Aeronautical Parts Research Articles

Experimental investigation of dry, wet and cryogenic boring of AA 7075 alloy

ABSTRACTIn this research work, an attempt has been carried out to examine (investigate) and study the dry, wet and cryogenic boring of AA 7075 alloy, which is predominantly used in transport applications in defense (aeronautical parts), oceanic and automaker industries. To ensure direct supply of the coolant, and real-time measurement of cutting temperature a modified boring bar is used (modification is carried out using EDM to accommodate placement of a thermocouple to obtain real-time measurement of temperature readings during the boring cycle). It is observed that during cryogenic boring of AA 7075 alloy there is a considerable reduction in the cutting force (Fc), cutting temperature (Tc) and surface roughness (Ra) by 56.16%, 84.70%, 58.98% compared to dry boring and 48.43%, 80.70%, 34.70% compared to wet boring, respectively. Decrease in Fc and Tc leads to a reduction in high stresses at localized points during machining and in turn curtail wear in workpiece and tool. Lubrication provided by cryogenic fluids also plays a sizable role in reduction of Fc and Tc. Reduction in lower Fc and Tc has a glaring effect on the surface characteristics of the hole produced during the boring process. Tool wear is reduced in cryogenic boring by 36.96% and 17.57% compared to dry and wet boring, respectively. Taguchi and ANOVA was carried out which helped in determining feed as an important parameter with respect to Fc and Ra during boring of AA 7075 under dry, wet and cryogenic conditions whereas speed as an important parameter in determining Tc in dry and wet conditions and feed for Tc in cryogenic boring condition. TOPSIS analysis highlighted speed of 770 rpm and feed of 0.055 mm/min as the most closest to ideal solution for all three different cutting conditions. Surface morphology study after boring of AA 7075 highlighted better surface characteristics in cryogenic bored surface compared to dry and wet boring. Roughness measured in AFM for tool used in boring highlighted a decrease in 86.79% and 66.01% in cryogenic boring in juxtaposition with dry and wet boring, respectively. A surge in compressive residual stress is observed in cryogenic bored surface by 10.41% and 3.5% in juxtaposition with dry and wet boring, respectively, highlighting an abatement in tensile residual stress and better workpiece integrity as compared to dry and wet boring conditions.

Wear resistance of cold sprayed Al alloys for aeronautical repairs

ABSTRACTAl–Cu alloys, like Al 2024, and Al–Si alloys, like Al F357 and Al C355, are used in aeronautic gearboxes and fuselage parts operating in severe conditions. It is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) could be an alternative as it is real solid-state processing technique. However, the repaired component should exhibit similar properties as the original substrate. This paper evaluates the wear performance of Al coatings CS onto the same Al substrates in sliding and oscillating conditions. The results were compared with the corresponding substrates. The wear rate of coatings processed using new conditions, developed to enhance the coatings performance, was similar or smaller than that measured in the substrate bulk alloys. For Al 2024 and Al C355 CS could be used for repairing, from the tribological point of view.

Cutting speed and feed-rate influence on fatigue behavior of dry machined UNS A97075 alloy

Fatigue behavior takes a special relevance in manufacturing aeronautical parts due to safety reasons. Considering friendly environmental techniques, dry machining results in higher severe cutting conditions, which may negatively affect the part surface integrity, depending on cutting parameters values applied. In this sense, surface finish can be related to fatigue behavior. Notwithstanding, there is a lack of research that evaluates how cutting parameters affect fatigue life of aeronautical aluminum alloys, and their relationship with geometrical deviations. This work aims to analyze cutting speed and feed-rate influence on fatigue behavior of aeronautical aluminum alloy UNS A97075-T6 dry turned specimens. In order to do this, several rotating bar bending fatigue test have been carried out. Surface roughness have been also analyzed through the arithmetical mean roughness value (Ra) and the mean roughness depth (Rz). Results obtained seem to indicate that an increase of feed-rate and cutting speed negatively affects the fatigue life of the tested specimens, taking surface conditions a special influence in this behavior.

