Advanced cutting tools and technologies for drilling carbon fibre reinforced polymer (CFRP) composites: a review

Carbon fibre reinforced polymer (CFRP) composites have excellent specific mechanical properties, these materials are therefore widely used in high-tech industries like the automobile and aerospace sectors. The mechanical machining of CFRP composites is often necessary to meet dimensional or assembly-related requirements; however, the machining of these materials is difficult. In an attempt to explore this issue, the main objective of the present paper is to review those advanced cutting tools and technologies that are used for drilling carbon fibre reinforced polymer composites. In this context, this paper gives a detailed review and discussion of the following: (i) the machinability of CFRP including chip removal mechanisms, cutting force, tool wear, surface roughness, delamination and the characteristics of uncut fibres; (ii) cutting tool requirements for CFRP machining; and (iii) recent industrial solutions: advanced edge geometries of cutting tools, coatings and technologies. In conclusion, it can be stated that advanced geometry cutting tools are often necessary in order to effectively and appropriately machine required quality features when working with CFRP composites.publishe

Study of temperature in the edge milling of carbon fiber-reinforced plastic (CFRP)/Ti6Al4V stack material for aerospace industry

With the advances of new technologies and new materials, aerospace, military and commercial aircraft industries are looking to decrease the fuel consumption by reducing weight into their structures and components. Hybrid or stacks of materials are used more often in airframes because of their outstanding mechanical properties such as high strength/weight ratio and, excellent corrosion and fatigue resistance that cannot be provided with metallic materials. Carbon Fiber-Reinforced Plastic (CFRP)/Titanium is the most used type of hybrid material for thermal-load applications in aviation, Ti6Al4V being the most popular of the titanium alloys. Usually, CFRP/Ti6Al4V plaque is assembled by rivets or bolts; however, there are some applications where both materials are bonded or cured together. Thus, the drilling process is not required as it usually happens, removing cost and weight from the airframe. The difference in machinability and the temperature invariability of each material makes achieving specified geometries and dimensional tolerances a real challenge. Therefore, this thesis studies the thermal effects on CFRP/Ti6Al4V in the process of edge milling. In particular, we study the tool-workpiece thermocouple method by using commercial thermocouples. Additionally, we study the effects of cutters while varying cutting speed, feed per tooth and radial depth of cut on the forces, roughness and tool wear for the different types of cutters. We found that, as opposed to what was previously thought, the feed factor is the most influent one regarding the cutting temperature for the CFRP and Ti workpiece instead of the cutting speed. It has been found that the temperature in the workpiece increases by decreasing feed per tooth and decreases by increasing the cutting speed, although this last factor is not as significant as the feed per tooth

Influence of Milling Process Parameters on Machined Surface Quality of Carbon Fibre Reinforced Polymer (CFRP) Composites Using Taguchi Analysis And Grey Relational Analysis

The article presents the milled surface quality of Uni-Directional Carbon Fibre Reinforced Polymer (UD-CFRP) composites from Taguchi’s and grey relational analysis. The novelty is demonstrating the possibility of detecting the surface defects in polymer composites during milling using SEM analysis. The material used for this study is UD-CFRP composite laminates and made by hand-layup process. All the milling operations were carried out using a solid tungsten carbide end milling tool and experiments conducted on CNC milling machine. Taguchi L9, 3-level orthogonal array was considered for experimentation. Analysis of Variance (ANOVA) was conducted to explore the significance of each individual input process parameters on multiple performance characteristics. Optimal process parameters are thoroughly validated by grey relational grade achieved by the grey relational analysis for multi performance characteristics. Finally, experimental results were correlated and analyzed with scanning electron micrographs using Scanning Electron Microscope (SEM)

Optimization of cutting parameters for finish end milling CFRP under vortex-cooled compressed air

Carbon fiber reinforced plastics (CFRP) offer several advantages in the aeronautical and automotive industry due to their combination of lightweight, high strength, and corrosion resistance. CFRP parts are usually produced in near-net-shape; however, additional machining processes are often required for achieving desired dimensional accuracy and surface finish. Thus, this work evaluates the influence of the cutting parameters in CFRP end milling to generate a better surface finish. The experiment was designed using a three-factor, three-level Box-Behnken considering feed rate (f), axial depth of cut (ap ), and cooling conditions (cc) as controllable factors, and roughness parameters (Ra , Rq , Rz , Rt ) as response variables (the occurrence of defects was evaluated qualitatively). Results indicated a strong influence of the quadratic effect of axial depth of cut and its interactions with feed rate and cooling condition on the roughness values and a milder but significant influence of the feed rate and cooling conditions. Multivariate analysis returned the optimum level of input parameters (f = 0.21 mm/rev and ap = 0.8 mm with cooled compressed air), resulting in Ra = 1.58 µm, Rq = 1.98 µm, Rz = 9.39 µm, Rt = 13.63 µm. Also, no defects were observed after machining under the optimum conditions

