Jacek Widłaszewski

Mechanically assisted laser forming of thin beams

Laser-assisted forming techniques have been developed in recent years to aid plastic working of materials, which are difficult in processing at normal temperatures due to a high brittleness, effects of high work-hardening or a high spring-back phenomenon. This paper reports initial experimental investigations and numerical simulations of a mechanically-assisted laser forming process. The research is aimed at facilitating plastic shaping of thin-walled parts made of high temperature resistant alloys. Stainless steel plate, 1 mm thick, 20 mm wide, was mounted in the cantilever arrangement and a gravitational load was applied to its free end. A CO2 laser beam with rectangular cross-section traversed along the plate, towards the fixed edge. Laser spot covered the whole width of the plate. Experiments and simulations using the finite element method were performed for different values of mechanical load and with constant laser processing parameters. Experimentally validated numerical model allowed analysis of plastic deformation mechanism under the hybrid thermo-mechanical processing. The revealed mechanism of deformation consists in intense material plastic flow near the laser heated surface. This behavior results mainly from the tension state close to the heated surface and the decrease of material yield stress at elevated temperature. Stress state near the side edges of the processed plate favored more intense plastic deformation and the involved residual stress in this region.

Laser forming of materials without external forces

Investigations on bending plates by use of laser beam with rectangular cross-section are presented. Permanent deformation of plate is obtained without external forces, solely under influence of thermal stress induced by local heating of the material. Laser beam of narrow rectangular cross-section was modeled as a linear heat source moving over the plate surface. Temperature distribution in the plastified layer of the material was taken into considerations. The bend angle was investigated as a function of laser beam parameters: power, cross-section geometric parameters, velocity with respect to the material and material parameters of bend plates. It has been proven that effective bending occurs when the material surface temperature is close to the melting temperature. Presented advanced analytical model can be applied in design and control of laser forming of developable surfaces, as well as in other laser processing technologies, hardening, for instance. Derived dependence for the bend angle and curvature can be reduced in special case to well-known expressions describing welding distortions.

Experimental and numerical investigation on laser-assisted bending of pre-loaded metal plate

The laser forming technique has an important disadvantage, which is the limitation of plastic deformation generated by a single laser beam pass. To increase the plastic deformation it is possible to apply external forces in the laser forming process. In this paper, we investigate the influence of external pre-loads on the laser bending of steel plate. The pre-loads investigated generate bending towards the laser beam. The thermal, elastic-plastic analysis is performed using the commercial nonlinear finite element analysis package ABAQUS. The focus of the paper is to identify how this pattern of the pre-load influence the final bend angle of the plate.The laser forming technique has an important disadvantage, which is the limitation of plastic deformation generated by a single laser beam pass. To increase the plastic deformation it is possible to apply external forces in the laser forming process. In this paper, we investigate the influence of external pre-loads on the laser bending of steel plate. The pre-loads investigated generate bending towards the laser beam. The thermal, elastic-plastic analysis is performed using the commercial nonlinear finite element analysis package ABAQUS. The focus of the paper is to identify how this pattern of the pre-load influence the final bend angle of the plate.