Method and device of layerwise manufacturing a three-dimensional object of a powdery material

Abstract

A polyamide powder is disclosed for use in a method of manufacturing a three-dimensional object by selectively solidifying layers of the polyamide powder at the locations corresponding to the cross-section of the object in the respective layer by application of electromagnetic radiation. The polyamide powder of the invention is reclaimed after manufacturing of an object and, then is treated with water or water vapor and subsequently dried. After treatment, the powder preferably can have a molar weight Mn (numeric average) of more than about 20,000 g/mol and a Mw (weight average) of more than about 40,000 g/mol. Also, the powder preferably has an excess of carboxylic end groups relative to amino end groups of at least 4:1 up to at most 200:1.

Claims

1. A recycled polyamide powder for use in a method of manufacturing a three-dimensional object by selectively solidifying layers of the recycled polyamide powder at the locations corresponding to the cross-section of the object in the respective layer by application of electromagnetic radiation, wherein the recycled polyamide powder has already undergone a manufacturing cycle and, prior to a further use in another manufacturing cycle, the powder is treated subsequently with water vapour and then the powder is dried, wherein after treatment the powder has a molar weight that is at least 5% less than before treatment.

2. The polyamide powder according to claim 1, further having a molar weight Mn (numeric average) of more than about 20,000 g/mol and a Mw (weight average) of more than about 40,000 g/mol. before the treatment with water vapour.

3. The polyamide powder according to claim 1, further having a molar weight Mn (numeric average) of 21,000-100,000 g/mol and a Mw (weight average) of 45,000-200,000 g/mol. before the treatment with water vapour.

4. The polyamide powder according to claim 1, further having a molar weight Mn (numeric average) of 22,000-50,000 g/mol and a Mw (weight average) of 50,000-150,000 g/mol. before the treatment with water vapour.

5. The polyamide powder according to claim 1, further having a molar weight Mn (numeric average) of 25,000-35,000 g/mol and a Mw (weight average) of 60,000-100,000 g/mol. before the treatment with water vapour.

6. The polyamide powder according to claim 1, further comprising an excess of carboxylic end groups relative to amino end groups of at least 4:1 up to at most 200:1 before the treatment with water vapour.

7. The polyamide powder according to claim 1, wherein after treatment the powder has a molar weight that is 10-70% less than before treatment.

8. The polyamide powder according to claim 1, wherein after treatment the powder has a molar weight that is 20-50% less than before treatment.

9. The polyamide powder according to claim 1, further comprising a molar weight (numeric average) after the treatment of less than about 40,000 g/mol and a M.sub.w (weight average) of less than about 100,000 g/mol.

10. The polyamide powder according to claim 9, further comprising an excess of carboxylic end groups relative to amino end groups after the treatment of about 2:1 up to about 3:1.

11. The polyamide powder according to claim 1, further comprising a molar weight (numeric average) after the treatment of 15,000-30,000 g/mol and a M.sub.w (weight average) of 35,000-70,000 g/mol.

12. The polyamide powder according to claim 1, further comprising a molar weight (numeric average) after the treatment of 17,000-25,000 g/mol and a M.sub.w (weight average) of 37,000-50,000 g/mol.

13. The polyamide powder according to claim 1, further comprising a molar weight (numeric average) after the treatment of 19,000-21,000 g/mol and a M.sub.w (weight average) of 38,000-45,000 g/mol.

14. The polyamide powder according to claim 1, further comprising an excess of carboxylic end groups relative to amino end groups after the treatment of about 2:1 up to about 3:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and effects of the invention are indicated in the description of an embodiment on the basis of the following figures.

(2) FIG. 1 shows a schematic view of an embodiment of the invention exemplified by a laser sintering device.

(3) FIG. 2 shows a test geometry of a piece to be laser sintered.

(4) FIG. 3 shows a piece which is laser sintered of 100% waste powder.

(5) FIG. 4 shows a laser sintered piece having no sink marks anymore and which is manufactured by the method of the present invention by recycled waste powder.

DETAILED DESCRIPTION OF THE INVENTION

(6) The laser sintering device according to FIG. 1 comprises a frame 1 which opens in the upper side and has therein a platform 2, which is movable in the vertical direction and supports the object 3 to be built-up and defines a building area. The platform 2 is adjusted in the vertical direction such that the layer of the object, which is to be solidified, lies in a working plane 4. Further, a dispenser 5 is provided to apply powdery building material 3a which is to be solidified by electromagnetic radiation. The building material 3a is supplied to the dispenser 5 from a storage container 6. Further, the device comprises a laser 7 generating a laser beam 7a, which is deflected by a deflection means 8 into an input window 9 and therefrom into the process chamber 10, and which is focussed to a predetermined point within the working plane 4.

