JP7554138B2 - Layered manufacturing method and layered manufactured body - Google Patents

Description

This disclosure relates to an additive manufacturing method and an additive manufactured body.

In order to create an overhanging part with a surface facing downward in the metal lamination direction using 3D additive manufacturing, which layers metal to create a product, the overhanging part is created and supports that support the overhanging part are also created. The supports need to be removed after creation, but in narrow areas that cannot be accessed by tools, it is often difficult to remove the supports using tools. As a method other than physically removing the supports using tools, Patent Document 1 describes a method of burning and removing supports using a thermal deburring device for burning and removing burrs generated during machining.

International Publication No. WO 2020/089303

However, according to the inventors' study of a method for burning and removing supports using a thermal deburring device, when the support has a shape that extends long in the depth direction relative to the surface exposed from the overhanging portion, the support can be burned and removed up to a certain distance in the depth direction from the exposed surface, but a phenomenon was observed in which part of the support remains at the back in the depth direction.

In view of the above, at least one embodiment of the present disclosure aims to provide an additive manufacturing method and an additive manufactured body that are capable of removing supports that have a shape that extends long in the depth direction.

In order to achieve the above object, the additive manufacturing method according to the present disclosure is an additive manufacturing method for forming a product by stacking metal, in which a semi-finished product of the product includes at least one overhang portion having a surface facing downward in the stacking direction of the metal, and a support supporting the overhang portion, the support having an exposed surface where the support is exposed from the overhang portion, and the additive manufacturing method includes a step of stacking the metal to form the semi-finished product, a step of forming at least one cavity portion in the support extending from the exposed surface toward the depth direction of the support, and a step of burning and removing the support.

In addition, the additive manufacturing object according to the present disclosure is a metal additive manufacturing object comprising at least one overhang portion having a surface facing downward in the stacking direction of the metal, and a support supporting the overhang portion, the support having an exposed surface where the support is exposed from the overhang portion, at least one cavity portion extending from the exposed surface toward the depth direction of the support is formed in the support , and a fuse is inserted into the at least one cavity portion .

The additive manufacturing method and additive manufacturing body disclosed herein can allow the flame to reach the back of the cavity and burn the supports located at the back of the support in the depth direction, making it possible to remove supports that have a shape that extends long in the depth direction.

FIG. 2 is a front view of a semi-finished product (additive manufactured body) manufactured by the additive manufacturing method according to the first embodiment of the present disclosure. FIG. 1 is a front view of a product manufactured by an additive manufacturing method according to a first embodiment of the present disclosure. 2 is a cross-sectional view taken along line III-III in FIG. 1. 1 is a flowchart of an additive manufacturing method according to a first embodiment of the present disclosure. 11 is a flowchart of some steps of a modified example of the additive manufacturing method according to the first embodiment of the present disclosure. 11 is a cross-sectional view of a semi-finished product (additive manufactured body) manufactured by the additive manufacturing method according to the second embodiment of the present disclosure. FIG. FIG. 11 is a cross-sectional view of a semi-finished product (additive manufactured body) manufactured by the additive manufacturing method according to embodiment 3 of the present disclosure. 13A to 13C are front views of a first lid portion, a second lid portion, and a third lid portion used in an additive manufacturing method according to embodiment 3 of the present disclosure. 11 is a flowchart showing some steps of an additive manufacturing method according to embodiment 3 of the present disclosure. 13A to 13C are diagrams for explaining the process of burning off supports in step S3 of the additive manufacturing method according to the third embodiment of the present disclosure. 13 is a cross-sectional view of a modified example of a semi-finished product manufactured by the additive manufacturing method of the present disclosure. FIG.

The additive manufacturing method and the additive manufactured body according to the embodiments of the present disclosure will be described below with reference to the drawings. Each embodiment described below shows one aspect of the present disclosure and does not limit the present disclosure, and can be modified as desired within the scope of the technical concept of the present disclosure.

(Embodiment 1)
<Configuration of product and layered object according to embodiment 1 of the present disclosure>
As shown in Fig. 1, an additive manufacturing object 1 according to the first embodiment of the present disclosure is a semi-finished product manufactured by stacking metals, and includes an overhanging portion 2 having a surface facing downward in the metal stacking direction, and a support 3 supporting the overhanging portion 2. By removing the support 3 from the semi-finished product by an operation described below, a product 10 as shown in Fig. 2 is completed. As shown in Fig. 1, the support 3 has a configuration with a larger specific surface area or a smaller apparent heat capacity than the overhanging portion 2, and has, for example, a lattice structure including many small cavities.

