JP2815301B2 - Stud welding quality judgment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to stud welding and, more particularly, to a method for detecting defects such as poor fusion of stud welds and judging their quality.

[0002]

2. Description of the Related Art In performing stud welding, welding defects may occur due to various factors in a process of joining a stud rod to a material to be welded. Japanese Patent Application Laid-Open No. Sho 49-4978 discloses a method for judging poor welding of such welds during stud welding.
No. 127840 is disclosed. This method captures the stability of the arc current or arc voltage as a primary factor of welding failure, detects the arc current and arc voltage, and when the current value within a set time is equal to or greater than a predetermined value, or when the voltage value is equal to or less than a predetermined value. In this case, the current relay or the voltage relay is operated to detect the welding failure.

A similar technique is disclosed in Japanese Patent Application Laid-Open No. 63-16507.
No. 7 discloses this. This method is a method of detecting an axial movement amount of a stud during stud welding, constantly monitoring the movement amount, and immediately detecting a defective joint due to an insufficient movement amount.

[0004]

The above-mentioned prior art can exert a certain effect in detecting a defective joint, but it has been difficult to detect a fusion defect at a joint. Such a defective fusion defect has a crack 16 formed inside the joint portion 15 as shown in FIG. 4, and there is a possibility that the joint portion may be damaged from this crack in the future.

The above-mentioned defect is not detected by a voltage relay as disclosed in Japanese Patent Application Laid-Open No. 49-127840, and such a defect cannot be removed even if the amount of movement of the stud shaft is sufficiently given. The above defect could not be recognized only by detecting the movement amount as disclosed in JP-A-63-165077. An object of the present invention is to provide a method capable of detecting such a fusion defect and judging a joint defect appropriately.

[0006]

In order to achieve the above object, the present invention provides the following method for determining the quality of a stud weld. That is, the gist of the present invention is that an arc is generated at the tip of the stud rod to be welded and the molten pool is formed, and then, when the stud rod is pushed into the molten pool and welded, the axial movement state of the stud rod is set. In the method of detecting the arc voltage immediately before the pressing of the stud bar is started and detecting the arc voltage at the time of pressing the stud bar, the quality of the stud welding portion is determined by monitoring the arc voltage. An arc voltage within 0.3 seconds before the start of pushing of the stud bar is detected, and when it is monitored that the value of the arc voltage is zero, the quality of the weld is determined to be a poor weld.

[0007]

The inventors of the present invention have conducted various studies on the cause of the above-mentioned defective fusion defect in the stud rod welding portion. As a result, the defect occurs when the arc voltage becomes close to zero immediately before the defect is pushed into the molten pool of the stud rod. This led to the completion of the present invention. That is, in stud welding, an arc is generated between the material to be welded and the stud bar to form a molten pool therebetween, and then, when the stud bar is pushed into the molten pool and joined, the stud bar is When the arc voltage of a predetermined value is lowered simultaneously with the pushing of the stud bar when the stud bar is pushed into the molten pool, and the arc voltage becomes zero when the molten pool of the stud bar comes into contact, the above-described defective fusion defect does not occur. .

However, immediately before the stud rod is pushed into the molten pool, for example, when the molten pool hangs down and is connected (short-circuited) to the stud rod (this phenomenon is particularly encountered in the case of a laterally large diameter stud rod welding). ), The short-circuit current flows, but the arc voltage becomes zero and no arc is generated. In such a state, the outer peripheral portion of the molten pool is cooled, and a solidified region is generated on the surface of the molten pool. When a stud rod is pushed into such a molten pool, as shown in FIG. The stud bars do not fuse, and a crack 16 is formed in the joint 15.

The crack 16 is thus formed when the arc voltage becomes zero immediately before the stud rod is pushed into the molten pool, preferably within at least 0.3 seconds. Even if the stud bar and the molten pool are short-circuited during the arc generation before this time, an arc is often generated again thereafter, and in such a case, a defective fusion defect does not occur.

[0010] Therefore, in order to surely find the defective fusion defect, it is necessary to accurately grasp the stud bar pushing time. Thus, in the present invention, detection of the moving state of the stud bar and detection of the arc voltage are essential requirements. That is, in order to detect a fusion defect defect at the joint, the axial movement state of the stud bar during arc generation is detected, and the arc voltage immediately before the pushing of the stud bar into the molten pool is detected. It is necessary to monitor the fluctuation of the arc voltage.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
FIG. 1 shows a block diagram of a circuit embodying the present invention.
Show. Stud bar 3 set in stud gun 2 is controlled
Pushing and pulling into the workpiece 1 is controlled by the control device 7
Also, the stud bar 3 is moved by the connecting plate 4
Potentiometer provided in the stud gun via
And is linked to the axis 5 of the motor 6. Therefore stud rod
3 is detected by the potentiometer 6. sand
That is, the potentiometer 6 is provided with a constant voltage power supply 61.
The movement of the stud bar is monitored as a voltage value.
Of the A / D converter 12 of the switching device 11 ₁Taken into
You.

