JP2017179517A - Residual stress reduction system for laminated molding, residual stress reduction method for the same, and residual stress reduction program for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a residual stress reduction technique for lamination molding capable of reducing residual stress generated in a molding.SOLUTION: A residual stress reduction system for lamination molding comprises: a control information input section 2 input with control information used for control of the lamination molding for irradiating a beam to metallic powder to be laminated and forming a molding 20; a residual stress analysis section 3 analyzing residual stress generated in the molding 20 based on the control information before a start of the lamination molding; a control information correction section 7 correcting the control information based on the residual stress analyzed; and a control information output section 8 outputting the control information after correction.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a layered modeling technique for forming a modeled article by irradiating a metal powder to be stacked with a beam.

  There is an additive manufacturing technique in which a metal powder is partially irradiated with a laser to be temporarily melted and cured immediately, and further, a metal powder is laminated, and this is repeated to form a target object. Such additive manufacturing technology is expected as a technology that can perform near net shape molding that can obtain a shape close to the final product, but it is still a developing technology, and it is not necessarily possible to form a molded product of quality as designed Not limited to this, repeated trial and error is repeated until the desired model is completed, and the layered modeling is repeated over and over again.

  Therefore, it is a wasteful trial by preliminarily calculating the curing depth and the curing width of the portion to be cured based on laser irradiation, and performing a simulation in advance based on these data and the three-dimensional data of the target object. Attempts to eliminate the need for mistakes.

Japanese Patent No. 4739507

  However, since the modeled object is formed by stacking the parts that are cured based on the laser irradiation, residual stress is generated in all parts of the modeled object. When the completed model is cooled to room temperature, there is a problem that the model is distorted or deformed by residual stress. In Patent Document 1, no consideration is given to the residual stress generated in the molded article.

  The embodiment of the present invention has been made in view of such circumstances, and an object of the present invention is to provide a residual stress reduction technique for additive manufacturing capable of reducing the residual stress generated in a model.

  The residual stress reduction system for additive manufacturing according to the embodiment of the present invention includes a control information input unit to which control information used for control of additive manufacturing for irradiating a beam to the metal powder to be stacked to form an object, A residual stress analysis unit that analyzes the residual stress generated in the modeled object based on the control information before the start of the additive manufacturing, and a control information correction unit that corrects the control information based on the analyzed residual stress; And a control information output unit that outputs the control information after the correction.

  The embodiment of the present invention provides a residual stress reduction technique for additive manufacturing capable of reducing the residual stress generated in a model.

The block diagram which shows a prior analysis apparatus. The flowchart which shows a prior analysis process. The perspective view which shows the three-dimensional structure of the molded article formed with an additive manufacturing apparatus. The graph which shows the evaluation result of residual stress. The perspective view which shows the molded article supported by the pin-shaped support part. The perspective view which shows the molded article supported by the lattice-shaped support part. The graph which shows the evaluation result of the residual stress which arises on the surface of a molded article. The graph which shows the evaluation result of the residual stress produced in the interface of a molded article and a support part. The graph which shows the relationship between the heat input with an electron beam, and a residual stress. The graph which shows the relationship between the beam diameter of an electron beam, and a residual stress. The graph which shows the relationship between the beam scanning speed of an electron beam, and a residual stress. The graph which shows the relationship between temporary sintering temperature and residual stress. The graph which shows the relationship between after-heating time and residual stress. The graph which shows the relationship between the heat input with an electron beam, a residual stress, and a man-hour. The graph which shows the relationship between temporary sintering temperature, a residual stress, and a man-hour. The graph which shows the relationship between after-heating time, a residual stress, and a man-hour. The graph which shows the relationship between the shape of a support part, a residual stress, and a man-hour.

  Hereinafter, this embodiment is described based on an accompanying drawing. The code | symbol 1 of FIG. 1 is a prior analysis apparatus for analyzing previously the residual stress which arises in a molded article before forming a molded article by additive manufacturing. In the present embodiment, the additive manufacturing apparatus 10 is used that forms an object by irradiating an electron beam to the metal powder to be stacked. Moreover, in this embodiment, forming a rectangular parallelepiped shaped article 20 (see FIG. 3) will be exemplified and described below.

  The additive manufacturing apparatus 10 according to the present embodiment has hardware resources such as a CPU, a RAM, a ROM, and an HDD, and information processing by software is realized using the hardware resources when the CPU executes various programs. Computer. And the layered modeling apparatus 10 performs control which forms the molded article 20 which has a predetermined | prescribed three-dimensional shape by processing the various information input.

  More specifically, the additive manufacturing apparatus 10 is provided with a powder supply unit that supplies metal powder in which a metal material that is a material of the target object 20 is powdered. A metal powder is supplied from the powder supply unit onto the powder bed, and a wiper blade or a roller for flattening the upper surface of the supplied metal powder is provided.

