A PROCESS FOR PRODUCING A THREE-DIMENSIONAL (3D) OBJECT EMPLOYING GRANULATES

Abstract

The present invention relates to a process for producing a three-dimensional (3D) object by employing a three-dimensional (3D) printing process wherein a granulate having an particle size in the range of 0.2 to 1 mm is used as a starting material to be printed within said 3D printing process, employing a 3D extrusion printer. In one preferred embodiment, the process according to the present invention is employed for producing a 3D greenbody. The invention further relates to 3D objects as such and the corresponding processes for obtaining such 3D objects, in particular a 3D green body, a 3D brown body and a 3D sintered body.

Claims

1.-12. (canceled)

13. A process for producing a three-dimensional (3D) object by employing a three-dimensional (3D) printing process comprising the steps a) to e) as follows: a) providing at least one granulate having a particle size in the range of 0.2 to 1 mm, b) feeding the at least one granulate with at least one screw located at least partially inside the housing of a three-dimensional (3D) extrusion printer towards at least one nozzle of the 3D extrusion printer, c) heating the at least one granulate inside the housing of the 3D extrusion printer, d) extruding the at least one heated granulate obtained in step c) through the at least one nozzle in order to obtain at least one extruded strand, e) forming the 3D object layer by layer from the at least one extruded strand obtained in step d), wherein the at least one granulate is selected from a granulate comprising at least one inorganic powder and at least one polymer.

14. The process according to claim 13, wherein the 3D extrusion printer comprises at least one screw and at least one nozzle and the screw feeds the at least one granulate in vertical direction or in an angle of not more than 60?, preferably of not more than 45?, different to the vertical direction towards the nozzle, more preferably the screw feeds the at least one granulate in vertical direction towards the nozzle.

15. The process according to claim 13, wherein i) the at least one granulate employed in step a) is placed in at least one storage container which may be positioned partially or completely inside of the three-dimensional (3D) extrusion printer, and/or ii) the housing of the 3D extrusion printer comprises at least one inlet for feeding the granulate into the housing, at least one screw for transporting the granulate from the storage container to the nozzle, at least one heating element and at least one nozzle, preferably the at least one nozzle, the at least one heating element and at least a part of the at least one screw are positioned within at least one printing head of the housing of the 3D extrusion printer, and/or iii) the heating of the at least one granulate according to step c) is carried out within at least one printing head of the 3D extrusion printer and the at least one printing head contains at least a part of the at least one screw employed within step b) and at least one nozzle, and/or iv) the at least one screw employed within step b) is a heatable screw.

16. The process according to claim 13, wherein the at least one granulate is selected from i) a granulate comprising at least one polymer, preferably at least one thermoplastic polymer, ii) a granulate comprising at least one inorganic powder and at least one polymer, the inorganic powder is a powder of at least one inorganic material selected from the group consisting of a metal, a metal alloy and a ceramic material, iii) a granulate comprising at least one core material (CM) coated with a layer of at least one shell material (SM), iv) a granulate comprising at least one fibrous filler (FF) and at least one polymer, preferably the fibrous filler (FF) is at least one carbon fiber, or v) a granulate comprising at least one thermoplastic polyurethane.

17. The process according to claim 13, wherein the at least one granulate is a mixture (M) comprising (a) from 40 to 75% by volume of an inorganic powder (IP) based on the total volume of the mixture (M), (b) from 25 to 60% by volume based on the total volume of the mixture (M) of a binder (B) comprising (b1) from 50 to 98% by weight of at least one polyoxymethylene (POM) based on the total weight of the binder (B), (b2) from 2 to 35% by weight of at least one polyolefin (PO) based on the total weight of the binder (B), (b3) from 0 to 40% by weight of at least one further polymer (FP) based on the total weight of the binder (B).

18. The process according to claim 17, wherein i) the mixture (M) comprises as component (c) from 0.1 to 5% by volume of at least one dispersant based on the total volume of the mixture (M), and/or ii) the inorganic powder (IP) is a powder of at least one inorganic material selected from the group consisting of a metal, a metal alloy and a ceramic material, and/or iii) component (b1) is a polyoxymethylene (POM) copolymer which is prepared by polymerization of from at least 50 mol-% of a formaldehyde source (b1a), from 0.01 to 20 mol-% of at least one first comonomer (bib) of the general formula (II) ##STR00003## wherein R.sup.1 to R.sup.4 are each independently of one another selected from the group consisting of H, C.sub.1-C.sub.4-alkyl and halogen-substituted C.sub.1-C.sub.4-alkyl; R.sup.5 is selected from the group consisting of a chemical bond, a (CR.sup.5aR.sup.5b) group and a (CR.sup.5aR.sup.5bO) group, wherein R.sup.5a and R.sup.5b are each independently of one another selected from the group consisting of H and unsubstituted or at least monosubstituted C.sub.1-C.sub.4-alkyl, wherein the substituents are selected from the group consisting of F, Cl, Br, OH and C.sub.1-C.sub.4-alkyl; n is 0, 1, 2 or 3; and from 0 to 20 mol-% of at least one second comonomer (b1c) selected from the group consisting of a compound of formula (III) and a compound of formula (IV) ##STR00004## wherein Z is selected from the group consisting of a chemical bond, an (O) group and an (OR.sup.6O) group, wherein R.sup.6 is selected from the group consisting of unsubstituted C.sub.1-C.sub.8-alkylene and C.sub.3-C.sub.8-cycloalkylene, and/or iv) the further polymer (FP) is at least one further polymer (FP) selected from the group consisting of a polyether, a polyurethane, a polyepoxide, a polyamide, a vinyl aromatic polymer, a poly(vinyl ester), a poly(vinyl ether), a poly(alkyl (meth)acrylate) and copolymers thereof.

