Wire for forming foam metal body and formation method of foam metal body

Abstract

To provide a wire for forming a foam metal body and a formation method of a foam metal body that achieve high quality of the foam metal body formed by the WAAM method.SOLUTION: In a wire 1 for forming a foam metal body, a metal precursor 4 that foams when heated is used as a core material 2. In the wire 1 for forming the foam metal body, the metal precursor 4 foams when heated by arc K or the like, and a foam metal body P containing fine independent air holes with a high porosity can be formed on a target object S. Accordingly, high quality of the foam metal body P formed by the WAAM method can be achieved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a wire for forming a metal foam body and a method for forming a metal foam body. [Background technology]

[0002] Metal foams made from materials such as aluminum are lightweight and strong, making them promising media for metal 3D printers. A well-known 3D modeling method is additive manufacturing (hereinafter referred to as "AM"), which involves repeatedly layering metal foams onto an object.

[0003] An example of a conventional technique related to the AM method is the method for forming a porous aluminum layer described in Patent Document 1. In this conventional method, an arc is generated on an aluminum or aluminum alloy substrate using an AC power source, and aluminum or aluminum alloy powder is introduced into the arc to form a porous aluminum layer on the substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-114054 Summary of the Invention [Problem to be solved by the invention]

[0005] Among AM methods, Wire Arc Additive Manufacturing (WAAM), which involves repeatedly layering metal foam onto an object by welding wire-shaped material with arc heating, has been attracting attention in recent years. WAAM has the advantage of using relatively inexpensive wire and is easy to handle, and there is a demand for even higher quality metal foams formed using WAAM.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a wire for forming a metal foam body and a method for forming a metal foam body that will further improve the quality of the metal foam body formed by the WAAM method. [Means for solving the problem]

[0007] The gist of the present disclosure is as follows.

[0008] [1] A wire for forming metal foam, with a core made of a metal precursor that foams when heated.

[0009] This metal foam forming wire uses a metal precursor that foams when heated as a core material. When heated with an arc, for example, the metal precursor foams, forming a metal foam with high porosity and fine, closed pores on the target object. This further improves the quality of metal foams formed using the WAAM method.

[0010] [2] The wire for forming a metal foam body according to [1], wherein an outer shell made of a weldable alloy is provided to cover the circumferential surface of the core material. In this case, the outer shell can protect the metal precursor during the production of the wire for forming a metal foam body. Therefore, the production yield of the wire for forming a metal foam body is improved. Furthermore, by forming the outer shell made of a weldable alloy, bonding between the metal foam body and the target object is supported when the metal precursor is heated. Therefore, it is possible to increase the lamination strength of the metal foam body to the target object.

[0011] [3] The wire for forming a metal foam body according to [2], wherein the outer shell material is made of an alloy of the metal contained in the metal precursor. In this case, the weldability of the outer shell material is further improved, and it is possible to further increase the lamination strength of the metal foam body to the target object.

[0012] [4] The wire for forming a metal foam body according to any one of [1] to [3], wherein the metal precursor contains a foaming agent and a thickener, thereby enabling an improvement in the porosity and further miniaturization of the closed pores contained within the metal foam body formed using the wire for forming a metal foam body.

[0013] [5] A method for forming a metal foam body, which comprises generating an arc on an object, heating a metal foam body forming wire described in any one of [1] to [4] with the arc to foam it, and performing build-up welding while laminating a metal foam body on the object.

[0014] In this method for forming a metal foam body, the above-mentioned metal foam forming wire is heated with an arc to foam the metal precursor while overlay welding is performed on the object, and the metal foam body is layered on the object. This allows a metal foam body with high porosity and containing fine, closed pores to be formed on the object. This further improves the quality of metal foam bodies formed by the WAAM method. [Effects of the Invention]

[0015] According to the present disclosure, it is possible to further improve the quality of metal foam bodies formed by the WAAM method. [Brief explanation of the drawings]

