JP7494824B2 - Additive manufacturing device and additive manufacturing method - Google Patents

Description

The present invention relates to an additive manufacturing device and an additive manufacturing method.

There is a known technology for forming a shaped object by melting a powdered metal material (see, for example, Patent Document 1). In the additive processing device described in Patent Document 1, a metal layer is formed on a workpiece by solidifying the molten metal powder and the workpiece. In this device, the thickness of the layer that is formed is measured, and the command value for the next layer to be formed is controlled based on the difference between the measured value and a predetermined command value.

The additive manufacturing device described in Patent Document 2 is a hybrid machine equipped with both additive manufacturing and machining functions. This device can grasp the area and shape of the molten part where the metal powder is molten without solidifying by monitoring from above with a thermo viewer. Non-Patent Document 1 discloses a method for generating control data that determines and reproduces a cutting path for cutting an additive manufacturing object.

JP 2021-31704 A Japanese Patent No. 6626788

Haruhiko Niitani and five others, "Development of a deposition-based 3D metal additive manufacturing device", [online], 2018, Mitsubishi Heavy Industries Technical Review vol. 55 No. 3 (2018) Industry & Social Infrastructure Special Feature, [Retrieved September 1, 2021], Internet <https://www.mhi.co.jp/technology/review/pdf/553/553090.pdf>

The technology described in Patent Document 1 measures the thickness of stacked layers and corrects the number of layers to achieve the target accuracy. By using this technology, it is possible to make the shape of a molded object closer to the desired shape. However, this technology is premised on ensuring dimensional accuracy by processing the object after molding. Therefore, when the shape of the object is complex or when processing after molding is difficult, it is difficult to create a highly accurate object even using the technology in Patent Document 1.

The techniques described in Patent Document 2 and Non-Patent Document 1 ensure precision by machining after additive manufacturing. In Patent Document 2, the thermoviewer captures the molten part as a surface, but the molten part itself is a three-dimensional shape with thickness. Therefore, the technique described in Patent Document 2 lacks information about the shape of the molten part. In other words, there is a risk that sufficient information is not obtained to control the shaping. The technique described in Non-Patent Document 1 is mainly about cutting processing, and does not take into consideration active control of the dimensions themselves during additive manufacturing.

The present invention has been made to solve the above-mentioned problems, and aims to improve the shape accuracy of the object while minimizing the processing of the object after additive manufacturing.

The present invention has been made to solve the above-mentioned problems, and can be realized in the following form : An additive manufacturing apparatus comprising: a stage on which an object is placed, a nozzle for supplying raw material powder for forming the object, an irradiation unit for irradiating the raw material powder supplied from the nozzle with a laser beam to form the object, and a control unit for controlling the additive manufacturing apparatus, wherein either the stage or the irradiation unit can be moved to change a relative position between them, and the control unit forms the object by stacking the raw material powder on the stage by changing the relative position, calculates an error in the vertical direction between a melted portion of the object and a reference position determined according to the elapsed time from the start of modeling using an image of the object on the stage, and changes a moving speed for changing the relative position using the calculated error. The present invention can also be realized in the following form.

(1) According to one aspect of the present invention, there is provided an additive manufacturing apparatus. The additive manufacturing apparatus includes a stage on which an object is placed, a supply unit that supplies raw material for forming the object, an irradiation unit that irradiates the supplied raw material with laser light to form the object, and a control unit that controls the additive manufacturing apparatus, and either the stage or the irradiation unit can be moved to change their relative positions, and the control unit stacks the raw material on the stage by changing the relative positions to form the object, calculates an error between a melted portion of the object and a preset reference position using an image of the object on the stage, and changes the movement speed to change the relative position using the calculated error.

According to this configuration, as the distance between the relative positions gradually increases, a model is formed in which the raw materials are stacked on the stage. Furthermore, the moving speed of the stage and the irradiation unit to change their relative positions is appropriately changed using an error calculated using an image of the model. By changing the moving speed, the model being formed is modeled so that it approaches the design value, compared to when the model is formed while the moving speed is constant. As a result, the shape accuracy of the three-dimensional model is improved, and continuous modeling is performed stably. In particular, the dimensional accuracy of models made of materials that are brittle and cannot be processed, and models made of materials that are hard and difficult to process after modeling is improved. In addition, according to this configuration, additional processing of models with complex three-dimensional shapes after modeling is unnecessary or the amount of additional processing is reduced. In other words, by using this configuration, the shape accuracy of the model is improved while suppressing processing of the model after additive manufacturing.

(2) In the additive manufacturing device of the above aspect, the control unit may identify a height parallel to the vertical direction of a vertex of the molten portion from an image of the object, calculate the difference from the reference position to the identified height as the error, and change the moving speed for changing the relative position along the vertical direction in accordance with the error.
According to this configuration, the moving speed for changing the relative position along the vertical direction is changed according to the error while the output intensity of the laser light and the supply amount of powder material are not changed. This changes the height of the material to the apex to be newly layered on the model per unit time. Therefore, according to this configuration, it is possible to further improve the shape accuracy of the model according to the calculated error.

(3) In the additive manufacturing device of the above aspect, the control unit may accelerate the speed in a direction in which the distance between the relative positions along the vertical direction increases when the error is greater than zero, and may decelerate the speed in a direction in which the distance between the relative positions along the vertical direction decreases when the error is less than zero.
According to this configuration, when the error is greater than zero, the modeling has progressed further than the reference position. Conversely, when the error is less than zero, the modeling has not progressed further than the reference position. In either state, the speed at which the distance between the relative positions increases or decreases is controlled, so that the height of the molten part at a certain time can be brought closer to the reference position.

(4) In the additive manufacturing device of the above aspect, the control unit may identify a width of the molten portion parallel to the horizontal direction from an image of the object, calculate a volume of the molten portion when the shape of the molten portion is defined as an elliptical hemisphere using the identified width and height, and change an output intensity of the laser light irradiated by the irradiation unit in accordance with a comparison between the calculated volume of the elliptical hemisphere and a preset volume of the elliptical hemisphere.
According to this configuration, when the output intensity of the laser light changes, the amount of material newly laminated in the molten part of the model changes. In this configuration, the amount of material further laminated in the molten part is controlled according to the volume of the elliptical hemisphere regarded as the volume of the molten part. This makes it possible to further improve the shape accuracy of the model.

