JPH05123873A - Resistance welding control method - Google Patents

Abstract

PURPOSE:To control resistance welding by the resistance value variation of a threshold value of expulsion and surface flash and a welding current value by executing determination by the change of a resistance value between electrode tips to obtain the threshold value of expulsion and surface flash. CONSTITUTION:When a welding current is subjected to feedback control so that the variation of a secondary side resistance value during welding attains the preset resistance value variation, on both values initialized, the generation of expulsion and surface flash for every welding is determined by the sudden change of the resistance value between the electrode tips and the next welding current value is obtained to perform welding again. The threshold value of expulsion and surface flash of materials to be welded is then obtained and the resistance value variation and the welding current value at the limit time are automatically programmed in a computer as the initialization data to control resistance welding. Consequently, the quality of welding can be made uniform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for automatically compensating for a decrease in current density due to wear of an electrode tip or the like without attaching a special additional device to the outside and for maintaining a uniform welding quality. Regarding the automation of its initial settings.

[0002]

2. Description of the Related Art Conventionally, the occurrence of dust in the welded portion causes the resistance value between the electrode tips to decrease, and the dust has been generated in the welded portion due to a slight change in the load power factor of the welding machine. Is detected and the welding current is controlled so as to have a current value in the vicinity of the occurrence of dust.

[0003]

In this case, since the load power factor is represented by the ratio of the resistance component and the reactance component of the load, the change amount of the load power factor represents the relative change amount of the resistance value and the reactance. However, it does not detect the amount of change in the resistance value itself.Therefore, it can be applied to a welder in which the welding cable kicks due to the repulsive force due to the welding current and the inductance component changes, or where the inductance changes depending on the welding location. Cannot be used, and the magnitude of the amount of change in the resistance value varies depending on the magnitude of the power factor angle and the inductance, and there is a drawback that several parameters must be adjusted by cut-and-try as an initial setting. As a result, in the actual work, there is no choice but to find the dust limit due to dust being generated during the welding work, and welding control cannot be performed unless dust is generated. In that case, not only the strength of the welded portion is deteriorated and the appearance is deteriorated, but also the occurrence of dust is not preferable in terms of work safety. Therefore, the purpose of the present invention is to
The amount of change in the secondary resistance value of the welding transformer can be easily detected, and the quality of welding can be made uniform without being affected by wear of the electrode tip, etc., and dust does not occur during welding work. It is to provide a resistance welding control method capable of performing a welding operation in an optimum state.

[0004]

That is, according to the present invention, the secondary voltage of the welding transformer is measured by measuring the primary voltage and the primary current of the welding transformer at the timing when the rate of change of the primary current during welding is zero. While calculating the side resistance value, 2 during welding
There is a resistance welding control method in which the welding current is feedback-controlled so that the change amount of the secondary side resistance value becomes a preset change amount of the resistance value. In this case, the resistance change amount and the welding current value of the initial setting are determined by determining whether the resistance value between the electrode tips changes abruptly for each welding to determine the next welding current value, and then again. While welding, the dust limit value of the object to be welded is obtained, and the resistance change amount and welding current value at the dust limit are automatically programmed in the computer as initial setting data.

[0005]

In the resistance welding control configured as described above, the amount of change in the resistance value and the welding current value are set at the dust limit before the actual welding work is performed, so that dust is generated at each trial welding. Judgment is made based on whether the resistance value between the electrode tips has changed abruptly, and in the state where no dust is generated, increase the next welding current value and perform welding again to obtain the dust limit value of the workpiece. The amount of change in resistance value at the limit of dust and the welding current value are automatically programmed in the computer as initial setting data. In this way, the welding work is started in the state where the resistance change amount and the welding current value corresponding to the optimum welding are initialized, and the primary current change rate during welding is 0, for example, welding for each cycle of the power supply. At the peak of the current waveform, the primary side voltage and primary side current of the welding transformer are measured to calculate the secondary side resistance value of the welding transformer,
The welding current is feedback-controlled so that the change amount of the secondary side resistance value during welding becomes the preset change amount of the resistance value.

[0006]

As a result, according to the present invention, in the initial setting of welding control, the resistance change amount ΔR value of the dust limit is programmed with an absolute value, and welding is performed at the dust limit of the optimum state where dust is not generated during welding work. It is possible to control, which makes it possible to make the quality of the welding uniform without being affected by wear of the electrode tip, etc., and moreover, to keep the finish of the welding including the strength and the appearance to be the most uniform. effective.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the structure of an embodiment of the present invention will be described with reference to the drawings. Figure 1 shows the secondary resistance of the welding transformer WT as 1.
The block circuit diagram to detect on the secondary side is shown, and the primary current transformer CT
Is an air-core CT for detecting the current flowing through the primary side of the welding transformer WT. A differential signal of the actual current waveform is input to this circuit, and this differential signal is restored to the current waveform by the integrating circuit IC. .. The primary voltage input is a signal obtained by stepping down the welding power source by the transformer MT for measuring instrument and the level thereof is adjusted by the amplifier circuit AMC. These current and voltage signals are converted from the waveform of the primary current transformer CT by the sample and hold circuit SHC. While the sampling signal is sampled and held for each timing signal of di / dt = 0 detected by the / dt = 0 detection circuit DDC, this timing signal is input to the microcomputer MC to generate an interrupt, and the A / D converter ADC converts the timing signal. The A / D converted current and voltage data is sampled, and the secondary resistance value R of the welding transformer WT is calculated by the microcomputer MC from the sampled data by the following equation.

