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# First Approach to a Theoretical Framework for Carbon Footprint Management in the Aerospace Manufacturing Industry

Lucia Recio Rubio<fnref n="1" />,<fnref n="2" />(✉) ID, Amanda Martin-Mariscal<fnref n="1" />, and Estela Peralta<fnref n="1" /> ID

**Abstract.** Reducing CO₂ emissions from aircraft and other artifacts, as well as minimizing the environmental footprint during their manufacture, is one of the current challenges facing the aerospace industry. This implies that all manufacturing companies related to the industry are faced with the need to implement strategies to manage and control emissions during their supply chain. Under this scenario arises the proposal of a conceptual framework integrated in a Product Lifecycle Management (PLM) environment based on the digital control of manufacturing, oriented to the fulfillment of carbon emission reduction objectives. The theoretical proposal is based on the use of an industrial Digital Twin (DT), combining the use of a digital model, a physical model, a CO₂ model, and a life cycle analysis (LCA) module. Those models work in an integrated way to estimate and control the carbon footprint with the goal of being able to reduce it. This study seeks to discern which are the appropriate measurement parameters in the CO₂ model. Starting from the proposed combined measures of manufacturing activities, support tasks, management tasks and industry suppliers. That will allow estimating the carbon footprint produced in the manufacture of each part through an LCA database.

**Keywords:** PLM · Carbon footprint · Digital twin · Aerospace industry · Sustainability

## 1 Introduction

Circular economy, cleaner production or green manufacturing are sustainable strategies on which research has been conducted in recent years, due to society's growing concern to be more careful with the planet.

In this research line, the aerospace industry included action plans to commit to sustainability in both final products and manufacturing processes. Among these commitments is a movement to decarbonize the entire aerospace industry that includes the objectives of carbon neutral growth from 2020 and a 50% reduction in CO₂ emissions by 2050, comparing with those recorded in 2005 [1]. This sector produces 2.5% of the world's energy-related CO₂ emissions [2, 3], reaching 3.8% in the EU [4]. In addition, it

<footnote n="1">¹ MyM Group, Cadiz, Spain
lrecio@us.es</footnote>

<footnote n="2">² University of Sevilla, Sevilla, Spain</footnote>
should be noted that emissions from the sector will increase annually by 5% until 2030, which may amount to as much as 22% by 2050 [5, 6], which in impact data amounts to 2.6 billion tons of CO₂ [7].

After reviewing the literature in search of application methods of these sustainable strategies, it was observed that although the subject is of interest, there are no frameworks that allow the implementation of carbon footprint management systems to the assembly and manufacturing processes industry.

The management of the carbon footprint is closely linked to the concept of “eco-efficiency”. Eco-efficiency is understood as the ability to create more for less, as pointed out by Moreira [8], or as Clark [9] said, the ability to deliver goods and services at competitive prices that meet the needs of the industry and provide quality of life, progressively reducing the ecological impact and resource intensity throughout the life cycle.

Other authors, such as Oliva, wanted to apply this term eco-efficiency to the industrial domain and defined it as “reducing the consumption of resources, raw material, energy, waste and air emissions while maintaining or reducing the costs for manufacturing a product. For an assembly process, it is a question of balance of environ-mental and economic benefits in an integrated way” [10].

Currently, the latest advances in eco-efficiency have led to innovative circular economy strategies, which help to improve functionalities such as the management of effi-ciency and cost evaluation of assembly processes or the simulation and optimization of processes as shown in the 3-Layers Model [10, 11]. In the same way that the terms associated with the circular economy have been the subject of study in recent years, other concepts such as digital transformation or digital continuity of industrial companies have been core in the proposals and advances in the sector [12, 13].

With this knowledge, it is possible to understand how the management of an envi-ronmental impact is carried out in the industrial sector. First, the search for methods to assess the environmental impact is of interest, such as Life Cycle Assessment (LCA), standardized in ISO 14040: 2006 [14]. These methods make it possible to optimize the impacts through plan, do, act and check. Second, it is of great interest to carry out impact management by taking advantage of the industry’s digital transformation trends [15]. This transformation enables sustainable and collaborative management in an agile and flexible way, one of the main challenges for organizations in the implementation of circular economy strategies.

