Patent Description:
In the abovementioned technical field, patent literature <NUM> discloses a technique by which the measurement value of the fluidity complying with JIS Z <NUM> is set at <NUM> to <NUM> sec/<NUM> as a condition when using WC-base hard metal particles as lamination shaping granules. Also, non-patent literature <NUM> describes the standards of JIS Z <NUM> as a metal powder-fluidity measurement method.

<CIT> discloses that primary powder particles whose main component is aluminum and whose particle diameter is between <NUM> and <NUM> are bound together using an organic binder to form secondary powder particles having a particle diameter of <NUM> to <NUM>. Similarly, primary powder particles whose main component is iron and whose particle diameter is between <NUM> and <NUM> are bound together using an organic binder to form secondary powder particles having a particle diameter of <NUM> to <NUM>, Thus, an alloy powder having excellent fluidity can be obtained, and a sintered alloy material having high dimensional accuracy can be produced with these secondary powder particles.

<CIT> discloses a copper powder initiating heat shrinkage behavior at a heating temperature of <NUM> or less by a heat shrinkage behavior measurement from room temperature to <NUM> by using a TMA (thermomechanical analysis) device, where maximum shrinkage rate C(%) of the copper powder is larger than maximum shrinkage rate C(%) of the copper and maximum shrinkage rate Cm (%) of mixture copper satisfies the following formula C-(C-C)×<NUM>≤Cm≤C+<NUM> when the mixture copper is prepared by adding the copper powder to the copper which initiates no heat shrinkage behavior at the heating temperature of <NUM> or less.

<CIT> discloses an aluminum particle group consisting of aluminum particles, having average circularity of the aluminum particle group of <NUM> or more and average particle diameter Dof the aluminum particle group of <NUM> or more and less than <NUM> in an observed image when the aluminum particle group is observed by using a scanning type electron microscope and satisfying A×<NUM>≤B and D.

<CIT> discloses that the powder for molding of the present invention is to be used for a powder bed melt-binding process and comprises powder containing a ceramic material and/or metal, and a thermoplastic binder. The thermoplastic binder contains at least one compound selected from the group consisting of petroleum wax, fatty acids, fatty acid esters, fatty acid amides and polyvinyl acetal. The thermoplastic binder has a melting point or a glass transition point in a range of <NUM> or higher and <NUM> or lower. The powder for molding preferably has a Hausner ratio (a ratio of (tap density)/(bulk density)) of <NUM> or more and <NUM> or less.

<CIT> discloses spherical TC4 titanium alloy powder used for laser 3D printing and a preparation method thereof. Titanium alloy powder particles are in a sphere shape, the grain size is <NUM>-<NUM>, the oxygen content is <NUM>%-<NUM>%, the apparent density is <NUM>-<NUM>/cm<<NUM>>, and the liquidity of the powder with the grain size being <NUM>-<NUM> is <NUM>-<NUM>/<NUM>. The powder with the grain size being <NUM>-<NUM> can be used for powder laying method laser 3D printing, and the powder with the grain size being <NUM>-<NUM> can be used for powder feeding laser 3D printing. According to the preparation method, an electrode titanium bar of which one end is a conical tip is made from titanium alloy and is placed in a induction melting chamber to rotate, induction melting is started at the same time, and when liquid drops are formed by the tip, the titanium bar rotates and perpendicularly moves downwards; the alloy liquid drops are atomized into the powder in an atomizing chamber through inert gases by regulating and controlling the atomizing air pressure and induction parameters; and then collection is conducted through a powder collection device, and the powder with different grain sizes is screened and preserved in a vacuum mode.

Unfortunately, the measurement of the fluidity complying with JIS Z <NUM> 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.

The present invention provides a technique of solving the above-described problem.

The present invention is defined in independent claim <NUM>. One example aspect provides a method of evaluating whether powder for lamination shaping can be spread into a uniform powder layer in the lamination shaping, wherein the powder is evaluated using, as a flowability of the powder, an adhesive force of the powder calculated from a failure envelope obtained by a shear test.

Another example not covered by the claims but helpful for understanding 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, 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.

<FIG> is a view showing a schematic configuration example of a laminating and shaping apparatus <NUM> of this example embodiment. The laminating and shaping apparatus <NUM> includes an emission mechanism <NUM> for an electron beam or fiber laser 101a, a hopper <NUM> as a powder tank, a squeegeeing blade <NUM> for forming a powder bed by spreading a powder by a predetermined thickness, and a table <NUM> that repetitively moves down by a predetermined thickness in order to perform lamination. The squeegeeing blade <NUM> and the table <NUM> cooperate with each other to generate a powder laminated portion <NUM> having a uniform predetermined thickness. Each layer is irradiated with the fiber laser 101a based on slice data obtained from 3D-CAD data, thereby melting a metal powder (in this example embodiment, a metal powder, particularly a copper powder or a copper alloy powder) and manufacturing a laminated and shaped product 105a.

