JP2002316268A - Method for estimating nugget diameter in resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for estimating the nugget diameter during the welding with high accuracy. SOLUTION: A regression line, an intersection of the line of the inclination 0 with the regression line of maximum inclination (imaginary saturation point), the imaginary saturation time T1 to the imaginary saturation point, and the displacement h between electrodes from the imaginary saturation point to the hold release are obtained from the displacement between electrodes from the hold start to the hold release as an approximation shown in the formula (1). Then, multiple regression formula shown in (2) is obtained from the imaginary saturation time T1, the inclination θ1 of the regression line of maximum inclination, the intercept HT0 of the regression line of maximum inclination of the time axis 0, and the coefficients a, b and c in the formula (1). T1, θ1, HT0, a, b, and c are obtained from the displacement between the electrodes during the welding, and the nugget diameter y is calculated from the formula (2). h=a×T<2> +b×T+c...(1), and y=r0+r1×a+r2×b+r3×c+r4×T1+r5×θ1+r6×HT0...(2), where r0 to r6 are partial regression coefficients.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for estimating the diameter of a nugget formed after welding in resistance welding represented by spot welding.

[0002]

2. Description of the Related Art Conventionally, as a method of estimating a nugget diameter for the purpose of quality control and quality improvement in resistance welding, particularly spot welding, a method of estimating a nugget diameter while a welding current is flowing (a nugget generation process)
Various methods utilizing the thermal expansion of a welding member have been developed.

[0003] In particular, the technique disclosed in Japanese Patent Application Laid-Open No. 2000-79482 is a very useful invention capable of estimating a nugget shape from the displacement between electrodes during welding.

[0004]

However, in the technology described in the above publication, only the displacement from the start of energization to the saturation of the displacement between the electrodes is used, so that the inclination of the strike angle of the welding gun is large. When the welded member having a large gap is welded, or the like, the actual nugget diameter does not match the estimated value.

Accordingly, an object of the present invention is to provide a method for estimating a nugget diameter which can extremely accurately estimate a formed nugget diameter in resistance welding represented by spot welding.

[0006]

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

(1) The displacement between the electrodes from the start of holding of the workpiece to be welded by the welding gun to the release of the hold is measured, and a regression line from the start of holding to the point where the displacement is saturated is determined. An intersection between the saturated point and a straight line having a slope of 0 that comes into contact is obtained, and an approximate expression that approximates the amount of displacement from the amount of displacement from the intersection to the release of the hold is obtained. From the time, the slope of the regression line, the value of the intercept of the regression line, and the approximate expression, a multiple regression equation is created, and the nugget diameter in resistance welding is calculated by calculating the nugget diameter by the multiple regression equation. Estimation method.

(2) From the displacement between the electrodes measured from the start of the hold of the member to be welded by the welding gun to the release of the hold, the horizontal axis is the time axis T and the vertical axis is the displacement h at regular time intervals. And the point where the slope of the regression line becomes 0, and the intersection of the regression line having the slope of 0 and the regression line having the largest slope among the regression lines obtained so far. And the time from the start of energization on the time axis T at the intersection is defined as a virtual saturation time T1.
And a step of obtaining an approximate expression shown in the following expression (1) that represents the inter-electrode displacement amount h from the intersection to the hold release as a function of time T:
Using the virtual saturation time T1, the slope θ1 of the maximum slope regression line, the intercept HT0 of the maximum slope regression line on the time axis 0, and the coefficients a, b, and c in the equation (1), the following (2) Calculating the multiple regression equation shown in the equation, the virtual saturation time T1 obtained from the displacement between the electrodes measured during welding, the slope θ1 of the regression line having the maximum slope, and the regression of the maximum slope on the time axis 0. From the value HT0 of the intercept of the straight line and the coefficients a, b, and c of the approximate expression shown in Expression (1),
A method for estimating a nugget diameter in resistance welding, comprising calculating a nugget diameter y during welding using the multiple regression equation shown in equation (2).

