How to Join Fiber-Reinforced Composite Parts: An Experimental Investigation

A coupler has been developed to prevent windshield wiper systems from being damaged by excessive loads that can occur when the normal wiping pattern is restricted. Unlike the traditional steel coupler used in wiper systems, the composite coupler will buckle at a prescribed compressive load threshold and become extremely compliant. As a result, the peak loading of the coupler and the entire wiper system can be greatly reduced. The coupler is composed of a pultruded composite rod with injection-molded plastic spherical sockets attached at either end. The sockets are used to attach the coupler to the crank and rocker of the windshield wiper linkage. Because the loads exerted on a coupler vary in magnitude and direction during a wiping cycle, the joint between the sockets and the pultruded composite rod must be robust. The paradigm for attaching sockets to steel couplers (i.e. over-molding the sockets around holes stamped into the ends of traditional steel couplers) was tested and found to produce inadequate joint strength. This paper details the methodology that was employed to produce and optimize an acceptable means to join the injection-molded sockets to the fiber glass pultruded rods. Specifically, a designed experiment based on the Robust Design Strategy of Taguchi was used to identify the process, processing parameters, and materials that yield a sufficiently strong joint at a reasonable manufacturing cost without damaging the integrity of the underlying composite structure.