JP3858476B2 - Quality judgment method and apparatus for spot welding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a quality determination method and apparatus for spot welding.
[0002]
[Prior art]
Spot welding is used in various fields such as joining of panel members constituting an automobile body (see, for example, JP-A-9-89825). Confirming whether or not spot welding has been properly performed, that is, confirming the quality of spot welding is performed.
[0003]
One method for confirming the quality of spot welding is based on a change in resistance value between electrodes. More specifically, the elapsed time from the start of energization to the maximum resistance value is a predetermined threshold value. It is determined whether the quality is good or not according to whether or not it is smaller. To elaborate on this point, with the passage of time, the resistance value decreases at the initial stage due to an increase in the surface contact of the base material as a member to be welded. After that, the resistance value is reduced by enlarging the current-carrying area (nugget expansion). And that the elapsed time until the resistance value becomes maximum is small, it is considered that the heat generation during that time is sufficiently performed, it is determined that the quality is good, and conversely, the elapsed time is large, Since the heat generation during that time is not sufficiently performed, it is determined that the quality is defective.
[0004]
[Problems to be solved by the invention]
If the quality of spot welding is determined based on the resistance value change only by the elapsed time until the resistance value reaches the maximum value as in the past, even if it is determined to be good quality, it may actually be defective quality. On the other hand, even if it is determined that the quality is poor, it actually occurs that the quality is actually good. For example, even if it is considered that the elapsed time is small and the amount of heat generated until this time is sufficient, the amount of heat generated after the resistance value becomes maximum may be too small, resulting in poor quality. Even when the elapsed time is large and the amount of heat generated up to this point is considered to be small, there is a case where the resistance value rises until the resistance value reaches the maximum, that is, the amount of heat generation is large, that is, the heat generation amount is large, resulting in good quality .
[0005]
The present invention has been made in view of the above circumstances, and its purpose is to perform quality determination with higher accuracy when determining quality of spot welding based on a change in resistance value between electrodes. An object of the present invention is to provide a quality determination method and apparatus for spot welding that can be performed.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the following solution is adopted in the method of the present invention. That is, as described in claim 1 in the claims,
A first step of detecting a change in resistance value between electrodes during spot welding;
A second step of obtaining a comparison result of whether the elapsed time from the start of energization to the maximum resistance value is smaller or larger than a predetermined time set in advance;
A third step of determining whether the quality of welding is good or not based on different resistance value change states when the comparison result is large and small;
It is supposed to be equipped with. Preferred embodiments based on the above solution are as described in claims 2 to 5 in the claims.
[0007]
In order to achieve the above object, the following solution is adopted in the device of the present invention. That is, as described in claim 6 in the scope of claims,
Resistance value change detection means for detecting a resistance value change between electrodes during spot welding;
Elapsed time determination means for determining an elapsed time from the start of energization to the maximum resistance value based on the detection result of the resistance value change detection means;
A magnitude determination means for determining whether the elapsed time determined by the elapsed time determination means is smaller or larger than a predetermined time set in advance;
When the determination result by the size determination means is large and when it is small, the quality determination means for determining quality of welding based on different resistance value change states;
It is supposed to be equipped with. A preferred mode based on the above solution is as described in claim 7 and subsequent claims.
[0008]
【The invention's effect】
According to the first aspect, the quality determination is made more accurately by allocating the quality determination condition depending on whether the elapsed time when the resistance value is maximum is smaller or larger than the predetermined time as the threshold value. Is possible.
[0009]
According to the second aspect, the degree of increase in the resistance value is further examined even when the amount of heat generated until the resistance value is maximized is considered to be small, that is, when it is basically determined to be defective quality. As a result, it is possible to prevent a situation in which it is erroneously determined that the quality is defective even though the quality is good.
According to the third aspect, even when it is considered that the heat generation amount until the resistance value reaches the maximum is small, that is, when it is basically determined that the quality is poor, the resistance value increases and the resistance value decreases. By further examining the degree, it is possible to prevent a situation in which it is erroneously determined to be defective quality although it is good quality.
[0010]
According to the fourth aspect, the degree of decrease in the resistance value is further examined even when the amount of heat generated until the resistance value is maximized is considered to be large, that is, when the quality is basically determined to be good. Thus, it is possible to prevent a situation in which the quality is erroneously determined to be good quality although it is defective quality.
According to the fifth aspect, the elapsed time until the resistance value reaches the maximum is obtained by eliminating the influence of the variation in the resistance value as much as possible and taking into account the tendency of the resistance value to increase and decrease before and after the resistance value becomes the maximum. This is preferable for more accurately determining quality and determining quality quality based on this elapsed time.
