Layering method for forming a circumferential layer using a metal 3D printer

Abstract

This invention provides a layering method for forming a circumferential layered section using a metal 3D printer while suppressing the occurrence of differences in height in the circumferential direction. [Solution] The method for forming a circulating layer in a metal 3D printer 1 of the present disclosure, in which a nozzle 6 for stacking metal material during one rotation is moved at a predetermined angle θ, includes a first stacking step of moving the nozzle 6 in a first circulating direction to stack metal material, and a second stacking step of moving the nozzle 6 in a second circulating direction opposite to the first circulating direction to stack metal material, wherein the first stacking step and the second stacking step are performed alternately.

Description

Technical Field

[0001] The present disclosure relates to a lamination method for forming a circumferential lamination part by moving a nozzle for laminating a metal material at a predetermined angle during one round in a metal 3D printer and laminating it.

Background Art

[0002] Patent Document 1 discloses a modeling method of modeling an object on a base plate with a metal 3D printer using an arc welding-based metal melting lamination method, in which a base plate is attached on a modeling table, and the case of modeling a cylindrical object is shown in an embodiment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, when forming a cylindrical shape such as a cylindrical shape, in accordance with the target cylindrical shape, lamination is performed while rotating a nozzle for laminating a metal material.

[0005] And, when the height of the circumferential lamination part formed by such circumferential lamination is high and the number of circumferential lamination times is large, there is a problem that a high place and a low place in the circumferential direction are formed.

[0006] The present disclosure has been made in view of such circumstances, and one object thereof is to provide a lamination method for forming a circumferential lamination part with suppressed occurrence of differences in height in the circumferential direction by a metal 3D printer.

Means for Solving the Problems

[0007] The present disclosure is a method for forming a circulating layer by moving a nozzle for stacking metal material during a single rotation in a metal 3D printer at a predetermined angle, The aforementioned lamination method is A first lamination step involves moving the nozzle in a first circumferential direction to laminate the metal material, The process includes a second lamination step of moving the nozzle in a second lamination direction, which is opposite to the first lamination direction, to laminate the metal material, The first stacking step and the second stacking step are performed alternately. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a lamination method for forming a circumferential laminated portion using a metal 3D printer while suppressing the occurrence of differences in height in the circumferential direction. [Brief explanation of the drawing]

[0009] [Figure 1] This is a side view of the metal 3D printer according to the first embodiment of the present disclosure. [Figure 2] Figure 1 is a side view of the metal 3D printer with the nozzle removed from the manipulator. [Figure 3] Figure 1 is a front view of the metal 3D printer with the nozzle removed from the manipulator. [Figure 4] This is a top view illustrating the movement of the nozzle when forming a typical circumferential layer. [Figure 5] This is a schematic side view illustrating the state when lamination is performed while moving the nozzle in the forward direction. [Figure 6] This is a schematic side view illustrating the state when lamination is performed while moving the nozzle in the backward direction. [Figure 7] This diagram schematically shows the state of the circumferential layer when lamination is performed with the nozzles oriented in the same direction during lamination. [Figure 8] This figure illustrates a method for forming a circumferential layer using a metal 3D printer according to the first embodiment of the present disclosure. [Figure 9] FIG. is a diagram schematically showing a circumferential laminated portion formed by the lamination method according to the first embodiment of the present disclosure. [Figure 10] FIG. is a diagram for explaining a lamination method for forming a circumferential laminated portion with a metal 3D printer according to the second embodiment of the present disclosure.

MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, embodiments for implementation (hereinafter referred to as "embodiments") will be described in detail with reference to the accompanying drawings. Throughout the description of the embodiments, the same elements are denoted by the same numbers or symbols.

[0011] <<First Embodiment>> The metal 3D printer 1 according to the first embodiment of the present disclosure and the lamination method for forming a circumferential laminated portion with the metal 3D printer 1 will be described with reference to FIGS. 1 to 9.

[0012] FIG. 1 is a side view of the metal 3D printer 1 according to the first embodiment of the present disclosure. FIG. 2 is a side view of the metal 3D printer 1 of FIG. 1 with the nozzle removed from the manipulator 2. FIG. 3 is a front view of the metal 3D printer 1 of FIG. 1 with the nozzle removed from the manipulator 2.