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 shapin 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.

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 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 <NUM>, and a powder having an insufficient squeegeeing property is basically excluded from the lamination shaping powder.

A powder having a sufficient squeegeeing property requires the following conditions.

The flowability is evaluated by using the flow rate (FR) complying with JIS Z <NUM> as disclosed in patent literature <NUM> and non-patent literature <NUM>. However, the measurement of the fluidity complying with JIS Z <NUM> 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 <NUM> to <NUM> is generally used as a powder for lamination shaping, but the use of a finer powder of <NUM> 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 <NUM>, 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.

In this example embodiment, therefore, as a standard of the flowability, not the method complying with JIS Z <NUM> that makes measurement results unstable but the adhesive force with which measurement results are stably obtainable is used as an evaluation criterion of the flowability and combined with other evaluation targets.

The adhesive force is calculated based on the shearing force test as disclosed in non-patent literature <NUM>.

<FIG> is a view showing the arrangement of a shearing stress measurement unit <NUM> for measuring the shearing stress in this example embodiment. The shearing stress measurement unit <NUM> measures the shearing stress by a rotary cell method. A rotary cell <NUM> including a blade attached to its lower portion is placed inside an external cell <NUM>, and a powder to be measured is packed in the upper portion of the external cell <NUM>. While a predetermined normal stress is applied from the rotary cell <NUM> to the external cell <NUM>, the shearing stress is measured from the torque of the rotary cell <NUM>.

<FIG> is a graph showing a method of obtaining the adhesive force based on the shearing stress measured by the shearing stress measurement unit <NUM>. As shown in <FIG>, a line obtained by plotting the shearing stress measured by the shearing stress measurement unit <NUM> when shear occurs under each normal stress is called a failure envelope, and a powder layer slips if a shearing stress stronger than the failure envelope is applied. A shearing stress when the normal stress is <NUM> (zero) on the failure envelope (e.g., <NUM>) is calculated as the adhesive force between particles.

In this example embodiment, an evaluation criterion of the squeegeeing property of a lamination shaping powder was analyzed by comparing numerical values of the squeegeeing property evaluation conditions including the adhesive force with evaluation results indicating whether the actual squeegeeing property is sufficient in lamination shaping.

<FIG> is a view showing a jig <NUM> for testing the squeegeeing property in this example embodiment. An upper view <NUM> of <FIG> is a view showing the jig <NUM> from its upper surface, and a lower view <NUM> of <FIG> is a view showing the jig <NUM> from its bottom surface. The jig <NUM> is called a doctor blade or an applicator, and obtained by forming a gap by processing one surface of a metal block. The jig <NUM> can apply a paint or ink with a predetermined film thickness.

In this example embodiment, the two ends of the jig <NUM> having an application width of <NUM> and an application thickness of <NUM> were picked up, and the jig <NUM> was pressed against the table <NUM> of the laminating and shaping apparatus <NUM> 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 <NUM> and the squeegeeing property obtained by the laminating and shaping apparatus <NUM> was confirmed by squeegeeing a powder by using the laminating and shaping apparatus <NUM>.

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, (<NUM>) the apparent density changes in accordance with the type of lamination shaping powder or the type of metal, but (<NUM>) the <NUM>% particle size and (<NUM>) the flowability (adhesive force) fall within similar ranges regardless of the type of laminating and shaping apparatus or the type of metal. In evaluation by (<NUM>), the flowability (adhesive force) is essential, and at least one of (<NUM>) the <NUM>% particle size and (<NUM>) the apparent density restricts the conditions of a lamination shaping powder.

In this example embodiment, a lamination shaping powder can be evaluated by stable criteria. In addition, the stable criteria make it possible to easily find a powder usable as a lamination shaping powder.

That is, when the adhesive force of a powder calculated from the failure envelope obtained by a shear test using a powder rheometer is <NUM> kPa or less, it is possible to obtain a high-density homogeneous laminated and shaped product having a sufficient flowability with which a uniform powder layer can be spread. If the adhesive force of a powder calculated from the failure envelope obtained by the shear test using the powder rheometer is larger than <NUM> kPa, the squeegeeing property of the powder becomes insufficient.

Also, if the <NUM>% particle size measured by the laser diffraction method is less than <NUM>, the powder causes surface defects, e.g., violently scatters and adheres to the manufacture product again. If the <NUM>% particle size is larger than <NUM> in lamination shaping using a laser beam, or if the <NUM>% particle size is larger than <NUM> in lamination shaping using an electron beam, the surface of the manufacture 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.

