Plastic welding is one of the most widely used technologies in the industry today to permanently join parts together. There are several plastic welding technologies: hot body, hot gas, friction, and ultrasound and also laser welding. Laser beam welding is good for welding very small plastic parts because of the size of the laser beam. The laser beam passes through the transparent part of the plastics and stops on the underlying part. At this point, the joint begins to heat until the two parts are joined together. To keep the temperature constant and for the long-term quality of the weld, this process must be monitored.