PROCESS FOR MELTING/SINTERING POWDER PARTICLES FOR LAYER-BY-LAYER PRODUCTION OF THREE-DIMENSIONAL OBJECTS

Abstract

A process for melting/sintering powder particles for layer-by-layer production of three-dimensional objects is performed by a)applying a layer of a powder material solidifiable under the action of electromagnetic radiation, b) heating the powder material to not more than 10 K below the melting point according to DIN 53765 by a radiation from a heat-radiating element whose maximum radiation intensity is at a wavelength of 5000 nm or at longer wavelengths, c) selective melting/sintering of at least a region of the powder material which corresponds to the cross section of the three-dimensional object, d)repeating steps a) to c) until the three-dimensional object is obtained.

Claims

1. A process for layer-by-layer production of three-dimensional objects, said process comprising: a) applying a layer of a powder material solidifiable under the action of electromagnetic radiation, b) heating the powder material to not more than 10 K below the melting point according to DIN 53765 by a radiation from a heat-radiating element whose maximum radiation intensity is at a wavelength of 5000 nm or at longer wavelengths, c) selective melting/sintering of at least a region of the powder material which corresponds to the cross section of the three-dimensional object, d) repeating steps a) to c) until the three-dimensional object is obtained.

2. The process according to claim 1, wherein the irradiation power of the heat-radiating element is at least 2000 W/m.sup.2 based on the vertically projected area of the powder bed that is to be heated.

3. The process according to claim 1, wherein the area of the heat-radiating element is at least 100% of the vertically projected area of the powder bed that is to be heated.

4. An apparatus for layer-by-layer production of three-dimensional objects, comprising: heat-radiating elements, whose area, which give off the electromagnetic rays to the surface of the powder bed, is at least 100% of the vertically projected area of the powder bed which is bounded by the build frame.

5. The apparatus according to claim 4, wherein the heat-radiating elements are configured such that the intensity maximum of the radiation from the heat-radiating elements is at a wavelength of at least 5000 nm.

6. The apparatus according to claim 4, wherein the heat-radiating elements are configured such that the total emissivity in the direction of the face normal of the heat-radiating elements is at least 0.2.

7. A three-dimensional object, produced by a process according to claim 1.

8. The process according to claim 1, wherein the powder material has an absorptivity at wavelengths above 5000 nm of at least 0.8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention provides a process for layer-by-layer production of three-dimensional objects, wherein in a first step a height-adjustable build platform (6) is lowered into a build frame (10) and using an apparatus (9) a layer of a material solidifiable under the action of electromagnetic radiation is applied to the build platform (6), wherein the powder material is supplied by means of a powder metering device (7). Excess powder material is pushed into an overflow container (8). In a second step the powder material is heated via a heating system consisting of radiant heating means (2), temperature measuring device (11) and temperature controller (12). The heating of the powder material is effected by means of a radiation having a maximum radiation intensity at a wavelength of 5000 nm or longer wavelengths. The heating of the powder material is preferably effected by means of a radiation having a maximum radiation intensity at a wavelength of 5250 nm or longer wavelengths, particularly preferably 6000 nm or longer wavelengths. The heating of the powder material is especially preferably effected by means of a radiation having a maximum radiation intensity at a wavelength of 7000 nm or longer wavelengths. In a third step an electromagnetic-radiation-emitting radiation source (1) is used to effect selective melting/sintering at the desired locations on the surface of the powder bed (3). These steps are repeated until a three-dimensional object (4) is formed layer by layer. After termination of the build process and any necessary cooling of the powder cake (5) the three-dimensional object (4) may be removed from the powder cake.

[0015] The wavelength of the maximum radiation intensity should vary by less than 20%. It is preferable when the wavelength of the maximum radiation intensity varies by not more than 10%. It is particularly preferable when the wavelength of the maximum radiation intensity varies by not more than 5%.

[0016] Heat-radiating elements having a maximum radiation intensity at a wavelength of over 5000 nm are regarded as sluggish and rapid temperature control therefore appears difficult to achieve. It was found that, surprisingly, simultaneous irradiation of the surface of the powder bed with high-surface-area heat-radiating elements from different directions makes it possible to achieve rapid heating of the surface of the powder bed even with electromagnetic radiation having a maximum intensity at a wavelength of 5000 nm or higher wavelengths. The irradiation power is preferably at least 2000 W/m.sup.2 based on the vertically projected area of the powder bed that is to be heated. The vertically projected area of the powder bed also corresponds to the area of the build region which is bounded by the build frame. The irradiation power is particularly preferably at least 3000 W/m.sup.2 based on the vertically projected area of the powder bed that is to be heated. The area of the heat-radiating elements which gives off the electromagnetic rays to the surface of the powder bed is at least 100% of the vertically projected area of the powder bed that is to be heated. The area of the heat-radiating elements which gives off the electromagnetic rays to the surface of the powder bed is preferably at least 150% of the vertically projected area of the powder bed that is to be heated. The area of the heat-radiating elements which gives off the electromagnetic rays to the surface of the powder bed is preferably at least 200% of the vertically projected area of the powder bed that is to be heated.

