Three-dimensional shaping device

Abstract

This invention provides a three-dimensional molding apparatus and method that improve molding accuracy in three-dimensional molding, which involves repeatedly melting and solidifying powder and then cutting it to form a three-dimensional object. [Solution] In a powder bed type three-dimensional molding apparatus, a laser is irradiated onto metal powder to melt and solidify the powder, forming thin layers, and these thin layers are stacked to create a three-dimensional object. At this time, the molding accuracy of the object is improved by cutting off the formed layers after each predetermined layer has been formed, such as 10 layers. The cutting data that defines the cutting shape uses a shape S3 obtained by reflecting the displacement d1 between the desired shape S1 and the shape S2 whose deformation has been predicted by simulation onto shape S1. Alternatively, the deformation of shape S3 may be further predicted to obtain a displacement d2 between it and shape S1, and a shape S5 that reflects this displacement may be used as the cutting data.

Description

Technical Field

[0001] The present invention relates to a technique for improving the shaping accuracy in three-dimensional shaping, which forms a three-dimensional shaped object by repeating the shaping of melting and solidifying powder with a laser, an electron beam, or the like, and the cutting thereof.

Background Art

[0003] For example, Patent Document 1 discloses a technique for performing layer shaping and cutting of the formed layers while repeating them when forming a structure by laminating thin layers. Patent Document 2 discloses a technique for making cutting easier by assuming distortion due to residual thermal stress during shaping of a laminate, forming each layer larger than the original shape, and forming portions protruding from the shape of the original shaped object to have low strength. Thus, attempts have been made to improve the accuracy of three-dimensional shaping by repeating shaping and cutting.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even when repeatedly performing molding and cutting, if the layers finished by cutting are subsequently deformed by thermal stress, the molding accuracy cannot be maintained. On the other hand, if cutting is performed only after waiting for each layer to stop deforming due to thermal stress, another problem arises: increased molding time. The above-mentioned problems are common to additive manufacturing, regardless of the method of layering thin layers. In view of these problems, the present invention aims to improve the accuracy of three-dimensional fabrication while suppressing an increase in fabrication time. [Means for solving the problem]

[0006] The present invention A three-dimensional modeling device for creating three-dimensional objects, An input unit for reading the shape data of the aforementioned molded object, A molding unit that melts and solidifies powder to form a part of the molded object according to the shape data, A moving mechanism for moving the part and the molding part relative to each other so that the next part is formed by adding to the already formed part, A cutting section for cutting off the formed portion, The system includes a control unit that controls the molding process performed by the molding unit and the moving mechanism, and the cutting process performed by the cutting unit, to repeatedly execute these processes in order to create the molded object. The control unit can be a three-dimensional molding apparatus that predicts the deformation that occurs in the part due to the stress associated with the molding after the cutting, and performs the cutting based on cutting data that has been corrected to conform to the shape data after the deformation has occurred.

[0007] In this invention, a three-dimensional object is formed by repeatedly performing molding and cutting based on shape data set without considering deformations that may occur during molding. At this time, cutting can be performed by applying a correction to the shape of the object based on the deformation caused by stress during molding. Therefore, even if the shape of the object deviates from its original shape during cutting, the original shape of the object will be realized after deformation occurs. By doing so, according to the present invention, cutting can be performed to realize the shape of the fabricated object without waiting for deformation to stop occurring in the already formed parts of the fabricated object. In other words, it is possible to improve the fabrication accuracy while suppressing an increase in fabrication time.

[0008] In 3D printing, it is possible to perform machining after all the printing is complete to finish the shape of the object. However, this method has the drawbacks of being time-consuming to machine and placing a heavy burden on the tools. Furthermore, depending on the shape of the object, such as deep grooves, it may not be possible to machine it after printing with conventional tools. In contrast, the present invention has the advantage of avoiding these problems because machining is performed during the printing process.

[0009] This invention can be applied to various three-dimensional fabrication methods using powder melting and solidification, such as PBF (Powder Bed Fusion) and DED (Directed Energy Deposition). The molding and cutting processes can be performed at any time. Alternatively, the molding process may be repeated a predetermined number of times before cutting is performed. In this invention, cutting data may be generated by a three-dimensional molding device, or data generated by an operator may be loaded into the three-dimensional molding device. Alternatively, cutting data may be generated by a device other than a three-dimensional molding device.

[0010] In the present invention, The system may also include a cutting data generation unit that predicts deformation due to stress through simulation and generates the cutting data by reflecting the results of the prediction in the shape data.

[0011] By predicting the deformation caused by stress on the original shape of the object and incorporating a deformation in the opposite direction into the cutting data, the original shape of the object can be achieved as a result of the deformation. It is not necessary to directly reflect the deformation obtained from the prediction; calculations such as multiplying by a weighting coefficient may be applied before reflecting the deformation. Various well-known methods can be applied to simulations that predict deformation. The cutting data generation unit may be located within the three-dimensional molding apparatus, or it may be located in a separate device, server, etc. The same applies in the following cases.

[0012] As mentioned above, when using simulations, The cutting data generation unit may predict the deformation that occurs in the cutting data through the simulation and update the cutting data by reflecting the difference between the deformed shape and the shape data.

[0013] Even if cutting data is set to reflect the predicted deformation, various error factors may prevent the shape of the fabricated object from being accurately realized after deformation. According to the above embodiment, deformation can be predicted based on the cutting data, and if the shape of the fabricated object cannot be realized, the cutting data can be set to reflect that difference. In this way, it becomes possible to realize the shape of the fabricated object with greater accuracy after deformation. Furthermore, updating the cutting data based on deformation prediction may be performed not only once, but two or more times. For example, it may be repeated until the difference between the deformed shape and the original shape of the fabricated object converges to a predetermined range.

[0014] In addition to methods using simulations, the present invention also uses: The system may also include a cutting data generation unit that predicts the deformation caused by the stress based on a database that stores past molded objects and the deformations caused by the stress in those molded objects, and generates the cutting data by reflecting the result of the prediction in the shape data.

