A Review of Current Trend in Sustainable Manufacturing
ABSTRACT 1.
Sustainability in manufacturing requires a view not just on the product, and the manufacturing processes involved, but also the entire supply chain, including the manufacturing systems across multiple product life-cycles. This requires improved models, metrics for sustainability evaluation, and optimization techniques at the product, process, and system levels. This paper presents an overview of recent trends and new concepts in the development of sustainable products, processes and systems also supply chain sustainability. In particular, recent trends in developing improved sustainability scoring methods for products and processes, and assessment of machining and optimization techniques for sustainable manufacturing processes.
2. INTRODUCTION
Sustainability in manufacturing defined also as sustainable development. Sustainable manufacturing meets the needs of the present without compromising the ability of future generations to meet their own needs.[1]There is now a well-recognized need for achieving overall sustainability in industrial activities, arising due to several established and emerging causes: diminishing non-renewable resources, stricter regulations related to environment and occupational safety/health, increasing consumer preference for environmentally- friendly products, etc. In particular, the manufacturing sector, which lies at the core of industrial economies, must be made sustainable in order to preserve the high standard of living achieved by industrialized societies and to enable developing societies to achieve the same standard of living sustainably. Further, the sustainability improvement effort must yield benefits at all elemental levels involved: environmental, economic, and societal. The most widely accepted general definition of sustainable development is provided by the United Nations’ Brundtland
Commission [2]:
‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs.’ However, during practical implementation the result of each sustainability enhancement exercise must be specific to that situation, while also attempting to maintain the holistic objective given by the above-mentioned definition. A significant problem with manufacturing is that changes cannot be made quickly to the process, product, and system or to the supply chain. While costs can be estimated based on market prices, the changes in these prices are affected by a variety of different types of information, much of it nonnumeric. During the oil price spike of 2008, issues such as oil reserves, production delays, and political/war issues caused variations in the price. By monitoring the behaviour of these issues, decisions in the supply chain can be made early to lower the impact on the bottom line.
The ability to fuse the information that impacts the process is referred to as Level 3 fusion [3].
Hence, efforts to make manufacturing more sustainable must consider issues at all relevant levels
– product, process, and system – and not just one or more of these in isolation. At the product level there is a need to move beyond the traditional 3R concept promoting green technologies
(reduce, reuse, recycle) to a more recent 6R concept forming the basis for sustainable manufacturing (reduce, reuse, recover, redesign, remanufacture, recycle), since this allows for transforming from an open loop, single life-cycle paradigm to a theoretically closed-loop,

multiple life-cycle paradigm [4]. At the process level there is a need to achieve optimized technological improvements and process planning for reducing energy and resource consumptions, toxic wastes, occupational hazards, etc., and for improving product life by manipulating process-induced surface integrity [5]. At the system level there is a need to consider all aspects of the entire supply chain, taking into account all the major life-cycle stages
– pre-manufacturing, manufacturing, use and post-use – over multiple life-cycles [6].Considering the complexities involved in the above-mentioned focus areas for sustainable manufacturing, optimized solutions, and corresponding underlying models, are necessary. This paper presents an overview of recent trends, and new challenges, for achieving sustainability at the product, process and system levels, with a focus on modelling and optimization aspects.
3. BACKGROUND
According to The National Council for Advanced Manufacturing (NACFAM) in the U.S. [1] sustainable manufacturing includes the manufacturing of ‘‘sustainable’’ products and the sustainable manufacturing of all products. The former includes manufacturing of renewable energy, energy efficiency, green building, and other ‘‘green’’ & social equity-related products, and the latter emphasizes the sustainable manufacturing of all products taking into account the full sustainability/total life-cycle issues related to the products manufactured. Since manufacturing is the core operation in a product’s supply chain, when considering physical products, designing the system and promoting sustainability in its operations must centre on a sustainable manufacturing approach by focusing on a broader, innovation-based 6R methodology to not only reduce, reuse and recycle (3R Methodology) but also to recover, redesign, and remanufacture the products over multiple life-cycles [4].
In the 6R methodology, reduce mainly focuses on the first three stages of the product life-cycle and refers to the reduced use of resources in pre-manufacturing, reduced use of energy and materials during manufacturing and the reduction of waste during the use stage [7]. On the other hand, reuse refers to the reuse of the product or its components, after its first life-cycle, for subsequent life-cycles to reduce the usage of new raw materials to produce such products and components [7]. Recycle involves the process of converting material that would otherwise be considered waste into new materials or products [7]. The process of collecting products at the end of the use stage, disassembling, sorting and cleaning for utilization in subsequent life-cycles of the product [4] is referred to as recover. The act of redesigning products to simplify future post-use processes through the application of techniques, such as Design for Environment (DfE), to make the product more sustainable is referred to as redesign while remanufacture involves the re-processing of already used products for restoration to their original state or a like-new form through the reuse of as many parts as possible without loss of functionality [4]. Figure 1 shows the evolution of different manufacturing concepts and their contributions to stakeholder value, and the proposed closed-loop system involving 6Rs [8] .