  Furthermore, a beam irradiation unit for irradiating an electron beam is provided on the upper surface of the flattened metal powder. A specific portion of the metal powder irradiated with the electron beam is temporarily melted and cured immediately by the beam irradiation unit. Then, the metal powder is again supplied from the powder supply unit, and the upper surface thereof is flattened, and beam irradiation is performed again. By repeating this, the shaped article 20 is formed.

  Further, the portion where the metal powder is cured based on the beam irradiation is controlled based on the three-dimensional structure information of the modeled object 20. For example, beam irradiation is controlled so as to form a state in which the shaped article 20 is horizontally cut. And whenever it laminates | stacks a metal powder, beam irradiation is repeated and these rounded parts are laminated | stacked and the molded article 20 is formed.

  In the present embodiment, the metal powder is partially melted by using an electron beam as a heat source in the metal powder, but other heat sources may be used. For example, the metal powder may be obtained by using a laser beam as a heat source. It may be partially melted.

  As shown in FIG. 3, the modeled object 20 of the present embodiment has a rectangular parallelepiped shape, for example. Note that a plurality of pores 33 are formed in the shaped article 20. When trying to manufacture a molded article 20 having a complicated configuration having a plurality of pores 33 by a conventional metal member manufacturing technique using a mold, the number of manufacturing processes will be excessive, but the additive manufacturing technique will be increased. By using it, even the modeled object 20 having a complicated configuration can be easily manufactured.

  As shown in FIGS. 5 and 6, when forming the shaped article 20, the base plate 30 is fixed in advance on the powder bed before the metal powder is supplied onto the powder bed. The base plate 30 is a metal plate material that serves as a base of the modeled object 20. The modeled object 20 is formed on the base plate 30 in a state where the modeled object 20 is supported via the support portions 31 and 32. In addition, the support parts 31 and 32 are cut away after the molded article 20 is formed. In the present embodiment, two types of patterns of support portions 31 and 32, which are a support portion 31 having a plurality of pin shapes (see FIG. 5) and a support portion 32 having a lattice shape (see FIG. 6), are illustrated. Moreover, when modeling each molded article 20, the structure other than the support parts 31 and 32 is the same.

  In the present embodiment, the lower surface of the modeled object 20 is connected to the support parts 31 and 32, but the shapes of the support parts 31 and 32 have various shapes depending on the shape of the target modeled object 20. . For example, the support portions 31 and 32 may be provided so as to cover the entire periphery including the upper surface and the side surface of the molded article 20.

  Further, in the process of additive manufacturing using the additive manufacturing apparatus 10, the electron beam moves at high speed, and the metal powder is melted and cured. Since the modeled object 20 is formed by such an operation, all parts of the modeled object 20 are the same as the parts welded by the electron beam. Therefore, residual stress (tensile stress) is generated in all parts of the shaped article 20. When such a residual stress is generated in the shaped article 20 and cooled to room temperature, the shaped article 20 is distorted or deformed.

  In particular, the residual stress generated in the molded article 20 made of a metal material is very large, and a large residual stress that may distort the base plate 30 may occur. In addition, due to the occurrence of residual stress, the molded article 20 may be peeled off from the support parts 31 and 32, or the support parts 31 and 32 may be peeled off from the base plate 30.

  Therefore, in this embodiment, before starting the modeling of the modeled object 20, the residual stress generated in the modeled object 20 is analyzed in advance by simulation, and the residual stress reduction that reduces the residual stress generated in the modeled object 20 based on this analysis. A system is provided.

  As shown in FIG. 1, the pre-analysis apparatus 1 as an example of the residual stress reduction system is generated in a control information input unit 2 to which control information used for control of additive manufacturing of the additive manufacturing apparatus 10 is input, and a modeled object 20. The residual stress analysis unit 3 that analyzes the residual stress based on the control information before the start of additive manufacturing, and the inherent strain generated in the three-dimensional structure having various shapes in advance are analyzed in advance. The strain which determines whether the distortion which arises in the molded article 20 by a residual stress is below a predetermined threshold value based on the database 4 which collected data, and the result of having analyzed control information in the residual stress analysis part 3 The determination unit 5, the final determination unit 6 that determines whether or not the modeled object 20 that is layered based on the control information satisfies the final determination requirement, the control information correction unit 7 that corrects the control information, and the control information And a control information output unit 8 for outputting the layer molding apparatus 10, the. Moreover, you may provide structures other than these structures. For example, a display unit that displays predetermined information may be provided.

  The pre-analysis apparatus 1 has hardware resources such as a CPU, a RAM, a ROM, and an HDD, and a computer in which information processing by software is realized using the hardware resources when the CPU executes various programs. Consists of.

