JPH01273673A - Capacitor type stud welding method - Google Patents

Abstract

PURPOSE:To decrease weld heat input and to improve welding quality by providing plural power supply units and discarding the residual current energy successively when the supply current and weld time of respective capacitors attain respective set values. CONSTITUTION:The plural power supplies A, B are provided and charging voltage regulators 1, 7 and the capacitors 2, 8 are respective disposed thereto. The energy charged in the capacitor 2 is supplied by a switch element 3 to a weld zone 4 and the energy of the capacitor 2 is discarded as the heat generation of a resistor 6 by a switch element 5 when the current value and weld time thereof attain the set value I1, T1. The similar operation is then repeated in the power supply unit B of the 2nd stage to control the welding current I and the weld time T to a required min. limit. The weld heat input is thereby decreased and the thermal strain and damage of the weld zone are minimized. The welding quality is, therefore, improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to capacitor stud welding for welding a bar-shaped metal to a mating metal.

(Prior technology) A simple and convenient method for welding a small-diameter rod-shaped metal to a fully bent member.
The condenser stud welding method is widely used because it takes a short time and has relatively little effect on welding heat. These welding methods perform welding by discharging energy stored in a capacitor with a constant capacity according to electrical circuit constants. Typical examples of the current waveforms are shown in Figures 2, 3a, 3b, and 3. 4
This is shown in the figure.

Figure 2 shows the result of normal spontaneous discharge, and Figures 3a and 3b show the results of JP-A No. 50-30764 and JP-B No. 48.
Figure 4 is a composite of two to three current waveforms with shifted timings as proposed in Publication No. 36819, etc., and Figure 4 is a current waveform from a power supply with different lance turns ratios according to Japanese Patent Publication No. 48-36820. It is a composite of

These methods can provide a welding current that is suitable for the purpose of forming a strong welded joint, but it is difficult to reduce the effects of welding heat because they lack the ability to control the welding heat input to the necessary minimum. Furthermore, if the circuit constants of the current-carrying circuit including the welding point change, the current waveform changes, which tends to make it difficult to obtain good welding results. The causes of variations in circuit constants include the way the welding cable is arranged, the distance between the power supply point to the welding member and the welding point, etc., and variations are often unavoidable during daily welding work. For this reason, when there is a risk that the current will drop due to the above fluctuations, the current is set to be higher in advance to prevent a drop in the strength of the welding member. However, in this case, high current conditions tend to occur and the weld heat-affected zone widens, resulting in a result that is not suitable for stud welding to thin steel plates where aesthetics are important. On the other hand, if too much emphasis is placed on the outside a of the weld and the current is set too low, the strength of the weld may not reach the target value.

(Problems to be Solved by the Invention) In stud welding, there is a required minimum current that is determined depending on the thickness of the rod-shaped metal to be welded, and there is also a necessary minimum time for continuing the current. FIG. 5 schematically shows the relationship between the discharge current from a conventional capacitor and the ideal welding current. In the figure, 16 is a conventional current waveform, and 17 is an ideal current waveform. In order to satisfy the maximum value IO of waveform 17 and its period To, a large current IP that far exceeds In is required. A current that significantly exceeds To flows for a long time.

If the current exceeds the value required to obtain joint strength, the electromagnetic force will cause the molten metal to scatter, or it will have a significant thermal effect on the vicinity of the weld.

The purpose of the present invention is to supply the minimum necessary current to the welded part to obtain joint strength, thereby achieving sufficient joint strength and minimizing thermal effects, and obtaining a welded part with an excellent appearance. can be,
It is an object of the present invention to provide a stud welding method in which the current waveform is controlled so that the maximum value of the welding current and the duration of the current are as close as possible to the ideal waveform 17 shown in FIG.

(Means for solving the problem) The gist of the present invention is to supply welding current from the first-stage capacitor unit, and discard the energy remaining in the first-stage capacitor when the supplied current and energization time reach preset constant values. At the same time, the supply of welding current is started from the next stage capacitor, and when the supply current and energization time reach a separately set fixed value, the energy remaining in the next stage capacitor is discarded. The present invention is directed to a capacitor type stud welding method, which is characterized in that the steps are sequentially performed.

(Function) The control method which is a feature of the present invention will be explained below with reference to FIG.

Prepare at least two or more sets of power supply units that supply energy to the welding area, and increase this number as necessary. A case where there are two sets of power supply units will be explained.

The first power supply A is connected to a capacitor 2 via a charging voltage regulator 1.
The energy charged in the switch element 3 at the start of welding
It is supplied to the welding part 4 via. It has the function of consuming the energy remaining in the capacitor 2 at this point as heat generated by the resistor 6 via the resistor 6 in the switch cable 5 in accordance with the control signal from the subsequent node. - The power source B of the power tube 2 supplies the energy charged in the capacitor 8 via the charging voltage regulator 7 to the welding part 4 via the switch element 9 in accordance with a first control signal. Thereafter, the energy remaining in the capacitor 8 at this point is released by the switch element 10 via the resistor 11 in accordance with the second control signal, and is consumed as heat generated by the resistor 11.

