Patent Description:
A technique of controlling a welding robot to manufacture an additively-manufactured object constituted by a multi-layered weld bead is developed (see, for example, Patent Literatures <NUM> and <NUM> and Non-patent Literature <NUM>).

Patent Literature <NUM> describes a method of adjusting a target position, a welding current, a welding voltage, and the like of a welding torch when welding iron poles for construction, by measuring a shape of a welded weld bead in real time with a laser sensor and selecting welding conditions from a database according to the measured bead shape.

Non-patent Literature <NUM> describes a method of adjusting a height and a width of a weld bead to be formed in additive manufacturing with molten wires, by controlling a welding voltage and a welding speed according to a bead shape measured by a laser sensor.

Patent Literature <NUM> describes a method for adjusting a target position for next bead formation in multi-layer welding. In this method, a shape of a weld bead formed on a flat plate is measured, and a bead shape approximation function is obtained from the measurement result. Then, a bead shape prediction function of a weld bead formed when there is an inclined wall plate on both sides of the bead is obtained using this bead shape approximation function.

It is described that the target position for the bead formation is set to either a position of a minimum bead height or a position of an intersection of the bead and the inclined wall plate according to the obtained bead shape prediction function.

<CIT>, according to its abstract, discloses a metal laminating and molding method, wherein a <NUM>-dimensional molded object is formed by sequentially laminating a plurality of metal layers. The metal laminating and molding method is accomplished by repeatedly performing a unit process including a metal layer laminating process of laminating the metal layer constituted by welding beads formed through arc welding and a removal process of removing impurities from a surface of the metal layer laminated in the metal layer laminating process. When the unit process is repeated, the metal layer laminating process is performed again such that a new metal layer is laminated on the surface of the metal layer from which impurities have been removed in the removal process.

As described above, it is necessary to accurately control the width and the height of each weld bead so as to manufacture an additively-manufactured object with high accuracy. Therefore, as in Patent Literature <NUM> and Non-patent Literature <NUM>, when measuring the shape of the formed weld bead and then performing feedback control of the bead formation position, welding conditions, and the like in the next step, in order to shorten a tact time of the step, the measurement is required to be in real time and in a high speed. However, in general, when measuring the bead shape using a laser sensor, variation in detected values is generally large due to light receiving sensitivity of the sensor, linearity of the bead, and the like. Therefore, it takes time to perform stable measurement, and it is difficult to speed up the measurement.

When controlling a tip position of a welding torch to form the weld bead, a groove can be used in normal groove welding to enable highly accurate positioning. However, when manufacturing an additively-manufactured object by padding, there is no absolute positioning reference such as a groove. Therefore, the bead shape approximation function cannot be obtained based on the position of the inclined side plate arranged on both sides of the bead as in Patent Literature <NUM>. In addition, the approximation calculation of the bead shape becomes complicated, approximation accuracy is lowered, and accuracy of the predicted bead shape is lowered. Furthermore, since the formed weld bead changes depending on conditions such as a protrusion length of a welding wire (filler metal) that protrudes from a tip of the torch, and a close distance to a surrounding bead, the target position for the bead formation may be displaced, or welding may become unstable due to adhesion of spatter.

Accordingly, an object of the present invention is to provide an additive manufacturing method capable of accurately obtaining the target position for the bead formation and manufacturing an additively-manufactured object with high accuracy.

According to the present invention, an additive manufacturing method of depositing weld beads formed by melting and solidifying a filler metal while moving a welding torch attached to a robot tip shaft is defined in claim <NUM>, the additive manufacturing method including:.

Further preferred embodiment of the present invention are defined in the dependent claims.

According to the present invention, the target position for the bead formation can be obtained correctly, and the additively-manufactured object can be manufactured with high accuracy.

Here, a procedure for manufacturing an additively-manufactured object constituted by a plurality of layers of weld beads using an additive manufacturing device that deposits the weld beads formed by melting and solidifying a filler metal will be described.

<FIG> is a configuration diagram of an additively-manufactured object manufacturing device.

An additive manufacturing device <NUM> having this configuration includes a manufacturing device <NUM>, a controller <NUM> that performs integrated control of the manufacturing device <NUM>, and a power supply device <NUM>.

