JP2018193586A - Powder bed evaluation method - Google Patents

Abstract

To provide a powder bed evaluation method capable of evaluating the uniformity of a distribution of a powder material in a powder bed when a three-dimensional molded product is produced by irradiating an energy line on the powder bed.SOLUTION: A powder bed evaluation method performs: an imaging step of acquiring an image by imaging a surface of a constituent layer during a powder supply step and a molding step, when a three-dimensional molded product is produced by alternately repeating the powder supply step for forming a constituent layer of a powder bed by paving a powder material in layer, and a molding step of solidifying the powder material of an irradiated part by irradiating an energy line while scanning on a surface of a constituent layer; and an evaluation step of acquiring evaluation data that detected a nonuniform position of a distribution of the powder material in the constituent layer based on the image acquired in the imaging step.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a powder bed evaluation method, and more particularly, to evaluate the uniformity of the distribution of powder material in a powder bed when irradiating the powder bed with an energy beam such as a laser beam to produce a three-dimensional structure. It is about the method.

  In recent years, development of additive manufacturing (AM) has been remarkable as a new technique for manufacturing a three-dimensional structure. As one type of additive manufacturing technology, there is an additive manufacturing method using solidification of powdered material by irradiation with energy rays. The additive manufacturing method using a powder material includes a selective laser melting method (SLM), a selective laser sintering method (SLS), an electron beam melting method (EBM), and the like. Can be mentioned. In these methods, a powder material made of resin, ceramics, metal, or a composite material thereof is supplied onto a base material to form a powder bed, and based on three-dimensional design data, A predetermined position on the floor is irradiated with an energy beam such as a laser beam or an electron beam. Then, the powder material of the irradiated part is solidified by melting and re-solidification or sintering, and a shaped body is formed. By repeatedly supplying powder material to the powder bed and modeling by irradiation with energy rays, a three-dimensional model is obtained by sequentially forming the modeled body in layers.

  In the obtained three-dimensional structure, a structure in which the distribution of constituent materials is not uniform, such as voids, is generated at the position corresponding to the surface of each layer when the material supply to the powder bed and the irradiation of energy rays are performed in layers. There is a case. It is desirable to suppress the generation of such a non-uniform structure as much as possible. For example, in Patent Document 1, by causing a static magnetic field to act perpendicularly to the surface of the metal powder layer and suppressing Marangoni convection caused by surface tension on the surface of the molten pool, the cause of the occurrence of deposit surface ripple defects, etc. We are trying to eliminate.

JP 2017-25401 A

  In the production of a three-dimensional structure by irradiating the powder bed with energy rays, the reason why a structure in which the distribution of the constituent materials is not uniform is generated inside the three-dimensional structure is the energy described in Patent Document 1. In addition to the phenomenon that occurs during the irradiation of rays, there can be various factors. Among them, the state of the powder bed before irradiation with energy rays can also greatly affect the state of the obtained three-dimensional structure. Assessing the state of the powder bed as a premise to take measures to suppress the influence of the state of the powder bed on the state of the three-dimensional structure, and further, evaluating the state of the powder bed, and the resulting three-dimensional structure It is important to investigate the correlation between these conditions. For example, if the distribution of the powder material on the surface of the powder bed is non-uniform, the non-uniformity may be reflected as the non-uniform distribution of the constituent materials in the three-dimensional structure.

  The problem to be solved by the present invention is to provide a powder bed evaluation method capable of evaluating the uniformity of the distribution of the powder material in the powder bed when producing a three-dimensional structure by irradiating the powder bed with energy rays. There is to do.

  In order to solve the above-mentioned problems, a powder bed evaluation method according to the present invention includes a powder supply step in which a powder material is spread in layers to form a constituent layer of a powder bed, and irradiation is performed while scanning energy rays on the surface of the constituent layer. Then, when the three-dimensional structure is manufactured by alternately repeating the modeling process for solidifying the powder material in the irradiated region, the surface of the constituent layer is between the powder supply process and the modeling process. An image capturing step for capturing an image and acquiring an image, and an evaluation step for acquiring evaluation data for detecting a portion where the distribution of the powder material in the constituent layer is non-uniform based on the image acquired in the image capturing step are performed. Is.

  Here, based on the images obtained in each of the photographing steps corresponding to a plurality of powder supply steps, in the evaluation step, the evaluation data is represented in three dimensions and the distribution of the powder material in the powder bed. Good to get as.

  In addition, irradiation data indicating a position where the energy beam is irradiated in the modeling process is superimposed on the evaluation data obtained in the evaluation process, and the distribution of the powder material in the powder bed is determined by the three-dimensional modeled object. It is good to associate with the position in.

  And in the said evaluation process, it is good to match the distribution of the space | gap in the said three-dimensional structure, and the distribution of the said powder material in the said powder bed.

  Then, in the evaluation step, for the image obtained in the photographing step, extraction of information on the distribution of the powder material by filtering processing and identification of a portion where the distribution of the powder material is not uniform by binarization And in this order.

  In the method for evaluating a powder bed according to the above invention, when the powder material is spread on the surface of the powder bed that encloses the three-dimensional structure being formed, and when a constituent layer of the powder bed is newly formed, the surface of the constituent layer , And a portion where the distribution of the powder material is not uniform is detected based on the obtained image. Thereby, if the distribution state of the powder material is non-uniform in the constituent layers due to the shape of the three-dimensional structure, the supply conditions of the powder material, etc., the non-uniform distribution is quantitatively detected. be able to. Based on the obtained information, for the three-dimensional structure to be manufactured, the degree of uniformity of the distribution of the constituent materials is estimated, and each process of additive manufacturing including powder bed formation is performed. It becomes possible to verify and improve such conditions.

  Here, based on the images obtained in each of the imaging processes corresponding to a plurality of powder supply processes, in the evaluation process, when acquiring the evaluation data as data indicating the distribution of the powder material in the powder bed in three dimensions It is easy to perform verification and interpretation regarding the distribution state of the powder material in the powder bed by sequentially forming the layers in a layered manner and forming the three-dimensional object in three dimensions.

