Fundamental properties of laser lap welding of thermoplastic materials are studied. It is found that shearing strength of the welded portion increases with the laser fluence but it abruptly decreases by the instability of the welding surface and the formation of a bubble followed by the splash of vaporized plastics. When an absorbent, such as aluminum powder and/or a thin stainless-steel wire, is inserted between two transparent thermoplastic plates, these plates can be welded with combining the absorbent. This is a new laser lap welding for transparent thermoplastic plates, and it can wrap an inorganic material in the welded portion.
