JP2018123381A - Mixed powder containing two powders of different particle sizes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a powder for performing sintering lamination molding with higher accuracy, and a method of producing the same.SOLUTION: A mixed powder containing a first powder and a second powder which are formed from the same material and have different particle size distributions, is used for sintering lamination molding. The ratio of a central particle size of a first particle size distribution to a central particle size of a second particle size distribution is larger than 3 and smaller than 5.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a powder and a method for producing the powder. For example, the powder can be suitably used for a powder that can be used in a sintered additive manufacturing technique and a method for producing the powder.

  In the international standard, additive manufacturing technology called “Additive Manufacturing” and generally called “3D printer” or the like is known. This modeling technique makes it possible to generate a modeled object having a complicated shape without using a mold such as a mold or a mold.

  In the additive manufacturing technique, first, data indicating the shape of a desired object is manufactured by, for example, three-dimensional CAD (Computer Aided Design), and the data is divided into a plurality of layers orthogonal to a predetermined direction. While generating plate-shaped objects corresponding to the respective layers, the plate-shaped objects are simultaneously laminated and adhered. By repeating such an operation, the entire modeled object can be generated.

  A plurality of methods are known for additive manufacturing technology, and one of them is a powder sintering method. In the additive manufacturing technology of the powder sintering method, the layered powder is melted and solidified by heating to produce a plate-shaped object of each layer, and at the same time, it is attached to the plate-shaped object of the layer immediately below Laminate.

  In the additive manufacturing technology, there is a known problem that gas porosity is easily generated due to voids between powders by the mechanism of melting and solidifying the powder.

  There is also a known problem that the melted part may fall down. Such a phenomenon is caused when the powder in the state supported by the powder head, such as the upper wall surface of the hollow portion, is supported by the powder head, among the desired shaped objects. The voids may be crushed and generated.

  In relation to the above, Patent Document 1 (Japanese Patent Publication No. 2006-534234) discloses that a three-dimensional article is formed through continuous fusion of at least one powder layer portion supplied onto a work table in a construction chamber. A description of how to do this is disclosed. The method includes the following steps. That is, providing at least a first powder tank and at least a second powder tank. Supplying a first type of powder having a first particle size distribution in a first powder tank; Supplying a second type of powder having a second particle size distribution different from the first particle size distribution into the second powder tank, wherein the minimum particle size in the second particle size distribution is Smaller than the smallest particle size in the first particle size distribution. Distributing the first sub-layer of the first type of powder on the worktable. Dispensing a second sub-layer of the second type of powder on top of the first sub-layer of the first type of powder, the first and second sub-layers being at least 1 Forming one of the two powder layers. Fusing the first and second sub-layers with a high energy beam from a high energy beam source to form a first cross-sectional configuration of the three-dimensional article.

  Non-Patent Document 1 (Michitaka Suzuki, Akira Yagi, Kazuo Watanabe, Toshio Oshima, “Estimation of Porosity of Three-Component Spherical Particle Random Packing Layer”, Chemical Engineering Papers Vol. 10, No. 6, published in 1984 Pp. 721 to 727) discloses a method for analytically calculating the proportion of voids generated between particles in a space filled with a plurality of types of particles having different diameters.

Special table 2016-534234 gazette

Michitaka Suzuki, Akira Yagi, Kazuo Watanabe, Toshio Oshima, “Estimation of Porosity of Three-Component Spherical Particle Random Packing Layer”, Chemical Engineering Vol. 10, No. 6, published in 1984, pp. 721-727

  Provided are a powder for performing sintered additive manufacturing with higher accuracy and a method for manufacturing the same. Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

  The means for solving the problem will be described below using the numbers used in the (DETAILED DESCRIPTION). These numbers are added to clarify the correspondence between the description of (Claims) and (Mode for Carrying Out the Invention). However, these numbers should not be used to interpret the technical scope of the invention described in (Claims).

  The powder according to one embodiment is a powder used for sintered additive manufacturing. This powder comprises a first powder and a second powder. Here, the first powder (1) has a first particle size distribution. The second powder (2) has the same material as the material of the first powder and a second particle size distribution different from the first particle size distribution. The ratio of the first center particle size of the first particle size distribution to the second center particle size of the second particle size distribution is greater than 3 and less than 5.

  The manufacturing method of the powder by one Embodiment is a manufacturing method of the powder used for sintering type | mold additive manufacturing. The method includes providing a first powder, preparing a second powder, and mixing the first powder and the second powder. Here, the first powder has a first particle size distribution. The second powder has a second particle size distribution that is the same as the material of the first powder and that is different from the first particle size distribution. The ratio of the first center particle size of the first particle size distribution to the second center particle size of the second particle size distribution is greater than 3 and less than 5.

  According to the one embodiment, sintering type additive manufacturing can be performed with higher accuracy.

