JPS59185581A - Resistance spot welding method and apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Relating to a resistance spot welding method and apparatus for passing current to a workpiece between electrodes to form a joint, in zero resistance spot g welding the aligned surfaces of the workpiece are
The electrical resistance of the workpieces, which are held together under force by electrodes, is used to generate heat and are joined together at one or more spots. The surfaces in contact with each other in the area of current concentration are heated by short pulses of low voltage, intense lightning to form molten nuggets of weld metal. When the current is turned off: the electrode force is maintained while the weld is rapidly cooled and solidified.

After each weld, the electrode is withdrawn, typically after a fraction of a second.

Resistance welding has increased in popularity significantly since 1935. The reason why resistance spot welding has become popular is due to the following factors: Resistance spot welding allows for speedy bath welding and can be integrated into large-scale production and assembly lines along with automation and other manufacturing operations. The fact is that even in cases where resistance spot bathing can be adopted. However, despite these advantages, spot welding has significant drawbacks. That is, there is a drawback in that it is impossible to control the process to a satisfactory degree in order to achieve uniform and good welding. The reason for this is that there are a large number of parameters that need to be controlled or that change from weld to weld. For example, voltage, current, pressure, heat loss,
These include shunt formation, electrode wear, and workpiece material thickness and composition. Some of these parameters are difficult or virtually impossible to control.

Attempts have been made for several years to automatically control the resistive spot seeding process by controlling the electrical energy and thus the heat generated. An electric θ't sensor is used to form a feedback connection for the purpose of maintaining a constant welding current. In addition, to compensate for power supply voltage fluctuations or impedance fluctuations, a turtle pressure pot device is added. However, all of these feedback coupling systems are based on monitoring process conditions according to set reference values derived on the basis of safety standards. Therefore, the actual welding process parameters that can be used to control the parameters are not discussed.

A large number of spot contacts are controlled by a time oscillator that controls four basic steps. The four basic steps are: 1. Close the electrode and apply force (suppression time).

Second, apply and maintain current (welding time).

Sixth, cut off the bath current. Maintain the electrode force until the weld nugget solidifies (hold time).

Fourth, open the electrode (at end 1i').

The time required for the above steps can be adjusted empirically to achieve optimal results.

During all subsequent spot m-connection operations. remains constant. It is generally assumed that the welding time is long enough to bring the metal into a bath melt state. However, this is not necessarily the case with wealth. As the degree of electrode wear increases, the time required to induce bath melting increases, and in some cases, the preset
The welding time may be longer than the welding time.

In such a case, the indentation will not reach the required goose fraction value, resulting in a defective weld.

The basic object of the invention is to provide a resistive spotted connection method and device of the type mentioned at the outset, which can be adapted to the situation existing in each case.

According to the present invention, this problem is solved as follows. That is, during bath melting of the workpiece, a pressing force that varies as a function of the depth of penetration by the electrode is applied to the workpiece by the electrode, the welding valve opening pressure is detected, and a welding signal is generated as a measure of the pressing force, The welding signal is processed in order to form a signal for a change in the pressing force acting on the workpiece.

According to the invention, as an apparatus for carrying out the method of the invention:
a pair of electrodes for accommodating the workpiece therebetween, a device for moving one electrode toward the other electrode for applying a pressing force to the workpiece, and a device for moving one electrode toward the other electrode for applying a pressing force to the workpiece; The device includes a device that causes a current to flow through the workpiece to the other electrode, and a device that controls the duration of current application to the workpiece, and controls the penetration depth of the electrode into the workpiece when the current melts the workpiece. A force transmission device that applies a force that changes as a function to a movable electrode is incorporated into the pressing force generation device, a transmission device that detects the force applied by the force transmission device and generates a welding signal indicative of the force, and a signal. A processing device is provided, the signal processing device being coupled to the transmission device to generate a signal for a change in the pressing force acting on the workpiece.

Advantageous embodiments of the invention are described in the dependent claims.

The non-invention is based on the fact that the necessary condition for forming a bath contact actually exists; i.e., the necessary condition for forming a bath contact is that the metal must reach the bath melt state. This means that it will not happen. Bath Welding 1 - Failure to bring the metal to the temperature required for bath melting will result in a poor weld or no bath welding at all. The detection of the molten phase is dependent on the bath welding process but not on fixedly defined parameters.

