[[alternative]]The Study on the Integrated Inventory Models for Stochastic Demand and Controllable Lead Time

計畫編號：NSC92-2416-H032-001研究期間：200308~200407研究經費：558,000[[sponsorship]]行政院國家科學委員

An Integrated Single Vendor-Buyer Stochastic Inventory Model with Partial Backordering under Imperfect Production and Carbon Emissions

This paper develops an integrated single vendor single buyer inventory model with imperfect quality and environmental impact. The demand during lead time is assumed to be stochastic and follows the normal distribution. An integrated system with controllable lead time and logarithmic investment to reduce the defective percentage is discussed in this model.100% error-free screening process is adopted by the buyer to separate defective and non-defective items. We assume that shortages are allowed and are partially backordered at the buyer’s end. Logistics management is the component of supply chain management that focusses on how and when to get raw materials, intermediate products and finished goods from their respective origins to their destinations.Thus, transportation play a major role in supply chain. As transportation increases, it affects the weather by the matter of carbon emission.The fixed and variable carbon emission cost for both vendor and buyer is considered. The prime motive is to determine the optimal policies regarding optimal order quantity, reorder point, lead time and the number of lots delivered in a production run by minimizing the expected total cost of the system. Finally, a numerical example is provided to demonstrate the model

Benefits and challenges with coordinated inventory control at Volvo Parts

Coordinated inventory control is a concept within inventory management where decisions are based on stock and demand situations throughout a whole system of interconnected warehouses and inventories, and where control parameters are simultaneously determined and set at all installations. This thesis is a part of a larger research collaboration project in coordinated inventory control where NGiL (Next Generation Innovative Logistics), a Lund based research institute, and Volvo Parts AB in Gothenburg participate. Volvo Parts handles the aftermarket distribution, sales and related services for the Volvo Group companies and has centrally controlled complex multi-level warehouse structures and routines. These warehouse structures are well suited for a coordinated inventory control approach. A new multi-level inventory control model has been developed by NGiL especially for the Volvo Parts supply chain in Europe. The model utilizes advanced mathematical concepts to mimic Volvo Parts inventory systems consisting of several dealers and warehouses on a market. The model optimizes the reorder points at all locations with the aim of minimizing the total costs of the system while still maintaining or increasing today’s service to end customers. The purpose of this thesis is to prepare for this pilot study by analyzing the information systems, processes, structures and routines at Volvo Parts, design methods for extraction and calculation of the necessary parameters, select an appropriate market and to perform a selection of suitable spare parts and accessories to be included in the pilot study. A suitable market for the pilot study and a method to select and classify 100 parts with all necessary parameters are the main results of the thesis. The study is performed as an action research project, meaning that the authors are stationed at Volvo Parts headquarters in Gothenburg and observe the daily work, perform the necessary data extractions from the IT systems themselves and conduct interviews on a daily basis. The gathered data is a combination of primary and secondary quantitative data from the IT systems and calculations, as well as a lot of primary qualitative data from interviews and observations. The authors also function as mediators between NGiL researchers and Volvo Parts personnel. The developed model is concluded to be a good representation of the reality of Volvo Parts’ supply chain on the selected market Spain, and the authors do not see any large obstacles in a generalization to other Volvo Parts markets with the same structure or even other companies. The one major discrepancy between the NGiL model and current Volvo Parts control methods is how service levels are measured and how goals on these service levels are achieved. We have also performed a simulation study for some of the selected parts and found that the potential for cost reductions is significant and that the optimized solution fulfills target service levels in almost all cases. We also found out that there are no clear correlations or patterns between the cost reduction and any of the part characteristics that were studied, implying that a larger simulation study or a real life pilot study is necessary in order to further investigate the full potential of the NGiL model

[[alternative]]The Impact of Quality and Lead Time on the Supply Chain Model

計畫編號：NSC93-2416-H032-002研究期間：200408~200507研究經費：333,000[[abstract]]由於電腦網路技術的進步及實體運輸系統的發達，「供應鏈管理」近年來逐漸發展 成一重要的領域。供應鏈管理的基本原則是利用有效率的方法，整合價值鏈上的買賣雙 方，賣方能夠在適當的時間，生產適當數量的高品質商品，並在適當的期間內送達買方 手上，使得整體系統成本最小化。基於這個理念，供應鏈的上下游廠商之間必需要建立 策略聯盟關係，利用一些有效率的方法，提升商品、服務及資訊分享的水準，才能真正 發揮供應鏈營運的績效。 再者，長久以來，存貨模式大都是基於買方或賣方單方面的考量，來探討生產及訂 購策略等問題，如此往往使雙方資訊無法整合而造成損失。近年來，及時化的製造策略 受到廣泛利用，由於其專注於買方與賣方的整合，因此需要買方與賣方能夠充分合作， 方可利用雙方資訊的整合，訂定合理的長期採購合約，做到真正的及時化採購，從而降 低相關存貨系統的總成本。 本計劃是一為期二年的個別型計劃。本計劃之第一年主要是考慮當需求不確定，且 前置時間的長度可控制及買方收到的批量中含有不良品的情況下，如何整合買方和賣方 的製造與訂購策略，並提出兩個整合存貨模型。在本研究中，首先我們採全部檢查(full-lot inspection)的策略來檢查批量中的不良品項。針對此檢查策略，我們假設前置時間內的 需求量服從常態分配，其次探討前置時間內需求量的機率分配為未知的情形，並且利用 大中取小分配不拘程序求解。我們亦分別針對此兩種情形(前置時間內需求量的機率分 配為常態分配或分配不拘)建立求得最適生產、訂購策略之演算法，並利用數值範例說 明買賣雙方整合後的利益，確實是高於整合前的個別利益。同時，本研究也將分析各參 數變動對於決策所造成的影響，作為提供給管理者之重要參考依據。 第二年：我們進一步考慮利用部份檢查(sub-lot inspection)策略於買賣雙方之整合存 貨模式。此外，我們亦探討數量折扣(quantity discount)在供應鏈模式中之影響。如同第 一年計劃，假設前置時間內的需求量服從常態分配及機率分配為未知的情況。並分別對 存貨數學模型找出最佳解。針對上述的存貨模型，分別就聯合決策、買方主導與賣方主 導等三種情況推導買、賣方之最適批量;並探討在何種情況下的存貨總成本為最小。最 後，以數值範例來說明其使用之方法，並顯示其所能帶來的經濟效益。[[sponsorship]]行政院國家科學委員

