Prem Vrat

A methodology for joint optimization for maintenance planning, process quality and production scheduling

Performance of a manufacturing system depends significantly on the shop floor performance. Traditionally, shop floor operational policies concerning maintenance scheduling, quality control and production scheduling have been considered and optimized independently. However, these three aspects of operations planning do have an interaction effect on each other and hence need to be considered jointly for improving the system performance. In this paper, a model is developed for joint optimization of these three aspects in a manufacturing system. First, a model has been developed for integrating maintenance scheduling and process quality control policy decisions. It provided an optimal preventive maintenance interval and control chart parameters that minimize expected cost per unit time. Subsequently, the optimal preventive maintenance interval is integrated with the production schedule in order to determine the optimal batch sequence that will minimize penalty-cost incurred due to schedule delay. An example is presented to illustrate the proposed model. It also compares the system performance employing the proposed integrated approach with that obtained by considering maintenance, quality and production scheduling independently. Substantial economic benefits are seen in the joint optimization.

Joint consideration of production scheduling, maintenance and quality policies: a review and conceptual framework

Performance of a manufacturing system depends on its ability to simultaneously meet several requirements such as: quick response to market demand, high product quality, low manufacturing costs and timely deliveries; which in turn strongly depend on performance at the shop floor level. In the past, the shop floor level operational policies in the context of scheduling, maintenance and quality have been examined in isolation. However, it is hypothesised that these three aspects of operations planning may also have some interaction effect and hence joint consideration of various policy options pertaining to quality, maintenance and scheduling on the performance of the manufacturing system is an important area for investigation. In this paper, a review of literature addressing the joint consideration of these three aspects is presented and research gaps are highlighted. As a preliminary work, some numerical investigations are also presented to highlight the importance of joint consideration of these three aspects. Finally, a conceptual methodology is presented that can lead to further developments in this field. Some potential research areas in this context are identified.

A methodology for simultaneous optimisation of design parameters for the preventive maintenance and quality policy incorporating Taguchi loss function

The performance of a production system depends on the breakdown-free operation of equipment and processes. Maintenance and quality control play an important role in achieving this goal. In addition to deteriorating with time, equipment may experience a quality shift (i.e. process moves to out-of-control state), which is characterised by a higher rejection rate and a higher tendency to fail. This paper develops an integrated model for joint optimisation of preventive maintenance interval and control parameters incorporating the Taguchi loss function. We consider two types of maintenance policies: minimal corrective maintenance that maintains the state of the equipment without affecting the age and imperfect preventive maintenance that upgrades the equipment in between ‘as good as new’ and ‘as bad as old’ condition. The proposed model enables the determination of the optimal value of each of the four decision variables, i.e. sample size (n), sample frequency (h), control limit coefficient (k), and preventive maintenance interval (t PM) that minimises the expected total cost of the integration per unit time. A numerical example is presented to demonstrate the effect of the cost parameters on the joint economic design of preventive maintenance and process quality control policy. The sensitivity of the various parameters is also examined.

A model for optimal maintenance interval incorporating the cost of rejections in manufacturing

Purpose – The purpose of this paper is to develop a model that incorporates the effect of rejection cost on optimal maintenance planning decisions. Such a model will help in further modelling the interrelationships between preventive maintenance and quality control policy.Design/methodology/approach – In this paper a model is developed for obtaining optimal preventive maintenance interval based on block replacement policy to incorporate the effect of rejection cost. An illustrative example is presented to compare economic performance of the proposed model (M2) and the conventional model (M1). Model M1 stands for optimal preventive maintenance interval without considering the rejection cost and model M2 stands for optimal preventive maintenance interval considering the rejection cost. The comparison is done for different production rates, costs of rejection and cost of lost production. The impact of control chart parameters on preventive maintenance decision is also studied.Findings – In this paper it is f...

Economic paper blending optimization model with competing materials

Purpose – Demanding customers, legislation and raw materials shortages in the modern world have forced companies to minimize the systems environmental impact. The paper seeks to analyze the economic impact of blending in sustainable paper industries in countries such as India.Design/methodology/approach – A linear programming model for a paper supply chain is proposed to minimize paper manufacturing cost by optimally blending wood pulp and after‐use paper under various conventional supply chain constraints. The issues of quality, environmental concern and reusability in the paper industry have also been taken into account.Findings – Improving quality of after‐use paper by proper recovery network reduces the manufacturing cost. Increasing proportion of wood fiber in the finished paper decreases the cost, even at the cost of degradation in the environment. Thus, it is up to the manufacturer to reflect its degree of environmental concern to the government and society by assigning appropriate environmental a...

Analysis of barriers hindering the implementation of reverse supply chain of electronic waste in India

India is the fifth biggest producer of electronic waste (e-waste) across the globe but still 95% of the e-waste is handled by the unorganised sector in an unscientific way severely impacting the environment and health. There are many social, economic and environmental benefits linked with reverse supply chain (RSC) of e-waste. The study aims to identify and analyse the barriers hindering the effective implementation of RSC of e-waste in India based on a comprehensive literature review and interaction with the experts. Interpretive structural modelling methodology has been utilised to find out the mutual influences among the barriers. The analysis reveals: legal issues, lack of awareness, and lack of infrastructure as the major barriers to RSC of e-waste. The study provides very useful insights to facilitate policy decisions to promote e-waste recycling in India like implementing monitoring and control systems across the e-waste supply chain, need for a dedicated e-waste etc.

Bio‐immune systems analogy for effective managerial decision making in conflicting environment

Purpose – The purpose of this paper is to investigate the analogy of the human immune system with the economic auction theory.Design/methodology/approach – The paper develops an analogy of bio‐immune system with competitive bidding in auction, then develops a model of the situation and discusses its managerial implications.Findings – The human immune system can be benchmarked to model decision making under competitive environment, such as biddings in auctions and obtains gainful insights.Practical implications – Various engineering, management, social science, and defense and security‐related applications of the model are suggested.Originality/value – The paper presents a novel and innovative model with tremendous potential for varied applications.

Dynamic analysis of a global supply chain using system dynamics approach

Supply chain management (SCM) plays a vital role in the growth of the industry, survival in the market, in the production rate and the dynamic interaction among the suppliers and customers. This paper analyses a supply chain model and the dynamic interaction between its variables using system dynamic approach. A causal loop diagram has been developed to identify the relationship between the variables of supply chain system. Under different delay conditions, the policy experimentation is carried out considering various global economies and their degree of development. The model results have been discussed and validated based on the questionnaire results. A detailed sensitivity test is carried out to examine the robustness of the model. The paper has addressed many important issues related to demand, delay time, inventory, GDP growth, SCMI and degree of development of India and their implications are useful in devising strategic policy and decision making scenario of Indias new liberalised economy.

Circular economy model of gold recovery from cell phones using system dynamics approach: a case study of India

Cell phones waste is the fastest growing electronics waste across the globe. Still in developing nations like India, most of this waste is routed to the unorganized sector causing irreparable damage to environment and health. This study has highlighted the economic, environmental and social benefits that India can gain by recycling the gold contained in discarded cell phones in an environmentally sound manner. In this work, system dynamics (SD) approach has been employed to develop a model of circular flow of gold in cell phones from manufacturing stage to recycling stage. Using the SD model developed, nine scenarios have been simulated and behavior trends of various variables under consideration are studied which provide very useful insights to facilitate policy decisions to promote cell phones recycling in India.