KR20010002300A - Method for detecting expulsion generating state - Google Patents

Abstract

PURPOSE: A method for checking an expulsion of a spot welder is provided to accurately check the expulsion using a dynamic resistance value. CONSTITUTION: First, the dynamic resistance value of a spot welder is sensed during welding. Then, the probability of the expulsion is detected with the variation of a dynamic resistance value from the next cycle after detecting a maximum value to a final conductive cycle. When the probability of the expulsion is more than a predetermined value, a system decides whether the expulsion happens or not. Then, the expulsion is accurately checked with using the dynamic resistance value.

Description

How to determine the occurrence of pulsation in a spot welder {METHOD FOR DETECTING EXPULSION GENERATING STATE}

The present invention relates to a welding current control device of a spot welder, and more particularly, to accurately detect whether or not an occurrence of an impulse is generated by using a copper resistance value when determining whether an expansion occurs to perform an automatic stepper function. The present invention relates to a method for determining the occurrence of expulsion of a spot welder.

Resistance spot welding (hereinafter referred to as spot welding) is a process in which a large current (8,000A to 30,000A) is supplied between base electrodes by pressing two or more thin sheets between the electrode tips with air pressure. It is a welding method that can obtain a simple and clean joint by melting and joining the contact part of the base material by Joule heat using contact and compression resistance. There are many factors that determine welding quality in this spot welding, but among them, the welding current, energization time (or energization cycle), and electrode pressing force are three basic factors.

1 is a view showing a typical dynamic resistance curve in spot welding, Figures 2a to 2b is a view showing a change in the dynamic resistance characteristics when the welding current is changed in a state in which the pressing force is kept constant, a welding base material The results obtained using two layers of cold rolled steel sheets 1.0 mm thick, which are commonly used in production, are shown.

Welding quality is generally a series of melting start (point a), nugget growth (point b), and indentation (point c) as the energization cycle increases, as shown in FIG. It is stabilized through the process. At time point d, an expulsion occurs. If the welding time is longer than necessary or the welding current is too large, the melt spreads, and the weld specimens around the melt cannot sustain the electrode force. In this case, an expulsion occurs and molten metal is ejected between the specimens, and at this time, the dynamic resistance is rapidly reduced. Here, the explosion phenomenon ensures the size of the nugget sufficient, it is used as a guarantee for the welding quality, but such an expulsion gives the operator anxiety about the disaster, there is a risk of damage to the welding equipment. Therefore, the optimum welding condition that can produce the highest welding strength with the least energy is considered to be the welding condition immediately before the expulsion occurs.

Therefore, the optimum welding quality should only be performed until the dynamic resistance value increases to some degree of slope and then falls to the value immediately before the impulse occurs after having the maximum value Rmax. If the heat input (determined by the welding current and the number of energizing cycles, but once the number of energizing cycles is fixed. Therefore, the heat input corresponds to the welding current value) is insufficient, the dynamic resistance value as shown in FIG. Since the maximum dynamic resistance value Rmax does not drop to an appropriate dynamic resistance value, the welding quality cannot be guaranteed. On the contrary, when the heat input is excessive, as shown in FIG. 2B, the copper resistance value changes rapidly from the maximum dynamic resistance value Rmax, which is not preferable.

However, the user cannot set the welding current value while checking the change of the dynamic resistance value one by one, and in particular, when the electrode tip wears, the current value decreases as it wears, and thus the current value needs to be increased. That is, when performing welding, it is necessary to automatically provide a desirable welding current value according to the characteristics of the welding machine and the base metal, and in response to this need, Patent Application Nos. 94-3146 and 96-29481 provide an automatic stepper. Suggested a function. In the automatic stepper function, the user sets the welding reference RBI number and the reference explosion occurrence number. The welding criterion RBI is the number of times the welding is performed, and the reference explosion occurrence number is the number of times the expulsion should be generated within the set welding criterion RBI. In the state where these reference values are set, welding is performed a number of times corresponding to the welding reference RBI number, and the number of occurrences of expulsion and the number of reference occurrences that occur when the welding is performed are compared. As a result of the comparison, the welding current is excessive when the number of occurrence of the pulverization is greater than or equal to the reference occurrence, and the welding current is lowered to a preset ratio. However, when the number of occurrences of the pulsation is less than or equal to the reference occurrence, the welding current is preset. By increasing the ratio, the welding current is near the impulse generation threshold.

