Aero-engine Casing Research Articles

Development and performance of heat insulation coatings for hot rolling of titanium alloy and superalloy rings

In recent years, with the continuous development of the equipment manufacturing industry, the seamless rings made of high-performance titanium alloys and superalloys have been widely used. These seamless rings mainly include aeroengine casing rings, carrier rocket capsule rings, gas turbine rings, oil/gas pipeline rings and so on. The metal ring hot rolling technology has become an irreplaceable manufacturing technology with its characteristics of low material consumption, high efficiency and high performance [1,2].However due to the special features of titanium alloys and superalloys, they have poor thermal processing plasticity and high processing sensitivity, thus cracks occur easily during metal temperature drop in hot rolling process. At the same time, the metal surface oxidation in the heating process also affects the surface quality and rolled parts performance. Therefore, using heat insulation and protective coatings is the most effective and easiest solution for the problem.In view of the above problems, Beijing Tianlichuang Glass Technology Development Co., Ltd. has successfully developed the water-based heat insulation coatings for titanium alloy & superalloy hot rolling at different rolling processes (different temperatures and different holding times). The coatings are coated on the metal surface at room temperature and dried before the billets are sent to furnace for heating. During the heating process, the coatings can prevent metal oxidation at high temperature and preserve heat during the billet transfer & rolling process without generating lubrication effect. These heating preservation coatings use a variety of crystalline non-metallic oxides, minerals and non-crystalline glass powders as major solid base materials, and blended with additives, adhesives and water to create suspensions, then applied to metal surface via brushing or spraying before heating. When design coating formulas, in order to realize good compatibility with the metals and right high temperature viscosity & expansion coefficient so as to achieve perfect match with different hot rolling processes, we should consider specific hot rolling process of titanium alloy & superalloy rings, that is, heating temperature, holding time, furnace atmosphere, and hot rolling condition.The heat insulation coatings can solve the problem of billet heat preservation & protection in the titanium alloy / superalloy ring hot rolling process, meanwhile reduce the surface cracks after hot rolling, making the metal easier to obtain even and fine microstructures. Also, the coatings are easy to use, non-toxic and environment friendly.

Splat analysis of plasma sprayed (Al + Ni + h(BN)) homogenized mixture for improvement of abradable resistance on aero-engine inner casing surface

In the past few years, there is a global need for engine manufacturers to give high performance and long durable engines by using good quality of materials. Previously, engine manufacturers have applied protective coatings to increase the life and performance of the aero engine. Today, a wide variety of parameters in environmental and material design challenges together with the component design of engines demanded towards the economic protective coating processes. In an aero engine, the protection against wear inside the inner surface casing is a great challenge. Present work is focused on the study of improvement of abradable resistance on aero-engine inner case materials by using a plasma spraying technique. Different wt% of (Al + Ni+(h)BN) homogenized powder mixture and sodium silicate as an inorganic binder is used for spraying. The surface property analysis of plasma sprayed coating has been characterized using, optical microscopy, scanning electron microscopy, X-Ray diffraction and Vicker hardness tester. It was found that the coating using (Al + Ni+(h)BN) homogenized powder is successful in finding optimum stand-off distance which can increase the life span of the aero-engine casing.

Bayesian identification of bolted-joint parameters using measured power spectral density

A Bayesian method for the optimal estimation of parameters that characterize a bolted joint based on measured power spectral density is proposed in this article. Due to uncertainties such as measurement noise and modelling errors, it is difficult to identify joint parameters of a bolted structure accurately with incomplete measured response data. In this article, using the Bayesian probability framework to describe the uncertainty of the joint parameters and using the power spectrum of the structural response of the single-point/multi-point excitation as measurements, the conditional probability density function of the joint parameters is established. Then, the Bayesian maximum posterior estimation is performed by an optimization method. Two simplified bolted-joint models are built in the numerical examples. First, the feasibility of the proposed method in the undamped model is proved. Then, taking advantage of multi-point excitation, the identification accuracy of the proposed method in the damped model is improved. The numerical results show that the proposed method can accurately identify the stiffness and damping characteristics of joint parameters with good robustness to noise. Finally, the joint parameters of the finite element model for an aero-engine casing are identified by the proposed method with satisfactory accuracy.

