One-Way-Assembly accelerates aerospace manufacturing but risks leaving drilling burrs at the interfaces of mechanical joints. The detrimental impact of burrs on fatigue strength is widely recognized in the literature, but the mechanisms driving this "knock-down" remain unclear. This study investigates this phenomenon using open-hole Ti-6Al-4V specimens. The experimental campaign systematically decouples the effects of macrogeometric stress concentration, residual stresses, and burr tip microgeometric features. Results revealed a non-monotonic relationship between burr size and the fatigue "knock down," leading to rejecting the macroscopic stress concentration hypothesis. Similarly, stress-relief heat treatments failed to mitigate the fatigue "knock-down," ruling out residual stresses as a governing factor. Instead, a unified failure mechanism was identified. All detrimental configurations collapsed into a single S-N cluster. Striation counting confirmed this cluster aligns with the material's pure crack propagation behavior, demonstrating that sharp burr tip features severely shorten the crack nucleation phase.

Burr formation is a major concern in the drilling of aeronautical components, as it negatively affects assembly quality and fatigue life. In the context of Industry 4.0, digital twins are expected to enable the prediction of burr formation and the active control of drilling processes. However, this requires robust predictive models, for which the selection of appropriate input variables and signal features is a fundamental step. In this work, axial force and torque signals acquired during Ti6Al4V drilling with the same cutting tool under four tool conditions were analysed, and after machining, the corresponding burr height at the hole exit was measured. The relevant descriptors were identified using a signal-processing methodology that extracts temporal and spectral domain features related to signal amplitude, energy, power, and dynamic behaviour. The results show that axial force-based descriptors extracted from the stable phase of drilling exhibit a relationship with burr height, following power-law trends with coefficients of determination up to R-squared higher than 0.83, although this behaviour is largely governed by the separation between wear levels. Comparable performance was obtained using the force at tool breakthrough, highlighting the potential for developing a digital twin to anticipate burr formation before the exit phase, an important capability for future real-time monitoring and control strategies.

In the context of cleaner, safer, and more cost-effective machining processes, supercritical carbon dioxide (sCO₂) has emerged as a promising alternative to conventional cutting fluids, particularly for drilling titanium alloys such as Ti-6Al-4V. The dual role of sCO₂, simultaneously providing localized cooling and assisting chip evacuation, underlines its potential to extend tool life, reduce cutting forces, and improve overall process sustainability. Nevertheless, the optimal operating conditions for sCO₂ jets in drilling remain undefined, and the direct influence of jet morphology on heat transfer mechanisms is not yet fully clarified.The present study intends to contribute to this understanding through an experimental investigation of the thermal performance of sCO₂ jets. Results show that the jet structure is essentially dependent on the upstream conditions. Due to the complicated jet structure under these conditions, the nozzle-to-plate distance is an important parameter, and the evolution of the supersonic structure in function of the nozzle-to-plate distance is evaluated. The cooling behavior is found to be directly related to the structure of the underexpanded jet and thus to the upstream parameters and the impinging distance. To investigate this phenomenon, high-speed Schlieren imaging was carried out under varying initial pressures and temperatures. The visualizations provided detailed insights into the jet structure and revealed the presence of three successive regions: laminar, transitional, and turbulent. Infrared images are also used to evaluate the jet cooling ability in a hot cylindrical tube for varying upstream conditions. Building on these results, future work will focus on the influence of the expansion distance on the jet cooling efficiency.

In recent years, materials have evolved across all fields. The goal is to develop materials that are increasingly resistant while also being lightweight, stainless, and tough. All these mechanical and physical properties require increasingly complex microstructures, which can directly affect the cutting process. Adding additive manufacturing to this equation—with its ability to produce even more complex structures—makes mastering the cutting process difficult and its prediction nearly impossible.The objective of this paper is to investigate, in the case of an additively manufactured stainless steel (316L) produced using different manufacturing routes, the relationships between microstructure and the cutting process. The analyses are based on the observation of the cutting process through post-mortem examinations of chips, chemical analyses of material evolution, as well as microstructural characterizations such as EBSD tests. In addition, a specific setup was developed to ensure that each test applies a mechanically oriented load with respect to the build plane. Finally, the cutting process partly relies on the creation of a crack initiated by the tool. This crack then becomes the beginning of the shear within the primary shear zone. One possible indicator of machinability is toughness. Part of this study therefore explores the impact of toughness modification on the cutting process.

