JPH07276075A - Method for detecting abnormality at welding time - Google Patents

Abstract

PURPOSE:To securely detect welding abnormality even when a welded material is a thin plate by periodically measuring a current value and a voltage value at welding time and finding how many times the difference between a measured value at a certain time of time and a subsequently measured value exceeds a reference value. CONSTITUTION:An arithmetic part 20 averages current values and voltage values measured by a measurement part 17 at specific intervals. The arithmetic part 20 calculates the absolute value of the difference between the 1st voltage value and subsequent voltage values. When the value exceeds the reference value more than a specific number of times, welding abnormality is decided. A 1st and a 2nd reference values are set and a specific time and a specific frequency are set corresponding to both the reference values to securely detect two kinds of welding abnormality differing in voltage variation pattern. With the 1st reference value, welding abnormality like a melting fall where large voltage variation is caused as a single shot in a short time is detected. With the 2nd reference value, welding abnormality such as decentering and unevenness of beads wherein small voltage variation is caused successively many times in a long time is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting abnormality during welding, and more particularly to a method for detecting abnormality during welding when performing DC TIG welding.

[0002]

2. Description of the Related Art When an abnormality occurs during welding, it is useful to accurately detect the abnormality and take some measures to improve the quality of welding. In DC TIG welding, there is a method of continuously measuring the current and voltage at the time of welding and detecting a place where the measured value deviates from a certain range as an abnormal portion of welding.

Specifically, since the TIG welding power source has a constant current characteristic, for example, when the material to be welded immediately below the arc is burnt out, the arc length becomes long, and as a result, the voltage rises rapidly even though the current is constant. From this, it is possible to detect that an abnormal portion of welding has occurred.

[0004]

Since this change in voltage corresponds to the change in arc length, even if there is no abnormal welding, there is a deviation in the set height of the material to be welded, wear of the electrode rod, The voltage also changes due to floating of the material to be welded during welding. Therefore, in such a case, it is necessary to provide a dead zone within a certain voltage range so that it is not determined to be abnormal.

However, when the material to be welded is a thin plate, the applied welding current and voltage are low, and the size of defects such as burn-through is also small. As a result, the voltage does not change even if an abnormality occurs. It will be small. Therefore, when an abnormality occurs, the voltage range, that is, the dead zone may not be exceeded, and there is a problem that the abnormality cannot be detected.

For example, FIG. 3 shows an example of a welding current value and a voltage value detected during TIG welding of a thin plate.
An allowable upper limit value and an allowable lower limit value are set for each. During welding, the current value shifts at a constant value as shown. Since the voltage value fluctuates due to various causes as described above, it is necessary to provide a certain range between the upper limit value and the lower limit value so that the fluctuation is not regarded as an abnormality. However, in this case, when the voltage values fluctuate due to the anomalies 1 to 4 as shown in the figure, the anomalies 1 and 4 can be detected because the voltage values at that time deviate from the upper limit value and the lower limit value. The anomaly 2 and the anomaly 3 have a problem that the voltage value at that time does not deviate from the upper limit value or the lower limit value, so that this cannot be detected as an abnormality.

Therefore, the present invention solves such a problem, and when the size of the defect of welding abnormality is small due to the fact that the material to be welded is a thin plate or the like, the voltage change at that time is small. The purpose is to ensure that this welding abnormality can be detected.

[0008]

In order to achieve this object, the method of the present invention measures the voltage value at the time of welding cyclically a plurality of times, and the voltage value measured at a certain time is compared with other values thereafter. When the absolute value of the difference from the measured voltage value exceeds the reference value for a predetermined number of times or more within the predetermined time after the time point, it is determined that the welding is abnormal.

Further, according to the present invention, the first reference value and the second reference value smaller than the first reference value are set,
A first predetermined time and a first predetermined number of times are set corresponding to the first reference value, and a second predetermined time longer than the first predetermined time is set corresponding to the second reference value. Time and the first
And a second predetermined number of times greater than the predetermined number of times is set, and the absolute value of the difference exceeds the first reference value within the first predetermined time, the first predetermined number of times or more, If the absolute value of the difference exceeds the second reference value and the second predetermined number of times or more occur within the second predetermined time, it may be determined that the welding is abnormal. it can.

