US3564895A

US3564895A - Drawing apparatus and method

Info

Publication number: US3564895A
Application number: US768826A
Authority: US
Inventors: Gunther E Pfanner; George A Bohmann
Original assignee: Fairchild Hiller Corp
Current assignee: Fairchild Hiller Corp
Priority date: 1968-10-18
Filing date: 1968-10-18
Publication date: 1971-02-23
Anticipated expiration: 1988-02-23

Abstract

APPARATUS FOR DRAWING ARTICLE FROM BLANKS WHICH CONTRAIN NO EXCESS MATERIAL, COMPRISES A PUNCH, DRAW RING, AND INNER AND OUTER PRESSURE PADS. THE OUTER PRESSURE PAD HOLDS THE BLANK DURING THE INITIAL STAGE OF THE DRAWING PROCESS. THE INNER PRESSURE PAD IS APPLIED TO THE ARTICLE AFTER SUCH INITIAL STAGE AND INCLUDES A PRESSURE SURFACE HAVING A SHAPE MATING WITH THE DRAW RADIUS OF THE ARTICLE FORMED DURING THE PROCESS.

Description

Feb. 23, 1971 PFANNER L 3,564,895

DRAWING APPARATUS AND METHOD Filed Oct. 18, 1968 INVENTORS GUNTHER E. PFANNER GEORGE A. BOHMANN 7L 5 'AT TORNEYS United States Patent 3,564,895 DRAWING APPARATUS AND METHOD Gunther E. Pfanner, Huntington, and George A. Bohmann, New Hyde Park, N.Y., assignors to Fairchild Hiller Corporation, Farmingdale, N.Y., a corporation of Maryland Filed Oct. 18, 1968, Ser. No. 768,826 Int. Cl. B21d 24/08 US. Cl. 72-351 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for drawing article from blanks which contain no excess material, comprises a punch, draw ring, and inner and outer pressure pads. The outer pressure pad holds the blank during the initial stage of the drawing process. The inner pressure pad is applied to the article after such initial stage and includes a pressure surface having a shape mating with the draw radius of the article formed during the process.

This invention relates to apparatus for hot-drawing materials where it is highly desirable to employ a minimum blank size.

There is considerable evidence indicating that titanium would be a highly desirable material from which to fabricate helmets for military purposes. From a practical viewpoint with regard to mass production considerations, a hot-forming process is preferable to a cold-forming one. Consequently, it has been proposed to employ a hotdrawing apparatus for the purpose of manufacturing titanium helmets. However, prior art hot-drawing techniques unavoidably produce a substantial amount of waste material. This is not a serious matter when working with relatively inexpensive metals such as steel and aluminum, but in the case of a more expensive metal such as titanium (or beryllium) this question of waste is important since, in the case of helmets, the waste which must be ultimately trimmed to form the finished article may comprise as much as twenty percent of the entire blank.

Accordingly, the main object of the present invention is to provide apparatus which can be used for drawing articles, where substantially the entire blank is formed to the desired shape and there is virtually no leftover waste material.

Briefly, in accordance with the invention, apparatus for drawing articles includes a heated punch, draw ring, and inner and outer pressure pads for retaining a blank during the process. The outer pressure pad is applied to the blank to be drawn during the initial phase of the process and the inner pressure pad is applied during the final stage. The surface of the inner pad which contacts the blank is shaped to mate with the draw radius of the article formed during the process whereby it is unnecessary to include a special flange or other excess portion of the blank to hold the blank during the process.

The invention is described in further detail below with reference to the attached drawings, wherein:

FIG. 1 is a side sectional view of a preferred embodiment of the invention; and

FIGS. 2A to 2D are diagrammatic illustrations showing the different steps in a drawing process according to the invention.

The apparatus according to a preferred embodiment of the invention is shown in FIG. 1 prior to drawing an elliptical blank to form, for example, a helmet. The apparatus includes a heated cylindrical punch 12 the dome of which is shaped to correspond to the desired shape of the helmet and a draw ring 14, which is also heated, extending downwardly from a fixed support member 16.

3,564,895 Patented Feb. 23, 1971 Punch 12 is hydraulically operated by standard means (not shown) to draw the blank 10 into the draw ring 14.

Blank 10 is restrained during the process by an annular outer pressure pad 18 and an annular inner pressure pad 20 positioned between the outer pad 18 and punch 12. The inner pressure pad 20 is made flexible by radial slots 21 suitably milled through its bottom and inner surfaces. The means (not shown) are provided to heat the inner and outer pressure pads.

The outer pressure pad 18 rests on a circular base plate 22 which is coupled by actuator rods 24 to respective hydraulic cylinders 26 so that the pad 18 can be urged against the blank 10 and bottom portion of draw ring 14. Outer pad 18 may be movable within a cylindrical guide 27. The inner pressure pad 20 is mounted on a plurality (e.g. eight) of base segments 29 each of which is mounted on top of the interior end of a respective lever 30. Each lever 30 is pinned at 32 to a pair of lugs 34 extending upwardly from the base plate 22. The outer ends of the levers 30 are connected to respective actuator rods 36 which are controlled by hydraulic cylinders 38 supported on separate L-shaped brackets 40 secured to the the bottom of base plate 22. This arrangement removes the cylinders 38 from the heated portions of the apparatus. Actuation of the flexible inner pressure pad 20 by independent hydraulic systems enables variable control of the peripheral restraining force applied to the blank. This assures an even draw and, if desired, can assist in shaping the finished article by changing the rate of feeding the blank. The continuous slotted pad 20 (as opposed to a segmented one) produces an even graduation in the forces applied by areas of pad 20 in which adjacent base segments 29 are applying different forces.

The inner lip 42 of the draw ring 14 is formed to a radius of curvature R which defines the draw radius of the article formed during the process. The corresponding upper surface 44 of inner pressure pad 20, which is the surface which contacts blank 10, is shaped to a mating radius of curvature R which is slightly greater than R to account for the presence of blank 10 between the pad 20 and draw ring 14. This is an important feature of the invention, as will become more apparent below during the description of the drawing process.

Punch 12, draw ring 14 and

pressure pads

18 and 20 may all be heated by means of conventional cartridge type heaters embedded therein. The temperature of each of the individual components may be controlled separately and automatically by means of thermocouples suitably embedded in the respective parts. The means and criteria for controlling the temperature of these parts will be known by those skilled in the art. Preferably, the punch temperature will be maintained several hundred degrees lower than the temperature of the draw ring to aid in reducing thinout.

The drawing sequence as applied by the apparatus of FIG. 1 is illustrated in FIGS. 2A to 2D. In FIG. 2A, the blank 10 is placed in position between the punch 12 and draw ring 14. The outer pressure pad 18 is actuated to hold the blank 10 against draw ring 14 (FIG. 2B), and then punch 12 is actuated to initiate a partial draw of the blank 10 into the draw ring 14.

When the blank 10 has been drawn sufiiciently to form the draw radius R (FIG. 2C) the segments of the inner pressure pads are then actuated by the hydraulic cylinders 38 thereby clamping the blank 10 against the similarly shaped inner lip 42 of draw ring 14. The process is then completed (FIG. 2D) by fully extending the punch 12 through draw ring 14 during which the edges of the blank 10 will be pulled from between the outer pressure pad 18 and draw ring 14. However, since the edges of blank 10 will still be retained by the segments of the inner pressure pad 20, the draw can be completed. Because the segments of the inner pressure pad are contoured to correspond to the draw radius of the article formed during the drawing process, the blank can be retained against the draw ring 14 until the entire edge has been pulled past the innermost point of contact of the pressure pad 20. Actually, in the case of a helmet as shown in FIG. 2D where it is desirable to include a slight flange, it is not necessary to draw the edge beyond the inner pressure pad.

There are various ways in which the movement of the inner pressure pad 20 can be synchronized with the position of the punch relative to the draw ring. Preferably, the sequence is programmed to occur as a single smooth draw controlled, for example, by cams which are actuated by the movement of the punch.

Obviously, the invention has utility regardless of the nature of the drawn article. Its main advantage is in permitting the use of minimum size blanks such that no trimming of excess material is required after drawing. This not only reduces the cost of material but also reduces the processing costs (by avoiding the trimming and related steps) and increases the percentage of deformation due to drawing rather than stretching, thereby minimizing thin-out.

What is claimed is:

1. Apparatus for drawing an article, including a draw ring, a punch adapted to push a blank into said draw ring, and an outer pressure pad for holding the edge of the blank at least during the initial drawing operation, the improvement comprising an inner flexible pressure pad between said punch and outer pressure pad for holding said blank at least during the terminal portion of the drawing operation, a surface of said inner pressure pad being adapted to contact said blank under pressure, said surface being shaped to mate substantially with the draw radius of the blank when it is drawn by said punch into said draw ring, and means for applying dilferential pressures to circumferentially spaced portions of said inner pressure pad, the inner pressure pad being sufficiently flexible to provide a substantially non-incremental variation in pressure between circumferentially displaced regions of said inner pressure pad when different forces are applied to said circumferentially spaced regions.

2. Apparatus according to claim 1, wherein said inner pressure pad comprises a continuous ring having a plurality of radially extending slots.

3. Apparatus according to claim 2, wherein said slots do not extend through the surface of said inner pressure pad adapted to contact said blank.

4. Apparatus according to claim 3, wherein said means for applying differential pressures comprises a plurality of segments contacting respective portions of a surface of said inner pressure pad opposite said first named surface and means for applying substantially independent forces to said segments. 7

References Cited UNITED STATES PATENTS 3,420,089 1/1969 Myers 72-351 FOREIGN PATENTS 480,594 8/1929 Germany 72-350 280,900 5/1952 Switzerland 72351 RICHARD J. HERBST, Primary Examiner