Recent advances in drilling of carbon fiber–reinforced polymers for aerospace applications: a review

Drilling is considered as one of the most challenging problems in aerospace structures where stringent tolerances are required for fasteners such as rivets and bolts to join the mating parts for final assembly. Fiber-reinforced polymers are widely used in aeronautical applications due to their superior properties. One of the major challenges in machining such polymers is the poor drilled-hole quality which reduces the strength of the composite and leads to part rejection at the assembly stage. In addition, rapid tool wear due to the abrasive nature of composites requires frequent tool change which results in high tooling and machining costs. This review intended to give in-depth details on the progress of drilling of fiber-reinforced polymers with special attention given to carbon fiber–reinforced polymers. The objective is to give a comprehensive understanding of the role of drilling parameters and composite properties on the drilling-induced damage in machined holes. Additionally, the review examines the drilling process parameters and its optimization techniques, and the effects of dust particles on human health during the machining process. This review will provide scientific and industrial communities with advantages and disadvantages through better drilled-hole quality inspection

INNOVATIVE DRILLING TECHNOLOGIES FOR ADVANCED MATERIALS

Carbon fibre reinforced polymer (CFRP) composites are among the most widely used composite materials in the aerospace industry, thanks to the high specific mechanical properties offered. These composites combine the fundamental aeronautical requirements of lightness and strength, which have sparked great research interest in improving the properties and the production process of composite materials. CFRP composites can be manufactured in near net shape; however, they often require further machining processes such as drilling, particularly for joining purposes. Fibre orientation plays a fundamental role in CFRP composite materials, affecting the mechanism of chip formation and the quality of the cut surface and making machining of CFRP a challenging task. Proper optimisation of the drilling process can substantially improve CFRP parts quality, which may be affected by several faults generated during the process. In order to simplify the assembly operations and reduce manufacturing costs, efforts are increasingly spent with the aim to optimise CFRP drilling

An experimental investigation of ultrasonic assisted milling (UAM) of carbon fibre reinforced polymer (CFRP) and the effect of machining on the BMI 5250-4 matrix resin

Milling of Carbon Fibre Reinforced Polymer (CFRP) is necessary for component accuracy prior to assembly of aircraft. Recently, ultrasonic assisted milling (UAM) which combines conventional machining (CM) with ultrasonic vibration on the cutting tool, has shown beneficial outcomes with respect to the machinability of some metals, however, limited UAM of CFRP has been reported. In this thesis, milling (CM and UAM) of a CFRP incorporating Bismaleimide 5250-4 (BMI 5250-4) resin was carried out in a wide range of cutting parameters and environments (dry, conventional cutting fluid (CCF) and CO2 cryogenic). Machinability was examined in terms of tool wear, cutting forces and surface roughness. In terms of machinability with conventional cutting tools, machining in a CO2 had a positive effect on tool life, despite an increase in cutting forces, compared to CCF and dry. UAM was found to reduce cutting forces by up to 10 %, compared with CM, however, this did not yield any benefit in terms of tool wear and/or workpiece surface roughness. When dry machining employing an abrasive diamond tool, CFRP material adhesion was a feature. The application of UAM in this instance yielded, reduced workpiece adhesion on the cutting tool and improved workpiece surface roughness. Machining of CFRP must be performed below the glass transition temperature (Tg) of the resin to avoid the degradation of the properties of the matrix resin. In this research new findings in the temperature initiated during machining and the consequential effects on the polymer utilised Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) which is well established in polymer characterization. FTIR and DSC was carried out to investigate the effect of machining on the chemical and material properties of BMI 5250-4 such as Tg and changes to matrix resin chemical bonding, which has been closely associated with degradation of the machined part. Further analysis of the machined surface by DSC indicated that the Tg of the matrix resin had been exceeded during the machining process and led to degradation of the BMI 5250-4 in some cases. An observed reduction of the maleimide double bond (C=C) at 825 cm-1 wavelength by FTIR signified that further post-curing of BMI 5240-4 had occurred which suggested that a higher cutting temperature was developed at the machine tool tip than recorded with the infrared camera. CM dry machining, FTIR analysis also confirmed the formation of isocyanate-derived products (C≡N) at 2250 cm-1 wavelength, a bond associated with the point at which BMI 5240-4 is thermally degraded having experienced temperatures in the range 400 to 600 °C. This result suggests that when CM dry machining the actual cutting temperature experienced by the BMI 5240-4 was at least 400 °C. The formation of isocyanate-derived products was not observed for UAM dry machining, suggesting that ultrasonic vibration of the cutting tool may reduce the cutting temperature in the primary shear zone, however this temperature reduction was insufficient to arrest observed post curing effects and shift in the Tg. Other aspects of the FTIR analysis revealed that despite the improvements to workpiece surface roughness when milling with CCF there was an increased presence of moisture (-OH bond) in the BMI 5240-4 resin which may have a detrimental effect on the durability of the material over time. Machining CFRP has been enhanced by the introduction of the chemical analysis. It suggests that DSC and FTIR exploration of the thermal history of the CFRP can provide more information about the temperature than typical thermal measurement during machining such as thermal cameras and thermocouples. The management of the milling process of CFRP can now be related to the management of the temperature at the tool tip and the effect on polymer characteristics. As a consequence, milling of CFRP in CO2 exhibited improvement in tool wear, an observed reduction in cutting temperature, and sustenance of the chemical properties of BMI 5250-4. However, there was no significant benefit in additionally employing UAM in a CO2 environment. The research has provided a new insight in the milling of polymer composites and could be beneficial in avoiding thermal degradation of the machined part, maintaining the quality of machined part and avoiding scrap parts at the end of machining processes

