Analysis Of Torque In 6061-T6 Aluminum BTFSW

Bobbin tool friction stir welding is a new welding technology developed in recent years.It has been widely used in many fields such as aerospace, defense industry and so on. In this paper, 7.8mm thick 6061-T6 aluminum was tested by different options by bobbin tool friction stir welding. Propose an algorithm which can be used to detect the gap, combined with torque analysis by process parameters such as forward resistance, temperature and comparison of torque characteristics. Four kinds of combination by concave and convex shoulder were tested for welding and the weld appearance and mechanical properties were researched after welding. Change in torque and the impact of torque on welding were researched emphatically.One kind of snap-in type friction stir head was designed independently. The distance between the two shoulders can be changed by the upper key and the lower key of different length. The head can adapt to different thickness and has good vibration resistance. The head can effectively prevent the distance change between the shoulders by bolt. We designed the new tooling to change sliding friction into rolling friction. This can make the measured forward resistance more accurate.BTFSW experiment was conducted in two conditions as with gap and non-gap. the characteristic parameters of torque was analyzed. Low frequency torque at steady state became smaller as the speed rose and became larger as the welding speed increased. Torque signal had oscillation characteristics throughout the welding process. And oscillation period became larger as the speed decreased. The gap would make overall trend of the torque original waveform reduce. Low frequency torque will be significant decline at the gap position. Periodic oscillation torque signal could cause torque signal shock substantially.Oscillations of torque signal at the gap position were more substantial than torque signal at non-gap position. When the welding speed was lower than 200 mm/min, the wavelet transform algorithm was able to detect the gap which was wider than 0.3mm reliably.The combination C and D formed the best weld between the different combinations of the shoulders. The tensile strength of the joint of combination C was the best and accounted about 74.4% of the base material. The raised shoulder made plastic metal flow into the weldcenter more favorably. Hardness distribution of weld nugget zone was quite uniform. The hardness of the concave shoulder was lower than the raised shoulder. Size of the grains of the concave shoulder was close to the raised shoulder. However, at both sides of the heat affected zone, hardness of the concave shoulder was larger than the raised shoulder and size of the grains of the concave shoulder were smaller than the raised shoulder. Torque of the double concave shoulders was the maximum between the four combinations and it was independent of the rotational speed. The raised shoulder was more likely to cause torque oscillations when the rotational speed was nearby. When the shoulders were selected inappropriately, the torque would be larger and the production of heat would increase. Also it would cause blocking, fin and make the weld thinner. When torque oscillated abnormally,it would cause fatigue fracture of stirring needle and be a direct result of welding failure.When the shoulders were selected appropriately, torque would be relatively stable and the heat was suitable for welding. Also there would not be cases such as weld metal blocking.And the weld surface was smooth and clear after the experiment.