Metal additive manufacturing method and device

Abstract

To provide a metal additive manufacturing method due to additive manufacturing capable of performing an adjustment process in series with the additive process with good controllability and accuracy.SOLUTION: The present invention relates to a metal additive manufacturing apparatus and method for modeling a metal additive manufacturing object by supplying a metal material onto a modeling stage and moving a localized melted part by an irradiated heat source. The device includes a movement control unit that positions a tip of a pressing tool at the rear in a moving direction of the local melting part, and freely maintains and controls a separation distance of the tip from the modeling stage, and it is characterized in that it slides following the movement of the local melting part while pressing the tip against the metal material. The method involves sliding the tip following the movement of the local melting part while pressing the tip against the metal material, in the movement control unit that positions the tip of the pressing tool at the rear in the moving direction of the local melting part, and freely maintains and controls the separation distance of the tip from the modeling stage.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for metal additive manufacturing using additive manufacturing. [Background technology]

[0002] A metal additive manufacturing (AM) method is known in which a supplied metal material is locally melted and solidified while a heat source, such as an arc discharge or laser, is moved to form tracks, which are then stacked horizontally and / or vertically to form a three-dimensional structure. However, if voids are formed inside the material during the melting and solidification process, the mechanical properties of the structure will be reduced. Therefore, a method has been proposed in which tracks are formed by applying plastic deformation during the melting and solidification process to collapse the voids.

[0003] For example, Non-Patent Document 1 discusses the so-called "bottleneck problem" in arc discharge additive manufacturing (AAM), where a large energy input causes the molten metal to flow, generating shrinkage voids and cracks, and causing residual stress and deformation, and then proposes a hot rolling process to address this problem. Plastic deformation is imparted by multiple cylindrical rollers behind the torch that supplies the metal wire, thereby restoring mechanical strength.

[0004] Furthermore, Patent Document 1, like Non-Patent Document 1, discloses a method in which a large energy source such as a plasma thermal fusion lamination gun using arc discharge or a gas-shielded laser gun is used to move a micro-roller in synchronization with the movement of the gun, thereby plastically deforming the surface of the area immediately after solidification behind the molten pool in situ, thereby controlling rolling and cooling accordingly, and performing deformation correction, removal processing, and / or finishing processing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-108960 [Non-patent literature]

[0006] [Non-Patent Document 1] "Improvement in Geometrical Accuracy and Mechanical Property for Arc-Based Additive Manufacturing Using Metamorphic Rolling Mechanism"; Yang Xie, Haiou Zhang, and Fei Zhou; Journal of Manufacturing Science and Engineering, NOVEMBER 2016, Vol. 138. Summary of the Invention [Problem to be solved by the invention]

[0007] In additive manufacturing (AM), it is difficult to control the initial pores formed during the manufacturing process, so it is desirable to provide a series of adjustment (plastic processing) processes in addition to the additive process. In particular, in AM processes that require high shape accuracy and mechanical properties, it is also necessary to be able to precisely and controllably perform the adjustment processes in each of the additive processes.

[0008] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a metal additive manufacturing method and apparatus that can accurately and controllably carry out an adjustment process in series with an additive process. [Means for solving the problem]

[0009] The device according to the present invention is a metal additive manufacturing device that supplies metal material onto a manufacturing stage and moves a local melted area caused by an irradiated heat source to manufacture a metal additive manufacturing object, and is characterized in that it includes a movement control unit that positions the tip of a pressing tool behind the direction of movement of the local melted area and freely maintains and controls the distance of the tip from the manufacturing stage, pressing the tip against the metal material while sliding it in accordance with the movement of the local melted area.

[0010] According to this feature, plastic deformation that can greatly contribute to improving mechanical properties can be easily and accurately imparted by sliding the tip of a pressing tool as a series of additional processes, so-called "ironing."

[0011] In the above-described invention, the tip may be made of a high-melting-point metal having a melting point of 2000°C or higher. The high-melting-point metal may be one selected from the group consisting of niobium, tantalum, molybdenum, and tungsten, or an alloy based on one of these. In the above-described invention, the pressing tool may have a tip formed from a part of a rod-shaped body made of the high-melting-point metal. The tip may have a partially spherical three-dimensional curved surface. This feature allows hot plastic deformation behind the localized molten zone to be sufficiently imparted so as to significantly contribute to improving mechanical properties, while suppressing a decrease in tool life and ensuring stable sliding of the tip.

