Remanufacturing and LCA: A Synergistic Approach Combining Structural Reliability, Sustainability, and Life Multi-Cycle Improvement

Abstract

Achieving sustainability is a strategic challenge for manufacturing. This study investigates the environmental and economic benefits of remanufacturing as a circular strategy to extend the lifetime of mechanical components while ensuring structural integrity, safety, and compliance with EU regulations. A mechanical synchronizer shaft used in the continuously variable transmission (CVT) of earth-moving machinery is analysed through a comparative life cycle assessment (LCA). Three scenarios are modelled: (i) the production of a new component; (ii) the remanufacturing of a discarded (at the end of its nominal life) component, considering the current remanufacturable rate of the inspected discarded lot (53.6%); and (iii) the remanufacturing of a discarded component assuming an improved remanufacturable rate (85%). Industrial data combined with Ecoinvent datasets are used to model cradle-to-grave impacts through SimaPro^®. Results show that a remanufactured component significantly decreases the global warming potential compared with a new component. However, when accounting for the actual remanufacturable rate achievable in practice, the reduction in the global warming index is more limited, highlighting the need to improve remanufacturability to unlock the full environmental benefits. A parametric LCA model integrating the DfRem approach is developed to evaluate how increasing the initial shaft diameter enables multiple remanufacturing cycles. Over multiple remanufacturing cycles, the improved design demonstrates substantial cumulative emission savings compared with repeated production of new components, also confirming the long-term environmental benefits of remanufacturing strategies. In addition to the environmental analysis, a cost evaluation is carried out to evaluate the economic feasibility of the different scenarios. The results confirm that higher remanufacturable rates not only reduce greenhouse gas emissions but also lower overall production costs, providing a comprehensive perspective on the benefits of remanufacturing-oriented design.

1. Introduction

In the current industrial and regulatory context, the transition towards circular economy models requires a fundamental rethinking of design strategies, where environmental sustainability becomes a structural constraint rather than a secondary objective. Mechanical components, as critical elements of machines, play a central role since their reliability and durability directly affect both safety and performance. While the traditional design has been limited to optimising costs and mechanical properties within a predetermined service life, the increasing need to reduce environmental impacts highlights the relevance of strategies, such as remanufacturing, to extend the product lifetime. Remanufacturing, as a strategy for enhancing the sustainability of mechanical systems, has gained increasing attention in the scientific literature. Although the Regulation EU 2024/1781 has introduced a new meaning to the term, we will refer to the most common one, which is recognised as an industrial process through which an end-of-life product is restored to a condition equal to or superior to its original state, with structural reliability equivalent to that of a newly manufactured component [1].

The Regulation formally recognises this role by defining standardised criteria for durability, recyclability, and circularity, requiring remanufactured products to meet performance and quality standards equivalent to new ones. Within this framework, integrating remanufacturing into LCA becomes essential. LCA provides a standard methodology (ISO 14040/14044) [2,3] for assessing the environmental impacts throughout the entire life cycle of a product or process, but its application to regeneration presents specific challenges, such as multiple useful lives, variable remanufacturable rates (i.e., the share of components that remain geometrically and technically suitable for reprocessing after service), the damage accumulated during use, and the energy requirements of remanufacturing processes [2,3]. To address these issues, it is necessary to link process-level information with system-level assessments in order to support technically and environmentally sound design decisions. The relevance of integrated design tools is therefore emphasised, combining mechanical simulations, structural analyses, and LCA/LCC models that enable designers to evaluate the environmental and economic consequences of their design choices in real time [4]. The concept of DfRem is therefore central. It requires anticipating, already in the design stage, the conditions that enable multiple remanufacturing cycles while preserving safety and performance. This entails defining structural acceptability thresholds and accounting for the trade-offs between increased material or energy use in the initial production and the environmental benefits of extended reuse. The design phase must consider such additional factors, as they may offset environmental gains [5], and the overall benefit remains highly sensitive to the balance between the initial property enhancement and remanufacturable rates [6]. As highlighted in a previous study [7], structural and functional validation must thus be complemented by environmental and economic assessments in order to enable truly circular design practices.

This study addresses the aforementioned challenge by situating the mechanical design within the LCA framework. First, it examines the regulatory and conceptual background. Then, it reviews the state of the art and methodological gaps. Finally, it explores the practical implications through a case study.

1.1. State of the Art: Remanufacturing Evaluation Through LCA and LCC

LCA is the recognised methodology for evaluating the environmental impact of products throughout their entire life cycle. It provides an objective basis for strategic and design decisions within the framework of a circular economy. Alongside the environmental dimension, the need to integrate the economic perspective through LCC has become increasingly relevant. The integration between LCA and LCC, known as LCSA, enables a joint evaluation of environmental, economic, and social aspects. Remanufacturing applied to industrial mechanical components has shown that it can reduce environmental impacts by more than five-fold compared to new production, while also achieving cost reductions of approximately 50%, confirming the long-term economic viability of the strategy [8]. Woodward [9] emphasised the importance of LCC for accurate life cycle planning, while Hunkeler and Swarr [10,11] established the methodological foundations and guidelines for its integration with LCA. The combination of these two methodologies has become an essential decision support tool for companies seeking to balance economic competitiveness with environmental impact reduction.

