Patrick R. Philipoom

DYNAMICALLY ADJUSTING THE NUMBER OF KANBANS IN A JUST-IN-TIME PRODUCTION SYSTEM USING ESTIMATED VALUES OF LEADTIME

Abstract In a Just-in-Time (JIT) production system with Kanbans, as used by the Japanese, the number of Kanbans employed at each workcenter remains relatively constant from month to month even though demand may change, This occurs because of the unique (and stable) conditions inherent in the production environment of Japanese firms. However, a number of American firms have considered or attempted the implementation of a JIT system without a similar production environment, thus, necessitating that the number of Kanbans at each workcenter be adjusted periodically. In this paper, a procedure for dynamically adjusting the number of Kanbans at workcenters in an unstable production environment is presented and analyzed. The adjustment methodology is presented in a step-by-step manner. This is followed by three examples presented within the context of a simulation model of a hypothetical shop. The first example will illustrate the methodology while the last two examples will demonstrate how well the methodology ...

An investigation of the factors influencing the number of Kanbans required in the implementation of the JIT technique with Kanbans

Abstract Japanese production environments exhibit a number of characteristics not present in many American firms that contribute to the success of the just-in-time (JIT) system with Kanbans. However, because of the advantages of a JIT system with Kanbans many firms have attempted implementation without the existence of the appropriate production environment to do so. The purpose of this paper is first to identify those factors that will influence the number of Kanbans required at a workcentre for the production manager implementing a JIT system in an uniquely American production environment. The factors that will be identified include the throughput velocity (i.e. the rate at which items flow through a workcentre machine), the coefficient of variation in processing times (i.e. the degree of variability of processing times), the machine utilization (i.e. the availability of slack time on a machine), and, autocorrelation of processing times (the degree to which successive processing times on a specific mach...

Capacity-based order review/release strategies to improve manufacturing performance

Given the increased emphasis by manufacturing organizations to reduce work-in-progress inventories thereby shortening their manufacturing lead times, more attention is being given to the control of the materials released to the shop floor. The control of input into the shop is one of the activities associated with order review/release (ORR). A common assumption of the published literature on ORR is that all orders received by the shop will be accepted, regardless of shop conditions. In this paper, this assumption is relaxed such that in times of high shop congestion, it may be better to reject an order to allow the customer to seek another supplier than to accept the order and deliver it to the customer late. When the shop is highly congested, accepting all orders will jeopardize the ability of the shop to meet customer due dates. In an industry that demands fast and reliable turnaround of customer orders, not meeting due dates may result in customers placing their orders with other more reliable supplier...

Machine dedication and process flexibility in a group technology environment

Abstract This study investigates changes in inventory and customer service performance of a job-shop that desires to adopt a Group Technology (GT) philosophy in its shop floor operations. Simulation methodology is pursued to explore tradeoffs in shop performance between the routing flexibility of non-dedicated machines in a functional job-shop and the setup efficiency of dedicated machines in shops that have machine cell layouts. Further, traditional and GT-based scheduling procedures are investigated in these different shops to determine the conditions under which a GT philosophy may be profitably employed only in layout decisions, only in scheduling decisions, or in both layout and scheduling decisions. Results from this study show that shop layout choice is not a simple decision that can capitalize either on the high routing flexibility of the functional job-shop or on the setup efficiency advantages of a cell shop. The tradeoffs between routing flexibility and setup efficiency must be made carefully. The impact of demand variability on performance is also dependent on the type of layout. In general, product volume variability more adversely affects the performance of functional job-shops, while product mix variability has greater impact on the performance of cell shops. Finally, sensitivity analysis is performed to show that maintaining balance between the utilization of machines is a major determinant of performance, and consequently the best layout.

Modeling simultaneous worker learning and forgetting in dual resource constrained systems

Abstract This paper addresses issues related to modeling worker learning and forgetting effects in Dual Resource Constrained (DRC) systems. The learn-forget-learn (LFL) model of Carlson and Rowe (Carlson, J.C., Rowe, A.J., 1976. Industrial Engineering 8, 40–47) is used to critically evaluate several worker training related issues that are associated with the learning and forgetting phenomenon. A numerical analysis is performed on the LFL model within a DRC system to gain insights into the nature of relationships between the extent of worker flexibility, forgetting rates, attrition rates, and flexibility acquisition policies. Results suggest that in the presence of higher attrition and forgetting rates, a worker may not be able to achieve full efficiency in as little as two different departments. Thus acquiring even incremental worker flexibility under such conditions may be infeasible. We also show that managers can use different flexibility acquisition policies designed in this study to reduce relearning losses and consequently improve the system performance.

