. At the same time, the coating assembly (50) is moved over the printing areas (60A) or bed (30) to recoat the patterns with a further layer of a powder material. The printing areas or powder beds are re-irradiated and re-coated once and again, in an alternate fashion, by repeating the steps on two or a multiple number of printing areas or powder beds to achieve the simultaneous manufacturing of two or more 3D objects.