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Laser transmission welding of absorber-free thermoplastics using dynamic beam superposition

So far, the main approach to weld absorber-free thermoplastics is exploiting their intrinsic absorption by choosing a proper wavelength of the laser. In order to melt the joining partners spatially restricted at the interface usually optics with a high numerical aperture are used. However, practice shows that the heat affected zone (HAZ) extends over a large area along the beam axis regardless of the optics used. Without clamping or convective cooling thermally induced expansion of the material can cause blowholes or deformation of the irradiated surface. To reduce the thermal stress on the part surface a dynamic beam superposition is investigated with the laser beam performing a precession movement.