JPH03472A - Method and equipment for ac tig welding - Google Patents

Abstract

PURPOSE:To maintain the depth of penetration at a fixed value even if the torch position is not controlled by a torch moving mechanism when the arc voltage is changed by changing frequency of the AC output corresponding to variation of the arc voltage. CONSTITUTION:In TIG welding, a DC voltage value (i) before being converted into AC by a secondary inverter circuit 9 is detected by a current detection circuit 7 and a pulse control circuit 3 is subjected to feedback control via an error amplifier 4 so that the detected value is coincident with a value I set by an output current setter 8, by which an output current value is maintained at a fixed value. The AC frequency generated by the secondary inverter circuit 9 and an electrode plasma time ratio are controlled by a driving circuit 10 based on an output signal of a square wave generator 12 and the fixed AC output is impressed on between a welding torch 13 and base metal 14. A function generator 16 sends a signal to regulate the AC frequency to the square wave generator 12 according to the prescribed relation between the arc voltage and the AC frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC TIG welding method and apparatus used for welding aluminum, its alloys, etc.

[Conventional technology]

It is widely known that welding results are greatly influenced by welding conditions. For example, the relationship between penetration depth and welding conditions is expressed by the Jackson O equation, where k: constant determined by the welding method I: welding current ■: welding speed vl: For Ando and Hase, the establishment of arc voltage is the "welding arc phenomenon"
Expanded edition, Sangyo Publishing (1967), p. 368-369
It is introduced in etc.

As is clear from Jackson's equation, in TIG welding using non-consumable electrodes, the arc voltage (1) greatly affects the penetration depth. As described in Japanese Patent Application Laid-Open No. 49-20044, the torch position is feedback-controlled by taking the deviation between the arc voltage and the set voltage to obtain a predetermined penetration depth.

[Problem to be solved by the invention]

However, in order to control the torch position so as to keep the arc voltage, or arc length, constant, a torch moving mechanism consisting of a slide base and a drive motor is required, which makes the device complex and requires a horizontally fixed tube. In automatic welding equipment, etc., the space around the welding part is narrow, so there may be restrictions on its use.

SUMMARY OF THE INVENTION An object of the present invention is to provide an AC TIG welding method and apparatus that can maintain the penetration depth at a predetermined value without controlling the torch position using a talk moving mechanism when the arc voltage changes. be.

[Means for Solving the Problems] In order to achieve the above object, the AC TIG welding method of the present invention uses an arc generated by applying an AC output of a welding power source between a non-consumable electrode and a base metal. The present invention is characterized in that the frequency of the AC output is changed in accordance with an increase or decrease in arc voltage when welding the base metal.

Specifically, the frequency of the AC output may be changed approximately in proportion to the arc voltage.

In order to carry out the above method, the AC TIG welding device of the present invention has a means for converting direct current into alternating current with a variable frequency, and maintains a constant value of the direct current before being converted to alternating current even if the alternating current frequency changes. means for detecting an arc voltage, and means for defining an output frequency of the orthogonal conversion means according to a detected value of the arc voltage according to a predetermined relationship between the arc voltage and the AC frequency, the AC output of the orthogonal conversion means being connected to an electrode.・It is designed to be applied between the base materials.

[Effect]

The welding current, welding speed, and arc length are kept constant, but the frequency of the AC output applied between the electrode and the base metal (hereinafter referred to as AC frequency) is varied to create an arc that has a close relationship with the penetration depth. When the pressure is measured, it is as shown in Figure 3, and as the AC frequency increases, the arc pressure increases and approaches the arc pressure in DC welding.

An example of the effect that changes in arc pressure due to AC frequency have on penetration depth is shown in Figure 4. When the AC frequency is higher than the commercial frequency, the penetration depth becomes deeper, and when it is lower than the commercial frequency, the penetration depth becomes deeper. Penetration depth becomes shallower.

In FIG. 4, considering AC welding at a commercial frequency, the penetration depth increases from Po to P when the arc voltage changes from the reference value ■1° to ■a+. Also, the arc voltage is V. When changing from Po to Vat, the penetration depth decreases from Po to P+.

