Laser welding process

There are two process variants for laser beam welding plastics: overlap welding and butt-welding.

Overlap welding

The parts to be welded are held together with a moderate clamping force. The laser beam passes through one of the parts which is transparent to laser radiation with a wavelength in the near infra-red region between 800 and 1100 nm.

The laser radiation is absorbed in the top-layer of the other part. This top-layer is heated and heat is transferred to the upper part. The surface layers of both parts melt, and after cooling and solidification a reliable bond is formed.

In general, parts that are transparent to near infra-red laser radiation are also visibly transparent, whereas laser-absorbing parts usually have an opaque appearance (colored or black). However, there are a few exceptions to this and these can be used to increase the freedom of the design with regard to color.

Overlap welding process

Butt welding

Butt welding is not the ideal configuration for polymer welding although most of the early papers published on laser welding refer to this variant.

Due to the low thermal conductivity of polymers (contrary to metals) only those parts of the work piece will be molten where the laser energy is absorbed. In order to achieve a strong weld seam, a melt has to be created throughout the whole joining volume. This puts important restrictions on the laser absorption of both parts, and consequently on their pigmentation.

Butt welding