The support 3 has an exposed surface 3a exposed from the overhang portion 2. As shown in FIG. 3, the support 3 has a shape that extends long from the exposed surface 3a in the depth direction. The support 3 has a cavity 4 formed so as to extend from the exposed surface 3a toward the back side in the depth direction of the support 3. Although FIG. 3 shows one cavity 4 formed, two or more cavities 4 may be formed. In addition, the length of the cavity 4 is arbitrary as long as it extends from the exposed surface 3a toward the depth direction of the support 3, and may have, for example, 1/3, 1/2, or 2/3 of the length of the depth direction of the support 3, or may penetrate the support 3 in the depth direction. In addition, the cavity 4 is not necessarily limited to a shape that extends straight, and may have a shape that has some curvature or bend. Furthermore, the inner peripheral surface that defines the cavity 4 has the same configuration as the lattice structure of the support 3. In other words, to form cavity 4, a surface that is denser than the lattice structure (a surface that does not contain many cavities) is not formed.

<Additive manufacturing method according to embodiment 1 of the present disclosure>
Next, an additive manufacturing method according to the first embodiment of the present disclosure will be described with reference to Figures 1 to 3 and the flowchart of Figure 4. In step S1 of this additive manufacturing method, metal is laminated to form an additive manufactured body 1 as a semi-finished product. For example, a powder bed type additive manufacturing device (3D printer) can be used to laminate metal by a known method used in three-dimensional additive manufacturing, such as laser melting or electron beam melting.

In step S2 following step S1, a hollow portion 4 is formed in the support 3. As in the flowchart of FIG. 3, in a form in which step S2 is performed after step S1, the hollow portion 4 is machined (e.g., drilled) in the support 3 after the additive manufacturing body 1 is manufactured. Step S2 is not limited to this form, and may be a form in which steps S1 and S2 are performed simultaneously, that is, a form in which the hollow portion 4 is formed during the manufacturing of the additive manufacturing body 1, or in other words, a form in which the support 3 is manufactured so that the hollow portion 4 is included in the support 3. In the former form, the support 3 can be designed without considering the hollow portion 4, and therefore the design of the support 3 can be simplified compared to the latter form. On the other hand, in the latter form, the hollow portion 4 is formed during the manufacturing of the additive manufacturing body 1, and therefore the number of steps in the additive manufacturing method can be reduced compared to the former form.

In step S3 following step S2, the support 3 is burned to remove it from the layered product 1. Step S3 can be performed, for example, using a known thermal deburring device. This device has a configuration in which a container having a space capable of accommodating the layered product 1 is provided with a supply path for supplying a combustible gas (e.g., methane) and oxygen to the space, and a plug for emitting sparks is provided within the space. The layered product 1 is accommodated in the space inside the device, and the flame generated by the combustion of the combustible gas in the space causes metallic combustion of the support 3, thereby embrittling the support 3 and making it easy to remove it from the layered product 1. After removing the layered product 1 from the device, the embrittled support 3 is removed from the layered product 1 to complete the product 10.

In the above-mentioned study by the present inventors, when the support 3 has a shape that extends long in the depth direction relative to its exposed surface 3a as shown in FIG. 3, a phenomenon was observed in which a part of the support 3 remains at the back side in the depth direction. The present inventors considered that the cause of this was that when the flame passes through the support 3 on the front side, heat is absorbed by the support 3, causing the flame to disappear and the flame cannot advance further back. To solve this problem, in the additive manufacturing method according to embodiment 1 of the present disclosure, a hollow portion 4 is formed in the support 3.

When a cavity 4 is formed in the support 3, the cavity 4 becomes a path for the flame, and the flame can reach the back of the cavity 4 and burn the support located at the back of the support 3 in the depth direction, so that the support 3 having a shape that extends long in the depth direction can be removed.

