Over-riveting is a hidden but extremely harmful process defect. Compared to cracking, it is not as obvious, but the damage is internal; excessive plastic deformation of the structure destroys the material’s crystal lattice structure, severely reducing joint performance. Accurately identifying and systematically preventing over-riveting is a critical process step in ensuring long-term product reliability.
- How to Accurately Identify Over-Riveting
Visual Inspection: The rivet head is abnormally flattened, losing its standard shape, showing irregular “flashing,” coating cracking or peeling, and bulging or depressions.
Dimensional Measurement: Rivet height or diameter consistently below the lower specification limit.
Process Data Analysis: Analyze recorded force and displacement curves to identify riveting anomalies such as abnormally high peak force, jagged or secondary peaks at the end of the curve.
- Serious Consequences of Over-Riveting
Reduced Riveting Strength: Excessive cold working makes both the rivet and the base material brittle, significantly reducing the impact toughness and fatigue strength of the joint, making it prone to brittle fracture under dynamic loads.
Induced Microcracks: High internal stress can induce hidden microcracks within the material or at the interface, creating a risk of long-term failure.
Functional Damage: For joints with sealing or conductive requirements, excessive deformation can damage the integrity of the contact surface.
Surface Damage: Over-riveting can cause surface scratches or damage to the coating, affecting the appearance and leading to corrosion, impacting performance.
Accelerated Equipment Wear: Long-term operation under overload conditions will significantly shorten the service life of the punch and spindle bearings.
- Scientifically Setting and Maintaining the “Process Window”
“Window Exploration” Experimental Method: Use experimental design to systematically change force and stroke parameters while observing the forming results. Determine the minimum stroke for acceptable riveting and the force/stroke values at which over-riveting occurs. The optimal operating point should be set in the middle region, away from the extreme values.
Intelligent Control for Hard Protection: On Suntop Technology ST-MSF series equipment, a “position-force” hybrid control mode can be used. The machine performs real-time monitoring; if the force reaches the protection limit before the end of the stroke, the machine will immediately stop and issue an alarm, thus preventing over-riveting at the execution level. Data-based early warning: The peak force of each rivet is incorporated into SPC (Statistical Process Control) monitoring. If the average peak force shows a slow upward trend, the system can provide an early warning and give a prompt.
Conclusion:
Preventing “over-riveting” must shift from relying on subjective judgment to control based on data and scientific methods. A robust process design can be achieved by defining a safety window, utilizing closed-loop control for hard protection, and combining it with statistical process monitoring.