However, regarding remanufacturing, the quality of LCA studies strongly depends on the proper definition of system boundaries, allocation rules, and—most importantly—the ability to model the actual variability of industrial processes, including the remanufacturable rates and efficiency losses across successive cycles [12,13]. Remanufacturing is a key strategy for reducing environmental impact, as it restores products to an “as-new” condition while maintaining the added value and reducing greenhouse gas emissions by up to 50% and energy consumption by about 25% compared to new production [14,15,16]. Nevertheless, the literature highlights that these benefits are often overestimated, since many studies assume constant and ideal remanufacturable rates, neglecting the structural degradation and technical constraints that emerge over multiple remanufacturing cycles [17]. In practice, remanufacturing success rates (i.e., the proportion of returned components that successfully pass inspection, reprocessing, and functional validation, and are therefore restored to service in an as-new operational condition) can be significantly lower due to geometric constraints, structural defects, or excessive wear, which necessitate the introduction of new parts and consequently reduce net environmental savings. The recent literature has thus shifted its focus from the simple “new vs. remanufactured” comparison toward a multi-cycle perspective, better reflecting the industrial reality. In this view, a product is not remanufactured only once but undergoes several remanufacturing cycles during its service life, experiencing progressive structural and functional degradation. Studies on mechanical components [18] have shown that, when considering three consecutive remanufacturing cycles, cumulative CO₂ emissions can be reduced by approximately 35% compared to exclusive new production. However, multi-cycle modelling is crucial to understanding the real benefits of remanufacturing over long time horizons, as the effectiveness of the strategy depends not only on the initial quality of the component but also on the reverse logistics efficiency and diagnostic accuracy of used components. In this context, data quality plays a fundamental role: variability in energy and material costs, as well as uncertainty regarding residual component performance, can significantly influence results. This underscores the need for parametric models and sensitivity analyses to manage uncertainties and ensure robust decision-making. Within this framework, DfRem aims to facilitate regeneration processes from the earliest design stages through the targeted choices of materials, joints, tolerances, and assembly strategies [19]. An interesting study [20] proposes an evolution of this concept through the remanufacturing co-design approach. This approach simultaneously improves the design and regeneration decisions throughout the product life cycle. It allows for the integration of design variables and regeneration processes while taking into account the variability of the damage, costs and emissions across cycles. It has been observed that investing in additional material to enable future machining operations is only beneficial above a certain component return rate threshold (≈15%).

Despite these advancements, most studies still neglect the quantitative modelling of the remanufacturable rate decay over time and the combined effect of structural degradation and design strategies. Over multiple remanufacturing cycles, the improved design demonstrates substantial cumulative emission savings compared with the repeated production of new components, also confirming the long-term environmental benefits of remanufacturing strategies.

In summary, the literature converges on recognising remanufacturing as an effective lever for sustainability, although the results strongly depend on the type of component, process characteristics, and actual remanufacturable rate. The innovation of this work lies in introducing a model that explicitly accounts for the real remanufacturable rate and its progressive decay over successive cycles, while simultaneously integrating structural reliability, environmental performance, and cost assessment within a unified framework for life cycle improvement.

1.2. Objective and Research Questions

This study proposes an integrated methodological framework that combines LCA and LCC within the principles of DfRem, aiming to assess the environmental and economic implications of structural design choices in remanufactured mechanical components. There is a direct relationship between a component’s ability to maintain its structural and functional properties over time and the economic and environmental efficiency of its remanufacturing process. This work quantifies this relationship using a representative industrial case study. The research is applied to the synchronizer shaft of a continuously variable transmission (CVT) for heavy machinery. The analysis is conducted in two main stages:

a. A comparative LCA–LCC evaluation between the production of a new component and the remanufacturing of an EoL one.

b. A parametric scenario analysis, exploring how variations in structural parameters—particularly the initial shaft diameter—affect the achievable number of remanufacturing cycles, as well as the corresponding environmental and economic trade-offs.

The study introduces a multi-cycle model based on a decreasing geometric law that accounts for the progressive decline in remanufacturable rates due to structural and dimensional constraints. This model enables the quantification of how mechanical sizing parameters influence both sustainability performance and remanufacturing feasibility. The ultimate goal is to identify the optimal balance between increased structural robustness (and thus material use) and the long-term gains in environmental and economic efficiency achieved through repeated remanufacturing. Accordingly, the research focuses on how structural design parameters influence the environmental and economic efficiency of remanufacturing and which configuration maximises sustainability across multiple life cycles.

2. Materials and Methods

The approach adopted in this work is outlined below: a brief introduction to the component under study is provided, along with a presentation of the methods used in the analysed scenarios.

2.1. Case Study

Specifically, the component analysed in this study is a synchroniser shaft, which is part of a mechanical transmission system used in earth-moving machinery. The CVT transmission, with a total mass of approximately 700 kg, is composed of around 170 different part numbers (p/n). The remanufacturing operations are framed with reference to the CVT transmission data collected in

Table 1. Quality data relating to machines.

Transmission Data CVT
Evaluation period	2019–2023
Production of new parts	12,750
Remanufacturing data monitored from 2019 to 2023	153
Weight [kg]	697.0
Intensity compared to total production [%]	1.2
Intensity compared to spare parts sales [%]	88
Remanufactured cost/New cost [%]	86

.

The synchroniser shaft (Figure 1) plays a fundamental role in gear shifting, ensuring a smooth engagement between different gear ratios. It is a high-precision component subjected to elevated torsional loads and cyclic stresses and is designed to deliver high performance and long-term durability.

The synchroniser shaft is robustly designed. This means it is not usually prone to frequent catastrophic failures. However, it experiences progressive wear resulting from repeated torsional stresses during gear shifts, sliding and toothed couplings (with hub, sleeve, and gear), as well as from localised friction in features such as bearing seats, keyways, and splines. The synchroniser shaft was selected as the focus of the present LCA as it represents a structurally resilient component that nevertheless poses specific challenges in the remanufacturing process. Data collected between 2019 and 2023 from 153 remanufactured mechanical transmissions revealed that 82 synchroniser shafts were deemed suitable for remanufacturing. This corresponds to a remanufacturable rate of approximately 54%, highlighting the component’s strategic relevance from both environmental and techno-economic standpoints. The observed damage was typically localised and mechanically repairable through conventional processes such as grinding, metal deposition, and polishing, while the base steel exhibited high strength and excellent machinability. These characteristics make the synchroniser shaft a strong candidate for remanufacturing.

Accordingly, this study aims to assess the environmental impact of remanufacturing this component in comparison with its production from primary raw materials, thereby providing actionable insights for improving processes within a circular manufacturing framework. The characteristics are reported in

Table 2. Characteristics of the component under investigation.

Material	Hardening Steel
Synchroniser shaft mass	15.7 kg
Remanufacturing data monitored from 2019 to 2023	82

.

2.2. Structure of the Work and Analysed Scenarios

The research was organised into two main parts, each addressing a different set of objectives. The first part focuses on analysing the current situation and evaluating the environmental performance of new and remanufactured components. The first part of the work is composed of three main phases:

-

Phase 1: Comparison between new and remanufactured shafts. A complete LCA (cradle-to-grave) was carried out for both components, including the materials, production processes, surface treatments, assembly, and end-of-life management.

