CN1264638C - Method and equipment of improving GMAW arc strike process - Google Patents

Abstract

The invention discloses a method and equipment for controlling the arc striking process of gas metal shielded welding—the method and equipment for improving the arc striking process of metal gas shielded welding. The method is as follows: (1) starting the welding equipment (11); (2) striking the arc (12); (3) detecting the output current (13); (4) judging that the output current i is at two given current values i ₁ and i Which section between ₂ (14); (5) If i<i ₁ , perform current negative feedback control; if i ₁ <i<i ₂ , keep the constant voltage source working mode (16); if i>i ₂ , for current negative feedback control. After adopting this control method, the melting speed of the welding wire is also stable due to the stable welding current after the GMAW starts the arc, so there will be no welding spatter. The device consists of a controllable voltage source (6), load (7), current/voltage converter (8) and current negative feedback control circuit (5), (7) and (8) are connected in series to the two outputs of (6) Between the terminals, the output terminal of (8) connects the input terminal of (5), and the output terminal of (5) is connected on the control terminal of (6). It has the advantages of novel design, reliable operation and great popularization value.

Description

Method and Equipment for Improving the Arc Striking Process of Metal Gas Shielded Welding

technical field

The invention relates to a method for controlling the arc striking process of metal gas shielded welding, and also relates to equipment applying the method.

Background technique

Due to the advantages of low cost, high efficiency, and easy automation, GMAW (gas metal arc welding) has become the most widely used joining process in metal processing and manufacturing. There are also some problems in the application of GMAW, welding spatter is one of them. Because welding spatter may cause the following serious problems: 1. For some processed parts on the workpiece to be welded, such as: with threaded holes or other similar matching holes, welding spatter may damage the quality of the thread or matching holes and even cause the entire workpiece to be scrapped ;2. The spatter attached to the nozzle of the welding torch and the contact tip will affect the normal feeding of the shielding airflow and the welding wire, so it has to be shut down frequently for cleaning or replacement, which is a great loss to the efficiency of high-efficiency automatic welding; 3 . For the welding positioning fixture used in mass production, when the workpiece is replaced, some welding spatter will have the opportunity to scatter on the welding positioning fixture, thereby affecting the positioning accuracy of the fixture. For robots or other automated welding systems, it will cause batches of workpieces due to welding The seam position deviation is too large and it is scrapped. Therefore, reducing welding spatter has always been a concern in the application of GMAW, especially in the manufacture of automobile bodies and parts. It is well known that the welding spatter of jet transfer mode GMAW is close to zero, so it is widely used in the welding process that requires high quality. However, in the welding application of automobile body machine parts, a confusing and perplexing problem is: even with jet transfer, the actual amount of welding spatter is still relatively large. The study found that the welding spatter of GMAW in jet transition mode mainly occurs at the initial stage of arc ignition. Because the GMAW welding machine currently used in industry, although the stable droplet transfer form can be set as jet transfer through welding parameter settings, it still takes a certain transition time from welding arc ignition to stable jet transfer, ranging from several hundred Milliseconds, up to a few seconds. For long applications where the welding time of the weld is long, the instability time of hundreds of milliseconds or even seconds is negligible relative to the total welding time. However, for the welding of automobile bodies and parts, generally the welds are very short and the number of welds is large. For GMAW automobile body welding applications, the welding time of a large number of short welds is generally within 5 seconds, so the arc ignition process accounts for a large proportion of the entire welding process, and its impact on the entire welding process becomes particularly prominent. Therefore, it is of great significance to study the influence of arc ignition process on welding spatter and improve the arc ignition process of GMAW to reduce welding spatter to improve the manufacturing level of automobile body. According to the basic principle of GMAW, the welding current should be smooth and stable during the jet transition, while the current waveform is a very unstable short-circuit transition form at the beginning of the arc ignition, which shows that the welding current between the start of the GMAW arc ignition and the stable jet transition It takes a certain amount of time, which is called welding arc ignition instability time. In the initial stage of arc ignition, there is a mixture of irregular short-circuit transition and particle transition, so a high welding spatter rate must be generated at this stage. The necessary condition for a stable jet transition is that the wire feeding speed is balanced with the melting speed of the welding wire, and the melting speed of the welding wire depends on the welding current. The root cause of the inability to achieve a stable jet transition at the initial stage of GMAW arc ignition is that the welding current is unstable . Due to the characteristics of GMAW welding, in order to keep the arc length constant, it is required to use a constant voltage power supply to obtain the self-regulation function of the arc, and the resulting problem is that the current of the constant voltage power supply at the initial stage of arc ignition is uncontrollable and unstable. The problem is reflected in two aspects, one is the initial stage of short-circuit arc ignition, the short-circuit current is too large, and the wire feeding speed is low, the welding wire is easy to melt in segments due to overheating; The arc current is low and cannot reach the critical current value of the jet transition.

