JP4290448B2 - Resistance welding control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to resistance welding used for spot welding, and in particular, estimates the temperature of a welded part during resistance welding by heat conduction calculation, and this welded part temperature estimated value becomes substantially equal to a predetermined temperature change target pattern. The present invention relates to an improvement in resistance welding control method for increasing and decreasing the welding current value.
[0002]
[Prior art]
In resistance spot welding, in which a plurality of stacked materials to be welded are pressed and energized by a pair of electrodes, in order to obtain good quality of the welded portion, the nugget diameter must be formed within an appropriate range; It is important that no scatter occurs during welding. In particular, in resistance welding of galvanized steel plates and high-tensile steel plates, which are frequently used recently, the nugget diameter is likely to fluctuate and the scattering tends to occur. Therefore, various control methods for suppressing these occurrences have been proposed.
[0003]
In order to optimize the nugget diameter and prevent the occurrence of scattering, it is necessary to optimize the temperature change of the welded part during resistance welding according to the material and thickness of the material to be welded. That is, by controlling the welding current so that the temperature change of the welded portion from the welding start time to the welding end time follows a predetermined temperature change target pattern according to the above welding conditions, an appropriate scattering of the nugget diameter is achieved. Good welding quality can also be obtained. In such temperature pattern tracking current control, it is necessary to measure the temperature change of the weld during resistance welding, but it is difficult to directly measure the temperature change because the weld is not visible from the outside. For this reason, many methods have been proposed in which the temperature change of the weld is calculated in real time by heat conduction calculation to obtain the estimated temperature of the weld.
[0004]
The heat conduction calculation method includes a method using a differential equation and a finite element analysis method, a method of calculating an average temperature estimated value based on an energy balance model of a welded part, and the like. In these heat conduction calculation methods, the welding current temperature estimated value is calculated by inputting the welding current value, the welding voltage value, and the physical constants of the electrode and the workpiece to be welded.
[0005]
FIG. 6 is a time change diagram of the weld temperature estimated value Tc showing an example of the temperature pattern following current control described above. In the figure, the horizontal axis represents the elapsed time t from the start of welding as one cycle of commercial power supply (reciprocal of 50 Hz or 60 Hz) = 1 cycle (cyc). The left vertical axis represents the weld temperature estimated value Tc [° C.] and the temperature change target pattern Tp [° C.], and the right vertical axis represents the effective value Irm [A] of the welding current as the control operation amount. Is. In the temperature pattern tracking current control, the weld temperature estimated value Tc at each elapsed time is calculated, a temperature deviation ΔT = Gain · (Tp−Tc) from the temperature change target pattern Tp is calculated, and welding is performed according to this output value. The effective value Irm of the current is increased or decreased so that the weld temperature estimated value Tc follows the temperature change target pattern Tp. As a result, the temperature change of the welded portion is optimized, and good welding quality can be obtained in which proper scattering of the nugget diameter does not occur (see, for example, Patent Document 1).
[0006]
[Patent Document 1]
Japanese Patent No. 3212296
[Problems to be solved by the invention]
In the above-described temperature pattern tracking current control, it is necessary to set a temperature change target pattern in advance according to the combination of the material and thickness of the plurality of workpieces. For this purpose, the temperature change target pattern must be created by repeating the experiment for each welding condition. However, there are many materials such as mild steel, galvanized steel, high-tensile steel, stainless steel, aluminum alloy etc. as the material of the material to be welded, and the plate thickness is 0.8mm, 1.0mm, 1.2mm, 1.6mm etc. There are many. Furthermore, there are two, three, etc. sheets to be welded. For this reason, the welding conditions which combined these become a huge number. It is practically difficult to create a temperature change target pattern by performing experiments for each of the enormous number of welding conditions. For this purpose, several types of standard welding conditions are selected, and temperature change target patterns under these standard welding conditions are created by experiments. When the actual welding conditions deviate from the standard welding conditions, the temperature change target pattern of the near standard welding conditions is used as it is or is used after fine adjustment on site. Therefore, the temperature change target pattern is not optimal for the actual welding conditions, and there is a problem that the welding quality varies. As described above, particularly in resistance welding of galvanized steel or high-strength steel, the welding quality varies further due to large fluctuations in welding quality.
