Design for Sustainable Manufacturing : Approach , Implementation , and Assessment

The implementation of sustainable systems is an essential requirement in modern manufacturing, in order to minimize the environmental and health concerns, and conserves energy and natural resources. The sustainable manufacturing approach is identified through three main levels, namely: product, process, and system scales. The interactions among these levels provide the required sustainable target. To achieve a sustainable manufacturing system, it is very important to understand and define the concepts and needs related to the sustainability approach. In addition, defining and understanding the implementation steps as well as the assessment method to build a sustainable manufacturing system is required. In this work, a study discussing the sustainable manufacturing approach is presented in terms of concepts, implementation steps, and assessment methods.


Introduction
It is a well-acknowledged fact that the major environmental concerns have arisen because of the pollution and consumption of natural resources.Thus, the implementation of sustainable systems is an essential requirement in modern manufacturing to address these concerns and to present effective solutions.There is no universal definition for the term sustainability; however, the most acceptable illustration of this term was proposed by Norway's previous Prime Minister and Director-General of the World Health Organization (WHO), Gro Harlem Bruntland, who expressed it as "meeting the needs of the present without compromising the ability of future generations to meet their own needs" [1].Jawahir and Wanigarathne showed that the main aspects of sustainability are focused on the environmental, economic, and social directions, in order to achieve better requirements through effectively utilizing available resources [1][2][3].
Each sustainable aspect has specific objectives that should be achieved in order to create and implement the efficient term of sustainability.The main objectives of social sustainability are focused on health improvement, safety, quality of life enhancement, and ethics.When looking at the environmental sustainability, clean air, water, soil, regulations implementation, and eco-balance efficiency support this goal.With respect to economic sustainability, the main pillars are product and process development, new employment, and large-scale new business opportunities [1,4].
The concept of sustainable manufacturing is identified and analyzed through three main levels, namely: product, process, and system levels, as shown in Figure 1.The interaction among these levels provides the required sustainable target.With regard to the product level, the perspective of sustainable manufacturing focuses on the new 6R approach (i.e., re-duce, re-design, re-use, re-cover, re-manufacture, and re-cycle) instead of the 3R approach (i.e., reduce, reuse, and recycle), as it theoretically achieves a closed loop and multiple life-cycle paradigms [5][6][7].At the process level, reducing energy consumption, hazards, and toxic waste is accomplished through using an optimized technological process associated with an effective process planning methodology, while using an efficient supply chain system considering all life-cycle stages (i.e., pre-manufacturing, manufacturing, use, and post-use) provides an effective sustainable system [3,8,9].The expectations of a sustainable manufacturing process are concluded as follows [1,2,4] sustainable manufacturing focuses on the new 6R approach (i.e., re-duce, re-design, re-use, re-cover, re-manufacture, and re-cycle) instead of the 3R approach (i.e., reduce, reuse, and recycle), as it theoretically achieves a closed loop and multiple life-cycle paradigms [5][6][7].At the process level, reducing energy consumption, hazards, and toxic waste is accomplished through using an optimized technological process associated with an effective process planning methodology, while using an efficient supply chain system considering all life-cycle stages (i.e., pre-manufacturing, manufacturing, use, and post-use) provides an effective sustainable system [3,8,9].The expectations of a sustainable manufacturing process are concluded as follows [1,2,4]:  Therefore, in this work, a review study that discusses the sustainable manufacturing approach is presented in terms of concepts, implementation techniques, and assessment methods.

Sustainable Manufacturing Elements
The evolution of sustainable manufacturing is shown in Figure 2. It can be seen that sustainable manufacturing evolves through several generations, namely: traditional manufacturing; lean manufacturing; green manufacturing; and, in its most developed phase, sustainable manufacturing [10,11].Therefore, in this work, a review study that discusses the sustainable manufacturing approach is presented in terms of concepts, implementation techniques, and assessment methods.

