Guojun Zhang

A novel shallow oil chamber hybrid journal bearing with adjustable oil chamber depth was designed based on piezoelectric ceramics, inspired by conventional shallow oil chamber bearing structures. The computational fluid dynamics method is used to analyze the bearing characteristics of shallow oil chamber bearings, including the volume flow, the seal oil pressure, load capacity and stiffness. An experimental platform equipped with signal acquisition device and piezoelectric ceramic control device was developed. The eddy current sensors collected the displacement signal at the shaft end. The required voltage was calculated by the displacement signal. The piezoelectric ceramics elongated or shortened, causing a displacement of the same magnitude in the depth of the oil chamber, thereby controlling the radial displacement of the shaft. The adjustment effect of this bearing was verified by experiment for no-load and 500 N load at 200–1000 rpm, with a baseline initial oil chamber depth of 20 and an oil supply pressure of 2 MPa. The results showed that compared with the case without adjustment, the accuracy in Y direction has increased from 8.9 μm to 1.9 μm (max. 78.4%) after adjustment. Under the above load conditions, the displacement can be controlled below 2 μm, indicating a significant improvement in shaft vibration resistance.

Electron beam powder bed fusion (EB-PBF) Ti6Al4V often exhibits high vertical surface roughness, limiting its use in high-end applications. In this study, an infrared continuous-wave laser was applied to precisely polish the vertical surface. An orthogonal design identified the optimal condition as 10,400 kW/cm² power density, 800 mm/s scanning speed, and one pass, achieving a minimum Sa of 0.24 μm and a 98.03% reduction compared with the as-built surface. To address the adhered semi-molten particle characteristics of EB-PBF sidewalls, a molten-pool-dynamics-based polishing model was developed and validated, yielding an error as low as 1.24%. Simulations indicate that power density governs the final morphology by controlling molten pool coverage, scanning speed affects polishing efficiency via thermocapillary force, and polishing time influences surface quality by triggering or avoiding melt splashing.

Silica fiber-reinforced silica aerogel (SFRSA) has low dielectric constant, light weight and high temperature resistance characteristics, making it one of the preferred materials for heat-resistant absorptive layers on the surfaces of high-speed aircraft. However, due to its ultra-high porosity, poor rigidity, and sensitivity to organic solvents, existing machining and chemical etching processes struggle to achieve patterned preparation of metallic layers on aerogel substrates. In order to address this issue, the present study employs femtosecond laser etching of the metal layer on the SFRSA surface. Orthogonal experiments were conducted to analyze the impact of different laser process parameters on the etching quality. With straightness as the primary factor, the optimal process parameters obtained were a laser power set to 2.15 W, a laser etching speed of 200 mm/s, and a laser etching time of 9. This achieved an etching width of 26.16 μm, a heat-affected zone of 39.16 μm, and straightness of 7.9 μm. Finally, Raman spectroscopy was used to study laser-ablated samples; thermogravimetric analysis (TGA) and Pyrolysis-Gas Chromatography–Mass Spectrometry analysis (Py-GC-MS) were employed to investigate the changes in the metal layer at high temperatures. A compositional analysis was conducted, revealing a decrease in carbon content within the etched region following laser ablation. The production of CO₂ gas and surface oxidation indicated that laser etching primarily operates via a photothermal mechanism.

The temperature rises of the oil film in hydrostatic bearings at high speed lead to a reduction in load capacity, accuracy, and stability. In this paper, a superhydrophobic/oleophobic surface with a micro-bulge structure is proposed. The surface is prepared by laser cross-scanning and chemical modification. The contact angle (CA) of the surface is 138 deg and the boundary condition of the surface is modified from non-slip to slip condition. The relationship between the slip length and the height of the micro-bulge structure is established by rheological experiments. By the simple partial simulations, the validity of the temperature rise reduction on the superhydrophobic/oleophobic surface is verified. Then a bearing test rig was set up to measure the temperature and load capacity of bearings at multiple points, and the performance of smooth primary surface/structured oleophobic surface thrust bearings was compared. Results show that the structured bearing has a lower oil film temperature and higher load capacity than the smooth bearing. The prepared oleophobic surface can effectively suppress the temperature rise at high-speed conditions and significantly increase the bearing load capacity.