[0015] For example, a method can be adopted in which a shaped object is shaped without predicting deformation, the deformation that occurs is actually measured with a three-dimensional measuring instrument or the like, and cutting data is created to cancel out the deformation. By doing so, based on the data generated in past shaped objects, cutting data can be set accurately by predicting deformation. Also, it may be possible to achieve this with a lighter load than simulation. In addition, as a method of using past data, deformation may be predicted by a statistical method or machine learning or the like.

[0016] In the present invention, The control unit may cause the cutting to be performed by excluding a portion due to shaping for a predetermined number of processes from the immediately preceding process among the shaping repeatedly performed by the shaping unit and the moving mechanism.

[0017] The portion shaped in the immediately preceding process may be affected by heat when new shaping is performed in subsequent processes. Therefore, even if such a portion is cut, there is also a possibility of causing unexpected deformation due to new heat. According to the above aspect, since cutting is performed by excluding the immediately preceding several processes, it is possible to avoid such an influence. The processes to be excluded can be arbitrarily determined according to the method of three-dimensional shaping, the shaped object, and the like.

[0018] In the present invention, The cutting unit may use a tool having a lollipop shape.

[0019] The lollipop shape refers to a tool having a spherical blade with a diameter larger than the diameter of the shaft formed at the tip of the shaft. By doing so, even when a part of the shaped object protrudes, cutting can be performed while avoiding interference, so that the accuracy can be improved by cutting for more diverse shaped objects. The lollipop shape is particularly useful when creating a model by layering thin layers, especially when removing several layers from the immediate vicinity. In such cases, the layers beneath are cut while the remaining thin layers that are not to be cut protrude. However, a lollipop-shaped tool can easily cut while avoiding interference with these protruding layers.

[0020] In the present invention, The aforementioned molding section is The mechanism involves melting and solidifying the powder on a base plate on which the molded object is placed, thereby forming a thin layer that constitutes a part of the molded object. A heater is provided for heating the base plate. The control unit may control the heating by the heater so that the warping of the base plate due to the molding process remains below a predetermined required value.

[0021] When building objects by layering thin layers on a base plate, the base plate may warp, which can lead to a decrease in the accuracy of the printed object. According to the above embodiment, by appropriately heating the base plate with a heater, it is possible to suppress the warping of the base plate and the distortion of the printed object. The above embodiment can also be applied so that the amount of warping and other deformation of the molded object after it has been separated from the base plate is less than or equal to the required value.

[0022] In the above embodiment, heating by the heater can be controlled in various ways. For example, heating conditions may be set to reduce warpage to below a predetermined level based on past molding data. Alternatively, heating conditions may be set based on the warpage of the base plate determined by simulation. In simulations that predict the deformation of the molded object, if the deformation of the base plate is also taken into consideration during the analysis, the results may be used. Furthermore, since the warpage of the base plate is highly correlated with the heater heating conditions and the contact area with the printed object, these correlations may be expressed in advance in the form of functions, maps, and tables, and the heater heating conditions that result in warpage being below the required value may be determined based on these correlations. In addition to the contact area with the printed object, other parameters representing the size and shape of the printed object, such as height, may also be considered. Furthermore, a strain sensor or other sensor for detecting deformation may be attached to the base plate itself, and the heating of the heater may be feedback-controlled so that the warpage detected by the sensor is below a required value.

[0023] In the present invention, also, The control unit may set the cutting height range in the lamination direction of the thin layer according to the set temperature of the heater and the area of ​​the thin layer to be bonded to the base plate.

[0024] When layering thin layers, if the edges of the thin layers are not aligned, the edges of the fabricated object may become rough. Machining can reduce the roughness of the edges of the fabricated object and improve the surface quality. However, in order to improve the surface quality of the edges, it is preferable to perform machining while considering the deformation that occurs in the thin layers during fabrication, as well as the effects of heat and deformation from subsequent layers. Deformation of thin layers can occur primarily due to either shrinkage or expansion compared to the initial molding stage. When shrinkage is the primary cause, there is a risk that the thin layer may not maintain its original shape if it shrinks after cutting. Therefore, it is preferable to perform cutting only within a range where further shrinkage is not expected during subsequent molding. On the other hand, when expansion is the primary cause, there is a risk that the cut thin layer may expand further during subsequent molding. Therefore, it may be preferable to perform cutting again on the thin layer even after the initial cutting is complete. It was found that these deformation tendencies are influenced by the temperature of the heater that heats the base plate and the area of ​​the thin layer bonded to the base plate. Therefore, in the above embodiment, the cutting height range in the lamination direction is set according to these parameters, making it possible to improve the surface quality according to the deformation tendencies occurring in the thin layer.

[0025] The cutting height range can be set in various ways. For example, if shrinkage deformation is expected based on parameters such as heater temperature, the cutting height range may be set to the area below the top surface of the existing thin layer, at a predetermined distance. Conversely, if deformation with an expansion tendency is expected to occur, the cutting height range may be set to a predetermined range from the top surface, including the previously cut layer.

[0026] The various features of the present invention described above do not necessarily have to be all present, and some may be omitted or combined as appropriate. Furthermore, the present invention can be configured in various forms other than the three-dimensional molding apparatus described above. For example, a three-dimensional modeling method that creates a three-dimensional object using a three-dimensional modeling device, (a) A step of reading the shape data of the molded object, (b) A step of melting the powder and solidifying it to form a part of the molded object according to the shape data, (c) Repeat step (b) so that the next part is formed by adding to the already formed part, (d) a step of cutting the formed portion, Step (d) above is, A three-dimensional fabrication method may also be used, which involves predicting the deformation that will occur in the part due to the stress associated with the fabrication after the cutting, and performing the cutting based on cutting data that has been corrected to conform to the shape data after such deformation has occurred.

[0027] This three-dimensional fabrication method can achieve the same effects as those described for the three-dimensional fabrication device. Furthermore, the various features described for the three-dimensional fabrication device are also applicable.

[0028] The present invention may be configured as a computer program for controlling a three-dimensional molding apparatus using a computer. Alternatively, it may be configured as a computer program for generating cutting data, which is a key part of the process, using a computer. That is, a computer program for a three-dimensional molding apparatus that repeatedly performs the process of forming parts of a three-dimensional object by melting and solidifying powder, and then cutting the formed parts, to create the object, wherein the computer generates data for cutting by computer. A function to read the shape data of the aforementioned molded object, A function that predicts the deformation that will occur in the part due to the stress associated with the molding after the cutting, and generates cutting data that has been corrected to conform to the shape data after such deformation has occurred. This may also be a computer program that implements this using a computer.

