ADDITIVE MANUFACTURING PRESSURE DEVICE, PROCESS AND OBTAINED PARTS THEREOF

Abstract

A laser sintering device for producing parts composed of powder materials is disclosed, the device including a mechanism which allows for porosity control during production of parts made with the materials. A method of producing a three-dimensional object is also provided, which includes the steps of disposing a layer of a powder material on a target surface, applying pressure to a powder material layer and directing an energy beam over a selected area of the powder material layer, wherein the powder is sintered or melted, and repeating the steps to form the three-dimensional object. The resultant three-dimensional objects made of powder material are also described.

Claims

1. A laser sintering device for producing parts comprised of powder materials, wherein said device comprises a mechanism which allows for porosity control during production of parts made with said materials.

2. The device as recited in claim 1, wherein said materials are selected from the group consisting of metals, ceramics, vitreous materials, polymeric materials and combinations thereof.

3. The device as recited in claim 1, wherein said materials are selected from the group consisting of polyolefins, polyvinyl chloride, polytetrafluoroethylene, ultra-high molecular weight polyethylene and combinations thereof.

4. The device as recited in claim 1, wherein the powder material comprises ultra-high molecular weight polyethylene.

5. The device as recited in claim 1, wherein said device includes a movable closing cap which works as a bulkhead.

6. The device as recited in claim 5, wherein said bulkhead is comprised of a mechanically resistant material able to bear pressure.

7. The device as recited in claim 5, wherein said bulkhead is transparent to a laser beam.

8. The device as recited in claim 1, wherein said mechanism applies pressure during laser sintering.

9. The device as recited in claim 8, wherein the pressure is from about 0 to 300 MPa.

10. The device as recited in claim 9, wherein the pressure is from about 5 to 80 MPa.

11. The device as recited in claim 10, wherein the pressure is from about 5 to 30 MPa.

12. The device as recited in claim 5, wherein said bulkhead is comprised of a material transparent to a laser beam.

13. The device as recited in claim 5, wherein said bulkhead is comprised of a material selected from the group consisting of germanium, zinc selenite and gallium arsenide.

14. The device as recited in claim 4, wherein parts made of ultra-high molecular weight polyethylene have a porosity index of from about 0 to 1.

15. The device as recited in claim 14, wherein parts made of ultra-high molecular weight polyethylene have a porosity index of from about 0.3 to 1.

16. The device as recited in claim 15, wherein parts made of ultra-high molecular weight polyethylene have a porosity index of from about 0.6 to 1.

17. The device as recited in claim 5, wherein the bulkhead comprises an insulating material containing an isotropic heating conductor.

18. The device as recited in claim 17, wherein said insulating material is an epoxy resin.

19. A method of producing a three-dimensional object comprising the steps of: (a) disposing a layer of a powder material on a target surface; (b) applying pressure to the powder material layer; (c) directing an energy beam over a selected area of the powder material layer, wherein the powder is sintered or melted; and (d) repeating said steps (a)-(c) to form the three-dimensional object.

20. The method as recited in claim 19, further comprising the step of disposing a bulkhead over the powder material after disposing the layer of the powder material on the target surface.

21. The method as recited in claim 19, wherein step (c) occurs under pressure.

22. The method as recited in claim 19, wherein steps (b) and (c) occur sequentially.

23. The method as recited in claim 20, wherein said bulkhead is transparent to the energy beam.

24. The method as recited in claim 20, wherein said bulkhead is comprised of a material transparent to a laser beam.

25. The method as recited in claim 20, wherein said bulkhead is comprised of a material selected from the group consisting of germanium, zinc selenite and gallium arsenide.

26. The method as recited in claim 20, wherein the bulkhead comprises an insulating material containing an isotropic heating conductor.

27. The method as recited in claim 26, wherein said insulating material is an epoxy resin.

28. The method as recited in claim 19, wherein said powder material is selected from the group consisting of metals, ceramics, vitreous materials, polymeric materials and combinations thereof.

29. The method as recited in claim 19, wherein said powder material is a polymeric material selected from the group consisting of polyolefins, polyvinyl chloride, polytetrafluoroethylene, ultra-high molecular weight polyethylene and combinations thereof.