[0013] <Metal 3D Printer 1> As shown in FIGS. 1 to 3, the metal 3D printer 1 includes a manipulator 2, a base portion 3 for fixing the manipulator 2, a table 4 attached on the base portion 3, a base material 5 provided on the table 4, and a nozzle 6 (see FIG. 1) attached to the tip of the manipulator 2.

[0014] Incidentally, the metal 3D printer 1 includes a wire supply mechanism that supplies a metal wire WR (described later) to the nozzle 6, a gas supply mechanism for the shielding gas supplied to the tip of the metal wire WR (the portion melted by the heat of arc discharge), and a power source for arc discharge. Although not shown in the figure, the wire supply mechanism, the gas supply mechanism, and the power source may be common ones used in metal 3D printers.

[0015] [Manipulator 2] The manipulator 2 will be mainly described with reference to FIGS. 2 and 3. The manipulator 2 includes a manipulator base 21 fixed to the base portion 3, a swing head 22, a lower arm portion 23, an upper arm portion 24, a wrist portion 25, and a neck swing portion 26.

[0016] (Manipulator base 21) The manipulator base 21 is a fixing portion for fixing the manipulator 2 so that it does not fall over or the like, and is fixed to the base portion 3 with bolts B1 in a state of being disposed on the base portion 3.

[0017] (Swing head 22) As shown in FIG. 2, the swing head 22 is rotatably connected to the manipulator base 21 about a first axis VA parallel to the vertical direction.

[0018] (Lower arm portion 23) As shown in FIG. 2, the lower arm portion 23 is rotatably connected to the swing head 22 (see arrow AR1) with the base end portion having a second axis parallel to the horizontal direction orthogonal to the vertical direction as a rotation center RC1.

[0019] (Upper arm portion 24) As shown in FIG. 2, the upper arm portion 24 is rotatably connected to the lower arm portion 23 (see arrow AR2) with the base end portion having a third axis parallel to the second axis as a rotation center RC2.

[0020] (Wrist portion 25) The wrist portion 25 is connected to the tip of the upper arm portion 24 so that its base end can pivot (see arrow AR3 in Figure 3).

[0021] (Swivel section 26) As shown in Figure 2, the swivel section 26 is provided at the tip of the wrist section 25 so as to be able to swivel (see arrow AR4) in one direction perpendicular to the longitudinal direction of the wrist section 25.

[0022] The oscillating unit 26 has a rotation mechanism (not shown) that rotates the attachment (in this example, the nozzle 6) attached to the oscillating unit 26 relative to the oscillating unit 26 (see arrow AR3 in Figure 3).

[0023] [Base section 3] As shown in Figures 1 to 3, the base section 3 is a pedestal constructed by combining H-beams to securely hold the manipulator 2 and table 4. However, it is not limited to H-beams; any structure that can securely hold the manipulator 2 and table 4 in an appropriate positional relationship is acceptable.

[0024] Furthermore, the underside of the base section 3 is equipped with casters (wheels) for use during transport and adjusters to prevent movement during use.

[0025] [Table 4] Table 4 is mounted on the base 3 so as to be positioned at an appropriate distance from the manipulator 2, in order to properly perform the molding (hereinafter also referred to as layering) using molten metal from the nozzle 6 attached to the tip of the manipulator 2.

[0026] In this embodiment, the table 4 is fixed to the base portion 3 with bolts (not shown) while positioned on the base portion 3.

[0027] The suspension bolts visible in the diagram are provided for connecting shackles and other components that connect to the wires and other components of the lifting device used when moving table 4.

[0028] [Base material 5] The base material 5 is a substrate that serves as the target for the initial layering of metal material when using the metal 3D printer 1. It is detachably fixed to the table 4 with bolts B2 so that it can be removed from the table 4 along with the laminated body (not shown) after layering.

[0029] In the first embodiment, the base material 5 is placed on the table 4, but the table 4 itself may be used as the base material 5, and a laminate (not shown) may be formed by laminating on the table 4.

[0030] However, the substrate (base material 5 in this example), which serves as the target for initially laminating the metal material, may be reused after the laminate (not shown) is removed by cleaning its surface (e.g., surface polishing), but it may also be discarded without being reused.

[0031] Therefore, the target substrate (base material 5 in this example) often serves as a disposable, supplementary component (also called a supplementary component) in the metal 3D printer 1.

