Reducing carbon emissions in manufacturing requires the adoption of sustainable practices. In CNC machining, sustainability can be improved by optimizing machining parameters and cutting tool paths to reduce material waste and energy use. Investing in energy-efficient CNC machines and using virtual simulations can further enhance efficiency and identify areas for improvement. These strategies not only lower environmental impact but also reduce operational costs and improve resource utilization. This overview highlights current advancements in sustainable CNC machining, showcasing both environmental and economic benefits. Embracing these practices is essential for a cleaner, more efficient manufacturing future.
Mohsen Soori , Fooad Karimi Ghaleh Jough , Roza Dastres , Behrooz Arezoo d
Introduction
Manufacturing environments face various challenges, including economic, social, environmental, and technical issues. Among the environmental concerns are the depletion of natural resources and climate change [1]. As a key contributor to carbon emissions, the manufacturing sector is under increasing pressure from both economic and environmental fronts to adopt low-carbon manufacturing strategies [2]. Environmental objectives such as reducing carbon emissions, conserving energy and natural resources, and minimizing environmental impact are closely interconnected [3]. To meet these objectives, manufacturing systems are adopting strategies aimed at reducing pollution, lowering raw material consumption, improving energy efficiency, and increasing the reuse and recycling of waste materials—key steps toward sustainable production [4].
Sustainable manufacturing involves producing goods in ways that minimize environmental harm and optimize the use of energy and resources. This focus on sustainability is increasingly critical, as manufacturers are urged by both regulators and consumers to provide eco-friendly products [5]. In addition, sustainable practices enhance the safety of workers, communities, and products. Because sustainability impacts a broad spectrum of industrial sectors, it has emerged as a major area of research and development [6]. The adoption of sustainable manufacturing technologies offers companies practical approaches to improving their performance across social, environmental, and economic dimensions.
During specific manufacturing operations, sustainable or green manufacturing focuses on reducing the consumption of energy and water, limiting emissions, optimizing cutting fluid supply pressures, lowering costs, and minimizing safety risks and waste generation [7]. To build a sustainable and clean energy future, manufacturers must be able to evaluate and compare existing technologies based on their sustainability performance. Green manufacturing—another term for sustainable manufacturing—aims to reduce waste, align with environmental expectations of consumers, and cut down energy and material expenses, resulting in greener products [8]. Achieving these goals requires redesigning processes, products, and operational strategies to reduce both energy and material usage. Given the rising costs of global resources and increasing stakeholder demands, sustainable manufacturing has become essential for modern industries [9].
Machining is a vital manufacturing process that plays a significant role in advancing sustainable production on the shop floor. Sustainable machining can be defined as a process that remains effective over time while maintaining productivity and minimizing negative impacts. It encompasses the long-term preservation of social, economic, environmental, and technological aspects of the machining process to ensure overall sustainability [10].
By conserving energy and natural resources, sustainable machining reduces waste and its adverse environmental impacts. This approach is commonly referred to as a form of “green manufacturing” [11]. To promote sustainability, decision-makers must monitor, assess, and optimize the performance of machining systems using advanced technologies. One effective tool is modeling and simulation (M&S), which allows manufacturers to predict the outcome of implementing new systems or processes without disrupting ongoing operations [12].
The machining industry holds a central position within the industrial sector and contributes significantly to the global economy. Therefore, reducing energy consumption in machining-related processes has become a major focus in environmentally responsible manufacturing [13]. Research into low-carbon machining techniques is necessary to enhance resource efficiency by lowering carbon intensity in production [14].
Machine tools are the primary contributors to energy use in industrial settings. As such, managing their energy consumption efficiently is a strategic method for energy conservation [15]. Studies analyzing the background operational loads—such as spindles, jog functions, coolant pumps, computers, and fans—have shown that these components account for over 30% of the total energy input during machining operations. Thus, using intelligent control systems to reduce energy usage during idle periods can lead to significant savings. Additionally, cutting parameters and tool paths can greatly influence carbon emissions [16].
Sustainability in manufacturing can be evaluated through three core factors: the energy required for operations, the materials consumed, and the time needed to complete tasks [17]. To ensure sustainable machining, it is essential to measure and analyze these parameters when designing an efficient manufacturing system. Cutting tools play a crucial role by removing material to form specific features and surfaces while optimizing energy use. Sustainable practices emphasize non-polluting methods that conserve resources, support economic viability, and prioritize the well-being of workers—while addressing social, environmental, and economic dimensions [18].
