To overcome the incoordination between production plan and its schedule in the classic from-top-to-down
approach, a mixed integer programming model of integrated production planning and scheduling is presented for synchronous
automobile assembly line. A Lagrangian relaxation method is developed for the proposed model which is decomposed into
planning and scheduling sub-problems, etc. The scheduling sub-problem is modeled as a time-dependent traveling salesman
problem(TDTSP) which is solved by using a dynasearch algorithm. The average direction strategy is employed to solve the
Lagrangian dual problem, and simulation results show the effectiveness of the proposed model and algorithm.