[0032] Therefore, instead of using the table 4 as the target for initially laminating the metal material, it is preferable to place a base material 5 on the table 4 as a component that can be used as a supplementary material, as in the first embodiment, and then perform lamination on the base material 5.

[0033] Furthermore, although the first embodiment shows the case where the base material 5 is in the shape of a plate, the base material 5 is not limited to being in the shape of a plate, and the shape can be selected as needed.

[0034] For example, when combining multiple molded objects to create a single structure, the base material 5 may have a shape suitable for assembling the molded objects (for example, a shape that has a bonding structure for joining the molded objects in addition to the layered surface).

[0035] In this way, the base material 5 is not treated as disposable, but can be effectively utilized as one of the structural components in the fabrication of the structure.

[0036] [Nozzle 6] Nozzle 6 is a nozzle that melts the metal wire WR (described later) that is being fed out by the heat of the arc discharge while injecting a shielding gas (for example, carbon dioxide, argon, etc.) so as to surround the fed-out metal wire WR.

[0037] In other words, in the first embodiment, an arc welding type metal 3D printer is used as the type of metal 3D printer 1.

[0038] However, the nozzle 6 is not limited to a nozzle that melts metal powder using the heat of an arc discharge as described above; it may also be a nozzle that melts metal powder by spraying it in a way that collects the metal powder while irradiating it with a laser.

[0039] In other words, metal 3D printer 1 may be a directed energy deposition metal 3D printer.

[0040] Furthermore, the nozzle 6 may be a nozzle that binds metal particles together by spraying a mixture of metal powder and air at a speed of three times or more the speed of sound.

[0041] In other words, metal 3D printer 1 may be a metal 3D printer using the supersonic deposition method.

[0042] <Lamination Method> Next, a method for forming a circumferential layer using the metal 3D printer 1 of the first embodiment of this disclosure will be described.

[0043] Figure 4 is a top view illustrating the movement of the nozzle 6 when forming a typical circumferential stacking section, and is a schematic diagram showing the case where a cylindrical body with a rectangular cross-section is formed as a circumferential stacking section.

[0044] Figure 4 shows a case where a circumferential laminated section is formed by rotating the nozzle 6 counterclockwise from the lamination start position ST, as indicated by the dotted arrow.

[0045] In this case, the nozzle 6 moves forward from the stacking start position ST, away from the installation position of the manipulator 2 (see manipulator base 21), as indicated by the solid arrow FD.

[0046] Note that the side closer to the installation position of manipulator 2 (see manipulator base 21) may be referred to as the rear side, and the side further away may be referred to as the front side.

[0047] Furthermore, the direction of movement towards the front is sometimes referred to as the forward direction, and the direction of movement towards the rear is sometimes referred to as the backward direction.

[0048] Next, the nozzle 6 moves laterally, perpendicular to the forward direction, as indicated by the solid arrow LD1, and then moves backward, as indicated by the solid arrow RD, towards the installation position of the manipulator 2 (see manipulator base 21), that is, it moves in the backward direction.

[0049] Next, nozzle 6 moves laterally, perpendicular to the retraction direction, as indicated by the solid arrow LD2, and returns to the lamination start position ST, thus completing one orbital movement for lamination.

[0050] Generally, this circular movement is performed the number of times required to stack the metal material to achieve the height required for the circumferential stacking section, thereby forming the circumferential stacking section.

[0051] Thus, when forming a circumferential layer, the layers stacked in one rotation include layer LY1 (described later), which is stacked by moving the nozzle 6 in the forward direction (solid arrow FD direction), and layer LY2 (described later), which is stacked by moving the nozzle 6 in the backward direction (solid arrow RD direction).

[0052] Figure 5 is a schematic side view showing the state when lamination is performed while moving the nozzle 6 in the forward direction (solid arrow FD direction).

[0053] Figure 6 is a schematic side view showing the state when lamination is performed while moving the nozzle 6 in the backward direction (direction of the solid arrow RD).

[0054] As shown in Figure 5, when lamination is performed while moving the nozzle 6 in the forward direction (direction of the solid arrow FD), the nozzle 6 moves in the forward direction (direction of the solid arrow FD) with the nozzle 6 tilted backward by a predetermined angle θ, and the molten metal material consisting of metal wire WR is laminated so as to form a layer LY1 behind the tip of the nozzle 6.