[0011]
According to claim 6, there is provided a quality judgment device capable of obtaining the effect corresponding to claim 1.
According to claim 7, there is provided a quality judgment device capable of obtaining the effect corresponding to claim 2.
According to claim 8, there is provided a quality judgment device capable of obtaining the effect corresponding to claim 3.
According to the ninth aspect, there is provided a quality judgment device capable of obtaining the effect corresponding to the fourth aspect.
According to the tenth aspect, the quality determination capable of obtaining the effect corresponding to the fifth aspect is provided.
According to the eleventh aspect, the change in resistance value between the electrodes can be easily determined from the relationship between the voltage between the electrodes and the current flowing through the electrodes.
[0012]
FIG. 1 shows a typical example in which the resistance value between a pair of electrodes changes during spot welding. Reference numerals (a) to (d) in FIG. ) To (d). That is, in FIG. 2, 1 and 2 are base materials as members to be welded, and 3 and 4 are electrodes for spot welding. In FIG. 1, at the initial stage of spot welding, a resistance value decrease due to an increase in contact area between the base materials 1 and 2 appears. Thereafter, the resistance value is increased due to the temperature rise of the energizing path (generation of Joule heat). A nugget 5 (see FIGS. 2C and 2D) is generated in the vicinity of the maximum resistance value, and the nugget 5 is grown to a desired and sufficient size at the end of energization. In the embodiment, the energization time is a fixed 15 cycles (1 cycle = 1/60 seconds), and the resistance value detection is performed every 0.5 cycle.
[0013]
FIG. 3 shows an example for detecting a change in resistance value as shown in FIG. 1. The voltage between the electrodes 3 and 4 is detected, and the current flowing through the electrodes is detected, and the detected voltage is detected. The resistance value between the electrodes is determined from the current and the current. Note that a toroidal coil 6 is attached to one of the electrodes 3 in order to detect a current flowing through the electrode.
[0014]
First, in order to detect the voltage between the electrodes, the voltage between the chips (between the electrodes) is sampled through the A / D converter 7 ((a) in FIG. 3), and then the induced voltage is removed (in FIG. 3). (B)) Finally, the effective voltage value is calculated (every 0.5 cycle in FIG. 3C). In addition, the induced voltage is sampled through the A / D converter 7 ((d) in FIG. 3), and the current is then integrated to determine the current value ((e) in FIG. 3). The value current is calculated (in FIG. 3, (f), every 0.5 cycle). The resistance value (change) is determined based on the effective value voltage and effective value current obtained as described above (in FIG. 3, (g), every 0.5 cycle).
[0015]
The change in resistance value between the electrodes obtained as described above is input to a pass / fail determination unit ((h) in FIG. 3), and the pass / fail determination unit determines pass / fail of spot welding as described later. Is done. As a premise for determining the quality of spot welding, the elapsed time from the start of energization until the resistance value reaches the maximum value (peak value) is determined, and this elapsed time is determined as follows. That is, as shown in FIG. 4, when the resistance value increases, that is, increases, the characteristic line indicating the maximum inclination of the resistance value increase is determined as α, and the characteristic line indicating the maximum inclination of the resistance value decrease is determined as β. It is determined. Then, the elapsed time up to the time corresponding to the intersection γ of both characteristic lines α and β is determined as the elapsed time at which the resistance value is maximized. In addition, each part from (a) to (h) in FIG. 3 is a block diagram showing control parts according to function in a control unit (controller) configured using a microcomputer. It is.
[0016]
FIGS. 5 to 8 are for explaining that a determination error is likely to occur when the quality of spot welding is determined only by the elapsed time at which the resistance value is maximum. First, FIG. 5 shows a welding example in which the energization diameter expands with the melting of the base materials 1 and 2, and the process in which the numbers 1, 2, and 3 in FIG. 5 grow the nugget 5. FIG. 6 shows how the resistance value changes at that time. The characteristic of the resistance value change in this case is that the elapsed time until the resistance value reaches the maximum is short (short), and the energization diameter increases as the nugget diameter grows, and the resistance value decreases.
[0017]
Next, FIG. 7 shows a case where the energized diameter spreads in the initial stage and the melting spreads in the vertical direction (the overlapping direction of the base materials 1 and 2), and the state of resistance change at that time is shown in FIG. It is. The feature in this case is that the resistance diameter due to heat generation is moderated because the current diameter is secured in the initial stage, and the elapsed time until the resistance value is maximized is long (long). Since the expansion is small, the decrease in resistance value is small.
