Additive manufacturing method

Abstract

To provide a lamination molding method allowing for manufacturing a dense molded body irrespectively of properties of a powder.SOLUTION: A lamination molding method for lamination-molding a powder by fusing it with a laser, includes performing lamination molding under a molding condition of the following Expression (1) using a ratio ρ / ρ' of true density ρ (g / cm3) to bulk density ρ' (g / cm3) of a powder, a melting point of the powder, and a material factor A dependent on specific heat. 0.5A(ρ / ρ')≤P / (v×d×h)≤1.5A(ρ / ρ') ... (1), where P is laser output (W), v is a laser scan rate (mm / s), d is a laser scan pitch (mm) and h is a lamination pitch (mm).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an additive manufacturing method. [Background technology]

[0002] Patent Document 1 discloses a technology for additive manufacturing in which a first layer of powder is dispensed onto a target surface, a laser beam is selectively irradiated onto that portion to provide energy and sinter it, a second layer of powder is dispensed onto the first layer of powder, and a laser beam is similarly irradiated onto it to sinter it, and these operations are repeated as many times as necessary. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 1-502890 Summary of the Invention [Problem to be solved by the invention]

[0004] In the additive manufacturing technique described in Patent Document 1, depending on the properties of the powder used, it may be difficult to obtain a high-density molded body under given additive manufacturing conditions.

[0005] An object of the present invention is to provide an additive manufacturing method that can produce a high-density shaped object regardless of the properties of the powder. [Means for solving the problem]

[0006] The inventors conducted extensive research to develop an additive manufacturing method that can produce high-density objects regardless of the properties of the powder. As a result, they discovered that it is effective to determine the manufacturing conditions based on the ratio of the true density to the bulk density of the powder.

[0007] The present invention was completed based on these findings and provides the following means.

[0008] (1) An additive manufacturing method for additive manufacturing by melting powder with a laser, True density of powder ρ (g / cm 3 ) and bulk density ρ´ (g / cm 3 The additive manufacturing is performed under the manufacturing conditions of the following formula (1), which uses the ratio ρ / ρ' of the powder and the material coefficient A, which depends on the melting point and specific heat of the powder. The density of the resulting molded body is 95% or more of the true density. An additive manufacturing method characterized by: 0.5A(ρ / ρ´)≦P / (v×d×h)≦1.5A(ρ / ρ´) …(1) where P is the laser output (W), v is the laser scanning speed (mm / s), d is the laser scanning pitch (mm), and h is the layer pitch (mm). Therefore, the material coefficient A is expressed by the following equation (2) when the specific heat is c (J / kg / K), the melting point is m (K), the heat of fusion is q (kJ / mol), the molecular weight is MW (g / mol), the absorption coefficient is a, and the thermal conductivity is λ (W / m / K). A=a(5.2×(c×m / ρ / 10 6 +q×ρ / MW)+1.3λ) …(2)

[0009] (2) The additive manufacturing method according to (1), characterized in that the diameter of the powder particles is 0.2 mm or less.

[0010] (3) The additive manufacturing method according to (1) or (2), wherein the powder is produced by a water atomization method. [Effects of the Invention]

[0011] According to the present invention, an additive manufacturing method is provided that can manufacture a high-density shaped body regardless of the properties of the powder. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a photograph showing the particle shape of powder formed by gas atomization. [Figure 2] 1 is a photograph showing the particle shape of powder formed by water atomization. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail. In this embodiment, a shaped object of a desired shape is formed by additive manufacturing of powder. An appropriate material is selected as the powder for additive manufacturing depending on the component to be formed. Typically, a shaped object can be formed using a metal powder. Examples of metal powders include iron-based alloys, Ni-based alloys, and Cr-based alloys.

[0014] In additive manufacturing, a first layer of powder is formed on the target surface, a laser is selectively irradiated on that area to apply energy and melt it, a second layer of powder is formed on the molten first layer, and a laser is irradiated on it to melt it in the same way, and this process is repeated as many times as necessary to form a shaped object.

[0015] The molding conditions at this time include the laser output P (W), laser scanning speed v (mm / s), laser scanning pitch d (mm), and layer pitch h (mm). Increasing the laser output P increases the energy supplied to the powder. In this case, the energy actually supplied to a unit volume of powder is P / (v × d × h).

[0016] Regarding powder, gas atomized powder has generally been used for additive manufacturing. Gas atomized powder is formed by dropping molten metal and spraying an inert gas (e.g., Ar gas) from a nozzle onto the dropped molten metal to form powder. The shape of the powder particles is close to spherical, as shown in Figure 1.

[0017] On the other hand, water atomized powder is known as a powder that can be produced more cheaply. Water atomized powder is produced by spraying water onto dripped molten metal. However, the grain shape of water atomized powder is irregular, as shown in Figure 2, unlike gas atomized powder. When additive manufacturing is performed using such water atomized powder, the density of the resulting molded object is low, even if the additive manufacturing conditions are the same as those used for additive manufacturing using gas atomized powder.

[0018] After investigating the reasons why high-density objects cannot be obtained by additive manufacturing using water-atomized powder, we concluded that this is because the powder shape of water-atomized powder is irregular, resulting in a lower bulk density than gas-atomized powder.