КЕРУВАННЯ ЕФЕКТИВНІСТЮ ПРОЦЕСУ ХОЛОДНОГО НАПИЛЮВАННЯ ЗАХИСНО-ВІДНОВЛЮВАЛЬНИХ ПОКРИТТІВ НА МАГНІЄВІ СПЛАВИ

The crucial task of developing the technology of low pressure cold gas–dynamic spraying and its wide application in the aviation, automotive and other industries is the possibility of obtaining coatings with given properties and deposition efficiency as great as practicable. To do this requires it is necessary to study the effect of complex parameters on coating deposition.An important characteristic of cold gas–dynamic spraying is deposition efficiency – the ratio of weight increment of the sample (weight of the coating) to the weight of powder used to produce the coating. Dependence of the deposition efficiency on the parameters of cold spraying, such as gas stagnation temperature and total pressure, material, shape and size of the powder particles, stand–of–distance, etc., allows a deeper understanding of the nature of the cold gas–dynamic spraying process, and as a consequence, to establish how these parameters effect on coating properties.The effect of stagnation temperature, total pressure and stand–of–distance on the cold spraying coating deposition efficiency on magnesium alloy utilized powder mixture based on aluminum was established. As a result of the deposition efficiency calculation, the optimal sputtering parameters ensuring the maximum deposition efficiency were established. It is shown that changing of the stagnation temperature has the greatest effect on the efficiency of coating formation. Stand–of–distance is the second most influential parameter, and the change in working pressure has the least effect. It is shown that with increasing temperature, the particle velocities increase during the deposition process, since the local speed of sound in the nozzle depends on the local flow temperature.The obtained results are the basis for the development of technological recommendations and processes for the formation of protective and restorative coatings on aeronautical part made of magnesium alloys during maintenance, repair and overhaul. Further optimization of the geometry of the nozzle, the composition of the powder mixture and the particle size is necessary to obtain deposition efficiency as great as practicable.

Flexible Abrasive Tools for the Deburring and Finishing of Holes in Superalloys

Many manufacturing sectors require high surface finishing. After machining operations such as milling or drilling, undesirable burrs or insufficient edge finishing may be generated. For decades, many finishing processes have been on a handmade basis; this fact is accentuated when dealing with complex geometries especially for high value-added parts. In recent years, there has been a tendency towards trying to automate these kinds of processes as far as possible, with repeatability and time/money savings being the main purposes. Based on this idea, the aim of this work was to check new tools and strategies for finishing aeronautical parts, especially critical engine parts made from Inconel 718, a very ductile nickel alloy. Automating the edge finishing of chamfered holes is a complicated but very important goal. In this paper, flexible abrasive tools were used for this purpose. A complete study of different abrasive possibilities was carried out, mainly focusing on roughness analysis and the final edge results obtained.

Cost analysis of alternative automated technologies for composite parts production

Composite material usage in aircraft has been rising since the 1990s, with significant increases in manufacturing productivity and repeatability due to automation in the production of aeronautic parts made of composite materials, becoming a strong driver for widespread adoption of composites in this industry. Automated Tape Layup (ATL) and Automated Fibre Placement (AFP) are two of the most important automated manufacturing technologies within aeronautics composites, although their cost implications and economic comparison have not been widely studied. This paper presents an economic evaluation of ATL and AFP technologies. Using process-based cost models, the manufacturing process of a horizontal stabiliser is modelled, determining for each technology the associated consumption and use of resources and their implications towards the part final cost. Results show that ATL is less expensive than AFP, due to lower material costs, although with less material efficiency and slower cycle time.

On the determination of thermal degradation effects and detection techniques for thermoplastic composites obtained by automatic lamination

Automatic lay-up and in-situ consolidation with thermoplastic composite materials is a technology under research for its expected use in the profitable manufacturing of structural aeronautical parts. This study is devoted to analysing the possible effects of thermal degradation produced by this manufacturing technique.Rheological measurements showed that there is negligible degradation in PEEK for the temperatures reached during the process. Thermogravimetric analysis under linear heating and constant rate conditions show that thermal degradation is a complex process with a number of overlapping steps. A general kinetic equation that describes the degradation of the material with temperature has been proposed and validated. Attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed that there is no remarkable degradation. The use of a combination of in-situ and ex-situ experimental techniques, including kinetic modelling, not only provides reliable information about degradation but also allows setting optimal processing conditions.

