JP2005186118A - Arc start method for ac tig welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a proper initial cleaning area, reduce electrode consumption, and suppress generation of arc cut-off, in starting arc in AC TIG welding. <P>SOLUTION: After the arc start, an initial electrode positive current Ipi of an initial electrode positive period Tpi and the initial electrode negative current Ini during the initial electrode negative period Tni are supplied. In order to form the proper initial cleaning area, the initial electrode positive current Ipi larger than the stationary electrode positive current Ip and the initial electrode positive period Tpi are made to vary in accordance with the average welding current, and the product of the initial electrode negative period Tni and the initial electrode negative current Ini is within the range of 0.6 to 1.6 of the product of the initial electrode positive period Tpi and the initial electrode positive current Ipi. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an arc start method for AC TIG welding for improving the welding quality of an arc start portion in AC TIG welding.

  AC TIG welding is mainly used for welding aluminum materials. FIG. 9 is a typical waveform diagram of the welding current Iw in a steady state in AC TIG welding. During a predetermined electrode plus period Tp from time t1 to t2, the non-consumable electrode has a positive polarity (hereinafter referred to as an electrode positive polarity EP) with respect to the base material, and a predetermined electrode plus current Ip is energized. During a predetermined electrode minus period Tn at subsequent times t2 to t3, the non-consumable electrode has a negative polarity with respect to the base material (hereinafter referred to as an electrode negative polarity EN), and a predetermined electrode negative current In is energized. During the electrode plus period Tp, the oxide film on the surface of the base material is removed by the cleaning action, and during the electrode negative period Tn, the heat input to the base material is increased and sufficient penetration is formed. The electrode minus ratio (EN ratio) is defined as Tn / (Tp + Tn), and is usually set to about 70% in many cases.

  In AC TIG welding, it is common to apply a high frequency high voltage between a non-consumable electrode and a base material to start an arc. In the steady state after the arc start, the welding current Iw described above is applied to perform welding. One example for improving the welding quality at the time of arc start is described in Patent Document 1. FIG. 10 is a waveform diagram of the welding current Iw in the prior art described in Patent Document 1. A high-frequency high voltage is applied to start an arc with an electrode plus polarity EP at time t1, and the energization of the initial electrode plus current Ipi during the initial electrode plus period Tpi and the energization of the initial electrode minus current Ini during the initial electrode minus period Tni are timed. Repeat several cycles until t2. After that, welding is performed by repeatedly applying a steady electrode plus current Ip during the steady electrode plus period Tp and energizing an electrode minus current In during the steady electrode minus period Tn. In this prior art, the AC frequency 1 / (Tpi + Tni) during the initial period Ti from time t1 to t2 is set lower than the AC frequency 1 / (Tp + Tn) in the steady state after time t2. According to this, it is described that the occurrence of arc break immediately after the arc start can be suppressed and a good welding quality of the arc start portion can be obtained.

Japanese Patent Laid-Open No. 3-5078

The prior art described above with reference to FIG. 10 has the following problems.
(1) A sufficient cleaning area cannot be formed immediately after the arc start. The reason for starting the arc with the electrode positive polarity EP and energizing the initial electrode plus current Ipi is to remove the oxide film by this energization to form the initial cleaning area. That is. When an arc start is started from the electrode negative polarity EN, an oxide film may be caught in the molten pool formed by energizing the initial electrode negative current Ini, resulting in a defective weld bead. By the way, when the average value of the steady welding current Iw is changed, the size of the molten pool is changed, so that an appropriate initial cleaning region is also different. Therefore, it is necessary to change the initial electrode plus current Ipi and the initial electrode plus period Tpi for forming the initial cleaning region in accordance with the change in the average value of the steady welding current Iw. However, since the conventional technology does not have such an interlocking function, the initial cleaning region immediately after the arc start is not sufficiently formed, and an oxide film is caught in the molten pool, which may result in a defective bead.

(2) Increase in electrode consumption at arc start and occurrence of arc breakage The set values of initial electrode minus current Ini and initial electrode minus period Tni with respect to the set values of initial electrode plus current Ipi and initial electrode plus period Tpi are predetermined. If this relationship is not satisfied, the amount of electrode consumption at the time of arc start increases and arc breakage is likely to occur. However, in the prior art, there is no description about the relationship between these two.