Figure 1
4. PRODUCT SUSTAINABILITY
Numerous energy and material input and output streams involved in a product’s life, the necessity of considering the total product life-cycle in order to evaluate a product’s sustainability score for comparison and selection between different alternative designs, or between different productions scenarios, are well recognized. An extensive analysis of streamlined life-cycle analysis (SLCA) methods is presented in a pioneering textbook covering various methodologies, including matrix approaches using target plots, for five major product life-cycle stages: premanufacture, manufacture, product delivery, use, and recycling [9]. In more recent work the simplified total life-cycle of a product was assumed to consist of four key stages – premanufacturing, manufacturing, use and post-use – since product delivery was considered as only one among the several delivery activities involved in all stages of the product’s life-cycle [8]. To achieve multiple product life-cycles with the goal of near-perpetual product/material life, design

and manufacturing practices for next-generation products must consider these product life-cycle stages using a more innovative 6R approach, as described above.
4.1. Current trend of product sustainability
Trend of current product sustaining. Life-cycle assessment (LCA) attempts to quantify the overall environmental and economic impact – in terms of material and energy consumption. – over the entire lifecycle of a product, from material extraction to eventual disposal at end of life.
Despite its immense promise, the practical application of LCA as a tool for evaluating design alternatives for consumer products has fallen short of its potential implementation because it can sometimes become a vast exercise that gets bogged down in excessive detail. Several notable attempts have been made to simplify LCA for various practical applications [10]. However, since the simplifications implemented need to be based on assumptions that are unique to each situation, there is a need for considerable innovative thinking and decision making from engineering and management teams involved in sustainability exercises. De Silva et al. [11] presented a case study involving simplified sustainability assessment of competing design alternatives of a commercial printer. Six major sustainability elements – environmental impact, functionality, manufacturability, recyclability and re-manufacturability, resource utilization/economy, societal impact – were further classified into 24 sub-elements, which were assigned to44 different influencing factors for the product. These factors were categorized as possessing either high, medium, or low importance or the overall product sustainability score was evaluated using available data and weights assigned based on surveys of manufacturers and consumers. As shown in Table 1 , manufacturers and consumers had very different perspectives on the importance of different sustainability elements.
[12]
Table 1
5. SUSTAINABLE PROCESS IN MANUFACTURING
The applications of sustainability principles in manufacturing processes are presented in this section using machining as an example. Machining is one of the most important and major manufacturing processes. The indirect impact of machining, due to its effect on surface
Integrity, and hence on product life, is even greater. Moreover, as economic factors induce shorter product cycles, and more flexible manufacturing systems, the importance of machining is expected to increase even further
.

