JPS63123578A - Welding current control method for resistance welding equipment - Google Patents

Abstract

PURPOSE:To improve the quality by storing the reference electricity amt. found from the electricity amt. of an electrification initial part, peak part and electrification last part among the electricity amt. of the case of welding plural times and controlling the welding current with tracing this electricity amt. CONSTITUTION:The material to be welded in welded in plural times and the voltage between electrodes while under respective welding time cycle is inputted to a microcomputor 6 via a detection circuit 4 for voltage between electrodes and A/D convertor 5. The voltage value on each half cycle is stored by calculating it by the computor 6. In case of welding thereafter it is performed by controlling the electricity amt. with comparing the voltage between electrodes with the stored voltage. With this method, the reliability for the welding quality is widely improved.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention detects the state of the welded part during AC resistance welding,
In particular, the present invention relates to a welding current control method for a resistance welding device that can control the welding current according to the growth of nuggets.

[Conventional technology]

In general, in resistance welding, the welding quality is determined by various electrical quantities: voltage, current, resistance, which is the voltage divided by the current, electric power, which is the product of voltage and current, and the value integrated over the current application time for these K. It has long been well known that there is a deep relationship between

Therefore, the amount of electricity when welding the material to be welded under the optimum welding conditions is received from at least the two electrodes that hold the material to be welded, and this is stored as the standard amount of electricity. Various methods have been proposed for controlling the welding current so as to trace the standard quantity of electricity based on the quantity of electricity detected during welding.

For example, when the material to be welded is welded under optimal welding conditions, the amount of electricity is detected from an electrode or secondary conductor, and this detected amount of electricity is the amount of electricity most closely related to the welding quality of the material to be welded (voltage and current are Resistance, which is the voltage divided by the current, electric power, which is the product of the voltage and current, and furthermore, the value integrated over the energization time, etc.) and stored, and then detected during subsequent welding and processed in the same way. The welding current is determined by comparing the above memorized quantity of electricity to obtain the difference between the two quantities of electricity, and using this difference in quantity of electricity to automatically trace the standard quantity of electricity stored above. Equipment for resistance welding (Special Publication No. 56-29632 [Resistance Welding Method and Apparatus])
In a resistance welding control method that controls the welding current by manipulating the firing angle of a switching element, the voltage between the welding electrodes is monitored during welding, and the voltage between the welding electrodes is monitored for each power cycle after a certain period of time from the start of energization. The difference value ■ between the voltage I and the reference value ■ (the voltage value between welding electrodes for each power cycle when a good welding result is obtained) is detected, and the difference value and the firing angle of the switching element are calculated in advance. A manipulated variable is programmed, and the manipulated variable of the firing angle of the switching element corresponding to the difference value ■ is derived from the program and operated. From K, the welding electrode voltage ■ is made to follow the reference value UK. (% Publication No. 61-2477 "Resistance welding control method"), etc., most of the time, the amount of electricity (voltage between electrodes, etc.) when welding the materials to be welded under optimal welding conditions is used as the standard amount of electricity. This is a method in which the information is stored in a memory circuit.

However, with this method, when the material to be welded is, for example, sheet metal fitted together (the body and chassis of an automobile), there are large variations in the welding conditions, such as variations in the gap between the plates and the presence or absence of oil stains. Therefore, even under optimal welding conditions, welding using the standard amount of electricity obtained from welding a single material to be welded cannot handle all materials to be welded, and it is not possible to eliminate welding defects. .

For this reason, the amount of electricity obtained by welding multiple times (5 to 10 times), for example, the average value of the interelectrode voltages Vtl to ■tn, is determined every half cycle and is stored as the reference voltage Vs (standard amount of electricity). By having the circuit memorize every half cycle from a keyboard or the like, it is possible to perform good welding even if there are variations in welding conditions due to variations in the shape of the welded material, dirt, etc.

[Problem that the invention seeks to solve]

However, it is very time-consuming and inefficient to obtain the average value of the results of welding a plurality of times and store it in the memory circuit every half cycle.

