JPS59225889A - Resistance welding method of steel plate treated with high resistance film on surface - Google Patents

Abstract

PURPOSE:To obtain a weld nugget having stable and high quality by detecting the inter-chip resistance at the time when the weld nugget begins to form and controlling the weld time with said resistance value as a reference. CONSTITUTION:The change ratio of the inter-chip resistance is successively compared at every prescribed cycle, and when the change rate attains the value smaller than a set reference value A, the inter-chip resistance at the point of that time as a reference value B is held in a holding circuit 5 for the reference value of the inter-chip resistance and an arithmetic circuit 6 for stopping current conduction is operated so as to start the integration with time of the difference between said value and the succeeding inter-chip resistance. The current conduction is stopped by the next timer circuit 7 for stopping the current conduction according to the output signal therefrom and sure control is thus automatically accomplished so as to form a weld nugget having good quality.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to lap resistance welding methods such as spot bath welding of surface-treated steel sheets with a synchrometal resistive coating, and more particularly to adaptive control of weld nuggets in spot welding VC.

Recently, Synchro Metal has been widely used in automobiles.In general, Synchro Metal has an insulating coating.
In spot welding of +l・fl 4, the initial value of the bath welding current and its current -2 rise rate are delicate, and explosions often occur between the electrode tips at the beginning of the welding energization period [4 This may damage the surface of the material or cause the tip of the tip to melt and carbonize.
Welding this glaze is even more difficult.

On the other hand, as shown in Figure 1, the waveform of the chip-to-chip resistance of a so-called polished mild steel plate that has not been surface-treated shows an increase during the 2nd to 3rd cycles after the start of energization, and then increases during the 3rd to 4th cycles. It reached a peak around S: 11μ, and a welding nugget began to form, and from then on,
As the bath nugget grows, the chip-to-chip resistance gradually decreases.

Recent experiments have shown that the waveform of the interchip resistance in the case of a surface-treated copper plate with a high-resistance film such as synchrometal is
As shown in the figure, from time t1 to t2, there is a section where the rate of decrease in the inter-chip resistance is large, and section 11, where the rate of decrease from t2 onwards is much smaller than the section 11-12.
It is certain that there are two intervals of 1.

The waveform of the inter-tick resistance in FIG. 2 can be explained as follows. In the section from energization to time t1, the coating of the surface-treated 1I heat insulation thread cannot be removed by energization. This is a section where high resistance is exhibited due to insufficient resistance, and from section tl to t
2, this film is suddenly torn, and the resistance between grooves is @,
This is an area where the amount decreases sharply.

Furthermore, as the current is continued, the insulator is completely removed, and weld nuggets begin to be generated from the second current application time t2, and after t2, as the nuggets grow, the rate of decrease in the inter-chip resistance decreases to the interval t1. - It becomes very small compared to t2 and gradually decreases.

By the way, as an adaptive control method to obtain a proper welding nugget by detecting the inter-chip resistance and detecting the generation state of bath welding nuggets from the percentage sign of its waveform and stopping the current supply, the following method is adopted. has been done.

As one method, as shown in FIG. The resistance 1111/\R is %1
There is an adaptive control method that completely stops energization when the welding occurs and obtains a suitable weld nugget.

In this case, Vζ is set during energization, for example, at 3
After ~4 cycles, the local maximum (iM', )'max
occurs, and from this point a weld nugget begins to form, and as the weld nugget continues to grow due to the applied current,
If the inter-chip resistance gradually decreases, the local maximum value may be sample-held and used as the reference value for dividing the resistance. The waveform of the inter-resistance has a high resistance of 41 cycles due to the high-resistance IIIA at t1 years after the start of energization, and when this waveform is held at its peak in the same way as for mild steel, the value of l'l is held and this is used as the reference value. As one person,
Since a predetermined %R is calculated, the %R reaches a predetermined value before the welding nugget is fully formed, and the current supply is stopped, resulting in a defective weld. As an example, without comparing and determining the change reduction rate of the chip-to-chip resistance, sample and hold the local maximum value Pmax of the chip-to-chip resistance, use this as a reference value, and calculate the difference from the chip-to-chip resistance from then on. Pmax shown in Figure 1 is a method in which the energization time is adjusted so that the integral value becomes a predetermined integral value, and when this is reached, the energization is stopped to obtain an appropriate nugget. There is also an adaptive control method in which when the area C of the diagonally shaded portion of the triangle formed by Q and Q reaches a predetermined value, the current supply is stopped and welding is completed. In this case as well, this is fine in the case of mild steel, but in the case of synchrometal, the local maximum value PI is peak held at time t1 as shown in Figure 2, and from this point onwards the interchip resistance Time integration of the difference is started, and before enough nuggets are generated, vcpv
When the r value reaches a certain value, the current supply stops, making it impossible to obtain a proper weld nugget.

The present invention provides a method that eliminates such welding defects and allows reliable adaptive control even for high-resistance coating surface-treated copper plates.