Abstract Machining processes produce unwanted remainders of material on the free edges which are called burrs. In particular, the drilling process generates an entry burr and a typically larger exit burr. When drilling stacks of several workpieces, exit and entry burrs are produced simultaneously at the interfaces. The presence of burrs can degrade the static and fatigue strength of the parts and assemblies containing them. An example concerns the burrs formed at the interface during the drilling of multistacks in One-Way-Assembly processes, where deburring is not systematically applied. The effect on fatigue can be significant. Reductions of up to 70% in fatigue life have been reported, even though the explanatory rationale is not clear. This article reviews existing works on burrs, focusing on drilling burrs. A description of the morphology of different types of burrs and of measurement technologies is given. Burr formation mechanisms and their modeling are reviewed. Burr control strategies and the main deburring technologies are examined. The limited literature on the effects of burrs on the static and fatigue strength of mechanical assemblies is also explored.

Precision in surgical bone drilling is essential for restoring bones mobility and function. However, the intricate nature and fiber-reinforced composite structure of bones inherently pose drilling-induced mechanical damage to the bone surface, affecting the primary stability necessary for implant anchorage and therefore leading to implant failure. The critical need for enhanced hole quality and damage reduction has spurred investigations into the optimal drilling parameters, novel drilling tools and alternative machining techniques. This study rigorously investigates the effect of the cutting speed and feed rate during axial drilling employing a center drill. It extends toward a comprehensive analysis of forces, temperature and mechanical damage, with a particular emphasis on delamination assessment. Then, the optimal parameters are established using the Tool-Material Couple (COM) optimization strategy. Subsequently, a novel approach of orbital drilling in bones is introduced for hole quality enhancement when compared to the conventional technique. This investigation serves as a foundational step for a more comprehensive study that ventures into the innovative application of orbital drilling in orthopedics.

Wheelchair fencing is an opposition sport on a specific wheelchair, with a fixed distance between the two athletes. As for other Paralympic sports, different categories exist for the different pathologies of the athletes. Searching for biomechanical performance criteria is of primary interest for coaches, recruiters and trainers. Such performance criteria have been highlighted for able-bodied fencers but not for para-fencers. Through transposition, the corresponding parameters for para-fencers would be the weapon speed and the ability to move the trunk forward and backward on their wheelchair. Therefore, the objective of this study was to determine performance criteria for para-fencers. Eleven French para-fencers performed fencing activities with a motion capture system while facing each other, with their own equipment. Different activities were realised to quantify the allonge, the weapon speed, and the torso motion. Only the correlation between the range of motion of the torso and the mass of the athletes wielding an épée was significant (p=0.02). The comparison between the different categories showed significant differences for the torso motion, which was not found for the weapon speed. Future studies, with a larger cohort, might help validate, or not, tendencies found in this study.

Bone drilling poses intricate challenges due to its high hardness, strength, and anisotropic composite structure. In the dynamic field of orthopedics, advancing surgical drilling techniques is imperative for optimizing precision and implant stability. As drilling methods have progressed from conventional to robot-assisted machining, some new possibilities are now appearing. While orbital drilling has been pivotal in aerospace for reduced forces and superior hole quality, its application in bone drilling remains unexplored. This study pioneers the introduction of orbital drilling for bone machining, aiming to unveil its potential to improve processing quality. Experimental investigations were conducted on cortical femur bone to evaluate its mechanical behavior and the geometry of the holes, encompassing parameters such as hole aperture, roundness, cylindricity and delamination. Employing full factorial statistical analysis, the study systematically elucidates the influence of cutting speed and feed rate on hole quality. Results reveal the potential of orbital drilling in mitigating its defaults and could significantly contribute to improving surgical outcomes in orthopedic procedures. (c) 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the CIRP BioM 2024