Contents of the invention

In order to overcome the defect that GMAW has large welding spatter during the initial welding period of arc ignition, a method and equipment for GMAW arc ignition process that can reduce the amount of welding spatter in the arc ignition stage are provided. The technical scheme of the present invention is as follows: a method for improving the arc striking process of gas metal shielded welding, which is realized through the following steps: (1) starting the welding equipment 11; (2) striking the arc 12; (3) detecting the output current 13 (4) judge which interval section 14 the output current i is between two given current values i ₁ and i ₂ ; (5) if i<i ₁ , then carry out negative feedback control to the output current of the welding equipment, and adjust The output voltage of the welding equipment, so that the output current remains constant, and the welding equipment works in the constant current source mode 15; if i ₁ <i<i ₂ , the welding equipment maintains the constant voltage source mode 16 under the original given voltage value ; If i>i ₂ , negative feedback control is performed on the output current of the welding equipment, and the output voltage of the welding equipment is adjusted to keep the output current constant, and the welding equipment works in the constant current source working mode 17 . After adopting this control method, since the welding current is stable after GMAW strikes the arc, the melting speed of the welding wire is also stable, which can quickly reach a balance with the wire feeding speed of the welding wire, so welding spatter will not occur, and when GMAW reaches the jet transition point After the stable working period, the working mode of constant voltage source ensures the constant arc length, which can provide suitable short-circuit current and stable welding current at the initial stage of arc ignition.

The present invention also provides equipment applying the above method: a device for improving the arc striking process of gas metal shielded welding, which is controlled by a controllable voltage source 6, a load (welding arc) 7, a current/voltage converter 8 and negative feedback The circuit 5 is composed of a load 7 and a current/voltage converter 8 connected in series between the two output terminals of the controllable voltage source 6, the output terminal of the current/voltage converter 8 is connected to the input terminal of the negative feedback control circuit 5, and the negative feedback control circuit The output terminal of 5 is connected to the control terminal of the controllable voltage source 6 . When the equipment is working, the current/voltage converter 8 collects the signal of the output current, and converts the signal into a voltage signal input negative feedback control circuit 5 for comparison, amplification and feedback, thereby outputting the control corresponding to the method of the present invention signal to control the working mode of the controllable voltage source 6, so as to improve the spattering condition of the GMAW during the arc striking period. The invention has the advantages of novel design, reliable operation and great popularization value.

Description of drawings

Fig. 1 is a flow chart of the steps of the method of the present invention, Fig. 2 is a schematic structural view of the device of the present invention, Fig. 3 is a schematic structural view of the third embodiment, Fig. 4 is an output characteristic diagram of the device of the present invention, and Fig. 5 is a structure of the fourth embodiment Schematic diagram, FIG. 6 is a schematic structural diagram of Embodiment 5.

