Cadena de aprovisionamiento

How successfully does JIT handle machine breakdowns in an automated manufacturing system?
¨ Mustafa Ozbayrak Gultekin Cagil and Cemalettin Kubat
The authors
¨ Mustafa Ozbayrak is Lecturer, Department of Systems Engineering, Brunel University, Uxbridge, UK. Gultekin Cagil and Cemalettin Kubat are both Assistant Professors in the Department of Industrial Engineering, Sakarya University,Adapazari, Turkey.

Introduction
Just-in-time (JIT) practices have proved efficient and powerful in running the operations of manufacturing shop floors. When a JIT control system is coupled with a reliable and automated manufacturing system, it can be considered as a competitive asset helping to create a streamlined manufacturing organisation. The benefits of successful JIT implementations, such asreduced work in progress (WIP) and inventory, better cycle time and on time delivery are well documented. However, relatively little work has been carried out on JIT performance in manufacturing systems where unexpected or unscheduled interruptions, such as machine or material handling system breakdowns, are possible. This study is concerned with such unexpected interruptions and analyses the robustnessof different modes of JIT control to unexpected breakdowns. Scheduling a manufacturing system can be one of the most complex tasks in managing an operation. Several different types of resources have to be dealt with simultaneously, and resources have their own variable characteristics, which add to the complexity of the problem. Ideally schedules should be reactive with strategies or contingencyplans “just in case” something unpredictable happens. If this approach is not adopted then, after a disruption, the pre-planned schedule often becomes inapplicable. Therefore, schedules chosen need to be dynamic, stochastic and discrete in order to truly model a manufacturing environment. Many scheduling systems assume that machines work continuously during a manufacturing period. However, thiscould be far from the truth. Machines and equipment stop during production regularly or irregularly for various reasons, such as breakdowns, maintenance, reworks and part/tool changeovers. To obtain more accurate schedules, corrective actions have to be taken into account to cater for “randomness”. This paper presents a simulation model to schedule jobs considering natural interruptions/ randomnessand to measure the effects of these interruptions on a flexible manufacturing system (FMS) performance. JIT is chosen as a planning and control system in the FMS. Although JIT has proven to be a highly successful strategy in managing the manufacturing planning and control there is a little research on how a JIT system handles equipment failure in an automated system such as FMS. We, therefore, havesimulated a
Received: September 2002 Revised: January 2003 Accepted: March 2003

Keywords
Breakdowns, Just in time, Industrial performance, Manufacturing industries, Manufacturing systems

Abstract
Scheduling a manufacturing system can be one of the most complex tasks in managing an operation. Planning and control systems such as just in time (JIT) can aid scheduling. However, planning andcontrol tools require a fairly stable shopfloor environment to get the best out of them. Many system designs and schedules only consider 100 per cent reliability in machines, and do not take into account random interruptions. In this paper, a simulation model was created to investigate machine and material handling system breakdown problems in a JIT-driven flexible manufacturing system. Resultsshow that compromises have to be made with JIT control in order to get the best system performance.

Electronic access
The Emerald Research Register for this journal is available at www.emeraldinsight.com/researchregister The current issue and full text archive of this journal is available at www.emeraldinsight.com/1741-038X.htm

Journal of Manufacturing Technology Management Volume 15 ·...