To facilitate the implementation of carbon footprint management systems in the industry 4.0 context, the objective of this work is to propose a process-oriented frame-work based on circular economy strategies. The framework supports the implementation of a PLM system to carry out the management of the carbon footprint, specifically, for those dedicated to manufacturing processes. This is an innovative proposal that inte-grates the circular economy and takes advantage of the challenges of Industry 4.0 and of the tools of the Product Lifecycle Management (PLM) environments.

To this end, the paper is structured as follows: Sect. 2 reviews previous studies in the field of PLM, Industry 4.0, and its link to sustainability strategies. Section 3 presents the proposal of the framework for carbon footprint management in Industry 4.0 components highlighting the contribution and benefits of the research. Finally, Sect. 4 provides a discussion of the results and summarizes the conclusions of the work, establishing future
lines of work. Throughout the study, the terms carbon footprint, CO₂ footprint, carbon contribution, CO₂ emissions, among others, will be used as synonyms to improve the richness and the readability of the paper.

## 2 Background

The large volume of data to be managed by companies in the product life cycle (quality, prevention, corporate social responsibility, costs, time, materials, human re-sources, environmental damage, etc.) makes the use of IT technologies indispensable to carry out their activities. In this field, multiple research projects have emerged to manage product and processes information through PLM environments [16]. Specifically, the aerospace industry devotes part of its interest and research efforts (time and investment) to green plans, integrating sustainability with the digitization of its processes, as for example Airbus does with its Digital, Design, Manufacturing & Services (DDMS) project [17].

PLM as enabler for Industry 4.0 has attracted much attention in the last decade, both from the industrial world and from academia and research. This recent upsurge is due to the potential benefits that PLM can offer in the face of today's design and manufacturing challenges, however, this is still a distant promise for most organizations [18]. PLM could be defined as a systematic concept of integrated management of product-related information and processes throughout the entire product lifecycle, from initial conception to end-of-life [19, 20], all managed through the methods and tools provided by the integrated collaborative platform or environment that is the PLM system itself. This collaborative management is one of the goals of Smart Factories where it is intended to achieve effective interoperability between all assets and information systems [21].

Product lifecycle management enables the development and control of information through the efficient storage, processing, collection, and distribution of data throughout the lifecycle of products (design, manufacturing, logistics, use and end-of-life), processes and resources (planning, execution, and disposal) in an organization. In this way, and with the goals of Industry 4.0, PLM systems become essential to achieve optimal interconnection and manage digital data together with other available enablers [22]: Internet of Things (IoT), cloud, big data, smart sensors, artificial intelligent, real-time data or robotics [23]. It requires agile, dynamic, and collaborative databases, whose functions can be covered by PLM systems. Furthermore, it makes it possible to handle the digital models of Cyber-physical systems (CPS), thanks to the integration of increasingly consolidated CAx techniques. In view of this integrated management, it could be said that the development of PLM has been highly dependent on the evolution and assimilation of computer-based software or product solutions, starting with computer-aided design or computer-aided manufacturing applications (CAD, CAM or CAE), passing through applications related to Enterprise Resource Planning (ERP), Customer Relationship Management (CRM) or Supply Chain Management (SCM) [20, 24].

Analyzing the studies on carbon footprint management in manufacturing and specifically in the aerospace industry, proposals are limited. Traditionally, they are aimed at managing energy use to minimize greenhouse gas (GHG) emissions with strategies for combustion efficiency, gearing ratios in engines, or redesigning wing aerodynamics [25].
Some PLM software (Siemens, Dassault Systèmes or Autodesk) do include carbon footprint calculation modules (such as Environmental Impact Calculator or Product Carbon Footprint), but they focus on calculating the system's contribution to the client change category as a product life cycle impact. It is necessary to incorporate a comprehensive system that considers, in addition to the calculation to minimize the impact, the management of holistic strategies and other key innovations for the minimization of CO₂ emissions. That can be implemented in the manufacturing process contributing to the other stages of the life cycle, such as the production of lighter, fuel efficient, less polluting and more aerodynamic next generation aircraft, closed-loop recycling, carbon-neutral technologies, waste management, hybrid-electric architectures, new manufacturing processes, new materials, sustainable alternative fuels, among others [26, 27]. From this review, it can be appreciated that the development of tools for environmental management is still under progress.

