Chang Seong Ko

The spatial and temporal consolidation of returned products in a closed-loop supply chain network

As cost pressures continue to mount in this era of economic slowdowns, a growing number of firms have begun to explore the possibility of managing product returns in a more cost-efficient and timely manner. However, few studies have addressed the problem of determining the number and location of initial collection points in a multiple time horizon, while determining the desirable holding time for consolidation of returned products into a large shipment. To fill the void in such a line of research, this paper proposes a mixed-integer, nonlinear programming model and a genetic algorithm that can solve the reverse logistics problem involving both spatial and temporal consolidation of returned products. The robustness of the proposed model and algorithm was tested by its application to an illustrative example dealing with products returned from online and retail sales.

Development of mathematical models for the container road transportation in Korean trucking industries

Abstract This study deals with some practical problems of the container road transportation in Korean trucking industries. We examine the workflow in container transportation and then develop mathematical models integrating the various operating and design characteristics of the containers. Several types of formulations are developed utilizing the standard formulations of well known TSP (Traveling Salesman Problem) and VRP (Vehicle Routing Problem). Heuristic algorithms are also presented to solve the models. An example problem is illustrated to explain how to apply the models to the real world through the data set collected from a container trucking company in Korea.

Operator-scheduling using a constraint satisfaction technique in port container terminals

In port container terminals, the efficient scheduling of operators of handling equipment such as container cranes, yard cranes, and yard trucks is important. Because of many complicated constraints, finding a feasible solution, as opposed to the optimal solution, within a reasonable amount of computing time can be considered satisfactory from a practical point of view. The major constraints include the following: restrictions on the minimum workforce assignment to each time slot, the maximum total operating time per operator per shift, the minimum and maximum consecutive operating times for an operator, types of equipment that can be assigned to each operator, and the available time slots for each operator or piece of equipment. The operator-scheduling problem is defined as a constraint-satisfaction problem, and its solution is obtained by utilizing a commercial software. An actual problem, collected from a container terminal in Pusan, Korea, is solved through the solution procedure proposed in this study.

Determination of cutoff time for express courier services: a genetic algorithm approach

As the result of an explosive growth in e-tailing, telemarketing, and television home-shopping industries, the demand for the direct shipment of purchased goods by express couriers has increased over the last several years. The success of an express courier service often depends heavily on the direct marketing firms ability to extend its cutoff time (deadline) for direct home deliveries coordinated by service centers near customers. Such an extension of cutoff time, however, may prolong consolidation holding time at the consolidation terminal and subsequently disrupt the timely delivery of products to customers. To make a trade-off between cutoff time extension and delivery delays, we propose an integer programming model and its genetic algorithm solution procedure that allows express couriers, such as UPS, FedEx, and DHL, to maximize their profit generated by direct home deliveries. To demonstrate the practicality and efficiency of the proposed model and solution procedure, we conducted a case study involving an express courier in Korea.

A closed-loop recycling system with a minimum allowed quality level on returned products

This paper deals with a closed-loop recycling system in which a stationary demand is satisfied by remanufactured products as well as newly manufactured products. In this system, only those used products that satisfy a minimum allowed quality level are bought back from customers for recycling. Thus the collection rate of used products is expressed as a function of the quality level and the unit bought-back price. It is assumed that the cycle consists of a single remanufacturing run and a single manufacturing run, both in Economic Production Quantity settings. Treating the quality of recycled products as a random variable, we develop a mathematical model with the objective of minimising the production and inventory costs. The decision variables are the length of the cycle, the minimum allowed quality level and the unit bought-back price of used products. To illustrate the validity of the model, sample problems are solved.

A strategic alliance model with a regional monopoly of service centres in express courier services

Since the 1990s, the demand for the direct shipment of purchased goods by express couriers has increased as the result of an explosive growth in the e-tailing, telemarketing and TV home-shopping industries, which has caused the emergence of an excessive number of express courier companies over the last several years. This increasing number of companies leads to severe competition among small- and medium-sized companies and a greater number of facilities and delivery vehicles for faster service, which may result in the waste of national resources. Furthermore, it is often the case that the facilities and delivery vehicles owned by individual companies are operated with a low utilisation rate. It has been suggested that cooperative strategic alliances in the operation of facilities and delivery vehicles may be beneficial especially for small- and medium-sized companies to overcome financial problems and improve declining profitability by reducing or eliminating overlapping investments. This study proposes a network design model for strategic alliances that share service centres. An integer programming model and its solution procedure based on maxmin and maxsum criteria are also developed respectively. The applicability and efficiency of the proposed model are demonstrated through an illustrative numerical example.

Managing product returns in customer-centric e-tail environments

Owing to liberal customer service policies and the rapid product obsolescence resulting from ever-shortening product life cycles, product returns have become daily routines for many retailers. As product returns slow down the retailers supply chain and consequently affect the retailers bottom line, a growing number of retailers have begun to explore the possibility of managing product returns in a more cost-efficient and timely manner. Such a possibility includes the determination of the number and location of initial collection points and the establishment of the desirable holding time for consolidation of returned products into a large shipment. With this in mind, this paper proposes a mixed-integer programming model and a genetic algorithm that can solve the reverse logistics problem involving consolidation of returned products. The validity of the proposed model and algorithm was tested by their application to an illustrative example dealing with products returned from online retail sales.

An agent-based framework for global purchasing and manufacturing in a shoe industry

Global competition is forcing the present day industry to produce high quality product more fast and inexpensively. The need for fast information exchange has increased among the remote locations for the cooperation and coordination. In this study, a virtual global manufacturing system in a shoe company is constructed that distributes production schedule among remote places, acts as a bridge between the headquarters and manufacturing plants, distributes tasks and collates different solutions between demand and supply using an agent. It generates an order and a procurement plan. An order-supply agent is proposed and implemented to automate the process of ordering and supplying of goods in a shoe making company from the Internet environment.

A case study for determining standard time in a multi-pattern and short life-cycle production system

Abstract This study presents two approaches for determining standard time in a multi-pattern and short life-cycle production system. We explain the approaches through conducting a case study on a tableware manufacturing company, gathering field data on the company that represent the characteristics of the multi-pattern and short life-cycle production system. In the first approach, based on the production field data, new weights for each variable in function and difficulty grade categories are estimated and corresponding model for determining standard time is developed. In the second approach, the standard time is determined based on the existing weights for each variable in two categories. Multiple regression models are developed for each approach. Based on standard time data, a conversion table reflecting the comprehensive difficulty is generated and used for differentiating the items produced by each worker.

Manufacturing cell formation in the presence of flexible cell locations and material transporters

Abstract The effect of cell locations and material transporters in the formation of manufacturing cells is investigated in this paper. Automated guided vehicles (AGVs) using a tandem configuration are considered and a first-come-first-served (FCFS) principle is applied for transporting the material between machines or between the input/output (I/O) and a machine. Using the time taken to perform material transfers as a suitable measure, a polynomial programming model is developed for the problem. As the model can be shown strongly NP-hard, a higher-level heuristic algorithm based upon a concept known as ‘tabu search’ is presented. An example problem is solved to further demonstrate that cell locations indeed have a significant impact when material transfers are used in the design of manufacturing cells.