(5) In the additive manufacturing apparatus of the above aspect, the control unit may calculate, as the volume of the preset elliptical hemisphere, the volume of an elliptical hemisphere whose diameter is the horizontal width of the reference position in the design value of the object and whose height is half of the diameter, calculate a lower limit volume and an upper limit volume by multiplying the preset volume of the elliptical hemisphere by an allowable accuracy, and if the calculated volume of the elliptical hemisphere of the molten part is larger than the upper limit volume, reduce the output intensity of the laser light irradiated by the irradiation unit, and if the calculated volume of the elliptical hemisphere of the molten part is smaller than the lower limit volume, increase the output intensity of the laser light irradiated by the irradiation unit.
According to this configuration, when the volume of the elliptical hemisphere of the molded object is larger than the preset upper limit volume of the elliptical hemisphere, the molten part has more material layered than the design value. On the other hand, when the volume of the elliptical hemisphere of the molded object is smaller than the preset lower limit volume of the elliptical hemisphere, the molten part has less material layered than the design value, and is therefore insufficient. When there is more or less material layered in the molten part, the output intensity of the laser light is adjusted, so that the shape of the molten part can be brought closer to the design value. As a result, the shape accuracy of the molded object can be further improved.

(6) In the additive manufacturing apparatus of the above aspect, the control unit may identify a width of the molten portion parallel to the horizontal direction from an image of the object, and may not need to change the moving speed for changing the relative position along the vertical direction from an initial value, regardless of the magnitude of the error, from the start of manufacturing of the object until the identified width reaches a design diameter.
According to this configuration, since the shape of the object at the start of modeling is unstable, the object is modeled at a constant moving speed from the start of modeling until the width of the molten part reaches the designed diameter, which makes it possible to prevent the shape of the object from becoming unstable due to the influence of fine adjustment due to errors.

(7) In the additive manufacturing apparatus of the above aspect, the control unit may stop manufacturing of the object when the identified width does not fall below the diameter of the design value for a predetermined time after the identified width exceeds the diameter of the design value, even though the moving speed has changed.
If the width of the molten part reaches a preset value after the start of molding and the width of the molten part does not fall below the diameter of the design value despite a correction for a predetermined time, the width of the molten part may continue to increase. In this case, according to the present configuration, the molding of the object is stopped, thereby making it possible to prevent the molding of an object with a different shape from the target shape.

(8) In the additive manufacturing device of the above aspect, the control unit may identify, from an image of the object, a width of the molten portion parallel to the horizontal direction and a height of a vertex of the molten portion parallel to the vertical direction, calculate a volume of the molten portion when the shape of the molten portion is defined as an ellipsoidal hemisphere using the identified width and height, and may abort the manufacturing of the object if the calculated volume of the ellipsoidal hemisphere of the molten portion does not exceed a predetermined volume within a predetermined time after starting the manufacturing of the object.
The shape of the object at the start of modeling is unstable. Therefore, if the volume of the elliptical hemisphere of the molten part does not reach a preset volume even after a predetermined time has passed, the molten part may become even smaller. In this case, according to the present configuration, the modeling of the object is stopped, thereby preventing the modeling of an object with a different shape from the target shape.

(9) The additive manufacturing apparatus according to the above aspect may further include an image acquisition unit that acquires an image of the molten portion in the model.
According to this configuration, it is possible to consistently perform operations from image acquisition to control of the moving speed without acquiring an image of the molten portion from another device.

(10) According to another aspect of the present invention, there is provided an additive manufacturing method. In this additive manufacturing method, an information processing device includes an image acquisition step of acquiring an image of a model placed on a stage, a modeling step of irradiating a raw material supplied from a supply unit with laser light from an irradiation unit to model the model on the stage, a calculation step of calculating an error between an apex of the melted part in the model and a preset reference position using the image of the model, and a position control step, in which either the stage or the irradiation unit can be moved to change their relative positions, the modeling step stacks the raw material on the stage by changing the relative position to model the model, and the position control step changes the moving speed for changing the relative position using the calculated error.

The present invention can be realized in various forms, for example, in the form of an additive manufacturing device, a 3D printer, a laser modeling device, a system including these devices, an additive manufacturing method, a laser processing method, a computer program for executing these devices and methods, a server device for distributing this computer program, a non-transitory storage medium on which a computer program is stored, etc.

1 is a schematic diagram of an additive manufacturing apparatus according to an embodiment of the present invention. FIG. 4 is an explanatory diagram of a reference position. FIG. 4 is an explanatory diagram of a molten portion of a shaped object. FIG. 4 is an explanatory diagram of an example of each parameter. FIG. 11 is an explanatory diagram of a change in the descending speed of the stage. 1 is a graph showing a time series change in the volume of an elliptical hemisphere of a fusion zone. FIG. 13 is a schematic side view of an object in the process of being manufactured according to the embodiment. FIG. 11 is a schematic side view of an object in the middle of being manufactured according to a comparative example. 1 is a flowchart of an additive manufacturing method according to the present embodiment. 1 is a flowchart of an additive manufacturing method according to the present embodiment. 13 is a flowchart of a modified additive manufacturing method.

<Embodiment>
1. Configuration of additive manufacturing device:
FIG. 1 is a schematic diagram of an additive manufacturing apparatus 100 according to an embodiment of the present invention. The additive manufacturing apparatus 100 of this embodiment melts a metal raw material powder with a laser beam and stacks the molten raw material powder on a stage 30. When the temperature of the stacked raw material powder is lowered, it solidifies and forms an object OB. The additive manufacturing apparatus 100 stacks the molten raw material powder to form an object OB of a predetermined shape by three-dimensionally moving the stage 30 relative to the laser head 10 that irradiates the laser beam LS. In this embodiment, the object OB being modeled is photographed, and the moving speed of the distance between the laser head 10 and the stage 30 is controlled using various dimensions of the object OB identified from the photographed image, thereby forming a predetermined object OB.

