Quality Assurance of Rivet Joint with Metal Process Rivets

Visual Inspection

Visually the rivets through the metal mold (Figure 1) were extremely satisfactory. Due to the contact surface with the smooth and regular cast aluminum of the mold the surface finish of the final part was excellent presenting few irregularities.

In addition, due to the consistency of the positioning of the mold aided by guide pins and its high precision of manufacture by machining in the CNC milling machine, there were almost no burrs.

Figure 1 - Rivets made by metallic mold

Source: Own

           Dimensional Inspection

However, they were not satisfactory in the dimensional aspect. Due to the need to heat the metal mold prior to initiating the process in order to retard the solidification of the aluminum due to the heat exchange, the expansion of the rivet wells was stronger than the contraction of the aluminum during solidification (disregarded in the design of the mold having in mind the very dilation thereof)

This resulted in rivets considerably larger than expected, with growths of up to 7% in diameter. This defect altered the design of the riveted joint since the holes for the rivets, before 7 mm, had to be increased to 7.5 mm, changing the mechanical resistance of the same.

In addition to the dimensional defect due to dilatation, the lack of a massalote for the mold has resulted in occasional small, undesirable rebuttals for the final result of the joint.