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TIG welding has the following advantages:1) Argon gas can be effectively isolated from ambient air, It does not dissolve in metal, and it does not react with metal; the arc can clear the surface oxide film automatically in TIG. Therefore, we can succeed in welding non-ferrous metals which are easy oxidation、nitridation and have lively chemical properties,stainless steel and various alloys.2) Tungsten arc is stable, even in very small welding current (<10A),The arc can still be stable combustion,which is particularly applicable to weld sheet metal and thin sheet material.3) Heat source and filling wire can be controlled separately, so it is easy to adjust heat input value, and it can weld in any positions.4) Filling wire does not pass current, so it does not produce spatter, the forming weld is beautiful.Due to the above-mentioned advantages,TIG welding can be used in welding almost all metals and alloys, in particular, it is widely used in welding aluminum, magnesium, titanium, copper and other non-ferrous metals and their alloys, as well as stainless steel, heat-resistant steel and so on. Its welding process is very stable, arc admission is relatively easy to control, and welding quality is higher. But it is very difficult to ignite.In TIG, there are two ways to ignite: Contacting Short Circuit Igniting, Non-Contacting High Frequency、High Voltage Igniting and High Voltage Pulse Igniting.Contacting Short Circuit Igniting manner, while having the advantages of simple equipment, low cost, but the tungsten loss is large when Igniting,the top of tungsten is easy to be destroyed,and the tungsten and workpiece are easy to pollute each other, often causing visco-tungsten, tungsten inclusion in the welding seam phenomenon. The impacts of visco-tungsten, tungsten inclusion in the welding seam phenomenon phenomenon to welding quality, production costs and production efficiency are as follows:(1)Because of the arc does not ignite successfully when igniting, Tungsten is bonding in the groove and the welding seam is polluted, formating tungsten inclusion defect and resulting in a decline in the welding quality;(2)The thermal expansion coefficient of tungsten inclusion in weld metal is very different from weld metal,and the shape is irregular, which will produce large internal stress leading to cracks, the harmful effect is no less than the slag defect in the process of electrode arc welding;(3)As a result of these defects, resulting in welding seam pollution need to re-grind, The tungsten need to re-grind and replace. Welding and other work should be re-started. which not only increasing the workload of fitter、welder and extending their work hours,but also increasing the production costs and declining the labor productivity.Even though take the way of Non-Contacting High Frequency、High Voltage Igniting and High Voltage Pulse Igniting manner, the igniting effect is well and the performance is stable, which can prevent thin workpiece burning, tungsten burning and tungsten inclusion in the welding seam phenomenon. but the former is harmful to people’s health,and there is interference on the surrounding environment, not only interfering with radio,television,communications receiver,but also causing Mechani-cal and electrical equipment, electronic devices work disorders, and even damaging; the latter applies to the welding power source, especially the new inverter power source,There are high-voltage breakdown problems. So research and development of new ways of igniting technology to overcome the above disadvantages has great significance.This paper designs a inverter welding power source with the function of Lifting-Igniting base on the original advantages of TIG welding. To improve the burning of tungsten and tungsten inclusion in the welding seam phenomenon.In this paper, I design the overall structure of the welding inverter system, including the main circuit、the Lifting-Igniting control circuit, protection circuit, rectifier filter circuit and so on. Focusing on the use of PWM and PFM combining control methods, and making an in-depth analysis of the principle. The general process of Lifting-Igniting is:When the tungsten is contacting with workpiece , PWM and PFM control mode simultaneously play the role, a small controlled current flow from arc welding circuit, preheat tungsten, but don’t make its melting, so no tungsten melting into the workpiece; subsequently lifting tungsten and leaving workpiece ,only a separate PWM mode play the role, the system adjust quickly to working voltage and current, the welding machine start normal welding job.Through the adoption of specific experiments, Detect the waveform in specified points of circuit, the waveform analysis shows that the inverter welding power source has achieved the desired design requirements; experiments simultaneously measured the external characteristic curve of inverter welding power source at different current profile, the external characteristic curves are constant-current within the Po-type, which is fit for the expected design requirements; through the technology experiments, make comparative analysis on the igniting arc success rate, the degree of tungsten loss and the workpiece surface situation respectively, The experimental results show that the Lifting-Igniting control system has a high igniting arc success rate of 93.3%, the tungsten loss and burning of workpiece surface obviously less than ordinary contact arc. These results show that the TIG Lifting-Igniting welding system has achieved the desired design requirements.Through practical applications, such Lifting-Igniting system has good usability, which is not only able to produce good quality welds、has greatly improved the tungsten loss problem and the work efficiency, but also with simple structure、lightweight installation、easy use and lower cost. TIG Lifting-Igniting method is a simple and reliable, superior performance and effective manner.
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