V. Mariappan

Combined Taguchi and dual response method for optimization of a centerless grinding operation

Abstract Offline quality control has been widely accepted as a key to high quality products at low price. The concept of robust design using Taguchi methodology is versatile and its application is not limited to any specific area. However, Taguchi techniques have their own shortcomings. Other methodologies like dual response methodology for process optimization have also been used with success. This paper presents a successful application of combined Taguchi and dual response methodology to determine robust condition for minimization of out of roundness error of workpieces for centerless grinding operation. From the confirmation runs, it was observed that this approach led to successful identification of optimum process parameter values.

Multiple response optimization for improved machined surface quality

Abstract Work material and cutting and tool parameters have a significant effect on the post-machining condition of a machined component. A case study from industry has been selected where it was observed that work hardening of machined surface leads to distortion of thin sections of the component. A multiple response optimization methodology has been used to identify robust cutting and tool parameter settings to minimize the variation and average value of the surface hardness and to minimize the depth of work hardening of the machined surface. The work material used is CuZn40Al2, which is also the material of the actual component.

Availability analysis of transmission system using Markov model

Technologically advanced transmission system operates economically only if a high rate of availability of the system is achieved. Therefore, it is very important to integrate the analysis of systems reliability and availability into the process of planning and designing the structure of a transmission system. This article discusses the availability modelling and analysis of transmission lines. As the failure phenomenon is stochastic and data analysis reveals negative exponential behaviour, Markov model has been found more appropriate in this study. The study involves live case of Goa Electricity Department. The code written in MATLAB 7.0 for data analysis is used for the Markov model. The Laplace transition matrix involved in stochastic modelling has been solved by using algorithm developed in MATLAB 7.0. Besides, failure interaction physically taking place in the field is also taken into account in the analysis. Component level failure mode effect analysis of extra high voltage transmission lines have also been developed and reported with appropriate results and discussions.

Integrated graphical model to evaluate multi-criteria maintenance policies for degradable systems

This paper deals with a system developed that will investigate on the (failure) data input of a given system to decide on its maintenance policies, specifically between breakdown maintenance and preventive maintenance (PM), which can restore the system either by repair or replacement as may be applicable. The system developed has the genesis of Kay’s work. Working on the basic limitations of Kay’s work, a complete system is developed as an integrated graphical tool to be suitable for degradable systems wherein repairing or replacement as applicable, considering three important criteria as suggested by Kay. After evaluating what type of maintenance is possible, the system developed optimizes for optimal period in case of PM is preferred. The algorithm involved in the development of the graphical tool is coded in Matlab 7.0 for in between Weibull shape parameters and numerical integration. The details of the research methodology and analytical issues involved are all presented appropriately in the paper. The system has been applied to four test cases and the utility of the tool has been explained through stepwise procedure and flow chart in the paper with appropriate results and discussions.

An integrated statistical analysis for process improvement

The paper deals with the implementation of Six Sigma methodology on manufacturing of shafts used in submergible pump. The paper showcases the study carried out on the grinding machine used in manufacturing process. The manufacturing unit was suffering from poor quality level due to high rejections of submergible pump systems. The initial study on the grinding machine revealed highly significant variance and a low value of process capability index. As robust design is one of the salient modules of Six Sigma Management, appropriate experiments were designed, conducted and analyzed to resolve the said problem. Details of the study carried out are reported in the paper. The end results of the study were confirmed with the manufacturer that the rejection level of the final output i.e. submergible pumps is substantially reduced by realigning the process with the parameters recommended by the analytical study. For further reduction in variance of the process a detailed Gauge R&R was applied. The outcome of the analysis is reported in the paper.

Capacity management of an electricity service centre using simulation

In todays competitive power market integrated with industrial growth, capacity management becomes a perennial technical issue. Power utilities lose customers when they lack sufficient capacity to provide their demanded service which severely affects the business process of the industries. Interruption time is one of the key characteristics of quality service and customer satisfaction. Higher the frequency of it may even force customer to switch over, resulting in a situation of loss of customer. While additional capacity improves service quality, but the cost for providing capacity increases. Electrical service centre of Goa Electricity Department is a customer complaint redressing mechanism hence its modelling becomes essential for investigating its efficacy. Thus the whole scenario gets placed in non-exponential and dynamic, wherein the classical stochastic models become transcendental. Using discrete event simulation, the working of electrical customer service centre was modelled and coded in general purposes simulation system.

