Securing a second object to a first object

According to an aspect of the invention, a method of mechanically securing a first object (1) comprising a thermoplastic material in a solid state to a second object (2) with a generally flat sheet portion, with a perforation (20) of the sheet portion, and with the sheet portion having an edge (21) along the perforation is provided, wherein the first object is positioned relative to the second object so that the edge is in contact with the thermoplastic material and wherein mechanical vibration energy is coupled into the assembly comprising the first and second objects until a flow portion of the thermoplastic material due to friction heat generated between the edge and the thermoplastic material becomes flowable and flows around the edge to at least partially embed the edge in the thermoplastic material. After the mechanical vibration stops, the thermoplastic material is caused to re-solidify, whereby the resolidified thermoplastic material at least partially embedding the edge anchors the first object in the second object.