A method for additive manufacturing of a hollow body, a hollow body created by the method, and an inflow control device comprising same

Abstract

A method for providing a hollow body (1), comprising: - creating the hollow body (1) by means of an additive manufacturing apparatus, wherein the hollow body (1) being created with at least one aperture (5) in a portion of the hollow body (1) to allow extraction of a powder from within the hollow body (1), - creating filler material (3) adjacent to the at least one aperture (5) for filling the at least one aperture, wherein the filler material (3) is created by the additive manufacturing ap- paratus; - extracting any powder from within the hollow body; - disconnecting a powder supply to the additive manufacturing apparatus, and melting the filler material (3) by means of a laser (L) forming part of the additive manufacturing apparatus, wherein the laser (L) is programmed to repeatedly print a plurality of imagi- nary disks (D) at the exact same location.

Description

[0001] A METHOD FOR ADDITIVE MANUFACTURING OF A HOLLOW BODY, A HOLLOW BODY

[0002] CREATED BY THE METHOD, AND AN INFLOW CONTROL DEVICE COMPRISING SAME

[0003] The present invention is related to a method for creating a hollow body. More specifically, the invention is related to a method for creating a hollow body by means of additive manufacturing, and a hollow body created by means of the method.

[0004] Additive manufacturing uses data computer-aided-design (CAD) software or 3D object scanners to direct hardware to deposit material, layer upon layer, in precise geometric shapes. Additive manufacturing adds material to create the object. By contrast, creating an object by traditional means, it is often necessary to remove material through milling, machining, carving, shaping or other means.

[0005] Publication EP 3903991 Al discloses a three-dimensional deposition method and an object provided by the method. The method comprises a step of supplying a powder toward an outer peripheral surface of a shaft rotated during depositing, irradiating the powder with a laser beam, and sintering or melting and solidifying at least a part of the powder irradiated with the laser beam to form a formed layer, so as to form a three-dimensional object body in which an internal space communicates with an exterior through an opening. The method further comprises a step of discharging a residue such as the powder in the internal space from the opening to an exterior; and a step of emitting the laser beam toward an end surface of the opening to melt and solidify the formed layer, so as to close the opening.

[0006] Publication EP 3148731 Al discloses a method for manufacturing a turbomachine component comprises the following steps: (a) producing by additive manufacturing a plurality of separate segments of the turbomachine component, having a skin surrounding an empty volume corresponding to a massive part of the turbomachine component; assembling the separate segments of the turbomachine component together forming a semifinished component, with an empty cavity therein; filling cavity of the semi-finished component with a bulk flowable material; densifying and solidifying the bulk flowable material in the cavity.

[0007] In this document additive manufacturing is also denoted 3D-printing.

[0008] Although any object can be created by means of additive manufacturing (3 D-pri nti ng), the present invention is directed towards creation of a hollow body, and particularly towards 3D-printing of a hollow body in the form of a ball.

[0009] In the industry, there is a need for balls with low overall density and sufficient strength to withstand high pressure. Such balls may be used for various applications. One example where such balls are needed is in the oil and gas industry, where balls can be used as flotation elements in autonomous inflow control technologies to restrict inflow of undesired fluids, like water and gas from the reservoir. Such balls must have overall densities between the densities of the different fluids they are designed for controlling. In order to stop excessive inflow of gas, a ball with a density between that of oil and gas must be used, and it must also be able to withstand the high reservoir pressure. An example of an autonomous inflow control device utilizing such balls is disclosed in patent publication No. US 11,111,756 B2 to the applicant.

[0010] Disclosed herein is a method for making strong light-weight balls by the use of a 3D- printer. The balls are hollow with a thin 3D-printed wall made from a powder of for example Inconel®, titanium or any other material that can be 3D-printed from powder. Balls for use in the above-mentioned US 11,111,756, may typically have a diameter in the range of 15-30 mm, and a wall thickness typically in the range of 0.3 - 1.5 mm.

[0011] The balls are printed layer by layer using a common 3D-printing technique where a thin layer of the powder material is added to a building platform. There, a powerful laser beam melts the powder precisely at certain points specified by the computer-generated 3D model. Next, the construction platform is lowered, and another layer of powder is added. The material is melted once again, which connects it to the layer below at the specified points.

[0012] Some sagging may occur during printing, which can cause the balls to become oblate with uneven wall thickness. However, such a sagging can be corrected for in the ball design, such that the printed balls become perfectly spherical with even wall thickness. The correction may for example be based on measurements of the warp created by the 3D- printing process.

