Analysis of short wavelength infrared radiation during laser welding of plastics

In this paper, a new measurement system and a new approach in calculation for infrared (IR) radiation investigation in quasi-simultaneous transmission laser welding of plastics are presented. The measurement system is based on a MW/SWIR (medium-wave/short-wave IR) camera and optical filters narrowing the spectral region to SWIR. The measured signals contain radiation from the melted zone in between the semitransparent and absorbing polymers, as well as radiation from the surface and interior of the semitransparent polymer. The new calculation approach was developed to distinguish between these signals. It is based on simplification of the process to two places with two temperatures (surface and molten interface) and knowledge of the spectral optical properties of the material, filters, and camera response. The results of measurement and calculation for three different optical filters and polyoxymethylene samples with two thicknesses are shown and discussed. Good agreement is obtained for the calculation variant using normal transmissivity of the semitransparent polymer.