Patent Application
20240181549
The present invention relates to an additively manufacturing method, an additive manufacturing device, and a program for building an additively manufactured object.
In recent years, there is an increasing need for shaping using a 3D printer as means for production, and research and development are proceeding toward practical use of shaping using a metal material. A 3D printer that builds a metal material uses a heat source such as laser beams, electron beams, and arcs to melt a metal powder or a metal wire, and deposits the molten metal to create an additively manufactured object. For example, Patent Literature 1 describes a technique in which, when an additively manufactured object is manufactured by depositing weld beads obtained by melting and solidifying a wire-like metallic material (filler metal), a welding output current and a filler metal feed speed are sampled, a distance from a contact tip of a welding torch to a welding base material is estimated based on the sampled information, and a welding speed and a filler metal feed speed are adjusted such that error of a bead height is small.
Patent Literature 1: JP2018-158382A
However, the adjustment of the height of the weld layer described in Patent Literature 1 is not always appropriately performed. For example, when any variation occurs in welding conditions, an operation of adjusting the occurred variation may be performed by maintaining a set value of a specific welding condition that causes the variation as it is and changing set values of the other welding conditions. Here, an expected adjustment operation may not be performed.
For example, regarding the filler metal feed speed at which the filler metal is supplied to the welding torch, a control system of the device during bead formation sets the speed to feed the filler metal. When the set values of the other welding conditions change depending on the filler metal feed speed, a command value set by the control is used for drive control in many cases assuming that the command value is the same as an actual filler metal supply speed.
Therefore, when the command value of the control is different from the actual feed speed due to some factor, appropriate drive control is not performed. As a result, the height of the weld layer varies, and a shape error occurs in the additively manufactured object.
Accordingly, an object of the present invention is to provide an additively manufacturing method, an additive manufacturing device, and a program form building an additively manufactured object in which a feed speed of a filler metal can be accurately grasped, a height of a weld bead can be more accurately managed, and a high-accuracy additively manufactured object can be obtained.
The present invention has the following configurations.
According to the present invention, a feed speed of a filler metal can be accurately grasped, and a height of a weld bead can be more accurately managed. As a result, a high-accuracy additively manufactured object can be obtained.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
An additive manufacturing device 100 having the present configuration is a device for manufacturing an additively manufactured object 11 and includes a welding robot 13, a robot controller 15, a power supply unit 17, a filler metal supply unit 19, a shape sensor 27, a sensor controller 21, and a control unit 23.
The welding robot 13 is an articulated robot, in which a filler metal M is continuously suppliable to and supported in a welding torch 25 attached to a tip axis of a robot arm. Any position and any posture of the welding torch 25 can be three-dimensionally set in a range of degree of freedom of the robot arm.
The welding torch 25 includes a shield nozzle (not illustrated) and is supplied with shielding gas from the shield nozzle. An arc welding method used herein may be any of a consumable electrode type such as shielded metal arc welding or CO2 gas arc welding or a non-consumable electrode type such as TIG welding or plasma arc welding, and is appropriately selected depending on the additively manufactured object to be prepared.
For example, in the consumable electrode type, a contact tip is disposed in the shield nozzle, and the filler metal M to which a melting current is supplied is held in the contact tip. The welding torch 25 generates an arc from a tip of the filler metal M in a shielding gas atmosphere while holding the filler metal M.
In the welding robot 13, the shape sensor 27 is provided in the vicinity of the welding torch 25. The shape sensor 27 may be a laser sensor that detects reflected light of irradiated laser light to acquire height information or may be a camera that can measure a three-dimensional shape. The sensor controller 21 outputs a shape profile of the additively manufactured object 11 (weld bead described below) that is acquired based on an output of the shape sensor 27 to the control unit 23.
The robot controller 15 drives each of the units of the welding robot 13 in response to a command from the control unit 23. The power supply unit 17 supplies a welding current and a welding voltage to the welding torch 25 of the welding robot 13 through the robot controller 15.
