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The determination principle should be based on the requirement of the index value, that is, if the index value should be selected as larger as possible, the level corresponding to the maximum k should be taken for the index value, smaller is better, the level corresponding to the minimum k should be taken and if the index value is required to be moderate, the level corresponding to the appropriate k should be taken. The optimal combination of scanning speed factor, scanning power factor and slice thickness factor is determined according to the magnitudes of k1, k2, and k3.
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Hence, the primary and secondary relationship of the factors is: laser power > scanning speed > slice thickness. The second is the scanning speed factor, and the final is the slice thickness factor. This column is used for the arrangement of laser power factors, indicating that the effect of laser power factors on the bending strength of the sintered parts is the most important. In Table 3.55, the range in the first column is 10.883, which is the largest one of all ranges. The judgment principles: where there is a large range, the corresponding factor will have the greater effect on the experimental results. (3.23) R 1 = k 1 − k 3 = 90.283 − 79.400 = 10.883Īccording to the magnitude of the range R, the effect of each factor on the test results can be judged. This gives rise to consistency in mechanical properties and dimension of the part fabricated by melting powders ( 9, 10). If the melt pool width changes from the predefined value, laser power is automatically varied (increased or decreased) to control the size of melt pool. In order to carry out process control in the system, laser power has been mostly used as a controlling parameter to cause change into the system online. Using higher laser power than required may ablate the metallic powder and degrade the polymer powder so finding a process window for a given material is important. If the aim is to melt the powder partially then less power is required. If we want to completely melt it, then more power is required.
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Laser power also depends upon our aim with powders. For the same laser power, with a decrease in spot size, higher laser energy density is achieved, which could be used to process higher melting point materials. The selection of power is not done independently but depends upon other process parameters and spot size. SLS/SLM machines are equipped with laser of power from 50 to 400 W. Polymers could be processed in 5 W while for ceramics, 500 W could be needed. Its magnitude depends upon the type of materials processed. Laser power is the main parameter in the process. Kumar, in Comprehensive Materials Processing, 2014 10.05.3.2.1 Laser Power The laser bending below a certain laser power is not possible due to reversible elastic effect or the threshold energy ( Chen, Wu, & Li, 2004a).
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This reduces the difference between plastic deformation at the top and bottom surface which leads to a decrease in bend angle at higher power ( Kant & Joshi, 2012a). Second, at high power, the peak temperature at the bottom surface is also high. First, the melting occurs in the irradiated region at higher power and the applied heat energy gets consumed in the phase transformation instead of worksheet bending ( Lawrence et al., 2001). After attaining peak, the bend angle decreases with an increase in laser power which is mainly due to two reasons. The increase in bend angle with laser power is due to more heat absorption which causes a higher peak temperature and hence more plastic deformation at the scanned surface ( Kant, Joshi, & Dixit, 2013b). In general, the bend angle increases with an increase in laser power, attains a peak, and then decreases with further increase in the laser power. Laser power controls the amount of energy absorbed into the work sheet. Dixit, in Materials Forming and Machining, 2016 4.4.1 Laser power