JPH0796375A - Method and device for controlling welding current of resistance welding machine - Google Patents

Abstract

PURPOSE:To provide the method and device for controlling the welding current of the resistance welding machine capable of obtaining a nugget having an optimum shape in respective welding points under different energizing condition of a welding current at the time of welding plural works of the same shape having the plural welding points under the different energizing conditions of the welding current. CONSTITUTION:At the time of welding the works having the same shape under the different energizing conditions of the welding current for every welding point, a square waveform is corrected on a waveform correction circuit 76 based on a generating state of expulsion and surface flash which is detected on an expulsion and surface flash detection circuit 55 and an expulsion and surface flash generation limiting current arithmetic circuit 70 obtains an expulsion and surface flash generation limiting current value based on this corrected square waveform. Based on the expulsion and surface flash generation limiting current value, a new waveform consisting of a high current value and a low current value is then generated by a CPU58, the high current value of this new waveform is corrected by the generating state of expulsion and surface flash which is detected on the expulsion and surface flash detection circuit 55 and the welding point of the same part having the same shape is welded. Accordingly, high welding strength can be obtained stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling a welding current of a resistance welding machine, and more specifically, it continuously applies a plurality of workpieces of the same shape having a plurality of welding points having different welding current energization conditions. The present invention relates to a welding current control method and device for a resistance welding machine to be welded.

[0002]

2. Description of the Related Art Conventionally, a plurality of welding points set on a work such as a car body of an automobile are sequentially and continuously welded by a resistance welding machine. In this case, the number of work pieces to be welded,
If the conditions such as the welding points such as the end or center of the work, the pitch between the welding points, the thickness of the work to be welded and the material of the work to be welded differ from welding point to welding point, A welding current waveform is set, and a method is used in which the energizing current follows the set current waveform.

On the other hand, it is known that a high welding strength can be obtained by passing a welding current in the vicinity of the spatter generation limit current value. Further, a welding current having a waveform composed of a high current value and a low current value is generated. It is known that by energizing, generation of dust is suppressed and a high quality nugget can be obtained.

[0004]

However, in the method of welding with the welding current having the waveform set for each welding point in the above-mentioned prior art, the wear of the electrode tip cannot be detected, so that the welding current conduction condition is When workpieces of the same shape having different welding points are continuously welded, the welding current waveform cannot be sufficiently controlled for each welding point, and high welding strength cannot be stably obtained. There is a problem.

The present invention has been made to solve such a conventional problem, and a resistance welding machine capable of obtaining a nugget having an optimum shape at each welding point under different welding current energization conditions. An object of the present invention is to provide a welding current control method and device.

[0006]

In order to achieve the above object, a first invention is a welding current control method for a resistance welding machine, in which works of the same shape having a plurality of welding points are sequentially welded for each work. In, a welding current having a waveform stored in advance is supplied to a predetermined welding point of the work to detect the presence or absence of spatter during welding, and the waveform of the welding current is corrected based on the presence or absence of the spatter. A first step; a second step for obtaining a scattering occurrence limit current value based on the corrected waveform; and a high current value larger than the scattering occurrence limit current value based on the scattering occurrence limit current value. The third step of generating a new welding current waveform having a low current value smaller than the scattering occurrence limit current value, and the welding current of the new welding current waveform at the same portion as the predetermined welding point of the workpiece. Wa The fourth step of supplying the welding current to the welding point and detecting the presence or absence of spatter during welding, and the high current of the new welding current waveform based on the presence or absence of spatter detected in the fourth step. A fifth step of correcting the value and supplying the welding current generated based on the corrected waveform to the welding point of the same portion of the work of the same shape.