[0013] After the printing is completed, powder will be left inside the balls. In order to remove this powder, an aperture (open hole) is left on the top of the printed ball. After powder removal, the aperture has to be filled in a manner that maintains even wall thickness and ball strength. Hitherto, the aperture on the top of the ball has been filled by using a laser welding technique where a separate filler material is added during the welding process. However, experiences show that such a laser welding technique for filling the aperture does not provide the desired properties of the ball. The most critical discrepancy recurring is insufficient filling of the aperture, i.e., the depth of the weld appears to be insufficient.

[0014] Publication EP 3888820 Al discloses a method for manufacturing an object comprising an opening that communicates with a hollow internal space. The method may include a step of discharging a metal powder from the internal space and mounting a plug in the opening and welding the plug to the object.

[0015] Publication FR 3026034 Al discloses additive fabrication of hollow bodies by selective melting of powder such as e.g. Selective Laser Sintering. The method includes the formation of a hole for enabling removal of unsintered powder from the interior of the item. The hole is shaped so that the opening is smaller on the inner surface compared to the outer surface. After the powder has been discharged, the hole is closed by methods such as welding, brazing, or soldering.

[0016] There is therefore a need for an improved method of filling the aperture in the top por- tion of a 3D-printed ball.

[0017] The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

[0018] The object is achieved through features, which are specified in the description below and in the claims that follow.

[0019] The invention is defined by the independent patent claims. The dependent claims define advantageous embodiments of the invention.

[0020] In a first aspect of the invention there is provided a method for providing a hollow body, wherein the method comprises:

[0021] - creating the hollow body by means of an additive manufacturing apparatus, wherein the hollow body being created with at least one aperture in a portion of the hollow body to allow extraction of a powder from within the hollow body,

[0022] - creating filler material adjacent to the at least one aperture for filling the at least one aperture, wherein the filler material is created by the additive manufacturing apparatus;

[0023] - extracting any powder from within the hollow body; and

[0024] - disconnecting a powder supply to the additive manufacturing apparatus, and melting the filler material by means of a laser forming part of the additive manufacturing apparatus, wherein the laser is programmed to repeatedly print a plurality of imaginary disks at the exact same location.

[0025] By melting the filler material by means of a laser forming part of the additive manufacturing apparatus, the hollow body is surrounded by protected atmosphere, typically an ar- gon-atmosphere. Thereby a substantially perfect welding atmosphere is provided. Further, by using the laser of the additive manufacturing apparatus to melt the filler material, the filler material is melted with high precision and on the exact same position as the body was created. It should be mentioned that no powder is supplied to the hollow body when melting the filler material.

[0026] Thus, the filler material is melted by a process wherein a beam of the laser of the additive manufacturing apparatus is programmed to repeatedly print a plurality of sub-disks at the exact same location. Thereby, the melting process imitates an additive manufacturing process, but with the differences that no powder is added, and the beam of the laser is programmed to sweep the exact same area repeatedly during melting of the filler material, meaning that the so-called building platform of the additive manufacturing apparatus is stationary during the repeated melting process of the filler material.

[0027] Preferably, the at least one aperture is created to be smaller at an inner surface of the hollow body than at an outer surface of the hollow body. Thus, the at least one aperture may be defined by a slanted surface between the inner surface of the hollow body than at the outer surface of the hollow body. Preferably, said surface may have a conical shape.

[0028] A slanted surface facilitates positioning of the filler material, in that the filler material may be created as protrusions extending outwardly from a portion of a perimeter the of the at least one aperture between the inner surface of the hollow body and the outer surface of the hollow body.

[0029] Preferably, the method may comprise creating the filler material by means of a plurality of mutually spaced elements of filler material for the aperture or each of the apertures. An advantage of creating a plurality of elements of mutually spaced filler material, is a larger surface area of the filler material. A larger surface of the filler material facilitates faster melting of the filler material when exposed to the laser beam.

[0030] The method may comprise, prior to exposing the filler material to the laser beam of the additive manufacturing apparatus, heating the hollow body. By heating the hollow body, gas within the hollow body expands. When the gas expands, some of the gas will evacuate through the at least one aperture. Thereby, a risk of gas penetrating through the melted filler material is considerably reduced. A gas penetrating through the filler material when being in melted state may be detrimental to the quality of the weld.