Analysis of milling in composite material by non-destructive methods

In aerospace industry, composite materials offer several advantages, such as high weight-to strength ratio and corrosion resistance. Aerospace materials are costly and have high safety standards, frequently using non-destructive testing in order to evaluate the material without incurring in further damage. Acoustic emission is a non-destructive testing method, which allows the signal processing to evaluate material performance during mechanical tests for determining material defects, for example. This study focused in the machining process of composite plates, in terms of surface finishing evaluation with comprehension of process phenomenology using non-destructive testing. Manufacturing processes are complex, especially the machining of composite materials, due to their specific properties and characteristics. The detection and prediction of surface finishing and occurrence of defects during manufacturing using non-destructive techniques is industrially useful, in terms of increasing automated manufacturing systems to increase productivity and quality control. The aim of this study is to show the possibility of online monitoring of the cutting process and to understand mechanism behind variables of control, with comparisons of different milling parameters and focusing in their impacts in acoustic emission signals, infrared thermography and surface finishing. The results indicates the relationship between cutting process and acoustic emission signals, with a key differentiation of other studies because it shows the not only the capability of detecting anomalies during cutting process and to predict surface quality by acoustic emission signal analysis, but also that is possible to develop new methods of monitoring in real time machined surface of composite parts quality using acoustic emission signals.Na indústria aeroespacial, polímeros reforçados com fibra de carbono oferecem diversas vantagens, como uma melhor relação entre resistência por peso ou mesmo resistência a corrosão. A análise de sinais obtidos pela emissão acústica tem sido bem sucedida para avaliar ensaios mecânicos e também para determinar defeitos no material. Esse trabalho é focado no processo de usinagem por fresamento de materiais compósitos de resina epóxi e fibra de carbono, em termos de avaliação da qualidade superficial e com compreensão da fenomenologia do processo por ensaios não destrutivos, principalmente emissão acústica e análise de temperatura por infravermelho. Durante o processo de usinagem, o monitoramento do processo com vistas à detecção e predição da qualidade superficial e ocorrência de defeitos é industrialmente útil, podendo aumentar a automatização dos sistema de fabricação, incrementar a produtividade e prover maior controle de qualidade. O objetivo deste estudo foi de mostrar que é possível implementar um sistema de monitoramento em tempo real do processo de corte, com o entendimento dos mecanismos e variáveis de influência. As comparações dos diferentes parâmetros empregados durante o fresamento e seus efeitos nos sinais obtidos pela técnica de emissão acústica e variações de temperatura, permitiram relacionar esses métodos com a qualidade superficial. Os resultados indicam que os ensaios não destrutivos podem servir de indicativo para o estado de qualidade superficial das placas de fibra de carbono-epóxi, também são sensíveis às alterações dos parâmetros de usinagem. Além disso, a análise por emissão acústica obteve melhor desempenho do que a análise por termografia infravermelho no monitoramento do fresamento desses materiais

Milling/routing of carbon fibre reinforced plastic (CFRP) composites

The research relates to a study on the routing/slotting of CFRP composites of the type used in aerospace applications. Following a literature review, 3 phases of experimental work were undertaken to evaluate the effects of key process variables on the machinability of CFRP. The influence of varying operating parameters, tool material and cutting environment were initially investigated in Phase 1 work. The results showed that use of PCD was critical and highlighted the importance of chilled air in maintaining adequate tool life and acceptable workpiece integrity. Delivery of chilled air through a single-nozzle arrangement generally led to an increase in forces and delamination with the twin-nozzle configuration showing superior workpiece surface roughness. Phase 2 work detailed the effect of workpiece lay-up configuration on cutting forces, temperature and surface integrity following slotting and routing. Plies in the 45 direction generally exhibited the highest level of surface damage following machining. Experiments in Phase 3 showed that relatively small helix angles (± 3) had a negligible effect on tool life, forces and temperature. In addition, cutters with a single relief angle were found to have lower stability in operation compared to tools with a secondary clearance angle, with detrimental effects on surface roughness