H = a × T2 + b × T + c (1) y = r0 + r1 × a + r2 × b + r3 × c + r4 × T1 + r5 × θ1 + r6 × HT0 (2) where y is a nugget diameter and r0 to r6. Is the partial regression coefficient.

[0010]

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 a regression line is obtained from the measured displacement. Find the intersection, and then calculate an equation that approximates the amount of displacement between the electrodes from the intersection to the hold release, and calculate the multiple regression equation based on the time to reach the intersection, the slope of the regression line, the intercept of the regression line, and the approximate expression. By calculating the nugget diameter using this multiple regression equation, in addition to the data from the start of energization to the saturation point, a multiple regression equation was established using an approximate equation that represents the displacement between the electrodes in the contraction region after the end of energization. By that
It is possible to reduce the estimation error due to the influence of the hitting angle and the gap of the electrode tip, and to estimate the nugget diameter with high accuracy.

According to the present invention, the displacement between the electrodes is measured during welding, and a regression line is obtained at regular time intervals from the measured displacement. The intersection between the straight line and the regression line with the maximum slope is defined as the virtual saturation point, the time required to reach the virtual saturation point is determined as the virtual saturation time, and the displacement between the electrodes from the virtual saturation point to the hold release is calculated. Calculate the approximate quadratic polynomial approximation, set a multiple regression equation based on the slope of the maximum regression line, intercept value, virtual saturation time, and the coefficient of the approximation equation, and calculate the nugget diameter using this multiple regression equation. In addition to the data from the start of energization to the saturation point, a multiple regression equation was established using an approximate expression that represents the amount of displacement between electrodes in the contraction region after the end of energization. Regardless of the influence of It is possible to estimate the nugget diameter accuracy.

[0013]

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

<Apparatus Configuration> 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 raised and lowered by a pressure closing device 18 composed of a servomotor or the like. 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 which 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 composed of, for example, an encoder.

The electrode position detecting device 19 detects a 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 stored in the storage circuit 26, and is used for estimating and controlling a nugget diameter described later.

The storage circuit 26 also stores welding conditions for performing welding, a multiple regression equation obtained as described later, and the like.

The operation of the closing device 18 is controlled by a 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
9 to determine the inter-electrode displacement from the position information of the electrode tip 12a detected by step 9, as described later, estimating the nugget diameter based on the obtained inter-electrode displacement, and further performing welding based on the estimation result. The energizing conditions such as the amount of energizing current and the energizing time during the operation are changed.

The central processing unit 20 is provided with a display (not shown) and the like, and displays a result of estimating a nugget diameter and energizing conditions.

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.

<< Estimation of Nugget Diameter >> A method of estimating a nugget diameter in resistance welding performed by the apparatus configured as described above will be described in detail.

FIG. 2 is a flowchart showing a procedure of a method for estimating a nugget diameter, and FIG. 3 is a schematic view showing a model of a displacement between electrodes for explaining this method.

In the welding operation by the above-mentioned apparatus, first, the welding member 10 is held by the welding gun 11 at a predetermined pressure, and energization of the electrode tips 12a and 12b is started under predetermined energizing conditions.

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

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

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

From the measured inter-electrode displacement, a regression line is obtained at regular time intervals twidth, and the slope and intercept of the obtained regression line are stored (S3).

The regression line determined here is a two-dimensional line with the horizontal axis representing the time axis T and the vertical axis representing the displacement h (see FIG. 3). In addition, the intercept of the regression line is an intercept of 0 on the time axis of the regression line. Also, the slope θ1 of the regression line
Represents the thermal expansion rate dh / dt.

The regression line obtained by this is h = θ1
× T + HT0. Here, in the equation, h is the displacement amount, T is time, θ1 is the slope, and HT0 is the value of the intercept.

