ON SOME FACTORS AFFECTING THE JUST-IN-TIME PRODUCTION SYSTEM OUTPUT VARIABILITY - A SIMULATION STUDY USING TAGUCHI TECHNIQUES

The main objectives of this research were to analyze the effect of dif ferent maintenance policies, machines unreliability, and some other fa ctors on the Just-In-Time (JIT) production system output variability o r stability. Maintenance policies of type I and II which were introduc ed by Proshan and Hunter, and maintenance policy III, which was introd uced by Makabi Hajime et al., were considered in this study and their effect on the JIT production system were analyzed. In this research, m athematical predictive and integrative models were developed to demons trate the effects of different maintenance policies (A), machine unrel iability (B), ratio of preventive maintenance time to processing time (D), production line size (C), processing time variability (E) and rat io of minimal repair time to preventive maintenance time (F) on the pr oduction line output variability (PLV) in a JIT production system envi ronment. Functional relationship between the dependent variable PLV an d die independent variables A, B, C, D, E and F were developed. Using the Taguchi approach in this experimental design all main factors used in this experiment were tested at three levels each using on L27 orth ogonal plan, then all main factors and their first order interactions were tested using an L32 orthogonal plan of experiment. Discrete-event simulation, using the GPSS/H simulation language, was employed in ord er to collect the needed data. The analysis of the data showed that un der different situations, different maintenance policies do not have t he same effect on the production line performance. With regard to the PLV, maintenance policy III led to a higher variation than policy II, except at the level where the number of machines is less than or equal to 5. The results of this study also demonstrate that the production line performance under policy II is more sensitive to the change on th e ratio of minimal repair time to preventive maintenance time when und er policy III the same production line performance is more sensitive t o production line size. Therefore, the results of this study should he lp the user in choosing a maintenance policy as a function of the prod uction process parameters in order to decrease production line output variability and improve productivity and stability.