In order to avoid such problems, the inter-chip resistance that decreases from the position of Pl is compared sequentially, even in one cycle angle, and when the resistance change rate reaches a preset rate of change, that is, the reference value A, The present invention is characterized in that the value of the inter-chip resistance at that point in time is set as the reference value of the inter-chip resistance which will gradually decrease thereafter, and the reference value B is used as the starting point for performing the weld nugget adaptive control.

Hereinafter, an apparatus for carrying out the entire method of the present invention will be explained based on the embodiment shown in FIG. In the figure, code (1),
+23 indicates the electrode tip of the spot welder.

(3) is an interchip resistance detection circuit. This circuit (3)
The inter-tip resistance is detected by dividing the voltage l'lJj detected from both ends of the electrode tip by the welding current. (4
) is an interchip resistance reference detection circuit, and this circuit (4
) is explained based on Figure 4, that is,
The resistance values a, b, c... of the inter-chip resistance waveform are as follows:
■After holding the sample for each cycle, it is stored in the memory of the microcombinator, and the following calculations are performed for each cycle, and the values are used to calculate the inter-tick resistance when enough weld nuggets grow. Decreasing side 6- Yes, that is, comparison with reference value A is 1.

n,,:l:,,lnb-c-q,,dd-e6-7f
'a + 'Tj + c + -■-r
e, that is, now, the value of 11n is -f: Nezoredan -W
= o, a.

b-c c7 d-e'-1,-
=(1,8,.-=0.2. Shoulder 1---0.15
, q''' = (1,04, then if the standard value A for sufficient weld nugget growth is set to -0,04, the inter-chip resistance value that changes from time to time during the welding process will be equal to the previous standard f, When hiA reaches 0.04 or less, a full hold signal to create a reference value B and a signal to start operation of the energization stop calculation circuit are transmitted.

(5) Using the full hold circuit, all bases fv and values B corresponding to the second local maximum value are created. (6) receives the operation start signal from the interchip resistance reference value detection circuit (4), calculates t, 1 to tf (reference value B-1 ()), and compares the calculation result with the reference value C. After comparison, a timer 1 stop signal is sent to the next timer energization 1 stop circuit (7).

The above standard value c (4) represents the area of the shaded part in Figure 2 and has a correlation with the thickness of the weld nugget.In other words, the standard value C is an integral value that indicates the depth of the weld nugget. It is.

With the above structure bV, in FIG.
From t2 to t2, the change in inter-chip resistance decreases at a large rate, and since the period from t2 to ta is a weld nugget growth period, the change rate C' in inter-chip resistance is small, so the predetermined cycle is For example, compare the rate of change in resistance between chips sequentially every cycle, and when the rate of change becomes smaller than the set value t and standard value A, the rate of change in resistance between chips at that time ((1 resistance as standard value B Hold the inter-chip resistance reference value hold circuit (5) and set V so that the difference between the inter-chip resistance and the subsequent time is 15 rl.
Here, the 9th circuit (6) for stop operation is made by ILR#, and according to this output signal, the next timer energization stop circuit (7) stops the energization at the energization time t8 and produces a welding nugget of good quality. Raw) Automatically performs a certain KIJ to make it grab.

Above, +: Inconsistency with the method of development 1 can sometimes cause weld nuggets to grow at about While monitoring the ever-changing rate of inter-chip resistance, the inter-chip resistance at the time when weld nuggets begin to grow is detected, and the entire energization time is controlled based on this resistance value, resulting in stable, high-quality weld nuggets. Obtainable.

[Brief explanation of the drawing]

Figure 1 is a graph showing an example of conventional adaptive control, showing changes in the inter-chip resistance waveform of a polished steel plate, and Figure 2 is a graph showing the inter-chip resistance of spot bath welding of a high-resistance surface-treated tuna l plate. Figure 3 is a graph showing the complete picture of the control method related to waveform changes and non-firing ψ], Figure 3 is an electrical block diagram of the device for carrying out the method of the present invention, and Figure 4 is a diagram showing the inter-chip resistance reference value detection. Function/operation 'f' of circuit (4): This is a rough diagram showing inter-chip resistance waveforms for explanation. FIG. 5 is a rough diagram showing changes in the inter-chip resistance waveform of a polished steel plate to explain another example of conventional adaptive control. -9--531 Fig. 1 m-Electrification time Fig. 2 Fig. 3] Fig. 5 Energization time Fig. 4 max △R %R = sieve xloO'u

Claims (1)

[Claims] In resistance welding of surface-treated steel sheets with high-resistance coatings, -
1- During the process of generating a bath contact nugget while removing the insulating coating of the steel plate, the inter-chip resistance that fades is compared sequentially at each predetermined cycle, and the reduction rate of the inter-chip resistance is determined to a preset reference value. When A is reached, the current inter-chip resistance is held at that point, and the reference value for the inter-chip resistance that continues to decrease thereafter is set to a reference value, and the reference value B is used as the starting point for performing weld nugget adaptive control. A resistance welding method for high-resistance coating surface-treated steel sheets.