517 research outputs found
Supply Chain Innovation for Parts Inventory Optimisation
No full textThe Ph.D. project focuses on spare parts supply chain optimisation and it is related to the innovation of a European spare parts Supply Chain. The project first focused on the single warehouses, and then a global perspective was taken, looking at the whole supply chain.
In the local perspective, the optimisation of the operational processes was considered. The objective was the improvement of the service level/inventory trade-off. Three main phases of the inventory management have been considered: the forecasting process (i.e., the methods used to predict future unknown demand), the planning process (i.e., setting inventory targets and issuing replenishment orders to suppliers) and the allocation process (i.e., giving the available inventory to customers according to their orders and their priority). Various algorithms have been proposed to improve the single inventory for all the three phases, both for fast and slow moving products.
In the global perspective, we studied the demand variability propagation in the supply chain (i.e., the Bullwhip Effect), which is one of the main causes of inefficiency and of cost increase. The identification of the bullwhip effect and of its potential influencing factors were the main topics we focused on, both from an empirical and a theoretical point of view. From the empirical standpoint, we proved that dealers tend to decouple supply and demand and, when they are given incentives to forward-buy, they may prefer to forward-buy fast moving items, especially during the switches from promotional to non-promotional periods. Instead, from the theoretical point of view, we proved that not knowing the demand process parameters increases the bullwhip effect. Also, an analytical approximation of the bullwhip was derived
An effective approach for total completion time minimization subject to makespan constraint in permutation flowshops
No full textThis article addresses the permutation flowshop scheduling problem with the objective of minimizing the total completion time subject to a makespan constraint. The makespan is related to system utilization while the total completion time is related to the waiting time, and hence to the work in process (WIP); in real contexts, focusing on both total completion time and makespan allows a good trade-off between WIP and utilization to be found. Two local search algorithms are developed in the paper and, by using an extensive computational experience on literature benchmark instances, they are proved to be able to find good solutions both for regular and no-wait flowshops
Integrating machine scheduling and transportation resource allocation in a job shop: a simulation approach
No full textIn scheduling problems with fixed routing, usually the transportation of jobs among the machines is not considered (i.e., the transportation time between two stages is negligible, and the number of transportation resources is unlimited). However, in real contexts, this assumption can be unrealistic, especially when human supervision is needed for transportation, and hence not considering transportation can lead to low quality scheduling solutions. This paper considers a job shop in which transportation resources are limited and free to move among all the machines (no fixed routes). The aim is the integration of machine scheduling and transportation resource allocation, i.e., to decide for each machine the job sequence, and for each free transportation resource the routing. Due to the complexity of the problem, a Discrete Event Simulation approach is used to compare different scheduling and transportation resource allocation policies through scenario analysis
Dynamic inventory rationing: how to allocate stock according to managerial priorities. An empirical study
No full textAn empirical investigation on the antecedents of the bullwhip effect: Evidence from the spare parts industry
No full textSupply chain effectiveness and costs are affected by the demand variability, especially in the upstream echelons. The propagation of demand variability moving upstream in the supply chain has been widely studied in the literature and it is known as the Bullwhip Effect phenomenon. In this paper, the bullwhip effect in a European automotive spare parts chain is identified, with the aim of shedding some light on how demand variability propagates in different groups of products. We considered more than 30,000 products, characterised by different technical characteristics, demand classes and planning parameters.
The results showed that the considered supply chain is affected by the bullwhip effect. Additional analyses suggested that the bullwhip effect is larger for fast moving products rather than for slow movers. Hence, dealers tends to decouple supply and demand and, when they are given incentives to forward-buy, they may prefer to forward-buy fast moving items. Moreover, as the dealers tend,to exploit the promotional benefits by forward-buying in the final period of promotions, frequent switches from promotional to non promotional periods tend to increase the propagation of the demand variability
An empirical investigation of the bullwhip effect on a complex three-echelon supply chain
No full textExploring the interplay of costs and flow time in server allocation for flow lines with parallel non-identical machines
No full textThe Server Allocation Problem is a significant challenge in manufacturing systems involving deciding the number and version of machines for each stage. This optimization problem is of utmost importance when there is a trade-off between minimizing investment costs and flow time while achieving target performance, such as a minimum throughput. Manufacturing systems often employ hybrid flow lines, with non-identical machines at each stage. This paper analyzes the trade-off between minimizing costs and flow time when allocating servers in hybrid flow lines by proposing a bi-criteria approach that uses an efficient pattern-based problem representation and a Variable Neighborhood Search solution algorithm. The objectives are to minimize total cost and flow time while ensuring a target throughput. A metric for comparing obtained solutions is proposed, providing insights for practical implementation. A comprehensive numerical analysis is conducted, to validate the proposed approach and demonstrate its applicability in real-world manufacturing settings
Implementing Job Sequencing in a CONWIP fully automated assembly line
No full textElectric vehicle production poses several challenges from the manufacturing point of view due to the uncertainty in the price and availability of raw materials and the frequent fluctuations of market demand. Moreover, mass customisation requires flexible and reconfigurable manufacturing systems, while the automation of the assembly lines to achieve a higher throughput rate and the complexity of job handling require conveyors and carousels. This paper investigates the implementation of job sequencing policies through conveyor loops to improve the flexibility and reconfigurability of a realistic CONWIP assembly line while avoiding upstream and downstream variability propagation. Scenario analysis evaluates how different job sequencing strategies and WIP control can impact the average and standard deviation of the shift throughput, the average job flow time, and the probability of deadlocks on an assembly line for stators of electric engines
Circular economy at scheduling level: influencing factors and impacts on system performance
No full textIn manufacturing systems, Circular economy (CE) strategies to recover returned end-of-life prod-ucts can reduce raw material purchasing costs and lead times while improving environmental performance. However, CE strategies may undermine production planning, control, and inventory management activities, and there is a lack of scientific evidence about the impact on work-in-progress (WIP) and overall performance. This paper uses Discrete Event Simulation to analyse the factors influencing the exploitation of returned products under different CE strategies and priority rules. The experiments investigate the impacts on makespan, virgin raw material consumptions, and WIP at the scheduling level in a realistic production and assembly system where production is coupled with disassembly, repairing, remanufacturing, and reusing. The results highlight the importance of production control strategies in limiting the negative impacts of CE strategies on WIP, makespan,and materials consumption. Moreover, frequent rescheduling is required due to the high variability affecting the systems implementing CE strategies
Managing different demand classes in a spare parts inventory: a practical dynamic allocation strategy
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