device for ultrasonic welding, comprising - a sonotrode with at least one, preferably at least two welding surfaces , wherein the sonotrode can be excited to ultrasonic vibrations with respect to a longitudinal axis (L) and the welding surface extends parallel to the longitudinal axis (L), - a temperature control device for controlling the temperature, in particular for cooling and/or heating, of the sonotrode , with - a feed channel through which a temperature control fluid can be introduced into the sonotrode , - at least one flow channel running inside the sonotrode , which is fluidly connected to the feed channel , - at least one heat transport device running inside the sonotrode , which is thermally coupled to the temperature control fluid flowing through the flow channel , - a discharge channel through which the temperature control fluid can be discharged from the sonotrode and which is fluidly connected to the flow channel , characterised in that - the heat transport device is designed and arranged to transport heat along the longitudinal axis (L), - the sonotrode has at least one bore with an inner wall which at least partially delimits the flow channel , - a guide element is arranged in the bore in such a way that it divides the bore at least along part of its length into a first temperature control channel and a second temperature control channel , so that the temperature control fluid can be guided at least partially from the feed channel in a first direction (R1) along the longitudinal axis (L) through the first temperature control channel and then in a second direction (R2) opposite to the first direction (R1) through the second temperature control channel and to the discharge channel . - a sonotrode with at least one, preferably at least two welding surfaces , wherein the sonotrode can be excited to ultrasonic vibrations with respect to a longitudinal axis (L) and the welding surface extends parallel to the longitudinal axis (L), - a temperature control device for controlling the temperature, in particular for cooling and/or heating, of the sonotrode , with - a feed channel through which a temperature control fluid can be introduced into the sonotrode , - at least one flow channel running inside the sonotrode , which is fluidly connected to the feed channel , - at least one heat transport device running inside the sonotrode , which is thermally coupled to the temperature control fluid flowing through the flow channel , - a discharge channel through which the temperature control fluid can be discharged from the sonotrode and which is fluidly connected to the flow channel , - a feed channel through which a temperature control fluid can be introduced into the sonotrode , - at least one flow channel running inside the sonotrode , which is fluidly connected to the feed channel , - at least one heat transport device running inside the sonotrode , which is thermally coupled to the temperature control fluid flowing through the flow channel , - a discharge channel through which the temperature control fluid can be discharged from the sonotrode and which is fluidly connected to the flow channel , - the heat transport device is designed and arranged to transport heat along the longitudinal axis (L), - the sonotrode has at least one bore with an inner wall which at least partially delimits the flow channel , - a guide element is arranged in the bore in such a way that it divides the bore at least along part of its length into a first temperature control channel and a second temperature control channel , so that the temperature control fluid can be guided at least partially from the feed channel in a first direction (R1) along the longitudinal axis (L) through the first temperature control channel and then in a second direction (R2) opposite to the first direction (R1) through the second temperature control channel and to the discharge channel . <EOS>