Increase in weldable material thickness in laser lap welding of fluoroplastics (Improving infrared absorption/transmission balance by changing laser wavelength)

Abstract

Fluoroplastics have a very high absorptivity to the CO2 laser (oscillation wavelength: 10.6 μm) widely used industrially, so that only the surface layer of their substrates irradiated with the laser can be melted. It is difficult to weld the overlapping parts with a thickness exceed 1mm deep enough. This study deals with the CO laser welding method for plastics assisted by a solid heat sink transparent to infrared laser beam. The CO laser beam (wavelength: 5.7 μm) is possible to penetrate fluoroplastic sheet deeper than CO2 laser beam due to the decrease in absorption of fluoroplastics at that wavelength. Firstly, heat transfer analysis was conducted to investigate the influence of the difference in transmission / absorption characteristics of the plastic material on the temperature distribution inside the welded sheets during laser irradiation. Secondly, by using the CO laser, an experimental examination of lap welding of PFA sheets with a thickness of 1 mm was carried out. It was impossible to weld them using a CO2 laser due to its high absorbance. It was conducted an observation of the internal cross section and evaluating the tensile strength of welded sheets. Under suitable laser irradiation conditions, melting of the interface between the upper and lower sheets was confirmed. In addition, it was confirmed by a tensile test that the welding performance is guaranteed by breaking the base material while the welded line is held integrally.

Keywords

• laser welding
• fluoroplastic
• pfa
• laser transparent heat sink
• co laser
• absorption coefficient