The gross mechanical efficiency of the manual wheelchair propulsion movement is particularly low compared to other movements. The energy losses in the manual wheelchair propulsion movement are partly due to energy losses associated with the wheelchair, and especially to the rolling resistance of the wheels. The distribution of mass between the front rear wheels and the caster wheels has a significant impact on the rolling resistance. The study of the caster wheels cannot therefore be neglected due to their involvement in rolling resistance. Thus, this study aimed to evaluate the power dissipated due to rolling resistance by different caster wheels, at different speeds and under different loadings on various terrains. Four caster wheels of different shapes, diameters, and materials were tested on two surfaces representative of indoor sports surfaces at four different speeds and under four loadings. The results showed a minimal dissipated power of 0.4±0.2W for the skate caster, on the parquet, at 0.5 m/s and under a loading of 50 N. The maximal mean power dissipated was 43.3±27.6W still for the skate caster, but on the Taraflex, at 1.5 m/s and under loading of 200 N. The power dissipated on the parquet was lower than the one on the Taraflex. The Spherical and Omniwheel caster wheels dissipated less power than the two other casters. This study showed that caster wheels cannot be neglected in the assessment of gross mechanical efficiency, particularly in light of the power dissipated by athletes during propulsion.

Bone drilling is a critical procedure in orthopedic surgery, essential for bone fixation. However, achieving consistently high-quality, damage-free holes remains a challenge, even with advanced drilling tools and techniques, as the process is conventionally performed manually using axial drilling units. This study introduces orbital drilling, a robot-assisted technique, as a novel approach in orthopedic applications to enhance the quality of drilled holes by addressing and mitigating drilling-induced mechanical damage. A comparative analysis of orbital and axial drilling techniques is conducted to elucidate the kinematics of both methods and assess the improvements in hole quality parameters achieved through orbital drilling. For the first time, forces generated during orbital drilling in bones are systematically monitored, and delamination damage at both the entry and exit points of the drilled bone tissue is comprehensively analyzed using advanced digital image processing techniques. Additionally, hole geometry is characterized using Coordinate Measuring Machines (CMM). Results demonstrate that orbital drilling reduces average forces by approximately 85% compared to axial drilling, due to improved load distribution and a reduced contact area. Using a multi-criteria decision-making approach (AHP-TOPSIS), the study reveals that orbital drilling significantly improves machining accuracy, including circularity, cylindricity, and aperture, while minimizing delamination damage, enhancing surface quality, and mitigating microcracks. Analysis of variance (ANOVA) further indicates that, in orbital drilling, cutting speed has a lower impact, whereas feed rate-related parameters play a more significant role compared to axial drilling. These findings represent a substantial advancement in addressing the current challenges associated with bone drilling and provide key insights into the mechanical failure mechanisms involved.

Industry 4.0 is the need of the hour in current global market scenario and all the processes are moving toward automation and smart manufacturing. In machining, smart techniques implementation depends on developing a database for decision-making, which is the case for stack drilling in aerospace industry. In this application, choosing one optimal condition for several materials is a challenge due to their different machinability. Hence, material identification techniques are suitable approaches for adapting the cutting parameters in real time, which improves tool life, hole quality, and productivity. In that regard, the goal of the present paper is to create a specific force data map for axial drilling and circular milling processes based on its experimental force and power measurements. To do that, experiments were separately carried out on Titanium and Aluminum workpieces in a range of cutting speed and feed conditions. The results show that specific cutting and feed forces for each material can be identified on distinct regions of the map, without thresholds overlapping. Given that, these maps can be used as a signature to distinguish two metallic materials in real time machining. In this case, the specific data points at the interface layers may offer advantage to accurately identify tool position unlike monitoring gradient of feed forces while drilling stacked materials. Therefore, smart machining techniques seeking cutting parameters optimization can be implemented for a particular material.

