An electromagnetically actuated friction welder produces orbital motion at interfaces between parts (usually of thermoplastic material) to bond the parts by fusion generated by friction. This welder can also be operated alternatively to produce reciprocating vibratory forces thereby providing flexibility as to the selection of an orbital or reciprocating mode, depending upon the joint to be welded. The velocity of motion is controllable preferably around the resonant frequency of the driven structure by adjusting the frequency of the AC power which operates the electromagnetic drive motor of the welder. A plate which carries one of the parts to be welded and which is driven is flexurally mounted for movement in an orbital plane or planes containing the interfaces without substantial tilting by an array of stiff members, such as rods, located around the drive motor, attached to the plate at one end and to a tubular structure at the opposite ends thereof. The tubular structure is desirably attached to a massive support carried by the frame of the welder.