Mechanical strength of thermoplastics and composite thermoplastics welded by laser – a review

Thermoplastic welding is currently well implemented in the market, with several competitive and suitable processes, ranging from simple hot plate to ultrasonic welding. By its side, laser welding of plastics is still in a relatively early stage of research. This process is one of the most recent in the welding of thermoplastics and of great interest in the market. The welding technique is based on heating the thermoplastics by transmitting heat in the form of radiation. This is due to the ability of certain plastics to absorb the beam. Usually, one of the parts to be welded must be transparent and the other opaque to radiation. These two parts are kept under pressure as the laser beams are transmitted through the transparent part. The laser beam is concentrated in the joint area of the opaque part, heating and melting it. There are relatively few scientific studies on the joining of thermoplastics by laser and, in the case of thermoplastic matrix composites, there are even fewer. The main conclusion is that the mechanical strength of a laser welded joint is in the range of 30-50 MPa, a value that is frankly weak when compared to the value that the base material can handle and which is usually more than double for thermoplastics and 10 times for composites. Although the fusion process is contactless, one of the great limitations of laser welding of plastics is the need to exert pressure on the joint, which conditions and complicates the execution of a weld. However, despite everything, it is certain that laser welding presents mechanical strength values superior to those of a bonded connection and the processing time is much shorter, therefore, it is clear the interest on the process.