JP2002316270A - Method for deciding weld condition and device for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for deciding a weld condition by which the generation of a spatter and a weld defect are clearly decided. SOLUTION: The method for deciding the weld condition is characterized by the fact that the amount of displacement between electrodes during a welding with a welding gun is measured, the measured amount of displacement between electrodes is detected as a generation of the spatter when the measured amount of displacement between electrodes varies over a predetermined value, and the normal/defective condition of welding is decided depending on whether the generation of the spatter is before or after the amount of displacement between electrodes reaches a saturated point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a welding state in resistance welding and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, in resistance welding, particularly in spot welding, the amount of electrode displacement of a welding gun during welding has been measured. This inter-electrode displacement is used, for example, for estimating a nugget diameter, and is used for determining a welding state (for example, Japanese Patent Laid-Open No. 11-58029).

[0003]

However, if spatter occurs during welding, the displacement between the electrodes fluctuates greatly. Therefore, it is necessary to estimate the nugget diameter and judge the welding quality using the displacement between the electrodes. There is a problem that can not be.

[0004] In addition, there is a problem that the generation of spatter itself does not relate to what leads to poor welding, and when spatter is generated, it is not always possible to judge that welding is defective.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for judging a welding state capable of clearly judging the occurrence of spatter and defective welding.

[0006]

The object of the present invention is achieved by the following means.

(1) The displacement between the electrodes during welding by the welding gun is measured, and when the measured displacement between the electrodes exceeds a predetermined value, the occurrence of the variation is detected by the electrode. A welding state determination method, which determines the quality of welding based on whether the inter-displacement amount reaches before or after reaching a saturation point.

(2) The method for judging a welding state further comprises:
When the variation in the inter-electrode displacement exceeds a specified value, a loss amount of the material to be welded is calculated from the variation, and when the calculated loss amount is larger than a predetermined value of a predetermined loss amount, It is characterized by determining that welding is defective.

(3) Measuring means for measuring the displacement between the electrodes during welding by the welding gun, and determining whether or not the displacement between the electrodes measured by the measuring means has exceeded a predetermined value. Sputter detection means for detecting the occurrence of spatter, quality judgment means for judging the quality of welding by comparing the time of spatter occurrence detected by the spatter detection means and the time when the displacement between the electrodes has reached a saturation point And a welding state determining device.

(4) The pass / fail determination means further calculates a loss amount of the material to be welded from the fluctuation amount of the displacement between the electrodes detected by the sputter detection means, and the calculated loss amount is a predetermined loss amount. The welding characteristic is determined to be defective when the value exceeds the specified value.

[0011]

According to the present invention, the following effects can be obtained for each claim.

According to the first aspect of the present invention, the displacement between the electrodes is measured during welding, and when the measured displacement fluctuates beyond a specified value, this is regarded as the occurrence of spatter. Since the welding state is determined depending on whether the position is before or after the saturation point, it is not only necessary to detect the occurrence of spatter from the displacement between the electrodes, but also to accurately determine welding defects caused by spatter. it can.

According to the second aspect of the present invention, when the variation of the displacement between the electrodes exceeds a specified value, the loss of the workpiece is calculated from the variation, and the calculated loss is calculated in advance. Welding is judged to be defective if the loss exceeds the specified value of the specified loss amount.Welding defect is judged from the amount of the member to be welded lost due to the occurrence of spatter corresponding to the loss of the member to be welded. can do.

According to the present invention, the displacement measuring means measures the displacement between the electrodes during welding, and detects the occurrence of spatter from the displacement measured by the spatter detecting means. Decided to determine the welding condition depending on whether the spatter generation position was before or after the saturation point. Therefore, it was not only possible to detect spatter generation from the displacement between the electrodes, but also to accurately determine welding defects caused by spatter. can do.

According to the fourth aspect of the present invention, the pass / fail judgment means calculates the loss amount of the material to be welded from the fluctuation amount of the displacement amount between the electrodes when spatter is detected, and calculates the loss amount. Welding failure is determined when the loss exceeds the predetermined value of the loss amount, and welding failure is determined based on the amount of welded member lost due to the occurrence of spatter corresponding to the loss amount of the welded member. Can be determined.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

FIG. 1 is a block diagram showing a schematic configuration of a welding apparatus for performing spot welding according to the present invention.

