An ultrasonic welding system comprising: an ultrasonic welding stack movable, in response to control inputs, to initiate a welding operation by applying vibrational energy to a workpiece; one or more sensors (32, 36) adapted to measure at least one control variable and to output a control signal corresponding to the at least one control variable; and a motion control system coupled to and adapted to cause a controlled advancing movement of the ultrasonic welding stack, the motion control system being responsive to the control inputs based on one or more control signals received from the one or more sensors (32, 36) to initiate the welding operation, wherein the motion control system is adapted to perform the following steps: subsequent to the initiating of the welding operation, optionally initially delaying any advancing movement of the ultrasonic welding stack until one or more of the control signals indicate that respective control variables satisfy a predetermined condition, subsequent to the optional initial delay and in response to the predetermined condition being satisfied, causing the ultrasonic welding stack to advance in accordance with a weld profile, characterized in that the motion control system is adapted to perform the following steps: subsequent to the ultrasonic welding stack moving in accordance with the weld profile, causing the ultrasonic welding stack to stop advancing movement and maintain a stationary position in response to an occurrence of a predetermined delay initiating condition, and in response to an occurrence of a predetermined delay terminating condition, resuming advancing movement of the ultrasonic welding stack in accordance with the weld profile, wherein vibrational energy continues to be applied to said workpiece while said ultrasonic welding stack is stopped and while the advancing movement of the welding stack continues. an ultrasonic welding stack movable, in response to control inputs, to initiate a welding operation by applying vibrational energy to a workpiece; one or more sensors (32, 36) adapted to measure at least one control variable and to output a control signal corresponding to the at least one control variable; and a motion control system coupled to and adapted to cause a controlled advancing movement of the ultrasonic welding stack, the motion control system being responsive to the control inputs based on one or more control signals received from the one or more sensors (32, 36) to initiate the welding operation, wherein the motion control system is adapted to perform the following steps: subsequent to the initiating of the welding operation, optionally initially delaying any advancing movement of the ultrasonic welding stack until one or more of the control signals indicate that respective control variables satisfy a predetermined condition, subsequent to the optional initial delay and in response to the predetermined condition being satisfied, causing the ultrasonic welding stack to advance in accordance with a weld profile, characterized in that the motion control system is adapted to perform the following steps: subsequent to the ultrasonic welding stack moving in accordance with the weld profile, causing the ultrasonic welding stack to stop advancing movement and maintain a stationary position in response to an occurrence of a predetermined delay initiating condition, and in response to an occurrence of a predetermined delay terminating condition, resuming advancing movement of the ultrasonic welding stack in accordance with the weld profile, wherein vibrational energy continues to be applied to said workpiece while said ultrasonic welding stack is stopped and while the advancing movement of the welding stack continues. subsequent to the initiating of the welding operation, optionally initially delaying any advancing movement of the ultrasonic welding stack until one or more of the control signals indicate that respective control variables satisfy a predetermined condition, subsequent to the optional initial delay and in response to the predetermined condition being satisfied, causing the ultrasonic welding stack to advance in accordance with a weld profile, characterized in that the motion control system is adapted to perform the following steps: subsequent to the ultrasonic welding stack moving in accordance with the weld profile, causing the ultrasonic welding stack to stop advancing movement and maintain a stationary position in response to an occurrence of a predetermined delay initiating condition, and in response to an occurrence of a predetermined delay terminating condition, resuming advancing movement of the ultrasonic welding stack in accordance with the weld profile, wherein vibrational energy continues to be applied to said workpiece while said ultrasonic welding stack is stopped and while the advancing movement of the welding stack continues.