Materialen

Laserweldable Materials

Thermoplastics are plastics that can be remelted. As a result, they can be welded. Thermoplastics can be divided into two categories:

Amorphous thermoplastics
Semicrystalline thermoplastics

Assuming that there are no additives, amorphous thermoplastics are transparent within the visual range. By contrast, semicrystalline thermoplastics appear opaque to milky to the human eye. In principle, thermoplastics of the same type can be welded together using a laser. Nevertheless, attention must be paid to the optical properties.

The table below lists the material combinations that can be laser welded. In addition to these combinations, the range can also be expanded by using modified blends.

Leister Material Combination — Click on chart for full resolution (pdf)

Optical Properties

The optical properties of plastics play a key role in determining the results of the laser radiation welding process. On one side, you have to have a welding material that is transparent to the laser radiation and on the other one that absorbs it.

All thermoplastics are transparent to laser radiation, unless there are additives. Nevertheless, a distinction is drawn between amorphous and semicrystalline thermoplastics. In the case of amorphous thermoplastics, the radiation transmits with virtually no losses even when the material is thick. However, when semicrystalline thermoplastics are used, the crystallites interrupt and reflect the radiation. This results in a level of dispersion that depends primarily on the degree of crystallinity and the thickness to be penetrated by the radiation.

The figure below shows a spectral analysis for a transparent PA. In the wavelength range of 800 - 1100 nm, the plastic is actually even more transparent than in the visual range (400 - 700 nm).

Optical Penetration Depth

The optical penetration depth provides a way of measuring the properties of the absorbent joining material. This describes how deeply the radiation penetrates the surface of the plastic before heat is generated.

Ideally, the optical penetration depth should be in the µm range (as illustrated by the case at the top of the figure below). If there is not enough absorber, this tends to result in volume absorption. As a result, the entire thickness of the material heats up. The third case describes excessive surface reflection, which means that the radiation cannot penetrate the surface at all. Consequently, both cases tend to have a negative effect on the process.

The generation of heat during welding results in a heat-affected zone, which can be viewed under a microscope by cutting thin sections.

Thus, the welding seam design is very easy to manage. To put it loosely, all that is required is physical contact between the components in the welding zone. However, it is not as straightforward as that: The components should be designed for laser compatibility. You can request guidelines from us or obtain them from the DVS German Welding Society (guideline 2243).