The time interval width is preferably about 50 to 120 msec, more preferably about 60 to 10 msec, in order to obtain a multiple regression equation to be described later.
0 msec, more preferably about 60 msec.

Here, the reason why the regression line is calculated at regular time intervals is to know the saturation point of the thermal expansion that changes every moment from the obtained slope of the regression line. It is determined that the thermal expansion has become saturated when the value becomes zero.

Then, when the slope of the obtained regression line becomes 0 (S4), the regression line and the regression line having the largest slope among the regression lines obtained up to that point are determined. An intersection is obtained, and a value of this intersection on the time axis is obtained. Here, this intersection is called a virtual saturation point.

The arrival time (virtual saturation time T1) from the start of energization to the intersection on the time axis, the slope θ1 of the regression line having the largest slope, and the value HT0 of the intercept are obtained (see FIG. 3).
(S6).

Thereafter, sampling of the displacement is further performed under the same conditions as above until the hold is released (end of welding) (S7, S8).

Then, from the displacement from the intersection to the release of the hold, a second-order polynomial approximation expressed by the following equation (1) is obtained which approximates the value of the displacement during this time (S9).

H = a × T2 + b × T + c (1) In the equation (1), h is the displacement and T is the time.

Subsequently, the multiple regression shown in the following equation (2) using the virtual saturation time T1, the slope θ1 of the regression line having the largest slope, the intercept value HT0, and the coefficients a, b, and c in the equation (1). An equation is obtained (S10).

Y = r0 + r1 × a + r2 × b + r3 × c + r4 × T1 + r5 × θ1 + r6 × HT0 (2) where y is a nugget diameter and r0 to r
6 is a partial regression coefficient. Note that the partial regression coefficients r0 to r6 in this multiple regression equation are values obtained from ordinary mathematical methods and numerous experimental results, and vary depending on the thickness of the welding member to be welded, the diameter of the electrode tip, or energizing conditions. .

A multiple regression equation is obtained from a plurality of samples that have been actually welded by the above procedure. The multiple regression equation thus obtained is stored in the storage circuit 26 in advance.

At the time of welding, the displacement between the electrodes is measured while performing the welding, and the virtual saturation time T is set in the same manner as in steps S1 to S9.
1, the slope θ1 of the regression line having the largest slope, the value HT0 of the intercept,
Then, the coefficients a, b, and c in the equation (1) are obtained, and these values are entered into the multiple regression equation shown in the equation (2), which has been obtained by the above-described procedures, to calculate the nugget diameter.

Next, a description will be given of the result of comparison between the actually measured value and the estimated value of the nugget diameter at the time of actually performing welding.

As a member to be welded, two cold-rolled steel sheets having a thickness of 1.6 mm are used, and two cold-rolled steel sheets 51 and 52 are laminated as shown in FIG. ,
A spacer 53 is inserted between the members to be welded, and a gap S = 2 m
m, a gap having a spacing of K = 20 mm, a gap having no gap (without a spacer), and a striking angle of 0 to 0
Spot welding was performed with various changes between 10 degrees, and the multiple regression equation represented by the equation (2) was created by the procedure described above.

Using the same plate material as described above, the hitting angles 0 (no hitting angle) and 10
The sample of the degree (having a striking angle) was welded, and the actual measured value of the nugget diameter at this time, the estimated value according to the present invention (Example), and the estimated value according to the technique disclosed in JP-A-2000-79482 (Comparative Example) Were compared.

The welding samples were (1) no gap, no hitting angle,
(2) No gap and hit angle, (3) No gap and hit angle, (4)
The welding conditions for each sample were 7.5 kA for (1) and 8.3 for (2).
kA, (3) is 7.8 kA, and (4) is 7.3 kA. The energization time is 3 cycles of up slope and 14 cycles of main energization. The applied pressure is 3528N (3
60 kgf).

