Patent Publication Number: US-2022234285-A1

Title: Am apparatus

Description:
TECHNICAL FIELD 
     The present application relates to an AM apparatus. The present application claims priority under the Paris Convention to Japanese Patent Application No. 2019-123764 filed on Jul. 2, 2019. The entire disclosure of Japanese Patent Application No.  2019 - 123764  including the specification, the claims, the drawings, and the abstract is incorporated herein by reference in its entirety. 
     BACKGROUND ART 
     There are known techniques for directly fabricating a three-dimensional object based on three-dimensional data on a computer that expresses the three-dimensional object. Known examples thereof include the Additive Manufacturing (AM) technique. As one example, in the AM technique using metal powder, each layer of the three-dimensional object is fabricated by, toward the metal powder deposited all over a surface, irradiating a portion thereof to be fabricated with a laser beam or an electron beam serving as a heat source, and melting and solidifying or sintering the metal powder. In the AM technique, a desired three-dimensional object can be fabricated by repeating such a process. 
     CITATION LIST 
     Patent Literature 
     PTL 1: International Publication No. 2015-151839 
     PTL 2: Japanese Patent Application Public Disclosure No. 2018-123381 
     SUMMARY OF INVENTION 
     Technical Problem 
     An AM apparatus using the metal powder as the material gradually forms each layer of the fabricated object by scanning the beam layer by layer, and therefore the fabrication time increases as the size of the fabricated object increases. As one of objects of the AM apparatus, a reduction in the fabrication time is desired. One conceivable measure for reducing the fabrication time is to thickly deposit the metal powder all over the surface in one layering process to fabricate a thick layer in one layering process. However, thickly depositing the metal powder all over the surface necessitates a certain time for a heat amount to move to the inside due to the thermal conductive property of the material, thereby raising a possibility that the fabrication cannot be conducted appropriately with the metal powder layer melted only on the surface thereof and the inside thereof remaining unmelted. Another conceivable measure for reducing the fabrication time is to increase the irradiation energy and the scanning speed of the beam. However, increasing the irradiation energy of the beam causes an excessive increase in the temperature of the surface of the metal powder layer to thus facilitate the occurrence of fume and spatter. The occurrence of fume and spatter may, for example, cause a defect in the fabricated object and/or cause a failure in the beam irradiation system, thereby making it impossible to maintain stable fabrication. Therefore, one of objects of the present application is to provide a technique for reducing the fabrication time while preventing or reducing the occurrence of fume and spatter in the AM apparatus. 
     Solution to Problem 
     According to one aspect, an AM apparatus configured to manufacture a fabricated object is provided. This AM apparatus includes a beam source configured to irradiate a material of the fabricated object with a beam, an adjustment device configured to adjust an intensity of the beam, a beam adjustment mechanism configured to adjust a beam size on the material, and a fabrication recipe determination device. The fabrication recipe determination device is configured to determine the intensity of the beam and the beam size on the material based on a property of the material of the fabricated object. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates an AM apparatus for manufacturing a fabricated object according to one embodiment. 
         FIG. 2  schematically illustrates a temperature and a state change when SUS is heated. 
         FIG. 3  illustrates a temperature increase when heat is being transmitted from the surface of material powder downward when the surface of the material is irradiated with a beam. 
         FIG. 4  is a graph schematically indicating an increase in the temperature of a lower surface when the surface of SUS used as the material is heated. 
         FIG. 5  schematically illustrates how the material powder is layered in n layers. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following description, embodiments of an AM apparatus for manufacturing a fabricated object according to the present invention will be described with reference to the attached drawings. Identical or similar components may be indicated by identical or similar reference numerals in the attached drawings, and redundant descriptions regarding the identical or similar components may be omitted in the description of each of the embodiments. Further, features described in each of the embodiments are also applicable to other embodiments in so far as they do not contradict each other. 