Furthermore, in the present invention, the allowable upper limit value and the allowable lower limit value are set for the current value and the voltage value during welding, respectively,
The current value during welding is also measured periodically multiple times,
It is to be determined that welding is abnormal even when at least one of the measured current value and the measured voltage value continuously deviates from the allowable upper limit value to the allowable lower limit value within a certain time from a certain point in time. You can

[0011]

In this way, the reference value can be set with a magnitude corresponding to the voltage change at the time of an abnormal condition to be detected, regardless of the allowable upper limit value and the allowable lower limit value of the voltage value.
This abnormality will be reliably detected. In addition, since the welding abnormality is judged only when the reference value is exceeded a predetermined number of times within a predetermined time set in advance, these are determined according to the pattern of voltage fluctuation that can usually occur when the abnormality exists. By setting the predetermined time and the number of times, it is possible to reduce the possibility of false detection.

Setting a first reference value and a second reference value,
By setting the predetermined time and the predetermined number of times corresponding to the respective reference values, both two types of welding abnormalities having different voltage fluctuation patterns can be reliably detected. Specifically, the first reference value is used to detect a welding abnormality such as burn-out that occurs during a relatively short time in which a large voltage change occurs,
Further, the second reference value is used to detect a welding abnormality such as off-centering or uneven bead, in which a small voltage change occurs continuously a number of times in a relatively long time.

By detecting that the current value and the voltage value at the time of welding deviate from the permissible upper limit value or the permissible lower limit value, it is determined that there is an abnormality when any one of the abnormalities is detected, Various abnormalities that may occur during welding are reliably detected.

[0014]

FIG. 2 shows the schematic construction of a welding apparatus for carrying out the method of the present invention. Here, 11 is a TIG welding machine, the welding torch 13 is electrically connected to the torch side terminal 12, and the ground side terminal 14 is made of a thin material to be welded.
15 are electrically connected. The TIG welding machine 11 is provided with a protective device 16 in parallel.
The voltage measuring unit 17 is connected. This current / voltage measuring unit
In FIG. 17, 18 is a voltage measuring terminal and 19 is a current measuring terminal. The current / voltage measuring unit 17 is connected to the calculating unit 20, and the calculating unit 20 is further connected to the recording unit 21. A display lamp 22 is arranged in parallel on the recording unit 21.

FIG. 1 shows changes in the current value and the voltage value measured by the measuring section 17 during welding work, and the horizontal axis thereof represents the elapsed time from the arc start time, that is, the position of the weld section from the start point. The measuring unit 17 can continuously measure the current value and the voltage value at a pitch of 0.001 seconds.

The arithmetic unit 20 can average the current value and the voltage value measured by the measuring unit 17 at intervals of 0.1 second, and can give a serial number to each average value immediately after the arc start. Here, the i-th current value is Ai and the i-th voltage value is Vi. Further, the calculation unit 20 determines that the i-th voltage value V
i, and the i + jth and i-th after the i-th
The absolute value of the difference between the + kth voltage value V (i + j) and V (i + k), that is, | Vi−V (i + j) | and | Vi−V (i +
k) | can be calculated respectively.

Further, the arithmetic unit 20 determines whether or not the following conditions (1) to (4) are satisfied. That is, (1) Ai <lower limit value or Ai> upper limit value is
Whether it occurred continuously for a certain time t1 seconds or more (2) Vi <allowable lower limit value, or Vi> allowable upper limit value,
Whether it occurs continuously for a fixed time t2 seconds or more (3) Whether it becomes | Vi-V (i + j) |> (first reference value) n times or more at the first predetermined time t3 (4) It is determined whether or not | Vi−V (i + k) |> (second reference value) has occurred m times or more in the second predetermined time t4.

Here, the allowable upper and lower limit values of the current value and the voltage value, the times t1, t2, etc. can be set in the calculation unit 20 based on the plate thickness of the workpiece 15 and the welding conditions. The j value and the k value, the first and second reference values, the times t3 and t4, the numbers of times n and m, and the like can be similarly set.

In the conditions (3) and (4), the second reference value is set to a value smaller than the first reference value, the second predetermined time t4 is set longer than the first predetermined time t3, The second predetermined number of times m is set to a value larger than the first predetermined number of times n. The reason why the different conditions are set in this way is to reliably detect two types of welding abnormalities having different voltage fluctuation patterns, as will be described later. Therefore, in the conditions (3) and (4), the j value and the k value are set separately. The j value and the k value are constants determined by the minimum defect size generated based on the plate thickness of the material 15 to be welded and the welding speed at that time, and are obtained by confirmation experiments.