The filler metal supply unit 19 includes: a reel 29 around which the filler metal M is wound: and an encoder 31 that measures a feed speed of the filler metal M drawn from the reel 29 and fed to the welding robot 13.
As the filler metal M, various commercially available welding wires can be used. For example, wires defined by solid wires (JIS Z 3312) for MAG and MIG welding of mild steel, high strength steel, and low temperature service steel or flux cored wires (JIS Z 3313) for arc welding of mild steel, high strength steel, and low temperature service steel can be used.
The control unit 23 integrally controls each of the above-described units of the additive manufacturing device 100. The control unit 23 is configured by a computer device including a CPU, a memory; a storage, and the like, and builds the additively manufactured object 11 by executing a program (building program) on the memory or the storage.
In the additive manufacturing device 100, the control unit 23 drives the welding robot 13 and the power supply unit 17 by executing the building program stored in the memory or the storage. That is, the control unit 23 drives the welding robot 13 and the power supply unit 17 according to a procedure (bead formation path) set by the building program, moves the welding torch 25 along the bead formation path, heats the filler metal M by arc welding at the torch tip, and deposits the molten filler metal M on a base plate 33. As a result, a linear weld bead that is a melt-solidified product of the filler metal M is formed on the base plate 33, and the weld bead is sequentially deposited to build the additively manufactured object 11. The building program is an instruction code set where procedures such as the movement of the welding robot 13 or the control of the power supply unit 17 are sequentially recorded, and the control unit 23 sequentially executes the instruction codes of the building program.
That is, the welding robot 13, the robot controller 15, and the power supply unit 17 described above function as a bead forming unit 35 to build the additively manufactured object 11.
A configuration of the additive manufacturing device 100 described herein is merely exemplary; and another configuration may be adopted. For example, by fixing the welding torch 25 and moving the base plate 33 or by moving the welding torch 25 and the base plate 33, the welding torch 25 and the base plate 33 may move relative to each other to build the additively manufactured object 11.
The heat source that melts the filler metal M is not limited to the above-described arc. For example, a heat source using another method such as a heating method using an arc and a laser in combination, a heating method using a plasma, or a heating method using an electron beam or a laser may be adopted. When the filler metal M is heated by an electron beam or a laser, the amount of heat can be controlled more finely, and the state of the weld beads can be more accurately maintained, which can contribute to further improvement of the quality of the additively manufactured object.
Next, a procedure of building the additively manufactured object using the additive manufacturing device 100 having the above-described configuration will be described.
The control unit 23 includes a filler metal feed speed measuring unit 41, a reference welding speed setting unit 43, a bead height measuring unit 45, a correction value setting unit 47, and a welding speed determination unit 49, and causes each of the units to function as schematically described below such that an additively manufactured object having a desired shape is built by the bead forming unit 35.
The filler metal feed speed measuring unit 41 measures a filler metal feed speed at which the filler metal M is fed to the welding torch 25 based on an output of the encoder 31 during the formation of the weld bead.
Although the details will be described below; the reference welding speed setting unit 43 refers to a database DB representing a relationship between the measured filler metal feed speed and a reference welding speed set for the filler metal feed speed to acquire the corresponding reference welding speed based on the measured filler metal feed speed from a predetermined conversion formula, correspondence table, or the like that is prepared in advance.
The bead height measuring unit 45 measures a height of the formed weld bead based on information regarding the shape profile that is created by the sensor controller 21 based on the output from the shape sensor 27.
The correction value setting unit 47 acquires a welding speed correction value with which the height of the weld bead to be formed is adjusted based on a difference between the measured height of the weld bead and a height of a tip of the filler metal M that protrudes from the tip of the welding torch 25.
The welding speed determination unit 49 corrects the reference welding speed with the welding speed correction value and determines a welding speed for forming the weld bead of which the height is adjusted.
The control unit 23 outputs a command for moving the welding torch at the determined welding speed to form the weld bead to the bead forming unit 35, and forms the weld bead while adjusting the bead height.