Further, in a second aspect of the present invention, there is provided a welding current control device for a resistance welding machine in which workpieces of the same shape having a plurality of welding points are sequentially welded to each other. Is supplied to the predetermined welding point of
Dispersion generation limit current value calculating means for obtaining the dispersion generation limit current value based on the waveform corrected by the presence or absence of the dispersion generation detected during welding, and based on the dispersion generation limit current value, the dispersion generation limit current value Welding current waveform generating means for generating a new welding current waveform consisting of a larger high current value and a lower current value smaller than the scattering occurrence limit current value, and a welding current based on the new welding current waveform Welding current supply means for supplying to a welding point of another work at the same site as the predetermined welding point of the work, and spatter occurrence detecting means for detecting the presence or absence of spatter due to the welding current supplied to the work by the welding current supply means. And a waveform correction unit that corrects the high current value of the new welding current waveform based on the presence or absence of occurrence of the detected scattering, and the corrected new welding voltage. And supplying a welding current that is generated based on the waveform welding points of the same site of the same shape of the workpiece.

[0008]

In the method and apparatus for controlling the welding current of the resistance welding machine according to the present invention, a welding current having a pre-stored waveform is supplied to a predetermined welding point of a work, and the welding current is controlled based on whether or not scattering occurs during welding. The waveform is modified, and the scatter occurrence limit welding current value calculating means obtains the scatter occurrence limit welding current value based on the modified waveform.

Next, a new welding current waveform consisting of a high current value larger than the dispersion generation limit current value and a low current value smaller than the dispersion generation limit current value is formed on the basis of the dispersion generation limit current value. Generated by the waveform generating means, the welding current supply means supplies the welding current based on this new welding current waveform to the welding point of the other workpiece at the same site as the predetermined welding point of the workpiece, and the scattering occurrence detection means Detects the occurrence of scattering when welding current is applied.

The waveform correction means corrects the high current value of the new welding current waveform based on the presence or absence of the detected scattering, and the welding current generated based on the corrected waveform has the same shape. Supply to the welding point of the same part of the work.

Therefore, the respective welding points are welded with the welding current having a waveform in which the high current value is corrected for each same portion.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A welding current control method for a resistance welding machine according to the present invention will be described below in detail with reference to the accompanying drawings in connection with a device for carrying out the method. .

FIG. 1 is a block diagram showing the overall construction of a resistance welding machine 20 embodying the present invention.

The resistance welding machine 20 includes a converter circuit 22 for converting an alternating current output from an alternating current power source 21 into a direct current, an inverter circuit 24 for converting the direct current into a high frequency alternating current, and a welding for transforming and rectifying the high frequency alternating current. The transformer circuit 26, the welding gun portion 28 that holds the work W, and the welding controller 3 that controls the welding current supplied to the work W.
With 0 and.

Further, the resistance welding machine 20 has a current I ₁ on the primary side of the welding transformer circuit 26 (hereinafter referred to as a primary current) I ₁
Primary current detector 32 for detecting the
6, a secondary current detector 34 for detecting a secondary current (hereinafter referred to as a secondary current) I ₂ , a keyboard 36 for inputting welding conditions and the like to the welding controller 30, and the welding conditions are displayed. A display device 38 and an FDD 39 for writing / reading data to / from a floppy desk which is an external storage means are provided.

The welding gun section 28 has movable gun arms 40 and 41 for holding the work W, and electrode tips 42 and 43 fixed to the movable gun arms 40 and 41.
A cylinder 44 that drives the movable gun arms 40 and 41 to open and close freely, and an air pressure source 48 is connected to the cylinder 44 via an electromagnetic switching valve 46. The switching operation of the electromagnetic switching valve 46 is controlled by the welding controller 30.

FIG. 2 is a block diagram showing the structure of the welding controller 30.

The welding controller 30 includes an analog / digital (hereinafter referred to as A / D) conversion circuit 50 for converting the primary current I ₁ detected by the primary current detector 32 into a digital value, and a secondary current detector. Secondary current I ₂ detected by 34
A / D conversion circuit 52 for converting the
A detection current selection circuit 54 for selecting either the primary current I ₁ output from the / D conversion circuit 50 or the secondary current I ₂ output from the A / D conversion circuit 52, and a detection current selection circuit. A dispersion detection circuit 55 for detecting the presence or absence of dispersion from the primary current I ₁ or the secondary current I ₂ selected by 54, and a corrected current value for correcting the peak value I _N of the reference square waveform described later. [Delta] I _N, the lateral continuous generation number m ₁ of scattering for determining the appropriateness of welding current shape waveform, a continuous non-occurrence number m ₂ and the reference of Chile Chile occurrence limit current I _SS
And a welding condition storage circuit 56 for storing