       FIG. 1  schematically illustrates an AM apparatus for manufacturing a fabricated object according to one embodiment. As illustrated in  FIG. 1 , an AM apparatus  100  includes a process chamber  102 . A buildup chamber  106  is attached to a bottom surface  104  of the process chamber  102 . A lift table  108  is installed in the buildup chamber  106 . The lift table  108  is movable in the vertical direction (a z direction) by a driving mechanism  110 . The driving mechanism  110  may be, for example, a pneumatic or hydraulic driving mechanism or may be a driving mechanism including a motor and a ball screw. An inlet and an outlet for introducing and discharging protective gas into and out of the process chamber  102  may be provided, although they are not illustrated. 
     In one embodiment, an XY stage  112  is disposed on the lift table  108  as illustrated in  FIG. 1 . The XY stage  112  is a stage movable in two directions (an x direction and a y direction) in parallel with the plane of the lift table  108 . A base plate  114  for supporting a material of a fabricated object is disposed on the XY stage  112 . 
     A material supply mechanism  150  for supplying the material of the fabricated object is disposed above the buildup chamber  106  in the process chamber  102 . The material supply mechanism  150  includes a storage container  154  for holding powder  152  used as the material of the fabricated object, such as metal powder, and a movement mechanism  160  for moving the storage container  154 . The storage container  154  includes an opening  156  for discharging the material powder  152  onto the base plate  114 . The opening  156  can be, for example, a linear opening  156  longer than one side of the base plate  114 . In this case, the material powder  152  can be supplied to the entire surface of the base plate  114  by configuring the movement mechanism  160  so as to move in a range longer than the other side of the base plate  114  in a direction perpendicular to the line of the opening  156 . Further, the storage container  154  includes a valve  158  for controlling the opening/closing of the opening  156 . 
     Only one storage container  154  is disposed in  FIG. 1 , but a plurality of storage containers  154  may be disposed as one embodiment. In the case where the plurality of storage containers  154  is disposed, each of the storage containers  154  may be used to hold a different material or may be used to hold the material powder  152  that is the same material but has a different particle diameter. 
     In one embodiment, the AM apparatus  100  includes a laser light source  170 , and a scanning mechanism  174 , which guides a laser  172  emitted from the laser light source  170  toward the material powder  152  on the base plate  114 , as illustrated in  FIG. 1 . Further, the AM apparatus  100  illustrated in  FIG. 1  includes an adjustment device  171  for adjusting the intensity of the beam to be applied. This adjustment device  171  can be configured to adjust the power of electricity to be supplied to the laser light source or the electron beam source. Further, the AM apparatus  100  illustrated in  FIG. 1  includes a beam shaper  173  for adjusting the shape and the profile of the beam to be applied. In the illustrated embodiment, the laser light source  170 , the adjustment device  171 , the beam shaper  173 , and the scanning mechanism  174  are disposed in the process chamber  102 , but all or a part of them may be disposed outside the process chamber  102 . The scanning mechanism  174  can be formed by an arbitrary optical system, and is configured to be able to irradiate an arbitrary position of a fabrication plane (a focus plane) on the base plate  114  with the laser  172 . 
     In one embodiment, the AM apparatus  100  includes a temperature detector  175  for measuring the temperature of the irradiation position of the beam. The temperature sensor  175  can be any non-contact type temperature sensor, and may be realized by, for example, employing a method that irradiates a weld pool while superimposing a laser for the measurement on the optical axis of a laser for melting the metal with use of a monochromatic radiation thermometer that works with a measurement wavelength of approximately 650 nm, and receives reflected light on a detection element such as silicon. The laser for the measurement uses a wavelength different from the wavelength of the laser for the melting. Temperature data measured by the temperatures sensor  175  is transmitted to a control device  200 . In one embodiment, the control device  200  may control the output of the beam based on the temperature of the beam irradiation position measured by the measurement sensor  175 . Mild melting that will be described below can be realized by, for example, controlling the irradiation energy of the beam in such a manner that the temperature of the beam irradiation position falls within a range of the melting point of the material +2% to 10%. 