FIG. 1 is a partial cross-sectional view showing a configuration example of a sintered additive manufacturing apparatus. FIG. 2 is a flowchart showing an example of a sintering type additive manufacturing method using the sintering type additive manufacturing apparatus of FIG. FIG. 3A is a diagram for explaining the first squeezing of the powder in the flowchart shown in FIG. 2A. FIG. 3B is a diagram for explaining the first melting and solidification of the powder in the flowchart shown in FIG. 2A. FIG. 3C is a diagram for explaining the second squeezing of the powder in the flowchart shown in FIG. 2A. FIG. 3D is a diagram for explaining the second melting / solidification of the powder in the flowchart shown in FIG. 2A. FIG. 4A is a cross-sectional view illustrating an example of a portion of a modeled article that does not have a sintered portion underneath. FIG. 4B is a cross-sectional view illustrating an example of a state immediately before melt-sintering powder for forming an upper wall surface included in a modeled object without a sintered portion therebelow. FIG. 4C is a cross-sectional view showing an example of a state immediately after melt-sintering a powder for forming an upper wall surface included in a modeled object without a sintered portion therebelow. FIG. 5A is a diagram illustrating an example of a space in which coarse powder is disposed around coarse powder that is a target particle. FIG. 5B is a diagram illustrating an example of a space in which fine powder is arranged around coarse powder that is a target particle. FIG. 5C is a diagram illustrating an example of a space in which coarse powder is arranged around fine powder that is a target particle. FIG. 5D is a diagram illustrating an example of a space in which fine powder is arranged around the fine powder that is the target particle. FIG. 6 is a diagram for calculating the porosity of the space in which the second particles having the second particle diameter are arranged around the first particles having the first particle diameter. FIG. 7 is a diagram for explaining a method of calculating the local porosity. FIG. 8A shows that the number of voids per unit area of the cross section varies depending on the particle size ratio when a mixed powder obtained by mixing two kinds of powders having different particle sizes is sintered. It is a graph to show. FIG. 8B is an example of a cross section of a shaped object obtained by sintering a mixed powder having a particle size ratio of 1. FIG. 8C is an example of a cross section of a shaped article obtained by sintering a mixed powder having a particle size ratio of 2. FIG. 8D is an example of a cross section of a shaped object obtained by sintering a mixed powder having a particle size ratio of 3.4. FIG. 9A is a graph showing an example of a particle size distribution of a powder obtained by mixing two types of particles. FIG. 9B is a diagram for explaining a method of calculating a mixing ratio of each powder from a mixed powder obtained by mixing two kinds of powders. FIG. 9C is a diagram for explaining a method of calculating a mixing ratio of each powder from a mixed powder obtained by mixing two kinds of powders.

  With reference to an accompanying drawing, the form for carrying out the powder by the present invention and the manufacturing method of this powder is explained below.

  First, in order to better understand the problem of the present invention, an additive manufacturing apparatus for realizing a sintered additive manufacturing technique and a sintered additive manufacturing method using the additive additive manufacturing apparatus will be described. FIG. 1 is a partial cross-sectional view showing a configuration example of a sintered additive manufacturing apparatus 1000.

  The components included in the sintered additive manufacturing apparatus 1000 shown in FIG. 1 will be described. 1 includes a control unit 1001, a heating unit 1002, a powder supply unit 1003, a coater 1004, a modeling table 1005, a modeling frame 1006, and a storage unit 2000. . The storage unit 2000 is included in the sintered additive manufacturing apparatus 1000 in the configuration example illustrated in FIG. 1, but is an external device connected to the sintered additive manufacturing apparatus 1000 in another exemplary configuration. May be.

  The shape and connection relationship of each component of the sintered additive manufacturing apparatus 1000 shown in FIG. 1 will be described. First, the powder supply unit 1003 stores a powder 1007 that is a material for generating the model 3000. The powder supply unit 1003 may be fixed to a main body (not shown) of the sintered additive manufacturing apparatus 1000, but more preferably is supported so as to be movable in the horizontal direction by a driving device (not shown). This driving device is electrically connected to the control unit 1001 and moves the powder supply unit 1003 in the horizontal direction under the control of the control unit 1001. The powder supply unit 1003 is also electrically connected to the control unit 1001 and drops the powder 1007 downward under the control of the control unit 1001.

  The modeling table 1005 is a table for supporting the powder 1007 on the surface thereof. Therefore, in order to receive the powder 1007 falling from the powder supply unit 1003, it is desirable that the modeling table 1005 is disposed below the powder supply unit 1003 so that the surface thereof is horizontal. The shape of the modeling table 1005 is, for example, a rectangular parallelepiped, and the shape of the surface of the modeling table is, for example, a rectangle. The modeling table 1005 is supported by a driving device (not shown) so as to be movable in the vertical direction. This drive device is electrically connected to the control unit 1001 and moves the modeling table 1005 in the vertical direction under the control of the control unit 1001.