<Modification of the additive manufacturing method according to the first embodiment of the present disclosure>
1, the cross-sectional shape of the cavity 4 is depicted as a square, but is not limited to a square, and may be a rectangle, a polygon other than a square, a circle, an ellipse, or any other cross-sectional shape. However, the size of the opening 4a is important so that the flame can reach the back of the cavity 4 without being extinguished at the opening 4a in the exposed surface 3a of the cavity 4. For this reason, the additive manufacturing method according to the first embodiment preferably includes a step of determining the size of the opening 4a before step S1.

Next, step S10 for determining the size of the opening 4a will be described in detail with reference to FIG. 5. Step S10 includes step S11 for acquiring a range of Peclet numbers based on the shape of the opening 4a, and step S12 for calculating the size of the opening 4a so that the Peclet number is within the range acquired in step S11. In step S11, the cross-sectional shape of the cavity 4 formed in the support 3 is specified in advance, and the range of Peclet numbers within which the flame does not disappear at the opening 4a of the cavity 4 having the specified cross-sectional shape in the state of the flame in the thermal deburring device to be used is acquired in advance, for example by experiment.

The Peclet number is defined by the following formula (1): where Pe _1,u is the Peclet number, ρ _u is the density of the unburned mixture, SL is the laminar burning velocity, C _p,u is the specific heat of the unburned mixture, δ _q1 is the quenching distance, and λ _u is the thermal conductivity of the unburned mixture.

The quenching distance δ _q1 is directly related to the size of the opening 4a. The quenching distance means the limit value of the representative dimension of the passage where quenching occurs. In other words, if the size of the opening 4a is larger than the quenching distance determined by the operation described later, the flame can reach the depths of the cavity 4 without being extinguished at the opening 4a.

The question arises as to what length the quenching distance should be for the opening 4a. If the shape of the opening 4a is a circle, the radius of the circle is the quenching distance. If the shape of the opening 4a is an ellipse, the minor axis of the ellipse is the quenching distance. If the shape of the opening 4a is a rectangle, the shortest distance of the perpendicular lines extending from the intersection of the two diagonals to each side is the quenching distance. If the shape of the opening 4a is any other polygon or arbitrary shape, the quenching distance is the shortest distance from the center of gravity of the shape to the edge that defines the opening 4a.

In step S11, the range of the Peclet number at which the flame does not disappear at the opening 4a of the cavity 4 having the specified cross-sectional shape is obtained. Then, in step S12, the quenching distance δ _q1 that brings the Peclet number into the range is calculated based on the above formula (1), and the size of the opening 4a in the specified cross-sectional shape of the cavity 4 that makes the quenching distance larger than the calculated value δ _q1 is determined.

This modified example reduces the risk of the flame disappearing at the opening 4a and allows the flame to reach the depth of the cavity 4, and since the supports 3 at the rear of the supports 3 in the depth direction can be burned, the supports 3 that have a shape that extends long in the depth direction can be removed.

(Embodiment 2)
Next, an additive manufacturing method according to embodiment 2 will be described. The additive manufacturing method according to embodiment 2 differs from embodiment 1 in that a fuse is inserted into the hollow portion 4. In embodiment 2, the same components as those in embodiment 1 are given the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, unless otherwise specified, the configuration of the modified embodiment of embodiment 1 can also be applied to embodiment 2.

<Configuration of Layered Object According to Second Embodiment of the Present Disclosure>
6 , in the layered object 1 according to the second embodiment of the present disclosure, a fuse 20 is inserted into the cavity 4, preferably all the way to the back of the cavity 4. The other configurations are the same as those of the first embodiment.

<Additive manufacturing method according to embodiment 2 of the present disclosure>
The additive manufacturing method according to the second embodiment of the present disclosure includes a step of inserting the fuse 20 into the cavity 4 before step S3 (see FIG. 4) of burning and removing the support 3. Other operations are the same as those of the first embodiment. When the fuse 20 is ignited by a flame, the fuse 20 burns toward the back of the cavity 4. As a result, in the cavity 4, the combustible gas is burned by the sparks scattered from the fuse 20 and a flame is generated, so that the flame can be reliably reached to the back of the cavity 4. In particular, even if the additive manufacturing method does not include step S10 and the size of the opening 4a is inappropriate or the state of the flame of the thermal deburring device changes due to an abnormality in the device, etc., and the flame disappears at the opening 4a, according to the second embodiment, the flame can be reliably reached to the back of the cavity 4.

