JP3263631B2 - First layer welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically and adaptively controlling welding conditions at a tacking position in an initial layer welding of arc welding in order to eliminate welding defects such as defective fusion at the tacking position.

[0002]

2. Description of the Related Art Conventionally, first-layer welding after tacking is performed by a welder while monitoring the welding condition, so that not only skill is required but also poor fusion at the beginning and end of the tacking portion. Was easy to produce welding defects. In particular, the initial layer welding of butt welding requires skill, and it is difficult to perform welding from only one side, and it is necessary to gouge the back surface, grind the back surface, and perform welding after shaping. Recently, there have been many cases where welding is performed by automatic machines or robots.However, since welding is performed under constant welding conditions regardless of the presence of a tacked portion, single-side welding cannot be performed. The mainstream is welding excluding the first layer and welding to members that do not require much quality.

[0003]

SUMMARY OF THE INVENTION In view of the above technical problems, the present invention has been developed in order to perform high-quality first layer welding. The present invention is to provide a first layer welding method capable of performing welding under optimum welding conditions by changing welding conditions at an end portion. To explain in more detail, the present invention sets welding conditions such as welding speed, welding current, welding voltage and the like to the optimum conditions of the starting portion at the moment when the tacking bead is overlapped with the starting end of the tacking bead. On the tacking bead, the optimal welding conditions according to the height of the tacking bead, and immediately before the end of the tacking, the optimal welding conditions at the end of the tacking are the original welding conditions if the tacking bead disappears. And automatically controls the welding conditions to be always optimal.

[0004]

First, a first related aspect of the present invention.
The technology relates to a method of automatically controlling the welding conditions at the tacking position (starting point, tacking part, end part) at the time of arc welding or other first layer welding before welding, and optically in the welding line direction. While moving the system detecting means (for example, laser slit optical sensor or laser sensor) with a traveling carriage or a robot, the cross section of the groove is captured by a light cutting method in which light scanning is performed across the groove, and from now on, a temporary bead The height is obtained by an image processing apparatus, and the presence or absence of the tacking is determined by a computer by relative comparison with the portion without the tacking bead, and this is determined at the tacking position (starting end, tacking portion, end end). The teaching data is prepared in advance by selecting conditions that become the optimum welding conditions, stored in a memory in the computer for each of the temporary bead positions, and after the pre-sensing is completed, the temporary mounting position is determined based on the teaching data. of It is intended to play back control of the contact.

Next, a second related art of the present invention relates to a method of automatically controlling during welding, and optically scans the groove by an optical system detecting means in the forward direction of welding during welding. The groove section is captured by the light cutting method, the height of the tacking bead is determined from this by an image processing device, and the presence or absence of the tacking is determined by a computer by comparing with the portion without the tacking bead. The optimum welding conditions are selected for each traveling position and tacking bead position, teaching data is created in advance, and when the welding reaches the sensor sensing position, welding at the tacking position is performed using the welding conditions at that position. Is controlled by playback.

According to the first aspect of the present invention , an image pickup means such as a visual sensor is used in place of the light cutting method. In the method of automatically controlling the welding conditions of the part and the end part during welding, the groove at the front position in the welding progress direction during welding
The welding condition of the tacked bead is imaged by the imaging means, the distance to the base material is measured by a distance meter, and the height of the tacked bead is determined from these by an image processing device. The computer is used to determine the presence or absence of tacking relative to the part, and the optimum welding conditions are selected for each tacking bead position, and the welding at the tacking position is controlled based on the welding conditions. And

According to a second aspect of the present invention , an arc sensor for controlling a welding current to be constant without using a light cutting method or a visual sensor is used. , The tacking position (start, tacking, end)
In the method of automatically controlling the welding conditions during welding,
During welding, the distance to the upper surface of the base material is measured with a distance meter together with the welding current, and while controlling the protrusion length of the welding torch using an arc sensor that controls the current to be constant, Measure the distance from the top surface of the base material with the distance sensor, and determine the distance to the base material in the part without the tack bead and the tack.
The height of the tacked bead is determined from the difference in the distance to the base metal of the portion where the bead is located, and the optimum welding conditions are selected for each position of the tacked bead based on the tacked bead height. Is used to control the welding at the tacking position.