  The modeling frame 1006 is arranged so as to surround the periphery of the surface of the modeling table 1005 and to be in close contact with the periphery of the surface of the modeling table 1005 so that the powder 1007 laid on the surface of the modeling table 1005 does not fall outside. Has been. Further, the shape inside the modeling frame 1006 has a shape of a side surface of a straight column having the shape of the surface of the modeling table 1005 as a bottom surface so that the modeling table 1005 can slide in the vertical direction inside the modeling frame 1006. It is desirable.

  The coater 1004 is supported by a drive device (not shown) so as to be movable in the horizontal direction. This driving device is electrically connected to the control unit 1001 and moves the coater 1004 in the horizontal direction under the control of the control unit 1001. The coater 1004 horizontally adjusts the upper surface of the powder 1007 supplied on the modeling table 1005 by moving in the horizontal direction. Such an operation is called squeezing. When the surface of the powder 1007 is prepared by squeezing, it is desirable that excess powder is excluded outside beyond the upper end of the modeling frame 1006. Therefore, it is desirable that the upper end portion of the modeling frame 1006 is horizontal, and the lower end portion of the coater 1004 is moved in the horizontal direction so as to slide with respect to the upper end portion of the modeling frame 1006.

  The heating unit 1002 is disposed above the modeling table 1005 and irradiates the powder 1007 supported on the surface of the modeling table 1005 with a heat ray 5000 such as a laser beam or an electron beam. The heating unit 1002 is electrically connected to the control unit 1001, and the range of the surface of the modeling table 1005 that is irradiated with the heat ray 5000 is controlled by the control unit 1001.

  The storage unit 2000 stores shape information indicating the desired shape of the model 3000. The storage unit 2000 is electrically connected to the control unit 1001 and outputs the entire shape information of the modeled object or a part divided for each layer in response to a request from the control unit 1001.

  An example of the overall operation of the sintered additive manufacturing apparatus 1000 according to the configuration example shown in FIG. 1, that is, the sintered additive manufacturing method will be described. FIG. 2 is a flowchart showing an example of a sintering type additive manufacturing method using the sintering type additive manufacturing apparatus 1000 shown in FIG.

  The flowchart shown in FIG. 2 includes a total of six steps from the 0th step S100 to the 5th step S105. The flowchart of FIG. 2 starts from the 0th step S100.

  In the 0th step S100, the sintering type additive manufacturing apparatus 1000 starts its operation, that is, the additive manufacturing method. Following the 0th step, the first step S101 is performed.

  In the first step S101, shape information indicating the desired shape of the model 3000 is prepared. Here, the shape information may be created in advance by an external design apparatus or the like and then stored in the storage unit 2000. The shape information may be decomposed for each layer of the layered modeling, and the shape information for each layer may be stored in the storage unit 2000. Here, the thickness of each layer is set based on the particle size distribution of the powder 1007 to be used, the material of the powder 1007 to be used, the output intensity of the heating unit 1002, the user's desire, and the like. Following the first step S101, a second step S102 is executed.

  In the second step S102, powder 1007 is laid. Here, first, the vertical position of the modeling table 1005 is adjusted such that the difference between the height of the surface of the modeling table 1005 and the height of the upper end of the modeling frame 1006 is equal to the set layer thickness. The Next, the powder supply unit 1003 supplies one layer of powder 1007 onto the surface of the modeling table 1005, and the coater 1004 performs squeezing. FIG. 3A is a diagram for explaining the first squeezing of the powder in the flowchart shown in FIG. 2A. In FIG. 3A, the first layer 1008 is in a state immediately after the powder 1007 is laid on the modeling table 1005 and its surface is squeezed by the coater 1004 moved along the direction 4000. Following the second step, a third step S103 is performed.

  In the third step S103, the laid powder 1007 is melted and solidified. Here, the control unit 1001 reads out the shape information of the first layer 1008 that is the uppermost layer portion of the powder 1007 at that time from the shape information stored in the storage unit 2000. The control unit 1001 controls the heating unit 1002 so as to selectively heat a range corresponding to the shape information of one layer of the laid one layer of powder. The heating unit 1002 is controlled by the control unit 1001 to heat, melt, and solidify a portion of the laid layer of powder 1007 that constitutes the desired shaped article 3000. At this time, the heating unit 1002 irradiates the heat ray 5000 toward the portion to be heated in the powder 1007. The heat ray 5000 may be, for example, a laser beam or an electron beam. 3B is a diagram for explaining the first melting / solidification of the powder 1007 in the flowchart shown in FIG. 2A. 3B, the model 3000 is in a state immediately after a part of the powder 1007 laid as the first layer 1008 is heated by the hot wire 5000 irradiated from the heating unit 1002, and melted and solidified. Following the third step S103, a fourth step S104 is executed.

