In automatic butt welding of relatively thin plates, it is important to control welding conditions in order to obtain a sound full penetration weld. Recently, it was reported that there was an intimate relationship between the oscillation of the molten pool and penetration. Therefore, the oscillation phenomena of the weld molten pool were analyzed and the estimation of penetration by detecting frequency of the molten pool was attempted. In this study, a new oscillating method, Pulsed Assist Gas (PAG) oscillating method is proposed. The natural frequency of molten pool was measured from the molten pool oscillation detected by arc sensor. A control system, which controled welding current on the basis of oscillation frequency measured, was constructed. Main results obtained are summarized as follows: 1) In order to oscillate molten pool during TIG arc welding of thin steel plate, Pulsed Assist Gas (PAG) oscillating method was proposed and effectiveness of this method was confirmed. 2) The PAG oscillating method was superior to conventional pulsed current oscillating (PC) method in amplitude of oscillation and robustness of frequency measurement. 3) Applying PAG oscillating method and detecting oscillation of arc voltage, the peculiar frequency of the oscillation of molten pool could be detected. 4) A system to control weld penetration using the principle of detecting the peculiar frequency of the molten pool was constructed and the effectiveness of the system was demonstrated.
Thermal spray conditions have important effects on the formation mechanism of a coating lamination. When thermal spray distance or power is changed, there is an increasing chance of defect being generated during coating formation. Thermal spray distance was chosen from each of 80, 100, 150 and 200 mm. The cavitation erosion strength of the sprayed coatings under the above conditions was examined. The evaluation of cavitation erosion of Al2O3 coatings was investigated by magnetostrictive cavitation test at a frequency of 20 kHz and at a horn amplitude of 50 μm. Cavitation erosion at the thermal spraying distance case of 200 mm was five times greater than that at the distance of 80 mm. The results of X-ray diffraction showed that α-Al2O3 tended to disappear when thermal spraying distance was the longest case of 200 mm. This is attributed to the temperature decrease of particles. The following factors are considered as the reason of the above phenomena. When the distance between the substrate and spraying nozzle is long, the flight time of particles becomes longer. During that time, the heat capacity of particle decreases, which in turn reduces the expansion rate and cohesion strength. Gas hole was made to be an origin, and it seemed to propagate the fracture damage for defects, voids or cracks, etc.
In order to measure the heat input (quantity of heat) generated during friction welding, a new type calorimeter of acryl resin was developed, and applied to friction welding of a stainless steel. The heat input measured during friction welding was in good agreement with the values calculated from the measured values of friction torque, burn-off length, rotation speed and pressure. Being classified into friction and deformation heat inputs, the friction heat input was much greater than the deformation heat input through the friction and upset stages.
An investigation has been made of the feasibility of friction stir welding of dissimilar lap joint of an aluminum plate to a copper plate, which is difficult to weld by fusion welding methods because of the formation of brittle intermetalic compounds (IMC). The joint strength depended strongly on the depth of the pin tip relative to the copper surface; when the pin did not penetrate to the copper surface the joints showed very weak fracture loads, whereas slight penetration of the pin tip to the copper surface increased the joint strength significantly. Although the level of bond strength was quite low, it exhibited a general tendency to increase with a rise in the rotation speed. Various microstructures with different morphologies and properties were observed in the stirred zone of aluminum and Al/Cu interfacial region. Comparison of the fracture location with the microstructure suggests that IMC formed in the interfacial region was responsible for the low strength of the joints. X-ray diffraction from the fracture surfaces indicated that Al4Cu9, AlCu, and Al2Cu were main intermetallic compounds formed in the interfacial region.