Fault diagnosis is a crucial task to guarantee reliability and reduce losses and production cost in smart machining in the Industry 4.0. In order to do so, it is necessary to implement a fault diagnoser that does not use a large amount of memory and which is capable of detecting the occurrence of a fault in a fast manner. In this paper, we propose a timed automaton model, called Timed Automaton with Timing Intervals and Outputs (TATIO), which is suitable for fault diagnosis. The TATIO model represents a typical drilling process on a CNC machine which uses an ISO code for programming and is obtained by identification of timing intervals associated with the time instants that the events occur in the system. The fault diagnoser uses only the spindle power and Z position read directly from the system controller and does not need any additional sensor. The proposed diagnoser is capable of detecting the use of a wrong cutting speed for a specific workpiece material, the use of a material different from the expected, and the occurrence of a wrong sequence of events executed by the system.

Hole making on stacked aerospace materials is a major operation during aircraft assembly which poses significant challenges during manufacturing because of different material machinability. Strategies involving smart machining including adapting proper cutting conditions using real time monitoring can lead to significant improvements. This paper is a continuation of our research that uses data map methodology characterized by different specific force regions for workpiece material identification. In this article, spindle power is monitored utilizing CNC machine internal sensor during helical milling of Aluminium and Titanium alloys in a aerospace stack for estimating cutting coefficients. Our previous research addressed the material detection in circular milling of Aluminium and Titanium alloys independently using a force dynamometer. The result shows the applicability of data map technique consisting of axial force coefficients for material identification in helical milling and highlights the significance of stack sequence .

The orbital drilling process is a very complex machining operation. Due to the helical path of the tool in the material and the tool geometry that can be very complex, the geometry of the chip is very variable along the cutting edge and during a revolution of the tool. This complexity leads to variable cutting forces during drilling and makes it difficult to model and estimate for different tool geometries. The aim of this study is, therefore, to use a modelling of the orbital drilling process in order to study the influence of the geometry of the tool and the cutting conditions on the cutting forces. The final objective is to identify their impact on the quality of the drilled hole and, thus, to control the final quality. First, the chip geometry is modelled from the cutting parameters and the macro-geometry of the tool. It needs to determine the tooth trajectory into the material for each point of the cutting edge. Cutting force models, based on the instantaneous chip thickness, are then implemented. An experimental study validates the modelling by cutting force measurements carried out during orbital drilling tests. From this modelling, it is now possible to study the influence of the geometry of the cutting tool on the forces in order to control the loading on the tool and therefore the final quality of the drilled hole.

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The development of intelligent techniques based on real-time monitoring for machining applications is one of the challenges of Industry 4.0, as in the Aerospace Industry. Drilling is the most used process before the assembly of airplane sheets, that nowadays are composed of different layers of materials with different optimized cutting conditions. The fault diagnosis during drilling stack materials is important to reduce cost and improve the process quality. Using a machine-tool, it is important that the fault diagnoser does not use a large amount of memory and be capable of detecting faults in a fast manner. In this paper, we propose a timed automaton model representing the drilling process of a Titanium plate on a CNC machine, which is suitable for fault diagnosis without any additional sensors. The diagnoser uses only the spindle power and Z axis displacement read directly from the system controller. The target faults in this case are: (i) excessive tool-wear or tool breakage; (ii) the tool finds an off-centered hole while producing a blind-hole; (iii) the tool finds an under layer of a different material, as it occurs in a bi-layer material; and (iv) the plate thickness is below the desired one and a though hole is produced. The results show that the model is capable of identifying all faults and it could be used to alert a problem on the sequence of machining holes in the industry

Abstract The orbital drilling process is a very complex machining operation. Due to the helical path of the tool in the material and the sometimes very complex tool geometry, the geometry of the chip is very variable along the cutting edge and during a revolution of the tool. tool. This complexity explains why the cutting forces are very variable during drilling and they are very difficult to model and estimate for different tool geometries. The aim of this study is therefore to develop a cutting force model taking into account the geometry of the tool and the cutting conditions. The final objective is to control the final quality of the machined borehole. First, the geometry of the chip is modeled from the cutting parameters defining the trajectory and from the macro-geometry of the tool. Cutting force models, based on the instantaneous chip thickness and applied to the drilling, are then implemented. An experimental study validates the modeling by cutting force measurements carried out during orbital drilling tests. From this modeling, it is now possible to study the influence of the geometry of the cutting tool on the forces in order to control the loading on the tool and therefore the final quality of the drilling.