| Aero tube is one of the most important components in the aircraft. At present, the manual TIG(Tungsten Inert Gas) welding mode is widely used in the manufacturing process for welding tube at home, the welding work is intensive, the welding quality is not stable, which can’t be able to satisfy the demand of CAD/CAM digital manufacturing. Considering the backward mode of production, the purpose of this paper is to establish a digital assembly and welding test system of aero tube, the key technologies included in the system, such as the assembly deviation compensation between the aero tube and the flange, the thermal deformation error compensation in the welding process are studied.Firstly, in view of the inconsistent shape and the thin wall of the aero tube, a general flexible digital assembly and welding test system, which can adapt to the different space shape of aero tube, is established. The main features include: a) the flexible positioning and installation of aero tube; b) the automatic assembly deviation compensation of aero tube and flange; c) the real-time compensation of the welding thermal deformation error.Using an assisted three dimensional measuring machine, a closed coordinate system chain, including the sensor coordinate system, three-dimensional coordinate system, the base coordinate system of robot, the tool coordinate system, is established to calibrate the hand-eye relationship. Four-point calibration method is used to calibrate the relative position relationship between the base coordinate system of welding robot and assembly robot, which realizes the unification of the coordinate frame in the system.The definition of digital welding is expounded from two aspects of generalized and narrow sense respectively. The motion path of the welding and assembly robot is planned by the off-line programming system, which is used to execute the preliminary assembly and welding task in the system. The causes of the robotic off-line programming path deviation are analyzed.The character and law of the variation stream of tube size are analyzed in the multi-stage manufacturing process of aero tube. For the particularity of variation stream in the multi-stage manufacturing process of aero tube, using the accurate location of aero tube and flange to build the inversion model of size deviation, through adjusting the assembly deviation size of the flange relative to the tube, the deviation compensation idea that a variety of deviation is compensated using a deviation is proposed.The strategy by measuring the relative position deviation of the aero tube and flange to compensate the assembly deviation is proposed. When the flange rotates around its own coordinate system located in the end face, the angle between the axis of tube and flange decreases first and then increases. Using the symmetrical change of the angle in the rotation process, the axis of the aero tube and flange is parallel through two rotations within the tolerance limits of ±0.5°.The strategy by measuring the relative position relationship between the laser stripe and aero tube to compensate the assembly deviation is proposed. When the stripe of structured light intersects with the cylinder, with the increase of the angle between the cylindrical bus-bar and the laser plane, the projection of the laser plane on the cylinder gradually tends to be a circular arc. Using this character adequately, the laser plane can be exactly adjusted to the posture where it is perpendicular to the axis of aero tube firstly, then, the flange can be adjusted to the posture where it is perpendicular to the laser plane, at last, the adjustment of the assembly posture deviation between the aero tube and flange is completed within the tolerance limits of ±0.5°~ ±1.5°. When parallel translation of the laser plane relative to the cylinder, the distance between the laser sensor and the cylinder decreases first and then increases, the minimum value happens to be at the diameter of the cylinder, and to be symmetric on both sides of the diameter. Using the symmetric law, the position deviation between the aero tube and flange has perfectly been corrected within the tolerance limits of ±0.20 mm.The transformation of model data in the digital manufacturing system of aero tube has been realized by the position relationship between the robots in the system, which reduces the follow-up planning path deviation of the welding robot. A novel off-line automatic compensation algorithm based on a visual sensor resulting from the bend forming size deviation of aero tube is proposed. When the welding torch moves along the planning path of horizontal seam for a circle, using the lateral and vertical distances between the welding torch and welding seam in the end of tube acquired by the laser vision sensor, the off-line automatic compensation for the bend forming size deviation of aero tube is completed. After the compensation, the range of lateral deviation is ±0.60 mm between the welding torch and the seam, while, the range of vertical deviation is ±0.64 mm.Finally, the welding thermal deformation of aero tube is simulated using the numerical simulation software Marc, the welding path deviation caused by the thermal deformation is loaded into the off-line planning path. Based on the analysis of the look-ahead problem of the structured-light,the“teaching and playing”robot is developed to the intelligent welding robot system with the ability of tracking the position and posture of the welding torch in real time. The relationship model between the deviation about the torch and the centerline of seam collected by the laser vision sensor and the adjustment quantity of the torch is deduced. The welding look-ahead time of the small diameter tube is determined. Drawing lessons from the tracking reference point character of the lap seam, the lateral feature recognition of the thin-walled tube seam is completed. The tracking results show that the range of the lateral deviation and the height deviation is ±0.20 mm between the welding torch and the seam, which satisfies the requirement of the digital welding of aero tube. |
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