Patent Application
20230286074
The present invention relates to a system for manufacturing an additively-manufactured object built by depositing weld beads based on a depositing plan, a method for manufacturing an additively-manufactured object, and a program for manufacturing an additively-manufactured object.
Patent Literature 1 discloses a welding quality determination method capable of determining welding quality of a welded product welded by lap welding, which is non-penetration welding. This method is a welding quality determination method for determining welding quality of a welded product obtained by joining a first material to be welded and a second material to be welded by irradiating the first material to be welded with a laser beam while the first material to be welded and the second material to be welded are superimposed on each other, in which: a welded portion in which the first material to be welded and the second material to be welded are laser-welded by irradiation of a laser beam is a portion solidified after the first material to be welded and the second material to be welded are molten; the welded portion is formed by welding in which a molten region of the second material to be welded does not reach a surface of the second material to be welded that is opposite to the first material to be welded during the laser welding; and the welding quality of the welded product is determined based on a height of a weld bead formed on a laser beam irradiated surface of the first material to be welded in the welded portion.
Patent Literature 2 discloses a system and a method for providing positional feedback for additive manufacturing. One or two of an output current, an output voltage, an output power, an output circuit impedance, and a wire feed speed are sampled during an additive manufacturing process in producing a current layer. A plurality of instantaneous contact tip-to-work distances (CTWD) are determined based on at least one or two of the output current, output voltage, output power, output circuit impedance, and wire feed speed. An average CTWD is determined based on the plurality of instantaneous CTWDs. A correction factor that is used to compensate for any error in the current layer height is generated based at least on the average CTWD.
Patent Literature 1: JP2018-79502A
Patent Literature 2: JP2019-107698A
Width and height of each weld bead must be controlled in order to create an additively-manufactured object with high precision. A feedback control method regarding a shape of the weld bead using laser sensor information or current and voltage information is proposed. Patent Literature 1 measures a bead height by a laser sensor to perform feedback control. Patent Literature 2 monitors an output current, a wire feed speed, and the like to perform feedback control of a distance between a tip and a work (height information).
However, depending on different additively-manufactured objects, there is a possibility that a bead cannot be measured by the laser sensor, and it is difficult to perform feedback control by the laser sensor in that range.
The present invention relates to a technique for obtaining an appropriate bead shape of a weld bead when manufacturing an additively-manufactured object obtained by depositing a plurality of weld beads formed by melting and solidifying a filler metal using an arc on a base material.
Present invention is a system for manufacturing an additively-manufactured object obtained by depositing weld beads based on a depositing plan, the system including: a torch that is provided on a robot arm; a first measurement unit that is mounted on the torch and that directly measures, in a non-contact manner, a base shape of a base portion on which the weld beads are deposited; a second measurement unit that measures at least one of a current, a voltage, and a filler metal supply rate when the weld beads are deposited, and estimates the base shape from history change thereof; and a control unit that selects at least either of a measurement result by the first measurement unit or by the second measurement unit and corrects control of at least one of the robot arm, the current, the voltage, and the filler metal supply rate.
The control unit may compare the measurement result by the first measurement unit and the measurement result by the second measurement unit with predetermined threshold values, respectively, and correct the control by switching selection of the measurement result when a deviation value from the threshold value exceeds a predetermined value.
The control unit may compare a moving distance of the torch, a measurement position of the first measurement unit, and a measurement position of the second measurement unit with positions on the depositing plan to switch the selection of the measurement result.
The first measurement unit may be a laser sensor, and a laser beam of the laser sensor may be emitted forward or backward with respect to a scanning direction of the torch.
A value obtained by averaging the measurement result over a predetermined period of time may be compared with the threshold value.
The measurement result by the second measurement unit may be selected when a mounting direction of the laser sensor as seen from the torch is not same as the scanning direction of the torch.
