Ultrasonic welding applications for baseball cap

25 Jun '08

4 min read

A New Zealand manufacturer of multifunctional baseball caps is opting for the ultrasonic welding technology from TECHSPAN GROUP.

While typical ultrasonic welding applications are to be found primarily in areas such as the automotive, packing, or textile industries, as well as in medical technology, items for the leisure and adventure sector are not one of the classic applications. This case concerns a baseball cap with integrated, solar-powered LEDs which act as headlamps in the dark - a patented product from the company 2C-Light.

Sensitive high tech electronics
A built-in electronics board takes over the energy management and control of the different light modes. The board is permanently welded into the two part visor made from PPC material, making it dust and water-proof. In addition to qualitative requirements, the welded seam is also subject to visual specifications.

No bubbles should be visible on the seam on the transparent sun visor and the plastic should not be stained a milky colour. Alternative welding processes such as hot plate, vibration, or laser technology were rejected after the evaluation phase. It was particularly the low investment and operational costs as well as short welding cycle times of 3 - 4 seconds which tipped the balance.

Firsthand application-specific advice
RINCO ULTRASONICS AG and TECHSPAN GROUP were involved as early as the design and project phase and full use was therefore made of the applications engineer's profound specialized knowledge and its many years of experience. Thus it was possible to adapt the design of the join area to suit the requirements of ultrasonic welding technology in order to achieve ideal welding results.

Is ultrasonic welding of PPC possible?
Polypropylene Random Copolymers (PPC) are polypropylene, where the structure has been changed due to the incorporation of another monomer molecule, generally ethylene. High transparency, flexibility, impact strength and a reduced melting point compared to PP homopolymers are characteristics of PPC.

As a result of its high flexibility, the soft material is regarded as problematic for ultrasonic welding. Nevertheless, the engineers at RINCO ULTRASONICS AG succeeded in designing the welding tools so that the application could be carried without any problems using the 20kHz ultrasonic welding machine Dynamic 3000 Series.

Tool construction as the focus
One very important aspect is the coordination between the ultrasonic welding machine and the tool, the so-called horn and anvil. The anvil ensures the correct and precise placing of the two sun visor halves with the sensitive electronic board. The height difference (concavity) was a particular challenge, as the acoustic laws of tool design set certain limits.

The parts are co-injected with PPC being the primary material, and a soft-touch thermoplastic rubber being the secondary material. This soft-touch material adjacent to the welding seam, which has a design function, made the construction and manufacture of the two tool forms even more complex.