5.1. Sustainability assessment of machining
As for the case of product design, a major hurdle for implementing sustainable process design is evaluating the process sustainability index conveniently. Since there is no universally accepted definition for sustainable machining, a recent work describes it as a process that leads to:
(i) improved environmental friendliness, (ii) reduced cost, (iii) reduced power consumption,
(iv) reduced wastes, (v) enhanced operational safety, and (vi) improved personnel health [5].
Based on these six interacting elements, a new model has been developed for comprehensive evaluation of machining process sustainability for optimizing machining performance using a hybrid model [13] . While three of the sustainability elements as Machining cost, Power consumption and waste management can be modelled using analytical techniques because of their deterministic nature, modelling of the other three elements – safety, health and environment
(SHE) – requires non-deterministic means, such as fuzzy logic [13] .
6. SUSTAINABLE SUPPLY CHAINS
The application of sustainability principles at the system level, beginning with the supply chain, is presented in this section. As discussed in the previous sections, product and process sustainability must be integrated and coordinated across all life-cycle stages. These life-cycle stages span across the supply chain, and therefore, for overall sustainability in business operations, sustainable supply chains are a necessity. This implies that a closed-loop systems approach must be followed in the planning and management of sourcing, procurement, conversion (manufacturing), and logistics activities involved during all four life-cycle stages while explicitly considering the environmental and societal impacts, in addition to the economic benefits alone [6].
6.1. Sustainable supply chain model
Though the term ‘supply chain management’ itself ‘crystallizes concepts about integrated planning’ [13], it has been approached, for a very long time, as not unifying but coordinating the operations of (a) independently managed entities (b) who seek to maximize profits (only) individually. This point of view is a major obstacle to achieving sustainability in supply chain operations. To the contrary, for sustainability, supply chains must be designed and managed as an integrated system. The 6R methodology provides a means to achieve this integration across all life-cycle stages. Closed-loop flow in supply chains, is heavily dependent on the product

design; while almost 80% of a product’s costs are determined during design [14] the reuse, remanufacturing and recycle costs (and therefore reverse flows) of the product are heavily influenced by the number/ variety of materials used, design for ease of disassembly and whether product-inherent information is included in the product to make recovery and re-processing easier [15]. Therefore, in sustainable supply chains the strategic optimization of the supply chain design and product design must be intrinsically linked. This enables the design of a sustainable product, by application of SLCA, as discussed in earlier sections, and the system infrastructure to produce, deliver, recover and re channel these products through multiple life-cycles.
6.2. New challenges
Most of the existing research on sustainable supply chain design-related aspects has a narrow focus on cost minimization, profit maximization or some form of economic value-addition
(single objective). Comprehensive models that integrate the 6R approach and environmental and societal considerations, in addition to economic benefits, are necessary to promote the design and managing of sustainable supply chains. One of the major challenges in developing such models is the lack of metrics to quantify the extent of environmental and societal impacts on supply chain operations (i.e., across the total life-cycle). There has also been very limited work on integrating product design (or the total life-cycle) with system and supply chain design, which is essential for achieving overall sustainability. Therefore, further research is needed to address how to concurrently evaluate product and supply chain designs from a triple bottom line perspective.
7. CONCLUSION
The new world of sustainable technologies and work practices is undoubtedly a challenging and exciting emerging reality for the manufacturing industries. Key drivers of compliance, community expectations, risks, costs and market competition will ensure that those who don’t adapt will be left behind. This paper presents an overview of some recent trends and new concepts that are rising for evaluating the sustainability contents at the product, process and system levels for enabling sustainable manufacturing. It further highlights the fact that although achieving overall sustainability requires a holistic view spanning the entire supply chain, including manufacturing systems and processes, and involving multiple product life-cycles, this requires improved product performance models, predictive process models and optimization of individual manufacturing processes, as well as optimization of the entire closed-loop supply chain operations. Some recent trends in developing improved and simplified sustainability scoring methods for product and process design, and in developing predictive models and optimization techniques for sustainable manufacturing.

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