The core challenge in plastic fuel tank welding is not making the weld, but avoiding damage to the EVOH barrier layer (0.1–0.2 mm). This article explains HDPE semi-crystalline behavior, hot plate and ultrasonic welding processes, penetration control, fast changeover, and integrated automation. Yuanwang Intelligence, with nearly 20 years of experience, delivers complete fuel tank welding lines to automakers like VW, GM, BMW, and Mercedes-Benz.