An ensemble-learning model for failure rate prediction

n/

conwip card setting in a flow shop system with a batch production machine

A B S T R A C T This paper presents an analytical technique to determine the optimum number of cards to control material release in a CONWIP system. The work focuses on the card setting problem for a flow-shop system characterised by the presence of a batch processing machine (e.g. a kiln for long heat treatment). To control production, two different static approaches are developed: the first one is used when the bottleneck coincides with the batch processing machine and the second one is proposed when the bottleneck is another machine of the flow shop. In both contexts, by means of the appropriate model, one can optimize the performance of the flow- shop by maximizing the throughput and keeping the work in process at a minimum level. Numerical examples are also included in the paper to confirm the validity of the models and to demonstrate their practical utility

Stochastic overall equipment effectiveness

International audienceThis paper focuses on the Overall Equipment Effectiveness (OEE), a key performance indicator typically adopted to support Lean Manufacturing and Total Productive Maintenance. Unfortunately, being a deterministic metric, the OEE only provides a static representation of a process, but fails to capture the real variability of manufacturing performances. To take into account the stochastic nature of the OEE, an approximated procedure based on the application of the Central Limit Theorem is presented: the OEE is considered as a stochastic random variable and its probability density function (pdf) is generated through the aggregation of the pdf of the basic causes of waste. Notwithstanding its approximated nature, the procedure can be applied in most practical cases, since the accuracy is assured provided that the average OEE is lower than 90% and the variability of the losses is high. The validity of the approach has been also confirmed by an industrial application included in the paper. Obtained results demonstrate that the Stochastic OEE can help in battling variation, for it allows to identify the hidden losses that account for most of the variability and to estimate the impacts of potential corrective actions in terms of both efficiency and efficacy

Safety Stock Management in Single Vendor-Single Buyer Problem under VMI with Consignment Stock Agreement

In 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

The House of Reliability

Purpose – The purpose of this paper is to provide a structured methodology for performing build-in reliability (BIR) investigation during a new product development cycle. Design/methodology/approach – The methodology in this paper represents an extension of the Quality Functional Deployment/House of Quality (QFD/HoQ) concepts to reliability studies. It is able to translate the reliability requisites of customers into functional requirements for the product in a structured manner based on a Failure Mode And Effect Analysis (FMEA). Besides, it then allows it to build a completely new operative tool, named House of Reliability (HoR), that enhances standard analyses, introducing the most significant correlations among failure modes. Using the results from HoR, a cost-worth analysis can be easily performed, making it possible to analyse and to evaluate the economical consequences of a failure. Findings – The paper finds that the application of the proposed approach allows users to identify and control the design requisites affecting reliability. The methodology enhances the reliability analysis introducing and managing the correlations among failure modes, splitting the severity into a detailed series of basic severity aspects, performing also cost/worth assessments. Practical implications – It is shown that the methodology enables users to finely analyse failure modes by splitting severity according to the product typology and the importance of each Severity criterion according to laws or international standards. Moreover the methodology is able to consider the “domino effects” and so to estimate the impact of the correlation between the causes of failure. Finally a cost/worth analysis evaluates the economical consequences of a failure with respect to the incurred costs to improve the final reliability level of the product. Originality/value – The paper proposes a completely new approach, robust, structured and useful in practice, for reliability analysis. The methodology, within an integrated approach, overcomes some of the largely known limits of standard FMECA: it takes into account multiple criteria, differently weighted, it analyses the product considering not only the direct consequence of a failure, but also the reaction chain originated by a starting failure

An Integer Linear Programming Approach to Maintenance Strategies Selection

Purpose - 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

A 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)

Optimization of POLCA controlled production systems with a simulation-driven Genetic Algorithm

The present work is meant to show the effective capability of optimizing an unbalanced Paired-Cell Overlapping Loops of Cards with Authorization (POLCA)-controlled production system by means of a heuristic algorithm. This objective is suggested by the fact that one of the most significant issues when using card-driven production control systems is represented by the optimized setting of the large number of cards within the control loops. This is particularly true in the case of unbalanced systems, where the number of cards may vary significantly among the different loops. Little law is usually adopted in literature to infer this number from historical data, but the obtained number is usually far from the optimum. Indeed, in real-world applications, the systems to be controlled are designed to process units with very different routings, each with different probability to occur. In all these situations, they result particularly difficult to set correctly. To this aim, in the present work a Genetic Algorithm is used. The objective is that of finding the correct number of cards and to reduce the overall Total Throughput Time and the average Work In Process. The proposed approach may provide a valid support tool to overcome these limitations, making the most of POLCA capabilities in many manufacturing configurations