Detailed ways

Specific Embodiment 1: The present embodiment will be specifically described below with reference to FIG. 1 . It is realized through the following steps: (1) starting the welding equipment 11; (2) striking the arc 12; (3) detecting the output current 13; (4) judging that the output current i is between two given current values i ₁ and i ₂ (5) If i<i ₁ , carry out negative feedback control on the output current of the welding equipment, adjust the output voltage of the welding equipment, so that the output current remains constant, and the welding equipment works in a constant current source Mode 15; if i ₁ <i<i ₂ , the welding equipment maintains the constant voltage source working mode at the original given voltage value 16; if i>i ₂ , negative feedback control is performed on the output current of the welding equipment to adjust the welding The output voltage of the equipment, so that the output current remains constant, and the welding equipment works in the constant current source mode 17.

Specific Embodiment 2: The present embodiment will be specifically described below with reference to FIG. 2 . This embodiment is composed of a controllable voltage source 6, a load 7, a current/voltage converter 8 and a negative feedback control circuit 5, the load 7 and the current/voltage converter 8 are connected in series between the two output terminals of the controllable voltage source 6, The output terminal of the current/voltage converter 8 is connected to the input terminal of the negative feedback control circuit 5 , and the output terminal of the negative feedback control circuit 5 is connected to the control terminal of the controllable voltage source 6 .

Specific Embodiment Three: The present embodiment will be specifically described below in conjunction with Fig. 3 and Fig. 4. The difference between this embodiment and Embodiment 2 is that the negative feedback control circuit 5 is composed of a nonlinear current feedback amplifier 5-1 and a subtractor 5-2. , the first level signal U1, the second level signal U2 and the third level signal U3, the level of the third level signal U3 is higher than the level of the second level signal U2, the nonlinear current feedback amplifier 5 One input terminal of -1 is connected to the output terminal of the current/voltage converter 8, and the other two input terminals of the nonlinear current feedback amplifier 5-1 are respectively connected to the output terminals of the third level signal U3 and the second level signal U2, The output terminal of the nonlinear current feedback amplifier 5-1 is connected to the subtracting terminal of the subtractor 5-2, the output terminal of the first power supply P1 is connected to the adding terminal of the subtractor 5-2, and the output terminal of the subtractor 5-2 is connected to the The control terminal of the control voltage source 6. Refer to Fig. 4 for the working principle of this embodiment, the core of Fig. 3 is the nonlinear current feedback amplifier 5-1, the output of the amplifier is composed of the output of the current/voltage converter 8, the second power supply P2 and the third power supply for current setting The power supply P3 is jointly determined, and the amplification factors are different in different stages, so it is called a nonlinear amplifier. The output voltage of the controllable voltage source 6 is determined by the sum of the set value of the first power supply P1 used for voltage setting and the output value of the nonlinear current feedback amplifier 5-1. The second level signal U2 and the third level signal U3 respectively correspond to two given current values i ₁ and i ₂ , that is, the current values corresponding to points B and C in FIG. 4 . When the current value detected by the current/voltage converter 8 is greater than the current setting i ₁ and smaller than the current setting i ₂ : the output of the nonlinear current feedback amplifier 5 - 1 is zero, that is, the amplification factor is zero. At this time, the output of the subtractor 5-2 is always equal to the given value of the first level signal U1, the output voltage of the controllable voltage source 6 is also determined by the first level signal U1, and the external characteristic of the power supply is a constant voltage source, as shown in Fig. 4 middle BC segment. When the current value detected by the current/voltage converter 8 is less than the current setting _i1 : the output of the nonlinear current feedback amplifier 5-1 is negative, and at this time the output of the subtractor 5-2 is equal to the first level signal U1 The sum of the given value and the output of the nonlinear current feedback amplifier 5-1, at this time, the reduction of the output current increases the input of the controllable voltage source through the effect of negative feedback, so the output voltage also increases, and the output current is kept constant, that is Form the constant current characteristics of the AB section. When the current value detected by the current/voltage converter 8 is greater than the current setting _i2 : the output of the nonlinear current feedback amplifier 5-1 is positive, and at this moment the output of the subtractor 5-2 is equal to the first level signal U1 The difference between the given value and the output of the nonlinear current feedback amplifier 5-1, at this time, the reduction of the output current reduces the input of the controllable voltage source through the effect of negative feedback, so the output voltage also decreases, and the output current is kept constant, that is The constant current characteristics of the CD segment are formed. In this embodiment, the controllable voltage source 6 is an inverter power supply, and the output voltage can be effectively controlled by changing the conduction time of the active elements (IGBT or MOSFET) in the inverter power supply.

