JPS605389B2 - Flash welding power waveform adjustment method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for adjusting a welding power source waveform in order to obtain a good welded product in flash welding.

Generally, in flash welding, single-phase alternating current at commercial frequency is used as the power source, but in this case, flash occurs only in the high voltage section of each sine wave half cycle, and the zero cross point where the polarity of each voltage waveform changes. Flushing stops due to insufficient voltage over a fairly long section before and after. Even during this pause period, the objects to be welded are brought together by the moving electrode, and during this period the short circuit area increases, and the first flash that occurs after the pause is a coarse flash because the large short circuit part is fused and welded. In addition to roughening of the end face, since flash welding is usually performed in the atmosphere, oxidation of non-contact parts progresses during the period when the flash is not in use, which has a negative effect on the welding result. It is already known that if the power supply waveform is made into a rectangular wave in order to overcome these difficulties, a continuous flash will occur and a good welded product can be obtained. However, in order to obtain a square wave as a power source for flash welding, the equipment is complicated and expensive, as it requires first obtaining direct current from a commercial power source using a forward converter, and then switching it between positive and negative using an inverter etc. to create a square wave power source. There were drawbacks. The present inventors have endeavored to simplify the power supply device with the prerequisite of obtaining welding quality substantially equivalent to that of a rectangular wave power source. It has been found that by energizing the transformer by discharging from a pre-charged capacitor, it is possible to obtain welding quality that is substantially equivalent to that obtained using a square wave power source.

In other words, the present invention has two
By controlling the charging and discharging of the set of capacitors, during the high voltage period of each sine wave half cycle of the AC voltage of the power supply, the welding transformer is energized from the commercial power source and the capacitor is charged, and the AC voltage is A flash welding power waveform adjustment method characterized in that a welding transformer is energized by the discharge current from the capacitor during the low voltage period of each sine wave half cycle, and an apparatus for implementing the method, In a flash welding device that supplies power from a commercial power source to a welding transformer via two sets of thyristors or ignitrons connected in antiparallel, two sets of capacitor charging/discharging circuits in which a capacitor and its discharge control device are connected in series are connected to each other. The present invention provides a flash welding power waveform adjusting device characterized in that it is connected in parallel with the primary winding of a welding transformer in the opposite direction.

The present invention will be explained in detail below. FIG. 1 shows an example of a device for carrying out the present invention, in which AC voltage from a commercial power supply 1 is applied to a welding transformer 3 via two sets of ignitrons or thyristors 2, 2' connected in antiparallel. A conventional welding device that performs flash welding by applying a voltage to the primary side of the transformer and applying the secondary side output of the transformer to the workpiece 4 includes a capacitor 5, 5' and a reverse conduction thyristor 6, 6'. This is a newly inserted circuit that is surrounded by a dotted line.

The principle of operation will be explained with reference to the relationship diagram of the voltage waveform applied to the primary side of the transformer, the firing signal of each element, and the conduction state shown in FIG. The waveform indicated by the dotted line in Fig. 2 is the voltage waveform of the commercial power supply 1, but the reverse conduction syringe 6 of Fig. 1 is ignited at point A in the figure, and the voltage is transferred from the capacitor 5 charged in the previous cycle. The welding transformer 3 is energized by the discharge current up to point B in FIG.

Since the voltage of the commercial power supply 1 becomes higher than the voltage of the capacitor 5 after point B, conduction of the ignitron 2 starts at point B, and thereafter, the capacitor 5 is charged and the welding transformer 3 is energized by the commercial power supply. Next, between the CDs, the voltage of the capacitor 5 is higher than the commercial power supply, so during this time, the discharge current of the capacitor 5 causes the welding transformer to
energize. Therefore, since the ignitron 2 naturally extinguishes at point C, current can be prevented from flowing backward from the capacitor 5 to the commercial power supply. Next, the thyristor 6 is forcibly extinguished at the point ○ where the polarity of the commercial power supply voltage changes, and thereafter the same operation is performed by the ignitron 2', the reverse conduction thyristor 6', and the capacitor 5', although the current polarity is reversed. Then, voltage ABC'〇 is applied to the welding transformer.

To be exact, there is a pause of several to tens of French seconds between D and A'. In FIG. 2, F indicates the forward flow of the thyratrons 6 and 6', B indicates the reverse flow, and C indicates conduction of the ignitrons 2 and 2'. In the method of the present invention, the capacitances of the capacitors 5 and 5' are set to such an extent that the voltage applied to the welding transformer 3 is lowest at B and B', and at the same time, sufficient voltage to generate a flash can be secured on the secondary side of the transformer. The size should be selected as follows.