[0008]
Therefore, the present invention provides a resistance welding control method capable of automatically generating an optimum temperature change target pattern corresponding to various combinations of the material and plate thickness of the material to be welded.
[0009]
[Means for Solving the Problems]
In order to solve the above-described problem, the invention of claim 1 estimates the temperature of the weld during resistance welding by heat conduction calculation, and this weld temperature estimate is substantially equal to a predetermined temperature change target pattern. In the resistance welding control method of performing welding by performing temperature pattern tracking current control to increase or decrease the welding current value,
The maximum temperature is set according to the material of the material to be welded, the welding end time is calculated by a predetermined relational expression with the material and thickness of the material to be welded as input, and the temperature pattern following current control system with the maximum temperature as input The temperature at the end of welding is calculated according to a predetermined relational expression so that the temperature is stable, and the maximum temperature arrival time is calculated according to a predetermined relational expression so that the temperature pattern tracking current control system is stabilized with the welding end time as an input. To calculate
The temperature change target pattern automatically increases from a predetermined initial temperature corresponding to the peripheral temperature at the start of welding to the maximum temperature at the maximum temperature arrival time and then decreases to the welding end temperature at the welding end time. It is the resistance welding control method characterized by being produced | generated.
[0010]
Further, in the invention of claim 2, the relational expression for calculating the welding end temperature Tpe with the maximum temperature Tpm as an input is Tpe = Tpm-E, and E is determined from the stability of the temperature pattern following current control system. Constant,
The relational expression for calculating the maximum temperature arrival time Tm using the welding end time Te as an input is Tm = Te × D, and D is within the range of 0.5 to 1.0, and the temperature pattern tracking current control system is stable. It is a constant determined from sex.
The resistance welding control method according to claim 1, wherein:
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
[Embodiment 1]
FIG. 1 is a diagram showing a temperature change target pattern generation method according to Embodiment 1 of the present invention. In the figure, the horizontal axis indicates the elapsed time t [cyc] from the welding start time, and the vertical axis indicates the target temperature [° C.]. Hereinafter, a description will be given with reference to FIG.
[0013]
First, the target temperature Tp = Tps when the welding start time t = 0 is set. The initial temperature Tps is set to a predetermined value (for example, 20 ° C.) corresponding to the peripheral temperature. Next, the maximum temperature Tpm is a constant determined by the material of the material to be welded. For example, in the case of steel, Tpm = 1500 ° C. The welding end time Te is calculated by the following equation.
Te = A × B + C
Here, A is a total value [mm] of the thicknesses of the stacked welded materials, B is a coefficient determined by the material of the welded materials, and C is a correction value when the welded material is plated. It is. For example, B = 5 for steel and C = 2 for galvanizing. Therefore, for example, when two sheets of mild steel with a plate thickness of 1.2 mm and not galvanized are stacked, the welding end time Te = (1.2 + 1.2) × 5 + 0 = 12 [cyc]. Similarly, in the case where two galvanized steel sheets having a thickness of 1.2 mm are stacked, the welding end time Te = (1.2 + 1.2) × 5 + 2 = 14 [cyc].
[0014]
The time Tm to reach the maximum temperature Tpm is calculated by the following equation.
Tm = Te × D
Here, D is a constant determined from the control stability in the temperature pattern tracking current control system, and is set in the range of about 0.5 to 1.0. Further, the welding end temperature Tpe is calculated by the following equation.
Tpe = Tpm-E
Here, E is also a constant determined from the above control stability, for example, E = 100 [° C.].
[0015]
Therefore, when the material and thickness of the material to be welded are input, the maximum temperature Tpm and the welding end time Te are first calculated. Subsequently, the maximum temperature arrival time Tm and the welding end temperature Tpe are calculated from these. The temperature change target pattern Tp rises from the initial temperature Tps at the welding start time t = 0 to the maximum temperature Tpe at the maximum temperature arrival time Tm, and then at the welding end time Te. It is automatically generated by the approximate expression so as to decrease to the end temperature Tpe. In this case, an approximate expression of about 1st to 4th order is used. Since the trajectory of the ascending curve and the descending curve affects the above control stability, the order of the approximate expression is set in relation to the control stability. The welding quality is not significantly affected by these curves, and the maximum temperature Tpm and its arrival time Tm are important.