Specific Embodiment 4: The present embodiment will be specifically described below with reference to FIG. 5 . The difference between this embodiment and the third embodiment is that the subtractor 5-2 is the third integrated operational amplifier A3, and the nonlinear current feedback amplifier 5-1 is composed of the first integrated operational amplifier A1, the second integrated operational amplifier A2, the first Composed of diode D1 and second diode D2, the output end of the current/voltage converter 8 is connected to the non-inverting input end of the first integrated operational amplifier A1 and the second integrated operational amplifier A2, the second level signal U2 and the third The output terminals of the level signal U3 are respectively connected to the inverting input terminals of the first integrated operational amplifier A1 and the second integrated operational amplifier A2, the output terminal of the first integrated operational amplifier A1 is connected to the cathode of the first diode D1, and the second integrated operational amplifier A1 is connected to the negative pole of the first diode D1. The output terminal of the operational amplifier A2 is connected to the anode of the second diode D2, the cathode of the second diode D2 is connected to the positive pole of the first diode D1 and the inverting input terminal of the third integrated operational amplifier A3, and the third integrated operational amplifier The non-inverting input terminal of the amplifier A3 is connected to the output terminal of the first power supply P1, and the output terminal of the third integrated operational amplifier A3 is connected to the control terminal of the controllable voltage source 6 . In the figure: A1, A2 and A3 are differential amplifiers. The current feedback signal Uif is added to the noninverting input terminals of A1 and A2 at the same time. When U ₂ < U _if < U ₃ , the output of A1 is positive, and the output of A2 is negative. At this time, both diodes D1 and D2 are cut off, so the output voltage = 0, and the control voltage of the controllable voltage source 6 has nothing to do with the current and is constant voltage characteristics; when U _if < U ₂ , the outputs of A1 and A2 are both negative, at this time diode D1 is turned on and D2 is cut off, the control voltage of the controllable voltage source 6 rises with the drop of U _if , forming a current negative feedback, and obtaining Constant current characteristics; when U _if > U ₃ , the outputs of A1 and A2 are both positive, at this time diode D1 is cut off and D2 is turned on, and the control voltage of the controllable voltage source 6 decreases with the rise of U _if , which also constitutes a current negative feedback , to obtain constant current characteristics. In order to obtain good constant current characteristics, the above-mentioned current negative feedback link must have a suitable gain. When the conversion coefficient of the current/voltage converter 8 is 1V/100A, and the amplification factor of the controllable voltage source 6 is 10, A1 and A2 When the magnification factor K1=K2=100 and the magnification factor K3=1 of A3, good constant current characteristics can be obtained.

Embodiment 5: This embodiment will be specifically described below in conjunction with FIG. 6 . The difference between this embodiment and embodiment two is that the negative feedback control circuit 5 is made up of a D/A conversion circuit 5-4, a microprocessor (single-chip microcomputer or DSP) 5-5 and an A/D conversion circuit 5-6, A The input end of the /D conversion circuit 5-6 connects the output end of the current/voltage converter 8, and the output end of the A/D conversion circuit 5-6 connects the input end of the microprocessor (single-chip microcomputer or DSP) 5-5, and the microprocessor The output end of the device (single-chip microcomputer or DSP) 5-5 is connected to the input end of the D/A conversion circuit 5-4, and the output end of the D/A conversion circuit 5-4 is connected to the control end of the controllable voltage source 6. In this embodiment, the negative feedback control of the output current of the welding equipment and the logic judgment of constant voltage source and constant current switching are completed through the computer program running in the microprocessor (single chip microcomputer or DSP), so as to realize the purpose of the present invention.

