Supply chain design to guarantee quoted lead time and inventory replenishment: model and insights

Do lead time constraints only lead to re-think and re-optimise the inventory positioning along the supply chain or can they impact on the design of the supply chain itself? To answer such a question, we integrate the lead time constraints in a multi-echelon supply chain design model and challenge the difficulty of combining in the same model the long-term decisions (facility location, supplier selection) with the midterm decisions (inventory placement and replenishment, delivery lead time). The model guarantees the respect of the quoted lead time associated with each customer order and the replenishment of the different stocks (raw materials, intermediate and final products) in the different stages of the supply chain between any pair of consecutive orders. We use the model to investigate the impact of the quoted lead time and customer’s order frequency on supply chain design decisions and costs. Some of our results indicate that the lead time constraints can lead to bringing the sites of manufacturing and distribution close to the demand zone and to select local suppliers in spite of their higher cost.     

基于提前期的多周期通用件库存模型

在单一周期库存模型的基础上，建立了多周期的通用件库存模型，对无通用件和有通用件的库存模型进行了比较研究，在模型中重点考虑提前期对通用件库存系统的影响，并以风神汽车有限公司有关数据进行了数据分析，揭示出基于提前期的单一周期模型中得出的结论并不能直接套用到多周期模型中，也就是说采用通用件并不总是能够降低库存水平和成本的，这个结论纠正了理论界认为单一周期库存模型的结论普遍适用的观点；研究基于提前期的通用件库存库存模型也是对通用件库存模型没有考虑提前期影响的一个扩展研究。     

An optimal consignment stock production and replenishment policy with controllable lead time

This paper considers a single-vendor and single-buyer production system in which the lead-time is controllable with an extra investment under a long-term agreement between the two trading partners. The vendor produces at a finite rate, ships the outputs in lots of equal size within a production cycle, and delays those shipments for a certain period when the buyer’s inventory approaches the capacity limits. Therefore, the arrival of these shipments does not lead to an increase in the buyer’s inventory. Meanwhile, the buyer holds the payment until the complete consumption of the products. The holding cost consists of a storage component and a financial component. A joint EOQ/EPQ model is then established under cases where the buyer’s unit storage holding cost might be greater or less than that of the vendor to jointly determine the number of shipments, the size of each shipment, the number of delayed shipments, and the lead time that minimise the yearly joint total expected cost (JTEC) of the system. An efficient solution procedure is provided to solve the non-linear integer optimisation model that defined the system under consideration. A method to determine the integer global optima from the real global optima is also presented. Two numerical experiments are conducted to illustrate the procedure and the results show that considering the combined effect of adopting a consignment stock policy and lead time crashing opportunities may lead to a better result than any of these two policies considered separately.     

季节性产品的两级供应链产量-提前期决策模型

以具有明显季节性的空调产品为研究对象,研究单一周期、单一产品类型的由空调制造商和经销商组成的两级供应链系统,分析了空调企业普遍存在的淡季产量决策误差大、旺季产能不足等问题,结合实践提出了季节性产品MTO-MTS集成的生产模式;并且建立了需求不确定条件下该生产模式的成本模型,给出了不同参数条件下提前期的取值规律,以及不同条件下最优提前期对应的最优产量和各项成本及其变化趋势,为季节性产品生产决策中提高交付的响应性提供了依据.     

Single-period assortment and stock-level decisions for dual sales channels with capacity limits and uncertain demand

This paper addresses a dual channel, clicks-and-mortar retailer's problem of determining which among a set of products with seasonal demand will occupy limited retail shelf space, which products will be offered via an online channel, and which items will be available through both channels. Using a consumer choice model in which the set of products offered influences each product's demand in each channel, we consider stocking and price decisions under uncertain demand in a single-period setting with a constraint on the probability of stocking out. The resulting model is a large-scale, chance-constrained, two-stage stochastic programme. We propose a sample average approximation (SAA) method that permits quickly arriving at near-optimal solutions for this complex problem class. We also exercise the proposed model to gain insights on the problem's key tradeoffs and properties of optimal solutions.     

A basic model for co-ordinating a four-level supply chain of a product with a vendor,multiple buyers and tier-1 and tier-2 suppliers

This paper investigates the co-ordination of order quantities amongst the players in a four-level supply chain with a centralised decision process. The first level of the supply chain consists of multiple buyers, the second level of a vendor (manufacturer), the third level consists of multiple tier-1 suppliers, and the fourth level consists of multiple tier-2 suppliers. Each supplier supplies one or more items that are components of the product produced by the manufacturer. The model developed in this paper guarantees that the local costs for the players either remain the same as before co-ordination, or decrease as a result of co-ordination. A mathematical model is developed, with numerical examples presented and results discussed.     