[0029] Furthermore, a computer program for a three-dimensional molding apparatus that fabricates a three-dimensional object by repeatedly melting and solidifying powder to form parts of the three-dimensional object and cutting the formed parts, wherein the computer program generates data for cutting by computer, A function to read the shape data of the aforementioned molded object, A function that predicts deformation due to stress based on a database that stores past molded objects and the deformation caused by the stress on those molded objects, and generates the cutting data by reflecting the result of the prediction in the shape data. This may also be a computer program that implements this using a computer. [Brief explanation of the drawing]

[0030] [Figure 1] This is a schematic diagram illustrating the configuration of the three-dimensional molding apparatus in the embodiment. [Figure 2] This is an explanatory diagram showing the molding process in the embodiment. [Figure 3] This is an explanatory diagram showing an example of the tool shape for the cutting section. [Figure 4]This is a flowchart of the molding process. [Figure 5] This is an explanatory diagram showing how to set the heater temperature. [Figure 6] This is an explanatory diagram showing how cutting data is generated. [Figure 7] This is a flowchart of the cutting data generation process. [Figure 8] This is an explanatory diagram showing the deformation that occurs in each layer. [Figure 9] This is an explanatory diagram showing how to set the cutting height range in relation to shrinkage tendencies. [Figure 10] This is an explanatory diagram showing how to set the cutting height range in response to expansion tendencies. [Figure 11] This is an explanatory diagram showing the results of the improved accuracy. [Figure 12] This is an explanatory diagram showing the results of improving surface quality. [Modes for carrying out the invention]

[0031] An embodiment of the present invention will be described using the case of fabrication by powder bed fusion as an example. The present invention is applicable not only to this method but also to various fabrication methods that melt and solidify powder, such as the DED (Directed Energy Deposition) method.

[0032] A. Equipment configuration: Figure 1 is a schematic diagram illustrating the configuration of the three-dimensional molding apparatus in the embodiment. The three-dimensional molding apparatus 10 of this embodiment includes a molding table 14 for forming an object and a recoater 13 that reciprocates over it. A substrate called a base plate is placed on the molding table 14, and molding is performed on it. The metal powder that will be used as the raw material for the object is stored in a hopper 12. When the recoater 13 reciprocates during molding, the surface of the base plate is covered with the metal powder used for molding to a nearly uniform thickness. The three-dimensional molding apparatus 10 is equipped with a laser irradiation unit 11 as a mechanism for heating and melting the metal powder. The laser irradiation unit 11 comprises a laser light source and a mechanism for moving the irradiation area according to the shape of the object being molded. In the area irradiated by the laser irradiation unit 11, the metal powder melts, and then solidifies as it cools, forming a thin layer that constitutes part of the molded object. The above parts can be collectively referred to as the molding unit, in the sense that they are components for forming a thin layer. The three-dimensional printing apparatus 10 is equipped with a moving mechanism 15 that moves the build table 14 downwards. After forming a thin layer, the build table 14 is moved downwards by one layer, and metal scattering by the recoater 13 and melting and solidification by the laser irradiation unit 11 are performed, allowing the next layer to be stacked on top of the already formed thin layer. The three-dimensional printing apparatus of this embodiment can create three-dimensional objects on a base plate by repeatedly forming thin layers and stacking them in this manner.

[0033] The three-dimensional molding apparatus 10 in this embodiment repeatedly performs thin-layer molding and cutting to improve accuracy. The three-dimensional molding apparatus 10 is equipped with a cutting unit 20 as a mechanism for cutting. The cutting unit 20 is retracted as shown in the figure when thin-layer molding is performed, and then moves onto the molding table 14 to perform cutting when the cutting process begins.

[0034] The three-dimensional molding apparatus 10 is equipped with a control device 30 to control the molding and cutting processes described above. While these can be configured in hardware, in this embodiment they are configured in software by incorporating computer programs that realize the functions shown in the illustration into a computer equipped with a CPU and memory.

[0035] The data input unit 31 reads the shape data of the printed object. Since the shape of each layer is required during printing, the shape data may be the shape data of each layer that makes up the printed object. Alternatively, the 3D printing apparatus 10 may read data representing the 3D shape of the printed object and generate shape data for each layer. The data input unit 31 also reads cutting data that defines the shape of the cut. As will be described later, in this embodiment, shape data and cutting data are different. Shape data is data that represents the shape of the object to be produced, while cutting data is data used for cutting performed during the production process. In the case of three-dimensional fabrication using the melting and solidification of powder, deformation may occur in the object due to thermal stress, so the cutting data is set to take into account deformation after cutting and to realize the shape to be produced as a result of the deformation. The cutting data may be generated by the three-dimensional molding apparatus 10, but in this embodiment, it is generated by a separately prepared cutting data generation device 50. The configuration of the cutting data generation device 50 will be described later.

[0036] The lamination control unit 35 controls the supply of powder by the recoater 13, the laser irradiation unit 11, and the movement by the moving mechanism 15 to form a thin layer. The cutting control unit 34 controls the cutting unit 20 to perform cutting based on cutting data during the molding process. The heater control unit 33 controls the heater provided on the build plate 14 so that the temperature of the build plate 14 is at an appropriate temperature. It is known that the temperature of the build plate 14 affects the warping of the base plate and, consequently, the accuracy of the printed object. In this embodiment, the temperature of the build plate 14 is controlled so that the printed object can be made with sufficient accuracy. The molding control unit 32 integrally controls the heater control unit 33, the cutting control unit 34, and the layering control unit 35 to create an object according to the shape data.

[0037] As explained earlier, in this embodiment, the process of creating a molded object involves repeatedly performing thin-layer fabrication and cutting. The cutting data that defines the shape to be cut may be generated by the three-dimensional molding apparatus 10, but in this embodiment, it is generated by the cutting data generation device 50. The cutting data generation device 50 is constructed in software by installing computer programs to implement each of the illustrated functions on a computer or server equipped with a CPU, memory, etc. These functions can be implemented on a single computer, or they can be implemented on multiple computers or servers connected via a network.

