Measurements of Forces and Selected Surface Layer Properties of AW-7075 Aluminum Alloy Used in the Aviation Industry after Abrasive Machining

Analysis of the Effectiveness of Removing Surface Defects by Brushing

The paper presents the results of a study on the effectiveness of removing surface defects by brushing. Damage to machine components usually begins on their surface or in the surface layer area. This determines the development of methods, conditions, and process parameters that will positively affect the stereometric and physical properties of the surface layer. Experiments were conducted in which surface defects were generated on a specially designed test stand. By controlling the load and speed of the defect generator it was possible to affect the geometry, depth, and width of the surface defect. A FEM simulation of the brushing treatment was carried out in order to determine the effect of fibers passing through a surface defect in the form of a groove with a small depth and width. It was shown that for certain conditions of brushing treatment, surface defects could be removed effectively. Moreover, the microhardness of the surface layer after the brushing process was analyzed. Changes in microhardness due to brushing reached up to 50 μm for EN AW-2024 aluminum alloy and up to 150 μm for AZ91HP magnesium alloy. The results demonstrated that brushing was an effective method for strengthening the surface layer and that the value of strengthening in the area of defects depended on the effectiveness of their removal.

Lapping Quality Prediction of Ceramic Fiber Brush Based on Gaussian-Restricted Boltzmann Machine

Although ceramic fiber brushes have been widely used for deburring and surface finishing, the associated relationship between process parameters and lapping quality is still unclear. In order to optimize the lapping process of ceramic fiber brushes, this paper proposes a multi-layer neural network based on the Gaussian-restricted Boltzmann machine (GRBM), and verified its prediction effectiveness. Compared with a traditional back-propagation neural network, its prediction error was reduced from 7.6% to 4.5%, and the determination coefficient was increased from 0.96 to 0.98, respectively. The comparison results showed that the proposed model can better grasp the relationship between process parameters and machining quality, which can be used as a decision-making foundation for lapping-process optimization.

Improving the Corrosion Resistance of Aluminum Alloy by Creating a Superhydrophobic Surface Structure through a Two-Step Process of Etching Followed by Polymer Modification

A multifunctional aviation aluminum alloy with good superhydrophobicity and corrosion resistance was prepared by a two-step process of etching followed by polymer modification. Meanwhile, micro- and nanostructures formed on the processed sample. Compared with bare sample, the static liquid contact angle on the as-prepared sample was increased by 100.8°. Further polarization tests showed that the corrosion potential of such a sample increased, and the corrosion current density decreased obviously, thus suggesting that the corrosion resistance of the modified sample was significantly improved. The same conclusion was confirmed by subsequent impedance testing. The work is of great economic value and practical significance to enhance the corrosion resistance of aviation actuator materials and also lays a foundation for future hydrophobic application research in aeronautical engineering.

Milling of Three Types of Thin-Walled Elements Made of Polymer Composite and Titanium and Aluminum Alloys Used in the Aviation Industry

The machining of thin-walled elements used in the aviation industry causes may problems, which create a need for studying ways in which undesirable phenomena can be prevented. This paper presents the results of a study investigating face milling thin-walled elements made of titanium alloy, aluminum alloy and polymer composite. These materials were milled with folding double-edge cutters with diamond inserts. The results of maximum vertical forces and surface roughness obtained after machining elements of different thicknesses and unsupported element lengths are presented. The results of deformation of milled elements are also presented. The results are then analyzed by ANOVA. It is shown that the maximum vertical forces decrease (in range 42-60%) while the ratio of vertical force amplitude to its average value increases (in range 55-65%) with decreasing element thickness and increasing unsupported element length. It is also demonstrated that surface roughness deteriorates (in range 100% for aluminum, 30% titanium alloy, 15% for CFRP) with small element thicknesses and long unsupported element lengths. Long unsupported element lengths also negatively (increasing deformation several times) affect the accuracy of machined elements.

