Methods of and apparatus for forming hollow metal articles

A method executed by a computer system as part of a computer-implemented program for optimizing pressure-time history for a process for forming a workpiece from an initial hollow metal preform into a hollow metal article within a die by subjecting the workpiece to net internal fluid pressure such that the workpiece expands into contact with an article-shape-defining wall of the die, while avoiding failure of the workpiece, comprising the steps of

• (a) selecting a first set of process parameters including temperature and preform material properties and dimensions;
• (b) determining, from said first set of parameters, at least one first failure criterion limiting pressure-time conditions to which the workpiece may be subjected without failure;
• (c) iteratively performing finite element analyses on the workpiece, based on the first set of parameters and the determined first failure criterion, at each of a plurality of different values of pressure-time conditions (P, t), to determine first pressure-time boundary conditions (Pb1, tb1) for the process;
• (d) determining a second set of process parameters corresponding to said first set of process parameters but modified by deformation imposed on the workpiece by subjection to said first pressure-time boundary conditions (Pb1, tb1);
• and
• (e) repeating steps (b) and (c) to determine, from said second set of process parameters, at least one second failure criterion and to determine, by iteratively performed finite element analyses based on the second set of parameters and the determined second failure criterion, second pressure-time boundary conditions (Pb2, tb2) for the process.

A process for forming a hollow metal article of defined shape and lateral dimensions, comprising the steps of

• (a) disposing a hollow metal preform having a closed end in a die cavity laterally enclosed by a die wall defining said shape and lateral dimensions, the preform closed end being positioned in facing relation to one end of the cavity and at least a portion of the preform being initially spaced inwardly from the die wall, and
• (b) subjecting the preform to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said defined shape and lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity,
• wherein the improvement comprises:
• (c) performing step (b) by subjecting the preform to a succession of sets of pressure-time conditions (p, t), respectively having successively decreasing values of net internal fluid pressure, said succession of sets of pressure-time conditions being within predetermined boundary conditions for the process.

A process for forming a hollow metal article of defined shape and lateral dimensions, comprising

• (a) disposing a hollow metal preform having a closed end in a die cavity laterally enclosed by a die wall defining said shape and lateral dimensions, with a punch located at one end of the cavity and translatable into the cavity, the preform closed end being positioned in proximate facing relation to the punch and at least a portion of the preform being initially spaced inwardly from the die wall;
• (b) under control of a computer, subjecting the preform to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said defined shape and lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity;
• and
• (c) translating the punch into the cavity to engage and displace the closed end of the preform in a direction opposite to the direction of force exerted by fluid pressure thereon, deforming the closed end of the preform;
• wherein the improvement comprises:
• (d) determining, for said preform, a failure criterion limiting pressure-time conditions to which the workpiece may be subjected without failure;
• (e) by iteratively performing finite element analyses on the preform, developing a pressure-time history for the preform comprising an initial value of net internal fluid pressure, an initial time interval during which said initial value is to be applied to the preform, a plurality of sequential time intervals following said initial interval, and a corresponding plurality of successively lower values of net internal fluid pressure to be respectively applied to the preform during said plurality of sequential time intervals, wherein the values of internal fluid pressure and the durations of the time intervals are such that the failure criterion is never exceeded throughout said pressure-time history;
• (f) supplying, to said computer, said pressure-time history;
• and
• (g) performing step (b) by subjecting the preform to said pressure-time history.

Apparatus for forming a hollow metal article of defined shape and lateral dimensions from a hollow metal preform having a closed end, comprising

• (a) die structure providing a die cavity for receiving the preform therein with at least a portion of the preform being initially spaced inwardly from the die wall and the preform closed end facing one end of the cavity, said cavity having a die wall defining said shape and lateral dimensions;
• (b) a punch located at one end of the cavity and translatable into the cavity such that the closed end of a preform received within the cavity is positioned in proximate facing relation to the punch;
• (c) a fluid pressure supply for subjecting a preform within the cavity to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said defined shape and lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity;
• and
• (d) a computer for controlling at least one of supply of fluid pressure and translation of the punch;
• wherein the improvement comprises:
• (e) at least one sensor positioned at a location in the die wall to sense contact of the preform with the die wall at that location, the sensor supplying information representative of the sensed contact to the computer, and computer control of the process being responsive to the supplied contact information.