Claims (5)

1. A method for improving the arc striking process of gas metal shielded welding, characterized in that it is realized through the following steps: (1) starting the welding equipment (11); (2) striking the arc (12); (3) detecting the output Current (13); (four) judge which interval section (14) the output current i is between two given current values i ₁ and i ₂ ; (five) if i<i ₁ , the output current of the welding equipment Perform negative feedback control to adjust the output voltage of the welding equipment so that the output current remains constant, and the welding equipment works in the constant current source mode (15); if i ₁ <i<i ₂ , the welding equipment operates at the original given voltage value Keep the constant voltage source working mode (16); if i>i ₂ , carry out negative feedback control on the output current of the welding equipment, adjust the output voltage of the welding equipment, so that the output current remains constant, and the welding equipment works in the constant current source Working mode (17). 2. A device for improving the arc striking process of gas metal shielded welding, characterized in that it consists of a controllable voltage source (6), a load (7), a current/voltage converter (8) and a negative feedback control circuit (5) The load (7) and the current/voltage converter (8) are connected in series between the two output terminals of the controllable voltage source (6), and the output terminal of the current/voltage converter (8) is connected to the negative feedback control circuit (5). The input terminal of the negative feedback control circuit (5) is connected to the control terminal of the controllable voltage source (6). 3. A device for improving the arc-starting process of gas metal shielded welding according to claim 2, characterized in that the negative feedback control circuit (5) consists of a nonlinear current feedback amplifier (5-1), a subtractor (5- 2), the first level signal (U1), the second level signal (U2) and the third level signal (U3), the level of the third level signal (U3) is higher than the second level signal ( U2), an input terminal of the nonlinear current feedback amplifier (5-1) is connected to the output terminal of the current/voltage converter (8), and the other two input terminals of the nonlinear current feedback amplifier (5-1) are respectively Connect the output terminals of the third level signal (U3) and the second level signal (U2), the output terminal of the nonlinear current feedback amplifier (5-1) is connected with the subtraction terminal of the subtractor (5-2), and the first The output terminal of the level signal (U1) is connected with the addition terminal of the subtractor (5-2), and the output terminal of the subtractor (5-2) is connected with the control terminal of the controllable voltage source (6). 4. A device for improving the arc striking process of MIGMA welding according to claim 3, characterized in that the subtractor (5-2) is the third integrated operational amplifier (A3), and the nonlinear current feedback amplifier (5 -1) Composed of a first integrated operational amplifier (A1), a second integrated operational amplifier (A2), a first diode (D1) and a second diode (D2), the current/voltage converter (8) The output terminal is connected to the non-inverting input terminals of the first integrated operational amplifier (A1) and the second integrated operational amplifier (A2), and the second power supply (P2) and the third power supply (P3) are respectively connected to the first integrated operational amplifier (A1) and the second integrated operational amplifier (A1). The inverting input terminal of the second integrated operational amplifier (A2), the output terminal of the first integrated operational amplifier (A1) is connected to the cathode of the first diode (D1), and the output terminal of the second integrated operational amplifier (A2) is connected to the second The positive pole of the diode (D2), the negative pole of the second diode (D2) connects the positive pole of the first diode (D1) and the inverting input terminal of the third integrated operational amplifier (A3), and the third integrated operational amplifier The noninverting input terminal of (A3) is connected with the output terminal of the first power supply (P1), and the output terminal of the third integrated operational amplifier (A3) is connected with the control terminal of the controllable voltage source (6). 5. A device for improving the arc striking process of MIGMA welding according to claim 2, characterized in that the negative feedback control circuit (5) consists of a D/A conversion circuit (5-4), a microprocessor (5 -5) and the A/D conversion circuit (5-6), the input end of the A/D conversion circuit (5-6) is connected to the output end of the current/voltage converter (8), and the A/D conversion circuit (5- 6) the output end of the microprocessor (5-5) is connected to the input end of the microprocessor (5-5), the output end of the microprocessor (5-5) is connected to the input end of the D/A conversion circuit (5-4), and the D/A conversion circuit ( 5-4) the output terminal is connected with the control terminal of the controllable voltage source (6).

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