Transient Performance Analysis of Serial Production Lines

TRANSIENT PERFORMANCE ANALYSIS OF SERIAL PRODUCTION LINES by Yang Sun The University of Wisconsin-Milwaukee, 2015 Under the Supervision of Professor Liang Zhang Production lines with unreliable machines and finite buffers are characterized by both steady-state performance and transient behavior. The steady-state performance has been analyzed extensively for over 50 years. Transient behavior, however, is rarely studied and remains less explored. In practice, a lot of the real production systems are running partially or entirely in transient periods. Therefore, transient analysis is of significant practical importance. Most of the past research on production systems focuses on discrete materials flow which utilities Markov chain analysis. This dissertation is devoted to investigate the effects of system parameters on performance measures for transient serial production line with other machine reliability models. The reliability models investigated in this dissertation are exponential and no-exponential (Weibull, Gamma, Log-normal). In a real production line system, machine reliability models are much more difficult to identify. Strictly speaking, it requires the identifications of the histograms of up- and downtime, which requires a very large number of measurements during a long period of time. The result may be that the machines\u27 real reliability model on the factory floor are, practically, never known. Therefore, it is of significant practical importance to investigate the general effects of system parameters on performance measures for transient serial production line with different reliability models. The system parameters include machine efficiency e, ratio of N and Tdown (K), machines\u27 average downtime Tdown, and coefficient of variation CV. The performance measures include settling time of production rate (t_sPR), settling time of work-in-process (t_sWIP), total production (TP), production loss (PL). The relationship between the performance measures and system parameters reveals the fundamental principles that characterize the behavior of such systems and can be used as a guideline for product lines\u27 management and improvement. Most previous research studies are limited to two or three machine system due to the technical complexity. Furthermore, presently there are no analytical tools to address the problems with multiple machines and buffers during transient periods. This dissertation addresses this problem by using simulations with C++ programming to evaluate the multiple machines (up to 10) and buffers and demonstrate the transient performance at different conditions. The simulation method does not only provide quantified transient performance results for a given production line, but also provides a valuable tool to investigate the system parameter effects and how to manage and improve the existing production line

Efficient buffer design algorithms for production line profit maximization

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 447-465).A production line is a manufacturing system where machines are connected in series and separated by buffers. The inclusion of buffers increases the average production rate of the line by limiting the propagation of disruptions, but at the cost of additional capital investment, floor space of the line, and inventory. Production lines are also a special case of assembly/disassembly systems as well as closed-loop systems. This thesis makes contributions to production system profit maximization. The profit of a production line is the revenue associated with the production rate minus the buffer space cost and average inventory holding cost. We assume that machines have already been chosen and therefore our only decision variables are the buffer sizes and the loop population. The difficulties of the research come from evaluation and optimization. We improve evaluation of loop systems. The optimization problem is hard since both the objective function and the constraints are nonlinear. Our optimization problem, where we consider the nonlinear production rate constraint and average inventory cost, is new. We present an accurate, fast, and reliable algorithm for maximizing profits through buffer space optimization for production lines, and extend the algorithm to closed-loop systems and production lines with an additional maximum part waiting time constraint. A nonlinear programming approach is adopted to solve the optimization problem. Two necessary modifications are proposed to improve the accuracy of the existing loop evaluation method before optimization of loops is studied. An analytical formulation of the part waiting time distribution is developed for two-machine one-buffer lines. It is used in the profit maximization for production lines with both the production rate constraint and the maximum part waiting time constraint. Numerical experiments are provided to show the accuracy and efficiency of the proposed algorithms. Finally, a segmentation method and an additive property of production line optimization are studied. They enable us to optimize very long lines rapidly and accurately.by Chuan Shi.Ph.D