Taebok Kim

Optimization of welding parameters for resistance spot welding of TRIP steel with response surface methodology

Many automotive companies are endeavouring to reduce the weight of the car body in response to various environmental issues. One initiative is the development of TRIP (Transformation Induced Plasticity) steels with a high strength and ductility. Resistance spot welding is a complex process, which requires specific optimal welding conditions based on experimental data. However, the trial-and-error method to determine the optimal conditions requires a large number of experiments, and so response surface methodology has been employed to overcome this problem. The second-order model was used here. This has been used in the resistance spot welding process of the TRIP steel and galvanized TRIP steel with a zinc-coated layer to optimize the welding parameters. The welding current, welding time, and welding force were selected as input variables, and the shear strength and indentation were selected as output variables.

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.

Determination of the optimal production policy and product recovery policy: The impacts of sales margin of recovered product

In this article, we consider the problem of jointly determining both the manufacturers selling quantity and the recovery rate of used products in a single-manufacturer–single-retailer supply chain. The types of recovery of used products might be either product recovery or component recovery. Also, since two types of finished products, i.e. either original product or recovered product, might have different sales margins in a market, the optimal recovery policy should be established according to the operational setting for resource recovery. This problem is formulated as a profit maximisation problem. We propose the solution procedure for deriving the optimal solution and numerical examples are provided to illustrate our approach. From the numerical results, we observed that the economical recovery policy can be classified into three modes, i.e. no-recovery, partial-recovery and full-recovery. And, it is analysed that how the optimal recovery policy might be characterised according to the key operational parameters such as the production capacity and recovery rate.

Coordinating a supply chain with a heterogeneous vehicle fleet under greenhouse gas emissions

Purpose – This paper studies a supply chain consisting of multiple suppliers and a single buyer. It considers the case where a set of heterogeneous trucks is used for transporting products, and develops a mathematical model that coordinates the supply chain. The purpose of this paper is to minimise the costs of producing and delivering a product as well as carbon emissions resulting from transportation. In addition, the authors analyse how imposing a tax on carbon emissions impacts the delivery of products from the suppliers to the buyer. Design/methodology/approach – It is assumed that heterogeneous vehicles are used for transporting products, which have different performance and cost attributes. A mathematical model that considers both operating costs and carbon emissions from transportation is developed. The impact of vehicle attributes on lot sizing and routing decisions is studied with the help of numerical examples and a sensitivity analysis. Findings – The analysis shows that considering carbon emi...

Shipment consolidation in a multiple-vendor-single-buyer integrated inventory model

This paper studies the case of a single buyer sourcing a product from multiple vendors. To reduce transportation and handling costs, the buyer has the option to assign vendors to groups. The vendor groups then deliver their batches jointly to the buyer. The paper shows that consolidating shipments may lead to a significant reduction in total cost. Numerical studies indicate that deliveries should be scheduled in such a way that the buyer receives large shipments at the beginning of the delivery cycle and small shipments at its end. The results also suggest that vendor groups with high (low) production capacities should be scheduled to deliver their shipments towards the end (beginning) of the delivery cycle.

Integrated product and container inventory model for a single-vendor-single-buyer supply chain with owned and rented returnable transport items

This study considers a single vendor supplying a single retailer with a finished product packed in returnable transport items (RTIs), such as containers, pallets or crates, to facilitate its safe shipment. Once received at the retailer’s site, the RTIs are emptied, cleaned, repaired if needed and returned to the vendor to be used for the next shipment. Because of unexpected events, such as damage of RTIs and/or shortage of labour to empty RTIs, the RTI return time is considered stochastic in this study. In case the return of empty RTIs is delayed, the vendor has the option to rent RTIs from a nearby service provider to avoid disruptions in the delivery schedule and finished product shortages at the buyer’s premise. We formulate the problem of coordinating the flow of both the finished product and RTIs and minimising the supply chain wide costs as a mixed-integer non-linear programme. For a convex objective function, we develop an efficient solution procedure that generates the optimal replenishment cycle, the optimal number of RTIs and the optimal number of trucks. The general optimisation model and the solution procedure are illustrated for the case where the RTI return time is exponentially distributed. In addition, we conduct an experimental study to assess the impact of the problem parameters on the decision variables. It is found that renting RTIs is especially beneficial in case both shortage cost and the risk of late RTI returns are high. In addition, the average RTI return time is found to be critical for the performance of the supply chain.

Green Supply Chain Management Practices' Effect on the Performance of Turkish Business Relationships

This paper provides a first-hand understanding about the procedures taken by Turkish business firms and their logistics providers and supply chain business firms to operate in an environmentally friendly supply chain. The main point of the study is to examine the influence of both external and internal parties on green supply chain management (GSCM) practices in business firms. The result of this research is very important to promote performance of Turkish business relations in their green perspectives. In order to find the correct answers, comprehensive questionnaire forms were designed. We collected data from 2014 May to 2015 July through Turkish companies. More than 180 companies contributed in this extensive research. Then the derived data were analyzed using statistical methods. One of the important inferred results is that the third party logistics service providers influence firms to have a proactive green behavior.

Economical production and transshipment policy for coordinating multiple production sites

In this article, we study the coordination mechanism dealing with a production–transshipment policy across the multiple regions supplying multiple products. It is assumed that each production site has its own dedicated demand region consuming multiple products. The main concern is how to determine both the production quantity and the lot-apportioning policy while minimising the relevant supply chain cost. This decision issue is formulated as a non-linear mathematical model to determine several relevant decision variables. We propose the solution procedure for deriving the production–transshipment policy minimising the overall supply chain cost.

Composite sourcing policy for multiple products on a single production facility

In this paper, we address the composite sourcing policy of a single production facility where customers order quantity can be made internally as well as externally. The surplus production capacity within a common production cycle can be utilised for in-sourcing of demand of other suppliers. We regard the traditional economics lot scheduling problem as a capacity allocation problem. Therefore, the decision problem is to determine the lot sizes as well as the composite sourcing policy for three production modes such as out-sourcing, in-sourcing and in-house making. We develop the mathematical model of the resulting decision problem and propose the solution procedure to determine the economic operating policy.

Design of flexible capacity plan for multiple items in a single production facility

In this paper, we consider the problem of determining production lot size and capacity requirement plan for multiple products, which is produced on a single production facility. Traditionally, the production capacity in such production system is assumed fixed. However, the economical verification of either capacity expansion or capacity reduction should be involved in the design of such production systems. In this paper, we incorporate the cost/benefit aspects in a capacity expansion and reduction decision. We develop the mathematical model dealing with this decision problem and propose an effective solution procedure. We expect that this kind of decision problem can be utilised as an alternative framework for make-or-buy decisions. Following an illustrative example, we discuss the managerial implications obtained from this study and further extensions of this generic model.