For example, a welding member 10 in which a plurality of plate members or the like are overlapped is sandwiched and pressed by electrode tips 12a and 12b attached to a welding gun 11 from above and below.

On the other hand, the electrode tips 12a and 12b, on the other hand, are movable up and down in the figure, and are controlled to move up and down by a pressure closing device 18 composed of a servomotor or the like. 10 is pressed at a predetermined pressure.

A welding current is supplied from the power supply circuit 15 to the electrode tips 12a and 12b while the welding member 10 is pressed against the electrode tips 12a and 12b.

The current amount of the welding current and the conduction time (welding time) are controlled by a current control circuit 16 that operates based on a command from the central processing unit 20.

The position of the electrode tip 12a is detected by an electrode position detecting device 19 such as an encoder.

The electrode position detecting device 19 detects slight vertical movement of the electrode tip 12a during welding,
This is measured as a displacement between electrodes due to thermal expansion during welding with the fixed electrode tip 12b. The measured inter-electrode displacement is temporarily stored in the storage circuit 26, and the central processing unit 20 determines the welding state from the data of the inter-electrode displacement.

The storage circuit 26 stores welding conditions for performing welding, a specified value for determining the presence or absence of spatter, and the like.

The operation of the closing device 18 is controlled by the central processing unit 20.
Is controlled by the closing pressure control circuit 22 which operates based on the command of

The displacement of the electrode tip 12a detected by the electrode position detecting device 19 is controlled by the closing pressure control circuit 22 for controlling the position of the pressure closing device 18 via the electrode position detecting circuit 24.
And is also used for controlling the pressing force by the electrode tips 12a and 12b.

The central processing unit 20 includes the electrode position detecting device 1
The displacement between the electrodes is obtained from the position information of the electrode tip 12a detected by the step 9, and as described later, the presence or absence of spatter and the quality judgment of the welding are performed from the obtained displacement between the electrodes.

Further, the central processing unit 20 is provided with a display (not shown) and the like, and displays a result of the determination of the welding state.

The welding device shown in FIG. 1 is only for explaining the schematic configuration of the welding device for the purpose of describing the present embodiment, and in an actual welding device,
For example, there are various types such as those held by an operator and those used as an end effector of a robot, but the basic configuration is the same as that described above, and the present invention is limited to the welding apparatus as described above. Instead, it can be applied to various welding devices.

Next, a detailed description will be given of a method for determining whether or not spatter has occurred and whether or not the welding state is good or bad during welding performed by the apparatus configured as described above.

First, the displacement between the electrodes and the occurrence of spatter will be described.

FIG. 2 is a schematic diagram showing the inter-electrode displacement, with the vertical axis representing the inter-electrode displacement and the horizontal axis representing the time. In this figure, a shows a case where welding is performed normally without spatters, and b shows a case where spatters are generated.

When no spatter occurs, the displacement between the electrodes gradually rises due to the thermal expansion of the welded portion, reaches a saturation point, and contracts when the current is terminated, as shown in a, after the start of current supply (time 0). On the other hand, when the spatter occurs, the displacement between the electrodes fluctuates rapidly as shown by b. In this embodiment,
It is assumed that sputter has occurred when the sudden change in the inter-electrode displacement is greater than a predetermined value.

In order to judge the quality of welding due to the generation of the spatter, the present embodiment provides two criteria.

The first criterion is to judge whether or not the displacement between the electrodes has reached a saturation point. this is,
If spatter occurs in the process of expanding the nugget before the saturation point, the generation of the nugget is often hindered by the spatter, and such a case is determined to be highly likely to have poor welding. . On the other hand, if spatter occurs after the saturation point, since the nugget has already entered the shrinkage process, it has little direct effect on the nugget formation. do not do.

To determine whether or not the saturation point has been reached, for example, a regression analysis of the displacement between the electrodes is performed, and a point at which the slope of the regression line becomes zero is defined as the saturation point.

