Methods of and apparatus for forming hollow metal articles

• US 20050252263A1
• Filed: 05/09/2005
• Published: 11/17/2005
• Est. Priority Date: 05/14/2004
• Status: Active Grant

• Current Assignee: Montebello Packaging, a division of Great Pacific Enterprises, L.P.
• Original Assignee: Novelis Incorporated (Hindalco Industries Limited)
• Inventors: Shi, Yihai, MacEwen, Stuart R., Mallory, Robert William, Moulton, James D., Hamstra, Peter
• Granted Patent: US 7,191,032 B2
• Time in Patent Office: Days
• US Class Current: 72/55
• CPC Class Codes: B21D 26/033 Deforming tubular bodies corrugating tubes by applying fluid pressure B21D15/03, B21D15/10
• CPC Class Codes: B21D 26/041 Means for controlling fluid parameters, e.g. pressure or temperature
• CPC Class Codes: B21D 26/047 Mould construction B21D26/037 - B21D26/045 take precedence
• CPC Class Codes: B21D 26/049 Deforming bodies having a closed end
• CPC Class Codes: B21D 51/26 cans or tins; Closing same in a permanent manner making outlet arrangements B21D51/38; welding or soldering B23K

Abstract

In hydroforming of hollow metal articles in a die, such as pressure-ram-forming procedures, a method of decreasing cycle time of the forming process, while ensuring acceptable product properties and avoiding failures, by modeling the process using finite element analysis to establish a pressure-time history that optimizes the forming operation and applies failure limits to selected variables such as minimum wall thickness or maximum strain rate, and transferring this pressure-time history to a computer controlling the forming process. Thermocouple and/or continuity sensors are incorporated into the die wall and connected to the computer so as to provide active feedback from the die to the control of the process.

Claims

1. 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 set of process parameters including temperature and preform material properties and dimensions;

(b) determining, from said set of parameters, at least one failure criterion limiting pressure-time conditions to which the workpiece may be subjected without failure; and

(c) iteratively performing finite element analyses on the workpiece, based on the selected set of parameters and the determined failure criterion, at each of a plurality of different values of pressure-time conditions (P, t), to determine pressure-time boundary conditions (P_b, t_b) for the process,

wherein each value of pressure-time conditions comprises a value of net internal fluid pressure (P) and a time interval (t) over which the last-mentioned value of net internal fluid pressure is applied to the workpiece.

2. A method according to claim 1, wherein said failure criterion is selected from the group consisting of minimum wall thickness, strain, and strain rate.

3. A method according to claim 1, wherein step (c) includes selecting a time interval and iteratively performing said finite element analyses on the workpiece at each of a plurality of different pressure values, to determine, as a boundary condition, a value of maximum net internal fluid pressure to which the workpiece can be subjected for said time interval without failure.

10. 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) supplying, to said computer, pressure-time boundary conditions determined for said process by the method of claim 1, and

(e) performing step (b) by subjecting the preform to pressure-time conditions corresponding to the pressure-time boundary conditions determined by the method of claim 1.

11. A process according to claim 10, further including the steps of sensing contact of the preform with a preselected location in the die wall and supplying information representative of the sensed contact to the computer, and wherein computer control of the process is responsive to the supplied contact information.

12. A process according to claim 10, further including the steps of sensing temperature conditions to which the preform is subjected during performance of the process and supplying information representative of the sensed temperature conditions to the computer, and wherein computer control of the process is responsive to the supplied temperature information.

13. A process according to claim 10, wherein said hollow metal article is a metal container.

24. 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 inner end of the cavity;

(b) subjecting the preform to net internal fluid pressure under control of a computer 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;

(c) translating the ram to displace said other end of the preform toward the closed end of the die cavity;

(d) supplying, to said computer, pressure-time boundary conditions determined for said process by the method of claim 1, and

(e) performing step (b) by subjecting the preform to pressure-time conditions corresponding to the pressure-time boundary conditions determined by the method of claim 1.

4. 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 (P_b1, t_b1) 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 (P_b1, t_b1); 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 (P_b2, t_b2) for the process.