  In addition, when the irradiation data indicating the position where the energy beam is irradiated in the modeling process is superimposed on the evaluation data obtained in the evaluation process, and the distribution of the powder material in the powder bed is associated with the position in the three-dimensional structure. When there is a part where the distribution of the powder material is not uniform in the powder bed, the part can correspond to a specific position in the three-dimensional structure. As a result, the location where the distribution of the constituent material is uneven in the three-dimensional structure is estimated with high accuracy, and the cause of the non-uniformity in the distribution of the powder material in the powder bed is included in the powder bed. Thus, it is possible to accurately verify the correlation between the non-uniformity of the powder bed and the shape of the three-dimensional structure, such as whether or not the shape of the already formed three-dimensional structure exists in the lower layer.

  In the evaluation process, when the distribution of the voids in the three-dimensional structure and the distribution of the powder material in the powder bed are associated with each other, the three-dimensional structure is caused by the uneven distribution of the powder material in the powder bed. It is possible to estimate the presence of voids in the interior and to verify the correlation between the nonuniformity of the distribution of the powder material in the powder bed and the voids in the three-dimensional structure.

  Then, in the evaluation process, for the image obtained in the photographing process, extraction of information on the distribution of the powder material by filtering processing and identification of the nonuniform distribution of the powder material by binarization are performed in this order. When performed, the non-uniform distribution of the powder material in the powder bed can be easily detected with high accuracy.

It is a figure explaining an example of the additive manufacturing apparatus which applies the powder bed evaluation method concerning one Embodiment of this invention. It is an example of the picked-up image which image | photographed the surface of the powder bed, (a) is a favorable surface, (b) is the surface where the exposure of a three-dimensional structure is seen, (c) is the exposure and powder bed of a three-dimensional structure. It shows the surface where the depression is seen. It is a figure explaining preparation of a three-dimensional distribution image and a section picture, (a) shows the state where a plurality of photography pictures were laminated, (b) shows a three-dimensional picture, and (c) shows a section picture near the surface. . It is a figure explaining the quantitative analysis in a cross-sectional image, (a) is an unprocessed image, (b) is an image after filtering, (c) is an image after binarization, (d) is the tertiary of unevenness distribution Original display. It is a figure which shows the design shape of the sample modeling thing produced in an Example, (a) is a block-shaped sample modeling thing, (b) has shown the beam-shaped sample modeling thing. It is a figure which shows the comparison of the laminated image which shows the nonuniformity of distribution of powder material, and the cross-sectional photograph of the obtained three-dimensional structure about the case where each powder material of an Example is used. It is a figure which shows the relationship between the nonuniformity rate in a powder bed, and the porosity in a three-dimensional structure. It is a figure which shows the modification of the design shape of a sample modeling thing, (a) has shown the block-shaped sample modeling thing, (b) has shown the beam-shaped sample modeling thing.

  Below, the powder bed evaluation method concerning one Embodiment of this invention is demonstrated in detail. A powder bed evaluation apparatus according to an embodiment of the present invention irradiates a powder bed on which a powder material is spread with an energy beam such as a laser beam and an electron beam in a predetermined two-dimensional pattern, thereby forming a modeling layer (a layered modeling object) In the additive manufacturing apparatus for creating a three-dimensional structure by sequentially repeating the process of forming the), the distribution state of the powder material in the powder bed is evaluated.

[Stacking equipment]
First, an example of an additive manufacturing apparatus 1 to which a powder bed evaluation method according to an embodiment of the present invention is applied will be briefly described.

  FIG. 1 shows an outline of the additive manufacturing apparatus 1. The additive manufacturing apparatus 1 performs additive manufacturing for a powder material by a selective laser melting method (SLM). The additive manufacturing apparatus 1 includes a powder bed container 10, a powder supply device 20, a laser irradiation device 30, a camera 40, and a control device 50. In the additive manufacturing apparatus 1, the powder bed B is formed in the powder bed container 10 using the powder supply apparatus 20, and the surface of the powder bed B is irradiated with a laser beam using the laser irradiation apparatus 30, thereby three-dimensional modeling. A product P is manufactured.

  The powder bed container 10 includes a base material 11 and a side wall 12. The powder material can be accommodated in the space surrounded by the base material 11 and the side wall 12 and the powder bed B can be held. The base material 11 which becomes the bottom surface of the powder bed container 10 is driven in the vertical motion M1 by a driving device (not shown).

  The powder supply device 20 includes a tank 21, a powder supply path 22, and a blade 23. The powder supply path 22 and the blade 23 are integrally held by a common holding part 24, and the in-plane motion M2 of the holding part 24 in the horizontal plane is driven by a driving device (not shown). The tank 21 can store the powder material and supply the powder material to the powder supply path 22 at a predetermined supply speed. The powder supply path 22 has an opening at the lower end, and the powder material supplied from the tank 21 can be discharged from the opening to the powder bed container 10 by gravity. The blade 23 is made of an elastic material such as rubber, and is a plate-like member having an edge at the tip. By moving the blade 23 in a horizontal plane so that the edge is in contact with the surface of the powder bed B, the blade 23 moves. The surface of the powder bed B can be smoothed (squeezing).

  When the powder material is supplied to the powder bed container 10 using the powder supply device 20, the powder is supplied while driving the in-plane motion M2 of the powder supply device 20 so that the powder supply path 22 is the front and the blade 23 is the rear. The powder material is discharged from the opening of the supply path 22. Thereby, the layer of the powder material discharged from the powder supply path 22 is squeezed by the blade 23 immediately after the discharge.

  The laser irradiation device 30 includes a laser unit 31 and a galvano scanner 32. The laser unit 31 generates a laser beam by laser oscillation. The wavelength and energy density of the laser beam may be selected so that the powder material to be used can be melted. Moreover, what is necessary is just to set a beam diameter according to the space precision requested | required of the three-dimensional structure P to be manufactured.