(Embodiment 3)
Next, an additive manufacturing method according to embodiment 3 will be described. The additive manufacturing method according to embodiment 3 is a modification of embodiment 1 or 2 in which a plurality of hollow portions 4 are formed in the support 3. Below, embodiment 3 will be described by making such a modification to embodiment 1, but embodiment 3 can also be configured by making such a modification to embodiment 2. In embodiment 3, the same components as those in embodiment 1 are given the same reference numerals, and detailed description thereof will be omitted. Furthermore, unless otherwise specified, the configuration of the modified embodiment of embodiment 1 can also be applied to embodiment 3.

<Configuration of Layered Object According to Third Embodiment of the Present Disclosure>
7, in the layered product 1 according to the third embodiment of the present disclosure, a plurality of cavities 4 are formed in the support 3, i.e., one first cavity 31 and two second cavities 32, 32 that are shorter in length in the depth direction of the support 3 than the first cavity 31. The arrangement of the first cavity 31 and the second cavity 32 is not particularly limited, but for example, they can be formed in the support 3 so that the first cavity 31 is located between the two second cavities 32, 32. Both the first cavity 31 and the second cavity 32 form openings 31a and 32a in the exposed surface 3a. The other configurations are the same as those of the first embodiment.

<Additive manufacturing method according to embodiment 3 of the present disclosure>
The additive manufacturing method according to the third embodiment of the present disclosure differs from the first embodiment in step S3 (see FIG. 4), but the other steps are the same as those of the first embodiment. In the third embodiment, two types of lids, i.e., a first lid 33 and a second lid 34, as shown in FIG. 8, are used in step S3. The first lid 33 has a first through hole 33a that communicates with the first cavity 31 (see FIG. 7) when the first lid 33 is attached to the additive manufacturing body 1 (see FIG. 7) so as to close the exposed surface 3a (see FIG. 7). The second lid 34 has second through holes 34a, 34a that communicate with the second cavities 32, 32 (see FIG. 7) when the second lid 34 is attached to the additive manufacturing body 1 so as to close the exposed surface 3a.

As shown in FIG. 9, step S3 in the additive manufacturing method according to embodiment 3 of the present disclosure includes a preparation step S21 of preparing the first lid portion 33 and the second lid portion 34, a first burn-removal step S22 of burning and removing the support 3 with the first lid portion 33 attached to the additive manufacturing body 1, a second burn-removal step S23 of burning and removing the support 3 with the second lid portion 34 attached to the additive manufacturing body 1 after the first burn-removal step S22, and a third burn-removal step S24 of burning and removing the support 3 with neither the first lid portion 33 nor the second lid portion 34 attached to the additive manufacturing body 1 after the second burn-removal step S23.

As shown in FIG. 10, in the first burning removal step S22, the exposed surface 3a is closed by the first lid portion 33, so that only the inside of the thermal deburring device and the first cavity portion 31 are in communication through the first through hole 33a formed in the first lid portion 33. When a flame is generated inside the thermal deburring device in this state, the flame enters the first cavity portion 31 through the first through hole 33a and propagates to the back of the first cavity portion 31, causing the support 3 further inside than the back end of the first cavity portion 31 to burn, or a pressure wave or detonation is generated in the first cavity portion 31, destroying the support 3 further inside than the back end of the first cavity portion 31 due to the pressure wave. The layered product 1 can be removed from inside the thermal deburring device, and the embrittled or destroyed support 3 can be removed.

In the next second burning removal step S23, since the exposed surface 3a is closed by the second lid portion 34, only the inside of the thermal deburring device and the second cavity portion 32 are in communication through the second through hole 34a formed in the second lid portion 34. When a flame is generated inside the thermal deburring device in this state, the flame enters the second cavity portion 32 through the second through hole 34a and propagates to the back of the second cavity portion 32, causing the support 3 further inside than the back end of the second cavity portion 32 to burn, or detonation occurs in the second cavity portion 32 and the support 3 further inside than the back end of the second cavity portion 32 is destroyed by a pressure wave. The layered product 1 can be removed from inside the thermal deburring device, and the embrittled or destroyed support 3 can be removed.