-

Phase 2: Average shaft with actual remanufacturable rate (53.6%). This scenario is based on factory data from 153 remanufactured transmissions, 82 of which contained remanufactured shafts. The process is modelled as a weighted combination of new and reprocessed components.

-

Phase 3: Sensitivity analysis with increasing remanufacturability rates. Hypothetical scenarios (70%, 85%, and 100%) were simulated to assess the effect of improving the remanufacturable rate on the environmental impact.

The second part of the study introduces a parametric LCA model to assess how design choices affect long-term remanufacturing performance. Industrial data showed that many shafts were unsuitable for remanufacturing due to excessive wear, which reduced critical dimensions below acceptable limits. To address this, the shaft was redesigned with a slightly larger initial diameter, adding extra material to allow repeated reprocessing without compromising functionality. This enabled an analysis of the trade-off between increased initial mass, structural safety, and higher remanufacturable rates. Environmental performance was initially assessed by comparing a single remanufacturing cycle followed by a new production cycle with two consecutive new production cycles. The model was then extended to a multi-cycle scenario, in which initial production is followed by three remanufacturable cycles, introducing a degradation factor to represent the progressive decline in remanufacturing success rates over time. This part of the work is composed as follows:

-

Phase 1: Comparison between one cycle of remanufacturing + one new cycle versus two consecutive new production cycles.

-

Phase 2: An evaluation of a multi-cycle scenario, in which the shaft underwent three consecutive remanufacturing cycles after its initial production, for a total of four life cycles. This was compared against the baseline of four entirely new production cycles.

The study concludes with an integration of the environmental perspective and an economic assessment. This was achieved by using the LCC methodology and considering the same system boundaries as in the LCA. Two alternative processes were compared: new production against remanufacturing.

2.3. LCA Modelling

2.3.1. Functional Unit

The functional unit is defined as a fully operational component over the entire service life of the machine, assumed to be 20 years. This assumption is consistent with industrial practice and aligns with commonly accepted definitions of remanufacturing, which require restoring products to an “as-new” functional condition. In line with these definitions—i.e., returning a used product to at least its original performance with an equivalent warranty—this study assumes that a properly remanufactured shaft achieves a service life comparable to that of a new component.

It is important to note that the shaft was not designed for infinite life, but rather for a finite fatigue life during which the safety factor (SF) does not fall below the prescribed minimum threshold. Consequently, each remanufacturing cycle is assumed to restore the structural integrity of the component to a level that ensures the safety factor remains above the design limit throughout operation. This assumption is coherent with fatigue theory and with mechanical design principles for components subjected to cyclic loading, according to which durability is ensured as long as the accumulated damage remains below the critical value.

This assumption holds provided that the remanufacturing process includes appropriate NDT and machining operations capable of fully removing the damaged surface layers generated during the previous service cycle, thereby restoring the surface condition and geometry to a state equivalent to that of the new component.

This interpretation is consistent with BSI/ISO guidance on remanufacturing terminology and practice, as well as with EU/JRC reporting on value-retention processes, which state that remanufactured products are expected to perform as-new. Accordingly, the comparison between new and remanufactured components is based on functional equivalence in terms of performance and durability, assuming that remanufacturing operations restore the component to a condition that guarantees the same remaining service life as a new one.

2.3.2. System Boundaries

The analysis of the new production process was conducted following a cradle-to-grave approach, encompassing raw material extraction, material processing, component manufacturing, logistics, and end-of-life management including disposal, recycling, or energy recovery. In terms of the remanufacturing process, a gate-to-grave approach was adopted. This considered the product returns and reverse logistics, including the collection of end-of-life products and the distribution of remanufactured ones. It also considered the remanufacturing process itself, as previously described, as well as end-of-life management through disposal, recycling, or energy recovery. Auxiliary activities and infrastructures were excluded from the analysis, as well as the use phase, due to the high variability of user operating models, which prevents a reliable generalisation.

2.4. Life Cycle Inventory (LCI)

The LCI considers two system configurations: the production of a new component and its remanufacturing.

For the new component, secondary data were sourced from the scientific literature and from the Ecoinvent 3.10 database within SimaPro^®. The geographical scope was set to Europe; where European datasets were unavailable, global datasets were used. The system includes raw material extraction and steel production, forging, machining (rough and finish turning, assembly), heat and surface treatments, quality control, transport, water use, and end-of-life management (95% recycling, 5% landfill).

For the remanufacturing process, primary data were collected from a specialised remanufacturing company in Italy. The system includes transport for reverse logistics (200 km), cleaning, NDT, re-machining by grinding, partial heat treatment to restore functionality, replacement of worn parts, final assembly, and waste treatment.

The used shaft is modelled as a neutral input flow (i.e., no environmental burden from material production). Therefore, new steel production was excluded from the system boundaries, while electricity use, replacement parts and end-of-life management (95% recycling, 5% landfill) were not.

Table 3. Inventory of “new” and “remanufacturing” processes of the shaft.

Process Phase	Included in “New” LCI	Included in “Remanufacturing” LCI
Raw material	Steel production, low-alloyed	Not included
Forming	Included	Not required
Machining/ re-machining	Rough + finish turning	Grinding/re-machining
Heat and Surface treatment	Carburising, quenching and tempering	Heat treatment for functional restoration
Cleaning and inspection	NDT	Cleaning + NDT
Assembly	Included	Included
Transport	Transport, lorry, EURO 6	Transport, lorry, EURO 6
End-of-life treatment	Recycling (95%)/landfill disposal (5%)	Recycling (95%)/landfill disposal (5%)
Process parameters	-	-Material removal: 0.20 mm per side; -Magnetic Particle Inspection + Ultrasonic Testing ≥ 0.2 mm; -stress-relief 180–220 °C, 2 h; -run-out(maximum permissible misalignment) ≤0.03 mm
Data source	Ecoinvent 3.10 (EU/Global)	Company—specific data + Ecoinvent 3.10 (EU/Global)

reports the input data for both the production of the new shaft and its remanufacturing process.