Sustainable Manufacturing Elements
The evolution of sustainable manufacturing is shown in Figure 2. It can be seen that sustainable manufacturing evolves through several generations, namely: traditional manufacturing; lean manufacturing; green manufacturing; and, in its most developed phase, sustainable manufacturing [10,11].The 6R approach adds three new elements to modify the classic approach (3R); these elements are recover, redesign, and remanufacture.The recover stage deals with collecting end-of-life products through post-use activities.On the other hand, the redesign element provides sufficient environmental consideration by simplifying the future post-use processes, while the product performance can be improved through the remanufacture element, as it works on saving natural resources, energy, cost, and on reducing the generated waste [1,2].One of the most important aspects of building and enhancing sustainable manufacturing systems is obtaining some basic keys for implementation.It can be seen from the open literature [4,[12][13][14] that implementation of the sustainable model is addressed by three major phases, as follows: -Research: to develop, evaluate, and examine the specific sustainability requirements, such as energy and resource use, pollution, and climate change impacts.This phase of the model has a high potential as it helps to ensure sustainability at the pre-competitive level and focuses on the manufacturing environmental issues; -Development: to improve the environmental performance, such as environmental footprint assessment, life cycle analysis, and design for environment, by using appropriate methods and tools [15,16]; -Commercialization: to refine the previous phases and co-operate with suppliers, vendors, and customers.

Sustainable Manufacturing: Needs and Concepts
To achieve a sustainable manufacturing system, it is very important to understand and define the needs related to the sustainability approach.It can be seen from the open literature [12,17,18] that building a sustainable manufacturing system can be accomplished by employing three basic keys, which are used to describe and define the sustainable manufacturing needs, namely: -Information: to make an effective assessment by providing the required quantitative and qualitative information; -Management and culture: to encourage and develop a sustainability-oriented culture in the organization through specialized sustainable departments inside the companies; -Procedures: to ensure applying the objectives and strategies for sustainable organization effectively.The 6R approach adds three new elements to modify the classic approach (3R); these elements are recover, redesign, and remanufacture.The recover stage deals with collecting end-of-life products through post-use activities.On the other hand, the redesign element provides sufficient environmental consideration by simplifying the future post-use processes, while the product performance can be improved through the remanufacture element, as it works on saving natural resources, energy, cost, and on reducing the generated waste [1,2].One of the most important aspects of building and enhancing sustainable manufacturing systems is obtaining some basic keys for implementation.It can be seen from the open literature [4,[12][13][14] that implementation of the sustainable model is addressed by three major phases, as follows: - Research: to develop, evaluate, and examine the specific sustainability requirements, such as energy and resource use, pollution, and climate change impacts.This phase of the model has a high potential as it helps to ensure sustainability at the pre-competitive level and focuses on the manufacturing environmental issues; -Development: to improve the environmental performance, such as environmental footprint assessment, life cycle analysis, and design for environment, by using appropriate methods and tools [15,16]; -Commercialization: to refine the previous phases and co-operate with suppliers, vendors, and customers.

Sustainable Manufacturing: Needs and Concepts
To achieve a sustainable manufacturing system, it is very important to understand and define the needs related to the sustainability approach.It can be seen from the open literature [12,17,18] that building a sustainable manufacturing system can be accomplished by employing three basic keys, which are used to describe and define the sustainable manufacturing needs, namely: -Information: to make an effective assessment by providing the required quantitative and qualitative information; -Management and culture: to encourage and develop a sustainability-oriented culture in the organization through specialized sustainable departments inside the companies; -Procedures: to ensure applying the objectives and strategies for sustainable organization effectively.
Additionally, a number of needs are required to improve the manufacturing sustainability performance.These needs are summarized as follows [12,[19][20][21]: -Concepts: present comprehensive analysis of the economic, social, and environmental clusters, as well as other relevant considerations; -Methods and tools: development, improvement, and enhancement of smart tools and methods to support the concept of sustainability; -Data: to support the environmental impact and sustainability assessments, more detailed, comprehensive and robust data are needed across the overall product life cycle; -Manufacturing practices: to build sustainable indicators for measuring and monitoring purposes to increase the sustainability awareness among suppliers and customers; -Government policies: to achieve incorporation between companies and government through sustainable programs, and environmental factors-clean processes policy; -Research: academic and industrial research is needed to enhance the sustainability system by focusing on the manufacturing, design, and environmental aspects; -Integration: for all previous needs to achieve an integrated system, which represents the environmental, economic, and societal sustainable aspects.