FIG. 5 is a drawing showing the amount of displacement of each sample, and FIG. 6 is a diagram showing measured values of the nugget diameter of each sample, estimated values according to the present invention (Example), and JP-A-2000-79.
482 is a chart showing estimated values (comparative examples) by the technique disclosed in 482. In FIG. 5, the displacement is represented by the number of pulses of the encoder, and is 1.22 μm per pulse. In FIG. 6, “residual” is an actual measured value−estimated value.

As can be seen from FIG. 5, the change tendency of the inter-electrode displacement varies depending on the presence or absence of the gap and the presence or absence of the striking angle. In particular, the tendency until reaching the saturation point is greatly different. On the other hand, the portion after the saturation point (this is referred to as a contraction region) shows almost the same contraction tendency. In the present invention, the tendency of the contraction region is represented by a second-order polynomial approximation formula, and its coefficient is incorporated into a multiple regression formula, thereby increasing the nugget estimation accuracy.

As is clear from FIG. 6, regardless of the presence or absence of a plate gap and the presence or absence of a hitting angle, the results of the examples according to the present invention are smaller than those of the comparative examples, regardless of the presence or absence of the gap. It can be seen that the estimation accuracy of the nugget diameter is high.

As described above, according to the present embodiment, it is possible to estimate the nugget diameter with high accuracy irrespective of the presence or absence of a plate gap and the hitting angle.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating a procedure of a method for estimating a nugget diameter.

FIG. 3 is a schematic diagram showing a model of a displacement between electrodes.

FIG. 4 is a drawing for explaining measurement of a sample.

FIG. 5 is a diagram showing a displacement between electrodes.

FIG. 6 is a drawing comparing an estimated value and a measured value of a nugget diameter.

[Explanation of symbols]

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

Claims (2)

[Claims] An inter-electrode displacement between a start of holding of a workpiece to be welded by a welding gun and a release of the hold is measured, and a regression line from the start of holding to a point where the amount of displacement is saturated is obtained. Obtain an intersection of the saturated point and a straight line having a slope of 0, which is in contact with, and obtain an approximate expression that approximates the amount of displacement from the amount of displacement from the point of intersection to the release of the hold, and the time from the start of energization to the point of intersection. Estimating the nugget diameter in resistance welding, wherein a multiple regression equation is created from the slope of the regression line, the value of the intercept of the regression line, and the approximation equation, and the nugget diameter is calculated by the multiple regression equation. Method. 2. A horizontal axis represents a time axis T and a vertical axis represents a displacement amount h at predetermined time intervals based on an inter-electrode displacement amount measured from a start of holding of a member to be welded by a welding gun to a release of the hold.
The step of obtaining a regression line when the regression line becomes zero. When the slope of the regression line becomes zero, the intersection of the regression line having the slope of zero and the regression line having the largest slope among the regression lines obtained so far. Determining the time from the start of energization of the intersection on the time axis T as a virtual saturation time T1; and calculating the inter-electrode displacement h from the intersection to the hold release as a function of time T. The following (1) expressed as
Obtaining an approximate expression of the expression; the virtual saturation time T1, the inclination θ1 of the regression line having the maximum inclination, the value HT0 of the intercept of the regression line having the maximum inclination on the time axis 0, and the coefficients a and b in the expression (1). , C to find a multiple regression equation shown in the following equation (2), a virtual saturation time T1 obtained from the displacement between the electrodes measured during welding, and a slope θ1 of the maximum slope of the regression line. From the value HT0 of the intercept of the regression line having the maximum slope on the time axis 0, and the coefficients a, b, and c of the approximate expression shown in the equation (1),
(2) A method for estimating a nugget diameter in resistance welding, wherein a nugget diameter y during welding is calculated using the multiple regression equation shown in equation (2). h = a.times.T2 + b.times.T + c (1) y = r0 + r1.times.a + r2.times.b + r3.times.c + r4.times.T1 + r5.times.1 + r6.times.HT0 (2) (where, y is a nugget diameter and r0 to r6 are polarized It is a regression coefficient.)