Study On Laser Shock Forming Process For Titanium Plate Based On The Binary Optics

The Laser shock forming(LSF) process is a new type of sheet metal forming technology. It mainly produces plastic deformation for sheet metal by force effect induced by laser shock wave interaction between laser and material. The high strength titanium plate is an important structural material in aerospace industry. Utilizing the ideal distribution of laser beam intensity by the binary optical device, the forming performance of the titanium sheet can be improved in laser shock forming, which is one of the research focus in the plastic forming process for titanium plate.In this paper, the combination of theoretical analysis, process test and numerical simulation was adopted. In the different LSF parameters(different laser energy, the light intensity distribution, etc.), the forming limit and forming quality were analyzed for three types of titanium plate such as TA1, TA2 and TC4 with the sheet thickness of 0.1 mm. Firstly, the deformation rule of plastic forming process and the cause of forming defects were simulated by ABAQUS software, and the influence of the different laser beam intensity distribution on LSF was compared; secondly, the binary optical device was self-made,and the laser shock forming process test was done based on the optimization of the process parameters; then, by means of the spectral confocal displacement sensor, the forming contour, forming depth bar chart and surface rough degree graph of the sheet metal specimen were drawn according to the measurement results. Analysis shows that the experimental results are in agreement with the simulation results.The main work and results of the paper were as follows:(1)The concept of the binary optics and its application in the high power laser manufacturing process were introduced, and the design scheme of the binary optical device to improve the quality of the output beam was put forward.(2)The binary optical element was made which effective modulation area was circular with the diameterΦ20mm, the pixel size 40 μm ′ 40 μm and the eight order based on the improved GS algorithm, the ring spot with the outer diameter Φ10 mm and the inner diameter Φ4 mm was obtained, and the intensity distribution relation was given.(3)The influence of the different laser intensity distribution under the condition of the circular Gaussian beam, the low-frequency ring spot with/without the strong center laser energy on the sheet metal forming limit and forming quality was emphatically studied according to the theory of light intensity distribution in the laser shock forming. The LSF experiments and performance test of threekinds of titanium plate were carried out. The comparison results showed that the flatness of the forming contour of the plate specimen was the best, the forming depth was largest and the surface roughness was least under low frequency ring spot without the center strong laser energy.(4)Taking the low-frequency ring spot as the laser intensity distribution as an example, the LSF process for a square plate with a thickness of 0.1 mm was numerically simulated, the stress fields at different time and residual stress field in the forming process were obtained, and the forming contour was consistent with the experimental results, which shows that the simulation model was feasible.(5)The experiment and numerical simulation analysis of the influence of the pulse laser parameters on the forming depth of the titanium plate after laser shock forming were done. The larger the laser energy, the greater the impact number, the larger the spot outside diameter, the greater the forming limit depth of the sheet metal, however, the pulse width has little effect on the forming limit depth.(6) The fracture problem of titanium plate under laser shock was studied. The fracture occurred at two locations, one was the center of the laser spot loading area, which was mainly caused by excessive tensile stress; another was the inner and outer diameter edge of the laser spot loading area, which is mainly caused by the stress concentration. The LSF under the ring spot was applied to avoid the stress concentration and prevent premature rupture of the plate.