High-speed laser welding of plastic films

Deep penetration welding of polymers can be carried out at high speed with relatively low laser power. This results from an efficient coupling of CO 2 laser radiation to polymers that leads to volume heating. A brief review of energy coupling and heat transfer effects in polymers under CO 2 laser welding conditions is given. Some examples of low power (10 to 100 watt) CO 2 welding of polypropylene and polyethylene at depth,s of up to 1.5 cm are discussed

CO2 laser welding of polymers

CHAPTER 2 – Laser Cutting

This paper deals with a novel CO 2 laser plastic welding procedure developed from the point of view of heat transfer containing simultaneous radiation and conduction processes and also gives a brief review of plastic welding development to date. The principle and features are shown by both the experiments using CO 2 laser as a radiation source and numerical simulation considering heat transfer phenomena in simultaneous radiation and conduction in welding process. The feasibility of the proposed procedure is confirmed by applying the overlapped same plastic films with combination of infrared radiation absorbing heating and thermal diffusion cooling processes. A solid material transparent to infrared radiation with a high thermal diffusivity is used as a heat sink in contact with the irradiated surface of overlapped thermoplastics during radiation heating. The procedure is able to achieve both high welding strength and excellent surface appearance without causing surface thermal damage as often suffered in conventional direct infrared radiation welding process. In addition, pigmentation in welding material to increase absorption of radiation is unnecessary for this method.

Radiative heat transfer in plastic welding process

Laser transmission welding offers significant benefits over conventional welding techniques enabling single-stage rapid plastic joining. The quality of laser transmission welded products is commonly assessed by measuring the weld penetration depth, hardened weld boundary, and inspecting the formation of porosity. However, the existing methods of verification are inevitably accompanied by destruction of the specimen. Thus, non-destructive quality assessment methods for laser transmission welding have gained attention recently. Here, we demonstrated an extended industrial application of 860 nm wavelength-based spectral domain optical coherence tomography for the non-destructive inspection of the aforementioned quality parameters of laser transmission welded industrial plastic materials, i.e., polycarbonate and acrylonitrile butadiene styrene copolymer. The acquired cross-sectional resolution and volumetric and intensity profiles sufficiently contributed to the quality assessment procedure, revealing the weld boundary and porosity formation, and thus confirming the potential applicability of optical coherence tomography for the quality inspection of laser transmission welded products.

Non-Destructive Identification of Weld-Boundary and Porosity Formation During Laser Transmission Welding by Using Optical Coherence Tomography

Of all the types of lasers now available, the CO 2 laser is particularly suitable for materials working. It has a very high efficiency (15–20%) and a high out-put power (up to several kW). When the laser light is focused by means of a lens or a mirror, a c.w. power density of more than 10 9 W cm -2 can be attained. The laser need not be used in vacuum. The CO 2 laser is a suitable cutting tool for numerous materials. These include metals such as titanium or steel; combustible materials such as paper, textiles and wood; and plastics. The CO 2 laser can also cut hard and brittle materials such as aluminum oxide and silicon carbide. If metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width, however, is determined by the size of the laser spot. Another important field of application is the growth of single crystals. Experiments are reported in which the CO 2 laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. A comparative study of laser and electron beam techniques is included.

K. Gürs

Papers

Cutting and welding using a CO2 laser