The manufacturing device <NUM> includes a welding robot <NUM> including a tip shaft provided with a welding torch <NUM>, and a filler metal supply unit <NUM> that supplies a filler metal (welding wire) M to the welding torch <NUM>. The manufacturing device <NUM> forms a weld bead B while the welding robot driving the welding torch <NUM> to move.

The tip shaft of the welding robot <NUM> is provided with a non-contact shape sensor that moves integrally with the welding torch <NUM>. As the non-contact shape sensor, a laser shape sensor <NUM> that detects a three-dimensional shape by a light section method, a pattern projection method, or the like is used here, but the detection method is not limited.

The welding robot <NUM> is a multi-joint robot, and the welding torch <NUM> attached to the tip shaft of a robot arm is supported so that the filler metal M can be continuously supplied. A position and a posture of the welding torch <NUM> can be freely set three-dimensionally within a range of degrees of freedom of the robot arm.

The welding torch <NUM> includes a shield nozzle (not shown), and a shield gas is supplied from the shield nozzle. An arc welding method may be 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 the additively-manufactured object to be produced.

For example, in the case of the consumable electrode type, a contact tip is disposed inside the shield nozzle, and the contact tip holds the filler metal M to which a melting current is supplied. The welding torch <NUM> holds the filler metal M and generates an arc from a tip of the filler metal M in a shield gas atmosphere. The filler metal M is fed from the filler metal supply unit <NUM> to the welding torch <NUM> by a feeding mechanism (not shown) attached to the robot arm or the like. When the welding torch <NUM> is moved and the continuously fed filler metal M is melted and solidified, the linear weld bead B, which is a melted and solidified body of the filler metal M, is formed on a base portion <NUM>.

The base portion <NUM> is made of a metal plate such as a steel plate, and is basically larger than a bottom surface (lowermost layer surface) of an additively-manufactured object W. Note that the base portion <NUM> is not limited to have a plate-like shape, and may be a block-like, bar-like, columnar-like, or other shape base.

As the filler metal M, any commercially available welding wire can be used. For example, a wire specified by solid wires for MAG and MIG welding of mild steel, high strength steel and low temperature service steel (JISZ <NUM>), flux cored wires for arc welding of mild steel, high strength steel and low temperature service steel (JISZ <NUM>), or the like can be used.

The controller <NUM> includes a CAD/CAM unit <NUM>, a track calculation unit <NUM>, a storage unit <NUM>, and a control unit <NUM> connected to the CAD/CAM unit <NUM>, the track calculation unit <NUM>, and the storage unit <NUM>.

The CAD/CAM unit <NUM> receives shape data (CAD data and the like) of the additively-manufactured object to be produced, and creates a deposition track plan indicating a procedure for manufacturing the additively-manufactured object in cooperation with the track calculation unit <NUM>. This deposition track plan is analytically obtained based on various conditions such as shape, material, and heat input from the input shape data and based on an appropriate algorithm so that deposition can be efficiently performed.

In creating the deposition track plan, first, the shape data is divided into a plurality of layers to generate layer shape data indicating a shape of each layer. Then, a movement track and welding conditions of the welding torch <NUM> are determined according to the generated layer shape data, and a driving program for the welding robot <NUM> and the power supply device <NUM> for forming the weld bead B is generated. This driving program implements operations corresponding to the deposition track plan. Various data such as the driving program and the welding conditions are stored in the storage unit <NUM>.

The control unit <NUM> drives the welding robot <NUM>, the power supply device <NUM>, and the like by executing the driving program stored in the storage unit <NUM>, thereby forming the weld bead B. That is, the control unit <NUM> drives the welding robot <NUM> to move the welding torch <NUM> along the set track of the welding torch <NUM>, and forms the weld bead B by melting the filler metal M protruding from a tip of the welding torch <NUM> with an arc according to the set welding conditions. Then, a plurality of weld beads B are formed on the base portion <NUM> to be adjacent to each other to form a weld bead layer <NUM>, and deposition of a next layer of the welding bead layer <NUM> on this welding bead layer <NUM> is repeated. In this way, the additively-manufactured object W having a desired shape is manufactured.