The environmental impact assessment was carried out using two complementary methods from the ReCiPe 2016 framework: the Midpoint (H) and the Endpoint (H) approaches, both based on the European normalisation and weighting set (Europe H/A).

The ReCiPe 2016 Midpoint (H) method allows a detailed evaluation of environmental impacts through eighteen specific categories, including climate change (expressed in kg CO₂ equivalent), fossil resource scarcity (kg oil equivalent), water consumption (m³ of freshwater used), terrestrial acidification (kg SO₂ equivalent), and human toxicity (kg 1,4-DCB equivalent). This midpoint-level analysis provides a disaggregated view of environmental pressures, highlighting contributions from greenhouse gas emissions, resource depletion, water use, and toxic emissions.

The ReCiPe 2016 Endpoint (H) method aggregates these impacts into three areas of protection: human health, ecosystems, and resources. Results are expressed, respectively, in DALY (Disability-Adjusted Life Years) for human health, PDF·m²·year (Potentially Disappeared Fraction of species per area and time) for ecosystem quality, and USD2013 for resource depletion.

This endpoint approach provides a synthetic view of the overall environmental burden, yielding a single score expressed in millipoints (mPt), which enables a direct comparison between different design or process alternatives.

2.5. Design Strategy: DfRem

As anticipated, within this context the DfRem strategy aims to develop components specifically designed to facilitate future remanufacturing processes. The case study considers the hypothesis that the synchroniser shaft will be redesigned with an increased initial diameter, moving from the current 42 mm to 43 mm and 44 mm. This modification allows for repeated grinding operations (0.2 mm per side) over multiple remanufacturing cycles. The increase in diameter results in greater stiffness and, consequently, a higher structural safety factor (SF). However, the geometric erosion caused by successive remanufacturing cycles progressively reduces the critical section diameter, leading to increased stresses and a corresponding decrease in the effective safety factor. To ensure that the remanufactured component maintains an SF ≥ 1.3 even after one or more reworking cycles, it is proposed to increase the initial shaft diameter from 42 mm to a maximum of 44 mm. Although this adjustment entails an increase in mass and environmental impact during the initial production phase, it preserves structural integrity throughout the extended life cycle of the component.

2.5.1. Empirical Data and Study Scenarios

Industrial data collected from a batch of 153 remanufactured transmissions indicate that, in the current configuration (42 mm diameter), only 82 shafts were successfully reused, corresponding to 53.6%. Most rejections were linked to failures in non-destructive testing, primarily due to excessive geometric reductions or the presence of localised cracks. Taking as an example a rotating mechanical shaft subjected to cyclic fatigue, the case study presented in the following section illustrates that each remanufacturing cycle inevitably involves grinding and reworking operations that progressively reduce the load-bearing cross-section. This leads to a gradual decrease in the fatigue life safety factor. The component is originally designed with a defined safety factor; however, each subsequent machining step reduces this factor, introducing a technical limit to the maximum number of sustainable remanufacturing cycles. After each machining operation, the shaft diameter decreases by a certain amount ${∆}_{dmachining}$ and can continue to be re-machined only until $d\ge d^{*}$, where $d^{*}$ represents the minimum allowable diameter for the specific application (Figure 2).

The DfRem can be simplified to an oversizing of the component, which leads to a safety coefficient that decreases over time without ever falling below the design value. The number of remanufacturing cycles is a function of the shaft diameter, according to the following equation:

$$N\left(d\right)={\displaystyle \frac{d-d^{*}}{{∆}_{dmachining}}}$$

(1)

where $d$ is the initial shaft diameter, $d^{*}$ is the minimum allowable diameter below which the component no longer meets functional and structural requirements, and $\mathsf{\Delta }{d}_{\mathit{machining}}$ represents the average diameter reduction required per remanufacturing cycle (due to grinding or re-machining to remove wear and restore tolerances). This formulation provides the maximum theoretical number of remanufacturing cycles, assuming constant material removal per cycle and no premature rejection due to defects or damage.

However, this design improvement entails a higher initial material demand and manufacturing effort—resulting in increased embodied energy and greenhouse gas emissions during the first production stage, as well as the utilisation phase. The trade-off between these two opposing effects determines the overall life cycle efficiency of the component. This relationship establishes a quantitative link between mechanical sizing parameters (such as diameter, mass, and allowable stress) and life cycle indicators (such as global warming potential, material consumption, and cost). In this sense, the improvement of structural design for remanufacturing becomes a multi-objective problem—balancing durability, remanufacturing feasibility, and sustainability performance. The parametric model developed in this work aims precisely to capture this interdependence and to identify the design configurations that maximise both environmental and economic benefits. By increasing the initial diameter first to 43 mm and then to 44 mm, and consequently the initial mass, the defect tolerance would increase, leading to a potential remanufacturable rate of 76% and 85%, respectively. The 76% and 85% values are assumed estimates rather than empirically validated data and are used to explore the potential effect of increasing the initial mass on the remanufacturable rate. This design modification is assumed to result in a mass increase of, respectively, 1.66% and 3.33% for the component. In this work, the variation in the shaft diameter is introduced as a global parametric design variable rather than as a modification applied to a specific functional surface. The entire external profile of the shaft is uniformly scaled from the minimum diameter section, without altering the functional geometry of shoulders, splines, or mating interfaces.

This choice reflects the industrial context of the case study: in the remanufactured transmission, all components mounted on the shaft (e.g., bearings, gears, synchroniser elements) are replaced at each remanufacturing cycle. These elements are standardised parts with finite life, and adapting their internal diameter to match a slightly larger shaft is technically straightforward and represents only a marginal cost compared with the value of the shaft itself.

For this reason, the focus of the study is not on proposing a redesign of a specific surface, but on evaluating—in a controlled and generalisable way—how an increased machining allowance (expressed through a larger starting diameter) influences remanufacturing feasibility, number of allowable cycles, and consequent environmental performance.

2.5.2. Parametric LCA Evaluation Scenarios

Based on these assumptions, three comparative scenarios are proposed:

-

S1: baseline shaft (Ø42 mm, +0% mass), 1 remanufacturing cycle, remanufacturable rate = 53.6%;

-

S2: reinforced shaft (Ø43 mm, +1.66% mass), 1 cycle, remanufacturable rate = 76%;

-

S3: further reinforced shaft (Ø44 mm, +3.33% mass), 1 cycle, remanufacturable rate = 85%.

