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Process control using reliability based control charts

Jacob J. K., Sreejith P. S.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

498-504

EN

Purpose: The paper presents the method to monitor the mean time between failures (MTBF) and detect any change in intensity parameter. Here, a control chart procedure is presented for process reliability monitoring. Control chart based on different distributions are also considered and were used in decision making. Results and discussions are presented based on the case study at different industries. Design/methodology/approach: The failure occurrence process can be modeled by different distributions like homogeneous Poisson process, Weibull model etc. In each case the aim is to monitor the mean time between failure (MTBF) and detect any change in intensity parameter. When the process can be described by a Poisson process the time between failures will be exponential and can be used for reliability monitoring. Findings: In this paper, a new procedure based on the monitoring of time to observe r failures is also proposed and it can be more appropriate for reliability monitoring. Practical implications: This procedure is useful and more sensitive when compared with the λ-chart although it will wait until r failures for a decision. These charts can be regarded as powerful tools for reliability monitoring. λr gives more accurate results than λ-chart. Originality/value: Adopting these measures to system of equipments can increase the reliability and availability of the system results in economic gain. A homogeneous Poisson process is usually used to model the failure

2

Need for incorporating reliability and availability in payback calculations

Shouri P. V., Sreejith P. S.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

816-821

EN

Purpose: The paper presents a method of payback calculation based on the process valuation model by incorporating reliability and availability. The paper also presents a comparison of calculation of payback periods using the conventional method with the method that uses the valuation model. Design/methodology/approach: The value of the system is arrived by considering the present worth of expected future cash flows. The model takes into consideration the system availability, in addition to the other cost elements like investment cost, and maintenance as well as operating cost. Findings: Calculation of pay back using valuation model was compared with the conventional method. The valuation model method proves to be a better tool in making safe decisions. Practical implications: In order to arrive at the economic feasibility of the new proposal the benefits that can be derived over the lifetime as well as the operating and maintenance costs are compared with the investment to be made. However, quite often the change in reliability of the proposed new design as a result of the change in system configuration or change in system components or both of these factors are not taken into consideration. Originality/value: Any new proposal for modification of the existing process or equipments should prove itself to be economically feasible for gaining acceptance for implementation.

3

Cell attachment on ion implanted titanium surface

Sreejith P. S., Yarlagadda P. K.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 31, nr 2

373-377

EN

Purpose: Of outmost importance for the successful use of an implant is a good adhesion of the surrounding tissue to the biomaterial. In addition to the surface composition of the implant, the surface topography also influences the properties of the adherent cells. In the present investigation, ion implanted and untreated surfaces were compared for cell adhesion and spreading. Design/methodology/approach: The surface topography of the surfaces were analyzed using AFM and the cell studies with SEM. Findings: The results of our present investigation is indicative of the fact that ion implanted titanium surface offer better cell binding affinity compared to untreated/polished surface. Practical implications: Success of non-biodegradable implants will first and foremost depend on biocompatibility, followed by the capacity of the surface topography of the implants to evince desired cell matrix, surface cell matrix interactions. In the present study, the cell growth on ion implanted Ti material is analyzed and discussed. Originality/value: In this paper, we have utilized ion implantation technique, which will produce nano-texturing of the surface without producing any detrimental effects to both the dimensions and properties of the implants.