The present invention has been made in view of the above-mentioned difficulties.
The standard amount of electricity to be stored in the memory circuit can be determined with a simple operation, and the standard amount of electricity can be easily set to correspond to various heat inputs depending on the welding characteristics of the welding material, and the welding current can be adjusted. The purpose of this invention is to provide a welding current control method that automatically controls the welding current.

[Means for solving problems]

The welding current control method for a resistance welding device according to the present invention includes: determining the average value of the amount of electricity obtained from at least both welding electrodes every half cycle when welding the welded material a plurality of times, and storing it as a standard amount of electricity; In a method of performing resistance welding using a welding current that is controlled to automatically trace the memorized standard quantity of electricity by comparing the quantity of electricity obtained during subsequent welding and the difference between the quantities of both types obtained. , for each of the electrical quantities when welding multiple times, calculate the average value of the electrical quantity at at least two points out of the three points of the initial energization part, the peak part, and the final energization part, and on the line connecting these points with a straight line. The amount of electricity determined every half cycle from 2000 to 2000 is the standard amount of electricity, or the point obtained by calculating the average value of the amount of electricity at at least two points, and these points and any point arbitrarily set for preheating or postheating. The welding current is characterized in that the quantity of electricity obtained every half cycle from a straight line connecting the lines is stored as a standard quantity of electricity, and the welding current is controlled so as to automatically trace this standard quantity of electricity.

[For production]

For each quantity of electricity when welding the material to be welded multiple times, find the average value of the quantity of electricity at at least two of the three points: the initial part of energization, the peak part, and the final part of energization, and connect these points with a straight line. Determine the amount of electricity for each half cycle from the dotted line or a line connecting these points with a point arbitrarily set for preheating or postheating, store this in the memory circuit as the standard amount of electricity, and store this standard electricity in the memory circuit. 5. Control the welding current to automatically trace the amount.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Figures 1 to 3 show mild steel (SP) with a plate thickness of 1.0 ms.
CC), using a CF type electrode with a tip diameter of 5.0 W, the inter-electrode voltage and inter-electrode voltage obtained when resistance welding was performed under the welding conditions of a pressurizing force of 190 KII, a welding current of 6.00 OA, and a current application time of 10 cycles. It shows the time course of resistance and welding current. As is clear from these figures, each curve draws a y-linear curve from the initial energization portion to the final energization portion C, sandwiching the peak portion a.

Therefore, instead of calculating the average value of the amount of electricity obtained from at least both welding electrodes every half cycle and using it as the standard amount of electricity when welding the material to be welded multiple times as in the conventional example, a. It is conceivable to define the standard quantity of electricity by connecting the three points b and C with a straight line.

Figure 4 shows the case where lightning and interelectrode voltage Vt are used as the quantity of electricity, and the three points of energization initial part b, peak part a, and energization final part C are connected with a straight line and the standard interelectrode voltage Vs is used. However, when comparing both type pressures Vt and Vs, the interelectrode voltage V
At t, there is a large difference between the voltage change degree β during the nugget rapid expansion period and the voltage change degree γ during the cooling period, and therefore the welding current changes suddenly to follow this difference, causing welding problems such as the occurrence of dust. have an unfavorable effect on quality. Therefore, if the peak part a of the interelectrode voltage Vt and the final energization part C are connected with a straight line to form the standard interelectrode voltage Vs, the degree of voltage change α at this Vs will be constant, and there will be no sudden change in the welding current and dust etc. can be prevented from occurring. Furthermore, if it is desired to adjust the standard interelectrode voltage Vs based on the welding results etc., this can be easily done by changing α.

As mentioned above, the standard quantity of electricity is defined as the line connecting the three points of the initial energization part, the peak part, and the final energization part of the quantity of electricity obtained from at least both welding electrodes when welding the material to be welded multiple times. Therefore, it is possible to easily set a standard amount of electricity that can accommodate various heat inputs depending on the welding characteristics of the materials to be welded.

Figures 5 to 7 show cases where the interelectrode voltage is used as a standard quantity of electricity, and voltage waveforms for various thermal controls are added to the basic interelectrode voltage that changes b-a-c. be. Fig. 5 shows an example in which a gentle preheating step (up slope) during the heating period Kb-b' of b-a is added, and Fig. 6 shows an example in which a preheating step (preheating step) during the heating period 1cb-b'-o of b-a is added. ) is added, and FIG. 7 is an example in which the post-heat treatment type of CcL is added to the cooling period of C.