  The control information input to the control information input unit 2 includes the three-dimensional structure information of the model 20 and the three-dimensional structure information of the support units 31 and 32 for fixing the model 20 to the base plate 30. The three-dimensional information is design information designed using CAD (computer-aided design) or the like. The layered modeling apparatus 10 performs control to form the modeled object 20 and the support units 31 and 32 having a predetermined shape based on the input three-dimensional structure information. In addition, the value of the residual stress which arises in the molded article 20 changes according to the shape of the support parts 31 and 32. That is, residual stress can be reduced by appropriately changing the three-dimensional structure information of the support portions 31 and 32.

  The control information is beam information related to electron beam control, and includes output information indicating the output value of the electron beam, diameter information indicating the diameter of the electron beam, profile information indicating the nature of the electron beam, and electron beam. Scanning speed information indicating the scanning speed of the scanning beam and scanning sequence information indicating the scanning order of the electron beams. Further, the beam information includes information on the environment when the beam irradiation is performed, and includes composition information and temperature information of the atmosphere around the beam, and information on the thickness of the laminated metal powder.

  Note that the amount of heat input incident on the metal powder by the electron beam is specified based on the output information. Moreover, the hardening depth, hardening width, etc. of metal powder are specified based on output information, diameter information, profile information, scanning speed information, and the like. Moreover, the modeling time etc. of the molded article 20 are specified based on scanning speed information or scanning sequence information. Depending on the beam information, the value of the residual stress generated in the shaped article 20 is different. That is, residual stress can be reduced by appropriately changing the beam information. The additive manufacturing apparatus 10 controls the electron beam based on the input beam information. Note that these pieces of beam information may be information that changes in chronological order according to the formation site and the formation order of the shaped article 20.

  In addition, the control information is pre-sintering information when performing pre-sintering by irradiating the metal powder with an electron beam with a lower output than the main sintering immediately before performing the main sintering. Including. By performing this preliminary sintering, the metal powder immediately before melting is heated to a predetermined temperature. So-called preheating is performed. The metal powder heated to a predetermined temperature by this preliminary sintering is suitably melted in the main sintering. In addition, the value of the residual stress which arises in the molded article 20 according to the temperature based on temporary sintering, what is called temporary sintering temperature, and temporary sintering time which is time from performing preliminary sintering to performing main sintering. Is different. That is, residual stress can be reduced by appropriately changing the preliminary sintering temperature. The additive manufacturing apparatus 10 controls temporary sintering using an electron beam based on the input temporary sintering information. Note that these pieces of beam information may be information that changes in chronological order according to the formation site and the formation order of the shaped article 20.

  The control information includes post-heat information such as a post-heating time and a post-heat temperature from the time when the model 20 is completed until the metal powder remaining around the model 20 is removed. In addition, when performing layered modeling, the part hardened | cured based on irradiation of the electron beam in metal powder has predetermined | prescribed calorie | heat amount. Further, in the middle of the layered modeling, the periphery of the modeled object 20 is covered with metal powder, and is insulated from the so-called outside. Therefore, a predetermined temperature is maintained without the amount of heat of the modeled object 20 escaping to the outside. Then, after the shape of the model 20 is completed on the powder bed, the metal powder is removed after maintaining the model 20 covered with the metal powder for a predetermined time.

  The post-heating time of the present embodiment indicates the time from the time when the shaped article 20 is completed, that is, the time when the irradiation of the electron beam is completed until the metal powder around the shaped article 20 is removed. In addition, the value of the residual stress which arises in the molded article 20 changes with post-heat time. That is, residual stress can be reduced by appropriately changing the post-heating time. The additive manufacturing apparatus 10 performs various controls such as a powder bed based on the input post-heating time.

  Further, the control information includes material property information of the metal powder that is the material of the modeled object 20. This material property information includes thermal property values such as thermal conductivity and specific heat, and mechanical property values such as Young's modulus, yield strength, linear expansion coefficient, and work hardening coefficient. As these physical properties, those expressing temperature dependency from room temperature to the melting temperature of the material and hysteresis accompanying phase transformation can be used. Depending on the physical properties of the metal powder, the value of the residual stress generated in the shaped article 20 varies. The material physical property information includes physical property information in a state where the metal powder is melted and physical property information in a state where the metal powder is cured. The additive manufacturing apparatus 10 performs various controls based on the input material property information.

  The control information input unit 2 includes a three-dimensional structure information input unit 21 to which three-dimensional structure information is input, a beam information input unit 22 to which beam information is input, and a preliminary sintering information input to which preliminary sintering information is input. Unit 23, post-heat information input unit 24 to which post-heat information is input, and material physical property information input unit 25 to which material physical property information is input. Various types of information included in the control information may be individually input to the control information input unit 2, or control information including all information may be input to the control information input unit 2.