In the present invention, it is used to control bath contact parameters. As a result of the measurement, as soon as the bath melt state is reached, the electrodes pressed against the workpiece begin to penetrate into the metal and move towards each other.

The facts have been revealed. Therefore, such electrode movement (penetration depth) is only about an inch percent of the plate thickness;
The melt phase is sensitive or wet.

The diagram in FIG. 1 is transcribed from r'RwMA Resistance Welding Manual Ji 3rd Edition, Volume 1, Page 122.

The diagram in FIG. 1 shows the relationship between the electrode penetration depth e, the breaking load of the weld joint (tensile shear 5 degrees b), and the weld nugget diameter d0) when welding is carried out under different welding currents 1. According to the above-mentioned reference, bath contact is 0.074 countries (o, o 29 inches 9
Made of annealed steel with a thickness of . At that time, an A-type (pointed tip) electrode with a tip diameter of 0.655 cm (4 inches) was used, and the electrode pressure was approximately 3 inches.
5! 1.4 kilobond [kp] (755 pounds [l!
bs)) corresponding to the force of 1,055 kp/C'n;'
(15,000 pounds per square inch Cpsi) and weld time was 6 cycles. According to the diagram in Figure M1, at the optimum current value (13.50 OA) the diameter of the weld nugget was approximately equal to the diameter of the electrode tip. Increasing the current beyond 15,500 A did not significantly increase the weld nugget diameter, but rather markedly increased the electrode penetration depth. The tensile shear failure load increases rapidly until the optimum current is reached, and becomes slightly lower as the current increases to values slightly above 1·4.00 OA. The penetration depth is
When the bath welding current is 15,500 A, it is about 2% of the plate thickness, or when the welding current is 14. Approximately 10 slightly exceeding DOOA
%.

As is clear from the diagram of FIG. 1, detecting bath melting and subsequent movement of the electrode ('intrusion of intrusion') is a potentially preferred method for detecting bath contact conditions.

However, attempts have been made to utilize the detection of electrode moving bodies for the purpose of controlling the welding process, but these attempts have not been successful. The reason is 0.00254 cm (
This is because it is difficult to accurately and repeatably detect small travel distances of spot bath contact electrodes, on the order of 0,001 inches).

The present invention indirectly detects the working distance of the electrode by making use of the fact that the mechanical force (pressure force 9) acting on the electrode changes when the welded part is in a bath-molten state. The load generated on the electrode is generated from the pressing force and the reaction force acting from the plate, which is in balance with the pressing force and is opposite to the pressing force and has the same size.Therefore, the electrode is placed between the pressure source and the plate. The M9 merccal of the present invention is maintained immovably between the metal and the metal in the spot bath contact area (instead of the pressing force being kept constant as in other systems). There is a possibility that the magnitude of the pressing force will change as a function of whether it is melted or bath melted.

As soon as the metal enters the molten state, the electrodes begin to move towards each other. This reduces the load on the electrode. Changes in the magnitude of this I'6T load can be easily detected using electrical strain gauges or other pressure transmitters. Furthermore, typical changes in electrode force are on the order of about 401 J. Therefore, an excellent signal-to-noise ratio can be obtained.

The present invention uses a pressing force system that satisfies the second-order differential equation % to produce the required change in the magnitude of the load.

A force system using spring-loaded electrodes is a good example of such a system. The force exerted by the spring tilt is a function of the spring stiffness K and the static displacement X of the spring. A change in the static spring displacement (caused by melt initiation) causes a change in the force acting on the electrode. The resulting signals indicative of changes in force at the electrodes are processed electronically and the processed signals are used for control or monitoring of the welding process. In this way, defective welds are detected and all necessary adjustments can be made in the welding process in order to eliminate defects in subsequent welds.

Next, the present invention will be explained in detail with reference to the drawings with reference to embodiments.

