Sustainable manufacturing through empowering machine tools with IoT innovations: a literature review

In the 21st century, sustainability takes the front seat as one of the main objectives while designing and developing new technologies. Machine tools have significant contributions in fuelling all four industrial revolutions. One of the major stepping stones to the fifth Industrial Revolution is making these machine tools sustainable. In this paper, we review the major developments driven by the integration of internet of things (IoT) in the field of machine tools which contribute to achieving a sustainable future. This integration of IoT in machine tools is also significant in contributing to different sustainable development goals of the United Nations. Through this work, we aim to reach a better understanding of current improvements in machine tool operations and ecosystem achieved through IoT innovations. The future research directions that are opening in this domain and their scope and limitations are also covered.


Introduction
Sustainability in manufacturing operations is now a primary objective among world economies, to reduce carbon emissions and ensure continued excellence in designing and fabricating newer technologies.The idea behind sustainability goals is to ensure that how we meet the needs of the current generation is not detrimental to the life and needs of the future generations [1].Manufacturing is one of the main contributors in satisfying the needs of recent generations of humanity.A good majority of manufacturing operations are performed using machine tools.One of the ways to improve upon the environmental impact of machine tools is to integrate them with new age technologies like internet of things (IoT) which will monitor and control their working.Much research is currently being undertaken in this direction.

Machine tools
Machine tools are the industrial equipment that are used to cut raw materials into finished components of different shapes.Different types of machine tool operations including turning, boring, milling, and grinding will be used in this transformation from the raw material to the finished product.Machine tools have been a key driver in technology development for humans over the last two centuries, playing a major role in all four industrial revolutions, including Industry 4.0.Some of the current innovations undergoing machine tools are energy efficiency [2], multi functionality [3], miniaturization [4], and making them intelligent [5].Making machine tools more energy efficient and intelligent are necessary developments towards achieving goals of Industry 5.0 and for a sustainable future.One of the ways to 1324 (2024) 012088 IOP Publishing doi:10.1088/1755-1315/1324/1/012088 2 achieve this is by integration of IoT sensors and actuators with machine tools to establish systems for energy monitoring and management, machine control, and minimize material usage.

Internet of things (IoT)
Internet of things, abbreviated as IoT, deals with connecting devices (or things) to the internet so that they can communicate with each other and take smart decisions.Such a network of connected smart devices ranging from household appliances to industrial machinery can improve our personal and work life.IoT is helping humanity in a variety of aspects including flood risk mitigation [6], rail accident prevention [7], landslide warnings [8], early earthquake warning [9], and other disaster management.
The introduction of IoT can lead to radical innovations in the industrial environment [10].Soldatos et al. [11] reports that future manufacturing will focus on flexibility, newer production models, neardemand-production, and better engagement of manpower, all of which depends heavily on IoT innovations.Moreover, IoT technology is key towards the development of smart factories, automation, remote monitoring, augmented reality (AR), and other tools that enhance work environment and productivity [12].Information technology tools have already been found to improve manufacturing in the automobile industry [13].Such benefits can be extended to manufacturing industries dependent on machine tools.

Sustainable manufacturing
Sustainable manufacturing deals with efficient use of energy and resources in manufacturing to minimize resultant greenhouse gas emissions and material wastage and to maximize production yield and quality.Machado et al. [14] summarizes through their review paper that digital technologies like IoT are essential to achieve sustainability in manufacturing and transitioning to a petroleum-free circular economy.Sustainability goals become even more relevant with the realization that resources are only finite [15].Daniyan et al. [16] suggests the use of life cycle analysis (LCA) approach to achieve sustainability goals in machine tools.One of the solutions they suggested in the LCA approach is implementation of IoT in machine tools.
This paper intends to cover different research developments and future research directions in the field of integration of IoT with machine tools.There are some review works discussing importance of IoT in sustainable manufacturing.However, the importance of this review work stands out as there are not many available reviews, in the open literature, on the impact of IoT integration in machine tools towards achieving sustainability.Moreover, this work contributes to some of the important Sustainable Development Goals (SDGs) of the United Nations.The relation of this work to the different SDGs are discussed as follows.
1. SDG 9 (Industry, Innovation, and Infrastructure): The IoT integration in machine tools leads to innovation in manufacturing processes and sustainable industrial processes.

