Date of Award
Doctor of Philosophy (PhD)
G. John Miltenburg
The popularity of Just-In-Time (JIT) methods in manufacturing has been rising steadily for the last two decades. U-shaped lines, or U-lines, are an important component of many JIT systems. While production on these lines is similar, in many respects, to that on other configurations, the U shape has significant impact on station assignments, line efficiency and production characteristics of the line. An important decision related to U-line production is the assignment of tasks to stations, the U-line balancing problem. This thesis explores aspects of U-line balancing including the nature of different U-line balancing problems, the production characteristics of U-lines and the efficiency of different solution algorithms. The investigation into U-line balancing begins with the simplest problem, balancing a single U-line constrained only by precedence relationships and the cycle time. The efficiency of U-lines compared to straight lines and the effectiveness of different optimal solution algorithms is evaluated. An effective branch and bound algorithm is identified. It forms a basis for solving more complex problems. One of the differences between U-lines and straight lines relates to the effect of operator travel and station layout on station feasibility. Consideration of operator travel is the second topic explored. Since JIT facilities often include numerous U-lines operating in close proximity, there is an opportunity to increase operator efficiency by constructing stations which contain tasks from more than one U-line. Simultaneous balancing of more than one line is introduced as the two U-line balancing problem and extended to N U-line balancing. If access to U-lines is restricted to the opening of each U-line, the first problem may be solved optimally for typical problems. The complexity of N U-line balancing dictates the use of heuristics solution algorithms. The nature of JIT production frequently requires the mixing of production of several product models on a single line. One of the difficulties with mixed-model production is that different models require different production resources and task processing times vary from one model to the next. During mixed-model production station times will fluctuate, a condition termed model imbalance. Mixed-model production on U-lines is examined and solution algorithms which smooth the degree of model imbalance are offered. The particular advantages of U-lines for mixed-model production are explored. In the final section the problem of U-line balancing is extended to include consideration of stochastic task processing times. A constrained version of this problem may be solved using dynamic programming. For general stochastic U-line balancing problems a heuristic solution is found by employing a simulated annealing algorithm. In this thesis a number of advantages of U-lines over straight lines are illustrated. These advantages provide an incentive for the incorporation of U-lines into manufacturing processes.
Sparling, David Hamilton, "Topics in U-line balancing" (1997). Open Access Dissertations and Theses. Paper 3427.