  The galvano scanner 32 is composed of a combination of optical components such as mirrors, and can irradiate a predetermined position on the surface of the powder bed B formed in the powder bed container 10 with the laser beam emitted from the laser unit 31. In the galvano scanner 32, the irradiation position of the laser beam on the surface of the powder bed B can be two-dimensionally scanned by adjusting the alignment (angle, arrangement, etc.) of each optical component. The galvano scanner 32 receives design data, for example, three-dimensional CAD data, in which a position to be irradiated with a laser beam is set according to the design shape of the three-dimensional structure P to be manufactured, from a control unit 50 such as a computer. The laser beam is scanned according to the design data.

  The camera 40 is attached above the powder bed container 10 and can take an image of the surface of the powder bed B. The camera 40 only needs to obtain an image reflecting the powder distribution on the surface of the powder bed B, and can capture the entire surface of the powder bed B within one field of view by photographing at a fixed point. Is preferred. The camera 40 outputs the obtained captured image to the control device 50. In addition, in this type of additive manufacturing apparatus 1, during the modeling, for the purpose of monitoring defects and abnormalities in the component members and powder bed of the apparatus, confirming whether the modeling is proceeding normally, etc. In many cases, a camera for photographing the surface of the powder bed B is provided, and here, such a camera may be used as it is. Moreover, in order to assist photographing of the powder bed B by the camera 40, an illumination device that irradiates light on the surface of the powder bed B, such as a flash device, may be provided as appropriate.

  Next, a method for manufacturing the three-dimensional structure P using the layered manufacturing apparatus 1 described above will be described. Prior to production, a powder material to be a raw material of the three-dimensional structure P is prepared in the tank 21 of the powder supply device 20. As the powder material, a material made of metal, ceramics, cermet or the like can be used. Preferably, a metal is used. What is necessary is just to select the specific component composition of a powder material according to the material of the three-dimensional structure P to be manufactured. Further, the particle size of the powder may be appropriately selected in consideration of the spatial accuracy required for the three-dimensional structure P, the ease of forming the powder bed B, etc., but the material powder generally used in the SLM The average particle size of is about 15 to 60 μm.

  The manufacture of the three-dimensional structure P is sequentially performed in layers. That is, in the powder bed B, a process of forming a constituent layer B1 filled with a powder material in a thin layer and irradiating the surface of the constituent layer B1 with a laser beam to form a modeling layer that is a layered solidified product. repeat. By sequentially stacking such modeling layers, a three-dimensional model P having a three-dimensional shape can be completed.

  Specifically, first, the constituent layer B1 of the powder bed B is formed on the base material 11 of the powder bed container 10 in the powder supply step. At this time, the powder material is discharged from the powder supply path 22 of the powder supply device 20, and the surface of the portion where the powder material is discharged is squeezed by the blade 23, and the powder material is spread in layers.

  When the formation of the constituent layer B1 is completed, the camera 40 performs a photographing process of photographing the surface of the constituent layer B1 and acquiring an image. The acquired image is sent to the control device 50.

  And the laser beam is irradiated from the laser irradiation apparatus 30 to the surface of the formed component layer B1, and a modeling process is performed. At this time, irradiation is performed while scanning a laser beam with a predetermined two-dimensional pattern based on design data input from the control device 50. The design data used here is three-dimensional CAD data formed by dividing the shape of the three-dimensional structure P to be manufactured into a thin layer structure corresponding to each of the constituent layers B1. In the portion of the powder bed B which is irradiated with the laser beam in the plane of the constituent layer B1, a substance constituting the powder material such as metal is heated and melted by the laser beam. When the irradiation of the laser beam at the site is completed, the irradiated site is cooled, and the once melted material is solidified (re-solidified) at the site. Thereby, a modeling layer corresponding to the constituent layer B1 for one layer is formed. The formed modeling layer has a shape corresponding to the two-dimensional pattern obtained by scanning the laser beam according to the design data in the plane of the constituent layer B1.

  Thus, the formation of the one modeling layer constituting the three-dimensional structure P is completed. In this state, the formed modeling layer is surrounded by the powder material and contained in the powder bed B.

  Next, the powder supply process is performed again. At this time, first, the motion M1 of the base material 11 of the powder bed container 10 is driven to lower the position of the entire powder bed B downward. Then, discharge of the powder material and squeezing by the blade 23 are performed to form a new constituent layer B1. At this time, the new component layer B1 is laminated on the surface of the existing powder bed B including the previously formed modeling layer. Before forming the new constituent layer B1, the distance by which the substrate 11 is moved downward may be set so that the height position of the surface of the powder bed B does not change before and after the new constituent layer B1 is formed. If the thickness of the constituent layer B1 to be formed is the same every time, the substrate 11 may be moved downward by a distance equal to the thickness of the constituent layer B1. The thickness of the constituent layer B1 is preferably set to be equal to or larger than the average particle diameter of the material powder, and is generally about 20 to 200 μm in the SLM method.

  When the new component layer B1 is completed, the imaging process is executed again, and the surface of the component layer B1 is imaged and the image obtained by the imaging is transferred to the control device 50. As described above, since the height position of the surface of the constituent layer B1 is the same as that in the previous photographing process due to the movement of the base material 11, a photographed image having substantially the same quality under the same photographing conditions. Can be obtained.

  Then, again, the surface of the constituent layer B1 is irradiated with a laser beam to execute a modeling process. At this time, the laser beam scan is based on the data corresponding to the layer above the layer formed in the previous modeling process among the design data consisting of the three-dimensional structure P divided into a thin layer structure. Done. At this time, in the design data, if the shape of the next lower layer and the shape of the newly formed layer are continuous, the melting and re-solidification of the powder material by this laser irradiation has already been formed and the powder bed A new modeling layer is formed in a state where it occurs immediately above the surface constituting the three-dimensional structure P included in B and is joined to the existing three-dimensional structure P. As described above, since the height position of the surface of the constituent layer B1 is the same as in the previous modeling process due to the movement of the base material 11, if the laser irradiation is performed under the same conditions, the powder material is melted. And recoagulation proceeds in substantially the same way.