[0016]
FIG. 2 is a diagram illustrating an example of characteristics generated by the above-described temperature change target pattern generation method. The characteristic L1 is a case where two sheets of 1.2 mm thick non-galvanized mild steel are stacked. Characteristic L2 is a case where two sheets of 1.0 mm thick non-galvanized mild steel are stacked. Characteristic L3 is obtained when three galvanized steel sheets having a thickness of 1.0 mm, 1.0 mm, and 1.6 mm are stacked. Thus, the optimum characteristics can be automatically generated according to various welding conditions by the temperature change target pattern generation method of the first embodiment.
[0017]
[Embodiment 2]
FIG. 3 is a diagram showing a temperature change target pattern generation method according to Embodiment 2 of the present invention. In the figure, the horizontal axis indicates the elapsed time t [cyc] from the welding start time, and the vertical axis indicates the target temperature [° C.]. Hereinafter, a description will be given with reference to FIG.
[0018]
In the figure, the calculation method of the maximum temperature Tpm and the welding end time Te is the same as that in the first embodiment. Therefore, when the material and thickness of the material to be welded are input, the maximum temperature Tpm and the welding end time Te are calculated. The temperature change target pattern Tp is automatically generated by an approximate expression so as to rise from the initial temperature Tps at the welding start time t = 0 to the maximum temperature Tpm at the welding end time Te. In this case, an approximate expression of about 1st to 4th order is used. Since the trajectory of the ascending curve affects the control stability, the order of the approximate expression is set in relation to the control stability. The welding quality is not significantly affected by this curve, and the maximum temperature Tpm and the welding end time Te that is the arrival time are important.
[0019]
FIG. 4 is a diagram illustrating an example of characteristics generated by the above-described temperature change target pattern generation method. Characteristic L4 is a case where two sheets of 1.2 mm thick non-galvanized mild steel are stacked. Characteristic L5 is a case where two sheets of 1.0 mm thick non-galvanized mild steel are stacked. Characteristic L6 is a case where three galvanized steel sheets having thicknesses of 1.0 mm, 1.0 mm and 1.6 mm are stacked. Thus, the optimum characteristics can be automatically generated according to various welding conditions by the temperature change target pattern generation method of the second embodiment.
[0020]
The second embodiment corresponds to the case where D = 1.0 and E = 0 ° C. in the first embodiment. The proper use of the first embodiment and the second embodiment is selected in relation to the control stability as described above. The selection is made in consideration of the control stability of the entire resistance welding apparatus.
[0021]
FIG. 5 is a block diagram of a welding power source device for carrying out the first and second embodiments. Hereinafter, each circuit will be described with reference to FIG.
[0022]
The thyristor SCR receives the commercial AC power supply AC as an input and performs phase control so that the effective value Irm of the welding current Iw becomes a predetermined value according to a drive signal Dv described later. The transformer TR steps down to a voltage value suitable for resistance welding. The pair of electrodes 1a and 1b pressurize a plurality of materials to be welded 2, and a welding current Iw is passed through the electrodes and a welding voltage Vw is applied.
[0023]
The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The weld temperature estimated value calculation circuit TC receives the current detection signal Id and the voltage detection signal Vd as input, calculates the heat constant using the predetermined physical constants of the welding material and the electrode, The temperature estimation signal Tc is output.
[0024]
The welding condition setting circuit WC sets the material and thickness of each material to be welded and outputs a welding condition setting signal Wc. The temperature change target pattern generation circuit TP receives the welding condition setting signal Wc (material and plate thickness) as an input, generates a temperature change target pattern by the above-described temperature change target pattern generation method, and at an elapsed time from the welding start time. A corresponding target temperature signal Tp is output. The temperature error amplification circuit ET amplifies an error between the target temperature signal Tp and the weld temperature estimation signal Tc, and outputs a temperature error amplification signal ΔT = Gain · (Tp−Tc).