SDG 12 (Responsible Consumption and Production): IoT and machine tool integration
promotes responsible consumption and production by reducing material wastage, optimizing resource consumption, and minimizing defects and errors.3. SDG 11 (Sustainable Cities and Communities): Smarter and sustainable cities and communities requires IoT integration with their manufacturing processes to promote resource usage efficiency and reduce environmental impact.4. SDG 13 (Climate Action): Energy efficiency and waste reduction achieved through IoT integration with machine tools aligns with the goal of fighting climate change and its negative impacts.

SDG 8 (Decent Work and Economic Growth): The implementation of IoT in machine tools
can improve the working conditions and safety for operators of these machines.This also leads to an increase in work efficiency and productivity, leading to economic growth.

IoT integrated machine tools: implementation
The implementation of IoT in machine tools is a complex procedure as the technologies associated with machine tools and IoT vary significantly.The different steps in this integration are listed in Figure 1 and explained in the following subsections.

Sensors for data acquisition
Machine tools can be fitted with different sensors for measurement of temperature, power consumption, vibration, and other important indicators.These sensors need to be placed strategically such that they can take readings continuously without human assistance, provide no hindrance to the working of machine tool or any other damage, and should not get damaged themselves while the machine works.

Connectivity
The data collected by the sensors needs to be sent for data processing.Connectivity devices such as Wi-Fi, ethernet or cellular transmission aids in this function.The connectivity channel should offer minimum latency as a delay in data and information transfer can lead to a reduction in production efficiency.

Data processing and analytics
Different data analytic tools are used to analyze the raw data sent through the connectivity component.These tools analyze real-time data to generate useful information that will be used by operators to make intelligent decisions towards improving productivity.After data analysis, the information output is transferred to human-machine interfaces (HMI) so that it can be received by the operator.

Human-machine interface (HMI)
The useful information that is output after data analysis will be of little use if it is not provided to the operator efficiently.Human-machine interfaces (HMI) are technologies through which this is made possible.Liu and Xu [17] reports that the HMIs can be formed to comprise of PCs, laptops, smart phones, tablets, and wearable devices that enable operators to get real-time information and make efficient decisions.

IoT integrated machine tools: applications
The integration of IoT with machine tools offers numerous beneficial applications.Some of these 4 applications are listed in Figure 2 and are explained in the following subsections.

Energy efficient systems
Manufacturing processes consume one-third of all energy generated in the world and therefore, it is necessary that these processes are made energy efficient.IoT integration with manufacturing systems enables control and management of the energy consumption by these manufacturing systems [18].IoT sensors enable real-time monitoring of energy consumption and losses for different systems of machine tools.Zhang [19] suggests that one of the solutions for achieving energy efficiency in machine tools is to develop intelligent machines that can automatically control machining parameters.This can lead to reduced machining times and material wastage.Zampou et al. [20] developed an energy-aware information system utilizing IoT sensors and data analytics for energy monitoring and reduction of energy utilization.The information system (IS) developed in this work enabled the researchers to perform real-time analysis of the huge amount of data collected using the sensors and make intelligent decisions.

Wearable technology devices for operators
Wearable technology is a subset of IoT devices that comes in close contact with humans and enables close monitoring of their vitals and enhancing their productivity.Di Pasquale et al. [21] reported that wearable devices are of critical importance to ensure the mental and physical well-being of the workers in a manufacturing environment.However, they also reported that the deployment of wearable devices also faces challenges such as breach of privacy, need for technological developments, government regulations, and higher initial cost for setup.Wearable devices such as augmented reality (AR) glasses enable the machinist to work to get real time status of the machine tools they are working on and real time schematics of the machining process.This enables them to fabricate better products along with ensuring minimal downtime due to the breakdown of machine tools.AR wearable also allows video conferencing with experts during the machining process, to get instructions to enhance the process and perform repairs.

Remote monitoring
Remote monitoring is another beneficial application that enables the operator to monitor the working of machine tools without being in proximity.This enables the operator to control multiple machine tools simultaneously and thereby increase productivity of the shop floor.Liu et al. [22] established an intelligent monitoring system for machine tools using IoT to form a connection between the enterprise information systems (EIS) and these machines.

Quality control
IoT devices also help in quality control by monitoring the machining process for any defects in the components fabricated.Quality improvement is also achieved by means of optimizing the machining parameters for better quality and giving real-time inputs to the operators for controlling the machining process.Christou et al. [23] showed the use of advanced data analytic tools towards reduction of product defects in manufacturing industry.