For each scenario, the environmental impact is quantified as Global Warming Potential (kg CO₂ eq), normalised both to mass and to the overall functionality of the component (expressed as equivalent service-life hours). The resulting parametric LCA model identifies the balance between initial oversizing, facilitation of remanufacturing, and environmental impact of the life cycle (

Table 4. Evaluation scenarios.

Scenario	% Remanufacturable Rate	Total Mass (kg)	Mass Allocated to New Production (kg)	Mass Allocated to Remanufacturing (kg)
S1	53.6%	1570	7285	8415
S2	76%	1623	3895	12,335
S3	85%	1676	2514	14,246

).

The last two columns indicate the proportional allocation of the total shaft mass between the new production process and the remanufacturing process, according to the remanufacturable rate. As the remanufacturable rate increases, the balance progressively shifts towards a higher share of remanufactured mass and a lower share of newly produced mass.

3. Results Analysis

The following section presents and discusses the results of the previously described scenarios, highlighting the environmental implications and comparative performance of the different configurations analysed.

3.1. First Part

3.1.1. Phase 1: Comparison Between New and Remanufactured Shaft

The following results are derived from the comparison between a new shaft and a remanufactured one (Figure 3).

The graph shows the comparison between the new and remanufactured synchroniser shafts based on damage assessment using the ReCiPe 2016 Endpoint (H) method. The impacts are divided into three macro-categories: human health, ecosystems, and resources. The results highlight that the remanufactured component provides a significant environmental advantage in two of the three areas considered:

Human health: A slight drawback is observed in this category, where the remanufactured component has a marginally higher impact. This is attributed to mechanical operations during the reworking, cleaning, and treatment stages, which may increase exposure to non-carcinogenic toxic substances.

Ecosystems: In this category as well, remanufacturing shows a lower impact, primarily due to the reduction in emissions and discharges associated with metallurgical production and raw material extraction, both of which negatively affect biodiversity and the quality of natural habitats.

Resources: The impact of the new component is twice as high as that of the remanufactured one. This reflects the intensive use of virgin materials and energy-demanding manufacturing processes for the new component, whereas the remanufactured one drastically reduces the consumption of natural resources through the reuse of an existing component.

The results obtained using the ReCiPe 2016 Endpoint (H) method are consistent with those generated by the ReCiPe 2016 Midpoint (H) method, as illustrated in Figure 4.

The environmental performance of the synchroniser shaft was evaluated using the ReCiPe 2016 Midpoint (H) method, which considers a comprehensive set of 18 environmental impact categories. This method allows a detailed characterisation of specific environmental mechanisms, providing fine-grained insight into environmental burdens across the life cycle.

However, for practicality and clarity of interpretation—particularly in the context of industrial remanufacturing decision-making—the discussion focuses on five midpoint indicators of primary relevance for mechanical components and metalworking systems: global warming, terrestrial acidification, human carcinogenic toxicity, fossil resource scarcity, water consumption. These impact categories represent those most commonly referenced in LCA studies on metal components, energy-intensive processes, and circular manufacturing systems, and they offer a balanced overview of climate, resource, toxicity, and operational water impacts. The full set of midpoint results is nonetheless available and consistent with the trends discussed below.

The comparison between the new and the remanufactured synchroniser shafts highlights a clear environmental advantage associated with remanufacturing, particularly in terms of global warming mitigation and fossil resource conservation. In both categories, the remanufactured solution shows substantially lower impacts, mainly due to the avoidance of primary steel production and energy-intensive manufacturing processes. This confirms the strong alignment of remanufacturing with circular economy principles, where extending the service life of components reduces reliance on virgin resources and lowers greenhouse gas emissions.

However, the analysis reveals trade-offs in other environmental categories. Human carcinogenic toxicity is slightly higher for the remanufactured component, primarily due to the cleaning, surface restoration, and grinding activities, which involve chemical use and localised emissions. A similar trend is observed in terrestrial acidification, influenced by the reverse logistics flows and electricity-based operations performed during remanufacturing. Furthermore, water consumption is higher in the remanufacturing scenario, as cleaning and cooling processes are required to restore the used part to an “as-new” functional condition.

Despite these localised increases, the overall balance clearly favours remanufacturing. The most significant result is observed for global warming, where the remanufactured shaft generates approximately 100 kg CO₂-eq compared to 183 kg CO₂-eq for a new shaft, corresponding to a ≈45% reduction in climate impact. This evidence reinforces remanufacturing as an effective strategy to reduce environmental burdens while maintaining component performance and material circularity. These results will be further analysed in the following sections through scenario-based evaluation and sensitivity analysis.

3.1.2. Phase 2: Average Shaft with the Actual Remanufacturable Rate of 53.6%

While the previous analysis assumes that the shaft is 100% recovered and reused in a remanufactured transmission, this scenario models the process as a weighted combination of new production and remanufacturing based on real industry data.

It addresses the key question: given the current remanufacturable rate of 53.6%, what is the true environmental impact of each synchroniser shaft leaving the system?

To assess the actual environmental benefit generated by the remanufacturing of the shaft, an LCA comparison is conducted across three distinct scenarios:

• Production of a new shaft using virgin raw materials.
• Complete remanufacturing of the shaft.
• An intermediate, real-world scenario in which only 53.6% of shafts are remanufactured, while the remaining 46.4% are replaced with newly produced components.

The graph in Figure 5 illustrates the environmental impact of the three scenarios in terms of Global Warming Potential (GWP), expressed in kilograms of CO₂ equivalent per synchroniser shaft.

The full production of a new component results in the highest impact, with 183 kg CO₂ eq. In comparison, remanufacturing lowers emissions to 100 kg CO₂ eq (−45%), while the intermediate scenario, based on the actual remanufacturable rate of 53.6%, leads to an impact of 139 kg CO₂ eq (−24%). These findings demonstrate that, even under non-ideal operational conditions, remanufacturing delivers significant environmental benefits. The “average shaft” model accurately represents the behaviour of the real system, providing a valuable tool for informed decision-making based on concrete data. Furthermore, this analysis enables sensitivity assessments to estimate the potential additional reductions in environmental impacts that could be achieved by increasing the remanufacturable rate beyond 53.6%.

