برنامه ریزی فرایند برای زنجیره تامین تولید هوافضای مدار بسته و کاهش اثر زیست محیطی

A considerable amount of work has recently been applied to the development of processes to reduce negative environmental impacts of disposal products. Different waste reduction options such as direct reuse, repair, refurbishing, cannibalization, and remanufacturing were introduced to overcome these shortages. This paper studies an integrated system of manufacturing and remanufacturing using a capacitated facility in the aerospace industry, where products are returned after certain flight hours or cycles for overhaul. A mixed integer linear programming model is developed to maximize profit considering manufacturing, remanufacturing set-up, refurbishing, and inventory carrying costs. The model was tested through a set of experimental data. Further sensitivity analysis was conducted aiming at revealing the effects of certain factors on inventory carrying cost, profit, amount of scrap, and inventory turnover ratio.

In recent years, increasing environmental concerns, the price of raw materials, and government legislations, aiming at conservation of energy and natural resources, landfill reduction, pollution reduction, and creating new jobs and skills (Gray and Charter, 2006 and McConocha and Speh, 1991), have resulted in companies to reduce their material wastes. The earlier approach, which was introduced in the 1970’s, was the recovery/recycling of materials such as waste paper, glass and metals. Wastewater treatment and waste-to-energy (WTE) are reestablishing themselves as attractive technology options to promote low carbon growth among other renewable energy technologies (Amoo and Fagbenle, 2013 and Kusiak and Wei, 2011). However, recycled products lose their added values; most of the time closed-loop recycling is not possible because of the purity of the recovered materials. Also, many energy taking activities would be required to transform a recycled product into raw materials. To overcome these deficiencies, different waste reduction options such as direct reuse, repair, refurbishing, cannibalization, and remanufacturing were studied (Thierry, Salomon, Van Nunen, & Van Wassenhove, 1995). Remanufacturing is “a process of recapturing the value added to the material when a product was first manufactured” (Gray & Charter, 2006). In order to have a successful remanufacture, the following parameters are required: market demand for remanufactured products, technology to remanufacture, stable product technology, standard interchangeable parts, and a lower remanufacture cost than the price of a new product (Lund, 1998). Dowlatshahi (2005) identifies strategic factors in the remanufacturing system and Guide (2000) lists the characteristics that make remanufacturing complex. Ijomah (2009) introduces a paradigm shift from product sales to service business model where a company’s needs are much more closely tied to customers’ needs. The new model looks at the following factors differently: product price, quantity of spares, reliability, customer expectation, source of profit, and incentive to overhaul. It also lists the difference between the new and old business model for aircraft engine life cycle costs. Companies create different strategies to encourage customers to buy remanufactured products. For example, up to 40% of part price is reimbursed by Caterpillar to the dealers that return parts and engines depending on their conditions (http://www.product-life.org/en/archive/case-studies/caterpillar-remanufactured-products-group). In aerospace industry, where safety and performance are the main concern and repairs are highly regulated, the general opinion is that remanufacturing has the least appeal. However, considering high price of raw materials and the low tolerance for manufactured components in aerospace which causes high percentage of defects, remanufacturing and component saving through “transforming” could be applied in imperfect production systems to reduce the amount of material scraps and inventory carrying cost. In some cases such as landing gear tires, remanufactured components may even have longer life cycles due to thicker retread rubber. By definition, an aviation product overhaul involves cleaning, carefully inspecting, and repairing or replacing components to meet service limits. It is usually a good idea to request that components used in the overhauled product meet new limits. But it is entirely legal to place a used component that meets only service limits into an overhauled product as a replacement. To ensure safety, when used components are consumed more frequent inspection is required. Aftermarket services encourage major aerospace manufacturers to look at maintenance costs from different views and practices such as extending life of defective components through remanufacturing, which might not be profitable in the old business model, becomes a desirable alternative in the new business model. In this paper a general model is proposed, and the effects of some factors on profit, inventory carrying cost, and number of scrap components are studied. The model determines the number of components to be manufactured, repaired, remanufactured, transformed, or scrapped at each time period to satisfy demand for spare components and final products while maximizing profit. The remainder of this paper is organized as follows. Section 2 categorizes and summarizes some of the relevant literature. Section 3 defines the problem, where the closed-loop supply chain network is introduced and a mixed integer mathematical model is developed for a multi-product multi-period scenario. Section 4 provides the results of sensitivity analysis and Section 5 concludes the study with a summary, extensions, and directions for future research.

A general mathematical model to study the effect of remanufacturing and transforming on profit and scrap in the aerospace industry where customers return products for overhaul has been proposed. The model determines the quantity of components sent for two types of repair, remanufacturing, transforming, and scrap in the forward flow and repair, remanufacturing, cannibalization and scrap in the reverse flow. A numerical example has been presented to validate and analyze the mathematical model. Based on the result remanufacturing and transforming increase profit in spite of inventory carrying cost increase. This study is based on the assumption of a deterministic defect rate(s) for manufacturing of new components and disassembled components, and lead-times. An extension of the model could make these factors stochastic. Also, the model developed in this paper can be extended to include shop visits for repair. Finally, the proposed model has integer variables which make computational time long and it is very sensitive to input data. Since this is the first attempt in solving this type of problems, the main objective of this work was to propose a mathematical modelling approach for the considered manufacturing process with repair and remanufacturing activities. The developed model can be solved to optimality with acceptable computational time for the considered example problem which is based on real production cases. We plan to develop efficient solution methods in future work in this area so that much larger size problems can be tackled properly. Such solution methods can be based on heuristic, meta-heuristic, optimization, or the combinations of these approaches.