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Advanced Machining Processes and Operations
Published in V. K. Jain, Advanced Machining Science, 2023
In different TAMPs, the sources of heat generation are of different types. For example, in EDM, the heat is generated by a sparking phenomenon in the dielectric flowing in the Interelectrode Gap (IEG) (between the tool (cathode) and workpiece (anode)). In LBM, when a laser beam hits the workpiece surface it produces such a high intensity of heat that it can melt and even vaporize any material (excluding short pulse lasers such as femtosecond and picosecond lasers). With the help of the optics, the laser beam diameter can be increased or decreased, which also changes heat intensity on the laser beam spot. It is possible to have a laser beam in continuous mode or pulsed mode (nanosecond, picosecond, and femtosecond laser pulses). However, it should be noted that the machining efficiency of the laser beam is extremely low (less than 5% or so). Laser beams can be produced by solid, liquid, or gas as lasing materials [17–20].
Low-coherence interferometry
Published in Pablo Artal, Handbook of Visual Optics, 2017
If 1/e2 intensity distribution diameters are used instead of FWHM electric field amplitude diameters, the factor ln(2) in Equation 3.8 has to be omitted. With a beam diameter of ~1 mm, a transverse resolution of ~10–15 μm can be expected at the retina of a human eye, the same order as the transversal resolution obtained by SLOs. Increasing the beam diameter in healthy eyes with low aberration can improve the resolution (Pircher et al. 2006a); however for beam diameters beyond ~3–4 mm, the aberrations of the optical elements of the eye degrade the transversal resolution (for eyes with moderate to high aberrations, the useful limit of d is ~1–2 mm). Furthermore, a larger beam diameter reduces the depth of focus, requiring a careful focusing of the beam. Solutions to these problems are dynamic focusing (Lexer et al. 1999; Pircher et al. 2006b) and the use of AO that compensate the aberrations (Liang et al. 1997; Fernandez et al. 2001; Roorda et al. 2002; Zawadzki et al. 2005; Zhang et al. 2006; Felberer et al. 2014).
Digital holography
Published in Tomoyoshi Shimobaba, Tomoyoshi Ito, Computer Holography, 2019
Tomoyoshi Shimobaba, Tomoyoshi Ito
Figure 4.1 shows an example of an inline digital holography setup. Since the laser has a thin beam, we use a beam expander to make it an appropriate beam diameter to irradiate the entire object. In the beam splitter 1, the laser is split into two beams. The one is used for reference light and the other is irradiated on the object. The reference light and object light are synthesized by the beam splitter 2, and an interference fringe (hologram) is captured by the image sensor.
Selection of process parameters in a single-pass laser bending process
Published in Engineering Optimization, 2018
The parametric results for different laser beam diameters are shown in Table 4. It is seen that with the increase in laser beam diameter the production rate, i.e. scan speed and temperature zone size, increases, while the tensile residual stress, radius of curvature and line energy requirement decrease up to the 3 mm beam diameter and then increase for obtaining a desired laser bend angle.
Design performance optimization of laser beam welded joints made for vehicle chassis application using deep neural network-based Krill Herd method
Published in Welding International, 2023
Sanjay S. Surwase, Santosh P. Bhosle
The development of residual stress, strain and defects during the LBW process of vehicle chassis parts is a problem. The chassis members should be compact in design, weightless, fit into the existing designs, and bear different load conditions. Hence, LBW is performed on ASTM A302 alloy steel material, and the effect of different process parameters and input variable on output responses are studied. In order to do so, various techniques such as advanced ND based inspecting instruments, RSM, neural network based prediction and optimization processes are implemented. Besides, the experimentation has been predicted using hybrid DNN-KHO, and the results are compared using different algorithms.During the preliminary analysis, the ‘I’ section and the ‘T’ section are evaluated for load carrying capacity and the strain rate caused by the applied load. Preliminary analysis shows that the ‘I’ beam offered 18.2%, 27.7%, 92.92%, 36.2% and 29.4% lower strain during respective experimentations compared to the ‘T’ joint configuration. This confirms that the ‘I’ sections have high load carrying capacity while offering less strain. Hence, further experimentation has been conducted on the ‘I’ beam configuration, which has four Butt weld joints.The experimentation has been designed using RSM, BBD. In addition, ANOVA analysis and FIT statistics are performed to validate the designs’ authenticity. ANOVA analysis was not significant from lack of fit by 0.995, 0.5191, 0.5575 and 0.6345, respectively, for undercut, overlap, residual stress and total strain.A higher beam diameter delivers excess energy over the weld bead causing a high penetration depth and building weld geometry defects such as undercut. In contrast, a higher laser power limits the penetration and promotes the formation of a high quality weld bead.The beam diameter has the least effect on the reinforcement or overlap. But the welding speed was found to reduce penetration depth and take responsibility for forming overlap. While a moderate weld speed with a bit higher gas flow rate leads to better weld bead form. And a higher beam diameter creates more residual stresses in the region.The proposed DNN-KHO algorithm outperformed the prediction behaviour of other existing algorithms, such as RF-GWO, RF and DNN, by 21.53%, 45.428% and 41.31%, respectively, meaning that the proposed algorithm provided the closest results to the experimental data.Finally, LBW process parameters have been optimized using the DNN-KHO algorithm. The optimal parameters are achieved between 15 and 20 iterations, such as peak power 1362 (W), weld speed 28.2 (mm/s), gas flow rate 10.6 (l/min), beam diameter 1.3 µm, undercut 280.21 µm, overlap 218.16 µm, total strain 0.00199 mm/mm, residual stress 168.15 MPa, respectively.