JPS6120673A - Resistance welding method - Google Patents

Abstract

PURPOSE:To stablize uniformly a welding quality by changing the pressurizing force according to the ideal program on the changing relation between the resistance values among electrodes of various sorts of welding materials and the electrode pressurizing force in a resistance welding and by operating the welding with detecting the progress of the resistance between electrodes with high accuracy. CONSTITUTION:The changing relation of the variation in the resistance values among electrodes of resistance welding of various sorts of welding materials and the electrode pressurizing forces is programmed. With performing a resistance welding according to the program for the variation in electrode pressurizing forces which sharply shows the progress of the resistance values among electrodes thereof, the highest ranked resistance value is detected with high accuracy and the welding is finished after the prescribed hours. With forming a good welding nugget irrespective of the property of the welding material the welding quality is stabilized uniformly. The variation in the pressurizing forces thereof can be simply realized by an electricity and air pressure proportional transducing valve and microcomputor technique.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding method in which welding quality is guaranteed by detecting the voltage between electric currents during welding and controlling the welding current, the current application time, or both.

It has long been widely accepted that the transition of interelectrode resistance during welding has a good correlation with the growth of nuggets in the weld zone, and various adaptive control methods have been proposed to utilize this fact to ensure welding quality. , has been put into practical use.

FIG. 1 shows a typical example of the change in interelectrode resistance of a bare steel plate without surface treatment in general single-phase AC welding. FIG. 1a shows an unstable region immediately after the start of energization, and the behavior of the interelectrode resistance during this period depends on the degree of contact with the material to be welded, the state of surface contamination, etc. This surface contact resistance disappears in 1 to 2 cycles after the start of current supply, and the interelectrode resistance rapidly decreases. Next, in FIG. 1, an increase in the specific resistance of the material to be welded due to a rise in the temperature of the weld zone, a softening of the weld zone, and an expansion of the energized path area due to crushing progress simultaneously. During this period, the increase in weld resistance due to the increase in specific resistance exceeds the decrease in resistance due to the expansion of the current carrying path area, and as a result, the interelectrode resistance increases and reaches a maximum value near the end of this process. During this period, nuggets begin to form and grow. As shown in FIG. 1C, the current carrying path area continues to expand as the nugget grows, but the resistivity reaches a saturation value and becomes approximately constant, so the interelectrode resistance decreases.

In the conventional adaptive control method, based on the above fact, a predetermined current value is set in advance based on the viewpoint that the amount of decrease of the interelectrode resistance from the thickest point or its integral value has a deep correlation with the nugget diameter. The voltage between the electrodes is detected moment by moment during welding, and the transition of the resistance between the electrodes is determined by dividing this by the current value. Welding quality was guaranteed by cutting off the current when the corresponding value was reached.

However, although the adaptive control method described above is effective for bare steel sheets without surface treatment, it is difficult to weld surface-treated steel sheets such as galvanized steel sheets and synchrometal sheets, which have been in increasing demand in recent years. The kimono has a large effect on the behavior of the interelectrode resistance, and generally narrows the amount of displacement, resulting in a decrease in the accuracy of the detected amount and, in turn, a deterioration in welding quality.

As an example, FIG. 2 shows a typical example of the change in interelectrode resistance of an alloyed galvanized steel sheet. In the initial unstable region shown in FIG. 2a, the electrical resistance of surface zinc is lower than that of iron, so the interelectrode resistance is slightly lower than that of a bare steel plate. At the beginning of nugget formation and early growth as shown in Figure 2, the zinc around the weld zone melts and fills the gaps in the welding material, expanding the current carrying path area, resulting in a decrease in interelectrode resistance. slow the rise,
Moreover, the maximum value itself is also low. Finally, in the nugget growth process shown in Figure 2C, the current carrying path area has already been expanded by molten zinc, so even if the nugget diameter increases, the resulting decrease in interelectrode resistance is not as noticeable in the case of a bare steel plate. . Therefore, it has been extremely difficult to accurately detect the amount of decrease or its integral value because the occurrence of extremely thick dots is not clear and the rate of decrease in interelectrode resistance is slow.

