Microstructural investigation and hole quality evaluation in S2/FM94 glass-fibre composites under dry and cryogenic conditions

International audienceS2/FM94 glass fibre reinforced epoxy is an aerospace-grade composite currently bonded with aluminium alloys and installed in parts of the Airbus A380 fuselage. In addition to its abrasive and hard nature, S2/FM94 glass fibre is sensitive to thermal effects developed during the drilling process, and therefore using coolants becomes necessary. However, conventional oil and water-based coolants are not suitable for drilling of composites. Cryogenic coolants on the other hand are an attractive choice for machining composites and are environmentally friendly. In this study, a new environmentally friendly cryogenic cooling technique in a liquid nitrogen bath was used for the drilling of S2/FM94 glass fibre reinforced epoxy composite. The aim was to investigate the effect of drilling parameters and cryogenic cooling on cutting forces, surface roughness, hardness and delamination factor at hole entry and exit sides. The workpiece was drilled within a cryogenic bath. In this way, both cryogenic workpiece cooling and tool cooling were obtained. In addition, the drill geometry is fixed and only the cutting parameters (i.e. spindle speed and the feed rate) are varied under dry and cryogenic conditions. The results indicate that the spindle speed and cryogenic cooling had the most significant influence on the cutting forces and surface roughness parameters (R a and R z ), while the use of cryogenic cooling had the most significant influence on increasing the hardness and size of delamination at entry and exit sides of the holes

Impact characteristics of S2-glass fibre/FM94-epoxy composites under high and cryogenic temperatures: Experimental and numerical investigation

The aerospace industry uses glass fibre reinforced polymer (GFRP) composites to manufacture structural and non-structural parts of an aircraft as they possess superior strength to weight ratio and exceptional corrosion resistance. Commercial aircraft operate in a very wide temperature ranges from −54 to 55 °C. Potential GFRP laminates are susceptible to impact during aircraft operation, and the temperature at impact governs the nature of damage and failure mechanisms. As a result, the current study focuses on examining how aeronautical GFRP composites behave in various temperature environments that are encountered during high- and low-altitude operations. Using S2-glass fibre/FM94-epoxy unidirectional prepreg, GFRP plates were created. Drop weight impact tests were conducted at ambient (25 °C), high (50, 75, 100 °C), and low (−25, −55 °C) temperatures, as well as at various impact energies (75, 150, 225 J). The damages were assessed visually, along with their sizes. Each testing scenario's impact parameters, including the impact load, deflection, and energy absorption, were also examined. In Abaqus/Explicit, a coupled temperature-displacement numerical model was created to predict the onset of stress and damage. According to experimental findings, GFRP plates are stiffer and show less apparent damage at cryogenic temperatures (∼15−34 % lower displacement) than they do at other temperatures. Furthermore, it was observed that the matrix softens at high temperatures, showing larger damaged area at entry but with less obvious damage and increasing energy absorption, while semi-perforation occurred under cryogenic temperatures at entry with smaller damaged area. A strong correlation is shown between the experimental and FE data, confirming the capability of FE models to predict impact damage and deflections at different temperatures in the future

Optimisation of machining parameters in interrupted cylindrical grinding using the Grey-based Taguchi method

WOS:000322616900001Selection of machining parameters is very important to obtain desired accuracy with good surface quality in cylindrical grinding. The present study focused on the optimisation of the continuous and interrupted cylindrical grinding of AISI 4140 steel. The effects of three machining parameters, such as workpiece speed, depth of cut and the number of slot, on multiple performance characteristics (MPC), surface roughness and roundness error (RE), were investigated using Grey-based Taguchi method. The optimum parameter settings and the most influential factor are determined by both the Grey analysis and the analysis of variance. Both the surface roughness and the RE decrease with the decreasing of depth of cut and number of slot

The drilling machinability of 5083 aluminum under shallow and deep cryogenic treatment

WOS:000546172600012Cryogenic treatment is applied to improve the properties of materials. In this study, a comprehensive experimental investigation was conducted on the effects of shallow and deep precryogenic treatment with different holding times on the machinability performance of the 5083 aluminum (Al) alloy. For this purpose, shallow cryogenic treatment at -80 degrees C and deep cryogenic treatment at -196 degrees C were applied to the aluminum alloy for different time periods (15, 30 and 45 h). The performance outputs included tensile properties, thrust force, tool wear and surface topography. The highest tensile strength was observed in the sample kept in liquid nitrogen (N-2) for 45 h, while the effect of cryogenic treatment for 15 and 30 h on the mechanical properties of the other samples was observed to be limited. Moreover, cryogenic treatment increased the thrust force during the drilling operation; however, the treatment reduced the adhesion of the material to the drill bit and improved the surface quality. It can be concluded that cryogenic treatment has positive effects on the mechanical properties and machinability of the 5083 alloy

Değişik şekillerde aralıklı (kesikli) yüzeylerin, taşlanmasında oluşan şekil hatalarının deneysel incelenmesi