[0055] On the other hand, as shown in Figure 6, when lamination is performed while moving the nozzle 6 in the backward direction (direction of the solid arrow RD), the nozzle 6 moves in the backward direction (direction of the solid arrow RD) with the nozzle 6 tilted backward by a predetermined angle θ, and the molten metal material consisting of metal wire WR is laminated so as to form a layer LY2 in front of the tip of the nozzle 6.

[0056] Furthermore, the thickness (also called height) of the layered material differs depending on whether the nozzle 6 for laminating the metal material is tilted at a predetermined angle θ and moves forward while laminating, or moves backward while laminating.

[0057] Specifically, the thickness (height) of layer LY1, which is stacked while the nozzle 6 is moving forward, is thinner (lower) than the thickness (height) of layer LY2, which is stacked while the nozzle 6 is moving backward.

[0058] Figure 7 schematically shows the state of the circumferential layer when lamination is performed with the nozzle 6 having the same circumferential direction during lamination.

[0059] As shown in Figure 7, the thickness (height) of layer LY1, which is stacked while the nozzle 6 is moving forward, is thinner than the thickness (height) of layer LY2, which is stacked while the nozzle 6 is moving backward. Therefore, the circumferential stacked portion formed by these stacks has a height difference of δH in the circumferential direction.

[0060] For example, when forming layers with a thickness of approximately 2.6 mm, the thickness (height) of layer LY1 will be about 0.1 mm thinner (lower) than the thickness (height) of layer LY2.

[0061] If the required height of the circumferential layering section is 260 mm, then the nozzle 6 will be rotated 100 times while 100 layers are stacked. A simple calculation shows that the difference in thickness (height) between layer LY1 and layer LY2 will accumulate, resulting in a circumferential height difference δH of 10 mm in the circumferential layering section.

[0062] Therefore, in the first embodiment, in a layering method for forming a circumferential layered section by moving a nozzle 6 for layering metal material in one rotation of a metal 3D printer 1 at a predetermined angle θ (see Figures 5 and 6) in the forward direction (direction of the solid arrow FD in Figure 4) and the backward direction (direction of the solid arrow RD in Figure 4), the method of moving the nozzle 6 is devised to suppress the occurrence of height differences in the circumferential direction of the circumferential layered section, and this will be explained in detail below.

[0063] Figure 8 is a diagram illustrating a method for forming a circumferential layer using the metal 3D printer 1 of the first embodiment of the present disclosure, and corresponds to the dotted arrow in Figure 4 that shows the movement state of the nozzle 6.

[0064] As shown in Figure 8, the lamination method of the first embodiment includes a first lamination step (see left side of Figure 8) in which the nozzle 6 is moved in a first circumferential direction (counterclockwise direction in Figure 8) to laminate the metal material, and a second lamination step (see right side of Figure 8) in which the nozzle 6 is moved in a second circumferential direction (clockwise direction in Figure 8), which is the opposite direction to the first circumferential direction (counterclockwise direction in Figure 8), to laminate the metal material, with the first lamination step and the second lamination step being performed alternately each time a layer is formed.

[0065] Specifically, among the layers stacked to form the circumferential layer, the odd-numbered layers (1st layer, 3rd layer, ...) are formed in the first stacking step, and the even-numbered layers (2nd layer, 4th layer, ...) are formed in the second stacking step.

[0066] As can be seen in Figure 8, layer LY2 is formed on top of layer LY1, which is stacked in the first layer while moving the nozzle 6 in the forward direction (see the solid arrow FD direction on the left side of Figure 8), while moving the nozzle 6 in the backward direction (see the solid arrow RD direction on the right side of Figure 8).

[0067] Similarly, on top of layer LY2, which is stacked while moving the nozzle 6 in the backward direction (see the solid arrow RD direction on the left side of Figure 8) in the first layer, layer LY1 is formed while moving the nozzle 6 in the forward direction (see the solid arrow FD direction on the right side of Figure 8) in the second layer.

[0068] Figure 9 is a schematic diagram showing a circumferential laminated portion formed by the lamination method of the first embodiment according to this disclosure. In other words, it is a schematic diagram showing a circumferential laminated portion formed by alternately performing the first lamination step (see left side of Figure 8) and the second lamination step (see right side of Figure 8) for each layer, and corresponds to Figure 7.

