Yazar "Yildiz, Mehmet Selami" seçeneğine göre listele

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    Determination of the optimal warranty policy and period from the manufacturer's/seller's perspective
    (Taylor & Francis Inc, 2021) Mutlu, Hakan Tahiri; Yildiz, Mehmet Selami
    This study aims to determine the most appropriate warranty period and policy with the lowest warranty cost from the manufacturer/seller point of view. The warranty policy to be put forward and the warranty period to be offered under this policy should ensure customer satisfaction while at the same time causing a minimum cost to the manufacturer/seller. For this reason, the optimum warranty period within the scope of Free-Replacement Warranty (FRW) policy, Pro-Rata Warranty (PRW) policy, and Combined FRW/PRW policy which was the combination of those two warranty policies were tried to be determined. In the study which was done to determine the most appropriate warranty period, economic benefit and the benefit function obtained from warranty cost and dissatisfaction cost functions were used. While obtaining necessary formulas, exponential distribution, which was widely used in life tests as density function and gamma and inverse-gamma functions as prior distribution of the exponential distribution were used. To demonstrate the applicability and flexibility of the model, some typical sales models and numerical values for exponential lifetime distribution were used, and an algorithm was created to find the optimal solution. When all of the results were analyzed it was seen that Combined FRW/PRW policy was the most appropriate warranty cost as a result of testing the models obtained and it was also found that the warranty cost was almost 3% of the sale price. Within the frame of these obtained results, Combined FRW/PRW policy was suggested for the warranty service to be served with the product to the manufacturer/seller. If the warranty period number of revolutions were chosen almost g1=0.054., g2=0.120. the warranty cost will be in the minimum level and it will be almost 3% of the product sale price. The validity and accuracy of the proposed strategy was verified by a case study with a numerical sample providing a scientific basis.
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    Statistical Process Control Methods For Determining Defects of Denim Washing Process: A Textile Case From Turkey
    (Ege Univ, 2020) Ata, Serhat; Yildiz, Mehmet Selami; Durak, Ismail
    The denim garments, which are made with many different sewing patterns, are given the final appearance by applying industrial washing processes and these are turned into high value-added fashion products. In this study, denim fabric control performed in a textile company, washing department after weaving for one month was investigated and as a result, washing defects are examined by using statistical methods. Pareto analysis, cause and effect diagram, and P control graphs, which are statistical process control methods, were used to classify the defects seen as a result of quality control. In Pareto analysis, chemical repair (20, 52 %), blue floor (19, 86 %), chemical intensive (19, 56 %), light floor (10, 71 %), deep floor (7, 95%) are in first five places among 53 defects and account for 78, 6 % of total number of defects. Of the 53 defects encountered during the washing process, it is found that only five of these defects could be prevented during the washing process, thus reducing the total waste by about 80%. In cause and effect diagram, washing defects are divided into categories as chemical, foreground, intensity, repair, tinctorial and processual and sub-dimensions as causes are determined. In the Laney P control chart, all processes are determined under control.