Philip Y. Huang

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 ...

A comparative study of priority dispatching rules in a hybrid assembly/job shop

SUMMARY This paper reports on research conducted on the use of priority dispatching rules in a hybrid assembly/job shop which manufactures both single-component and multiple-component products. A simulation model was constructed and a large stale experiment performed. Statistical analysis of the simulation results indicated significant impact of both the priority rules tested, and the product-mix considered on shop performance. Among the 12 priority rules tested, the SPT (shortest processing time) rule and the ASMF-SPT (assembly jobs first with SPT as tie-breaker) rule performed very well with respect to measures like lateness, flow time, tardiness, staging time, and percent of jobs tardy. These findings lead to further investigation of a combined priority rule, MIXED, which implements the ASMF-SPT rule at all machine centres that process components of assembly jobs, and the SPT rule at the remaining machine centres which process non-component jobs. The additional research results yielded evidence that th...

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...

Using beam search techniques for sequencing mixed-model assembly lines

This paper introduces a beam search approach to sequencing mixed-model assembly lines and compares that approach to existing sequencing heuristics. The comparison study consists of over 400 test problems that vary in terms of number of product models, quantity of assembly, and degree of component commonality. The results show that beam search techniques are clearly superior to both the goal chasing algorithm (GCA) and Miltenburg and Sinnamons look ahead heuristic. The second half of this paper extends the beam search approach to allow two scheduling objectives: (1) minimizing parts consumption variation, and (2) minimizing workload variation. Termed filtered beam, this variation uses a filter to eliminate alternatives that exceed a predetermined threshold according to one objective, and then proceeds with the beam search for the second objective. As in the first case, optimization is not guaranteed; however, the filtered beam search provides a frontier of good trade-off solutions from which the decision maker can choose an acceptable sequence.

A multi-criteria decision model for the selection of a computerized manufacturing control system

The purpose of this paper is to describe and demonstrate a quantitative procedure for evaluating alternative computerized manufacturing control software packages that are being considered for possible purchase. The procedure considers both quantitative factors (i.e. costs) and qualitative factors (i.e. vendor reputation) that should be considered in the evaluation process. The various evaluation factors and criteria are identified and a procedure for quantifying the factors in commensurable unite is described. The procedure is demonstrated via an example.

Workload vs scheduling policies in a dual-resource constrained job shop

Abstract The purpose of this paper is to report on research conducted to examine the effectiveness of different scheduling policies in a dual-constrained job shop under various workload conditions. The standard assumption in most job shop scheduling research has been that a 90% utilization of the shop is achieved. However, since shop utilization levels vary widely, it was hypothesized that scheduling policies that are optimum under one load condition might not be as effective under other load conditions. The model for this simulation experiment represented a job shop constrained by both labor and machines. The shop contains four machine centers with random routing of jobs through the shop. Shop workload was defined at three levels: 70, 85 and 99% utilization. Four machine scheduling rules and three labor assignment rules were tested for each of the shop workload levels, with mean job flow time as. the performance criterion. The results of the 3 × 4 × 3 factorial experiment showed that the advantage of the SPT (shortest processing time) machine scheduling rule over other rules is diminished dramatically when shop utilization is reduced from 99 to 85% or below. This same observation holds for other rules considered. The LNQ (longest queue length) labor assignment rule outperformed other rules at the 99% utilization level, but yielded no significant difference in performance at the 85% and below workload levels.

Integrating the MRP-based control level and the multi-stage shop level of a manufacturing system via network simulation

Despite the increased attention recently to material requirements planning (MRP) in the research literature. MRP has frequently proved to be unsuccessful on actual implementation. One factor related to its unsuccessful implementation is that MRP systems are often not sufficiently analysed and tested within an actual shop scenario prior to implementation. In this paper, a network simulation model that integrates the MRP-based shop control level with the shop level in a manufacturing system is described, and its usage demonstrated within the context of a realistic shop scenario that encompasses multiple-level product structures, several-component items, job and assembly operations, machine setups and backordering. Five simulation experiments are conducted using the network simulation model, including cases in which: (1) all model parameters are constant (standard case), (2) product demand is varied, (3) set-up times are varied, (4) processing times are variable and (5) the worst cases from all the previous ...

Analysis of material and capacity requirements with Q-GERT

Abstract The purpose of this paper is to report on research conducted to develop a simulation model which incorporates the basic MRP logic into the modelled production process. The objective of the modelling effort is to provide information necessary for planning and controlling of the material and capacity requirements of a production process that includes stochastic processes. The modelling and analysis procedure exploits the fact that the structure of the production process can be logically modelled as a network flow process. The technique employed to facilitate the network modelling is Q-GERT (Graphical Evaluation and Review Technique) modelling and simulation language. A case application is presented to demonstrate a prototype model, followed by a report of the simulation results. The model is designed to provide answers and insights to the following questions: (1) how long must each production centre operate to yield the specified quantities of finished products, (2) what is the expected lead time r...