Welding daytime running light housings is tricky because of their asymmetrical shape, but one supplier found a solution, using ultrasonic welding.
Ultrasonic welding, if you’re not familiar with it, uses sound vibrations (with a frequency of 20,000 Hz or higher) to weld with a tool called a “sonotrode.” The heat created by the back-and-forth vibrations melts the part in a local area to form the weld. The system for this application was developed by Herrmann Ultrasonics (herrmannultrasonics.com). The company developed sonotrodes specific to the workpiece design; they are manually mounted into a fixture, then laser gauged to assure position. The entire process requires just 100 to 300 milliseconds.