[0017] FIG. 1 shows the in-principle construction of an apparatus for producing three-dimensional objects. The present invention further provides an apparatus for layer-by-layer production of three-dimensional objects. The apparatus comprises a build frame (10) having a height adjustable build platform (6), an apparatus (9) for applying a layer of a material solidifiable under the action of electromagnetic radiation to the build platform (6), a radiant heating means (2) and an electromagnetic radiation source (1) with which the solidifiable material is selectively melted/sintered. The radiant heating means consists of a heat source and of heat-radiating elements. The temperature control means in turn consists of a temperature measuring device (11) and a control unit (12). The temperature measuring device is advantageously a noncontact radiative thermometer.

[0018] The area of the heat-radiating elements (2) which give off the electromagnetic rays to the surface of the powder bed is altogether at least 100% of the vertically projected area of the powder bed which is bounded by the build frame (10). It is preferable when the area of the heat-radiating elements which give off the electromagnetic rays to the surface of the powder bed is at least 150% of the vertically projected area of the powder bed which is bounded by the build frame (10). It is particularly preferable when the area of the heat-radiating elements which give off the electromagnetic rays to the surface of the powder bed is at least 200% of the vertically projected area of the powder bed which is bounded by the build frame (10). The total emissivity in the direction of the face normal of the heat-radiating elements is at least 0.2. The total emissivity in the direction of the face normal of the heat-radiating elements is preferably at least 0.5. The heat-radiating elements are configured such that the intensity maximum of the radiation from the heat-radiating elements is at a wavelength of at least 5000 nm. The heat-radiating elements are preferably configured such that the intensity maximum of the radiation from the heat-radiating elements is at a wavelength of at least 5250 nm, particularly preferably of at least 6000 nm. The heat-radiating elements are especially preferably configured such that the intensity maximum of the radiation from the heat-radiating elements is at a wavelength of at least 7000 nm.

[0019] The heat-radiating elements are configured such that the intensity maximum of the radiation from the heat-radiating elements varies by not more than 20%. The heat-radiating elements are preferably configured such that the intensity maximum of the radiation from the heat-radiating elements varies by not more than 10%. The heat-radiating elements are configured such that the intensity maximum of the radiation from the heat-radiating elements particularly preferably varies by not more than 20%. The heating of the heat-radiating elements may be effected for example by induction, convection, conduction or electromagnetic radiation via a heat source. The radiant emittance of the heat-radiating elements is at least 500W/m.sup.2. The radiant emittance of the heat-radiating elements is preferably at least 1000W/m.sup.2. In the radiant heating means the heat source (14) and the heat-radiating elements (13) may be integrated in one component i.e. the heat source may be completely enclosed by the heat-radiating elements or the heat-radiating element (15) and the heat source (16) may exist as separate components. In a preferred embodiment the heat-radiating elements may be heated independently of one another in order to adjust the temperature distribution at the surface of the powder bed uniformly.

[0020] All powders known to those skilled in the art are in principle suitable for use in the apparatus according to the invention/the process according to the invention. Powders of polyamides, copolyamides, polyesters, copolyesters, polyether amides and polyether ketones are particularly suitable. Polymer powders having an absorptivity of greater than 0.8 at a wavelength of 5000 nm are particularly suitable. Polymer powders having an absorptivity of greater than 0.9 at a wavelength of 5000 nm are very particularly suitable. The three-dimensional objects produced by the processes according to the invention likewise form part of the subject matter of the present invention.

[0021] Even without further intimations, it is assumed that a skilled person will be able to utilize the above description to its widest extent. The preferred embodiments and examples are therefore to be interpreted merely as a descriptive disclosure which is by no means limiting in any way whatsoever. The present invention is elucidated in more detail below using examples. Alternative embodiments of the present invention are obtainable analogously.

[0022] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.

EXAMPLES

Example 1

Noninventive

[0023] A powder of polyamide 12 having the characteristics reported in Table 1 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 at room temperature (23° C.) to form a powder bed of 100 mm in height. A radiative heating means whose heat-radiating elements emit a radiation having an intensity maximum at a wavelength of 1400 nm heated the powder bed. The wavelength of the maximum radiation intensity varied by more than 30%. The area of the heat-radiating elements was 224 cm.sup.2. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 4.

