a method and apparatus for welding thermoplastic materials with a stir welding system using a rotating element pin or element with a geometry to induce frictional energy from the rotating element . a floating constraining surface that has a motion independent of the rotation the pin is used to constrain ejection of material from the zone where the weld is being formed . molten material is retained in the weld region , avoiding weakness and voids at the weld joint . optionally a system for introducing thermal energy into the weld zone in addition to the frictional energy is used . the system for introducing the thermal energy may be in association with the constraining shoe and / or the rotating tool , or a system independent of these .