Aluminum Company of America

James M Story

Andrew B Trageser

David A Dornfeld

George L Smith, Jr

Edwin H Spuhler

Matthew P Sklad

A method of forming a metal sheet workpiece into a three-dimensional object by subjecting the workpiece to a stretch forming process along at least two strain paths having slopes of opposite sign. The strain paths define a point on a forming limit curve that is shifted substantially from a forming limit curve generated by linear strain paths. The shift in forming limit curves allows a substantially higher strain state to be reached in the workpiece in comparison to a strain state achievable using linear strain paths to attain the same strain state in flowing metal into a die cavity. The three-dimensional object is formed by flowing workpiece metal into a die cavity in a manner that controls the position and magnitude of forces restraining the periphery of the workpiece such that metal flow into the cavity takes place along the strain paths having the slopes of opposite sign.

Strain path control in forming processes

A method of superplastically forming a part from a blank of material. The blank is placed between opposed die structures and heated to a superplastic forming temperature. Positive fluid pressure is supplied at an increasing rate against a front surface of a blank to stretch the same into a cavity of one of the dies to begin formation of the part. A positive fluid pressure is also applied against the back surface of the blank, and acoustical energy emitted by the material of blank resulting from the occurrence of cavitation in the material is sensed. The sensing of acoustical energy is employed to control one or more of the above parameters until the formation of the cavities substantially reduces or ceases altogether.

Control of cavitation in superplastic forming through use of acoustic

A method of forming an object having a relatively deep cavity from a superplastic metallic blank wherein a preform having a bottom portion and sides sloping upwardly and outwardly therefrom is first superplastically formed in a female mold. The preform is then attached to a male mold with the bottom portion of the preform in a snug fit with a top portion of the male mold which has outside dimensions equal to the cavity in the object and thereafter the preform is superplastically forced against the male mold to form the desired object.

Two-step superplastic forming method

A method of superplastically forming a part over period of a forming cycle in which a blank of the material is provided and heated to within a certain range of temperatures. An analytical model is provided that determines locations of the blank that will deform most rapidly when forming pressure is applied. As the forming pressure is applied, the displacements are monitored at such locations while the blank is being deformed. The strain rate is then calculated and feedback control is provided to affect the strain rate at such locations that will reduce the tendency of the blank or part to cavitate.

Strain rate control of superplastic forming

A blankholder having a central opening for applying pressure against the flange of a blank being drawn through a die in a draw press. The blankholder is divided into individual segments defined by its inner and outer peripheries, at least one continuous divisional line intermediate the inner and outer peripheries, and radii extending outwardly from the central axis. Each individual segment is provided with a different power source so that each segment can provide a force to the blank flange independent of the force being applied by any other segment.

Blankholder for a draw press

A method of removing or ejecting a part from a first die after the part has been superplastically formed in a cavity of the die at an elevated temperature such that the part sticks to the surfaces of the die. The method includes the steps of forming a flange of the part between opposed die surfaces and providing movable plate within the die cavity and a ring on the opposed surface of the first die that engages the flange and the part in the cavity in a uniform manner. The movable plate and ring are then translated away from the die surfaces to uniformly move the part from the first die after the dies are separated.

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Pittsburgh, PA, United States of America

James M Story