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.
Local heating of metal objects by means of a laser beam gives opportunity to obtain their permanent deformations in a controlled manner. Very small changes of the shape are utilized in mutual positioning of parts and subassemblies. This touch-less method has found applications in production of miniature electro-mechanical and electronic devices, entering the area of optoelectronics lately. Basic contructional solutions of support structures designed to utilize laser positioning technique are presented. The systems apply laser-induced bending deformations or contraction due to material upsetting. Bending under influence of heating by non-moving laser beam was analyzed with use of the finite element method. Steep temperature gradient on the cross-section of the object is needed to obtain permanent bending deformation in the direction of the heat source. Bending of a steel plate, 1 mm thick, was analyzed in a sequence of three cycles of heating and cooling. Time-run of the bending process resulting from the simulation is similar to those, observed in physical experiments. Precision of calculations is strongly influenced by the values of the absorption and thermal expansion coefficients.
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.