  The residual stress analysis unit 3 analyzes (evaluates) the residual stress generated in the completed molded article 20 based on the input control information. In the present embodiment, analysis using a finite element method (FEM) is performed. For example, after converting the three-dimensional structure information into an FEM model, an elastic analysis or a thermoelastic-plastic analysis is performed using the FEM model.

  In the present embodiment, the deformation of the FEM model is predicted using an inherent strain method or the like. This inherent strain method is a technique in which inherent strains (thermal strain, plastic strain, etc.) generated in the modeled object 20 for each layered manufacturing process and material are stored in a database, and elastic analysis is performed using these data. In addition, these data can be acquired by conducting an experiment or thermal elastic-plastic analysis in advance.

  In the database 4 connected to the residual stress analysis unit 3, analysis results of inherent strains generated in a three-dimensional structure having various predetermined shapes constituting a modeled object to be layered are stored in advance. By predicting the deformation of the FEM model based on these analysis results, the analysis time of the FEM model (calculation time of elasticity calculation) can be greatly shortened. In addition, the processing load necessary for analysis can be reduced. The database 4 may store not only the three-dimensional structure analyzed in advance but also information related to the modeled object 20 analyzed by the pre-analysis apparatus 1.

  The strain determination unit 5 has a value (strain value) when the modeled object 20 is deformed based on the residual stress generated in the modeled object 20 analyzed by the residual stress analyzing unit 3 below a predetermined threshold value. It is determined whether or not. This specific threshold value is a value for determining whether or not the deformation amount of the modeled object 20 is within an allowable range.

  Here, when the strain value is equal to or less than the threshold value, the input control information is sent to the final determination unit 6. On the other hand, if the strain value is not less than or equal to the threshold value, the input control information and the result analyzed by the residual stress analysis unit 3 are sent to the control information correction unit 7. The control information correction unit 7 corrects the input control information.

  The control information correction unit 7 includes a three-dimensional information correction unit 71 that corrects three-dimensional information, a beam information correction unit 72 that corrects beam information, a preliminary sintering information correction unit 73 that corrects preliminary sintering information, And a post-heat information correcting unit 74 that corrects the heat information. Based on the control information and the result of analysis by the residual stress analysis unit 3, the control information correction unit 7 is configured so that the strain value of the modeled object 20 is equal to or lower than the threshold value, that is, the residual stress is reduced. Correct the control information.

  The three-dimensional information correction unit 71 examines the structures of the support units 31 and 32 based on the three-dimensional structure information included in the control information, and identifies the structure in which the residual stress is reduced. For example, various support portions such as a plurality of pin-shaped support portions 31 (see FIG. 5), a lattice-shaped support portion 32 (see FIG. 6), and a plate-shaped support portion (not shown). Consider which is the best. Further, the optimum thickness and thickness of each part constituting the support parts 31 and 32 will be examined. Then, the three-dimensional structure information is corrected so as to correspond to the specified support units 31 and 32. If it does in this way, the three-dimensional structure of the support parts 31 and 32 can be corrected so that the residual stress which arises in the molded article 20 may be reduced.

  Note that various shapes of the support units 31 and 32 may be stored in advance in a storage unit such as a database, and the optimal structure of the support units 31 and 32 may be specified based on the stored information.

  In the present embodiment, the three-dimensional structure information of the target object 20 is not corrected, but the three-dimensional structure information of the object 20 is appropriately changed in consideration of the occurrence of deformation in advance. Also good. For example, when the modeled object 20 is deformed into a concave shape due to residual stress after completion, the modeled object 20 is formed in a convex shape in advance, and the modeled object 20 becomes a target shape due to the residual stress after completion. Anyway.

  In the present embodiment, the control information input to the pre-analysis device 1 includes the three-dimensional structure information of the predetermined support units 31 and 32 in advance, but the control information input to the pre-analysis device 1 The three-dimensional structure information of the support units 31 and 32 may not be included. In that case, the three-dimensional structure of the support portions 31 and 32 suitable for the three-dimensional structure of the shaped article 20 may be generated by the pre-analysis device 1.

  The beam information correcting unit 72 examines the control of the electron beam based on the beam information included in the control information, and specifies the control of the electron beam that reduces the residual stress. For example, consider the conditions that affect the residual stress, such as the output value of the electron beam, the diameter of the electron beam, the nature of the electron beam, the scanning speed of the electron beam, and the scanning order of the electron beam. Identify the optimal conditions. Then, the beam information is corrected so as to correspond to the specified condition. If it does in this way, control of a beam can be corrected so that the residual stress which arises in modeling object 20 may be reduced.

