Yushin Hong

An optimal production run length in deteriorating production processes

This paper presents an EMQ model which determines an optimal production run length in a deteriorating production process. It is assumed that the process is subject to a random deterioration from an in-control state to an out-of-control state with an arbitrary distribution and, thus, produces some proportion of defective items. An optimal production run length and a minimum average cost are derived in three deteriorating processes: constant, linearly increasing, and exponentially increasing. Several different results from those of previous research are obtained and discussed. A numerical experiment is carried out to see the behavior of the proposed model depending on the cost and process parameters. Some interesting behaviors are observed.

Optimal production run length and inspection schedules in a deteriorating production process

This paper presents an economic manufacturing quantity model which determines an optimal production run length and inspection schedules simultaneously in a deteriorating production process. It is assumed that a production process is subject to a random deterioration from the in-control state to the out-of-control state and, thus, produces some proportion of defective items. An optimal production run length and an optimal number of inspections are derived, and unique properties of the proposed model are discussed. A numerical experiment is carried out to examine the behavior of the proposed model and compare the proposed model to an existing model.

An extended EMQ model for a failure prone machine with general lifetime distribution

Abstract This paper presents an EMQ model which determines an optimal lot size in a failure prone machine. It is assumed that time between failures of a machine is generally distributed, and a machine is repaired instantaneously when it fails. Depending on various types of failure rate function of a machine, it is discussed how to determine an EMQ and prove its uniqueness. Variations of an EMQ depending on repair cost are also examined. Through numerical experiments, extensive investigations are carried out on the effects of repair cost and setup cost to an EMQ as well as average cost, and some interesting behaviors are observed.

Heuristic algorithms for buffer allocation in a production line with unreliable machines

Efficient heuristic algorithms are developed for the buffer allocation in a production line so as lo maximize the throughput. We focus on the unbalanced production line in which the mean processing time of each machine is not identical. The optimal buffer allocation problem is formulated as a multi-dimensional non-linear search problem with a linear resource constraint such that total capacity available is finite. The concept of standard and non-standard exchange vectors are introduced to develop two different versions of the algorithm. Since the objective function representing the throughput is not differentiable, we suggest the pseudo-gradient for obtaining improving directions. Numerical experiments show that the proposed algorithms work well even for the larger problems that could not have been handled as yet.

Joint economic production allocation and ordering policies in a supply chain consisting of multiple plants and a single retailer

This article discusses the production and ordering policies in a supply chain consisting of a single manufacturer and a single retailer. The retailer places orders based on the EOQ-like policy, and the manufacturer purchases raw materials and allocates them to the multiple plants in parallel to produce demand requirement from the retailer. The model is mathematically formulated, and the solution procedure is developed to determine the production cycle length, ordering quantity and frequency, and production allocation ratios for multiple plants. The closed forms of the production cycle length, ordering quantity, and frequency in terms of the production allocation ratios are obtained. It is also shown that the production allocation problem is NP-hard. An efficient and effective heuristic algorithm is proposed to determine the near-optimal production allocation ratios. A numerical experiment demonstrates that the proposed algorithm performs quite satisfactorily.

An extended optimal lot sizing model with an unreliable machine

This paper presents an extended EMQ model which determines an optimal manufacturing lot size for an unreliable machine. An average cost function is derived when the machine has an arbitrarily distributed time between failures and constant time to repair. Under the assumption that time between failures is exponentially distributed, the optimal lot size is determined and some properties of the proposed model are derived. Through numerical experiments, sensitivity analyses are carried out to examine the effects of machine parameters as well as cost parameters on the optimal lot size. It is observed that the optimal lot size does not always increase as the failure rate or the time to repair increases.

A simulation-based semiconductor chip yield model incorporating a new defect cluster index

This paper proposes a new cluster index that utilizes the defect location data on a wafer in terms of the coefficient of variation. The proposed cluster index is independent of the chip area and does not require assumptions on the distribution of defects. An extensive simulation is performed under a variety of cluster patterns and a yield prediction model is derived through the regression analysis to relate the yield with the proposed cluster index and the average number of defects per chip. The performance of the proposed simulation-based yield prediction model is compared with that of the well-known negative binomial model.

Pricing and ordering policies for price-dependent demand in a supply chain of a single retailer and a single manufacturer

This article discusses joint pricing and ordering policies for price-dependent demand in a supply chain consisting of a single retailer and a single manufacturer. The retailer places orders for products according to an EOQ policy and the manufacturer produces them on a lot-for-lot basis. Four mechanisms with differing levels of coordination are presented. Mathematical models are formulated and solution procedures are developed to determine the optimal retail prices and order quantities. Through extensive numerical experiments, we analyse and compare the behaviours and characteristics of the proposed mechanisms, and find that enhancing the level of coordination has important benefits for the supply chain.

A stock rationing policy in a (s,S)-controlled stochastic production system with 2-phase Coxian processing times and lost sales

Abstract This paper analyzes a (s,S)-controlled stochastic production system with multi-class demands and lost sales. Demands in each class are assumed to arrive according to a Poisson process, and the time required to process an item is assumed to follow a 2-phase Coxian distribution. For each class, a stock rationing level is set. When customers arrive, if the inventory level is lower than the predetermined rationing level, the demands are lost for future demands with higher priorities. A behavior of the production system is modeled as a continuous time Markov chain, and an efficient algorithm to calculate the steady-state probability distribution of the system is proposed. The average operating cost under the stock rationing policy is compared with the one without stock rationing. Numerical experiment shows that the proposed stock rationing policy reduces the average operating cost significantly, depending on the system parameters.

Continuous slab caster scheduling and interval graphs

We define and solve a scheduling problem for operating the continuous steel slab caster which converts molten steel into slabs. The nature of our problem has an interesting connection to a special class of graphs known as interval graphs. We show that our problem can be seen as a variant of the clique partitioning problem defined on interval graphs and develop an optimal algorithm for it.