  Therefore, in the present invention, (1) the initial cleaning area immediately after the arc start is always optimized, and (2) the arc of AC TIG welding that can reduce the amount of electrode consumption at the time of arc start and suppress the occurrence of arc breakage. Provides a starting method.

In order to solve the above-described problem, the first invention is to start an arc with an electrode positive polarity, and then energize a predetermined initial electrode plus current during a predetermined initial electrode plus period with the electrode positive polarity, Switch to electrode negative polarity and apply a predetermined initial electrode negative current during a predetermined initial electrode negative period, followed by a steady electrode positive current during a steady electrode plus period and a steady electrode during a steady electrode minus period. In the arc start method of AC TIG welding in which an electrode negative current is repeatedly applied,
Immediately after the arc start, in order to form an appropriate initial cleaning region on the surface of the base material, the initial electrode plus current and the initial electrode plus period which are larger than the steady electrode plus current are changed according to the average value of the welding current. And the multiplication value of the initial electrode minus period and the initial electrode minus current is within the range of 0.6 to 1.6 of the multiplication value of the initial electrode plus period and the initial electrode plus current. This is an arc start method for AC TIG welding.

  According to the first aspect of the invention, the initial electrode plus current Ipi and the initial electrode plus period Tpi are set so that the initial cleaning region is appropriate according to the average value of the welding current, and according to both values Ipi and Tpi. Therefore, the initial electrode minus current Ini and the initial electrode minus period Tni are set so that the multiplication value ratio Rnp falls within the proper range, so that an appropriate initial cleaning region is formed immediately after the arc start, and the amount of electrode consumption during the arc start is reduced. Reduction and suppression of arc breakage can be performed, and the welding quality of the arc start portion can be improved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a waveform diagram of a welding current Iw according to an embodiment of the present invention. Hereinafter, a description will be given with reference to FIG.

(1) Initial electrode plus period Tpi between times t1 and t2.
After starting the arc with the electrode positive polarity EP at time t1, a predetermined initial electrode positive current Ipi is applied during the predetermined initial electrode positive period Tpi from time t1 to t2 with the electrode positive polarity EP. This initial electrode plus current Ipi is set to a value larger than the steady electrode plus current Ip in order to form an appropriate initial cleaning region on the surface of the base material immediately after the arc start. In addition, since the size of the weld pool to be formed differs depending on the average value of the welding current Iw as described above, in order to form an appropriate initial cleaning region according to the average value of the welding current Iw, the initial electrode plus current Ipi In addition, it is necessary to change the initial electrode plus period Tpi according to the average value of the welding current Iw. The average value of the welding current Iw is the average value of the absolute values of the steady electrode plus current Ip and the steady electrode minus current In after time t3. Usually, since Ip = In is often the case, the average value of the welding current Iw in this case is equal to the electrode plus current Ip and the electrode minus current In. FIG. 2 shows an example of the relationship between the welding current average value, the initial electrode plus current Ipi, and the initial electrode plus period Tpi. When the welding current average value changes, the initial electrode plus current Ipi changes according to the characteristic L1, and the electrode plus period Tpi changes according to the characteristic L2.

