Brass alloy blending problem from quality and cost perspectives: A multi-objective optimization approach

WOS:000595657400032Brass alloy is a composition of copper and zinc and it also includes lead, iron, tin, aluminum, nickel, antimony if necessary. One of the basic problems in brass casting is to determine which pure and scrap materials will be mixed at what quantities; this problem is known as the blending problem. The ingredient ratios of pure materials are exactly known, however they are expensive. The scrap materials are cheaper than the pure ones with varying ingredient ratios. Stochastic mathematical models aiming to minimize blend cost have been developed in the literature. In the solutions of these models, some of the ingredient ratios exactly equal to the specification limits. Because of the variation, some of them may violate the specification limits and cause quality problems in the actual blends. There is only one study in the literature to solve the quality problem by maximizing the process capability index. However, the blend cost increases when the process capability index maximized. In this study, a multiobjective stochastic mathematical model, which aims both to minimize blend cost and to maximize process capability index, has been developed. The developed model has been converted to a deterministic non-linear counterpart by using chance-constrained programming. Then, fuzzy programming is used to transform the multiobjective model into a single objective one. A solution procedure has been proposed to use it effectively in real life applications. The developed model and solution procedure have been tested by the data supplied from a brass factory. The solution of the numerical example has shown that the developed model and solution procedure can be used successfully in real life applications

Estimating confidence lower bounds for Weibull percentiles

Birgoren, Burak/0000-0001-9045-6092WOS: 000184716300001

1999ネン トルコ セイブ ニ オコッタ ジシン ノ キョウシンドウ シミュレーション : トクセイカ シンゲン モデル ト イソウ イソン サイト オウトウ オ コウリョシタ トウケイテキ グリーン カンスウホウ

京都大学0048新制・課程博士博士(理学)甲第10630号理博第2772号新制||理||1403(附属図書館)UT51-2004-G477京都大学大学院理学研究科地球惑星科学専攻(主査)教授 入倉 孝次郎, 教授 岡田 篤正, 助教授 赤松 純平学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

Confidence interval estimation of Weibull lower percentiles in small samples via Bayesian inference

Birgoren, Burak/0000-0001-9045-6092WOS: 000400531500024Weibull distribution has been vastly used for modeling fracture strength of ceramic and composite materials. Confidence interval estimation of Weibull parameters and percentiles in small samples has been an important concern due to high experimental costs. It was shown previously that in classical inference the Maximum Likelihood Estimation Method is the best method among several alternatives for estimating 95% one-sided confidence lower bounds on the 1st and 10th Weibull percentiles, namely A-basis and B-basis material properties. This study proposes the Bayesian Weibull Method as an alternative using the information that ceramic and composite materials have increasing failure rates, which requires the Weibull shape parameter to be at least 1. Through Monte Carlo simulations, it is shown that the performance of the Bayesian Weibull Method is superior in that it achieves the precision levels of the Maximum Likelihood Estimation Method with significantly smaller sample sizes. (C) 2017 Elsevier Ltd. All rights reserved

A computer simulation for estimating lower bound fracture strength of composites using Weibull distribution

Birgoren, Burak/0000-0001-9045-6092WOS: 000220303300008Estimating confidence lower bound for fracture strength of composites is a key concern in design and manufacture, and the Weibull distribution has been widely used for this purpose. Previous simulation-based studies presented computational tools for these bounds involving tables or parametric equations, which lack generality and may contain simulation and curve-fitting errors. An alternative approach is to present a fast and effective simulation tool that can be directly used by the end-user. Such a tool is developed in this study for estimating the bounds using the Weibull distribution based on maximum likelihood estimation. This is a more versatile approach in that it allows the user to input any desired confidence level, failure probability, and simulation-run number. The tool is demonstrated by using fracture strength data obtained from ASTM D3039 tension tests of 19 identical carbon-epoxy composite specimens. The results are compared with those obtained from previously developed approaches. (C) 2004 Elsevier Ltd. All rights reserved

Joint optimization of quality and cost in brass casting using stochastic programming

Birgoren, Burak/0000-0001-9045-6092WOS: 000488498300001A critical process in brass casting is the blending of pure and scrap materials to satisfy specified metal ratios. The primary focus in such blending problems has always been cost minimization. The optimal blends produced by mathematical models use large amounts of scrap materials, which are cheaper but have high variations in ingredient ratios. This gives rise to quality problems. This study aims at joint optimization of cost and quality. A chance-constrained nonlinear mathematical model is developed for maximizing the minimum process capability level for a fixed cost. Then parametric programming is used to run the model for different costs to produce a Pareto-optimal frontier. An application to data from a brass factory showed that the frontier is highly nonlinear, enabling the decision maker to select a competitive process capability and cost value combination. The proposed approach is applicable to any blending problem in which ingredient amounts have statistical variation