  In 4th step S104, it is determined whether the molded article 3000 is completed. This determination can be made by, for example, determining whether the layer number of the powder 1007 laid last has reached the total number of layers by the control unit 1001. When it is determined that the modeled object 3000 is completed (YES), the fifth step S105 is executed after the fourth step S104. On the other hand, if it is determined that the model 3000 is not yet completed (NO), the control unit 1001 increments the layer number, and then the second step S102 is executed again after the fourth step S104. . FIG. 3C is a diagram for explaining the second squeezing of the powder in the flowchart shown in FIG. 2A. In FIG. 3C, the second layer 1009 is in a state immediately after the powder 1007 has been laid on the first layer 1008 and its surface has been squeezed by the coater 1004 that has moved along the direction 4000. Further, after the second step S102, the third step S103 is executed again. FIG. 3D is a diagram for explaining the second melting / solidification of the powder in the flowchart shown in FIG. 2A. In FIG. 3D, in the model 3000, a part of the powder 1007 laid as the second layer 1009 is heated and melted by the heat ray 5000 irradiated from the heating unit 1002, and is integrated with the model 3000 of the first layer 1008. It is in a state immediately after it has solidified and solidified.

  In the fifth step S105, the additive manufacturing method ends, and the sintered additive manufacturing apparatus 1000 ends its operation. The user can take out the molded object 3000 from the powder 1007 that has not been melted or solidified even when stacked.

As described above, the additive manufacturing technique using the sintered additive manufacturing apparatus 1000 according to the configuration example illustrated in FIG. 1 and the sintered additive manufacturing method according to the example of the flowchart illustrated in FIG. 1 has been described. Next, with reference to FIG. 4A-FIG. 4C, it demonstrates that the defect derived from the space | gap between powders may arise in a molded article in such a sintering type | mold additive manufacturing technique.
FIG. 4A is a cross-sectional view showing an example of a portion of the modeled product 3000 that has no sintered portion below it. This cross-sectional view shows a cross section by a plane parallel to the vertical direction, which is the direction in which the powder is laminated. The cross-sectional view of FIG. 4A shows a modeling table 1005, a modeled product 3000, an auxiliary support unit 3001, and a powder bed 4.

  The auxiliary support part 3001 is formed immediately above the modeling table 1005, and the modeled object 3000 is formed immediately above the auxiliary support part 3001. In other words, the model 3000 is supported on the model table 1005 via the auxiliary support unit 3001.

  The model 3000 illustrated in FIG. 4A is hollow and has a ring-shaped cross section around it. 4A is, for example, a cylindrical pipe that is orthogonal to the stacking direction and extends in a direction orthogonal to the paper surface. The unsintered powder remains inside the cylindrical pipe that is the model 3000. The powder in such a state is called a powder bed 4.

  Of the cylindrical pipe that is the model 3000, attention is paid to the inner surface portion of the upper portion. In FIG. 4A, this portion surrounded by a broken line is hereinafter referred to as an upper wall surface 3002. The molded object 3000 does not exist immediately below the upper wall surface 3002 and is supported by the powder bed 4.

  As shown in the upper wall surface 3002 of FIG. 4A, the portion supported by the powder bed 4 in the modeled product 3000 that is being layered is likely to have poor dimensional accuracy as compared to the other portions. There is a problem that the surface tends to be rough. The reason why such a phenomenon occurs will be described with reference to FIGS. 4B and 4C.

  FIG. 4B is a cross-sectional view showing an example of a state immediately before melt-sintering the powder for forming the upper wall surface 3002 included in the modeled product 3000 in a state where there is no sintered portion below. In the example of FIG. 4B, among the uppermost layer 1007A laminated immediately before the powder bed 4 which is a laminated powder, the portion to be sintered 3000C is supported by the powder bed 4 without the shaped article 3000 immediately below it. ing.

  FIG. 4C is a cross-sectional view showing an example of a state immediately after the powder for forming the upper wall surface 3002 included in the modeled product 3000 is melt-sintered with no sintered part below. In the example of FIG. 4C, the sintered portion 3000 </ b> C shown in FIG. 4B is melt-sintered into a model 3000. At this time, the volume of the model 3000 is smaller than the volume of the portion to be sintered 3000C by a part or all of the voids between the particles contained in the melt-sintered powder. In other words, in the laminated powder, a cavity is generated in the melted part and the periphery thereof, so that the melted part before sintering sinks into the powder bed 4 in the downward direction, that is, moves downward. Such a movement causes deterioration of dimensional accuracy and surface roughness in a portion of the sintered model 3000 such as the upper wall surface 3002.

(First embodiment)
In order to solve such a problem in the sintering type additive manufacturing technique, the inventor proposes to use a powder having fewer voids between particles. Furthermore, the inventor has found that a powder satisfying the following conditions has fewer voids between particles.

  As a first condition, the powder to be used is a mixed powder obtained by mixing two kinds of powders having different particle sizes or different particle size distributions. Here, the first powder having a relatively coarser particle size or particle size distribution is referred to as a coarse powder, and the second powder having a relatively finer particle size or particle size distribution is referred to as a fine powder.

  As the second condition, the particle diameter or center particle diameter of the coarse powder is D1, the particle diameter or center particle diameter of the fine powder is D2, and the ratio of D1 and D2 is expressed as “particle diameter ratio = D1 / When defined as “D2”, the particle size ratio is 3 or more and less than 5.

