company news about Ultrasonic Welding with Robotics

The effect of shrinking high-volume products and growing multiple versions of lower-volume products, especially in the automotive industry, have forced manufacturers to look for more flexible assembly solutions. Today’s requirements include maximizing flexibility and floor space and minimizing tool change setup time. The latest developments are flexible ultrasonic welding cells incorporating robotics for the assembly of multiple plastic components. This eliminates the need for time consuming set-up and tool changes.

One of the key features of such assembly solutions is six-axis robots. This component can be supplied by any robotics manufacturer, as long as the end-of-arm load and welding forces are taken into consideration when sizing the robot.
A second key feature is the specially designed end-of-arm weld head, utilizing two different (up to four) weld sonotrodes to accommodate different welding operations without tool change.

Compact ultrasonic actuators with low weight easily can be mounted on robot arms and are thus well-suited for fast and low-energy joining of plastic parts. Pre-loading the pneumatic cylinder of the actuator saves time – up to one second per weld spot. This is particularly noticeable in applications with many weld spots.

Robots are utilized in situations where several identical weld spots must be performed on one larger plastic component. Robot cells provide the highest flexibility with very low counts and high variant variety. However, the robot performs the welds step-by-step, which requires time. With the help of the pre-loaded concept, the sonotrode up/down travel times can be reduced and productivity of the robot is increased. Despite the reduced cycle times, the weld process achieved is impeccable.

In order to ensure repeatability of the weld process, the weld distance must not only be traveled by the robot itself, but also by the actuator. Otherwise, after reaching the weld end position, the robot would have to apply home position pressure at a consistent value during hold time (ultrasonic off). However, this cannot be realized with the required degree of precision and, what is more, elaborate programming of the robot motion sequence (position control without ultrasonic) would be required. The solution is to always integrate actuators when planning automation concepts. In this way, a repeatable weld process can be ensured during the plasticization and solidification phases.

The pre-loaded technology causes the robot with the pneumatically pre-loaded ultrasonic unit to travel towards the weld area and thus to pressurize the pneumatic drive cylinder of the actuator in joining direction. The ultrasonic generator now receives an external trigger signal from the robot controller. As soon as the programmed end coordinates of the robot motion are reached, the weld process of the ultrasonic system monitored by the weld process control is started: trigger process, ultrasonic welding and hold time. After expiry of the hold time, the robot receives a ready signal and lifts the sonotrode off the component by a few millimeters, before directly moving on to the next weld spot. During the lifting phase, the actuator is retracting into the pre-loaded end position. If no weld process controller is available, ultrasonic start is directly triggered by the robot controller (time delayed).

Another important component is a CNC controller, which controls all weld processes and interfaces with the robot. A separate, optimized weld program can be established for each weld position, providing the possibility to switch between weld modes, using different forces or amplitudes and setting individual min/max weld process control windows.
The controllers are equipped with an Ethernet port, allowing interfacing directly with plant networks or off-site QC departments via the World Wide Web for remote diagnostics. This also allows users to monitor and modify weld process parameters that provide closed-loop data collection and parts tracking.