[0012] In the above-described invention, the movement control unit may be characterized in that it controls the holding state of the pressing tool by either or both of fixed control for keeping the separation distance constant and constant pressure control for pressing the tip end against the metal material with a predetermined pressure. According to this feature, fixed control can simplify control while providing sufficient plastic deformation, while constant pressure control can simply control hot plastic deformation at a softened position at or above a predetermined temperature behind the locally molten zone.

[0013] Furthermore, a method according to the present invention is a metal additive manufacturing method in which a metal material is supplied onto a building stage and a local molten zone is moved by an irradiated heat source to form a metal additive manufacturing object, characterized in that the tip of a pressing tool is positioned behind the direction of movement of the local molten zone, and a movement control unit that freely maintains and controls the distance of the tip from the building stage causes the tip to press against the metal material and slide in accordance with the movement of the local molten zone.

[0014] According to this feature, plastic deformation that can greatly contribute to improving mechanical properties can be easily and accurately imparted by sliding the tip of a pressing tool as a series of additional processes, so-called "ironing."

[0015] In the above-described invention, the tip may be made of a high-melting-point metal having a melting point 1000°C or more higher than that of the metallic material. According to this feature, it is possible to impart sufficient hot plastic deformation behind the local molten zone so as to significantly contribute to improving mechanical properties, and it is also possible to suppress a decrease in tool life.

[0016] In the above-described invention, the holding state of the pressing tool may be controlled by either or both of fixed control for keeping the separation distance constant and constant pressure control for pressing the tip end against the metal material with a predetermined pressure. According to this feature, fixed control can simplify control while providing sufficient plastic deformation, while constant pressure control can simply control hot plastic deformation at a softened position at or above a predetermined temperature behind the locally molten zone.

[0017] In the above-described invention, the constant pressure control may include a step of providing a tapered shape at a pressing start position of the pressing tool. According to this feature, hot plastic deformation under constant pressure control behind the locally molten zone can be easily controlled. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a block diagram showing an example of a metal additive manufacturing apparatus according to the present invention. [Figure 2] FIG. 1A is a top view and FIG. 1B is a side view showing a stacking pattern A in a manufacturing test. [Figure 3] FIG. 10A is a top view and FIG. 10B is a side view showing stacking pattern B in a manufacturing test. [Figure 4] 1A and 1B are photographs showing the appearance of a metal additive manufacturing object formed by laminating metal and a target object, and a diagram showing the cutting position of a micro tensile test piece. [Figure 5] (a) A top view and (b) a photograph showing the shape of the micro-tensile test specimen. [Figure 6] 1 is a table showing the manufacturing conditions and test results of a metal additive manufacturing object in a manufacturing test. DETAILED DESCRIPTION OF THE INVENTION

[0019] A metal additive manufacturing apparatus and a metal additive manufacturing method as one embodiment of the present invention will be described with reference to FIG.

[0020] As shown in Figure 1, a metal additive manufacturing apparatus 10 includes a slide 1 that fixes a workpiece 5 and enables horizontal movement, an irradiation unit 2 that irradiates laser light L, a pressing tool 3, and a control unit 14 that controls the operations of these components. The workpiece 5 serves as a modeling stage for melting and layering a metal material 9 on its upper surface, and is fixed to the slide 1 so that its upper surface is approximately horizontal. The laser light L irradiated from the irradiation unit 2 is a heat source for melting the metal material 9 supplied onto the workpiece 5, and can form a local molten portion 8 by melting the metal material 9.

[0021] The locally molten zone 8 is a portion of the metal material 9 that has been locally melted or semi-molten due to heating by the laser light L, and is generally defined as a range within a circle having a diameter approximately three times the diameter of the irradiation spot from the center of irradiation by the laser light L. In practice, since the laser light L is moved relative to the metal material 9, the locally molten zone 8 is thought to be formed in a range that extends backward from the circle depending on the moving speed. Here, the semi-molten state refers to a state in which the temperature is equal to or higher than the solidus temperature of the metal material 9, and a solid and liquid coexist.