Advanced DIC for accurate part deflection measurement in a machining environment

Structural aluminium alloy parts used in aeronautics are manufactured in several steps, from forming processes and heat treatments to final machining. Some of the process steps generate residual stresses. For highly-alloyed thick aluminium plates manufactured with closed-die forging parts, material removal during machining can release residual stresses, leading to part deformations. Such deformations may lead to a geometrical non-conformity of the machined workpiece. It is thus of primary importance to control this phenomenon. For this purpose, the present work aims to define a reliable experimental technique to measure part deformations during the machining of large aeronautical parts. The backbone of the technique relies on Digital Image Correlation (DIC), which enables the non-destructive measurement of part deformations during machining. Moreover, DIC provides a full-field measurement in one shot. This is faster than other available measurement techniques. This work discusses more particularly problems related to the use of DIC in a machining environment for a large machined workpiece. Indeed, the technique involves using the entire captured image to compute the displacement field, and the large size of the studied workpiece can give rise to optical distortion, which can corrupt the results. In order to control optical distortion problems, a specific calibration method, which takes advantage of the machine tool environment, is proposed.

Optimization tolerancing of surface in flexible parts and assembly: Influence Coefficient Method with shape defects

Generally, a mechanical product must fulfill particular functions in accordance with the specification provided by the customer. A designer must find a solution with lower cost to answer the functional requirements. After the design stage, come the prototyping of the parts, but in case of the large structures of automotive and aeronautical parts, this step is impossible because of the large real dimension as well as the behavior of this type of parts during the positioning and during the assembly of all the mechanism.The aim of this article is to show the influence of geometrical shape differences in the assembly of flexible components in order to optimize the tolerancing of surface in flexible parts and assembly. first a presentation of the tolerance of deformable mechanisms through the illustration of the general problem, then we propose a new approach which takes into account shape defects based on the Influence Coeficient Method, after that we compare between a case study without takes into account shape defects and another one but this time taking into account shape defects always based on the Influence Coefficient Method.

Predicting failure in additively manufactured parts using X-ray computed tomography and simulation

In casting, molding, or additive manufacturing processes, there are some typical issues that can change the geometry of a part and cause porosity or other defects. With the aid of X-ray computed tomography (CT), internal discontinuities and geometry deviations can be accurately detected and visualized. However, the question remains in how far a given defect affects mechanical failure. We aim at bridging this gap by structural mechanics simulations based on CT images. In this study, we describe a method to predict the tensile strength and the location of crack initiation from the simulated stress distributions on the basis of local stress concentrations. We validate the method for tensile rods and real-life aeronautic parts which were additively manufactured from an AlSi10Mg aluminum alloy. Thirty-six specimens were manufactured in total, where different porosity patterns were deliberately inserted. The specimens were CT-scanned in high resolution. Structural mechanics simulations were carried out on basis of the CT images. An immersed-boundary finite elements code is used. The generation of a conforming simulation mesh is not required, making the code suitable especially for complex geometries like porous objects. The same test specimens were subjected to destructive physical tensile tests. We show that there is a very good correlation between the predicted and measured tensile strengths, and that the location of the first crack occurrence can be forecasted accurately.

Reverse engineering as a way to optimize and design parts produced by elastic-medium drawing

On the example of an aeronautical part of the classical form for a box-type part, optimization of the cavity elastic forming process using a cover with guaranteed clearance is considered, as well as classical optimization of a part based on modeling and optimization based on the technology of “technological reconstruction”. Schemes of classical cavity elastic forming process and cavity elastic forming process with guaranteed clearance are presented. The main aspects of using NURBS technology for restoring the shape of a part from a finite element mesh are described. The problems arising in the case of classical optimization using simulation and the ways of their solution using “technological reconstruction” are shown. The results of calculation in the form of gradients are presented: plastic deformations; thickness and quality zones based on the Keller-Goodwin limit strain curve.

Drilling of thick composite materials using a step gundrill

The assembly of aeronautical parts requires the machining of composite materials. Drilling is the most important process in the assembly. When drilling composite materials, a number of defects are generating. A solution, to reduce these defects, is to drill using a step gundrill. In this paper, drilling of thick composite plates using a step gundrill is studied. Delamination, which is considered the major drilling defect, is analytically modelled at the hole exit. The critical thrust force at delamination is then found dividing the plate under the tool into several zones corresponding to the tool active part. These results are experimentally validated. The optimal cutting conditions at delamination are finally determined using a cutting force model. This model uses the same zones decomposition as the analytical critical thrust force model. The results of this paper can be extended to other tools to find the optimal cutting conditions corresponding for delamination-free drilling.