Pre-positioning inventory and service outsourcing of relief material supply chain

Service outsourcing is very common in a commercial supply chain, and in humanitarian relief area, the transportation service is usually outsourced. To practice relief supply more effectively, it seems essential to enlarge outsourcing from shipping to more areas, and private enterprises could play a vital role. This paper examines the optimal pre-disaster order quantity of a certain relief commodity, based on a two-stage coordinated approach. Our findings show that the delay cost, shortage penalty cost, risk of supply shortage, salvage value, expected perishable rate, unit inventory cost and reactive price have significant impacts on the optimal amount of propositioned inventory. Moreover, the outsourcing strategies differ by types of relief commodities. For perishable supplies, proactive or reactive outsourcing would improve the benefits of buyer and supplier simultaneously. As for imperishable supplies, it is better to combine proactive insourcing approach and reactive outsourcing strategy. In view of some supplies whose monitoring cost is high, the insourcing approach is much better than the outsourcing approach.     

基于缩短多阶响应周期的Push/Pull结合的库存管理体系

在顾客化大量生产的环境下，响应速度是企业竞争力的关键，论文从缩短供应链多阶响应周期对库存管理产生的问题出发，建立Push/Pull结合的库存管理体系，阐述了其基本运行机制，并对运行机制中准时制(JIT)与快速响应(QR)结合、供应链延迟点等问题进行了分析，并建立数学模型对库存与响应周期之间的关系进行了研究。     

A comparison of alternative delivery structures in a dual sourcing environment

This paper studies the flow of material between two vendors and a buyer and develops alternative delivery structures with the intention of minimising total system costs. The proposed delivery structures employ alternative design features and give varying degrees of flexibility to the system as to the emergence of inventory and the allocation of inventory among both stages of the supply chain. The delivery structures are compared in a numerical study and it is shown that an increasing degree of flexibility in the delivery structure always leads to lower total system costs. Further, contextual factors that influence relative performance advantages of the structures are identified.     

基于提前期的需求信息放大效应定量研究

在m个分销商和一个制造商的两级供应链中考虑提前期对信息放大效应的作用,推导出分销商需求信息与最初客户群的需求信息之间的需求信息放大效应的表达式.实例分析证明在即使不存在提前期(或者提前期为零)的情况下仍然存在信息放大效应,单纯地压缩提前期不能真正减少信息放大效应的影响,提出实现企业之间的合作与实时信息共享是关键.     

Learning and screening errors in an EPQ inventory model for supply chains with stochastic lead time demands

This paper investigates the role of variable lead time, learning in production and screening errors in a vendor–buyer supply chain with defective items. The vendor–buyer supply chain is modelled for supplying a single item considering that the lots from vendor may contain some defective items. It is assumed that demand during lead time follows a normal distribution. Moreover, the production time at vendor’s facility is assumed to follow learning whereas buyer’s screening for defective items is prone to errors as well. Numerical examples are presented to illustrate the impact of different variables in the model. The analysis shows that delay in transportation lead time forces the buyer to carry more inventories to avoid shortages. Further, Type I error has a major impact on this cost. It was found that learning in production keeps on reducing the total cost of the supply chain up to a threshold.     

A constrained EPSAC approach to inventory control for a benchmark supply chain system

The design of an appropriate inventory control policy for a supply chain (SC) plays an essential role in tempering inventory instability and bullwhip effect. Several constraints are commonly encountered in actual operations so managers are required to take these physical restrictions into account when designing the inventory control policy. Model predictive control (MPC) appears as a promising solution to this issue, due to its capability of finding optimal control actions for a constrained SC system. Therefore, the inventory control problem for a benchmark SC is solved using the extended prediction self-adaptive control approach to MPC. To extend methodologies in our previous work, the control framework relies on generic process model and incorporates the physical constraints arising from practical operations to form the general constrained optimisation problems. The managers can choose from decentralised and centralised control structures according to specific informational and organisational factors of their SCs. The proposed control schemes in this study may be appropriate for industrial practice because the designed policy can bring a reduction of over 30% in operating cost and a significant increase of customer satisfaction level compared with that of the conventional policy.     