[0022] Other heat sources that can be used include electron beams and arc discharge. The pressing tool 3 slides its tip 3a against the track made of the softened metal material 9 after melting, thereby applying a so-called "ironing process," which causes hot plastic deformation of the metal material 9 and reduces initial voids and the like that are formed during the forming process.

[0023] Specifically, the feed table 1 is connected to a feed mechanism 11a so that the object 5 can be fed in at least one direction within a horizontal plane. The feed mechanism 11a can be, for example, a mechanism including a ball screw. The feed mechanism 11a is connected to a feed control unit 11 included in the control unit 14, and includes a driver that receives a signal related to the movement of the feed table 1 from the feed control unit 11 and operates the feed table 1.

[0024] By operating the feed mechanism 11a in this manner, the object 5 to be built is moved horizontally so as to feed the object 5 relative to the irradiation unit 2, and the locally molten portion 8 of the metal material 9 can be moved relatively relative to the object 5. In other words, while the locally molten portion 8 obtained by melting the metal material 9 supplied in a powder or other form is moved above the object 5, the metal material 9 is sequentially solidified to form tracks, which are then stacked horizontally and / or vertically to perform additive manufacturing, thereby forming a three-dimensional metal additive manufacturing structure. It is also preferable that the metal additive manufacturing apparatus 10 further includes a height adjustment mechanism that moves the feed table 1 vertically and a mechanism that adjusts the position in a direction perpendicular to the feed direction within a horizontal plane.

[0025] The irradiation unit 2 is connected to a laser control unit 12, and is capable of adjusting the output of the laser light L and switching it on and off. This makes it possible to obtain the above-mentioned local melted portion 8. The laser control unit 12 is also included in the control unit 14. It is also preferable to provide an angle adjustment mechanism (not shown) so that the irradiation angle of the laser light L can be adjusted.

[0026] Meanwhile, the press tool 3 is connected to a movement control unit 13 that controls the movement of the press tool 3 via a movement mechanism 13a that moves the press tool 3. The movement control unit 13 is also included in the control unit 14. The movement control unit 13 freely controls and adjusts the distance between the tip 3a of the press tool 3 and the surface of the object 5, which serves as the modeling stage. That is, the press tool 3 is suspended with its tip 3a pointing downward, held vertically movable by the movement mechanism 13a, and fixed at a position where the above-mentioned distance is a given value. For example, the movement mechanism 13a and the movement control unit 13 can be configured with a known servo mechanism. The distance is determined as appropriate depending on the thickness of the supplied metal material 9 and the amount of deformation to be imparted by the press tool 3.

[0027] Here, it is preferable that the movement control unit 13 be able to control the holding state of the pressing tool 3 using either or both of fixation control, which keeps the distance between the tip 3a and the surface of the object 5 constant, and constant pressure control, which presses the tip 3a against the track made of the metal material 9 with a predetermined pressure. Fixation control keeps the height of the track made of the metal material 9 constant after plastic deformation, allowing the adjustment process by plastic deformation to be carried out more accurately. Furthermore, constant pressure control makes it possible to keep the amount of plastic deformation of the metal material 9 constant after plastic deformation. Note that constant pressure control keeps the load on the pressing tool 3 constant, and does not matter what the pressure of the tip 3a on the metal material 9 is.

[0028] The pressing tool 3 is also designed to follow the movement of the locally molten zone 8. For example, it is preferable to space the pressing tool 3 a predetermined distance from the locally molten zone 8, as this facilitates control. Therefore, it is preferable to provide a mechanism for adjusting the horizontal (feed direction) position of the pressing tool 3 relative to the irradiation unit 2. This predetermined distance is determined so that the tip 3 a can be pressed against a portion of the track whose temperature has reached a predetermined range, in order to provide "ironing" to sufficiently process the track of the metal material 9 after the locally molten zone 8 has passed, thereby reducing voids and improving mechanical properties. Therefore, this predetermined distance is determined by various conditions, including the temperature within the predetermined range, such as the type of metal material 9, the feed rate, and the heat removal from the locally molten zone 8. Therefore, such a predetermined distance can be determined, for example, experimentally.