(7) Further, a control unit 11 is provided to control the components of the device in a coordinated manner to perform the building process.

(8) Outside the process chamber 10, a device 12 for treating non-solidified waste powder is provided. This device comprises a water vapour generating means (not shown), a heating means to bring the water vapour on a predetermined temperature and a drying means. The device for treating the waste powder 12 can be an autoclave, for instance. The drying means can be a hot air blower, for instance. The device for treating the waste powder further comprises a control (not shown) to adjust the temperature and the time of the treatment.

(9) The device 12 for treating the waste powder can optionally be connected with the process chamber and the storage container via a deliver system (not shown). Thereby, the non-solidified waste powder can be sucked and supplied again to the storage container after the treatment. The device 12 for treating the waste powder is optionally connected only with the storage container, so that the waste powder is supplied after removal of the object with the surrounding non-solidified material. In a further modification, the device 12 for treating the waste powder can also be integrated in the storage container.

(10) Optionally, the post treatment of the waste powder in the open frame (1) together with the pieces is conducted after the job. Herein, the complete open frame (replaceable frame) is removed from the laser sintering machine and subjected the post treatment process in a device 12.

(11) In a further modification, the device 12 for treating the waste powder is provided at a farther place, and the waste powder can be transported thereto and transported back to the laser sintering machine after the treatment as well.

(12) In the following, the method according to the invention is described. Preferably, polyamide-12 is used as the powder, as it is described in EP 0 911 142. The powder usually has a grit size of about 50 m to about 150 m. The powder may have additives such as riddle additives, pigments, fillers, flame resistants or further additives.

(13) The powder 3a is applied layer by layer from the storage container 6 onto the platform and onto a previously solidified layer, respectively, and solidified by the laser at the locations in the layer corresponding to the cross-section of the object. After manufacturing the object, non-sintered powder 3a surrounding the object is supplied to the device 12 for treatment of waste powder. Here, it is treated by water vapour for about 1 up to about 48 hours at temperatures of at least 130 C. and at most 10 C. below the melting point of the powder. For polyamide-12 and polyamide-11, the treatment is preferably performed at about 130 C. up to about 170 C. Thereafter, it is dried in a drying cabinet, which is part of the device 12. At the same time, the drying temperature is lower than 100 C., preferably between 50-70 C. The time and the temperature of the treatment depends on the age of the waste powder. The older the powder is, as the case may be when it has been used for some manufacturing processes before, the longer it must be treated. By increasing the temperature, the recovery can be accelerated. However, the required temperature is below the melting points so as to prevent baking of the powder grains.

(14) By aging in the laser sintering process, the molar mass of the polyamide is aggregated by post-condensation. The waste powder 3a supplied to the treatment device 12 has a noticeable higher molar weight than fresh powder. In accordance to the age and the temperature load, the molar weight of the waste powder is increased. For instance, the waste powder according to the present invention before the treatment has a molar weight M.sub.n (numeric average) of more than 20.000 g/mol, preferably of 21.000-100.000 g/mol, further preferred of 22,000-50,000 and most preferred of 25,000-35,000, and M.sub.w (average weight) of more than 40.000 g/mol, preferably of 45,000-200,000, further preferred of 50.000-150.000 and most preferred of 60,000-100,000. After the treatment, the recycled powder has a molar weight, which is at least 5%, preferably 10-70% and further preferred 20-50% below the molar weight of the waste powder. The recycled powder has an M.sub.n(numeric average) of less than 40,000 g/mol, preferably of 15,000-30,000 g/mol, further preferred of 17,000-25,000 and most preferred of 19,000-21,000, and M.sub.w (weight average) of less than 100,000 g/mol, preferably of 35,000-70,000 and further preferred of 37,000-50,000 and most preferred of 38,000-45,000.

(15) By aging during the laser sintering process, the balance between carboxylic end groups and amino end groups of polyamide-12 in a direction to an excess of one of both end groups, preferably of the carboxylic end group, can be shifted. The waste powder 3a supplied to the treatment device 12 has preferably an excess of one end group, preferably of the carboxylic end group, at least of 4:1 up to at most 200:1. In accordance to the age of the powder, the excess can be 4:1, 5:1, etc., 100:1 up to 200:1. By the treatment, the excess of end groups is preferably decreased.