[0069] As shown in Figure 9, in the lamination method of the first embodiment, thin (low height) layers LY1 formed while the nozzle 6 moves in the forward direction and thick (high height) layers LY2 formed while the nozzle 6 moves in the backward direction are alternately laminated.

[0070] Therefore, in terms of the height of the circumferential layer, it is the height formed by stacking layers of an intermediate thickness (height) between layer LY1 and layer LY2, for the total number of stacking cycles.

[0071] Furthermore, the layer LY3, which is stacked as the nozzle 6 moves in a lateral direction perpendicular to the forward and backward directions (see the solid arrow LD direction in Figure 8), is formed to connect the layer LY1, which is stacked while moving in the forward direction, and the layer LY2, which is stacked while moving in the backward direction.

[0072] Therefore, as can be seen in Figure 8, layers LY1 and LY2 appear alternately, resulting in a state where, after layer LY3 which becomes thicker (higher) towards the right in Figure 9, another layer LY3 which becomes thicker (higher) towards the left in Figure 9 is stacked.

[0073] Therefore, since this layer LY3 is also formed by stacking layers with an intermediate thickness (height) between layers LY1 and LY2 for the total number of stacking cycles, every part in the circumferential direction is in the same state as if it were formed from layers with an intermediate thickness (height) between layers LY1 and LY2, and the height of the circumferential stacking section becomes almost uniform in the circumferential direction.

[0074] As described above, the lamination method of the first embodiment can suppress differences in the height of the circumferential lamination portion.

[0075] Moreover, with the lamination method of the first embodiment, it is possible to suppress differences in the height of the periphery lamination without performing very subtle adjustments to lamination parameters (for example, adjustments to current, voltage, etc.) that suppress differences in layer thickness (height) of about 0.1 mm per layer.

[0076] In the above explanation, the first rotation direction was described as counterclockwise and the second rotation direction as clockwise, but this relationship can be reversed.

[0077] In other words, the first rotation direction may be clockwise, and the second rotation direction may be counterclockwise.

[0078] Furthermore, while the above describes a case where one layer is formed in the first lamination step (see left side of Figure 8), and then the procedure of forming one layer in the second lamination step (see right side of Figure 8) is repeated, it is also possible to form multiple layers in the first lamination step (see left side of Figure 8), and then repeat the procedure of forming multiple layers in the second lamination step (see right side of Figure 8).

[0079] However, if the second layering step (see Figure 8, right side) is performed after forming numerous layers in the first layering step (see left side of Figure 8) and creating a large difference in height, it becomes difficult to average out the heights.

[0080] Therefore, it is preferable to perform lamination in a way that does not result in significant height differences during the lamination process, with the first lamination step (see left side of Figure 8) consisting of 10 layers or less, and the second lamination step (see right side of Figure 8) consisting of 10 layers or less.

[0081] Furthermore, it is preferable that approximately half of the total number of layers stacked to form the circumferential layer are formed in the first stacking step (see left side of Figure 8), and approximately half of the layers are formed in the second stacking step (see right side of Figure 8).

[0082] However, for this to be possible, the number of layers formed in the first layering step (see left side of Figure 8) and the second layering step (see right side of Figure 8), which are performed multiple times, does not necessarily have to be the same.

[0083] For example, even if four layers are formed in the first lamination step (see left side of Figure 8) and six layers are formed in the next first lamination step (see right side of Figure 8), it is also possible to form six layers in the second lamination step (see left side of Figure 8) and then four layers in the next second lamination step (see right side of Figure 8).

[0084] Even in this way, 10 of the total 20 layers (half the layers) are formed in the first stacking step (see left side of Figure 8), and the remaining 10 layers (half the layers) are formed in the second stacking step (see right side of Figure 8).

[0085] <<Second Embodiment>> Next, a lamination method for forming the circumferential laminated portion of the second embodiment of this disclosure will be described with reference to Figure 10.

[0086] The lamination method of the second embodiment has the same basic configuration as the lamination method of the first embodiment. Below, we will mainly describe the differences from the first embodiment, and may omit explanations of similar points.

[0087] Figure 10 is a diagram illustrating a lamination method for forming a circumferential layer using the metal 3D printer 1 of the second embodiment of the present disclosure, and corresponds to Figure 8.