1 shows a schematic block diagram of the configuration of an additive manufacturing apparatus 100. As shown in FIG. 1, the additive manufacturing apparatus 100 includes a nozzle (supply unit) 20 that supplies raw metal powder, a laser head (irradiation unit) 10 that irradiates laser light LS, a stage 30 whose position can be changed with respect to the nozzle 20 and the laser head 10, a camera (image acquisition unit) 40 that acquires an image of an object OB formed on the stage 30, and a PC (Personal Computer) that controls each unit.
and a computer) 50.

The raw material powder supplied from the nozzle 20 is the raw material for forming the object OB. The amount of metal raw material powder supplied from the nozzle 20 is controlled by the PC 50. The laser head 10 forms the object OB by irradiating the raw material powder supplied from the nozzle 20 with laser light LS. The intensity of the laser light LS irradiated from the laser head 10 is controlled by the PC 50.

In this embodiment, the position of the stage 30 can be changed, while the positions of the laser head 10 and the nozzle 20 are fixed. In other words, the stage 30 can change its relative position with respect to the nozzle 20 and the laser head 10 by moving. By changing the distance between the laser head 10 and the stage 30, the object OB is formed from the raw material stacked on the stage. The movement amount and movement speed of the stage 30 are controlled by the PC 50. The camera 40 photographs the molten part MP at the tip of the object OB. The molten part MP is a part where the raw material powder supplied from the nozzle 20 is not solidified but is in a molten state. In this embodiment, the molten part MP is identified using the color of the reflectance, etc. of the photographed object OB, the movement of the unsolidified tip, etc. The resolution of the camera 40 in this embodiment is 0.1 mm.

1, the PC 50 includes a CPU (Central Processing Unit) 51, a storage unit 60, an input unit 70 that receives various inputs, and an output unit 80 that outputs images and sounds. The storage unit 60 includes a hard disk drive (HDD).
) The storage unit 60 stores three-dimensional computer-aided design (CAD) data of the object OB that is required to form the object OB. The input unit 70 in this embodiment is composed of a keyboard and a mouse. The CPU 51 is controlled in accordance with the input received by the input unit 70. The output unit 80 has a monitor that displays various images in accordance with control signals from the CPU 51, and a speaker that outputs sound.

The CPU 51 executes the functions of various programs by expanding the programs stored in a ROM (Read Only Memory) (not shown) into a RAM (Random Access Memory). The CPU 51 functions as an irradiation control unit 52 that controls the laser light LS irradiated by the laser head 10, a supply control unit 53 that controls the amount of raw material powder supplied from the nozzle 20, a movement control unit 55 that changes the position of the stage 30, a shape acquisition unit 57 that acquires CAD data of the object OB from the memory unit 60, and a calculation unit 56. Note that the irradiation control unit 52, movement control unit 55, and calculation unit 56 in this embodiment correspond to a control unit.

The shape acquisition unit 57 acquires the CAD data that is the basis of the object OB stored in the storage unit 60 in response to the input received by the input unit 70. The calculation unit 56 determines the initial control amount to be performed by the irradiation control unit 52, the supply control unit 53, and the movement control unit 55 when the object OB acquired by the shape acquisition unit 57 is formed. The calculation unit 56 also changes (corrects) each control amount when the object OB is formed, using the captured image acquired from the camera 40. Specifically, the calculation unit 56 calculates the error L(t) between the apex TP of the molten part MP melted in the object OB and a preset reference position, using the captured image of the object OB. The calculation unit 56 corrects each control amount using the calculated error L(t). Note that parameters such as accuracy, which will be described later and are used during the correction, are received via the input unit 70. The corrected control amount includes the movement amount and movement speed of the stage 30 by the movement control unit 55. Details of the apex TP of the molten part MP will be described later.

FIG. 2 is an explanatory diagram of the reference position. FIG. 2 shows an example of each parameter at time t including the reference position, which is calculated in advance by the calculation unit 56. The object OB to be formed in this embodiment is a rod-shaped member such as a coil having a circle with a cross-sectional diameter Dsta of 1 mm. FIG. 2 shows the reference position Z0(t) of the height that changes with time t, which is the time elapsed from the start of formation, the cross-sectional diameter Dsta of the object OB, the accuracy range allowed during manufacturing, the volume Vhsta of an elliptical hemisphere (elliptical hemisphere) of an ideal shape, the volume Vhsta_u of the elliptical hemisphere in the case of the upper accuracy limit, and the volume Vhsta_l of the elliptical hemisphere in the case of the lower accuracy limit. Each parameter shown in FIG. 2 is a numerical value that can be calculated in advance as a design value based on CAD data. The allowable accuracy range in this embodiment is set to -20% to +20%. The upper and lower limits of the allowable accuracy range are input via the input unit 70.

The volume Vhsta of the elliptical hemisphere is the volume of an elliptical hemisphere having a horizontal cross-sectional area of the object OB and a height that is half the horizontal radius. Therefore, the volume Vhsta of the elliptical hemisphere of the design value shown in FIG. 2 is expressed by the following formula (1).

The volume Vhsta_u of the elliptical hemisphere at the upper limit of accuracy is the volume when each length of the ellipse is +20%. On the other hand, the volume Vhsta_l of the elliptical hemisphere at the lower limit of accuracy is the volume when each length of the ellipse is -20%. The volumes Vhsta_u and Vhsta_l of the elliptical hemisphere set before molding are expressed by the following formulas (2) and (3), respectively.

Figure 3 is an explanatory diagram of the molten part MP of the object OB at time t. Figure 3 shows a schematic side view of the tip of the object OB at time t photographed by the camera 40. Note that the molten part MP shown in Figure 3 is hatched.