[0038] The molding database 51 stores molding data representing past molding results. The content of the molding data can be arbitrarily determined, but for example, it can include the shape of the molded object, cutting data during molding, and the magnitude of the distortion that occurred in the molded object. The shape of the molded object and cutting data may use a 3D shape, or they may be represented by parameters such as the thickness in the layering direction. The magnitude of the distortion may also be represented by parameters such as distortion in the layering direction or distortion within a layer.

[0039] The machine learning unit 53 generates a learning model using machine learning regression with respect to the molding database 51. The purpose of machine learning is to create a learning model that sets the cutting data so that the shape obtained after deformation following cutting of an object to be fabricated in the future is the desired shape. Therefore, machine learning is performed with shape, distortion, etc. as explanatory variables and cutting data as the dependent variable. Machine learning can be performed using various algorithms. The generated learning model is stored by the machine learning unit 53. Alternatively, instead of the machine learning unit 53, a function may be provided to set cutting data using statistical methods based on the molding database 51. For example, a method can be adopted that statistically determines the strain occurring in each three-dimensional direction of the molded object, using parameters such as the planar shape of the thin layer and the thickness of each part of the molded object.

[0040] The deformation prediction unit 52 performs the function of determining, through simulation or other means, what kind of deformation will occur in the object to be fabricated due to thermal stress and structural changes. Since various methods for deformation prediction simulation are well known, an appropriate method can be used.

[0041] The cutting data generation unit 54 generates cutting data by reflecting the results from the machine learning unit 53 and the deformation prediction unit 52 onto the shape data of the fabricated object. Either the machine learning unit 53 or the deformation prediction unit 52 may be used selectively depending on the fabricated object, or the results from both may be used. The generated cutting data is sent to the control device 30 and used in the cutting process.

[0042] Furthermore, the cutting data generation unit 54 may be configured to omit either the machine learning unit 53 or the deformation prediction unit 52, and the cutting data may be generated using only the remaining unit. Alternatively, the configuration of the cutting data generation unit 54 may be incorporated into the control device 30.

[0043] B. Three-dimensional modeling process: Figure 2 is an explanatory diagram showing the fabrication process in this embodiment. In this embodiment, thin layers are fabricated repeatedly (arrows SC1, SC2), and cutting (arrow SC3) is performed at predetermined timings. The process is described below. First, the thin-layer fabrication (arrow SC1) will be explained. The figure shows a state in which a thin layer 1a has been formed on the fabrication table 14. In this state, metal powder is supplied while moving the recoater 13 in the direction of arrow A. Then, the laser 11L is irradiated to melt and solidify the powder, forming a thin layer 1b. As a result, a state is formed in which a thin layer 1b is stacked on top of a thin layer 1a. The above process is repeated several times (arrow SC2). In this embodiment, 10 layers are formed by repeating the process. Subsequently, the cutting unit 20 moves onto the fabricated object and cuts the existing thin layer 1c (arrow SC3). Once the cutting is complete, the process returns to creating the thin layer (arrow SC1). As described above, three-dimensional fabrication is performed by repeatedly creating thin layers and cutting them. In this embodiment, cutting is performed every 10 layers, but the timing of the cutting can be determined arbitrarily. In addition, in this embodiment, the deformation of the thin layer is predicted and cutting (hereinafter, this cutting may also be referred to as finish cutting) is performed. In addition to this, intermediate cutting in the shaping process, that is, cutting in a state where the original shape has some allowance (hereinafter, this cutting may also be referred to as semi-finishing), may be interposed. In the following description, unless otherwise specified, cutting means finish cutting, but this is not intended to exclude performing semi-finishing.

[0044] FIG. 3 is an explanatory diagram showing an example of the tool shape of the cutting part. FIG. 3(a) shows a perspective view of a cutting tool 40 attached to the cutting part 20. As shown in the figure, the cutting tool 40 has a so-called lollipop shape in which a spherical blade part 41 is formed at the tip of the shaft 42. FIG. 3(b) is a side view of the cutting tool 40. The diameter d2 of the spherical blade part 41 is larger than the diameter d1 of the shaft 42 (d1 < d2). In addition, cutting blades are formed on the blade part 41 over the range of the angle ANG. The angle ANG can be arbitrarily determined, but in this embodiment, it is 220°. FIG. 3(c) schematically shows the advantages of the lollipop shape. When laminating and shaping the thin layers L1 and L2 as in this embodiment, as shown in the region S, the later-formed layer L1 may protrude beyond the existing layer L2. In such a situation, when cutting the existing layer L2, if it has a lollipop shape, since the blade part 41 is formed at a wide range of angles ANG, it is possible to avoid interference with the layer L1 and cut the layer L2. The same applies when cutting only the layer L2 without the layer L1 protruding. In this embodiment, as will be described later, cutting is performed excluding several layers from the top. Therefore, the lollipop-shaped cutting tool 40 is particularly useful.

[0045] C. Shaping process: Next, the process when shaping is performed by the three-dimensional shaping apparatus 10 of this embodiment will be described. FIG. 4 is a flowchart of the shaping process. It is a process executed by the control device 30 of the three-dimensional shaping apparatus 10. When processing begins, the 3D printing apparatus 10 first reads the shape data of the printed object (step S10). This shape data defines the shape of each thin layer when the printed object is constructed as a stack of thin layers. If the shape data is 3D data of the printed object, the 3D printing apparatus 10 needs to generate the shape data of the thin layers based on the 3D data.

[0046] Next, the three-dimensional molding apparatus 10 controls the temperature of the heater that heats the base plate (step S11). Figure 5 is an explanatory diagram illustrating the heater temperature setting. The horizontal axis shows the heater temperature, and the vertical axis shows the deformation of the base plate. The deformation of the base plate when it deforms upward is shown as a negative value, and the deformation when it deforms downward is shown as a positive value. Various stresses are generated in the formed object during the manufacturing process, and the base plate may deform as a result. The stress acting on the base plate is affected by the size of the object, more precisely, the contact area between the object and the base plate, and the temperature of the table heater that heats the base plate. Points p1 to p3 in the figure show the measurement results of the deformation of a certain object when the heater temperature is changed. According to this example, the relationship between heater temperature and deformation can be determined roughly as shown by the straight line L in the figure. Therefore, for this object, it is possible to determine the heater temperature at which the deformation is expected to be zero. If the printed object is different, the length of the straight line L will also be different. Furthermore, if the number of measurement points is increased, an approximate curve may be obtained instead of a straight line. Therefore, it is sufficient to identify the straight line L or approximate curve based on past identical or similar printing results and set the heater temperature accordingly. Returning to Figure 4, in step S11, the heater is controlled to reach the temperature set as described above.

