JPH07323376A - Resistance welding method of stud and device therefor - Google Patents

Abstract

PURPOSE:To exactly detect the weld defect of resistance welding of studs by calculating an electric resistance value and comparing this value with a reference value. CONSTITUTION:An upper electrode 1 and lower electrode 2 of a resistance welding device of studs are so arranged as to hold a panel 5 therebetween. A welding current is passed from the upper electrode 1 through the stud 3 and the panel 5 to the lower electrode 2 by a power source 6. A welding current supplying circuit is provided with a current detector 8 for detecting the voltage between the electrodes 1 and 2 and a current detector 9 for detecting the welding current. The detection outputs of these detectors 8, 9 are inputted to a weld zone electric resistance value calculating circuit 10. This circuit 10 calculates the electric resistance value of the weld zone in accordance with the welding voltage and welding current which are the detection outputs of the detectors 8, 9. This resistance value is compared with the reference value and the weld defect is judged when the resistance value is lower than the reference value. As a result, the weld defect of the weld zone is exactly detected. The perfect welding is executed by executing energization again in case of the weld defect.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to welding methods and apparatus for welding studs such as threaded studs or T-studs to panels such as body panels. In particular, the present invention relates to a stud resistance welding method and apparatus. More particularly, the present invention relates to a method and apparatus for detecting weld defects in resistance welding of studs.

[0002]

2. Description of the Related Art When a threaded stud or T stud is resistance-welded to a panel, an upper electrode for gripping the stud and pressing it against the panel and a lower portion on the opposite side of the panel facing the upper electrode. A welding device with electrodes is used. The tip of the stud is formed in a tapered shape, and the stud tip is melted by heat generation due to high electric resistance of the contact portion between the tip of the tapered portion and the panel, and is crushed to form a nugget and welded to the panel. If the formation of this nugget is small, the strength of the welded portion will be insufficient, resulting in poor welding.

[0003]

The conventional stud resistance welding method and device do not include means for accurately detecting a welding failure. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method and an apparatus capable of detecting welding defects.

[0004]

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, an electric resistance value of a welded portion is calculated based on a welding voltage and a welding current, and the electric resistance value is compared with a reference value. , Or a change in electric resistance value is compared with a reference pattern. Then, when the electric resistance value becomes lower than the reference value or the reference pattern, it is determined that the welding is defective. In a preferred aspect of the present invention, when it is determined that there is poor welding, the welding current is passed again to obtain good welding. That is, a stud resistance welding method according to an aspect of the present invention includes a stud that includes an upper electrode for gripping the stud and pressing it against the panel, and a lower electrode disposed on the opposite side of the panel and facing the upper electrode. The resistance welding device is used to measure the voltage between the upper electrode and the lower electrode and the welding current flowing between both electrodes during welding to obtain the electric resistance value of the welded part, and this resistance value is used as a reference. When the resistance value is lower than the reference value as compared with the value, it is determined that the welding is defective. Further, in a welding method according to another aspect of the present invention, the electric resistance value is monitored over a welding current energization period, and when the resistance value falls below a reference pattern by a predetermined amount or more during the welding current energization period, it is determined that welding is defective. To do.

Further, in one aspect of the resistance welding apparatus for a stud according to the present invention, the apparatus is arranged so that the upper electrode for gripping and pressing the stud against the panel and the opposite side of the panel facing the upper electrode. Lower electrode,
Voltage detecting means for detecting the voltage between the upper electrode and the lower electrode, current detecting means for detecting the welding current flowing between both electrodes, and electric power of the welded portion by receiving the detection output of the voltage detecting means and the current detecting means. A resistance value calculating means for calculating a resistance value and a welding failure detecting means for comparing a resistance value output of the resistance value calculating means with a reference value and generating a welding failure signal when the resistance value output is lower than the reference value are provided.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the stud resistance welding apparatus includes an upper electrode 1 and a lower electrode 2. Upper electrode 1 is stud 3
Has a cylindrical recess 4 into which the stud 3 is inserted and held. As shown in the figure, the stud 3 has a flange 3a having a tapered lower surface at the lower end, and is arranged so that the lower end surface of the upper electrode 1 contacts the upper surface of the flange 3a. The upper electrode 1 and the lower electrode 2 are
The panel 5 is arranged so as to sandwich the panel 5, and a power source 6 applies a welding current from the upper electrode 1 to the lower electrode 2 through the stud 3 and the panel 5. The welding current is controlled by the switch 7. The switch 7 is closed by the welding start signal and supplies a welding current between the electrodes 1 and 2 for a predetermined welding time. The welding current supply circuit is provided with a voltage detector 8 for detecting the voltage between the electrodes 1 and 2 and a current detector 9 for detecting the welding current. The detection outputs of the detectors 8 and 9 are input to the welding portion electric resistance calculation circuit 10. This circuit 10 calculates the electric resistance value of the welded portion based on the welding voltage and welding current which are the detection outputs of the detectors 8 and 9. The output of the circuit 10 is input to the comparator 11 and compared with the reference value from the reference value circuit 12.