  The first condition will be described with reference to FIGS. 5A to 5D and FIG.

  Non-Patent Document 1 (Michitaka Suzuki, Akira Yagi, Kazuo Watanabe, Toshio Oshima, “Estimation of Porosity of Three-Component Spherical Particle Random Packing Layer”, Chemical Engineering Papers Vol. 10, No. 6, published in 1984, pp 721-727) discloses a method for analytically calculating the ratio of voids generated between particles in a space filled with three types of spherical particles having different diameters.

  Here, the analysis conditions of Non-Patent Document 1 are simplified when only two types of spherical particles having different diameters are used, that is, when only coarse powder and fine powder are used. FIG. 5A is a diagram illustrating an example of a space in which the coarse powder 1 is arranged around the coarse powder 1 that is the target particle. FIG. 5B is a diagram illustrating an example of a space in which fine powder 2 is arranged around coarse powder 1 that is a target particle. FIG. 5C is a diagram illustrating an example of a space in which the coarse powder 1 is arranged around the fine powder 2 that is the target particle. FIG. 5D is a diagram illustrating an example of a space in which the fine powder 2 is arranged around the fine powder 2 that is the target particle.

When the four types of arrangement examples shown in FIGS. 5A to 5D are generalized, FIG. 6 is obtained. 6, around the first particle P1 with a first particle size D _P1, the space in which the second particles P2 and the third particles P3 having a second particle size D _P2 is located, the porosity It is a figure for calculating.

  With reference to FIG. 6, a method for calculating the porosity in a space in which the first particle P1, the second particle P2, and the third particle P3 having two types of particle sizes are in contact with each other will be briefly described. Detailed description will be given later.

  The first particle P1, the second particle P2, and the third particle P3 are all spherical. The center of the first particle P1 is the point O, the center of the second particle P2 is the point C, and the center of the third particle P3 is the point F. The first particle P1 and the second particle P2 are circumscribed at the point A, the second particle P2 and P3 are circumscribed at the point D, and the first particle P1 and the third particle P3 are circumscribed at the point G. . The points A, D, and G are all included in a virtual plane OCF that passes through the points O, C, and F.

  Consider a virtual sphere S1 centered on a point O and having a radius OD. The porosity in the phantom sphere S1 when N second particles P2 (or third particles P3 having the same second particle diameter) are in contact with the periphery of the first particles P1 is as follows: Is required. Such a number N is called a coordination number.

  First, consider a space shared by the phantom sphere S1 and the spherical second particle P2. Further, this shared space is divided into two spaces by a plane orthogonal to the straight line OC and passing through the point D. Here, one of the two spaces is a first missing sphere V1 that is a part of the phantom sphere S1, and the other is a second missing sphere V2 that is a part of the second particle P2. The volume of the first missing sphere V1 and the second missing sphere V2 is calculated by the formula described later. The volume of the phantom sphere S1 is also calculated by the formula. At this time, the porosity in the space around the first particle P1 is obtained by multiplying the sum of the volumes of the first missing sphere V1 and the second missing sphere V2 by the coordination number N in the volume of the phantom sphere S1. Equal to the percentage.

The porosity of the whole space calculated analytically in this way is called the theoretical powder porosity ε _c . At this time, a filling rate obtained by subtracting voids from the entire space is called a theoretical powder filling rate and is defined by 1−ε _c .

ここで、符号ｊは１または２であり、Ｓｖ_１は第１粒子Ｐ１の体積基準混合率であり、ε_１は第１粒子Ｐ１の空隙率であり、Ｓｖ_２は第２粒子Ｐ２の体積基準混合率であり、ε_２は第２粒子Ｐ２の空隙率である。 The theoretical powder porosity ε _c is the sum of products obtained by multiplying the local porosity ε _j when focusing on each of the j-th particles P _j by the volume-based mixing fraction Sv _j of the particles. Is calculated by

Here, the symbol j is 1 or 2, Sv ₁ is the volume reference mixing ratio of the first particle P1, ε ₁ is the porosity of the first particle P1, and Sv ₂ is the volume reference of the second particle P2. The mixing ratio, and ε ₂ is the porosity of the second particles P2.

ここで、βは局所的な空隙率と全体の空隙率との間の比例係数であり、理論値を実測値に補正するための係数である。比例係数βの具体的な算出方法については、後述する。 The local porosity ε _j in the vicinity of the j-th particle Pj is calculated by the following equation.

Here, β is a proportional coefficient between the local porosity and the overall porosity, and is a coefficient for correcting the theoretical value to the actually measured value. A specific method for calculating the proportionality coefficient β will be described later.

ここで、符号ｋは、１または２である。 Sa _k is the area reference mixing ratio of the k particles Pk, is calculated by the following equation.

Here, the symbol k is 1 or 2.