     In one embodiment, an electron beam source may be used instead of the laser light source  170 . In the case where the electron beam source is used, the scanning mechanism  174  includes a magnet or the like, and is configured to be able to irradiate an arbitrary position of the fabrication plane on the base plate  114  with an electron beam. 
     In the embodiment illustrated in  FIG. 1 , the AM apparatus  100  includes the control device  200 . The control device  200  is configured to control the operations of various kinds of operation mechanisms of the AM apparatus  100 , such as the above-described driving mechanism  110 , movement mechanism  160 , laser light source  170 , adjustment device  171 , beam shaper  173 , scanning mechanism  174 , and valve  158  of the opening  156 . The control device  200  can be formed by a general computer or a dedicated computer. 
     In one embodiment, the AM apparatus  100  includes a fabrication recipe determination device  202 . The fabrication recipe determination device  202  may be formed by the same hardware as the control device  200  or may be formed by dedicated hardware different from the control device  200 . The fabrication recipe determination device  202  is configured to determine a recipe of the AM process based on the properties of the material powder  152  to be used for the fabrication. The properties of the material powder  152  include, for example, the material and the particle diameter of the powder. The recipe determined by the fabrication recipe determination device  202  includes at least one of energy, power, a power density, a spot size, an irradiation time, and a scanning speed of the beam to be applied. 
     In one embodiment, the AM apparatus  100  can include a classifier  250  for classifying the material powder  152  based on the particle size. Desirably, the classifier  250  can classify the material powder  152  into a plurality of classes ranging over a narrow distribution of particle diameters. In one embodiment, it is effective to classify the material powder  152  in such a manner that the standard deviation is approximately 5% of the central particle diameter. 
     When a three-dimensional object is fabricated by the AM apparatus  100  according to the embodiment illustrated in  FIG. 1 , the procedure therefor is generally as follows. First, three-dimensional data D 1  of a fabrication target is input to the control device  200 . The control device  200  generates slice data for the fabrication based on the input three-dimensional data D 1  of the fabricated object. Further, the fabrication recipe determination device  202  or the control device  200  including the fabrication recipe determination device  202  generates execution data including fabrication conditions and the recipe. The fabrication conditions and the recipe include, for example, beam conditions, beam scanning conditions, and layering conditions. The beam conditions include voltage conditions, a laser output, and the like of the laser light source  170  in the case where the laser is used, or include a beam voltage, a beam current, and the like in the case where the electron beam is used. The beam scanning conditions include a scanning pattern, a scanning route, a scanning speed, a scanning interval, and the like. Examples of the scanning pattern include a pattern when the beam scans in one direction, a pattern when the beam scans in reciprocating directions, a pattern when the beam scans zigzag, and a pattern when the beam moves transversely while drawing a small circle. The scanning route determines, for example, in what order the beam scans. The layering conditions include, for example, a material type, an average particle diameter of the powder material, a particle shape, a particle size distribution, a layering thickness (a thickness in which the material powder is deposited all over the surface at the time of the fabrication), and a fabrication thickness coefficient (a ratio between the layering thickness and the thickness of the actually manufactured fabricated object). A part of the above-described fabrication conditions and recipe may be generated and changed according to the input three-dimensional data of the fabricated object or may be determined in advance independently of the input three-dimensional data of the fabricated object. 