(2) Initial electrode minus period Tni at times t2 to t3
At time t2, the polarity is switched to the electrode negative polarity EN, and a predetermined initial electrode negative current Ini is applied during a predetermined initial electrode negative period Tni. Here, the multiplication value ratio Rnp is multiplied by the multiplication value Tni × Ini of the initial electrode minus period Tni and the initial electrode minus current Ini and the multiplication value Tpi × Ipi of the initial electrode plus period Tpi and the initial electrode plus current Ipi. The ratio is defined as Rnp = (Tni × Ini) / (Tpi × Ipi). FIG. 3 is a diagram showing the relationship between the multiplication value ratio Rnp, the amount of electrode consumption at the time of arc start, and the number of occurrences of arc breakage. The figure shows the measurement of the amount of electrode wear and the number of arc breaks when the arc start is performed 100 times with an arc generation time of 1 second at an average welding current value of 100A. As shown in the figure, when the multiplication value ratio Rnp is less than about 0.6, the electrode consumption increases greatly. On the other hand, when the multiplication value ratio Rnp exceeds about 1.6, the number of occurrences of arc breaks greatly increases. Therefore, the multiplication value ratio Rnp needs to be within the range of 0.6 to 1.6 in order to reduce the amount of electrode consumption at the time of arc start and to suppress the occurrence of arc breakage. About this cause, the temperature rise of the non-consumable electrode at the time of an arc start has influenced greatly. That is, when the multiplication value ratio Rnp is less than the appropriate range, the non-consumable electrode is heated more than necessary and the temperature becomes too high, resulting in an increase in electrode consumption. On the other hand, when the multiplication value ratio Rnp exceeds the appropriate range, the temperature of the non-consumable electrode becomes too low to make it difficult for electrons to be emitted from the non-consumable electrode, and as a result, arc breakage is likely to occur. The figure shows the case where the welding current average value is 100 A, but the same tendency is observed in other cases. The temperature rise of the non-consumable electrode will be described in detail in FIGS.

(3) Period after time t3 At time t3, the process shifts to normal energization of welding current, energization of electrode plus current Ip during electrode plus period Tp at times t3 to t4, and electrode minus period Tn at times t4 to t5. The energization of the electrode negative current In is repeated.

  FIG. 4 is a diagram illustrating temporal changes in the welding current Iw and the temperature Et of the non-consumable electrode when the above-described multiplication value ratio Rnp is in the above-described appropriate range. As shown in FIG. 6A, after the arc start at time t1, an initial cleaning region is formed by energizing the initial electrode plus current Ipi, and as shown in FIG. It rises rapidly and reaches Et1. When the negative electrode EN is switched to the negative polarity EN at time t2 and the initial electrode negative current Ini is energized, electrons are released from the non-consumable electrode, so that energy is lost and the temperature of the non-consumable electrode drops to Et2. Thereafter, the temperature rises during the electrode plus period Tp and falls during the electrode minus period Tn. At this time, if the multiplication value ratio Rnp is within the proper range, the temperature Et2 is within the proper range, and the subsequent temperatures also change within the proper range. As a result, it is possible to obtain a good welding quality in which the amount of electrode consumption does not increase due to the temperature of the non-consumable electrode becoming too high, and on the contrary, arc breakage due to being too low is not generated.

  FIG. 5 is a diagram showing temporal changes in the welding current Iw and the temperature Et of the non-consumable electrode when the multiplication value ratio Rnp is smaller than the appropriate range. In this figure, the initial electrode plus current Ipi and the initial electrode plus period Tpi are the same as those in FIG. 4 described above. This is a case where only the initial electrode minus period Tni is shortened without changing the initial electrode minus current Ini in order to change the multiplication value ratio Rnp. Of course, the multiplication ratio Rnp may be changed by changing the initial electrode minus current Ini.

  In FIG. 4, the temperature Et1 is the same as that in FIG. 4, but the temperature Et3 is higher than the temperature Et2 in FIG. 4 because the initial electrode minus period Tni is shorter. As a result, since the temperature of the non-consumable electrode becomes too high, the amount of electrode consumption at the time of arc start increases. This state is the state of the multiplication value ratio Rnp <0.6 in FIG. 3 described above.

  FIG. 6 is a diagram showing temporal changes in the welding current Iw and the temperature Et of the non-consumable electrode when the multiplication value ratio Rnp is larger than the appropriate range. In this figure, the initial electrode plus current Ipi and the initial electrode plus period Tpi are the same as those in FIG. 4 described above. This is a case where only the initial electrode minus period Tni is lengthened without changing the initial electrode minus current Ini in order to change the multiplication value ratio Rnp. Of course, the multiplication ratio Rnp may be changed by changing the initial electrode minus current Ini.

  In FIG. 4, the temperature Et1 is the same as that in FIG. 4, but the temperature Et4 is lower than the temperature Et2 in FIG. 4 because the initial electrode minus period Tni is longer. As a result, since the temperature of the non-consumable electrode becomes too low, it is difficult for electrons to be emitted in the negative polarity of the electrode, and arc breakage is likely to occur. This state is the state of the multiplication value ratio Rnp> 1.6 in FIG.

