Algorithms for increasing labor productivity in U-shaped assembly systems

Manufacturers commonly produce high-volume products using assembly lines, where each unit becomes incrementally more complete as it moves through successive workstations on the assembly line. Most Western manufacturers arrange assembly lines in a straight-line layout, while their Japanese counterparts prefer U-shaped lines. According to proponents of just-in-time (JIT), U-shaped layouts often require fewer operators than comparable straight-line layouts, thus improving labor productivity.;This research examines several research issues concerning U-shaped assembly systems in two phases. The first phase, which forms the nucleus of this research, addresses the development and testing of exact solution procedures for the Simple U-Line Balancing (SULB) and Simple Assembly Line Balancing (SALB) problems. Two fathoming techniques, the Paired Tasks lower bound procedure and the Immediate Task Assignment dominance rule, are introduced in this research to improve the performance of our solution procedures. Provided these new solution procedures, the second phase examines questions pertaining to the level of labor productivity improvement that occurs when switching from a traditional straight-line layout to a U-shaped layout.;Developments of the first phase consist of a series of solution procedures coined as *U-OPT*. Results convincingly show that the performance of U-OPT is not only superior to existing SULB solution procedures, but U-OPT also performs quite well when solving the SALB problem. The newly developed Paired Task lower bound is largely responsible for the superior performance of U-OPT. The ITA dominance rule introduced in this research also enhances the performance of U-OPT, but its effect on the performance of solution procedures is not as pronounced. Without these two new fathoming criteria, the performance of U-OPT is comparable to the performance of the existing solution procedures examined when solving the SALB problem.;Results from the second phase of this research indicate that labor productivity of an assembly system will improve significantly under certain conditions by switching from a straight-line layout to a U-shaped layout. However, the level of labor productivity attained is quickly negated as the amount of operator travel increases when designing the spacial layout of the U-shaped line.