Forming Planning And Process Control Of Wire Arc Additive Manufacturing

Wire Arc Additive Manufacturing(WAAM)has attracted wide attention from research institutions due to its advantages of high deposition rate and millimeter resolution.WAAM is widely used in large near-net forming parts because of its high deposition rate and high cost performance,and become an efficient cladding process that can shorten the forming cycle.At the same time,WAAM conforms to the current development concept of green manufacturing,high efficiency,low carbon and low cost.At present,automatic additive manufacturing is mainly based on the welding method like GMAW,CMT and other wire contact forming circuits.There are relatively few studies on automation,GTAW and forming process control.Therefore,this paper takes the closed single-channel multi-layer thin-walled components formed by GTA-AM as the research object,which aims to improve the dimensional stability and forming quality of the deposited layer in the GTA-AM process.Based on the 3D model of the component,the control strategy of starting(extinguishing)arc at different positions was adopted to eliminates the defects of high arc starting end and low arc extinguishing end.At the same time,the visual sensing detection and closed-loop control of the deposited size were studied in depth.The research of this subject enriched the theoretical results of WAAM process control.By observing the single-layer forming morphology under various process parameters,the range of process parameters suitable for single-layer multi-layer forming was obtained.At the same time,the effects of deposition current,deposition speed and wire feeding speed on the forming of single-pass multi-layer structural parts were discussed in depth.The results showed that when the deposition current was lower than 70 A,it was basically not formed.When the deposition current was in the range of70～100A,the deposition current,deposition speed and wire feeding speed had a certain effect on forming.When the deposition current is greater than 100 A,the probability of flow phenomenon increased with the increase of deposition current,while the deposition speed and wire feeding speed have little effect on the forming.It was proved that the deposition current was the key factor to determine whether the single-pass multi-layer thin-walled structure can be formed.In this paper,the mathematical model of cladding layer size-process parameters was established by quadratic regression rotation combination design method.The predicted value of the model was in good agreement with the real value,which could well predict the relationship between the size of the deposited layer and the deposition process parameters in the actual test process.There was a delay in the actual forming process so that it was necessary to reduce the deposition current and wire feeding speed to void the ’collapse’ phenomenon caused by excessive heat accumulation.On the basis of the above research content,this paper analyzed the influence of the fixed wire deposition speed ratio and the variable wire deposition speed ratio on the forming quality.The ratio of wire is constant,when the deposition current increased the roughness of single-pass multi-layer structural parts and the forming quality decreased with other process parameters unchanged and feeding speed to deposition speed fixed.When the ratio of wire feeding speed to deposition speed changes,the deposition current was constant,the roughness of single-channel multilayer structure increased with the increase of deposition speed.Keeping the deposition speed constant,as the deposition current increased,the roughness of the structural parts decreased first and then increased.When the deposition current was 90 A,the roughness of the structural parts was the lowest and the forming quality was the best.A binocular vision sensor was designed.The detection width vision sensor and the detection height vision sensor were combined to detect the deposition size of GTA-AM process,and the obtained deposition layer size image was subjected to high-speed denoising,Sobel operator edge extraction and Hough transform fitting to realize the detection of the deposition layer size,which laid a foundation for the subsequent controller design and model design.The Cartesian space trajectory planning,joint space trajectory planning and ROS trajectory planning simulation were designed.The method of linear interpolation and circular interpolation under Cartesian space trajectory was studied.The unit quaternion is used to interpolate the attitude,which avoided the singularity problem while ensuring smooth transition.The comparative analysis of 3-5-3 mixed interpolation method and3-3-3 mixed interpolation showed the superiority of 3-5-3 mixed interpolation and avoided the flexible impact.The Rviz visualization platform was used to verify the model,Move It is used to test the robot,and a joint simulation platform is established with Gazebo to realize the parameter setting of the robot controller.Finally,the trajectory simulation was carried out in the ROS simulation system to realize the planning and control of the robot,and the effectiveness of the ROS system simulation was verified.Through the step response test of deposition current and deposition speed,the unidirectional input and output dynamic models of deposition layer process parameters and deposition size were established,and the characteristics of step response of deposition current and deposition speed were analyzed.It was found that the forming process had the characteristics of nonlinearity and time delay.In this paper,a single neuron self-learning controller and an adaptive controller were designed.The PSD controller took the width of the cladding layer as the output control quantity and the cladding speed as the input control quantity,and its performance is verified by simulation test and interference test.Adaptive control is based on the stability of the height of the deposited layer,and the distance between the tungsten electrode and the upper surface of the deposited layer was detected macroscopically and adjusted adaptively.In order to verify the effectiveness of visual sensing and closed-loop control,three geometric components of ’Box’,’Square Bottle’ and ’Bottle’ were formed by GTA-AM.The results showed that the structural parts were well formed,the forming quality was stable,the dimensional accuracy of the cladding layer was controlled within 0.4 mm,and the PSD control and adaptive control were effective.