Integrated production quality and condition-based maintenance optimisation for a stochastically deteriorating manufacturing system

This paper investigates the problem of optimally integrating production quality and condition-based maintenance in a stochastically deteriorating single- product, single-machine production system. Inspections are periodically performed on the system to assess its actual degradation status. The system is considered to be in ‘fail mode’ whenever its degradation level exceeds a predetermined threshold. The proportion of non-conforming items, those that are produced during the time interval where the degradation is beyond the specification threshold, are replaced either via overtime production or spot market purchases. To optimise preventive maintenance costs and at the same time reduce production of non-conforming items, the degradation of the system must be optimally monitored so that preventive maintenance is carried out at appropriate time intervals. In this paper, an integrated optimisation model is developed to determine the optimal inspection cycle and the degradation threshold level, beyond which preventive maintenance should be carried out, while minimising the sum of inspection and maintenance costs, in addition to the production of non-conforming items and inventory costs. An expression for the total expected cost rate over an infinite time horizon is developed and solution method for the resulting model is discussed. Numerical experiments are provided to illustrate the proposed approach

A framework for real-time product quality monitoring system with consideration of process-induced variations

Department of Human and Systems EngineeringAs industrial technologies develop, the manufacturing industry is globally changing in more automated and complex manners, and the prediction of real-time product quality has become an essential issue. Although many of the physical manufacturing activities are getting more automated than ever, there still exist many uncovered parameters that, either directly or indirectly, affect the product quality. In many manufacturing sites, the quality tests in their processes still rely on few skilled operators and quality experts, which requires a lot of time and human efforts to manage the product quality issues. In this thesis, thus, a real-time/in-process quality monitoring system for small and medium size manufacturing environments is proposed to provide the data-driven product quality monitoring system framework. The proposed framework consists of a product quality ontology model for complex manufacturing supply chain environments, and a real-time quality prediction tool using the support vector machine (SVM) algorithm that enables the quality monitoring system to classify the product quality patterns from the in-process production data. Additionally, we propose a framework for analysis of the quality inspection results from the monitoring system with respect to quality costs, including inspection and warranty costs. In addition, this thesis establishes a relationship between the warranty cost and the severity of customer-perceived quality. Finally, we suggest a future work that a prescriptive product quality assessment concept using the Hidden Markov Models (HMM) that analyze and forecast possible future product quality problems using production data from manufacturing processes based on data flow analysis. Also, a door trim production data in an automotive company is illustrated to verify the proposed quality monitoring/prediction model.ope

A study in joint maintenance scheduling and production planning

Master'sMASTER OF ENGINEERIN

A Comprehensive Methodology for Assessing the Quality of Solar Photovoltaic Systems

The goal of this project was to assist the Alternative Technology Association by providing an enhanced assessment methodology for solar photovoltaic systems, emphasizing the development of a quantifiable evaluation of reliability and performance. To realize this goal, we interviewed industry leaders, surveyed solar consumers, and researched factors affecting solar photovoltaic system quality. The project resulted in a more comprehensive assessment methodology to aid the ATA in providing consultations that examine the value of solar photovoltaic systems

Search, Obfuscation, and Price Elasticities on the Internet

We examine the competition between a group of Internet retailers that operate in an environment where a price search engine plays a dominant role. We show that for some products in this environment, the easy price search makes demand tremendously price-sensitive. Retailers, though, engage in obfuscation---practices that frustrate consumer search or make it less damaging to firms---resulting in much less price sensitivity on other products. We discuss several models of obfuscation and examine its effects on demand and markups empirically. Observed markups are adequate to allow efficient online retailers to survive.

Electronic Part Total Cost Of Ownership And Sourcing Decisions For Long Life Cycle Products

The manufacture and support of long life cycle products rely on the availability of suitable parts from competent suppliers which, over long periods of time, leaves parts susceptible to a number of possible long-term supply chain disruptions. Potential supply chain failures can be supplier-related (e.g., bankruptcy, changes in manufacturing process, non-compliance), parts-related (e.g., obsolescence, reliability, design changes), logistical (e.g., transportation mishaps, natural disasters, accidental occurrences) and political/legislative (e.g., trade regulations, embargo, national conflict). Solutions to mitigating the risk of supply chain failure include the strategic formulation of suitable part sourcing strategies. Sourcing strategies refer to the selection of a set of suppliers from which to purchase parts; sourcing strategies include sole, single, dual, second and multi-sourcing. Utilizing various sourcing strategies offer one way of offsetting or avoiding the risk of part unavailability (and its associated penalties) as well as possible benefits from competitive pricing. Although supply chain risks and sourcing strategies have been extensively studied for high-volume, short life cycle products, the applicability of existing work to long life cycle products is unknown. Existing methods used to study part sourcing decisions in high-volume consumer oriented applications are procurement-centric where cost tradeoffs on the part level focus on part pricing, negotiation practices and purchase volumes. These studies are commonplace for strategic part management for short life cycle products; however, conventional procurement approaches offer only a limited view for parts used in long life cycle products. Procurement-driven decision making provides little to no insight into the accumulation of life cycle cost (attributed to the adoption, use and support of the part), which can be significantly larger than procurement costs in long life cycle products. This dissertation defines the sourcing constraints imposed by the shortage of suppliers as a part becomes obsolete or is subject to other long-term supply chain disruptions. A life cycle approach is presented to compare the total cost of ownership of introducing and supporting a set of suppliers, for electronic parts in long life cycle products, against the benefit of reduced long-term supply chain disruption risk. The estimation of risk combines the likelihood or probability of long-term supply chain disruptions (throughout the part's procurement and support life within an OEM's product portfolio) with the consequence of the disruption (impact on the part's total cost of ownership) to determine the "expected cost" associated with a particular sourcing strategy. This dissertation focuses on comparing sourcing strategies used in long life cycle systems and provides application-specific insight into the cost benefits of sourcing strategies towards proactively mitigating DMSMS type part obsolescence

