טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYael Berstein
SubjectLot Splitting on a Reentrant Machine
DepartmentDepartment of Industrial Engineering and Management
Supervisors Mr. Rubinovitz Jacob (Deceased)
Mr. Masin Michael


Abstract

Lot splitting is a procedure of splitting lots into sublots. This procedure accelerates the flow of work by scheduling sublots of a same lot simultaneously on sequenced machines. Therefore, some performance measures such as makespan and flowtime may be improved. In spite of the benefits of lot splitting in flow shop and job shop environments, lot splitting was not applied in reentrant production systems. This research introduces lot splitting to the reentrant environment, considering mean flowtime and makespan as performance measures. Our model consists of a single reentrant machine where the product is processed in N different stages. The number of sublots processed consecutively in the same stage is our decision variable.  After finding structural properties of this production system, we develop three algorithms for lot splitting: the first deals with consistent and equal sized groups of sublots, the second assumes only consistent groups, and the third finds general solutions. The first two algorithms minimize mean flowtime and obtain good results in the performance measure and run time. Based on the Tradeoffs Programming approach, the third algorithm generates the complete efficiency frontier for both the mean flowtime and the makespan performance measures. A comprehensive computational experiment is performed for analyzing the tradeoff between the two objectives and evaluating the relative performance of the proposed algorithms. Our results show that lot splitting improves performance in reentrant environment.