  The pre-sintering information correction unit 73 examines the optimum pre-sintering temperature and pre-sintering time based on the pre-sintering information included in the control information, and pre-sintering temperature and pre-sintering that reduce the residual stress. Identify the settling time. Moreover, the range where temperature rises by temporary sintering, for example, temporary sintering depth, temporary sintering width, etc. are specified. Then, the preliminary sintering information is corrected so as to correspond to the specified preliminary sintering temperature and preliminary sintering time. If it does in this way, temporary sintering conditions can be corrected so that the residual stress which arises in modeling object 20 may be reduced. In addition, since temporary sintering is performed based on irradiation of an electron beam, the beam information may be appropriately corrected according to the correction of the temporary sintering information.

  The post-heat information correction unit 74 examines the optimal post-heat time and post-heat temperature based on the post-heat information included in the control information, and specifies the post-heat time and the post-heat temperature at which the residual stress is reduced. In addition, the inherent distortion which arises in the molded article 20 can be relieved according to a post-heating time or a post-heating temperature. That is, the post-heating time and post-heating temperature affect the generation of residual stress. Therefore, a strain relaxation curve may be made into a database using the afterheating time and afterheating temperature as a function. And based on this database, you may specify after-heating time and after-heating temperature. Then, the post-heat information is corrected so as to correspond to the specified post-heat information and the post-heat time. If it does in this way, after-heating conditions can be corrected so that the residual stress which arises in modeling object 20 may be reduced.

  Note that the various types of information studied by the three-dimensional information correction unit 71, the beam information correction unit 72, the pre-sintering information correction unit 73, the post-heat information correction unit 74, and the like are linked to each other. Other information may be modified as appropriate in accordance with the modification.

  In addition, the examination of the control information according to the present embodiment is a main examination requirement that the residual stress is reduced, but other points such as easiness of additive manufacturing and the removal of the support portions 31 and 32 are included. Ease, safety, manufacturing time, manufacturing cost, etc. are also considered requirements. In addition, it is necessary to consider the prevention of the charging (charge-up) of metal powder and the negative effects (smoke generation, etc.) caused by charging, the stability during modeling, the quality of the modeled object 20, the service life of the modeled object 20 It is said. Further, based on these examination requirements, the control information is modified so that the most rational and efficient additive manufacturing can be performed.

  In this embodiment, the material physical property information uniquely specified according to the material used for additive manufacturing is not corrected, but the optimal material physical property is also examined for this material physical property information. In addition, material properties that reduce residual stress may be specified. In addition, when the material physical property which reduces a residual stress is specified, you may display the material physical property information which shows an optimal material physical property on the display part of the prior analysis apparatus 1. FIG. Further, when the additive manufacturing apparatus 10 can hold a plurality of types of materials in advance, according to the correction of the material physical property information, an optimum material can be specified among the plurality of types of materials, and the specified materials are stacked. Modeling control may be performed.

  Based on the control information corrected by the control information correction unit 7, the residual stress analysis unit 3 performs the analysis again. Then, the strain determination unit 5 determines again whether or not the strain value of the shaped article 20 is equal to or less than a specific threshold value. Further, when the strain value is not less than the specific threshold value, the control information correction unit 7 corrects the control information again, and these controls are repeated until the strain value becomes less than the specific threshold value. Then, when the strain value becomes equal to or less than a specific threshold value, this control information is sent to the final determination unit 6.

  The final determination unit 6 determines whether or not the modeled object 20 that is layered and formed satisfies the final determination requirement based on the control information. The final determination requirement is a requirement that enables the most rational and efficient additive manufacturing. In the present embodiment, the final determination requirement is a man-hour that is a value obtained by quantifying the manufacturing time and labor (including the removal process of the support portions 31 and 32) necessary for manufacturing the shaped article 20. The final determination unit 6 determines whether or not this man-hour is equal to or less than a specified threshold value. Note that safety, manufacturing cost, and the like may be included in the final determination requirements.

  Here, when the man-hour is equal to or less than a predetermined threshold, control information is sent to the control information output unit 8. And this control information output part 8 outputs control information toward the additive manufacturing apparatus 10, and additive manufacturing is started based on this control information. On the other hand, if the man-hour is not equal to or less than the prescribed threshold, the input control information and the result analyzed by the residual stress analysis unit 3 are sent to the control information correction unit 7. The control information correction unit 7 corrects the control information. Then, these determinations and corrections are repeated, and when the man-hour is equal to or less than a predetermined threshold, the control information output unit 8 outputs this optimal control information to the additive manufacturing apparatus 10, and additive manufacturing is performed based on the control information. Is started.

  In the present embodiment, the correction of the control information is repeated until the strain value becomes equal to or less than a specific threshold value. However, the number of corrections of the control information may be limited to a predetermined number. For example, the control information may be corrected only once, and even if this correction is performed, if the distortion value does not fall below a specific threshold value, an output for informing that effect may be performed.

