Patent Application
20200254517
The present invention relates to a lamination shaping powder evaluation method and a lamination shaping powder therefor.
In the abovementioned technical field, patent literature 1 discloses a technique by which the measurement value of the fluidity complying with JIS Z 2502 is set at 10 to 25 sec/50 g as a condition when using WC-base hard metal particles as lamination shaping granules. Non-patent literature 1 also describes the standards of JIS Z 2502 as a metal powder-fluidity measurement method. In addition, patent literature 2 discloses a technique that evaluates the flowability of aluminum particles by criteria including the average roundness, the average particle size, and the satellite state.
Patent literature 1: Japanese Patent Laid-Open No. 2016-172904
Patent literature 2: Japanese Patent Laid-Open No. 2017-066432
Non-patent literature 1: Japanese Industrial Standards (JIS Z 2502: 2012), “Metallic powders-Determination of flow rate by means of a calibrated funnel”
Unfortunately, the measurement of the fluidity complying with JIS Z 2502 using the technique described in the above literature is unstable as a criterion of a lamination shaping powder because a fine powder probably usable for lamination shaping cannot be measured or the same powder can be measured or cannot be measured due to a slight change in measurement environment. This makes the evaluation of a lamination shaping powder insufficient. Also, the evaluation of the satellite adhesion ratio, the fine particle ratio, and the average roundness as the evaluation of the flowability of aluminum particles disclosed in patent literature 2 is not directly related to the evaluation of the squeegeeing property of a powder in a laminating and shaping apparatus.
The present invention provides a technique of solving the above-described problem.
One example aspect of the present invention provides a method of evaluating a squeegeeing property of powder for lamination shaping, wherein the squeegeeing property is evaluated using at least a satellite adhesion ratio of the powder and an apparent density of the powder.
Another example aspect of the present invention provides powder, which has been evaluated to be spread into a uniform powder layer in lamination shaping by the abovementioned method.
According to the present invention, the squeegeeing property of a lamination shaping powder can be evaluated by stable criteria.
Example embodiments of the present invention will now be described in detail with reference to the drawings. it should be noted that the relative arrangement of the components, the numerical expressions and numerical values set forth in these example embodiments do not limit the scope of the present invention unless it is specifically stated otherwise.
<<Manufacture of Laminated and Shaped Product>>
As described above, a manufactured product having an arbitrary shape can be obtained by melting and solidifying a lamination shaping powder by using the electron beam or fiber laser 101a as a heat source. For example, when using a copper powder, fine manufacturing can be performed in the fields of electric circuit connectors, heat sinks, and heat exchangers. However, the lamination shaping powder is not limited to a metal powder such as a copper powder.
«Manufacture of Lamination Shaping Powder»
The lamination shaping powder of this example embodiment can be manufactured by, e.g., “a rotating disk method”, “a gas atomizing method”, “a water atomizing method”, “a plasma atomizing method”, or “a plasma rotating electrode method”. In this example embodiment, “the gas atomizing method” was used among these methods. In this gas atomization, a gas such as helium, argon, or nitrogen was used, and a lamination shaping powder was manufactured by controlling powdering by adjusting the pressure and flow rate of the gas. However, a similar lamination shaping powder can also be manufactured by using another manufacturing method. The manufactured lamination shaping powder was classified by a predetermined classification size.
«Conditions Usable as Lamination Shaping Powder»
Conditions usable as a lamination shaping powder are presumably as follows:
Of these conditions, the squeegeeing property is a criterion for determining whether a powder can be used by the laminating and shaping apparatus 100, and a powder having an insufficient squeegeeing property is basically excluded from the lamination shaping powder.
«Evaluation Targets of Squeegeeing Property»
A powder having a sufficient squeegeeing property requires the following conditions.
«Evaluation of Flowability»
The flowability is evaluated by using the flow rate (FR) complying with JIS Z 2502 as disclosed in patent literature 1 and non-patent literature 1. However, the measurement of the fluidity complying with JIS Z 2502 is unstable as a criterion of a lamination shaping powder because a fine powder probably usable for lamination shaping cannot be measured or the same powder can be measured or cannot be measured due to a slight change in measurement environment. This makes the evaluation of a lamination shaping powder insufficient.