When the control unit <NUM> moves the welding torch <NUM> for bead formation, the laser shape sensor <NUM> measures a shape of the existing weld bead B that is already formed. The measurement by the laser shape sensor <NUM> may be performed at times other than the welding.

Here, in the additive manufacturing device <NUM> having this configuration, the track calculation unit <NUM> obtains a target position of the welding torch <NUM> for forming the weld bead to be formed next (hereinafter referred to as a torch target position) and welding conditions according to the created deposition track plan and the welding conditions, and a shape measurement result of the existing weld bead during deposition, and changes the deposition track plan and the welding conditions as necessary.

<FIG> is a flow chart showing a procedure for determining the torch target position and the welding conditions for the bead formation from the deposition track plan, the welding conditions, and the shape measurement result of the weld bead.

First, the weld bead is formed according to the deposition track plan created based on the inputted shape data (S <NUM>).

<FIG> is a schematic diagram showing a state of forming the weld bead B.

The welding robot <NUM> is driven to form the weld bead B while moving the welding torch <NUM>. At this time, the laser shape sensor <NUM> provided integrally with the welding torch <NUM> at the tip shaft of the welding robot <NUM> measures the shape of the existing weld bead B at a position downstream of a torch target position P in a welding direction WD.

The laser shape sensor <NUM> includes a laser emitting unit 23A and a detection sensor 23B. For example, when the measurement is performed by a light section method, a slit light L1 is emitted from the laser emitting unit 23A, and a reflected light L2 from the existing weld bead B is detected by the detection sensor 23B, which is an image sensor. A two-dimensional image detected by the detection sensor 23B includes a pattern corresponding to a height of the weld bead, and the shape of the weld bead is obtained from the pattern. Since the specific shape detection method is publicly known, description thereof is omitted here.

<FIG> is a schematic explanatory diagram showing a cross-sectional shape of the weld bead B and a position of the welding torch <NUM> when a welding position is viewed from a downstream side in the welding direction.

In this case, lower-layer weld beads B1, B2, and B3 and a weld bead B4 formed above the weld bead B1 are provided around the torch target position P where the weld bead is formed.

The laser shape sensor <NUM> emits the slit light L1 and detects reflected light from the weld beads B1 to B4 to obtain a shape of each weld bead around a tip of the torch. In <FIG>, from the measured shape of each weld bead, shape information including an apex P1 of the weld bead B2 located directly below an axis Ax of the welding torch <NUM>, and a narrow point P2 connected to a surface of the weld bead B4 disposed on a side of the welding torch <NUM> and a surface of the weld bead B2, is obtained.

<FIG> is a schematic explanatory diagram showing a state of forming a new weld bead along the existing weld beads shown in <FIG>.

According to the shapes of the existing weld beads B1 to B4 around the tip of the welding torch <NUM> shown in <FIG>, a torch target position of a weld bead B5 to be formed next shown in <FIG>, welding conditions during the bead formation, and the like are determined. If there is a difference between setting contents such as the determined torch target position and the welding conditions and setting contents such as the torch movement track in the initial deposition track plan and the welding conditions, the deposition track plan and the welding conditions are changed.

Here, a change procedure for the deposition track plan and the welding conditions described above will be described in detail.

<FIG> is an explanatory diagram showing a basic change procedure in stages (A) to (C) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead. Note that (A) to (C) of <FIG> show the shape in a cross section perpendicular to a longitudinal direction of the weld bead.

First, as shown in (A) of <FIG>, the laser shape sensor <NUM> measures a shape profile Pf of the existing weld bead (S2). Here, for simplification, a measurement example of one weld bead is shown. In addition to a line connecting a plurality of measurement points, the shape profile Pf may be a straight line or a curved line interpolated between the measurement points, or the like.

With reference to the deposition track plan, the torch target position P corresponding to the measured weld bead is extracted. First geometric information of the bead shape is extracted from the measured shape profile Pf and information on the extracted torch target position P (S3). The first geometric information means information including the shape profile Pf and the torch target position P, which are expressed in the same coordinate system by coordinate transformation of the shape profile Pf of the weld bead expressed in a sensor coordinate system by the laser shape sensor <NUM>, and the torch target position P expressed in a robot coordinate system of the welding robot <NUM> (see <FIG>).

