JP7207020B2 - Method for manufacturing metal article having three-dimensional structure - Google Patents

Description

The following disclosure relates to a method of manufacturing a metal article having a three-dimensional structure, and more particularly to a three-dimensional additive manufacturing process that includes efficiently removing supports for supporting overhang structures.

Three-dimensional additive manufacturing is a set of techniques for manufacturing articles having three-dimensional structures, commonly known under the name of 3D printing. Three-dimensional additive manufacturing has been particularly successful as a technology for modeling resin, and its equipment is commercially available for general consumers.

In the case of metals, unlike resins, means such as photo-curing and adhesion cannot be normally used, so the available shaping means are limited. Currently, methods of sintering or melting metal powders are common, examples of which include electron beam additive manufacturing, laser sintering, laser melting, and the like. According to these methods, for example, pure metal or alloy powder is leveled in a thin layer (bed) in a vacuum, and solidified by selectively sintering or melting the powder by irradiation with an electron beam or laser. By repeating this process, a three-dimensional metal article is formed in layers. Patent Literature 1 discloses a related technique.

Japanese Patent Publication No. 2009-544501

Metal powder is easily deformed during molding, so if you try to mold a structure that includes an overhang, it is necessary to include a member called a support that supports it so that it does not collapse. Also, solidification of the powder is not always completely selective, and pre-sintered powder tends to adhere to the periphery of the model. After molding, these must be removed, but since both the support and the pre-sintered body are made of the same material as the main body of the molded object, there is no simple means such as removing them by making use of the difference in physical properties. It depends. In addition, unlike resin, metal adheres firmly to the main body of the modeled object, so the removal work is extremely troublesome. That is, the need to remove the support and the pre-sintered body is a factor that significantly impairs productivity. Alternatively, one of the advantages of the three-dimensional additive manufacturing method is that a structure having a cavity inside can be easily manufactured, but there is a difficult problem that it is difficult to even remove the support inside the cavity. The techniques disclosed below have been made to solve these problems.

According to one aspect, a method for manufacturing a metal article having a three-dimensional structure includes three-dimensional additive manufacturing of a structure integrally including a plurality of plate-like supports that support the structure and a prototype of the article, immersing the structure in an etchant to remove the support , wherein in the step of additively manufacturing the structure, the edge of the support has a plurality of tooth profiles or teeth to bond only at the vertices thereof to the master, respectively; Shaping the structure in a wavy pattern and arranging the supports to form flow paths for the etchant.

Preferably, in the step of three-dimensional additive manufacturing, the structure is shaped such that the original mold includes excess material. More preferably, in the step of three-dimensional layered manufacturing, the structure is shaped so that the excess thickness is the same as or thinner than the support. More preferably, in the step of removing, the corrosive liquid is caused to flow along the channel. Alternatively preferably, one or more of the plurality of supports are positioned inside the master during the three-dimensional additive manufacturing step.

The etchant not only allows surface finishing of the shaped metal article, but also allows the support to naturally separate from the original mold, allowing the finishing process and the support removal process to be performed in parallel, significantly improving productivity. .

FIG. 1 is a conceptual elevation view of a three-dimensional metal additive manufacturing apparatus. FIG. 2 is an example of a target shape for three-dimensional metal additive manufacturing of an article, and is a view showing a cross section in elevation and a side view thereof, and the cross section of FIG. Corresponds to the IIA line. FIG. 3 is an enlarged partial elevation cross-sectional view of the target shape. FIG. 4 is a cross-sectional side view of the target shape, taken from line IV-IV of FIG. FIG. 5 is a schematic cross-sectional view of a modeled object and metal powder in the middle of modeling. FIG. 6 is a diagram showing a cross-section and a side view of a model taken out of metal powder. FIG. 7 is a schematic diagram showing a mode in which a model is immersed in a corrosive liquid stored in a liquid bath. FIG. 8 is an example of a three-dimensional metal additive manufacturing article, showing a cross section in elevation and a side view thereof.

Several exemplary embodiments are described below with reference to the accompanying drawings.

A method of manufacturing a metal article having a three-dimensional structure according to this embodiment generally comprises three-dimensional additive manufacturing of a structure and immersing the structure in an etchant. The structure integrally includes a plurality of plate-like supports that support the structure and the prototype of the article, but by immersing the structure in the corrosive liquid, the joints between the prototype and the supports are corroded, and the supports are naturally formed. to break away from the prototype. Also, the surface of the prototype becomes rough due to molding, but the surface is finished by corrosion. That is, the steps of surface finishing the shaped metal article and removing the support proceed in parallel.

Any known method can be used for three-dimensional additive manufacturing of a metal article, but for the sake of convenience, the present embodiment will be described below based on a process that utilizes a powder bed type electron beam additive manufacturing method. explain. Of course, other suitable methods could be used, such as by deposition, and instead of electron beams, lasers or other high energy particle streams could be used to sinter or melt the powder. Electron beam additive manufacturing is faster than laser manufacturing, but the surface of the as-built structure is relatively rough and requires finishing work, so it is particularly suitable for applying this embodiment. Conceivable.

