Study On Process Optimization And Control Of Additive Manufacturing With Double Electrode Micro Plasma Arc Welding

Wire and Arc Additive Manufacturing?WAAM?has been widely explored by the domestic and foreign researchers to fabricate large metal components due to its high deposition rate,high material utilization,and unlimited build volume in the shape and size of metal parts.However WAAM has been still applied in repairing and manufacturing the simple shaped metal parts because of the problems of process automation and control caused by heat build-up and dynamic changes in the sizes of the molten pool.In this thesis,the problems of heat build-up,process automation,and process control in WAAM are studied experimentally and theoretically.Firstly,Double Electrode Micro Plasma Arc Welding?DE-MPAW?additive manufacturing system is established under the real-time target environment of xPC Target.The comparative experiments of double electrode micro plasma arc welding and conventional micro plasma arc welding for depositing metal parts are carried out.The results show that the thermal control effects of bypass current on the substrate and deposition layers can improve the heat build-up in WAAM deposition process,decrease the width and penetration of the deposition layers,increase the height of the layers and enhance the deposition efficiency.Secondly,the dynamic deformation measurement system of DE-MPAW additive manufacturing is built by industrial CCD camera,coordinate plate,K-type thermal couple and suitable substrate restraint method.The dynamic deformation law and the effects of deposition path parameters on the deformation in DE-MPAW deposition process are studied by depositing 10^th layers single bead wall parts in same direction and reciprocating.The results show that the dynamic deformation camera measurement method based on the cantilever substrate constraint can effectively record the dynamic deformation in WAAM deposition process.With time goes on and the deposition layers increase,the dynamic deformation changes in zigzag shape and presents a trend of first increasing and then decreasing.WAAM deposition process with the reciprocating direction is good for improving heat build-up and deformation.Because it has lower average peak temperature,temperature gradient and deformation,compared with the deposition process in same direction.Moreover,DE-MPAW additive manufacturing curved parts deposition system is developed by getting UG/NX software system and DE-MPAW additive manufacturing system together.The experiments of depositing elliptical metal parts with 304L stainless steel and Inconel 625 nickel-based super alloy material are carried out by control the bypass current in this deposition system.The stainless steel ring parts are manufactured with this deposition system and milling technology together.The results show that with the same deposition parameters,it's available to get a well done deposited metal part in appearance by changing the bypass current to decrease the heat build-up of substrate and deposition layer.With the bypass current control and deposition path design,the different material curved surface parts can be automatically deposited in this system,especially in depositing Inconel 625 material.Finally,the relationship between the maximum critical wire feed rate,welding torch stand-off,current and voltage in DE-MPAW additive manufacturing deposition process are investigated experimentally.The circuit principles of deposition process based on different metal transfer models are analyzed.With these investigations,the adaptive height control system for DE-MPAW additive manufacturing is developed under real-time xPC Target environment.The experiments of depositing metal material on the step,slop,and cross shaped substrates,and depositing 25^th layers single wall part are conducted in this adaptive height control system.The results show that the adaptive height control system of DE-MPAW additive manufacturing make the deposition experiments with different shaped substrates and the fabrication of 25^thh layers single wall part come true by adjusting welding torch in the set scope and changing wire feed rate real-time.This control system improve the problems such as the predication of the deposition layer heights,layers slice design of metal model,and the re-melting and collapse of deposition layers.The adaptive height control system also optimizes the WAAM deposition process and enhances the stability of this deposition process.