  In the present embodiment, the control information is repeatedly corrected until the man-hour is equal to or less than a predetermined threshold. However, a plurality of types of control information whose man-hour is equal to or less than the predetermined threshold is acquired, and the control information Among them, the control information that can perform the additive manufacturing most rationally and efficiently may be determined.

  Next, the pre-analysis process executed by the pre-analysis apparatus 1 will be described with reference to FIG. In the description of each step in the flowchart, for example, a portion described as “Step S11” is abbreviated as “S11”.

  First, control information is input to the control information input unit 2 of the pre-analysis device 1 (S11: control information input step). Next, the residual stress analysis unit 3 executes a residual stress analysis process for analyzing (evaluating) the residual stress generated in the completed molded article 20 based on the control information input to the control information input unit 2 (S12). : Residual stress analysis step).

  Next, based on the residual stress generated in the modeled object 20 analyzed by the residual stress analyzing unit 3, the strain determination unit 5 specifies a predetermined value (strain value) when the modeled object 20 is deformed. It is determined whether it is below the threshold value (S13: strain determination step). If the strain value is not equal to or less than the specific threshold value, the process proceeds to S16. On the other hand, if the strain value is equal to or less than the specific threshold value, the process proceeds to S14.

  In S14, the final determination unit 6 determines whether or not the shaped article 20 that is layered and formed satisfies the final determination requirement based on the control information (final determination step: man-hour determination step). Here, when the final determination requirement is satisfied, the control information is output from the control information output unit 8 to the additive manufacturing apparatus 10 (S15: control information output step), and the preliminary analysis process is ended. On the other hand, if the final determination requirement is not satisfied, the process proceeds to S16.

  In S16, the control information correction unit 7 executes a control information correction process for correcting the control information (control information correction step). Then, after the control information is corrected, the process returns to S12, and the residual stress analysis unit 3 executes the residual stress analysis process again based on the control information corrected by the control information correction unit 7. Further, the strain value of the analyzed modeled object 20 is determined (S13), and these steps are repeated until the strain value becomes equal to or less than a specific threshold value. Next, it is determined whether or not the model 20 to be layered and formed based on the control information satisfies the final determination requirement (S14), and these steps are repeated until the final determination requirement is satisfied. When the final determination requirement is satisfied, control information is output from the control information output unit 8 to the additive manufacturing apparatus 10 (S15), and the preliminary analysis process is terminated.

  Next, experimental results showing the effectiveness of the residual stress reduction system of this embodiment will be described with reference to FIGS. Each graph shows an evaluation result analyzed by the residual stress analysis unit 3.

  FIG. 3 shows a three-dimensional structure of the modeled object 20. The modeled object 20 has a rectangular parallelepiped shape having a plurality of pores 33 and has dimensions of 30 mm (Z direction) × 50 mm (X direction) × 70 mm (Y direction).

  The material used in this experiment is a Ni alloy, and the heat source for additive manufacturing is an electron beam. Here, the Young's modulus (206828 MPa) at room temperature is input to the material property information input unit 25 as the material property information of the Ni alloy. In addition, the beam information input unit 22 receives, as beam information, a heat input amount (about 0.7 J / mm) based on beam output information and a beam scanning speed (about 200 mm / sec.). Furthermore, the lamination thickness (80 μm) of the metal powder supplied at a time by the powder supply unit is also input.

  FIG. 4 is a graph showing the evaluation results of the shaped object 20 having a reference shape. This evaluation result is a graph based on the evaluation line L1 (see FIG. 3) at the center of the surface 20A (upper surface) of the modeled object 20. As shown in this graph, in the evaluation line L1 of the surface 20A of the modeled object 20, it is evaluated that the residual stress (tensile stress) of the maximum stress (about 300 MPa) is generated in the center portion.

  5 and 6 show the three-dimensional structure of the support portions 31 and 32. FIG. Two types of support portions 31 and 32, which are a plurality of pin-shaped support portions 31 and a lattice-shaped support portion 32, are illustrated. The support portions 31 and 32 are fixed to the upper surface of the base plate 30, and the molded article 20 is fixed on the support portions 31 and 32.

  FIG. 7 is a graph showing an evaluation result based on the evaluation line L1 of the surface 20A of the modeled object 20. FIG. 8 is a graph showing an evaluation result based on the evaluation line L2 of the interface 20B which is a boundary between the molded article 20 and the support portions 31 and 32.