  In this way, the powder supply process → the photographing process → the modeling process → the downward movement of the base material 11 → the powder supply process →... By doing so, a three-dimensional structure P having a three-dimensional shape can be manufactured. Here, a photographing process is performed corresponding to the formation of each modeling layer, and a photographed image obtained by photographing the surface of the constituent layer B1 of the powder bed B formed in each powder supply process is obtained. In the present layered modeling apparatus 1, the powder bed evaluation method described below is executed on these captured images, and the distribution state of the powder material in the powder bed B used for manufacturing the three-dimensional structure P is evaluated. .

  The additive manufacturing apparatus 1 described here performs additive manufacturing by a selective laser melting method (SLM). However, a powder material such as a selective laser sintering method (SLS) and an electron beam melting method (EBM) is used. Even when other additive manufacturing methods are used as raw materials, the powder bed evaluation method described below can be similarly applied if a camera 40 capable of photographing the surface of the powder bed B is provided in each apparatus. . In the case of SLS, the powder material is mainly made of a resin material, the average particle diameter is about 20 to 80 μm, and the thickness of the constituent layer B1 of the powder bed B is about 60 to 180 μm. In the case of EBM, the powder material is mainly made of metal, the average particle size is about 45 to 110 μm, and the thickness of the constituent layer B1 of the powder bed B is about 50 to 200 μm. In the additive manufacturing apparatus 1 described here, the powder material is supplied to the powder bed B from above the powder bed B, and the surface of the powder bed B is smoothed by the blade 23. The surface of the powder bed B is photographed on each apparatus in the form in which the powder material is supplied from below the powder bed B as if the material 11 is pushed up, and in the form in which the surface of the powder bed B is smoothed by a roller. If the camera 40 which can be provided is provided, the powder bed evaluation method demonstrated below can be applied similarly.

  In addition to the three-dimensional structure P to be finally manufactured, the design data for defining the shape of the three-dimensional structure P to be manufactured is appropriately added with a structure for assisting the manufacture of the three-dimensional structure P. Also good. For example, FIG. 5 (a) and FIG. 5 (b) show the design shapes adopted in the following embodiments, and extend downward from the bottom of the block-shaped and beam-shaped three-dimensional structure P, respectively. A tooth-shaped support p1 is provided. The support p1 contributes to preventing deformation of the three-dimensional structure P during modeling. Moreover, generation | occurrence | production of the defect in the three-dimensional structure P can also be suppressed by the support p1. The support p1 is molded integrally with the three-dimensional structure P based on the design data in the modeling process. After all the modeling steps are completed, the support p1 is appropriately removed to obtain a three-dimensional structure P having a finally desired shape. Further, in FIGS. 8A and 8B, as a modification, a form in which a thin plate-like mesh portion p2 for connecting the supports p1 is provided in addition to the support p1. By providing the mesh part p2, the support p1 can be easily removed.

[Powder bed evaluation method]
Next, a powder bed evaluation method according to an embodiment of the present invention will be described. When this powder bed evaluation method manufactures the three-dimensional structure P by repeating the powder supply process, the imaging process, and the modeling process in order using the layered modeling apparatus 1 described above, the configuration of the powder bed B in the powder supply process. Each time the layer B1 is formed, the distribution state of the powder material in the powder bed B is evaluated based on a photographed image obtained by photographing the surface of the constituent layer B1 with the camera 40 in the photographing process. The captured image acquired by the camera 40 is sent to the control device 50, and an evaluation process is performed on the captured image by the control device 50.

(Non-uniformity of powder material distribution on the powder bed surface)
In the layered manufacturing apparatus 1, the powder material is supplied and the laser irradiation is performed in layers, and a new component layer B1 is formed on the surface of the powder bed B containing the three-dimensional structure P that has already been formed halfway. Laminated. Therefore, the three-dimensional structure P included in the powder bed B may affect the state of the newly formed component layer B1.

  For example, in a part where the three-dimensional structure P that has already been formed partway and is contained in the powder bed B protrudes upward, the powder material is sufficiently distributed in the next powder supply process compared to other parts. It may not be. In an extreme case, an exposed portion D1 may be formed in which the upper surface of the three-dimensional structure P is exposed on the surface of the constituent layer B1 to be formed next. Alternatively, the powder material may be stacked on the protruding portion of the three-dimensional structure P, and the layer of the powder material may be formed thicker at that portion. On the other hand, in the part where the upper surface of the three-dimensional modeling part included in the powder bed B is low, even if the powder material is supplied in the next powder supply process in the same manner as other parts, only that part. There is a case where a depressed portion (egre) D2 in which the surface of the constituent layer B1 is depressed downward is formed. Even after squeezing with the blade 23, the uneven distribution of the powder material such as the exposed portion D1 and the depressed portion D2 cannot often be completely eliminated. Further, during squeezing, the blade 23 forms a streaky non-uniform distribution on the surface of the constituent layer B1, or the squeezing is caused by the blade 23 being caught by the already formed three-dimensional structure P. In some cases, the nonuniformity of the distribution of the powder material may be increased.

(Construction of evaluation data)
If a non-uniform distribution of the powder material such as the exposed portion D1 and the depressed portion D2 is present in the constituent layer B1 of the powder bed B, such a non-uniform distribution is present in the photographed image acquired by the camera 40 in the photographing process. Reflected. FIG. 2 shows an example of a captured image. Here, metal powder is used as the powder material. In the image of FIG. 2 (a), there is substantially no non-uniform distribution such as the exposed portion D1 and the depressed portion D2, and the powder material has a high uniformity through squeezing with the blade 23. It is distributed over the entire surface of B. In the image of FIG. 2 (b), a large number of structures in which a bright part and a dark part are striped inside a long and narrow area inclined with respect to the side of the image are shown in a part surrounded by a broken line. It has been. These structures correspond to the exposed portion D1 where the metal surface corresponding to the upper surface of the three-dimensional structure P that has already been formed halfway is exposed. In the image of FIG. 2C, an exposed portion D1 that is observed as a dotted bright portion in the region indicated by the symbol A, and a depressed portion that is observed as a darkened portion in the region indicated by the symbol B. D2 is confirmed. In this way, by using the captured image acquired by the camera 40, the uniformity of the distribution of the powder material in the constituent layer B1 of the powder bed B can be evaluated.