[0019] That is, when additive manufacturing is performed using powder, the true density ρ (g / cm 3 ) and bulk density ρ´ (g / cm 3 The ratio ρ / ρ' is an important parameter in additive manufacturing; the larger ρ / ρ', i.e., the smaller ρ', the greater the energy required for additive manufacturing. Furthermore, the energy required to melt powder per unit volume varies depending on the powder's melting point and specific heat, and therefore also varies depending on the material coefficient A, which is a coefficient dependent on the powder's melting point and specific heat. The material coefficient A can be calculated, for example, using the following formula, where c is the specific heat (J / kg / K), m is the melting point (K), q is the heat of fusion (kJ / mol), MW is the molecular weight (g / mol), absorptivity (a), and λ is the thermal conductivity (W / m / K). However, the material coefficient A is not limited to the following formula: A=a(5.2×(c×m / ρ / 10 6 +q×ρ / MW)+1.3λ)

[0020] When the value of P / (v×d×h), which is the energy supplied to the powder per unit volume, the ratio ρ / ρ' of true density to bulk density, and the material coefficient A, which is related to the energy required to melt the powder per unit volume, satisfy the relationship of the following equation (1), the density of the molded body obtained by additive manufacturing will be 95% or more of the true density. 0.5A(ρ / ρ´)≦P / (v×d×h)≦1.5A(ρ / ρ´) …(1)

[0021] In the above formula (1), if P / (v×d×h) is less than 0.5A(ρ / ρ'), the powder will not melt sufficiently, and if P / (v×d×h) is more than 1.5A(ρ / ρ'), excessive energy will be imparted to the powder, and in either case, a high density of 95% or more of the true density will not be obtained. By keeping the value of P / (v×d×h) within the range of the above formula (1), the desired melting state will be achieved, and the density of the shaped body can be made 95% or more of the true density.

[0022] In the present invention, it is preferable that the diameter of the powder particles is 0.2 mm or less, which improves the powder spreadability and reduces the occurrence of molding defects.

[0023] By performing additive manufacturing so as to satisfy the above formula (1), it is possible to obtain a high-density molded body regardless of the shape of the powder.In addition, it is possible to obtain a high-density additive manufactured body even in the case of powder produced by the water atomization method, which has traditionally been difficult to perform high-density additive manufacturing on. [Example]

[0024] Next, an example will be described. Here, we used Fe-Ni alloy (true density 8.10 g / cm3) and Cr-Fe alloy (true density 7.20 g cm3) as powder materials. Gas-atomized and water-atomized powders were prepared from these materials, and additive manufacturing was performed under various manufacturing conditions to determine the density of the resulting objects. Table 1 shows the powder conditions, manufacturing conditions, and densities of the resulting objects. The manufacturing conditions used were the laser power P (W), laser scanning speed v (mm / s), laser scanning pitch d (mm), and layer pitch h (mm), as shown in equation (1) above. Furthermore, the material coefficient A, which depends on the powder's melting point and specific heat, was calculated using the following equation, where c is the specific heat (J / kg / K), m is the melting point (K), q is the heat of fusion (kJ / mol), MW is the molecular weight (g / mol), a is the absorption coefficient (a), and λ is the thermal conductivity (W / m / K), as described above. A=a(5.2×(c×m / ρ / 10 6 +q×ρ / MW)+1.3λ)

[0025] In Table 1, No.1~2、4~5、7~11 No. uses an Fe-Ni alloy as the powder material, and No. 13 to 24 uses a Cr-Fe alloy as the powder material. 1~2、4~5 , 13 to 18 are made using gas atomized powder, and No. 7 to 11 , 19 to 24 are made using water atomized powder. 1~2、4~5、7~11、13~24 Among them, No.1 2 , 7 to 9, 13 to 15, and 19 to 21 are examples of the present invention that satisfy the above formula (1), and Nos. 4 to 5 , 10~ 11 , 16 to 18, and 22 to 24 are comparative examples that do not satisfy the above formula (1).

[0026] As shown in Table 1, No. 1 to No. 2 are examples of the present invention. 2 , 7 to 9, 13 to 15, and 19 to 21 satisfied formula (1), and therefore the density of the shaped body reached the desired high density of 95% or more of the true density ρ, regardless of the powder material and powder manufacturing method.

[0027] In contrast, the comparative examples No. 4 5 , 10~ 11 , 16 to 18, and 22 to 24 did not satisfy formula (1), and therefore the density of the shaped body was less than 95% of the true density ρ, regardless of the powder material and powder manufacturing method.

[0028] [Table 1]

Claims

1. An additive manufacturing method for additive manufacturing by melting powder with a laser, comprising: The true density ρ (g / cm ３ ) and bulk density ρ' (g / cm ３ ) and a material coefficient A, which depends on the melting point and specific heat of the powder, and is expressed by the following formula (1): 0.5A (ρ / ρ')≦P / (v×d×h)≦1.5A (ρ / ρ')...(1) where P is the laser output (W), v is the laser scanning speed (mm / s), d is the laser scanning pitch (mm), and h is the layer pitch (mm). The material coefficient A is expressed by the following formula (2) where c is the specific heat (J / kg / K), m is the melting point (K), q is the heat of fusion (kJ / mol), MW is the molecular weight (g / mol), a is the absorptivity, and λ is the thermal conductivity (W / m / K). A=a(5.2×(c×m / ρ / 10 6 +q×ρ / MW)+1.3λ)…(2)

2. The layered manufacturing method according to claim 1, wherein the diameter of the powder particles is 0.2 mm or less.

3. 3. The layered manufacturing method according to claim 1, wherein the powder is produced by a water atomization method.

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