[0031] Creating the hollow body with one aperture, or two or more apertures, depends inter alia on the size and the complexity of the geometry of the hollow body. For a small hollow body having a form of a ball, for example a ball for use in an autonomous inflow control device as disclosed in the publication US 11,111,756 mentioned above, it may be suffi- cient with only one aperture to be able to extract powder from within the body. However, even for such a small ball it may be convenient with two or more apertures since two or more apertures allows for "blowing" powder out of the hollow body. For a hollow body having a form or size wherein extracting powder by means of gravity is inconvenient due to time needed for extracting powder, or being impractical for other reasons, two or more apertures are preferred.

[0032] In a second aspect of the invention, there is provided a hollow body created by means of the method according to the first aspect of the invention. The hollow body may be a ball.

[0033] In a third aspect of the invention, there is provided an autonomous inflow control device comprising a hollow body according to the second aspect of the invention. The autonomous inflow control device may for example be the valve disclosed in patent publication US 11,111,756 B2 to the applicant.

[0034] In the following is described an example of a preferred embodiment illustrated in the accompanying drawings, wherein:

[0035] Fig. 1 shows a cut through a top portion of a hollow body provided with an aperture and filler material protruding from a periphery of the aperture;

[0036] Fig. 2 shows in perspective a top portion of the hollow body provided with an aperture and filler material protruding from a periphery of the aperture;

[0037] Fig. 3 shows in a smaller scale a ball prior to melting the filler material, and a programmed imaginary operation layer for the laser; and

[0038] Figs. 4a - 4c show in larger a scale a melting process of the filler material.

[0039] Any positional indications refer to the position shown in the figures.

[0040] In the figures, same or corresponding elements are indicated by same reference numer- a Is. For clarity reasons, some elements may in some of the figures be without reference numerals.

[0041] A person skilled in the art will understand that the figures are just principal illustrations. The relative proportions of individual elements may also be distorted.

[0042] In the figures, reference numeral 1 denotes a hollow body, here in the form of a hollow ball 1, crated by means of a process that includes an additive manufacturing apparatus (not shown). In the following the process is denoted 3D-printing.

[0043] Filler material 3, in the figures shown as four vertical rods 3 near an aperture 5 having conical shape, has been printed when printing the ball 1. The aperture 5, which has also been printed when printing the ball, is created to be smaller at an inner surface 10 of the hollow body 1 than at an outer surface 11 of the hollow body 1. The rods 3, which in the embodiment shown protrude upwardly from a perimeter of the aperture 5 between the inner surface 10 of the hollow body 1 and the outer surface 11 of the hollow body 1 as seen for example in Fig. 2, serve as filler material in the laser welding process according to the method where the laser of the 3D-printer itself is used as laser welder. This means that after powder removal, the ball 1 is put back onto a so-called building platform inside the 3D-printer.

[0044] To melt the rods 3, i.e., to fill the aperture 5 by welding, the 3D-printer is programmed to "print" a thin disc-shaped layer that intersects the rods 3, wherein the disc-shaped layer has a diameter slightly larger than the top diameter 5' of the conical aperture, as best seen in Figures 4a-4c. The instructed print area for the laser L is indicated by dotted lines in Fig. 3 and shown as an imaginary disk D in Figures 4a-4b. It should be noted that the thickness or height of the disc D is shown exaggerated for illustrative purpose. A person skilled in the art will appreciate that a program of the 3D-printer requires that all objects to be printed have a volume. Thus, the imaginary disk D to be "printed" must have an area and a thickness.

[0045] To melt the rods 3, the 3D-printer is programmed to repeatedly print a predetermined number of sub-disks at the exact same position so that the sub-disks perfectly overlap each other. During the melting operation of the rods 3, i.e., the welding process, the laser of the 3D-printer repeatedly sweeps a bottom surface area of all sub-disks, one by one, until all of the predetermined number of sub-disks have been printed. Each of the subdisks is, as mentioned above, printed at the exact same position, meaning that the swept area of all sub-disks is at the same elevation. Thus, contrary to an ordinary printing process for creating an object, wherein a so-called building platform of the additive manufacturing apparatus is lowered for each printing layer, the building platform is kept stationary throughout the process of printing the predetermined number of the sub-disks to provide the imaginary disk D.