3.1.3. Phase 3: Sensitivity Analysis with Increasing Remanufacturable Rates (70%, 85%, 100%)

The sensitivity analysis is used to explore how design or operational choices influence one or more environmental indicators. For the synchroniser shaft, an “intermediate” scenario was modelled to reflect the current real-world situation, in which 53.6% of shafts are remanufactured out of a total of 153 remanufactured transmissions. However, this proportion may not remain constant over time. With process improvements and targeted investments in the selection, diagnostics, treatment, and collection of used components, it is reasonable to expect an increase in the remanufacturable rate, leading to greater environmental benefits. As shown in

Table 5. Sensitivity analysis scenarios.

Scenario	% Remanufacturable Rate	% New	Global Warming (kg CO2 eq)	% Reduction
Actual case (53%)	53.6%	46.4%	139	24%
Improved case 70%	70%	30%	125	31%
Improved case 85%	85%	15%	113	38%
Optimal case 100% (theoretical)	100%	0%	100	45%

below, the environmental impact decreases progressively as the percentage of remanufactured shafts increases.

The sensitivity analysis reveals an almost linear decreasing relationship between the remanufacturable rate, and the climate impact associated with the production of the synchroniser shaft. As the remanufacturable rate increases, the Global Warming Potential (GWP) indicator decreases significantly, reaching a maximum reduction of 45% in the theoretical case where all components are replaced with remanufactured ones. The current scenario, with a remanufacturable rate of 53.6%, already achieves a 24% reduction, demonstrating both the environmental value of the present strategy and the potential for further improvement in the future. The sensitivity analysis shows that increasing the remanufacturable rate improves environmental performance, quantifies the associated reductions in CO₂ emissions, energy use and resources, and provides a data-driven basis to justify investments in component recovery while strengthening sustainability strategies and communication.

3.2. Second Part

This section presents the results related to Part 2, focusing on the analysis of the DfRem approach and the multi-cycle scenario.

Phase 1: For each case, the environmental impacts are calculated and expressed in kilograms of CO₂ equivalent, considering the contributions from both the production of the new shaft and the remanufacturing process, weighted according to the actual success rate. The total Global Warming Potential (GWP) for each case, considering an extended service life, is therefore defined as: ‘production of a new component + remanufacturable weighted by the success rate’, that is:

$${\mathrm{GWP}}_{\mathrm{tot}}={\mathrm{GWP}}_{\mathrm{new}}· (1-\mathrm{p})+{\mathrm{GWP}}_{\mathrm{reman}}·\mathrm{p}+{\mathrm{GWP}}_{\mathrm{new}}$$

(2)

where GWP new is the impact of producing a new shaft, GWP reman is the impact of remanufacturing one shaft, and p is the proportion of components that can be successfully remanufactured. In

Table 6. Analysis results (new + remanufacturing).

Case	GWP New	GWP of the Reman Component	% Remanufacturable Rate	Weighted GWP Tot (New + Reman)	GWP (2 New) (kg)	Reduction (kg)
A (d = 42 mm)	183	139	53.6%	342.4	366	23.6
B (d = 43 mm)	189	124	76%	328.6	378	49.4
C (d = 44 mm)	195	124	85%	329.7	390	60.3

is indicated the reduction using remanufacturing.

Figure 6 shows the analysis comparing three configurations of the synchroniser shaft. Each configuration has an increasing mass and a different remanufacturing rate.

Case A (15.7 kg, 53.6% remanufacturable rate) achieves a net saving of 23.6 kg CO₂ eq compared to the production of two entirely new components.

Case B (16.23 kg, 76%) further improves the outcome, with a saving of 49.4 kg CO₂ eq, representing the best compromise between added mass and environmental benefit.

Case C (16.76 kg, 85%), while resulting in a slightly higher mixed GWP than Case B, delivers the greatest absolute net saving of 60.3 kg CO₂ eq, due to the high percentage of remanufactured components. However, the ratio between the additional mass and the environmental benefit is less favourable.

In summary, Case C is most advantageous in terms of absolute emission reduction, whereas Case B is more efficient and balanced. The design for remanufacturing should therefore carefully balance mass, service life, and remanufacturable rate to improve environmental impact over the product’s life cycle.

Phase 2: Extension to Multi-Cycle Remanufacturing.

In real-world scenarios, the remanufacturing of a component is not necessarily limited to a single cycle. If the component continues to meet the required structural, functional, and dimensional specifications, it can undergo multiple reworking cycles. However, with each additional cycle, the component is subject to the following:

-

Material removal, which reduces both the diameter and the residual mass;

-

An increasing risk of failing non-destructive testing (NDT);

-

A potential loss of compliance with the dimensional tolerances required for proper machine function.

These physical and technical factors establish a practical limit to the maximum number of permissible remanufacturing cycles. To more accurately represent the real behaviour of the system over time, a progressive decay hypothesis was introduced, describing a decrease in the remanufacturable success rate with each subsequent cycle. If p₁ is the success rate at the first remanufacturing cycle, the success rate at cycle n is defined as:

$${\mathrm{p}}_{\mathrm{n}}={\mathrm{p}}_1·{\mathrm{r}}^{(\mathrm{n}-1)}$$

(3)

where

-

${\mathrm{p}}_{\mathrm{n}}$= success rate at the $\mathrm{n}\text{-}\mathrm{th}$ remanufacturing cycle;

-

${\mathrm{p}}_1$ = initial success rate at the first cycle (baseline industrial value);

-

$\mathrm{r}$ = decay factor (<1) expressing the fractional reduction in success rate per cycle;

-

$\mathrm{n}$ = cycle index $(\mathrm{n}=1,2,3,\dots )$.

This formulation reflects the increasing likelihood of rejection as geometric tolerances tighten, wear accumulates, and fatigue damage progresses over successive regeneration cycles. In this study, a decay factor of r = 0.85 was adopted, corresponding to a conservative 15% reduction in successful remanufacturing probability per cycle to reflect a conservative yet technically plausible rate of decline. This choice is motivated by the following:

-

Documented reductions in recovery rates for rotating mechanical components across reuse cycles in industrial practice, driven by dimensional loss, surface degradation, and fatigue life exhaustion.