Next, the operation of the present invention and related technologies will be described.
First, the welding condition is imaged by an optical sensor such as a laser slit optical sensor or a laser sensor or a visual sensor, and the groove shape and the height of a temporary bead placed therein are calculated and processed by image processing. Calculate the height of the tack bead. In addition, while controlling the protrusion length of the welding torch using an arc sensor, the distance to the upper surface of the base material is measured by a distance sensor, and the temporary bead height is obtained from the difference in distance from the base material. You may. On the other hand, in advance, the optimal welding conditions according to the bead height at the beginning and end of the tacking and the bead height on the tacking part are compiled in a database, and this is determined according to the bead height at each tacking position. To select the optimum welding conditions from the database and perform welding with the values.

According to this method, the height of the tacking bead can be determined by the image processing apparatus, and welding can be performed under the optimum welding conditions corresponding to each tacking state. That is, the “plate thickness” T (Xi) at the traveling position Xi is compared with the “height from the base material surface to the groove bottom surface (or the tacking bead surface)” h (Xi), and T (Xi−1) ) ≒ h (Xi−1) & T (Xi) ≒ h (Xi) (1) If (here, i−1 represents the previous traveling position, the same applies hereinafter), it is determined that there is no tacking. If T (Xi)> h (Xi) (2), it can be determined that there is a temporary attachment. In this case, the tacked bead thickness Bt (Xi) is obtained by Bt (Xi) = T (Xi) -h (Xi) (3). Here, the tacked bead start end position Xis is a condition when T (Xis-1) ≒ h (Xis-1) & T (Xis)> h (Xis) (4), and the tacked bead end position Xie
T (Xie-1)> h (Xie-1) & T (Xie) ≒ h (Xie) (5)

In addition, the position Xim on the tacking bead is determined as follows: T (Xim-1)> h (Xim-1) & T (Xim)> h (Xim) (6) Thus, the presence or absence of the temporary attachment and its positional relationship can be determined. In addition, according to this judgment result, the database of welding conditions is provided for each of {1} no tacking, {2} tacking start end, {3} tacking portion, and {4} tacking end. Welding conditions corresponding to each can be selected. At this time, by storing a database of welding conditions according to the tacking bead height on the tacking portion, it is possible to output optimal conditions according to the height.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.

First, a first relation for understanding the present invention.
The technology will be described. FIG. 1 is a control block diagram of a first comparison, showing an example of a method of controlling before welding. Reference numeral 1 denotes a welding torch, which is configured so that welding conditions can be automatically controlled by a welding machine 13 via an overall control panel 11 as described later. The welding torch 1 is attached to a traveling device 15 and is configured to be able to move in three X-axis directions and weaving operation by a servo motor control panel 9 via an overall control panel 11.

Reference numeral 2 denotes a welding wire projecting from the tip of the welding torch 1, 3 denotes a welding arc, 4 denotes a first layer welding bead laid on a groove 5, 5 denotes a base material 5A, 5A a groove of a joint portion, and 14 denotes a groove. The molten pool, 16 is a temporary bead provided at an appropriate position of the groove 5,
Reference numeral 17 denotes a laser slit light irradiating unit that irradiates the laser slit light in a direction perpendicular to the welding direction so as to cross the groove 5, and the light shielding filter 7 is attached from a direction inclined by a predetermined angle from the irradiation direction. The light is received by the CCD camera 6 and the cross section of the groove is captured by a light cutting method. The laser slit light irradiating section 17 and the CCD camera 6 are integrally formed with the XY
It is attached to the Z three-axis moving part, and is configured to be movable in the direction of the welding line at the center of the groove 5. The signal from the CCD camera 6 is taken into the image processing device 10, where it is subjected to arithmetic processing so as to capture the groove section by the light cutting method, and the TV monitor 1
2 is received. Reference numeral 8 denotes a camera control panel.

Next, a control operation based on such a configuration will be described. After tacking, and before the first layer welding, the traveling device 15
While moving with a robot (or a robot) or the like, a laser beam is scanned across the groove 5 by the laser slit light sensors (17, 6), and a groove section is captured by a light cutting method as shown in FIG. The height h of the temporary bead 16 is determined by the image processing apparatus 10.