  In the present powder bed evaluation method, evaluation data for detecting a non-uniform distribution of the powder material in the powder bed B is constructed based on the photographed image of the constituent layer B1 as shown in FIG. Below, an example of the construction method of evaluation data is demonstrated.

(1) Creation of three-dimensional distribution image Three-dimensional distribution showing the distribution of the powder material in the powder bed B in three dimensions based on a two-dimensional photographed image of the surface of each component layer B1 as shown in FIG. An image can be obtained. FIG. 3 shows an example of creating a three-dimensional distribution image.

  In order to obtain a three-dimensional distribution image, in each of the photographing steps corresponding to the plurality of powder supply steps, the two-dimensional photographed image obtained for each constituent layer B1 is made to correspond to the stacking order of the constituent layers B1. Are sequentially laminated to obtain a laminated image. An example of a laminated image is shown in FIG. In the figure, the direction of squeezing is indicated by an arrow. From the viewpoint of analyzing the distribution of the powder material in the powder bed B with high accuracy, it is preferable to construct a laminated image using photographed images corresponding to all the constituent layers B1, but when the data capacity is limited, etc. In other words, a laminated image may be configured through thinning and extracting and using one photographed image for each of a plurality of images or averaging using an image for each of a plurality of images.

  FIG. 3B shows a three-dimensional distribution image obtained by three-dimensionally displaying the layered image obtained above. This corresponds to the distribution state of the powder material in the actual powder bed B formed as an assembly of the respective constituent layers B1 sequentially stacked in the additive manufacturing apparatus 1. In FIG. 3B, a large number of structures having irregularities inside the elongated region are seen on the surface. On the surface of the actual powder bed B from which this three-dimensional distribution image was obtained, a structure having irregularities is formed by the powder material and the surface of the three-dimensional structure P exposed on the surface. In the three-dimensional distribution image, Such a surface state is reproduced. The three-dimensional distribution obtained here does not indicate the distribution of the powder material in the powder bed B finally obtained by laminating the constituent layers B1 in multiple layers while sandwiching the modeling process by laser irradiation, The distribution of the powder material in the constituent layer B1 at the time when each constituent layer B1 is formed is accumulated. Although both distributions may match, they generally do not match.

  The distribution of the powder material in the cross section of the powder bed B can be analyzed by creating a cross-sectional image cut at an arbitrary position with respect to the obtained three-dimensional distribution image. In the three-dimensional distribution image of FIG. 3 (b), the cross section is displayed at the end, and FIG. 3 (c) shows an enlarged cross-sectional image in which a portion near the surface of the end is enlarged. According to the cross-sectional image of FIG. 3 (c), in the portion where the uneven uneven structure is seen on the surface of the three-dimensional distribution of the material powder, the uneven structure in which the brighter portion and the darker portion are mixed even in the lower part. Extends in a columnar shape. That is, it can be seen that the structure in which the distribution of the powder material is nonuniform exists in a columnar shape. This is interpreted as being due to the influence of the three-dimensional structure P formed as a columnar body.

(2) Quantitative Evaluation of Nonuniform Distribution of Powder Material Next, a method for analyzing the obtained three-dimensional distribution image and quantitatively evaluating the nonuniform distribution of the powder material in the powder bed B will be described. Although it is possible to visually recognize the presence of non-uniformity in the distribution of the powder material from the two-dimensional or three-dimensional image obtained above, the non-uniformity should be analyzed quantitatively. Thus, the distribution state of the powder material in the powder bed B can be analyzed more clearly.

  FIG. 4A shows a cross-sectional image created for the three-dimensional distribution image obtained in the same manner as described above. In FIG. 4A, processing and operation are not performed on the image other than the stacking and three-dimensionalization of the captured images taken by the camera 40, and the cutting of the cross section, and an unprocessed cross sectional image is obtained. In addition, the image of Fig.4 (a) was obtained with respect to the powder bed at the time of forming a beam-shaped sample by using powder A as a raw material in the following Example.

  The captured image as it is photographed by the camera 40 is non-essential and does not originate from the distribution of the powder material in the powder bed B, such as shadows, reflection of light on the surface of the powder bed B, noise during photographing, etc. Elements are superimposed. Such elements are inherited in the three-dimensional distribution image and the cross-sectional image. The presence of such non-essential elements in the image may hinder the quantitative analysis of the powder material distribution. Therefore, it is preferable to perform a process of removing such non-essential elements from the image and extracting essential information derived from the distribution of the powder material from the image. Such processing can be performed by, for example, image filtering processing. The filtering process is an operation for removing or extracting a predetermined structure in an image by processing image data according to a predetermined algorithm. Filtering methods for removing shadows, reflections, noise, and the like in an image are known, and can be applied here. Moreover, in each component layer B1 of the powder bed B, when the metal surface of the already formed part of the three-dimensional structure P is exposed, the structure in the image derived from such a metal surface is used as the powder material. Differentiating from the derived structure can also be performed by a filtering process.

  FIG. 4B shows a result of filtering processing performed on the unprocessed image in FIG. 4A and extracting essential information derived from the distribution of the powder material. Here, the contrast of the entire image is clearer than the unprocessed image of FIG. In the image, the distribution density of the powder material is higher as the region is brighter.

  Next, in the powder bed B, the location where the powder material is unevenly distributed is specified and extracted. For this purpose, binarization processing can be applied to the image. In the binarization process, a threshold value is set for the signal intensity that is considered to be non-uniform in the distribution of the powder material, and for each data point in the image, the signal intensity is equal to or greater than (or exceeds) the threshold value. Or less than the threshold value (or below the threshold value), and is replaced with two-level data (for example, 0 and 1) indicating each state. This makes it possible to determine whether or not a non-uniform distribution of the powder material occurs at each data point. If the signal intensity is greater than or equal to the threshold (or greater than the threshold), the non-uniform distribution is considered to occur, or if the signal intensity is less than the threshold (or less than the threshold), the non-uniform distribution is occurring What is considered is the type of non-uniform distribution that can occur, for example, whether a part with a lower density of the powder material is likely to occur than other parts, or conversely, a part with a higher density is more likely to occur, or the type of powder material Since it depends on the shooting conditions of the camera 40, etc., it may be selected as appropriate.

