Focus Like A Laser Beam PDF Free Download

Focused laser beam must match the parameters of the fiber for optimum coupling efficiency. In particular, two conditions should be met for maximum coupling efficiency: (i) The focused spot diameter (SD) of the laser beam should be less than or equal to the mode field diameter of the fiber being used (a). FOCUS LIKE A LASER BEAM. If you looked up the meaning of focus, you would find several definitions. Focus means attention on the right things. Focusing means concentrating attention or energy on something. To focus is to achieve maximum clarity or a distinct vision. When you focus you concentrate on something or a central point. If your laser is a 3.8W or 4.2W your laser shipped with focus set to 1.5″ if you bought it from us. The HF lens included in the kit has the smallest focus to closer to the work surface you get. On all of the lasers, the closer to 1″ you get the smaller your spot will be. Get Lasers and Laser Light Multiple Choice Questions (MCQ Quiz) with answers and detailed solutions. Download these Free Lasers and Laser Light MCQ Quiz Pdf and prepare for your upcoming exams Like SSC, Railway, UPSC, State PSC.

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Microstructure characteristics and mechanical properties of the magnesium and aluminium alloy laser weld bonded joint

L. Liu, inFailure Mechanisms of Advanced Welding Processes, 2010

8.2.3Influence of laser power

Laser beam power is the decisive factor in the penetration in an LWB joint. Figure 8.6 shows different penetrations with increasing laser beam power. The welding depth increases as the laser beam power increases. As the laser beam power exceeds 400 W, the penetration increases more quickly. Here, the laser welding mode in both aluminium and magnesium alloys is a keyhole model. The results of a tensile shear test on the joints are displayed in Table 8.3. A laser beam power of 350W produces a joint with the highest tensile shear strength.

Table 8.3. Tensile shear forces on LWB samples at different laser power

Laser power P (W)Tensile shear force F (kN, average)
2002.95
2604.12
3105.02
3505.98
4093.02
4512.44

Welding speed: 300 mm min−1; defocusing amount: –3 mm

Figure 8.7(a)–(c) shows the characteristics of the microstructure models with different laser beam powers in the LWB fusion zone. When the laser beam power reaches 260 W, a small part of the aluminium alloy is melted in the welding process and a magnesium–aluminium intermetallic layer appears at the bottom of the fusion zone.

An X-ray diffraction (XRD) pattern of the fracture, shown in Fig. 8.8, confirms the composition of Mg–Al intermetallics. Thus the joint, having poor mechanical properties, will fail at the intermetallics layer. When the laser beam power is increased to 350 W, a larger quantity of the aluminium alloy melts and more of the adhesive decomposes. Diffusion between magnesium and aluminium alloys is prevented by the decomposition of the adhesive and the thickness of the intermetallic layer decreases. This kind of joint will fail at the edge of the magnesium fusion zone.

X-ray diffraction analysis of the fracture shown in Fig. 8.9 confirms not many combinations of magnesium–aluminium intermetallics. This improves the mechanical properties of the joint. When the laser beam power is increased to 400 W, more aluminium alloys melt and the adhesive decomposes rapidly, with a complex effect on the fusion zone. The interme-tallic compounds are observed across almost the entire fusion zone. Many continuous cracks are observed in the high power LWB magnesium to aluminium joint. This results in inferior mechanical properties in this kind of joint.

As laser beam power is increased, the amount of melted aluminium increases. With low laser beam power, all the melted aluminium reacts with the melted magnesium forming Mg–Al intermetallic compounds at the bottom of the fusion zone. With higher laser beam power, more aluminium is melted and more adhesive decomposition occurs, preventing the diffusion between the melted magnesium and aluminium alloys. Thus the thickness of the intermetallic layer is reduced. As the laser beam power is increased further, the welding mode in aluminium alloy turns into a keyhole mode, where more alloy is melted, with a greater reaction between the melted magnesium and aluminium alloys. Here, the decomposition of the adhesive has a complex effect on the entire fusion zone, resulting in more Mg–Al intermetallics in the fusion zone. In the LWB process, the Mg–Al intermetallics and the microstructure in the fusion zone change as the laser beam power is varied, thus determining the properties of the joint. After numerous experiments, the welding parameters are optimized, as shown in Table 8.4, and the corresponding joint performance is exhibited in Fig. 8.10.

Focus Like A Laser Beam PDF Free Download Windows 10

Focus Like A Laser Beam PDF Free Download

Laser Beam In Medicine

Table 8.4. Welding parameters in laser weld bonding Mg alloy to Al alloy

Welding parametersQuantity
Laser power300~400W
Welding speed300~500 mm min−1
Defocusing amount−3 mm
Adhesive thickness0.1~0.2 mm
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URL: https://www.sciencedirect.com/science/article/pii/B9781845695361500081