Coated Rivet Dies: A Dramatic Improvement in Rivet Interference Profile 2016-01-2084
Successfully riveting aerospace fatigue-rated structure (for instance, wing panels) requires achieving rivet interference between a minimum and a maximum value in a number of locations along the shank of the rivet. In unbalanced structure, where the skin is much thicker than the stringer, this can be particularly challenging, as achieving minimum interference at the exit of the skin (D2) can often be a problem without exceeding the maximum interference at the exit of the stringer (D4). Softer base materials and harder, higher-strength rivets can compound the problem, while standard manufacturing variations in hardness of part and rivet materials can cause repeatability issues in the process. This paper presents a solution that has been successfully implemented on a production commercial aircraft. The application of a special coating on the stringer side die dramatically reduces interference at the exit of the stringer, which in some instances resulted in a reduction of over 38%. This allowed an increase in forming force to increase interference at the exit of the skin and made for a much more robust process. As well, variability of the process due to material and rivet variation was reduced. Comparisons of industry-standard uncoated, polished steel dies vs. the new, coated dies will be shown to illustrate the improvement in interference and process reliability.