[0016] [Figure 1] 1A is a schematic perspective view of a metal foam body forming wire according to an embodiment of the present disclosure, and FIG. 1B is a schematic cross-sectional view thereof. [Figure 2] FIG. 1( a ) is a schematic side view showing a method for forming a metal foam body according to one embodiment of the present disclosure, and FIG. 1( b ) is a schematic side view showing a method for forming a metal foam body according to another embodiment of the present disclosure. [Figure 3] 1 is a cross-sectional photograph of a metal foam body obtained in an example. [Figure 4] 1 is a photograph of the axial appearance of a metal foam body obtained in an example. [Figure 5] FIG. 10 is a diagram showing the relationship between the moving speed of a welding torch and porosity. [Figure 6] 10A and 10B are cross-sectional photographs of various metal foam bodies obtained by changing the moving speed of the welding torch. [Figure 7] 1(a) is a cross-sectional photograph of a laminate of the first and second layers of a metal foam body, and FIG. 1(b) is an enlarged cross-sectional photograph of the vicinity of the boundary surface between the first and second layers. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of a metal foam body forming wire and a method for forming a metal foam body according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0018] FIG. 1(a) is a schematic perspective view of a metal foam body forming wire according to an embodiment of the present disclosure, and FIG. 1(b) is a schematic cross-sectional view thereof. The metal foam body forming wire 1 shown in FIGS. 1(a) and 1(b) is a member used as a medium for a metal three-dimensional printer based on, for example, the WAAM method. When performing three-dimensional modeling using a metal three-dimensional printer, buildup welding is performed while the metal foam body forming wire 1 is heated by an arc or the like to foam (see FIGS. 2(a) and 2(b) described below). By repeatedly stacking metal foam bodies P on an object S, a structure of a desired shape is formed using the metal foam bodies P.

[0019] As shown in Figures 1(a) and 1(b), metal foam body forming wire 1 has a core material 2 and an outer shell material 3, and is, for example, long and circular in cross section. The outer diameter of metal foam body forming wire 1 can be designed appropriately depending on the specifications of a wire feeder in a three-dimensional printer to which metal foam body forming wire 1 is applied. In this embodiment, the outer diameter of metal foam body forming wire 1 is approximately 1.6 mm.

[0020] The core material 2 is a component that constitutes the main body of the metal foam forming wire 1. The core material 2 is composed of a metal precursor 4 that foams when heated. The metal precursor 4 is composed of a metal material such as aluminum. In addition to the metal material, the metal precursor 4 contains, for example, a foaming agent and a thickener. An example of the foaming agent is titanium hydride (TiH2) with a particle diameter of 45 μm or less. Other examples of the foaming agent include zirconium hydride (ZrH2), calcium carbonate (CaCO3), and calcium hydride (CaH2). An example of the thickener is alumina (Al2O3) with a particle diameter of 1 μm or less. Other examples of the thickener include silicon carbide (SiC), calcium oxide (CaO), and calcium aluminate (CaAl2O4).

[0021] The outer shell material 3 is a member that covers the circumferential surface of the core material 2. The outer shell material 3 functions as a mold for the core material 2 when manufacturing the metal foam body forming wire 1, and also functions to support the bonding between the metal foam body P and the object S when the metal foam body forming wire 1 is overlay welded to the object S. Examples of materials that make up the outer shell material 3 include alloys that have weldability. When the metal material that makes up the metal precursor 4 is aluminum, for example, an aluminum alloy is used as the material that makes up the outer shell material 3. The thickness of the outer shell material 3 is designed appropriately within a range that allows the above functions to be performed. The ratio of the thickness of the outer shell material 3 to the outer diameter of the core material 2 is, for example, about 1:5 to 1:100.

[0022] Next, a method for forming a metal foam body using the above-described metal foam body forming wire 1 will be described.

[0023] In the method for forming a metal foam body according to this embodiment, an arc K is generated on the target object S, the above-described metal foam body forming wire 1 is heated by the arc K, and the metal precursor 4 is foamed while being overlaid with metal build-up welding, thereby laminating the metal foam body P on the target object S. The target object S may be, for example, a metal substrate 12. The target object S may also include a metal foam body P that has already been formed.

[0024] The method for forming a metal foam body according to this embodiment is carried out using, for example, an arc welding device with an NC (Numerical Control) function or an arc welding device with a robot arm. In the example shown in FIG. 2(a), TIG (Tungsten Inert Gas) welding is used. The arc welding device 11A shown in FIG. 2(a) has a welding torch 13 incorporating a tungsten electrode 14. The target object S is, for example, an aluminum plate, and is placed on a stage. The tungsten electrode 14 and the target object S are electrically connected to an AC power source (not shown).

[0025] When forming a metal foam body P using arc welding apparatus 11A, metal foam body forming wire 1 is placed at a desired position on object S. A predetermined AC voltage is applied from an AC power source to tungsten electrode 14 and object S, generating an arc K between object S and the tip of tungsten electrode 14. Shielding gas G is then circulated inside welding torch 13, and supplied from the tip of welding torch 13 toward the position where arc K is generated. As shielding gas G, for example, argon (Ar) gas can be used.