The welding controller 30 includes a central processing unit (hereinafter referred to as CPU) 58, and a digital / analog (hereinafter referred to as D / A) which converts a welding current command value I _cmd output from the CPU 58 into an analog value. A conversion circuit 60 and a pulse width modulation (hereinafter referred to as PWM) circuit 62 that generates a pulse based on a signal output from the D / A conversion circuit 60 are provided, and the pulse generated in the PWM circuit 62 is the inverter. It is output to the circuit 24.

Further, the welding controller 30 stores a control program for controlling the resistance welding machine 20 in a read-only memory (hereinafter referred to as ROM) 64, and the CPU 58 temporarily stores the calculation result during calculation. readable and writable memory (hereinafter, RAM hereinafter) 66, a parameter for generating a high current value I _H of the welding current, high current supply time t _H for energizing the high current value I _H, the high current value I _H Fixed current [Delta] I _H in the case of modifying a parametrize for generating a low current value I _L of the welding current, the low current value I _L low current energization time t _L for energizing a welding transformer circuit 26 can supply A waveform generation parameter storage circuit 68 for storing a waveform generation parameter for generating a new welding current waveform consisting of the maximum value I _MAX of the welding current, and a scattering occurrence limit current value are calculated. Dispersion occurrence limit current value calculation circuit 70, keyboard 36, display device 38, FD
An interface (hereinafter, referred to as I / F) circuit 72 with the D39 and the electromagnetic switching valve 46 is provided.

Furthermore, the welding controller 30 is a welding current waveform storage circuit for storing a rectangular welding current waveform serving as a reference consisting of data of the energization time t and the peak value I _N , that is, a reference rectangular waveform. 74 and a waveform correction circuit 76 for correcting the reference welding current waveform and the like stored in the welding current waveform storage circuit 74 according to the occurrence state of scattering.

The operation of continuously welding a plurality of workpieces W having the same shape and having a plurality of welding points in the resistance welding machine 20 configured as described above will be described with reference to the flowcharts of FIGS. 3 and 4. To do.

When the operator inputs data indicating that the dispersion generated in the work W is detected by the secondary current I ₂ , for example, from the keyboard 36, this data is sent to the CPU 58 via the I / F circuit 72. Entered,
The CPU 58 outputs a selection signal for detecting the secondary current I ₂ to the detection current selection circuit 54.

[0024] In this case, the respective welding point P ₁₁ · P ₁₂ ... P _1n of the welding workpiece W ₁ shown in FIG. 5, then the welding point husband of the workpiece W ₂ s P ₂₁ to P _2n, ... workpiece W _n The welding points P _{n1 to} P _nn are sequentially welded to each other, and in this welding operation, in the present embodiment, the welding points at the same portion of the _respective works W _{1 to} W _n , for example, welding points P ₁₁ and P _n . ₂₁ ... Only the welding operation of P _n1 will be described as an example.

The program read from the ROM 64
Based on this, the CPU 58 outputs a drive signal for the electromagnetic switching valve 46.
When driven, this drive signal is transmitted via the I / F circuit 72.
It is output to the magnetic switching valve 46. This drive signal
Electromagnetic switching valve 46 is opened and the air pressure source 48
Pressure air is supplied to the da 44. To the pressure air
The movement of the cylinder 44 causes the gun arms 40 and 41 to move.
The electrode chuck attached to this gun arm 40, 41 is closed.
Workpiece W depending on top 42, 43₁Welding point P ₁₁Sandwiched
To be done.

Next, the data of the rectangular standard welding current waveform stored in the welding current waveform storage circuit 74 is stored in the CPU 58.
Command value I of the square-shaped welding current
_cmd is output to the D / A conversion circuit 60.

