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Carbon fiber reinforced plastic and titanium alloy (CFRP/Ti) stacks have been widely used as aerospace structures because of their excellent combination of physical properties. Interface damage caused by interface gaps, significantly different from that of metal/metal stacks, is a common problem in the through-hole drilling of CFRP/Ti stacks with l...
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... These phenomena become more prominent and noticeable for thin materials, resulting in a corresponding reduction in their flexural stiffness. Additionally, Luo et al. [4] and Panico et al. [5] highlighted that the interlayer gap influences the formation of burrs. To maintain structural integrity and assembly quality, it is necessary to remove the accumulated material and interface defects through operations such as disassembly, cleaning/deburring, and reassembly. ...
The aerospace industry's relentless pursuit of lighter, stronger, and more fuel-efficient aircraft has led to the widespread use of lightweight materials, particularly aluminum alloys, in aerospace engineering. This study focuses on the challenges associated with one-shot drilling without back-up forces of thin parts, a strategy aimed at reducing cycle, avoiding part separation for cleaning after drilling, and minimizing part assembly problems. Despite its effectiveness, problems persist with defects developing at the interface due to the interlayer gap phenomenon. This gap causes metal chips to accumulate and is influenced by both process parameters and the clamping conditions and methodologies. While existing literature primarily associates process parameters with burr measurements, this study delves into the often-overlooked influence of clamping strategies on the occurrence of interface defects. Through experimental drilling on a thin stack of Al7075-T6 and Al2024-T3, various clamping schemes were analyzed to assess their impact on burr height. The results were also correlated with the drill verse, thrust force, and torque. The objective is to increase know-how about these aspects and optimize clamping strategies for effective one-shot drilling, addressing gaps in current research.
... This could lead to the accumulation of metallic chip and/or carbon powder between the plates. Besides Luo et al. 7 pointed out that the interlayer gap has an effect on the interlayer burr formation in one shot drilling of unsealed plates. To preserve the structural integrity and quality of the assembly, the accumulated material and the interlayer burr at the interface must be removed through de-stacking, cleaning/deburring, and reassembly operations but these operations are time-consuming, non-value added and expensive. ...
... The complexity increases considerably in the case of hybrid stacks, where the different mechanical properties of the materials imply different machinability and therefore different optimal process parameters. [10][11][12] Although the process parameters affect the size of the interlayer burr, the condition that physically allows the generic insertion of material between two consecutive layers is the gap between them, as explained by Luo et al. 7 and Yin et al. 13 There are two main reasons contributing to the formation of the interlayer gap: the first is related to relative positioning errors of the parts and manufacturing tolerances, while the second is intrinsic to the dynamics of the process. Specifically, during the drilling of stacked layers, when the upper plate recovers its elastic deformation after being drilled, the pressure exerted by the drill bit on the lower plate induces elastic deformation in it as well. ...
In the aeronautical industry, one-shot drilling of stacked materials is a widely adopted and established solution. However, ongoing discussions persist, particularly regarding the issue of interlayer gap formation that arises when two or more unsealed materials are drilled together. This study aims to present a simplified and reproducible theoretical model based on the equation of the elastic curve applied to structural schemes that discretize and describe the interlayer gap phenomenon in the drilling process. The model is designed to estimate the extent of the interlayer gap phenomenon and predict the clamping force required for its reduction when an end-effector is employed as a clamping device during the drilling of stacked sheets. Experimental and finite element analyses were conducted to validate the results of the proposed theoretical model. Each model was developed and applied to a real structural unit of a fuselage panel, considering actual boundary conditions in terms of structural constraints and geometric features of the assembly. The results obtained in this study demonstrate that the proposed one-dimensional theoretical model consistently aligns with experimental and numerical observations obtained through finite element analysis. This offers an effective and readily implementable solution in an industrial context as a tool for sizing the clamping force exerted by a clamping device.
... This is particularly significant in thin stacks, where the spring back of the first drilled layer and the bending of the second layer, caused by the thrust force, can result in a noticeable interlayer gap, promoting the development of defects at the interface. [27,28] Instead, the burr at the bottom is larger and cannot always be removed due to assembly configuration. For this reason, a confocal Microscope (Sensofar S, 20× of magnification) was used to measure the burr height on both the top and bottom hole side and to observe the shape of the burr. ...