ε _{(j, k)} is a local porosity when the k-th particle Pk exists around the j-th particle Pj, and is calculated by the following equation.

ここで、αは、配位数の比例係数であり、理論値を実測値に補正するための係数である。比例係数αの具体的な算出方法については、後述する。 Here, N _{(j, k)} is the coordination number of the k-th particle Pk adjacent to the j-th particle Pj, and is calculated by the following equation.

Here, α is a proportionality coefficient of the coordination number, and is a coefficient for correcting the theoretical value to the actually measured value. A specific method for calculating the proportionality coefficient α will be described later.

ここで、線分ＢＥおよびＯＤの長さは、以下の式で算出される。なお、点Ｂは、直線ＯＣに直交し、かつ、点Ｄを通る平面と、直線ＯＣとが交わる点である。

V1 _{(j, k)} is the volume of the first missing sphere V1 and is calculated by the following equation.

Here, the lengths of the line segments BE and OD are calculated by the following equations. Note that the point B is a point where a plane orthogonal to the straight line OC and passing through the point D intersects the straight line OC.

ここで、線分ＡＢおよびＣＤの長さは、以下の式で算出される。

V2 _{(j, k)} is the volume of the second missing sphere V2, and is calculated by the following equation.

Here, the lengths of the line segments AB and CD are calculated by the following equations.

V _{(j, k)} is the volume of the phantom sphere S1, and is calculated by the following equation.

ただし、

なお、ガスアトマイズ方式で生成した粉末を、３５乃至４４μｍ（マイクロメートル）の範囲で狭分級した粉末の、タップ充填率を実測した値が約５７％であったことから、ここでは、単粒子を充填した際の実測空隙率を４３％とする。 The proportionality coefficient β is calculated by the following equation.

However,

In addition, since the measured value of tap filling rate of the powder produced by gas atomization method was narrowly classified in the range of 35 to 44 μm (micrometer) was about 57%, it is filled here with single particles. The actually measured void ratio is 43%.

ここで、

ここで、ｂは実測空隙率からの近似値を表す不定定数であり、以下の式で求められる。

The proportionality coefficient α is calculated by the following formula.

here,

Here, b is an indefinite constant representing an approximate value from the measured porosity, and is obtained by the following equation.

  By using the above formula, it is possible to calculate the estimated powder filling rate from the powder volume mixing rate for each particle size ratio of the two kinds of mixed powders. FIG. 7 is a graph comparing the estimated powder filling rate calculated from the powder volume mixing rate for each particle size ratio. The graph of FIG. 7 includes a total of six graphs of the first graph G1 to the sixth graph G6, and the horizontal axis indicates the volume mixing ratio of the first particles in percentage, and the vertical axis indicates The estimated powder loading is shown as a percentage.

  The first graph G1 shows the change in the estimated powder filling rate according to the volume mixing rate of the first particles when the particle size ratio is 1. When the particle size ratio is 1, it means that the particle sizes of the first particles and the second particles are equal, and the value of the estimated powder filling rate is constant regardless of the volume mixing ratio of the first particles.

  The second graph G2 shows the change in the estimated powder filling rate according to the volume mixing rate of the first particles when the particle size ratio is 2. Similarly, the 3rd graph G3, the 4th graph G4, the 5th graph G5, and the 6th graph G6 are the volume of the 1st particle in case the particle size ratio is 3, 4, 5 and 6, respectively. The change of the estimated powder filling rate according to the mixing rate is shown. From the graph of FIG. 7, as an overall trend, the larger the particle size ratio, the higher the peak value of the estimated powder filling rate, and the volume mixing rate of the first particles from which this peak value is obtained is also shown. It can be seen that it grows. Therefore, from the viewpoint of improving the estimated powder filling rate, it can be said that, when mixing two types of powders having different particle sizes, the higher the particle size ratio between the two, the better.

  However, from the viewpoint of melting the mixed powder, the particle size ratio is preferably suppressed to about 5 or less. This is because the coarse and fine powders having different particle sizes have different melting conditions, but the mixed coarse and fine powders are heated at the same time and under the same conditions. That is, if the melting conditions are matched to the fine powder, the coarse powder does not reach melting, and a defect may occur in the model 3000. In addition, if the melting conditions are matched to the coarse powder, there is a possibility that the modeling speed is lowered and the productivity is lowered, and even fine powder in an undesired region is melted, and the dimensional accuracy of the model 3000 may be lowered. Occurs. On the other hand, from the graph shown in FIG. 8A, it is considered that the higher the particle size ratio, the smaller the number of voids. In particular, when the particle size ratio is 5 or more, the number of voids is almost zero. Therefore, it is considered that there is no merit even if there is a demerit by making the particle size ratio higher than 5. In this respect, the particle size ratio is more preferably less than 4.8 and even more preferably less than 4.5.

  Further, from the viewpoint of voids generated in the sintered model 3000 after sintering, the particle size ratio is preferably about 3 or more. This will be described with reference to FIGS. 8A to 8D.