The welding current command value I _cmd is converted into an analog command value I _f by the D / A conversion circuit 60 and output to the PWM circuit 62. Further, the PWM circuit 62 pulse-width modulates it to a predetermined value. It becomes a pulse of frequency and duty cycle and is output to the inverter circuit 24.
The inverter circuit 24 generates a high frequency alternating current based on the pulse, and the high frequency alternating current is output to the welding transformer circuit 26. The high-frequency alternating current is transformed and rectified by the welding transformer circuit 26, and the work W is passed through the welding gun section 28.
Electric current is applied to _one welding point P ₁₁ (see FIG. 6) (step S1).

By this energization, the secondary current I ₂ detected by the secondary current detector 34 is input to the dispersion detection circuit 55 through the A / D conversion circuit 52 and the detection current selection circuit 54, and the dispersion detection circuit 55. Then, it is determined whether or not scattering has occurred (step S2). When it is determined that the dispersion has occurred, the CPU 58 determines whether or not the continuous occurrence number N ₁ of dispersion has reached the set value m ₁ (step S3).

As a result of the above judgment, when the continuous occurrence number N ₁ of dispersion has reached the set value m ₁ , the CPU 58 determines that the peak value I _{N of the} rectangular waveform is higher than the reference dispersion occurrence limit current value I _SS. is, corrected current value [Delta] I _N from the peak value I _N of rectangular shape waveform is subtracted by the waveform correction circuit 76 (I _N ← I _N -
ΔI _N) (step S4).

The peak value I _N obtained by this modification is used in step S1 for the work to be welded next, for example,
It is used as the peak value I _N of the rectangular waveform when welding the welding point P _i1 of the work W _i (see FIG. 6).

On the other hand, when it is determined in step S2 that the scattering does not occur, the CPU 58 determines whether or not the number N ₂ of continuous occurrence of scattering has reached the set value m ₂ (step S5), and the setting is made. When the value m ₂ is reached, it is determined that the peak value I _N is significantly lower than the scattering occurrence limit current value I _S. Based on this determination, the waveform correction circuit 76 adds the correction current value ΔI _N to the peak value I _N of the welding current (I _N ← I
_N + _{ΔI N)} (step S6).

[0032] In peak I _N is step S1 obtained by this modification, as the peak value I _N of square-shaped waveform when welding the welding point P _i1 of the workpiece W _i1 to be subsequently welded,
Used (see FIG. 6).

By repeating steps S1 to S6 described above, the peak value I _{N of the} rectangular waveform is corrected. Then, as a result of the determination in the step S3, when the continuous occurrence number N _{1 of} scattering does not reach the set value m ₁ , or as a result of the determination in step S5, the continuous non-occurrence number N _{2 of} scattering is the set value m ₂ Is reached, the CPU 58 determines that welding is being performed with the optimum peak value I _{N at} which spatter is sporadically generated, and based on the peak value I _N and the energization time t at this time. The scattering occurrence limit current value I _S is obtained by the scattering occurrence limit current value calculation circuit 70 (step S7).

Next, the waveform generation parameter storage circuit 68
A waveform generation parameter for generating a welding current waveform is read from the CPU 58 by the CPU 58, and a high current value I _H based on this waveform generation parameter and the scattering occurrence limit current value I _S obtained by the above calculation, High current value I _H
A new new welding current waveform having a low current value I _L of a low value is determined (step S8).

The low current value I _L determined on the basis of the waveform generation parameter is a value lower by the set value C ₁ than the scattering occurrence limit current value I _S obtained by the calculation in step S7, while the new welding current I The high current value I _H is determined so that the average value I _{A of the} waveform is higher than the scattering occurrence limit current value I _S by the set value C ₂ (see FIG. 7).

In this way, the welding current having the new welding current waveform thus determined is applied to the welding point P _{(i + 1) 1} of the work W _{(i + 1)} by the same action as in step S1 ₍ step S1 _).
9) The CPU 58 determines whether or not dispersion has occurred due to the secondary current I ₂ detected by the secondary current detector 34 (step S10).

When it is determined that the scattering does not occur, the waveform
The correction circuit 76 causes the waveform generation parameter storage circuit 68.
Corrected current value ΔI read from_HThere is a high welding current
Value I _HIs added to (I_H← I_H+ ΔI_H) (Step S
11), the high current value I obtained by this addition_HBut melted
Maximum value I that can be supplied from the contact transformer circuit 26_MAXWhether or not
Is determined by the CPU 58 (step S1)
2).

