Riveting is a mechanical joint method that could be used to join dissimilar materials having different melting points. Among the various riveting processes, self-piercing riveting(SPR) is suitable to join aluminum alloy and steel which have been being used for the automobile body. The SPR directly pierces the upper sheet and joins it to the lower sheet without a pre-hole.
As emission regulation of vehicles is being reinforced globally, the automobile industry needs to reduce the weight of vehicles to improve fuel efficiency and reduce emissions. Several studies have been conducted in the
automobile industry with the aim of body weight reduction. Lightweight materials and AHSS(Advanced High Strength Steel) have beam proved effective in improving both the performance and fuel economy of vehicle. Also using the AHSS is being tried to improve vehicle crash safety performance. In this regards, studies on the joint of dissimilar materials have attracted attention.
The joint of aluminium alloy and mild steel sheets are comparatively easy due to small difference of strength. But the joint becomes difficult with the increase in strength of the high strength steel sheet. Helical rivet was designed for joining aluminum alloy sheet to a steel sheet of over 1,000 MPa of tensile strength.
Each type of SPR needed different conditions such as rivet, anvil and sheet material etc. There was little research on the anvil and helical SPR miniaturization. Therefore, the following study was conducted.
For the anvil, a simple flat shape or dome shape has been used for a helical SPR anvil design, but the flat and dome type anvil have advantages and disadvantages. So a new shape of anvil that can improve the riveting strength is required.
To reduce the weight of vehicles, it is necessary to miniaturize the helical rivet size that can join soundly.
In this thesis, the new combined shape anvil and helical SPR miniaturization design have been suggested and simulated by using commercial FEM code DEFORM-3D. The simulated results were compared with experimental ones and conclude as follow;

Considering the advantages of each dome shape and flat shape, it is desirable to design the Helical SPR anvil in a combined shape of flat and dome.

1. Considering the elastic spring back between the anvil and the sheet after joint, the anvil should have draft angle and it is recommended to apply 7º.

2. When using flat and dome combined shaped anvil, the shearing separation load of CP1470 and Al6061 sheet is increased by 33% against dome type, while 8% against flat type. Also, the cross tension separation load is improved by 12.5% against dome type, while 20% against flat type.

3. Helical rivet aims to join with CP1470 sheet. So helical rivet should be used higher strength materials than upper sheet. The hardness of rivet should be Hv550.

4. Helical rivet size 6mm, rib thickness 2mm, center diameter 2.5mm is minimum so or more is recommended.