A preliminary investigation of multi-attribute based sequencing rules for assembly shops

This paper updates the current literature on assembly shop scheduling to include multi-attribute based sequencing rules that have recently been introduced and measures of shop performance that more accurately reflect managements view toward tardiness and inventory. In addition, a new set of sequencing rules, called importance ratio (IR), is proposed. The operation of a hypothetical assembly shop is simulated to test the performance of eight sequencing rules on three distinct sets of product structures. Four measures of system inventory and four measures of job tardiness are used to evaluate sequencing rule performance. The study shows that sequencing rules which incorporate attributes of both job shop and assembly shop scheduling do not necessarily produce the best performance. Moreover, multiple measures of inventory and tardiness performance do provide important insight into the operation and particular benefits of different sequencing rules. Finally, the importance ratio rules introduced are viable ca...

A mathematical programming approach for determining workcentre lotsizes in a just-in-time system with signal Kanbans

SUMMARY An essential condition necessary for the implementation of the Japanese just-in-time (JIT) technique with Kanbans is Small setup times relative to processing times. Without this condition bottlenecks occur at workcentres which delay production. However, the Japanese have developed a variation of the strict JIT technique that employs a special type of Kanban, referred to as a ‘signal Kanban’, at workcentres with relatively high setup times. While a normal Kanban triggers the production of larger than normal lots this altered version of the JIT technique provides an alternative approach for firms that desire to use the JIT technique, but are unable to reduce setup times at all workstations. The purpose of this paper is to describe the signal Kanban technique and demonstrate two versions of an integer mathematical programming approach for determining the optimal lotsizes to be used in conjunction with signal Kanbans. A simulation model is subsequently employed to test the effectiveness of the integer...

Due Date Assignment in a Multistage Job Shop

Abstract In a Materials Requirements Planning (MRP) system, component lead times are generally assumed to be known and constant. Since a requirement of a MRP system is that components finish on time, slack is often built into component lead times to insure that actual job flowtimes equal planned job lead times. In this study, job characteristics and shop characteristics are investigated to determine which has a greater impact on predicting job flowtimes. This is accomplished by determining which characteristic most greatly influences the deviation of planned job lead times from actual job flowtimes. After identifying those factors which have the greatest influence on the jobs flowtime, due date assignment rules are developed. A simulation study is then made to determine. which of the due date assignment rules perform best for varying product structures, as defined by various Bills of Materials (BOMs), and various shop conditions. Simulation test results are presented and discussed.

Labour flexibility and staffing levels in a dual-resource constrained job shop

In many manufacturing organizations, increasing process flexibility is becoming more important while the reliance on product cost to measure manufacturing performance is being lessened. As a result, companies are placing more emphasis on developing a cross-trained workforce in an effort to improve the flexibility of their operations. Having a cross-trained workforce allows managers to move workers around to adjust to temporary overloads in the shop. Another approach to increasing process flexibility is through the addition of labour to create a capacity buffer. Adding more labour improves flexibility since it reduces the average utilization in the shop thereby reducing the possibility of any overload occurring in the first place. This paper compares the benefits realized by the development of a multi-skilled workforce with the benefits realized by additional workforce staffing. Both strategies exhibit improvement in the simulation of a hypothetical dual resource constrained hybrid job-shop. Results sugges...

Sequencing rules and due date setting procedures in flow line cells with family setups

Abstract The purpose of this study is to investigate due date setting procedures and dispatching decisions in a flow line cell with family setups. In this environment, setups are not required when switching from a job in a given family to a job in the same family. However, switching from a job in one family to a job in another family requires a setup. Family setups in this shop are sequence independent. The dispatching decisions in this shop are threefold: (1) when should the decision to switch from one part family to another be made; (2) once the decision to switch families is made, how should the next part family be chosen (next family decision); and (3) how should the jobs within a family be prioritized (next job decision)? If the decision to switch classes can only be made after the current family is exhausted, the rule is called a class exhaustion rule. Otherwise the rule is a truncated rule. The results indicate that the due date setting procedure has a major impact on how dispatching should be performed in the shop. The family exhaustion procedure using the APT next family rule and the SPT next job rule is the best performer for mean flow time. When setup times are long, the SEQ due date rule using the family exhaustion procedure with the FCFS next family and the EDD next job rules performed well for due date criteria. When setup times are short, the EDD/T, Sawicki truncation rule and the family exhaustion rules performed well for due date criteria.