Design for Sustainable Manufacturing
In terms of design for sustainable manufacturing, several objectives should be considered to achieve the desired target for process, product, and system scales.These objectives are provided as follows [1,22,23]: Also, the term of "design for sustainable manufacturing" can be expressed as a unique loop, which includes the integration of information and substance loops across life cycle stages, as shown in Figure 3 [22].The main pillars of design for sustainable manufacturing, based on product and process levels are design for optimum environmental impact, design for resource utilization and economy, design for manufacturability, design for functionality, design for social impact, and design for recyclability and re-manufacturability.In terms of design for environmental impact [15,24], the main responsibility is dealing with environmental effects, co-balance, and efficiency.Regarding design for resource utilization and economy, it mainly concerns power consumption, energy efficiency, material utilization, operational cost, and using renewable energy resources [2,3,25].Additionally, the design for manufacturability [26] is related to improving the manufacturing methods, packaging, assembly, and transportation and storage techniques.Another pillar is design for functionality, which includes different aspects, such as durability, ease of use, serviceability, upgradability, ergonomics, function effectiveness, and reliability [2,27,28].Operation safety, health-wellness effect, and ethical responsibility are the main objectives related to the design for social impact [29][30][31].The last pillar is design for recyclability [32] and re-manufacturability [33,34], which is mainly focused on offering advanced and smart techniques for re-manufacturing and recycling operations to increase the efficiency of materials and energy use.

Practice and Implementation of Sustainable Manufacturing
Once the models, elements, and needs of sustainable manufacturing are defined, it is necessary to understand and obtain the required methodologies to implement an effective sustainable manufacturing system.In this section, the practice and recommendations for the implementation of sustainable manufacturing concepts are discussed.To achieve a sustainable manufacturing system, defining and implementing some practical aspects through the product, process, and system levels are required.Some of these aspects are summarized and presented as follows [35][36][37][38]: -Applying principles of utilized materials and inputs, which are non-hazardous and recyclable; -Developing and planning of production processes to reduce the consumption of energy, materials, and water; -Using renewable energy that does not affect the natural environment; -Developing product design to be reusable, re-manufacturable, or recyclable; -Expanding the design concepts of using fewer resources and applying easy-to-repair techniques; -Using efficient transportation and logistics systems.
The implementation steps to achieve the sustainable manufacturing approach are varied based on the implementation difficulty level.These steps are provided, as shown in Figure 4.

Practice and Implementation of Sustainable Manufacturing
Once the models, elements, and needs of sustainable manufacturing are defined, it is necessary to understand and obtain the required methodologies to implement an effective sustainable manufacturing system.In this section, the practice and recommendations for the implementation of sustainable manufacturing concepts are discussed.To achieve a sustainable manufacturing system, defining and implementing some practical aspects through the product, process, and system levels are required.Some of these aspects are summarized and presented as follows [35][36][37][38]: -Applying principles of utilized materials and inputs, which are non-hazardous and recyclable; -Developing and planning of production processes to reduce the consumption of energy, materials, and water; -Using renewable energy that does not affect the natural environment; -Developing product design to be reusable, re-manufacturable, or recyclable; -Expanding the design concepts of using fewer resources and applying easy-to-repair techniques; -Using efficient transportation and logistics systems.
The implementation steps to achieve the sustainable manufacturing approach are varied based on the implementation difficulty level.These steps are provided, as shown in Figure 4.