[0029] For example, if the metallic material 9 remains in a semi-molten state at the tip 3a of the pressing tool 3, which is a predetermined distance away from the locally molten portion 8, it is preferable from the viewpoint of easily crushing the pores by ironing and reducing the porosity. On the other hand, if the metallic material 9 is in a softened state after solidification at the same position, it is preferable from the viewpoint of imparting plastic processing by ironing and improving the mechanical properties of the base material.

[0030] As described above, the object 5 to be shaped is fed by the feed table 1. Meanwhile, the pressing tool 3 is disposed behind the movement direction of the local molten portion 8 and follows the movement of the local molten portion 8. Therefore, the pressing tool 3 is positioned in the feed direction of the object 5 to be shaped relative to the local molten portion 8. In other words, as shown in the figure, when the feed direction of the feed table 1 is set to the left, the pressing tool 3 is positioned to the left of the local molten portion 8. Note that a structure may also be used in which the object 5 to be shaped is fixed and feeding is applied to both the local molten portion 8 and the pressing tool 3.

[0031] Furthermore, as described above, the tip 3a of the pressing tool 3 is pressed against the high-temperature metal material 9 after melting. Therefore, the tip 3a is preferably made of a high-melting-point metal having a melting point of 2000°C or higher. It is also preferable that the tip 3a be made of a high-melting-point metal having a melting point 1000°C or higher than the melting point of the metal material 9. Examples of such high-melting-point metals include niobium, tantalum, molybdenum, and tungsten. The pressing tool 3 may be made of one selected from these metals or an alloy based on these metals. Using such a high-melting-point metal can prevent a decrease in the life of the pressing tool 3 and, further, can achieve stable sliding of the tip 3a, stabilizing plastic working.

[0032] Since such high-melting-point metals are relatively expensive, it is also preferable to configure the tip portion 3a by using a high-melting-point metal for a portion of the rod-shaped body. The shape of the tip portion 3a is not particularly limited as long as it can slide stably during the ironing process. For example, it may have a shape with a partially spherical three-dimensional curved surface, such as a hemisphere or a portion of an ellipsoid, or it may be a cut surface of a rod-shaped body such as a rectangular parallelepiped.

[0033] In the metal additive manufacturing apparatus 10, the slide 1, irradiation unit 2, and pressing tool 3 are preferably placed in a chamber that can provide an inert gas atmosphere to melt and solidify the metal material 9 and prevent oxidation of the metal material 9. The chamber also includes an inert gas supply source and a vacuum pump that evacuates the air from the interior space, facilitating purging of the inert gas. Argon gas, for example, can be used as the inert gas.

[0034] The metal additive manufacturing method using the metal additive manufacturing apparatus 10 is as follows.

[0035] First, the object 5 to be shaped is fixed on the slide 1, and after the atmosphere in the chamber is changed to an inert gas atmosphere, a metal material 9, such as metal powder, is spread on the object 5. The thickness of the metal material 9 spread on the object 5 is set to a constant value, such as 0.1 mm. It is also preferable to provide a tapered shape on the object 5 at the position where pressing by the pressing tool 3 begins, and a step of forming the tapered shape in advance may be included.

[0036] Next, the movement control unit 13 adjusts the vertical position of the tip 3a so that the distance from the surface of the object 5, which serves as the modeling stage, is a predetermined distance. Note that the horizontal position of the tip 3a of the pressing tool 3 with respect to the locally molten portion 8 has been adjusted in advance.

[0037] The laser control unit 12 controls the irradiation unit 2 to irradiate the laser light L, and at the same time, the feed control unit 11 controls the feed mechanism 11a to feed the feed table 1. This allows a local molten zone 8 to be formed in the metal material 9, while the tip 3a of the pressing tool 3 is pressed and slid against the track made by the molten metal material 9, thereby imparting plastic deformation by "ironing." During this process, the movement control unit 13 controls the distance between the tip 3a and the object 5 to be shaped and / or the pressing force against the track by performing the above-mentioned fixation control and / or constant pressure control.