[0026] In the example of Fig. 2(b), MIG (Metal Inert Gas) welding is employed. In the arc welding apparatus 11B shown in Fig. 2(b), a metal foam body forming wire 1 is passed through a welding torch 13, and the metal foam body forming wire 1 itself also functions as an electrode. As in the case of the arc welding apparatus 11A, the target object S is, for example, an aluminum plate, and is placed on a stage. An AC power source (not shown) is electrically connected to the metal foam body forming wire 1 and the target object S.

[0027] When forming a metal foam body P using the arc welding device 11B, a predetermined AC voltage is applied from an AC power source to the metal foam body forming wire 1 passed through the welding torch 13 and the object S, and an arc K is generated between the object S and the tip of the metal foam body forming wire 1. In addition, a shielding gas G is circulated inside the welding torch 13, and the shielding gas G is supplied from the tip of the welding torch 13 toward the position where the arc K is generated. As the shielding gas G, for example, argon (Ar) gas can be used.

[0028] In either of the arc welding devices 11A and 11B, when the metal foam body forming wire 1 is heated by the arc K generated at the tip of the welding torch 13, foaming of the metal precursor 4, which is the core material 2, and melting of the outer shell material 3 occur, and these solidify to form a metal foam body P on the target object S. By moving the welding torch 13 at a predetermined speed along the extending direction of the metal foam body forming wire 1, the metal foam body P is layered in a desired region on the target object S. By repeatedly layering the metal foam body P on the already formed metal foam body P as necessary, a three-dimensional structure of a desired shape is formed.

[0029] As described above, the metal foam body forming wire 1 according to this embodiment is configured with a metal precursor 4 that foams when heated as the core material 2. In this metal foam body forming wire 1, the metal precursor 4 foams when heated with an arc K, and a metal foam body P with high porosity and containing fine, closed pores can be formed on the target object S. This allows for even higher quality of the metal foam body P formed by the WAAM method.

[0030] In the metal foam body forming wire 1 according to this embodiment, an outer shell 3 made of a weldable alloy is provided to cover the circumferential surface of the core material 2. With this configuration, the metal precursor 4 can be protected by the outer shell 3 during the production of the metal foam body forming wire 1. This improves the production yield of the metal foam body forming wire 1. Furthermore, by forming the outer shell 3 from a weldable alloy, bonding between the metal foam body P and the target object S is supported when the metal precursor 4 is heated. This makes it possible to increase the lamination strength of the metal foam body P relative to the target object S. Note that the metal foam body forming wire 1 does not necessarily have to have the outer shell 3, and may be composed only of the core material 2 formed of the metal precursor 4.

[0031] In this embodiment, the outer shell material 3 is made of an alloy of the metal contained in the metal precursor 4. This further improves the weldability of the outer shell material 3, making it possible to further increase the lamination strength of the metal foam body P to the object S. Furthermore, in this embodiment, the metal precursor 4 is made to contain a foaming agent and a thickener. This makes it possible to improve the porosity and further reduce the size of the closed pores contained within the metal foam body P formed using the metal foam body forming wire 1.

[0032] [Example] Hereinafter, examples of the present disclosure will be described.

[0033] [Metal precursor production] Aluminum powder with a purity of 99% or higher and a particle size of 180 μm or less was prepared as the matrix material for producing the metal precursor. Titanium hydride (TiH2) powder with a particle size of 45 μm or less was prepared as the foaming agent, and alumina (Al2O3) powder with a particle size of approximately 1 μm was prepared as the thickener. 3 mass% of the titanium hydride powder and 1 mass% of the alumina powder were mixed with the aluminum powder and poured into a stainless steel mold. The mixed powder was hot-pressed at 798 K and 150 MPa for 180 minutes to obtain an aluminum metal precursor with a diameter of 15 mm and a length of 50 mm.

[0034] [Manufacturing wire for forming metal foam bodies] An A5052 aluminum alloy tube with an outer diameter of 19 mm, an inner diameter of 15.5 mm, and a length of 50 mm was prepared as the outer shell material. A metal precursor was inserted into the tube as a core material and subjected to swaging. For the swaging, a USD-10000 swaging machine manufactured by Yoshida Memorial Co., Ltd. was used, and a wire for forming a metal foam body with a diameter of 3 mm was obtained by swaging at room temperature. Further swaging was performed at room temperature using a USD-500 swaging machine manufactured by Yoshida Memorial Co., Ltd., which is capable of processing finer diameters, to obtain a wire for forming a metal foam body with a diameter of 1.6 mm.