A key strategy to reduce energy and material use is to enhance the productivity of both processes and machines. Manufacturing systems are increasingly being designed with a focus on eliminating, reducing, or recycling waste continuously. These goals can be achieved through improved water use, reduced energy and material waste, elimination of metalworking fluids, and better management of lubricants, swarf, and hydraulic oils. Techniques such as dry machining with coated tools and the selective use of cooling and lubrication fluids (CLFs) are also valuable in promoting sustainability [19]. Figure 1 illustrates the major factors to consider when implementing sustainable machining practices [20].
| Topic of research work | Papers | Finding/ Discoveries |
|---|---|---|
| Parameters optimization | [27] | To reduce the environmental impact during hard machining of AISI 304 stainless steel, the grey fuzzy coupled Taguchi method is applied. |
| [28] | Optimized machining parameters are determined to enable minimum quantity lubrication during milling of steel alloys. | |
| [29] | An optimization process is implemented to achieve sustainability in the machining of Inconel 625. | |
| Cutting tool paths optimization | [30] | Optimized cutting tool paths are developed to minimize operation time during the turning of POM-C cylindrical stocks. |
| [31] | Optimized machining parameters are used to minimize cutting tool degradation in CNC machining operations. | |
| [32] | A genetic algorithm is used to optimize cutting tool paths in the orthogonal turning of AISI 310S. | |
| Process planning | [33] | A comprehensive digital evaluation of low-carbon machining process planning is conducted using the fuzzy statistical method. |
| [34] | Multi-objective process planning is applied to enable sustainable CNC machining operations. | |
| [35] | The Internet of Things (IoT) is applied to develop a smart system based on STEP-NC for machine vision. | |
| Energy efficiency improvement | [36] | The optimization of resources is reviewed to enable sustainable CNC machining operations. |
| [37] | Energy monitoring, evaluation, optimization, and benchmarking during machining operations are reviewed to support sustainable manufacturing processes. | |
| [38] | Energy efficiency, carbon emissions, and machining characteristics are optimized to enable sustainable machining operations. | |
| Metal chips and swarf recycling | [39] | The recycling of Ti6Al4V machining swarf is studied to reduce the environmental impacts of CNC machining. |
| [40] | Machining waste is converted into metal powder feedstock for additive manufacturing to reduce environmental pollution from CNC machining. | |
| [41] | Metal powder is produced from machining chips to support sustainable CNC machining operations. | |
| Virtual simulatio | [42] | The application of digital twin is studied to enhance sustainability in intelligent manufacturing. |
| [43] | The application of virtual reality is studied to enhance manufacturing sustainability in Industry 4.0. | |
| [44] | Digital twin-enabled machining process modeling is introduced to enhance both productivity and sustainability in machining operations. |
To evaluate and enhance CNC machining within virtual environments, Soori et al. proposed several virtual machining approaches [45], [46], [47], [48]. In efforts to improve CNC machining performance, Soori et al. also reviewed the application of machine learning and artificial intelligence in machining operations [49]. To assess the impact of coolant on turning processes, Soori and Arezoo studied factors such as cutting temperature, tool wear, and surface roughness [50]. In examining ways to improve efficiency in component production through welding, Soori et al. [51] provided an overview of recent developments in friction stir welding techniques.
Focusing on five-axis milling of turbine blades, Soori and Asamel [52] explored the use of virtual machining technologies to reduce residual stress and deflection error. Similarly, to control cutting temperatures in the milling of difficult-to-machine materials, Soori and Asmael [53] introduced applications of virtualized machining systems. To enhance surface quality in turbine blade milling, Soori et al. [54] presented an improved virtual machining technique. Moreover, to minimize deflection errors in impeller blade milling, Soori and Asmael [55] developed specialized virtual milling procedures.
Karimi Ghaleh Jough and Sensoy [56] introduced meta-heuristic methods for evaluating the collapse risk of mid-rise steel moment frames, aiming to improve structural risk management. In a related study, they applied the FCM-PSO method to analyze the dependability of Steel Moment-Resisting Frames, improving the speed and accuracy of seismic fragility curve estimation [57]. Karimi Ghaleh Jough and Golhashem [58] assessed the out-of-plane behavior of non-structural masonry walls using finite element simulations, aiming to reduce axial compression through lightweight masonry components.
To improve accuracy under epistemic uncertainty, Karimi Ghaleh Jough and Beheshti Aval [59] developed seismic fragility curves using an adaptive neuro-fuzzy inference system based on the fuzzy C-means algorithm. Ghasemzadeh et al. [60] identified and contextualized key challenges in infrastructure projects, emphasizing the current limitations of BIM in this domain. Addressing epistemic uncertainty in seismic collapse analysis, Karimi Ghaleh Jough et al. [61] introduced a Group Method of Data Handling (GMDH) algorithm, which improves precision without increasing computation time.
Further improving fragility curve modeling, Karimi Ghaleh Jough and Ghasemzadeh [62] proposed an uncertainty interval analysis using a 3D-fragility curve method based on optimized fuzzy logic. Additionally, Karimi Ghaleh Jough [63] examined the role of steel wallposts in enhancing the out-of-plane performance of masonry walls, contributing to reduced modification factors in walls featuring wallposts.
