Method for operating an ultrasonic welding machine

A method for operating an ultrasonic welding machine, in which, during a welding process, a flat material is continuously moved through a gap formed between a sonotrode, which is vibrated at an ultrasonic frequency with a welding amplitude, and an anvil at a welding speed while a welding force is exerted onto the flat material by the anvil and/or the sonotrode,

• wherein during a welding phase, the ACTUAL temperature of the flat material is measured after the flat material has passed through the gap, the ACTUAL temperature is compared with a predetermined TARGET temperature, and the welding amplitude is varied on the basis of the comparison result;
• wherein, prior to the welding phase, during a start-up phase, the welding speed is increased from 0 to a predetermined welding speed value, a predetermined welding amplitude and predetermined welding force being sought, characterized in that, during the start-up phase, no variation of the welding amplitude on the basis of the comparison result takes place;
• and
• wherein prior to the start-up phase, during a standby phase, the welding amplitude and/or the welding force is held at a predetermined reduced welding amplitude value or at a predetermined reduced welding force value, the reduced welding amplitude and reduced welding force values being between 40 percent and 60 percent of the predetermined values sought during the start-up phase.