Lap joint method

The invention provides a lap joint method, a twin wire welding method and a system thereof for welding a groove. The twin wire welding method comprises the steps of: setting a tracking angle range of a tracking sensor according to the angle of the groove, wherein the tracking angle range comprises the angle of the groove, and the angle of the groove is the angle of the groove for welding lap jointed by upper sectional materials and lower sectional materials; setting a welding angle of a welding torch according to the angle of the groove, wherein the welding torch comprises a first welding wire and a second welding wire, the first welding wire is communicated with root penetration voltage, and the second welding wire is communicated with surface filling voltage; controlling the welding torch to not to open an arc, and verifying whether the welding angle is correct or not along the groove for welding under the guidance of the tracking sensor; if so, controlling the welding torch to openan arc, and welding along the welding track of the groove for welding according to the verified welding angle. The technical scheme of the invention overcomes the technical defects of inconvenient welding by the welding torch caused by the fact that the welding angle of the groove for welding is appropriately a right angle or an acute angle in the prior art.