Referring to FIG. 1, a three-dimensional metal additive manufacturing apparatus 1 generally includes a vertically extended housing 3, an electron gun 5 fixed to the top thereof, and an electron lens 7 for converging an electron beam B. and an elevating table 13 on which the metal powder M is placed.

The housing 3 is configured so that the inside can be kept in an appropriate vacuum. The electron gun 5 for emitting the electron beam B, the hopper 9 for supplying the metal powder M, the recoater 11 for leveling the metal powder M, and the elevating table 13 for placing the metal powder M are all placed in such a vacuum. Impurities are prevented from entering metal articles. The lifting table 13 is controllably lifted by a lifting device 15 .

The metal powder M consists of a pure metal such as pure titanium, or an alloy such as Ti-6Al-4V alloy, but may be any metal powder that can be sintered or melted by an electron beam. In the case of alloys, pre-alloyed powders are typically utilized, but mixtures of dissimilar metals may also be utilized and alloyed during sintering or melting.

The device 1 also comprises a controller 17 electrically connected to each element thereof. The controller 17 is generally a general-purpose computer equipped with a storage such as a hard disk drive or solid state drive, a temporary storage device such as a random access memory, and an arithmetic element, and controls each element in combination with appropriate algorithms. . The storage can store three-dimensional CAD (Computer Aided Design) data for modeling as well as programs for executing such algorithms. Based on the stored data, the controller 17 controls the electron gun 5, the electron lens 7, the hopper 9, the recoater 11 and the lifting device 15, thereby performing the three-dimensional layered manufacturing described below.

This embodiment will be described below based on an example of manufacturing an article 100 shown in FIG. The article 100 has a cavity H open to the outside and, as shown in FIG. 8(a), has an overhang in which the upper portion falls to the right in the figure with respect to its base. Needless to say, this is merely an example for convenience of explanation, and metal articles having various three-dimensional structures can be manufactured according to this embodiment.

Referring to FIG. 2, first, three-dimensional CAD data of the structure 21, which is a semi-finished product of the article 100, is prepared. The structure 21 comprises a master 23 approximating the shape of the article 100, a support 25 supporting the base of the master 23, a support 27 supporting the overhang, and a support 29 supporting the cavity H within it. including.

Support 25 is a thin, three-dimensional structure along the base of model 23 and may be unitary, as shown in the figures, or may consist of multiple pieces. Supports 27 and 29 are each a plurality of relatively thin plates appropriately aligned to support the overhang and cavity H, respectively. Each plate of support 27 may also consist of two or more pieces 27A, 27B, and each plate of support 29 may likewise consist of pieces 29A, 29B.

The placement and orientation of supports 25, 27, 29 are determined solely by mechanical considerations to support the structure, but may also include fluid considerations. That is, the supports 25, 27, 29 can be arranged in the direction in which the corrosive liquid flows or circulates in the later-described step of being immersed in the corrosive liquid. In the example shown in FIG. 2, a plurality of supports 27 are arranged in a direction from the entrance to the exit of the opening, and the support 25 surrounds the entrance (or exit) of the opening, in which direction the corrosive liquid flows. Construct the flow path. Similarly, a plurality of supports 29 are oriented along this direction to form a flow path for the etchant. Such an arrangement is advantageous for allowing fresh etchant to flow through each part of the model, thereby enabling uniform finishing. Such an arrangement is also particularly advantageous in delivering fresh etchant to the interface between the master 23 and the supports 27, 29, thereby encouraging the supports to erode away from the master 23.

Notwithstanding the above description, the placement, orientation and materials of supports 25, 27 and 29 can be determined based on individual considerations. For example, support 29 can be oriented along the direction of etchant flow and support 27 can be oriented differently. For example, regarding the support 27, it is possible to adopt a grid-like shape and arrangement by giving priority to consideration of dynamics or thermal deformation. Of course, it could also be the other way around, or various combinations are possible, such as only a portion of each of the supports 27, 29 having a rheological arrangement and other portions having a different arrangement.

The supports 25, 27, 29 may be fully bonded to the pattern 23 at their edge surfaces, but may have structures around the bonding to facilitate disengagement. For example, according to the example shown in FIG. 3, the edges of the supports 27, 29 delineate a number of teeth or corrugations 27S, 29S, each of which joins the pattern 23 only at its apex. With such a structure, the points of attachment tend to disappear due to corrosion, or the areas around the points of attachment tend to corrode preferentially due to their large surface area, thus causing the supports 25, 27, 29 to separate from the master 23 early. It is advantageous for

Mainly referring to FIG. 4, the original mold 23 can have a thickness T that includes an excess thickness slightly larger than the target shape in anticipation of the corrosion allowance. Here, the excess thickness can be the same as or about the same as the thickness t of the supports 25, 27, 29. When the supports 27 and 29 are removed or disappear, it can be determined that finishing is completed. Alternatively, if the supports 25, 27, 29 and the prototype 23 are point-bonded as described above, the supports 25, 27, 29 will come off early, so the excess thickness may be thinner.