In order to enhance accuracy during five-axis milling of turbine blades, Soori [64] presented a method for compensating deformation errors. To improve the quality of parts produced through abrasive water jet cutting, Soori and Arezoo [65] studied surface roughness and residual stress in cutting titanium alloy Ti-6Al-4V. The same alloy was analyzed by the authors in a separate study [66] to minimize cutting tool wear during drilling operations.
For better parameter optimization in machining operations, Soori and Asmael [67] summarized recent developments from the literature. Dastres et al. [68] explored RFID-based wireless manufacturing systems to boost energy efficiency, data quality, and production reliability throughout the supply chain. Revisiting machine learning and AI applications in CNC tools, Soori et al. [49] again highlighted their potential to increase operational efficiency and value-added outcomes.
To better manage residual stress during machining, Soori and Arezoo [69] presented a comprehensive review. They also used the Taguchi method to optimize machining parameters, aiming to reduce residual stress and improve surface integrity during the grinding of Inconel 718 [70]. Tool wear prediction methods were examined by the same authors [71] to extend cutting tool life. Soori and Asmael [72] investigated computer-assisted process planning to improve efficiency in part manufacturing.
In support of data-driven manufacturing, Dastres and Soori [73] examined advancements in web-based decision support systems. They also reviewed the use of artificial neural networks in improving engineering performance, including applications in risk analysis, drone control, welding, and computer-aided quality inspection [74]. For environmental protection, Dastres and Soori [75] discussed how information and communication technology can reduce the ecological impact of technological growth. They also proposed using Secure Socket Layer (SSL) technology to enhance online network and data security [76].
To identify gaps in current methodologies, Dastres and Soori [77] analyzed trends in web-based decision support systems. In terms of cybersecurity, they assessed recent developments in network threats [78]. Lastly, to broaden the application of image processing technologies, they provided an evaluation of image processing and analysis systems [79].
This review introduces a novel perspective on sustainable CNC machining operations by integrating sustainability principles into advanced machining practices. It compiles the latest developments in the field to guide analysis and optimization of machining processes. The study introduces innovative tools and concepts that manufacturers can adopt to significantly reduce the environmental footprint of CNC machining.
Optimizing cutting tool paths and machining parameters can help minimize energy consumption during operations. Recycling metal chips and swarf also contributes to lowering the environmental impact of machining. Additionally, implementing virtual simulations and optimization techniques can further enhance productivity and sustainability in CNC machining processes.
Parameters optimization
Optimizing CNC machining parameters is a vital aspect of modern manufacturing, aiming to enhance operational efficiency, product quality, and cost-effectiveness. Through strategic parameter optimization, manufacturers can achieve substantial improvements such as shorter cycle times, extended tool life, and better surface finishes of machined components [80].
Sustainability-oriented optimization focuses not only on technical performance but also on reducing waste, energy usage, and environmental impact—while maintaining or enhancing the quality of the final product [81,82]. This approach plays a pivotal role in reducing energy consumption, material waste, and adverse ecological effects, all while preserving or even increasing productivity and product performance [36].
The concept of sustainable machining integrates the “triple bottom line,” which considers economic, environmental, and social dimensions of manufacturing processes [83]. To optimize CNC machining operations sustainably, several key parameters must be addressed:
- Material Selection: The choice of machining materials greatly influences process sustainability. Environmentally friendly materials such as titanium, brass, and aluminum are preferable to traditional steel and plastic materials due to their recyclability and reduced environmental footprint.
- Cutting Parameters: Adjusting critical cutting variables—including cutting speed, feed rate, and depth of cut—can yield notable improvements in sustainability. Proper parameter selection helps reduce energy use and raw material consumption, while also improving surface quality and tool longevity. Machining quality and the effectiveness of heavy-duty CNC machine tools are highly sensitive to these parameters [84]. Specifically, selecting an optimal cutting speed for each material and operation can decrease both energy usage and waste. Similarly, controlling feed rate minimizes excessive material removal, while reduced depth of cut can further lower power consumption and material waste [85].
- Cutting Tool Selection: The sustainability of CNC machining is also affected by the tools used. Choosing high-durability tools with the right material and geometry reduces tool replacement frequency, minimizes downtime, and enhances process efficiency [86].
- Lubrication and Cooling: The use of suitable lubricants and coolants not only decreases friction and tool wear but also contributes to lower energy consumption and improved surface finish. Effective cooling strategies are essential for extending tool life and ensuring part quality [87].
- Waste Management: Responsible waste management is critical to sustainable machining. Recycling chips, swarf, and other by-products significantly decreases the environmental burden of CNC machining operations [88].
- Machine Maintenance: Maintaining CNC machines regularly ensures optimal performance, reduces energy consumption, and extends equipment life—thereby decreasing the frequency of machine replacement and contributing to resource conservation.
In the context of sustainable machining, a decision-making framework that integrates data clustering and multi-objective optimization allows for the identification of optimal cutting parameters tailored to various operational scenarios [89]. This method not only facilitates the selection of the most effective parameters for different situations but also enables smooth transitions between clusters or scenarios with minimal adjustments. As a result, the application of such strategies—combined with ongoing process monitoring and refinement—can significantly enhance the sustainability of CNC machining. This leads to a reduction in environmental impact while sustaining or even boosting productivity and profitability, as illustrated in Fig. 3 [90].