  As shown in these graphs, the residual stress generated on the surface 20 </ b> A of the modeled object 20 is not affected by the three-dimensional structure (shape) of the support parts 31 and 32, but between the modeled object 20 and the support parts 31 and 32. It is evaluated that the residual stress generated on the modeling object 20 side (the lower surface of the modeling object 20) at the interface 20B changes depending on the three-dimensional structure (shape) of the support portions 31 and 32. In addition, it is evaluated that the residual stress generated in the interface 20B between the modeled article 20 and the support portions 31 and 32 is smaller in the support portion 32 having a lattice shape than the support portion 31 having a pin shape.

  9 to 17 show the evaluation results of the residual stress generated at the center point P (see FIGS. 5 and 6) of the surface 20A of the shaped article 20. FIG. 9 to 16 show the evaluation results of the modeled object 20 modeled using the pin-shaped support part 31, and the modeled model 20 modeled using the grid-shaped support part 32 is the same. It is an evaluation result.

  FIG. 9 is a graph showing the relationship between the amount of heat input by the electron beam and the residual stress, FIG. 10 is a graph showing the relationship between the beam diameter of the electron beam and the residual stress, and FIG. 6 is a graph showing the relationship between the beam scanning speed and the residual stress. As shown in these graphs, the residual stress generated at point P of the shaped article 20 is not affected by the beam diameter, but is affected by the amount of heat input and the beam scanning speed. Further, it is evaluated that the larger the heat input amount and the slower the beam scanning speed, the smaller the residual stress generated at the point P of the shaped article 20.

  FIG. 12 is a graph showing the relationship between the preliminary sintering temperature and the residual stress. As shown in this graph, it is evaluated that the higher the temporary sintering temperature, the smaller the residual stress generated at the point P of the shaped article 20.

  FIG. 13 is a graph showing the relationship between post-heating time and residual stress. As shown in this graph, it is evaluated that the longer the post-heating time, the smaller the residual stress generated at the point P of the shaped article 20.

  Referring to the above evaluation results, in order to reduce the residual stress generated in the molded article 20, the three-dimensional structure of the support portions 31 and 32, the output of the electron beam, the beam scanning speed, the temporary sintering temperature, It can be seen that the modification (change) of the after-heating time is effective.

  14 to 17 are graphs showing the relationship between the amount of heat input, the pre-sintering temperature, the post-heating time, and the man-hour. Here, the man-hour is a value obtained by quantifying the manufacturing time and labor (including the removal process of the support portions 31 and 32) necessary for manufacturing the molded article 20. In this experiment, an allowable residual stress value is 270 MPa or less, and an allowable man-hour value is 1.1 or less when the reference man-hour value is 1.0.

  As shown in these graphs, if the post-heating time is corrected, the number of man-hours exceeds the allowable value. Therefore, it is evaluated that the correction of the post-heating time is irrational. Further, the amount of heat input based on the three-dimensional structure of the support portions 31 and 32, the output value of the electron beam, the beam scanning speed, and the like, and the pre-sintering temperature can reduce the residual stress while keeping the man-hours below the allowable value. It can be appreciated that it is reasonable to modify these values.

  From the above, the shape of the support portions 31 and 32 is suitable for the pin shape (see FIG. 17), and the heat input based on the electron beam is suitable for 1.0 J / mm (see FIG. 14). It is evaluated that 1000 ° C. is suitable for the temperature (see FIG. 15) and 0 h is suitable for the post-heating time (see FIG. 16).

  In the present embodiment, it is possible to evaluate the three-dimensional structure of the support portions 31 and 32 of the shaped article 20 that affects the residual stress, beam conditions, pre-sintering conditions, and post-heating conditions. Moreover, the influence of the allowable residual stress and man-hour can be evaluated quantitatively. As a result, the control information of the layered manufacturing apparatus 10 can be corrected so that the residual stress can be reduced most rationally.

  In the present embodiment, the prior analysis device 1 is a separate device from the additive manufacturing apparatus 10, but the prior analysis device 1 may be an apparatus that is integrated into the additive manufacturing apparatus 10. In that case, the control information output unit 8 of the pre-analysis apparatus 1 outputs control information to the control unit of the additive manufacturing apparatus 10.

  In the present embodiment, the strain value of the modeled object 20 analyzed by the residual stress analysis unit 3 is determined by the strain determination unit 5 to determine whether it is equal to or less than a specific threshold value. 5 may be omitted, and the input control information may be corrected by the control information correction unit 7 without fail.

  In the present embodiment, in the preliminary analysis process, it is determined whether or not the deformation amount (strain) of the modeled object 20 is in an allowable range, but the residual stress generated in the modeled object 20 is in an allowable range. It may be determined whether or not. Here, even if the residual stress is large, if the rigidity of the modeled object 20 is high, the amount of deformation (strain) of the modeled object 20 becomes small. Therefore, the determination value may be changed depending on the rigidity of the modeled object 20. That is, the determination value used in the pre-analysis process may be changed as appropriate according to changes in other parameters.