[0008] The difference ΔR in resistance value in one welding cycle from the maximum value of the resistance value R to the end of welding is also calculated.

Next, the operation of this embodiment will be described.
In the case of resistance welding control configured as described above, first, the resistance value change amount ΔR and the welding current value I
Is set as the dust limit, the occurrence of dust is determined for each trial welding by checking whether the resistance value between the electrode tips 1 and 1 has changed rapidly. While increasing I and performing welding again, the dust limit value of the workpiece 2 is determined, and the resistance change amount ΔR and the welding current value I at the dust limit are automatically programmed in the microcomputer MC as initial setting data. ..

That is, the initial value of the welding current I is the electrode tip 1
Is for resetting the current value I increased at the time of the work of replacing or polishing the tip 1, and therefore, this automatic setting operation is preferably performed after the replacement of the electrode tip 1 or the polishing of the tip 1. Therefore, first, a temporary welding current is set in a state where the operation mode of the welding control device 3 is set to [setting mode] (this value is updated for each welding in the setting mode), and a predetermined workpiece is welded. Weld two. At this time, inside the microcomputer MC, the occurrence of dust and the amount of change in resistance value ΔR are calculated, and the current value I for the next welding is set, and the determination result displayed in the teaching box at this time is [OK]. ], The current resistance value variation ΔR and the welding current value I are written in a predetermined program area of the microcomputer MC by pressing the [setting key], and the operation of [NG] is repeated.

The above control is shown in the flowchart for automatically setting the ΔR target value and the initial value of the welding current in FIGS. 2 and 3, and after setting the temporary welding current in step 101,
The system jumps to setting mode in step 102,
After the test welding step = 0 is set in step 103, welding is performed in step 104, and it is determined in step 105 whether or not dust has occurred. In the state where dust has occurred, the test welding step is performed in step 106. It is determined whether or not = 0, and if 0, step 1
The welding current value is set to -5% at 07, and NG at step 108.
After the determination, in step 109, it is determined whether or not all the test welding according to the setting mode processing flow is completed, and if not completed, in step 104, welding is performed again at a welding current value of -5%.

In step 105, it is determined whether or not dust has occurred in this welding, and in the state in which no dust has occurred, it is determined in step 110 whether or not the test welding step = 0, and if 0, step 111. In step 112, the welding current value is set to + 5%, NG is determined in step 108, and then in step 109, it is determined whether or not all the test welding is completed according to the setting mode process flow. In a state where the welding current value + 5% has not been completed yet, welding is performed again in a state of the welding current value + 5%.

In step 105, it is determined whether dust occurs in this welding. In the state where dust occurs, it is determined in step 106 whether the test welding step = 0.
When it is not 0, it is determined in step 113 whether or not the test welding step = 1, and when it is 1, after the test welding step = 2 is set in step 114, the welding current value is set to -1% in step 115, Step 10
After the NG judgment in step 8, it is judged in step 109 whether or not all the test welding according to the setting mode processing flow is completed, and in the state where it is not completed yet, the welding is performed again in the state of the welding current value -1% in step 104. To be done.

In step 105, it is determined whether or not dust has occurred in this welding. In the state in which dust has occurred, it is determined in step 106 whether or not the test welding step = 0.
If it is not 0, it is determined in step 113 whether or not the test welding step = 1, and if it is not 1, the welding current value is further set to -1% in step 115, and the same test welding as described above is repeated, and then step 105 If the occurrence of dust does not occur in the determination of the occurrence of dust in step 110, it is determined in step 110 whether the test welding step = 0, and if it is not 0, it is determined in step 116 whether the test welding step = 1 and not 1. In this case, it is determined in step 117 whether or not the test welding step = 2, and if it is 2, the test welding step = 3 is set in step 118, an OK determination is made in step 119, and then the setting mode is set in step 109. It is determined whether or not all the test weldings according to the processing flow are completed, and if they are not completed yet, welding is performed again in step 104. It is carried out.

