Research On Decoupling Control Model And Experiment Of Complicated Welding Seam Formation On The Free-form Surfaces

As the spacecraft is getting bigger and faster, the panel type components with aerodynamic shape complicated structure using multi-axial numerical control processing are increasing. With the restriction of space location of the spacecraft's structure, the effective double-side welding can not be operated, so the single-side welding is implemented. Therefore the modern welding is much more challenged for the well weld formation and high efficiency automatic control.As to this problem of aerospace manufacture, the accuracy control method of welding quality on the free-form surfaces is given in this paper. Firstly the relation between the front weld pool information (the front weld width and the pool length) and back pool width is concluded by heat resolution formula of welding. Then the quality of weld formation can be controlled through controlling the front weld pool information.The welding process is a coupling course with multi-factors such as high noise interference, big time lag and dynamic break. The stable control can not be achieved by the single variable control. So the MIMO model with the weld current and weld speed as inputs and the front width and pool length as outputs is confirmed by analysis the welding heat resolution formula. In order to overcome the disadvantage of testing method, the mathematic model is based by resolution method. Through the resolution formula, the function between input variable and output variable is acquired. The transfer function is calculated by fitting this function curve to the step response curve of the first-order system. For the two variable coupling control system, the feed-forward compensator is designed to decouple the coupling relation between the input and output. Then the two variable coupling system is decomposed to two single variable system. The PI control strategy is introduced to eliminate the deviation of the output signal and setting value. The Smith prediction compensator is designed to remove the effect of time lag on the system stable.Through the simulation experiment under the simulink of MATLAB, the couple relation is fully eliminated by the feed-forward compensator, the stable of system is well achieved by the PI controller and the time lag is overcome by the Smith prediction compensator.Take the workpiece with continuous varied thickness as the example of the free-form surfaces. The TIG welding experiment is designed to control the weld current according to the front pool width to acquire the stable back pool width. The experiment results validate the feasibility of achieving the stable back pool width through controlling the front pool width.