# 3 Materials and Methods

This section describes the framework for sustainability with the integration of a CO₂ model, managed through an LCA database, with the industrial Digital Twin of a manufacturing company and its application context. For the development of the conceptual proposal, the following steps were carried out and are explained in the following sub-sections:

* Development of the new carbon footprint estimation process oriented to Industry 4.0, composed of three interconnected models (physical model, digital model, and carbon model) (Sect. 3.1).

* Characterization of the carbon model differentiating into groups of activities that contribute to the carbon footprint and identification of sustainability indicators for each group of operations (Sect. 3.2).

## 3.1 Conceptual Framework Proposal

This conceptual framework is proposed for the estimation and management of the carbon footprint for a machining and metal forming company of aerospace parts.

Processes play a very important role when studying a machining plant, a proper characterization of them allows to know the production cost, processing time, product quality, production resources and environmental impact of the whole product. Focusing the interest on the carbon emission of the parts manufacturing process, the material flow, the energy flow and the environmental flow in the production and machining processes must be included in the study [28]. The characterization of manufacturing processes is strongly promoted to optimize the management of carbon emissions, showing special interest in the factors with the greatest influence on the carbon footprint in the machining process, such as materials, machinery, or personnel [29].

Derived from the commitments and objectives of circular economy and emission reduction set by the aerospace industry [30], the conceptual framework is proposed. Seeking, in the first place, to estimate the carbon footprint produced during the complete
manufacturing life cycle of the components of the supplier companies. To be able to provide, together with the manufactured parts, a study of the CO₂ footprint generated during manufacturing, aided with the use of an industrial Digital Twin. In addition to this objective, it is intended that the model serves to facilitate the control and monitoring of carbon consumption throughout the production chain. This contributes to carried out periodic continuous improvement processes to bring the company closer to the commitments of circular economy with the help of advances in industry 4.0.

The model is based on the use of a Digital Twin of an industrial plant. Figure 1 shows the architecture of the base model. It combines the use of a physical model, a digital model, and a CO₂ model, as well as an LCA database to work together to estimate, control and optimize carbon consumption and emissions.

<figure><img src="image_2.png" /><figcaption>Fig. 1. A conceptual framework for carbon footprint management (prepared by the authors)</figcaption></figure>

In the conceptual model shown in the figure above, you can see how the information flows, represented with arrows, derived from the real plant (physical model) and the digital plant (digital model) are managed and evaluated through the CO₂ model and the LCA database. The information collected from the actual situation and from the actual data history is collected and processed in the physical model. In addition, this information feeds the Digital Twin of the plant, where different scenarios are proposed, based on the information obtained, and process improvements are sought to reduce CO₂ emissions.

The next section is centered in the first approach to the components of the CO₂ model, which is the core of the framework, and to present the proposed parameters and indicators involved in the model, as well as the information expected to be obtained.
## 3.2 CO₂ Model

The next step of the characterization of the theoretical framework is to introduce the carbon model, which would be the engine for estimating and calculating the emissions generated during the production of each of the parts.

For the generation of this model, all operations related to the manufacture of the parts that may have a contribution to its carbon footprint are considered.

The first step to configure the model would be to study all the agents involved in the life cycle of the plant under study, identifying each of the tasks performed during manufacturing and the possible carbon contribution they may have.

In this way, aided by the job data obtained from the physical model and the digital model, it would be possible to map all the operations and processes involved in the CO₂ footprint of the plant.

Once the tasks involved have been identified, it is proposed to cluster them into groups differentiated by the type of activity and the relationship it has with the production process. So that it is easier to identify the sustainability indicators that can be measured in each of them.