The present invention has been made in order to solve this problem, and the electrode pressurizing force, which was conventionally applied at a constant value during welding, is changed to correspond to the type of material to be welded, that is, the material, plate thickness, surface treatment status, etc. Furthermore, in order to avoid narrowing the transition of the interelectrode resistance, test welding is performed on the target welding material in advance to promote nugget growth and to prevent the behavior of the interelectrode resistance from becoming noticeable during welding. The electrode pressure cover turn is determined, and the subsequent welding work is performed using the pressure cover turn to ensure the growth of the nugget.
There is a method that allows the transition of interelectrode resistance during welding to be detected with high precision and guarantees uniform welding quality.

FIG. 4 shows an embodiment in which the present invention is applied to welding of alloyed galvanized steel sheets, and will be described below with reference to the drawings. In Fig. 4, pressure waveform 1 indicates that welding was performed with a constant pressure according to the conventional adaptive control method, and waveform 2 shows the transition of interelectrode resistance in that case, and is the same as the waveform in Fig. 2. be. Waveform 3 is an appropriate pressing force waveform for the welding material obtained through experiments, and takes into consideration improvement in weldability and waveform 4, that is, improvement in detection accuracy of the transition of interelectrode resistance at that time. Compared to conventional adaptive control methods, it first compensates for the decrease in clear stream density due to the expansion of the energized path area brought about by molten zinc.

As a result, the temperature of the weld zone increases and the specific resistance also increases, resulting in an increase in the interelectrode resistance and a clear maximum point.

At this point, nuggets have already been generated and have started to grow, so from now on, the pressure is increased to prevent them from scattering.
Grow nuggets somewhat slowly. Waveform 3 as above
If energization is carried out, the interelectrode resistance will change as shown in waveform 4, which means that, for example, if the amount of decline from the maximum point or its integral value is detected, the accuracy will be much better than in the case of waveform 2. That is clear. Therefore, fluctuations in the growth rate of nuggets due to various disturbances can be detected more sensitively, good reproducibility can be obtained, and uniform welding quality can be guaranteed.

In order to find the appropriate pressure waveform, welding experiments should be conducted in advance for each type of welding material to ensure good welding quality.
In addition, the electrode pressurization cover pattern is determined while taking into consideration that the amount of displacement in the transition of the interelectrode resistance becomes large. In the past, changing the pressurizing force during a single welding operation required a large amount of money and was difficult to realize, but with recent advances in electropneumatic proportional conversion valves and microconbeater technology, etc. The background of the present invention is that progress has made this possible.

[Brief explanation of the drawing]

FIG. 2 is a typical example of the change in interelectrode resistance when a bare steel plate without surface treatment is energized with an appropriate constant current value. Moreover, FIG. 2 shows the results obtained by applying this method to an alloyed galvanized steel sheet. FIG. 3 is a cross-sectional view of a welded portion of an alloyed galvanized steel sheet showing a situation in which molten zinc suppresses sheet separation and expands the current carrying path area. In FIG. 4, waveforms 1 and 3 indicate the electrode pressing force, and waveforms 2 and 4 are changes in interelectrode resistance during welding, corresponding to waveforms 1 and 3, respectively. Figure 1 Figure 3 Figure 4 Procedural Amendment (OK) November 19, 1980 Commissioner of the Patent Office Manabu Shiga Patent Application No. 141749 of 1981 2 Name of the invention Resistance welding method 3 Person making the amendment Relationship to the incident Name of patent applicant Dengunsha Title Dengensha Seisakusho Co., Ltd. Correct "Figure !82" to "Figure 1" on page 7, line 13 of the detailed statement.

Claims (1)

[Claims] A resistance welding method characterized in that the generation of a weld nugget is ensured by changing the electrode pressurizing force according to the program during the actual welding period.