19. The process according to claim 13, wherein the granulate employed in step a) has i) a particle size in the range of 0.4 to 0.9 mm, and/or ii) a round shape, wherein the term round shape means that more than 50% of the respective particles have a sphericity of >0.7.

20. The process according to claim 13, wherein the length to diameter ratio of the at least one screw employed in step b) is below 12, preferably below 8.

21. The process according to claim 13, wherein the at least one granulate is transferred by gravity from the at least one storage container to the at least one screw, preferably the at least one storage container is positioned on the upper end of the at least one screw and the at least one storage container has an opening on its lower part in order to transfer the at least one granulate from the at least one storage container to the at least one screw.

22. The process according to claim 13, wherein the 3D object obtained in step e) is a three-dimensional (3D) green body.

23. The process according to claim 22, wherein step e) is followed by a step f), in which at least part of the binder (B) is removed from the three-dimensional green body to form a three-dimensional (3D) brown body.

24. The process according to claim 23, wherein step f) is followed by a step g), in which the three-dimensional (3D) brown body is sintered to form a three-dimensional (3D) sintered body.

Description

EXAMPLES

Inventive Example E1 and Comparative Examples C2 and C3

[0194] Provision of the at Least One Granulate (Step a))

[0195] Production of the Granulate

[0196] Catamold evo 316L pellets having a pellet size of 2 to 4 mm (C3) are grinded with a cutting mill to obtain a fine granulate. After grinding, the fine granulate is fractionated by sieving to obtain different fractions (0.5 to 1 mm (E1); 1 to 2 mm (C2)).

[0197] The Catamold evo 316L pellets comprise stainless steel 316L particles, polyoxymethylene (POM) as primary binder and polyethylene (PE) as secondary binder.

[0198] Production of the Three-Dimensional Object by Employing a Three-Dimensional Printing Process (Steps b) to e))

[0199] A series P printer from the 3D printer manufacturer Pollen AM is used as three-dimensional (3D) extrusion printer. The delta kinematic-type printer processes pellets or fine granulates; the print bed and printer space can be heated. Hardened steel nozzles are employed to minimize abrasion. To ensure a good adhesion to the build plate during printing and easy removal of parts after the print, a EZ-STIK HOT build plate from Geckotech is used.

[0200] Typical printing parameters are shown in table 1.

TABLE-US-00001 TABLE 1 Nozzle temperature [? C.] 210-240 Build plate temperature [? C.] 80-120 IR radiative heater [? C.] 0-240 Extruder temperature [? C.] 160-180 Layer height [mm] 0.1-0.2 Nozzle diameter [mm] 0.4-0.8 Print speed [mm/min] 900-2400

[0201] The different fractions of the fine granulate are each fed with a screw located at least partially inside the housing of the three-dimensional (3D) extrusion printer towards the nozzles of the 3D extrusion printer (step b)), and then heated inside the housing of the 3D extrusion printer (step c)). Subsequently, the heated fractions of the fine granulate obtained in step c) are each extruded through the nozzles in order to obtain at least one extruded strand (step d)), and from the at least one extruded strand, a 3D object (a three-dimensional (3D) green body) is formed layer by layer (step e)).

[0202] In FIG. 1, the 3D objects formed are shown. The 3D object a) is formed from the fraction having a particle size in the range of 0.5 to 1 mm (E1), the 3D object b) is formed from the fraction having a particle size in the range of 1 to 2 mm (C2) and the 3D object c) is formed from the pellets (C3).

[0203] As can be seen from FIG. 1, the fine granulate having a particle size in the range of 0.5 to 1 mm (E1) leads to a constant extrusion rate, printing line consistency and, therefore, to the smoothest surface. The larger the particle sizes are the more prominent is the layer appearance due to extrusion rate instabilities.

[0204] Preparation of Brown and Sintered Bodies

[0205] Step f)

[0206] After step e), at least part of the binder (B) is removed from the three-dimensional green body to form a three-dimensional (3D) brown body:

[0207] The debinding is done at 110? C. using HNO.sub.3 (>98%) in a 40 litre debinding furnace (Nabertherm CDB 40) with a nitric acid feed of typically 60 ml/h and a purging gas (nitrogen) throughput of 840 I/h.

[0208] The debinding process is finished when a minimal debinding loss of 5.7% is reached.

[0209] Step g)

[0210] After step f), the three-dimensional (3D) brown body is sintered to form a three-dimensional (3D) sintered body:

[0211] The sintering is done in an atmosphere with 100% clean and dry hydrogen (dewpoint <?40? C.). As sintering support Al.sub.2O.sub.3 with a purity of 99.6% is used. The following sintering cycle is used: [0212] 1) room temperature5 K/min600? C., hold 1 h, [0213] 2) 600? C.5 K/min1380? C., hold 3 h [0214] 3) furnace cooling

[0215] In the early stage of the sintering process remaining binder constituents are burnt off and the pyrolysis products is removed by a suction fan.