[0035] Figure 3 is a cross-sectional photograph of the wire for forming a metal foam body obtained in the example. This cross-sectional photograph was taken by cutting the wire for forming a metal foam body obtained in the above process and imaging the cut surface with a scanning electron microscope (SEM). As shown in Figure 3, a visible bond boundary was observed between the metal precursor, which is the core material, and the outer shell material, but in the evaluation test described below, no effect of the bond boundary on foaming was found. No cracks or the like were observed in either the cross section of the metal precursor or the cross section of the outer shell material. The relative density of the metal precursor was 99% or more.

[0036] [Formation of metal foam] A SainSmart Genmitsu 3018-PRO computer numerically controlled router and a Daihen 200PII DCTIG welding machine were used as an automatic welding system for the WAAM method. A 100 mm long test piece was cut from the wire used to form the metal foam body and placed on an aluminum plate stage. A 2.5 mm long arc was formed by the welding torch and placed above one end of the test piece. The arc current was set to 4 A, and the welding torch was moved from one end of the test piece to the other, forming the metal foam body. 99.99% pure argon gas was used as the shielding gas.

[0037] [Evaluation of metal foam] Welding torch movement speed V TSThe travel speed was varied between 120 mm / min and 620 mm / min, and three metal foam bodies were formed at each different travel speed. The resulting metal foam bodies were observed using a high-speed microscope MCHU30RS-CDC manufactured by Shodensha Co., Ltd., and the foaming behavior of the metal precursor was evaluated.

[0038] In this example, the porosity p is calculated by dividing the density of pure aluminum by ρ AL and the density of the metal foam is ρ f In this case, the density was calculated using the following formula (1): The density of the metal foam body was calculated using the Archimedes method.

number

[0039] The cross section of the obtained metal foam was observed with an optical microscope ECLIPSEMA100 manufactured by Nikon Corporation, and the circular equivalent diameter of the pores was calculated as the pore diameter d m The pore diameter d m was calculated by the following formula (2), where n is the number of pores and A is the pore cross-sectional area.

number

[0040] Local porosity p IA The local porosity p IA is the cross-sectional area of ​​the metal foam, A f In this case, it was calculated using the following formula (3).

number

[0041] Figure 4 is a photograph of the axial appearance of the metal foam body obtained in the example. The photograph was taken with a scanning electron microscope (SEM) of the side of the metal foam body obtained in the above process. As shown in Figure 4, the welding torch travel speed V TSWhen the welding speed was 120 mm / min, the resulting metal foam was relatively flat. This is thought to be because the metal precursor foamed due to the hydrogen gas generated from the titanium hydride particles, and then the heating time was prolonged due to the welding torch moving at a relatively slow speed, resulting in the hydrogen gas being released outside the aluminum.

[0042] On the other hand, movement speed V TS When the welding speed was 220 mm / min to 620 mm / min, humping (discontinuous bumps) was observed in the resulting metal foam. This is thought to be due to a phenomenon (arc jump) in which the surface of the metal foam expands toward the tip of the electrode when the welding torch moves at a relatively high speed. The humping in this example is also thought to be due to interruption of foaming. Such humping can be suppressed by increasing the viscosity of the metal precursor, increasing the arc current, and slowing down the welding torch movement speed.

[0043] Fig. 5 is a diagram showing the relationship between the moving speed of the welding torch and the porosity. As shown in Fig. 5, the porosity p is proportional to the moving speed V of the welding torch. TS In the range of 120mm / min to 320mm / min, the moving speed V TS It gradually increases as the welding torch travel speed V TS In the range of 320mm / min to 620mm / min, the moving speed V TS The porosity p gradually decreased as the welding torch travel speed V increased. TS The porosity of the metal foam can be increased by suppressing humping and drainage.

[0044] Figure 6 shows cross-sectional photographs of each metal foam body obtained by changing the welding torch moving speed. Each cross-sectional photograph shows the pore diameter (average pore diameter) d m and local porosity p IA As shown in Fig. 6, the welding torch moving speed V TS When the welding torch travel speed V is 120 mm / min. TSWhen the welding torch travel speed V was 620 mm / min, a dense region was observed in the cross section of the metal foam. TS When the welding torch travel speed V is 120 mm / min, it is thought that the drainage formed a dense area. TS When the heating rate was 120 mm / min, it is thought that the non-foamed region formed a dense region due to the short heating time.