The most distinctive feature of the present invention is that the standard electricity t(VS) can be easily stored in a memory circuit by having a linear configuration as described above. This point will be explained with reference to FIG.

FIG. 8 shows an embodiment of a device for implementing the welding current control method according to the present invention, in which 1 is a welding transformer, 3 and 3' are lead wires attached to welding electrodes 2 and 2', and 4 5 is an inter-electrode voltage detection circuit, 5 is an A/D converter, 6 is a microcomputer, and 7 is a standard electricity quantity setting mode and a welding current control mode used for multiple welding experiments to determine this standard electricity quantity. Keyboard circuit for switching and setting a program in advance for increasing or decreasing the conduction angle of the thyristor in order to control the welding current so that the standard electricity quantity is automatically traced, 8 is when the predetermined pressing force is reached. 9 is a microcomputer, an I10 circuit that controls the firing angle of a thyristor connected to the output side of the computer 6, and 10 is a thyristor circuit.

Next, the operation will be explained.

First, the standard electricity setting mode is selected using the keyboard circuit 7, the workpiece is welded multiple times, and the inter-electrode voltages Vtt to Vtn during each welding energization cycle are detected by the inter-electrode voltage detection circuit 4 and A/D converted. input to the micro combinator 6 via the device 5.

The microcomputer 6 stores the voltages at the initial energization part, peak part a, and final energization part C of the interelectrode voltages Vtl to Vtn, calculates the average value for each point, and calculates the average value of these three points. The voltage value for each half cycle on the straight line connecting the points is calculated and stored as the standard quantity of electricity Vs. Thereafter, the mode is switched to the welding current control mode to perform actual welding, and this interelectrode voltage vtn+1 is applied to the microcoder K. In the next energization of the thyristor, the conduction angle of the thyristor is increased by the set increase amount and energized. In the opposite case, reduce the conduction angle of the thyristor by the above reduction amount and energize it.
Control is performed to approach the standard electricity quantity Vs stored in the standard electricity quantity setting mode. By controlling the temperature to 5 in this manner, better welding results than K can be obtained.

FIGS. 9 and 10 are diagrams showing the results of welding with a welding current controlled to automatically trace the standard quantity of electricity Vs determined as described above. Figure 9 shows a cold rolled steel plate with a thickness of 1.2 wm and a cold rolled steel plate with a thickness of 3.2 wm as materials to be welded.
This is a diagram showing the inter-electrode voltage when continuous dot welding of a hot-rolled steel plate of 500 m in diameter using a dome-shaped electrode (radius of curvature of 20 m) with a diameter of 16 cans, where Vt is the voltage when the same type of material to be welded is welded 5 times. It is the average value of the inter-electrode voltage vtt to vts at the time, and VS
is a standard quantity of electricity (interelectrode voltage) set by connecting the two points a and C in the average interelectrode voltage Vt with a straight line. As is clear from the figure, the inter-electrode voltage vt' when welding is performed using this standard quantity of electricity Vs follows the standard quantity of electricity Vs well. In addition, at the initial stage of energization, there are large variations in the familiarity between the materials to be welded, the surface condition, or the resistance value between the welding electrode and the material to be welded, so in the example shown in FIG. It's cut off. Figure 10 shows a plot of the measured nugget diameter, which is a criterion for welding quality, when spot welding was performed 4245 times (number of welding points) using the standard electricity quantity Vs shown in Figure 9. The nugget exceeds the limit value of 5.5- set as the minimum nugget diameter, and from this it can be seen that there is no problem even if the standard air volume is replaced with a straight line as in the present invention.

In the above explanation, only the voltage between the electrodes when the materials to be welded were actually welded was stored in the microcomputer 6 as a standard quantity of electricity. To add a voltage waveform for control,
The interelectrode voltage stored in the microcomputer 6 is temporarily displayed on a display 11 such as a printer or a display, and the basic interelectrode voltage b - a - c (Figs. 5 to 7) K and the desired preheating are performed. The waveforms of the process (FIGS. 5 and 6) and the post-heating process (FIG. 7) are input from the keyboard circuit 7 and added.