... A higher point angle, up to 138 , yielded lower delamination damage and interlayer gap [71] compared with the 90 and double 90 / 130 point angles for PCD drills [167]. Luo et al. [181] developed a force-deformation coupling model to study the formation mechanisms of interface damage during drilling of CFRP/Ti stacks. The authors stated that imposing pressure on the stack surface by a clamping foot could reduce the interface damage of the stacks. ...
CFRP/Ti stacks have attracted considerable attention over the past decades as a promising alternative to individual fibrous composites and metallic alloys due to their improved properties and enhanced structural functions. Mechanical drilling is a compulsory but challenging process to shape these compound stacks to desired dimensions and target quality. Despite a large volume of studies already addressing the conventional twist drilling of CFRP/Ti stacks, a comprehensive understanding of their fundamental drilling mechanisms is still lacking. The present paper aims to report the state-of-the-art advances achieved in the fields of CFRP/Ti machining. Aspects including chip removal, damage formation, mechanical/thermal effects, influences of process conditions, hole quality attributes, and tool wear mechanisms are carefully reviewed. An emphasis is placed on the discussion of the interface drilling behaviors as well as the impacts of different drilling sequence strategies on the machining outputs of CFRP/Ti stacks. The current research limitations and future research perspectives are pointed out. The review paper could provide technical guidance for both scientific and industrial communities to achieve the damage-free drilling of CFRP/Ti stacks.
... The complexity increases considerably in the case of hybrid stacks where the different mechanical properties of the materials imply different machinability and therefore different optimal process parameters [12,13,14,15,16]. Although the process parameters affect the size of the interlayer burr, the condition that physically allows the generic insertion of material between two consecutive layers is the gap between them, as explained by B. Luo et al. [17] and S. Melkote et al. [11]. There are two main reasons that contribute to the formation of the interlayer gap: the first one is due to relative positioning errors of the parts and manufacturing tolerances, and the second one is intrinsic to the dynamics of the process; in fact, during the drilling stacked layer, when the upper plate recovers its elastic deformation when it is drilled through, the pressure exerted by the drill bit on the lower plate produces on it an elastic deformation. ...
Nowadays in different industrial fields, especially in aircraft manufacturing industry, the use of stacked material plays a relevant role. To allow the correct assembly of parts, one shot drilling is the best option to avoid misalignment and increase the productivity. In this context, the formation of the interlayer gap and its consequences in terms of final hole quality and structural integrity is a relevant aspect that need to be investigated and reduced. The growing push towards the implementation of automated drilling solutions offers the advantage of using the robot end effector for the minimization of this phenomenon, but few works offer a useful analytical study of the robot-workpiece interaction in terms of force based on real operating boundary conditions. This work aims to provide a simplified theoretical model to study the interlayer gap phenomenon and to predict the clamping force required for its reduction by using a robot end effector on metal stacked plates. Both experimental and finite element analyses were carried out in order to validate the results of the proposed theoretical model. The results obtained in this study showed that the proposed simplified one-dimensional theoretical model allow to obtain suitable results despite the complexity of the phenomenon studied.
... Some researchers have conducted conventional drilling (CD) experiments, trying to improve the drilling damage defects of CFRP/Ti stacks by selecting different process parameters and different bit geometries. They found that high spindle speed and low feed rate can effectively minimize drilling-induced defects, suppress the wear of drill bits, and reduce delamination defects and interface layer damage [9,10]. In addition, changing the drill bit geometry or bit type can effectively improve the drilling stability and chip-breaking performance and reduce the delamination defects [11][12][13][14]. ...