The calculation unit 56 identifies the vertically lowest position of the identified molten part MP as the height position Z(t) at time t. The calculation unit 56 also identifies the vertically highest position of the molten part MP as the apex TP of the molten part MP. The calculation unit 56 calculates the value obtained by subtracting the reference position Z0(t) from the apex TP of the molten part MP in the vertical direction as the height error L(t) at time t. The movement control unit 55 uses the error L(t) calculated by the calculation unit 56 to change the descending speed Vs of the stage 30. The calculation unit 56 further identifies the horizontal width Dhs(t) passing through the position Z(t) at time t as the width of the molten part MP. The calculation unit 56 further calculates the height Hho(t) from the position Z(t) to the apex TP.

Figure 4 is an explanatory diagram of an example of each parameter at time t. Figure 4 shows an example of specific numerical values of the error L(t), width Dhs(t), height Hho(t), and volume Vho(t) of the elliptical hemisphere of the molten part MP at time t. The calculation unit 56 calculates the volume Vho(t) of the elliptical hemisphere using the following formula (4).

The calculation unit 56 changes the moving speed (descent speed Vs) of the stage 30 in the vertical direction depending on whether the error L(t) at time t is positive or negative. Specifically, the calculation unit 56 of this embodiment calculates the error L(t) every time a predetermined time Δt elapses. If the error L(t) is not zero, the calculation unit 56 accelerates or decelerates the descent speed Vs of the stage 30 so that the error L(t+2Δt) after 2Δt elapses becomes zero. If the descent speed after acceleration or deceleration is defined as Vc, the following relational expression (5) holds.

Figure 5 is an explanatory diagram of the change in the descent speed Vs of the stage 30. Figure 5 shows a line L1 that changes the descent speed Vs of the stage 30 over time. The dashed line L2 is the time series change in the descent speed Vc calculated at time t. The dashed line L3 is the time series change in the descent speed Vc calculated at time (t + Δt). The dashed line L4 is the time series change in the descent speed Vc calculated at time (t + 2Δt). For example, as shown in Figure 4, when the error L (t) is +0.35 (mm) and Δt is 0.5 (seconds), the movement control unit 55 uses the calculation result of the calculation unit 56 to increase the descent speed Vs of the stage 30 so that it becomes the target descent speed Vc after time (t + 2Δt) has passed. In other words, when the error L(t) is greater than zero, the movement control unit 55 accelerates the speed in a direction in which the distance along the vertical direction of the stage 30 relative to the laser head 10 increases. On the other hand, when the error L(t) is less than zero, the movement control unit 55 decelerates the speed in a direction in which the distance along the vertical direction of the stage 30 relative to the laser head 10 decreases (the descent speed Vs is reduced). Note that in this embodiment, the movement speed of the stage 30 along the horizontal direction is determined by the CAD data of the object OB, and is not corrected regardless of the shape of the molten part MP.

The irradiation control unit 52 adjusts the output intensity of the laser light LS irradiated from the laser head 10 according to the width Dhs(t) and the volume Vho(t) of the elliptical hemisphere at time t calculated by the calculation unit 56. The output intensity of the laser light LS at the start of modeling is determined according to the CAD data of the object OB. In this embodiment, the irradiation control unit 52 reduces the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is larger than the volume Vhsta_u of the elliptical hemisphere with the upper limit of accuracy. On the other hand, the irradiation control unit 52 increases the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is smaller than the volume Vhsta_l of the elliptical hemisphere with the lower limit of accuracy.

FIG. 6 is a graph showing the time series change of the volume Vho(t) of the elliptical hemisphere of the molten part MP. FIG. 6 shows a curve C1 (solid line) which is the time series change of the volume Vho(t) when the output intensity of the laser light LS is controlled according to a comparison between the volume Vho(t) of the elliptical hemisphere of the molten part MP and the upper and lower limit volumes Vhsta_u and Vhsta_l of the elliptical hemisphere. FIG. 6 also shows the time series change of the volume Vho(t) of the elliptical hemisphere of the comparative example in which the laser light LS of a constant output intensity is irradiated regardless of the volume Vho(t) of the elliptical hemisphere of the molten part MP by a curve C2 (dashed line). As shown in FIG. 6, the volume Vho(t) of the elliptical hemisphere of the molten part MP of the embodiment falls within the range from the volume Vhsta_l of the lower limit of accuracy to the volume Vhsta_u of the upper limit of accuracy. On the other hand, the volume Vho(t) of the elliptical hemisphere of the molten part MP of the comparative example is the volume Vh of the upper limit of accuracy.
As time passes and the shape of the object OB in the comparative example exceeds sta_u, the shape of the object OB becomes larger.

Figure 7 is a schematic side view of the object OB of the embodiment in the middle of being formed. Figure 8 is a schematic side view of the object OB of the comparative example in the middle of being formed. In the objects OB shown in Figures 7 and 8, the molten parts MP are hatched. The object OB of the embodiment shown in Figure 7 has a cross section of a constant size regardless of its position in the height direction, except immediately after the start of forming. On the other hand, the volume of the molten part MP of the object OB of the comparative example shown in Figure 8 is much larger than that of the embodiment.

In this embodiment, the calculation unit 56 does not change the descent speed Vs of the stage 30 and the output intensity of the laser light LS from their initial values from the start of the formation of the object OB until the width Dhs(t) of the molten part MP reaches a preset value, regardless of the values of the width Dhs(t) and the volume Vho(t) of the elliptical hemisphere. In this embodiment, the diameter Dsta (Figure 2) is set as the preset value.

Furthermore, in this embodiment, in addition to controlling the descent speed Vs of the stage 30 and the output intensity of the laser light LS every time the above-mentioned specified time Δt has elapsed, the calculation unit 56 controls each part to stop the formation of the object OB when the following two conditions are satisfied from the start of formation:
Condition 1. When the volume Vho(t) of the molten portion MP does not reach the lower limit volume Vhsta_l even after the threshold time T1 has elapsed since the start of modeling. Condition 2. When the width Dhs(t) of the molten portion MP exceeds the diameter Dsta, the width Dhs(t+10Δt) does not fall below the diameter Dsta despite the descent speed Vs and the output intensity of the laser light LS being corrected a predetermined number of times (for example, 10Δt).

