Stage 1 of the process is used to accelerate the forming head rapidly until the forming peen makes contact with the top of the rivet. This ensures that the forming tool travel time is minimised as this is effectively wasted time in the riveting cycle. However, using fast acceleration is not good for forming high precision joints because excessive acceleration can lead to forming overshoot and uncontrolled riveting which usually results in variations in the quality of the riveted joint.
For this reason, as soon as the peen makes contact with the rivet, Stage 2 is inititated which instantaneously deccelerates the forming head to a pre-determined rate of advance which forms the rivet in a controlled manner until a final formed condition has been achieved. The final formed condition depends on the application and can be measured in terms of distance, force or time. Electronic devices including displacement transducers (LVDT) and load cells are used to provide direct feedback to the control system depending on the needs of the Design Engineer.
Stage 3 follows automatically during which the rivet head is created and fully formed. This normally takes place within a short period of time typically between 0.5 and 3 seconds duration. The exact parameters required for stage 3 depends on the material being riveted and the rotational speed of the forming head and the peen design.
Stage 4 is used to return the forming head back to a home position which allow the riveted assembly to be removed from the machine and the next components to be loaded. The time taken for this operation is minimised by rapidly retracting the head as soon as the previous stage is completed.