  FIG. 8A shows that the number of voids per unit area of the cross section varies depending on the particle size ratio when a mixed powder obtained by mixing two kinds of powders having different particle sizes is sintered. It is a graph to show. In the graph of FIG. 8A, the horizontal axis indicates the particle size ratio, and the vertical axis indicates the number of voids per unit area.

  A point R1 on the graph of FIG. 8A indicates the number of voids per unit area when the particle size ratio is 1. FIG. 8B is an example of a cross section of a shaped object obtained by sintering a mixed powder having a particle size ratio of 1. In the cross section of FIG. 8B, the black portions indicate voids.

  Similarly, points R2 and R3 on the graph of FIG. 8A indicate the numbers of voids per unit area when the particle size ratio is 2 and 3, respectively. FIG. 8C and FIG. 8D are examples of cross-sections of shaped objects obtained by sintering mixed powders having particle size ratios of 2 and 3.4, respectively.

  As a matter of course, the fewer voids generated in the sintered model 3000 after sintering, the better. However, for quality control of the model 3000, it is considered that the standard is satisfied if the number is 0.5 or less per square millimeter of the cross section. According to the graph of FIG. 8A, this criterion is met if the particle size ratio is greater than 3. In this respect, the particle size ratio is more preferably greater than 3.2 and even more preferably greater than 3.5.

  In the graph of FIG. 7, a solid line represents a third graph G3 indicating that the particle size ratio is 3 and a fifth graph G5 indicating that the particle size ratio is 5. In the graph of FIG. 7, a straight line L1 indicating 61.7% that is the peak value of the third graph G3 is further drawn. So far, the condition that the mixed powder should satisfy from the viewpoint of the particle size ratio has been described, but the condition that the mixed powder should satisfy from the viewpoint of the estimated powder filling rate can also be set. That is, the estimated powder filling rate of the mixed powder is preferably greater than 62%, more preferably greater than 63%, and even more preferably greater than 64%.

  In the present embodiment, a mixed powder that satisfies the conditions described above can be generated. That is, first, two types of powders having different particle sizes are prepared. Here, from the viewpoint of melting conditions, the two powders are preferably made of the same material. Also from the viewpoint of melting conditions, the ratio of the first particle size of the first powder to the second particle size of the second powder is preferably set to be smaller than 5. Furthermore, the particle size ratio is preferably set to be larger than 3 from the viewpoint of suppressing the generation of voids. Also from the viewpoint of the number of voids, the estimated powder filling rate is preferably set to be larger than 62%. Next, a mixed powder is obtained by uniformly mixing these two kinds of powders. By using the powder obtained in this way, it is possible to generate a modeled object by a sintered additive manufacturing technique with higher accuracy.

(Second Embodiment)
In the first embodiment, the particle size of the powder is treated as a single value because of the relationship described from the analytical viewpoint. However, in practice, it is rare that all particles contained in the powder have the same particle size, and generally the particle size exhibits a predetermined distribution. In particular, a powder produced with a predetermined particle size as a target can have a particle size distribution approximate to a lognormal distribution. In such a case, in the above expression indicating the conditions to be satisfied by the mixed powder, “particle size” may be read as “central value of particle size distribution (strictly, mode value of distribution)”.

  FIG. 9A is a graph showing an example of a particle size distribution of a powder obtained by mixing two types of particles. In the graph of FIG. 9A, the horizontal axis indicates the particle diameter of the mixed powder on the logarithmic axis, and the vertical axis indicates the volume ratio. The curve L shown in the graph of FIG. 9A has a total of two local peaks at the first particle size D1 and the second particle size D2. The volume ratio indicated by the local peak in the first particle diameter D1 is I1, and the volume ratio indicated by the local peak in the second particle diameter D2 is I2.

  In other words, if the particle size distribution of the existing powder is measured and, as a result, a plurality of local peaks are obtained as shown in the graph of FIG. 9A, the powder satisfies the above-mentioned mixed powder conditions according to the present embodiment. There is a possibility. With reference to FIG. 9B and FIG. 9C, the method for confirming whether the existing powder satisfies the conditions of the mixed powder according to the present embodiment will be described.

  FIG. 9B and FIG. 9C are diagrams for explaining a method of calculating a mixing ratio of each powder from a mixed powder obtained by mixing two kinds of powders.

  First, the particle size distribution of the powder to be confirmed is measured. At this time, the histogram section defining the particle size distribution range for each measurement is set to be narrower for smaller particle sizes and wider for larger particle sizes, in accordance with the log normal distribution graph drawn thereafter. It is preferable to set. Here, the description will be continued assuming that the graph shown in FIG. 9A is obtained as a semilogarithmic graph of the particle size distribution thus obtained.