Example 2

Noninventive

[0024] A polymer powder having the characteristics reported in Table 1 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 to form a powder bed of 100 mm in height. A radiative heating means having heat-radiating elements consisting of graphite foils which emits a radiation having an intensity maximum at a wavelength of 2000 nm heated the powder bed. The area of the heat-radiating elements was 775 cm.sup.2. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 5.

Example 3

Inventive

[0025] A polymer powder having the characteristics reported in Table 1 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 to form a powder bed of 100 mm in height. The powder bed was heated using a radiative heating means. The heat-radiating elements of the radiative heating means emit a radiation having an intensity maximum at a wavelength of 6200 nm. The wavelength of the maximum radiation intensity varied by less than 10%. The area of the heat-radiating elements was 1852 cm.sup.2. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 6. The temperature at the surface increased markedly more rapidly here compared to the noninventive examples. By contrast, the temperature at a depth of 20 mm increased only very slowly. It was thus possible to increase the temperature at the surface of the powder bed without excessively heating, and thus unnecessarily subjecting to thermal stress, the powder in lower powder layers.

Example 4

Inventive

[0026] A polymer powder having the characteristics reported in Table 2 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 to form a powder bed of 100 mm in height. The powder bed was heated using a radiative heating means. The heat-radiating elements of the radiative heating means emit a radiation having an intensity maximum at a wavelength of 5700 nm. The wavelength of the maximum radiation intensity varies by less than 10%. The area of the heat-radiating elements was 2466 cm.sup.2. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 7. The temperature at the surface increases markedly more rapidly here compared to the noninventive examples. By contrast, the temperature at a depth of 20 mm increases only very slowly. It was thus possible to increase the temperature at the surface of the powder bed without excessively heating, and thus unnecessarily subjecting to thermal stress, the powder in lower powder layers.

Example 5

Inventive

[0027] A polymer powder having the characteristics reported in Table 3 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 to form a powder bed of 100 mm in height. The powder bed was heated using a radiative heating means. The heat-radiating elements of the radiative heating means emit a radiation having an intensity maximum at a wavelength of 5000 nm. The wavelength of the maximum radiation intensity varies by less than 10%. The area of the heat-radiating elements was 2466 cm.sup.2. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 8. The temperature at the surface increased markedly more rapidly here compared to the noninventive examples. By contrast, the temperature at a depth of 20 mm increased only very slowly. It was thus possible to increase the temperature at the surface of the powder bed without excessively heating, and thus unnecessarily subjecting to thermal stress, the powder in lower powder layers.

Example 6

Inventive

[0028] A polymer powder having the characteristics reported in Table 1 was applied in a build region having dimensions of 35×35cm and an area of 1225cm.sup.2 to form a powder bed of 100 mm in height. The powder bed was heated using a radiative heating means. The heat-radiating elements of the radiative heating means emit a radiation having an intensity maximum at a wavelength of 7050 nm. The area of the heat-radiating elements was 1852 cm.sup.2. The wavelength of the maximum radiation intensity varies by less than 5%. The temperature at the surface of the powder bed and at a depth of 20 mm in the powder bed was measured and recorded. The results are reported in Table 9. The temperature at the surface increased markedly more rapidly here compared to the noninventive examples. By contrast, the temperature at a depth of 20 mm increased only very slowly. It was thus possible to increase the temperature at the surface of the powder bed without excessively heating, and thus unnecessarily subjecting to thermal stress, the powder in lower powder layers.

TABLE-US-00001 TABLE 1 polyamide 12 powder characteristics Value Unit Test type/test instrument/test parameter Polymer polyamide 12 Bulk density 0.456 g/cm.sup.3 DIN EN ISO 60. Particle size d50 58 μm Malvern Mastersizer 2000, dry measurement, metered addition of 20-40 g of powder using Scirocco dry dispersion instrument. Vibratory trough feed rate 70%, dispersing air pressure 3 bar. Sample residence time 5 seconds (5000 individual measurements), refractive index and blue light value fixed at 1.52. Evaluation by Mie theory. Particle size d10 32 μm Malvern Mastersizer 2000, see particle size d50 for parameters Particle size d90 86 μm Malvern Mastersizer 2000, see particle size d50 for parameters <10.48 μm 1 % Malvern Mastersizer 2000, see particle size d50 for parameters BET (spec. surface area) 7.1 m.sup.2/g ISO 9277, Micromeritics TriStar 3000, nitrogen gas adsorption, discontinuous volumetric method, 7 data points at relative pressures P/P0 from about 0.05 to about 0.20, dead volume calibration using He (99.996%), sample preparation 1 h at 23° C. + 16 h at 80° C. in vacuo, spec. surface area based on devolatilized specimen, evaluation by means of multipoint determination Melting point 1st heating 187 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Recrystallization temperature 139 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Material conditioning Material stored for 24 h at 23° C. and 50% humidity prior to processing/analysis