However, if the AC frequency is set to 25H2 when the arc voltage becomes ■, , the penetration depth becomes Po, and the arc voltage at the commercial frequency becomes ■. It can be set to the same value as the penetration depth in . Similarly, if the arc voltage is Va
ffi, the penetration depth does not change if the AC frequency is set to 250 Hz. That is, by changing the AC frequency approximately in proportion to the arc voltage as shown in FIG. 2, the penetration depth can be maintained at a predetermined value.

〔Example〕

An example of the configuration of a welding apparatus for implementing the TIG welding method of the present invention is shown in FIG. 1. In FIG. 1, 1.2 is a rectifier and a primary inverter circuit for converting commercial AC input into high frequency AC, respectively. So, -order inverter circuit 2
inputs the high frequency alternating current controlled by the pulse width control circuit 3 to the welding transformer 5. 6 is a rectifier for converting the secondary output of the transformer 5 into direct current, and 7 is a current value i converted to direct current.
9 is a secondary inverter circuit for converting direct current back into alternating current for performing alternating current welding. The output current value is determined by detecting the DC voltage value i before being converted to AC by the secondary inverter circuit 9 using the current detection circuit 7, and adjusting the output current value so that it matches the value I set by the output current setting device 8. , is maintained at a predetermined value by feedback-controlling the pulse control circuit 3 via the error amplifier 4.

The frequency and electrode plus time ratio (d) of the alternating current generated in the secondary inverter circuit 9 are the function generators 16 and d6. The function generators 16 and d6 generate a rectangular wave whose pulse frequency and pulse width are defined by the signal from the setting device 11. A predetermined alternating current output is applied between the welding torch 13 and the base material 14 under the control of the drive circuit IO based on the output signal of the welding torch 12 .

Reference numeral 15 denotes an arc voltage detection circuit, and based on the detected value V, a function generator 16 generates a signal defining the AC frequency into a rectangular wave according to a predetermined relationship between the arc voltage and the AC frequency as shown in FIG. to generator 12.

With such a configuration, the alternating current frequency is automatically changed in response to increases and decreases in arc voltage, and the penetration depth can be maintained at a predetermined value.

Although it is desirable that the alternating current frequency be changed approximately in proportion to the arc voltage according to a predetermined relationship as shown in FIG. 2, substantially the same effect can be obtained by changing it by linear approximation or in steps.

〔Effect of the invention〕

According to the invention. Since the penetration depth in AC TIG welding can be maintained at a predetermined value without performing torch position control, a torch moving mechanism composed of a slide base, a drive motor, etc. can be omitted.

The omission of the torch moving mechanism simplifies the welding equipment, and
It has the advantage of being able to make automatic welding equipment for fixed pipes used in confined spaces smaller and lighter.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of the configuration of a welding device for carrying out the TIG welding method of the present invention, and Fig. 2 shows an example of the relationship between arc voltage and AC frequency to maintain a constant penetration depth. FIG. 3, and FIG. 4 are explanatory diagrams of the phenomenon on which the present invention is based. 2... Output current control - next inverter circuit, 3...
Pulse width control circuit, 4... Error amplifier, 7... Current detection circuit, 8... Output current setting device, 9... Secondary inverter circuit for AC output, 10... Drive circuit, 12.・
- Rectangular wave generator, 13... Welding torch, 14... Base material, 15... Arc voltage detection circuit, 16... Function generator that defines AC frequency.

Claims (1)

[Claims] 1. In AC TIG welding, in which base metals are welded using an arc generated by applying AC output of a welding power source between a non-consumable electrode and a base metal, the frequency of the AC output is set to An AC TIG welding method characterized by changes in response to increases and decreases in voltage. 2. The AC TIG welding method according to claim 1, wherein the frequency of the AC output is changed approximately in proportion to the arc voltage. 3. In order to carry out the method according to claim 1 or 2, means for converting direct current into alternating current with variable frequency, and means for keeping the value of the direct current constant before being converted to alternating current even if the alternating current frequency changes. , comprising means for detecting an arc voltage and means for defining an output frequency of the orthogonal transformation means according to a detected value of the arc voltage according to a predetermined relationship between the arc voltage and the AC frequency, the AC output of the orthogonal transformation means being connected to an electrode or AC TIG welding equipment that applies voltage between base materials.