  Next, it is confirmed whether the graph of the particle size distribution obtained by measurement can be approximated as the sum of two lognormal distribution graphs. This confirmation can be performed, for example, by fitting by the least square method. Here, the description will be continued assuming that the first lognormal distribution graph F1 and the second lognormal distribution graph F2 shown in FIG. 9B are obtained as a result of the fitting by the least square method. Here, the first log normal distribution graph F1 represents the particle size distribution of the first powder, and the second log normal distribution graph represents the particle size distribution of the second powder.

  Next, the particle size ratio between the first powder and the second powder is calculated. FIG. 9B shows the curve L, the first lognormal distribution graph F1, and the second lognormal distribution graph F2 shown in FIG. 9A, and the horizontal axis indicates the particle size on the logarithmic axis. The vertical axis represents the volume ratio. As described above, in the fitting by the least square method, a result is obtained that the curve L is approximated to the sum of the first lognormal distribution graph F1 and the second lognormal distribution graph F2. The central value is read from the first lognormal distribution graph F1, and this is defined as the particle size D1. Similarly, the central value is read from the second lognormal distribution graph F2, and this is set as the particle size D2. At this time, the particle size ratio between the first powder and the second powder is calculated as the ratio of the particle size D1 and the particle size D2.

  Next, the volume mixing ratio of the first powder and the second powder is calculated. FIG. 9C shows the first lognormal distribution graph F1 and the second lognormal distribution graph F2 shown in FIG. 9B, and the horizontal axis shows the particle size by the logarithmic axis, and the vertical axis Indicates a volume ratio. However, for ease of viewing, the first lognormal distribution graph F1 and the second lognormal distribution graph F2 are separated by moving left and right so that the respective areas do not change. The area of the first lognormal distribution graph F1 is A1, and the area of the second lognormal distribution graph F2 is A2. At this time, the volume mixing ratio of the first powder and the second powder is calculated as a ratio of the area A1 and the area A2.

  When the particle size ratio (or the reciprocal number) calculated as described above is larger than 3 and smaller than 5, the powder satisfies the condition from the viewpoint of the melting condition. Further, when the powder filling rate is larger than 62%, the condition from the viewpoint of voids is satisfied. The powder filling rate may be obtained by actual measurement, or an estimated powder filling rate calculated from the particle size ratio (or the reciprocal thereof) and the volume mixing ratio calculated as described above may be used.

  The invention made by the inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say. In addition, the features described in the embodiments can be freely combined within a technically consistent range.

DESCRIPTION OF SYMBOLS 1 Coarse powder 2 Fine powder 4 Powder bed 1000 Laminate modeling apparatus 1001 Control part 1002 Heating part 1003 Powder supply part 1004 Coater 1005 Modeling table 1006 Modeling frame 1007 Powder 1007A Top layer 1008 First layer 1009 Second layer 3000 Model 3000C Sintering Planned part 3001 Auxiliary support part 3002 Upper wall surface 4000 Direction 5000 Heat ray A, B, C, D, E, F, G, O Point A1, A2 Area D1 First particle size D2 Second particle size D _P1 , D _P2 particle size F1 first log normal distribution graph F2 second log normal distribution graph G1 to G6 graph L curve L1 straight line I1, I2 volume ratio P1 first particle P2 second particle P3 third particle R1 to R3 point S1 virtual spherical surface V1 first missing Sphere V2 second missing ball

Claims (6)

A powder used for sintered additive manufacturing,
A first powder having a first particle size distribution;
A second powder having a second particle size distribution different from the first particle size distribution, the material being the same as the material of the first powder;
A powder having a median ratio of a first central particle size of the first particle size distribution to a second central particle size of the second particle size distribution of greater than 3 and less than 5. The powder according to claim 1, wherein
The overall particle size distribution of the powder is a log normal distribution that is the sum of a first log normal distribution and a second log normal distribution;
The first log normal distribution is the first particle size distribution;
The first central value of the first lognormal distribution is the first central particle size,
The second lognormal distribution is the second particle size distribution;
The second central value of the second lognormal distribution is the second central particle size. The powder according to claim 1 or 2,
A powder having an overall powder filling rate of greater than 62%. The powder according to claim 2, wherein
A ratio between a first area of a first logarithmic graph in which the first lognormal distribution is drawn under a predetermined condition and a second area of a second logarithmic graph in which the second lognormal distribution is drawn under the predetermined condition Is the area ratio,
A value corresponding to a volume-based mixing ratio equal to the area ratio of an estimated powder filling ratio corresponding to a particle size ratio equal to the median ratio is greater than 62%. A method for producing a powder for use in sintering additive manufacturing,
Providing a first powder having a first particle size distribution;
Providing a second powder having a second particle size distribution that is the same as the material of the first powder and different from the first particle size distribution;
Mixing the first powder and the second powder,
A method for producing a powder, wherein a ratio of a first central particle size of the first particle size distribution to a second central particle size of the second particle size distribution is larger than 3 and smaller than 5. In the manufacturing method of the powder of Claim 5,
The method for producing a powder further comprising setting a volume-based mixing ratio of the first powder and the second powder in a range in which an overall powder filling ratio of the powder is larger than 62%.

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