Although we may not want to admit it, most of us have a “chairdrobe.” When worn clothes are too clean to wash, but are no longer fresh enough to put back into the closet, we drape them over a chair to be donned on a later date.

Engineers at Bosch Home Appliances have come up with a clever new gadget that promises to help us with the chairdrobe problem. The FreshUp is a handheld, battery-powered device that uses plasma to remove unpleasant odors, bacteria and viruses from dry clothes without the need to wash them. When the plasma source is activated, the air is ionized directly at the fabric. Molecular chains are broken, and bacteria and viruses are destroyed. This permanently neutralizes odors without the use of chemicals.

The gadget is great for getting extra mileage out of clothing that’s clean, but might have absorbed unpleasant smells, such cigarette smoke, body odor and food smells. It’s also helpful for travelers, who might not have access to a washer and dryer.

The plasma is powerful enough to dissolve odor-causing molecules, but not so powerful that it destroys textile fibers. Photo courtesy Bosch Home Appliances

The plasma is powerful enough to dissolve odor-causing molecules, but not so powerful that it destroys strong or complex structures, such as textile fibers. The device removes odors from cotton, silk, cashmere, wool, linen, and polyester blends. It can be used on both sportswear and functional clothes. It can even be used on cushions or teddy bears. And, it can be safely used on clothes while they are being worn.

The device cannot be used on leather, fur, metal fibers, foam or any other non-textile surface, including skin, hair or animals.

FreshUp is a lozenge-shaped device measuring 6.5 inches long, with a 2-inch treatment area on its underside.

Bosch engineers chose ultrasonic welding as the most suitable assembly technology, since it produces strong and visually appealing joints. Herrmann Ultrasonics was involved in the project at an early stage and was able to develop a welding system that satisfied Bosch’s requirements.

The device is housed between two shells molded from MABS. Photo courtesy Herrmann Ultrasonics

Fixture Allows Flawless Assembly

During the development process, the aesthetic requirements for the assembly put Herrmann’s ultrasonic laboratory to the test. 

The two halves of the device’s case are molded from methyl methacrylate acrylonitrile butadiene styrene. MABS is a thermoplastic that combines the properties of methyl methacrylate and ABS. Known for its transparency, toughness and impact resistance, the material is used in a variety of applications, including medical devices, printer and copier parts, refrigerator drawers, and auto parts. It offers good chemical resistance; good mechanical strength and stiffness; good resistance to heat deformation; and easy processing. It can be printed upon, and it can be formulated to create visual effects, such as deep colors and sparkly finishes.

The material conducts ultrasonic vibrations very well, so that strong vibrations not only occur in the joining zone, but also in the entire component during the welding process. This caused marks to appear on the surface at various points where the component sits in the fixture.

To dampen the vibrations, the fixture was made of a special casting resin. This is an abrasion-proof, heat-resistant material with a hardness of 80 to 90 Shore, roughly equivalent to the hardness of skateboard wheels. The material is hard enough to hold the component in place, but soft enough to dampen the vibrations from the ultrasonic energy.

The fixture was made of a special casting resin. The material is hard enough to hold the component in place, but soft enough to dampen the ultrasonic vibrations. Photo courtesy Herrmann Ultrasonics

The low hardness of the resin also allows for subsequent adjustment of its three-dimensional shape. In this way, the ideal fit for the curved component could be created step-by-step by manual polishing and grinding.

Further optimization of the fixture was achieved by dividing it into four fixture segments instead of the usual two. This structure ensures that the component lies cleanly in the fixture and can be welded accurately by the sonotrode. At the same time, the divisions prevent damage to the material in the area of the parting lines. Together with the soft casting resin, the fixture reliably prevents any marring of the components.

Joint Trials via Video Calls

A special aspect of the project was that the design of the components was fixed from the start. This meant that only a small welding path of 0.3 millimeter was available—about half as much as would normally be used. It was not possible to adapt the injection-molding tool in the area of the energy direction without making changes to the appearance of the case.

To weld both components flush over the entire length, the welding process was jointly developed and optimized in an extensive design of experiments process with several evaluation loops. Graphs showing weld speed, time, collapse distance and other parameters were critical for optimizing the process.

The tests were carried out in Herrmann’s ultrasonic plastic welding laboratory, as well as at the customer’s site, and some of the tests were transmitted between locations via live video. Thanks to the close cooperation between engineers at Bosch and Herrmann, the right parameters were ultimately defined to ensure a strong and visually flawless joint.

For more information on ultrasonic welding, visit www.herrmannultrasonics.com.

For more information on ultrasonic welding, read these articles:
Potential Pitfalls in Ultrasonic Plastic Welding
Ultrasonic Welder Assembles Plastic Medical Device
Optimizing Ultrasonic Plastic Welds