Owing to their brittleness and heterogeneity, achieving carbon fiber-reinforced silicon carbide ceramic (Cf/SiC) composites with ideal dimensional and shape accuracy is difficult. In this study, unidirectional Cf materials were subjected to orthogonal grinding experiments using different fiber orientations. Through a combined analysis of the surface morphology and grinding force after processing, the mechanism underlying the effect of the fiber orientation on the surface morphology of the material was explained. The surface roughness of the material was less affected by the process parameters and fluctuated around the fiber radius scale; the average surface roughness (R a) in the direction of scratching parallel (SA) and perpendicular (SB) to the fiber direction was 4.21‒5.00 μm and 4.42‒5.26 μm, respectively; the material was mainly removed via the brittle removal mechanism; and the main defects of the fiber in the SA direction were tensile fracture and extrusion fracture; the main defects of the fiber in the SB direction were bending fracture, shear fracture, and fiber debonding. The grinding parameters influenced the grinding force in the order: depth of cut > feed rate > wheel speed. The grinding force increased with an increase in the feed rate or depth of cut and decreased with an increase in the wheel speed. Moreover, increasing the depth of cut was more effective in decreasing the grinding force and improving the material removal efficiency than adjusting the rotational speed of the workpiece and the rotational speed of the grinding wheel. The specific grinding energy decreased with an increase in the feed rate or depth of cut, and increased with an increase in the grinding wheel speed.
To enhance the performance of aero-engines, honeycomb seals are commonly used between the stator and rotor to reduce leakage and improve mechanical efficiency. Because of the thin-walled and densely distributed honeycomb holes, machining defects are prone to occur during manufacturing. Electrochemical grinding (ECG) can minimize machining deformation because it is a hybrid process involving electrochemical dissolution and mechanical grinding. However, electrolysis will generate excessive corrosion on the honeycomb surface, which affects the sealing capability and operational performance. In this study, an ECG method using an electrolyte of 10% (mass fraction) NaCl is proposed to machine the inner cylindrical surface of the honeycomb seal, and an eco-friendly inhibitor, sodium dodecylbenzene sulfonate (SDBS), is introduced to the electrolyte to inhibit corrosion of the honeycomb structure. A theoretical relationship between the voltage and feed rate during ECG is proposed, and the excessive corrosion of the honeycomb single-foiled segment is used as a measurement of the impact of electrolysis. The corrosion inhibition efficiency of SDBS on the honeycomb material in 10% (mass fraction) NaCl solution is evaluated through electrochemical tests, and the suitable feed rate and optimal concentration of SDBS are determined through ECG experiments. Additionally, the corrosion inhibition effect of SDBS is validated through four groups of comparative experiments. The results indicate that the inhibition efficiency of SDBS increases with increasing concentration, reaching the maximum of 73.44%. The optimal SDBS mass fraction is determined to be 0.06%. The comparative experiments show that excessive corrosion is reduced by more than 40%. This establishes ECG as an effective and environmentally friendly processing method for honeycomb seals by incorporating SDBS into a 10% (mass fraction) NaCl solution.
Silicon carbide fiber-reinforced silicon carbide composites are preferred materials for hot-end structural parts of aero-engines. However, their anisotropy, heterogeneity, and ultra-high hardness make them difficult to machine. In this paper, 2.5-dimensional braided SiCf/SiC composites were processed using a nanosecond pulsed laser. The temperature field distribution at the laser ablated spot is analyzed through finite element modeling (FEM), and the ablation behavior of the two main components, SiC fiber and SiC matrix, is explored. A plasma plume forms when the pulse energy is sufficiently high, which increases with growing energy. The varied ablation behavior of the components is investigated, including the removal rate, ablative morphology, and phase transition. The ablation thresholds of SiC matrix and SiC fiber are found to be 2.538 J/cm2 and 3.262 J/cm2, respectively.
Owing to the hard brittle phase organization in their matrixes, brittle materials are prone to the formation of pits and cracks on machined surfaces under extreme grinding conditions, which severely affect the overall performance and service behavior of machined parts. Based on the electroplastic effect of pulsed currents during material deformation, this study investigates electroplastic-assisted grinding with different electrical parameters (current, frequency, and duty cycle). The results demonstrate that compared to conventional grinding, the pulsed current can significantly decrease the surface roughness (S a) of the workpiece and reduce surface pits and crack defects. The higher the pulsed current, the more pronounced the improvement in the surface quality of the workpiece. Compared to traditional grinding, when the pulsed current is 1 000 A, S a decreases by 46.4%, and surface pit and crack defects are eliminated. Under the same pulse-current amplitude and frequency conditions, the surface quality continues to improve as the duty cycle increases. When the duty cycle is 75%, S a reaches a minimum of 0.749 μm. However, the surface quality is insensitive to the pulsed-current frequency. By investigating the influence of pulsed electrical parameters on the surface quality of brittle material under grinding conditions, this study provides a theoretical basis and technical support for improving the machining quality of hard, brittle materials.