Obtaining high surface quality in electrolyte jet machining TB6 titanium alloy via enhanced product transport

Numerous components used in the aerospace industry, such as helicopter rotor hubs and aero-engine casings, require high surface quality because they must endure extreme conditions. Most of those components are made of titanium alloy materials. However, it is difficult to obtain high surface quality for those titanium alloy materials by electrolyte jet machining owing to the high sensitivity of these materials to changes in the flow field. A disordered flow field will result in pitting corrosion and product accumulation, which will degrade the quality of the machined surface. It had been reported that specially designed structures at the tool end could improve the machined surface quality. In this study, several types of tools with different sloping structures at their ends were designed to enhance the machined surface quality in electrochemical jet macro machining. Numerical simulations were applied to investigate the influence of these sloping structures on the machining flow field distribution. The simulation results revealed that an upward-sloping inclined end could improve the electrolyte flow rate, reduce the dead zone, and limit the influence range of the electric field. In contrast, a downward-sloping inclined end caused flow field disorder, which resulted in serious pitting and electrolytic product accumulation. Experiments were also conducted to verify these results, which revealed that the electrolytic product transport capacity was improved and then high surface quality was obtained by the tool with an upward-sloping end face. The groove machined using this tool possessed a smoother surface, sharper edge, and lower surface roughness compared with grooves machined using other tools. In combination with a numerical control system, the proposed tool could be used to fabricate aerospace parts composed of titanium alloys, as the machined surface quality could meet the requirements for industrial production.

Research on counter-rotating electrochemical machining of convex structures with different heights

Counter-rotating electrochemical machining (CRECM) is an alternative method for the manufacture of aero-engine casing parts with complex convex structures. In previous studies, the revolving part with hollow windows was used as the cathode tool. However, only convex structures with the same height could be machined. In practice, there are usually differences in height between different convex structures on the surface of most casing parts. To machine convex structures of different heights by using CRECM, a specific cathode with concave cavities has been designed. The bottom surfaces of concave cavities are conductive, and the depths of concave cavities are changed according to the height of convex structures. The material of the workpiece in this study is Inconel 718. Forming processes of convex structures with the cathode are simulated by using the finite element method. Results show that during the processing, the top surface of the convex structure is gradually changed from stray corrosion at low current density to normal dissolution at high current density. The height of the convex structure increases and then approximately keeps constant with increasing amount of feed, and it also can be controlled by changing the depth of the concave cavity. Finally, convex structures of different heights on the cylindrical workpiece are machined experimentally, verifying the feasibility of the method.

An experimental and simulation study of impact resistance in sandwich structures casing

As the main force component on the aeroengine, casing is one of bases of the whole aeroengine, but it is extremely difficult to analyze the capacity of aeroengine casing impact resistance. An experimental and simulation study of impact resistance has been conducted on sandwich structures casing with aluminum honeycombs to identify and improve aeroengine casing impact resistance. Firstly, a Rent–Ipson model has been applied to analyze the energy of broken blades with impacting casing. Based on a sensing test technology, the experimental research on the impact of aluminum honeycomb sandwich panel with a conical head shape bullet and a hemispherical head shape bullet have been carried out. The experimental results provide a basis for subsequent simulation research. Then the impact resistance have been compared and analyzed from single structure casing, double layer structure casing, and sandwich structure casing, according to their loss of blade kinetic energy, casing deformation, and the variation of casing internal energy. Finally, the variation of energy has been discussed during blade impacting casing with various oblique angles. Our results show that the impact resistance of sandwich structure casing is better than single structure casing and double layer structure casing. Most importantly, the impact resistance of casing has been improved with the increase of blade impact oblique angle.

Counter-rotating electrochemical machining of a combustor casing part using a frustum cone-like cathode tool

An aero-engine casing is a thin-walled revolving part with many complex convex structures on its outer surface. It is usually made of difficult-to-cut materials such as nickel-based super alloy or titanium alloy, and may have a material removal ratio as high as 60–80%. Thus, manufacturing aero-engine casings via conventional machining methods is time-consuming and expensive. In this paper, a frustum cone-like cathode tool is used to manufacture a combustor casing part via counter-rotating electrochemical machining (CRECM). A mathematical model based on the CRECM process is established. A cathode design method is proposed based on optimizing the edge points of the concave window. The methods used to determine the three main frustum cone-like cathode tool parameters: the radius, the half cone angle, and the concave window angle, are described in detail. An experiment is performed using the frustum cone-like cathode tool in which a combustor casing part with complex convex structures is successfully machined. The surface is smooth and contains no flow tracks or rib-like remnants. Convex structures with various shapes can be fabricated using a single frustum cone-like cathode tool. The edges of the convex structures are trenchant and the dimensions of the machined convex structure meet the tolerance requirements. This indicates that the proposed CRECM process offers a superior machining ability to manufacture hard-to-machine combustor casing parts.