     The material powder  152  of the fabricated object, such as metal powder, is loaded into the storage container  154 . The lift table  108  of the buildup chamber  106  is moved to an upper position, by which the surface of the base plate  114  is adjusted so as to be positioned on the focus plane of the laser  172 . Next, the valve  158  of the opening  156  of the storage container  154  is opened and the storage container  154  is moved, and then the material powder  152  is evenly supplied onto the base plate  114 . The material supply mechanism  150  is controlled by the control device  200  so as to supply the material powder  152  onto the focus plane by an amount corresponding to one layer of the fabricated object (corresponding to the above-described “layering thickness”). Next, a fabricated object M 1  corresponding to one layer is created by emitting the laser  172  from the laser light source  170 , irradiating a predetermined range of the focus plane with the laser  172  by the scanning mechanism  174 , and melting and sintering the material powder at a predetermined position. At this time, the irradiation position of the laser  172  may be changed by also moving the XY stage  112  disposed on the lift table  108  if necessary. 
     After the fabrication corresponding to one layer is ended, the lift table  108  of the buildup chamber  106  is lowered by a distance corresponding to one layer. The material powder  152  is supplied onto the focus plane by the material supply mechanism  150  by an amount corresponding to one layer of the fabricated object again. Then, the fabricated object M 1  corresponding to one layer is created by causing the laser  172  to scan on the focus plane by the scanning mechanism  174  and melting and sintering the material powder  152  at a predetermined position. The targeted fabricated object M 1  can be entirely created from the powder  152  by repeating these operations. 
     In the following description, the determination about the fabrication conditions and the recipe by the AM apparatus according to one embodiment will be described in detail. As described above, it is desirable to reduce the fabrication time while preventing or reducing the occurrence of fume and spatter in the AM apparatus. Therefore, in the following description, a measure for reducing the fabrication time while preventing or reducing the occurrence of fume and spatter will be described. This measure will be described assuming that stainless steel (SUS) is used as the material powder  152  as one example. 
       FIG. 2  schematically illustrates a temperature and a state change when SUS is heated. As illustrated in  FIG. 2 , when being heated, SUS reaches a melting point (T 1 ) and transitions to a state in which a solid and liquid are mixed together. When being further continuously heated, SUS transitions to a state in which SUS is entirely liquefied. When being further heated, SUS reaches a boiling point (T 2 ) and transitions to a state in which liquid and gas are mixed together, and transitions to a state in which SUS is entirely gasified by being further heated.  FIG. 2  illustrates SUS having a melting point (T 1 ) of 1450° C. and a boiling point (T 2 ) of 2750° C. as one example, but it should be noted that a physical property such as the boiling point and the melting point varies depending on a difference in the composition even among SUS materials. Since a desired object is being fabricated by melting and solidifying the material powder in the AM technique, the material powder should be heated to the melting point or higher. 
       FIG. 3  illustrates a temperature increase when heat is being transmitted from the surface of the material downward when the surface of the material is irradiated with the beam.  FIG. 3  illustrates the material powder  152  irradiated with the beam in a state viewed from above and a state viewed from the side. As illustrated in  FIG. 3 , assume that the material powder  152  is irradiated with a beam having a diameter d.  FIG. 3  illustrates thermal conduction and a temperature increase in a region having an area ΔA and a thickness δ in the beam spot having the diameter d, and they will be described now. 
     A temperature (Ta( 0 )) of the surface of the material  152  before the beam irradiation is the same as a temperature (Tb( 0 )) of the lower surface of the material. This means Ta( 0 )=Tb( 0 ). A temperature Tb(t) of the lower surface of the material when an arbitrary time t has elapsed since the irradiation with the beam is expressed as follows. 
         Tb ( t )=( Ta ( t )− Ta (0))×(1−exp(− t/τc ))+ Tb (0)   Equation (1):
 