Practice and Implementation of Sustainable Manufacturing
Once the models, elements, and needs of sustainable manufacturing are defined, it is necessary to understand and obtain the required methodologies to implement an effective sustainable manufacturing system.In this section, the practice and recommendations for the implementation of sustainable manufacturing concepts are discussed.To achieve a sustainable manufacturing system, defining and implementing some practical aspects through the product, process, and system levels are required.Some of these aspects are summarized and presented as follows [35][36][37][38]: -Applying principles of utilized materials and inputs, which are non-hazardous and recyclable; -Developing and planning of production processes to reduce the consumption of energy, materials, and water; -Using renewable energy that does not affect the natural environment; -Developing product design to be reusable, re-manufacturable, or recyclable; -Expanding the design concepts of using fewer resources and applying easy-to-repair techniques; -Using efficient transportation and logistics systems.
The implementation steps to achieve the sustainable manufacturing approach are varied based on the implementation difficulty level.These steps are provided, as shown in Figure 4.The description of each implementation step is discussed in previous studies.The summary of these steps along with their descriptions are summarized as follows [39][40][41][42]: -Developing work practice and maintenance: This step is called the housekeeping step, and it is considered as a simple action to accomplish effective monitoring, inventory management, and scheduling in all production operations (e.g., reducing loss from leaks, keep equipment's maintaining properly, sustainable training programs).-Process optimization: In this step, development in manufacturing processes is required to minimize waste, conserve raw materials, and reuse waste materials.Examples of actions during these steps are changing the steps in a specific process, determining the optimal settings for each operation, and or rearranging machines' locations to minimize the total required movements.Also, the implementation of energy-efficient technologies offers significant effects, which support the sustainable manufacturing concepts.For example, using minimum quantity lubrication and dry cutting [43], cryogenic approach [44], waste management principles [45], modeling and optimization approaches [46,47], and artificial intelligence methods [48].-Raw material substitution: The main objective of this step is to replace hazardous materials and chemicals (high environmental impact) with sustainable materials (low health and environmental impact).The output of the current step contributes to reducing environmental and health concerns, as well as avoiding the regulatory costs associated with the storage and disposal of materials.-New technologies: This step depends on using more energy-efficient systems that enhance the environmental impact performance, as they have effective capabilities of saving heat and energy.However, for these technologies to have an effective impact to achieve sustainable systems, they need huge capital investment (i.e., initial costs problems).-New product design: This is considered the most difficult implementation step as it needs to transfer the whole system from the ground up to be greener (more sustainable).Some development keys to achieve this step are mentioned in Section 3; for example, smart methods, research, integration, and manufacturing practices.
It should be stated that many attempts have been presented in previous studies to implement the sustainable manufacturing concepts, and to link the sustainability aspects (e.g., energy consumption, environmental and health concerns, and waste management) with real manufacturing needs.Some of these studies are presented in Table 1.
Table 1.The link between the sustainable manufacturing concepts and recent technologies.ADI-austempered ductile iron; 6R approach-re-duce, re-design, re-use, re-cover, re-manufacture, and re-cycle.Reducing the health and environmental concerns associated with machining operations

Assessment of Sustainable Manufacturing Approach
Once the implementation stages are defined, it is also necessary to have a solid assessment model to evaluate the sustainability of the manufacturing systems.It has been obtained from the open literature that five major elements are mainly used to assess the sustainability aspects of the manufacturing systems.These elements are as follows: manufacturing costs, environmental impact, waste management, energy consumption, and personal health and safety, as has been mentioned in some previous studies [61][62][63][64].A summary for each element (i.e., sub-clusters, indicators, and measurements methods) is summarized as shown in Tables 2-6 [4,27,65].It has been obtained from previous studies [27,[66][67][68] that some of these elements (i.e., energy consumption, manufacturing costs, and waste indicators) can be modeled using analytical and numerical models; however, other elements, such as personal health and safety, as well as environmental impact [69], can be expressed depending on the designer's experience and judgment.A sustainability assessment schema that obtains the integration and analysis of all sustainable elements is provided, as shown in Figure 5.The assessment method can provide the optimal operating conditions (levels).It can be seen that the effective assessment method includes the integrated effect of all of the studied sustainable elements, as presented and discussed in some previous studies [61,70].After that, a suitable optimization methodology/loop (considering the system constraints) is employed to find the optimal/sustainable operating levels (acceptable sustainability level).The acceptable sustainability level is defined based on the designer's experience and judgment.Additionally, an assessment of sustainable manufacturing from the product perspective can be expressed by three main clusters, which are economic, environmental, and societal aspects, as mentioned in some previous studies [71,72].Regarding the economical cluster, it includes initial investment, direct and indirect costs, and economic growth benefits and financial losses.The environmental cluster, it focuses on the efficiency of the material and energy use, the end-of-life of the product, and the waste and emissions.In terms of the societal cluster, it assesses the health and safety impacts, employment benefits and characteristics, human rights implementation, and the societal impact regulations.Regarding the system and process levels, sustainability is described through the five pillars (i.e., manufacturing costs, personal health, waste management, energy consumption, and environmental impact), presented in Figure 5.In terms of the product level, another assessment method, which includes the economic, societal, and environmental consideration, can be used.Also, it should be stated that this work is mainly focused so as to achieve a sustainable manufacturing target through obtaining an interaction among the three sustainable manufacturing levels (i.e., system, process, and product).The desired interaction represents an important role for achieving the required expectations of the sustainable manufacturing.Additionally, an assessment of sustainable manufacturing from the product perspective can be expressed by three main clusters, which are economic, environmental, and societal aspects, as mentioned in some previous studies [71,72].Regarding the economical cluster, it includes initial investment, direct and indirect costs, and economic growth benefits and financial losses.The environmental cluster, it focuses on the efficiency of the material and energy use, the end-of-life of the product, and the waste and emissions.In terms of the societal cluster, it assesses the health and safety impacts, employment benefits and characteristics, human rights implementation, and the societal impact regulations.Regarding the system and process levels, sustainability is described through the five pillars (i.e., manufacturing costs, personal health, waste management, energy consumption, and environmental impact), presented in Figure 5.In terms of the product level, another assessment method, which includes the economic, societal, and environmental consideration, can be used.Also, it should be stated that this work is mainly focused so as to achieve a sustainable manufacturing target through obtaining an interaction among the three sustainable manufacturing levels (i.e., system, process, and product).The desired interaction represents an important role for achieving the required expectations of the sustainable manufacturing.
Applying sustainable manufacturing concepts offers various advantages; for example, it can reduce the energy consumption, decrease/eliminate the waste, improve the product durability, achieve better health and safety conditions, and enhance the system and processes overall performance.