Cutting tool paths optimization
Sustainable CNC machining practices include the optimization of cutting tool paths to minimize material waste, lower energy usage, and prolong the life of cutting tools [91]. By optimizing tool paths, manufacturers can achieve greater machining accuracy and efficiency while also reducing tool wear and material consumption. This approach is part of a broader sustainable machining strategy that not only focuses on tool path optimization but also takes into account material selection, machine performance, and effective waste management [36,92]. A flowchart illustrating the tool-path optimization process with a focus on carbon emissions is presented in Fig. 4.
To reduce energy consumption during hole machining operations, an advanced optimization method integrating cutting tool path and cutting parameters is proposed [94]. The flowchart illustrating the optimization process for minimizing energy usage in hole machining is presented in Fig. 5 [94].
Enhancing a manufacturing company’s efficiency can be achieved by minimizing processing time within its production system [95]. Both processing time and environmental impact are influenced by the choice of machining technology and parameters. Therefore, optimizing cutting tool paths and machining settings is essential to achieving reduced processing times and lowering environmental effects. The following are key strategies for optimizing cutting tool paths in sustainable CNC machining:
- Selecting the appropriate cutting tools: Choosing the correct tool is vital for effective tool path optimization. The tool must be suitable for the material, type of cut, and desired surface finish. Proper tool selection can minimize the number of passes required and reduce tool wear, leading to less waste and extended tool life [96].
- Utilizing high-quality cutting tools: Tools of higher quality can lessen machine wear, thereby reducing the energy required for operation. They also contribute to lower waste generation during the machining process [97].
- Optimizing cutting parameters: Parameters such as feed rate, spindle speed, and depth of cut greatly influence the efficiency of the tool path. Carefully optimizing these factors can decrease tool wear, enhance machining precision and efficiency, and minimize waste [98].
- Employing efficient cutting path strategies: The strategy selected for tool movement—such as zigzag, spiral, or contour cutting—can have a significant impact on the sustainability of the machining process. Choosing the right strategy helps reduce material waste, boost accuracy and efficiency, and prolong tool lifespan [99].
- Leveraging CAD/CAM software: CAD/CAM software can simulate and optimize the machining process before actual execution. This helps reduce material waste and ensures that the cutting tool operates at peak efficiency [100].
- Implementing adaptive cutting operations: Adaptive cutting techniques adjust the cutting tool path in real-time based on feedback from the machining process. This approach enhances material removal efficiency, reduces tool wear, and minimizes waste [101].
- Applying high-speed machining techniques: Techniques such as trochoidal milling can significantly cut down machining time, contributing to energy savings and waste reduction.
- Using simulation software: Simulation tools allow for pre-process optimization of the cutting path by modeling various cutting scenarios. This enables selection of the most efficient path for a given material and tool, enhancing accuracy and minimizing waste [102].
In summary, achieving sustainable CNC machining and optimizing tool paths involves deliberate attention to energy use, material efficiency, cutting strategies, and tool selection. Implementing these techniques contributes to environmentally friendly, cost-effective, and highly efficient machining operations.
Process planning
Process planning in CNC machining for sustainable manufacturing focuses on developing a machining strategy that not only ensures the production of high-quality components but also aims to reduce environmental impact, minimize waste, and enhance the efficient use of resources [103]. This planning process is critical for optimizing the overall manufacturing workflow to lower environmental burdens while sustaining or even improving both productivity and product quality [37,104].
To achieve these goals, an integrated approach that combines process planning with the optimization of cutting parameters is highly recommended. This approach supports energy-efficient CNC machining by reducing total energy consumption and helping to distribute machine workloads more evenly [105]. The synergy between process planning and cutting parameter optimization is visually represented in Fig. 6 [105].
Improving the Energy Performance of CNC Machining
Investigating the energy consumption in machining processes is essential not only for understanding its environmental impact but also for identifying related operational phenomena. The energy characteristics in CNC machining can vary widely, influenced by the design of the machining technique and the variety of operational procedures involved. Recent literature emphasizes the energy requirements associated with CNC machining, highlighting their variability and impact.
One notable application involves the indirect monitoring of tool conditions by measuring the electrical power consumption of the machine tool. This method has proven to be an effective, low-cost, flexible, and fast approach for evaluating tool condition [106]. It stands out as a reliable and adaptable technique for tool condition monitoring, offering both affordability and efficiency [107].
Extensive research at the process control level has aimed to improve the mechanics of tool-chip interaction and to reduce energy usage during machining. A promising strategy is to harness the energy-saving potential of machine tools. The discrepancy between the machine tool’s total energy consumption and the actual energy required for material removal indicates the total energy-saving potential in CNC metal cutting processes [108].
