Pulsed laser texturing for improved adhesive-bonded polyethylene (PE) joints

Nanosecond pulsed laser texturing was performed on pigmented polyethylene (PE) specimens with a 1064 nm fiber laser with the aim of improving adhesive-bonded joint strength. A Design-of-Experiments (DoE) was employed to optimize process parameters and determine the effects of average laser power, scanning velocity and hatch spacing on the resulting failure load of PE joints bonded with Teroson 9399. Failure load increased with laser energy dose up to the onset of macroscopic melting. Laser scanning strategies minimizing heat accumulation yielded best results as the energy dose could be increased as much as possible prior to onset of melting. The process exhibited highest sensitivity to heat accumulation in the laser scanning direction, favoring large pulse separation distances in the scanning direction and moderate pulse overlap in the lateral direction. With a focused spot diameter of 60 μm and a repetition rate of 20 kHz, a maximum failure load of 0.93 kN (1.49 MPa, standard deviation 0.01 kN) was achieved with a crossing-line laser scanning strategy, 25 μm hatch spacing, 3 W average power and 2500 mm/s scanning velocity. Under these conditions, purely cohesive failure took place yielding a 79% improvement in failure load over standard primed joints.