The principle involves cold forming a cylindrical pin with 3 grooves at 3 intervals of 120 °. This results in an expansion of the pin’s diameter.
When one inserts this pin into a hole carefully drilled to the nominal diameter, the grooves partially close and the metal flows between and into the grooves thus achieving a perfect fit between the pin and the hole. The tightening achieved is an elastic connection and not a simple gripping connection.
- fig. 1 – End view before insertion
- fig. 2 – Cross section of the pin in situ
Figures 1 and 2 show the deformation which results. The actual type of swelling may differ depending on the materials or machined parts involved.
The only characteristic to take into account is the bulging diameter (Dr), measured at the ring, i.e. the diameter of the circle marking out the most projecting points, however they are distributed.
Types of grooving:
– Constant grooving
– Progressive grooving
The shape of the groove required is recommended by the supplier.