[0047] Once the above processes are complete, the 3D printing apparatus 10 starts the printing process. First, the first thin layer is formed (step S12). As explained in Figure 2, the thin layer is formed by irradiating it with a laser according to the shape data, melting and solidifying the metal powder. This process is repeated until the printing of N layers (N is a natural number) is completed (step S13). As explained in Figure 2, in this embodiment, N=10.

[0048] Once the fabrication of N layers is complete (step S13), the 3D printing apparatus 10 executes a cutting data generation process (step S14) and then performs a cutting process, that is, a process of cutting the target layer based on the cutting data (step S15). The 3D printing apparatus 10 repeats the above process until the fabrication is complete (step S16).

[0049] The cutting data generation process will be described later. In this embodiment, the cutting data is generated during the manufacturing process, but it may also be prepared in step S10 before starting the manufacturing process. In the cutting process (S15), in this embodiment, a predetermined number of layers may be excluded from the layer immediately after molding, i.e., the top layer (hereinafter referred to as the "excluded area"), and cutting may be performed only on the layer below. The excluded area is an upper area, and is therefore susceptible to heat when the next thin layer is laminated. Even if the cutting is performed with high precision, deformation may occur between cutting operations, resulting in steps on the cut surface, i.e., the edge of the molded object. If the excluded area is made thicker, the cut portion will be less affected by the heat during the formation of subsequent layers. On the other hand, depending on the shape of the molded object, if the excluded area is made thicker, the excluded area may protrude significantly, making it difficult to cut the layer below the excluded area. The excluded area can be determined arbitrarily by considering these factors. The method of determining this will be described later. Furthermore, in the cutting process, not only finish cutting but also intermediate finishing may be performed.

[0050] D. Method for generating cutting data: Next, we will explain how to generate the cutting data. This corresponds to the process in step S14 of the molding process (Figure 4).

[0051] Figure 6 is an explanatory diagram illustrating the method for generating cutting data. Figure 6(a) shows an example of the desired shape S1 of the three-dimensional object. When performing three-dimensional fabrication by melting and solidifying powder, as in the example, deformation may occur in the fabricated object due to thermal stress generated during the fabrication process. Figure 6(b) shows an example of deformation. It shows an example where the left and right side walls have contracted due to deformation, as shown in shape S2, from the original state. A displacement d1 occurs between the original shape and the desired shape due to the deformation. In the example shown in the figure, deformation is schematically represented as occurring only on the left and right sides, but deformation can occur in various ways depending on the shape of the molded object. Such deformations can be predicted by simulation. According to this simulation, it is possible to predict the displacement d1 that will result from the deformation.

[0052] Therefore, the displacement d1 is reflected in the opposite direction to the desired shape S1 (shown as -d1 in the figure) to obtain shape S3. If the fabricated object is generated with shape S3, it is expected that deformation due to displacement d1 will occur afterward, resulting in the fabricated object of shape S1. From this perspective, shape S3 can be used as cutting data. Note that the example in the figure shows the displacement d1 being directly reflected in the reverse direction, but various calculations may be performed on the displacement d1, such as multiplying it by a weighting coefficient or correcting it so that the displacement d1 changes smoothly, before it is reflected.

[0053] As mentioned above, it is possible to use shape S3 as cutting data, but in this embodiment, further improvements in accuracy are being made. In other words, a deformation prediction simulation is performed again on shape S3. If shape S1 is obtained through this simulation, there is no problem, but the displacement d1 that occurs in shape S1 and the displacement that occurs in shape S3 are not necessarily the same, so a displacement d2 from shape S1 may occur, as shown in shape S4 in Figure 6(d). When a displacement d2 occurs in this way, as shown in Figure 6(e), the cutting data is set to shape S5, which reflects the displacement d2 in shape S3. This increases the likelihood of achieving shape S1 with greater accuracy than shape S3.

[0054] The process of performing a deformation prediction simulation on shape S5, and then updating the cutting data by reflecting the result and the displacement between shape S1, may be repeated. By repeating this process until the deformation prediction simulation result and the displacement between shape S1 fall within a predetermined range, the accuracy of the fabrication can be further improved. The extent to which cutting data is updated based on deformation prediction simulations depends on the required accuracy, and it is acceptable to use the initially obtained cutting data (shape S3 in Figure 6(c)).

[0055] Figure 7 is a flowchart of the cutting data generation process. This process is executed by the cutting data generation device 50 (see Figure 1) and generates cutting data in accordance with the concept explained in Figure 6.

[0056] When processing begins, the cutting data generation device 50 reads the shape data of the molded object (step S20). Next, it sets the initial cutting data (step S21). The shape data can be used as the initial value.

[0057] Next, the cutting data generation device 50 performs a deformation prediction simulation on the shape represented by the cutting data (step S22) and calculates the displacement relative to the shape data of the fabricated object (step S23). Referring to Figure 6, this corresponds to the process of calculating the displacement d1 (Figure 6(b)) as a result of predicting the deformation of the shape S1 in Figure 6(a). If this displacement converges, i.e., becomes smaller than a predetermined range (step S24), it is determined that the cutting data can be fabricated with sufficient accuracy, and the process is terminated.

[0058] On the other hand, if the displacement has not converged, the cutting data is updated based on the displacement (step S25). In terms of Figure 6, this corresponds to the process of determining the shape S3 by reflecting the displacement d1. Then, deformation prediction simulation (step S22) and displacement calculation (step S23) are performed again on this cutting data. Referring to Figure 6, this corresponds to the process of obtaining the shape S4 and displacement d2 in Figure 6(d).

