1,721,004 research outputs found
Improving Tool-Life Stochastic Control Through a Tool-Life Model Based on Diffusion Theory
No full textIt is known that estimating the wear level at a future time instant and obtaining an updated evaluation of the tool-life density is essential to keeping machined parts at the desired quality level, reducing material waste, increasing machine availability, and guaranteeing the safety requirements. In this regard, the present paper aims at showing that the tool-life model that Braglia and Castellano [23] developed can be successfully adopted to probabilistically predict the future tool wear and to update the tool-life density. Thanks to the peculiarities of a stochastic diffusion process, the approach presented allows deriving the density of the wear level at a future time instant, considering the information on the present tool wear. This makes it therefore possible updating the tool-life density given the information on the current state. The method proposed is then experimentally validated, where its capability to achieve a better exploitation of the tool useful life is also shown. The approach presented is based on a direct wear measurement. However, final considerations give cues for its application under an indirect wear estimate
Diffusion theory applied to tool-life stochastic modeling under a progressive wear process
No full textIn this paper a novel approach to the derivation of the tool-life distribution, when the tool useful life ends after a progressive wear process, is presented. It is based on the diffusion theory and exploits the Fokker-Planck equation. The Fokker-Planck coefficients are derived on the basis of the injury theory assumptions. That is, tool-wear occurs by detachment of small particles from the tool working surface, which are assumed to be identical and time-independent. In addition, they are supposed to be small enough to consider the detachment process as continuous. The tool useful life ends when a specified total volume of material is thus removed. Tool-life distributions are derived in two situations: (i) both Fokker-Planck coefficients are time-dependent only, and (ii) the diffusion coefficient is neglected and the drift is wear-dependent. Theoretical results are finally compared to experimental data concerning flank wear land in continuous turning of a C40 carbon steel bar adopting a P10 type sintered carbide insert. The adherence to the experimental data of the tool-life distributions derived exploiting the Fokker-Planck equation is satisfactory. Moreover, the tool-life distribution obtained when the diffusion coefficient is neglected and the drift is wear-dependent is able to well-represent the wear behavior at intermediate and later times
A novel operational approach to equipment maintenance: TPM and RCM jointly at work
No full textPurpose: The purpose of this paper is to present a new operational approach to equipment maintenance designed to exploit the complementary nature of total productive maintenance (TPM) and reliability-centered maintenance (RCM). Design/methodology/approach: This paper focuses on the operational aspect of the maintenance practice, proposing an equipment maintenance methodology that can be suitably adopted to define a new maintenance plan or check and improve an existing one. It integrates principles and methods of TPM and RCM and uses different tools to support decision-makers and operators. It proposes several worksheets which facilitate planning and implementing maintenance activities, that range from autonomous maintenance tasks to maintainability improvement actions. Findings: This paper exploits the complementary nature of TPM and RCM to design or improve maintenance plans for a generic system. The tools and worksheets presented can be helpful to practitioners and operators. Originality/value: While the integration of TPM and RCM is evidently a central issue in the maintenance management context, it has received limited attention in literature. To the best of the authors’ knowledge, it lacks a structured practical equipment maintenance methodology that exploits the complementary nature of TPM and RCM. Therefore, the approach presented in this paper would fill the current gap
A study on the importance of selection rules within unbalanced MTO POLCA-controlled production systems
No full textThe present paper is aimed at investigating, through simulation, the behaviour of the POLCA method when a Make-to-Order (MTO) production system is highly unbalanced, in terms of both routings and times. In particular, the study is addressed to verify (i) the effective capability of the POLCA method to improve the uncontrolled system and (ii) the impact of how orders are processed at each workstation, to show that POLCA performance can be further improved in such circumstances by adopting an appropriate selection rule. Germs and Riezebos (2010) proved that POLCA is very effective in reducing the Total Throughput Time (TTT) with respect to the corresponding unconstrained production systems. Owing to this, it appears evident that POLCA represents a valuable and effective Make-to-Order (MTO) production control method. However, they only considered balanced systems, hence some observations must be carefully addressed. In fact, often, in real world applications, the systems to be controlled are designed to process units with very different routings, each with significantly different probability to occur
An extension of the stochastic joint-replenishment problem under the class of cyclic policies
No full textThis paper presents an extension of the Joint-Replenishment Problem under the class of cyclic policies. The developed model includes stochastic demands, backorders-lost sales mixtures, and controllable lead times. With the objective of minimizing total system cost, we propose two heuristics. Numerical experiments investigate the algorithms performance and the model sensitivity
An Integer Linear Programming Approach to Maintenance Strategies Selection
No full textPurpose - The paper presents a RCM embedded integer linear programming approach (suited to the budget monetary resources allocation task) to the maintenance strategies mix selection for an industrial plant equipments.