     In this equation, τc represents a time constant, and is expressed as follows. 
       τ c =( m×c )× R    Equation (2):
 
     In this equation, each variable represents the following item.
     m: mass [kg]=ΔA×δ×ρ   ρ: density [kg/m 3 ]   c: specific heat [J/kg·K]   m×c: thermal capacity [J/K]   R: thermal resistance [K/W]   

     Further, the thermal resistance R is expressed as follows. 
         R =(δ/(λ×Δ A ))   Equation (3):
 
     In this equation, λ represents the following item.
     λ: thermal conductivity [W/m·K]   

     Further, the time constant τc can be expressed as follows based on the equation (2) and the equation (3). 
       τ c =(Δ A×δ×ρ×c )×(δ/(λ×Δ A ))=ρ× c×δ   2 /λ  Equation (4):
 
       FIG. 4  is a graph schematically indicating the increase in the temperature of the lower surface Tb when the surface Ta of SUS used as the material is heated. A curve L 1  in  FIG. 4  indicates a change in the temperature of the lower surface of the material when the material is irradiated with the beam under a condition that causes the temperature of the surface of the material to reach approximately the melting point (T 1 =1450° C.) due to the irradiation with the beam (the mild condition). That is, this condition corresponds to Ta(t)=1450° C. On the other hand, a curve L 2  in  FIG. 4  indicates a change in the temperature of the lower surface of the material when the material is irradiated with the beam under a condition that causes the temperature of the surface of the material to reach approximately the boiling point (T 2 =2750° C.) due to the irradiation with the beam (a strict condition). That is, this condition corresponds to Ta(t)=2750° C. Because the time constant τc is a condition determined based on the physical properties and the arrangement (the thickness δ) of the material, the lower surface of the material reaches the melting point (T 1 ) in a shorter time Δt when the material is irradiated with the beam under the strict condition as seen from the equation (1) and the graph illustrated in  FIG. 4 . In other words, as the beam output increases, the lower surface of the material reaches the melting point (T 1 ) in a shorter time Δt. Therefore, one conceivable measure for reducing the fabrication time in the AM technique is to increase the output of the beam and increase the scanning speed of the beam. However, as described above, increasing the irradiation energy of the beam causes an excessive increase in the temperature of the surface of the material powder layer to thus facilitate the occurrence of fume and spatter, and therefore may lead to, for example, a defect in the fabricated object and/or a failure in the beam irradiation system of the AM apparatus. Therefore, the present application is directed to contriving a method for reducing the fabrication time under the mild condition. 
     In the case of the beam irradiation under the mild condition, it is presumed that the surface temperature Ta(t) of the material reaches the melting point (T 1 =1450° C.) at some moment, and the surface temperature Ta(t)=T 1  (=1450° C.) is maintained for some time Δt during the irradiation with the beam. In the case of the mild condition based on such a presumption, the time Δt required for the temperature Tb(t) of the lower surface at the depth δ from the surface of the material to reach the melting point (T 1 =1450° C.) is calculated as follows. 
       Δ t≈ 4τ c= 4 ×ρ×c×δ   2 /λ  Equation (5):
 
     In the equation (5), Δt is set to a time taken until Tb(t) reaches approximately 98% of a temperature corresponding to the increase in the temperature of the surface (Ta(t)−Ta( 0 )) in the equation (1). More precisely, the time for which the surface temperature Ta(t) can be kept at T 1  (=1450° C.) is a time determined based on absorption of latent heat required for the material to transform from a solid to liquid and a diffused heat amount due to thermal conduction during that, and the surface temperature Ta(t) starts to rise after that. As a result, the temperature Tb(t) of the lower surface also rises and can reach the melting point or higher. Further, the mild melting intended by the present application can also be realized by a method that monitors the surface temperature Ta(t) and controls the irradiation energy of the beam in such a manner that the surface temperature Ta(t) falls within a range of the melting point of the material +2% to 10%. This method places emphasis on being able to make a parameter comparison (a qualitative comparison) and being also able to make a relative quantitative comparison with respect to the relationship among the density, the specific heat, the thermal conductivity, the thickness, and the required time Δt for each material with use of the equation (5). In one embodiment, the intensity of the beam and the beam size on the material may be determined in such a manner that the temperature of the lower surface of the material reaches the melting point with the irradiation time of the beam lasting for approximately 2τc to approximately 4τc to realize the fabrication under the mild condition. Alternatively, the intensity of the beam and the beam size on the material may be determined so as to realize the fabrication under the mild condition with the irradiation time of the beam lasting for approximately 3τc to approximately 4τc. 
     As seen from the equation (4) and the equation (5), τc is proportional to a square of the thickness δ of the material, and therefore reducing the thickness δ of the material leads to a reduction in the time constant τc, thereby also leading to a reduction in Δt as a result thereof. In other words, it is desirable to reduce the thickness δ of the material to reduce the fabrication time in the AM technique using the powder material. As one example, assuming that SUS is used as the material powder and the thickness δ of the material is δ=0.05 mm, the time constant τc is calculated to be τc=7900×590×0.05 2 ×10 −6 /17≈0.685 [ms], when the following substitutions are added to the equation (4).
     ρ=7900 [kg/m 3 ]   c=590 [J/kg·K]   δ=0.05×10 −3  [m]   λ=17 [W/m·K]   

