JPH0371985A - Capacitor type spot welding machine - Google Patents

Abstract

PURPOSE:To fix welding conditions and to improve welding quality by providing a residual magnetic flux extinguishing means separately from a switching element for excitation. CONSTITUTION:A capacitor 1 is charged to the polarity shown by the figure from a DC power source and a turn ratio of primary winding 21 and secondary winding 22 of a transformer 2 is made to a reciprocal ratio and an electrical current is doubled and a welding electrode 3 is connected to the secondary wiring 22 and the current il is applied to materials 31 and 32 to be welded which are welded to each other. The current il is extinguished and main thyristors 41 and 42 are turned off and then, the materials 31 and 32 to be welded are removed and the welding electrode 3 is made opened. when ignition signals are then given to auxiliary thyristors 51 and 32, the current is carried from the capacitor 1 to a parallel circuit of a capacitor 61 and a resistor 62 the primary wiring 21 a parallel circuit of a capacitor 64 and a resistor 63 the auxiliary thyristor 52 a capacitor 1 circuit. By this method, residual magnetic flux is extinguished and the welding conditions can be fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a capacitor type spot welding machine 2, particularly to a capacitor type spot welding machine with improved control of residual magnetic flux of a transformer.

[Conventional technology]

As a conventional capacitor type spot welding machine.

For example, there is one shown in FIG. To explain according to this diagram, the electric energy stored in the capacitor l with the polarity shown is activated by the welding signal to the thyristors 41 and 42, and current flows to the primary winding 21 of the transformer 2, and from the secondary winding 22. A welding current is sent in the direction 11 shown in the figure.

This current imparts power loss to the objects to be welded 31 and 32 which are sandwiched and connected via the electrodes 3, thereby causing welding. Then, the next welding signal turns on the thyristors 43 and 44, and a current flows in the primary winding 21 of the transformer 2 in the opposite direction to the previous one, and the welding current in the direction 12 shown in the figure is sent out from the secondary winding 22. . At this time, the residual magnetic flux of the transformer is canceled out.

[Problem to be solved by the invention]

However, in such a conventional capacitor type spot welding machine, four switching elements of the same capacity and weight are used, leading to an increase in cost. Furthermore, the direction of welding current changes alternately during each welding process, and when welding dissimilar metals or projection welding, welding results may vary depending on the polarity of the welding current. The present invention aims to eliminate the residual magnetic flux of the transformer while keeping the direction of the welding current constant.

[Means to solve the problem]

This invention aims to solve such problems.

In addition to the switching element for excitation, means for extinguishing or reducing residual magnetic flux is provided.

[Embodiment] An embodiment of the present invention will be explained below based on FIG. 1. In the figure, t is a capacitor, which is not shown in the figure, but is charged in advance from a DC power source to the polarity shown in the figure. 2 is a transformer, the secondary winding 21 of which is excited via main thyristors 41 and 42; The turns ratio between the primary winding 21 and the secondary winding 22 of the transformer 2 is approximately 60:I, and the current is multiplied to the inverse ratio of this ratio. The secondary winding 22 is connected to the welding electrodes and applies a current il to the objects to be welded 31 and 32 held between them, causing self-welding due to heat loss caused by the electrical resistance.

After the welding current if disappears and the main thyristor 41.42 is turned off, the workpiece 31.32 is taken out from between the welding electrodes 3, and then the welding electrodes 3 are left open. Then, the residual magnetic flux of the transformer 2 is eliminated as follows.

That is, first, a firing signal is given to the auxiliary thyristors 51 and 52. Then, from the capacitor l, the parallel circuit of capacitor 61 and resistor 62→, -th order winding 21→, capacitor 6
Parallel circuit of 4 and resistor 63→, capture thyristor 52→
, a current flows through the capacitor 1.

The current in this path can substantially eliminate the residual magnetic flux of the transformer 2 with a small current.

This returns to the initial state in which welding work can be performed again, and the objects to be welded 31 and 32 are newly held between the welding electrodes 3. In this way, the welding current can always be kept constant in the 11 direction.

Here, the magnitude of the current flowing through the auxiliary thyristors 51 and 52 is adjusted by the impedance formed by a capacitor and a resistor connected in series with these thyristors, respectively, so that the magnitude of the current flows as long as is permissible from the time length of the two welding intervals.