Estimating confidence lower bounds of Weibull lower percentiles with small samples in material reliability analysis

WOS: 000514814600023Weibull distribution is widely used in the modeling of mechanical properties such as tensile strength of ceramic and composite materials. The 95% one-sided confidence lower bounds on the 1st and 10th Weibull percentiles, namely A-basis and B-basis material properties, are important in reliability studies for understanding early failures and reducing risks. These lower bounds are generally estimated by small samples due to the high costs of the experiments, hence the precision of estimation remain low. Therefore, in the literature, many exact and approximate interval estimation methods for Weibull percentiles have been proposed for achieving better performance. In this study, a comprehensive comparison of the exact methods with Monte-Carlo simulations has been made. In addition, some methods developed for Weibull parameters are also included in this comparison since they can be used for exact lower bound estimation but have never used for this purpose in the literature. In the study, the lower bounds have been estimated by the maximum likelihood method, the Menon method and 25 different models of weighted/ unweighted least squares methods (such as improved estimators, interchanged axes), and average false coverage probabilities are used for the comparison criterion. According to the simulation results, the maximum likelihood and the weighted least squares method with Faucher & Tyson weight factors have very similar performances for sample sizes less than 8; and the maximum likelihood method has always shown the best performance for sample sizes greater than or equal to 20. However, it is emphasized that linear regression methods are more practical in terms of ease of calculation when performance differences are negligibl

The relationship between entrepeneurial management and financial performance: Evidence from the hotel industry in Canakkale Region

It is aimed in this study to present the relationship between the entrepreneurial management (i.e. the management philosophy of an organization's overall internal management systems and organizational processes encouraging strategic agility, flexibility, creativity and continuous innovation, which lets the organization follow a selected marketing strategy and play the 'game' better than its competitors/dictates its 'game') and financial performance. With a literature review, an empirical study has been conducted on hotel businesses in Canakkale Region in Turkey with Pearson and Spearman Correlations as well as multiple linear regressions to present the relationships between entrepreneurial management, which aims to stimulate all individuals, regardless of their hierarchial levels, in an organization to think and act like entrepreneurs to achieve above-average returns in the long run, and financial performance. The study reveals that there is a positive relationship between strategic orientation with satisfaction of overall financial performance, ROE and change in assets; resource orientation with satisfaction of overall financial performance and ROE; reward system with satisfaction of overall financial performance, ROI, change in sales, net profit margin, net profit level, net profit from operations and ability to fund growth as well as entrepreneurial culture with ROI and change in sales. Furthermore, the findings suggest that growth orientation is the most important variable to contribute the financial performance

A spreadsheet-based decision support tool for blending problems in brass casting industry

35th International Conference on Computers and Industrial Engineering -- JUN 19-22, 2005-2006 -- Istanbul, TURKEYBirgoren, Burak/0000-0001-9045-6092WOS: 000264037900018This paper has discussed development and implementation of spreadsheet-based decision support tools for modeling and solving blending problems in a large-scale brass factory in Turkey. The user interfaces have been designed in Microsoft Excel which is linked with Lingo modeling language and optimizer. One decision support tool was developed from a single-blend LP model and has been in use at the foundry; it is run several times a day by foremen to obtain optimal raw material quantities for melting operations. That the users were foremen without any engineering and optimization background posed a serious challenge to produce a decision support tool that is easily applicable at the foundry, for which spreadsheet interfaces have produced an effective solution. The paper has elaborated on difficulties faced in the development and implementation and their solutions as well as design of the interface. A similar tool has also been developed for master production planning, which has not been put to use yet. Issues have been discussed regarding its integration into the production planning system and its relationship with the single-blend tool. (C) 2008 Elsevier Ltd. All rights reserved

MODELING AND ANALYZING CUSTOMER DATA IN CUSTOMER RELATIONSHIP MANAGEMENT WITH ARTIFICIAL NEURAL NETWORKS

Birgoren, Burak/0000-0001-9045-6092WOS: 000273014200003Customers must keep customer satisfaction as a top priority in order to keep up with increasing competition. In order to achieve, they need to be able to analyze their customers properly and pay attention to their individual expectations. It is important for companies to maximize customer satisfaction and dependence. The success of Companies depends on the extent to how they manage to become 'indispensable' for their customers. It is related with how they determine important points for the satisfaction of their customers, and reflect it back accordingly. In order to make this assessment, companies must first consider their customers as groups. This study aims to analyze customer information, by artificial neural networks, which cannot be handled by mathematical models and optimization techniques, thus improve marketing process for determining important factors and their levels for customer satisfaction