2. Additive manufacturing flow:
9 and 10 are flowcharts of the additive manufacturing method of this embodiment. In the additive manufacturing flow shown in Fig. 9, first, the shape acquisition unit 57 acquires CAD data of one object OB from the storage unit 60 in response to an input received by the input unit 70 (step S1). The calculation unit 56 acquires, via the input unit 70, an allowable accuracy range during modeling, a predetermined time Δt at a fixed interval for performing correction, and a threshold time T1 for controlling the output intensity of the laser light LS (step S2).

The calculation unit 56 uses the acquired allowable accuracy range and the CAD data of the object OB to calculate the control amount of each part at the start of modeling (step S3). The calculation unit 56 uses the CAD data of the object OB to determine the horizontal and vertical movement amount and movement speed of the stage 30, and the output intensity of the laser light LS. The calculation unit 56 also uses the CAD data of the object OB and the allowable accuracy range to calculate various parameters including the reference position shown in FIG. 3.

The irradiation control unit 52, the supply control unit 53, and the movement control unit 55 start forming the object OB using the control amount calculated by the calculation unit 56, and the camera 40 starts photographing the object OB (step S4). The calculation unit 56 determines whether or not the threshold time T1 has elapsed since the start of forming the object OB (step S5). If the threshold time T1 has not elapsed (step S5: NO), the calculation unit 56 waits for the threshold time T1 to elapse.

When the threshold time T1 has elapsed (step S5: YES), the calculation unit 56 determines whether the volume Vho(t) of the molten part MP has reached the lower limit volume Vhsta_l (step S6). When the volume Vho(t) of the molten part MP has not reached the lower limit volume Vhsta_l (step S6: NO), the above condition 1 is satisfied, and the additive manufacturing flow ends as shown in FIG. 10.

When the volume Vho(t) of the molten part MP reaches the lower limit volume Vhsta_l (step S6: YES), the calculation unit 56 determines whether the width Dhs(t) of the molten part MP shown in FIG. 4 reaches the diameter Dsta (step S7). When the width Dhs(t) has not reached the diameter Dsta (step S7: NO), the additive manufacturing flow ends.

When the width Dhs(t) of the molten part MP reaches the diameter Dsta (step S7: YES), the calculation unit 56 calculates the error L(t) between the reference position Z(t) at time t and the apex TP of the molten part MP of the object OB photographed by the camera 40 (step S8). The calculation unit 56 identifies the molten part MP and the apex TP of the molten part MP from the photographed image of the object OB. The calculation unit 56 identifies the width Dhs(t) of the molten part MP from the identified molten part MP and apex TP. The calculation unit 56 calculates the height Hho(t) from the height position Z(t) of the molten part MP to the apex TP. The calculation unit 56 calculates the error L(t) and the volume Vho(t) of the elliptical hemisphere using the width Dhs(t) and height Hho(t).

The calculation unit 56 determines whether the calculated error L(t) is zero (step S9). If the error L(t) is zero (step S9: YES), the output intensity of the laser light LS does not change, and the process of step S11 in FIG. 10 is performed. If the error L(t) is not zero (step S9: NO), the movement control unit 55 changes the descent speed Vs of the stage 30 (step S10). The movement control unit 55 increases or decreases the descent speed Vs of the stage 30 to the descent speed Vc calculated from the above formula (5).

The calculation unit 56 compares the calculated volume Vho(t) of the elliptical hemisphere with the upper and lower accuracy limits of volumes Vhsta_u and Vhsta_l (step S11). It is determined whether the volume Vho(t) of the elliptical hemisphere is within the accuracy range from the lower limit volume Vhsta_l to the upper limit volume Vhsta_u. If the volume Vho(t) is within the accuracy range (step S12: YES), the process proceeds to step S15.

If the volume Vho(t) is outside the accuracy range (step S12: NO), the irradiation control unit 52 changes the output intensity of the laser light LS (step S13). In this embodiment, if the volume Vho(t) is larger than the volume Vhsta_u of the upper accuracy limit, the irradiation control unit 52 increases the output intensity of the laser light LS. On the other hand, if the volume Vho(t) is smaller than the volume Vhsta_l of the lower accuracy limit, the irradiation control unit 52 decreases the output intensity of the laser light LS.

After the output intensity of the laser light LS is changed, the calculation unit 56 determines whether a predetermined number of times of the predetermined time Δt have elapsed while the condition for changing the output intensity is satisfied (step S14). If it is determined that a predetermined number of times of the predetermined time Δt have elapsed (step S14: YES), the additive manufacturing flow ends. If it is determined that a predetermined number of times of the predetermined time Δt have not elapsed (step S14: NO), the calculation unit 56 determines whether the formation of the object OB has been completed (step S15). If it is determined that the formation of the object OB has not been completed (step S15: NO), the calculation unit 56 determines whether the predetermined time Δt has elapsed (step S16). If the predetermined time Δt has not elapsed (step S16: NO), the calculation unit 56 waits for the predetermined time Δt to elapse. If the predetermined time Δt has elapsed (step S16: YES), the processing from step S8 in FIG. 9 is repeated. In the process of step S13, if the formation of the object OB is completed (step S15: YES), the additive manufacturing flow ends.

3. Effects As described above, in the layered modeling apparatus 100 of this embodiment, the stage 30 can change its relative position with respect to the nozzle 20 and the laser head 10 by moving. The calculation unit 56 calculates the error L(t) between the apex TP of the melted portion MP melted in the modeled object OB and a preset reference position using the captured image of the modeled object OB. The calculation unit 56 corrects each control amount using the calculated error L(t). Therefore, in the layered modeling apparatus 100 of this embodiment, as the distance between the laser head 10 and the stage 30 increases, the modeled object OB in which the raw material is stacked on the stage 30 is stacked. Furthermore, the control amount such as the descending speed Vs of the stage 30 is appropriately corrected using the error L(t) calculated from the captured image. By this correction, the modeled object OB being modeled is modeled so as to approach the shape of the target design value, compared to when the modeled object OB is modeled with the moving speed kept constant. As a result, the shape accuracy of the three-dimensional modeled object OB is improved, and continuous modeling is performed stably. In particular, the dimensional accuracy of the object OB made of a material that is too brittle to be machined and the object OB made of a material that is too hard to be machined after modeling is improved. Furthermore, by using the additive manufacturing device 100 of this embodiment, additional processing of the object OB having a complex three-dimensional shape after modeling is unnecessary or the amount of additional processing is reduced. In other words, the shape accuracy of the object OB is improved while suppressing processing of the object OB after additive manufacturing.

