Ultrasonic spotwelding is used predominantly when, for instance, flat mouldings without weld preparation (ED) have to be welded (e.g. semi-finished products, thermoformed, blow moulded, extruded and large-surface mouldings).
The tip of the sonotrode penetrates through the upper part into the lower part. Heat is produced on the contract surfaces of the mouldings, as a result of which the material is plasticised and welded. The expelled plastic flows upwards and forms a ring shaped elevation. The back of the lower part remains largely free of marks. The mouldings can be fixed appropriately by hold-downs or clamping devices. The thickness of the moulding adjacent to the sonotrode should not exceed 8 mm. Spot welding can also be carried out with a moveable ultrasonic hand welding apparatus (welding gun).