  The result of binarizing the image of FIG. 4B is shown in FIG. Here, the distribution density of the powder material is lower in the darkly displayed area than in the brightly displayed area. Since the brightly displayed area and the darkly displayed area are mixed, it can be considered that a non-uniform distribution (unevenness) of the powder material occurs in the powder bed B. In this way, the location where the distribution of the powder material is non-uniform in the powder bed B can be identified through the binarization process.

  The distribution of unevenness of the powder material obtained for the cross-sectional image as described above can also be displayed three-dimensionally. In the cross-section corresponding to each position of the powder bed B, similarly, after filtering processing and binarization processing, the obtained cross-sectional images are arranged and displayed in a three-dimensional manner. It can be visualized in three dimensions. FIG. 4D shows an example of the three-dimensional distribution of unevenness thus obtained. Here, the area | region displayed with dark gray has shown that the density of powder material is lower than another site | part. It can be seen that such a region is distributed throughout the powder bed B.

  Further, in the two-dimensional image (FIG. 4C) or the three-dimensional image (FIG. 4D) obtained through filtering and binarization, the unevenness existence rate can be quantitatively estimated. What is necessary is just to calculate the area or the volume ratio that the part determined to have unevenness through binarization occupies the entire powder bed B in the image. For example, in the secondary dimensional image of FIG. 4C, the area occupied by the area where the density of the powder material is lower than that of the other areas that are darkly displayed is 24.9%.

  Here, a mode has been described in which a three-dimensional distribution image is created from a captured image obtained by the camera 40 and further a cross-sectional image, and the cross-sectional image is subjected to quantification of unevenness by image processing. Such image processing may be performed on a two-dimensional captured image obtained by the camera 40. In this case, layering, three-dimensionalization, and cross-sectional image creation may be performed on the image that has been processed previously. Alternatively, image processing may be performed on the three-dimensional distribution image formed based on the two-dimensional image obtained by the camera 40 while keeping the three-dimensional image.

(Correspondence between distribution of powder material in powder bed and shape of three-dimensional structure)
As described above, after evaluating the uniformity of the distribution of the powder material in the powder bed B as a raw material for forming the three-dimensional structure P, it is further converted into the shape of the three-dimensional structure P to be manufactured. Can be associated.

  As described above, in the modeling process for each layer, the position where the laser beam is irradiated is performed based on design data such as a three-dimensional CAD indicating the shape of the three-dimensional structure P to be manufactured. Therefore, by superimposing the design data on the distribution of the powder material obtained above, the distribution of the powder material on the powder bed B can be associated with the position on the three-dimensional structure P to be manufactured. That is, in the powder bed B, it is possible to associate which part of the entire three-dimensional structure P is a part where unevenness exists in the distribution of the powder material.

  In the powder bed B, the uneven portion where the distribution density of the powder material is low is reduced in the density of the constituent material or the constituent material is lost when the three-dimensional structure P is formed by receiving the laser irradiation. The probability of forming a void is high. By utilizing this, the distribution of the powder material in the powder bed B can be associated with the distribution of the voids in the three-dimensional structure P. Specifically, the distribution of the powder material in the powder bed B and the design data indicating the irradiation position of the laser beam are superimposed, and a portion where the density of the powder material in the powder bed B is low forms a void in the three-dimensional structure B. By considering that it becomes the site | part to be performed, in the three-dimensional structure P, the position where the space | gap is formed and the ratio which such a space | gap occupies for the three-dimensional structure P can be estimated.

  As described above, there is a correlation between the uneven distribution of the powder material in the powder bed B and the density of the constituent material in the manufactured three-dimensional structure P, which is also shown in a later example. However, since the powder material constituting the powder bed B is once melted and re-solidified to become a constituent material of the three-dimensional structure P, the unevenness ratio (unevenness ratio) in the powder bed B remains as it is, and the three-dimensional structure P However, the ratio of voids not filled with the constituent material (void ratio) is not necessarily obtained. Further, since the residual stress in the three-dimensional structure P also affects the formation of the void in the three-dimensional structure P, the degree of void formation also depends on the specific shape of the three-dimensional structure P. However, the unevenness ratio in the powder bed B and the void in the three-dimensional structure P are determined by a preliminary test or the like for forming the three-dimensional structure P having the same or similar shape using the powder bed B having various distribution states. If the correlation of the rates is quantitatively estimated, it is possible to quantitatively estimate the porosity in the three-dimensional structure P from the unevenness rate in the powder bed B. In addition, the porosity in the three-dimensional structure P used for matching with the unevenness ratio can be estimated by analyzing a cross-sectional photograph of the three-dimensional structure P, measuring the density, or the like.

(Use of information obtained by powder bed evaluation)
As described above, the distribution of the powder material in the powder bed B is analyzed by analyzing the distribution of the powder material in the powder bed B based on the photographed image obtained by photographing the surface of the constituent layer B1 constituting the powder bed B. Can be evaluated. In particular, in the powder bed B, a portion where the distribution of the powder material is non-uniform can be detected, and the non-uniformity can be quantitatively evaluated. If there is unevenness in the distribution of the powder material in the powder bed B that is the raw material for additive manufacturing, the unevenness is inherited as unevenness in the constituent material in the three-dimensional structure P obtained by irradiating the powder bed B with laser. The probability is high. Therefore, the uniformity of the distribution of the constituent material in the three-dimensional structure P to be manufactured can be estimated based on the information regarding the distribution of the powder material in the powder bed B obtained by the evaluation. If the density distribution of the constituent material is to be examined inside the manufactured three-dimensional structure P, it is necessary to cut and observe the three-dimensional structure P or perform non-destructive analysis using an analyzer. However, since the density distribution of the constituent material in the three-dimensional structure P can be estimated from the distribution state of the powder material in the powder bed B, such an analysis can be omitted. In addition, when the constituent layer B1 is sequentially formed and laser irradiation is performed to produce the three-dimensional structure P in layers, the distribution of the powder material on the powder bed B is analyzed in real time, and it is found that there are many unevennesses. Determines that a high-quality three-dimensional model P cannot be obtained even if the modeling is continued further, and stops the modeling. Evaluation can also be used.