Machining Distortion of Titanium Alloys Aero Engine Case Based on the Energy Principles

The simulation of a complete manufacturing process to produce an aero engine case, including forging, rolling, and machining processes, is analyzed via finite element software. The deformation of the turning and drilling processes is quantitatively studied using the energy principles. Firstly, simulations of multi-stage forging of aero engine case and machining-induced residual stress are conducted and verified via the residual stresses test in order to provide the initial elastic strain energy condition prior to machining processes. The effects of blank forging-induced residual stress and machining-induced residual stress on the deformation of titanium alloys aero engine case are investigated. Secondly, a potential energy expression for the machining processes is developed. The predicted results of turning and drilling simulations indicate that there is an optimal process in which the deformation and potential energy decline rapidly compared with the other processes and finally, gradually stabilize at the end of the process.

Analytical lump model for the nonlinear dynamic response of bolted flanges in aero-engine casings

Abstract Bolted flanges in aero-engine casings exhibit a nonlinear response when subjected to forced vibration. The current models for the structural dynamic analysis of bolted flanges are accurate, but they are cumbersome for the design of new structures. These models either require model updating from modal testing, or they require a large number of nonlinear elements. This study presents a new lump model that accounts for the nonlinear phenomena of partial clearance and friction, and has analytical parameters related to the flange geometry. The model was implemented in finite element analysis and compared with an experiment where a test structure is excited by an electromechanical shaker. The lump model predicts the structural response better than a traditional linear method; yet it does not require model updating, and it uses a very limited number of nonlinear elements. The model is therefore well suited for the early design phase of new aero-engine casings. This study supports the use of geometric lump models in the field of nonlinear structural dynamics.

Feature-based automatic NC programming for aero-engine casings

Traditional numerical control (NC) programming methods based on commercial computer-aided manufacturing systems usually require a large number of manual interactions with high-skilled experience, which not only results in low efficiency but also unstable machining quality. Especially since the structural complexity and machining requirements keep increasing, the NC programming is becoming a bottleneck problem in machining complex parts like aero-engine casings. This article proposes a feature-based automatic NC programming approach for aero-engine casings. A machining feature classification towards the geometric and machining characteristics of aero-engine casings is given. Then, a feature-based method to extract machining regions by considering the alternatives in selecting turning or milling operations is discussed. After the construction of machining operations, an undercut region detection method is also presented to evaluate the interim machining effects reasoned by each individual machining operation for excessive cutting avoidance. By implementing the proposed approach, a feature-based NC programming system is developed on a commercial computer-aided manufacturing platform and a real aero-engine casing is chosen to demonstrate the feasibility of the proposed approach.

Vibration isolation design for periodically stiffened shells by the wave finite element method

Periodically stiffened shell structures are widely used due to their excellent specific strength, in particular for aeronautical and astronautical components. This paper presents an improved Wave Finite Element Method (FEM) that can be employed to predict the band-gap characteristics of stiffened shell structures efficiently. An aero-engine casing, which is a typical periodically stiffened shell structure, was employed to verify the validation and efficiency of the Wave FEM. Good agreement has been found between the Wave FEM and the classical FEM for different boundary conditions. One effective wave selection method based on the Wave FEM has thus been put forward to filter the radial modes of a shell structure. Furthermore, an optimisation strategy by the combination of the Wave FEM and genetic algorithm was presented for periodically stiffened shell structures. The optimal out-of-plane band gap and the mass of the whole structure can be achieved by the optimisation strategy under an aerodynamic load. Results also indicate that geometric parameters of stiffeners can be properly selected that the out-of-plane vibration attenuates significantly in the frequency band of interest. This study can provide valuable references for designing the band gaps of vibration isolation.

Experimental and computational appraisal of the shape accuracy of a thin-walled virole aero-engine casing manufactured by means of laser metal deposition

Laser metal deposition (LMD) of metallic powders, especially of high-strength nickel based alloys, allows for the manufacturing of components of high shape complexity and load capacity. However, high temperature gradients, induced during laser processing may have an impact on the product quality, especially when it comes to the geometrical accuracy of thin-walled components. This paper aims to provide a modelling approach of the heat effects during LMD manufacturing of a thin-walled virole aero-engine structure, in order to calculate possible shape deviations compared to the target CAD geometry. Hereby, a model reduction method is facilitated which allows the finite element analysis of such larger components in reasonable time. Major process characteristics as heat input, molten region geometry, material deposition (i.e. layer thickness), temperature dependent material and powder properties, phase transformation, process sequence and convection effects are taken into account. The proposed model aims to decrease time consuming trial-and-error testing effort during process design and development by providing reliable results on the shape accuracy of components. The computed final shape of the final product was compared to 3D measurements on a real demonstrator virole component.