[0059] The cutting data generation device 50 repeatedly performs the above process until the displacement converges to a predetermined range (step S24). The cutting data generation device 50 also sets the cutting height range (step S26). As explained earlier in the cutting process (step S15 in Figure 4), in the cutting of this embodiment, it is not always necessary to cut all of the fabricated thin layers, but a certain exclusion area may be provided. The cutting height range refers to the range in the layering direction that is to be cut. The method for determining the cutting height range will be described later. The cutting data obtained through the above process is used in the cutting process of the three-dimensional molding apparatus 10 (see step S15 in Figure 4).

[0060] As an alternative, the deformation prediction simulation (step S22) and displacement calculation (step S23) in the cutting data generation process may utilize a molding database 51 (see Figure 1) that stores past molding results. Specifically, a method can be used to calculate displacement by machine learning by referring to the molding database 51. Alternatively, cutting data that reflects the displacement can be generated using machine learning. In addition to using machine learning, displacement can also be calculated and cutting data generated by statistical processing of the molding database 51. Furthermore, cutting data may be generated by combining both methods, such as using displacements obtained from deformation prediction simulations and averaging displacements obtained using machine learning or statistical methods.

[0061] E. How to set the cutting height range: Next, we will explain how to set the cutting height range. This is the process of the cutting data generation process (step S26 in Figure 7). First, we will explain what kind of deformation occurs in each layer when building by stacking thin layers, and then we will explain how to set the cutting height range taking that deformation into account. Figure 8 is an explanatory diagram showing the deformation that occurs in each layer. The deformation that occurs in each layer differs depending on the temperature of the base plate, etc. Figures 8(a) to 8(e) show deformations that occur when the temperature of the base plate is relatively low. Figure 8(a) shows a state in which layer LL2 is laminated on top of the already formed layer LL1. Note that layer LL1 may be a single thin layer formed in one molding process, or it may be a region consisting of multiple thin layers formed in multiple molding processes. In this embodiment, as explained in steps S12 and S13 of Figure 4, cutting is performed after N layers are formed, so it can be considered that these N layers form layer LL1. If the temperature of the base plate is relatively low, after layer LL2 is formed, shrinkage occurs in layer LL2 over time, as shown in Figure 8(b). Along with this shrinkage, the upper surface of layer LL1 also shrinks, and layer LL1 deforms into a trapezoidal shape with its upper base shorter than its lower base, as shown in the figure. In this state, suppose the end face of layer LL2 is cut with an end mill EM to the shape that should be obtained (the part shown by the dashed line in the figure), as shown in Figure 8(c). Next, layer LL3 is formed on top of layer LL2, as shown in Figure 8(d). Then, similar to what was shown in Figure 8(b), shrinkage occurs in layer LL3, and layer LL2 also deforms into a trapezoidal shape. When this process is repeated, at relatively low temperatures of the base plate, the end face SL of the fabricated object will not be flush, as shown in Figure 8(e), but will have a rough surface with overlapping trapezoidal shapes that widen downwards. This rough state is sometimes described as having low surface quality, while a smooth surface without irregularities is sometimes described as having high surface quality.

[0062] Figures 8(f) to 8(j) show the deformation of the base plate when the temperature is relatively high. Figure 8(f) shows the state in which layer LH2 is laminated on top of the already formed layer LH1. If the temperature of the base plate is relatively high, after layer LH2 is formed, as time passes, the structure of layer LH2 undergoes a martensitic transformation, as shown in Figure 8(g), causing layer LH2 to expand. The upper surface of layer LH1 also changes, dragged along by the expansion of layer LH2, and layer LH1 deforms into a trapezoidal shape, as shown in the figure, with the upper base longer than the lower base. In this state, suppose the end face of layer LH2 is cut with an end mill EM to the shape that should be obtained (the part shown by the dashed line in the figure), as shown in Figure 8(h). Next, layer LH3 is formed on top of layer LH2, as shown in Figure 8(i). Then, as shown in Figure 8(g), layer LH3 expands, and layer LH2 also deforms into a trapezoidal shape. When this process is repeated, if the base plate temperature is relatively high, the end face SH of the fabricated object will not be flush, as shown in Figure 8(j), but will have a rough surface with overlapping trapezoidal shapes that extend upwards.

[0063] The end face cutting is performed to suppress irregularities as shown in Figure 8 and improve surface quality. As explained in Figure 8, the manner of deformation that occurs in the layers differs depending on the temperature of the base plate, so it is preferable to change the cutting method according to the temperature of the base plate.

[0064] Figure 9 is an explanatory diagram illustrating the method for setting the cutting height range in relation to the shrinkage tendency. Figure 9(a) shows a state in which layer LL2 is laminated on top of the formed layer LL1. As shown in Figure 9(b), intermediate finishing is performed on the end face of layer LL2 by cutting with an end mill EM. In intermediate finishing, the cutting is stopped at a position that leaves a margin compared to the original shape. This has the advantage of reducing the amount of material removed in the finish cutting, which will be explained later, and also suppressing the amount of deformation that occurs in layer LL2 due to shrinkage. However, intermediate finishing is not an essential step and can be omitted. As shown in Figure 9(c), when LL3 is formed along layer LL2, layer LL3 shrinks as shown in Figure 9(d), and layer LL2 deforms accordingly. Layer LL3 is then given an intermediate finish as shown in Figure 9(e).

[0065] Subsequently, as shown in Figure 9(f), finish cutting is performed, that is, cutting to match the original shape. In Figure 9, deformation mainly occurs in each layer, so for example, if the top layer LL3 is cut, deformation will occur in layer LL3 during subsequent shaping, and there is a risk that layer LL3 will become smaller than its original shape. To avoid this, it is desirable that the finish cutting be performed with an upper limit that is offset by a predetermined height HLS in the layering direction, with the top surface as the reference (0 in the diagram). Furthermore, it is desirable that the lower limit of the cutting be the height HLE that reaches a layer unaffected by the molding process. The part below the height HLE is the part where the finish cutting is completed and does not require further finishing cutting, but it is acceptable to perform cutting on this part as well. The cutting may be performed from top to bottom or from bottom to top. Furthermore, since the cutting is performed while leaving the topmost layer LL3 intact, it is preferable to use a lollipop-shaped end mill EM2, as shown in the illustration.