To further reduce energy consumption, Jia et al. [109] introduced a multi-objective optimization of CNC turning process parameters by considering both transient and steady-state energy consumption. The optimization approach is illustrated in Fig. 7 using the Taguchi method and response surface methodology [109].
The potential for energy savings in machine tools can be applied in numerous ways. Monitoring energy usage is crucial for identifying opportunities to reduce consumption. By optimizing energy use, CNC machining operations can become more sustainable and energy-efficient [110]. One way to achieve this is by minimizing setup time, which can reduce both energy consumption and material waste. Streamlining the setup process ensures more efficient machine operation, decreasing the need for additional setup time.
Additionally, reducing the frequency of tool changes can save both time and energy. Grouping multiple tools together for simultaneous changes can help further optimize this process. Selecting the appropriate cutting tool for the material being machined not only lowers the energy required for cutting but also extends the tool’s lifespan. Optimization of cutting parameters and energy modeling during machining operations are recognized as powerful and effective energy-saving strategies.
However, it is important to note that only 15-25% of the total energy consumed by a machine during the material removal process is used for cutting itself when performing machining tasks [111]. A significant portion of the energy is expended by auxiliary devices such as the controller, fluid pump, and fan, along with other internal machine components.
Reducing energy consumption for the same machining task can also be addressed during the planning and scheduling stages by opting for smaller machine tools. Another method to minimize energy usage throughout the machining process involves selecting optimal cutting settings to reduce energy during the cutting phase [112]. Studies show that decisions regarding process parameters play a key role in determining the total energy consumption of a machine tool and its efficiency during a cutting operation [113]. Therefore, finding the ideal combination of process parameters for a specific cutting task can be simplified into a mathematical optimization problem.
- Upgrade to more energy-efficient equipment: Modern CNC machines are typically more energy-efficient than older models. If your equipment is outdated, consider upgrading to newer, energy-efficient machines that consume less power [114].
- Optimize cutting parameters: Fine-tuning cutting parameters can help lower the energy consumption of machines. For instance, reducing cutting speed or feed rate can save energy while still ensuring high-quality parts are produced.
- Use energy-efficient lighting: Replacing conventional lighting with LED lighting can decrease energy consumption in the shop. LED lights are more energy-efficient and have a longer lifespan, which leads to reduced energy costs and maintenance expenses [115].
- Implement a preventive maintenance program: Proper maintenance plays a significant role in improving the energy efficiency of equipment. Adopting a preventive maintenance program ensures that machines run efficiently, minimizing the energy they consume [116].
- Use renewable energy sources: Consider utilizing renewable energy sources like solar or wind energy to meet the energy demands of your facility. This approach reduces reliance on fossil fuels and can contribute to lowering greenhouse gas emissions [117].
- Implement energy-saving practices: Promote energy-saving habits among employees, such as turning off machines when not in use, using power-saving modes, and ensuring proper equipment maintenance [118].
- Supply chain management: A sustainable supply chain also contributes to reducing the energy required for CNC machining. This can be achieved by sourcing materials from environmentally conscious suppliers, reducing transportation distances, and optimizing inventory management [119].
By adopting these strategies, CNC machining operations can enhance sustainability and lower energy consumption, leading to cost savings and reduced environmental impact.
Recycling metal chips and swarf generated during CNC machining.
In metalworking, metal swarf refers to the metallic chips that remain after shaping processes. These small fragments, commonly known as metal chips or swarf, are produced during various CNC machining operations such as drilling, milling, and turning [39]. If not properly managed, these chips can accumulate rapidly, resulting in a substantial amount of waste.
A variety of specialized machining techniques—including boring, grinding, grooving, knurling, reaming, sawing, slotting, and tapping—contribute to the generation of swarf [120]. Recycling these metal chips or swarf is a sustainable and environmentally responsible approach. It not only minimizes waste and conserves valuable resources but can also provide financial benefits for manufacturing operations.
Below are some key steps and considerations for effectively recycling metal chips or swarf:
- Collection and Segregation: Begin by collecting metal chips and swarf in designated containers or bins during CNC machining processes. Make sure the material is free from contaminants such as oils or coolants. It’s important to separate different types of metals—like aluminum, steel, and brass—as they are often recycled separately for greater efficiency.
- Fluid Removal: Metal chips may retain cutting fluids or coolants depending on the machining process. These fluids should be removed before recycling. Equipment such as centrifuges, chip wringers, or other fluid-removal systems can be used to extract residual liquids effectively [121].
- Storage and Transportation: Once cleaned and segregated, store metal chips in suitable containers to prevent recontamination. Ensure proper handling and secure transportation when moving the materials to a recycling facility. Local scrap yards and metal recycling centers are typical destinations. During transport, it is crucial to secure the waste to avoid spills or accidents.
- Finding a Recycling Facility: Identify and contact local recycling facilities that accept metal machining waste. Some centers specialize in processing metal chips and swarf. Be sure to verify their acceptance criteria and preparation requirements before delivery.