[0088] The lamination start position ST, where the lamination process begins, is more prone to variations in layer thickness and other properties compared to the lamination process while moving the nozzle 6, and is therefore more likely to become a singularity.

[0089] Therefore, as in the first embodiment, if the lamination start position ST is always set to the same position, the shape of that part may become poor.

[0090] Therefore, in the lamination method of the second embodiment, the lamination start positions ST of the first lamination step and the second lamination step are distributed at different positions in the circumferential direction.

[0091] Specifically, as shown in the upper left of Figure 10, in the first lamination step, the lower left corner of the rectangular circumferential portion where the nozzle 6 (not shown) is moved is set as the lamination start position ST, and the first layer is laminated. Then, as shown in the upper right of Figure 10, in the first second lamination step, the position of the nozzle 6 (not shown) is moved to the lower right position of the rectangular circumferential portion before lamination begins.

[0092] Similarly, after one layer is laminated in the first second lamination step, the second first lamination step is performed as shown in the lower left of Figure 10. However, this time, the nozzle 6 (not shown) is moved to the upper right position of the rectangular circumferential portion before lamination begins.

[0093] Then, after one layer has been laid in the second first lamination step, the second second lamination step is performed, as shown in the lower right of Figure 10. However, at this time, the nozzle 6 (not shown) is moved to the upper left position of the rectangular circumferential portion before lamination begins.

[0094] Furthermore, if lamination is to be carried out again after the second lamination step is completed, the same lamination process as the first lamination step is performed again, so that the lamination start positions ST do not overlap consecutively. By distributing them to the four corners of the circumferential lamination section, the lamination start positions ST are distributed to different positions in the circumferential direction.

[0095] Thus, in the lamination method of the second embodiment, the lamination start position ST of the second lamination step is set to a different position from the lamination start position ST of the preceding first lamination step, and the lamination start position ST of the first lamination step is set to a different position from the lamination start position ST of the preceding second lamination step, thereby dispersing the lamination start positions ST in the circumferential direction.

[0096] Therefore, it is possible to suppress the occurrence of a degraded shape due to the repeated appearance of the stacking start position ST, which is prone to becoming a singularity, at the same location.

[0097] The above description has been based on specific embodiments of this disclosure, but this disclosure is not limited to the embodiments described above.

[0098] In the above embodiment, the case where the circumferential stacking portion is a cylindrical body with a rectangular cross-section was described, but the circumferential stacking portion may also be a cylindrical body with a ring-shaped cross-section.

[0099] Furthermore, in the case of a cylindrical body, the lamination method of the second embodiment can be implemented by distributing the lamination start positions ST to different positions in the circumferential direction.

[0100] It goes without saying that the surrounding laminated portion may also be a cylindrical body with other cross-sectional shapes (for example, elliptical, triangular, pentagonal, etc.).

[0101] Thus, this disclosure is not limited to the embodiments described above, and modifications and improvements to the embodiments are also included within the technical scope of the invention, which will be clear to those skilled in the art from the description of the claims. [Explanation of Symbols]

[0102] 1...Metal 3D printer, 2...Manipulator, 21...Manipulator base, 22...Swing head, 23...Forearm, 24...Upper arm, 25...Wrist, 26...Swivel, 3...Base, 4...Table, 5...Base material, 6...Nozzle, B1, B2...Bolts, LY1, LY2, LY3...Layer, RC1, RC2...Rotation center, ST...Layer start position, VA...First axis, WR...Metal wire, θ...Determined angle

Claims

1. A method for forming a circulating layer in a metal 3D printer by moving a nozzle for layering metal material during a single rotation at a predetermined angle, The aforementioned lamination method is A first lamination step involves moving the nozzle in a first circumferential direction to laminate the metal material, The process includes a second lamination step of moving the nozzle in a second lamination direction, which is opposite to the first lamination direction, to laminate the metal material, A lamination method in which the first lamination step and the second lamination step are performed alternately.

2. The first lamination step is performed with a number of layers of 10 or less. The lamination method according to claim 1, wherein the second lamination step is characterized in that the number of layers is 10 or less.

3. The lamination method according to claim 1 or claim 2, wherein the lamination start positions in the first lamination step and the second lamination step are distributed at different positions in the circumferential direction.

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