  As described above, the initial electrode minus current Ini and the initial electrode are set so that the multiplication ratio Rnp is within the above-described range in order to reduce the amount of electrode consumption at the time of arc start and to suppress the occurrence of arc breakage. It is necessary to set the minus period Tni.

  FIG. 7 is a block diagram of a welding power source for carrying out the present invention. Hereinafter, each circuit will be described with reference to FIG.

  The inverter circuit INV receives a commercial AC power supply AC (three-phase 200 V or the like) as an input, performs inverter control according to a current error amplification signal Ei described later, and outputs a high-frequency AC. The high frequency transformer INT steps down the high frequency alternating current to a voltage value suitable for an arc load. The rectifiers D1 to D4 rectify the stepped-down high frequency alternating current and convert it into a direct current output. The electrode plus transistor PTR is turned on during the electrode plus period by the electrode plus drive signal Pdr. The electrode minus transistor NTR is turned on during the electrode minus period by the electrode minus drive signal Ndr. Reactor WL smoothes welding current Iw. An arc 3 is generated between the non-consumable electrode 1 attached to the tip of the welding torch 4 and the base material 2.

  The current detection circuit ID detects an AC welding current Iw, converts it to an absolute value, and outputs a current detection signal Id. The current energization determination circuit CD determines that the arc starts and the welding current Iw is energized based on the current detection signal Id, and outputs a current energization determination signal Cd which becomes a high level. The electrode plus period setting circuit TPS has an electrode plus period that becomes a predetermined initial electrode plus period for the first time after the current energization determination signal Cd becomes High level and becomes a predetermined steady electrode plus period for the second time and thereafter. The setting signal Tps is output. The electrode minus period setting circuit TNS has an electrode minus which becomes a predetermined initial electrode minus period for the first time after the current energization determination signal Cd becomes High level and becomes a predetermined steady electrode minus period for the second time and thereafter. A period setting signal Tns is output. The polarity switching signal timer circuit TM outputs a polarity switching signal Tm which is at a high level during a period determined by the electrode plus period setting signal Tps and is at a low level during a period determined by the electrode minus period setting signal Tns. The drive circuit DR outputs an electrode plus drive signal Pdr for conducting the electrode plus transistor PTR when the polarity switching signal Tm is at a high level, and an electrode minus drive signal Ndr for conducting the electrode minus transistor NTR when the polarity switching signal Tm is at a low level. Is output.

  The electrode plus current setting circuit IPS has a predetermined initial electrode plus current for the first time after the current energization determination signal Cd becomes High level, and an electrode plus which becomes a predetermined steady electrode plus current for the second time and thereafter. The current setting signal Ips is output. The electrode minus current setting circuit INS has an electrode minus which becomes a predetermined initial electrode minus current for the first time after the current energization determination signal Cd becomes High level and becomes a predetermined steady electrode minus current for the second time and thereafter. The current setting signal Ins is output. The current setting switching circuit SI receives the polarity switching signal Tm and switches to the a side when the signal is at the high level, and outputs the electrode plus current setting signal Ips as the current control setting signal Isc, and when the signal is at the low level. Switch to the b side and output the electrode minus current setting signal Ins as the current control setting signal Isc. The current error amplification circuit EI amplifies an error between the current control setting signal Isc and the current detection signal Id, and outputs a current error amplification signal Ei. As a result, the welding current Iw having the current waveform described above with reference to FIG. 1 is applied according to the current control setting signal Isc.

  FIG. 8 is a flowchart showing a method for setting the initial electrode plus current Ipi, the initial electrode plus period Tpi, the initial electrode minus current Ini, and the initial electrode minus period Tni in FIG. Hereinafter, a description will be given with reference to FIG.