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Process constraints associated with the minimum allowable shaft diameter after re-machining and critical fatigue strength thresholds required to ensure compliance with mechanical safety margins.

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Alignment with degradation trends reported for remanufactured automotive and off-highway machine components, where rejection rates typically increase between 10 and 25% per cycle due to cumulative damage and inspection screening.

To acknowledge uncertainty, a sensitivity analysis on r was performed (not reported in the present paper to maintain focus on the proposed modelling framework), demonstrating that while the absolute magnitude of environmental benefits varies, the direction and consistency of the advantage of remanufacturing remain robust across realistic decay ranges. This confirms that the approach is valid within the operational limits dictated by geometry, material removal allowances, and fatigue performance criteria.

This approach realistically simulates the scenario in which, as the number of cycles increases, a growing proportion of components no longer meet the dimensional or structural requirements for remanufacturing, due to wear, cracking, or exceeding tolerance limits. The cumulative Global Warming Potential for a new shaft followed by three remanufacturing cycles is calculated as:

$${\mathrm{GWP}}_{\mathrm{tot}}={\mathrm{GWP}}_{\mathrm{new}}+\sum _{n=1}^3\left[p_i\cdot {\mathrm{GWP}}_{\mathrm{reman}}+\left(1-p_i\right)\cdot {\mathrm{GWP}}_{\mathrm{new}}\right]$$

(4)

In this formulation

-

${\mathrm{GWP}}_{\mathrm{new}}$ is the environmental impact of manufacturing a new shaft;

-

${\mathrm{GWP}}_{\mathrm{reman}}$ is the impact of remanufacturing one shaft;

-

$p_n$ is the remanufacturing success rate at cycle $n$;

-

$\left(1-p_n\right)$ represents the fraction of components that cannot be remanufactured at cycle $n$ and must therefore be replaced with new units.

The summation term accounts for the environmental impact of each remanufacturing cycle, weighted by the probability of successful recovery and including the impact of producing new components when remanufacturing is unsuccessful. The initial ${\mathrm{GWP}}_{\mathrm{new}}$ term represents the impact of manufacturing the first (original) shaft. This formulation captures the cumulative benefit of extending the service life through remanufacturing and the penalty associated with failures to recover components across successive cycles.

The results, in terms of GWP for the different cases, are reported in

Table 7. Analysis results: 1 new + 3 remanufacturing cycles.

Case	GWP New	GWP Reman	Initial Remanufacturable Rate (%)	GWP Tot (1 New + 3 Reman)	GWP 4 New	Reduction
A	183	139	53.6%	596.28	732	135.72
B	189	124	76.0%	562.33	756	193.67
C	195	124	85.0%	567.08	780	212.92

.

In the multi-cycle scenario (Figure 7), the net savings increase with the initial remanufacturable rate, confirming that a design strategy oriented towards remanufacturing enables cumulative benefits over successive cycles. Case A, while representing the baseline configuration, is less efficient in the long term. However, Case B proves to be the most balanced configuration, as it achieves a lower GWP while requiring only a modest increase in initial mass. Case C, despite having a higher initial mass, delivers the greatest absolute reduction in emissions, with a saving of −212.9 kg CO₂ eq compared to producing four entirely new shafts. This highlights how the adoption of DfRem strategies, combined with the realistic modelling of the remanufacturable success rate, can lead to a significant environmental improvement over the entire life cycle of the component.

4. LCC Analysis

For further investigation, an assessment is carried out not only from an environmental perspective but also from an economic one. This preliminary analysis compares two types of processes: the production of a new component versus the remanufacturing of an end-of-life component. The objective of the LCC analysis in this study is to evaluate the economic viability of remanufacturing a synchroniser shaft compared to its production using virgin raw materials. The analysis is carried out in parallel with the LCA, adopting the same system boundaries to ensure methodological consistency. The LCC model is developed following the guidelines of ISO 15686-5 [21], ensuring a structured and standardised approach to life cycle cost evaluation.

Costs were categorised into five main groups: acquisition/production costs (related to the fabrication of a new component or the remanufacturing process), logistics, operating costs (energy consumption, labour, and auxiliary materials), maintenance and downtime costs (direct and indirect costs), end-of-life costs (associated with disposal, recycling, and waste treatment).

For remanufactured components, additional elements were incorporated into the model to capture the specific dynamics of circular production, such as the core value, representing the economic benefit of recovering and reusing an end-of-life component, the inspection and reworking costs (depending on the actual remanufacturable success rate) and the reverse logistics costs (covering the collection and transportation of end-of-life components back to the remanufacturing facility).

This structure enables a comprehensive comparison between the two scenarios, ensuring that both the direct and indirect economic factors are considered in the evaluation of long-term sustainability.

4.1. Input Data and Economic Assumptions

The analysis is carried out starting with the collection of data for the six main phases of the remanufacturing process: cleaning and sandblasting, NDT inspections, final grinding, heat treatments, replacement of worn parts, and final assembly. Each phase is characterised by the following parameters:

-

Energy consumption (kWh) or mass of material removed (kg).

-

Processing time (hours or minutes).

-

Process description.

Based on these inputs, the following cost elements are calculated:

-

Energy: Energy consumption is directly derived from measurement data where available. In the absence of direct measurements, it is estimated using the removed material mass multiplied by a specific cutting energy of 2.5 MJ/kg (equivalent to 0.694 kWh/kg) and divided by machine efficiency, assumed at 75%.

-

Tooling: Tooling costs are estimated at EUR 2.00/kg of material removed; in general, tooling accounts for approximately 3% of the total manufacturing cost.

-

Waste disposal: Represents the cost of managing chips or residues, set at EUR 0.10/kg, consistent with average fees charged by recycling operators, including transportation costs.

-

Scrap revenue: A revenue of EUR 0.20/kg is assigned to steel chips. Although 2024 European scrap metal prices ranged between EUR 0.295/kg and EUR 0.345/kg, a conservative value was chosen to account for potential contamination or additional processing costs.