Substructure-based model updating using residual flexibility mixed-boundary method

Substructure method has been widely applied in dynamic analysis of complex structures due to high computational efficiency. On the basis of Residual flexibility mixed-boundary (RFMB) substructure method, a model updating approach is proposed in this paper. Four major steps of the RFMB model updating method are summarized as: 1) Substructuring: Dividing the whole structure into residual part and reduced part according to the junction surface; 2) reduction: Using the RFMB component mode synthesis approach to reduce the order of each substructures; 3) assembly: Residual structure analysis by using the reduced assemble matrix; 4) updating: Model updating by solving the optimization problem. Numerical simulation is conducted to verify the effectiveness by adopting a cantilever plate in case I. In case II, the proposed method is applied to identify the elastic parameter of interface of a bolted joint structure using experimental data. After parameter identification, the maximum error between numerical results and the experimental data decreases to 2.44 %. And three component mode synthesis model updating methods: Craig-Bampton (CB), Mixed-boundary (MB) without considering residual flexibility and RFMB model updating approach, are applied to update the same bolted joint structure for comparing the accuracy. For comparing the computational efficiency, the RFMB model updating approach is applied to the complicated aero-engine casing structure. In case III, the average time-consuming of the Whole finite element model (WFEM) is 5.15 times to the Residual finite element model (RFEM) in the single updating iteration. Results show that the proposed approach has better performance in the finite element model updating.

Dynamic finite element model validation of an assembled aero-engine casing

Structural dynamic model updating and validation of an aero-engine casing is critical to the design and development of an aircraft engine. It helps to identify the dynamic characteristics and reduce the response of the aero-engine. The modelling and parameter identification of joint are extremely difficult and important in structural dynamic analysis of the assembled aero-engine casing. In this paper, dynamic model validation technique was applied to update and validate the finite element model of an assembled aero-engine casing. First, modal test of individual casings and the assembled casing was performed by using the traditional acceleration sensors and a hammer. The modal frequencies and mode shapes were obtained by modal analysis tools. Second, the Inverse Eigen-sensitivity Method was used to correct frequency errors and MAC values of correlated mode pairs in the individual components to obtain validated models. Last, the bolt joints of two aero-engine casings were modelled by thin layer of shell elements. The material parameters or element properties of the thin-layer contact elements were updated to obtain reliable connection parameters. The results show that the errors of natural frequencies between the validated FE model of an assembled aero-engine casing and test data are within 7%, and the MAC values of main modes are above 70%, which can verify the feasibility and effectiveness of this approach.

Parametric modeling and updating for bolted joints of aeroengine casings

To establish accurate finite element (FE) model of bolted joint structures of aeroengine stator system (casings), this work implements the parametric FE modeling and updating of bolted joints of aeroengine stator system with multi-characteristic responses (multi-object). Firstly, the parametric FE modeling approach of bolted joint structure was developed based on the thin layer element method. And then the FE model updating thought of aeroengine stator system was developed based on the probabilistic analysis method. Finally, the parametric modeling and updating of the bolted joints of aeroengine stator system with multi-characteristic responses was completed by the optimization iteration calculation of objective function based on the proposed methods and the static stiffness testing data. Through the parametric modeling of bolted joint structures based on the thin layer method, the complexity of FE model of aeroengine casings with many bolted joint structures is reduced. As shown in the FE model updating of casings with multi-characteristic responses analysis, the static stiffness from the updated model are very close to the test data, in which the maximum relative error decreases to 3.9% from 30.52% and the others are less than 3%, so that the design precision of aeroengine stator system with the many and wide variety of bolted joints gets a great improvement. Moreover, the proposed methods of parametric modeling and model updating for multi-characteristic responses are validated to be effective in the simulation and equivalent of the mechanical characteristics of bolted joints in complex systems like aeroengine stator system.

Multi-blade effects on aero-engine blade containment

To study the effects of multi-blade interaction on the blade containment capability of the aero-engine casing, series of blade containment tests and the corresponding numerical analysis for the fan and the turbine components are carried out. Numerical models are validated through the correlation of the numerical results with the experimental data. Combined with the experiments and the FEM analysis, it is found that multi-blade effects enhance the penetration ability of the released blade for both the fan and the turbine components. Consequently, the containment capability of the casing is weakened for the fan stage. But for the turbine stage, the containment capability of the turbine casing varies significantly with deviation of the impact site, which is caused by the multi-blade effects. If the impact site moves to the circular groove on the inner wall of the turbine casing, the casing's containment capability is significantly enhanced; otherwise, the containment capability of the turbine casing remains weakened.

