Balancing just-in-time production units: The NU-line balancing problem

U-shaped production lines are a common component of Just-In-Time systems. When several U-lines operate in close proximity, an opportunity exists to balance two or more U-lines together and reduce the total number of stations required to operate the facility. The concept of a JIT production unit, where a number of U-lines produce and assemble parts for the same product line, is introduced. The problem of balancing a JIT Production Unit is considered as the NU-line balancing problem considering travel. This problem is modelled and heuristic solution algorithms are presented for both the general case, where U-line locations are not fixed, and for the fixed location case. A subproblem, the problem of assigning tasks to stations which may include tasks from more than one U-line, provides new challenges for operations managers. This new problem is the multi-line station assignment problem. The benefits of multiple U-line balancing are examined in an empirical study.