30. The method as recited in claim 19, wherein said powder material comprises ultra-high molecular weight polyethylene.

31. The method as recited in claim 19, wherein the pressure is from about 0 to 300 MPa.

32. The method as recited in claim 31, wherein the pressure is from about 5 to 80 MPa.

33. The method as recited in claim 32, wherein the pressure is from about 5 to 30 MPa.

34. A three-dimensional object comprised of powder material having a porosity index of from about 0 to 1.

35. The three-dimensional object as recited in claim 34, wherein the object has a porosity index of from about 0.3 to 1.

36. The three-dimensional object as recited in claim 35, wherein the object has a porosity index of from about 0.6 to 1.

37. The three-dimensional object as recited in claim 34, wherein said powder material is selected from the group consisting of metals, ceramics, vitreous materials, polymeric materials and combinations thereof.

38. The three-dimensional object as recited in claim 34, wherein said powder material is a polymeric material selected from the group consisting of polyolefins, polyvinyl chloride, polytetrafluoroethylene, ultra-high molecular weight polyethylene and combinations thereof.

39. The three-dimensional object as recited in claim 34, wherein said powder material comprises ultra-high molecular weight polyethylene.

40. The three-dimensional object as recited in claim 34, prepared by a selective laser sintering process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Like reference numerals denote like features throughout specification and drawings.

[0033] FIG. 1 illustrates four key components of Powder Bed Fusion, i.e., a laser scanning system, a powder delivery system, a roller or rake and a fabricated piston.

[0034] FIG. 2 illustrates an exemplary device comprising a movable closing cap (11) that works as a bulkhead (anteparo, in Portuguese).

[0035] FIG. 3 illustrates an exemplary bulkhead which can be comprised of a non-transparent material.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The present invention relates to a device able to apply pressure during the laser sintering process. The device introduces pressure in an ordinary sintering process, allowing for porosity control during production of parts made with UHMWPE.

[0037] Unlike temperature and time, pressure is the single key parameter important to produce solid parts of UHMWPE, that is not present in an ordinary laser sintering process.

[0038] Pressure is necessary for collapsing voids and allowing enough contact among porosity interfaces, important considerations for achieving reptation.

[0039] FIG. 2 illustrates the device comprising a movable closing cap (11) that works as a bulkhead (anteparo, in Portuguese). The bulkhead is comprised of any mechanically resistant material able to bear pressure and also be transparent to a laser beam (6). The bulkhead is moved by any motorized device able to position it in up (U) and down (D) positions.

[0040] In an embodiment of the present invention, the bulkhead is comprised of any material transparent to a laser beam such as, but not limited to, germanium (Ge), zinc selenite (ZnSe), gallium arsenide (GaAs), or any material transparent to a CO.sub.2 laser beam.

[0041] In further embodiments of the present invention, other materials can be used depending on the type of laser used.

[0042] In an additional embodiment of the present invention, the bulkhead can be comprised of a non-transparent material as shown in FIG. 3. The following identifiers are associated with this figure: [0043] 12—Non transparent bulkhead cap (lateral view). [0044] 13—Non transparent bulkhead cap (superior view). [0045] 14—Laser beam. [0046] 15—Insulating material. [0047] 16—Oriented thermal conductor

[0048] In this embodiment, the bulkhead is composed of a mechanically resistant and insulating material (15), containing an isotropic heating conductor (16). In this exemplary device, the laser shines each conductor point (14) in the bulkhead's top surface (12). In this way, heat will propagate along the isotropic conductor (16) to the bulkhead's bottom surface, heating a very restricted region of powder under pressure. This device was developed as an option to a transparent bulkhead. CO.sub.2 transparent materials are in general brittle and/or expensive.

[0049] In a further embodiment of present invention, the isotropic heating conductor (16) can be any oriented material having a high thermal conductivity in its main axis direction. Examples of oriented materials include, but are not limited to, carbon fiber, metal filament, graphite fiber, etc.

[0050] In a further embodiment of present invention, the insulating material (15) can be any mechanically resistant and insulating material such as, but not limited to an epoxy resin.