Next, a specific building procedure of the above-described additively manufactured object will be described in more detail.
The control unit 23 reads a building program corresponding to the shape of the additively manufactured object to be built, and drives each of the units of the additive manufacturing device 100 to form the weld bead based on the read building program (S11).
In the step (S11) of forming the weld bead, the weld bead is formed while moving the welding torch 25 using the welding robot 13, and the filler metal feed speed measuring unit 41 measures a filler metal feed speed Vwire of the filler metal M supplied to the welding torch 25 based on an output signal of the encoder 31 (S1a). The sensor controller 21 measures a shape profile based on the output signal of the shape sensor 27 that detects the height of the formed weld bead (S1b).
Next, the reference welding speed setting unit 43 refers to the database DB that is prepared in advance to acquire a reference welding speed Vweld_0(Vwire) corresponding to the measured filler metal feed speed Vwire(S2). The database DB stores a relationship between the filler metal feed speed Vwire and reference welding speed Vweld_0 capable of welding at the speed. The database DB may be a correspondence table between the filler metal feed speed Vwire and the reference welding speed Vweld_0 or may be a function Vweld_0(Vwire) or arithmetic equation of reference welding speed where the filler metal feed speed Vwire is a variable.
Examples of a method of calculating the reference welding speed Vweld_0(Vwire) include a method of calculating the reference welding speed Vweld_0 in real time from the filler metal feed speed Vwire measured during welding and a method of calculating the reference welding speed Vweld_0 from an average value of the filler metal feed speed Vwire during weld bead formation of a previous layer or a previous path.
As illustrated in
The characteristic illustrated in
H
0
=ha=C
1
+C
2Vwire+C3Vweld+C4Vwire2+C5Vweld2+C6Vwire Vweld Equation (1)
Here, when the effect of the squared term in Equation (1) is ignorable and the constant term is rearranged as D, a linear relationship between the welding speed Vweld and the feed speed Vwire is obtained as shown in Equation (2).
Vweld=(C2/C3)Vwire+D Equation (2)
Accordingly, when the feed speed Vwire varies, by changing the welding speed Vweld based on Equation (2), the difference between the planned height H0 and the estimated height ha can be reduced. With such configuration, the deviation between the planned height H0 and the estimated height ha is reduced, and finally the actual height and the planned height are easily matched to each other.
The planning line 51 is a target shape of the weld bead B, and a height H0 of the weld bead B corresponds to the height of the tip of the filler metal M that protrudes from the tip of the welding torch 25. The dimension of the height H0 is geometrically acquired from coordinate information based on which the welding robot 13 is driven.
The bead height measuring unit 45 acquires a difference (planned height error) Δh (=H0−H) between an actual value H of the height of the weld bead obtained from the information regarding the shape profile from the sensor controller 21 and the planned height H0 of the weld bead acquired from the building program (S3).
The correction value setting unit 47 acquires a welding speed correction value corresponding to the acquired planned height error Δh.
As illustrated in
For example, it is assumed that the welding speed where the planned height error Δh is 0 (the reference welding speed Vweld_0 acquired from the filler metal feed speed Vwire) is a welding speed Vweld_a1 shown at a point P1. If the planned height error Δh is generated by −δ, the welding speed is changed to a welding speed Vweld_a2 at a point P2 along a reference characteristic line L1 that is preset. Here, however, a correction amount Vweld(Δh) of the welding speed may become excessive such that the control of the bead height is unstable. Accordingly, using a characteristic line L2 obtained by intentionally reducing the gain (slope of the characteristic line) of the characteristic line L1, a welding speed Vweld_a3 at a point P3 corresponding to −δ is set.
Here, the gain of the characteristic line L2 is reduced to ¼ of the characteristic line L1. The gain is appropriately set based on findings by an experiment, analysis, or the like. It is preferable that the characteristic lines L1 and L2 and a characteristic line L3 described below are set in a range of ±30% with respect to the welding speed Vweld_a3 to set the upper limit of the correction amount.
