Effects of friction welding conditions on initial joining phenomena

Summary

This paper describes an investigation into the effects of friction welding conditions on the initial joining phenomena and joining mechanism in the first and second phases of friction welding on a continuous drive type friction welding machine using mild steel specimens. The results obtained may be summarised as follows:

1. At a friction pressure as low as around 35 MPa, the initial joining location shifts from the axial centre of the specimen towards its outside with an increasing friction pressure. If the friction pressure exceeds this value, however, it remains virtually constant.

2. The effect of the friction pressure on the time taken for initial joining to start is pronounced when the friction pressure is less than around 10 MPa. The time taken for joining to start then increases with a decreasing friction pressure. If the friction pressure exceeds this value, however, the time is little changed.

3. The initial joining location virtually coincides with the location where maximum traces are found on the faying surface and with the location where the maximum faying surface temperature is attained.

4. The torque values in the first and second phases of friction welding are virtually proportional to the faying surface contact area.

5. The mechanism responsible for shifting of the initial joining location due to any difference in the friction pressure not only stems from heat conduction, but is also due to temperature rise induced shifting of the friction location and plastic deformation of the faying surface.