- Cleaning and Separation: To enhance the quality and efficiency of recycling, thoroughly clean the collected chips and swarf to eliminate residues like oils, coolants, or other machining by-products. In some cases, this may require specialized cleaning equipment [122].
- Environmental Considerations: Certain materials used in CNC machining may be hazardous. It is essential to adhere to local environmental regulations and safety protocols when handling and recycling these substances [123].
- Sustainability Benefits: Recycling metal chips and swarf supports environmental sustainability by conserving natural resources, reducing energy use, and lowering greenhouse gas emissions when compared to producing metal from virgin raw materials. It also helps reduce the volume of waste sent to landfills [41].
Recycling metal chips and swarf is both environmentally responsible and economically advantageous for manufacturing operations. It promotes a more sustainable and conscientious approach to CNC machining and metalworking.
Eco-friendly cutting fluids and sustainable cooling methods.
To mitigate the effects of overheating during machining operations, cutting fluids are commonly used in metalworking processes. These fluids play a vital role in enhancing machining efficiency and extending tool life, ultimately reducing overall machining costs. However, CNC machining can also pose environmental risks due to the use of cutting fluids and cooling methods that may be harmful to ecosystems [124].
The vapors and mists generated during machining are hazardous to operators, prompting the enforcement of strict regulations to control exposure. Prolonged skin contact with cutting fluids has also been linked to the occurrence of skin-related illnesses, including skin cancer [125]. Therefore, robust environmental guidelines are essential for the proper disposal or recycling of used cutting fluids to prevent ecological harm. Additionally, handling and recycling various types of cutting fluids can incur substantial costs [126].
One effective approach to sustainable machining within industrial settings is the use of biodegradable or eco-friendly cutting fluids. These alternatives help prevent the emission of harmful gases during the machining process and reduce health risks for operators by minimizing skin exposure. Having contingency plans in place further enhances operational safety and reliability [127].
To ensure the safe and effective use of environmentally friendly cutting fluids, several strategies have been developed. High-quality coolants help reduce friction and heat generation, extending the life of cutting tools and decreasing energy consumption.
Notably, vegetable oil-based machining fluids enhanced with nanoparticles exhibit significantly better thermal and tribological properties compared to conventional vegetable-based options. These advancements contribute to improvements in energy efficiency, lower carbon emissions, and optimized machining performance. For example, Figure 8 illustrates the sustainable milling of Ti-6Al-4V, highlighting key benefits in machining parameters and environmental impact [38].
Below are several eco-friendly cooling methods and cutting fluids that support sustainable CNC machining operations:
- Vegetable-Based Cutting Fluids: Vegetable-based cutting fluids offer a sustainable alternative to conventional mineral oil-based options. Derived from natural sources such as soybean oil and canola oil, these fluids are biodegradable and non-toxic, making them safer for both operators and the environment [128].
- Recycling Cutting Fluids: Whenever possible, cutting fluids should be recycled. This involves filtering and treating used fluids to extend their service life and reduce the volume of waste generated.
- Mist Collection Systems: Mist collection systems capture airborne mist and smoke produced during machining operations, preventing air pollution in the workplace. When used in conjunction with fluid recycling systems, they significantly reduce overall waste [36].
- Optimized Toolpath and Tool Selection: Selecting the right tools and optimizing the toolpath can decrease heat generation during machining. As a result, the demand for cooling and cutting fluids is reduced, enhancing sustainability.
- High-Pressure Coolant Systems: These systems use a high-pressure jet to deliver coolant directly to the cutting area, improving cooling efficiency and reducing coolant consumption by up to 90% [129]. This method not only lowers fluid usage but also enhances machining performance.
- Dry Machining: In processes where feasible, dry machining eliminates the use of cutting fluids entirely. It relies on specialized cutting tools that produce minimal heat and friction, reducing or eliminating the need for coolants and minimizing environmental impact [130].
- Air Cooling: Air cooling utilizes compressed air to lower the temperature of both the workpiece and cutting tool. This method is particularly effective for low to medium-speed machining operations that produce limited heat.
- Closed-Loop Cooling Systems: Closed-loop systems recycle and reuse coolant, drastically reducing coolant consumption and minimizing waste output [131]. This approach is both cost-effective and environmentally responsible.
- Biodegradable Coolant Additives: Adding biodegradable additives to traditional cutting fluids can improve their environmental compatibility. These additives help enhance the biodegradability of fluids, thereby reducing their ecological footprint.
- By adopting these sustainable cutting fluids and cooling methods, CNC machining operations can minimize their environmental impact while preserving high efficiency and productivity.
Reduction of carbon emissions in CNC machining operations.
CNC machining operations contribute to carbon emissions primarily through energy consumption and waste generation. By focusing on reducing carbon emissions in sustainable CNC machining, companies can benefit both the environment and their bottom line, with potential cost savings and enhanced operational efficiency [132]. The goal is to decrease energy usage and carbon emissions while optimizing industrial processes [133]. Fig. 9 illustrates the sources of carbon emissions within the industrial sector [38].