A theoretical model for load prediction in rolling correction process of thin-walled aeronautic parts

In the aviation industry, flexural distortion of thin-walled aeronautic parts after machining processes is inevitable, especially for high-strength aluminum alloy. To satisfy the accuracy requirement for subsequent assembly processes, the distorted parts have to be corrected. Bilateral rolling operation has been proved to be an effective method for correcting the flexural distortion. However, this method is generally based on trial and error, and the quality of distortion correcting cannot be guaranteed. To solve this problem, finite element method (FEM) was first adopted to investigate the distortion feature after bilateral rolling process for T-shaped structures. The relationship between processing parameters and maximum deflection was then studied. An equivalent bending moment method was proposed to represent the effects of bilateral rolling on micro-plastic deformation and residual stresses. Besides, a theoretical model was established for distortion prediction. Furthermore, based on simulation results, the calculation formula of the equivalent load was deduced. Finally, the theoretical model and the equivalent bending moment method were verified by rolling correction experiments, which were used to calculate the rolling correcting load (rolling depth). The results show that the average reduction rate of deflection is 73.5%. This paper provides an effective theoretical model for predicting the correction load in rolling correction process for thin-walled aeronautic parts.

Topological optimization and manufacturing by Direct Metal Laser Sintering of an aeronautical part in 15-5PH stainless steel

DMLS (Direct Metal Laser Sintering) Additive manufacturing allows building topological optimized geometries with good mechanical properties and low weight. These features are appropriated for the aeronautical industry because the reduction of weight involves saving costs per trip. However, the manufacturing cost using SLM (Selective Laser Melting) or DMLS, is also high since titanium alloys powder is expensive. Therefore, this work aims to explore the possibility of using 15-5PH stainless steel powder to balance the mechanical properties, weight and cost of the part.

Non-Destructive Evaluation of Protective Coatings on AA2024-T3 Aluminum Alloy Used in Aeronautical Parts by Electrochemical Impedance Spectroscopy

Plasma treatments have faced growing interest as important strategy to modify the hydrophobic/hydrophilic characteristics of materials. However, challenges related to the plasma modification of polymers are the improvement of the chemical resistance without decreasing the mechanical resistance. In this letter, we present for the first time a plasma treatment, using Sulfur hexafluoride (SF6), analogous to vulcanization process, of natural rubber surface, which resulted in a chemical and tension resistance improvements. The natural rubber membranes were coated with glow discharge plasmas generated in sulfur hexafluoride (SF6) atmospheres at a total pressure of 160 mTorr and applying 70 W of radiofrequency. Plasma treatment increases the contact angles from 64° to 125° i.e. leading to a hydrophobic surface. The tension at rupture increased from 3.7 to 6.1 MPa compared to natural rubber without plasma treatment demonstrated by stress-strain investigation. These results provide a fast alternative approach to improve mechanical and chemical properties of rubber-based products.

Optimization study of dry peripheral milling process for improving aeronautical part integrity using Grey relational analysis

Dry machining is one of the reliable eco-friendly techniques since it enables avoiding the use of harmful/expensive cutting fluids, reducing part costs, and increasing productivity. This study attempts to optimize the dry peripheral milling conditions with regard to the surface finish and residual stress (RS) of machined aeronautical Al–Zn–Mg–Cu alloy. The proposed approach involves a multi-objective optimization of five machining parameters, including cutting tool geometry, milling mode, feed per tooth, cutting speed, and radial depth of cut. The multi-objective optimization approach is developed based on the Taguchi method combined with the Grey relational analysis (GRA). An improvement of the multiple performance characteristics by 104%, as compared to the initial cutting conditions, has been obtained using the proposed approach. The analysis of variance (ANOVA) has shown that the feed per tooth, the cutting speed, and the interaction between cutting tool and milling mode significantly influence the surface quality of dry peripheral milled parts. This study demonstrated that the dry peripheral milling of aluminum parts can be an efficient sustainable process in terms of part quality if the machining conditions are adequately selected and optimized.

Numerical prediction of distortions during machining of large aluminium aeronautical parts

Aluminium alloy structural aerospace parts are usually large monolithic parts machined from rolled plates or preformed parts. Previous to machining, several manufacturing steps (forming, heat treatments and mechanical stress relief operations) are performed, resulting in the creation of residual stresses. During machining, a redistribution of the residual stresses occurs due to the material removal. This residual stress redistribution is the main reason for machining errors such as dimensional variations and post‐machining distortions. In order to predict the mechanical behaviour of the workpiece during machining and the final part quality in taking into consideration both the machining parameters (fixture layout and machining sequence) and the residual stress redistribution, a specific numerical tool has been developed [1]. Using this numerical tool, an analysis of the influence of the initial residual stresses as well as of the fixture layout and the machining sequences (tool path) on the machining quality of parts machined from an AIRWARE®2050‐T84 alloy rolled plate is performed. The numerical results are compared with experimental ones in terms of both post‐machining distortions and dimensional errors. Similar results are obtained for both, showing that the developed numerical tool allows to predict dimensional and geometrical errors due to the redistribution of the residual stresses during machining. The machining of these cases and results obtained are then analysed, demonstrating the feasibility to adapt and to optimize the machining process plan to ensure conformity of the part with the tolerance specifications.

