In a previous study, a new metal flow joining method that enables a shaft and ring to be combined without the need for any specialized punch was examined. In this method, the shaft was loosely fitted on the ring, which has a step, and then pressed. Metal flow caused the shaft to be joined to the ring upon pressing. As a result, the maximum joining efficiency (i.e., the shaft return-proof load / joining load) of the new method was more than 25%. In this study, the method was examined in detail in the experiment using a JIS S45C shaft (soft shaft) and JIS SKD11 ring (hard ring). Specifically, the initial dimensions of the joining hole of the ring were evaluated. First, the effect of the step width at the hole on the shaft-return-proof load was investigated. For different step widths, an 18- or 19-mm-diameter hole was combined with a concentric 20-mm-diameter hole. Second, the effect of the radial clearance between the hole and shaft on the proof load was investigated. The size of the 20-mm-diameter hole was varied to create three clearances ranging from 0.015 mm to 0.055 mm. As a result of this study, the proof load and the joining efficiency were found to be increased by using a ring with a narrower step width. The proof load reached 1.3 times greater than that in the previous study. On the other hand, the proof load and the joining efficiency were not affected by the clearance, the tightness of which would be related to the cost and productivity of joining parts with holes.
