Papers by Author: Li Jun Yang

Abstract: Although the nanostructure machining by AFM probe assisted with laser has gain a great progress, few studies has been done on the optical fiber probe guiding the continuous laser to irradiate on AFM probe to machining nanostructure. Using this technology to create nanodot and nano-groove was presented in this paper. The law of how the experiment parameters influenced the results was summarized in the paper. The scale of nanodot is about 450nm, and nano-groove is about 40nm. When the fabrication is completed, the wear of the AFM probe was observed by SEM and drew a conclusion. In the method of nano machining by AFM Probe combining with a CW Laser, there will be a combined field to achieve the fabrication, and the method is better than mechanical characterization with AFM probe.

Abstract: In laser induced thermal crack propagation (LITP) cutting brittle materials, according to the laser absorption ability, materials are divided into the body absorption and surface absorption. This paper indicates the fracture mechanism of LITP cutting surface absorption brittle materials. The crack extension appears in the lower surface firstly in this stress distribution state, then the crack extends to the upper surface and the laser scanning direction with the LITP cutting. The stress field of cutting ZrO₂ ceramic is studied by finite element software ANSYS. The crack propagation process of cutting silicon wafer is studied by finite element software ABAQUS. According to the fracture mechanism, the curve cutting the ZrO₂ ceramic experiments and the cooling lower surface cutting the silicon wafer experiments are carried out in this paper. Optical microscope and laser scan confocal microscope (LSCM) photographs of the curve path the ZrO₂ ceramic and separation surface cutting the silicon wafer are obtained to examine the cutting quality. The quality of the curve path is very good. The quality of the separation surface in cutting the silicon wafer with the cooling lower surface is better than conventional environment.

Abstract: Owing to drilling capacity can reach micron grade, laser punching technology has been widely used in high-tech field. In this article, ultraviolet laser has been adopted to punch on polystyrene material, the ablation principle and heat transfer between ultraviolet laser and material are analyzed. Through the finite element simulation, microporous temperature field distribution can be obtained. At last, by experiments that use single factor method to get laser parameters on the effect of surface morphology and microporous depth/diameter ratio, the optimal laser parameters that satisfy requirements which are less slag and tapered micropore can be acquired.

Abstract: Drilling and cutting experiments in magnesium alloy sheet were conducted using water-jet guided laser. Morphology characteristics in processing areas were analyzed and compared with that of the conventional laser processing. The results show the processing areas are clean, with almost no molten residues attached and negligible heat damage in water-jet guided laser processing. The hole walls and cut surfaces are smooth and have some degree of slope, and are completely covered with dense protruding particles at microcosmic scale. However, with conventional laser, the processed areas are attached with a large number of residues, and obvious secondary solidified layers.

Abstract: Titanium is a class of material difficult to common machine. Laser processing is a feasible method for machining of titanium. This paper presents cutting investigation of industry pure titanium sheet with conventional laser and water-jet guided laser, and analyses their processing features by means of the surface morphology of kerf obtained from Scanning Electron Microscope. The result shows that the machining quality and cleanliness of water-jet guided laser processing is much better than conventional laser processing. The impact and cool effects of the high-speeds water jet are more effective to trim the cut surface and remove molten waster.

Abstract: In recent years, optical manipulators based on forces exerted by enhanced evanescent field close to near-field optical probes have provided the access to nonintrusive manipulation of nanometric particles. However, the manipulation capability is restricted to the intensity enhancement of the probe tip due to low emitting efficiency. Here a near-field optical trapping scheme using the combination of an optical fiber probe and an AFM metallic probe is developed theoretically. Calculations are made to analyze the field distributions including tip interaction and the trapping forces in the near-field region by applying a direct calculation of Maxwell stress tensor using three-dimensional FDTD. The results show that the scheme is able to trap particle at the nanoscale with lower laser intensity than that required by conventional near-field optical tweezers.

Abstract: This paper indicates the experiments of YAG laser cutting soda-lime glass with controlled fracture. The qualities of glass obtained by laser cutting and mechanical cutting are compared. The impact of laser power, scanning speed and spot size on the cutting quality is studied and the optimum laser parameters are given. Finally the experiments of laser cutting two-layer glasses, glass tube and laser cutting in curve paths are carried out. The results show that good cutting quality of glass can be acquired by YAG laser cutting.

Abstract: In laser cutting of glass with controlled fracture, thermal stress induces a fracture and the material is cleaved along the cutting path by fracture propagation. Compared with CO2 laser, YAG laser has many advantages in cutting glass with controlled fracture. As a volumetric heat source, YAG laser can penetrate through the glass. Therefore, the temperature distribution is uniform across the thickness of the glass and the fracture propagates from the top and bottom surface to the middle so that better cutting quality can be acquired and multi-layer glasses can be cut simultaneously. In this paper, a 1064nm YAG laser is applied to cut two-layer and four-layer glasses. Fracture propagation mechanism is studied by examining the temperature and stress fields using finite element software ANSYS11.0. Good cutting qualities of fracture surfaces for all the layer glasses are acquired and the cutting efficiency is greatly improved by this technique as well. Additionally, due to smaller laser spot size the glasses that are closer to the focal point have higher laser power density inside glass, which may lead to ablation and evaporation phenomenon. But lower laser power density is not enough for fracture initiation and expansion. Therefore, it’s important to find a proper laser power for all the layer glasses. Small tensile stresses on the top and bottom surfaces will make the material separate from up and down to middle, whereas the compressive stresses in the middle ensure stable fracture propagation. Moreover, the stable fracture propagation always lags behind the laser beam spot. High tensile stresses are distributed throughout the thickness of the glass in the leading and trailing edges, which leads to unstable fracture extension in the leading and trailing edges.

Abstract: Water-jet guided laser micromachining is the new development of laser machining. This paper analysis the action mechanism of the plasma shock wave and hollow erode effects in water-jet guided laser machining processing, on the base of the thermal effects of the laser and water-jet. And the numerical model on the action effects between the water-jet guided laser and the material was founded. Using the software ANSYS, the processing of the water-jet guided laser micromachining was simulated. This paper gave the investigation on the distributing of temperature field in processing of water-jet guided laser micromachining. And the results of the correlative experiment correspond with the simulation results.

Abstract: Water-jet guided laser micromachining is the new development orientation of laser machining. This paper set up the numerical model on the action between the water-jet guided laser and the material. By using the software ANSYS, simulated the processing of the water-jet guided laser micromachining. This paper gave the investigation on the machining laws and the distributing of temperature fielding in processing of water-jet guided laser micromachining. And the results of the correlative experiment prove the model aright. The result provided the theoretical foundation for the next research on the water-jet guided laser machining.