     Further, the time Δt is calculated to be Δt≈4×τc=2.74 [ms] from the equation (5). 
     When the material powder is used, an interface is present between a particle and a particle in the powder, and therefore contact resistance is present between the particle and the particle. Then, assuming that the contact resistance is expressed as the contact resistance≈δg/λg, the above-described thermal resistance R can be expressed as follows. 
         R ={(δ/ k )+(δ g/λg )}×(1 /ΔA )= R #×(1 /ΔA )   Equation (6):
 
     Now, R# is expressed as follows. 
         R #=(δ×λ g+δg ×λ)/(λ×λ g )   Equation (7):
 
     Because the thermal resistance R is expressed as (thickness/thermal conductivity)×(1/ΔA) as indicated by the equation (3), similarly, (δ×λg+δg×λ) and (λ×λg) in R# in the equation (7) can be deemed to be an “equivalent thickness” and an “equivalent thermal conductivity”, respectively. 
       FIG. 5  schematically illustrates how the material powder is layered in n layers of particles. Assuming that δ, λ, δg, and δg in each of the layers are the same, R# throughout all the n layers is expressed as follows. 
         R #=(δ× g+δg ×λ)× n /(λ×λ g )   Equation (8):
 
     When the above-described Δt is calculated assuming that Δ represents the equivalent thickness (δ×λg+δg×λ), Δt is calculated as follows. 
       Δ t≈ 4 τc= 4 ×ρ×c×δ×n ×(Δ× n )/(λ×λ g )=4 ×ρ×c×δ×n   2 /(λ×λ g )   Equation (9):
 
     As seen from the equation (9), τc and Δt are proportional to a square of n, which is the number of layers of powder particles, and therefore reducing the number n of layers leads to a reduction in the time constant τc, thereby also leading to a reduction in Δt as a result thereof. It is desirable to reduce the number n of layers of particles of the material powder to reduce the fabrication time in the AM technique using the powder material. 
     From the above-described analysis, it is desirable to reduce the thickness in which the material powder is layered to reduce the fabrication time while preventing or reducing the occurrence of fume and spatter in the AM technique using the material powder. Further, desirably, the number n of layers of powder particles to be layered is 1. Further, reducing the number n of layers of powder particles to be layered establishes such a state that an already fabricated lower layer can be observed via a gap between the powder particles when being viewed from the irradiation side. Therefore, it is considered that this reduction allows the AM apparatus  100  to directly irradiate the material powder to be melted and the material surface of the already fabricated lower layer with the beam, thereby being able to reduce the fabrication time. 
     Further, if the material powder has a wide distribution of particle diameters, the fabrication time increases because the scanning speed of the beam should be determined in correspondence with a large particle diameter. Therefore, a narrow distribution is desirable as the distribution of particle diameters of the material powder. In one embodiment, it is effective to classify the material powder  152  in such a manner that the standard deviation is approximately 5% of the central particle diameter. In one embodiment, the AM apparatus illustrated in  FIG. 1  can include the classifier  250 . A powder material having a narrow distribution of particle diameters can be prepared by using the classifier  250 . Further, material powder classified into a plurality of classes corresponding to different central particle diameters can be prepared. The fabrication can be conducted at an optimum scanning speed according to the central particle diameter by using different scanning speeds of the beam for the powder materials corresponding to the different central particle diameters. The material powder corresponding to the different central particle diameters can be held in the above-described respective storage containers  154 . 
     Further, it is desirable to set the scanning speed F of the beam as follows in consideration of the time taken until the heat is transmitted as far as the lower surface of the material powder, assuming that d represents the dimension of the beam spot in the beam scanning direction. 
         F≤d/Δt    Equation (10):
 