[0066] Note that in Figure 9(f), the upper limit height HLS of the cutting height range coincides with the top surface of layer LL2, and the lower limit height HLE coincides with the top surface of layer LL1. However, this is only one example. For example, deformation due to subsequent fabrication may not only occur in the topmost layer LL3, but may also affect the layer below it, LL2. In such cases, it is preferable to set the upper limit height HLS below layer LL2. Furthermore, even if the finish cutting of layer LL1 has been completed and no further deformation has occurred, it may be possible to eliminate the step difference at the boundary between layer LL1 and layer LL2 by cutting including layer LL1. From this perspective, the lower limit height HLE can be set to overlap the portion where the finish cutting has already been completed.

[0067] After the finishing cuts are completed and layer LL4 is formed, the state shown in Figure 9(g) is reached, and the steps in Figures 9(c) to 9(f) can be repeated. The above describes the finishing cuts primarily for cases where shrinkage-like deformation occurs. When shrinkage-like deformation occurs, the basic idea is to perform finishing cuts on the layers that are no longer affected by the deformation caused by the molding process.

[0068] Next, we will explain finish cutting when deformation primarily involves expansion. Figure 10 is an explanatory diagram illustrating how to set the cutting height range in relation to the expansion tendency. Figure 10(a) shows a state in which layer LH2 is formed on top of layer LH1. As explained earlier, when the base plate is at a relatively high temperature, layer LH2 expands due to martensitic transformation, as shown in Figure 10(b). Consequently, deformation also occurs in layer LH1. Therefore, finish cutting is performed on layers LH1 and LH2 as shown in Figure 10(c). In this case, the finish cutting is performed on the entire layers LH1 and LH2. That is, when the top surface of layer LH2 is taken as the reference (0 in the figure), the upper limit height HHS0 of the cutting height range may be set to coincide with the reference. The lower limit height can be the height HHE of the bottom surface of layer LH1, which is affected by the deformation. Once the finishing cut is complete, a layer LH3 is formed on top of it, as shown in Figure 10(d), and the process shown in Figures 10(b) and 10(c) can be repeated.

[0069] Figure 10(c) illustrates a cutting height range with an upper limit height HHS0 and a lower limit height HHS1, but the cutting height range can be set in various ways. For example, if deformation of layer LH2 is expected to occur due to subsequent molding, the cutting height range may be set excluding layer LH2. In such cases, the upper limit height can be set to HHS1, as shown in Figure 10(c). Furthermore, even if no deformation occurs in the layer below layer LH1 due to the fabrication of layer LH2, the lower limit height HHE of the cutting height range may be set lower than that of layer LH1. This makes it possible to make the boundary between layer LH1 and the layer below it even smoother. The above describes the finishing cuts primarily for cases where deformation tends to expand. When deformation tends to expand, the basic idea is to repeat the finishing cuts on a layer that has already undergone finishing cuts until no further deformation occurs due to subsequent molding.

[0070] The setting of the cutting height range (step S26 in Figure 7) is performed based on the concepts shown in Figures 9 and 10. For example, it is determined whether shrinkage or expansion is likely to occur based on the heater temperature of the base plate and the contact area between the printed object and the base plate. Past printing results can be stored in a database, and decisions can be made based on this. In either case, the upper and lower height limits can be set based on the concepts explained in Figures 9 and 10, respectively, based on the existing range to which the effects of deformation due to printing extend.

[0071] F. Effects and variations: According to the three-dimensional molding apparatus 10 and the molding method based thereon described in the examples, the molding accuracy of the molded object can be improved by using cutting data that predicts deformation, as described below. Figure 11 is an explanatory diagram showing the results of the accuracy improvement. Figure 11(a) schematically shows the fabricated object. The Y-axis was defined from the bottom to the top of the fabricated object, and the displacements XL and XR occurring in the lateral surfaces SL and SR at each part were measured.

[0072] Figures 11(b) and (c) show the displacements that occur in the fabricated object when the method of this embodiment is not followed, that is, when fabrication and cutting are performed using the shape data of the fabricated object as is. Figure 11(b) shows the displacement XL that occurred on the left side SL, and Figure 11(c) shows the displacement XR that occurred on the right side SR. Multiple measurement results are shown because measurements were taken at multiple locations along the depth direction of the fabricated object. As shown in Figures 11(b) and (c), it can be seen that the outward displacements XL and XR increase as you go upwards on both the left and right side SL and SR.

[0073] Figures 11(d) and (e) show the displacements that occur in the fabricated object when the cutting data is generated by reflecting the displacement predicted by deformation using the method of this embodiment. Figure 11(d) shows the displacement XL that occurred on the left side SL, and Figure 11(e) shows the displacement XR that occurred on the right side SR. As shown in Figures 11(d) and (e), it can be seen that the displacement is small relative to the shape data at all parts of both the left and right side SL and SR. Thus, it has been confirmed that the accuracy of the fabricated object can be improved according to the three-dimensional molding apparatus 10 and the molding method based thereon of this embodiment.

[0074] According to the three-dimensional molding apparatus 10 and the molding method based thereon described in the embodiment, the surface quality of the end face of the molded object can be improved by setting the cutting height range for finishing cuts based on the temperature of the base plate, etc. Figure 12 is an explanatory diagram showing the results of surface quality improvement. Figure 12(a) schematically shows a molded object that has undergone deformation mainly characterized by shrinkage. As explained earlier, the end face becomes a trapezoidal shape that widens downwards, resulting in unevenness. Figure 12(b) is a graph representing the state of that end face. The horizontal axis shows the position in the height direction relative to the base plate. The vertical axis represents the displacement of the end face in the outward direction as a positive value and the displacement in the inward direction as a negative value. As shown in Figure 12(b), it can be seen that as you go upwards, the position of the end face displaces from the outside to the inside, then at a certain point it discontinuously changes to an outward displacement, and then gradually displaces inward again. In other words, Figure 12(b) is a graph representing the end face shape of Figure 12(a). In this example, the roughness of the side surface is calculated to be Ra 1.00 μm.