Predictive maintenance
Machine tools having different sensors inside them, which monitor the internal conditions continuously, enable prediction of a breakdown much before it happens.This enables the operator to perform preventive maintenance measures and thereby, reducing the downtime of the machine.Liu et al. [24] developed an intelligent system for predictive maintenance of machine tools by combining technologies such as IoT, augmented reality (AR), and deep learning.

Worker safety
Worker safety while using large machine tools is a serious concern in industry and a good amount of safety instructions and training are given to the workers to prevent accidents.However, there are still instances of accidents even with these safety measures in place.IoT devices are crucial in this scenario as different sensors can monitor the vitals and the environment of workers and give signals or raise alarm much before an accident happens.Moreover, they closely monitor the machine tool against any breakdown that may lead to harming the workers.Gnoni et al. [25] implemented intelligent IoT systems and improved worker and plant safety in the production environment.

Future innovations and research directions
There are different future innovations and research directions possible in the domain of IoT and machine tool integration.Some of them are listed in Figure 3.They are also explained in the following subsections.

Integration of artificial intelligence (AI)
Artificial Intelligence (AI) can be used to improve analysis of data collected by sensors when IoT is integrated with machine tools.This enables better data predictions.Researchers are pursuing development in AI tools so that fully automated and intelligent machine tools can be developed, which improves productivity and reduces wastage.However, the implementation of both AI and IoT in machine tools can lead to significant cost improvements.Hence, a balance between additional costs and benefits must be reached before this implementation.

5G (or higher) connectivity
Latency is a major issue in any IoT application.Latency quantifies the delay in response due to the time taken for data to travel from source to destination and back after processing.Faster connections, such as 5G, can reduce latency significantly.However, the coverage issues and high cost of 5G technology poses serious challenges for its implementation for improving IoT integrated machine tools.

Digital twin technology
The data collected using IoT sensor can be used to develop digital twin or a virtual 'copy' of the machine tool, so that simulations of machine operations can be done under different conditions.Such simulations enable highly accurate breakage predictions.Luo et al. [26] successfully developed a digital twin (DT) IOP Publishing doi:10.1088/1755-1315/1324/1/0120886 for a computer numeric controlled machine tool (CNCMT) and was able to use it for fault analysis and prediction.

Human-centric technologies
Human-centric technologies, such as AR wearable, enable the machine operator to select optimal running conditions for the machine tool based on real-time data.Research is going on to improve humancentric technologies so that operators can improve their work and life quality.

Sustainable materials
Sustainable materials are those materials that are ecofriendly and reusable.They play a crucial role in reducing the environmental impact of machine tools and other manufacturing processes.Researchers are aiming to develop IoT innovations that can properly monitor and control the use of these materials during manufacturing, to promote a circular economy.

Cyber security
Cybersecurity is a major concern when integrating IoT with any traditional technology.Since security protocols for these technologies are still under development, there is always the danger of security breach and loss of data.Especially in a field like IoT integration with machine tools, all kinds of security protocols need to be properly placed before commercial use of this technology.

Super factories
Super factories are highly advanced factories that leverage new age cutting edge technologies such as IoT, AI, and other tools and integrated them seamlessly with machine tools to enable higher production and efficiency and lower energy and material wastage.Thus, super factories are a major aspect of a sustainable future.Shrouf et al. [27] reported that smart factories or super factories use IoT technology efficiently to enable energy management and optimization.

Edge computing
Edge computing enables data processing near the source of data, which in this case is machine tools.This reduces the time loss due to high latency in data transmission and enables quick decision making, which is essential for better productivity, minimal material wastage, and reduced downtime.

Summary
This paper covered in detail the integration of IoT in machine tools in terms of implementation, applications, and research directions.Such an integration is identified as necessary for fulfilling the goal of a sustainable future for manufacturing industry.Initially, the different steps in implementing IoT integration with machine tools are discussed in this work.Then the different applications offered by this innovative integration are discussed.This review paper also lists the future research directions scientists are taking to make the IoT and machine tool integration much more efficient and environment friendly.

Figure 1 .
Figure 1.Steps in IoT implementation in machine tools.

Figure 2 .
Figure 2. Different applications offered by IoT integration in machine tools.

Figure 3 .
Figure 3. Future research directions in IoT and machine tool integration.