On the other hand, as described above, in order to perform the conventional automatic stepper function, it is necessary to accurately detect the occurrence of the impulse. For this purpose, conventionally, the probability of occurrence of expulsion was used. The probability of occurrence of expulsion Epro detects the probability of occurrence of expulsion during welding by using a change amount of the dynamic resistance value, and is detected by the following equation (1).

Here, R _max means the maximum value of the copper resistance in the change curve of the copper resistance value, as shown in Figure 3, ΔR _max means the maximum value of the change in copper resistance every half cycle in every welding cycle, R _end means dynamic resistance in the last energizing cycle, and R _min means minimum value of dynamic resistance.

In other words, the probability of occurrence of expulsion Epro in Equation 1 is the difference between the maximum value R _max of the dynamic resistance value and the dynamic resistance value R _end of the last energizing cycle, and the change amount ΔR _max of the maximum dynamic resistance. Is set as the ratio of.

Since the probability of occurrence of explosion (Epro) literally means only the probability of occurrence of explosion, in order to finally determine that the occurrence of explosion, the probability of occurrence of explosion (Epro) should be more than a predetermined value. Therefore, conventionally, the test welding is carried out with a real material, and the judgment reference value which can determine that an expulsion generate | occur | produced is set, and it determines finally that an expulsion generate | occur | produced only when the expulsion generation probability Epro is more than a judgment reference value.

However, such a conventional occurrence probability detection method has a low reliability in the amount of change in dynamic resistance per half cycle under a noisy environment, which causes a lot of problems in application alone in a real environment. In addition, the applied welding machine also has a variable variation in dynamic resistance (R _max -R _end ) depending on the type of plate, and in the case where the variation width (R _max -R _end ) is very small, a small amount of noise changes the maximum dynamic resistance variation ( ΔR _max ) has a big influence, causing significant distortion in the occurrence probability (Epro) value. In other words, when the change resistance (R _max -R _end ) of the dynamic resistance is large, the influence by noise is small, but when the change resistance (R _max -R _end ) of the dynamic resistance is small, the influence by noise is large and it is determined whether or not an explosion occurs. There is a problem that cannot be judged accurately.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a method for determining the occurrence of an explosion in a spot welding machine, which can accurately detect whether or not an occurrence of an impulse is generated using a copper resistance value.

1 is a view showing the change in dynamic resistance of the spot welding machine,

2 is a view for explaining the relationship between the welding current and the dynamic resistance in the spot welder,

3 is a diagram illustrating a dynamic resistance change characteristic for explaining a conventional formula for detecting probability of occurrence of pulverization;

4 is a block diagram of an apparatus for determining welding current of a spot welder according to the present invention;

5 is a diagram illustrating a dynamic resistance change characteristic for explaining a formula for detecting an occurrence probability of pulsation according to the present invention;

FIG. 6 is a diagram illustrating the dynamic resistance change characteristic for explaining a formula for detecting an occurrence probability of expulsion according to the present invention. FIG.

<Description of the symbols for the main parts of the drawings>

10: welding machine

20: copper resistance detector

30: expulsion detector

In order to achieve the above object, the present invention, in the method of determining the occurrence of the impulse on the spot welding machine based on the change in the copper resistance of the base material during spot welding, the maximum value of the amount of change between the copper resistance and the copper resistance The occurrence of expulsion is determined on the basis of the amount of change in dynamic resistance from immediately after the maximum value of the change in liver to the last energization.

4 shows a schematic block diagram of the apparatus of the present invention. In the illustrated block diagram, reference numeral 10 denotes a general welding machine, and the welding current of the welding machine 10 is controlled by a welding current control signal of the expulsion detector 30 described later. The copper resistance value generated at the time of performing the welding by the welder 10 is detected by the copper resistance detector 20, and the detected copper resistance value is provided to the explosion detector 30.

The impulse detector 30 determines whether an impulse is generated using the method according to Equation 2, and provides a welding current control signal corresponding thereto to the welder 10.

Here, R _max means the maximum value of the copper resistance in the curve of the copper resistance value as shown in Figure 5, ΔR _max means the maximum value of the change in the copper resistance of the adjacent cycle, R _end in the last energizing cycle LD means the dynamic resistance, and LD means the standard deviation of dynamic resistance values from the cycle (t + 1) to the last energization cycle after the cycle where ΔR _max is sensed.