(16) Further preferred, the excess of the end groups, preferably of the carboxylic end group, is set between about 2:1 to about 3:1.

(17) A concrete embodiment uses a powder which is available under the trade name Primepart of EOS GmbH Electro Optical Systems, and which corresponds to the powder as described in EP-0 911 142 and has further additives. Fresh powder, which has not been used in a laser sintering process yet, usually has the following parameters: molar mass (numeric average) M.sub.n=19,600 g/mol, molar mass (weight average) M.sub.w=42,500 (g/mol). After the sintering process, the waste powder has the following parameters: M.sub.n=27,200 g/mol, M.sub.w=85,600 g/mol. This waste powder is treated for different times in the treatment device by hot vapour of 140 C. and, thereafter, it is dried. The treated waste powder has then values as indicated in the table. In accordance to the treatment time, it is possible to reset the molar weight of the fresh powder. It does not depend on the molar weight of the fresh powder and of the waste powder, respectively. Therefore, it is not essential whether the waste powder comes from one cycle or several cycles.

(18) TABLE-US-00001 molar mass determination (GPC) Samples Mn Mw fresh powder 19500 42600 waste powder 27200 85600 140 C., 1 h 25800 77100 140 C., 6 h 24500 70300 140 C., 12 h 20300 54000 140 C., 24 h 19100 48600

(19) The values have been determined by means of gel permeation chromatography (GPC) in hexafluoroisopropanol. The determination of the molar mass has been performed computer-aided by means of the so-called strip method. Herein, the eluted peak is divided in several equidistant volume slices which are identical with the measurement frequency. By the calibration, the elution volumes are then transformed to molar masses. As a calibration step standard, tightly distributed polymethyl methacrylate (PMMA) dissolved in HFIP has been used. The proper procedure and evaluation are known by the skilled person.

(20) The treated powder is then used for a new laser sintering process. The laser sintering pieces manufactured by the treated primepart-powder (laser sintering machine EOS P380, parameters mechanics, compromise, surface, for instance) has, in accordance to the location in the built-up area, noticeably less or no sink marks anymore as compared with waste powder. The check of the tendency of sink marks can be checked during laser sintering by a relative simple wedge test geometry having different inclined slopes of at least 15-30, and preferably of 0-50. In this respect, 0 corresponds to a vertical plane in the Z-axis of the building space. The minimum size of the wedge is 452530 mm (lengthwidthheight). A typical test geometry is depicted in FIG. 2.

(21) FIG. 3 shows a laser sintered piece manufactured of 100% waste powder of polyamide. The sink marks are clearly shown. FIG. 4 shows a laser sintered piece having the same geometry, wherein the powder has been subjected to the above mentioned treatment. Sink marks are not present.

(22) By the treatment of the waste powder, the melting point and the crystallization point, respectively, of the powder nearly remain constant or is slightly lowered. Generally, the decrease is 0-5 C. The melting- and crystallization point of the powder can be determined by dynamic difference calorimetry (DKK and DSC, respectively) according to DIN 53765.

(23) The treatment can either be conducted by the user of the laser sintering machine in the treatment device 12 or by a central unit comprising the treatment device 12 and receiving the waste powder for recycling.

(24) The method is not restricted to the use of polyamide-12. Other aliphatic polyamide such as polyamide-6, polyamide-11, polyamide-46, polyamide-66, polyamide-1010, polyamide-1012, polyamide-1212 as well as their copolymers and other partly aromatic polyamide such as polyamide-PA6T/6I, poly-M-xylylenadipinamide (PAMXD6), polyamide-6/6T, polyamide-PA6T/66, -PA4T/46 can be used as well. As a matter of principle, all polyamides can be used where an increase in the molar weight of non-solidified powder occurs by post-condensation during the laser sintering process in the process chamber.

(25) The method is also applicable to all plastic powders, where the non-solidified powder is subjected to an aging process in the process chamber resulting to a shift of the ratio of carboxylic end groups and amino end groups.

(26) The method and the device are not restricted to the laser sintering method and the laser sintering device, either. As a matter of principle, they are applicable to all methods of layerwise manufacturing a three-dimensional object, where conditions (high temperatures) act on the non-solidified powder in the process chamber which makes the powder aging. Further examples for these methods are mask sintering and electron beam sintering.

(27) The method is not restricted to a treatment only by water or water vapour. It is also possible to add further additives such as condensation catalysts or amide generating chain regulators in the treatment. Such catalysts and regulators are well-known by the skilled person.