Further, the present invention is a method for manufacturing an additively-manufactured object obtained by depositing weld beads based on a depositing plan, the method including: a step of using a first measurement unit that is mounted on a torch supported by a robot arm to directly measure, in a non-contact manner, a base shape of a base portion on which the weld beads are deposited; a step of using a second measurement unit to measure at least one of a current, a voltage, and a filler metal supply rate when the weld beads are deposited, and estimate the base shape from history change thereof; and a step of selecting at least either of a measurement result by either the first measurement unit or the second measurement unit and correcting control of at least one of the robot arm, the current, the voltage, and the filler metal supply rate.
Further, the present invention is a program that causes a computer to execute a procedure of a method for manufacturing an additively-manufactured object obtained by depositing weld beads based on a depositing plan for executing the method for manufacturing an additively-manufactured object, the program causing the computer to execute: a step of using a first measurement unit that is mounted on a torch provided on a robot arm to directly measure, in a non-contact manner, a base shape of a base portion on which the weld beads are deposited; a step of using a second measurement unit to measure at least one of a current, a voltage, and a filler metal supply rate when the weld beads are deposited, and estimate the base shape from history change thereof; and a step of selecting at least either of a measurement result by the first measurement unit or by the second measurement unit and correcting control of at least one of the robot arm, the current, the voltage, and the filler metal supply rate.
According to the present invention, an appropriate result can be selected among measurement results of a shape of a base portion measured by a first measurement unit or a second measurement unit, and an additively-manufactured object can be manufactured with high precision.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
The additive manufacturing device 11 includes a welding robot 19 including a tip shaft provided with a torch 17, and a filler metal supply unit 21 that supplies a filler metal (welding wire) M to the torch 17. The tip shaft of the welding robot 19 is provided with a shape sensor 23 constituting a first measurement unit, together with the torch 17.
The welding robot 19 is a multi joint robot, and the filler metal M is supported by the torch 17 mounted on a tip shaft of a robot arm in a continuously suppliable manner. A position and a posture of the torch 17 can be freely set three-dimensionally within a range of a degree of freedom of the robot arm.
The torch 17 includes a shield nozzle (not shown), and the shield nozzle supplies shielding gas. An arc welding method may be either a consumable electrode type such as shielded metal arc welding or carbon dioxide gas arc welding, or a non-consumable electrode type such as TIG welding or plasma arc welding, and is appropriately selected according to an additively-manufactured object to be manufactured.
For example, in the case of the consumable electrode type, a contact tip is disposed inside the shield nozzle, and the filler metal M to which a melting current is supplied is held on the contact tip. The torch 17 generates an arc from a tip of the filler metal M in a shielding gas atmosphere while holding the filler metal M. The filler metal M is fed from the filler metal supply unit 21 to the torch 17 by a feeding mechanism (not shown) mounted on the robot arm or the like. Then, when the continuously supplied filler metal M is melted and solidified while the torch 17 moves, a linear weld bead B, which is a melted and solidified body of the filler metal M, is formed on a base plate 51, and an additively-manufactured object W formed of the weld bead B is manufactured.
As shown in
The controller 13 includes a CAD/CAM unit 31, a track calculation unit 33, a storage unit 35, a deviation amount calculation unit 37, a correction unit 39, a second measurement unit 32, and a control unit 41 to which these units are connected. The controller 13 is implemented by a computer device including a CPU, a memory, a storage, and the like.
The CAD/CAM unit 31 inputs or creates shape data (CAD data and the like) of the additively-manufactured object W to be manufactured.
The track calculation unit 33 disassembles a shape model of three-dimensional shape data into a plurality of weld bead layers according to a height of the weld bead B. Then, for each layer of the disassembled shape model, a depositing plan is created, which defines a track of the torch 17 for forming the weld bead B and heating conditions for forming the weld bead B (including welding conditions for obtaining a bead width, a bead depositing height, and the like).
