The center axis of the riveting peen describes the surface of a cone, whose tip lies in the rivet – thus a circular motion.

This round movement creates a crescent-shaped contact surface on the rivet. The deformation is effected around the riveting head.

Orbital riveting is not as gentle as the radial riveting procedure. The hardening on the rivet is well visible after the process.

Explanation chart: 

A = center axis
K = cone
N = constant angle
KF = contact surface
 

On the following video clips you can recognize that the riveting tool is rotating – not so in radial riveting.