Furthermore, if the apparent density is less than <NUM>/cm<NUM>, 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.

In this example embodiment, a lamination shaping powder is evaluated by further taking account of the "satellite adhesion ratio" of the powder particles. The "satellite adhesion ratio" is the ratio of powder particles on which satellites are adhered, in all particles including powder particles on which no satellites are adhered.

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 manufacture 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, the satellite adhesion ratio was obtained by capturing a scanning electron microscope (SEM) image of powder particles, and counting powder particles on which satellites were adhered and powder particles on which no satellites were adhered. However, it is also possible, by image processing, to count powder particles on which satellites are adhered and powder particles on which no satellites are adhered.

According to this example embodiment, it is possible to more accurately evaluate whether a lamination shaping powder is usable.

By using Examples <NUM> to <NUM> according to this example embodiment and Comparative Examples <NUM> to <NUM>, 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.

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.

The shearing stress of a copper powder or a copper alloy powder was measured by using a searing stress measurement kit and input to Powder Rheometer FT4 (manufactured by Malvern Instruments), and the adhesive force was calculated in accordance with <FIG>. Table <NUM> shows the correspondence between the FR (sec/<NUM>) measurement results complying with JIS Z <NUM> and the adhesive force measurement results in Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>.

As is apparent from Table <NUM>, the adhesive force measurement result can be obtained even for a copper powder or a copper alloy powder that is "unmeasurable" in the FR (sec/<NUM>) measurement result. Therefore, even for a powder found to be unusable by the FR (sec/<NUM>) measurement result, it is possible to determine whether the powder is usable as a lamination shaping powder.

The <NUM>% particle size (µm) of a copper powder or a copper alloy powder of each of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was measured by the laser diffraction method (Microtrac MT3300: manufactured by MicrotrackBEL). Also, the apparent density (g/cm<NUM>) of the copper powder or the copper alloy powder was measured in accordance with JIS Z <NUM>.

The squeegeeing property of a copper powder or a copper alloy powder of each of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> was tested by using the jig <NUM> shown in <FIG>.

<FIG> is a view showing the test results of the squeegeeing properties of powders of Examples <NUM> to <NUM>. <FIG> is a view showing the test results of the squeegeeing properties of powders of Comparative Examples <NUM> and <NUM>. <FIG> and <FIG> show only some of the examples and the comparative examples, but the results of other examples and other comparative examples were also similar.

Table <NUM> shows the correspondence between the characteristics (the adhesive force, <NUM>% particle size, and apparent density) and the squeegeeing property test results of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>.

<FIG> shows a state in which the powders of Examples <NUM> to <NUM> and Comparative Example <NUM> were squeegeed in the laminating and shaping apparatus. As shown in <FIG>, when using a powder found to have a good squeegeeing property in Table <NUM>, squeegeeing in the laminating and shaping apparatus was also good. By contrast, when using a powder found to have an unsatisfactory or bad squeegeeing property in Table <NUM>, squeegeeing in the laminating and shaping apparatus was also unsatisfactory.

Accordingly, evaluation by the adhesive force, <NUM>% particle size, and apparent density as the squeegeeing property criteria disclosed in this example embodiment were found to be useful.

<FIG> are views showing scanning electron microscope (SEM) images for measuring the satellite adhesion ratios of the powders of Examples <NUM> to <NUM>. <FIG> are views showing scanning electron microscope (SEM) images for measuring the satellite adhesion ratios of the powders of Comparative Examples <NUM> to <NUM>. The satellite adhesion ratios of the powders of the examples and the comparative examples were obtained by using these scanning electron microscope (SEM) images.

Table <NUM> shows the correspondence between the characteristics (the adhesive force, <NUM>% particle size, apparent density, and satellite adhesion ratio) and the squeegeeing property test results of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM>.

Claim 1:
A method of evaluating powder for lamination shaping, wherein whether or not the powder is spread into a uniform powder layer on a table (<NUM>) of a laminating and shaping apparatus (<NUM>) in the lamination shaping is evaluated using an adhesive force of the powder calculated from a failure envelope (<NUM>) obtained by a shear test (<NUM>) of the powder, the shear test (<NUM>) being conducted by a powder rheometer,
the adhesive force is obtained as a shearing stress when a normal stress is zero on the failure envelope (<NUM>) at the powder rheometer,
wherein the powder is evaluated further using an apparent density of the powder, and
wherein if
the adhesive force is equal to or less than <NUM> kPa, and
the apparent density of the powder measured according to JIS Z <NUM> is equal to or more than <NUM>/cm<NUM>, the powder is evaluated to be spread into a uniform powder layer in the lamination shaping.