The welding machine (second core) itself is conventional, with important exceptions described below. This bath wetting machine consists of a fixed lower arm 12
and an electrode holder 10 having a movable upper arm 14. The bath current flows through the arm to two of the transformers 18.
The next winding 16 supplies the electrodes. The primary winding 20 of the transformer 18 is connected to the line 22, 24'faO: 60H when the switch 26 controlled by the hour oscillator is closed.
Powered by z alternating current. Time transmitter 28 controls the entire welding cycle. That is, the generation of a pressing force (hydraulic or mechanical) to move the movable arm in the direction of the fixed arm, the closing of the switch 26 to energize the workpiece W with the welding underflow between the electrodes E. control, the opening of the switch 26 to cut off the bath contact current, and the removal of the pressing force after the elapse of the hold time for the bath increase to solidify.

The pressing force F2 that actually acts on the workpiece is generated based on the force F1. The force F1 is slightly larger than the force F2 (and is generated by a suitable mechanical or hydraulic device. The member 60 transmitting the force F1 contacts a fixed stopper 62, which generates a pressing force F2. The transmission device for this is a spring 64. The force exerted by the spring 54 decreases as the length of the spring 64 increases. load cell) 36
Ha, spring 640 force F2. Therefore, the pressing force acting on the workpiece is detected. This force is a measure of the penetration of the electrode into the workpiece. Penetration of the electrode into the workpiece occurs when the weld point melts. When the electrode penetrates into the workpiece and the movable electrode approaches the fixed electrode, the spring 34 is lengthened and the force F2 is correspondingly reduced, so that the force described in iii is equal to the degree of penetration of the electrode into the workpiece. It will be a relief to your eyes.

The force detector 36 is configured to include four strain gauges connected to a bridge circuit (see Figure 2B). This circuit provides increased sensitivity and excellent temperature compensation. During the bathing cycle, the strain gauge
Because of the extremely strong electromagnetic field exposure, a low is provided to completely eliminate any harmful effects of the welding current during the welding cycle. An undercurrent sensor 58 (FIG. 2A) detects the bath contact alternating current in the secondary winding of the transformer 180. The current sensor 68 is connected via lines 40, 41 to two operational amplifiers 42.44 (eg National LM741). Operational amplifiers 42, 44 determine the point at which the welding current takes its minimum value (crossing the zero point). This information is fed to two monostable multi-by-breaks 46,48 (eg National LM555). These monostable multi-bibreaks 46.48 are connected to the transistor Q1 (fl
(e.g. Fairchild 2N6716) can be adjusted using potentiometers R1-R4. This adjustment is possible between 5% and 100% of the sinusoidal cycle. In this way, transistor Q supplies a driving DC current from north B to force detector 3 through line 50 only during periods when the harmful effects of the magnetic field are minimal.

The load signal generated by the force F2 is transmitted to the sense amplifier 52.
(e.g. National LF152), 60Hz
It is guided through a filter 54.

After the initial pressing force is applied to the workpiece, the switch 26
immediately before closing the switch 26 and starting welding, or simultaneously with closing switch 26 and starting welding.

In response to the signal provided on line 56 from the time oscillator, the I2J double signal from filter 54 is applied to sample and hold element 58 (flJ, National LF
198). 2 before the actual welding takes place.
The output value captured by the sample and hold element, which is an analogue of the I.
111) to one input side of the 111). This analog voltage is a reference voltage. The reference voltage does not change during the subsequent welding process. This is because the value of the reference rolling pressure is identified by the sample-and-hold amplifier. A second input of the comparator receives the amplified t-wave strain gauge signal via line 62. This strain gauge signal is
It is a function of subsequent changes in electrode loading and is compared to a reference signal during subsequent welding current cycles.

Biasing device RB causes comparator 58 to have a negative ρ when the variable load signal is greater than the captured reference signal.
Forced to 1 to generate output polarity. At some point during the welding phase, the metal begins to melt. As a result, the force F2 decreases. This decrease in force F2 causes the variable wagon signal to decrease and the amplitude of the load signal to be just around the reference signal. Comparator 60 now switches to positive output polarity.

Logic output level of comparator 60 (H, AND go) 6
4 (eg, Fairchild 10104). The other input value is the signal applied via line 66 from the main weld time transmitter 28.

When the time oscillator initiates bathing by closing switch 26 to supply current to the workpiece, a positive voltage signal is sent to the AND gate. As a result, A.N.
The D gate is connected to the comparator 6 so that the necessary second normal image signal is connected to the comparator 6.
Arrangements are made such that its output voltage changes as it comes from zero. The welding current period is controlled by the 1 hour oscillator (start) and the ifE polarity output value of the AND gate (stop). The time transmitter further interrupts the welding current when a predetermined overtime has elapsed. To provide a pure stop signal to the time oscillator, the AND gate flips 70
Trigger the whelk 68 (eg Fairchild 54/7470).

