Reliable joining of the spring wire to polymer composite for the micro-multi-functional actuator of cellular phones

The micro-multi-functional actuator (MFA) of a cellular phone is a mass-spring system which is resonated by electrical force at the fundamental natural frequency to generate and transmit the vibration signal to the customers. The MFA has two design requirements such as high vibration force transmission and long fatigue life.Generally, conventional multi-functional actuators have been manufactured using stamped metal plate springs using precision dies. Since cracks are often generated in the cut area of metal plate during stamping operation, fatigue failures of conventional MFA’s are inevitable.In this study, a new micro-multi-functional actuator was designed using a spring (music) wire which has a high fatigue endurance limit because the surface of music wire is finely surface-finished. After the static and dynamic characteristics of MFA were analyzed using finite element analysis with respect to the diameter and shape of the spring wire, its dynamic performance such as fundamental natural frequency, vibration force transmission and fatigue life, and adhesion characteristics between the wire and the composite molding were experimentally investigated with respect to manufacturing parameters such as surface treatment method of spring wire, injection molding temperature and pressure of polymer mold.