This paper describes work performed to model the dynamics of a system consisting of two manipulators bringing sheet metal components of a car-body into contact for welding. A sheet metal payload is first discretized into finite shell elements. The flexible payload dynamics are derived via the Lagrangian formulation and combined with the robot dynamics to form one robot-and-payload system. The system equations are simplified by first ignoring certain of the terms that describe the interaction between the flexible and rigid-body coordinates; and second, by applying Guyan reduction. The model developed is applied to simulate the mating of two halves of a car door under three control methods: PD control with gravity compensation, computed torque control, and master/slave hybrid position/force control.