[0075] Figure 12(c) schematically shows a molded object that has undergone deformation primarily characterized by expansion. As explained earlier, the end face becomes a trapezoidal shape that widens upwards, resulting in unevenness. Figure 12(d) is a graph representing the state of the end face. As shown in Figure 12(d), as you move upwards, the position of the end face shifts from the inside to the outside, then at a certain point it discontinuously changes to an inward displacement, and then gradually shifts outwards again. In other words, Figure 12(d) is a graph representing the end face shape of Figure 12(c). In this example, the roughness of the side surface is calculated to be Ra 0.48 μm.

[0076] Figure 12(e) shows the results when finish cutting is performed after setting the cutting height range as in this embodiment. Compared to Figures 12(b) and 12(d), it can be seen that the displacement fluctuation is clearly suppressed. In other words, in the example of Figure 12(e), it can be confirmed that the surface quality of the fabricated object is improved with reduced unevenness on the side surface. In the example of Figure 12(e), the surface roughness is calculated to be Ra 0.24 μm. Thus, according to this embodiment, it has been confirmed that the surface quality of the end face of the molded object can be improved by setting the cutting height range for finishing cuts based on the temperature of the base plate, etc.

[0077] The various features described in this embodiment do not necessarily have to be fully met, and some may be omitted or combined as appropriate. Furthermore, the present invention can be configured in various ways, not limited to the embodiments. The present invention is not limited to the powder bed method as shown in the examples, but can be applied to various molding methods that melt and solidify powder. [Industrial applicability]

[0078] This invention can be used to improve the accuracy of three-dimensional molding, which involves repeatedly melting and solidifying powder and then cutting it to form a three-dimensional object. [Explanation of Symbols]

[0079] 10 3D printing equipment 11 Laser irradiation area 12 Hoppers 13 Recorder 14. Build Table 15 Moving mechanism 20 Cutting part 30 Control device 31 Data Input Section 32 Molding Control Unit 33 Heater control unit 34 Cutting Control Unit 35 Stacked Control Unit 40 cutting tools 41 Blade part 42 axes 50 Cutting Data Generation Device 51. Modeling Database 52 Deformation prediction unit 53 Machine Learning Department 54 Cutting data generation unit

Claims

1. A three-dimensional modeling device for creating three-dimensional objects, An input unit for reading the shape data of the aforementioned molded object, A molding unit that melts and solidifies powder to form a part of the molded object according to the shape data, A moving mechanism for moving the part and the molding part relative to each other so that the next part is formed by adding to the already formed part, A cutting section for cutting off the formed portion, The system includes a control unit that controls the molding process performed by the molding unit and the moving mechanism, and the cutting process performed by the cutting unit, to repeatedly execute these processes in order to create the molded object. The control unit predicts the deformation that occurs in the part due to the stress associated with the molding after the cutting, and performs the cutting based on cutting data that has been corrected to conform to the shape data after the deformation has occurred.

2. A three-dimensional molding apparatus according to claim 1, A three-dimensional molding apparatus comprising a cutting data generation unit that predicts deformation due to the stress through simulation and generates the cutting data by reflecting the results of the prediction in the shape data.

3. A three-dimensional molding apparatus according to claim 2, The cutting data generation unit predicts the deformation that occurs in the cutting data through the simulation, and updates the cutting data by reflecting the difference between the deformed shape and the shape data.

4. A three-dimensional molding apparatus according to claim 1, A three-dimensional modeling apparatus comprising a cutting data generation unit that predicts deformation due to stress based on a database that stores past molded objects and the deformation caused by the stress in the molded object, and generates the cutting data by reflecting the result of the prediction in the shape data.

5. A three-dimensional molding apparatus according to claim 1, The control unit is a three-dimensional molding apparatus that performs the cutting process while excluding the portion of the molding process, which is repeatedly performed by the molding unit and the moving mechanism, from the molding process that is performed for a predetermined number of steps starting from the immediately preceding step.

6. A three-dimensional molding apparatus according to claim 1, The cutting section is a three-dimensional molding device that uses a lollipop-shaped tool.

7. A three-dimensional molding apparatus according to claim 1, The aforementioned molding section is The mechanism involves melting and solidifying the powder on a base plate on which the molded object is placed, thereby forming a thin layer that constitutes a part of the molded object. A heater is provided for heating the base plate. The control unit controls heating by the heater so that the warping of the base plate during molding is kept below a predetermined required value.

8. A three-dimensional molding apparatus according to claim 1, The aforementioned molding section is The mechanism involves melting and solidifying the powder on a base plate on which the molded object is placed, thereby forming a thin layer that constitutes a part of the molded object. A heater is provided for heating the base plate. The control unit sets the cutting height range in the stacking direction of the thin layer according to the set temperature of the heater and the area of ​​the thin layer to be bonded to the base plate.

9. A three-dimensional modeling method for creating a three-dimensional object using a three-dimensional modeling device, (a) A step of reading the shape data of the molded object, (b) A step of melting the powder and solidifying it to form a part of the molded object according to the shape data, (c) Repeatedly performing step (b) to form the next part by adding to the already formed part, (d) a step of cutting the formed portion, Step (d) above is, A three-dimensional fabrication method comprising the step of predicting the deformation that will occur in the part due to the stress associated with the fabrication after the cutting, and performing the cutting based on cutting data that has been corrected to conform to the shape data after the deformation has occurred.

10. A computer program for generating data for cutting by a computer for a three-dimensional molding apparatus that fabricates a three-dimensional object by repeatedly melting and solidifying powder to form parts of the three-dimensional object and cutting the formed parts, A function to read the shape data of the aforementioned molded object, A function that predicts the deformation that will occur in the part due to the stress associated with the molding after the cutting, and generates cutting data that has been corrected to conform to the shape data after such deformation has occurred. A computer program that realizes this using a computer.

11. A computer program for generating data for cutting by a computer for a three-dimensional molding apparatus that fabricates a three-dimensional object by repeatedly melting and solidifying powder to form parts of the three-dimensional object and cutting the formed parts, A function to read the shape data of the aforementioned molded object, A function that predicts deformation due to stress based on a database that stores past molded objects and the deformation caused by the stress on those molded objects, and generates the cutting data by reflecting the result of the prediction in the shape data. A computer program that realizes this using a computer.

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