• Transactions of Materials Processing
• /
• v.29 no.3
• /
• pp.157-162
• /
• 2020

Blind rivet nuts are increasingly used in automotive for the joining of sheets. Their application, however, requires appropriate design guides to prevent catastrophic events arising from the failure of joints. In this study, the shaft shape of a frequently used M8 blind rivet nut is optimized based on 3D numerical analysis of the blind rivet nut considering the characteristics of thread. The thread needs to be modeled to suitably consider the fastening of the M8 bolt after the crimping process. FE analysis showed that while the friction in the contact between crimp flange and plate has no significant effect on the crimp geometry, shaft thickness (t) and shaft height (h) are the most significant design variables. The parameter study including various combinations of t and h reveals that they affect the gap (the distance between the crimped flange and the plate that develops through riveting) and the load acting on the plate. The gap is an indicator of the tightening force. It is found that t is inversely proportional to the gap, and proportional to the load, whereas h is proportional to the gap and inversely proportional to the load. Based on our FE analysis results, we propose the range 0.062 < t/h < 0.1 to ensure sufficient fastening (high clamping load, small gap) of the M8 blind rivet nut. The design guide for determining the t/h ratio proposed in this study can be used for general quantitative analysis of the size and the t/h ratio of blind rivet nuts.

• Transactions of Materials Processing
• /
• v.29 no.6
• /
• pp.331-337
• /
• 2020

Blind rivet nuts (BRNs) are increasingly used in automotive industry because unlike conventional bolt fastening, BRN fastening requires access from one side only. Generally, fastening is conducted using automated units, but manual fastening may be resorted to in case of small quantities. Since the fastening direction is not exactly perpendicular to the sheet metal, the BRN axis is tilted with respect to the plate and may result in damage or incomplete fastening. As the tilt angle (clamping angle α) increases, undesired plate deformation occurs and the contact area of the plate with the BRN fastening area decreases, reducing the clamping effect. In this study, the reduction of the clamping effect with the α was investigated to ensure stable fastening force. M6 BRNs were used in the tests. The fastening force was measured as follows: the plate was cut in half through the center of the hole; the BRN was inserted into the hole and fastened; and the clamping angle a was measured (values, 0° ≤ α ≤ 9°). The force leading to the separation of the halves was measured using a universal testing machine (UTM). The maximum α range, in which the fastening force remains stable, was determined. Finite element (FE) analysis confirmed that the fastening force decreases approximately linearly with increasing α. Based on the experiment and FE analysis using various α, the fastening force was found to decrease with α. Further, the maximum tolerance for α that provides secure fastening without damage is suggested.