For example, a fine powder having an average particle size of 20 to 45 μm is generally used as a powder for lamination shaping, but the use of a finer powder of 20 μm or less is desirable in the future. A fine powder has a strong adhesive force and hence has a low flowability, and this makes it difficult to generate a powder layer necessary for lamination shaping. It is sometimes impossible to measure a fine powder like this by using JIS Z 2502, so this method is insufficient to properly evaluate the flow form of a powder for lamination shaping. If measurement is impossible, it becomes difficult to evaluate the powder as a lamination shaping powder. In practice, however, it is sometimes possible to laminate even an unmeasurable fine powder depending on an apparatus or a supply method, and this makes evaluation difficult.
For example, the flowability and the spreadability of a powder are hindered if the powder has a nonuniform shape due to strain or a large amount of satellites are adhered on the powder, and no uniform powder layer can be formed. Since this generates pores or decreases the density, a high-density high-quality homogeneous manufactured product cannot be obtained. A powder is ideally closer to a spherical shape in order to obtain a sufficient flowability and a sufficient spreadability. However, the manufacturing cost rises in order to obtain a powder having a higher spherical degree. The present inventors made extensive studies and have found that it is possible to ensure a sufficient flowability and a sufficient spreadability suitable for lamination shaping by controlling the satellite adhesion amount to a predetermined amount or less.
In this example embodiment, therefore, as a standard of the flowability, not the method complying with JIS Z 2502 that makes measurement results unstable but the satellite adhesion ratio with which measurement results are stably obtainable is used as an evaluation criterion of the flowability and combined with other evaluation targets. The “satellite adhesion ratio” of powder particles is the ratio of the number of powder particles on which satellites are adhered to the number of all particles including powder particles on which no satellites are adhered.
(Satellite Adhesion Ratio Measurement Method)
In this example embodiment, from a scanning electron microscope (EM) image obtained by capturing a manufactured powder, the satellite adhesion ratio of the whole powder was calculated by counting powder particles on which satellites were adhered and powder particles on which no satellites were adhered. Note that it is also possible to extract the number of powder particles on which satellites are adhered and the number of particles on which no satellites are adhered, by image processing of a scanning electron microscope (SEM) image, and calculate the satellite adhesion ratio of the whole powder.
(Evaluation of Squeegeeing Property)
In this example embodiment, the two ends of the jig 400 having an application width of 50 mm and an application thickness of 100 μm were picked up, and the jig 400 was pressed against the table 104 of the laminating and shaping apparatus 100 or against an equivalent horizontal plate and pulled at a predetermined velocity, thereby forming a powder layer. After that, whether a uniform powder layer was formed was observed. Note that this process was repetitively performed by changing the initial powder amount or the velocity.
In addition, the relationship between the squeegeeing property test using the jig 400 and the squeegeeing property obtained by the laminating and shaping apparatus 100 was confirmed by squeegeeing a powder by using the laminating and shaping apparatus 100.
«Evaluation Criteria of Squeegeeing Property»
From the relationship between the abovementioned characteristics measured from the powders, the squeegeeing property test using the jig, and the squeegeeing property obtained by the laminating and shaping apparatus, the following evaluation criteria were obtained when using a copper powder or a copper alloy powder.
Of the abovementioned three conditions, (2) the apparent density changes in accordance with the type of lamination shaping powder or the type of metal, but (1) the 50% particle size and (3) the flowability (satellite adhesion ratio) fall within similar ranges regardless of the type of laminating and shaping apparatus or the type of metal. Evaluation by (3) the flowability (satellite adhesion ratio) is essential, and at least one of (1) the 50% particle size and (2) the apparent density restricts the conditions of a lamination shaping powder.
«Effects of This Example Embodiment»
In this example embodiment, a lamination shaping powder can be evaluated by stable criteria. Also, the stable criteria make it possible to easily find a powder usable as a lamination shaping powder.
In addition, it is possible to spread a uniform powder layer, and obtain a high-density high-quality homogeneous manufactured product not having defects such as segregation and voids. It is also possible to reduce the material cost when using a copper powder or a copper alloy powder in lamination shaping.
That is, if the satellite adhesion ratio exceeds 50%, the squeegeeing property of the powder deteriorates. Also, the conductivity decreases, and this may hinder temporary sintering in a preheating step of electron-beam lamination shaping.
Furthermore, if the apparent density is less than 3.5 g/cm3, the packing property of the powder in the powder layer deteriorates, and the density of the manufactured product decreases because pores are formed in the manufactured product.
