Abstract: The principle and characteristics of AC/DC arc welding power supply are expounded. The research status of inverter technology, digital control technology and intelligent control technology of AC/DC arc welding power source is introduced in detail, and AC/DC arc welding is pointed out. The trend of power supply along the trend of high-performance digitalization and intelligence.

Key words : AC and DC; arc welding power source; digital; intelligent

CLC number : TG434 Document code: A

Aluminum and its alloys are usually welded by power frequency AC sinusoidal tungsten argon arc welding, but the arc stability of this welding power source is poor, and the positive and negative can not be used for alkaline electrode arc welding. In particular, it is difficult to obtain satisfactory weld quality for some of the more demanding welding work, such as aluminum thin-piece low-current welding, single-sided welding double-sided forming, and high-strength welding. With the development of high-power semiconductor components and power technology, AC/DC arc welding technology has been successfully applied in China in recent years, and the corresponding arc welding power source has been developed and produced [1].

AC/DC arc welding is an ideal arc welding method for thin-plate aluminum alloy, which can control the penetration depth of the weld and improve the welding efficiency. The AC/DC argon arc welding function is most suitable for the welding of aluminum and aluminum alloy, magnesium and magnesium alloy. It has atomization adjustment function, which can effectively break the oxide film on the surface of the workpiece; the weld bead is formed well and the surface is bright and beautiful [2] 3].

In recent years, non-metals such as aluminum alloys have been widely used in aerospace, automotive and civil industries due to their low temperature characteristics, light weight and high specific strength, and have become an important processing material [4]. With the development of science and technology, the application of thin-plate aluminum alloy in the industry is more and more extensive, and the welding quantity is also constantly expanding. Increasing welding productivity, ensuring product quality, automating and intelligentizing welding production are getting more and more attention from welding manufacturers, especially in robot welding where welding quality and precision are relatively high. Coupled with the integration of modern artificial intelligence technology, digital information processing technology, computer vision technology and other high-tech, it also promotes the development of high-speed welding and high-efficiency welding, digitization of welding control and intelligent control system.

1 AC and DC arc welding principle and characteristics

The main feature of AC and DC arc welding is that the time of current zero crossing is extremely short. The ratio of positive and negative half-wave energization time to current can be adjusted freely by electronic control technology. Therefore, it is used for the welding of aluminum and its alloys. It has the following characteristics in the welding process: the power supply is stable, and it is easy to re-ignite the arc when the current crosses zero. It is not necessary to add a stable arc high-voltage pulse or high-frequency electricity, and the influence of interference is small. And can adjust the ratio of positive and negative half-wave energization time to obtain the best penetration depth and cathode atomization, improve the life of the tungsten electrode; adjust the heat input on the workpiece, more effectively use the arc heat and arc force to meet a certain The special needs of these arc welding processes do not require the use of devices that eliminate the DC component.

Inverter AC/DC arc welding power source mainly consists of common DC arc welding power source and inverter main circuit. The inverter converts DC into AC, frequency is adjustable, positive and negative half-wave energization time ratio, positive and negative half-wave The current ratio can also be adjusted freely within a certain range. The principle is shown in Figure 1.

It can be seen from Fig. 1 that when S1 and S3 are triggered to turn on, and S2 and S4 are turned off, the DC power supply circuit is: +→S1→Arc→S3, so that a positive half-wave current is obtained in the arc, DC and the wire is positive. Yes, the arc is stable, and the depth of the stove is deep. It is easy to achieve wire melting and droplet transfer by effectively controlling the current. When S2, S4 are turned on, S1, S3 are turned off, the energizing circuit is -→S2→Arc S4, so that when the arc obtains a negative half-wave current, DC and the wire is negative, the arc climbs along the wire, and the arc does not Stable, the droplets are not easy to transition, the weld pool is shallow, and the arc climbs along the wire to promote the melting of the wire and reduce the heating effect of the arc on the molten pool to form a shallow melt depth. It can be seen that as long as the two sets of electronic components are controlled to turn on in turn, the direction of the arc current is switched, and by controlling the relative proportions of the length of the on-time of the two sets of power components and the energization time, the frequency and the positive and negative half-wave energization can be obtained. Proportional adjustable AC and DC. In the welding process, according to the size requirements of the weldment, the appropriate welding current frequency and the ratio of positive and negative half-wave energization time can be selected to control the quality of the weld, especially when welding the thin plate, to ensure that it does not appear. The molten pool forms a failure phenomenon and meets the requirements of welding quality.

2 DC arc welding inverter technology

The improvement and development of power electronic devices provide the most basic material basis for the rapid development of inverter technology. The emergence of a new superior power electronic device will inevitably lead to the development of inverter technology, which will inevitably lead to advanced Application and development of inverter technology in AC and DC arc welding power supply.

Since the successful production of thyristors in China in 1962, the variable-injection technology and inverter technology based on common thyristors and silicon rectifiers have been greatly developed, and the quality of devices has been greatly improved. Derivative thyristors are fast, two-way, The shutdown and inverter guiding devices have developed rapidly, and the output of the products has increased significantly. In the past 10 years, after careful design, plus research on process, testing, reliability and equipment, the device capacity has been greatly increased, and the static and dynamic characteristics have improved in the afternoon. China has designed and developed 1000A, 1200V, 30μs fast thyristors; 100A, 600V or more power switching transistors; 40, 60A, 1000V or more fast diodes. In addition, 50,100A high-power field-effect transistors and IGBTs began trial production in the early 1990s. At the same time, inverter technology and products have been widely used in frequency conversion speed regulation, regulated power supply, non-tip, electroplating power supply, electric resistance welding, arc welding power supply, electron beam power supply, medium and high frequency heating and heat treatment, and electrochemistry. Dozens of series and hundreds of specifications of this type of product. These include thyristor inverters with a unit capacity of 250,350kVA; uninterruptible power supply units with a single unit capacity of 1000kVA or more; IGBT type resistance welding inverters with 250kVA; IGBT type arc welding inverters with 33kVA; field effects of 15,30kVA Transistor type arc welding inverters, etc. [5].

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