Studies on laser forming of Ti–6Al–4V alloy sheet

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Abstract

In this paper, the processes of laser forming along linear irradiation paths and curved irradiation paths have been investigated and the effects of deformation parameters on the bending angle also have been studied for Ti–6Al–4V alloy sheets with poor deformability at ambient temperature. The tests show that laser curve bending produces a significant reduction in the achievable bending angle compared with laser linear bending under the same conditions of deformation, and the bending angle decreases with increasing path curvature. Furthermore, on the relatively smaller side of irradiation paths, a 3D deformation is generated and the sheet is extended and thinned slightly during laser curve forming. This is very different from the laser linear bending which produces a symmetrical deformation on the two sides of irradiation paths. The bending angle decreases sharply with an increase in the sheet thickness and increases with an increase in the sheet width, and is generally in proportion to the laser feed number. In addition, excessively high laser energy density will result in a reduction in the achievable bending angle and the microstructure changes of Ti–6Al–4V alloy.

Introduction

Laser forming with thermal stresses has been known for several years and is coming out of the development stage [1], [2], [3], [4], [5], [6], [7]. Mostly, the attention on laser forming has hitherto been focused on laser forming along linear irradiation paths, and the sheets employed in the laser forming process were mainly those of materials with good deformability at the ambient temperature, such as steel and aluminum. For the complex shaped or spatial parts, it should be more convenient and efficient if laser curve forming is applied instead of laser linear forming. This fact, recently, has been demonstrated by Hennige who used the laser curve forming process to form a spherical dome with material SAE 1008 instead of using the previous laser linear bending process [8]. However, to our knowledge, systemic studies on laser curve forming have not yet been reported. Fig. 1 shows a schematic diagram of the laser curve forming process of metal sheets.

One of the main advantages of the laser forming process is that it is capable of shaping hard and brittle metals thanks to the character of accumulative forming under the condition of thermal state [9], [10], [11], [12], [13], while traditional methods prove either inapplicable or very labor consuming. So, in this study, titanium alloy sheets with poor deformability at ambient temperature are taken as the research object and then the comparative studies of laser forming using linear irradiation paths and curved irradiation paths are carried out. In addition, the effect of deformation parameters on the bending angle and the effect of laser heat irradiation on the microstructure of the material are also investigated.

Section snippets

Experimental

The Ti–6Al–4V alloy was used for the present investigations. The sheets were of thickness between 0.8 and 2 mm, width between 20 and 50 mm, and length 50 mm. The irradiated surface of the sheets was coated thinly and uniformly with the coat Ti-3 to improve the heat absorption coefficient of the surface. The whole experimental process of laser forming was performed on a CO2 numerical control laser machine (NCLS-2125) with a maximum laser power of 3 kW. The laser beam mode is TEM00+TEM10. Gas argon

Comparison between laser linear bending and curve bending

Fig. 2 shows the effect of path curvature on bending angle. It can be seen that when compared with laser linear bending (1/R=0), the laser curve bending has a significant reduction in the achievable bending angle under the same conditions of deformation, and the bending angle decreases with increasing path curvature. The reason is that only partial inner stresses transfer from the heat stresses impact on the bending angle and others will cause the sheet 3D deformation during the laser curve

Conclusions

The laser linear and curve forming of the Ti–6Al–4V alloy sheet and the effect of laser irradiation on the microstructure of the materials have been studied systematically, and the following conclusions are drawn from this study:

  • (1)

    In comparison to laser linear bending, the laser curve bending produces a significant reduction in the achievable bending angle under the same conditions of deformation, and the bending angle decreases with increasing path curvature.

  • (2)

    On the relatively smaller side of

Acknowledgements

The authors are grateful to the National Natural Science Foundation of China for providing the science funds (Project No. 19872055) to enable the performing of this investigation.

References (14)

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