[0018]
In the case of FIG. 5, although the elapsed time is small, there is a case where the amount of heat generated after the resistance value is maximized is insufficient, resulting in defective quality, and such defective quality is erroneously determined as good quality. It is desirable to prevent the situation. In the case of FIG. 7, although the elapsed time is large, the rate of increase in the resistance value is sufficiently large, or the amount of decrease in the resistance value after the resistance value is maximized is sufficiently large. As a result, a sufficient amount of heat generation is ensured. In many cases, good quality is obtained, and it is desirable to prevent such a good quality from being erroneously determined as defective.
[0019]
FIG. 9 is a flow chart showing an example of spot welding quality judgment according to the present invention, and FIG. 9 will be described below. FIG. 9 shows the contents of control in the pass / fail judgment unit shown in FIG. It corresponds to. In the example of FIG. 9, the quality determination condition is basically changed depending on whether the elapsed time is longer or smaller than a predetermined time (predetermined threshold).
[0020]
First, in Q (step—the same applies hereinafter) 1, after monitoring the above-described change in resistance value, in Q2, a waveform parameter indicating the initial heat generation amount is calculated. In Q3, it is determined whether or not the initial heat generation amount is large (whether or not it is equal to or greater than a predetermined threshold value). If the determination in Q3 is NO, the initial energy is absolutely insufficient. Therefore, in Q13, it is determined as defective quality (NG determination).
[0021]
If YES in Q3, it is determined in Q4 whether the elapsed time until the resistance value becomes maximum is longer than a predetermined time (predetermined threshold value) set in advance. When the determination of Q4 is NO, it is basically the case of good quality, but the determination of FIGS. 5 and 6 is performed in consideration of the case of poor quality. That is, in Q5, whether or not the resistance value reduction amount (maximum reduction amount) from the maximum resistance value to the end of energization after the resistance value becomes maximum is large, more specifically, the resistance value reduction amount. Is greater than or equal to a predetermined threshold value α1. If the determination in Q5 is YES, the amount of heat generated after the resistance value is maximized is sufficiently secured, so that the quality is determined to be good in Q8 (OK determination).
[0022]
If the determination in Q5 is NO, further, in Q6, whether or not the resistance value decrease rate after the resistance value becomes maximum is large, that is, the maximum resistance value decrease rate is equal to or greater than a predetermined threshold value. Is determined. If the determination in Q6 is YES, the amount of heat generated after the resistance value is maximized is sufficiently large, and it is determined in Q8 that the quality is good. When the determination in Q6 is NO, it is determined in Q7 that the quality is defective.
[0023]
When the determination in Q4 is YES, it is basically considered that the quality is defective, but the determination of Q9 to Q11 is performed in consideration of the case of good quality. That is, in Q9, whether or not the resistance value decrease amount after the resistance value becomes maximum is large, that is, the maximum resistance value decrease amount may be a predetermined threshold value α2 (α2 = α1 or α2 <α1). Whether or not is greater than or equal to). If YES in Q9, whether or not the increase rate of the resistance value is large in Q10 until the resistance value becomes maximum, that is, whether or not the maximum increase rate of the resistance value is equal to or greater than a predetermined threshold value. It is determined whether or not. If the determination in Q10 is YES, in Q11, is the resistance value increasing acceleration until the resistance value reaches the maximum value, that is, whether the resistance value maximum increasing acceleration is equal to or greater than a predetermined threshold value? It is determined whether or not. If the determination in Q11 is YES, it is determined in Q12 that the quality is good. When the determination of Q9, Q10 or Q11 is NO, it is determined that the quality is defective.
[0024]
If FIG. 9 is supplementarily explained, Q6 is provided in order to further improve the accuracy of quality determination, and may be omitted. Q5 indicates the degree of decrease in the resistance value, and instead of the amount of decrease in the resistance value, it may be determined whether or not the rate of decrease in the resistance value is large (the resistance value decrease rate is When it is larger than a predetermined threshold value, the quality is judged as good). The determination may be made by both the resistance value decrease amount and the resistance value decrease rate. In this case, when the resistance value decrease amount is larger than a predetermined threshold value, or the resistance value decrease rate is a predetermined value. It may be determined that the quality is good when one of the conditions when the value is larger than the threshold value is satisfied (or condition setting, and in order to more positively exclude defective quality and It is also possible to set conditions.)