Discussions and Future Trends
Understanding the needs, implementation techniques, and assessment methods is crucial in order to accomplish an effective sustainable environment.Thus, this work discusses the sustainable manufacturing approach in terms of concepts, implementation, and assessment methods.Also, it should be stated that three main phases (i.e., research, development, and commercialization) are used to address the sustainable manufacturing approach in order to achieve the main sustainable manufacturing expectations (i.e., reduce the energy consumption, decrease/eliminate the waste, improve the product durability, achieve better health and safety conditions, and enhance the system and processes overall performance).Regarding the research gap, the needs and implementation techniques of the sustainable manufacturing still need to be implemented in an effective way.Thus, a detailed guideline to define the concepts and practice techniques of the sustainable manufacturing is required.In addition, developing artificial intelligence-based methods can effectively support achieving sustainable manufacturing concepts in all levels (i.e., system, process, and product).Furthermore, it is necessary to keep developing the current sustainable technologies (see Table 1) to achieve more benefits towards a sustainable manufacturing environment.

Summary
In this work, a review study that discusses the sustainable manufacturing approach is presented in terms of concepts, implementation techniques, and assessment methods.The interaction among the three sustainable levels (i.e., process, product, and system) provides the required sustainable target.The main expectations of building a sustainable manufacturing system are the following: to reduce the energy consumption, minimize the waste, improve the product durability, decrease the environmental and health concerns, enhance the quality of the product, and develop renewable energy resources.To accomplish these objectives, several needs (e.g., approach, methods, data, research, and integration) are required.Additionally, the implementation of the sustainable manufacturing approach requires employing several design aspects.These aspects are as follows: design for environmental impact, design for resource utilization and economy, design for manufacturability, design for functionality, and design for social impact.Furthermore, five main stages are required to successfully achieve an effective sustainable system.These stages include the following: developing work practice and maintenance, process optimization, raw material substitution, employing new technologies, and developing new product designs.Once the implementation stages are defined, it is also necessary to have a solid assessment model in order to evaluate the sustainability of manufacturing systems.It is obtained from the open literature that five major elements are mainly used to assess the sustainability aspects of the manufacturing systems.These elements are as follows: manufacturing costs, energy consumption, environmental impact, waste management, and personal health and safety.The integration and analysis of all sustainable elements provides the optimal operating levels, from a sustainability perspective.
Energy consumption reduction.-Waste elimination/reduction.-Product durability improvement.-Health hazards and toxic dispersion elimination.-Higher quality of manufacturing.-Recycling, reuse, and remanufacturing enhancement.-Development of renewable energy resources.

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Design for repair, reuse, and recycle.-Design for waste and hazards minimization.-Design for product disassembly.-Design for continuous improvements.-Design for energy efficiency.-Design for remanufacturing.-Design for optimal materials use.-Design for cost effectiveness.

Figure 4 .
Figure 4.The implementation steps of the sustainable manufacturing approach.

Figure 4 .
Figure 4.The implementation steps of the sustainable manufacturing approach.Figure 4. The implementation steps of the sustainable manufacturing approach.

Figure 4 .
Figure 4.The implementation steps of the sustainable manufacturing approach.Figure 4. The implementation steps of the sustainable manufacturing approach.

Author Contributions:
The three authors have together collected, discussed, and analyzed different parts of the information.H.H. compiled the first draft.Each of the authors have provided feedback.Each of the authors have reviewed and edited the different versions of the paper.