The proposed division of groups by task is as follows:

* **Manufacturing processes:** all the carbon contribution generated by the machinery and manufacturing processes themselves, i.e., the direct contribution to the carbon footprint of the part.

Within this grouping, sustainability indicators to be measured are identified, aided by Zhao's studies [31], such as:

- Raw material consumption

- Energy consumption (differentiating between renewable and non-renewable)

- Water consumption

- Consumption of additional materials

* **Support tasks:** All types of activities associated with production but not directly involved in the manufacture of the part (transport of materials, cleaning of machines, setting up the warehouse, etc.) but which do produce CO₂.

Some of the sustainability indicators to be measured in this group would be:

- Energy, materials, & water consumption in plant cleaning tasks.

- Energy, materials, & water consumption in machinery maintenance tasks.

- Energy consumption in transporting materials.

- Plant air conditioning

* **Administrative tasks:** All the tasks necessary for the plant to be in operation and continue with production, from reception, human resources, suppliers, etc.

The following sustainability parameters have been proposed for measurement:

- Energy consumption by supplier management.

- Energy consumption by human resources
- Energy consumption by communication personnel

- Energy consumption by management personnel.

To obtain, store and maintain all the data obtained from the sustainability indicators, both physical and digital models are needed as input, so that data can be measured in both cases, and the use of an LCA database that is able to cover all material flows such as inventory throughout the life cycle of all the processes carried out in the plant is necessary [32]. The required information flow is shown in Fig. 2 below.

<figure><img src="image_3.png" /><figcaption>Fig. 2. CO₂ model information flow (prepared by the authors)</figcaption></figure>

The expected output of the proposed carbon model is an estimate as accurate as possible of the carbon footprint of currently manufactured metal parts.

Once the actual footprint is obtained, the next objective is to take it as a starting point to, in conjunction with the other two models, realize periodic emission reductions thanks to the improvements generated in the Digital Twin scenarios that subsequently materialize in the actual industrial plant.

In this way, the conjunction of the three models, as shown in the conceptual framework, would allow organizations to meet their carbon footprint reduction commitments during their life cycle, aided by the implementation of a digital model supported by the advances of Industry 4.0 and the implementation of a PLM.

## 4 Discussion

Through this work, it was proven that information management with a PLM and virtual representation through an industrial Digital Twin are an important improvement to address the sustainability parameters of companies.

Through the above study and the development of the circular economy framework, it has become evident that the need to develop tools to support sustainability strategies is a reality in the aerospace industry.
Without the inclusion of technology and innovation in the environmental manage-
ment of the aerospace industry, it would not be possible to achieve the proposed sus-
tainability and emission reduction commitments. Therefore, it is necessary to bring
companies closer to Industry 4.0 and its benefits if merged with environmental strategies.

This study has provided a framework to work on for the estimation of the current
carbon footprint in a parts manufacturing company. It also opens the door to the periodic
management of these emissions through the joint use of the three models to achieve
reduction targets.

The possibility of being able to count on the collaboration of a real company for
its implementation provides this conceptual framework with an associated line of work
with which to continue researching and refining the proposal to achieve the development
of a functional tool. The next steps to follow in this line of action would be to launch
an industrial project based on this research. This project would allow us to test the
usefulness and reliability of the framework.

Being able to quantify and subsequently optimize the carbon footprint by using the
Digital Twin of the plant, allows small companies in the aerospace industry to comply
with the environmental requirements of the industry. This brings additional value to
organizations to strengthen their position as suppliers to large multinationals in the
sector.

In a future where digital transformation and continuity are indispensable and the
environment is a constant concern, it is of vital importance for companies to possess
tools that bring them closer to these goals in order not to be left behind compared to
other companies with the same target.

The industry seeks to improve and innovate in production and assembly lines, in
the manufacture of components and intermediate products, and thus favor the digital
transformation of companies thanks to Industry 4.0 tools and PLM environments.

**Acknowledgments.** The authors would like to recognize M&M Group colleagues and Seville University colleagues support during the development of this work and thank them for their contribution.

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