Junke Jiao

Numerical analysis of cutting glass by dual CO2- laser beams

Cutting brittle materials such as ceramics and glass by lasers or traditional saw method, costly fractures and associated damage such as chips and cracks can result. In most cases, these problems were caused as a result of the stress was not controlled properly and exceeded the critical value of the fracture. In this study, a dual-laser-beam method was proposed to avoid fractures in glass laser cutting, where an off-focused CO2-laser beam was scanning on the top surface of glass periodically and repeatedly and a preheated-band which has a proper temperature was built. This preheated-band will reduce the temperature gradients when the glass is cut by the focused CO2-laser beam. Under these conditions, glass can be cut with melting method without any fractures. The process of cutting glass by dual CO2-laser beams was simulated numerically with FEA method and the distribution of temperature and thermal stress was investigated. The relationships between the cutting parameters, such as laser beam diameter, laser power, cutting speed, and the profile of the cutting groove were also discussed. The result showed that thermal stress decreased with the increasing width of preheated-banding, and the smaller the diameter of laser beam, the better the quality of the cutting groove was in the same laser power situation.

Theoretical research of α-RF discharge in slab oxygen iodine lasers

A theoretical model is established to describe the α-RF discharge in slab Oxygen Iodine lasers, according to the continuity equation of electron density, the electron energy equilibrium equation and the continuity equation of current density. Assuming a Maxwellian energy distribution, the spatial distributions of electron density and electric field in RF plasma are obtained by numerical method. The effects of parameters on discharge characteristics have been analyzed. The results show that the current density has a big effect on the electron density in discharge area. The influences of excitation frequency on the maximum value of electric field and the thickness of boundary layer are also discussed. And the spatial distributions of electron energy and excitation efficiency of singlet delta oxygen have been calculated. The influences of gas mixture on the excitation efficiency of singlet delta oxygen are discussed. It provides references of parameters for slab discharge in singlet delta oxygen generating.

Optimization of the Microstructure and Mechanical Properties of a Laves Phase-Strengthened Hypoeutectic NiAl/Cr(Mo,W) Alloy by Suction Casting

A niobium (Nb)-doped NiAl/Cr(Mo,W) hypoeutectic alloy was prepared by conventional and suction casting methods. Its microstructure and compression properties were studied to evaluate the effect of a manufacturing process. A coarse primary NiAl phase and NiAl/Cr(Mo) eutectic cell are demonstrated to be the main components of a NiAl/Cr(Mo,W)–Nb hypoeutectic alloy. The Nb addition promotes the formation of a Cr2Nb Laves phase along the eutectic cell boundary. The suction casting significantly refines a NiAl/Cr(Mo) eutectic cell, primary NiAl phase, eutectic lamella, intercellular region, and Cr2Nb Laves phase. This casting provides the uniform distribution of a Cr2Nb Laves phase and increases the solid solubility of the alloy. At room temperature, the suction casting alloy reaches its yield strength, compression strength, and ductility of 1495 MPa, 2030 MPa, and 36%, respectively, which are approximately 50, 30, and 100% higher than those of the conventional casting alloy. A significant improvement of the mechanical properties at room temperature may be ascribed to optimization of the microstructure by suction casting. At 1273 K, the above alloy exhibits almost similar mechanical properties, which is mainly associated with an enlarged intercellular region.

Research on carbon fiber reinforced thermal polymer/stainless steel laser direct joining

To improve the numerical simulation accuracy of carbon fiber reinforced thermal polymer (CFRTP)/stainless steel laser direct joining (LDJ), a fitting formula of thermal contact conductance was established based on experiments in this paper. Taking into account the thermal contact resistance, a three-dimensional finite element thermal contact model of LDJ was established, and the theoretical simulation and experimental results were compared and analyzed. The result showed that the thermal contact model was more consistent with the reality compared with the traditional model. This thermal contact model could be used to characterize the influence of clamping pressure on the laser joining quality. When the laser power was 318 W and the clamping pressure was 0.1 MPa, the relative error of the melting width was 17.8% for the traditional model and 6.7% for the thermal contact model considering the thermal conductivity. The numerical simulation accuracy could be improved in the process of LDJ. With this numerical model, relationships between the thermal behaviors and the joining parameters were studied numerically. The CFRTP/stainless steel laser joining experiments were also carried out, and the result showed that the joint width measured agreed well with the numerical result.To improve the numerical simulation accuracy of carbon fiber reinforced thermal polymer (CFRTP)/stainless steel laser direct joining (LDJ), a fitting formula of thermal contact conductance was established based on experiments in this paper. Taking into account the thermal contact resistance, a three-dimensional finite element thermal contact model of LDJ was established, and the theoretical simulation and experimental results were compared and analyzed. The result showed that the thermal contact model was more consistent with the reality compared with the traditional model. This thermal contact model could be used to characterize the influence of clamping pressure on the laser joining quality. When the laser power was 318 W and the clamping pressure was 0.1 MPa, the relative error of the melting width was 17.8% for the traditional model and 6.7% for the thermal contact model considering the thermal conductivity. The numerical simulation accuracy could be improved in the process of LDJ. With this numerical...