As such, when the planned height error Δh is generated, a correction value with which the welding speed is adjusted (changed from Vweld_a1 to Vweld_a3) based on the planned height error Δh is set (S4). By correcting the welding speed with the correction value, the height of the weld bead to be formed can be more rapidly matched to the planned height while preventing overshoot and hunting.
In the additively manufacturing method having the present configuration, in addition to the above-described correction, by measuring the filler metal feed speed Vwire with the filler metal supply unit 19, the reliability of the set value of the welding speed Vweld_a1 is further improved.
For example, when the set value of the filler metal feed speed Vwire is set to Q1 illustrated in
Accordingly, in the present configuration, when the filler metal feed speed Vwire is actually measured and the measurement result is set to Q2, the reference welding speed Vweld_0 is set to R2 corresponding to Q2, and the filler metal feed speed is set to a welding speed corresponding to the planned height error Δh centering on R2. That is, a characteristic line L3 obtained by translating the characteristic line L2 to pass through a point P4 is set centering on the point P4 where the welding speed is corrected from the point P1 illustrated in
That is, the welding speed Vweld is set from Equation (3).
Vweld=Vweld_0(Vwire)+Vweld(Δh) (3)
Here, Vweld_0(Vwire) is a reference welding speed corresponding to the actual value of the filler metal feed speed, and Vweld(Δh) refers to the amount of the welding speed that is adjusted to increase or decrease to compensate for the planned height error Δh.
The more details will be described. For example, when a set value of the feed speed is set to Vwire_f0 and an actual value thereof is set to Vwiref1 (≠Vwire_f0), the planned height H0 and the estimated height ha are expressed by Equation (4) and Equation (5), respectively.
H
0
=C
1
+C
2Vwire_f0+C3Vweld+ Equation (4)
ha=C
1
+C
2Vwire_f1+C3Vweld+ Equation (5)
Accordingly, a difference between the planned height H0 and the estimated height ha is expressed by Equation (6).
|H0−ha|=|C2(Vwire_f0−Vwire_f1)+C4(Vwire_f02−Vwire_f12)+C6Vweld(Vwire_f0−Vwire_f1)|=f(Vwire_f1, Vweld) Equation (6)
Based on Equation (6), a value Vweld_1 to which the welding speed changes from the initial set value Vweld_0 to satisfy Equation (7) is searched for.
f(Vwire_f1, Vweld_0)>f(Vwire_f1, Vweld_1) (7)
Accordingly, the reference welding speed for compensating for the deviation in feed speed can be acquired, and the reference welding speed can be set while expecting the difference between the planned height and the estimated height to some extent. Regarding the difference |H0−ha| between the planned height H0 and the estimated height ha, a value that is realistically assumed according to the estimation accuracy may be provided in advance as an allowable upper limit value in the left side of Equation (7).
The acquired welding speed Vweld is changed in real time (S6). Accordingly, the procedures of S11 described above (each of the procedures of S1a and S1b to S6) are repeated until the formation of all the weld beads is completed (S12).
With the above-described configuration, when the set value of the filler metal feed speed and the actual filler metal feed speed do not match with each other, the occurrence of shape error caused by an inaccurate control can be prevented in advance, the correction to a planned accurate bead height can be reliably performed, and an additively manufactured object can be accurately built as designed.
It is preferable that the building procedure by the above-described additively manufacturing method is performed on all the weld beads to be formed. However, the building procedure may be applied to only a part of the building.
During the formation of the weld bead B, the thickness of the weld bead B in a starting edge portion 61 of the bead formation path is thicker than that in the other portions, and the thickness of the weld bead B in an end edge portion 63 thereof is thinner than that in the other portions. Therefore, in the starting edge portion 61 and the end edge portion 63, the bead height is required to be formed more accurately than the other portions. Accordingly, it is preferable that, in at least any one of the starting edge portion 61 and the end edge portion 63, the filler metal feed speed and the bead height described above are measured to determine the welding speed Vweld. Here, the entire additively manufactured object can be accurately built with a high dimensional accuracy regardless of the positions of the starting edge portion 61 and the end edge portion 63 of the weld bead.