For this input value, input only the value of the start point and end point (including the intermediate point if necessary) of the process to be added,
The value for each half cycle between pixels is determined by micro combinator 6.
It may be generated by the function generator function of , and may be input from the keyboard circuit 7 every half cycle.

〔Effect of the invention〕

As explained above and explained in 5, the welding current control method of the resistance welding device of the present invention is such that the welding current control method of the resistance welding device of the present invention is configured to control the amount of electricity during multiple welding to at least one of the three points of the initial part, the peak part, and the final part of the reverse electric current. Calculate the average value of the quantity of electricity at two points, connect these points with a straight line, and store the quantity of electricity found every half cycle on the line obtained as a standard quantity of electricity, and automatically trace this standard quantity of electricity. Since the welding current is controlled in such a way that it is possible to always obtain the optimum nugget without being affected by changes in the welding equipment, material to be welded, welding conditions, etc.
The reliability of welding quality can be greatly improved in that electrode damage due to excessive current and insufficient welding strength due to insufficient current are eliminated.

In addition, the amount of electricity when welding the materials to be welded is detected, and at least two of the initial energization part, peak part, and final energization part are detected.
Since the points are extracted and connected with straight lines and stored as the standard quantity of electricity, the standard quantity of electricity can be set with simple operations and in a short time. Preparation before welding becomes very easy.

Furthermore, since the standard quantity of electricity is in a linear configuration, it is easy to add various heat inputs for preheating and postheating, and the effects are outstanding.

[Brief explanation of the drawing]

Figures 1 to 3 are diagrams showing the time course of interelectrode voltage, interelectrode resistance, and welding current during resistance spot welding, respectively, and Figure 4 is a diagram for explaining the welding current control method according to the present invention. Standard electrical quantity (waveform) using interelectrode voltage as an example
Figures 5 to 7 are diagrams showing standard amounts of electricity according to various heat inputs used in the welding current control method according to the present invention, and Figure 8 is a diagram showing the welding current control method according to the present invention. FIG. 9 is a block diagram of a device for controlling the welding current, and FIG.
FIG. 0 is a diagram showing the transition of the nugget diameter when the welding current control method according to the present invention is implemented.

Claims (3)

[Claims] (1) Calculate the average value of the amount of electricity obtained from at least both welding electrodes when welding the material to be welded multiple times every half cycle, store it as a standard amount of electricity, and compare it with the amount of electricity obtained during subsequent welding. In a method of performing resistance welding using a welding current controlled to automatically trace the stored standard quantity of electricity by the difference between the two quantities of electricity obtained,
For each of the electrical quantities when welding multiple times, calculate the average value of the electrical quantity at at least two points out of the three points of the initial energization part, the peak part, and the final energization part, and from the line connecting these points with a straight line. A welding current control method for a resistance welding device, characterized in that the amount of electricity determined every half cycle is stored as a standard amount of electricity, and the welding current is controlled so as to automatically trace this standard amount of electricity. (2) When the material to be welded is welded multiple times, the average value of the amount of electricity obtained from at least both welding electrodes is determined every half cycle, stored as a standard amount of electricity, and compared with the amount of electricity obtained during subsequent welding. In a method of performing resistance welding using a welding current controlled to automatically trace the stored standard quantity of electricity by the difference between the two quantities of electricity obtained,
The points obtained by calculating the average value of the quantity of electricity at at least two points out of the three points of the initial energization part, the peak part, and the final energization part for each of the quantity of electricity when welding the plurality of times, and the preheating or post-heating point between these points and The amount of electricity obtained every half cycle from a straight line connecting arbitrarily set points for heat is stored as a standard amount of electricity, and the welding current is controlled so that this standard amount of electricity is automatically traced. Features: Welding current control method for resistance welding equipment. (3) The resistance welding apparatus according to claims 1 and 2, characterized in that the standard quantity of electricity is made variable by changing the slope of each line segment constituting the standard quantity of electricity. Welding current control method.