Browsing by Subject "Manufacturing cells."

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Open Access
Dynamic lot-sizing and scheduling in a cellular manufacturing system
(1993) Dağlıoğlugil, Orhan
In most of the production systems, lot-sizing and scheduling decisions are given in different levels of hierarchy, however there is a strong interaction between these decisions. Most of the existing models do not utilize the shop floor conditions in lot-sizing and scheduling decision dynamically, even though such a. decision might improve the system performance. In tins study, a dynamic lot-sizing and scheduling algorithm is suggested for cellular manufacturing systems, wliich utilizes a h}d)rid simulation/analytic modelling approach. The performance of the proposed algorithm is compared with the push and pull systems under different shop floor conditions.
Open Access
Polyhedral Approaches to Hypergraph Partitioning and Cell Formation
(1994) Kandiller, Levent
Hypergraphs are generalizations of graphs in the sense that each hyperedge can connect more than two vertices. Hypergraphs are used to describe manufacturing environments and electrical circuits. Hypergraph partitioning in manufacturing models cell formation in Cellular Manufacturing systems. Moreover, hypergraph partitioning in VTSI design case is necessary to simplify the layout problem. There are various heuristic techniques for obtaining non-optimal hypergraph partitionings reported in the literature. In this dissertation research, optimal seeking hypergraph partitioning approaches are attacked from polyhedral combinatorics viewpoint. There are two polytopes defined on r-uniform hypergraphs in which every hyperedge has exactly r end points, in order to analyze partitioning related problems. Their dimensions, valid inequality families, facet defining inequalities are investigated, and experimented via random test problems. Cell formation is the first stage in designing Cellular Manufacturing systems. There are two new cell formation techniques based on combinatorial optimization principles. One uses graph approximation, creation of a flow equivalent tree by successively solving maximum flow problems and a search routine. The other uses the polynomially solvable special case of the one of the previously discussed polytopes. These new techniques are compared to six well-known cell formation algorithms in terms of different efficiency measures according to randomly generated problems. The results are analyzed statistically.