Flip-flop 68 is locked upon receiving a positive pulse and remains in this state until reset by the bath time oscillator, providing a stop signal to the time oscillator via line 70.

The closed-loop control system described above can therefore be used to control the length of the welding cycle depending on the condition of the workpiece, rather than depending on some arbitrarily selected parameters. .

However, if it is desired to monitor the welding process (rather than to control it), when the selection switch 72 is switched to the monitoring mode of operation, the selection switch 72 can switch the feedback loop to a time oscillator. In the supervisory mode of operation, the welding time transmitter operates in a customary manner. Specifically, the welding time transmitter controls the welding cycle according to a fixed preset time transmitter. If no plastic (molten) phase is obtained during the welding cycle, the indicator 74 generates a perceptual alarm, thereby indicating a defective or unsuccessful weld.

According to another method of monitoring the welding cycle, one uses the time transmitter 28 after the initial pressing force has been applied to the workpiece, based on the idea of the invention, ie, indentation information as a criterion for good welding. A reference signal is conducted via line 76 to zumble hold element 78 in response to a time-defined command signal provided via line 80 from . The reference signal and weight signal are provided to an amplifier 82. The resulting amplified output signal is indicative of the load during the welding cycle, starting from the time welding current is applied to the workpiece. The complete waveform of the load on the electrode during the welding cycle is AD
Via a converter 84 (eg XICOM 1855) it is fed as input to a microcomputer 86 (eg XICOM 1868). The microcomputer 86 has
A pre-plotted "target" waveform of the complete weld is programmed. At the end of the welding cycle, microcomputer 86 performs the following;
Namely, a. Digital filtering of the waveform to obtain a smooth plot.

b. Comparing the detected waveform with the target waveform during welding.

C1 Send an "OK" signal when the detected waveform is within a predetermined programmed error range of the target waveform.

d. When the detected waveform does not correspond to the specifications.

Abandon welding.

Based on the rate of change of the load signal, which is an additional indication of the onset of the melt phase of the workpiece and is therefore suitable for monitoring the welding process,
You can also analyze waveforms.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the weld nugget diameter, the fracture strength of the welding part, and the depth of electrode penetration in a region where welding current is present, and Fig. 2A is a welding device used for detailed explanation of the present invention. FIG. 2B is a schematic diagram of a welding device provided for detailed explanation of the present invention. 1... Welding current, d... Welding spot diameter, b...
・Fracture load of welded joint, e...jQ pole penetration depth, E・
... Electrode, W ... Workpiece, F2 ... Pressing force, 1
0...electronic boulder, 12.14...arm, 16.
...Secondary winding green, 18...Transformer, 20...Primary winding, 26...Switch, 28...Time transmitter, 52 River stopper, 64...Spring, 66...・Strong deer detector, 68...' current sensor, 42.44...
Arithmetic J width unit, 46° 48... Monostable multipipe rake, 54... Filter, 58°゛° sample/hold element, 60... Comparator, 64... AND
gate, 68... flip-flop, 72... selection switch, 74... display device, 78 sample/hold element, 86-C microcomputer. r −′, agent Koto Ezaki 1, − agent Kyu Ezaki,” ′ , −−1′

Claims (1)

