Laura Mazzoldi

Vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme

This paper presents a joint economic lot size (JELS) model for coordinated inventory replenishment decisions under the vendor-managed inventory (VMI) with consignment stock (CS) agreement and an emission-trading scheme. The paper assumes a single product that flows along a two-level supply chain system, with a single vendor and a single buyer. The total cost of the system is the performance measure, which is the sum of the vendor’s and the buyer’s total costs. The total cost includes the set-up and order costs, inventory holding costs, greenhouse gases (GHG) emissions tax and penalty costs. A mathematical model is proposed to determine: (1) the vendor’s production lot size quantity; (2) the number of shipments sent by the vendor to the buyer in a cycle; and (3) the production rate that minimises the total cost of the supply chain. Some numerical examples are carried out, as well as comparisons with the traditional JELS model for a classic two-level supply chain. Results show that the performance of the system is better when it is operated under a VMI with CS agreement, which is capable of reducing the traditional inventory holding costs and, for some values of given parameters, the GHG emissions tax and penalty costs.

A joint economic lot size model with price and environmentally sensitive demand

This paper presents a joint economic lot size (JELS) model for coordinated inventory replenishment decisions considering price and environmentally sensitive demand. It assumes a single product that flows along a two-level supply chain (vendor–buyer). The buyer’s demand is linear and sensitive to the product’s price and its environmental performance. A capital investment is considered necessary to improve the production process resulting in an indirect improvement of the product’s environmental quality. A mathematical model is developed to represent this situation and solved to maximize the total profit of the supply chain for: (1) the vendor’s production lot size quantity and the number of shipments to the buyer, and (2) the selling price and the amount invested to improve the production process. Numerical examples are provided with their results discussed.

Multi-product economic lot scheduling problem with manufacturing and remanufacturing using a basic period policy

In this research we study the multi-product Economic Lot Scheduling Problem (ELSP) with manufacturing and remanufacturing opportunities. Manufacturing and remanufacturing operations are performed on the same production line. Both manufactured and remanufactured products have the same quality thus they fulfil the same demand stream. Tang and Teunter (2006) firstly studied this type of Economic Lot Scheduling Problem with Returns (ELSPR) and presented a complex algorithm for the optimal solution. More recently Teunter, Tang, and Kaparis (2009) proposed several heuristics to deal with the same problem using more computational efficient approaches. However, both studies have limited the attention to the common cycle policy with the assumption that a single (re)manufacturing lot is used for each item in each cycle. Relaxing the constraint of common cycle time and a single (re)manufacturing lot for each item in each cycle, we propose a simple, easy to implement algorithm, based on Segerstedt (1999), to solve the model using a basic period policy. Several numerical examples show the applicability of the algorithm and the cost savings.

A joint economic lot size model with third-party processing

A joint economic lot size model with third-party processing is studied.Aim of this work is to analyse the performance of different supply chain configurations.Results show that adopting a coordination policy between Vendor and Manufacturer can lead to a total cost saving.Results show that VMI with CS policy can additionally improve such results. This contribution presents a production-inventory model for a supply chain that incorporates three distinct entities a Vendor, a third-party external Manufacturer and a Buyer. The Vendor purchases raw materials from a supplier and performs preliminary manufacturing operations, the semi-finished goods are sent to a third-party Manufacturer for additional manufacturing operations then the products are sent back to the Vendor for final operations or assembly with other components and finally they can be sold to the customer. The study of this particular Supply Chain configuration has been inspired by an industrial case observed in the aeronautical sector.The aim of this work is to analyse the performance of different supply chain configurations with third-party processing for operations carried out by the Manufacturer. The first option is to consider a traditional production-inventory system where the Vendor and the Manufacturer follow a centralised traditional agreement policy. The second option involves a centralised Vendor Managed Inventory policy with consignment stock agreement between the Vendor and the Manufacturer. The objective is to determine the optimal lot size policy, i.e. traditional agreement or consignment stock agreement, in order to minimize supply chain total cost.Finished goods are assumed to have price-independent deterministic demand, while cost components are assumed to be constant over time. The analysis is carried out considering system total cost as the objective function to be minimized.

Supply chain network design under uncertain demand: robust and stable optimisation approaches

This paper is focused on the design of a supply chain taking into account the variability of the final customer demand: the traditional strategy for the network configurations so as to face such uncertainty, named robust approach, to seek the minimum expected total cost over the planning horizon. The novelty of this contribution resides in the investigation of an alternative way to face the uncertainty, named stable approach, which aim is to determine the minimum variability of transport and handling cost in the considered time horizon. The goal is the definition of the network configuration that can efficiently operate under the uncertainty of the customer demand, to this extent the solutions of the robust and the stable approaches have been compared. A numerical analysis has been performed over a realistic case study data and results of robust and stable and hybrid solutions have been reported.

Integrated Energy Value Analysis: A New Approach

The improvement of energy efficiency of 20 % is one of the three objectives of the EU Directive 20-20-20. To reach this goal, all production processes have to be analysed with reference to their energy consumption so as to identify actions aimed at removing or reducing energy wastes. From the Lean Production framework, the variation of the Value Stream Mapping (VSM), the Energy VSM (EVSM) is selected as a useful tool able to highlight the seven types of wastes identified by Ohno in Toyota Production System and energy wastes. This work aims at proposing a possible modification of the EVSM, which encompasses it within the Energy Audit and the Energy Balance Chart. The goal is to realize a deep energy analysis, highlighting energy wastes, in order to understand which corrective actions must be implemented or which corrections to energy reduction should be considered to reduce energy wastes.

Long Term Analysis of Energy Payback Time for PV Systems

The energy payback performance of an energy generating technology such as PV, is usually based on a single system considering static parameters for its evaluation. However it is recognized that performances of an installed systems decrease over time, while, on the other hand, the performances of new systems is expected to slightly increase over time. Additionally the energy required for manufacturing a new system has decreased significantly in the last years and additional decrease is expected in the near future; moreover the opportunity to recycle materials from dismantled PV installations is becoming massively investigated and some technologies are already on industrial scale. These dynamic aspects inspired the present work that firstly consider the calculation of the energy payback of PV systems that should drive the most sustainable decision regarding the optimal timing for dismissing of an old PV system and replacement with a new one.