The cutting of thick glass is extensively employed in aerospace, optical, and other fields. Although ultrafast laser Bessel beams are heavily used for glass cutting, the cutting thickness and cutting quality need to be further improved. In this research, the high-quality cutting of thick glass was realized for the first time using ultrafast laser perforation assisted by CO₂ laser separation. Initially, an infrared picosecond laser Bessel beam was employed to ablate the soda-lime glass and generate a perforated structure. Subsequently, a CO₂ laser was employed to induce crack propagation along the path of the perforated structure, resulting in the separation of the glass. This study investigates the influence of hole spacing, pulse energy, and the defocusing distance of the picosecond laser Bessel beam on the average surface roughness of the glass sample cutting surface. The optimal combination of cutting parameters for 6 mm thick glass results in a minimum surface roughness of 343 nm in the cross-section.

Carbon fiber reinforced polymer (CFRP) composites are widely used in the aerospace field because of their outstanding performance. Laser is an effective method for CFRP composite processing. However, there are corner errors and obvious thermal damage in laser corner cutting, which affect the cutting quality. This article mainly describes the corner error and thermal damage behavior, and the effect of anisotropy of nanosecond UV laser when cutting different corners of CFRP plates. Select six corner angles to perform a full factorial experiment with a right-angled triangle hole cutting under the horizontal and vertical baselines and different laser repetition rates. The results show that there are obvious corner errors and heat affected zone (HAZ) and matrix recession (MR) in laser corner cutting. The corner error always shows that the cut-in error is smaller than the cut-out error (28.06% on average), and the cut-in error and HAZ decrease with the increase of the corner angle, but the difference between the cut-in and the cut-out error increases with the increase of the corner angle. In vertical baseline cutting, the corner error can be reduced to a certain extent, but the HAZ (average 38.42%) is seriously increased, and the thermal damage of linear cutting under a large pulse repetition rate is increased. The large laser repetition rate increases the thermal damage due to the increase of the overlap rate of adjacent pulses but has less effect on the corner error, especially the cut-in error.

Laser-induced plasma micro-machining (LIPMM) process does well in fabricating high-quality surface microstructures of hard and brittle materials. However, the liquid medium is overheated to induce lots of bubbles to defocus the laser beam, reducing machining stability, and explosive behavior of bubbles destroys the surface quality. Thus, the static and dynamical behaviors of bubbles in LIPMM are comprehensively investigated in this article. First, a series of mechanisms including bubble generation and growth, bubble motion and explosion, and the effect of bubbles behavior on machining characteristics were explained. Second, a volume of fluid (VOF) model of bubble motions in laser-induced plasma micro-machining was established to simulate the dynamical behavior of bubbles under different depths of water layer, which reflect the growth of microbubbles, the aggregation of multiple bubbles, and the floating movement of bubbles. Then, a series of experiments were carried out to reveal bubble static behaviors, and further bubble explosion behaviors on surface integrity, surface defects, and hardness were analyzed. The increase of laser frequency leads to the increase of the maximum attached bubble size. Obstructed by bubble dynamical behaviors, a discontinuous section and the unablated area are observed in the microchannel. The elastic modulus and surface hardness of surface impacted by explosion bubbles are reduced. This research contributes to better understanding bubble behavior related to machining performances in LIPMM of single-crystal silicon.

Curved glass is widely used in 3C industry, and the market demand is increasing gradually. Glass molding process (GMP) is a high-precision, high-efficiency 3D glass touch panel processing technology. In this study, the processing parameters of fingerprint lock glass panels were deeply analyzed. This paper first introduces the molding process of the glass panel, discusses the glass forming device, and explains the heat conduction principle of the glass. Firstly, it introduces the forming process of the glass panel, discusses the glass forming device, and explains the heat conduction principle of the glass. Secondly, the simulation model of a fingerprint lock glass plate was simulated by MSC. Marc software. The stress relaxation model and structure relaxation model are used in the model, and the heat transfer characteristics of glass mold are combined to accurately predict the forming process of glass components. The effects of molding temperature, heating rate, holding time, molding pressure, cooling rate and other process parameters on product quality characteristics (residual stress and shape deviation) were analyzed through simulation experiments. The results show that, in a certain range, the residual stress is inversely proportional to the bending temperature and heating rate, and is directly proportional to the cooling rate, while the shape deviation decreases with the increase of temperature and heating rate. When the cooling rate decreases, the shape deviation first decreases and then increases. Furthermore, a verification experiment is designed to verify the reliability of the simulation results by measuring and calculating the surface roughness of the formed products.