As a result of the above judgment, if I _H ≤I _MAX ,
It is determined that the welding transformer circuit 26 can supply the high current value I _H obtained by the addition, and this new welding current waveform is applied to the welding point P _{(i )} of the workpiece W _{(i + 2)} to be welded next in step S9. ₊₂₎ Used as a new welding current waveform when welding ₁ .

As a result of the determination in step S12, I _H ≤
When not I _MAX , the CPU 58 causes the electrode chips 42, 4 and
3 deteriorates, the contact resistance with the work W increases, and the high current value I _H obtained by the addition is the welding transformer circuit 26.
Is determined to have exceeded the maximum value I _MAX that can be supplied, and a signal for instructing the grinding (chip dressing) of the electrode tips 42, 43 is output to the display device 38 (step S1).
3) Then, the execution of this flowchart ends.

On the other hand, when the scattering occurs in the determination of step S10, if the high current value I _H of the welding current is high, the CPU 58
The correction current value ΔI _H is subtracted from the high current value I _H of the welding current by the waveform correction circuit 76 (I _H ← I
_H- ΔI _H ) (step S14).

Next, the CPU 58 causes the high current value I _H , the high current conduction time t _H , and the low current value I _H obtained by the above subtraction.
_The average value I _A is calculated based on _L and the energization time t ₁ ,
It is determined whether this average value I _A is larger than the scattering occurrence limit current value I _S obtained in step S7 (step S15).

As a result of this judgment, I_A≧ I_SIf so, before
High current value I obtained by subtraction _HNew welding current including
Grow good quality nugget by applying welding current based on waveform
This waveform is determined by the CPU 58 to be able to
Is the work W to be welded next in step S9
_{(i + 3)}Welding point P_{(i + 3) 1}New welding current waveform when welding steel
Used as.

In step S15, I _A ≧ I _S
If not, the CPU 58 determines that the nugget cannot be grown sufficiently, that is, sufficient shear tensile strength is not obtained, and the energization start time of the high current value I _H is shifted by a predetermined time t ₁ Is generated by the waveform correction circuit 76 (step S16).

Next, it is judged whether or not the energization start time of the high current value I _H has reached the limit at which the current can be shifted (step S
17) If the limit is not reached, the welding current based on the shifted waveform is supplied to the work W in step S9, while if the energization start time reaches the shiftable limit, the process returns to step S1. The current is supplied again based on the reference rectangular waveform stored in the welding current waveform storage circuit 74, and a new scattering limit current value I _S is obtained by executing step S7.

In this way, steps S8 to S17 are repeatedly executed, and the welding current generated based on the new welding current waveform consisting of the high current value I _H and the low current value I _L is supplied to the work W and scattered. Generation is suppressed and a high quality nugget can be obtained.

[0046] As described above, in the present embodiment is welded welding point P ₁₁ to P _1N husband of the workpiece W ₁ s are sequentially next workpiece W ₂ of the welding points each P ₂₁ to P _2n, ... workpiece W _When the welding points P _{n1 to} P _{nn of n} are sequentially welded, the welding points of the same part in the _respective workpieces W ₁ , W ₂ , ..., W _n , for example, welding points P ₁₁ , P ₂₁ ,. The waveform of the welding current supplied to P _n1 is supplied based on the waveform corrected when welding the welding points at the same site.

Therefore, the respective welding points on the work W are the number of overlapping work W, the welding point portions on the work W such as the end portion or the central portion, the pitch between the welding points, the thickness of the work W to be welded, Also, even when the welding current energization conditions are different for each welding point, such as the material of the workpiece W to be welded, each welding point has the same energization condition when the same portion of another workpiece W is welded. Welding can be performed by applying a welding current based on each of the modified new welding current waveforms.

[0048] Incidentally, it is possible to have been detected by the secondary current I ₂ the presence of occurrence scattering in this embodiment, to detect the presence or absence of the occurrence scattering similarly as secondary current I ₂ by the primary current I _1.