Post-Machining Deformations of Thin-Walled Elements Made of EN AW-2024 T351 Aluminum Alloy as Regards the Mechanical Properties of the Applied, Rolled Semi-Finished Products

The paper presents an evaluation of post-machining deformations of thin-walled elements as regards the mechanical properties of the applied, rolled semi-finished products. Nowadays, wrought aluminum alloys, supplied primarily in the form of rolled plates, are widely applied in the production of thin-walled integral parts. Considering the high requirements for materials, especially in the aviation sector, it is important to be aware of their mechanical properties and for semi-finished products delivered after plastic working to take into account the so-called “technological history” concerning, inter alia, the direction of rolling. The study focused on determining the influence of the ratio of the tension direction to the rolling direction on the selected mechanical properties of the EN AW-2024 T351 aluminum alloy depending on the sample thickness and its relation to the deformation of thin-walled parts. Based on the obtained results, it was found that the sample thickness and the ratio of the tension direction to the rolling direction affected the mechanical properties of the selected aluminum alloy, which in turn translated into post-machining deformations. Summarizing, the textured surface layer had a significant impact on the mentioned deformation. Greater deformations were noted for samples made of a semi-finished product with a thickness of 5 mm in comparison to 12 mm. It was the result of the influence of the surface layer, which at lower thickness had a higher percentage of contents than in thicker samples.

Numerical and Experimental Research on the Brushing Aluminium Alloy Mechanism Using an Abrasive Filament Brush

Abrasive filament brushes have been widely used in surface processes for a wide range of applications, including blending, edge-radiusing, and polishing. However, the associated brush mechanics of material removal is still not clear. In order to analyze the brush grinding of aluminium alloy, this paper constructed a kinematic model of a single filament, simulated the scratch process of a single abrasive grain, and investigated the brush force and material removal based on the finite element approach. The simulated result shows that the brush grinding can be changed from elastic-plastic deformation to chip formation when increasing the brush speed to 1000 r/min. The normal and tangential forces increase linearly and quadratically with the increase in the rotation speed (500-5000 r/min), respectively, and increase linearly with the increase in the penetration depth (0.1-1 mm), which is consistent with the experiment results. In addition, the amount of material removal initially increases with the increase in penetration depth, and then decreases. This paper provides a new approach to understanding the process of material removal and is helpful for the selection of reasonable brush parameters in the intelligent grinding control application.

Microstructure and Properties of Electroless Ni-P/Si3N4 Nanocomposite Coatings Deposited on the AW-7075 Aluminum Alloy

The article presents the results of mechanical and tribological tests of Ni-P/Si₃N₄ nanocomposite coatings deposited on the AW-7075 aluminum alloy using the chemical reduction method. The influence of the chemical composition on the Vickers microhardness determined by the DSI method was examined. The nanocomposite layers were made of Si₃N₄ silicon nitride in a polydisperse powder with a particle size ranging from 20 to 25 nm. The influence of the content of the dispersion layer material on the adhesion to the substrate was analyzed. The abrasive wear was tested and determined in the reciprocating motion using the "ball-on-flat" method. The surface topography was examined by the contact method with the use of a profilometer. Based on the obtained test results, it was found that the Ni-P/Si₃N₄ layers produced in the bath with the Si₃N₄ nanoparticle content in the amount of 2 g/dm³ are more resistant to wear and show greater adhesion than the Ni-P/Si₃N₄ layers deposited in the bath with 5 g/dm³ of the dispersion phase. NiP/Si₃N₄ layers provide protection against abrasive wear under various loads and environmental conditions.

Ultimate Load-Carrying Ability of Rib-Stiffened 2024-T3 and 7075-T6 Aluminium Alloy Panels under Axial Compression

Stringer-stiffened panels made of aluminium alloys are often used as structural elements in the aircraft industry. The load-carrying capacity of this type of structure cannot relieve the reduction in strength in the event of local buckling. In this paper, a method of fabrication of rib-stiffened panels made of EN AW-2024-T3 Alclad and EN AW-7075-T6 Alclad has been proposed using single point incremental forming. Panels made of sheets of different thickness and with different values of forming parameters were tested under the axial compression test. A digital image correlation (DIC)-based system was used to find the distribution of strain in the panels. The results of the axial compression tests revealed that the panels had two distinct buckling modes: (i) The panels buckled halfway up the panel height towards the rib, without any appreciable loss of rib stability, and (ii) the rib first lost stability at half its height with associated breakage, and then the panel was deflected in the opposite direction to the position of the rib. Different buckling modes can be associated with the character of transverse and longitudinal springback of panels resulting from local interaction of the rotating tool on the surface of the formed ribs.