     To further reduce the fabrication time, the scanning speed F of the beam can be increased by shaping the beam in such a manner that the beam spot has an elliptic shape and the major axis direction thereof extends in the scanning direction. Further, it is more desirable to shape the beam in such a manner that the beam profile has a top-hat shape than a Gaussian shape. Shaping the beam into the top-hat shape allows the beam to yield further average melting. The shape of the beam can be adjusted by the above-described beam shaper  173 . 
     As described above, the AM apparatus  100  illustrated in  FIG. 1  includes the fabrication recipe determination device  202 . In one embodiment, the fabrication recipe determination device  202  has the following functions. The fabrication recipe determination device  202  holds the following data as setting values.
     a standard beam diameter or a length in the scanning direction: d 0     a standard beam width (a width perpendicular to the scanning direction): w 0     a standard beam output: P 0     

     The fabrication recipe determination device  202  calculates the time constant τc based on the material and the particle diameter of the material powder  152 , and the thickness in which the material powder  152  is deposited all over the surface. 
     The fabrication recipe determination device  202  calculates the time Δt required to melt the material powder  152  deposited all over the surface. The time Δt is calculated as follows. 
       Δ t=a 1×4 ×τc [sec]  Equation (11):
 
     In this equation, a 1  represents a correction coefficient, and is assumed to be, for example, 1.0. 
     A beam irradiation area S is calculated according to S=d×w based on the length d of the beam in the scanning direction and the width w of the beam perpendicular to the scanning direction. The fabrication recipe determination device  202  calculates minimum thermal energy Q required to heat the material powder  152  deposited all over the surface in the layered thickness δ to the melting temperature Δt with the beam irradiation area S=d×w. Q is calculated from the following equation. 
         Q=a 2 ×S×δ×ρ×c×ΔT [ J]   Equation (12):
 
     In this equation, a 2  represents a correction coefficient, and is assumed to be, for example, 1.0. 
     The fabrication recipe determination device  202  calculates the beam scanning speed F according to F=d 0 /Δt as an initial calculated value. 
     Supposing that the AM apparatus  100  attempts to fabricate some region having a width ΔY and a depth ΔX within some time ta based on the three-dimensional data D 1  input to the control device  200 , the fabrication recipe determination device  202  operates in this case in the following manner. 
     The fabrication recipe determination device  202  calculates a time tcal taken for the fabrication of this region according to the following equation. 
         tcal=a 3×(Δ X/F )×(Δ Y/w 0)[sec]  Equation (13):
 