The first and second control signals will be explained using the circuit shown in FIG. 1 and the welding current waveform shown in FIG. 6.

The first power source A has a current detector 18 and sends a signal of welding current to a first control signal generator 19, which outputs a welding current and a constant constant of the market time. When the value is reached, the first control signal 20 is generated.

That is, at the start of welding, the switch element 3 is turned on, the energy of the capacitor 2 begins to be supplied to the welding part 4, and the current 12 begins to flow. The first control signal is issued at the 0 point, which satisfies two conditions: the current 12 reaches a constant value 11 and the constant time T1 has elapsed since the start of welding. This signal turns on switch element 5 and switch element 9. As a result, the current supplied to the welding part from the capacitor 2 is cut off, the current 13 that had conventionally flowed to the welding part is discarded as heat generated by the resistor 6, and the supply of welding current from the capacitor 8 begins. Further, the second power source B has a current detector 21, and sends a welding current signal to a second control signal generator 22. When the value is reached, the second control number 23 is generated.

That is, the second control signal is issued at point D, where two conditions are satisfied: the current supplied from the capacitor 8 to the welding part 4 reaches a constant value (2) and the constant time T2 has elapsed. As a result, the current supplied from the capacitor 8 to the welding section is cut off, and the current 14 that conventionally flowed to the welding section is discarded as heat generated by the resistor 11. Through such a process, a composite current 15 having a shape close to the ideal current waveform 17 shown by the dotted line in FIG. 5 is created.

According to this method, only the minimum amount of energy accumulated in the capacitors 2 and 8 necessary for stud welding is combined and supplied to the welding part, and energy unnecessary for welding is discarded without being supplied to the welding part. It becomes possible.

If the rod-shaped metal to be stud-welded is steel, the current density of the rod-shaped metal will be 110 to 250 A/tm''.
ec.

There is an appropriate setting value within the range of . If it falls below this range, the weld will be incomplete, and if it exceeds this range, the effect of welding heat will become significant, increasing thermal damage to the weld, or the molten metal will scatter violently, reducing the strength of the weld. It becomes like this.

It is necessary to select appropriate values for the current value and the current application time for generating the first control signal and the second control signal depending on the cross-sectional area and material of the metal rod to be stud-welded.

(Example) A steel bolt with a diameter of 5 nnφ was stud-welded to the back surface of a 1.6-thick steel plate with the following settings.

11 = 3KA, T1 = 3msec, 1:2 = 3
KA, 2 = 0.2m5ec After welding, the strength of the joint was determined by a torsion test, and it was found to be strong enough to be twisted from a steel bolt.

In addition, the maximum temperature of the steel plate surface at the welded part is 150°C,
The period during which this maximum temperature was 1i11i'Ig was 50 m.
It was 5ec.

Comparing this result with the conventional method, the maximum temperature was about 172 in the conventional method, and the time until the maximum temperature became 150° C. or less was about 177.

(Effects of the invention) Unlike the conventional energization method using natural discharge, the present invention is a method of controlling the current value and the energization time to the minimum value necessary for welding, so the welding heat input is significantly reduced compared to the conventional method. Not only is it possible to perform stud welding, it is also possible to perform extremely reliable stud welding.

Therefore, even when welding to a thin steel plate, thermal distortion is extremely small, and when welding to a painted steel plate, damage to the painted surface due to heat can be suppressed to a minimum.

Although the present invention has been described above using a connection method in which the polarity of the rod-shaped metal to be welded is (+), it goes without saying that the same effect can be obtained even if the polarity is reversed.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a current control circuit implementing the present invention, Figure 2 is a circuit diagram of a current control circuit implementing the present invention;
3a, 3b, and 4 are waveform diagrams of t'lYs currents emitted from capacitor power supplies that have been proposed in the past,
FIG. 5 is a waveform chart showing the discharge current from a conventional capacitor and an ideal welding current, and FIG. 6 is a waveform chart showing the current supplied from the capacitor to the welding part. A: First power supply B: Second power supply 1.2: Charging voltage regulator 2, 8: Capacitor 3.9: Switch element for supplying welding current 4: Stud welding part S, tO: Capacitor unnecessary for welding Switch element 6.11: Resistor 1 that consumes capacitor energy
2: Welding current 13.14: Electricity d color that conventionally flows in the welded part 15: Combined welding current I+, I2: Set current value TI, T2: Set energization time C
: First control signal generation point D: Second control signal generation point 16: Conventional current waveform 17: Ideal current waveform 18
．． 21 Cffi current ratio detector: First control signal generator 20: First control signal 22: Second control signal generator 23: Second control signal p: Maximum value of conventional current waveform ■. : Current value of ideal current waveform Patent applicant Nippon Steel Corporation Nikaisha

Claims (1)

[Claims] Welding current is supplied from the first-stage capacitor unit, and when the supply current and energization time reach preset values, the energy remaining in the first-stage capacitor is discarded, and the welding current begins to be supplied from the next-stage capacitor. A capacitor type stud welding method characterized in that each capacitor unit is made to sequentially perform an operation of discarding the energy remaining in the next stage capacitor when the supplied current and energization time reach a predetermined value set separately.