Re-scheduling in a production line of the Varitronix Limited

Pao Yue-kong Library Electronic Theses Database

Re-scheduling in a production line of the Varitronix Limited

 

Author: Lee, Wai-yan
Title: Re-scheduling in a production line of the Varitronix Limited
Degree: M.Sc.
Year: 1999
Subject: Assembly-line methods -- Case studies
Production scheduling -- China -- Hong Kong -- Case studies
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Management
Pages: vi, 188 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1568946
URI: http://theses.lib.polyu.edu.hk/handle/200/1765
Abstract: In this dissertation, an intensive analysis of the re-scheduling policy for a production line of Varitronix Limited has been performed. Varitronix Limited is a local LCD manufacturing company, which has two production lines at present. One is in China Mainland and the other one is in Hong Kong. Both of these are very similar to each other, so this dissertation only concentrates on the production line in Hong Kong for easy monitoring. Everyday, Varitronix Limited spends a sum of production cost for frequent re-scheduling of orders in production. The facing problem is that the current re-scheduling policy, Earliest Due Date method with left-shift, is rather subjective. It is used because a manufacturing manager suggests it according to his past experience only. Therefore, the main objective of this dissertation is to find an improved re-scheduling policy for Varitronix Limited such that the total costs associated with frequent re-scheduling in the production line would be less than that of the current re-scheduling policy (EDD with Left-shift). Theoretically, the optimal policy for re-scheduling problem can be found. However, the time required to find the optimal policy is impractical in real life. The running/solving time for a real life re-scheduling problem is very long because there are too many constraints in a problem. Therefore, some new re-scheduling policies are developed and investigated in this dissertation. Past research reveals that there are many common scheduling methods such as Shortest Processing Time method (SPT) and Longest Processing Time method (LPT). In this dissertation, these common methods are also applied to obtain new re-scheduling policies to solve the problem. At the same time, some heuristic re-scheduling policies are also developed. Their performances are compared with the current re-scheduling policy. Data that include unit price, market rental price, processing time for different models, prices of materials, labor cost, etc. are collected accordingly. With these data and the order data records in 3 previous months, the total cost of the production schedule per each day is calculated by applying each of the above re-scheduling policies as an experiment in this dissertation. The best performance re-scheduling policy, Heuristic Re-scheduling Policy with Sorted Start/Finish Date (HP-SF), is chosen for solving our problem. In order to test the effectiveness of HP-SF, a simulation analysis is carried out to compare its performance with that of the current re-scheduling policy. The results show that HP-SF is better than the current re-scheduling policy by a calculated improvement percentage from the results of the simulation. And the 90% confidence interval is also obtained to estimate the mean of the improvement percentage of HP-SF compared to the current policy. In the simulation, the total cost of the optimal re-scheduling policy is also obtained for each simulated day. These figures are compared to the total cost associated with HP-SF by the measure of relative error. Same as above, the 90% confidence interval is obtained to estimate the mean of the relative error of HP-SF compared to the optimal. The results are satisfied by the management of Varitronix Limited.

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