In addition, the calculation unit 56 of this embodiment calculates the value obtained by subtracting the reference position Z0(t) from the apex TP of the molten part MP in the vertical direction as the height error L(t) at time t. The movement control unit 55 uses the error L(t) calculated by the calculation unit 56 to change the descent speed Vs of the stage 30 along the vertical direction. The descent speed Vs of the stage 30 changes according to the error while the output intensity of the laser light LS and the supply amount of powder material do not change. This changes the height of the material newly layered on the model OB per unit time. Therefore, in the additive manufacturing device 100 of this embodiment, the shape accuracy of the model OB can be further improved according to the calculated error L(t).

In addition, when the error L(t) is greater than zero, the movement control unit 55 of this embodiment accelerates the speed in a direction in which the distance along the vertical direction of the stage 30 relative to the laser head 10 increases. On the other hand, when the error L(t) is less than zero, the movement control unit 55 decelerates the speed in a direction in which the distance along the vertical direction of the stage 30 relative to the laser head 10 decreases. When the error L(t) is greater than zero, the modeling has progressed further than the reference position Z0(t). Conversely, when the error L(t) is less than zero, the modeling has not progressed further than the reference position Z0(t). In either state, the position Z(t) at time t can be brought closer to the reference position Z0(t) by increasing or decreasing the descending speed Vs of the stage 30.

In addition, the calculation unit 56 of this embodiment further specifies the horizontal width Dhs(t) passing through the position Z(t) at time t as the width of the molten part MP. The calculation unit 56 calculates the height Hho(t) from the position Z(t) to the apex TP. The calculation unit 56 calculates the volume Vho(t) of the elliptical hemisphere using the above formula (4). The irradiation control unit 52 adjusts the output intensity of the laser light LS according to the width Dhs(t) at time t and the volume Vho(t) of the elliptical hemisphere calculated by the calculation unit 56. When the output intensity of the laser light LS changes, the amount of material layered on the molten part MP of the modeled object OB changes. In the additive manufacturing device 100 of this embodiment, the amount of layers further layered on the molten part MP is controlled according to the volume Vho(t) of the elliptical hemisphere regarded as the volume of the molten part MP. This can further improve the shape accuracy of the modeled object OB.

In addition, the irradiation control unit 52 of this embodiment reduces the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is larger than the volume Vhsta_u of the elliptical hemisphere with the upper limit of accuracy. In addition, the irradiation control unit 52 increases the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is smaller than the volume Vhsta_l of the elliptical hemisphere with the lower limit of accuracy. A state in which the volume Vho(t) is larger than the volume Vhsta_u is a state in which the molten part MP has an excess of material stacked therein compared to the design value. On the other hand, a state in which the volume Vho(t) is smaller than the volume Vhsta_l is a state in which the molten part MP has an insufficient amount of material stacked therein compared to the design value. When there is a large or small amount of material stacked in the molten part MP, the output intensity of the laser light LS is adjusted, so that the shape of the molten part MP can be brought closer to the design value. As a result, the shape accuracy of the object OB can be further improved.

In addition, the calculation unit 56 in this embodiment does not change the descent speed Vs of the stage 30 and the output intensity of the laser light LS from their initial values from the start of the formation of the object OB until the width Dhs(t) of the molten portion MP reaches the diameter Dsta, which is a preset design value, regardless of the values of the width Dhs(t) and the volume Vho(t) of the elliptical hemisphere. In this embodiment, since the shape of the object OB at the start of formation is unstable, the object OB is formed at a constant descent speed Vs from the start of formation until the width Dhs(t) of the molten portion MP reaches the diameter Dsta. This makes it possible to prevent the shape of the object OB formed from becoming unstable due to the influence of fine adjustment due to the error L(t).

In addition, in this embodiment, the calculation unit 56 stops the formation of the object OB if the width Dhs(t) of the molten portion MP exceeds the diameter Dsta, even if the descent speed Vs and the output intensity of the laser light LS are corrected a predetermined number of times (e.g., 10Δt), and the width Dhs(t+10Δt) does not fall below the diameter Dsta (condition 2 above). If the width Dhs(t) reaches the diameter Dsta after the start of formation, and the width Dhs(t+10Δt) does not fall below the diameter Dsta despite a predetermined number of corrections, there is a risk that the width Dhs(t) will continue to increase. In this case, by stopping the formation of the object OB, it is possible to suppress the formation of an object OB with a shape different from the target shape.

In addition, the calculation unit 56 in this embodiment stops the formation of the object OB if the volume Vho(t) of the molten portion MP does not reach the lower limit volume Vhsta_l even after the threshold time T2 has elapsed since the start of formation (condition 1 above). In this embodiment, the shape of the object OB at the start of formation is unstable. Therefore, if the volume Vho(t) does not reach the lower limit volume Vhsta_l even after the threshold time T2 has elapsed, there is a risk that the molten portion MP will become even smaller. In this case, by stopping the formation of the object OB, it is possible to prevent the formation of an object OB with a shape different from the target shape.

The camera 40 of this embodiment also captures images of the molten part MP. Therefore, the additive manufacturing device 100 of this embodiment can perform operations from image capture to controlling the descent speed Vs of the stage 30 in an integrated manner without acquiring images of the molten part MP from another device.