The second criterion is that even if spatter occurs, welding failure is not considered as long as the loss of the nugget forming portion is small. At this time, the loss amount serving as a criterion for determination needs to be obtained in advance by experiments. For example, when there is a change in the amount of displacement between the electrodes, the amount of change (displacement difference) is measured to determine how much the finished nugget diameter has decreased from the case where there is no change, and this displacement difference and the nugget diameter are measured. Table data is created in relation to the amount of decrease in the distance between the electrodes, and thereafter, by referring to this table data, the loss amount of the member to be welded is calculated from the displacement difference in the displacement amount between the electrodes. Then, a displacement difference at which a decrease in the nugget diameter at which a welding failure such as insufficient strength occurs occurs is used as a criterion for determining the amount of loss.

Note that a specified value for confirming the occurrence of spatter is also obtained in advance by an experiment.
In this case, similarly to the creation of the table data, the completed nugget diameter is associated with, for example, the displacement difference between the electrode displacement amounts, and the displacement difference at which the reduction in the nugget diameter is recognized is sputtered. The specified value for confirming the occurrence of

FIG. 3 is a drawing showing a typical example in the case where spatter has occurred.

First, as shown in FIG. 3A, when spatter occurs before the saturation point, the displacement rapidly changes before the inclination θ of the regression line becomes zero. The loss amount is calculated from the displacement difference, and if the loss amount is large, it is determined that the welding is defective. On the other hand, as shown in FIG. 3B, after the inclination θ of the regression line becomes 0, ie,
If spatter occurs after reaching the saturation point, it is determined that welding is good.

Next, a description will be given of a procedure for determining the welding state due to the above-mentioned generation of spatter.

FIG. 4 is a flowchart showing a procedure for determining the welding state.

In the welding operation by the above-mentioned device, first, the welding member 10 is held by the welding gun 11 at a predetermined pressure, and at the same time, energization is started to the electrode tips 12a and 12b under predetermined energizing conditions (S
1).

The measurement of the position of the electrode tip 12a is started simultaneously with the start of the hold and the energization, and the displacement difference between the electrode tips 12a and 12b, that is, the displacement between the electrodes, is measured from the positional displacement.

At this time, the measurement frequency is sampled and stored continuously or at very short time intervals of about 0.5 msec or about 1 to 5 msec (S
2).

It should be noted that the sampling interval is not limited to such a time interval, but may be set as appropriate in accordance with a later-described regression line calculation time interval.

From the measured inter-electrode displacement, a regression line is determined at regular time intervals “twidth”, and the slope of the determined regression line and the displacement difference are stored (S3). Note that the displacement difference is the difference between the previous sampling value and the current sampling value.

Subsequently, it is determined whether or not spatter has occurred based on the calculated displacement difference (S4). Here, when the displacement difference exceeds the specified value and the spatter has occurred, the spatter occurrence time is subsequently stored (S5), and it is determined whether or not the spatter has occurred before saturation (S6). Here, if the saturation time (step S13 described later) is not stored, it is determined that spatter has occurred before saturation, and the process proceeds to step S7. On the other hand, if the saturation time is stored,
Since the saturation time is stored before the occurrence of the spatter, in this case, the occurrence of the sputter is determined to be after the saturation, and the process proceeds to step S11, where the occurrence of the sputter is maintained.

If it is determined in step S6 that the occurrence of spatter is before saturation, the loss is calculated from the displacement difference obtained in step S3 (S6).
7). As described above, the loss amount is calculated from a data table created in advance.

Subsequently, it is determined whether or not the amount of loss exceeds a specified value and is excessive (S8). If the amount of loss is excessive, a warning is given that the strength is insufficient due to the occurrence of spatter (S8).
9). Then, this warning is transmitted to the display device or a higher-level control device (S10), and the process ends.

On the other hand, if it is determined in step S8 that the loss amount is not excessive, the fact that spatter has occurred is held (S11), and the process proceeds to step S12.

