The technology of ultrasonic welding appeared in the early 90s and has been under rapid development since then
. As the technology improves, the range of materials that can be joined together using this technique increases. At first only non-flexible plastics could be welded because their material properties allowed the efficient transmission of acoustic energy from part to part. Nowadays, less rigid plastics such as semi crystalline plastics can be welded because large amounts of acoustic energy can be applied to the welding zone. As the technology matures and becomes more versatile, it is likely to obsolete large classes of historical techniques for joining materials together.