A welding power source 8 is connected to the workpiece and the stud gun for generating an arc between the workpiece 1 and the stud bar 3. The on / off of the welding power source is controlled by the control device 7.
Done by A shunt 9 is provided in a circuit between the welding power source and the stud gun, and the arc current value is monitored by the A / D of the monitoring device 11 via the shunt and the amplifier 10.
It is taken into CH _{2 of} converter 12.

The arc voltage value is directly supplied from the +/- terminals of the welding power source 8 to the A / D converter 12 of the monitoring device 11.
CH ₃ Further, the control device 7 and the IO port 14 of the monitoring device 11 are connected,
The measurement start signal from the control device 7 is the I / O port 1
At 4, monitoring is started via the central processing unit 13.

In the above-described apparatus and circuit, the stud gun 2 moves the stud rod 3 to the work 1
After a predetermined time has elapsed, the stud bar 3 is pulled up a predetermined distance to generate an arc. After an arc is generated for a predetermined time and the stud bar 3 and the work 1 are melted to form a molten pool, the stud bar is pushed into the work to be welded in the molten pool.

The movement of pulling and pushing the stud bar 3 is performed based on a command from the control device. A measurement start command is transmitted from the control device to the monitoring device a little before the start of pulling up the stud bar. The arc current value, the voltage value, and the movement of the stud bar (the voltage signal input from the potentiometer is converted into the moving distance) accompanying the operation of the stud bar are measured and displayed on the monitoring screen.

FIGS. 2 and 3 show a stud bar (diameter 19 mm, length 1000 mm) on a pipe with an arc current of 1573.
3A, arc voltage 40V, arc time: 0.84 seconds, stud rod pulling distance: 2.42 mm, pushing distance: 6.5
7 shows a monitoring screen when stud welding is performed under a condition of 6 mm. In the embodiment shown in FIG. 2, the voltage dropped at the same time as the stud rod was pushed in. Therefore, there was no short circuit between the stud rod and the molten pool, and no defective fusion defect occurred in the welded portion.

On the other hand, in the embodiment of FIG. 3, the voltage becomes zero 0.12 seconds before the start of pushing of the stud bar, a short circuit occurs between the stud bar and the molten pool, and a defective fusion defect occurs in the welded portion. Was. Therefore, by observing the movement of the arc voltage immediately before the stud rod is pushed into each stud welding portion on the monitoring screen, it is possible to reliably know the fusion defect of the welding portion. When the stud welding portion is determined to be defective, stud welding is performed again or repair welding is performed using a manual welding rod.

[0018]

As described above, according to the method of the present invention, it is possible to surely know the fusion defect of the welded portion, which was difficult to confirm conventionally, during the stud welding. The industrial effect is enormous.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a monitoring screen obtained by the method of the present invention, showing a case where no defective fusion defect occurs.

FIG. 3 is a monitoring screen obtained by the method of the present invention, showing a case where a defective fusion defect occurs.

FIG. 4 is a partial cross-sectional front view showing a joint in a state where a defective fusion defect has occurred.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Material to be welded 2 ... Stud gun 3 ... Stud rod 4 ... Connecting plate 5 ... Shaft 6 ... Potentiometer 7 ... Stud gun control device 8 ... Welding power supply 9 ... Shunt 10 ... Amplifier 11 ... Monitoring device 12 ... A / D converter 13 central processing unit 14 IO port 15 joint 16 defective fusion defect

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-58-25877 (JP, A) JP-A-1-154877 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 9/20 B23K 9/073 550 B23K 9/095 515 B23K 31/00

Claims (3)

(57) [Claims] 1. An arc is generated at the tip of a stud rod and a material to be welded, and after forming a molten pool, when the stud rod is pushed into the molten pool and welded, an axial movement state of the stud rod is detected. Detecting the arc voltage immediately before the pushing of the stud bar is started, and judging the quality of the stud weld by monitoring the arc voltage at the time of pushing the stud bar. Quality judgment method. 2. The method for judging quality of stud welding according to claim 1, wherein an arc voltage within 0.3 seconds before the start of pushing of the stud bar is detected. 3. The method for judging quality of stud welding according to claim 1, wherein when it is detected that the value of the arc voltage immediately before the start of pushing of the stud bar is zero, the welded portion is judged to be defective in welding.