On the analysis of temperatures, surface morphologies and tool wear in drilling CFRP/Ti6Al4V stacks under different cutting sequence strategies

In drilling CFRP/Ti6Al4V stacks, the cutting sequence strategy, which determines the coupling effects of each phase machining, affects significantly the machinability of the sandwiched material as well as the tool wear characteristics. The present paper contributes to a scientific understanding of the effects of different cutting sequence strategies on the drilling performance of multilayer CFRP/Ti6Al4V stacks when using uncoated tungsten carbide and diamond-coated drills. Experimental quantification of the in-situ temperatures during the stack drilling was conducted using the method of infrared thermography camera and the instrumentation of drill bits by embedded thermocouples. Drilling forces, exit burr heights of the titanium holes, surface morphologies of the composite holes and tool wear signatures were analyzed. The results indicate that drilling from titanium to CFRP leads to higher magnitudes of the composite cutting temperatures while it benefits the reduction of the stack thrust forces, the improvement of the composite surface morphologies as well as the decrease of the exit titanium burr heights. Additionally, the coupling effects of drilling temperatures and chip adhesion are the influential factors leading to the disparate effects of the cutting sequence strategy on the drill wear progression. Drilling from titanium to CFRP reduces the drill adhesion and flank wear extents owing to the brushing effects of the composite drilling. The diamond-coated drills are confirmed superior to the uncoated ones in terms of lower drilling temperatures, lower drilling forces, minimal hole surface damage, less tool wear while machining the CFRP/Ti6Al4V stacks.publishe

Wear Mechanisms and Wear Model of Carbide Tools during Dry Drilling of CFRP/TiAl6V4 Stacks

The present contribution on tool wear during the drilling of carbon fiber composite materials (CFRP)/Ti stacks intends to determine (i) if the adhesion of titanium to carbide is mechanical or chemical, (ii) the possible di usion path, (iii) if the titanium is the only element involved in the adhesion and (iv) the role of the CFRP in this wear. The overall tool wear is not the sum of the wear in each material and there is a multiplicative e ect between them. It has been pointed out that the maximum temperature reached during drilling is higher than 180 C, 400 C and 750 C respectively in the CFRP and Ti plates alone and in the Ti part of the stack. As tungsten carbide CW is not in equilibrium with titanium above 250 C, the di usion path is CW/(Ti,W)C/Ti as confirmed by Auger analysis. For temperatures above 500 C, (Ti,W)C becomes very sensitive to oxidation allowing a friable oxycarbide (Ti,C,O) to form, which explains the erosion of the tool. The CW is therefore the weakest link in the drilling of CFRP/Ti stacks. Improving the performance of the tool involves the use of a coating, the development of a tool material having low chemical a nity with Ti and/or the use of cryogenic lubricant

Hybrid Composite-Metal Stack Drilling with Different Minimum Quantity Lubrication Levels

Hybrid stack drilling is a very common operation used in the assembly of high-added-value components, which combines the use of composite materials and metallic alloys. This process entails the complexity of machining very dissimilar materials, simultaneously, on account of the interactions that are produced between them, during machining. This study analyzed the influence of Minimum Quantity Lubrication (MQL) on the performance of diamond-coated carbide tools when drilling Ti/carbon fiber reinforced plastics (CFRP)/Ti stacks. The main wear mechanism observed was diamond-coating detachment, followed by fragile breaks in the main cutting-edge. The tests done with the lower lubrication levels have shown an important adhesion of titanium (mainly on the secondary cutting-edge) and a higher friction between the tool and the workpiece, producing higher temperatures on the cutting region and a thermal softening effect on the workpiece. These phenomena affect the evolution of cutting power consumption with tool wear in the titanium layer. Regarding the quality of the test specimen, no significant differences were observed between the lubrication levels tested.The authors acknowledge the financial support of Airbus Defense and Space, through the project Drilling Processes Improvement for Multi Material CFRP-Al-Ti Stacks, and the Ministry of Economy and Competitiveness of Spain through the grant PTA2015-10741-I and the project DPI2017-89197-C2-1-

Tool Wear Monitoring Based on Fractal Analysis of Cutting Force Signals While Machining Titanium Alloy Within CFRP/Titanium Stack