Carbon fiber–reinforced plastics (CFRP)/titanium alloy (Ti) stacks are extensively applied in the aerospace industry due to their excellent mechanical properties. However, their poor machinability poses great challenges. In this study, longitudinal-torsional ultrasonic vibration drilling (LT-UVD) is innovatively introduced to improve the quality of CFRP/Ti drilling. First, the separation mode of LT-UVD is analyzed by kinematic equations. Then, an experimental platform is built based on the LT-UVD vibration actuator to perform CFRP/Ti drilling experiments. The thrust force, interface temperature, hole wall quality, hole defects, Ti chip morphologies, and tool wear in LT-UVD are experimentally compared against conventional drilling (CD) and longitudinal ultrasonic vibration drilling (L-UVD). The experimental results show that, compared with CD and L-UVD, the thrust force of CFRP in LT-UVD decreases by 20.36–40.55% and 2.04–14.61%, while the thrust force of Ti decreases by 19.08–24.83% and 1.95–9.34%. Moreover, a relatively low maximum interface temperature is achieved in LT-UVD. In addition, the hole size accuracy, surface roughness for the hole’s inner surface, and delamination factor are improved in LT-UVD. Fiber pullout defects, chip-breaking performance, and tool wear of CFRP are improved due to torsional vibration in LT-UVD. Finally, according to the high-speed camera, damage forms of the interface area are different when drilling CFRP/Ti stacks with various drilling sequences.
... Thus, stacked components constituting CFRP and titanium alloys are widely used in the aircraft industry owing to their outstanding physical and mechanical properties including high strength-to-weight ratio and exceptional corrosion resistance [7][8][9]. Moreover, the application of CFRP has gradually expanded from non-critical parts (i.e., in radomes, fairings, doors, etc.) to main bearing parts (i.e., wings and fuselage), hence requirements for the machining quality of CFRP, as well as its related stacks have increased [10,11]. Within these applications, thin-walled parts assembled using CFRP/Ti stacks, such as wing panels, are prone to deformation during hole-making operations, resulting in defects including burrs, delamination, and chip inclusion between layers, which significantly reduce the assembly quality and efficiency [9][10][11][12][13]. ...
... Moreover, the application of CFRP has gradually expanded from non-critical parts (i.e., in radomes, fairings, doors, etc.) to main bearing parts (i.e., wings and fuselage), hence requirements for the machining quality of CFRP, as well as its related stacks have increased [10,11]. Within these applications, thin-walled parts assembled using CFRP/Ti stacks, such as wing panels, are prone to deformation during hole-making operations, resulting in defects including burrs, delamination, and chip inclusion between layers, which significantly reduce the assembly quality and efficiency [9][10][11][12][13]. ...
... Optimizing the layout of the support points and applying pressure feet are common methods for suppressing damage in stack drilling [11,15]. The former can improve the rigidity of the processing system, thereby reducing the amount of deformation. ...
Hole-making of stacks composed of carbon-fiber-reinforced plastic (CFRP) and titanium alloy under Low-frequency vibration-assisted drilling (LFVAD) is beneficial to both machining quality and tool wear. However, complicated deformation of the bottom Ti layer and even severe interfacial damage appears under the thrust forces with periodic fluctuations. Owing to lack of theoretical guidance in suppressing the deformation, this study established an analytical model to explain the influence of the fluctuating thrust force on the deformation of the workpiece. Data from validation trials performed on the CFRP/Ti stacks show that the deformation and thrust forces exhibit the same fluctuation behavior. The prediction errors of the average value and vibration amplitude of the Ti deformation were within 0.9 % and 10.7 %, respectively. Finally, a case study was conducted to optimize the drilling parameters in LFVAD of CFRP/Ti stacks based on the proposed model. As a result, the CFRP delamination damage was reduced by 17.0 %, and the stack drilling efficiency increased by 40.8 %.
... Дослідження останнього десятиліття, зосереджені на забезпеченні параметрів якості отворів у пакетах вуглепластик/ титановий сплав, вивченню впливу різних факторів. Здебільшого дослідження були присвячені вивченню зношування свердла [23][24][25][26][27], впливу покриття ріжучого інструменту на зношування [28][29][30], режимів різання [31], геометрії свердла [32,33], динамічні характеристики вуглепластику [34], стратегії та техніки свердління, а саме: однопрохідне свердління [35], свердління з ступінчастою геометрією свердла [20], свердління пілотного отвору [36], кріогенне свердління [37,38], техніка малого змащення (MQL) [39], спіральне свердління [40]. ...