Techniques for Thin-Walled Element Milling with Respect to Minimising Post-Machining Deformations

The paper examines the impact of selected machining techniques and the semi-finished product technological history on deformations of thin-walled elements made of EN AW-2024 T351 aluminium alloy after milling. The following techniques have been implemented: High Performance Cutting, High Speed Cutting, conventional finishing (CF) and combinations of these techniques. As for the semi-finished product technological history, the rolling direction has been analysed. It has been assumed that it can be relevant in relation to the cutting tool feed direction and, in consequence, exert considerable impact on the stress, as well as deformation following machining. The interest in this issue proceeds from significant challenges faced by the industry, particularly in the aerospace sector. The analysis of results obtained has shown that milling in the direction perpendicular to the rolling direction results in larger deformations than milling in the parallel direction. Additionally, it has been revealed that applying a correctly selected machining technique makes it possible to minimise post-machining deformations of thin-walled elements.

Adhesion and Corrosion Resistance of Micro-Arc Oxidation/Polyurethane Composite Coating on Aluminum Alloy Surface

The adhesion and bonding performance of waterborne polyurethane (PU) coating on aluminum alloy surface was improved in this study. To achieve this objective, the effects of different sodium silicate concentrations on the aluminum alloy micro-arc oxidation (MAO) layer and the adhesion strength and corrosion resistance of MAO-PU composite coating before and after modification by MAO treatment of the 7050 aluminum alloy were studied. The experimental results showed that the modification of the MAO membrane layer by a silane coupling agent could significantly improve the adhesion strength and corrosion resistance of the composite coating. Moreover, the maximum adhesion strength was obtained when the concentration of sodium silicate was 12 g L−1.

Selected Properties of the Surface Layer of C45 Steel Parts Subjected to Laser Cutting and Ball Burnishing

In this article, we report the results of experimental studies on the impact of ball burnishing parameters on the roughness, microstructure and microhardness of the surface layer of laser-cut C45 steel parts. We also analysed the distribution of residual stresses generated in the surface layer of these parts. Laser-cut parts often require finishing to improve the quality of their surface. The tests performed in this study were aimed at assessing whether ball burnishing could be used as a finishing operation for parts of this type. Ball burnishing tests were performed on an FV-580a vertical machining centre using a mechanically controlled burnishing tool. The following parameters were varied during the ball burnishing tests: burnishing force F_n, path interval f_w and the diameter of the burnishing ball d_n. Ball burnishing of laser-cut C45 steel parts reduced the surface roughness parameters Sa and Sz by up to 60% in relation to the values obtained after laser cutting. Finish machining also led to the reorganization of the geometric structure of the surface, resulting in an increase in the absolute value of skewness Ssk. This was accompanied by an increment in microhardness (maximum microhardness increment was ΔHV = 95 HV0.05, and the thickness of the hardened layer was g_h = 40 µm) and formation of compressive residual stresses in the surface layer.

Properties of the Surface Layer After Trochoidal Milling and Brushing: Experimental Study and Artificial Neural Network Simulation

The aim of this study was to investigate the effect of milling and brushing cutting data settings on the surface geometry and energy parameters of two Mg alloy substrates: AZ91D and AZ31. In milling, the cutting speed and the trochoidal step were modified (vc = 400–1200 m/min and str = 5–30%) to investigate how they affect selected 2D (Rz, Rku, Rsk, RSm, Ra) and 3D (Sa, Sz, Sku, Ssk) roughness parameters. The brushing treatment was carried out at constant parameters: n = 5000 rev/min, vf = 300 mm/min, ap = 0.5 mm. The surface roughness of specimens was assessed with the Ra, Rz, and RSm parameters. The effects of the two treatments on the workpiece surface were analyzed comparatively. It was found that the roughness properties of the machined surface may be improved by the application of a carbide milling cutter and ceramic brush. The use of different machining data was also shown to impact the surface free energy and its polar component of Mg alloy specimens. Complementary to the results from the experimental part of the study, the investigated machining processes were modelled by means of statistical artificial neural networks (the radial basis function and multi-layered perceptron). The artificial neural networks (ANNs) were shown to perform well as a tool for the prediction of Mg alloy surface roughness parameters and the maximum height of the profile (Rz) after milling and brushing.