TABLE-US-00002 TABLE 2 polyamide 106 powder characteristics Value Unit Test type/test instrument/test parameter Polymer polyamide 106 Bulk density 0.438 g/cm.sup.3 DIN EN ISO 60. Particle size d50 66 μm Malvern Mastersizer 2000, dry measurement, metered addition of 20-40 g of powder using Scirocco dry dispersion instrument. Vibratory trough feed rate 70%, dispersing air pressure 3 bar. Sample residence time 5 seconds (5000 individual measurements), refractive index and blue light value fixed at 1.52. Evaluation by Mie theory. Particle size d10 48 μm Malvern Mastersizer 2000, see particle size d50 for parameters Particle size d90 91 μm Malvern Mastersizer 2000, see particle size d50 for parameters <10.48 μm 1 % Malvern Mastersizer 2000, see particle size d50 for parameters BET (spec. surface area) 5.3 m.sup.2/g ISO 9277, Micromeritics TriStar 3000, nitrogen gas adsorption, discontinuous volumetric method, 7 data points at relative pressures P/P0 from about 0.05 to about 0.20, dead volume calibration using He (99.996%), sample preparation 1 h at 23° C. + 16 h at 80° C. in vacuo, spec. surface area based on devolatilized, specimen evaluation by means of multipoint determination Melting point 1st heating 242 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Recrystallization temperature 196 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Material conditioning Material stored for 24 h at 23° C. and 50% humidity prior to processing/analysis

TABLE-US-00003 TABLE 3 PEEK powder characteristics Value Unit Test type/test instrument/test parameter Polymer PEEK Bulk density 0.438 g/cm.sup.3 DIN EN ISO 60. Particle size d50 66 μm Malvern Mastersizer 2000, dry measurement, metered addition of 20-40 g of powder using Scirocco dry dispersion instrument. Vibratory trough feed rate 70%, dispersing air pressure 3 bar. Sample residence time 5 seconds (5000 individual measurements), refractive index and blue light value fixed at 1.52. Evaluation by Mie theory. Particle size d10 48 μm Malvern Mastersizer 2000, see particle size d50 for parameters Particle size d90 91 μm Malvern Mastersizer 2000, see particle size d50 for parameters <10.48 μm 1 % Malvern Mastersizer 2000, see particle size d50 for parameters BET (spec. surface area) 5.3 m.sup.2/g ISO 9277, Micromeritics TriStar 3000, nitrogen gas adsorption, discontinuous volumetric method, 7 data points at relative pressures P/P0 from about 0.05 to about 0.20, dead volume calibration using He (99.996%), sample preparation 1 h at 23° C. + 16 h at 80° C. in vacuo, spec. surface area based on devolatilized specimen, evaluation by means of multipoint determination Melting point 1st heating 242 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Recrystallization temperature 196 ° C. DIN 53765 Perkin Elmer DSC 7 heating/cooling rate 20K/min Material conditioning Material stored for 24 h at 23° C. and 50% humidity prior to processing/analysis

TABLE-US-00004 TABLE 4 Example 1 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 32 24 1 39 25 1.5 44 26 2 51 27 2.5 55 28

TABLE-US-00005 TABLE 5 Example 2 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 34 24 1 41 24 1.5 47 25 2 54 26 2.5 60 27

TABLE-US-00006 TABLE 6 Example 3 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 41 23 1 57 23 1.5 68 23 2 79 24 2.5 90 24

TABLE-US-00007 TABLE 7 Example 4 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 40 23 1 55 23 1.5 66 24 2 75 24 2.5 86 24

TABLE-US-00008 TABLE 8 Example 5 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 39 23 1 53 24 1.5 64 24 2 73 24 2.5 83 25

TABLE-US-00009 TABLE 9 Example 6 temperature measurement Uppermost 20 mm below Time of powder layer powder surface measurement temperature data temperature data in min point in ° C. point in ° C. 0 23 23 0.5 44 23 1 59 23 1.5 71 23 2 82 23 2.5 94 24

[0029] German patent application 102016205053.2 filed Mar. 24, 2016, is incorporated herein by reference.

[0030] Numerous modifications and variations on the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.