The actual size varies depending on the cross-sectional area of the object to be welded, the butting speed, the power supply voltage, etc., but it is usually on the order of several thousand to tens of thousands of microfarads. Furthermore, it is natural that thyristors can be used in place of the ignitrons 2, 2' in the method of the invention. As described above, the present invention provides a relatively simple method and device for constantly supplying a voltage sufficient to cause a flash to a workpiece, even though the voltage waveform has considerable irregularities. ), similar to the square wave method, a continuous flash is generated, resulting in good welding results.

Comparing the system of the present invention with a rectangular wave power supply system, it is found that while a rectangular wave system requires a conversion device for converting alternating current to direct current, the present invention does not require it; The number of large-capacity semiconductor elements is only half of those used in inverter devices, which are essential for square wave systems. That is, the present invention provides an effect substantially similar to that of a rectangular wave by inserting a relatively simple device into a normal flash welding machine, and its industrial effects are extremely significant. The effects of the method of the present invention will be explained in more detail below using Examples. Example The apparatus shown in FIG. 1 includes a normal flash welding machine (conventional method) without the part surrounded by dotted lines, a flash welding machine with the part surrounded by dotted lines inserted, that is, the apparatus of the present invention, and an additional 14% 3. Flash welding, in which the pulsating flow including the nopple is switched between positive and negative by an inverter and an alternating current with a waveform similar to the square wave of 50 days 2 is applied to the primary side of the welding transformer.
Thickness 2. Stainless steel plates of 3 lengths (cross-sectional area: 60 degrees) were butt-welded, and after grinding the welded part smooth, the strength of the welded part was evaluated by a tensile test.

The welding conditions are that the secondary no-load voltage is 7.2V (its effective value in the conventional method, the effective value of the input voltage before waveform adjustment in the method of the present invention, and its average value in the case of a waveform similar to a rectangular wave), and the flash The time was set to 3 seconds, the flash length was 8 cycles, the upset length was 2.5 cycles, and the number of upset energization cycles was set to 1.0 cycles. Further, the capacitance of the capacitor in the device of the present invention was set to 6000 F. 3Z welds were each welded using each method, and Table 1 shows the average and minimum values of the tensile strengths after grinding the weld burrs. As shown in the results in the same table, in the conventional method, not only the average value of the tensile strength of the welded parts is low, but also some parts have extremely low strength, which poses a problem in the reliability of welding.

Many cold-reinforced parts were observed on the fracture surface (low-strength specimens), and many of the specimens using the conventional method developed arm fractures during the tensile test. These phenomena are thought to be due to the fact that in the conventional method, the flash generation stops before and after the zero-crossing point of the AC waveform. On the other hand, with the method of the present invention, a tensile strength equivalent to that of a rectangular wave can be obtained, and both the average value and the minimum value of the strength are high, and the reliability of welding is high. All fractured shapes in the tensile test showed structural failure. Table 1

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of the device of the present invention, and Fig. 2 shows the relationship between the no-load voltage waveform on the primary side of the welding transformer whose waveform was adjusted by the method of the present invention, and the ignition signal and conduction status of each element. It is a diagram. 1... Commercial AC power supply, 2, 2'... Ignitron or thyristor, 3... Welding transformer, 4
...Object to be welded, 5,5'...Capacitor,
6,6'... Reverse conduction thyristor. Figure 1 Figure 2

Claims (1)

[Claims] 1. By controlling the charging and discharging of two sets of capacitors inserted in the primary side of the welding transformer, welding can be performed from the commercial power source during the high voltage period of each sine wave half cycle of the AC voltage of the power source. Flash welding characterized by energizing a transformer and charging the capacitor, and energizing the welding transformer with a discharge current from the capacitor during the low voltage period of each sine wave half cycle of the AC voltage. power waveform adjustment method. 2. In a flash welding device that supplies power from a commercial power source to a welding transformer via two sets of thyristors or ignitrons connected in antiparallel, two sets of capacitor charging/discharging circuits each having a capacitor and its discharge control device connected in series are connected to each other. A power waveform adjustment device for flash welding, characterized in that it is connected in parallel with the primary winding of a welding transformer in the reverse direction.