How is ultrasonic welding used for to make safe and durable toys?

Jon Lawson

With their iconic smiles and varied outfits, Playmobil figures entertain and fascinate children around the world. Product safety is writ large at Playmobil. To ensure safe play, head coverings of the infant series 1.2.3 are welded onto the figures’ little heads with ultrasound. The toy maker relies on customised ultrasonic welding equipment from Weber Ultrasonics. In an automated process, the system welds different types of head covering into place at a six-second pace and then checks the quality of the weld.

In the early 1970s Horst Brandstätter, at this time the sole owner of today’s geobra Brandstätter Stiftung & Co. with headquarters in Zirndorf near Nuremberg in Germany, asked his head developer Hans Beck to design a new play system. In 1974 Playmobil took the world’s playrooms by storm when it launched figures of a Native American, construction worker and knight. Since then more than 5,700 variants of this creative, award-winning toy system have been produced for imaginative roleplays in historical and modern scenarios. Over the years, more than three billion women, men, girls, boys and babies in widely varying outfits and with numerous accessories have been developed. As product safety is so important, every article is tested prior to production for break resistance – for example, in external testing laboratories. The plastic and dyes also are examined to ensure their harmlessness for children and every product is certified.  

High safety requirements in figure manufacturing

The figures are manufactured in the Playmobil factory on Malta. Very high safety requirements are met there too. For example, the head covering on the little playmates of the infant series 1.2.3 has to be firmly attached to the head to prevent a child from swallowing the small pieces. The permanent connection is made with an ultrasonic welding process.

Given the complexity of the welding job and its high quality criteria, the Playmobil managers responsible for the project turned to Weber Ultrasonics, developer and manufacturer of ultrasound components and systems for ultrasonic welding, cutting and cleaning. The company was chosen because it could advise Playmobil of the ideal part geometry for welding while the shapes of heads and head coverings were being developed. Playmobil also relied on Weber Ultrasonics to help coordinate the ultrasonic components, welding processes and system engineering.  

On the basis of the modular welding platform Saphir, Weber Ultrasonics adapted two highly flexible, compatible systems to meet Playmobil requirements. Each is equipped with an innovative generator and control concept that allows the complete capture, monitoring and documentation of processing parameters. If required, other functions and processes can be added. At Playmobil the systems have integrated safety functions, mechanical quality control by means of a tension test and height control, plus product marking and sorting.
The newest system has been designed to process 600 parts per hour. It consists of the welding unit with an indexed workpiece support. Downstream is the testing and marking area with a rotary indexing table with four part-specific workpiece supports. The welding system is equipped with two sonotrodes for different sized heads (adult or child) and 16 workpiece supports for varied head coverings. Thanks to the flexible system design, only a corresponding tool is required for the processing of new types of head coverings. With the welding modes Time, Energy, Absolute Distance and Relative Distance stored in the control unit, parameters for new welding programs can be set quickly and easily. The operator can specify which parameters can and cannot be freely changed in a pre-defined area. Indexing saves time when a change has to be made to the workpiece support for welding or the rotary plate on the testing unit. No re-adjustment is required.

Fully automated welding, testing and sorting

After the head and head covering have been manually joined and placed in the part-specific tool, the welding process can ensue, with the defined and monitored parameters – power, time and energy – for each head. A light curtain serves as a safety guard. When welding is completed, a gripper transports the head to the testing area and positions it in the workpiece support for the tension test with adjustable force. For example, while the head covering is gripped, a pulling force of about 150 Newton is applied to the head. The plate moves to the marking station where a height control takes place at the same time. If the part passes the test, a sonotrode with adjusted force applies a system-specific mark. If the part fails the test, the sonotrode applies increased force to destroy the part. In the fourth station a gripper removes the head and puts it into a good parts box or into one of two rejected parts boxes. The parts that failed the tension test are sorted from parts whose welding parameters or height are outside defined tolerances.  
At Playmobil the systems are operated in three shifts. All welding parameters and test results for each part are captured and stored. Among other things, the data show whether changes have occurred in the process. To ensure a quick return to operation in such cases, the systems are integrated in a network. Technicians from Weber Ultrasonics can log into the systems remotely and resolve problems or make software updates. This service contributes to Playmobil’s satisfaction with the ultrasonic welding systems. The proof is in the form of an order for the third system.

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