When any one of the conditions (1) to (4) is satisfied, it is determined that a welding abnormality has occurred. Further, these detection results are recorded in the recording unit 21, and if it is detected that an abnormality has occurred, the display lamp 22 is turned on at that time and the operator is notified of that fact.

Next, a specific example will be described with reference to FIG. It is assumed that the materials 15 to be welded having a thickness of 1.0 mm are butt-welded with each other, and the welding condition is a welding current of 100 A,
The welding speed is 900 mm / min. In addition, condition (1)-
With respect to (4), the following values are input to the arithmetic unit 20.・ Regarding condition (1), allowable upper limit of current value 105A, allowable lower limit of current value 95A, constant time t1 2 seconds ・ Regarding condition (2), allowable upper limit of voltage value 13V, allowable lower limit value of voltage 10V, constant time t2 2 seconds -Regarding condition (3), first reference value 0.8V j value 4 First predetermined time t3 3 seconds First predetermined number of times n 1 times-Regarding condition (4) second reference value 0.4V k value 2 Second predetermined time t4 8 seconds Second predetermined number of times m 3 times In FIG. 1, whether welding is being performed on the work material 15 at an appropriate welding current value, that is, the welding current value is its allowable upper limit value. Is 105A and the lower limit is 95A
It is determined by the condition (1) whether or not it falls within the range between and. For example, during welding, the current value increases for some reason as shown in part A of the figure, and if it exceeds the allowable upper limit value, burn-through occurs. Therefore, if the state of exceeding the permissible upper limit continues for a certain time t1 or 2 seconds or more,
It is determined that the welding is abnormal, the fact is recorded in the recording unit 21, and the display lamp 22 is turned on. At this time, as shown in the section B, the voltage value simultaneously exceeds the allowable upper limit value of 13 V, and therefore the condition (2) is also satisfied. Therefore, by detecting the establishment of any of these conditions (1) and (2), it is possible to detect the occurrence of welding abnormality at this time.

Whether or not welding is being performed on the material 15 to be welded at an appropriate welding voltage value, that is, the welding voltage value falls within the range between its allowable upper limit value of 13V and its allowable lower limit value of 10V. It is determined by the above condition (2). Material to be welded 15 and welding torch 13 during welding
If there is a gradual deviation in the height direction between the and, that is, if there is a gradual deviation in the set height of the material to be welded 15 or the consumption of the electrode rod, these exceed a certain amount. If this happens, poor fusion will occur and welding will be abnormal. That is,
In this case, if the welding voltage exceeds the permissible upper limit value as shown in part D of FIG. 1 and the state continues for 2 seconds or more, which is the constant time t2, it is determined that the welding is abnormal.

The portion C in FIG. 1 is the material to be welded 15 during welding.
And a welding torch 13 when a deviation in the height direction occurs abruptly, that is, the deviation of the set height of the material 15 to be welded, the rise of the material to be welded, etc. . If these exceed a certain amount, the bead shape becomes defective and the welding becomes abnormal. In this case, based on the condition (3), the i-th voltage value Vi, that is, the voltage value before the fluctuation occurs, and the i + 4th voltage value V (i + 4) (j = 4) and the absolute value of the difference, that is, |
Vi-V (i + 4) | may exceed the first reference value of 0.8V once in the first predetermined time t3 of 3 seconds, which is the first predetermined number n. Can be checked. In this C part, the voltage fluctuation of 1.1V is 1 within 0.4 seconds.
Since it has occurred, the condition (3) is satisfied and it is determined that the welding is abnormal.

In the section C, as shown in the figure, the voltage value falls below the allowable lower limit value of 10 V for a fixed time t2 of 2 seconds or more, and the condition (2) is also satisfied.
Therefore, the welding abnormality is detected by either the condition (3) or (2).

When a welding abnormality occurs to the extent that the welding voltage does not fall outside the allowable upper and lower limit range, that is, when a small size of burnout occurs, the welding abnormality is determined by the conditions (3) and (4). Is done.

Portion E in FIG. 1 shows a case where a small amount of burnout occurs in the gap between the butted parts 15 to be welded when the voltage is gently changing within the allowable range. In this case, the condition (3) is applied in the same manner as above, and 0.
Since there was one voltage fluctuation of 9V, it is determined that the welding is abnormal. As described above, the condition (3) is applied to the detection of a welding abnormality when a relatively large voltage change such as a burnout occurs sporadically within a relatively short time.