<Modifications of the above embodiment>
The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

[Modification 1]
In the above embodiment, an example of the additive manufacturing device 100 has been described, but the configuration of the additive manufacturing device 100 can be modified. For example, the additive manufacturing device of another embodiment may not be equipped with the camera 40. In this case, the additive manufacturing device may control the stage 30, etc., using an image of the molten part MP of the object OB captured by another device. The camera 40 that captures the image of the molten part MP may be a thermograph. The thermograph may identify a part of the object OB that is at or above a preset temperature as the molten part MP. The image acquisition unit that captures the image of the molten part MP may be a well-known device within a range in which the molten part MP can be identified. The resolution of the camera 40 is preferably 0.1 mm or less, but may be 0.1 mm or less within a range in which the molten part MP can be identified.
. It may be more than 1 mm.

The raw powder supplied from the nozzle 20 may be made of metal or other materials. The output intensity of the laser light LS may be controlled according to the raw powder. A well-known combination may be applied to the combination of the raw powder and the laser light LS. In the above embodiment, the relative positions of the laser head 10, the nozzle 20, and the stage 30 are changed by the three-dimensional movement of the stage 30 relative to the laser head 10 and the nozzle 20, but the method of changing the relative positions can be modified. For example, the laser head 10, the nozzle 20, and the stage 30 may all be configured to be movable. The position of the nozzle 20 relative to the laser head 10 may be changed according to the shape of the object OB to be formed, for example.

In the above embodiment, the shape acquisition unit 57 acquires the CAD data that is the basis of the object OB from the storage unit 60, but the method of acquiring the data on the shape of the object OB can be modified. For example, the PC 50 may not include the storage unit 60, and may acquire the data of the object OB to be modeled from another storage device or the like via wireless communication.

In the above embodiment, specific examples of the predetermined time Δt and the upper and lower limits of accuracy are given, but these numerical values can be modified. For example, the user may input any number via the input unit 70. In addition, there may be a predetermined numerical value associated with the predetermined time Δt and accuracy for the shape data of the modeled object OB.

In the above embodiment, the molten portion MP is identified using the reflectance of the object OB and the movement of the tip of the object OB, but the method of identifying the molten portion MP can be modified. For example, the unsolidified molten portion MP generates fluctuations that are characteristic of liquids. Therefore, the calculation unit 56 may identify the fluctuations using photographed images of the object OB along a time series, and identify the portion where the fluctuations are occurring as the molten portion MP. In this case, the calculation unit 56 may identify the portion of the fluctuations and the molten portion MP using a learning model generated by machine learning using artificial intelligence.

In the above embodiment, the calculation unit 56 controls the descent speed Vs of the stage 30 using the error L(t), but the controlled parameters can be modified. For example, the error L(t) may be the difference in height from the reference position to the position Z(t) of the molten part MP, instead of the difference in height from the reference position to the apex TP of the molten part MP. Also, the difference between another position of the molten part MP and the reference position may be used as the error L(t). The calculation unit 56 may control the descent acceleration of the stage 30, or may control the speed or acceleration along the horizontal direction in accordance with the descent speed Vs.

In the above embodiment, the width Dhs(t) of the molten portion MP of the object OB was identified, and control was performed using the width Dhs(t), but each control may be performed using only the error L(t) without identifying the width Dhs(t). In the above embodiment, the volume Vhsta_u of the upper limit elliptical hemisphere and the volume Vhsta_u of the lower limit elliptical hemisphere were calculated from the upper and lower limit allowable accuracies, but the numerical values of the volumes Vhsta_u and Vhsta_l themselves may be input. In addition, the calculation unit 56 may identify the maximum diameter of the molten portion MP as the width Dhs(t). A learning model generated by machine learning may be used to identify the width Dhs(t).

[Modification 2]
Fig. 11 is a flowchart of an additive manufacturing method according to a modified example. In the additive manufacturing flow of the modified example shown in Fig. 11, the processes from step S21 to step S24 are the same as the processes from step S1 to step S4 in the additive manufacturing flow (Fig. 9) of the above embodiment. Therefore, in the modified example, the processes from step S25 onwards will be described.

When the formation of the object OB and the camera 40 start capturing images (step S24), the calculation unit 56 determines whether or not a predetermined time Δt has passed since the start of formation (step S25). If the predetermined time Δt has not passed (step S25: NO), the calculation unit 56 waits for the predetermined time Δt to pass. If the predetermined time Δt has passed (step S25: YES), the calculation unit 56 calculates the error L(t) (step S26).

If the calculated error L(t) is not zero (step S27: NO), the movement control unit 55 uses the calculation result of the calculation unit 56 to change the descent speed Vs of the stage 30 (step S28). After the change in the descent speed Vs or if the error L(t) is zero in the processing of step S27 (step S27: YES), the calculation unit 56 determines whether or not the formation of the object OB is completed (step S29). If the formation is not completed (step S29: NO), the processing from step S25 onwards is repeated. If the formation is completed (step S29: YES), the additive manufacturing flow ends. The processing of step S24 corresponds to the image acquisition process. The processing from step S25 to step S29 corresponds to the formation process. The processing of step S26 corresponds to the calculation process. The processing of step S28 corresponds to the position control process.

Unlike the additive manufacturing flow of the above embodiment, as in the additive manufacturing flow of the modified example shown in FIG. 11, it is not necessary to determine whether the width Dhs(t) of the molten part MP has reached the diameter Dsta after the start of manufacturing. In addition, the output intensity of the laser light LS, which is the process from step S9 to step S11 in FIGS. 9 and 10 of the above embodiment, does not need to be controlled, and the subsequent determination using the threshold time T1 in step S12 does not need to be made. On the other hand, the output control of the laser light LS in the process from step S9 to step S11 is performed, and the subsequent determination using the threshold time T1 in step S11 does not need to be made.

In the process from step S9 to step S11 of the above embodiment, the irradiation control unit 52 controls the output intensity of the laser light LS according to the comparison result between the width Dhs(t) and the diameter Dsta, and the comparison result between the volume Vho(t) and the upper and lower limit volumes Vhsta_u and Vhsta_l. However, the control may be performed according to the comparison result between the width Dhs(t) and the diameter Dsta. Specifically, the irradiation control unit 52 reduces the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is larger than the volume Vhsta_u of the elliptical hemisphere with the upper limit of accuracy. On the other hand, the irradiation control unit 52 may increase the output intensity of the laser light LS when the volume Vho(t) of the elliptical hemisphere at time t is smaller than the volume Vhsta_l of the elliptical hemisphere with the lower limit of accuracy.

