The most important material properties for applying the laser welding process
are the optical properties of the parts to be joined. In most cases overlap
welding is used. For this variant of laser welding, one part has to be
transparent and the other should absorb the laser. Since most polymers are
transparent to infrared laser radiation, absorbing additives are needed in the
absorbing part of the joint. For colored parts which do not absorb in the IR
spectrum, special IR absorbing additives should be used with a low level of
visible color. The most well-known organic IR absorbing material is carbon.
The IR laser radiation penetrates the transparent part and irradiates the
interface between the product parts. In many polymers there are several
phenomena, which lead to scattering of the incoming IR radiation. Sources of
light scattering are mineral fillers, glass fibers or crystallite structures
of the polymers. An example of a strongly scattering material is
Arnite PBT. All these phenomena result in a broader intensity distribution
at the weld area.
Welds of dissimilar materials can be made as long as the materials have some
degree of compatibility.