[0038] After the irradiation of the laser light L is stopped by the laser control unit 12, feeding is performed a predetermined distance, and then the feeding control unit 11 stops the feeding, completing the formation of one track. If necessary, track formation is repeated in the same manner, and tracks are stacked in the horizontal and / or vertical directions to perform additive manufacturing, thereby forming a three-dimensional metal additive manufacturing object.

[0039] Here, the "ironing" process, in which the tip 3a slides against the softened track, is thought to impart a different stress state to the softened metal material 9 than, for example, pressing using a roller. While pressing using a roller only applies a pressing force perpendicular to the track surface, "ironing" imparts a horizontal force near the track surface due to the frictional force generated by the sliding in addition to the pressing force. While the mechanism behind this stress state is currently unknown, it is known that it significantly reduces porosity in the metal additive manufacturing product obtained by stacking the tracks, thereby improving the mechanical properties. This will be discussed later. It is preferable to reduce porosity so that the porosity in the cross section of the metal additive manufacturing product is 10% or less.

[0040] As described above, the metal additive manufacturing apparatus 10 can precisely and with good control the additional process of forming a local molten portion 8 in the metal material 9 and moving it to obtain a track, as well as the associated adjustment process using "ironing."

[0041] [Manufacturing test] Next, a manufacturing test in which tracks were actually formed and layered using the metal additive manufacturing apparatus 10 to obtain a metal additive manufacturing object by metal layering will be described with reference to FIGS. 2 to 6. FIG.

[0042] As shown in Figures 2 and 3, a circular object 5 (see Figure 4) with a tapered shape 5a at one end was prepared, and a path for forming a track on its surface was determined. Note that the x and y directions in the figure are horizontal, and the z direction is vertical. The x direction is the direction in which the local melted portion 8 and the pressing tool 3 are moved relative to the object 5 (the direction in which the laser light L is scanned), and is opposite to the feed direction. The tapered shape 5a was formed at the pressing start position of the pressing tool 3. When such a tapered shape is given, by controlling the movement control unit 13 under constant pressure, the tip 3a of the pressing tool 3 moves along the tapered surface of the object 5, automatically obtaining the separation distance from the surface of the object 5. In other words, this facilitates position control of the pressing tool 3. The slope of the tapered shape 5a was set to 1 / 10. The layering pattern will be described later.

[0043] The tracks were formed with a thickness of 0.1 mm in the longitudinal direction (x direction) of the laminated pattern, and multiple tracks were formed parallel to each other at a 0.15 mm pitch in the y direction, resulting in an overall width of 3.6 mm. Multiple layers with a width of 3.6 mm were formed, resulting in an overall thickness of 1 mm for laminated pattern A (see Figure 2) and 1.5 mm for laminated pattern B (see Figure 3). In laminated pattern A, the paths for forming tracks on adjacent layers were aligned in the y direction. Meanwhile, in laminated pattern B, the paths on adjacent layers were offset in the y direction by half a pitch.

[0044] Furthermore, it is preferable to provide a tapered shape at the end of the track formation start side of each lamination pattern so as to extend and maintain the tapered shape 5a of the object 5, allowing the tip 3a of the pressing tool 3 to move along the tapered shape. Therefore, to maintain the tapered shape not only in the object but also in the laminated portion, the area where the track formation start position of each layer may be machined, or the track formation start position may be shifted backward with each lamination. Using this lamination pattern, a metal additive manufacturing structure 6 (see Figure 4) was obtained.

[0045] Maraging steel powder was used as the metal material 9, and tracks were formed with the laser light L output set to 126 W, a spot diameter of φ0.2 mm, a feed rate of 15 mm / s, and a horizontal distance of 1.0 mm between the local melted portion 8 and the tip 3a. The additive manufacturing was performed in an argon gas atmosphere.

[0046] As shown in Figures 4 and 5, micro-tensile test pieces 7 were cut out of the obtained structures 6, avoiding the tapered shape 5a. The micro-tensile test pieces 7 were tensile test pieces with a total length of 15.4 mm and a parallel cross section of 1.0 mm wide and 0.4 mm thick. The cross section (yz plane) of each structure 6 was observed to determine the porosity. The porosity was calculated by taking a cross-sectional photograph, binarizing the image of the photograph, and then calculating the area ratio of the portion corresponding to the pores.

