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 and the welding surface extends parallel to the longitudinal axis, - 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, - 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 along the longitudinal axis through the first temperature control channel and then in a second direction opposite to the first direction 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 and the welding surface extends parallel to the longitudinal axis, - 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, - 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 along the longitudinal axis through the first temperature control channel and then in a second direction opposite to the first direction through the second temperature control channel and to the discharge channel.