Development of a laser-based pre-damage for metal-polymer caps for sealing medical ampoules

The closure of injection vials is realized by multi-material crimp caps consisting of aluminum and polymer. To improve the handling, previous investigations have determined which force for opening is perceived as comfortable and can be achieved with one hand. The potential of both material properties is utilized to develop a hybrid joining process which facilitates the opening of the vials. Undercut microstructures are introduced into the metal by laser radiation, which are filled by injection molding and ensure a microform-fit connection. This method leads to the elimination of adhesives and bonding agents, which require special regulations in medical technology. The aim of this research is to develop laser-based structuring for the aluminum sheet that ensures a reliable metal-polymer joint and breaks under a defined force. The challenge is to identify laser parameters that do not create a cutout or damage the thin aluminum sheet. A mechanical analysis is done by using a tensile testing machine in four different push-through arrangements to validate the opening forces. As a result, the targeted forces for single-handed opening of the injection vial are achieved. The metal-polymer joint remains connected while the flared cap is split open at an introduced pre-damage.