| Brittle and hard materials have excellent mechanical and thermal mechanical properties, such as high strength, high hardness, corrosion resistance and oxidation resistance, etc. But brittle and hard materials are with high brittleness, low fracture toughness and its elastic limit is very close to strength, the material is very difficult to be machined. A new method of ultrasonic-assisted laser machining in anhydrous conditions or in water is put forward in this paper. Experiments are carried out on hard and brittle materials of Si3N4 ceramic, Si C ceramic, hard alloy and W-Zr C composite, especially Si3N4. SEM, microscope and other detection methods are used to study the effects of the machining method on etched depth and surface quality. The results show that method of ultrasonic-assisted laser machining underwater is effective. The paper is to provide an efficient and high-precision method for some hard and brittle materials.The main work and conclusions of this paper are as follows:(1)The ultrasonic-assisted laser machining experimental system is studied and designed. The system is built to research etching process and mechanism of ultrasonic-assisted laser machining. To assure the machining quality, only the designed ultrasonic vibration platform has displacement in Z-axis direction, others are constrained.(2) First, the experiments are performed with Si3N4 using ultrasonic-assisted laser machining in the air. Ultrasonic-assisted laser machining is compared with single source laser etching. The influences of laser parameters and ultrasonic parameters on etching quantity and quality of Si3N4 are studied. SEM, two-dimensional imaging instrument and EDS are used for micro and macro analysis and elemental composition analysis of surface slags of machined surface. The results show that the depths of vibration-assisted laser etching is substantially greater than those without vibration, but the V-grooves are filled with slags and no significant differences between the etched surface are found under both two conditions.(3) Given the results under anhydrous conditions, water flow is introduced in this combined machining. Water can increase the cooling rate and the cavitation effect is applied to clean machined surface. The effect is significant. Select appropriate processing parameters and the effects of laser current, laser frequency, ultrasonic power and laser pulse width on surface quality and etching depth are studied. The results show that surface machined underwater is cleaner and better and there are fewer slags; Better surface quality is obtained with clean surface and smaller slag particles in vibration-assisted laser etching. The etching depths by vibration-assisted laser are substantially greater than the case without vibration.(4)Some hard and brittle materials of Si C, hard alloy, W-Zr C are machined by ultrasonic-assisted laser machining in anhydrous conditions and water conditions. There is no significant difference among the surface morphology of holes of Si C ceramics machined in laser in for conditions of water participation, no water, no vibration and without vibration. For hard alloy machining, there are no slags and pores are regular on etched holes by laser under water, but irregular holes with thick recast layer are formed in anhydrous conditions. Holes got by vibration-assisted laser machining in water are more regular and the machined surfaces are smooth. Laser machining is used to machined W-Zr C composite material under anhydrous conditions. The etched grooves are filled with slags. Very poor quality is obtained. Figure [45] table [6] reference [87]... |
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