Influence of Processing Parameters on Laser Direct Joining of CFRTP and Stainless Steel

The CFRTP and the stainless steel were joined by the fiber laser, and the effect of processing parameters on the joint quality was investigated in detail. The heat-affected zone on the stainless steel and the microstructure of the joint interface were examined and analyzed. The results showed that the laser joining process refines the microstructure of the fusion and heat-affected zones in the stainless steel. And the tensile strength of the joint was affected greatly by the laser power and scanning speed but slightly by the clamping pressure. With the PPS additive, the joint shear strength could be improved, and the optimal PPS additive thickness is 300 μm. With the best parameters, joint with a shear strength of 15–17 MPa could be obtained as the laser power is 320–350 W, the scanning speed is 4-5 mm/s, the clamping pressure is about 0.5 Mpa, and the additive PPS thickness is about 300 μm.

Research on microstructure properties of the TiC/Ni-Fe-Al coating prepared by laser cladding technology

In this paper, the laser cladding method was used to preparation the TiC reinforced Ni-Fe-Al coating on the Ni base superalloy. The Ti/Ni-Fe-Al powder was preset on the Ni base superalloy and the powder layer thickness is 0.5mm. A fiber laser was used the melting Ti/Ni-Fe-Al powder in an inert gas environment. The shape of the cladding layer was tested using laser scanning confocal microscope (LSCM) under different cladding parameters such as the laser power, the melting velocity and the defocused amount. The microstructure, the micro-hardness was tested by LSCM, SEM, Vickers hardness tester. The test result showed that the TiC particles was distributed uniformly in the cladding layer and hardness of the cladding layer was improved from 180HV to 320HV compared with the Ni-Fe-Al cladding layer without TiC powder reinforced, and a metallurgical bonding was produced between the cladding layer and the base metal. The TiC powder could make the Ni-Fe-Al cladding layer grain refining, and the more TiC powder added in the Ni-Fe-Al powder, the smaller grain size was in the cladding layer.

A research on CFRP and stainless steel joining with fiber lasers

Carbon fiber reinforced plastic (CFRP) has been widely used in aerospace, shipping and automobile, et al. However, realizing a high strength joint between the CFRP and metals is still an unsolved industrial problem. In this study, an experimental investigation on the mechanism of laser direct joining between 304 stainless steel and CFRP was carried out, and a method to strengthen the joint by filling PPS laminae between metal and CFRP was present. The effect of the laser power and the traveling speed on the joint strength were studied. The strength of joint was also tested by using electro-mechanical universal testing. Experimental results showed that: (1) Cross-sectional photos revealed that the melted PPS flowed into micro-cavity of metal surface and a mechanical bonding was formed. (2) The shear strength reached 15.7MPa when the energy density was 45.71J/mm2, which was determined by the power of 320W, the traveling speed of 5 mm/s, and the defocusing distance of 20 mm. The simulation of temperature field was conducted to provide theoretical support for the experimental results. These results showed that the bonding strength of the metal-CFRP could be improved by filling PPS laminae between the CFRP and the 304 stainless steel in the welding process.Carbon fiber reinforced plastic (CFRP) has been widely used in aerospace, shipping and automobile, et al. However, realizing a high strength joint between the CFRP and metals is still an unsolved industrial problem. In this study, an experimental investigation on the mechanism of laser direct joining between 304 stainless steel and CFRP was carried out, and a method to strengthen the joint by filling PPS laminae between metal and CFRP was present. The effect of the laser power and the traveling speed on the joint strength were studied. The strength of joint was also tested by using electro-mechanical universal testing. Experimental results showed that: (1) Cross-sectional photos revealed that the melted PPS flowed into micro-cavity of metal surface and a mechanical bonding was formed. (2) The shear strength reached 15.7MPa when the energy density was 45.71J/mm2, which was determined by the power of 320W, the traveling speed of 5 mm/s, and the defocusing distance of 20 mm. The simulation of temperature fie...

Experimental Study on Laser High-Speed Micro-Processing

To study the characteristics of material removal with high power ultra-short pulsed lasers, a 300 W picosecond laser was used to make microgrooves in cooper and steel. The effects of laser power, laser frequency, scanning layers, and scanning velocity on the width and depth of the grooves were analyzed. The material removal rate of picosecond laser was compared with that of a 10 W nanosecond laser. The results showed that high power high frequency ultra-short pulsed lasers have good potential in high speed micromachining. Evidence showed that ps laser machining could be more efficient than nanosecond machining. There are issues to be solved to make high power ultra-short pulsed lasers the dominating process for high speed micromachining.Copyright

A Numerical Study on Welding Stainless Steel With Lasers

The technique to weld stainless steel with fiber lasers was investigated. The main objective of this study was to determine the influence of the welding parameters, such as laser power, defocusing amount, velocity, on weld characteristics. The mathematical model was put forward. And, the temperature and thermal stress distribution in the welding process was calculated by ANSYS. Through numerical prediction, the theoretical effects of laser parameters to the welding quality were analyzed.Copyright

Sealing glass ampoules with CO 2 lasers

Glass ampoules were always sealed by melting in the presence of a flame to create closures. Some poisonous gases were generated in this sealing process that pollute the injection drug and are physically harmful. In this study, CO(2) lasers were proposed for sealing glass ampoules. Because of the clean noncontact sealing process with lasers, there was nearly no pollution of the injection drug. To study in detail the principle of this sealing process, a mathematical model was put forward, and the temperature and the thermal stress field around the ampoules neck were calculated by ANSYS software. Through experimental study, 1 ml and 5 ml ampoules were sealed successfully by a dual-laser-beam method. The results show that a laser source is an ideal heat source for sealing glass ampoules.