[0046] When the welding process commences, there is no powder on the building platform, and the powder source is disconnected or emptied, such that the 3D-printer ends up sweeping through a "volume" of the imaginary disc D with its laser beam, as explained above, without actually printing anything. This adds heat to the swept area, and the rods 3 melt and fill the aperture 5.

[0047] Fig. 4a illustrates a start of the welding process and shows a programmed operating area (the disk D) for the laser of the 3D-printer. As mentioned above, the thickness or height of the disk D is shown exaggerated. Figures 4b and 4c illustrate by arrows how the four rods 3 melt when subject to the laser beam of the 3D-printer when "printing" the sub-disks without any powder being supplied. Fig. 4c illustrates how the molten bath 3' fills the aperture 5. For clarity, the imaginary disk D shown in fig. 4b is not shown in fig. 4c.

[0048] In a process of filling an aperture 5 for a ball intended for use in an autonomous inflow control device as disclosed in the publication US 11,111,756, the number of sub-disks was seventeen, i.e., the beam of the laser L of the 3D-printer swept the exact same area seventeen times without adding any powder. The time needed for this welding operation was about two seconds.

[0049] The bottom of the conical aperture 5 has sufficiently small diameter to prevent molten rod material from penetrating into the internal ball volume. A diameter of the bottom of the aperture may for example be in the range of 0.8 - 1.2 mm. When melting the rods 3 by the laser beam of the additive manufacturing apparatus, heat is added, as mentioned above. While heat is added, gas trapped inside the ball will expand and evacuate through the molten rod material. Such an evacuation of gas may be detrimental to the weld because it may lead to rupture or uneven wall thickness and therefore a weak point. This can be avoided by pre-heating the ball such that gas expands and partly evacuates before the welding process commences. The 3D-printer may be used for this pre-heating operation, too.

[0050] The method according to the invention may also be applicable for other geometries than balls. The number of rods 3 can be different from four, and they may have a shape being different from the circular rods 3 shown in Fig. 2. The four rods 3 shown in Fig. 2 have a larger combined surface area than for example two rods comprising the same total volume of filler material. The larger surface area of the rods, the better with respect to the melting process. The additive manufacturing apparatus may be programmed for providing individual imaginary discs having different shapes and thicknesses. Typically, if the thickness is increased, the number of imaginary discs placed at the same location can be reduced accordingly such that the total amount of energy becomes similar.

[0051] From the disclosure above, it will be clear that the process of printing the hollow body, and the subsequent process of welding the aperture provided during the printing process by melting the printed filler material, is provided solely by means of the additive manufacturing apparatus. Thus, the process of completing the hollow body is based on programming the additive manufacturing apparatus. Therefore, the method according to the invention provides an even quality that is difficult, if not impossible, to achieve by a prior art method.

[0052] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise", and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

C l a i m s1. A method for providing a hollow body (1), the method comprises:- creating the hollow body (1) by means of an additive manufacturing apparatus, wherein the hollow body (1) being created with at least one aperture (5) in a portion of the hollow body (1) to allow extraction of a powder from within the hollow body (1), the method further comprising:- creating filler material (3) adjacent to the at least one aperture (5) for filling the at least one aperture, wherein the filler material (3) is created by the additive manufacturing apparatus;-extracting any powder from within the hollow body;- disconnecting a powder supply to the additive manufacturing apparatus, and melting the filler material (3) by means of a laser (L) forming part of the additive manufacturing apparatus, c h a r a c t e r i s e d i n that the laser (L) is programmed to repeatedly print a plurality of imaginary disks (D) at the exact same location.

2. The method according to claim 1, wherein the at least one aperture (5) is created to be smaller at an inner surface of the hollow body (1) than at an outer surface of the hollow body (1).

3. The method according to claim 1 or 2, wherein the filler material (3) is created as a protrusion extending outwardly from a portion of the at least one aperture (5) between an inner surface of the hollow body (1) and an outer surface of the hollow body (1).

4. The method of any of the any one of the preceding claims, comprising creating the filler material (3) by means of a plurality of mutually spaced elements of filler material (3) for the aperture (5) or each of the apertures.

5. The method according to any of the preceding claims, wherein the method further comprises, prior to melting the filler material (3), heating the hollow body (1).

6. A hollow body (1) created by means of the method according to any one of the preceding claims.

7. The hollow body (1) according to claim 6, wherein the hollow body is a ball (1).

8. An autonomous inflow control device comprising a hollow body (1) according to claim 6 or 7.

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