In step S4, when it is determined that the displacement difference is less than the specified value, and in step S1
1 and thereafter, in step S12, the
It is determined whether or not the slope obtained in step 3 is 0. If the slope is 0, the time at that time is stored as the saturation time (S13), and the process proceeds to step S15. On the other hand, if the inclination is not 0, it is determined whether welding is completed or not (S14), and if not completed, the process returns to step S3 and continues. On the other hand, if welding is completed, it is determined whether or not spatter has occurred from the holding state in step S11 (S15), and if spatter has occurred, the information is given (S16). If it is normal (S17), it is transmitted to the display device or a higher-level control device (S10), and the process ends.

FIG. 5 is a diagram showing a change in the displacement between the electrodes when welding is actually performed. In the figure, data a shows no sudden change in the displacement between the electrodes, and the welding is completed in a normal state. On the other hand, in the data b and c, the amount of displacement between the electrodes has a sharp change, and spatter has occurred in this portion. Data b indicates that spatter occurred before saturation, and data c indicates that spatter occurred after saturation.

When the finished nugget diameter was measured for the welded product from which each of these data was obtained, b, in which spatter occurred before saturation, had a significantly smaller nugget diameter than a, which ended normally. It turned out that the possibility of shortage was large. On the other hand, the value of c where spatter occurred after saturation was almost the same as that of a which ended normally.

From this result, it can be seen that it is possible to judge a welding defect based on the position where spatter is generated.

In FIG. 4, the vertical axis indicates the amount of displacement between the electrodes, which is the number of pulses of the encoder, and the horizontal axis is time.

As described above, according to the present embodiment, it is possible to accurately determine not only the occurrence of spatter but also the welding failure due to the occurrence of spatter from the measurement result of the displacement between the electrodes.

The embodiment of the present invention has been described above.
The present invention is not limited to such an embodiment. For example, in the above-described embodiment, after the occurrence of spatter, the loss amount of the member to be welded is calculated from the difference in the displacement amount between the electrodes at that time, and it is determined that the welding is defective only when the loss amount is excessive. However, instead of this, by using a displacement difference that may cause welding failure as a specified amount for determining the occurrence of spatter, a displacement difference that may cause welding failure is used. Is detected before the saturation point, it may be directly determined that poor welding occurs. In the above-described embodiment, the welding state is determined in real time during welding. However, only the data of the displacement between the electrodes is collectively inspected after the end of welding to determine the quality of each welding point. You may do so.

For the detection of the saturation point, instead of a regression line, a graph representing the change in the inter-electrode displacement may be created and the slope of a straight line tangent to the graph curve may be used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a spot welding apparatus.

FIG. 2 is a diagram for explaining a displacement between electrodes and generation of spatter.

FIG. 3 is a drawing showing generation of spatter.

FIG. 4 is a flowchart showing a procedure for determining a welding state.

FIG. 5 is a drawing showing a change in the displacement between electrodes when welding is actually performed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... welding member, 11 ... welding gun, 12a, 12b ... electrode chip, 20 ... central processing unit, 26 ... memory circuit.

Claims (4)

[Claims] An electrode displacement during welding by a welding gun is measured, and when the measured displacement between electrodes exceeds a predetermined value, the variation occurs between the electrodes. A welding state determination method, wherein the quality of welding is determined depending on whether the displacement amount reaches before or after reaching a saturation point. 2. The method according to claim 1, further comprising: calculating a loss amount of the material to be welded from the variation amount when the variation in the inter-electrode displacement amount exceeds a specified value, and determining the calculated loss amount. 2. The welding state determination method according to claim 1, wherein when the loss is larger than a predetermined value of the loss amount, it is determined that the welding is defective. 3. A measuring means for measuring an inter-electrode displacement during welding by a welding gun, and a spattering method based on whether or not the inter-electrode displacement measured by the measuring means fluctuates beyond a predetermined value. A spatter detecting means for detecting the occurrence of spatter, a good or bad judgment means for judging the quality of welding by comparing the time of occurrence of spatter detected by the spatter detecting means with the time when the displacement between the electrodes reaches a saturation point. A welding state determination device, comprising: 4. The pass / fail determination means further calculates a loss amount of the material to be welded from a variation amount of the inter-electrode displacement amount detected by the sputter detection means, and the calculated loss amount is a predetermined loss amount. 4. The welding state determination device according to claim 3, wherein when it is larger than a specified value, it is determined that the welding is defective.