Design/methodology/approach - The developed approach allows to determine the optimal maintenance strategies mix for a set of equipments in a more quantitative way than the classic RCM approach. The proposed model takes into account, for each potential failure determined using the FMECA and for each admissible strategy, the costs and the potential RPN reduction. Finally, an industrial case concerning an Italian paper-mill plant is reported to demonstrate the effectiveness of the approach presented.
Findings - The paper finds that the application of the proposed approach allows to optimally allocate the budget monetary resources, determining which suitable maintenance practice apply to each failure, taking into account the costs of each strategy and the potential reduction of the RPN.
Practical implications - The proposed model permits to assign (during the budget monetary resources allocation task) to each failure the optimal strategy, among a set of suitable maintenance practices, considering the costs and the estimated RPN reduction.
Originality/value - The paper proposes a completely new RCM embedded approach to the maintenance strategies selection, in order to optimally allocate the budget monetary resources. This model overcomes the limits of the traditional RCM approach, taking into account quantitative aspects, i.e. the compatibility constraint between failures and policies, the maintenance strategies costs, and the RPN estimated reduction
A note concerning physical space occupation costs in Vendor Managed Inventory with consignment agreement models
No full textA new analytic formulation of the Vendor Managed Inventory with consignment agreement is proposed. It represents a modified and more realistic version of the model proposed in Braglia and Zavanella (2003). The evaluation of the stockholding related costs is herewith substantially revisited to consider the requirements of a standard VMI relationship with consignment agreement. In particular, the physical space occupation cost held by the buyer is introduced as a component of the overall holding cost and is referred to the maximum stock level, rather than to the average value, as proposed in the past literature. Finally, an implicit analytical solution is given and compared to the original one obtained by Braglia and Zavanella (2003)
Corrigendum to “Safety stock management in single vendor-single buyer problem under VMI with consignment stock agreement” [Int. J. Prod. Econ. 154 (2014) 16–31] (International Journal of Production Economics (2014) 154 (16–31), (S0925527314001224), (10.1016/j.ijpe.2014.04.007))
No full textSafety Stock Management in Single Vendor-Single Buyer Problem under VMI with Consignment Stock Agreement
No full textIn this paper a new analytical approach to safety stock management, within single buyer–single vendor framework under VMI with consignment agreement, is presented. In particular, the cost of the safety stock is evaluated adopting a logistic approximation of the standard normal cumulative distribution. The service level is put in relation to the dimension of the single shipment, to the average demand on the buyer and to the number of admissible stockouts. Once the mean joint total cost function is defined, on the basis of the model of Braglia and Zavanella, (2003. Int. J. Prod. Res. 41, 3793–3808) modified according to Braglia et al. (2014. Int. J. Logist. Syst. Manage. forthcoming 2014), a minimum cost solution (within a predefined domain) is derived. Moreover, a numerical study is carried out. First, a sensitivity analysis is shown. Then, the model of Braglia and Zavanella, (2003. Int. J. Prod. Res. 41, 3793–3808), in its original expression, is compared with both Hill (1997. Eur. J. Oper. Res. 97, 493–499), Hill (1999. Int. J. Prod. Res. 37, 2463–2475) and Hill and Omar (2006. Int. J. Prod. Res. 44, 791–800). In particular, the comparison considers the equal-sized shipments case without delayed deliveries taking into account different reciprocal values for the stockholding costs
A novel game theory based exit selection model in emergency conditions
No full textIn this paper, a new game theory based approach for the evacuees exit selection in emergency conditions is presented. It is founded on the theoretical concepts of multi-stage games with perfect information. In particular, an evacuee is a player and the available actions for a generic player are the accessible emergency exits. The developed mathematical model involves several psychological parameters, in order to make the emergency exit choice also affected by the individual character. Moreover, an evacuation simulation model incorporating this novel approach is shown. The model involves many other parameters and aspects attempting to obtain a satisfactory representation of the actual evacuation process and of the human behavior in emergency conditions. Finally, the effectiveness of the model is demonstrated with a simulative study
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