Laser Transmission Welding of Thermoplastics: Analysis of the Heating Phase

Abstract

In laser transmission welding, the parts to be joined are brought into contact prior to welding, and the heating and joining phases take place simultaneously. The laser beam of the N d: YAG laser penetrates the transparent part being joined and is converted into heat by the absorbing part. The transparent part is similarly heated and plasticized by means of heat conduction, thereby ensuring that the parts are welded together.When the heating phase was analyzed, it was seen that if the part that absorbs the laser beam has a high absorption constant, this process phase can be readily described by a physico-mathematical model, by analogy to single-sided heat impulse welding. A comparison of calculated and measured melt layer thicknesses showed that, by introducing a correction factor, it is possible for this model to be successfully used for the case of a low absorption constant as well.

Laser markability of PVC coated automotive electric cables

“…This heating affected less and less volume as it moved outwards, this is why the cross section of the zones heated with the laser looks like triangles pointing outwards. The transparent layer can similarly heated and plasticized by means of heat conduction [48], but at the boundary of the red and the transparent layer so much heat was generated that gas was produced due to thermal decomposition, and its pressure separated the two layers; a similar explanation is described by Zelenska et al [76]. The cross section of the black cable is shown in Figure 6.…”

“…Markings must satisfy certain technological criteria, such as visibility, legibility, durability or laser markability [42][43][44][45], but marking speed (cycle time) is also a basic criterion in industrial applications. During laser marking of thermoplastics, various interactions take place in the polymer, some of which are hardly known as the pulse time of the laser can be measured in µs, ns, ps or fs [46][47][48][49][50][51], but the temperature during marking can reach up to 800°C [8]. Thermoplastics without fillers or pigments can be divided into three main groups according to their suitability for laser marking: - Members of group 1 absorb laser rays well, therefore they are carbonized and the marking will be dark.…”

Laser and Microwave Welding – The Applicability of New Process Principles

“…There are essentially two different processes that can be employed for the laser welding of plastics. These are, firstly, the so‐called laser butt welding process,6 where the joining surfaces of the parts to be welded are heated via a system of mirrors (Figure 4) and then pressed together in the molten state and joined. It is also possible to use an array of laser diodes to heat each of the joining surfaces.…”

“…The second and much more interesting process variant is the laser transmission welding 7. The condition that needs to be fulfilled for this variant is that one of the parts to be joined must be transparent to the wavelength of the laser light employed, while the other has a high absorption (Figure 5).…”

“…Figure 7 highlight the influence of the welding parameters of laser power and scanning velocity on the mechanical strength of laser‐transmission‐welded double‐T specimens (AWS specimens) 7…”