company news about Pre-loaded ultrasonic welding systems

Pre-loading means that the cylinder already has been extended via an intelligent pneumatic system when the weld tool gets in contact with the material. Therefore, the machine immediately can start the welding process. The time saved in applications with many weld spots may be significant. The joining of acoustic foam for an engine compartment with up to 20 weld spots is an example that is more and more frequently realized by means of robots. In this case, time savings per application may amount to as many as 20 seconds.

In more detail, a pre-loaded system consists of a primary drive (cam, servo, robot, etc.) and a secondary, pneumatic drive. In the secondary drive, pressure continuously is applied to the pneumatic cylinder of the actuator. Thus, the cylinder of the actuator is in extended condition. The pressure in the cylinder corresponds to the trigger force required for the application. The actuator is in pressurized condition, which is called “pre-loaded.” The primary drive moves the “pre-loaded” actuator to the weld area, lowers the sonotrode onto the plastic part to be welded to form contact with the surface and travels over the contact point of the cylinder so that the cylinder piston of the actuator is pushed back. The resulting pressure increase in the cylinder is vented via a pneumatic pressure regulator (precision pressure regulator or proportional valve) in order to keep the pressure in the cylinder at a consistent level. Subsequent to the primary travel reaching its end position, the trigger is initiated and the weld process is started. The buffered pneumatic cylinder now performs the weld stroke. The required weld force is defined by the pneumatic pressure regulator or proportional valve. After the weld (end of hold time), the entire actuator is moved back from the weld area by the primary drive. During this travel, the actuator moves back to its extended pre-loaded position and then is ready for the next weld cycle.

One example for the use of pre-loaded systems is for applications with very large quantities and repeated production of the same or similar plastic parts, where fast-operating automated rotary systems or linear transfer machines frequently are used. These systems operate in time-optimized cycles; they are partly cam-controlled and partly servo-controlled, with cycle times of a second or less per assembly. The paramount purpose of such production systems is to exploit the full cycle-reduction potential up to the last millisecond and thus to increase the parts output. If an ultrasonic welding process is integrated, all requirements for cycle time must be met. The ultrasonic welding process, which only takes a few milliseconds, combined with the pre-loaded concept, which drastically reduces the sonotrode up/down travel times, meets this demand with a high degree of reliability for millions of parts. In general, the actuators are mounted on a carriage, which is driven either by a cam drive or a servo-controlled direct drive (primary shaft).

Another typical setup involves automated assembly systems where the pre-loaded technology causes the primary shaft with the pneumatically pre-loaded actuator to travel towards the weld area and thus to pressurize the pneumatic drive cylinder of the actuator. The ultrasonic generator now receives an external trigger signal from the overriding machine controller (PLC). As soon as the primary shaft reaches its end position, the weld process of the ultrasonic system monitored by the HU weld process control is started: trigger process, ultrasonic welding, hold time after expiry of the hold time, the main machine controller (PLC) receives a ready signal and moves the primary shaft back to home position. While retracting, the actuator is pushed into the pre-loaded end position. If no weld process controller is available, ultrasonic start is directly triggered by the machine controller (time delayed).