Three-dimensional CAD data of the structure 21 as described above is created and input to the controller 17 . The controller 17 controls the three-dimensional metal additive manufacturing apparatus 1 based on the input data.

That is, referring to FIG. 5 in combination with FIG. 1, the metal powder M supplied from the hopper 9 is horizontally and evenly flattened by the recoater 11 to form a powder bed MB, which is a thin powder layer. Alternatively, the recoater 11 itself may have the function of supplying the metal powder M. An electron beam B emitted from an electron gun 5 and converged by an electron lens 7 is incident on the powder bed MB, selectively melting and solidifying the powder bed MB. Under the control of the controller 17, the electron beam B is scanned two-dimensionally, thereby forming one layer.

When one layer of modeling is completed, the elevating table 13 is lowered by one layer under the control of the controller 17, and the metal powder M supplied from the hopper 9 is leveled horizontally and evenly by the recoater 11 to form a new layer. A powder bed MB is laminated on top of the previous layer. The electron beam B is scanned again under the control of the controller 17 to form the next layer.

By repeating the above steps, the structure 21 is gradually three-dimensionally laminated. As can be easily understood from FIG. 5, a support 27 is formed in advance immediately below the overhang portion in the structure 21 according to the CAD data. Since this supports portions of the overhangs that will be formed later, the structure 21 is additively manufactured without compromising its shape.

The heat input by electron beam B is not necessarily confined to its focal point, but has a thermal effect on its surroundings. Therefore, the metal powder M around the shaped body 31 also tends to be slightly sintered or melted. The modeled body 31 immediately after being layered and manufactured often takes a form in which the entirety of the structure 21 is covered with the temporary sintered body 33 as shown in FIG. 6, for example. Whether or not the pre-sintered body 33 adheres and its amount depend on various conditions such as the properties of the metal powder M, the energy density of the electron beam B, and the like. Moreover, the cavities in the structure 21 are filled with the metal powder M regardless of whether or not the temporary sintered body 33 adheres.

Since the temporary sintered body 33 is normally hardened only by a very weak cohesive force, it can be easily removed by air blowing, blasting, brushing or manual work. However, since the modeled body 31 has such a form immediately after being layered and manufactured, its surface inevitably has a considerable degree of roughness, and it is often not suitable for practical use as it is shaped. Finishing is therefore usually necessary to obtain a smooth surface.

After the temporary sintered body 33 and the metal powder M are removed, or with the shaped body 31 still attached, the shaped body 31 is housed in a suitable basket 43 and immersed in the corrosive liquid 45 stored in the liquid tank 41 . When the metal powder M is pure titanium or a titanium alloy, the corrosive liquid 45 is nitric acid or hydrofluoric acid, depending on the type of metal.

The corrosive liquid 45 may be left to convection caused by bubbling or the like, but may be given a flow using a pump, screw, or the like. The orientation of the modeled body 31 in the cage 43 is determined in consideration of the direction of flow of the corrosive liquid 45 . As already mentioned, the supports 25, 27, 29 arranged in the direction of flow guide the corrosive liquid 45, so that the entire molded body 31 is evenly corroded, and the connection points with the supports 25, 27, 29 are preferentially attached. corroded by

The supports 25, 27, 29 are released from the structure 21 at the same time as the finish machining by the etchant is completed, thereby obtaining the article 100 shown in FIG. According to this embodiment, since the support can be removed in parallel with the finishing process without requiring a special process for removing the support, good productivity can be expected.

Although several embodiments have been described, modifications or variations of the embodiments are possible based on the above disclosure.

A method for three-dimensional metal additive manufacturing is provided that does not require a special step for removing the support.

1 three-dimensional metal additive manufacturing apparatus 3 housing 5 electron gun 7 electron lens 9 hopper 11 recoater 13 lifting table 15 lifting device 17 controller 21 structure 23 prototype 25, 27, 29 support 27A, 27B, 29A, 29B piece 27S, 29S Tooth shape or corrugation 31 Shaped body 33 Temporary sintered body 41 Liquid tank 43 Basket 45 Corrosive liquid 100 Article B Beam H Cavity M Metal powder MB Powder bed t Thickness T Thickness

Claims (5)

A method of manufacturing a metal article having a three-dimensional structure, comprising:
Three-dimensional additive manufacturing of a structure integrally including a plurality of plate-shaped supports that support the structure and the prototype of the article,
immersing the structure in an etchant to remove the support , the method comprising:
In the step of three-dimensional additive manufacturing, the structure is shaped so that the edges of the support form a plurality of tooth shapes or corrugations so that each edge of the support is connected to the master only at its vertices. and arranging to form a. 2. The method of claim 1, wherein in the additively three-dimensional manufacturing step, the structure is built such that the master includes excess material. 3. The method of claim 2, wherein the three-dimensional additive manufacturing step builds the structure such that the excess wall is the same thickness or thinner than the support. 2. The method of claim 1 , wherein the step of removing comprises flowing the etchant along the flow path. 5. The method of any one of claims 1 to 4 , wherein the step of additively manufacturing includes placing one or more of the plurality of supports inside the master.

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