Laser parameters and different materials have great influence on laser melting unit. Studies have shown that when the scanning speed is accelerated, the cross-sectional area of the unit body decreases; When the laser peak power increases, the cross-sectional area increases; However, the unit size and frequency have little relationship with the defocus amount. On the other hand, the cross-sectional area and hardness of the unit are greatly affected by the thermal conductivity of the material and alloy elements.
Considering the thermal fatigue and wear properties of various types of gray cast iron materials, it is necessary to control the laser parameter variables in order to better study the relationship between materials and laser melting unit. Therefore, in the experimental design, through the orthogonal test of a kind of gray cast iron material, the best laser processing parameters are obtained, and then the same laser parameters are used in the processing of all laser melting units.
On the basis of gradual attempt and research, the laser scanning speed is limited to 2mm / s and the laser spot diameter is 1.2mm. The orthogonal experimental parameters of laser current, pulse width and frequency are optimized. Orthogonal test is a scientific method to deal with multi factor test. Orthogonal test design uses orthogonal table to arrange the test evenly and reasonably, and then scientifically analyze the experimental results through the method of mathematical statistics.
| No. | Current (A) | Pulse width (ms) | Frequency (Hz) | Depth / width ratio | Pores and cracks |
| 1 | 125 | 8 | 15 | 0.23 | No |
| 2 | 125 | 6 | 13 | 0.21 | Yes |
| 3 | 125 | 4 | 11 | 0.21 | Yes |
| 4 | 120 | 4 | 15 | 0.26 | Yes |
| 5 | 120 | 8 | 13 | 0.21 | No |
| 6 | 120 | 6 | 11 | 0.24 | Yes |
| 7 | 115 | 6 | 15 | 0.34 | No |
| 8 | 115 | 4 | 13 | 0.33 | Yes |
| 9 | 115 | 8 | 11 | 0.30 | Yes |
Three factors a, B and C are selected, and three levels are selected for each factor. The results are shown in Table 1 and figure. Group 7 has the best aspect ratio and no obvious pore cracks, so the laser parameters used in this study are those of group 7, as shown in Table 2.
| Pulse Duration | Frequency | Current | Laser spot diameter | Scanning speed |
| 6.0ms | 15Hz | 115A | 1.2m | 2mm/s |