Bojin Qi

Study on Electromagnetic Force in Arc Plasma With UHFP-GTAW of Ti-6Al-4V

Ti-6Al-4V titanium alloy is processed by ultrahigh-frequency pulsed gas tungsten arc welding (UHFP-GTAW), and the correlation between electromagnetic force and pulsed welding efficacy is studied. A mathematical model is formulated to analyze the macroscopic and internal electromagnetic forces. The axial and radial electromagnetic forces inside the arc plasma are evaluated with arc constriction. Meanwhile, the arc profile is also experimentally observed by a camera system to be the experimental evidence for the pinch effect. Owing to arc constriction during the UHFP-GTAW process, the axial component of the macroscopic electromagnetic force decreases, and the arc area diminishes, reducing the root radius. Therefore, larger axial pressure is found. The radial electromagnetic force inside the arc plasma is the most important factor for arc constriction. In addition, the reduced root radius makes the radial electromagnetic force to get reduced with increased pulsed frequency. The attenuation coefficient of magnetic force could be a key parameter for evaluating strength of the arc constriction. With decreased root radius with the UHFP-GTAW, the axial electromagnetic force inside the arc plasma can be maintained at a high level, which affects surface and mobility of the molten pool. The electromagnetic force is observed to have a close correlation with the root radius of the arc, which depends on the pulsed frequency.

The Effect of Hybrid Ultrasonic Pulse Current Parameters on VPTIG Arc Pressure and Weld Formation

Based on a novel arc welding device which can provide hybrid ultrasonic pulse current, the effect of hybrid pulsed current parameters on the arc pressure and weld formation during the aluminum alloy welding process was investigated. The experiment results show that, compared with normal VPTIG process, hybrid ultrasonic pulse VPTIG process gets greater arc pressure. Under the condition of keeping the RMS of positive current unchanged, lowering duty ratio has an evident effect on increasing arc pressure. At proper frequency range, increasing the pulse frequency and decreasing the pulse duty ratio can increase the depth and width of the weld, improve weld penetration rate correspondingly, and be beneficial to improve weld quality.

Study on Fast-Convert Ultrasonic Frequency Pulse TIG Welding Arc Characteristic

Based on ultrasonic frequency pulse tungsten inert-gas (TIG) welding for 0Cr18Ni9Ti austenitic stainless steel, the influence of pulse level parameters was investigated on the field of arc characteristic and arc force. The experimental results show that the pulse level parameters could have huge impact to arc characteristic and arc force. With the increased frequency of pulse level, arc plasma has a more obvious pinch effect, which causes the enhance of arc voltage. Similarly, the arc force can be improved obviously compared with that during conventional direct current (DC) TIG welding. By contrast, the sensitivity of welding characteristic to pulse current level frequency would reduce while the duty of pulse peak current increased.

Arc force and shapes with high-frequency pulsed-arc welding

ABSTRACT Arc plasma is the source of heat and force for molten pool with dynamics fluid and convections. The arc force is studied with shape surveillance and force measurement during pulsed welding process. The results indicated that the average force increased by 42–57%. And the pressures were 322 Pa (conventional welding), 409 Pa and 517 Pa (pulsed welding). Imaging process is carried out for energy distribution analysis. The core region ratio increased up to 51%, compared with 43.7% by conventional welding. The arc pressure derivation was produced and the error was discussed. The increased arc force happens with arc constriction during pulsed welding. It is supposed to create surface depression of molten pool, enhance the fluidity and improve the heat convections.

ANALYSIS AND COMPARISON OF ALUMINUM ALLOY WELDED JOINTS BETWEEN METAL INERT GAS WELDING AND TUNGSTEN INERT GAS WELDING

Surface contamination usually occurs during welding processing and it affects the welds quality largely. However, the formation of such contaminants has seldom been studied. Effort was made to study the contaminants caused by metal inert gas (MIG) welding and tungsten inert gas (TIG) welding processes of aluminum alloy, respectively. SEM, FTIR and XPS analysis was carried out to investigate the microstructure as well as surface chemistry. These contaminants were found to be mainly consisting of Al2O3, MgO, carbide and chromium complexes. The difference of contaminants between MIG and TIG welds was further examined. In addition, method to minimize these contaminants was proposed.

The effect of pulsed frequency on the plasma jet force with ultra high-frequency pulsed arc welding

Plasma jet force is considered to be the key component of the arc force during arc welding. This is known to be the important factor for surface penetration into the molten pool. With pulsed welding technology, the arc plasma constricts significantly which affects the plasma jet force. The experimental results in this work indicate that the arc force increases with increasing pulse frequency. The plasma jet force is found to be the most important contributor to a larger arc force during ultra high-frequency pulsed gas tungsten arc welding (UHFP-GTAW). In this work, the reason for the increasing force is studied with support from a mathematical model. The plasma jet force was recognized to change with the distribution coefficient a at various pulse frequencies. With increasing frequency, the value of the distribution coefficient decreases. As known, the distribution coefficient represents attenuation of the curve. The results suggest that with a high pulse frequency, a high level of plasma jet force occurs in a constricted arc plasma and significant attenuation of the plasma jet force can be found. In contrast, the plasma jet force was low with little attenuation during conventional gas tungsten arc welding (C-GTAW).