[Claims] (υ In a resistance spot welding method in which a workpiece is pressed between a pair of electrodes and a current is passed through the workpiece between the electrodes to form a welded part, Electrode (f,) Penetration depth by K (6
), the pressing force (F2) changes as a function of the electrode (E)
In addition to the workpiece (W), the welding valve opening pressure (F2)
detecting, generating a welding signal as a measure of the pressing force (F2), and processing the welding signal to form a signal for a change in the pressing force (F2) acting on the workpiece (W). A resistance spot welding method characterized by: (2) Welding signal processing detects the workpiece (
Sample the reference signal that indicates the pressing force acting on W).
comparing the welding signal with the reference signal and the welding signal, and forming an output signal for whether and when a predetermined change in the opening pressure (F2) of the weld formation occurs; Claim No. 1 (1) having the step of
The resistance spot welding method according to item 1. (3) When an output signal is generated indicating a predetermined change in the pressing force (F2) that occurs when the electrode (E) enters the workpiece (W) at the start of melting of the weld, the workpiece (W)
The resistance spot welding method according to claim (2), wherein energization is terminated. (4) The output signal is monitored to see if there is a change in the pressing force (F2) that indicates the start of melting of the weld. Resistance spot welding method according to claim 2, which is perceptually displayed. (5) A strong deer detector (5) where the welding signal is electrical
6), which transmits a direct current pulse to a strain detector (36) in phase with a selected corresponding portion near zero of the cycle of the welding current; The resistance spot welding method according to any one of item (4). (6) A step of sampling and holding a reference signal for the pressing force still acting on the workpiece (W) for the first time. The steps of comparing the reference signal and the bath contact signal, the step of generating a digital output waveform of the welding valve opening pressure, and the step of comparing the output waveform with a target waveform of an ideal welding process are signal processing steps. Claim No. (
The resistance spot welding method described in item 1). In a resistance spot welding device that applies current to the workpiece between the electrodes in order to press the workpiece between the pair of electrodes and form a bath contact, a pair of electrodes for holding the workpiece between them. and a device for moving one electrode in the direction of the other electrode in order to apply a pressing force to the workpiece, and a current flow from one electrode through the workpiece to the other electrode to form the weld. and a device for controlling the energization period of the workpiece, as a function of the penetration depth (e) of the electrode CEJ into the workpiece (W) when the current melts the workpiece (W). A force transmission device (54) that applies a changing force (F2) to a movable electrode
and a transmission device (66) which is incorporated into the pressing force generation device, detects the force (F2) exerted by the force transmission device (64), and generates a welding signal instructing the force (F2). A signal processing device (54, 58, 60,) is provided, and the signal processing device (54, 58, 60,) is coupled to the transmission device (36) and has a signal processing device No. A resistance spora)/mo damping device characterized in that it is made to occur. (8) The resistance spot welding device according to claim (7), which includes a force transmitting device and a spring (34). (9) Claim (7) or (8) in which the transmission device includes an electrical strong deer detector (36)
) The resistance spot weld DI described in item DI. a@ A device (58) that samples and bolds a reference signal, which is the peak of the pressing force acting on the workpiece (W) before melting the weld zone, and a device (36) that transmits the signal during the formation of the weld zone. mW (60) in order to compare No. 1H generated by the reference signal with a reference signal and to generate an output signal when a predetermined change in the valve opening pressure of forming the weld occurs. Resistance spot welding device according to claim No. 1 (Hatsufun). ) A resistance spot bath wetting device according to claim M00). (121) A resistive spot bath wetting device according to claim 101, further comprising a device (74) for monitoring the output signal and for indicating whether a predetermined change in the pressing force has occurred. αJ According to any one of claims (9) to αp, comprising a device (Ql) for transmitting a direct current pulse to a force detector in phase with a selected corresponding part of the cycle of the welding current. The resistance spot welding device according to the description.αa A current sensor circuit (38) for detecting the welding current in the secondary winding gauze (16) of the welding transformer and a current in the current sensor circuit (58) actuate the welding current. The point at which the minimum value is obtained is confirmed, and the pair of operational amplifiers (42, 44) supplying an output signal as an instruction to that effect, and the transistor receives the output signal of each operational amplifier (42, 44). A pair of monostable multipipe lakes (46°48) supplying base current to (Ql) and a DC source (B0)
and is provided in a device for transmitting current to the force detector (36),
A transistor (Ql) is provided in the line (50) supplying direct current to the force detector (66), and only when the welding current is approximately zero and therefore the harmful influence of the magnetic field of the welding current is minimal. , a resistance spot welding device according to claim 2, characterized in that a current is supplied to the force detector (66). aω A device for sampling and holding a reference signal that is a measure of the initial suppression force (F2) acting on the workpiece! (
78), a device for comparing the signal generated by the transmission device during the welding process with a single signal, and for generating a digital output waveform indicating changes in the pressing force, and a device for optimizing the welding process. A calculation device (78
), and a device (86) for receiving the digital output waveform of the monitored annotation process and for comparing the target waveform and the digital output waveform, in the signal processing device. Resistance spot welding equipment as described in .