In step 105, it is determined whether or not dust is generated in this welding. If no dust is generated, it is determined in step 110 whether or not the test welding step = 0.
If it is not 0, it is determined in step 116 whether the test welding step = 1, and if it is not 1, it is determined in step 117 whether the test welding step = 2 or not.
If not, after the test welding step = 2 is set in step 120, the welding current value is set to + 1% in step 121, NG judgment is made in step 108, and then all test welding by the setting mode process flow is completed in step 109. It is determined whether or not it is determined that the welding current value is + 1% and welding is performed again in step 104 when the welding is not completed.

As described above, the dust limit value of the object to be welded 2 is obtained from the change in the resistance value of the entire secondary circuit shown in FIG. 5 as shown in FIG. 6 by the welding in which the welding current value is increased or decreased, and in this state, The setting mode process flow ends and returns to the main routine. At step 122, the resistance value variation ΔR and the welding current value I at the limit of dust are automatically programmed in the microcomputer MC as initial setting data, and at step 123. The setting mode is released.

The resistance value variation ΔR for each welding point thus obtained is displayed in the teaching box of the resistance welding control device 3 in units of μΩ, and in the case of manual setting, it is best to change the setting of welding conditions. The monitor value at the time of welding is read and written in the program area of the resistance change amount ΔR target value of the microcomputer MC, whereby the setting work before welding work is completed.

As described above, the welding work is started in the state where the resistance value variation ΔR and the welding current value I corresponding to the optimum welding are initially set, and the rate of change of the primary current during welding is 0. The primary side voltage and primary side current of the welding transformer WT are measured at the peak of the welding current waveform for each cycle of the power source shown in FIG. 7 to calculate the secondary side resistance value R of the welding transformer WT, and for each welding. The resistance value change amount ΔR calculated in step 1 is averaged with the resistance value change amount ΔR at the past several dots, and the averaged resistance value change amount ΔR is compared with the initial setting resistance value change amount ΔR target value and averaged. If the resistance change amount ΔR is less than the resistance value change amount ΔR target value, the welding current I is increased, and if it exceeds, the welding current is decreased to set the change amount ΔR of the secondary side resistance value R in advance. So that the resistance change amount ΔR becomes The welding current I is feedback controlled. As a result, this resistance welding can always be performed in the optimum state of the dust limit, and the finish of the welding can be kept uniform.

That is, welding is performed in step 201 of the welding current value control system shown in FIG.
In step 202, it is determined whether or not dust is generated during the welding process. If it is determined that dust is not generated, or if it is a temporary phenomenon that does not continuously occur in step 203, ΔR is determined in step 204. Value and the ΔR average value of the past several hit points are calculated, and ΔR is calculated in step 205.
It is determined whether or not the value is equal to or less than the ΔR lower limit value (see FIG. 6), and if it is less than the above, there is a setting error or some abnormality, so in step 206, an abnormality such as blank driving or welding failure is notified, and the ΔR value is the ΔR lower limit. If it is not less than the value, it is determined in step 207 whether or not the ΔR value and the ΔR average value are + 10% or more of the ΔR target value.
After 1%, the next welding is repeated. If the ΔR target value is + 10% or less, it is determined in step 209 whether the ΔR value and the ΔR average value are −10% or less of the ΔR target value. The next welding is repeated as it is without changing the value, and when the ΔR target value is -10% or less, the welding current rate is increased by + 1% in step 210 and the next welding is repeated.

[Brief description of drawings]

FIG. 1 is a secondary resistance detection block circuit diagram of resistance welding.

FIG. 2 is a flowchart of an initial setting operation of resistance welding.

FIG. 3 is a flowchart of a setting process mode for resistance welding.

FIG. 4 is a flowchart of welding current value control for resistance welding.

FIG. 5 is a waveform diagram of a secondary circuit resistance value [μΩ] in an energization cycle of resistance welding.

FIG. 6 is a waveform diagram of a secondary circuit resistance value [μΩ] for obtaining a dust limit ΔR of resistance welding.

FIG. 7 is a waveform diagram of a primary welding current and a welding voltage in resistance welding.

[Explanation of symbols]

 1 Electrode tip 2 Welding object 3 Welding control device CT Primary current transformer WT Welding transformer IC Integrating circuit MT Measuring instrument transformer MC Microcomputer AMC Amplifying circuit SHC Sample hold circuit DDC di / dt = 0 Detection circuit ADC A / D conversion vessel

Claims (2)

[Claims] 1. The primary side voltage and primary side current of the welding transformer are measured at the timing when the rate of change of the primary current during welding is 0 to calculate the secondary side resistance value of the welding transformer and at the same time during welding. 2. The resistance welding control method, wherein the welding current is feedback-controlled so that the change amount of the secondary side resistance value in step 1 becomes a preset change amount of resistance value. 2. The occurrence of dust for each welding is determined by determining whether the resistance value between the electrode tips has changed abruptly, the next welding current value is obtained, and the dust limit value of the workpiece is determined while performing welding again. A resistance welding control method characterized in that the resistance change amount and the welding current value at the dust limit are automatically programmed into a computer as initial setting data.