In the above embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware. The present invention is not limited to the above embodiment, and can be implemented in various aspects without departing from the gist of the present invention.

Although this aspect has been described above based on the embodiment and modified examples, the embodiment of the above-mentioned aspect is intended to facilitate understanding of this aspect and does not limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

10...Laser head (irradiation unit)
20...Nozzle (supply section)
30... Stage 40... Camera (image acquisition unit)
51...CPU
52... Irradiation control unit (control unit)
55...Movement control unit (control unit)
56...Calculation unit (control unit)
57: Shape acquisition unit 60: Memory unit 70: Input unit 80: Output unit 100: Additive manufacturing device C1, C2: Curve Dhs(t): Width of melted part at time t Dsta: Diameter L(t): Error at time t L1: Linear change L2, L3, L4: Dashed lines LS: Laser light MP: Melted part TP: Apex of melted part OB: Model T1: Threshold time Δt: Predetermined time Vs, Vc: Descending speed (moving speed)
Vho(t)...volume of the elliptical hemisphere at time t Vhsta...volume of the elliptical hemisphere Vhsta_u...volume of the upper limit of the elliptical hemisphere Vhsta_l...volume of the lower limit of the elliptical hemisphere Z0(t)...reference position Z(t)...height position of the molten part at time t

Claims (10)

An additive manufacturing apparatus, comprising:
a stage on which the model is placed;
a nozzle for supplying a powder of a raw material for forming the object; and
an irradiation unit that irradiates the raw material powder supplied from the nozzle with laser light to form the object;
A control unit that controls the additive manufacturing apparatus;
Equipped with
Either the stage or the irradiation unit can be moved to change a relative position therebetween;
The control unit is
The raw material powder is layered on the stage by changing the relative position to form the object; and
calculating, using an image of the object on the stage, an error in a vertical direction between a melted portion of the object and a reference position that is determined according to an elapsed time from a start of modeling ;
An additive manufacturing apparatus that uses the calculated error to change a moving speed for changing the relative position. The additive manufacturing apparatus according to claim 1 ,
The control unit is
Identifying a height of a vertex of the fusion zone parallel to a vertical direction from the image of the object;
Calculating the difference between the reference position and the specified height as the error;
An additive manufacturing apparatus that changes a moving speed for changing the relative position along a vertical direction in accordance with the error. The additive manufacturing apparatus according to claim 2,
The control unit is
If the error is greater than zero, accelerating the velocity in a direction that increases the distance between the relative positions along the vertical direction;
When the error is smaller than zero, the velocity is reduced in a direction in which the distance between the relative positions along the vertical direction decreases. The additive manufacturing apparatus according to claim 2 or 3,
The control unit is
Identifying a width of the molten portion parallel to a horizontal direction from the image of the object;
Calculating the volume of the molten portion when the shape of the molten portion is defined as an elliptical hemisphere using the specified width and height;
an additive manufacturing device that changes an output intensity of the laser light irradiated by the irradiation unit in response to a comparison between the calculated volume of the elliptical hemisphere and a preset volume of the elliptical hemisphere. The additive manufacturing apparatus according to claim 4,
The control unit is
calculating, as the volume of the predetermined elliptical hemisphere, a volume of an elliptical hemisphere having a diameter equal to a horizontal width of the reference position in a design value of the object and a height equal to half of the diameter;
calculating a lower limit volume and an upper limit volume by multiplying the preset volume of the elliptical hemisphere by an allowable accuracy;
When the calculated volume of the elliptical hemisphere of the molten portion is larger than the upper limit volume, the output intensity of the laser light irradiated by the irradiation unit is reduced,
an additive manufacturing apparatus that increases an output intensity of the laser light irradiated by the irradiation unit when the calculated volume of the elliptical hemisphere of the molten portion is smaller than the lower limit volume. The additive manufacturing apparatus according to any one of claims 1 to 5,
The control unit is
Identifying a width of the molten portion parallel to a horizontal direction from the image of the object;
An additive manufacturing device that does not change the moving speed for changing the relative position along the vertical direction from an initial value until the specified width reaches a design diameter from the start of manufacturing of the object, regardless of the magnitude of the error. The additive manufacturing apparatus according to claim 6,
The control unit stops the formation of the object when the identified width does not fall below the diameter of the design value for a predetermined time after the identified width exceeds the diameter of the design value, despite the movement speed changing. The additive manufacturing apparatus according to any one of claims 1 to 7,
The control unit is
Identifying a width of the molten portion parallel to a horizontal direction and a height of a vertex of the molten portion parallel to a vertical direction from the image of the object;
Calculating the volume of the molten portion when the shape of the molten portion is defined as an elliptical hemisphere using the specified width and height;
an additive manufacturing device that stops manufacturing of the object when the calculated volume of the elliptical hemisphere of the molten part does not exceed a preset volume within a predetermined time from the start of manufacturing of the object. The additive manufacturing apparatus according to any one of claims 1 to 8, further comprising:
An additive manufacturing apparatus comprising: an image acquisition unit that acquires an image of the molten portion in the object. An additive manufacturing method, comprising:
an image acquiring step of acquiring an image of the object placed on the stage;
a modeling step of irradiating a laser beam from an irradiation unit onto the raw material powder supplied from a nozzle to form the model on the stage;
a calculation step of calculating, by using an image of the object, an error in a vertical direction between an apex of a melted portion in the object and a reference position that is determined depending on the elapsed time from the start of modeling ;
A position control process;
Equipped with
Either the stage or the irradiation unit can be moved to change a relative position therebetween;
the modeling step includes stacking the raw material powder on the stage by changing the relative position to model the model,
The position control step uses the calculated error to change a moving speed for changing the relative position.

Images