Tacking device

A tacking structure comprising a first member formed of a thermoplastic resin;

• a second member to be tacked to said first member;
• a tacking member formed of a thermoplastic resin compatible with that of a thermoplastic resin forming said first member to be attached, said tacking member having a fusible plate and a pin having a bulged tip and projecting from a lower surface of the fusible plate;
• and
• a retaining member which is formed of another material having a sufficient rigidity greater than a material of the tacking member, having a substantially cylindrical body provided with a plurality of catches on its outer circumference;
• the tacking member being rotated at a high rotating speed or vibrated with the fusible plate when pressed against said first member so that an upper surface of the fusible plate will be fused by frictional heat to weld the tacking member to said first member, the pin being inserted in a central hollow of the retaining member so that an expanded tip of the pin is caught by the retaining member to combine the tacking member and the retaining member, and the retaining member being forced into a hole formed in said second member so that the catches engage with the edge of the hole for attachment of said first member to said second member;
• wherein the fusible plate of the tacking member is provided on its upper surface with a small rigid conical positioning protrusion at a center of the upper surface, and a plurality of concentric circular ridges formed about the positioning protrusion, and the tacking member is joined to the first member at a predetermined position by rotational friction welding.