Here, as shown in FIG.
6B, the average bead height h of the portion without the tacking bead 16 becomes equal to the plate thickness T, and the tacking bead is compared with the portion with the tacking bead 16 in FIG. When there is 16, the average bead height h is a value smaller than the plate thickness T, and it can be determined whether or not there is a temporary attachment. The average bead height h is the left end (X
bl, Ybl) to the right end (Xbr, Ybr) and the difference between the coordinate value of (Ytl + Ytr) / 2 on the upper surface of the groove.

At this time, the light cutting line in the light cutting method is an image obtained by observing the image radiated by the laser slit light irradiating section 17 from the CCD camera 6 at an oblique angle. Because the magnification ratio of the value is different, the camera coordinate system
It is needless to say that the coordinate system is used after being converted to the above coordinate system. Similarly, the laser slit optical sensors (17, 6) also convert the rotation angle θ of the mirror and the distance r from the mirror imaged on the CCD device by the diffused light from the base material 5A to the base material 5A into XY coordinates. , A conversion from the camera coordinate system to the actual mm coordinate system is required. This is determined by the computer of the overall control panel 11, and as shown in FIG. 5, this is determined for each traveling position of the traveling device 15 by the position of the tacking bead 16, ie, {1} non-temporarily attaching portions 21, {2}. } The tacking start end 16a, {4} tacking upper portion 16b, and {3} tacking end portion 16c are determined.

That is, the "plate thickness" T (Xi) at the traveling position Xi (the current traveling position is represented by Xi) and the "height from the surface of the base material 5A to the bottom surface of the groove 5 (or the surface of the tacking bead 16)". H (Xi), T (Xi-1) ≒ h (Xi-1) & T (Xi) ≒ h (Xi) (1) If T (Xi-1) ≒ h (Xi) ≒ h (Xi) Xi)> h (Xi) (2) If it is, it can be determined that the portion has a temporary attachment, that is, the temporary attachment bead 16. In this case, the tacked bead thickness Bt (Xi) is obtained by Bt (Xi) = T (Xi) -h (Xi) (3).

Here, the starting end 16a of the tacking bead 16
Xis is a condition when T (Xis-1) ≒ h (Xis-1) & T (Xis)> h (Xis) (4), and the end 1 of the tacking bead 16
Xie of 6c is as follows: T (Xie-1)> h (Xie-1) & T (Xie) ≒ h (Xie) (5) The position Xim of the tacked upper portion 16b is determined as follows: T (Xim-1)> h (Xim-1) & T (Xim)> h (Xim) (6) This makes it possible to determine the presence or absence of the temporary bead 16 and its positional relationship.

Also, a database of welding conditions is stored in each of the {1} non-temporary attachment portion 21, the {2} temporary attachment start end portion 16a, the {4} temporary attachment upper portion 16b, and the {3} temporary attachment end portion 16c. Therefore, the corresponding welding conditions are selected according to each judgment result. At this time, in {4} tacking upper part 16b,
By having a database of welding conditions according to the temporary bead height h, it is possible to output optimum conditions according to the height. The optimum welding conditions held in the database are welding speed ν, current Α, voltage V, weaving condition Wi of welding torch 1 and the like. The weaving conditions are defined as the weaving width WX shown in FIG. 8 from Xbl to Xbr in FIGS. 6A and 6B, and in the case of the third embodiment described later, the widths Wa and Wb of the lower end of the molten pool 14 in FIG. Is obtained, and the weaving width WX can be controlled by controlling the value in proportion to this.

Based on the above, teaching data is selected from the database in accordance with the state of the temporary attachment, and data necessary for moving a robot or the like, such as welding conditions including operation data, is stored for each welding travel position. Is prepared in advance and stored in a memory in the computer for each traveling position Xi. After completion of the pre-sensing, the welding is performed by the welding machine 13 via the overall control panel 11 based on the teaching data. Playback control is performed by the servo motor control panel 9. At this time, the traveling position Xi and the sensing position have a sensing position deviation Ls as shown in FIG. 1, and the traveling position Xi ′ (Xi ′ = Xi) taking this Ls into account.
+ Ls), it is necessary to record data and correct the deviation of the sensing position. At the time of sensing, the traveling position Xi is changed from (Xi-Ls) to (Xend-Ls
) (Where Xend: welding end point position).

