Influence of Laser Spot Shape on Welding of Thin Thermoplastics

摘要

Lap welding of thin thermoplastics at very high speeds has been studied and the influence of laser beam spot shape, dimensions, and position relative to sample displacement were analysed. A 2700 W CO_2 laser was used and a rotating drum allows plastic samples, with thickness between 0.1 and 0.01 mm, to reach constant linear velocities up to 20 m s~(-1). The focusing system, using spherical or cylindrical lenses, and adjusted towards or away of the sample, produced on the thermoplastic, laser spots of circular or elliptical contour with several dimensions. This allowed changing spot area, laser energy density and the interaction time of the beam on the sample. Influence of each of them on welding parameters was analysed. The influence of an angular deviation between welding direction and elliptical spot position on the sample was also studied. Experimental results show that weld strength increases for larger beam spot diameters, and that elliptical beam spots increase weld efficiency, allowing higher processing speeds or decreasing required laser power. Consequence of angular deviation of elliptical beam spot relative to sample movement direction is also an increase of weld strength, but maximum welding speed decreases.