Here, in order to make the torch target position P correspond to the shape profile Pf, the following is performed. First, a welding position is obtained in consideration of inclination (posture) of the welding torch <NUM> at a torch tip position on the robot coordinate system of the welding robot. That is, a set value of a distance ΔL (see <FIG>) from the tip of the torch to the existing weld bead directly below is offset to the torch tip position. The offset position is the welding position of the welding torch <NUM>, and this position is defined as the torch target position P. Then, the torch target position P in the robot coordinate system is coordinate-transformed into the sensor coordinate system. In this way, the shape profile Pf of the sensor coordinate system and the torch target position P are associated with each other in the same coordinate system.

Next, second geometric information corresponding to the extracted first geometric information is extracted (S4). Here, the second geometric information is information on a target shape of the weld bead and the torch target position in the deposition track plan used when forming the weld bead whose bead shape is measured as described above.

(B) of <FIG> shows a target shape Ts of the weld bead and the torch target position P defined by the deposition track plan when forming the weld bead having the shape profile Pf shown in (A) of <FIG>.

Then, the first geometric information and the second geometric information are compared with each other to calculate a deviation amount between the two (S5). That is, a deviation amount between the measured shape of the weld bead and the target shape is obtained.

(C) of <FIG> shows a deviation amount ΔH in height between the shape profile Pf shown in (A) of <FIG> and the target shape Ts shown in (B) of <FIG>. The deviation amount ΔH is a height difference between an apex of the shape profile Pf and an apex of the target shape Ts, and the apex of the shape profile Pf is determined using a height of a measurement point near the apex. Note that the shape profile Pf and the target shape Ts here are arranged so that each torch target position P is at the same position.

The deposition track plan is updated by changing at least one of a bead height Bh and a bead width Bw (see <FIG>) in the target shape Ts of the weld bead B defined by the deposition track plan so that the deviation amount ΔH in height is reduced (S6). Here, the deposition track plan may be updated by changing various parameters such as the torch target position and a bead cross-sectional area, in addition to changing the bead height Bh and the bead width Bw.

The welding conditions are changed according to an update result of the deposition track plan (S7). Examples of the welding conditions include a position of the welding torch, a posture of the welding torch, a welding speed, a welding voltage, a welding current, and a feeding speed of the filler metal. At least one of these conditions is changed, or a combination of any two or more is changed.

Then, a weld bead is formed under the changed deposition track plan and welding conditions (S8). The above steps are repeated until the additively-manufactured object is completed (S9).

It is not always necessary to recognize the tip position of the welding torch, the position of the weld bead, and the shape of the existing weld bead. Recognition of the above may be necessary only at a required position, or only one of the above may be preferentially recognized. For example, when manufacturing an additively-manufactured object including weld beads that form a frame and weld beads that fill an inside of the frame, in manufacturing the frame where comparatively thin welding beads are deposited, it is necessary to precisely adjust a position of each bead, so the position and shape described above are always recognized. On the other hand, in manufacturing to fill the inside of the frame, since it is necessary to fill the inside of the frame without gaps, recognition of the cross-sectional area of the weld bead is prioritized over adjusting the torch position.

<FIG> is a cross-sectional diagram showing the shape of the weld bead.

Preferably, the first geometric information and the second geometric information described above include at least one of the bead height Bh, the bead width Bw, a bead cross-sectional area A in the cross section perpendicular to the bead longitudinal direction, a geometric feature point near the torch target position, and a cross-sectional shape approximation curve indicating a bead outer shape of the weld bead B, whose details will be described later.

Here, the geometric feature point is a feature point extracted from the existing weld bead disposed around the welding torch <NUM>, as shown in <FIG>, and includes the apex P1 of a convex shape of the existing weld bead B2 and the narrow point P2 formed by recessing a bead outer surface inward between the weld bead B2 and another weld bead B4 adj acent to the weld bead B2. Before formation of the weld bead B3, between a pair of points P3a and P3b at widthwise end portions of the weld bead B2, the geometric feature point also includes the point P3a that intersects with a lower layer surface (here, the base portion <NUM>) on which the welding bead B2 is formed.