Also, if the 50% particle size measured by the laser diffraction method is less than 3 μm, the powder causes surface defects, e.g., violently scatters and adheres to the manufactured product again. If the 50% particle size is larger than 75 μm in lamination shaping using a laser beam, or if the 50% particle size is larger than 250 μm in lamination shaping using an electron beam, the surface of the manufactured product roughens and causes an appearance defect. Alternatively, a melt pool formed in a powder layer during beam irradiation does not reach a solidified layer immediately below the pool. Since this causes insufficient melting and solidification, a shaping defect occurs.
In this example embodiment, a lamination shaping powder is evaluated by further taking account of the “adhesive force” of the powder particles. The “adhesive force” is calculated based on a shearing force test.
For example, a fine powder having an average particle size of 20 to 45 μm is generally used as a powder for lamination shaping, but the use of a finer powder of 20 μm or less is desirable in the future. A fine powder has a strong adhesive force and hence has a low flowability, and this makes it difficult to generate a powder layer necessary for lamination shaping. It is sometimes impossible to measure a fine powder like this by using JIS Z 2502, so this method is insufficient to properly evaluate the flow form of a powder for lamination shaping. If measurement is impossible, it becomes difficult to evaluate the powder as a lamination shaping powder. In practice, however, it is sometimes possible to laminate even an unmeasurable fine powder depending on an apparatus or a supply method, and this makes evaluation difficult.
The flowability of a fine powder is low because the adhesive force between particles forming a fine powder is strong and the kinetic energy of the particles is very low. It is known that the adhesive force of a powder relatively increases as the particle size decreases. The adhesive force functions as binding power that hinders the flowability of a powder. On the other hand, the kinetic energy is proportional to the mass, but the mass of a particle is proportional to the cube of the particle size, so the kinetic energy of a fine particle becomes very low. Consequently, the gravity and the inertia force necessary to move particles become low and cannot exceed the adhesive force as binding power. This makes it impossible to cause the flow of a powder.
«Measurement of Adhesive Force»
In this example embodiment, the adhesive force with which measurement results are stably obtainable is further used as an evaluation criterion of the flowability and combined with other evaluation targets.
(Adhesive Force Measurement Method)
«Effects of This Example Embodiment»
According to this example embodiment, it is possible to more accurately evaluate whether a lamination shaping powder is usable.
By using Examples 1 to 15 according to this example embodiment and Comparative Examples 1 to 6, the evaluation criteria of the lamination shaping powder evaluation method of this example embodiment will be verified from the relationship between the evaluation results of evaluated lamination shaping powders, the squeegeeing property test using the jig, and the squeegeeing property of the laminating and shaping apparatus.
«Manufacture of Lamination Shaping Copper Powders»
By using gases such as helium, argon, and nitrogen as gas atomization of a gas atomizing method, copper powders or copper alloy powders were generated by controlling powdering by adjusting the pressure and flow rate of each gas, and the evaluation criteria of the lamination shaping powder evaluation method of this example embodiment were verified. However, the following examples can be referred to even for another powder or another metal powder.
«Measurement of Satellite Adhesion Ratio»
As is apparent from Table 1, the satellite adhesion ratio measurement result can be obtained even for a copper powder or a copper alloy powder that is “unmeasurable” in the FR (sec/50 g) measurement result. Therefore, even for a powder found to be unusable by the FR (sec/50 g) measurement result, it is possible to determine whether the powder is usable as a lamination shaping powder.
«Measurements of 50% Particle Size and Apparent Density»
The 50% particle size (μm) of a copper powder or a copper alloy powder of each of Examples 1 to 15 and Comparative Examples 1 to 6 was measured by the laser diffraction method (Microtrac MT3300: manufactured by MicrotrackBEL). Also, the apparent density (g/cm3) of the copper powder or the copper alloy powder was measured in accordance with JIS Z 2504.
<<Test of Squeegeeing Property>>
The squeegeeing property of a copper powder or a copper alloy powder of each of Examples 1 to 15 and Comparative Examples 1 to 6 was tested by using the jig 400 shown in
Table 2 shows the correspondence between the characteristics (the satellite adhesion ratio, 50% particle size, and apparent density) and the squeegeeing property test results of Examples 1 to 15 and Comparative Examples 1 to 6.
«Results of Squeegeeing by Laminating and Shaping Apparatus»
Accordingly, evaluation by the satellite adhesion ratio, 50% particle size, and apparent density as the squeegeeing property criteria disclosed in this example embodiment were found to be useful.
«Measurement of Adhesive Force»
The shearing stress of a copper powder or a copper alloy powder was measured by using a searing stress measurement kit shown in
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/030510 | 8/25/2017 | WO | 00 |
