The robot ultrasonic welding improves the welding efficiency and stability of engine cover and soundproof cotton in automobile mold production, and realizes the automation of welding between soundproof cotton and engine cover. The robot ultrasonic welding has high quality tight welding joint. Ultrasonic spot welding is used to transfer heat to the soundproof cotton material, melamine and non-woven fabric through ultrasonic welding head, and the required effect is achieved by hot pressing deformation. After welding, the surface of the product is smooth and the connection is firm, which can highly meet the requirements of product welding quality.