Effect of Tool Geometry on Strength of Friction Stir Spot Welded PTFE Sheets

In the present study, friction stir spot welding of PTFE sheets is investigated. Due to the special propertiesof this polymer, its welding is a challenging task. According to the primary tests, the friction stir spot weldingof PTFE is possible, however, it requires more dwell time, i.e. a dwell time of at least ۶ min is required toachieve a joint with an acceptable strength. All specimens were welded with a tool rotational speed of ۱۲۵۰rpm, and a dwell time of ۹ min. Two tool geometries including a conventional tool with a cylindrical pinand a pinless tool were investigated. The spot-welded samples with the pinless tool have no keyhole. Eachtool was used to spot weld two different samples with different tool shoulder plunge depths of ۰.۱ and ۰.۲mm. The tensile-shear test was used to evaluate the tensile strength of the welded samples. The resultssuggest that friction stir welding is a joining method that could be used to join PTFE sheets successfully.Although the welding time is an issue that may hinder the application of this method to join PTFE sheets.The pinless tool produces joints with higher strength. Increasing the plunge depth also increases the jointstrength. The highest strength that was obtained by spot-welded samples is ۳۷۳.۷ N which was obtained bythe sample that was welded with the pinless tool and a plunge depth of ۰.۲ mm.

Keywords:

Friction stir spot welding , Keyhole , Tensile-shear test , PTFE , Pinless tool