Micromilling has been extensively employed in different fields such as aerospace, energy, automobiles, and healthcare because of its efficiency, flexibility, and versatility in materials and structures. Recently, nanofluid minimum quantity lubrication (NMQL) has been proposed as a green and economical cooling and lubrication method to assist the micromilling process; however, its effect is limited because high-speed rotating tools disturb the surrounding air and impede the entrance of the nanofluid. Cold plasma can effectively enhance the wettability of lubricating droplets on the workpiece surface and promote the plastic fracture of materials. Therefore, the multifield coupling of cold plasma and NMQL may provide new insights to overcome this bottleneck. In this study, experiments on cold plasma + NMQL multifield coupling-assisted micromilling of a 7075-T6 aluminum alloy were conducted to analyze the three-dimensional (3D) surface roughness (S a), surface micromorphology, burrs of the workpiece, and milling force at different micromilling depths. The results indicated that, under cold plasma + NMQL, the workpiece surface micromorphology was smooth with fewer burrs. In comparison with dry, N2, cold plasma, and NMQL, the S a values at different cutting depths (5, 10, 15, 20 and 30 μm) were relatively smaller under cold plasma + NMQL with 0.035, 0.036, 0.041, 0.043 and 0.046 μm, which were respectively reduced by 38.9%, 45.7%, 45.9%, 47% and 48.9% when compared to the dry. The effect of cold plasma + NMQL multifield coupling-assisted micromilling on enhancing the workpiece surface quality was analyzed using mechanical analysis of tensile experiments, surface wettability, and X-ray photoelectron spectroscopy (XPS).
It is necessary to improve the surface performance of bearing rings and extend the service life of bearings. In this study, ultrasonic vibration-assisted grinding (UVAG) was applied to process GCr15SiMn bearing steel, considering the effects of grinding-wheel wear, overlap of abrasive motion tracks under ultrasonic conditions, elastic yield of abrasives, and elastic recovery of the workpiece on the machined surface. In addition, a novel mathematical model was established to predict surface roughness (R a). The proposed model was validated experimentally, and the predicted and experimental results showed similar trends under various processing parameters, with both within an error range of 12%–20%. The relationships between the machining parameters and R a for the two grinding methods were further investigated. The results showed that increases in the grinding speed and ultrasonic amplitude resulted in a decrease in R a, whereas increases in the grinding depth and workpiece speed resulted in an increase in R a. Furthermore, the R a values obtained using the UVAG method were lower than those of conventional grinding (CG). Finally, the influence of ultrasonic vibration on the surface topography was investigated. Severe tearing occurred on the CG surface, whereas no evident defects were observed on the ultrasonically machined surface. The surface quality was improved by increasing the ultrasonic amplitude such that it did not exceed 4 μm, and a further increase in ultrasonic amplitude deteriorated the surface topography. Nevertheless, this improvement was superior to that of the CG surface and was consistent with the variation in R a.
Particle-reinforced metal matrix composites (PMMCs) exhibit exceptional mechanical properties, rendering them highly promising for extensive applications in aerospace, military, automotive, and other critical sectors. The distinct physical properties of the matrix and reinforcement result in a poor machining performance, particularly owing to the continuous increase in the particle content of the reinforcement phase. This has become a major obstacle in achieving the efficient and precise machining of PMMCs. The grinding process, which is a highly precise machining method, has been extensively employed to achieve precision machining of metal matrix composites. Firstly, the classification of PMMCs is presented, and the grinding removal mechanism of this material is elaborated. Recent studies have examined the impact of various factors on the grinding performance, including the grinding force, grinding temperature, grinding force ratio, specific grinding energy, surface integrity, and wheel wear. The application status of various grinding methods for PMMCs is also summarized. Finally, the difficulties and challenges in achieving high-efficiency precision grinding technology for PMMCs are summarized and discussed.
Ti2AlNb intermetallic alloys, which belong to the titanium aluminum (TiAl) family, are currently being extensively researched and promoted in the aerospace industry because of their exceptional properties, including low density, high-temperature strength, and excellent oxidation resistance. However, the excellent fracture toughness of the material leads to the formation of surface defects during machining, thereby affecting the quality of the machined surface. In this study, Ti2AlNb intermetallic alloys were subjected to side-milling trials to investigate the influence of tool coating and tool wear on both the machined surface quality and chip morphology. Specifically, the tool life, machined surface roughness, surface morphology, surface defects, and chip morphology were investigated in detail. The results indicated that the tool coating provided a protective effect, resulting in a threefold increase in the service life of the coated end mill compared to that of the uncoated one. A coated end mill yields a superior machined surface topography, as evidenced by reduced roughness and a more consistent morphology. Tool wear has a significant effect on the morphology of machined surfaces. The occurrence of material debris and feed marks became increasingly severe as the tool wore off. The chip morphology was not significantly affected by the tool coating. However, tool wear results in severe tearing along the chip edge, obvious plastic flow on the non-free surface, and a distinct lamellar structure on the free surface.