a new method of friction welding , particularly suitable for manufacturing blisks and blums for gas turbine engine rotors , in which the disc or drum rotor is angularly reciprocated while the airfoil blades are pressed radially against the rotor circumference . a machine for carrying out the method has a workpiece holder and a counterbalancing member mounted for angular reciprocation and coupled together by torque transfer means to constitute a resonant system . in operation the machine is driven at or near its natural frequency of oscillation . the natural frequency can be tuned by adjusting the stiffness of the torque transfer means . the machine also includes a drive mechanism .