ÖZETDEĞİŞİK ŞEKİLLERDE ARALIKLI (KESİKLİ) YÜZEYLERİN, TAŞLANMASINDA OLUŞAN ŞEKİL HATALARININ DENEYSEL İNCELENMESİTaşlama işlemi, genellikle metal malzemelerin en son işlemlerinde gerekli yüzey kalitesini ve ölçüsünü elde etmek için yapılır. Maliyeti yüksek olduğu için dikkat edilmesi gereken aşamadır. Çeşitli makinelerin esas çalışma yüzeylerinin sürekliliği farklı şekilde aralıklarla kesilmiş olabilir. Böyle süreksizliklere sahip olan yüzeylerin işlenmesi sonucunda süreksizlik yerleri etrafında yüzey şekil hataları ortaya çıkar. Aralıklı çalışma yüzeyine sahip olan makine parçalarının çalışma yüzeylerinin son imalat işlemlerinde şekil hatalarının incelenmesi, bu hataların azaltılması veya yok edilmesi imalat işlemlerinde çok önemlidir. Şekil hataları bulunan elamanlarda, kullanıldığı bağlantıların sızdırmazlığının bozulması, parçaların temas yüzeylerinin küçülmesi, aşınması ve parçaların çalışma süresinin kısalması gibi istenmeyen durumlar ortaya çıkabilir.Taşlama işlemlerinde iş parçası yüzeylerinde; iş parçasına uygun taşın seçilmemiş olması, taşın bilenmemiş olması, taş baskı kuvvetinin yüksek olması, uygun ilerlemenin verilmemesi ve soğutmanın istenilen şekilde yapılamamasından dolayı mikro çatlaklar ve yanmalar meydana gelebilir. Yüzey taşlama işlemlerinde iş parçasının yüzey şekli incelendiğinde, düz bir yüzey yerine taş yarıçapına bağlı çukurların oluştuğu görülebilir. Taşın geometrik büyüklükleri ve taşın aşınması bu şekil bozuklukları üzerine tesir etmektedir. Süreksiz yüzeylerin taşlanarak bitirme işleminde geometrik hataların oluşmasını etkileyen esas faktörlerden en önemlisi, işleme alanında kesme kuvveti etkisiyle ortaya çıkan elastik yer değişmelerdir. Bu çalışmada, aralıklı yüzeylerin taşlanmasında ortaya çıkan şekil hatalarının oluşmasına neden olan faktörler incelenerek, taşın yüzey aralık boşluğuna giriş-çıkış prosesinde iş parçasında oluşan şekil hataları ölçülmüştür. Taşlama parametrelerinin şekil hatasına etkisi belirlenmiş ve şekil hatasını mimimize ederek optimum taşlama şartları belirlenmesi ve hataların matematiksel modellenmesi için Taguchi ve Response Surface metodolojisi kullanılmıştır. ABSTRACTEXPERIMENTAL INVESTIGATION OF SHAPE ERRORS ON GRINDING INTERRUPTED SURFACES OF DIFFERENT SHAPESThe procedure of grinding is generally used in the last step of metallic materials machining to have necessary surface quality and measurement. Since it costs much this is an attentive phase. The continuity of working surfaces of various machines might be cut with different intervals. As a result of machining these interrupted surfaces surface shape errors appear around them. To investigate the working surfaces’ shape errors on interrupted working surfaces, to reduce or to get rid of these errors are very crucial in manufacturing. In the components with shape errors one can face with undesirable cases such as fault of sealing, reducing in components’ contact surfaces, wear and reduction of proper working of duration components.In working surfaces during grinding period; micro cracks and burns may occur due to selection of inappropriate grinding wheel for working material, not sharpening the grinding wheel, grinding wheel’s intense press of force, giving inappropriate feed and finally cooling in an undesired way. If workpiece surface shape in the procedure of surface grinding is investigated, it will be noticed that instead of a smooth surface there will be holes dependent on grinding wheel’s radius. Grinding wheel’s geometrical size and its wear will have an effect on these shape errors. While grinding process the most important cause of shape errors in interrupted surfaces is elastic displacement change which is an effect of cutting force.In this study, the factors that result in surface errors during grinding procedure in interrupted surfaces are examined so that surface errors have been measured during grinding wheel entry and exit to surface interval hole. The effect of grinding parameters on shape errors was determined. Finally, Taguchi and response surface methodology have been used to determine optimum grinding conditions for minimizing the shape errors and to make mathematical modeling of these errors

Analysis of cutting forces at different spindle speeds with straight and helical-flute tools for conventional-speed milling incorporating the effect of tool runout