RÉSUMÉ L’usinage orbital comporte plusieurs avantages par rapport au perçage axial, particulièrement pour les matériaux difficiles à usiner tels que les alliages de titane. Parmi les avantages, on compte une réduction des bavures, une délamination atténuée et une force de coupe diminuée. L’industrie aérospatiale emploie de plus en plus de structures en matériaux composites en alliages légers à base de titane, en aluminium, et autres. Les propriétés mécaniques de ces alliages apportent une grande rigidité, une résistance importante à la corrosion, un poids faible et une forte résistance à la traction. Toutefois, l’usinage d’empilements de matériaux est difficile en raison des combinaisons diverses des mécanismes d’usure des outils. Afin de répondre aux exigences industrielles, plusieurs chercheurs se sont appliqués pour améliorer l’usinage des empilements hybrides. Par contre, tous les travaux se sont concentrés sur l'analyse des signaux acquis pendant l’usinage de composites impliqués dans ces empilements hybrides. Il en résulte que de l’information utile de l’usinage des matériaux homogènes dans les empilements se trouve négligée. Cette recherche examine l’usinage orbital d’un empilement hybride commun dans l’industrie aérospatiale, soit d’une matière plastique renforcée par des fibres de carbone et du titane. L’étude est consacrée à des pièces en alliage de titane afin d’exploiter les informations des signaux obtenus lors de l'usinage de matériaux homogènes qui sont présents dans des empilements multimatériaux. Les efforts de coupe représentent un des indicateurs les plus importants pour le suivi en ligne de l’état des outils vu leur sensibilité aux transitions d’états de la coupe. Par conséquent, les efforts de coupe sont davantage analysés ces dernières années. Or, l’analyse fractale des efforts de coupe durant l’usinage orbital d’empilements comprenant des alliages de titane CFRP/Ti est une méthode utile pour la caractérisation de la morphologie des signaux en vue de prévoir l’usure des outils. Afin d’exploiter cette avenue, la présente étude examine la « rugosité » des efforts de coupe en fonction du temps, à l’aide de la dimension fractale. La dimension fractale, ainsi que d’autres paramètres fractaux ressortant de la régularisation mathématique, sont évalués afin d’identifier des stades d’usure distincts servant à estimer l’usure et à augmenter la qualité de l’usinage. De plus, un indice fractal est proposé comme paramètre statistique visant le suivi de l’usure des outils durant l’usinage d’alliages de titane. Ceci est accompli afin de réduire la nécessité d’effectuer des essais de coupe à longues durées et d’améliorer le système de surveillance.----------ABSTRACT Orbital drilling has advantages over axial drilling, especially for difficult-to-cut materials like titanium alloys. Reduced burr size, less fiber delamination and reduced cutting force are some of these advantages. In the aerospace industry, the utilization of hybrid structures made of composites and of lightweight metals such as titanium or aluminium alloys is increasing due to their excellent mechanical properties, including: high stiffness, high corrosion resistance, low weight and high tensile strength. However, machining these multi-material stacks is challenging due to the combination of diverse wear mechanisms which accelerate tool wear. Researchers have been working on the machining of hybrid stacks to provide industry requirements, but all the research has focused on the analysis of the signals acquired during the machining of composite involved in the hybrid stacks; in contrast, useful information from the machining of homogenous materials during machining of the hybrid stacks has been missed. This study investigates orbital drilling of one of the popular hybrid stacks in the aerospace industry, carbon fiber reinforced plastics (CFRP) with Ti-6Al-4V titanium alloy stack, and it has focused on the titanium alloy parts to ply the unexploited information from signals obtained during machining the homogenous materials within multi-material stacks. Cutting force signals are one of the most significant indicators for online tool condition monitoring as consequence of high sensitivity to shifts between cutting states, and has prompted more monitoring of cutting force signals in recent years. Fractal analysis of cutting force signals acquired during the orbital drilling of titanium alloy while machining CFRP/Ti stack is a useful technique to characterize signal features and predict tool wear. In this study, the irregularity and “roughness” of the cutting force signal during titanium alloy machining is characterized in terms of fractal dimension. The fractal dimension and other fractal parameters based on regularization analysis are calculated to identify distinct wear stages, estimate the tool wear and prevent low machining quality. In addition, a fractal index is proposed as a statistical parameter to monitor tool wear during titanium alloy machining to mitigate the need for long machining tests and to improve the monitoring process

Influence of cutting conditions in drilling of CFRP/Al stacked composites

152-164Composite laminates are gorgeous for several applications such as aerospace and aircraft structural components due to their excellent properties. Typically, mechanical drilling has been important machining operation for components made of composite laminates. Nevertheless, laminated composites are considered as hard-to-machine material which results in low drilling efficiency and drilling-induced delamination which is undesirable. This paper reviews the experiments during drilling of CFRP/Al stacked and sandwich composites. The machinability facets of these material stacks has been generally used in aerospace applications, it has been studied based on impact of drill material, drill geometries, and drilling process parameters such as speed and feed. Composite material requires high spindle speed and low feed rate, whereas drilling aluminum requires stability between speedsto feed rate. The review reports essential results and gap in the collected literature for CFRP/Al stacked and sandwich composites. A compromise between several parameters is required during drilling of multi-material stacks. The problems and solutions allied to drilling of multi-material stacks are deliberated and the directions in which the research on drilling of multi-materials may be carried out are suggested in this paper. It is intended to assist readers to acquire a thorough view on mechanical drilling of laminated composite

Influence of cutting conditions in drilling of CFRP/Al stacked composites

Composite laminates are gorgeous for several applications such as aerospace and aircraft structural components due to their excellent properties. Typically, mechanical drilling has been important machining operation for components made of composite laminates. Nevertheless, laminated composites are considered as hard-to-machine material which results in low drilling efficiency and drilling-induced delamination which is undesirable. This paper reviews the experiments during drilling of CFRP/Al stacked and sandwich composites. The machinability facets of these material stacks has been generally used in aerospace applications, it has been studied based on impact of drill material, drill geometries, and drilling process parameters such as speed and feed. Composite material requires high spindle speed and low feed rate, whereas drilling aluminum requires stability between speedsto feed rate. The review reports essential results and gap in the collected literature for CFRP/Al stacked and sandwich composites. A compromise between several parameters is required during drilling of multi-material stacks. The problems and solutions allied to drilling of multi-material stacks are deliberated and the directions in which the research on drilling of multi-materials may be carried out are suggested in this paper. It is intended to assist readers to acquire a thorough view on mechanical drilling of laminated composite

Method of hole shrinkage radial forces measurement in Ti6 Al4V drilling

This work deals with the phenomenon of hole shrinkage during Ti6Al4V drilling. Indeed, the shape and dimensions of the drilled hole, as well as the heat generated by the operation depend on this phenomenon which is caused by multiple factors, including the relaxation of internal residual stresses, thermal expansion and diverse thermome chanical loads applied to the workpiece and the tool. Nevertheless, the present study focuses only on the mechanical aspect and especially aims atshowing the development of an innovative method to measure the radial forces induced by the hole shrinkage phenomenon