多级分销网络设计及库存控制整合优化模型

从供应链集成的角度出发,基于多目标规划,根据排队论探讨了随机性需求下多级分销网络设计与库存控制的整合优化问题,提出了多级分销网络设计和库存控制整合优化的多目标规划模型.针对遗传算法收敛速度慢、易陷入局部最优等缺点,采用了基于并列选择法的遗传-模拟退火算法混合优化策略.实验证明,模拟退火算法提高了遗传算法的全局搜索能力,改善了遗传算法的求解性能.     

Quality improvement practices and the effect on manufacturing firm performance: Evidence from Mexico and the USA

A comparison of organizations in Mexico and the USA demonstrates that, for these two countries, different quality improvement approaches are related to actual quality and financial performance. For 345 firms multiple quality improvement variables are correlated with seven quality measures, four financial measures, and one operating performance measure. Results suggest that in both countries an increase in employee involvement leads to improved quality-a decrease in internal failure costs, the percentage of items defective, and costs of quality. In Mexico an increase in employee knowledge about quality improvement and customer focus also leads to improved quality (as measured above). In the USA, but not in Mexico, the quality improvement approach relates to financial performance. An increase in senior executive leadership and an increased emphasis upon both design and conformance in the USA leads to an improved return on assets and increased net profit. In each country similar distributions from respondents regarding individual items that improve quality can be found, yet statistical modelling demonstrates country-specific models best explain quality improvement/performance relationships. This suggests culture-specific quality improvement models are necessary to better understand how quality may be improved globally.     

基于随机提前期的通用件安全库存管理

研究了随机提前期与通用件安全库存的关系，并建立它们之间的函数关系，通过数学分析得出可以通过控制内部提前期相关的因素来控制通用件安全库存水平的结论，建立了提前期对安全库存影响的决策规则，并以实际数据进行了案例分析。     

A closed loop outsourcing decision model for developing effective manufacturing strategy

The case study deals with aligning production capacity for a US manufacturer of industrial thermal transfer bench-top printer, by exploring various insourcing and outsourcing options based on production, cost and delivery capabilities. A modelling framework is devised which aids in selecting an effective manufacturing strategy that considers key enablers and barriers to successful outsourcing. The proposed model is closed loop, which stresses regular re-evaluation of the existing outsourcing strategy. It models the total product cost for the product currently being manufactured in the US and compares the total costs if it were manufactured offshore in countries such as, Malaysia, China, Slovakia and Mexico. The analysis from the model shows moving manufacturing of the product to Mexico results in the largest business benefit of about $400 savings per unit compared to other countries studied. A closer look at China in the future could be considered as the economic, social and security risks may change enough to warrant re-evaluation of this option. To get a clearer picture of how Mexico rates against Malaysia in the existing state, these risks may be reviewed as an extra data point to finalise the decision to move manufacturing of industrial thermal transfer bench-top printers to Mexico.     

Model predictive control for inventory management in biomass manufacturing supply chains

This paper presents a centralised model predictive control strategy applied to biomass inventory control in sugarcane industries. Sugarcane industries are important renewable energy producers and an adequate inventory control of their feed material (biomass) can improve energy production. Simple linear discrete-time models with dead-time are developed to predict the controlled variable behaviour. Two layers are used in the controller, in the upper one performance is optimised by an linear programming (LP) algorithm and a multivariable generalised predictive controller (GPC) or multivariable generalised predictive controller with dead-time compensation (DTC-GPC) is used in the lower level. Simulation results in general show that the proposed controllers globally optimise the system behaviour and find an optimal ordering amount for keeping stock levels. In cases of plant/model mismatch DTC-GPC can have a significant and positive impact on the control of stock levels adding one more parameter for achieving minimised oscillatory performances (bullwhip effect).     

A graph-based model to measure structural redundancy for supply chain resilience

Globalisation and lean initiatives increase the vulnerabilities of the supply chains (SC), where disruptions in any plant in a supply chain network (SCN) can propagate throughout the whole SCN. Redundancy is part of the SC re-engineering to improve supply chain resilience (SCRES). This paper presents a conceptual model of an SCN using graph theory, considering the relationships between plants and materials. Based on the model, the structural redundancy of the SCN is measured, which is used to assess SCRES. This assessment approach focuses on the resilience of the SCN against disruptions. Case studies are discussed to illustrate the applicability of this model and show that increasing structural redundancy of the SCN improves SCRES against disruptions.