WOS:000861274800001This paper is concerned with the experimental investigation and mechanistic prediction of cutting forces for flat-end milling with tool runout. The effects of the tool geometry, the workpiece material and cutting parameters such as spindle speed, tool engagement and cutting direction are investigated. The mechanistic force model uses the trochoidal flute path to calculate the undeformed chip thickness. Average cutting force and linear regression model are applied for identifying the coefficients of the force model, and tool runout parameters are established from the radii of all flutes at the free end of the cutting tool. A series of milling processes are conducted on AZ31 Magnesium (Mg) alloy and titanium alloy (Ti6Al4V) to analyze the instantaneous cutting force curves, amplitudes of cutting forces and peak forces over a wide range of conventional spindle speeds, namely 600, 1200 and 3000 rev/min. It is found that the values of the cutting force coefficients are higher at lower spindle speed and decrease with an increase in spindle speed, especially when machining Ti6Al4V alloy. For the edge force coefficients, it is observed a slight variation when using cutting tools with different helix angles. Besides, the cutting force amplitudes strongly depend upon the workpiece material. The helix angle has a significant influence on the transverse force amplitude at the spindle speed of 600 rev/min. The cutting forces obtained mechanistically are also substantiated by comparison with measurements

Effect of dipped cryogenic approach on thrust force, temperature, tool wear and chip formation in drilling of AZ31 magnesium alloy

WOS:000547373000003Magnesium alloys tend to have inflammable nature and chip self-ignition at high cutting speeds under dry machining condition, although they can be easily machined with good surface quality. In the drilling process, cooling and lubrication have a critical impact as it controls heat generation, tool wear, surface quality, and cutting force. In the present study, drilling tests on AZ31 magnesium alloy were performed with dry and cryogenic conditions at various feed rates and cutting speeds. The effect of dipped cryogenic application during drilling on thrust force, temperature, tool wear, and chip formation were investigated. The results showed that the applied cryogenic drilling method provided less tool wear, smaller chips and reduced amount of adhesions. Drilling tests performed in the cryogenic envi- ronment increase the thrust forces by 32 %-39 % compared to dry cutting. Spark and chip ignition were not observed even at high cutting speeds during dry cutting.This work was supported by Commission of Scientific Research Projects of Karamanoglu Mehmetbey University, Karaman-Turkey (Project No. 04-YL-17)

Cryogenic drilling of carbon fiber-reinforced composite (CFRP)

WOS:000491292400012In order to reduce the adverse effects on the environment and economy and to avoid health problems caused by the excessively used cutting lubrications, cryogenic machining is drawing more and more attention. In this work, a novel cryogenic machining approach was applied for drilling of carbon fiber-reinforced polymers (CFRPs). According to this approach, CFRP was dipped into the liquid nitrogen (LN2) and it was machined within the cryogenic coolant directly. Various machinability characteristics on thrust force, delamination damage, tool wear, surface roughness, and topography were compared with those obtained with dry condition. This experimental study revealed that the novel method of machining with cryogenic dipping significantly reduced tool wear and surface roughness but increased thrust force. Overall results showed that the cryogenic machining approach in this study improved the machinability of CFRP

Identification and modeling of cutting forces in ball-end milling based on two different finite element models with Arbitrary Lagrangian Eulerian technique

WOS:000407815500115This paper presents two different finite element (FE) models with Arbitrary Lagrangian Eulerian (ALE) technique to evaluate the effectiveness of FE modeling for estimating the cutting forces in ball-end milling. The milling forces are modeled using a unified mechanics of the cutting approach, which is based on the shear stress, friction coefficient and chip thickness ratio provided through the orthogonal cutting process. Two-dimensional (2D) FE models of the orthogonal cutting are designed for estimating the milling forces using this approach, and explicit dynamic thermo-mechanical analyses are performed to determine the orthogonal cutting data from a set of cutting and material parameters. The oblique transformation approach is used to carry the orthogonal cutting data to the milling cutter geometry. Simulations are numerically and analytically carried out for machining of 20NiCrMo5 material with a tungsten carbide tool and the estimated forces are compared to measured ones. The estimation of milling forces is accurately achieved by the unified mechanics of cutting approach with orthogonal cutting data based on the ALE technique using Eulerian-Lagrangian boundaries. Good agreements between the estimated and measured outcomes reveal an obvious knowledge of an efficient and accurate FE model for determining the ball-end milling forces

Analysis of flat-end milling forces considering chip formation process in high-speed cutting of Ti6Al4V titanium alloy

WOS:000512987800003This paper proposes a unified numerical and analytical approach to predict flat-end milling forces considering the chip morphology and cutting force in high-speed cutting of titanium alloy (Ti6Al4V). A two-dimensional finite element (FE) model of the orthogonal cutting process is developed by applying a displacement-based ductile failure criterion. With this FE model, the segmented chip formation is analyzed. The mesh dimension is investigated as an effective factor in the chip segmentation. The numerical results demonstrate that the chip morphology is significantly affected from the mesh dimension while the average cutting force varies slightly with the mesh dimension. The mesh dependency of the chip morphology can be decreased by applying the non-local progressive damage model involving the intrinsic material length. An attempt is also made for modeling and prediction of cutting forces in high-speed flat-end milling. The milling force constants which are generally derived from experimental calibrations are required to predict the milling forces by using the unified mechanics of cutting approach. Here, the numerical FE simulations are carried out to characterize the milling force constants. The milling forces predicted analytically are validated by comparing with those obtained from the experimental study. Finally, the behavior of the milling forces can be effectively analyzed through the proposed approach based on the chip formation proces