A cross-sectional area of a weld bead for the existing weld bead can also be determined by the welding conditions during the bead formation. The bead cross-sectional area A is equal to a cross-sectional area of a newly introduced metal material for the bead formation. For example, when the weld bead is approximated by an elliptical model, the bead cross-sectional area A changes according to a short axis of the elliptical model and a height from a base (lower layer). Note that the cross-sectional area referred to here means a volume per unit length of the weld bead, and is represented by the following Formula (<NUM>).

A cross-sectional area of the weld bead to be formed next may be obtained by, for example, using an arc centered at the torch target position P as an outline of the weld bead and using an area inside the arc as the cross-sectional area of the weld bead. However, a method for calculating the cross-sectional area is not limited to this.

According to this additive manufacturing method, the deposition track plan is updated according to the difference in bead height between the deposition track plan and an actual weld bead formation result, and the welding conditions are changed accordingly, so that it is possible to form the next weld bead with high accuracy. Since the weld bead is formed according to the deposition track plan based on feedback of the actual bead formation result, it is possible to stably implementing manufacturing with an accuracy of an order of <NUM>, for example.

Next, other change procedures for the deposition track plan and the welding conditions based on the basic change procedure described above will be sequentially described.

<FIG> is an explanatory diagram showing a first change procedure in stages (A) to (C) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead.

A cross-sectional area of the shape profile Pf in the cross section perpendicular to the longitudinal direction of the weld bead shown in (A) of <FIG> is set as Apf, and a cross-sectional area of the target shape Ts of the weld bead defined by the deposition track plan shown in (B) of <FIG> is set as Ats.

In this change procedure, as shown in (C) of <FIG>, a difference Df between the cross-sectional area Apf of the shape profile Pf and the cross-sectional area Ats of the target shape Ts is used as a deviation amount, and the deposition track plan is changed so that this deviation amount is reduced. Then, according to the updated deposition track plan, the welding conditions are changed as necessary.

According to this procedure, since an area difference between the shape profile Pf and the target shape Ts is reduced, even if the shape profile Pf has a locally large shape difference from the target shape Ts, it is possible to appropriately reduce the deviation amount without being greatly affected by this local shape difference.

<FIG> is an explanatory diagram showing a second change procedure in stages (A) to (C) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead.

In this change procedure, as shown in (A) of <FIG>, a cross-sectional shape approximation curve Cpf is obtained by approximating the shape profile to a curve model by regression calculation. Any curve such as a parabola, a cubic or higher function, and a spline curve can be used as the curve model. For example, a curve model of Z = aY<NUM> + bY +c (a, b, and c are coefficients) is used to perform fitting with the measured shape profile Pf (Yj, Zj). For fitting, a publicly known method such as a method of least squares or a method of steepest descent can be adopted.

Then, the cross-sectional shape approximation curve Cpf and the target shape Ts shown in (B) of <FIG> are superimposed with each other to make the torch target positions P match as shown in (C) of <FIG>, and then a distribution of the deviation amount ΔH in height between the cross-sectional shape approximation curve and the target shape is obtained. The deposition track plan is changed so that this deviation amount ΔH is reduced. Then, according to the updated deposition track plan, the welding conditions are changed as necessary.

According to this procedure, since the shape profile is approximated to the curve model, the bead shape can be recognized more precisely, and a bead center position, the bead height, and the like of the shape profile can be obtained more accurately. Therefore, the weld bead to be formed next can be formed with higher accuracy.

<FIG> is an explanatory diagram showing a third change procedure in stages (A) to (C) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead.

In this change procedure, as shown in (A) of <FIG>, the cross-sectional shape approximation curve Cpf obtained by approximating the shape profile to the curve model by regression calculation is set so that a cross-sectional area Ac of a region surrounded by the cross-sectional shape approximation curve Cpf becomes equal to the cross-sectional area Ats of the target shape Ts shown in (B) of <FIG>. For this calculation, for example, a constrained least squares method can be adopted. This constrained least squares method is a method of performing approximation processing under a constraint that the cross-sectional area Ac formed by the cross-sectional shape approximation curve Cpf as a model curve and the cross-sectional area Ats predefined by the deposition track plan match with each other, when minimizing an objective function representing an error amount.

