OPTIMISATION OF PRODUCTION PLANNING AND CONTROL IN JOBSHOPS

Abstract

Smooth production planning and control in jobshops has been hindered by inherent problems and peculiarities that surround management decisions in meeting the organisational objectives while satisfying the customers' requests. In solving these problems and streamlining the peculiarities, this study has developed mathematical models for eight strategic decisions that are pertinent in effective production planning and control in jobshops. These strategic decisions are: Demand Management, Manpower Planning, Tools and Equipment Planning, Material Requirement Planning, Job Scheduling, Cost Estimation, Due Dates, and Floor Shop Control and Record Management. Demand Management Model that was developed, determined the optimal forecast hour of demand and the optimal quantity of materials needed in the planning horizon using Exponential Smoothing Technique as the basis. The Manpower Planning Model determined the optimal number of manpower and its associated cost. The model permits internal transfer of full-time and part-time manpower with utilisation of excess and make up for shortage labour-hour, which served as control measure. Tools and Equipment Planning Model was also developed through which the optimal quantity of Tools and Equipment and cost, based on purchase, hire or contract strategy were determined. The development of Materials Requirement Planning Model was done and the optimal quantity and cost of material were determined based on modified Economic Order Quantity Model. A job-scheduling model was among the models developed to determine the commencement time and minimise the make span with inclusion of a dynamic operational schedule and re-schedule of jobs based on priority and first-come first-served principle. Cost Estimation Model based on modification of Aderoba (1997a)'s model with inclusion of bargaining permissibility was developed. A due-date model was formulated by modifying Akinnuli and Aderoba's (2000) model to include uncertainty in due dates and job crashing through adjustment of manpower, tools and equipment, and the scheduled jobs. A shop floor control and record management tools were designed to assign shop-order priority and work-in-progress quantity information for effective control in the areas of job location, shop order, accounting, efficiency and facility productivity. The tools track and monitor the flow of jobs, tools and equipment, material and manpower in the system. The eight (8) models were integrated using a heuristic method to evolve a hybrid model. Based on this, a software, JOBSIS_2007, in PHP (Hypertext Preprocessor) programming language, which costs maximum of 16% of the existing proprietary softwares, was developed for rapid implementation of the model. The validity of the model was tested using a jobshop located in Osogbo, Osun State, Nigeria. The period used for this purpose was classified into pre-implementation and implementation period. Pre- and Post- implementation results were compared using ANOVA, with the results from the implementation period. Based on this, it was revealed, among other things, that the model developed has enhanced capacity utilisation, improved marginal profit and created adequate records and documentations for planning . and control of production activities in the company. This study finally recommended salient points that could promote efficient usage of the model.