[0045] As shown in Figure 6, the welding torch travel speed V TS Pore ​​diameter d when the flow rate is 120 mm / min m is 250 μm, and the welding torch moving speed V TS Pore ​​diameter d when the flow rate is 220 mm / min m is 260 μm, and the welding torch travel speed V TS Pore ​​diameter d when the flow rate is 320 mm / min m The welding torch moving speed V TS Pore ​​diameter d when the flow rate is 420 mm / min m is 290 μm, and the welding torch travel speed V TS Pore ​​diameter d when the flow rate is 520 mm / min m is 450 μm, and the welding torch travel speed V TS Pore ​​diameter d when the flow rate is 620 mm / min m was 250 μm.

[0046] In general, the average pore size decreases as the porosity increases. TS When the flow rate is 320 mm / min, the pore diameter (average pore diameter) d m The maximum pore size was 560 μm. The average pore size of aluminum foams obtained by conventional powder metallurgy and foaming methods is on the order of several mm. In this example, an average pore size that is one order of magnitude smaller than the average pore size of aluminum foams obtained by conventional methods was achieved, confirming that a metal foam with high porosity and containing fine, closed pores can be formed on a target object.

[0047] As shown in Figure 6, the welding torch travel speed V TS Local porosity p when IAis 41%, and the welding torch travel speed V TS Local porosity p when IA is 61%, and the welding torch travel speed V TS Local porosity p when IA The welding torch moving speed V TS Local porosity p when IA is 55%, and the welding torch moving speed V TS Local porosity p when IA is 71%, and the welding torch travel speed V TS Local porosity p when IA was 43%.

[0048] In this embodiment, the welding torch moving speed V TS When the flow rate is 320 mm / min, the local porosity p IA This result suggests that the local porosity p IA It was confirmed that a metal foam body with a high porosity of 80% or more could be obtained.

[0049] [Lamination test of metal foam] A 10 mm long test piece was cut from the metal foam forming wire, and a first layer of a metal foam body was formed on a plate stage at a moving speed of 220 mm / min and an arc current of 6 A. Next, a 10 mm long test piece was cut from the metal foam forming wire, and a second layer of a metal foam body was formed on the first layer at a moving speed of 220 mm / min and an arc current of 6 A. The densities of the first and second layers were measured to calculate the porosity, and the cross sections of the first and second layers were observed with an optical microscope.

[0050] FIG. 7(a) is a cross-sectional photograph of a laminate of the first and second layers of a metal foam body. FIG. 7(b) is an enlarged cross-sectional photograph of the vicinity of the boundary between the first and second layers. As shown in FIGS. 7(a) and 7(b), the first and second layers are bonded to such an extent that the bond boundary is not visible, despite the fact that aluminum has the property of forming a thick iron oxide in air. These results confirm that the method for forming a metal foam body using the metal foam body forming wire of the present disclosure enables three-dimensional modeling with sufficient layer strength.

[0051] The average pore size of the first layer was 49 μm, that of the second layer was 134 μm, and the average pore size of both layers was 86 μm. It is presumed that the pores in the first layer were crushed due to the low viscosity of the metal precursor. On the other hand, the pores in the first layer did not connect with the pores in the second layer, and no coarsening of the pores was observed. In order to achieve three-dimensional fabrication with high porosity using the WAAM method, it is thought that ensuring the viscosity of the aluminum that serves as the base for the metal precursor is also important. [Explanation of symbols]

[0052] 1...wire for forming metal foam body, 2...core material, 3...outer material, 4...metal precursor, K...arc, P...metal foam body, S...target object.

Claims

1. A wire for forming metal foam, with a core made of a metal precursor that foams when heated.

2. The wire for forming a metal foam body according to claim 1 , further comprising an outer shell member made of a weldable alloy, the outer shell member covering the circumferential surface of the core member.

3. The wire for forming a metal foam body according to claim 2 , wherein the outer shell material is made of an alloy of the metal contained in the metal precursor.

4. The wire for forming a metal foam body according to claim 1 , wherein the metal precursor contains a foaming agent and a thickener.

5. Generate an arc on the object, A method for forming a metal foam body, comprising heating the wire for forming a metal foam body according to any one of claims 1 to 4 with the arc, and performing build-up welding while foaming the metal precursor, thereby laminating the metal foam body on the object.

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