Frame cross member assembly and welding method thereof

The invention provides a frame cross member assembly and a welding method thereof. The frame cross beam assembly comprises a beam body assembly, a left supporting frame and a right supporting frame; the beam body assembly comprises a bottom plate, a front plate, a rear plate, a left end cover and a right end cover; the front plate and the rear plate are arranged on the two sides of the bottom plate in the front-back direction, and the rear plate comprises a top wall part, a first side wall part and a second side wall part. The top wall part is arranged between the first side wall part and thesecond side wall part, the top wall part is located above the bottom plate, the second side wall part is connected with the front plate, the two ends of the front plate are provided with a first protruding part and a second protruding part respectively, and the left end cover and the right end cover are arranged at the two ends of the bottom plate in the left-right direction; in the vertical direction, the first protrudin