  In step ST1, a steady electrode plus current Ip, a steady electrode plus period Tp, a steady electrode minus current In, and a steady electrode minus period Tn suitable for the workpiece are set. In step ST2, the welding current average value is calculated from Ip, Tp, In and Tn. As described above, when Ip = In, the welding current average value is equal to Ip and In. In step ST3, the average value of the welding current is input, and the initial electrode plus current Ipi and the initial electrode plus period Tpi are calculated by a predetermined function as described above with reference to FIG. In step ST4, the above-mentioned Ipi and Tpi are input, and the initial electrode minus current Ini and the initial electrode minus period Tni are calculated by a predetermined function so that the multiplication value ratio Rnp becomes a predetermined value. For example, if Ipi = Ini and the multiplication value ratio Rnp = 1.2 (value in the range of 0.6 to 1.6), it can be calculated by Tni = Tpi × 1.2. When Tni = Tpi, it can be calculated by Ini = Ipi × 1.2.

It is an electric current waveform diagram which shows the arc start method of the alternating current TIG welding which concerns on embodiment of this invention. It is a figure which shows an example of the relationship between the welding current average value which concerns on embodiment of this invention, initial electrode plus electric current Ipi, and initial electrode plus period Tpi. It is a figure which shows the relationship between the multiplication value ratio Rnp which concerns on embodiment of this invention, the amount of electrode consumption at the time of an arc start, and the frequency | count of occurrence of arc breakage. In embodiment of this invention, it is a figure which shows the time change of the welding current Iw and the temperature Et of a non-consumable electrode when the multiplication value ratio Rnp is an appropriate value. In embodiment of this invention, it is a figure which shows the time change of the welding current Iw and the temperature Et of a non-consumable electrode when the multiplication value ratio Rnp is a value smaller than an appropriate value. In embodiment of this invention, it is a figure which shows the time change of the welding current Iw and the temperature Et of a non-consumable electrode when the multiplication value ratio Rnp is a value larger than an appropriate value. It is a block diagram of the welding power supply for implementing this invention. 8 is a flowchart showing a method for setting an initial electrode plus current Ipi, an initial electrode plus period Tpi, an initial electrode minus current Ini, and an initial electrode minus period Tni in the welding power source of FIG. It is a current waveform figure in the steady state of the alternating current TIG welding in a prior art. It is a current waveform figure at the time of the arc start of the alternating current TIG welding in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Non-consumable electrode 2 Base material 3 Arc 4 Welding torch CD Current energization discrimination circuit Cd Current energization discrimination signal D1-D4 Rectifier DR Drive circuit EI Current error amplification circuit Ei Current error amplification signal EN Electrode minus polarity EP Electrode plus polarity Et Non-consumption Electrode temperature ID Current detection circuit Id Current detection signal In (steady) electrode minus current Ini Initial electrode minus current INS Electrode minus current setting circuit Ins Electrode minus current setting signal INT High frequency transformer INV Inverter circuit Ip (steady) electrode plus Current Ipi Initial electrode plus current IPS Electrode plus current setting circuit Ips Electrode plus current setting signal Isc Current control setting signal Iw Welding current Ndr Electrode minus drive signal NTR Electrode minus transistor Pdr Electrode plus drive signal PTR Electrode plus transistor Rnp Multiplication value ratio SI Current Setting Constant switching circuit Ti initial period TM polarity switching signal timer circuit Tm polarity switching signal Tn (steady) electrode minus period Tni initial electrode minus period TNS electrode minus period setting circuit Tns electrode minus period setting signal Tp (steady) electrode plus period Tpi Initial electrode plus period TPS Electrode plus period setting circuit Tps Electrode plus period setting signal WL Reactor

Claims (1)

After starting the arc with the positive polarity of the electrode, energize the predetermined initial electrode positive current during the predetermined initial electrode positive period with the positive electrode polarity, and then switch to the negative polarity with the electrode during the predetermined initial electrode negative period. Arc starting method of AC TIG welding in which a predetermined initial electrode minus current is energized, and then a steady electrode plus current during a steady electrode plus period and a steady electrode minus current during a steady electrode minus period are repeatedly energized In
Immediately after the arc start, in order to form an appropriate initial cleaning region on the surface of the base material, the initial electrode plus current and the initial electrode plus period which are larger than the steady electrode plus current are changed according to the average value of the welding current. And the multiplication value of the initial electrode minus period and the initial electrode minus current is within the range of 0.6 to 1.6 of the multiplication value of the initial electrode plus period and the initial electrode plus current. An arc start method for AC TIG welding that is characterized.

Images