Fixture for welding automobile sheet metal part

The invention discloses a fixture for welding an automobile sheet metal part, and relates to the technical field of automobile sheet metal part machining. The fixture comprises an underframe, two supports, a cross beam, a first connecting piece, a clamping box, a first fastening piece and a detection part. The two supports are symmetrically and fixedly connected to the top of the underframe; the cross beam is arranged between the two supports; the first connecting piece is fixedly connected to the cross beam; the clamping box is arranged at the lower end of the first connecting piece, and is provided with an installation groove; the first fastening piece is in threaded connection with the clamping box; and the detection part comprises a sliding rod arranged between the two supports, the sliding rod is positioned below the cross beam, a first sliding block is connected to the sliding rod in a sliding mode, an infrared lamp is arranged on the first sliding block, and a scale line is arranged on the surface of t