The deviation amount calculation unit 37 compares the depositing plan generated by the track calculation unit 33 with a measured value obtained by the shape sensor 23. Then, a deviation amount between a shape based on the depositing plan and a shape based on the measured value in the portion serving as the base during formation of the weld bead B is calculated.
The correction unit 39 corrects, based on the deviation amount calculated by the deviation amount calculation unit 37, the welding conditions based on the depositing plan during formation of the weld bead B.
The second measurement unit 32 acquires a current and a voltage during formation of the weld bead B from the power supply device 15, and acquires a filler metal supply rate, which is a rate at which the filler metal (welding wire) M is supplied to the torch 17, from the filler metal supply unit 21. Therefore, the second measurement unit 32 can estimate and measure a shape of a base portion (a base shape) that serves as the base during formation of the weld bead B from history change in these values. The shape sensor 23 constituting the first measurement unit directly measures the base shape in a non-contact manner using a medium such as a laser beam, whereas the second measurement unit 32 indirectly measures the base shape from numerical values such as the current, voltage, and filler metal supply rate during formation of the weld bead B.
The control unit 41 executes a manufacturing program stored in the storage unit 35 to drive the welding robot 19, the power supply device 15, and the like. That is, the welding robot 19 moves the torch 17 in response to a command from the controller 13 and melts the filler metal M with an arc to form the weld bead B on the base plate 51.
Note that the base plate 51 is made of a metal plate such as a steel plate, and is basically larger than a bottom surface (a surface of a lowermost layer) of the additively-manufactured object W. The base plate 51 is not limited to a plate shape, and may be a base of other shapes such as a block body or a rod body.
Any commercially available welding wire can be used as the filler metal M. For example, a wire specified by solid wires for MAG welding and MIG welding of mild steel, high strength steel, and low temperature service steel (JISZ 3312), flux-cored wires for arc welding of mild steel, high strength steel, and low temperature service steel (JISZ 3313), or the like can be used.
Next, an example of an additively-manufactured object manufactured by a manufacturing method according to the present embodiment will be described.
As shown in
Next, a case of building the additively-manufactured object W will be described.
The filler metal M is melted while the torch 17 of the additive manufacturing device is moved by being driven by the welding robot 19. Then, the weld beads B1 made of the melted filler metal M are supplied and deposited on the base plate 51 to build the frame portion having a substantially rectangular shape in a plan view, which is formed by the weld beads B1 deposited on the base plate 51.
The weld beads B2 are formed inside the frame portion 53. The weld beads B2 are formed in a width direction in the frame portion 53. Accordingly, the weld bead layers BL constituted by the plurality of weld beads B2 formed in parallel are formed in the frame portion 53. Then, the weld bead layers BL are deposited inside the frame portion 53, so that the internal molded portion 55 is built.
According to this manufacturing method, since the internal molded portion 55 is built inside the frame portion 53 after the frame portion 53 is built, the internal molded portion 55 can be efficiently built by the weld beads B2 having a large cross-sectional area.
Width and height of each weld bead must be controlled in order to create the additively-manufactured object W with high precision using the manufacturing system 100 for additively-manufactured objects, and it is desirable to perform feedback control regarding a shape of the weld bead using laser sensor information or current and voltage information. For example, a bead height is measured by the laser sensor to perform the feedback control.
However, depending on a shape of the additively-manufactured object, there is a possibility that a bead cannot be measured by the laser sensor, and it is difficult to perform feedback control by the laser sensor in that range.
Even in this state, it is possible to measure values such as the current, voltage or filler metal supply rate during deposition of the weld beads. Therefore, the second measurement unit 32 can estimate the bead shape of the weld bead from history change of these values, and can obtain the distance estimate de from the torch 17 to the base plate 51.