Long-term reliability of photovoltaic c-Si modules - A detailed assessment based on the first Italian BIPV project

Assessing the long-term reliability of PV systems is important for understanding their energy and cost efficiency. Typically, estimates and predictions are based on indoor tests and accelerated ageing. However, fluctuating and differently interacting outdoor factors such as solar radiation, dust, and shadowing in real environment can impact the actual performance. This paper examines alterations related to ageing of c-Si PV modules, firstly by classifying the main factors that affect aged c-Si PV modules and then assessing the impact on their performance degradation by analysing a pilot BIPV system at Politecnico di Milano after 20 years of actual operation. Such system, which is highly representative since is the first public BIPV plant funded in Italy, was carefully and continuously monitored during its operating life. In particular, according to the visual/IR inspection carried out after the 20th year of operation, the main observed alteration in the modules were discoloration of the encapsulant, delamination, and chalking of the backsheet. The I-V characterization shown that all sampled modules had an overall degradation rate of less than 20 %, which is within the warranty limit, although in many cases the degradation rate over time shows a non-linear trend. Only one module experienced a severe fault that caused the complete loss of functionality. Obtained results confirm the reliability of c-Si technology, stressing the importance of a careful monitoring especially after the 15th year, when an increase of the degradation rate might occur

Reputations, Relationships and the Enforcement of Incomplete Contracts

This paper discusses the literature on the enforcement of incomplete contracts. It compares legal enforcement to enforcement via relationships and reputations. A number of mechanisms, such as the repeat purchase mechanism (Klein and Leffler (1981)) and efficiency wages (Shapiro and Stiglitz (1984)), have been offered as solutions to the problem of enforcing an incomplete contract. It is shown that the efficiency of these solutions is very sensitive to the characteristics of the good or service exchanged. In general, neither the repeat purchase mechanism nor efficiency wages is the most efficient in the set of possible relational contracts. In many situations, total output may be increased through the use of performance pay and through increasing the quality of law.contract, law and economics, reputation, repeated games, incomplete contracts, transactions costs, institutional economics, contract enforcement

Optimised solder interconnections in crystalline silicon (c-Si) photovoltaic modules for improved performance in elevated temperature climate

A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.The operations of c-Si PV modules in elevated temperature climates like Africa and the Middle East are plagued with poor thermo-mechanical reliability and short fatigue lives. There is the need to improve the performance of the system operating in such regions to solve the grave energy poverty and power shortages. Solder interconnection failure due to accelerated thermo-mechanical degradation is identified as the most dominant degradation mode and responsible for over 40% of c-Si PV module failures. Hence the optimisation of c-Si PV module solder interconnections for improved performance in elevated temperature climate is the focus of this research. The effects of relevant reliability influencing factors (RIFs) on the performance (thermo-mechanical degradation and fatigue life) of c-Si PV module solder interconnections are investigated utilising a combination of ANSYS finite element modelling (FEM), Taguchi L25 orthogonal array and analytical techniques. The investigated RIFs are operating temperature, material combination and interconnection geometry. Garofalo creep relations and temperature dependent Young’s Modulus of Elasticity are used to model solder properties, EVA layer is modelled as viscoelastic while the other component layers are modelled using appropriate constitutive material models. Results show that fatigue life decays with increases in ambient temperature loads. A power function model =721.48−1.343, was derived to predict the fatigue life (years) of c-Si PV modules in any climatic region. Of the various ribbon-contact material combination models investigated, Silver-Silver, Aluminium-Aluminium, Silver-Aluminium and Aluminium-Silver are the top four best performing solder interconnection models with low deformation ratios, , normalised degradation values, 1. Further findings indicate that only the solder layer demonstrates good miniaturisation properties while the standard dimensions for ribbon and contact layers remain the best performing geometry settings. Additionally, from the Taguchi robust optimisation, the Aluminium-Silver ribbon-contact material combination model (ribbon = 180μm, solder = 56μm, contact = 50μm) demonstrated the best performance in elevated temperature climate, reduced solder degradation by 95.1% and is the most suitable substitute to the conventional c-Si PV module solder interconnection in elevated temperature climate conditions – in terms of thermo-mechanical degradation. These findings presented provide more insight into the design and development of c-Si PV modules operating in elevated temperature climates by providing a fatigue life prediction model in various ambient conditions, identifying material combinations and geometry which demonstrate improved thermo-mechanical reliability and elongated fatigue life.Schlumberger Faculty for the Future Foundation (FFTF