[0051] In order to apply pressure over the top of the powder bed (1), the bulkhead (11) is fixed in the D position by means of a clamp (not shown) to bear pressure imposed by a fabrication piston (4). The fabrication piston (4) is moved by any suitable driver such as a servo-hydraulic system, electro-fuse system, etc. The pressure is set according to the following Equation 1.

P=F/S  Equation 1

Where:

[0052] P is the pressure, in MPa.
F (FIG. 2) is the force, in N.
S (FIG. 2) is the surface in m.sup.2.

[0053] In an additional embodiment of the present invention, the process to produce parts made of UHMWPE is described by the following steps: [0054] a) In the first step, the powder reservoir (2) is completely filled with UHMWPE powder and the powder bed (1) is empty. The fabrication piston is at the upper position and the bulkhead is at the U position; [0055] b) Then, the powder delivery piston is moved one layer up while the fabrication piston is lowered one layer; [0056] c) The roller (8) pushes the powder layer from the powder reservoir (2), spreading it over the powder bed (1); [0057] d) The bulkhead goes to the D position and is fixed in this position by mean of a clamp; [0058] e) The fabrication piston applies a pre-defined force F on the powder layer; [0059] f) A specific time is allotted for the compressive force to produce a cold sintering; [0060] g) The laser (7) is switched on and the scanner directs the laser beam on the pre-defined surface of the pressurized powder bed; [0061] h) A specific time is allotted for the compressive force to produce a hot sintering; [0062] i) The laser is switched off and a specific time is set, so that the layer can be cooled; [0063] j) The bulkhead is moved to the U position; [0064] k) The roller (8) goes to the home position; and [0065] l) The steps from b to k are repeated until the part (9) is finished.

[0066] The present invention describes a part produced for any powder that can be sintered, such as metals, ceramics, vitreous materials, polymeric materials, and combinations thereof.

[0067] In a preferred embodiment, any polymeric powder can be used, such as polyolefins, polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE), UHMWPE, and combinations thereof.

[0068] In a particularly preferred embodiment, an UHMWPE is used.

[0069] The present invention further relates to a part made of UHMWPE that is produced by laser sintering under different pressure levels. The pressure will define the amount of porosity of the final part.

[0070] In a further embodiment of the present invention, a pressure range from 0 to 300 MPa is desirable, with a range of 5 to 80 MPa preferred, and a range from 5 to 30 MPa particularly preferred.

[0071] In an additional embodiment of the present invention, the Porosity Index (PI), according to the following Equation 2, defines the level of part porosity:

[00001]$\begin{array}{cc}\mathrm{PI}=\frac{{\rho }_{\mathrm{part}}}{{\rho }_{\mathrm{pol}}}& \mathrm{Equation}.Math..Math.2\end{array}$

[0072] Where: [0073] PI is the porosity index. ρ.sub.part is the density of a part produced by the process described in the present invention, in kg/m.sup.3 at room temperature (23° C.). [0074] ρ.sub.pol is the density of polymer, in kg/m.sup.3 at room temperature (23° C.).

[0075] The effect of pressure on the mechanical and tribological properties of UHMWPE has been previously studied. The mechanical and tribological properties increase asymptotically with applied pressure. The pressure is necessary to keep the porous wall in contact, allowing the reptation process to occur.

[0076] In an additional embodiment of the present invention, a part made of UHMWPE has a porosity index (PI) from 0 to 1, with a porosity index from 0.3 to 1 preferred, and a porosity index from 0.6 to 1 particularly preferred.

[0077] The present invention further relates to a method of producing a three-dimensional object comprising the steps of: (a) disposing a layer of a powder material on a target surface; (b) applying pressure to the powder material layer; (c) directing an energy beam over a selected area of the powder material layer, wherein the powder is sintered or melted; and (d) repeating steps (a)-(c) to form the three-dimensional object. This method may further comprise the step of disposing a bulkhead over the powder material after disposing the layer of the powder material on a target surface. Step (c) may occur under pressure, steps (b) and (c) may occur sequentially, and the bulkhead may be transparent to the energy beam.

[0078] The foregoing is provided for purposes of illustrating, explaining, and describing embodiments of this invention. Modifications and adaptations to these embodiments will be apparent to those skilled in the art and may be made without departing from the scope or spirit of this invention.

[0079] Although the subject matter has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments, which may be made by those skilled in the art.