[0047] As shown in FIG. 6, under conditions 1 and 3, no "ironing" was performed using the pressing tool 3, i.e., no adjustment by plastic processing to reduce voids was performed, while under conditions 2 and 4, "ironing" was performed.

[0048] The results of the tensile tests using micro-tensile test pieces showed that conditions 2 and 4 had much higher tensile strength than conditions 1 and 3. In other words, the tensile strength could be improved by ironing compared to when ironing was not performed.

[0049] Furthermore, in the case of lamination pattern A, the porosity was 20.6% under condition 1, but was extremely small at 6.9% under condition 2. Similarly, in lamination pattern B, the porosity was 16.0% under condition 3, but was extremely small at 2.9% under condition 4. In other words, more pores were crushed when ironing was performed than when ironing was not performed. It can also be seen that this result corresponds well to the results of the tensile test.

[0050] As shown above, in manufacturing tests, it was found that structures made from metal additive manufacturing products obtained by stacking tracks that had been subjected to ironing processing could achieve low porosity and high tensile strength.

[0051] Regarding the lamination pattern, it was confirmed that the tensile strength was increased and the porosity was reduced in lamination pattern B, in which the path positions in adjacent layers were shifted by half a pitch.

[0052] Although typical embodiments of the present invention have been described above, the present invention is not necessarily limited thereto, and a person skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the appended claims. [Explanation of symbols]

[0053] 1 feed table 2. Irradiation unit 3 Pressing tools 9 Metal materials 10 Metal additive manufacturing equipment 14 Control Unit

Claims

1. A metal additive manufacturing apparatus that supplies a metal material onto a manufacturing stage and moves a locally melted portion caused by an irradiated heat source to manufacture a metal additive manufacturing object, A metal additive manufacturing device characterized in that it includes a movement control unit that positions the tip of a pressing tool behind the direction of movement of the local molten portion and freely maintains and controls the distance of the tip from the manufacturing stage, and presses the tip against the metal material while sliding it in accordance with the movement of the local molten portion.

2. The metal additive manufacturing apparatus according to claim 1, wherein the tip is made of a metal with a high melting point of 2000°C or higher.

3. 3. The metal additive manufacturing apparatus according to claim 2, wherein the high-melting-point metal is one selected from the group consisting of niobium, tantalum, molybdenum, and tungsten, or an alloy based on one of these metals.

4. 4. The metal additive manufacturing apparatus according to claim 3, wherein the pressing tool has a tip formed from a part of a rod-shaped body made of the high-melting-point metal.

5. The metal additive manufacturing apparatus according to claim 4, wherein the tip portion has a partially spherical three-dimensional curved surface.

6. The metal additive manufacturing device according to any one of claims 1 to 5, characterized in that the movement control unit controls the holding state of the pressing tool using either or both of fixed control that keeps the separation distance constant and constant pressure control that presses the tip end against the metal material with a predetermined pressure.

7. A metal additive manufacturing method for manufacturing a metal additive manufacturing object by supplying a metal material onto a manufacturing stage and moving a locally melted portion caused by an irradiated heat source, the method comprising: A metal additive manufacturing method characterized by positioning the tip of a pressing tool behind the direction of movement of the local molten portion, and using a movement control unit that freely maintains and controls the distance of the tip from the manufacturing stage, pressing the tip against the metal material while sliding it in accordance with the movement of the local molten portion.

8. The metal additive manufacturing method according to claim 7, wherein the tip portion is made of a high-melting-point metal having a melting point that is 1000° C. or more higher than the melting point of the metal material.

9. The metal additive manufacturing method according to claim 7 or 8, characterized in that the holding state of the pressing tool is controlled by either or both of fixed control that keeps the separation distance constant and constant pressure control that presses the tip portion against the metal material with a predetermined pressure.

10. The metal additive manufacturing method according to claim 9, wherein the constant pressure control includes a step of providing a tapered shape at a pressing start position of the pressing tool.

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