5. A method according to claim 4, including repeating steps (d) and (e) to determine a plurality n of pressure-time boundary conditions wherein 3<

n; and

wherein, for each integer i such that 3<

i<

n, the ith set of process parameters corresponds to the (i-1)th set of process parameters but modified by deformation imposed on the workpiece by subjection to the (i-1)th pressure-time boundary conditions (P_bi-1, t_bi-1), the ith failure criterion is determined from the ith set of process parameters, and the ith pressure-time boundary conditions (P_bi, t_bi) are determined by iteratively performed finite element analyses based on the ith set of parameters and the determined ith failure criterion, thereby to determine n successive sets of pressure-time boundary conditions ({P_b1, t_b1}, . . . {P_bn, t_bn}) collectively constituting an optimized pressure-time history for said process.

6. A method according to claim 5, wherein at least one set of pressure-time boundary conditions is determined by iteratively performed finite element analyses as aforesaid at each of a plurality of values of pressure (P) for a preselected value of time (t).

7. A method according to claim 5, wherein at least one set of pressure-time boundary conditions is determined by iteratively performed finite element analyses as aforesaid at each of a plurality of values of time (t) for a preselected value of pressure (P).

8. 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) 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,

wherein the improvement comprises:

(c) supplying, to said computer, an optimized pressure-time history for said process determined by the method of claim 5, and

(d) performing step (b) by subjecting the preform to n successive sets of pressure-time conditions respectively corresponding to n successive sets of pressure-time boundary conditions ({p_b1, t_b1}, . . . {P_bn, t_bn}) constituting said optimized pressure-time history determined by the method of claim 5.

9. 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.

14. 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.

15. A process according to claim 14, wherein said failure criterion is a limiting value of strain rate.

16. 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.

17. Apparatus as defined in claim 16, wherein said sensor comprises an electrical conductor exposed at the die wall at said location, said conductor being connected to said computer such that when the preform comes into contact with the die wall, an electrical circuit is closed, contact information is supplied to said computer.

18. Apparatus as defined in claim 16, further including at least one sensor for sensing temperature conditions to which the preform is subjected during performance of the process and supplying information representative of the sensed temperature conditions to the computer, and wherein computer control of the process is responsive to the supplied temperature information.

19. 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.

20. A process according to claim 19, wherein the die wall comprises a fixed portion adjacent said closed end of the cavity and a movable portion slidable axially of the die cavity and arranged for movement with the ram toward the closed end of the die cavity from an initial position at which said fixed and movable portions are spaced apart to a limiting position at which said fixed and movable die wall portions are contiguous, the step of translating the ram causing the movable portion of the die wall to move therewith from said initial position to said limiting position.

21. A process according to claim 19, wherein the closed end of the die cavity is closed by a punch translatable into the cavity.

22. A process according to claim 21, wherein the preform closed end is positioned in proximate facing relation to the punch, and including the step of 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.

23. A process according to claim 20, wherein translation of the ram is under control of a computer, and further including the steps of sensing contact of the preform with a preselected location in the die wall and supplying information representative of the sensed contact to the computer, computer control of the ram translation being responsive to the supplied contact information.

25. 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.

26. Apparatus as defined in claim 25, wherein the die wall comprises a fixed portion adjacent said closed end of the cavity and a movable portion slidable axially of the die cavity and arranged for movement with the ram toward the closed end of the die cavity from an initial position at which said fixed and movable portions are spaced apart to a limiting position at which said fixed and movable die wall portions are contiguous, the step of translating the ram causing the movable portion of the die wall to move therewith from said initial position to said limiting position.

27. Apparatus as defined in claim 26 wherein said die structure includes an enlarged indentation, for slidably receiving said movable portion of the die wall, spaced from the closed end of the cavity by the fixed die wall portion.

28. Apparatus as defined in claim 26, further including a punch closing said closed end of the die cavity.

29. Apparatus as defined in claim 28, wherein the punch is translatable 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.

30. Apparatus as defined in claim 26, further including a computer for controlling movement of the ram, and a sensor for sensing contact of the preform with a preselected location in the die wall and supplying information representative of the sensed contact to the computer.

31. 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.

32. A process according to claim 31, wherein said second die cavity is formed in a static die.

33. A process according to claim 31, wherein said second die cavity is provided with a punch located at one end of the cavity and translatable into the cavity, and wherein step (d) further comprises positioning the workpiece closed end in proximate facing relation to the last-mentioned punch and translating the punch into the cavity to engage and displace the closed end of the workpiece in a direction opposite to the direction of force exerted by fluid pressure thereon, thereby to form said workpiece into an article having said final shape and final lateral dimensions.

34. 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.

35. A process according to claim 34, wherein said alloy is an Al—

Mg—

Si alloy.