  In this embodiment, in the determination in the pre-analysis process, it is determined whether or not it is “threshold or less”, but this determination may be a determination of “whether it is less than the threshold” or “ Or “whether or not a threshold value is exceeded”.

  In this embodiment, the residual stress generated in the modeled object 20 is reduced by performing the pre-analysis process and correcting the control information, but only the tensile stress that reduces the strength of the modeled object 20 is reduced. The compression stress that improves the strength of the shaped article 20 may not be reduced. Further, the control information may be corrected so that the compressive stress generated in the shaped article 20 increases. Further, the control information may be modified so that only the residual stress that is not intended by the designer is reduced and only useful residual stress is generated.

  According to the embodiment described above, the residual stress analysis unit 3 that analyzes the residual stress generated in the modeled object based on the control information before the start of the layered modeling, and the control that corrects the control information based on the analyzed residual stress. By having the information correction unit 7, it is possible to reduce the residual stress generated in the modeled object.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Prior analysis apparatus, 2 ... Control information input part, 3 ... Residual stress analysis part, 4 ... Database, 5 ... Strain determination part, 6 ... Final determination part, 7 ... Control information correction part, 8 ... Control information output part, DESCRIPTION OF SYMBOLS 10 ... Laminate shaping apparatus, 20 ... Modeling thing, 20A ... Surface, 20B ... Interface, 21 ... Three-dimensional structure information input part, 22 ... Beam information input part, 23 ... Pre-sintering information input part, 24 ... Post heat information input , 25 ... Material property information input part, 30 ... Base plate, 31, 32 ... Support part, 33 ... Fine pore, 71 ... Three-dimensional information correction part, 72 ... Beam information correction part, 73 ... Temporary sintering information correction part, 74: Post-heat information correction unit.

Claims (8)

A control information input unit to which control information used for control of layered modeling for irradiating a beam to the metal powder to be stacked to form a modeled object; and
A residual stress analysis unit that analyzes residual stress generated in the modeled object based on the control information before the start of the additive manufacturing;
A control information correction unit for correcting the control information based on the analyzed residual stress;
A control information output unit for outputting the control information after the correction;
A residual stress reduction system for additive manufacturing, comprising: The control information includes three-dimensional structure information of the modeled object and three-dimensional structure information of a support unit for fixing the modeled object to a base plate,
The residual stress reduction system for additive manufacturing according to claim 1, wherein the control information correction unit corrects at least the three-dimensional structure information of the support unit based on the analyzed residual stress. The control information is beam information related to the control of the beam, and includes output information indicating the output value of the beam, diameter information indicating the diameter of the beam, profile information indicating the property of the beam, and scanning speed of the beam. Including at least one of scanning speed information and scanning sequence information indicating the scanning order of the beam,
The residual stress reduction system for additive manufacturing according to claim 1, wherein the control information correction unit corrects the beam information based on the analyzed residual stress. The control information is presintering information when performing presintering by irradiating the metal powder with the beam and irradiating the beam with a lower output than the main sintering immediately before performing the main sintering. Including
The additive stress reduction system for additive manufacturing according to any one of claims 1 to 3, wherein the control information correction unit corrects the preliminary sintering information based on the analyzed residual stress. The control information includes after-heating time information until the metal powder remaining around the modeled object is removed from the time when the modeled object is completed,
The additive stress reduction system for additive manufacturing according to any one of claims 1 to 4, wherein the control information correction unit corrects the post-heating time information based on the analyzed residual stress. The residual stress analysis unit is preliminarily analyzed for inherent strain generated in a three-dimensional structure constituting the shaped object having a predetermined shape, and a database that collects these analysis results is connected,
The said residual stress analysis part analyzes the said residual stress by performing the elastic calculation using a finite element method based on the said control information and the said database, In any one of Claims 1-5 The residual stress reduction system for additive manufacturing described. A control information input step in which control information used for control of layered modeling for irradiating a beam to the metal powder to be stacked to form a modeled object,
A residual stress analysis step for analyzing the residual stress generated in the modeled object based on the control information before the start of the additive manufacturing;
A control information correction step for correcting the control information based on the analyzed residual stress;
A control information output step for outputting the control information after the correction;
A method for reducing residual stress in additive manufacturing, characterized by comprising: On the computer,
A control information input step in which control information used for control of layered modeling for irradiating a beam to the metal powder to be stacked to form a modeled object,
A residual stress analysis step for analyzing the residual stress generated in the modeled object based on the control information before the start of the additive manufacturing;
A control information correction step for correcting the control information based on the analyzed residual stress;
A control information output step for outputting the control information after the correction;
Is a residual stress reduction program for additive manufacturing.

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