As shown in (C) of <FIG>, the deposition track plan is changed so that a topmost portion Pa of the cross-sectional shape approximation curve Cpf in which the cross-sectional area Ac is equal to the cross-sectional area Ats coincides with the target formation position of the weld bead, which is a topmost portion Pb of the target shape Ts. In other words, the target formation position of the weld bead is corrected so that the topmost portion Pa of the cross-sectional shape approximation curve corresponding to the formed weld bead coincides with the topmost portion Pb of the target shape Ts. Then, according to the updated deposition track plan, the welding conditions are changed as necessary.

According to this procedure, the weld bead to be formed next can be formed with high accuracy by a simple process of matching the topmost portion Pa of the cross-sectional shape approximation curve with the topmost portion Pb of the target shape Ts.

<FIG> is an explanatory diagram showing a fourth change procedure in stages (A) and (B) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead.

In this change procedure, as shown in (A) of <FIG>, the cross-sectional shape approximation curve Cpf is obtained by approximating the shape profile to the curve model by regression calculation.

Next, as shown in (B) of <FIG>, the target formation position of the weld bead is corrected so that the deviation amount ΔH, which is the difference between a height of an optional point on the cross-sectional shape approximation curve Cpf over the entire cross-sectional shape approximation curve Cpf and a height of an outline of the target shape Ts corresponding to the optional point, is reduced. Then, according to the updated deposition track plan, the welding conditions are changed as necessary.

According to this procedure, since the deviation amount ΔH is determined using the cross-sectional shape approximate curve Cpf, the correction can be performed more stably and accurately than when the deviation amount ΔH is determined using the shape profile shown in <FIG>, and the weld bead can be formed with higher accuracy.

<FIG> is an explanatory diagram showing a fifth change procedure in stages (A) and (B) for changing the deposition track plan and the welding conditions for forming the new weld bead according to the shape of the existing weld bead.

In this change procedure, as shown in (A) of <FIG>, the cross-sectional shape approximation curve Cpf obtained by approximating the shape profile to the curve model by regression calculation is changed so that the deviation amount ΔH, which is the difference between the height of an optional point on the cross-sectional shape approximation curve Cpf and the height of the outline of the target shape Ts corresponding to the optional point is reduced as shown in (B) of <FIG>.

The deposition track plan is changed so that the position of the cross-sectional shape approximation curve Cpf matches the target formation position of the weld bead, which is the target shape Ts. That is, the deposition track plan is changed so as to match the topmost portion Pa of the cross-sectional shape approximation curve corresponding to the formed weld bead with the topmost portion Pb of the target shape Ts. Then, according to the updated deposition track plan, the welding conditions are changed as necessary.

According to this procedure, the deviation amount ΔH in the bead height is reduced, and the position of the cross-sectional shape approximation curve Cpf with the reduced deviation amount ΔH in the bead width direction is matched with the target formation position, so that the weld bead to be formed next can be formed with high accuracy.

Next, a method for forming the weld bead with higher accuracy will be described.

In the embodiments described above, the weld bead is formed on the flat base portion, but here, a case where the weld bead is formed on a circumferential surface of the base portion will be described.

<FIG> is an explanatory diagram showing a state of the welding torch <NUM> provided on the welding robot <NUM> forming the lower-layer weld bead B1 and the upper-layer weld bead B2, and the laser shape sensor <NUM> measuring the bead shape.

A cylindrical base portion 25A is rotationally driven in a direction Rt shown in <FIG> about a central axis O, and the weld bead B is formed by the welding torch <NUM> on a circumferential surface of an outer periphery of the base portion 25A. The laser shape sensor <NUM> attached to the welding robot <NUM> is disposed on an upstream side in a rotation direction of the base portion 25A (the downstream side in the welding direction) to measure the shape of the existing weld bead B <NUM>.

The laser shape sensor <NUM> measures the shape of the weld bead B1 from a two-dimensional image obtained by detecting the reflected light L2. The shape is a shape of a bead cross section parallel to the reflected light L2 at a measurement point Pm. The reflected light L2 is parallel to an axis (torch axis) Ax of the welding torch <NUM>. A central angle of an arc connecting the torch target position P on the base portion 25A shown in <FIG> and the measurement point Pm is set as θ.