The first burn-off step S22 and the second burn-off step S23 result in the support 3 at the rear side relative to the exposed surface 3a being removed. In the next third burn-off step S24, a flame is generated inside the thermal deburring device with neither the first lid portion 33 nor the second lid portion 34 attached to the layered object 1, and the remaining support 3 is embrittled by metal combustion caused by the flame. The layered object 1 is removed from inside the thermal deburring device and the embrittled support 3 is removed, thereby removing all of the supports 3 from the layered object 1 and producing the product 10 (see FIG. 2).

According to the third embodiment, it is possible to remove even supports 3 that extend long in the depth direction and have a large cross-sectional area in the depth direction.

In the third embodiment, there is one first cavity 31 and two second cavities 32, but this is not limiting, and the number of first cavities 31 and second cavities 32 can be changed as appropriate depending on the size of the support 3. Also, instead of forming two types of cavities with different lengths, three or more types of cavities with different lengths (i.e., a third cavity, etc.) may be formed depending on the depth length of the support 3.

In each of the first to third embodiments, as shown in FIG. 3, for example, the exposed surface 3a and the end surface of the layered product 1 where the exposed surface 3a is exposed are flush with each other, but this is not limited to the above. As shown in FIG. 11, the exposed surface 3a may be recessed in the depth direction relative to the end surface of the layered product 1. In the third embodiment, when the layered product 1 includes an exposed surface 3a of this type, it is preferable that the first lid portion 33 and the second lid portion 34 each have a surface that contacts the exposed surface 3a, and may be configured to have a protruding portion that fits into the recess of the layered product 1, and this protruding portion contacts the exposed surface 3a.

The contents described in each of the above embodiments can be understood, for example, as follows:

[1] An additive manufacturing method according to one aspect includes:
An additive manufacturing method for forming a product (10) by layering metal, comprising the steps of:
The semi-finished product (layered product 1) of the product (10) is
At least one overhang portion (2) having a surface facing downward in the lamination direction of the metal;
a support (3) that supports the overhang portion (2), the support (3) having an exposed surface (3a) where the support (3) is exposed from the overhang portion (2);
The additive manufacturing method includes:
A step (S1) of stacking the metal to form the semi-finished product (1);
A step (S2) of forming at least one cavity portion (4) in the support (3) extending from the exposed surface (3a) toward a depth direction of the support (3);
and a step (S3) of burning off the support (3).

According to the additive manufacturing method disclosed herein, the flame can reach the back of the cavity to combust the supports located at the back of the support in the depth direction, making it possible to remove supports that have a shape that extends long in the depth direction.

[2] A method for additive manufacturing according to another aspect is the additive manufacturing method according to [1],
The cavity (4) is formed during the shaping of the semi-finished product (1).

With this configuration, the cavity is formed during the molding of the semi-finished product, which reduces the number of steps in the additive manufacturing method compared to when the cavity is formed in the support after the semi-finished product is molded.

[3] A further aspect of the additive manufacturing method is the additive manufacturing method of [1],
The cavity (4) is formed in the support (3) after shaping of the semi-finished product (1).

This configuration allows the support to be designed without taking into account the cavity, simplifying the support design.

[4] A further aspect of the additive manufacturing method is the additive manufacturing method according to any one of [1] to [3],
The method further includes a step (S10) of determining a size of an opening (4a) of the cavity portion (4) on the exposed surface (3a) before the step (S1) of shaping the semi-finished product (1),
This step (S10) is
A step (S11) of obtaining a range of Peclet numbers based on the shape of the opening (4a);
and determining (S12) the size of the opening (4a) so that the Peclet number falls within the range.

This configuration reduces the risk of the flame disappearing at the opening and allows the flame to reach the back of the cavity, and since the supports at the back in the depth direction can be burned, supports that have a shape that extends long in the depth direction can be removed.

[5] A further aspect of the additive manufacturing method is the additive manufacturing method according to any one of [1] to [4],
The method further includes a step of inserting a squib (20) into the cavity (4) prior to the step (S3) of burning off the support (3).

This configuration allows the flame to reliably reach the back of the cavity and reliably combust the supports located at the back of the support in the depth direction, making it possible to remove supports that extend further in the depth direction.

