Kankaanpää Unit - Projects

High frequency welding for Electronics Packaging and Protection "HEPP"

Work done 06/2008 - 01/2009
Project team: Emma Kaappa, Sanni Santavirta, Manu Myry, Tapio Karinsalo
Extent of work: 7 person months, Research the possibilities of this technology and find a suitable HF-welding machine
Funding: Prizztech, Clothing Plus ltd
Results: Two to four HF-welded test cases, technology report
Contact: Emma Kaappa

Project purpose is to encapsulate electronics with textiles and elastomer materials using high frequency welding. The main aim is to research the advantages and possibilities of this technology and to find suitable HF-welding machine for our purposes. This project is finding a new way to integrate electronics into textiles. Biggest advantage in HF-welding is selective heating of materials. The research is carried out by the TUT Kankaanpää Unit between 14.04.2008-31.01.2009. The project is funded by Prizztech and Clothing Plus ltd.

High frequency welding, also called radio frequency (RF) welding or sealing, heat sealing, and dielectric welding or sealing, uses high frequency (13 to 100 MHz) electromagnetic energy to generate heat in polar materials, resulting in melting and weld formation after cooling. A high intensity radio signal is used to impart increased molecular motion in two similar or dissimilar polymers. This causes the materials to rise in temperature, resulting in melting and increased polymer chain mobility. Ultimately, the polymer chains of the two materials penetrate their interface and become entangled, forming a weld. The technology itself is quite old and common, but to take advantage of it in textile joining is quite new thing.

The HR welding press has two plates - a moveable one, and a fixed one also called a bed. During the process, the press lowers the moveable platen and closes the electric circuit to apply certain amount of HF power. The parts to be welded are placed in a set of metal dies or electrodes which are usually operated by a compressed air cylinder to apply a preset amount of pressure at the joint area. HF energy flows through the materials and the polar materials heat and melt. The joint cools under pressure and releases the welded assembly. Basically the welder is a big capacitor where the welded material is in the middle.

High frequency welding is useful for sealing and welding plastics such as polyvinyl chloride (PVC), thermoplastic polyurethanes (TPU), ethylene-vinyl acetate (EVA), nylons (polyamide PA), some ABS resins and special grades of polyolefins (PP, PE, PET).

Our aim is to research the possibilities of this technology in joining high tech textiles and flexible electronics and compare it to traditional technologies such as heat lamination. The biggest advantage of HF-welding is the selective heating of materials. One interesting aspect also is the welding of 3D-shapes.

The test samples that we sent to be welded by welder manufacturers were encouraging. In some of the samples the seams were close the invisible and the fabric was intact. With better material selection and welding parameter tuning it´s possible to make the seam even better. We have set out to produce two to four test samples with our own 8kW welding machine, that demonstrate the possibilities of this technology in combining textiles with other materials and also electronics.

Updated , Hokkanen Mirja