[0049]

In the welding current control method and apparatus for a resistance welding machine according to the present invention, when workpieces of the same shape having a plurality of welding points are sequentially welded for each workpiece, the respective welding points are different from those of other workpieces. Since welding is performed with a welding current with a waveform in which the high current value has been corrected by welding the same part, even if the welding current energization conditions differ for each welding point, the optimum welding current is supplied to each welding point. As a result, a nugget having a stable shape can be generated.

Further, by correcting the high current value of the waveform having the high current value and the low current value based on the scattered occurrence state, there is an effect that a high welding strength can be stably obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a resistance welding machine for carrying out the present invention.

2 is a block diagram showing a configuration of a welding controller in the resistance welding machine of FIG. 1. FIG.

FIG. 3 is a flow chart for explaining a method of welding the welding points of the same part of the work of the same shape in the resistance welding machine of FIG.

FIG. 4 is a flow chart for explaining a method of welding the welding points of the same part of the work of the same shape in the resistance welding machine of FIG.

FIG. 5 is a view for explaining each work of the same shape that is continuously conveyed in the resistance welding machine of FIG.

FIG. 6 is a diagram illustrating a square-wave welding current supplied to a work in the resistance welding machine of FIG. 1;

FIG. 7 is a diagram illustrating a welding current having a waveform including a high current value and a low current value applied to a work in the resistance welding machine of FIG. 1.

[Explanation of symbols]

20 ... Resistance welding machine 24 ... Inverter circuit 26 ... Welding transformer circuit 28 ... Welding gun part 30 ... Welding controller 34 ... Secondary current detector 40, 41 ... Movable gun arm 42, 43 ... Electrode tip 50, 52 ... A / D conversion Circuit 54 ... Detection current selection circuit 55 ... Dispersion detection circuit 56 ... Welding condition storage circuit 58 ... CPU 64 ... ROM 66 ... RAM 68 ... Waveform generation parameter storage circuit 70 ... Dispersion occurrence limit current value calculation circuit 74 ... Welding current waveform storage circuit 76 ... Waveform correction circuit

Claims (2)

[Claims] 1. A welding current control method for a resistance welding machine, in which workpieces of the same shape having a plurality of welding points are sequentially welded for each workpiece, wherein a welding current having a waveform stored in advance is applied to a predetermined welding point of the workpiece. The first step of supplying and detecting the occurrence of spatter during welding, and correcting the waveform of the welding current based on the presence or absence of the spatter, and the spatter occurrence limit current value based on the corrected waveform And a new welding current waveform consisting of a high current value larger than the dispersion generation limit current value and a low current value smaller than the dispersion generation limit current value based on the dispersion generation limit current value. And a welding current of the new welding current waveform is supplied to a welding point of another workpiece at the same site as the predetermined welding point of the workpiece to detect the occurrence of scattering during welding. The high current value of the new welding current waveform is modified based on the fourth step of performing the above, and the presence or absence of the scattering detected in the fourth step, and the high current value of the new welding current waveform is generated based on the modified waveform. Fifth welding current is supplied to the welding point of the same part of the work of the same shape
And a welding current control method for a resistance welding machine. 2. A welding current control device of a resistance welding machine, which sequentially welds workpieces of the same shape having a plurality of welding points for each workpiece, wherein a welding current having a pre-stored waveform corresponds to a predetermined welding point of the workpiece. Supply occurrence limit current value calculation means for obtaining the occurrence limit current value of occurrence of dispersion based on the waveform corrected by the presence or absence of occurrence of occurrence of dispersion detected during welding; Welding current waveform generation means for generating a new welding current waveform consisting of a high current value larger than a limit current value and a low current value smaller than the scattering occurrence limit current value, and welding based on the new welding current waveform A welding current supply means for supplying an electric current to a welding point of another work at the same site as the predetermined welding point of the work, and a welding current supplied to the work by the welding current supply means. And a waveform correction unit that corrects the high current value of the new welding current waveform based on the detected presence or absence of the dispersion. A welding current control device for a resistance welding machine, characterized in that a welding current generated based on the new welding current waveform is supplied to a welding point on the same portion of a work having the same shape.