Strategic role of capacity management in electricity service centre using Markovian and simulation approach

In today’s competitive power market integrated with industrial growth, capacity management becomes a perennial technical issue. Power utilities lose customers when they lack sufficient capacity to provide their demanded service which severely affects the business process of the industries. Interruption time is one of the key characteristics of quality service and customer satisfaction. While additional capacity improves service quality, but the cost for providing capacity increases. Thus, the capacity management is having a conflicting role with the utility effectiveness. The important strategy role of capacity management should be arriving at a point wherein it is optimally economical and maximising the customer satisfaction. A live case of Electrical Service Centre of Goa Electricity Department is modelled using Markov model by a code written in MATLAB 7.0 and the working of Electrical Service Centre was modelled in general purposes simulation system. Results, conclusions and future scope are discussed.

Collaborative optimal preventive maintenance schedule using goal programming

From the published literature, it was found that there is a scope to develop models to select between preventive maintenance (PM) and breakdown maintenance (BDM) with optimal schedule. But an organisation using multiple criteria decides to embark PM with a value of its optimal schedule common to all the criteria chosen. To this effect,a system has been developed to determine collaborative schedule for an equipment taking into consideration of those three criteria. This system consists of three phases. Input phase using a developed and published method by the authors provides the information whether or not PM is preferable and optimal schedule for that criterion chosen. Criteria importance through inter-criteria correlation (CRITIC) method is used to evolve weights without subjectivity. Goal-programming has been used to derive a single common schedule for PM, in optimisation phase. The system was applied to cases and the analysis carried out is reported in the paper.

Power Weibull system for business management

When competing brands are nearly identical, it is very difficult, in many instances, to choose a particular product solely on the basis of the product-related characteristics. With traditional Weibull, it is not possible to make clear distinction between the modes of failures revealing bathtub profile. Maintenance policies, in particular, will primarily be based on these modes of failure, missing which or mixing which will result in undesirable and detrimental consequences. To this effect, a system is developed incorporating bathtub hazard-rate function, using which effective failure data analysis can be carried out and effective maintenance policy and warranty decisions can be arrived at. The system is developed in MATLAB 7.0 platform. Development of the system and its applicability are discussed in the paper. The system was applied to a case and results obtained are discussed.

Multi-state failure phenomenon and analysis using Semi-Markov Model

Purpose Degraded failures and sudden critical failures are quite prevalent in industries. Degradation processes commonly belong to Weibull family and critical failures are found to follow exponential distribution. Therefore, it becomes important to carry out reliability and availability analysis of such systems. From the reported literature, it is learnt that models are available for the situations where the degraded failures as well as critical failures follow exponential distribution. The purpose of this paper is to present models suitable for reliability and availability analysis of systems where the degradation process follows Weibull distribution and critical failures follow exponential distribution. Design/methodology/approach The research uses Semi-Markov modeling using the approach of method of stages which is suitable when the failure processes follow Weibull distribution. The paper considers various states of the system and uses state transition diagram to present the transition of the system among good state, degraded state and failed state. Method of stages is used to convert the semi-Markov model to Markov model. The number of stages calculated in Method of stages is usually not an integer value which needs to be round off. Method of stages thus suffers from the rounding off error. A unique approach is proposed to arrive at failure rates to reduce the error in method of stages. Periodic inspection and repairs of systems are commonly followed in industries to take care of system degradation. This paper presents models to carry out reliability and availability analysis of the systems including the case where degraded failures can be arrested by appropriate inspection and repair. Findings The proposed method for estimating the degraded failure rate can be used to reduce the error in method of stages. The models and the methodology are suitable for reliability and availability analysis of systems involving degradation which is very common in systems involving moving parts. These models are very suitable in accurately estimating the system reliability and availability which is very important in industry. The models conveniently cover the cases of degraded systems for which the model proposed by Hokstad and Frovig is not suitable. Research limitations/implications The models developed consider the systems where the repair phenomenon follows exponential and the failure mechanism follows Weibull with shape parameter greater than 1. Practical implications These models can be suitably used to deal with reliability and availability analysis of systems where the degradation process is non-exponential. Thus, the models can be practically used to meet the industrial requirement of accurately estimating the reliability and availability of degradable systems. Originality/value A unique approach is presented in this paper for estimating degraded failure rate in the method of stages which reduces the rounding error. The models presented for reliability and availability analyses can deal with degradable systems where the degradation process follows Weibull distribution, which is not possible with the model presented by Hokstad and Frovig.