A process for forming a hollow metal article of defined shape and lateral dimensions, comprising

• (a) disposing a hollow metal preform having opposed ends, one of which is closed, in a die cavity laterally enclosed by a die wall defining said shape and lateral dimensions, the cavity having an axis and a closed inner end faced by the preform closed end, at least a portion of the preform being initially spaced inwardly from the die wall, and a ram translatable axially of the cavity toward the closed inner end and arranged to exert force on the other end of the preform in a direction toward the closed end of the cavity;
• (b) subjecting the preform to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said defined shape and lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity;
• and
• (c) translating the ram to displace said other end of the preform toward the closed end of the die cavity.

Apparatus for forming a hollow metal article of defined shape and lateral dimensions from a hollow metal preform having opposed ends of which one is closed, comprising

• (a) die structure providing a die cavity having an axis and a die wall defining said shape and lateral dimensions, for receiving the preform therein with at least a portion of the preform being initially spaced inwardly from the die wall and the preform closed end facing one end of the cavity, said one end of the cavity being closed;
• (b) a ram translatable axially of the cavity toward the closed inner end and disposed to exert force on the other end of the preform in a direction toward the closed inner end of the cavity;
• and
• (c) a fluid pressure supply for subjecting a preform within the cavity to internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said defined shape and lateral dimensions to the preform, said fluid pressure exerting force, on said closed preform end, directed toward said one end of the cavity.

A process for forming a hollow metal article of defined shape and defined final lateral dimensions, comprising

• (a) disposing a hollow metal preform having a closed end in a first die cavity laterally enclosed by a die wall defining a first shape and first lateral dimensions, smaller than said defined final lateral dimensions, with a punch located at one end of the cavity and translatable into the cavity, the preform closed end being positioned in proximate facing relation to the punch and at least a portion of the preform being initially spaced inwardly from the die wall;
• (b) subjecting the preform to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said first shape and first lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity;
• and
• (c) translating the punch into the cavity to engage and displace the closed end of the preform in a direction opposite to the direction of force exerted by fluid pressure thereon, deforming the closed end of the preform, thereby to form said preform into a workpiece having said first shape and first lateral dimensions and having a closed end;
• wherein the improvement comprises:
• (d) thereafter placing the workpiece in a second die cavity defining said final shape and final lateral dimensions and subjecting the workpiece therein to net internal fluid pressure to expand the workpiece to said final shape and final lateral dimensions.

A process for forming a hollow metal article of defined shape and defined final lateral dimensions, comprising

• (a) disposing a hollow metal preform having a closed end in a first die cavity laterally enclosed by a die wall defining a first shape and first lateral dimensions, smaller than said defined final lateral dimensions, with a punch located at one end of the cavity and translatable into the cavity, the preform closed end being positioned in proximate facing relation to the punch and at least a portion of the preform being initially spaced inwardly from the die wall;
• (b) subjecting the preform to net internal fluid pressure to expand the preform outwardly into substantially full contact with the die wall, thereby to impart said first shape and first lateral dimensions to the preform, said fluid pressure exerting force, on said closed end, directed toward said one end of the cavity;
• and
• (c) translating the punch into the cavity to engage and displace the closed end of the preform in a direction opposite to the direction of force exerted by fluid pressure thereon, deforming the closed end of the preform, thereby to form said preform into a workpiece having said first shape and first lateral dimensions and having a closed end;
• wherein the improvement comprises:
• (d) said workpiece being made of a precipitation-hardening alloy.