The physical meaning in Equation 2 is as follows. First, as a result of analyzing the dynamic resistance waveform, it can be seen that when an explosion occurs, the standard deviation of the dynamic resistance value from the next cycle (t + 1) at the time of occurrence of the explosion to R _end is extremely small. Therefore, when the expulsion occurs in Equation 2, the denominator decreases according to the degree, and since the ΔR _max is relatively large, the total amount has a large value. On the contrary, when no pulsation occurs, the amount of deviation since the cycle in which ΔR _max is sensed is large, so that the value of the overall occurrence is reduced by that amount, thereby overcoming the ΔR _max reliability problem due to noise.

Another method of detecting the occurrence probability of expulsion is to detect as equation (3).

In the above formula, ST denotes resistance values on the straight line when connected with a straight line from the time when ΔR _max appears to the last welding cycle instant (t _end ) as shown in FIGS. 6A and 6B, and R indicates the time when ΔR _max appears. It means the dynamic resistance value of the moments sampled from (t) to the last welding cycle moment (t _end ). In addition, since Dev means a command to obtain a standard deviation amount, Equation 6 represents a standard deviation amount of deviation amounts between the virtual copper resistance value ST and the sampled copper resistance value R.

The reason why the occurrence probability Epro can be detected by Equation 3 can be clearly seen from FIGS. 6A and 6B. FIG. 6A illustrates a case where an explosion does not occur, and FIG. 6B illustrates a case where an explosion occurs. As shown in FIG. 6A, when the occurrence of an explosion occurs, the probability of occurrence of the explosion (Epro) by Equation 3 is high. However, when the expansion does not occur, the wing of Equation 3 is calculated as shown in FIG. 6B. The reason for this is that the probability of occurrence of spuron is lowered. This is because when the impulse does not occur, the copper resistance becomes stable, i.e., gradually decreases since the maximum dynamic resistance value R _max enters the cooling stage. This is because it has a characteristic to.

Therefore, it will be preferable to use Equation 2 or Equation 3, rather than Equation 1, to determine whether occurrence of an expulsion is performed.

The expulsion detector 30 that detects an occurrence occurrence probability by Equation 2 or 3 compares the detected occurrence occurrence probability with a predetermined reference value. Here, the reference value should be set to a value (expansion occurrence probability value) that can be determined that expulsion has occurred by performing test welding with a real material.

The explosion detector 30 compares the number of occurrences of expulsion detected within a predetermined number of RBIs, and when the number of occurrences of the impulse is greater than or equal to the reference occurrence number, the welding current is excessive. The welding current control signal for lowering the welding current to the preset ratio is provided to the welder 10. However, when the number of occurrences of the pulsation is less than or equal to the reference expulsion number, the welding current control signal for lowering the welding current to the preset ratio is provided to the welder ( 10) to ensure that the welding current is near the impulse generation threshold.

As described above, in the present invention, the probability of occurrence of pulverization can be judged more precisely, and thus an optimum welding condition can be easily detected.

Claims (3)

In the method of judging the occurrence of expulsion of the spot welder based on the change in the dynamic resistance of the base material during spot welding, Determination of whether the occurrence of an impulse on the basis of the amount of change in dynamic resistance from immediately after the maximum value of the change amount between the copper resistance and the change value between the copper resistance until the last energization Way. The method of claim 1, The occurrence of the expulsion is calculated using the amount of change in the copper resistance from immediately after the maximum value of the change amount between the copper resistance and the change value between the copper resistance until the last energization. Epro), (ΔR _max is the maximum value of dynamic resistance change every cycle, and LD is the deviation of dynamic resistance values from the next cycle to the last energizing cycle of the cycle where ΔR _max is detected.) The method of determining the occurrence of explosion in a spot welder, wherein the occurrence of expansion is determined when the probability of occurrence of occurrence of explosion is greater than a predetermined value. The method of claim 1, The occurrence of the expulsion is calculated using the amount of change in the copper resistance from immediately after the maximum value of the change amount between the copper resistance and the change value between the copper resistance until the last energization. Epro), (ST is the resistance value when connecting ΔR _max from the last welding moment (t _end ) in a straight line, R is the moment when ΔR _max is sampled from the time of the final welding cycle (t _end ). Is the copper resistance value, and Dev is the standard deviation. The method of determining the occurrence of an explosion in a spot welder, wherein the occurrence of expansion is determined when the probability of occurrence of occurrence of expansion is greater than or equal to a predetermined value.