  In addition, by detecting the unevenness of the distribution of the powder material in the powder bed B and quantitatively evaluating it, the conditions for forming the powder bed B can be verified, and the cause of giving such unevenness can be analyzed, Based on the analysis result, conditions for forming the powder bed and the like can be improved, and unevenness in the powder bed B can be reduced. The causes of unevenness in the distribution of the powder material in the powder bed B include the characteristics of the powder material (particle size, particle shape, surface treatment, etc.), the supply speed of the powder material, the configuration of the blade 23 (material and shape), and squeezing. The moving speed of the blade 23 at the time, the thickness of each constituent layer B1, etc. can be mentioned. For example, by changing any of these parameters and comparing the distribution unevenness of the powder material in the powder bed B, it is possible to estimate what parameter causes the distribution non-uniformity. By adjusting the parameters, uneven distribution of the powder material can be reduced. In addition, as described above, the shape of the lower portion of the three-dimensional structure P that is already formed often affects the formation of the exposed portion D1 and the depressed portion D2 in the constituent layer B1 of the powder bed B. If possible, the distribution unevenness of the powder material may be reduced by changing the design shape of the three-dimensional structure P.

  On the other hand, although the uniformity of the distribution of the powder material in the powder bed B is high, the void ratio may be high in the obtained three-dimensional structure P. In such a case, it can be presumed that factors other than the distribution of the powder material in the powder bed B are generating voids in the three-dimensional structure P. Such factors include physical properties of materials such as metals constituting the powder material, and laser beam irradiation conditions. In such a case, the change of the type of powder material to be used and the laser beam irradiation conditions (wavelength and energy density) may be considered.

  In the powder bed B, any specific analysis method for detecting unevenness in which the distribution of the powder material becomes non-uniform based on the captured image of each component layer B1 may be used. After extracting essential image information indicating the distribution of the powder material by filtering processing, and using a method of identifying unevenness by binarization processing, the presence of unevenness in the powder bed B can be detected with high accuracy and simplicity. Can be detected. Moreover, it is easy to quantify the unevenness ratio in the powder bed B. Since the surface of each of the constituent layers B1 of the powder bed B is photographed, the amount of photographed images to be processed may become enormous. However, unevenness is automatically generated by filtering and binarization. Can be efficiently executed collectively on the captured image data processing. Even if the type of powder material composing the powder bed B and the photographing conditions with the camera 40 change, the same method can be used to adjust the parameters used for the filtering process and the threshold value for binarization. Can be quantitatively detected.

  The evaluation of the distribution of the powder material in the powder bed B can be performed on a two-dimensional photographed image obtained for each constituent layer B1 of the powder bed B, and is obtained by stacking such two-dimensional images. By evaluating the three-dimensional information to be obtained, the three-dimensional structure P is formed in a three-dimensional manner by stacking the modeling layers, and the distribution of the powder material in the powder bed B is evaluated. It becomes easier to verify and interpret the influence on the obtained three-dimensional structure P. Furthermore, the design data used for laser irradiation and the three-dimensional distribution image of the powder material in the powder bed B are superimposed, and the powder as the raw material is made to correspond to the shape of the three-dimensional structure P and the distribution of the powder material in the powder bed B. It is possible to accurately estimate a location where the distribution of the constituent materials of the three-dimensional structure P is non-uniform due to uneven material distribution. In addition, the correlation between the distribution of the powder material in the powder bed B and the shape of the three-dimensional structure P can be verified accurately, the improvement in the uneven distribution of the powder material in the powder bed B and the three-dimensional structure P It becomes possible to improve the uniformity of the constituent materials. In particular, by quantitatively associating the unevenness ratio in the powder bed B and the void ratio in the three-dimensional structure P, the position and ratio of the voids in the three-dimensional structure P caused by the unevenness in the powder bed B are quantitatively determined. To estimate the correlation between the distribution of the powder material in the powder bed B and the void in the three-dimensional structure P, and to improve the conditions of each process related to additive manufacturing based on the results of the investigation Is possible.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Test method]
(Preparation of sample model)
Using the SLM method, a sample model was produced using metal powder as a raw material. A metal 3D printer (SLM280HL) manufactured by SLM Solutions was used for the preparation of the sample model.

The following four types of metal powders were prepared as material powders.
・ Powder A: Gas spray powder of Fe-based alloy (average particle size: 45 μm)
-Powder B: High-pressure water spray powder of Fe-based alloy (average particle diameter: 45 μm)
・ Powder C: Powder A mixed with 0.05% nano silica ・ Powder D: Ni-based alloy powder (average particle size: 45 μm)

  Based on the three-dimensional CAD data used for laser irradiation when producing the sample model, the shape of the sample model is shown in FIG. Using each of the material powders, two types of sample shaped objects were created: a block shape sample in FIG. 5A and a beam shape sample in FIG. 5B. Each sample has a support (p1) at the bottom.

  In the production of the sample model, the thickness of each constituent layer sequentially laminated on the powder bed was 50 μm. Moreover, the energy density of the laser beam irradiated at the time of modeling is shown in FIG.

(Evaluation of powder bed unevenness)
A photographed image acquired for each constituent layer of the powder bed during the preparation of the sample shaped object is laminated to form a three-dimensional distribution image, which corresponds to the design data as shown in FIG. And the cross-sectional image of the position corresponding to a BB cross section was created. And the filtering process was performed with respect to the cross-sectional image. In FIG. 6, an image after processing is shown in the “stacked image” column. In the region corresponding to the cross section indicated by the broken line in the image, the higher the uniformity of the brightness of the data points, the higher the uniformity of the distribution of the powder material in the powder bed. For example, as in the beam A sample of powder A, bright and dark parts are mixed in a streak in the region, indicating that the distribution of the powder material is non-uniform and uneven. ing. Furthermore, after performing the binarization process, the area of the region that appears dark in the image was estimated, and the unevenness rate was calculated as a ratio to the area of the entire cross section.
The value of the obtained unevenness rate is shown together with the “stacked image” column in FIG.