The magnitude of the current flowing through the auxiliary thyristors 51 and 52 can be limited. Therefore, the auxiliary thyristors 51 and 52 can have a sufficiently medium current capacity compared to the main thyristors 41 and 42.

Note that a resistor 7 connected in parallel to the primary winding 2I of the transformer 2
1 and capacitor 72 in series acts as a voltage snubber for this primary winding 21.

FIG. 2 shows another embodiment of the present invention, in which elements having the same numbers as those in the embodiment shown in FIG. 1 correspond to the same elements. In the figure, the electric charge stored in the capacitor l is made conductive by firing of the thyristor 41, and current flows through the primary winding 21 of the transformer 2, thereby exciting it. At this time, the secondary winding 22
is the workpiece 3 connected to the welding electrode and held between the welding electrodes.
A current 11 is applied to 1.32 to cause self-welding due to heat loss caused by the electrical resistance.

After the welding current direction disappears and the main thyristor 41 turns off, the welding electrode 3 is first turned off in order to eliminate the residual magnetic flux of the transformer 2.
Open between. Next, a firing signal is given to the auxiliary thyristor 51. Then a capacitor! From capacitor 61 and resistor 6
Parallel circuit with 2 →, Urasuke thyristor 51 →, 3rd winding 2
3→, current flows through the capacitor l. The current in this path can eliminate the residual magnetic flux of the transformer 2 with a small current. This returns to the initial state in which welding work is possible again, and the welding current flowing through the objects to be welded 31 and 32 is always constant in the direction of if.

Although this embodiment requires the addition of a third winding.

It has the advantage of allowing a greater degree of freedom in design conditions and reducing the number of thyristors used as switching elements by half.

Note that a resistor 7 connected in parallel to the third winding 23 of the transformer 2
5 and capacitor 76 act as a voltage snubber for this third winding 23. Further, a series body of a resistor 73 and a diode 74 connected in parallel to the main thyristor 41 and a series body of a resistor 77 and a diode 78 connected in parallel to the auxiliary thyristor 51 each act as a voltage snubber.

In the above embodiments, the switching means is not limited to Cyrisk, but also bipolar transistors, field effects)
・Of course, transistors, GTOs, etc. can be used.

Further, the impedance means is not limited to the parallel combination of a resistor and a capacitor as shown in this embodiment, but may be only a resistor or only a capacitor.

Furthermore, a non-linear element can also be used if necessary.

Furthermore, in the second embodiment, the residual magnetic flux of the transformer was controlled using the capacitor's capacitor charge that supplies welding energy, but it is also possible to supply it from another energy source. Furthermore, the disappearance of residual magnetic flux can be realized not only by direct current but also by a method of supplying from an alternating current source.

〔Effect of the invention〕

As described above, according to the present invention, the size and number of switching elements can be reduced, resulting in economical operation. In addition, since the welding current for each welding operation can be applied to the workpiece in only one direction, the welding conditions are constant, and especially when welding dissimilar metals, the quality improvement -L can be achieved.

[Brief explanation of drawings]

FIG. 1 shows a capacitor type spot welding machine which is one embodiment of the invention, and FIG. 2 shows another embodiment of the invention. FIG. 3 shows an example of a conventional capacitor type spot welding machine. i... Capacitor. 2...Transformer, 21...-Secondary winding 22...Secondary winding, 23...Third winding 3...Welding electrode, 31.32...Welded object 41, ,42.4
3.44...Main thyristor 51, 52...Auxiliary thyristor

Claims (4)

[Claims] (1) A capacitor charged by a DC power source, a transformer connected to be excited by a discharge current from the capacitor via a first switching means, and connected to a secondary winding of the transformer, A capacitor type spot welding machine comprising a pair of electrodes that sandwich a workpiece to be welded, and reverse excitation means that is activated after the first switching means is turned off. (2) A capacitor type spot welding machine according to claim 1, characterized in that a demagnetizing means is provided in place of the reverse excitation means. (3) The capacitor type spot welding machine according to item 1, wherein the reverse excitation means comprises an impedance means and a second switching means that are connected in series with each other. (4) A first characterized in that the reverse excitation means is comprised of a third winding of the transformer and a second switching means.
Capacitor type spot welding machine described in section.