In the additively manufacturing method having the present configuration, the bead height of the weld bead is estimated and acquired from the filler metal feed speed and is acquired by measuring the formed weld bead, and the deviation from the planned height, that is, the error of the bead height is acquired. The error of the bead height can be acquired for each layer of the weld bead or for each bead formation path and further by comparison to a previous layer or a previous bead formation path.
For example, it is preferable that, when the filler metal feed speed Vwire is measured and the reference welding speed corresponding to the measured filler metal feed speed is set to the reference speed (welding speed) at which the welding torch is relatively moved, the difference between the actual value and the planned height of the height of the formed weld bead is acquired in real time such that the reference welding speed changes depending on the acquired difference.
As a result, even when the height of the weld bead varies depending on welding conditions, welding positions, and the like while compensating for the variation in filler metal feed speed from the set value with respect to the reference welding speed, by measuring the variation in real time and adding the correction amount of the welding speed to the reference welding speed to compensate for the variation, the weld bead having an appropriate planned height can be formed at all times. As a result, an additively manufactured object made of a plurality of weld beads can be built with high shape accuracy. By performing the compensation depending on the welding speed, the building can be controlled independently of a heat source such as an arc.
The present invention is not limited to the above-described embodiment, and combinations of the configurations of the embodiment and changes and applications based on the description of the specification and well-known techniques by those skilled in the art can be expected from the present invention and are included in the range for which protection is sought.
As described above, the present specification discloses the following features.
In the additively manufacturing method, the reference welding speed is set based on the measured value of the filler metal feed speed, and the welding speed obtained by correcting the set reference welding speed such that the height of the weld bead is appropriately maintained is determined. When the weld bead is formed at the determined welding speed, the bead height is adjusted as planned, and an additively manufactured object having a high shape accuracy can be obtained.
In the additively manufacturing method, the welding speed for reducing the deviation between the planned height and the estimated height of the weld bead is set. Therefore, the weld bead having a planned bead height can be formed.
In the additively manufacturing method, even when the set value of the filler metal feed speed and the actual filler metal feed speed are different from each other, the welding speed is changed depending on the difference. Therefore, the weld bead having a planned bead height can be formed at an appropriate welding speed.
In the additively manufacturing method, the formation of the weld bead is not likely to be affected by a local variation in height.
In the additively manufacturing method, the bead height is accurately acquired for each layer of the weld bead or for each bead formation path, and the weld bead having a height close to a planned height can be formed with higher accuracy as compared to a case where a plurality of weld beads are collectively measured to adjust the bead height.
In the additively manufacturing method, the welding speed can be corrected to a welding speed for reducing the error of the weld bead from the planned height.
In the additively manufacturing method, by acquiring the difference between the planned height and the actual height in a region where the variation in bead height is relatively large, the height can be adjusted as planned over the entire weld bead.
In the additive manufacturing device, the reference welding speed is set based on the measured value of the filler metal feed speed, and the welding speed obtained by correcting the set reference welding speed such that the height of the weld bead is appropriately maintained is determined. When the bead forming unit forms the weld bead at the welding speed, the bead height is adjusted as planned, and an additively manufactured object having a high shape accuracy can be obtained.
In the program, the reference welding speed is set based on the measured value of the filler metal feed speed, and the welding speed obtained by correcting the set reference welding speed such that the height of the weld bead is appropriately maintained is determined. When the weld bead is formed at the welding speed, the bead height is adjusted as planned, and an additively manufactured object having a high shape accuracy can be obtained.
The present application is based on Japanese patent application No. 2021-070002 filed on Apr. 16, 2021, the content of which is incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-070002 | Apr 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/017744 | 4/13/2022 | WO |