Further, as shown in FIG.
The welding torch 1 is moved by the vertical shaft 18 according to the thickness Bt of the base material 6 (in the case of an articulated robot, an arbitrary axis is moved to
By moving the welding wire 2 above the surface A (by the height of the bead), the protrusion length L of the welding wire 2 can be made constant and welding can be stably performed. In other words, FIG.
8B shows a simulation diagram during welding of the tacking upper portion 16b. In the tacking upper portion 16b, the height Yb of the vertical shaft 18 is (Yb = Ya +
Bt).

Here, the tacking bead thickness Bt is equal to the plate thickness T.
From the relationship between and the average bead height h, Bt = T−h (8) Further, the weaving width WX shown in FIG.
Is obtained by calculating Xbr-Xbl in FIG. 6 and controlling with a value proportional to Xbr-Xbl, so that weaving width control is also possible. In this way, the height position Yb of the vertical axis is obtained as Yb (Xi) for each traveling position, and this is stored as teaching data, and stable welding can be performed by performing playback control.

Next, a second related technique will be described.
FIG. 2 is a control block diagram of a second related technology of the present invention ,
One example of a control method during welding is shown. To explain the difference between FIG. 2 and FIG. 1, a laser slit optical sensor (17, 6)
Further, a laser sensor 20 and a laser sensor control panel 19 are used instead of the camera control panel 8. The laser sensor 20 scans the laser spot light so as to cross the groove 5 by rotating the laser spot light by a predetermined angle by a scanning mirror such as a polygon mirror, and then receives irregularly reflected light from the base material 5A by a built-in CCD element. The sensor attempts to obtain a groove cross-sectional shape based on the rotation position of the scanning mirror and the light receiving position of the CCD element. Similarly to the laser slit optical sensor, the laser sensor 20 is also driven by the rotation angle θ of the deflecting mirror and the irregularly reflected light from the base material 5A.
It is necessary to convert the distance r from the mirror imaged on the CD element to the base material 5A into XY coordinates, and from the camera coordinate system to the actual mm coordinate system).

The control operation of this embodiment is the same as that of the embodiment shown in FIG. 1 and will not be described in detail. A laser sensor 20 is disposed on the laser beam, and the laser beam is scanned across the groove 5 by the laser sensor 20 while moving the laser sensor 20 in the welding line direction by the traveling device 15 (or a robot) or the like. The height of the tacking bead 16 is determined by the image processing apparatus 10 from this, and the presence or absence of the tacking is determined by a computer by comparing the height with the portion without the tacking bead 16. When the welding torch 1 reaches the sensing position of the sensor 20, the optimal welding conditions are selected for each traveling position (the position of the tacking bead) and teaching data is created in advance. The over switch 1 is for playback control.

That is, the playback control is performed on the welding torch 1
Of the welding time (welding speed ν, current A, voltage V, weaving condition of the welding torch 1) from the database according to the state of the tacking bead 16 thickness Bt using the time delay of the welding to reach the sensing position of the sensor 20. Wi etc.)
Is selected and teaching data is created in advance, and the travel position Xi
The welding conditions are stored in a memory in the computer every time, and the welding conditions are controlled by the welding machine 13 through the overall control panel 11 based on the teaching data for which the pre-sensing is completed. Is what you do. At this time, the traveling position Xi and the sensing position are shown in FIG.
As shown in the figure, there is a sensing position shift Ls, and this Ls
It is necessary to record the data as the traveling position Xi ′ (Xi ′ = Xi + Ls) in consideration of the above, and to correct the deviation of the sensing position.

That is, first, the running position is sensed from Xi-Ls, and teaching data for the sensing distance is obtained up to the welding start position Xi without emitting the arc 3. From here, arc 3 is started and welded to Xend. The welding operation data is based on the current position Xi taught in advance.
"Sensing distance delay control" is performed using the teaching data obtained by sensing Ls before.