(Evaluation of voids in the sample model)
Each actually formed sample was cut at a position corresponding to the AA cross section and the BB cross section in FIG. 5 to obtain a cross section. In FIG. 6, a photograph of the cross section is shown in the “cross section” column. In the photograph, a region that is darkly observed like a hole in the cross section is a void. The total area of such voids was estimated from the photograph, and the void ratio was calculated as a ratio to the total area of the cross section. The value of the obtained porosity is shown together with the column of “cross section” in FIG.

[Results and discussion]
(Correlation between powder bed unevenness and porosity of sample molding)
FIG. 6 shows a cross-sectional image (laminated image) showing the distribution of the powder material on the powder bed and a cross-sectional photograph of the actually produced sample model for the case where a sample model of each shape is prepared using each metal powder. (Cross section) contrast is shown. Both correspond to the AA cross section and the BB cross section in FIG.

Looking at FIG. 6, except for the case where the energy density of the powder D is 25.0 J / mm ³ , the degree of mixture of light and dark in the laminated image of the powder bed is large, and the distribution unevenness of the powder material in the powder bed is large, In the cross-sectional photograph of the sample object, it can be seen that there are many hole-like voids distributed. In order to confirm this tendency, FIG. 7 shows a plot of the unevenness rate and the porosity value calculated from each image.

  According to FIG. 7, it can be confirmed that there is a positive correlation between the unevenness ratio in the powder bed and the void ratio in the cross section of the sample shaped article. In the figure, the result of linear approximation of the data points is also shown by a broken line, but a good approximation is established to some extent, and between the unevenness ratio in the powder bed and the void ratio in the cross section of the sample object It can be said that there is a linear relationship. Thus, the fact that a linear relationship is observed between the unevenness of the powder material in the powder bed and the gap formed in the sample shaped article obtained using the powder bed as a raw material means that the voids in the sample shaped article are main. This indicates that the main cause is the uneven distribution of the powder material in the powder bed as a raw material.

  On the other hand, focusing on the case where a block-shaped sample is prepared using powder D, the uniformity of the distribution of the powder material in the powder bed is almost the same, but the energy density of the laser beam used for modeling is low. The porosity is increased. This indicates that, for at least the case where powder D is used as a raw material, the formation of voids in the sample specimen to be produced is not only due to uneven distribution of the powder material in the powder bed, but also due to laser irradiation conditions. . For example, the behavior of melting and re-solidification during laser irradiation due to the material properties of the alloy that constitutes the powder material depends on the energy density of the irradiated laser, and that dependency is related to the formation of voids. Can be interpreted.

(Relationship between sample shape, porosity and unevenness)
When FIG. 6 is seen, except the case where powder D is used as a raw material, the tendency for the nonuniformity of a powder bed and the porosity in a sample molded object to become large in a beam-shaped sample is seen rather than a block-shaped sample. . In other words, when preparing a beam-shaped sample, the powder material unevenness in each constituent layer of the powder bed is larger than when preparing a block-shaped sample, and as a result, the porosity of the sample model obtained by laser irradiation is higher. It is getting bigger. This is interpreted that the beam-shaped sample is more susceptible to thermal deformation due to laser irradiation than the block-shaped sample. In layered modeling, when forming a new component layer by laying a powder material on a sample model in the process of formation, the sample model in the process of forming is subjected to thermal deformation, thereby forming a structure on the model model. It can be considered that the powder material becomes difficult to be uniformly distributed in the layer.

  In the case of using the powder D, the unevenness ratio of the powder bed and the porosity of the sample shaped object are hardly changed between the block-shaped sample and the beam-shaped sample. This means that for powder D, the material properties specific to powder D (physical properties of the alloy material itself) and powder characteristics (related to the shape and size of the powder) in the distribution of the powder material in the powder bed and the formation of voids in the sample model Characteristic) has a larger influence than the sample shape. Consideration regarding the correlation between the unevenness ratio of the powder material and the void ratio of the sample shaped article also suggests the magnitude of the contribution of the material properties.

  The embodiments and examples of the present invention have been described above. The present invention is not particularly limited to these embodiments and examples, and various modifications can be made.

DESCRIPTION OF SYMBOLS 1 Layered modeling apparatus 10 Powder bed container 11 Base material 20 Powder supply apparatus 22 Powder supply path 23 Blade 30 Laser irradiation apparatus 31 Laser unit 32 Galvano scanner 40 Camera 50 Control apparatus B Powder bed B1 Component layer D1 Exposed part D2 Depressed part P Tertiary Original model

Claims (5)

A powder supplying process for forming a constituent layer of a powder bed by spreading powder materials in layers, and a modeling process for irradiating the surface of the constituent layer while scanning with energy rays to solidify the powder material in the irradiated part And alternately, to produce a three-dimensional structure,
A photographing step of photographing the surface of the constituent layer to obtain an image between the powder supply step and the modeling step;
An evaluation step of acquiring evaluation data in which a portion where the distribution of the powder material in the constituent layer is not uniform is acquired based on the image acquired in the photographing step.   Based on the images obtained in each of the imaging steps corresponding to a plurality of powder supply steps, the evaluation data is acquired as data indicating the distribution of the powder material in the powder bed in three dimensions in the evaluation step. The method for evaluating a powder bed according to claim 1.   The irradiation data indicating the position where the energy beam is irradiated in the modeling process is superimposed on the evaluation data obtained in the evaluation process, and the distribution of the powder material in the powder bed is determined in the position in the three-dimensional modeled object. The powder bed evaluation method according to claim 1, wherein the powder bed evaluation method is associated with each other.   The powder bed evaluation according to any one of claims 1 to 3, wherein in the evaluation step, the distribution of voids in the three-dimensional structure and the distribution of the powder material in the powder bed are associated with each other. Method.   In the evaluation step, for the image obtained in the photographing step, extraction of information on the distribution of the powder material by filtering processing, identification of a portion where the distribution of the powder material is not uniform by binarization, The powder bed evaluation method according to any one of claims 1 to 4, wherein the powder bed is performed in this order.