Papers by Author: Xiang Feng Li

Abstract: In the process of modeling the squashed piece of powders for the simulation of the temperature field of laser cladding, the metallurgical model and the pore model were proposed separately. The effects of the organizational form, the contact resistance and the thickness of the squashed piece of powders on the temperature were considered. Different values of physical parameters of the squashed piece of powders were converted, different contact resistances were calculated and the laser absorptivity for different process parameters of laser cladding was determined. The temperature curves of six typical nodes and the temperature gradient of two nodes in the molten pool of the substrate were discussed from different aspects.

Abstract: According to the airplane landing gear anti-fatigue manufacturing, a new data acquisition system for cold extrusion of internal threads was developed based on LabVIEW platform. And the acquisition, presentation and storage of the data including the torque moment, temperature and tap vibration for cold extrusion process of internal threads were realized. The problem that the data lost during the acquisition was resolved by using the producer/consumer design mode. The experiment that cold extrusion of internal threads in Q460 high strength steel which size is M22×1.5 was completed, and the result shows that the system is reliable and meets the requirements of the measurement.

Abstract: Simple genetic algorithm has shortcomings of poor local search ability and premature convergence. To overcome these disadvantages, simulated annealing algorithm which has good local search ability was combined with genetic algorithm to form simulated annealing genetic algorithm. The tests by two commonly used test functions of Shaffer’s F6 and Rosenbrock show that simulated annealing genetic algorithm outperforms the simple genetic algorithm both in convergence rate and convergence quality. Finally, the simulated annealing genetic algorithm was firstly applied in a practical problem of balancing and sequencing design of mixed-model assembly line, once again, the solution results show that simulated annealing genetic algorithm outperforms the simple genetic algorithm. Meanwhile, it provides a new algorithm for solving the design problem of mixed-model assembly line.

Abstract: In this work, the elastic constant and natural frequency of NCD and non-NCD coated AFM probes were simulated using ANSYS. The results indicated that after depositing 1～2μm thick NCD films on the silicon probes, the elastic constant and natural frequency were both increased, yet within the prescribed limit: when the cantilevers had the same total thicknesses (3μm, 3.5μm and 4μm), the elastic constant and the natural frequency of the NCD coated probes were increased by 96%～107% and 28%～30% respectively, compared with the silicon probes.

Abstract: Firstly, taking the stability of the forestay bar as the restraint, the section area of the forestay bar was optimized from 1800 mm2 to 1178 mm2, with reduced weight of 16.1%. Secondly, the equivalent load of the forestay bar was obtained by using dynamics simulation software. Finally, the stress field and the fatigue life of the forestay bar were simulated. The results show that stress of the forestay bar with 929MPa can meet the requirement for its material strength, and fatigue life of 51200 times also satisfies the request of the nose landing gear. That is, material property of the forestay bar is utilized more than before, and its weight decreased successfully.

Abstract: Three NiCoCrAlY coatings strengthened by different contents of nano-SiCp (nanometric SiC particles)were prepared on Ni-based superalloy substrates using crosscurrent CO2 laser, and the thermal shock test of these coatings was conducted by cycling between 1050°C and room temperature (10-15°C). The spalled area in the oxide scale of coatings after 10 thermal shock cycles and the thermal shock cracks in the cross-section of coatings after 100 thermal shock cycles were investigated using SEM, OM, and other means. The results show that the thermal shock resistances of NiCoCrAlY coatings are improved after adding nano-SiCp. Among nano-SiCp-added coatings, the coating added with 1.0 wt% nano-SiCp performs best. After 10 thermal shock cycles, there is a slight spallation whose area is only 2.65% in the oxide scale of the coating; after 100 thermal shock cycles, no internal crack is observed in the cross-section, and the amount and size of propagating cracks are slight.

Abstract: Boron-doped micro-nanocrystalline diamond coating may be successfully prepared on Mo substrate with DC arc plasmas jet deposition device. Along with the increase of doped-boron concentration in the film, two-point resistance measurement indicates that film resistance presents exponential decrease; Raman spectrum test shows that, the characteristic peak value of diamond 1332cm-1 in the spectrum moves toward low frequency, the semi-height width of diamond peak, peak D and peak G, etc. in the spectrum is expanded, and the component of non-diamond bonds such as sp2, etc. in the film is increased; SEM and AFM observation shows that, increasing the doped-boron concentration could further subdivide the crystal grains in the film, and is beneficial for the growth of nano- or ultra-nano-crystalline diamond film; film annealing test shows that, micro-nanocrystalline diamond film with higher doped-boron concentration has better thermal stability than the micro-nanocrystalline diamond film without doped boron.

Abstract: Effects of running state and spindle speeds on the sound signals produced from a drill press are investigated. And the obtained sound signals by using of a sound level meter are analyzed in both time domain and frequency domain. It is evident that there is more high frequency energy for drilling sound signals with load than without load. And spindle speeds still affect their energy distribution of drilling sound signals. Using wavelet decomposition and wavelet packet decomposition, drilling sound signals are decomposed into a number of frequency bands. And energy percentages of the divided frequency bands are extracted to be the effective characteristics to recognize spindle speeds. Meanwhile, training error of different BP networks is compared to obtain the effective network for recognition spindle speeds. By using of the obtained network structure named 16-30-5, the study rate for training samples and the recognize rate for testing samples are all above 95%.

Abstract: The synthesis of nanocrystalline diamond film on polycrystalline molybdenum substrates was carried out by using of self-made hot filament chemical vapor deposited (HFCVD) system. Positive bias voltage on the grid electrode on top of hot filaments and negative bias voltage on the substrate were applied. High purity and extremely smooth nanocrystalline diamond films were successfully prepared by using the double bias method. Raman, SEM, XRD and AFM results show that the diamond films obtained have grain sizes less than 20nm, nucleation density higher than 1011cm-1. The mechanism of double bias is also discussed in this paper. The positive grid bias increases the active, decomposition and ionization of hydrogen and methane molecules, while negative substrate bias helps positive carbon-containing ions bombard the substrate that leads to the high nucleation density of the diamond film.

Abstract: Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra<0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.