     In this equation, a 3  represents a correction coefficient, and is assumed to be, for example, 1.2. The correction coefficient a 3  corresponds to an overlap in the direction of the width w when the beam scans. 
     If the time tcal is tcal≤ta, the fabrication recipe determination device  202  determines that the fabrication can be conducted with the standard beam dimensions (d 0  and w 0 ) and the beam scanning speed F kept at the initial calculated value. 
     On the other hand, if the time tcal is tcal&gt;ta, the fabrication recipe determination device  202  determines the beam dimensions (d and w) that satisfy tcal≤ta by changing the length d of the beam in the scanning direction and/or the width w of the beam perpendicular to the scanning direction. For example, the width w is changed to reduce tcal while fixing the scanning speed F. On the other hand, the length d is changed to reduce tcal while increasing the scanning speed F. 
     For the correction coefficients a 1 , a 2 , and a 3 , optimum values may be determined from a simulation and/or an experiment. 
     The fabrication recipe determination device  202  determines the output P of the beam generation source in proportion to the beam area S, and determines the recipe so as to keep the energy density constant. Further, if the fabricated object has a fine shape, the fabrication recipe determination device  202  determines the recipe so as to conduct the fabrication while reducing the beam dimensions (d and w) and reducing the power P of the beam so as to keep the energy density constant. 
     Having described the embodiments of the present invention based on the several examples, the above-described embodiments of the invention are intended to only facilitate the understanding of the present invention, and are not intended to limit the present invention thereto. It is apparent that the present invention can be modified or improved without departing from the spirit thereof, and includes equivalents thereof. Further, each of the components described in the claims and the specification can be arbitrarily combined or omitted within a range that allows it to remain capable of achieving at least a part of the above-described objects or bringing about at least a part of the above-described advantageous effects. 
     At least the following technical ideas can be recognized from the above-described embodiments.
     [Configuration 1] According to a configuration 1, an AM apparatus for manufacturing a fabricated object is provided. This AM apparatus includes a beam source configured to irradiate a material of the fabricated object with a beam, an adjustment device configured to adjust an intensity of the beam, a beam adjustment mechanism configured to adjust a beam size on the material, and a fabrication recipe determination device. The fabrication recipe determination device is configured to determine the intensity of the beam and the beam size on the material based on a property of the material of the fabricated object.   [Configuration 2] According to a configuration 2, in the AM apparatus according to the configuration 1, the property of the material of the fabricated object includes a density (ρ), specific heat (c), a thermal conductivity (λ), and a thickness (δ).   [Configuration 3] According to a configuration 3, in the AM apparatus according to the configuration 1 or the configuration 2, the fabrication recipe determination device is configured to determine the intensity of the beam and the beam size on the material in such a manner that the material of the fabricated object reaches a melting temperature with an irradiation time of the beam lasting for approximately 2τc to approximately 4τc, assuming that τc represents a time constant of thermal conduction of the material of the fabricated object.   [Configuration 4] According to a configuration 4, in the AM apparatus according to any one of the configuration 1 to the configuration 3, the fabrication recipe determination device determines the intensity of the beam and the beam size on the material in such a manner that a surface of the material of the fabricated object has a temperature within a melting point +2% to 10%.   [Configuration 5] According to a configuration 5, in the AM apparatus according to any one of the configuration 1 to the configuration 4, the material of the fabricated object is powder. The AM apparatus further includes a classifier configured to classify the powder into a plurality of classes corresponding to different particle diameters.   [Configuration 6] According to a configuration 6, in the AM apparatus according to the configuration 5, the fabrication recipe determination device is configured to determine the intensity of the beam and the beam size on the material according to a particle diameter of the powder.   [Configuration 7] According to a configuration 7, a method for manufacturing a fabricated object by an AM technique is provided. This method includes a step of preparing a material of the fabricated object, a step of determining an intensity of a beam and a beam size on the material based on a property of the material of the fabricated object, and a step of irradiating a surface of the material with the beam according to the determined beam intensity and beam size.   [Configuration 8] According to a configuration 8, in the method according to claim  7 , the property of the material of the fabricated object includes a density (ρ), specific heat (c), a thermal conductivity (λ), and a thickness (δ).   [Configuration 9] According to a configuration 9, in the method according to the configuration 7 or the configuration 8, the intensity of the beam and the beam size on the material are determined in such a manner that the material of the fabricated object reaches a melting temperature with an irradiation time of the beam lasting for approximately 2τc to approximately 4τc, assuming that τc represents a time constant of thermal conduction of the material of the fabricated object.   [Configuration 10] According to a configuration 10, in the method according to any one of the configuration 7 to the configuration 9, the intensity of the beam and the beam size on the material are determined in such a manner that a surface of the material of the fabricated object has a temperature within a melting point +2% to 10%.   [Configuration 11] According to a configuration 11, in the method according to any one of the configuration 7 to the configuration 10, the material of the fabricated object is powder. The method further includes a step of classifying the powder into a plurality of classes corresponding to different particle diameters.   [Configuration 12] According to a configuration 12, in the method according to the configuration 11, the intensity of the beam and the beam size on the material are determined according to a particle diameter of the powder.   

     REFERENCE SIGNS LIST 
     
         
           102  process chamber 
           106  buildup chamber 
           108  lift table 
           110  driving mechanism 
           112  stage 
           114  base plate 
           150  material supply mechanism 
           152  material powder 
           154  storage container 
           160  movement mechanism 
           170  laser light source 
           171  adjustment device 
           172  laser 
           173  beam shaper 
           174  scanning mechanism 
           200  control device 
           202  fabrication recipe determination device 
         D 1  three-dimensional data 
         M 1  fabricated object