SOLID STATE (FRICTION WELDING):INFLUENCES of IN-SITU PRE-HEAT

Friction welding dates back to the early 1950’s when companies commercialize rotary fiction welding for joining a wide range of metallic products. Friction welding is a solid-state welding process that generates heat through mechanical friction between workpieces in relative motion to one another. The mechanism for such heating is known to transition from sliding friction to one based on continual plastic deformation.  The transition between these heating regimes is characterized by a short duration spike in the shear loads necessary to maintain the desired relative motion. Because no melting occurs, the benefits associated with friction welding are significant and have been well documented. 

These instantaneous high shear loads govern designs for current welding system solutions.  This work investigates the use of in-situ heating for mitigating such shear loads.  A hybrid system has been developed that incorporates in-situ pre-heat and conventional friction welding.  Studies have been conducted to define relationships between processing conditions and resulting shear load variations for some representative material systems (Titanium, steels, Al-alloys).  

An evaluation was performed on the mechanical properties and metallurgical changes in the microstructure. The transverse sectional view of the welds in the as-welded condition along with micro structural details in the center and fusion boundary region of welds are presented. 

The results were compared to samples produced by a conventional friction welding process (no pre-heat).  The metallographic changes and mechanical properties were similar in comparison.  The pre-heating had a significant impact on the process parameters and resulting forces.