Fig. 10 depicts a quantitative approach for evaluating the carbon emissions of CNC machining equipment [134].
Several strategies can be employed to reduce carbon emissions and enhance sustainability in CNC machining operations. Here are some recommendations:
- Energy-Efficient Equipment: Utilize energy-efficient CNC machines and equipment that consume less energy and generate fewer carbon emissions, contributing to a reduction in overall environmental impact [135].
- Renewable Energy: Consider integrating renewable energy sources such as solar panels, wind turbines, or other green energy solutions to power CNC machines and equipment, further minimizing the carbon footprint of operations [136].
- Material Selection: Opt for sustainable and eco-friendly materials, including recycled or biodegradable options. These materials help reduce waste and decrease carbon emissions during the production process.
- Waste Reduction: Implement waste reduction practices such as recycling, reusing, or repurposing materials. These strategies not only help minimize waste but also reduce the carbon emissions associated with material disposal and processing [137].
- Process Optimization: Optimize CNC machining processes to minimize material waste and lower energy consumption. Techniques like toolpath optimization, reducing machining time, and using cutting tools with longer lifespans can all contribute to more efficient operations [138].
- Transportation Optimization: Streamline transportation logistics to reduce the carbon emissions generated by the movement of raw materials, finished products, and waste, further lowering the overall environmental impact of machining operations [139].
Virtual simulation and analysis of CNC machining processes.
Virtual simulation and analysis of CNC machining operations play a crucial role in optimizing machining processes, reducing waste, conserving energy, and minimizing material usage [140]. By leveraging virtual simulations, operators can evaluate different machining strategies and tool paths before implementation, allowing them to detect and correct potential issues in the production process [141]. This ensures that the process plan and NC program are accurate and complete before assigning tasks to the shop floor.
CNC simulation and analysis also help predict and prevent collisions during machining operations, thereby improving safety in CNC machining environments [142]. Virtual technology can simulate actual working conditions and identify possible collisions or other complications that may arise during the machining process [143]. Before initiating the actual machining process, both users and CNC design engineers can test a range of performance-related characteristics of CNC machine tools with Cartesian configurations using advanced virtual CNC modules [144].
Additionally, the simulation software can optimize the cutting toolpath for a given part, reducing the amount of material that needs to be removed [145]. Another significant benefit of virtual simulation is the ability to assess the environmental impact of machining operations. This includes analyzing energy consumption, CO2 emissions, and the waste materials generated during CNC machining [146]. The gathered data can then be used to pinpoint areas where sustainable practices can be incorporated into CNC machining, thereby reducing its environmental footprint.
Once the tool path is optimized and confirmed, the engineer can validate the entire NC process using a model of the machining center, which includes tool changers and material handling equipment. As a result, the need for costly trial-and-error cuts is minimized, saving both time and money during CNC machining operations [147]. The primary objectives of employing virtual machining systems include maximizing machine utilization, improving product quality, reducing time and costs, and minimizing the risk of expensive machine tool accidents [148].
Moreover, virtual simulation allows operators to optimize key cutting parameters—such as cutting speed, feed rate, and depth of cut—thereby reducing energy consumption and extending tool life [149]. By analyzing virtual simulation results, operators can identify opportunities to reduce waste and enhance sustainability. For example, they may optimize the removal of material or adjust cutting fluid usage to minimize environmental impact [43].
In summary, virtual simulation and analysis of CNC machining operations improve process efficiency, sustainability, and product quality. These technologies help reduce costs, minimize waste, and lower the environmental impact of CNC machining. Virtual simulation is an essential tool for implementing sustainable practices in CNC machining operations, contributing to both economic and environmental benefits.
Trend
As companies increasingly focus on reducing their environmental impact, sustainable CNC machining operations are gaining greater importance. The challenge is to achieve high productivity and profitability while minimizing environmental effects. One promising area of research is the development of control techniques in Computer-Aided Process Planning (CAPP) and NC code generation to enable energy-efficient control of CNC machines.
Various factors—such as inertia, thermal effects, sequential setups, and safety considerations—play a role in determining the most appropriate control method. The significance of each factor may vary depending on the specific machining operation. Achieving sustainable machining requires adopting a variety of techniques and strategies, and researchers have identified alternatives to conventional methods that can help meet sustainability goals.
These sustainable methods not only improve worker health but also reduce machining costs and mitigate environmental impacts. Some of the most promising techniques include cryogenic cooling, dry cutting, high-pressure coolant systems, biodegradable lubricants, and minimal quantity lubrication (MQL). Additionally, hybrid nano cutting fluids are gaining attention for their potential in various machining processes. The performance of these fluids can be further explored, particularly in relation to the size and shape of the nanoparticles mixed into the base fluids.
