Laser forming of aerospace alloys

Abstract

Laser forming has emerged as a candidate process for rapid prototyping of sheet metal. The dimensional accuracy of rapid prototypes is a topical issue. As the dimensions of a laser formed part depend on the temperature field induced in the workpiece, it is imperative that the correct selection of laser processing parameters be made. In this work a parametric investigation into the factors influencing the laser forming process on plates of an α-β titanium and a high strength AlCuMg aluminium alloy is reported. The influence of the energy parameters on the bend angle is examined empirically and compared with an analytical model. The effects of varying the energy supplied to the plate surface and hence the temperature gradient through the plate thickness are examined by altering the traverse velocity of the plate for a range of laser powers and beam diameters.Results from the experimental work show that the plastic strain, the bend angle and hence the dimensions of the part are critically dependent on the energy supplied to the workpiece surface. An optimum traverse velocity is identified for some power densities in terms of maximising the bend angle achieved per scan. The digressive course of the bend angle with increasing the number of scans over the same track is evident. This is attributed to a partial burn-off of the graphite coating used to increase the absorptivity of the samples, and an increase in the section modulus of the samples due to the thickening of the material along the bending edge. Edge effects are apparent in the samples. They are pronounced when the plate is heated slowly and the beam diameter is large compared to the thickness of the sample. It is shown that these effects can be minimised by varying the line energy supplied to the plate surface with in plate location.Conclusions drawn from this work indicate that the dimensions of the final part and the rate of bending can be controlled primarily from the temperature field. In addition, other factors, such as the increase in the section modulus and the edge effects, influence the accuracy of the process.Laser forming has emerged as a candidate process for rapid prototyping of sheet metal. The dimensional accuracy of rapid prototypes is a topical issue. As the dimensions of a laser formed part depend on the temperature field induced in the workpiece, it is imperative that the correct selection of laser processing parameters be made. In this work a parametric investigation into the factors influencing the laser forming process on plates of an α-β titanium and a high strength AlCuMg aluminium alloy is reported. The influence of the energy parameters on the bend angle is examined empirically and compared with an analytical model. The effects of varying the energy supplied to the plate surface and hence the temperature gradient through the plate thickness are examined by altering the traverse velocity of the plate for a range of laser powers and beam diameters.Results from the experimental work show that the plastic strain, the bend angle and hence the dimensions of the part are critically dependent on the en...