SCREW FASTENING STRUCTURE WITH HIGH-STRENGTH SELF-FORMING SCREW

摘要

To provide a screw fastening structure for enhancing the strength of a bolt and fatigue strength by reducing the machining process without altering the shape of an associated member, and for achieving downsizing by keeping the fitting length of a thread almost the same as that of the prior art, thus contributing remarkably to weight reduction of a vehicle. A self-forming screw (1) having a strength 14T produced by form rolling before heat treatment is employed as a fastening bolt, and the self-forming screw is driven into a member (4) having an as-cast, nonthreaded rough hole (5). In a screw fastening structure to which a fixing member (6) is fastened, the catch rate of a female screw and a male screw formed by a self-form is 75-90%, the fitting length of the screw and the rough hole is d-2.5d (d is screw diameter), and no clearance appears at the contact surface of the male and female screws because of self-forming screw fastening.