Generalised cutting force model including contact radius effect for turning operations on Ti6Al4V titanium alloy

Current constraints on aeronautical parts have led to the introduction of materials like titanium alloys as well as new part geometries featuring large dimensions and reduced thickness. Inappropriate cutting forces during turning operations could lead to high deflections and damage to the machine. In order to ensure the respect of final part geometry and the optimal use of resources, cutting forces have to be known, to anticipate the deformed shape during and after machining operations on thin parts. Current models are offering a solution which can be optimised by the modelling influence of the ploughing effect on cutting forces. Therefore, a mechanistic model is developed in order to improve the prediction of cutting forces during turning operations on titanium alloy Ti6Al4V: this model includes the effect of the clearance face contact radius and comprises two main steps. First, the effect of the clearance contact radius and the effect of the cutting edge lead angle are determined independently, via a direct identification method based on elementary cutting tests. Secondly, this analysis is extended to cutting trials in boring, cylindrical turning and face turning. Then, based on a mechanistic approach, a model is defined according to the previous results and the coefficients are identified thanks to cutting trials in real conditions. The results of the proposed model are then compared to a commonly used model which takes into account mostly the uncut chip thickness effect. It is demonstrated that the proposed cutting force model provides a more accurate prediction of cutting forces.

Influence of the machining sequence on the residual stress redistribution and machining quality: analysis and improvement using numerical simulations

The manufacturing of aluminium alloy structural aerospace parts involves multiple steps, the principal ones being the forming (rolling, forging etc.), the heat treatments and the machining. During this last step, the final geometry of the part is obtained. Before machining, the workpiece has therefore undergone several manufacturing steps resulting in unequal plastic deformation and metallurgical changes which are both sources of residual stresses. On large and complex aluminium alloy aeronautical parts, up to 90 % of the initial workpiece volume can be removed by machining. During machining, the mechanical equilibrium of the part is in constant evolution due to the redistribution of the initial residual stresses.The residual stress redistribution is the main cause of workpiece deflections during machining as well as of post-machining distortion (after unclamping). Both can lead to the non-conformity of the part with the geometrical and dimensional tolerance specifications and therefore to a rejection of the part or to additional conforming steps. In order to improve the machining accuracy and the robustness of the process, the effect of the residual stresses has to be considered for the definition of the machining process plan. In this paper, a specific numerical tool [2] allowing to predict workpiece deflections during machining and post-machining distortion is used to study the influence of the machining sequence on the machining quality in taking into consideration the initial residual stresses. A first machining process plan defined as the reference case is simulated. Simulation results are then compared with experimental ones showing the feasibility to use the developed tool to predict the machining quality depending on the initial residual stresses, the fixture layout and the machining sequence. Using the computational tool, a method to optimise the machining quality depending on the initial workpiece and on the machining sequence is presented. A machining process plan allowing to respect the tolerance specifications is then defined. This demonstrates the feasibility to adapt and to optimise the machining process plan to ensure conformity of the part with the tolerance specifications.

Quick fabrication of aeronautical complicated structural parts based on stereolithography

Investment casting based on stereolithography (SL) has the characteristics of short production cycle and low cost, which is especially suitable for fabricating complex aeronautical parts without metal dies. But there are some problems during the fabrication process, such as low surface accuracy caused by the staircases of resin prototype, shell cracking caused by higher thermal stress during the sintering process and so on. Taking an engine turbine stator as a fabrication example, the surface accuracy of resin prototype under the effect of coating method was investigated using the laser confocal microscopy; what’s more, both theoretical analysis and finite element analysis (FEA) were combined and compared to reveal the thermal stress field of ceramic shell during pyrolyzing and sintering process under different situation. It was founded that the surface staircases of the resin prototype was eliminated and the surface quality was improved after coating process, the thermal stress was decreased and shell cracking was avoided by sintering the ceramic shell with the inner hollow resin prototype under the heating rate of 5°C/min. The result showed that, the metal turbine stator had high dimensional accuracy of CT4-CT6 and had a good surface finish within Ra 3.2.