Therefore, the major difference between the first embodiment and the second embodiment shown in FIG. 1 is that the former completes all sensing before welding and creates all teaching data before welding. In the latter case, when the arc point reaches the sensing position while sensing in advance by the sensing distance (sensing position shift Ls) and performing sensing by the sensing distance Ls at all times in advance while welding based on the data, the sensing is performed in advance. There is a difference that welding is performed using the data. In this case, the former requires welding time instead of being unaffected by the arc 3. On the other hand, the latter has a difference in that it is susceptible to arcs instead of being able to efficiently perform welding without requiring welding time, and it is necessary to respond to arc light in sensors and image processing.

[0028] Next, a description will be given of a first embodiment of the present invention. FIG. 3 shows a first embodiment corresponding to the first aspect of the present invention.
The control block diagram of embodiment is shown and it is an example of the method of controlling during first layer welding using a visual sensor. Related Techniques in Figure 1
The difference from the technique is that the CCD camera 6 is used as a visual sensor (a sensor for imaging a welding situation), and the distance meter 23 that can measure the distance HP to the base material 5A such as a laser displacement meter or an eddy current sensor is a CCD camera. 6 together with the XYZ three-axis moving part of the traveling device 15
Is movable in the direction of the welding line at the center of the groove 5, and the distance meter 23
Is configured so that the distance HP to the upper surface of the base material 5A near the groove 5 can be measured. CCD during welding in the forward direction during welding
As shown in FIGS. 7A and 7B, the camera ( visual sensor ) 6 captures images of the welding conditions of the groove 5 without the tacking bead 16 (a) and with the tacking bead 16 (b). The height h of the tacking bead 16 is determined by the image processing apparatus 10.

Here, a welding torch 1, a welding wire 2,
The arc 3, the welding pond 14, and the like can be recognized by the image processing device 10 and the TV monitor 12. Here, the distance from the lower end of the welding torch 1 to the lower end of the welding wire 2 is obtained as the protrusion length L. The vertical shaft 18 is operated so that the protrusion length L is always constant (in the case of an articulated robot, an arbitrary axis is moved to operate vertically so as to have a constant protrusion length from the surface of the base material 5A). Thus, as shown in FIG. 8, the height Y of the vertical shaft 18 is controlled so that the protrusion length La becomes equal to the protrusion length Lb when the temporary bead 16 is present. That is, the height Yb of the vertical axis when there is the tack bead 16 is obtained by the following equation: Yb = Ya + △ L (△ L: change in the projection length L) (9) Next, the presence or absence of the tacking beads 16 is checked from these.

As shown in FIG. 8, the distance HP to the upper surface of the base material 5A is measured by the distance meter 23. Temporary bead 5
Assuming that the distance to the base material 5A in the portion without A is HPa and the distance to the base material 5A in the provisional portion is HPb, the provisional bead thickness Bt is obtained by Bt = HPb−HPa (10) . This is calculated by the computer of the overall control panel 11, and the position of the tacking bead 16 is obtained for each traveling position of the traveling device 15 in the same procedure as in the above embodiment.
, Welding conditions are controlled by the welding machine 13, and the welding torch operation control is performed in real time by the servo motor control panel 9 during welding, and playback control is performed based on the data.

Next, a second embodiment will be described.
FIG. 4 shows a second embodiment corresponding to the second aspect of the present invention .
The control block diagram of embodiment is shown and it is an example of the method of controlling during initial layer welding using an arc sensor. Conventionally, there is an arc sensor that detects a welding current A during welding and controls the current to be constant. Here, it is known that the current A and the protrusion length L are in a proportional relationship. ,
Therefore, in this embodiment, if the current is high, the protrusion is lengthened, and if the current is low, the calculation is controlled by the welding current control panel 22 having an arc sensor function so as to shorten the protrusion, and is controlled via the overall control panel 11. A command is given to the welding machine 13 to perform the first layer welding. Thereby, the protrusion is made constant, and stable welding can be performed.

On the other hand, in order to optimize welding conditions other than the protrusion length at the temporary attachment portion, the presence or absence of the temporary attachment bead 16 is determined by using the distance meter 23 in this embodiment to the upper surface of the base material 5A in the same manner as in the third embodiment. Is measured by the distance meter 23. When the protrusion length control is performed by the arc sensor, the distance between the base material 5A and the portion where there is no tack bead 16 is set to HP.
a, assuming that a distance between the base material 5A and a certain portion of the tacking bead 16 is HPb, the tacking bead thickness Bt is obtained by Bt = HPb−HPa (10).

