Solutions to dynamic facility layout problems: Development of Dynamic From Between Chart (DFBC) and its applications to continuous layout modeling
Manufacturing facility layout is determined by minimizing the Material Handling (MH) cost associated with the manufacturing of products. A manufacturing facility operates in a dynamic environment where the production rates and product mix are continuously changing. In addition, the introduction of new products/machines and removal of existing products/machines render the existing layout completely unreliable to yield improved productivity. Hence, it is often necessary to analyze the current layout and redesign the layout in accordance with the constantly changes in demand. Existing methods for the analysis of redesign uses multiple, static, and tabular from-to charts. These charts assume and exhibit the timely demand as a discrete invariable quantity. A new tool, “Dynamic From Between Chart (DFBC)” that allows easier visualization of the changes in product rates and mix is introduced and developed in this research. DFBC models the production rate changes using a continuous function. The development process of the new tool, the formulation of the cost function and its application to the solution of Dynamic Facility Layout Problems (DFLP) for multiple time periods is presented with the use of a case study. The solution methodology uses a tradeoff analysis between increased MH cost and the rearrangement cost for the transition from existing layout to a new layout. To further authenticate and strengthen the developed methodology, real world case studies are considered and evaluated. Importance of any department flow over the other departments (crossover) occurs only if there is variation in the flow volumes between relative departments. In previous research, the redesign is carried out at the end of specific time period in a given time horizon. In most instances, the need for redesign or change in flow occurs somewhere during the period and identifying such crossover points will assist to yield better savings. In addition, the exact time at which the layout should be modified can be determined. For large size problems, the number of crossover points sited in DFBC will be large and evaluating each of these points to identify the point of change in layout will be tedious and time consuming. Thus, along with the methodology to identify the crossover points a concept of Upper bound and Lower bound (UB–LB) to discover the set of redesign points which may warrant a change in layout has been developed. Further analysis is necessary to detect the point(s) that initiate the change. Limiting the solution space facilitates the evaluation of large size problems by reducing and simplifying the computation. Multiple case studies are considered and evaluated to indicate the applicability of the concept. It is also evident in current manufacturing paradigms that the introduction of new products/machines and removal of existing products/machines in-between the time horizon induces huge flow variations between departments. Previous research on DFLP does not deal with models which adopt such scenarios. In this research the application of DFBC to analyze the impact of introduction of new products/machines and removal of existing products/machines in between the time horizon is considered. The ability of the DFBC to address such scenarios is evaluated using a case study. Finally, the possible extensions of this research are listed along with the conclusions on the proposed approach.
Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering