STRETCH-FORMING MACHINE AND METHOD

Abstract

A stretch-forming machine of the type wherein a pair of opposed curving jaw assemblies grip opposite end edge portions of a metal sheet for initially stretching the metal sheet into a yield state and forming the metal sheet into a predetermined curved configuration. Each jaw assembly includes a jaw having an array of adjacent grippers or groups of grippers moveable relative to each other to define a part of the curve of the jaw and adapted to extend along one side edge of the metal sheet from adjacent a first corner to adjacent a second corner of the sheet, a moveable yoke connected to the jaw, a pivot connecting the yoke to a beam way, and at least one actuator connected to the yoke for pivoting the jaw about the pivot to urge the grippers at opposing ends of the gripper array away from the pivot while the grippers adjacent a centerline of the gripper array remain approximately stationary. The pivot and the actuator cooperate to stretch the outer corners of the metal sheet while substantially minimizing elongation along the centerline of the metal sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

FIG. 1 is a simplified top plan view of a curving jaw stretch-forming machine of the type on which the invention of the application is utilized;

FIG. 2 is a side elevation of the stretch-forming machine shown in FIG. 1;

FIG. 3 is a simplified fragmentary end view of one side of a curving jaw showing the range of up and down motion of the array of grippers carried on the jaw;

FIG. 4 is a side elevation of a jaw of the stretch-forming machine;

FIG. 5 is an enlarged, partial side elevation of the jaw shown in FIG. 4;

FIG. 6 is a view similar to FIG. 5 showing the optimum jaw location and pivot motion of the jaw shown in FIG. 5;

FIG. 7 is a side elevation view showing the location of the jaw at normal stretch;

FIG. 8 is a pivot motion and side elevation view showing the location of the jaw at optimum edge areas stretch;

FIG. 9 is a partial sequential perspective view, with parts broken away and exaggerated edge wrinkling, showing movement of the outboard jaws applying additional stretch to the edge portions;

FIG. 10 is a schematic of a stretch-formed part illustrating edge stretch-forming compensation; and

FIG. 11 is a perspective view of an aircraft showing an exemplary stretch-formed part location.

Claims

1. In a stretch-forming machine of the type wherein a pair of opposed curving jaw assemblies grip opposite end edge portions of a metal sheet for initially stretching the metal sheet into a yield state, and forming the metal sheet into a predetermined curved configuration, the improvement wherein each jaw assembly comprises: a) a jaw comprising an array of adjacent grippers moveable relative to each other to define a part of the curve of the jaw, and adapted to extend along one side edge of the metal sheet from adjacent a first corner to adjacent a second corner of the sheet;b) a moveable yoke connected to the jaw;c) a pivot connecting the yoke to a beam way; andd) at least one actuator connected to the yoke for pivoting the jaw about the pivot to urge the grippers at opposing ends of the gripper array away from the pivot while the grippers adjacent a centerline of the gripper array remain approximately stationary, thereby further stretching outer corners of the metal sheet while substantially minimizing elongation along the centerline of the metal sheet.

2. The stretch-forming machine according to claim 1, further including a moveable die upon which the metal sheet is formed into a predetermined curved configuration.

3. The stretch-forming machine according to claim 2, further including a bulldozer assembly moveable relative to the die for forming the metal sheet.

4. The stretch-forming machine according to claim 1, further including respective hydraulic cylinders adapted to move the grippers or groups of the grippers relative to each other to form the opposite ends of the metal sheet into predetermined curved configurations.

5. The stretch-forming machine according to claim 1, further including at least one respective hydraulic cylinder carried by each yoke and adapted to urge each yoke along the beam way.

6. The stretch-forming machine according to claim 1, further including at least one respective hydraulic cylinder carried by each yoke and adapted to move each jaw relative to each respective yoke.

7. A stretch-forming machine comprising a pair of opposed curving jaw assemblies for gripping opposite end edge portions of a metal sheet, each jaw assembly including: a) a jaw comprising an array of adjacent grippers moveable relative to each other to define a curve in which a center gripper is positioned at an apex of the array intermediate two opposed end grippers of the array;b) a moveable yoke connected to the jaw;c) a pivot connecting the yoke to a beam way, the axis of the pivot being defined as the intersection of: i) a line tangent to the curve of the array at a point located within the center gripper; andii) a plane defined by the center gripper and the two end grippers; andd) at least one actuator connected to the yoke for pivoting the jaw about the pivot, thereby further stretching outer corners of the metal sheet while substantially minimizing elongation along a centerline of the metal sheet.

8. The stretch-forming machine according to claim 7, further including a moveable die upon which the metal sheet is formed into a predetermined curved configuration.

9. The stretch-forming machine according to claim 8, further including a bulldozer assembly moveable relative to the die for forming the metal sheet.

10. The stretch-forming machine according to claim 7, further including respective hydraulic cylinders carried adapted to move the grippers or groups of the grippers relative to each other in order to form the opposite ends of the metal sheet into predetermined curved configurations.

11. The stretch-forming machine according to claim 7, further including at least one respective hydraulic cylinder carried by each yoke and adapted to urge each yoke along the beam way.

12. The stretch-forming machine according to claim 7, further including at least one respective hydraulic cylinder carried by each yoke and adapted to move each jaw relative to each respective yoke.

13. The method of stretch-forming a metal sheet comprising the steps of: a) providing a stretch-forming machine of the type wherein a pair of opposed curving jaw assemblies grip opposite end edge portions of a metal sheet to be formed into a predetermined curved configuration, each jaw assembly including a jaw comprising an array of adjacent grippers moveable relative to each other to define a part of the curve of the jaw and adapted to extend along one side edge of the metal sheet from adjacent a first corner to adjacent a second corner of the sheet, a moveable yoke connected to the jaw, a pivot connecting the yoke to a beam way, and at least one actuator connected to the yoke for pivoting the jaw about the pivot;b) stretching the metal sheet to a yield state by retracting the jaws rearwardly away from each other;c) forming the metal sheet into a desired curvature over a die; andd) pivoting the jaws about the pivots using the at least one actuator to urge the grippers at opposing ends of the gripper array away from the pivot while the grippers adjacent a centerline of the gripper array remain approximately stationary, thereby further stretching outer edges of the metal sheet while substantially minimizing elongation along the centerline of the metal sheet.

14. The method of stretch-forming a metal sheet according to claim 13, further including the step of forming the metal sheet over a bulldozer assembly, the bulldozer assembly being moveable relative to the die.

15. The method of stretch-forming a metal sheet according to claim 13, further including the step of utilizing computer-controlled servo-feedback technology to define and control the shape of the metal sheet to be formed.

16. The method of stretch-forming a metal sheet according to claim 13, wherein the metal sheet is stretched to a yield state by urging the yokes away from each other along the beam way by at least one respective hydraulic cylinder carried by each yoke.

17. The method of stretch-forming a metal sheet according to claim 13, wherein the metal sheet is stretched to a yield state by retracting the jaws within their respective yokes by at least one respective hydraulic cylinder carried by each yoke.

18. The method of stretch-forming a metal sheet according to claim 13, further including the step of forming the opposite ends of the metal sheet into predetermined curved configurations using respective hydraulic cylinders adapted to move the grippers or groups of grippers relative to each other.