Development of a test planning methodology for performing experimental model validation of bolted flanges

This work presents a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures. Considering the great number of coupled mechanical structures and research studies on this subject, the authors focused this research work on bolted flanges of aircraft engine casings. In fact, the coupling of engine casings is generally obtained by a large number of joints which assure the correct sealing at the flanges’ interfaces. From a finite element (FE) modelling perspective, joints are often modelled by either rigid connections or springs, otherwise incurring a very expensive computational time. This modelling approach is not a problem when dealing with low amplitude levels of vibrations. For higher levels of vibrations, joints and flanges cannot be considered rigidly connected and that exerted flexibility at the joints’ area can determine nonlinear dynamic behaviour. This work aims to study the dynamic behaviour of bolted flanges by using modal testing performed under controlled response amplitude. Two test structures, (1) a simple bolted flange test case and (2) a sector of a Rolls-Royce aero-engine casing, are tested under high level of vibrations. Both test structures are modelled by FE method, and nonlinear elements are used for modelling the flanges’ interfaces so as to perform prediction of nonlinear responses. These predictions are eventually correlated with the measured data.

Chatter stability prediction in four-axis milling of aero-engine casings with bull-nose end mill

An analytical model for chatter stability prediction in bull-nose end milling of aero-engine casings is presented in this paper. And the mechanics and dynamics variations due to the complex cutter and workpiece geometry are considered by analyzing the effects of the lead angle on the milling process. Firstly, the tool-workpiece engagement region is obtained by using a previously developed method and divided into several disk elements along the tool-axis direction. Secondly, a 3D dynamic model for stability limit calculation is developed and simplified into a 1D model in normal direction considering only the dominant mode of the workpiece. Then the cutting force coefficients, the start and exit angles corresponding to each disk element are determined. And the total stability lobe diagram is calculated using an iterative algorithm. Finally, several experimental tests are carried out to validate the feasibility and effectiveness of the proposed prediction approach.

Novel Dispersion Curves Extraction Method for Waveguides Affected by Nonuniform Transient Temperature Field

Guided waves sensitivity to environmental and operational conditions, especially temperature fluctuations, is one of the major problems when the method is considered for real engineering applications. The aim of this paper is to propose a novel dispersion curves extraction method for waveguides affected by nonuniform transient temperature field. Essentially, the method is based on a simple and robust approach, consisting in a few series of modal analyses for a representative part of the inspected structure. To consider the effect of temperature, a thermal stress calculation based on finite element method is presented. In this way, for different wave lengths, the mode shapes and corresponding natural frequencies can be obtained by solving some thermal-eigenvalue problems. To test the theoretical thermal effect of the dispersion curves a experiment on an isotropic plate is conducted. Those theoretical dispersion curves, consisting of only dominant modes, are compared with dispersion curves obtained from experiment. Finally, this method is used to extract the dispersion curves of the aero-engine casing considering the nonuniform temperature field. The results not only give us insight to how temperature affects Lamb wave velocities in different frequency ranges but also will help those extracting dispersion curves for waveguides affected by nonuniform transient temperature field.

An investigation of the relationship between wear and contact force for abradable materials

Abradable linings are frequently used on the inside of aero-engine casings. During the operation of engine, the rotating blades may strike the lining of the casing. The wear mechanisms present during these incursions have been re-produced on a scaled test rig platform. Previously, characterisation of the wear has been performed using a stroboscopic imaging technique in order to identify the different wear mechanisms at the incursion conditions investigated. In the present study, a dynamometer has been included in the test arrangement allowing the measurement of the contact force. This approach has then been combined with sectioning of the abradable test samples, in order to investigate the material response to the different incursion conditions. The wear results, the cutting force and material structure post-incursion show a high degree of correlation. At low incursion rates, significant consolidation and solidification of abradable material was observed, whilst at the same time adhesive transfer to the blade was recorded along with a low tangential to normal force ratio. At high incursion rates, little solidification and consolidation was observed, together with negligible adhesion and a higher tangential force, suggesting a cutting mechanism. Transitions in material behaviour, wear mechanism, and force ratio were observed at the same incursion condition, further highlighting the link between the different experimental measurements.