FIG. 2 (a) shows a welding current waveform. The welding current is controlled by the switch 7 for a predetermined welding time,
An electric current is applied between the electrodes 1 and 2. Figure 2 (b) shows a typical change in the electrical resistance of the weld in the case of poor welding. When the welded nugget is not sufficiently formed due to the abnormal collapse of the tip taper portion of the flange 3a of the stud 3, the electric resistance value sharply decreases after the start of energization as shown in the figure. If the reference value of the electric resistance value is set as shown by A in the figure,
This welding failure can be detected by the comparator 11. Comparator 1
The welding failure signal from 1 is input to the stud 7. Upon receipt of this welding failure signal, the stud 7 closes the welding circuit again and energizes when the energization period for welding ends. FIG. 2 (c) shows a reference pattern representing changes in the electrical resistance value of the welded portion in the case of normal welding, which is empirically required. Instead of the comparator 11 in the welding circuit of FIG. 1, it is possible to provide a monitor circuit for monitoring the output of the welding portion electric resistance calculating circuit 10 during the welding period. This monitor circuit compares the output of the weld electric resistance calculation circuit 10 with the reference pattern shown in FIG. 2 (c), and when the amount of deviation from the reference pattern exceeds a predetermined value, it judges that welding is defective. Generates a welding failure signal. That is, this monitor circuit constitutes a welding failure determination means. As in the circuit of FIG. 1, a welding failure signal from the monitor circuit is input to the switch 7 and when the energization period for welding is over, the welding circuit is closed again to energize.

[0008]

According to the stud resistance welding method and apparatus of the present invention, it is possible to accurately detect a welding defect in a welded portion, and in the case of a welding defect, it is possible to obtain complete welding by re-energizing. Become.

[Brief description of drawings]

FIG. 1 is a schematic view of a resistance welding device for a stud showing an embodiment of the present invention.

FIG. 2 is a chart showing welding current and electric resistance value of a welded part, where (a) shows a typical example of the welding current and (b) shows electric resistance value of the welded part in the case of poor welding. Shows a change, (c)
Indicates the change in electric resistance value in the case of normal welding.

[Explanation of symbols]

 1 ... Upper electrode, 2 ... Lower electrode, 3 ... Stud, 3a ... Flange, 5 ... Panel, 6 ... Power supply, 7 ... Switch , 8 ... Voltage detector, 9 ... Current detector, 10 ... Weld portion electrical resistance calculation circuit, 11 ... Comparator, 12 ... Reference value circuit.

Claims (6)

[Claims] 1. Welding using a resistance welding device for a stud, comprising an upper electrode for gripping and pressing a stud against a panel, and a lower electrode arranged opposite the panel on the opposite side of the panel. In addition, the voltage between the upper electrode and the lower electrode and the welding current flowing between the electrodes are measured to obtain the electric resistance value of the welded portion, and the resistance value is compared with a reference value to obtain the resistance value. Is less than the reference value, it is determined that the welding is defective. 2. Welding using a resistance welding device for a stud, comprising an upper electrode for gripping and pressing a stud against a panel, and a lower electrode arranged opposite the panel on the opposite side of the panel. In addition, the voltage between the upper electrode and the lower electrode and the welding current flowing between the both electrodes are measured to obtain the electric resistance value of the welded portion, and the resistance value is monitored over the welding current energization period to perform the welding. A resistance welding method for a stud, wherein when the resistance value is lower than a reference pattern by a predetermined amount or more during a current-carrying period, it is determined that welding is defective. 3. The resistance welding method for a stud according to claim 1 or 2, wherein when the welding is judged to be defective, the energization for welding is performed again. 4. An upper electrode for gripping and pressing a stud against a panel, a lower electrode arranged opposite to the upper electrode on the opposite side of the panel, and between the upper electrode and the lower electrode. A voltage detecting means for detecting a voltage, a current detecting means for detecting a welding current flowing between the both electrodes, and a resistor for receiving an output of the voltage detecting means and the current detecting means to calculate an electric resistance value of a welded portion. A stud comprising: a value calculating means; and a welding failure detecting means for comparing a resistance value output of the resistance value calculating means with a reference value and generating a welding failure signal when the resistance value output is lower than the reference value. Resistance welding equipment. 5. An upper electrode for gripping and pressing a stud against a panel, a lower electrode arranged opposite to the upper electrode on the opposite side of the panel, and between the upper electrode and the lower electrode. A voltage detecting means for detecting a voltage, a current detecting means for detecting a welding current flowing between the both electrodes, and a resistor for receiving an output of the voltage detecting means and the current detecting means to calculate an electric resistance value of a welded portion. A value calculation means and a welding defect in which this electric resistance value is compared with a reference pattern over a welding current energization period, and a welding defect is judged to be a welding defect when the resistance value falls below a predetermined amount from the reference pattern during the welding current energization period. A resistance welding device for a stud, comprising: a determining means. 6. The stud resistance welding apparatus according to claim 4 or 5, further comprising means for receiving a welding failure signal from the welding failure detection means and restarting a welding cycle. Resistance welding equipment.