У цій роботі представлені та проаналізовані результати експериментального дослідження по вивченню впливу технологічних параметрів (режимів різання) на геометричну точність отворів та температурне розширення свердла в процесі свердління. Планування експерименту здійснювалось за методикою Тагучі за варіювання швидкості різання, подачі та часу відтермінування на трьох рівнях. Контрольованими параметрами була точність отворів, що вимірювалась за координатним методом на координатно-вимірювальній машині. Крім того у процесі свердління контролювався температура свердління за допомогою бездротового пристрою WICUTEM, що поєднав метод штучної термопари та технологію Bluetooth. Перевірка гіпотези про вплив температурного розширення свердла та точність отворів в залежності від технологічних параметрів здійснювалась за допомогою методу скінчених елементів.
... CFRP often requires secondary machining, such as drilling and peripheral milling. The purpose of drilling is to meet the need for a large number of assembly connection holes [4]. The purpose of peripheral milling is to meet the strict requirements for the size, shape and position accuracy of key components and to reduce tears, burrs and other defects [5,6]. ...
When constant parameters are used for peripheral milling CFRP, it is difficult to meet the requirement of high quality, so variable parameters machining is proposed. First, the response surface method was used to explore the effect of changing cutting conditions on the interaction of spindle speed, cutting depth and feed speed on radial force. The surface topography and roughness after the test were observed and analyzed. The results show that defects are more likely to occur at the entrance and the exit area than the central area. Taking the minimum radial force as the experimental goal, the optimal parameters combination was obtained and used for finite element and experimental verification. Second, the variable parameters milling were used the cemented carbide tool and PCD tool. The radial force, surface topography and roughness were analyzed and the optimized variable parameters combination was obtained. The results show that the high spindle speed, low feed speed and low cutting depth are beneficial to improve the surface quality at the entrance and the exit area when the machining parameters at the centra area remain unchanged. Meanwhile, when the parameters change abruptly, the fluctuation of the radial force at the variable parameters area is decreased. The variable parameters compared to constant parameters, the surface roughness of the machining with the cemented carbide tool at the entrance area by 29.7% and 7.4%, respectively and the machining with PCD tool at the exit and the entrance area decreased by 60.5%, 43.5% and 38.8%, 51.9%, respectively. Compared with the cemented carbide tool, the radial force of the PCD tool is more stable and the surface quality is further improved.
... Meanwhile, due to the exist of interlayer gap which gives growing space for burrs, chip may enter into the gap and causes damage at the interface of the stacks. 9,10 Normally, there are three sources of non-coaxiality, that is, pure bending, horizontal displacements and local deformation. 11 Besides, mechanical damage can be observed at the CFRP hole exit, owing to the invading of Ti-6Al-4 V entry burrs. ...
Hole-making for Carbon Fiber Reinforced Plastics (CFRP)/Ti-6Al-4V stacks is crucial for the assembling strength of aircraft structure parts. This work carried out experimental work for helical milling (HM) of the stacks with sustainable cooling/lubrication (dry, MQL and cryogenic) conditions. Cutting forces and temperatures at the CFRP layer, Ti-6Al-4V layer and the interface of stacks were obtained by a developed measuring system. The temperatures in CFRP machining at cryogenic condition varied from -167 °C to -94 °C, which were much lower than those at dry and MQL conditions. The maximum temperature near the interface of stacks for the ninth hole was higher than 240 °C due to heat conduction from Ti-6Al-4V layer. The hole quality, hole diameter and tool wear mechanism at different cooling/lubrication conditions were presented and discussed. MQL condition generated mainly extrusion fracture for the fibers, due to the reduced friction effect compared with dry condition. MQL was helpful to reduce the feed mark at the hole surface of Ti-6Al-4V alloy. The flank wear of cutting edge at MQL condition was better than those at dry and cryogenic conditions. Cryogenic cooling contributed to better CFRP surface with smaller delamination and hole entrance damage due to the increased resin strength and fiber brittleness. The damage near the entrance of CFRP were analyzed by the contact state of cutting edges and fibers. Additionally, hole diameters near the exit of CFPR layer were larger than other test positions. This work provided feasible processes for improving hole quality and tool life in hole-making of CFRP/Ti-6Al-4V stacks.