In the state of (A) in
On the other hand, (B) of
Positions where the measurement by the shape sensor 23 is obstructed as shown in (B) of
Note that in the above description, an example of recognizing the distance from the first measurement unit or the second measurement unit to the base plate 51 is described. In this example, the surface shape of the base plate 51 is the base shape. On the other hand, for example, when the weld beads B2 are built on the base plate 51, the first measurement unit or the second measurement unit recognizes the distance to the weld beads B2. That is, the surface shape of the weld beads B2 becomes the base shape. Although the base on which the weld beads are formed is made of various members depending on different situations, the present embodiment can be applied to any member. The same applies to the following description.
According to the present embodiment, at a measurement location where there is an obstacle for the laser beam L such as the frame portion 53, information of the second measurement unit 32 such as the current, voltage, or filler metal supply rate during deposition of the weld bead is monitored to acquire and compensate for the information of the base shape. On the other hand, when the current, voltage, or filler metal supply rate is temporarily disturbed due to surface unevenness, surface slag, disturbance, or the like, the height information can be obtained by the non-contact measurement from the shape sensor 23, which is the first measurement unit. As a result, it is possible to acquire appropriate information on the base portion on which the weld bead is to be built, and to manufacture an additively-manufactured object with high precision.
The control unit 41 can accurately recognize the position at which the switching between the first measurement unit and the second measurement unit is performed even before manufacturing by comparing the moving distance of the torch 17, the measurement position of the shape sensor 23, which is the first measurement unit, and the measurement position of the second measurement unit with the positions on the depositing plan.
Note that even without using the depositing plan, the control unit 41 can compare the measurement result by the first measurement unit and the measurement result by the second measurement unit with predetermined threshold values, respectively, and can correct the various controls described above, such as the control to the robot arm, by switching the selection of the measurement result when a deviation value from the threshold value exceeds a predetermined value.
According to the present embodiment, since the first measurement unit and the second measurement unit acquire abnormal values for different reasons, it is possible to switch to the other one if a determination is made using a threshold value and there is an abnormality. The threshold value in this switching judgment may be adjusted in consideration of accuracy or robustness of each measurement unit.
The control unit 41 may perform the above-described comparison with the threshold value based on a value obtained by averaging the measurement results of the first measurement unit and the second measurement unit over a predetermined period of time. The averaging can reduce effects from noise, outliers, and the like, so that a stable measurement result can be obtained.
An example of the first measurement unit is the shape sensor 23, and the laser beam L of the shape sensor 23 is emitted forward or backward with respect to a scanning direction (advancing direction) of the torch 17.
The shape sensor 23 can measure the shape of the weld bead B with high precision. In the case of forward irradiation, unevenness on the surface of the weld bead B serving as the base can be monitored, and in the case of rearward irradiation, the height of the weld bead B immediately after deposition can be confirmed. Note that in monitoring the current, voltage, and filler metal supply rate, the height directly below the torch 17 is recognized.
Note that when the shape sensor 23 is fixed to the torch 17, the shape sensor 23 cannot always measure a shape of a depositing path on the track. For example, when an extending direction of the laser beam L and the scanning direction of the torch 17 are orthogonal to each other as shown in (A) of
That is, when the mounting direction of the shape sensor 23 as seen from the torch and the scanning direction of the torch 17 are the same as in the case of (A) in
In the case of (B) in
In the present embodiment, the frame portion 53 is exemplified as an object that blocks the laser beam from the shape sensor 23, but the object that blocks the laser beam is not limited to the frame portion 53. When the shape sensor 23 cannot measure the base shape due to an object blocking the laser beam, the control unit 41 can use the measurement result by the second measurement unit 32.
The present invention is not limited to the above embodiment, and may be appropriately modified, improved, or the like. Materials, shapes, sizes, numerical values, forms, numbers, arrangement positions, and the like of components in the above embodiment are set as desired and not limited as long as the present invention can be achieved.
It should be noted that the present application is based on a Japanese patent application (Japanese Patent Application No. 2020-123861) filed on Jul. 20, 2020, the content of which is incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-123861 | Jul 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/025685 | 7/7/2021 | WO |