As the weld bead B2 is formed while rotating the base portion 25A, the weld bead B1 at the measurement point Pm reaches the torch target position P. In this case, the shape of the weld bead B1 measured at the measurement point Pm is not the shape in the cross section including the torch axis Ax, but a shape in a cross section including a straight line Lm inclined rearward in the welding direction by an angle θ from the torch axis Ax.

Therefore, the measured shape of the weld bead B1 is projected and transformed so as to be the shape in the cross section including the torch axis Ax at the torch target position P. Since the projective transformation is a known transformation process for geometrically inclining the angle θ, description of the transformation process is omitted.

Accordingly, the shape of the weld bead measured at the measurement point Pm is converted into a cross-sectional shape corresponding to the position of the torch axis Ax at the torch target position P. As a result, it is possible to change the welding track plan accurately, and to form the weld bead with higher accuracy.

<FIG> is an explanatory diagram showing changes in a welding state by (A) and (B) when there is an error in the measured bead shape.

As shown in (A) of <FIG>, if a measurement error occurs in the shapes of the existing weld beads B2 and B4 near the torch target position P, a distance S1 between the weld bead B2 and a torch tip position and a distance S2 between the weld bead B4 and the target position P will differ from assumed distances. In this case, as shown in (B) of <FIG>, The arc Arc becomes unstable, such as when an actual protrusion length (exposed length) of the filler metal M changes and the arc Arc is displaced according to a distance between the surrounding existing weld bead and the filler metal M. As a result, there is a risk that shape accuracy of the weld bead to be formed is lowered.

<FIG> is a graph schematically showing a change characteristic of the welding current with respect to the protrusion length of the filler metal.

A change in the protrusion length of the filler metal M not only causes the generated arc to become unstable, but also affects the welding current. That is, the longer the protrusion length, the smaller the welding current, and the smaller the formed weld bead tends to be. Therefore, as described above, by measuring the shape of the existing weld bead with high accuracy, fluctuations in the welding conditions can be reduced and a highly accurate weld bead can be formed.

In the above, the shape of the weld bead is expressed using the bead height, the bead width, and the cross-sectional shape approximation curve indicating the bead cross-sectional area the bead outer shape of the weld bead, but parameters indicating the shape are not limited to these.

Claim 1:
An additive manufacturing method of depositing weld beads (B) formed by melting and solidifying a filler metal (M) while moving a welding torch (<NUM>) attached to a robot tip shaft, the additive manufacturing method comprising:
a step of measuring a shape profile (Pf) of an existing weld bead (B) by a non-contact shape sensor provided on the robot tip shaft integrally with the welding torch (<NUM>), during manufacture of an additively-manufactured object (W) by forming the weld beads (B), based on a deposition track plan that defines a target position (P) of the welding torch (<NUM>) and a shape of the weld beads (B);
a step of extracting first geometric information of a bead shape from the shape profile (Pf) and the target position (P) of the welding torch (<NUM>);
a step of extracting second geometric information corresponding to the first geometric information from the deposition track plan and calculating a deviation amount (ΔH) between the first geometric information and the second geometric information;
a step of updating the deposition track plan by changing at least one of a bead height (Bh) and a bead width (Bw) in a cross section perpendicular to a bead longitudinal direction of the weld bead (B) defined by the deposition track plan, according to the deviation amount (ΔH); and
a step of changing a welding condition according to an update result of the deposition track plan, wherein
the first geometric information and the second geometric information include information on at least one of a geometric feature point near the target position (P) of the welding torch (<NUM>), the bead height (Bh), the bead width (Bw), a bead cross-sectional area (A) of the weld bead (B), or a cross-sectional shape approximation curve (Cpf) indicating a bead outer shape of the weld bead (B), and
the geometric feature point includes any one of
an apex (P1) of a convex shape of the existing weld bead (B2),
an end point (P2) of a narrowed portion formed by recessing a bead outer surface inward between the weld bead (B2) and another weld bead (B4) adjacent to the weld bead (B2), or
a point (P3a) where an end portion of the weld bead (B2) in a width direction and a lower layer surface on which the weld bead (B2 is formed intersect.