The following research areas hold promise for advancing sustainable CNC machining operations:
- Material Selection: Research could explore more sustainable materials for CNC machining, such as recycled or bio-based alternatives, that can replace less environmentally friendly options. The focus should be on materials that are either recyclable or biodegradable, as these can significantly reduce the negative environmental impact of the machining process.
- Energy Efficiency: Studies could examine strategies for enhancing the energy efficiency of CNC machines. This includes optimizing operating parameters, using more efficient motors and drives, and incorporating energy-saving technologies to reduce overall energy consumption.
- Waste Reduction: Research could focus on minimizing waste in CNC machining operations. This might involve optimizing cutting parameters to reduce scrap and developing new recycling methods for materials such as metal chips and coolant, further contributing to a sustainable process.
- Life Cycle Assessment (LCA): A comprehensive life cycle assessment (LCA) could evaluate the environmental impact of CNC machining operations, from raw material extraction to end-of-life disposal. This approach would help identify areas for improvement and guide efforts to make the process more sustainable.
- Lean Manufacturing: Applying lean manufacturing principles to CNC machining operations can help reduce waste, optimize production processes, and improve overall efficiency. Research could focus on how lean practices can be implemented to drive sustainability within machining operations.
- Renewable Energy: Research could investigate the feasibility of utilizing renewable energy sources, such as solar and wind power, to supply energy to CNC machining operations, reducing reliance on fossil fuels and lowering carbon emissions.
- Monitor and Optimize Machine Utilization: By closely monitoring machine utilization and optimizing production schedules, CNC operations can reduce idle time, lower energy consumption, and minimize material waste. Research could focus on methods to enhance machine efficiency and ensure optimal resource use.
- Supply Chain Sustainability: Efforts to promote sustainability throughout the CNC machining supply chain could include collaborating with suppliers to source more sustainable materials, reducing transportation-related emissions, and implementing green logistics practices to minimize environmental impact.
- Virtual Simulation and Tool Optimization: Virtual simulation and analysis can be employed to optimize the use of cutting tools. By modeling the machining process and analyzing tool wear, the simulation software can determine the optimal time for tool replacement, helping to reduce waste and the cost of tool replacements.
- Operator Training and Engagement: Studies could explore the impact of operator training and engagement on sustainability in CNC machining operations. The goal would be to identify best practices for raising awareness and promoting sustainable behavior among machine operators.
By exploring and addressing these research areas, we can foster the development of sustainable CNC machining operations and play a key role in creating a more sustainable future.
Conclusion
CNC machining is a commonly used manufacturing technique that automates the creation of precision components, frequently utilized in industries like aerospace, automotive, and medical devices. Sustainable CNC machining focuses on incorporating efficient, eco-friendly processes into the production of these components. Such operations not only contribute positively to the environment but can also lead to cost savings and enhanced competitiveness in an increasingly sustainability-driven world. Below are some key steps for planning a sustainable CNC machining process:
- Design for Sustainability: The first step in sustainable CNC machining process planning is to design products with sustainability in mind. This includes considering the environmental impact of the product throughout its lifecycle, including energy consumption, material selection, and end-of-life disposal. The goal is to minimize material waste and energy usage while maximizing the use of recyclable materials.
- Material Selection: Choosing the right materials is crucial in sustainable CNC machining. Opting for materials with lower environmental footprints, such as recycled or bio-based materials, is ideal. Additionally, selecting materials that can be easily recycled or safely disposed of at the end of the product’s life cycle should be prioritized.
- Energy-efficient Machining: CNC machining is energy-intensive, so it is vital to adopt energy-efficient methods. This can be achieved by utilizing high-efficiency cutting tools, optimizing cutting parameters to reduce energy consumption, and implementing coolant systems that minimize energy use during machining operations.
- Waste Reduction: The precision component production process often generates significant waste. Sustainable CNC machining process planning should incorporate strategies to reduce waste, such as recycling metal chips and coolant fluids, and minimizing scrap material.
- Green Supply Chain: A sustainable CNC machining operation relies on a green supply chain. This involves collaborating with suppliers who use environmentally friendly materials and processes and who are committed to sustainability, helping to ensure that sustainability principles are upheld throughout the production cycle.
- Reusable Tooling: Investing in high-quality, durable cutting tools that can be sharpened or reconditioned rather than discarded after one use contributes to more sustainable CNC machining practices. This reduces waste and lowers the demand for new tools, which conserves resources.
- Monitoring and Reporting: Continuous monitoring and reporting of the environmental impact of CNC machining operations are essential for sustainability. By tracking energy use, waste, and emissions, businesses can identify areas for improvement and implement strategies to reduce their environmental impact.
- Coolant Management: Proper coolant management is critical for both machine performance and sustainability. Recycling and filtering coolant fluids can reduce waste, minimize environmental contamination, and lower overall resource consumption in machining operations.
- Education and Training: Training CNC machine operators and staff on sustainable machining practices is essential for reducing environmental impacts. Educating workers on energy-saving techniques, waste reduction, and the importance of sustainable practices can help implement more eco-friendly machining operations.