Research On New Arc Process In Robot Welding Of Shield Machine Parts

With the development of China,the population in the downtown have a high density.As a convenient transportation,the subway can improve traffic conditions,and at the same time provide rapid,on time and safe service.Therefore,the shield tunneling machines which are used for underground tunnel undoubtedly play an increasingly important role in nowadays.The current production of shield tunneling machine is mainly produced by manual which has low production efficiency and poor welding quality.Therefore,the production efficiency will be greatly improved when the robot welding is applied in shield machine.Shield machine parts are complicated,so there is no guarantee of ideal stem elongation because of structure limit when use robot welding.Long stem elongation often cause incomplete fusion problems in root welding.At the same time,the thick plates in shield machine need to reduce the heat input and residual stress while ensuring the efficiency of the deposition.Therefore,through the study of these problems in the robot welding of shield machine,it will have great practical values for the automatic welding of shield machine.Firstly,the arc process for robot root welding is studied.The arc process of PMC(Pulse Multi Control)is used for root welding.This arc process can realize mixed transition mode with pulse drop transition and short circuit transition by reducing the arc length.The cold-heat welding effect reduces the heat input effectively.Compared with the arc process of Pulse,PMC has higher peak current which leads to greater penetration.Then,the root welding test of T-joint in shield machine is performed by using the arc process of PMC.The fusion of the root welding is good.For the single V45° groove,there appears the problem of incomplete fusion with the stem elongation of 27 mm.Secondly,according to problem of incomplete fusion with the stem elongation of 27 mm,the function of constant penetration control in PMC is studied.With a constant arc length,the arc process of PMC increases the penetration by increasing the wire feed speed,and then increase the average current.When the stem elongation is 22 mm,the constant penetration is basically realized.When the stem elongation is 27 mm,it reaches 80% of the normal penetration.Through the welding of single V45° groove once again,the incomplete fusion problem is effectively solved.Then,the arc processes for robot filling welding are studied.The arc processes of LSC(Low Spatter Control)and Universal are compared in this part.Through the effective waveform control,the splash is controlled and the deposition efficiency of both arc processes is over 87%.The short circuit transition of LSC is more obvious,and more short circuit transitions are realized in the same average current.So the welding heat input is effectively reduced with the arc process of LSC.At the same time,LSC realizes a smaller weld forming coefficient due to the smaller penetration when it has the same deposition with arc process of Universal.In the end,the arc process of LSC is used in multi-layer multi-path welding.The formula of deposition is established in this part.Then the parameter selection and weld arrangement are carried out according to the requirement of feet size of T-joint in shield structure.The result shows that the actual feet size is closed to the specified feet size and the formula of deposition has a high reliability.The actual welding of shield machine structure is good.Through the filling welding of single V45° groove with arc process of LSC,the fracture of tensile specimen is appeared in parent metal.The tensile specimen has good tensile properties.