[6] A further aspect of the additive manufacturing method is the additive manufacturing method according to any one of [1] to [5],
The cavity (4) includes at least one first cavity (31) and at least one second cavity (32) having a length in the depth direction shorter than that of the first cavity (31),
The step (S3) of burning and removing the support (3) comprises:
a preparation step (S21) of preparing a first lid portion (33) having a first through hole (33a) formed therein and communicating with the first cavity portion (31) when the first lid portion (33) is attached to the semi-finished product (1) so as to close the exposed surface (3a), and a second lid portion (34) having a second through hole (34a) formed therein and communicating with the second cavity portion (32) when the second lid portion (34) is attached to the semi-finished product (1) so as to close the exposed surface (3a);
a first burning and removing step (S22) of burning and removing the support (3) in a state where the first cover portion (33) is attached to the semi-finished product (1);
a second burn-off step (S23) of burning off the support (3) in a state in which the second lid portion (34) is attached to the semi-finished product (1) after the first burn-off step (S22);
After the second burn-off step (S23), a third burn-off step (S24) is included in which the support (3) is burned off without either the first lid portion (33) or the second lid portion (34) being attached to the semi-finished product (1).

This configuration makes it possible to remove supports that extend long in the depth direction and have a large cross-sectional area in the depth direction.

[7] A layered object according to one aspect,
A metal additive manufacturing body (1),
At least one overhang portion (2) having a surface facing downward in the lamination direction of the metal;
a support (3) that supports the overhang portion (2), the support (3) having an exposed surface (3a) where the support (3) is exposed from the overhang portion (2);
At least one cavity (4) extending from the exposed surface (3a) toward the depth direction of the support (3) is formed in the support (3).

The additive manufacturing body of the present disclosure allows the flame to reach the back of the cavity and combust the supports located at the back of the support in the depth direction, making it possible to remove supports that have a shape that extends long in the depth direction.

1. Laminated object (semi-finished product)
2 Overhang portion 3 Support 3a Exposed surface 4 Cavity portion 4a Opening 10 Product 20 Fuze 31 First cavity portion 32 Second cavity portion 33 First cover portion 33a First through hole 34 Second cover portion 34a Second through hole

Claims (7)

An additive manufacturing method for forming a product by layering metal, comprising the steps of:
The semi-finished products of the above-mentioned products are
At least one overhang portion having a surface facing downward in a lamination direction of the metal;
a support for supporting the overhang portion, the support having an exposed surface where the support is exposed from the overhang portion;
The additive manufacturing method includes:
building up the metal to form the blank;
forming at least one cavity in the support, the cavity extending from the exposed surface toward a depth direction of the support;
and burning away the support. The additive manufacturing method according to claim 1, wherein the cavity is formed during the manufacturing of the semi-finished product. The additive manufacturing method according to claim 1, wherein the cavity is formed in the support after the semi-finished product is manufactured. prior to the step of shaping the workpiece, determining a size of an opening of the cavity at the exposed surface;
This step is
obtaining a range of Peclet numbers based on the shape of the aperture;
The additive manufacturing method according to any one of claims 1 to 3, further comprising determining a size of the opening so that the Peclet number is within the range. The additive manufacturing method according to any one of claims 1 to 4, further comprising the step of inserting a fuse into the cavity before the step of burning off the support. The cavity includes at least one first cavity and at least one second cavity having a length in the depth direction shorter than that of the first cavity,
The step of burning off the support comprises:
a preparation step of preparing a first lid portion having a first through hole formed therein and communicating with the first cavity portion when the first lid portion is attached to the semi-finished product so as to close the exposed surface, and a second lid portion having a second through hole formed therein and communicating with the second cavity portion when the second lid portion is attached to the semi-finished product so as to close the exposed surface;
a first burn-off step of burning off the support while the first lid portion is attached to the semi-finished product;
a second burn-off step of burning off the support while the second lid portion is attached to the semi-finished product after the first burn-off step;
The additive manufacturing method according to any one of claims 1 to 5, further comprising a third burn-off step of burning off the support without attaching either the first lid portion or the second lid portion to the semi-finished product after the second burn-off step. A metal additive manufacturing body,
At least one overhang portion having a surface facing downward in a lamination direction of the metal;
a support for supporting the overhang portion, the support having an exposed surface where the support is exposed from the overhang portion;
An additive manufacturing body, wherein at least one cavity extending from the exposed surface toward the depth direction of the support is formed in the support , and a fuse is inserted into the at least one cavity .

Images