Integrated supply chain inventory model with quality improvement involving controllable lead time and backorder price discount

For the past four decades the integrated vendor and buyer supply chain inventory model has been an interesting topic, but quality improvement of defective items in the integrated inventory model with backorder price discount involving controllable lead time has been rarely discussed. The aim of this paper is to minimize the total related cost in the continuous review model by considering the order quantity, reorder point, lead time, process quality, backorder price discount and number of shipment as decision variables. Moreover, we assume that an investment function is used to improve the process quality. The lead time demand follows a normal distribution. In addition, the buyer offers backorder price discount to motivate the customers for possible backorders. There are some defective items in the arrival lot, so its treatment is also taken in account in this paper. We develop an iterative procedure for finding the optimal values of decision variables and numerical example is presented to illustrate the solution procedure. Additionally, sensitivity analysis with respect to major parameters is also carried out

Development of an inventory management policy at Wurth Portugal

This project is carried out in a company that sells equipment and provides maintenance services for this equipment. The project's objective was to reduce equipment repair time by increasing the availability of parts to carry out these repairs. Having identified that the lack of parts for repair delays the completion of repairs, the current stock management policy was studied and taking into account the variability in demand and supply, a new stock management policy was proposed to the company to combat current irregularities. In addition, potential supply risks related to suppliers and delivery times were also identified and a supply risk mitigation policy was proposed. The current stock management policy for machine substitution parts was analyzed and the respective supply risks were identified. Data evaluation was carried out through observation, interviews and focus groups in the company's purchasing, logistics and technical services departments. The replacement parts were divided by classes through the ABC analysis (sales volume) in order to select those with the highest degree of importance, the so-called class A. Therefore, a suggestion for improving the management of the class A substitution parts stock was proposed. A proposal for mitigating the supply risk was also prepared. The proposals were implemented, leading to a substantial improvement throughout the machine repair process.O presente projeto é realizado numa empresa de venda de equipamento e prestação de serviços de manutenção desses equipamentos. O objetivo do projeto foi a redução do tempo de reparação dos equipamentos por via do incremento da disponibilidade de peças para realização dessas mesmas reparações. Tendo-se identificado que a falta de peças para reparação adia a conclusão das reparações, a política de gestão de stock em vigor foi estudada e tendo em conta a variabilidade na procura e abastecimento, foi proposta à empresa uma nova política de gestão de stock para combater as irregularidades atuais. Para além disso, também foram identificados os potenciais riscos de abastecimento relacionados com fornecedores e prazos de entrega e proposta uma política de mitigação do risco de abastecimento. Foi analisada a atual política de gestão de stock de peças de substituição de máquinas e identificados os respetivos riscos de abastecimento. A avaliação dos dados foi feita através de observação, entrevistas e grupos focais nos departamentos de compras, logística e serviços técnicos da empresa. As peças de substituição foram dividas por classes através da análise ABC (volume de vendas) com o intuito de selecionar as com maior grau de importância, as denominadas de classe A. Assim sendo, foi proposto uma sugestão de melhoria de gestão do stock de peças de substituição de classe A. Também foi elaborada uma proposta de mitigação do risco do abastecimento. As propostas foram implementadas, originando uma melhoria substancial ao longo do processo de reparação de máquinas

Optimation economic order quantity method for a support system reorder point stock

The success of a company is measured by the ability to provide goods and services at the right time and place. Besides, one of the factors of the company's progress is also supported by inventory management which functions to control the company's inventory by neither hoarding lots of products nor running out of products. The development of technology requires a company's inventory management that is fast, precise and accurate to support its’ performance. In fact, some companies have difficulty in determining the stock of their goods production so that it impedes the fulfillment of consumer needs in the event of high market demand. This study is to determine the reorder point stock of a company that determines the number of purchases and sales of the company's products, therefore the amount of expenses and income can be presented to the board of directors to be followed up quickly and accurately. The method used is a statistical approach to the economic quantity model where safety stock analysis is first performed. This method is used to put the company's products to the inventory so that there are no excess or even shortages of products. System development method used is a user centered design, which is the most suitable to the study. The output of the activity is information in the form of advice to the company leaders in making decisions about production planning, controlling stock inventory, detailing market demand quickly, precisely and accurately and developing a decision support system that is made by taking into account the details of user needs