[0025]
The temperature error integration circuit SDT integrates the temperature error amplification signal ΔT and outputs a current setting correction signal ΔIs. The initial current setting circuit IS outputs a predetermined initial current setting signal Is. The adder circuit AD adds the initial current setting signal Is and the current setting correction signal ΔIs, and outputs a current control setting signal Isc = Is + ΔIs = Is + ΣΔT. Therefore, the current control setting signal Isc is increased or decreased by feedback control.
[0026]
The current effective value calculation circuit IRM calculates the effective value of the current detection signal Id as an input, and outputs the current effective value signal Irm. The current error amplification circuit EI amplifies an error between the current control setting signal Isc and the current effective value signal Irm and outputs a current error amplification signal Ei. The drive circuit DV outputs a drive signal Dv for controlling the phase of the thyristor SCR in accordance with the current error amplification signal Ei.
[0027]
【The invention's effect】
According to the resistance welding control method of the present invention, the optimum temperature change target pattern can be automatically generated according to various combinations of the material and thickness of the material to be welded, so that the temperature change target pattern can be easily set. And always good welding quality can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a temperature change target pattern generation method according to Embodiment 1 of the present invention.
FIG. 2 is a diagram showing an example of a temperature change target pattern generated by the first embodiment of the present invention.
FIG. 3 is a diagram showing a temperature change target pattern generation method according to Embodiment 2 of the present invention.
FIG. 4 is a diagram showing an example of a temperature change target pattern generated by the second embodiment of the present invention.
FIG. 5 is a block diagram of a welding power source apparatus according to the present invention.
FIG. 6 is a diagram showing temporal changes in the weld temperature estimation value Tc, the temperature change target pattern Tp, and the welding current effective value Irm when the temperature pattern tracking control of the prior art is performed.
[Explanation of symbols]
1a, 1b Electrode 2 Material to be welded AC Commercial AC power supply AD Adder circuit DV Drive circuit Dv Drive signal EI Current error amplifier circuit Ei Current error amplifier signal ET Temperature error amplifier circuit ID Current detection circuit Id Current detection signal IRM Current effective value calculation circuit Irm welding current effective value, current effective value signal IS initial current setting circuit Is initial current setting signal Isc current control setting signal Iw welding currents L1 to L6 characteristics SCR thyristor SDT temperature error integration circuit t elapsed time TC welding temperature estimation value calculation circuit Tc Weld temperature estimation (value / signal)
Te welding end time Tm maximum temperature arrival time TP temperature change target pattern generation circuit Tp temperature change target pattern, target temperature (signal)
Tpe welding end temperature Tpm maximum temperature Tps initial temperature TR transformer VD voltage detection circuit Vd voltage detection signal Vw welding voltage WC welding condition setting circuit Wc welding condition setting signal ΔIs current setting correction signal ΔT temperature deviation, temperature error amplification signal

Claims (2)

The temperature of the weld zone during resistance welding is estimated by heat conduction calculation, and temperature pattern follow-up current control is performed to increase or decrease the weld current value so that the weld temperature estimate is approximately equal to the predetermined temperature change target pattern. In the resistance welding control method for welding,
The maximum temperature is set according to the material of the material to be welded, the welding end time is calculated by a predetermined relational expression with the material and thickness of the material to be welded as input, and the temperature pattern following current control system with the maximum temperature as input The temperature at the end of welding is calculated according to a predetermined relational expression so that the temperature is stable, and the maximum temperature arrival time is calculated according to a predetermined relational expression so that the temperature pattern tracking current control system is stabilized with the welding end time as input. To calculate
The temperature change target pattern automatically increases from a predetermined initial temperature corresponding to the peripheral temperature at the start of welding to the maximum temperature at the maximum temperature arrival time and then decreases to the welding end temperature at the welding end time. A resistance welding control method generated. The relational expression for calculating the welding end temperature Tpe with the maximum temperature Tpm as an input is Tpe = Tpm−E, where E is a constant determined from the stability of the temperature pattern following current control system,
The relational expression for calculating the maximum temperature arrival time Tm using the welding end time Te as an input is Tm = Te × D, and D is within the range of 0.5 to 1.0, and the temperature pattern tracking current control system is stable. It is a constant determined from sex.
The resistance welding control method according to claim 1.

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