-

New material: For the “Replacement parts” phase, the cost of steel is set at EUR 0.80/kg. This value is higher than the average price of hot-rolled coil steel in Italy (approximately EUR 0.55–EUR 0.59/kg in 2024) to reflect the use of alloyed and heat-treated steels.

-

Labour: For the final assembly, a specialised operator in the automotive sector is assumed, with an average company labour cost of EUR 42/h. Eurostat data show that in 2024, the European average industrial labour cost was EUR 33.5/h, with comparable figures reported for the Italian manufacturing sector.

-

Electricity: The electricity rate is set at EUR 0.25/kWh, aligned with the industrial consumer prices in the Eurozone. According to Eurostat, in the second half of 2024, non-domestic electricity prices ranged from EUR 0.0767/kWh (Finland) to EUR 0.2578/kWh (Cyprus).

-

Overhead costs: A 15% overhead rate is applied to direct costs to cover general expenses such as administration, logistics, and non-attributable maintenance. The managerial literature typically suggests overhead percentages between 10 and 20% of total production value.

-

CAPEX: Capital expenditure (machine depreciation) was not included in the current calculations, as the analysed operations represent only a small fraction of total equipment usage. However, the model allows for the introduction of an hourly capital cost if desired, by allocating a machine value across the number of processed parts.

These economic assumptions establish a framework for converting physical quantities into monetary values. While realistic, they remain sensitive to fluctuations in energy markets, raw material prices, and labour costs, requiring periodic updates to maintain accuracy.

4.2. Life Cycle Costing Inventory (LCCI)

The following table summarises the physical quantities associated with each remanufacturing phase (

Table 8. Quantities of remanufacturing phase.

Phase	Brief Description	Main Data Type	Value
Cleaning and sandblasting	Removal of surface contaminants by wheel blasting	Electricity consumed	2.0 kWh
NDT checks	Magnetic and ultrasonic inspections to detect defects	Electricity consumed	0.5 kWh
Final grinding	Removal of worn layer by grinding	Mass removed	0.7 kg
Heat treatments	Controlled heating and cooling to restore microstructure	Electricity consumed	20.0 kWh
Replaced parts	Replacement of irreparable material sections	Mass replaced	0.3 kg
Final assembly	Reassembly and functional testing of reconditioned component	Labour time	3 h

). Energy-based phases report the consumption directly in kWh, while material-based phases indicate the mass of material removed or replaced (kg).

Results

The results of the LCC analysis for each phase are shown in the table below (

Table 9. Results of LCC Analysis for remanufactured shaft.

Phase	Quantity	Energy (kWh)	Direct Cost (EUR)	Overhead (EUR)	Total Cost (EUR)
Cleaning and sandblasting	2.0 kWh	2.000	0.500	0.075	0.575
NDT checks	0.5 kWh	0.500	0.125	0.019	0.144
Final grinding	0.7 kg	0.648	1.492	0.224	1.716
Heat treatments	20.0 kWh	20,000	5.000	0.750	5.750
Replaced parts	0.3 kg	–	0.240	0.036	0.276
Final assembly	3 h	–	114,000	17,100	131,100
Total		23,148	121,357	18,204	139,561

). All values are expressed in euros.

The analysis of the results shows that the final assembly phase overwhelmingly dominates the total cost, amounting to EUR 131.10 (94% of the total). This is primarily due to the high cost associated with specialised labour. Energy-intensive phases, such as heat treatments, make a moderate but non-negligible contribution (EUR 5.75; 4.1% of the total), reflecting the relatively low cost of industrial electricity. The final grinding phase, while modest in absolute terms (EUR 1.716), presents a complex cost structure as it combines multiple cost elements, including energy, tooling, waste disposal, and scrap revenue. Initial phases such as cleaning and NDT inspections have a negligible impact on total costs. Finally, the replacement of worn parts results in a marginal cost (EUR 0.276), due to the very limited quantity of new material required.

5. Conclusions and Future Developments

In many cases, the failure of a mechanical component can compromise the overall safety of the machinery; therefore, efforts to enhance environmental sustainability through remanufacturing must be accompanied by a rigorous consideration of structural reliability.

This study assessed the environmental potential of remanufacturing the synchronizer shaft of a mechanical transmission, analysing both single-cycle and multi-cycle scenarios through a parametric LCA model based on industrial data. The model integrates component geometry, dimensional modifications for remanufacturing, and the gradual decline in process efficiency across cycles. Results show that remanufacturing yields a clear environmental advantage even after a single reuse, with CO₂-equivalent emissions significantly lower than those of producing a new component. This benefit increases over successive remanufacturing cycles, assuming a remanufacturable decay factor of 0.85. Among the three shaft designs examined (42, 43, and 44 mm), the 43 mm configuration offered the best trade-off between environmental impact, remanufacturable rate, and mass, while the 44 mm design achieved the highest cumulative savings due to its enhanced remanufacturing suitability. The findings confirm that the Design for Remanufacturing (DfRem) is an effective approach to improving both technical and environmental performance, provided that functional and residual performance limits are properly assessed. The proposed model serves as a decision support tool to align design strategies with circular economy objectives, guiding engineers in balancing mechanical performance, remanufacturing potential, and environmental impact throughout the product life cycle. Replacing even small amounts of primary steel with remanufactured parts substantially reduces energy consumption and CO₂ emissions: for instance, avoiding the production of 0.3 kg of new steel can save roughly 15.6 MJ (≈4.3 kWh) of energy. Remanufacturing is therefore confirmed to be both environmentally and economically advantageous compared to full replacement. The resulting benefit translates not only into lower emissions but also into substantial cost savings, as energy is a major cost driver in steel production. From an industrial perspective, these savings justify investments in component collection, inspection, rework, and quality control systems. Increasing the remanufacturable rate directly improves profitability by reducing the material procurement costs, lead times, and exposure to raw material price volatility. Although not covered in this study, further improvements could be achieved by implementing a lean-oriented final assembly, real-time energy monitoring on grinding and sandblasting equipment, heat recovery technologies during thermal treatments, systematic data acquisition from the shop floor, and periodic updating of LCC models to reflect fluctuations in energy, labour and material costs.

Future work should extend the analysis to the entire transmission system and incorporate real-time energy monitoring, heat recovery, and improved waste management to further enhance process sustainability and data accuracy.