As described above, the welding sensor 1
Is performed, and the distance from the upper surface of the base material 5A is measured by the distance meter 23 .
Distance HPA to the base material 5A in the non-existing part and the tacking bead
16 to the base material 5A
The difference is determined as the thickness Bt of the tacking bead 16 based on the difference . This is calculated by the computer of the overall control panel 11, and the position of the tacking bead 16 is obtained for each traveling position of the traveling device 15 in the same procedure as in the above embodiment. 13, the welding torch operation control is performed by the servo motor control panel 9 in real time during welding, and playback control is performed based on the data.

[0034]

As described above, according to the present invention,
It is possible to determine the presence or absence of a tack bead by sensing the welding status and perform welding under welding conditions suitable for it, providing high-quality welding and eventually reducing man-hours by unsupervised operation and unmanned welding. Become.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a first related art of the present invention,
An example of a method of controlling before first layer welding using a light section method will be described.

FIG. 2 is a control block diagram of a second related technology of the present invention,
An example of a method of controlling during first layer welding using a light cutting method will be described.

FIG. 3 shows a first embodiment corresponding to the first aspect of the present invention .
The control block diagram of embodiment is shown and it is an example of the method of controlling during first layer welding using a visual sensor.

FIG. 4 shows a second embodiment corresponding to the second aspect of the present invention .
The control block diagram of embodiment is shown and it is an example of the method of controlling during initial layer welding using an arc sensor.

FIG. 5 shows a longitudinal section of the tacking bead in the groove.

FIGS. 6A and 6B are cross-sectional views of a light-cut image groove according to the related art of the present invention shown in FIGS. 1 and 2, wherein FIG.
(B) shows the presence of a tack bead.

FIGS. 7A and 7B are conceptual diagrams of a welding state imaging monitor using a visual sensor according to the first embodiment of the present invention, wherein FIG. 7A shows no temporary beads and FIG.

FIGS. 8A and 8B are conceptual diagrams of a welding situation illustrating a difference depending on the presence or absence of a tack bead, FIG.
Indicates that there is a tack bead.

[Explanation of symbols]

 Reference Signs List 1 welding torch 2 welding wire 3 arc 4 welding bead 5 groove 5A base material 6 CCD camera 7 light shielding filter 8 camera control panel 9 servo motor control panel 10 image processing device 11 overall control panel 12 TV monitor 13 welding machine 14 weld pool 15 Traveling device 16 Temporarily attached bead 17 Laser slit light irradiation unit 18 Vertical axis 19 Laser sensor control panel 20 Laser sensor 21 No temporary attachment 22 Welding current control panel 23 Distance meter

Continuation of the front page (51) Int.Cl. ⁷ identification code FI B23K 9/127 509 B23K 9/127 509A (56) References JP-A-7-266044 (JP, A) JP-A 9-57446 (JP, A) JP-A-5-329646 (JP, A) JP-A-63-84772 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 9/095 B23K 9/127

Claims (2)

(57) [Claims] 1. A method for automatically controlling welding conditions at a tacking position (a start end, a tacked portion, and an end portion) at the time of initial layer welding of arc welding during welding. Bead with groove in front position
Image of the welding condition of the
Measure the distance with a distance meter and calculate the height of the
Is determined by an image processing device, and the part without the tacking beads
And make a computer to determine the presence or absence of tacking
Select the optimal welding conditions for each tacking bead position.
And controlling the welding at the tacking position based on the welding conditions . 2. A method for automatically controlling welding conditions at a tacking position (a starting end, a tacking portion, and an end portion) during initial layer welding of arc welding during welding, together with a welding current during welding. , Distance to the top surface of the base material
And control the current to be constant.
Using a sensor to control the welding torch protrusion length
Control the distance to the top surface of the base material using a distance sensor.
Measure the distance to the base material without the tack bead and the tack
Temporary attachment based on the difference in the distance to the base material of the part with the bead
Find the bead height and temporarily attach it based on the tacked bead height.
Optimum welding conditions are selected for each bead position and
A first layer welding method, characterized in that welding at a tacking position is controlled by contact conditions .