[0025]
When YES is determined in Q4, it is not necessary to determine Q12. Moreover, although the resistance value increasing speed at Q10 indicates the resistance value increasing rate, the resistance value increasing rate may be the resistance value increasing amount. Further, although Q9 may be omitted, it is preferable to set Q9 in order to more surely prevent erroneous determination of defective quality as good quality. In any case, when the determination in Q4 is YES, it is a process of picking up good quality, so it is preferable to set in a direction in which conditions for determining good quality are tightened. That is, the condition that is determined to be good quality when NO is determined in Q4 is the or condition of a plurality of condition settings, whereas the condition that is determined to be good quality when YES is determined in Q4 is When a plurality of conditions are set, it is preferable to set the and condition.
[0026]
The elapsed time until the resistance value reaches the maximum is not determined as shown in FIG. 4, but the time until the point indicating the maximum resistance value among the detected resistance values at each sampling time is determined as it is, as in the past. It may be. The object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing an example of a change in resistance value in spot welding.
FIG. 2 is an explanatory view showing a welding state in each welding progress state in the characteristic diagram of FIG. 1;
FIG. 3 is a diagram showing an example of a control system for detecting a change in resistance value and determining quality.
FIG. 4 is a diagram illustrating a preferable example of determining an elapsed time until the resistance value becomes maximum.
FIG. 5 is a simplified cross-sectional view showing an example of a nugget growth process.
6 is a diagram showing a change in resistance value in FIG. 5;
FIG. 7 is a simplified cross-sectional view showing another example of the nugget growth process.
FIG. 8 is a diagram showing a change in resistance value in FIG. 7;
FIG. 9 is a flowchart showing a control example for quality judgment according to the present invention.
[Explanation of symbols]
1, 2: Base material 3, 4: Electrode 5: Nugget 6: Toroidal coil

Claims (11)

A first step of detecting a change in resistance value between electrodes during spot welding;
A second step of obtaining a comparison result of whether the elapsed time from the start of energization to the maximum resistance value is smaller or larger than a predetermined time set in advance;
A third step of determining whether the quality of welding is good or not based on different resistance value change states when the comparison result is large and small;
A method for judging quality in spot welding, characterized by comprising: In claim 1,
When the comparison result in the second step is large, the resistance value change state in the third step is the degree of increase in the resistance value.
A quality judgment method in spot welding characterized by the above. In claim 1,
When the comparison result in the second step is large, the resistance value change state in the third step is a resistance value increase degree and a resistance value decrease degree.
A quality judgment method in spot welding characterized by the above. In claim 1,
When the comparison result in the second step is small, the resistance value change state in the third step is the degree of decrease in the resistance value.
A quality judgment method in spot welding characterized by the above. In any one of Claims 1 thru | or 4,
The elapsed time until the resistance value reaches the maximum is determined as the time at which the maximum slope of the resistance value rises and the maximum slope of the resistance value reduction intersects.
A quality judgment method in spot welding characterized by the above. Resistance value change detecting means for detecting a resistance value change between electrodes during spot welding;
Elapsed time determination means for determining an elapsed time from the start of energization to the maximum resistance value based on the detection result of the resistance value change detection means;
A magnitude determination means for determining whether the elapsed time determined by the elapsed time determination means is smaller or larger than a predetermined time set in advance;
When the determination result by the size determination means is large and when it is small, the quality determination means for determining quality of welding based on different resistance value change states;
A quality determination apparatus in spot welding, comprising: In claim 6,
When the determination by the size determination means is large, the quality determination means is configured to determine quality quality based on the increasing speed of the resistance value.
A quality determination apparatus in spot welding characterized by the above. In claim 6,
When the determination result by the size determination means is large, the quality determination means is configured to determine quality based on the resistance value increasing speed and the resistance value decrease amount.
A quality determination apparatus in spot welding characterized by the above. In claim 6,
When the determination result by the size determination means is small, the quality determination means is configured to determine quality quality based on the amount of decrease in the resistance value.
A quality determination apparatus in spot welding characterized by the above. In any one of Claims 6 thru | or 9,
The elapsed time determining means is configured to determine the time that is the intersection of the maximum slope of resistance value increase and the maximum slope of resistance value decrease as the elapsed time,
A quality determination apparatus in spot welding characterized by the above. In any one of Claims 6 thru | or 10,
The resistance value change detecting means is
Voltage change detection means for detecting a change in voltage between the electrodes;
Current change detection means for detecting a change in current flowing through the electrode;
Resistance value change determining means for determining a change in resistance value based on the voltage change detected by the voltage change detecting means and the current change detected by the current change detecting means;
Composed of,
A quality determination apparatus in spot welding characterized by the above.

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