Portion F in FIG. 1 shows how the voltage fluctuates when the bead height becomes uneven due to the center deviation during welding. In this case, based on the condition (4), the i-th voltage value Vi, that is, the voltage value before the fluctuation occurs, and the i + 2-th voltage value V (i + 2) (k after the i-th voltage value)
= 2), the absolute value of the difference, that is, | Vi−V (i + 2) |
However, if the voltage exceeds 0.4V which is the second reference value,
It is checked whether the second predetermined number of times m, that is, three times, occurs within the predetermined time t4 of 8 seconds. In this part C, the voltage fluctuation of 0.5 V was made four times within 8 seconds, so that the condition (4) is satisfied and it is determined that the welding is abnormal. As described above, the condition (4) is applied to the detection of a welding abnormality when a small voltage change occurs a large number of times continuously in a relatively long time, such as an out-of-center position or an uneven bead.

By doing the above, it is possible to detect all kinds of welding abnormalities including the abnormal welding portion having a small defect size, and to control the welding quality online. As a result, it is possible to eliminate the inspection of the welded portion in the post process. Further, for example, when a welding abnormality occurs, a signal to that effect is output to the outside, and the signal is input to an emergency stop circuit of a welding apparatus such as a welding robot, so that the welding operation can be stopped when the abnormality occurs. Therefore, it is possible to prevent the need for reworking as in the case where the welding work is continued after the occurrence of the abnormality.

[0029]

As described above, according to the present invention, the voltage value at the time of welding is periodically measured a plurality of times, and the difference between the measured voltage value at a certain time point and the other measured voltage values thereafter is determined. When the absolute value exceeds the reference value occurs a predetermined number of times or more within a predetermined time after the time point, it is determined to be a welding abnormality, therefore, regardless of the allowable upper limit value and the allowable lower limit value of the voltage value, Within the range of the allowable upper limit value and the allowable lower limit value, the reference value can be set based on the voltage change according to the abnormality to be detected, so that the abnormality can be reliably detected. In addition, since the welding abnormality is judged only when the reference value is exceeded a predetermined number of times within a predetermined time set in advance, these are determined according to the pattern of voltage fluctuation that can usually occur when the abnormality exists. By setting the predetermined time and number of times, it is possible to prevent erroneous detection from occurring.

According to the present invention, two kinds of reference values are
Since it is set together with the predetermined time and the predetermined number of times corresponding to each reference value, it is possible to reliably detect both two types of welding abnormalities having different voltage fluctuation patterns.

Further, according to the present invention, it is also detected that the current value and the voltage value at the time of welding deviate from the allowable upper limit value or the allowable lower limit value, and when any one kind of abnormality is detected, it is abnormal. Therefore, it is possible to reliably detect various abnormalities that may occur during welding.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a current value and a voltage value at the time of welding for explaining a method of an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a welding device for carrying out the method.

FIG. 3 is a diagram showing an example of a current value and a voltage value for explaining a conventional method for detecting an abnormality during welding.

[Explanation of symbols]

 11 TIG welding machine 15 Welding material 17 Current / voltage measuring unit 20 Computing unit 21 Recording unit 22 Indicator lamp

Claims (3)

[Claims] 1. The voltage value at the time of welding is periodically measured a plurality of times, and the absolute value of the difference between the measured voltage value at a certain time point and the other measured voltage values thereafter exceeds a reference value. When it occurs more than a certain number of times within a certain time after that point,
A method for detecting abnormality during welding, which is characterized by determining that the abnormality is welding. 2. A first reference value and a second reference value which is a value smaller than the first reference value are set, and a first predetermined time and a first reference time are set in correspondence with the first reference value. A predetermined number of times of 1, and a second predetermined number of times longer than the first predetermined number of times and a second predetermined number of times greater than the first predetermined number of times corresponding to the second reference value. And is set so that the absolute value of the difference exceeds the first reference value within the first predetermined time.
And the absolute value of the difference is the second
2. The welding abnormality is determined in at least one of a case where the reference value exceeds the second predetermined number of times within the second predetermined time. Abnormality detection method during welding. 3. An allowable upper limit value and an allowable lower limit value are set respectively for a welding current value and a voltage value, and the welding current value is periodically measured a plurality of times to measure the measured current value and the measured current value. At least one of the voltage value is determined to be a welding abnormality even when continuously deviating from a permissible upper limit value to a permissible lower limit value within a certain time from a certain time point. Item 1. A method for detecting an abnormality during welding according to Item 1 or 2.